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1994 Tertiary coal belt in eastern Kalimantan, Indonesia: the influence of coal quality on coal utilisation Bukin Daulay University of Wollongong
Recommended Citation Daulay, Bukin, Tertiary coal belt in eastern Kalimantan, Indonesia: the influence of coal quality on coal utilisation, Doctor of Philosophy thesis, Department of Geology, University of Wollongong, 1994. http://ro.uow.edu.au/theses/1413
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TERTIARY COAL BELT IN EASTERN KALIMANTAN, INDONESIA: THE INFLUENCE OF COAL QUALITY ON COAL UTILISATION
A thesis submitted in (partial) fulfilment of the requirements for the award of the degree of
DOCTOR OF PHILOSOPHY
from
THE UNIVERSITY OF WOLLONGONG
by
BUKIN DAULAY (B.Sc, A.G.P., Bandung; M.Sc (Hons), Wollongong)
Department of Geology March 1994 This thesis contains original research work carried out by the author except where otherwise acknowledged. The work has not been previously submitted for a higher degree to any other University or similar institution
Bukin Daulay ABSTRACT Eastern Kalimantan has the second largest coal resources in Indonesia after Bukit Asam and Ombilin Coalfields of Sumatera, but currently has the highest coal production. It is also the area forecast to have the highest growth rate in production to the year 2000.
The Kutei, Barito, Asem Asem and Tarakan Basins developed as a result of rifting in the Makassar Strait during the mid-Tertiary. The basins have cratonic and back-arc (retro- arc) settings with similar depositional histories from the Eocene through to the Middle Miocene. Coal was deposited in both Eocene and Miocene sequences in depositional environments ranging from fluviatile to deltaic. Economic coal deposits of Miocene age occur in all basins but economic Eocene coals occur only in the Barito and Asem Asem Basins.
The aim of this study was to evaluate lateral and vertical variations in coal thickness and to study the chemical and physical (including petrographic) properties to provide valuable input for short and long term planning for the utilisation of the coals of this important coal mining district.
Vitrinite and liptinite are the dominant macerals in both Eocene and Miocene coals. Inertinite is a minor component but it is higher in Miocene coals. Typical ratios for vitrinite to liptinite are higher in Miocene coals (8 to 15) than for Eocene coals (5 to 10). Mineral content is low in most of the coals except in some Eocene coals where it is abundant.
Five types of exsudatinite have been recognised in the present study on the basis of morphology and mode of occurrence. Veins of exsudatinite are typically associated with telovitrinite whereas lensoidal exsudatinite is associated with detrovitrinite and resinite. Both liptinite and meta-exsudatinite can be distinguished within coals that have been subjected to contact alteration.
The rank of the Miocene coals ranges from soft brown coal to high volatile bituminous (Rvmax of 0.30% to 0.71%) whereas for Eocene coals it ranges from subbituminous to high volatile bituminous (Rvmax of 0.43% to 0.66%). Thus, unlike most of the Miocene coals, the Eocene coals show only a small range of coal ranks. Miocene coals in Sangatta area have been altered to semi-anthracite by igneous intrusion.
Most of the eastern Kalimantan coals are suitable for feedstocks in combustion and conversion (liquefaction and gasification) processes. Combustion is the most important present day use for coals but suitability of coals for combustion is restricted by the contents of minerals, sulphur, liptinite and inertinite as well as rank.
The Miocene coals from Sangatta, Mahakam and Berau are the best coals for pulverised fuel combustion processes followed by the Tanjung (both Miocene and Eocene) and Pasir (Eocene) coals. Of the coals currently mined, or likely to be mined in eastern Kalimantan, Asem Asem, Satui and Senakin coals are considered to be the least suitable coals for pulverised combustion, because they have high moisture (Asem Asem), liptinite (Satui) and mineral matter (Senakin).
The exceptionally high sulphur in some coals will produce high concentrations of S02 when combusted. Nevertheless, the Satui and Senakin coals are of sufficiently high quality to be used for power generation in Indonesia and the Asem Asem coal could be used to fuel a "mine mouth" power station. The Satui and Senakin coals are only marginally suitable for export under current market conditions. All Miocene coals and the Eocene coals from Satui are suitable as feedstocks for liquefaction and gasification processes. The economic of the use of eastern Kalimantan coals for both gasification and liquefaction processes is dependent upon using the solid residues produced for subsequent combustion in power generation. However, in order to use the residues for combustion specifically designed char-fired plants will have to be built. Sangatta, Senakin, Pasir and Tanjung (Eocene) coals are suitable for low-temperature (600°C to 700°C) carbonisation to produce chars. Good quality cokes, on the other hand can only be produced from coals with Rvmax in the range from 1.0% to 1.40% and the vitrinite content should be <75% and >50%. Accordingly, none of the eastern Kalimantan coals can be used as coke oven charges although selected coals such as Sangatta, Pasir, Senakin, Tanjung (Eocene) can be used as a minor component in coke blend. In the last two years most of the coal production from eastern Kalimantan was allocated for exports but in the next few years an increasing proportion of production from this area is likely to be used for additional coal-fired plants in Java. ACKNOWLEDGEMENTS
The research project was carried out at the Department of Geology, University of Wollongong, through tenure of a scholarship funded by the Australian International Development Assistance Bureau (AIDAB).
I wish to express my deep gratitude to both my supervisors Dr AC Hutton and Associate Professor Brian G. Jones for their suggestions of this study, encouragement, patient guidance, constructive discussion and general assistance throughout the study. I am also grateful to my earlier supervisor, Dr Alan C. Cook for visiting thefield area and providing general advice.
The author wishes to thank Associate Professor A.J. Wright, Head of the Department of Geology and also all academic staff for their assistance during this study. I would like to express my sincere gratitude to all technical staff for their help, especially Messrs Aivars Depers, David Carrie, John Paterson, Max Perkins, Mrs R. Varga and Mrs B.R. McGoldrick.
I wish to thank the former Research and Development Director of the State Coal Mining (Perusahaan Umum Tambang Batubara) Jakarta, Dr M. Kusna, for providing an assess to coal mines along the eastern coast of Kalimantan. My special thanks go to the managements and all staff of P.T. Adaro Indonesia, P.T. Arutmin Indonesia, P.T. Berau Coal, P.T. Bukit Baiduri, P.T. Kaltim Prima Coal, P.T. Kideco Jaya Agung, P.T. Kitadin, P.T. Multi Harapan Utama, P.T. Tanito Harum and P.T. Utah Indonesia for permission to collect coal samples from mine faces and also providing shallow drill hole samples.
Special appreciation is addressed to Mr. Frank S. Wojtaszak and Ms. Norma L. Buckman, the present and former Regional Directors of AIDAB, training officers and social workers who gave the author valuable assistance during the study. Also my thanks go to the postgraduate students of the Department of Geology who provided advice during many informal discussions.
Finally, I am indebted to my wife Lely, son Dany Ardiansyah and daughter Tishi Tania for their companionship, patient support and encouragement throughout my study. TABLE OF CONTENTS Page ABSTRACT
ACKNOWLEDGMENT
LIST OF FIGURES
LIST OF TABLES
LIST OF PLATES
CHAPTER ONE INTRODUCTION 1
1.1 GENERAL 1 1.2 ATMS OF THE STUDY 2 1.3 GEOGRAPHICAL LOCATION 3 1.4 PREVIOUS STUDIES 5 1.4.1 Regional Geology 5 1.4.2 Coal-related Investigations 6 1.5 SUMMARY 10 CHAPTER TWO GEOLOGICAL SETTING 11
2.1 REGIONAL GEOLOGICAL SETTING OF INDONESIA 11 2.2 REGIONAL GEOLOGY OF EASTERN KALIMANTAN 12 2.2.1 Stratigraphy and Sedimentation in 13 the Tarakan Basin 2.2.2 Stratigraphy and Sedimentation in 17 the Kutei Basin 2.2.3 Stratigraphy and Sedimentation in 19 the Barito and Asem Asem Basins 2.3 SUMMARY 21 CHAPTER THREE COAL POTENTIAL 23
3.1 GENERAL 23 3.2 DEPOSITION OF COAL 24 3.2.1 Barito and Asem Asem Basins 25 3.2.2 Kutei Basin 27 3.2.3 Tarakan Basin 28 3.3 COAL AND PEAT RESOURCES 29 3.3.1 Coal Resources 29 3.3.2 Peat Resources 31 3.4 CHEMICAL ANALYSES 31 3.4.1 Chemical Data for Eastern Kalimantan Coals 32 3.4.2 Comparison Between Eastern Kalimantan 36 and Other Coals 3.5 HARDGROVE GRINDABILITY INDEX (HGI) 38 3.6 SUMMARY AND CONCLUSIONS 39 CHAPTER FOUR COAL PETROLOGY 41
4.1 GENERAL jl 4.2 COAL TYPE *J 4.2.1 Miocene Coals ™ 4.2.2 Eocene Coals ^9 4.3 COAL RANK 52 4.3.1 Miocene Coals ^3 411 Pnrpnp Co3ls 4.4 SPATIAL AND TEMPORAL VARIATIONS IN COAL TYPE 56 4.5 EXSUDATINITE IN EASTERN KALIMANTAN COALS 63 4.5.1 Types of Exsudatinite 6^ 4.6 RANK VARIATIONS 68 4.7 COAL FACES AND DEPOSITIONAL ENVIRONMENTS 71 4.8 COALIFICATION AND THERMAL HISTORY 72 4.8.1 Geothermal Gradient 73 4.8.2 Palaeotemperatures 74 4.8.3 Estimation of Maximum Cover 75 4.9 SUMMARY AND CONCLUSIONS 76 CHAPTER FIVE MINERAL MATTER 79
5.1 NATURE AND OCCURRENCE OF MINERAL MATTER 79 IN COAL 5.2 ANALYTICAL PROCEDURES 81 5.2.1 Optical Microscopy 82 5.2.2 X-ray Diffraction 82 5.2.3 Scanning Electron Microscopy (SEM) 83 5.3 MINERAL COMPOSITION 84 5.3.1 Clay Minerals 85 5.3.2 Quartz 87 5.3.3 Pyrite and Related Minerals 88 5.3.4 Carbonate Minerals 90 5.4 FACTORS CONTROLLING MINERAL CONTENT 92 5.5 SUMMARY AND CONCLUSIONS 95 CHAPTER SIX COAL QUALITY AND UTILISATION 97
6.1 COAL QUALITY 97 6.2 COAL UTILISATION 100 6.2.1 Combustion 102 6.2.2 Liquefaction 112 6.2.3 Gasification 119 6.2.4 Carbonisation 123 6.3 SUMMARY AND CONCLUSIONS 129 CHAPTER SEVEN COAL PRODUCTION AND CONSUMPTION 133
7.1 COAL PRODUCTION 133 7.1.1 General 133 7.1.2 Indonesian Coal Production 134 7.1.3 Comparison Between Coal Production in 137 Indonesia and Other Countries 7.2 COAL CONSUMPTION AND PROJECTIONS 140 7.2.1 Electricity Generation 141 7.2.2 Cement Plants 143 7.2.3 Small Industries 145 7.2.4 Residential Consumption 146 7.2.5 Exports 146 7.3 COAL'S SHARE OF PRIMARY ENERGY CONSUMPTION 153 7.4 THE FUTURE OF COAL CONVERSION 155 7.4 SUMMARY AND CONCLUSIONS 160 CHAPTER EIGHT SUMMARY AND CONCLUSIONS 163 8.1 CONCLUSIONS 164 8.2 FURTHER WORK 171
REFERENCES 173
APPENDED 1 PETROGRAPHIC DATA OF COALS FROM EASTERN KALIMANTAN
APPENDK 2 VITRINITE REFLECTANCE DATA OF COALS FROM EASTERN KALIMANTAN LIST OF FIGURES
Figure Description ^ 191 1.1 Location map of study area *r 1.2 Coal contractor agreement areas in eastern Kalimantan iyz 2.1 Present and Cenozoic tectonic features of southeast Asia J93 2.2 Structural elements of eastern Kalimantan J94 2.3 General geological map of eastern Kalimantan j^j 2.4 Generalised stratigraphic columns for eastern Kalimantan 196 2.5 Distribution of subbasins in northeastern Kalimantan 197
3.1 Coal and peat deposits in Indonesia *jj° 3.2 Distribution of coal deposits in eastern Kalimantan 199 3.3 Generalised stratigraphic column of Senakin and Satui 200 coal deposits 3.4 Generalised stratigraphic column of Mahakam coal deposits 201 3.5 Generalised stratigraphic column of Sangatta coal deposits 202 3.6 Generalised stratigraphic column of Berau coal deposits 203 3.7 Coal resources in eastern Kalimantan 204 3.8 Relationship between inherent moisture and calorific value, 205 eastern Kalimantan 3.9 Relationship between calorific value and volatile matter, 206 eastern Kalimantan 3.10 Relationship between volatile matter and inherent moisture, 207 eastern Kalimantan 3.11 Relationship between volatile matter and H/C ratio, 208 eastern Kalimantan 3.12 Van Krevelen diagram for eastern Kalimantan 209
4.1 Mean petrographic composition, eastern Kalimantan coals 217 4.2 Petrographic composition of coals from eastern Kalimantan 218 4.3 Petrographic analyses of coals from eastern Kalimantan, 219 showing means and ranges 4.4 Mean maceral and mineral matter in coals from 220 eastern Kalimantan 4.5 Vitrinite composition of coals from eastern Kalimantan 221 4.6 Mean vitrinite composition in coals from eastern Kalimantan 222 4.7 Mean inertinite composition in coals from eastern Kalimantan 223 4.8 Mean liptinite composition in coals from eastern Kalimantan 224 4.9 Vitrinite reflectance vs vitrinite content in coals from 225 eastern Kalimantan 4.10 Range of vitrinite reflectance values from Miocene coals, 226 eastern Kalimantan (293 readings) 4.11 Range of vitrinite reflectance values from Eocene coals, 227 eastern Kalimantan (86 readings) 4.12 Vitrinite reflectance histogram for heat-affected coal 228 from Sangatta 4.13 Vitrinite reflectance histogram of a normal Sangatta coal 229 4.14 Selected petrographic composition of Tertiary coals from 230 Indonesia and other countries 4.15 Range of vitrinite contents of coals from eastern Kalimantan 231 List of Figures (cont.)
4.16 Mean maceral and mineral composition of Miocene and 232 Eocene coals, eastern Kalimantan 4.17 Mean proportion of vitrinite subgroups in Miocene and 233 Eocene coals, eastern Kalimantan 4.18 Ratio of telovitrinite to detrovitrinite, eastern Kalimantan 234 coals 4.19 Relationship between vitrinite reflectance and suberinite 235 content, eastern Kalimantan coals 4.20 Present land surface vitrinite reflectance of coals from 236 eastern Kalimantan 4.21 Relationship between vitrinite reflectance and coal thickness, 237 Asem Asem and Senakin coals 4.22 Relationship between vitrinite reflectance and coal thickness 238 for Berau and Satui coals 4.23 Facies-critical maceral association for coals from 239 eastern Kalimantan 4.24 Relationship between temperature estimated from coal rank 240 and coal age data and present estimated well/basin temperatures for some Indonesian Tertiary basins
5.1 Frequency distribution of mineral matter in eastern 249 Kalimantan coals 5.2 Proportion of mineral matter in eastern Kalimantan coals 250 5.3 Mineral content of coals from eastern Kalimantan 251 5.4 Mean abundances of mineral matter by coalfield, eastern 252 Kalimantan coals 5.5 X-ray diffraction pattern of a shaly coal from Senakin 253 5.6 X-ray diffraction pattern of a shaly coal from Sangatta 254 5.7 Pyrite abundance and location in coal seam, Berau coals 255 5.8 Pyrite abundance and location in coal seam, Sangatta coal 256 5.9 Percentage of mineral matter in Eocene and Miocene coals, 257 eastern Kalimantan 5.10 Abundance of mineral matter in Eocene and Miocene coals, 258 eastern Kalimantan 5.11 Relationship between pyrite and vitrinite, eastern Kalimantan 259 coals 5.12 Relationship between pyrite and inertinite, eastern Kalimantan 260 coals 5.13 Relationship between pyrite and total mineral matter, 261 eastern Kalimantan coals 5.14 Relationship between inertinite and total mineral matter, 262 eastern Kalimantan coals
6.1 Relationship between average Hardgrove Grindability Index 265 and average vitrinite reflectance, eastern Kalimantan coal 6.2 Relationship between average Hardgrove Grindability Index 266 and average mineral matter, eastern Kalimantan coals 6.3 Relationship between average ash fusion temperature 267 and average volatile matter, eastern Kalimantan coals 6.4 Relationship between average Hardgrove Grindability Index 268 and average inherent moisture, eastern Kalimantan coals 6.5 Average oil yield of Miocene, Eocene and all seams 269 eastern Kalimantan coals List of Figures (cont.)
6.6 Relationship between pyrolysis oil yield and reactive 270 macerals, eastern Kalimantan coals 6.7 R-mode dendogram of eastern Kalimantan coals 271 6.8 Relationship between pyrolysis oil yield and liptinite, 272 eastern Kalimantan coals 6.9 Relationship between pyrolysis oil yield and resinite, 273 eastern Kalimantan coals 6.10 Relationship between pyrolysis oil yield and suberinite, 274 eastern Kalimantan coals 6.11 Relationship between pyrolysis oil yield and exsudatinite, 275 eastern Kalimantan coals 6.12 Relationship between pyrolysis oil yield and vitrinite 276 reflectance, eastern Kalimantan coals 6.13 Rate of gasification as a function of temperature 277 6.14 Optimum ratio of reactives to inerts for each vitrinite type 278 6.15 Predicted coke stability of selected eastern Kalimantan coals 279 6.16a Generalised relationship of coke strength and rank: 280 coal type constant 6.16b Generalised relationship of coke strength and vitrinite: 280 rank constant 7.1 World coal reserves 290 7.2 Asian coal reserves 291 7.3 Coal reserves in ASEAN countries 292 7.4 Indonesian coal production, 1940-1992 293 7.5 Contribution of eastern Kalimantan coal to Indonesian 294 total coal production 7.6 Coal production growth rate, Indonesia 295 7.7 Projected coal production in Indonesia, 1993-2000 296 7.8 World coal production 297 7.9 Production, consumption and export of Indonesian coals, 1992 298 7.10 Indonesian coal consumption, 1971-1992 299 7.11 Projected coal consumption, Indonesia 300 7.12 Existing and projected coal-fired plant capacities in OECD 301 and non OECD countries and Indonesia 7.13 Existing and projected cement production and associated 302 coal consumption, Indonesia 7.14 Indonesian coal exports 303 7.15 Coal exports from Indonesia as a percentage of production 304 7.16 Comparison between coal consumption and coal exports 305 7.17 World coal exports 306 7.18 Primary energy resources in Indonesia 307 7.19 Primary energy production from different sources, Indonesia 308 7.20 Comparison between primary energy production from different 309 sources in Indonesia and some other countries 7.21 Proportion of electricity production from different sources, 310 Indonesia LIST OF TABLES
Table Description Page
3.1 Estimation of coal resources from eastern Kalimantan 210 3.2 Estimation of Indonesian coal resources 211 3.3 Chemical analyses of eastern Kalimantan coals 212 3.4 Average ultimate analyses of eastern Kalimantan coals 213 3.5 Chemical analyses of Indonesian coals 214 3.6 Chemical analyses of coals from some countries 215 3.7 Hardgrove grindability index of selected eastern 216 Kalimantan coals
4.1 Australian classification system for coals 241 4.2 Summary of petrographic data in eastern Kalimantan coals 242 4.3 Microlithotypes in coals from eastern Kalimantan 243 4.4 Vitrinite subgroups in eastern Kalimantan coals 244 4.5 Inertinite macerals in eastern Kalimantan coals 245 4.6 Liptinite macerals in eastern Kalimantan coals 246 4.7 Summary of mean vitrinite reflectance for eastern 247 Kalimantan coals 4.8 Occurrences and characteristics of exsudatinite in 248 eastern Kalimantan coals
5.1 Mineral matter in eastern Kalimantan coals 263 5.2 Total and pyritic sulphur, eastern Kalimantan coals 264
6.1 Comparison between Mahakam and Pasir coals 281 6.2 Ash analyses of eastern Kalimantan coals 282 6.3 Properties of coals with potential for conversion to liquids 283 6.4 Ash fusion temperature, eastern Kalimantan coals 284 6.5 Modified Fischer assay results of selected eastern 285 Kalimantan coals 6.6 Data matrix for eastern Kalimantan coals for cluster analysis 286 6.7 Product-moment matrix for eastern Kalimantan coals for 287 cluster analysis 6.8 Calculated coke stabilities of selected eastern Kalimantan 288 coals 6.9 Summary of quality and utilisation potential, eastern 289 Kalimantan coal
7.1 Existing and projected coal production in Indonesia 311 7.2 World coal production by regions 312 7.3 Existing and projected coal consumption in Indonesia 313 7.4 Existing and planned additions of coal-fired plants in 314 Indonesia, 1984-2000 7.5 Typical characteristics of coal used in coal-fired plants 315 and cement industries 7.6 Existing and projected cement production and associated 316 coal consumption, Indonesia 7.7 Estimation of primary energy resources in Indonesia 317 7.8 Primary energy supply in Indonesia and other selected 318 countries LIST OF PLATES Page
PLATE 1 319 PLATE 2 320 PLATE 3 321 PLATE 4 322 PLATE 5 323 PLATE 6 324 PLATE 7 325 PLATE 8 326 CHAPTER ONE INTRODUCTION
1.1 GENERAL
The coal deposits along the eastern coast of Kalimantan are, after those in Sumatera, the second biggest coal resource in Indonesia. Exploitation of coal in Kalimantan has a long, but spasmodic history. Mining first started around 1850 but terminated in 1941 due to a lack of demand as a result of the limited number of consumers. It is only recently that mining has again become a major industry for this island of Indonesia and this reflects changes in government policy.
Increasing domestic use of coal as a substitute for oil, in order to maximise export earnings from oil, has been one of the main objectives of the Indonesian energy policy since 1976.
A presidential instruction in 1976, decreed that coal use in electricity generation and cement industries was to be maximised. By the end of the 1980s, Indonesian coal production, with a small output from eastern Kalimantan, and domestic consumption had increased steadily.
However, until recently, major parts of the coal resources and reserves remained undeveloped.
Coal is the largest primary energy resource in Indonesia, but crude oil is still the main primary energy consumed. This is because, among other things:
i. the characteristics of the coals (including geology and quality) are not well understood; ii. the demand for, and marketing strategies of, coal (particularly from eastern 2
Kalimantan) are well behind those of oil;
Hi. alternative uses and technological knowledge of eastern Kalimantan coals, and
Indonesian coals in general, such as for their applicability conversion in
liquefaction, gasification and low-temperature carbonisation processes, have not
been developed.
1.2 AIMS OF THIS STUDY
Indonesia, like many developing countries, has vast resources of coal that have been exploited in a non-systematic manner with selective mining taking the shallow, easily-
obtained coal and little attention has been given to coal quality, differences in properties
and coal resources at greater depths. Exploration to date has produced additional data but
these have not been used in integrated studies and the exploitation of Indonesian coal has
a long way to go before it reaches the efficiency and maximisation such as in the United
States of America, Australia, South Africa and Canada. Additional studies are required to
determine suitable export markets. Most of the coal mined in Sumatera is destined for
domestic markets because of historical reasons and infrastructure related to the high
population densities of Sumatera and nearby Java. However, the low population density,
and the lack of industry and infrastructure in eastern Kalimantan dictates that coal from this
part of Indonesia is a prime export commodity.
This laboratory-based study was initiated to collect petrographic data on coals from eastern
Kalimantan and integrate this with the large, unprocessed data base that has accumulated
through exploration programs. The study has the potential to make a significant
contribution to the knowledge and exploitation of eastern Kalimantan coal and should
provide a framework for later studies. 3
The major objective of this study is to evaluate variations in the quality and quantity of coals in eastern Kalimantan to provide a better understanding of these coals, in terms of technical considerations, so as to optimise the potential utilisation strategies of the coal.
The study is based on published and unpublished data as well as original data for samples collected from outcrop, mining faces and shallow boreholes in Tertiary (Eocene and
Miocene) coal measures.
The main aims of the study are:
1. To evaluate lateral and vertical variations in the thickness and chemical composition of coal seams in relation to the depositional environments.
2. To examine coal type and rank variations.
3. To evaluate spatial and temporal variations in coal type.
4. To outline local and regional coalification and thermal history.
5. To determine types and abundances of mineral matter.
6. To assess alternative methods of utilising coal.
7. To assess the potential coal consumption, particularly domestic use as well as export.
8. To assess coal supply and demand.
1.3 GEOGRAPHICAL LOCATION
The study area is located along the eastern coast of Kalimantan, Indonesia which can be reached by regular flights to the main district towns and then by car or boat to the more remote localities.
The area has a tropical climate with temperatures ranging between 24°C and 33°C; the mean annual temperature of 27°C. Average rainfall is 160 mm per month with 4 approximately 10 rainy days per month; maximum rainfall occurs during the months of
November through April. Elevation of the coalfields along the eastern coast of Kalimantan ranges between 5 and 300 metres above sea level.
Apart from mining industries (mainly oil, coal and gold) the major private industries along the eastern coast of Kalimantan are agriculture, fishing and commercial timber mills. The region is largely covered with tropical rainforest vegetation. Five vegetation groups are present - primary rainforest, secondary rainforest, brackisli/mangrove swamp, freshwater swamp and cultivated/deforested land. These vegetation types, or at least the brackish/mangrove community, appear to have been in place before human habitation as mangrove pollen has been recorded from the Eocene coal measures of Asem Asem and
Barito Basins.
The main geomorphological features of the study area are lowlands and swamps along the east coast and broad, gently- to steeply-sloping hilly land in the western, southern and northern parts. Well-defined lineations in the hilly land, appearing on air photos and satellite imagery, are related to a series of long, broad synclines and anticlines. The western, southern and northern edges of the area are composed of steep highlands where pre-Tertiary and Early Tertiary rocks are exposed. Basement faulting, penecontemporaneous with or after basin development, may be responsible for these morphological features.
Samples, mainly coal and shaly coal from clay partings, were collected from the following coalfields:
- Senakin, Satui, Pasir and Asem Asem Coalfields in the Asem Asem Basin;
- Tanjung Coalfield in the Barito Basin;
- West Busang, North Busang, Mahakam, Ambalut and Sangatta Coalfields in the
Kutei Basin; and 5
- Berau Coalfield in the Tarakan Basin.
The coalfields of eastern Kalimantan were divided, for this study, into eight regions from north to south: the Berau, Sangatta, Mahakam, Pasir, Tanjung, Senakin, Satui and Asem
Asem regions (Figure 1.1). It was then possible to subdivide the coals into Miocene coals from Berau, Sangatta, Mahakam and Asem Asem and Eocene coals from Pasir, Senakin and
Satui. Both Eocene and Miocene coals occur in Tanjung Coalfield.
1.4 PREVIOUS STUDIES
1.4.1 Regional Geology
Early reports on the regional geology, stratigraphy and structure of eastern Kalimantan have been given by Rutten (1914), Krol (1920; 1925), Leupold and Van Der Vlerk (1931),
Koolhoven (1935) and Beltz (1944) with the most comprehensive analysis of the geology of the area given by Van Bemmelen (1949). Since 1970, several important geological aspects of eastern Kalimantan have been investigated by Katili (1973; 1975), Samuel and
Muchsin (1975), Koesoemadinata (1978), Koesoemadinata et al. (1978), Hamilton (1979) and Hartono (1984). A basis for coal exploration in the region was presented by Strauss et al. (1976) and Strauss and Atkinson (1981).
Additional specific studies were undertaken by Supriatna et al. (1980), Rustandi et al.
(1981), Sikumbang and Heryanto (1981) and Umar et al (1982); the data in these reports were used by the Geological Research Development Centre, Bandung, to produce geological maps of the area at a scale of 1:250,000. Further work was carried out by Marks et al.
(1982), Situmorarig (1982), Williams (1986) and Pieters et al. (1987). 6
1.4.2 Coal-related Investigations
Coal deposits in eastern Kalimantan were recognised and delineated by Dutch geologists between 1800 and the 1940s (for example, Van Bemmelen, 1949; Sigit, 1959; 1963). The first commercial coal production in Indonesia started around 1850 and involved small private companies in the Tenggarong district along the Mahakam River, the Kelai River and
Berau regions of northeastern Kalimantan, and the northern part of Pulau Laut in southeastern Kalimantan (Sigit, 1963; 1981; Johannas, 1983). Miocene coals were mined from both eastern and northeastern Kalimantan whereas Eocene coals were produced from southeast Kalimantan.
Indonesian coal production was approximately 100,000 tonnes a year in 1850. Since that time, production has steadily increased with the development of other mines, both in
Sumatera and Kalimantan. The coal was utilised mainly for electricity generation, steam locomotives, steam ships and export to the Southeast Asian region. Traditionally coal was also used to produce town gas, steam and industrial heating.
The two largest coal mines in Sumatera (Ombilin in West Sumatera and Bukit Asam in
South Sumatera) were operated by the Netherlands Indies Government. Ombilin coal mine was started in 1892 and achieved a maximum annual production of approximately 665,000 tonnes in 1931. Coal mining in the Bukit Asam region commenced in 1919 and production reached 863,700 tonnes in 1941. Thus, as a result of the operation of Ombilin and Bukit Asam mines, with virtually no production from Kalimantan, Indonesian coal production reached nearly two million tonnes annually in 1940 and 1941. This coal production was allocated mainly for exports, because of limited domestic consumers.
After this time, production patterns and markets changed dramatically. Unfortunately, between World War U and the early 1970s, Indonesian coal production declined because 7 of the relatively low world price of oil compared to that of coal. The operation of coal mines in eastern Kalimantan was terminated completely in the 1970s. However, both
Ombilin and Bukit Asam mines in Sumatera continued to produce with the aid of
Government subsidies; production was only for domestic consumption.
After the first oil crisis in 1973, intensive coal exploration was carried out in Sumatera and
Kalimantan. By 1975, coal had become a very important component of the Indonesian
Government's long term energy strategy and policy which was based on four main priority areas:
i. the need to compile an inventory of resources after evaluation of currently exploited resources arid extensive exploration of unexploited areas; ii. diversification of energy types; iii. conservation of energy sources; and iv. indexation of supplies.
Emphasis on diversification for maximum coal utilisation in thermal electricity plants and kiln firing in the cement industry were the corner-stones of the policy changes.
Since 1975, many workers carried out coal investigations, particularly in Sumatera and
Kalimantan, including Siregar (1975), Koesoemadinata (1978), Koesoemadinata et al.
(1978), Johannas (1983) and Katili (1983). Investigations of the coal geology of
Kalimantan have been carried out by Land and Jones (1987) and Strauss (1988).
Since 1981, as part of the energy strategy program, the Indonesian Government has invited foreign companies to become engaged in exploration, development and production of coal in Indonesia, particularly in eastern Kalimantan, through co-operative contracts. These 8 contracts are formal agreements between foreign companies and Perusahaan Umum
Tambang Batubara (abbreviated to Perum Tambang Batubara), the State Coal Company, which acts on behalf of the Indonesian Government. Contracts, which are based on
Presidential Instruction No. 49, decreed in 1981 (Johannas, 1986; Perum Tambang Batubara,
1987; Prijono, 1987), have resulted in substantial investment and exploration, leading to operation of mines, by the foreign companies.
To date, nine contracts have been signed for the eastern coast of Kalimantan (Figure 1.2).
These are contracts with:
P.T. Aratmin Indonesia
P.T. Utah Indonesia
P.T. Kaltim Prima Coal
P.T. Kideco Jaya Agung
P.T. Adaro Indonesia
P.T. Berau Coal
P.T. Chung Hua Exploration Co.
P.T. Tanito Harum
P.T. Multi Harapan Utama.
Besides these international companies, five national private companies also carry out coal mining activities in eastern Kalimantan.
Most of the coal and shaly coal samples in this study were collected from contract areas.
The most extensive drilling in recent exploration programs was confined to depths of 100 to 200 metres; thus deep-seated seams, intersected during oil exploration and proving programs, were excluded from resource evaluations. Pre-feasibility studies in most coalfields (except Asem Asem) included infra-structure, port site, marine engineering, 9 mining and marketing investigations. Most contractors carried out test combustion programs with satisfactory results.
Three contractors, P.T. Arutmin Indonesia, P.T. Multi Harapan Utama and P.T. Tanito
Harum, commenced production in 1988. The largest mines, including Sangatta, started in
1992 (Chapter 7).
In addition to the important shallow coal measures sequences known from exploration by the nine foreign contractors and five national private companies, thick sequences of coal measures have been found in other areas during the course of oil and natural gas exploration (Pertamina U.E.P., 1976; 1981), particularly in the Tarakan Basin. P.T. Utah
Indonesia (1978) also discovered coal-bearing beds, probably of Eocene to Oligocene age, in the northern Tarakan Basin (close to the border between Indonesia and Malaysia).
These seams are approximately 1 metre thick and typically have high sulphur contents.
Initial studies of the petrology/petrography of Indonesian coals were conducted by Stach
(1953), on coal from Bukit Asam Coalfield, followed by Bourdin et al. (1964) who studied coal from eastern Kalimantan. A more comprehensive petrographic study was carried out by Daulay (1985) and this was published by and Daulay and Cook (1988) as part of a wider study in which coal type and rank variations in selected Indonesian Tertiary coal basins, in relation to sedimentary and tectonic setting and palaeoclimate, were evaluated.
More recent work by Panggabean (1991), as part of his PhD research, investigated the petroleum source-rock and reservoir-rock potential and depositional environments of the
Early Tertiary sequences in the Asem Asem and Barito Basins . 10 1.5 SUMMARY
Eastern Kalimantan has the second largest coal resources in Indonesia behind the Bukit
Asam and Ombilin Coalfields area of Sumatera. In line with the national energy policy guidelines, extensive geological investigations of coal from the eastern coast of Kalimantan have been carried out since 1981. As a result, large coal deposits of both Eocene and
Miocene age have been discovered. Coal production commenced from several eastern
Kalimantan coalfields after 1988 but significant production has been achieved only since
1992.
Despite the extensive geological base, few studies have examined the organic petrography of the coals and tried to relate this to coal utilisation. This study will use laboratory data and data from unpublished reports to evaluate lateral and vertical changes in coal properties on a regional basis for the Tarakan, Kutei, Barito and Asem Asem Basins and will develop basic data to assess alternative uses of the coals and thus provide a technical framework to optimise coal utilisation both for domestic markets and export. 11
CHAPTER TWO GEOLOGICAL SETTING
2.1 REGIONAL GEOLOGICAL SETTING OF INDONESIA
It is widely accepted that the Indonesian islands resulted from the evolution and convergence of three main plates: the northward-moving Indian-Australian Plate, the westward-moving Pacific Plate and the relatively stationary Eurasian Plate (Figure 2.1;
Hamilton, 1979; Katili, 1973; 1978; 1989; CCOP-IOC, 1980). Subduction of the Indian-
Australian Plate beneath the Eurasian Plate lead to the development of a major magmatic arc system which is divided into two segments, the Sunda Arc in the west and the Banda
Arc in the east. These arcs are associated with a series of subduction zones which have migrated, with time, in response to changes in the tectonic setting of the Indonesian region
(Hamilton, 1979).
As a result of the interaction between the three lithospheric plates mentioned above,
Koesoemadinata and Pulunggono (1974) and Koesoemadinata et al (1978) divided
Indonesia into two tectonic regions that contain Tertiary sedimentary basins: western
Indonesia, with the Sunda landmass as the continental core, and eastern Indonesia with the
Sahul Shelf as the continental core. In contrast to the geological evolution of western
Indonesia, which has been relatively simple since at least the Early Tertiary, the geological history of the eastern Indonesian region appears to have been much more complex (Bowin et al, 1980; Silver et al, 1985).
Plate collision was responsible for the development of basement faulting in the continental crust and subsequent differential movement resulted in basin deeps and highs. Erosion and 12 sedimentation in the basins was controlled by vertical differential movement. The relative rates of subsidence and deposition controlled the occurrence and thickness of coal deposits.
2.2 REGIONAL GEOLOGY OF EASTERN KALIMANTAN
Many papers discussing the tectonics of Indonesia have presented theories to explain the origin of the Tertiary basins in Kalimantan, particularly those along the east coast of
Kalimantan. Workers (such as Beltz, 1944; Van Bemmelen, 1949; Samuel and Muchsin,
1975; Audley-Charles, 1976; Rose and Hartono, 1978; Katili, 1973; 1975; 1978; 1989;
Hamilton, 1979; Situmorang, 1982, and Daly et al, 1987) contributed greatly to the evolution of ideas on the tectonic history of the island. Some of the authors suggested that a mid-Tertiary spreading centre existed in the Makassar Strait whereas others depicted western Sulawesi juxtaposed with eastern Kalimantan before the opening of the Makassar
Strait. Katili (1978), Hamilton (1979) and Situmorang (1982) argued strongly that the rifting and opening phases of the Makassar Strait were followed by lateral movement of approximately 200 km.
As a result of the tectonic activities explained above, four main Tertiary sedimentary basins, and associated coal deposits, are recognised along the east coast of Kalimantan. From north to south respectively, they are the Tarakan, Kutei, Barito and Asem Asem Basins
(Figure 2.2). Initially the basins developed as a single large depocentre during the Early
Tertiary, only becoming separated by uplifted zones (such as the Mangkalihat Ridge and the Semporna, Kuching, Laut and Meratus Highs) in the later stages of basin development, that is, during the Late Miocene orogenic activity (Hamilton, 1979; Sikumbang, 1986).
The Tarakan, Kutei, Barito and Asem Asem Basins are cratonic and back-arc (retro-arc) basins which are associated with the Tertiary southeast-directed subduction zone in 13 northwest Kalimantan (which is no longer active) and which developed in the eastern part of the island and the adjacent Makassar Strait. Large-scale thrusting and continuous movement of unconsolidated mudstone in the basins have been interpreted as being caused by the slightly westward movement of Sulawesi (Katili, 1978; Hamilton, 1979).
Sedimentation was fairly continuous throughout the Tertiary and still occurs offshore today.
In general terms, the sediment was deposited in the four basins as regressive sequences with the locus of thickest sedimentation moving eastwards, although, at any given locality, several regression-transgression cycles have been recognised in oil and gas exploration programs (Pertamina U.E.P. rv, 1976).
The Tertiary sequences of the Tarakan, Kutei, Barito and Asem Asem Basins overlie strongly-deformed Cretaceous rocks consisting of an ophiolite complex, metamorphic and volcanic rocks. Marine sedimentary rocks (Koolhoven, 1935; Sikumbang, 1986) underlie the Tertiary coal deposits and probably form the basement of the Tertiary basins over most of eastern Kalimantan.
The four basins have a related depositional history ranging in age from Eocene through the
Middle Miocene (Figure 2.3). The similarities in sedimentation between the basins are illustrated in Figure 2.4.
2.2.1 Stratigraphy and Sedimentation in the Tarakan Basin
The Tarakan Basin, which is on the coast of northeastern Kalimantan, is an arcuate depression, concave to the east where it opens into the Makassar Strait/Sulawesi Sea. The basin which has both an onshore and an offshore component, is flanked to the west by the pre-Tertiary strata of the Kuching High. To the south, the Tarakan Basin is separated from the Kutei Basin by the east-trending Mangkalihat Ridge/Suikerbrood High. The basin 14 extends north of the Indonesian-Malaysian border where it terminates at a subduction zone in the Semporna High (Figure 2.2).
The initial depositional history recorded in the Tarakan Basin began with a widespread marine transgression, during the Eocene and continued until the Early Miocene when the
Kuching High, to the west, was gradually uplifted, moving the palaeoshoreline progressively eastward (Rowley, 1973; Samuel, 1980; Achmad and Samuel, 1984; Akuanbatin et al,
1984; Williams, 1986). During the Middle Miocene, a regressive phase resulted in deposition of dominantly constructive deltaic deposits which prograded eastwards over prodelta and bathyal deposits.
According to Achmad and Samuel (1984) and Williams (1986), basin subsidence was rapid during the Miocene and Pliocene, although overall, sedimentation outstripped subsidence.
Thick sequences of deltaic sediment were deposited with the depocentres shifting progressively eastward with time.
The Tarakan Basin can be divided into four sub-basins; from north to South, these are the
Tidung, Tarakan, Berau and Muara Sub-basins (Figure 2.5).
Tidung Sub-basin
This northernmost, mostly onshore sub-basin extends onto the Semporna High to the north and developed from the Late Eocene to the Middle Miocene. It is separated from the
Berau Sub-basin to the south by the Sekatak Berau Ridge. The Tidung Sub-basin contains sandstone, siltstone, claystone and thin brown coals deposited in an easterly prograding delta system which, during the Pliocene, merged with a delta system to the south (Achmad and Samuel, 1984). 15
Tarakan Sub-basin
This sub-basin developed primarily offshore but includes several large islands (such as
Bunyu and Tarakan). It was filled with a very thick sequence of post-Miocene terrigenous sediment which unconformably overlies all previous sequences and structures. The basin onlaps the southeastern part of the Tidung Sub-basin and the northeastern part of the Berau
Sub-basin. Many of the offshore islands represent upfolded Pliocene sediments deposited in a deltaic sequence.
Muara Sub-basin
The Muara Sub-basin lies offshore of the Mangkalihat Ridge. It contains a marine sequence of primarily reef and other carbonate strata. It has no coal potential.
Berau Sub-basin
This southernmost sub-basin also developed during the Late Eocene to Middle Miocene period and has a similar depositional history to that of the Tidung Sub-basin. This is the most important sub-basin with respect to coal, as most of the coal-bearing strata in northeastern Kalimantan, including the Berau Coalfield, occur in the Berau Sub-basin.
Pertamina U.E.P. rv (1976) noted that coal-forming environments had developed since the
Late Miocene in both the northern and southern onshore sections of the sub-basin.
The Berau Sub-basin is separated from the Kutei Basin to the south by the Mangkalihat
Ridge/Suikerbrood High which has been a structural high since the Eocene. To the west,
Berau Sub-basin onlaps the Kuching High with its core of highly deformed pre-Tertiary strata. The Sekatak Berau Ridge, a topographically high area since the Oligocene, separates the Berau Sub-basin from the Tidung Sub-basin to the north.
According to Achmad and Samuel (1984) and Williams (1986) the Berau area has 16 undergone three main periods of deformation. The most dynamic period of deformation occurred in pre-Eocene time when existing basement strata were intensely folded and faulted. The second period of deformation occurred during the Oligocene when the Early
Tertiary sequence was folded, faulted and intruded. The final period of deformation occurred during the Pliocene. Achmad and Samuel (1984) suggested that the Berau area is a downthrown block of Miocene rocks which is bounded on the south, west and north by faults.
Pre-Tertiary, Eocene and Oligocene sedimentary rocks are present in the Tanjung Redeb area but none are found in the Berau Coalfield (Lati, Kelai and Binungan areas). The
Eocene and Oligocene sediments are dominantly marine,fine-grained clastic rocks with rare volcanic units, although non-marine sandstones and minor coal deposits occur immediately above the basal Tertiary unconformity (Achmad and Samuel, 1984).
The oldest rocks present in the Berau Coalfield are of Miocene age and belong to the
Sterile Formation. This formation is composed of marine mudstone, siltstone and sandstone. The sandstone is massive and fine- to very fine-grained and it is interbedded with mudstone and siltstone. Burrows are common in all lithologies.
The Sterile Formation conformably underlies the coal-bearing Berau Formation although the contact between the formations is difficult to place in the Berau Coalfield. The Berau
Formation, at least 400 metres thick, contains interbedded mudstone, siltstone, sandstone and coal. Shell fossils, plant impressions, coalflakes and burrows are common, particularly in the mudstone.
Gravel deposits, possibly Pleistocene in age, are found unconformably overlying the older
Miocene units. Stream valleys are filled with recent alluvial deposits probably derived from 17 the surrounding Berau Formation, as evidenced by the clasts of coal found in these deposits.
2.2.2 Stratigraphy and Sedimentation in the Kutei Basin
The Kutei Basin is partly onshore in the eastern part of the island and offshore in the adjacent Makassar Strait (Figure 2.2). Numerous publications (for example, Gerard and
Oesterle, 1973; Samuel and Muchsin, 1975; Rose and Hartono, 1978; Nuay et al, 1985;
Carbonel and Moyes, 1987; Ott, 1987; Caratini and Tissot, 1988) described the Kutei Basin in considerable detail, particularly the nature of the Mahakam River deltaic complex which presently progrades into the Makassar Strait, as it has done since Early Miocene time.
Covering some 60,000 km2, with a Miocene to Pleistocene sequence up to 9,000 metres thick, the Kutei Basin is the largest and deepest Tertiary basin in eastern Kalimantan, and
Indonesia in general. The tectonism which gave the basin its present configuration was probably confined largely to the Late Pliocene, although fluctuating movement of positive elements occurred at least from Late Oligocene time. Some of the tectonic elements used to define the basin antedate it and some are post-depositional.
The Kutei Basin is bounded to the south by the Laut High, to the southwest by the
Meratus High, to the northwest by the Kuching High and to the northeast by the
Mangkalihat Ridge/Suikerbrood High. The Laut High, Meratus High and Mangkalihat
Ridge/Suikerbrood High had little influence on depositional patterns except for a period of temporary uplift in the Late Oligocene. The highs were raised to their present position by
Late Pliocene and Quaternary movements.
The Laut and Meratus Highs occupy onshelf positions and received a moderate thickness of sediment, whereas the Mangkalihat Ridge/Suikerbrood High was near the axis of deepest 18
Early Tertiary subsidence (Samuel and Muchsin, 1975; Williams, 1986; Ott, 1987). The
Kuching Arc was transgressed in the Early Tertiary and it is likely that the arc was uplifted during the Oligocene because the outliers now remaining on the arc have been mapped as
Eocene or Early Tertiary (Samuel and Muchsin, 1975; Rose and Hartono, 1978).
Tertiary sedimentation within the Kutei Basin appears to have occurred in two distinct phases:
1. The first phase was during the Eocene-Oligocene period during which time the basin was generally the site of deposition of a thick siliciclastic sequence, much of which is shale, deposited in deep (bathyal) water. Coarser siliciclastic strata are locally associated with the shale sequence but these are mostly confined to the western basin area.
Samuel and Muchsin (1975), Allen et al. (1976), Rose and Hartono (1978), Van De Weerd et al (1987) and Pieters et al (1987) stated that the provenance area for the coarse clastic detritus was largely from the stable shelf areas to the north (Mangkalihat Ridge/Suikerbrood
High region; Figure 2.2) and from the Sunda Shield to the south. The Kuching High is believed to have been a very low relief feature and a minor contributor of sediment at that time. Indeed, the Kuching High may not have been a provenance area for clastic detritus during the Eocene-Oligocene time (Rose and Hartono, 1978) and the basin may have been entirely open to the west.
2. The second phase of deposition was characterised by deposition of an extensive series of alluvial and deltaic deposits which commenced in the Early Miocene and prograded eastwards. This sedimentation pattern, which still continues, is represented by the modern delta complex at the mouth of the Mahakam River. The primary provenance area of this sedimentary complex appears to be to the west (Kuching High, Figure 2.2), with evidence 19 of less input from the northern and southern sediment provenance areas which were more important during the earlier Eocene-Oligocene period.
The Early Tertiary rocks of Kutei Basin consist of basal coal-bearing, quartzose sandstone and mudstone units, which grade into marine mudstone and limestone (Samuel and
Muchsin, 1975; Marks et al, 1982). Oligocene rocks are widely distributed over the basin.
The units are commonly composed of limestone and calcareous sediment of the Tuyu and
Berai Formations (Figure 2.4).
Miocene rocks consist of three formations, which from oldest to youngest, respectively, are the Pemaluan, Pulubalang and Balikpapan Formations. The most prospective coal-bearing unit is the Balikpapan Formation, especially in the vicinity of the Mahakam River and the
Pinang Dome (Sangatta area) in northern part of the basin. The Balikpapan coal measures are mainly deltaic and floodplain fades. Other Miocene rocks also contain coal seams, but these are very thin and few in number.
The Pliocene Kampung Baru Formation has similar lithotypes to the Balikpapan Formation but normally does not occur inland indicating that it is younger than the Balikpapan
Formation. The formation also contains coal measures but the coals are predominantly thin and of very low rank.
2.2.3 Stratigraphy and Sedimentation in the Barito and Asem Asem Basins
The Barito and Asem Asem Basins lie in southeastern Kalimantan and are separated by
Mesozoic structural features. The Barito Basin is bounded by the Sunda Shield to the west and the Meratus High, a belt of melange and ophiolites, to the east. To the north, the basin is separated from the Kutei Basin by the South Kutei Boundary Fault (also called the
Paernoster High) whereas to the south, the basin merges with the East Java Basin offshore. 20
The Asem Asem Basin (which was previously called the Pasir Sub-basin of the larger Kutei
and Barito Basins) is separated from the Barito Basin by the Meratus High to the west.
The basin is bounded by the Paternoster Platform and the Laut High in the east, and the
South Kutei Boundary Fault (the Paternoster High) in the north (Figure 2.2).
Bishop (1980), Siregar and Sunaryo (1980) and Kusuma and Nafi (1986) stated that
Tertiary sedimentation in both the Barito and Asem Asem Basins was completed as a single
major transgressive-regressive cycle, interrupted only by minor local sub-cycles and
variations. The transgressive nature of the Eocene Tanjung Formation, which blankets the
basement and has a fairly low relief, was deposited in a shallow marine to deltaic
environment and comprises a sequence of coarse clastic rocks interbedded with shale and
rare coal beds. The marine influence increased throughout the Oligocene and into Early
Miocene time, resulting in deposition of the extensive limestone and marl deposits of the
Berai Formation.
The centre of the Barito and Asem Asem Basins subsided rapidly, whereas both the continental core (to the west) and the proto-Meratus High (in the east) were uplifted. The strata belong to the Warukin and Dahor Formations, which represent paralic and deltaic sequences, on the highs.
Orogenic activity in the Plio-Pleistocene resulted in a strong westward movement of the
Meratus High, which folded and thrust the basinfill into a series of tight anticlines that were, in part, controlled by basement features (Siregar and Sunaryo, 1980).
P.T. Arutmin Indonesia (1986) recognised three units in the Tanjung Formation. The oldest unit comprises basal sandstone, pebble conglomerate, beds of massive red claystone and mudstone and coarse- to medium-grained quartz-lithic sandstone with large scale cross- 21 bedding. The second unit, referred to as the Eocene coal measures, contains coal seams interbedded with laminated sequences of fine-grained sandstone, siltstone and shale. The unit generally fines upward and grades into the overlying unit. The third unit is a marine
Eocene unit of marl, mudstone and clayey sandstone with minor thin limestone beds towards the top.
The overlying Berai Formation (Oligocene to Early Miocene age) consists of a thick sequence of limestone, marl and fine-grained clastic strata. It is a time equivalent unit of the Pemaluan Formation in the Kutei Basin. The Berai Formation comprises claystone, marl and thin limestone beds. The distinction between the two formations is based largely on facies and lithological differences (Rustandi et al, 1984).
The overlaying marine Berai (limestone and marl) was succeeded by the Warukin
Formation (Middle Miocene) which was deposited during a regressive phase of the Tertiary transgressive-regressive cycle. This unit comprises soft, fine-grained clastic rocks with siltstone, sandstone and brown coal seams up to 40 metres thick.
The Dahor Formation (Pliocene to Pleistocene) consists of poorly-consolidated sandstone and minor fine-grained clastic sequences with brown coal seams. Quaternary deposits include alluvium, estuarine muds and coastal sands.
2.3 SUMMARY
Tertiary rifting and crustal extension in the Makassar Strait had an important effect on the development of the Tarakan, Kutei, Barito and Asem Asem Basins along the east coast of
Kalimantan. The four basins have similar depositional and structural histories. The basins began to develop during an Eocene transgression which was part of the major transgressive- 22 regressive cycle, which in turn consisted of many smaller transgressions and regressions, that affected sedimentary basins throughout Southeast Asia during the Tertiary. The marine transgression reached a peak in the Late Oligocene in the western part of the Kutei Basin and in the early Middle Miocene in the eastern part of the basin.
The sedimentary rocks are predominantly of clastic origin with some carbonate deposition
(particularly in the Barito and Tarakan Basins). Tectonic uplift of the Kuching High during the Late Oligocene resulted in deposition of regressive deltaic sequences infilling the Kutei and Tarakan Basins. These were accompanied by a west to east shoreline migration of the main depositional centres.
The Meratus Mountains were uplifted during the Late Miocene and from that time contributed clastic sediment to the Barito and Asem Asem Basins. Carbonate strata were best developed on more stable areas in the south, particularly in the Barito Basin and on the Paternoster Platform.
23
CHAPTER THREE
COAL OCCURRENCES AND CHEMICAL ANALYSES
3.1 GENERAL
Although coal-bearing sequences are present in a wide range of Indonesian basins (Figure
3.1) ranging from Permo-Carboniferous through to Tertiary in age (Van Bemmelen, 1949;
Koesoemadinata, 1978; Johannas, 1983; Katili, 1983), only the Tertiary coals are of economic importance. Mesozoic coal deposits are normally less than one metre thick and have been reported in Sulawesi and Irian Jaya (Panggabean, pers. comm.; Surono, pers. comm.). Permo-Carboniferous deposits are not well documented and are unlikely to be investigated further in the short to medium term. Of the Tertiary coals, minor coal resources, generally less than 10 million tonnes, are found in Java, Sulawesi, Mollacass and
Irian Jaya. Significant economic coal deposits occur only in the Tertiary basins of
Sumatera and eastern Kalimantan.
Koesoemadinata et al. (1978), Sigit (1981) and Strauss (1988) recognised, based on age and quality, two main'groups of economic Tertiary Indonesian coal deposits: Paleogene (Eocene and Oligocene) and Neogene (Miocene, Pliocene and Pleistocene) coals. However, it is the
Eocene and Miocene coals, both in eastern Kalimantan and for Indonesia as a whole, which have the greatest potential for development.
The Eocene coals were deposited in environments which bear little relationship to the present geography, whereas the formation of Miocene coals was controlled by drainage patterns which were comparable to the present patterns. Thus, Eocene and Miocene coals 24 show some differences in coal geometry and quality including both chemical and physic characteristics.
The distribution of coal deposits in eastern Kalimantan is shown in Figure 3.2. Eocene coals are well developed in southeastern Kalimantan whereas Miocene and Pliocene coals are found along most of the eastern coastal region of the island.
Generally for both Miocene and Eocene coals, seams occur both in narrow steeply-dipping anticlinal and fault zones and in intervening syncline areas with shallow dips. No major structural dislocations are recognised within the coal deposits. However, some of the seams
(for example, Senakin, Sangatta and Mahakam coals) have splits, wash-outs, wedge-outs or discontinuities. Splitting probably resulted from channel activity associated with peat accumulation whereas discontinuities may have been caused by rapid lateral lithofacies changes. Local thickening of seams is observed in some coalfields due to seam wash outs. Variations in seam thickness are also associated with fold axes or faults, probably reflecting differential subsidence of the basement during peat deposition.
Because of the low rank and the elevation at which the coals crop out, some of the seams
(for example, Berau coals) have been burned or weathered. Little is left of the burned coal except at some locations where small stringers are still present. The effects of surface weathering are normally confined to changes in the moisture content, fluidity and surface properties, and a decrease in particle size and total sulphur content.
3.2 DEPOSITION OF COAL
In relation to coal deposition, Koesoemadinata and Pulunggono (1974), Koesoemadinata
(1978), and Koesoemadinata et al. (1978) noted that the most important sedimentary basins 25 in Indonesia are Paleogene intramontane and continental margin (or possibly retro-arc) basins, Neogene back-deep (retro-arc) basins and Neogene deltaic and continental margin basins. Using the above classification, coal deposits along the eastern coastal region of
Kalimantan occur in continental margin basins ranging from retro-arc basins, to the foreland basins (for example, Barito Basin) to passive continental margin basins adjoining rifts where the sequences were deposited in fluviatile to deltaic environments (such as Kutei and
Tarakan Basins)..
As for most other Indonesian coals, coal from eastern Kalimantan is autochthonous in origin as indicated by the occurrence of seat earths, plant root traces and low ash contents.
In addition, the floors of the seams are mostly shale and mudstone with gradational contacts into the coal. In some localities, for example, in the Berau and Asem Asem
Coalfields, root traces extend from the coal to several centimetres below it.
3.2.1 Barito and Asem Asem Basins
In the Barito and Asem Asem Basins, coal measures sequences occur in the Eocene
Tanjung Formation and in the Miocene-Pliocene Warukin Formation. The coal-bearing sequences, which have a total thickness of approximately 615 m (Siregar, 1975; P.T.
Arutmin Indonesia, 1986), consist predominantly of shale, mudstone, sandstone and limestone. The thickness of the seams ranges from 4 m to 9 m with an average of 5.9 m.
Dips range from 5° to 15° at outcrop.
Koesoemadinata et al (1978) stated that the Eocene coals in the Tanjung Formation were formed in intramontane basins as were other Paleogene coals in Indonesian basins (for example, Ombilin Coalfield in West Sumatera and Bayah Coalfield in West Java). More recently, Panggabean (1991) suggested that the Eocene coals in the Tanjung Formation were deposited in low-lying back swamps adjacent to a meandering river system (for the lower 26 seam) and in low-lying swamps and marshes associated with filled interdistributary bay sequences in a lower delta plain setting (for the upper seam).
The seams have been well documented in the Senakin, Sepapah, Sangsang and Satui areas, where, in some places, the seams have up to 8 splits separated by sandstone, siltstone and mudstone lenses (Figure 3.3). Splitting may have resulted from channel activity associated with peat accumulation.
Compared with the Senakin, Sepapah and Sangsang coals, the Satui coals contain fewer clay bands or partings.
The Miocene-Pliocene coals of the Warukin Formation have been well documented in the
Sarongga and Asem Asem areas. The thickness of the seams ranges from 1 m to 40 m.
These coals were probably deposited as raised swamps (Koesoemadinata et al, 1978; Land and Jones, 1987). Siregar (1975) argued that the area where coal was deposited was generally flat or gently rolling grassland although it is likely that grassland environments would be too dry for peat development. Exposures of the Miocene coals cropping out along the Asem Asem River indicate that it is a clean coal with only a few dirt bands thus supporting a raised swamp hypothesis for peat development.
Coal-bearing sequences in the Pasir area are in the basal Tanjung Formation (Eocene) and
Warukin Formation (Middle Miocene) of Asem Asem Basin. Tertiary units in this area have greater affinity with those in the Barito Basin than to those in the more northern
Kutei Basin. P.T. Utah Indonesia (1984a; 1984b; 1984c) identified four seams within a narrow 40 km belt at the northern end of the Meratus Mountains. Economic interest, however, is confined to the Kendilo seam which, geographically, occurs in three areas known as the Bindu, Betitit and Petangis deposits. Average thickness of the Kendilo seam 27 is 6.9 m at Bindu, 5.7 m at Betitit and 4.4 m at Petangis. The seam dips to the east at 10° to 25° (typically 14°). Significant faulting controls the coal seam geometry and may have controlled deposition of the peat prior to coalification.
Economic Miocene coal deposits in the Tanjung area are contained in the Warukin
Formation which is a sequence 400 m to 450 m thick comprising sandstone, siltstone, claystone and coal. Up to 11 seams have been identified in three prospective areas,
Tutupan, Wara and Paringin. The thickness of the seams varies between 2 m and 10 m with dips off the Meratus Mountains of approximately 30° towards the west. Thin Eocene seams (typically <1 metre thick) are also present in this area.
3.2.2 Kutei Basin
Seams in the Kutei Basin occur in the Early Miocene Pemaluan and Pulubalang Formations and the Miocene-Pliocene Balikpapan and Kampungbaru Formations. These coal-bearing sequences have been folded into north-northeast trending anticlines and synclines. The
Mahakam coal deposits are located in the Semalis, Busang and Gitas anticlinal zones, south of the Mahakam River. A schematic representation of the seams in the Mahakam area is shown in Figure 3.4. The thicknesses of the seams vary from a few centimetres to 3.7 m with dips ranging from 5° to 20°, but as can be seen in Figure 3.4, there are 30 to 40 seams, more than 0.5 metre thick, per kilometre of section.
The seams change rapidly across the axes of anticlines and synclines. Seam thinning occurs near the anticlines with erosional features being more pronounced closer to the axes, and hence, nearer the subcrop. Significantly thicker seams are developed in the synclinal areas. These features suggest that the deformation of the Tertiary sequence was penecontemporaneous with coal formation. 28
Coal deposits in the Sangatta area occur in the Miocene Pulubalang and Balikpapan
Formations. The prospective seams are concentrated in the Pinang Dome area which has been postulated as being of diapiric mudstone origin (Samuel and Muchsin, 1975; Rose and
Hartono, 1978). Synclinal structures exhibit a gentle plunge of approximately 6° and faults probably controlled the deposition of coal (Samuel and Muchsin, 1975; Koesoemadinata et al, 1978; Land and Jones, 1987).
In the Sangatta area, there are four main seams, namely the Prima, Sangatta, Pinang and
Kedapat seams (Figure 3.5). They show lateral variations in thickness with the Sangatta seam being the most persistent and recognisable seam. The thicknesses of the seams vary from 2.5 m to 9.4 m (average of 5.5 m) with dips of 5° to 16°. Slumping appears to have affected the seams locally, as shown by brecciation of the seam and incorporation of the enclosing sediment. In some places, thinner seams (<3 m) commonly thin laterally and grade into carbonaceous mudstone or shaly coal equivalents. Local tectonic activity may have affected the coal rank (see Chapter 4).
3.2.3 Tarakan Basin
The coal measures of the Tarakan Basin occur in the Berau Formation which contains at least 19 seams (Figure 3.6). The thicknesses of the seams range from a few centimetres up to 4.5 m with dips of 5° to 20°. Exposure of the seams is good and they can be traced in three geographic areas which correspond to structural zones formed by post-Miocene folding - Kelai, Lati and Binungan.
Most of the seams were deposited over sandstone which grades downwards into marine mudstone or siltstone. The seams are commonly overlain by burrowed or bioturbated mudstone which marks a transgressive marine sequence that terminated the coal swamps.
In some cases, the top of the coal contains sand-filled burrows but sandstone does not 29 overlie the coal. These features possibly indicate that the Berau Formation represents subsiding delta lobes and lagoonal deposits.
Numerous authors (for example, Samuel and Muchsin, 1975; Allen et al, 1976; Achmad and Samuel, 1984; Akuanbatin et al, 1984) argued that the deposition of seams in the
Kutei and Tarakan Basins took place in a terrestrial delta-plain, shifting over time, towards the east as a result of progradation. The distribution of peat, therefore, does not correspond to a time-equivalent interval, as been suggested for the back-deep basins of Sumatera, although the coal seams are generally positioned at the same stratigraphic level.
3.3 COAL AND PEAT RESOURCES
3.3.1 Coal Resources
Since 1981 extensive coal exploration had been conducted along the eastern coastal region of Kalimantan. According to Perum Tambang Batubara (1987) and Strauss (1988) drilling in this area totalled 3,546 holes which penetrated approximately 272,631 m, comprising:
- 62 holes totalling 7,037 m in Berau;
- 728 holes totalling 54,467 m in Sangatta;
- 436 holes totalling 19,867 m in Satui, Senakin and Asem Asem;
- 780 holes totalling 64,260 m in Pasir;
- 220 holes totalling 17,500 m in Tanjung; and
- 1320 holes totalling 109,000 m in Mahakam.
As a result of these extensive exploration activities, several areas with large inferred resources were delineated and these now contribute significantly to the measured and indicated resources and reserves available for use.
The United States Bureau of Mines and the United States Geological Survey classification 30 system (USGS, 1976) is followed when classifying coal resources in eastern Kalimantan.
According to this system, resources are related only to coal that is known to be useable under the technical and economic conditions prevailing at the time the assessment is made.
Thus, coal deposits that are either too deep, too thin or in which the quality is too poor to be worked on an economic basis at the present time, are not included in the calculations.
Clay partings less than 10 cm thick, however, are included because they are not separated out during the mining.
Present total resources of coal in eastern Kalimantan are 8.94 billion tonnes (Table 3.1,
Figure 3.7) which is approximately 24.6% of the total Indonesian coal resources (see Table
3.2; Sahminan et al, 1988; Busono, 1990; Perum Tambang Batubara, 1990; Soelistijo,
1990; Directorate of Coal, 1993). These resources can be classified into 1.98 billion tonnes measured, 5.00 billion tonnes indicated (including inferred) and 1.96 billion tonnes hypothetical (22.18%, 55.94% and 21.88% of the total for Kalimantan respectively). The above figures are expected to be confirmed at relatively higher levels of confidence after current exploration activities have been carried out by both overseas contractors and national private companies.
Comparing one basin to another, the highest coal resources occur in the Barito and Asem
Asem Basins (53.76% of the total Kalimantan resources) followed by the Kutei Basin
(42.12%) and the Tarakan Basin (4.12%). The low figure reported for the Tarakan Basin does not take into account deep seams. As noted in the previous chapter, additional deep seams have been discovered in many areas in the Tarakan Basin by oil companies during their exploration activities (Pertamina U.E.P., 1976; 1981) but given the present resources of Kalimantan there is little incentive to investigate these further. 31
3.3.2 Peat Resources
Peat deposits are also known to occur in lowland geographical environment of Indonesia with resources of approximately 16.1 million hectares. These are concentrated mostly in eastern and central Kalimantan (39% of the total), eastern Sumatera (60%) and Irian Jaya
(1%; Figure 3.1; Van De Meene, 1982; Busono, 1990). The thickness of the peat is normally more than 1 m; up to 16 m have been identified by Van De Meene (1982) in
Sumatera.
Peat has calorific values of approximately 10 MJ/kg and moisture contents of 90% to 94%.
Indonesian peat deposits represents approximately 8% of worldwide peat resources (which cover to approximately 200 million hectares). Of the tropical countries Indonesia has the largest peat resources (50%) followed by Venezuela (9%) and Malaysia (7.5%).
3.4 CHEMICAL ANALYSES
Chemical analyses will probably remain the most widely-used industry standard for comparing Indonesian coals for quite some time in the future as organic petrography is only now being introduced for coal analyses. For most practical purposes, three types of analyses are normally undertaken - proximate, ultimate and miscellaneous analyses.
Proximate analyses provide details of volatile matter, fixed carbon, ash and moisture content. Included in ultimate analyses are hydrogen, carbon, oxygen, nitrogen and sulphur values. Included" in miscellaneous analyses are calorific value, free swelling index and
Hardgrove Grindability Index (HGI)
Over 99% of the organic portion of the coal consists of hydrogen, carbon, oxygen, nitrogen and sulphur. With the exception of nitrogen, these elements are also found in many of the 32 mineral species which occur in coals, such as clay minerals, carbonates and sulphides.
Hydrogen and oxygen are the constituents of water which is found either as inherent moisture or free pore water.
Carbon, hydrogen and oxygen are of great importance when assessing the coking, gasification and liquefaction properties of coals whereas nitrogen and sulphur represent possible sources of pollution where coal is used for combustion.
Fixed carbon content is used as an index of the yield of coke expected from a coal on carbonisation, or as a measure of the solid combustible material that remains after the volatile fraction has been liberated.
3.4.1 Chemical Data for Eastern Kalimantan Coals
Table 3.3 shows typical chemical analyses of coals from eastern Kalimantan that have been collected from various reports and publications. Both Eocene and Miocene coals show some variation with respect to several chemical properties. In many cases the variations between various coals of Miocene age and Miocene versus Eocene age appear to be a function of rank differences between the Miocene and Eocene coals. In turn, rank is partly influenced by age and stratigraphic position and partly by regional rank variation (Chapter
4).
The most striking feature of the chemical data is some apparently anomalous values for the
Miocene Sangatta coal which diverge markedly from the other Miocene coals. For example, the range of fixed carbon values for Miocene coals generally range between
30.9% and 42.0% for most but for the Sangatta coals, the range is 47.0% to 54.0% (Table
3.3). The calorific values are also anomalous in that the Sangatta values range from 6800 to 7650 kcal/kg (average of 7100 kcal/kg) whereas for other Miocene coals, the values 33 range between 4344 and 6600 kcal/kg. Both of the above values from Sangatta reflect the higher rank of these coals compared to the other Miocene coals. The increase in rank is a function of the increased geothermal gradients caused by local hidden intrusions.
Although not shown in the chemical data, petrographic data (Chapter 4) show that close to the intrusions the rank increases markedly to semi-anthracite rank and it decreases away from the intrusions. Although chemical data are not available for a suite of such samples, there is little doubt that the above petrographic observations would be confirmed by chemical data.
In the following analysis of the chemical data, the Sangatta data are not included unless comment is warranted.
Specific energy is given as the gross calorific value, calculated on dry ash free basis (dafb).
Most of the eastern Kalimantan coals have relatively high specific energy although there are distinct differences in the chemical compositions of Eocene coals compared to Miocene coals. The average calorific values for Miocene coals range from 4680 kcal/kg (Asem
Asem coal) to 6350 kcal/kg (Mahakam coal), whereas for the Eocene coals, the values range between 6300 kcal/kg (Senakin coal) and 6800 kcal/kg (Satui coal). The range of variation in calorific values for Miocene coals (2420 kcal/kg) is much wider than the range for Eocene coals (500 kcal/kg) indicating that Eocene coals have a small range of coal rank. The wider- range in the variation is related to the wider range in the rank of the
Miocene coals. For example, Asem Asem coal has a rank of soft brown coal, based on fixed carbon, and a mean calorific value of 4680 kcal/kg whereas the mean calorific values of other Miocene coals ranges between 5830 and 6350 which correspond to higher ranks.
Average inherent moisture is much lower for the Eocene coals, where the range is between
3.5% (Senakin coal) to 7.0% (Satui coal), than for Miocene coals which show a wide 34 range, that is, 11.0% (Mahakam coal) to 27.7% (Asem Asem coal). These data suggest that inherent moisture is rank dependent.
Figure 3.8 shows, a positive correlation between calorific value and inherent moisture for eastern Kalimantan coals. The Eocene Pasir and Senakin coals plot well below the line of best fit. Both have fixed carbon values below that of other Eocene coals and this suggests that the coals have lower ranks than the other Eocene coals, thus accounting for the higher inherent moisture.
The fixed carbon and volatile matter contents of the Miocene coals are significantly different to those of the Eocene coals (Table 3.3). For Miocene coals, average fixed carbon ranges from 31.1% (Asem Asem coal, indicating that this is the coal with the lowest rank) to 44.0% (Mahakam coal), whereas for Eocene coals the average values are between 39.7% (Senakin coal) and 42.8% (Satui coal). Fixed carbon and volatile matter normally show an inverse relationship with each other since, as the rank of the coal increases, the fixed carbon content becomes higher. The Eocene Satui and Senakin coals
(Table 3.3) have lower fixed carbon values than expected from the rank of the coals as indicated by vitrinite reflectance.
Average volatile contents for Eocene coals range from 40.4% (Tanjung coal) to 41.5%
(Satui coal) whereas the average values for Miocene coals range from 37.6% (Asem Asem coal) to 40.0% (Mahakam coal). Figure 3.9 gives the relationship between calorific value and volatile matter and shows that the Eocene coals and Miocene Sangatta coal typically have higher calorific values than other Miocene coals and fall below the line of best fit.
Eocene coals exhibit quite variable volatile contents with the lower rank coals (lower fixed carbon contents) having lower volatile contents. One possible explanation could be variation in coal type where the coals with high volatile contents contain higher liptinite 35 contents derived from lipid-rich floral material. This hypothesis cannot be tested as the samples taken for organic petrography do not correspond with the samples on which the chemical analyses were made.
The relationship between volatile matter and inherent moisture in Figure 3.10 shows that for Eocene coals volatile matter increases approximately 1% for each 1% to 2% increase in inherent moisture. On the other hand, for the Miocene coals, volatile matter increases approximately 1% for each 5% to 12% decrease in moisture content.
Average ash content of Eocene coals ranges from 8% to 15% (typically 10%) and this is much higher than average ash contents of the Miocene coals which range between 4% and
7% (typically 5%). Ash contents of selected Sangatta and Tanjung (Miocene) coals are typically less than 2.0% which is thought to be the lowest ash content for any eastern
Kalimantan coal. The high ash content in the Eocene Senakin and Pasir coals is attributed to the presence of significant clay partings included in the samples.
In general, Eocene coals have higher sulphur contents, with values up to 3% in Pasir coals, than Miocene coals. The Berau coal is an exception and has an average of 1.3% sulphur with some samples having a sulphur content up to 9.9%, particularly in the upper part of the seam.
Table 3.4 summarises ultimate analyses data for the eastern Kalimantan coals. There is a slight variation in values between Miocene and Eocene coals. For example, carbon (C) content of Eocene coals (78.4% to 80.4%) is slightly higher than Miocene coals (71.3% to
79.5%) and corresponding oxygen values are lower. The relatively high carbon and low oxygen in Eocene coals are a function of rank. 36
For the higher rank Sangatta coals, the carbon content is 3.7% to 8.2% higher than for other Miocene coals and therefore these values are comparable to, or higher than, those of the Eocene coals, clearly showing the influence of rank.
Hydrogen content of Miocene coals (4.5% to 5.7%) is lower than for Eocene coals (5.9% to 6.1%). Variations in the hydrogen content are probably related to variations in the liptinite content of the tested samples because hydrogen is known to be closely related to volatile material (van Krevelen, 1981) which in turn is related to liptinite content. This is shown in Figure 3.11 where the volatile content is linearly related to H/C ratio. Van
Krevelen (1981) noted that coals having the same H/C value normally have the same basic structure and distribution of hydrogen in the structural unit.
Ratios of H/C and O/C for selected eastern Kalimantan coals are plotted on the van
Krevelen diagram (Figure 3.12). Asem Asem coals have the lowest H/C ratio and the highest O/C ratio. These coals have the lowest rank.
Nitrogen does not show significant variations (Table 3.4) with the average values for
Eocene coals only slightly higher (1.2% to 1.8%) than those for the Miocene coals (0.7%% to 1.6%). Saxby and Shiboaka (1986) noted that nitrogen is concentrated with progressive coalification. The data for eastern Kalimantan coals supports that observation.
3.4.2 Comparison Between Eastern Kalimantan and Other Coals
Although data for most Indonesian coal deposits are presented in Table 3.5, it is the data from Sumatera that should be compared to data for coals from eastern Kalimantan. Coals from Sumatera (especially Bukit Asam and Ombilin) are extensively used for the domestic scene and future development of facilities in the near term, such as electricity generating plants and new cement plants, will be similar to those operating now, or modified slightly 37 to take advantage of new technology.
Unlike for Eocene coals, chemical data for Miocene coals from eastern Kalimantan are remarkably consistent with that for Miocene coals from Sumatera (Table 3.5), excluding the coals from Bukit Asam (South Sumatera) which have been altered to semi-anthracite and anthracite rank by igneous intrusions (Daulay, 1985). Ash content of Eocene coals from eastern Kalimantan is relatively higher than that of Eocene coal from Ombilin (4.1% to 7.1%) but it is comparable to ash content of Eocene coals from Bayah, West Java.
Eocene coals from eastern Kalimantan are also slightly harder than other Eocene coals from elsewhere in Indonesia.
The data clearly show that the chemical properties of eastern Kalimantan coals are similar to the chemical properties of coals from Sumatera. Thus coals from eastern Kalimantan can compete with, substitute for or be used in conjunction with the coals from Sumatera.
Table 3.6 gives typically chemical analyses of subbituminous and bituminous coals from several countries. Data for coals from Australia, South Africa and India are added for completeness as these coals are generally bituminous coals and are less likely to compete for the same markets as the Indonesian coals unless as steaming coals. In this case,
Indonesian coals are unlikely to be at a disadvantage, as outlined in Chapter 7.
In general, calorific values of eastern Kalimantan coals are comparable with the values for coals from coals from Australia, South Africa, India, New Zealand and Japan. However, calorific values for eastern Kalimantan coals are higher than those of coals from Malaysia,
Spain and China.
The ash yield of eastern Kalimantan coals is similar to that of New Zealand and Australian 38
coals but is much lower than those for many other coals.
3.5 HARDGROVE GRINDABILITY INDEX (HGI)
It is likely that the use of pulverised coal will increase significantly as Indonesia builds
new electricity generating plants as most will use pulverised coal because this has been
found to be the best feedstock for coal-fired electricity generation. To select the best coal
for pulverising, the behaviour of the coal during grinding and the subsequent particle
characteristics need to be known. The effectiveness of a pulveriser to comminute coal is
influenced by many factors including the size of the coal feed, moisture content, the degree
to which the grinding elements are worn and the grain size of the final product. The
Hardgrove Grindability Index (HGI) which measures several properties including hardness,
strength, tenacity and fracture, is the most frequently-used test in the combustion industry
for measuring the mechanical strength and milling behaviour of a coal.
Although HGI data are available for eastern Kalimantan coals in unpublished reports, it
cannot be related to the samples used for this study. Therefore, the HGI of ten samples
from the group analysed by organic petrography was measured by SGS Australia Pty Ltd
in their Wollongong laboratory in accordance with the Australian standard AS 1038, Part
20. The SGS data (Table 3.7) were interpreted and compared with data from Sahminan et al. (1988) and .Perum Tambang Batubara (1990).
The average HGI value of eastern Kalimantan coals ranges from 34 to 58 showing that the coals fall into three categories:
very hard (<40) - Eocene Pasir, Satui and Senakin coals hard (40-55) - Eocene Tanjung coal, Miocene Berau, Mahakam, Sangatta and 39
Tanjung coals medium (>55) - Miocene Asem Asem coal.
It should be noted that some values in the range of HGIs for all coals in the very hard and medium categories overlap the hard category range.
The average HGI of Eocene coals varies from 34 to 40 whereas for the Miocene coals, the
HGI ranges between 46 and 58 suggesting that on average the Eocene coals are harder than the Miocene coals and would give a larger mean particle size for any given level of grinding.
The HGI values of Miocene coals from eastern Kalimantan are generally identical with values for other Miocene coals in Indonesia. However, the HGI values for the Eocene coals are typically lower (that is, the coals are tougher) than for other Indonesian Eocene coals.
3.6 SUMMARY AND CONCLUSIONS
Most of the economic coal deposits eastern Kalimantan were deposited along the continental margin in retro-arc basin settings, close to the foreland, or passive margin basins adjoining rifts. The environment of deposition for the coal measures sequences ranged from fluvial to deltaic.
The seam thicknesses vary from a few centimetres to 40 m and dips are mostly 5° to 20°.
Typically, Miocene seams are thicker than Eocene seams.
Chemical analyses show that the rank varies from soft brown coal to high volatile 40 bituminous with Eocene coals having slightly higher ranks than the Miocene coals.
Compared to the Eocene coals the Miocene coals, with the exception of those in the
Sangatta area, typically have lower ash, sulphur and calorific values which reflect the differences in rank.
The rank of Miocene Sangatta coal is much higher than that of other Miocene coals in eastern Kalimantan or Indonesian coals in general. This increased rank was caused by higher geothermal gradients and heat flows in the Sangatta area, compared to other areas, because of the influence of intrusions. Therefore, Miocene Sangatta coals have higher fixed carbon and calorific values than other eastern Kalimantan Miocene coals; such values that commensurate with their higher rank.
On an Indonesia-wide comparison, the coal resources of eastern Kalimantan are second only to those of Sumatera, which are almost entirely restricted to the Bukit Asam and Ombilin
Coalfields. 41
CHAPTER FOUR COAL PETROLOGY
4.1 GENERAL
Penological variation in coal can be considered in terms of two independent concepts - coal type and coal rank. Coal petrology is the study of the composition and technological behaviour of organic matter in coals, oil shales and other organic-rich rocks and is therefore essentially, the study of the above two concepts. The petrology, or more specifically, the petrography of coal can be assessed in terms of macerals (Stopes, 1935), microlithotypes
(Seyler, 1954) and/or lithotypes (Stopes, 1919; Seyler, 1954). The term maceral was originally introduced to distinguish organic from inorganic constituents in coal and each maceral is predominantly defined by morphology, source of material, colour and reflectivity
(Stopes, 1919; Stach, 1982).
The organic petrology of three hundred and seventy nine coal and clay parting (dirt bands) samples from eastern Kalimantan was examined for this study:
- 61 samples from Berau;
- 100 samples from Sangatta;
- 94 samples from Mahakam;
8 samples from Pasir;
- 10 samples from Tanjung;
- 34 samples from Asem Asem;
- 24 samples from Satui; and
- 48 samples from Senakin. 42
Sampling was based on the Australian Standard AS 1676 (Standards Association of
Australia, 1975).
Samples were prepared as polished particulate coal mounts and analysed using incident white light and fluorescence mode microscopy.
In this study, the coal petrographic terms used follow the Australian Standard AS 2856
(Standards Association of Australia, 1986; Table 4.1). The classification is based on the maceral nomenclature described by the International Committee for Coal Petrology
Handbook (1963; 1971; 1975) as modified by Smith (1981) and Standards Association of
Australia (1986). This system provides a better method for discriminating vitrinite macerals in coals from eastern Kalimantan than other systems in that it avoids using the rank- sensitive terms of huminite for material which has a reflectance less than 0.5%, and vitrinite, for macerals of similar origin but with a reflectance of greater than 0.5%. As will be discussed later, the rank of samples from the same seam in at least one basin in eastern
Kalimantan ranges from approximately soft brown coal to medium-low volatile bituminous coal.
Normally, point-counts of approximately 500 points, "on coal", for each block were taken.
Traverses were made perpendicular to the gravitational settling direction during mounting of the polished blocks. Step distance and traverse spacing were altered in relation to the grain size of the sample in order to obtain representative counts with approximately 90% of the area of each block covered during the point count; counts were only completed after a full traverse.
Microlithotype estimation was carried out for each coal sample and the classification follows the terminology given by Stach et al (1982). 43
In general discussions where specific maceral percentages are not required, the following maceral abundance categories used for macerals and microlithotypes are: dominant - >40.0% major - >10.0% to 40.0% abundant - >2.0% to 10.0% common - >0.5% to 2.0% sparse - 0.1% to 0.5% rare - <0.1% absent - 0%.
Vitrinite reflectance measurements were taken using a Leitz Ortholux microscope fitted with a Leitz MPV-I microphotometer. All measurements were carried out using plane polarised light of 546 nm wavelength in oil immersion with a refractive index of 1.518 at a temperature of 23 + 1°C. The microphotometer was calibrated against synthetic garnet standards (YAG 0.917% and GGG 1.726% reflectances) and a synthetic spinel standard
(0.413% reflectance).
The measurement of maximum reflectance of vitrinite follows the Australian Standard AS
2486 (Standards Association of Australia, 1989). The stage of the microscope was rotated to obtain the first maximum reading and then rotated through approximately 180° for the second maximum reading. Each pair of readings was averaged and the mean calculated to give mean maximum vitrinite reflectance in oil immersion (P^max). Readings were rejected if the pair of readings obtained were not within 5% relative of each other.
ICCP (1971; 1975) and Stach et al (1982) recommended that one hundred measurements should be taken to obtain the mean value. Determination of P^max standard deviations for a number of coals, obtained by varying the number of data points from 10 to 100, showed 44
that the standard error of the mean approaches the precision and accuracy of the
measurements of the standard where as few as twenty readings were taken. Therefore,
using this as a guideline, mostly fifty reflectance readings were taken on the eastern
Kalimantan coal and shaly coal samples to obtain the mean maximum reflectance.
Vitrinite reflectance measurements were made on telovitrinite, detrovitrinite and gelovitrinite
maceral subgroups with the number of measurements on each vitrinite subgroup based on
the proportion of each subgroup in the sample as determined by point counting. This
method ensures that the readings accurately represent the various populations of the vitrinite
being measured although vitrinite reflectance differences between vitrinite sub-macerals are
not significant. Using this method to determine mean maximum reflectance fits in with the
aims of the study, one of which is to assess the coal type and coal rank variations in
relation to coal utilisation.
4.2 COAL TYPES
Examination of hand specimens shows that coals from eastern Kalimantan are composed
mainly of clarain and vitrain bands. Thick vitrain bands are normally interbedded with
finely-striated bands of clarain (<5.0 mm). However, in some coals such as those from
Berau and Satui, thick clarain layers, up to 20.0 cm, can be identified. Fusain bands are
not common in any of the coals except in several samples from Mahakam, Sangatta and Tanjung (Miocene).
Layers of carbonaceous shale, siltstone and shale (clay partings) commonly alternate with
thick bands of coal, particularly in the Eocene coals of Satui and Senakin. Exsudatinite-
like material commonly occurs in the coal seams, particularly in the Mahakam and Sangatta coals with the thickness of the veins ranging from a few millimetres up to 4.0 cm (Plate 45 la). Microscope examination of the coal associated with this material reveals that the sample is commonly composed of abundant (up to 9.9%) exsudatinite. It has bright green to greenish-yellow fluorescence of high intensity and is mainly associated with vitrinite.
The maceral and mineral matter data for each of the 379 coal and shaly coal samples analysed are listed in Appendix 1. In general, organic petrological examination of eastern
Kalimantan coals (Figure 4.1) shows that all samples contain dominantly vitrinite (61.9% to 98.0%, average of 81.4%), sparse to major liptinite (0.2% to 33.3%, average of 10.1%), rare to major inertinite (<0.1% to 31.3%, average of 3.3%) and sparse to major mineral matter (0.2% to 29.6%, average of 5.2%; Chapter 5). Oil (mainly as oil hazes) is rare in some samples and normally has bright green to greenish-yellow fluorescence.
Volumetric percentages of maceral groups were converted to a mineral matter free basis
(mmfb) and these values are plotted on Figure 4.2. Figure 4.3 summaries the proportions of macerals and mineral matter in graphical form. Mean volumetric percentages and ranges of maceral contents and mineral matter for each coalfield are shown in Table 4.2 and
Figure 4.4.
Volumetric percentages of telovitrinite, detrovitrinite and gelovitrinite are shown in Figure
4.5, and Figure 4.6 shows the mean telovitrinite, detrovitrinite and gelovitrinite contents from each of the coalfields. The major variations in sub-maceral composition are significant only for telovitrinite and detrovitrinite (Section 4.4).
Clarke and vitrite are the major microlithotypes (Table 4.3) with minor duroclarite, vitrinertite (both vitrinite- and inertinite-rich microlithotypes) and inertite in some coal samples. 46
4.2.1 Miocene Coals Petrographically, Miocene coals are composed mainly of vitrinite with substantial liptinite and inertinite (see Appendix 1, Table 4.2, Figures 4.2, 4.3 and 4.4). Uncommon coal types are present in some of the Mahakam coals (for example, GM 23712 and GM 24403) and these contain anomalously high percentages of inertinite (31.3% and 18.3% respectively).
Mineral matter (mainly clay minerals, quartz, pyrite and carbonate; Chapter 5) is sparse to major; oil is rare in most coals.
Vitrite and clarite are the dominant microlithotypes with subordinate vitrinertite (both vitrinite- and inertinite-rich microlithotypes), duroclarite and inertite (Table 4.3). In some of the Mahakam, Tanjung and Sangatta coals vitrite and vitrinertite are dominant.
Vitrinite Vitrinite is dominant in all Miocene coals, ranging from 63.5% to 98.0% (average of
82.9%). The exception to this are several thermally-altered Sangatta coals where the average content is 95.0% (93.9% to 95.8%). The high vitrinite content in the latter coals probably is due to their high rank and therefore the identification of other macerals
(inertinite and especially liptinite) is difficult. Vitrinite mostly occurs as telovitrinite and detrovitrinite with gelovitrinite a minor component (Tables 4.2 and 4.4, Figures 4.5 and
4.6).
Telovitrinite, ranging from 0.04 mm to 0.20 mm in thickness, is major to dominant (16.6% to 85.6%, average of 42.4%) and consists predominantly of textinite, texto-ulminite, eu- ulminite and lesser telocollinite. Thin layers of telovitrinite are generally surrounded by a thick detrovitrinite groundmass (Plate lb) but some telovitrinite bands are interbedded with detrovitrinite. 47
Detrovitrinite is major to dominant (10.2% to 60.3%, average of 36.1%) in all Miocene coals and is commonly associated with liptinite. Attrinite and densinite are the most common detrovitrinite macerals with desmocollinite a minor component. Sparse to abundant gelovitrinite (0.1% to 9.9%, average of 4.4%) is disseminated throughout the telovitrinite and detrovitrinite with porigelinite occurring as thin bands within telovitrinite.
Inertinite
Inertinite is rare to major (<0.1% to 31.3%, average of 4.2%) in all Miocene coals and comprises predominantly semifusinite, inertodetrinite and sclerotinite (Tables 4.2 and 4.5,
Figure 4.7). Anomalously-high percentages of inertinite (up to 31.3%), however, occur in some of the Mahakam coals.
Rare to abundant semifusinite (Plate lc, <0.1% to 9.9%, average of 2.2%) is dominant over other inertinite macerals and commonly occurs as layers (up to 1.0 mm in length), lenses or isolated fragments. Semifusinite is generally associated with vitrinite (mainly telovitrinite); in some cases, cell lumen of semifusinite are filled with either resinite
(Section 4.5), fluorinite or mineral matter.
Inertodetrinite is rare to abundant (<0.1% to 7.4%, average of 0.9%) and is commonly associated with vitrinite and semifusinite. Sclerotinite, consisting of unilocular and bilocular teleutospores and sclerotia, is rare to abundant (<0.1% to 2.7%, average of 0.7%) and is generally scattered throughout the sample with local concentrations (Plate Id).
Fusinite, micrinite and macrinite are present in several samples but commonly accounts for less than 1.0% of the bulk coal. These macerals are commonly disseminated throughout the coals with the exception of some micrinite that forms distinct layers within telovitrinite. 48
Liptinite Liptinite averages 9.0% (0.2% to 30.9%) and comprises predominantly resinite, suberinite, liptodetrinite and cutinite with minor sporinite, fluorinite, exsudatinite and Botryococcus- related telalginite (Tables 4.2 and 4.6, Figure 4.8). Resinite is rare to major (<0.1% to
13.5%, average of 2.8%) and has bright greenish-yellow to dull orange fluorescence (Plates
le and If). It occurs as discrete bodies and lenses with some occurring as diffuse cell fillings in telovitrinite, semifusinite and sclerotinite.
Suberinite is rare to major (<0.1% to 13.0%, average of 3.1%) and commonly occurs as
distinct layers (0.05 mm to 0.40 mm thick) with greenish-yellow to orange fluorescence
although in some of the Sangatta coals the fluorescence is very weak brown or absent.
Cell walls of the latter type of suberinite are thinner than the more strongly fluorescing
suberinite. Suberinite commonly occurs in association with corpogelinite, rarely with
resinite and exsudatinite. In some samples (for example, Berau and Asem Asem coals)
suberinite has broken cell structure (Plates lg and lh) which may have occurred during the diagenesis of the peat.
Liptodetrinite is rare to abundant (<0.1% to 5.2%, average of 0.8%) in most samples and mainly occurs in clarite where it has greenish-yellow to orange fluorescence. Large fragments (typically >7 microns diameter) in some of the Berau and Asem Asem coals are included as liptodetrinite maceral because they cannot be assigned to any other liptinite maceral.
Rare to abundant cutinite (<0.1% to 3.8%, average of 0.8%), both crassicutinite (Plates 2a and 2b) and tenuicutinite, commonly occurs in association with vitrinite and resinite but in some cases it is associated with suberinite and exsudatinite. It generally has greenish- yellow to orange fluorescence, although some has very weak brown or no fluorescence, 49 particularly in the Sangatta coals.
Sporinite (including crassispores, pollen and sporangia) is rare to common (<0.1% to 1.8%, average of 0.5%) and has greenish-yellow to orange fluorescence. It commonly occurs in association with detrovitrinite, resinite and suberinite. The distinction between pieces of thick suberinite and sporinite within a single sample is difficult in some cases although the sporinite generally has yellow to orange fluorescence whereas suberinite fluoresces greenish- yellow to yellow.
Rare to abundant exsudatinite (<0.1% to 9.9%, average of 0.8%) occurs in most coals and commonly has bright greenish-yellow to orange fluorescence. It has various shapes and occurrences including infillings in fractures, bedding plane cavities and cell lumens (Section
4.5). Fluorinite is rare to abundant (<0.1% to 2.6%, average of 0.2%) in some coals and typically occurs as isolated bodies and lenses with bright green to greenish-yellow fluorescence of very strong intensity (Plates 2c and 2d).
Rare to sparse Botryococcus-itMtd telalginite (alginite A of Hutton et al, 1980 and Cook et al, 1981) with bright yellow to orange fluorescence is present in a few samples of the
Berau coal. It is commonly disseminated throughout the samples although some concentrations are present. Maximum percentages of the Botryococcus-velated telalginite is 0.4%.
4.2.2 Eocene Coals
As for Miocene coals, Eocene coals are typically rich in vitrinite with abundant liptinite.
Inertinite constitutes only a minor component of the coals except in a few samples where it is abundant (see Appendix 1, Table 4.2, Figures 4.2, 4.3 and 4.4). Mineral matter
(mainly clay minerals, quartz and pyrite) are present in substantial amounts in most coals; 50 oil is a trace component in some samples.
Vitrite and resinite-rich clarite are the dominant microlithotypes whereas duroclarite and vitrinertite (vitrinite-rich) constitute minor microlithotypes (Table 4.3). Trace inertite and liptite microlithotypes are present in some samples, particularly in Satui coals.
Vitrinite
Vitrinite averages 79.4% (61.9% to 93.9%) and occurs mainly as telovitrinite and
detrovitrinite with a minor component of gelovitrinite (Tables 4.2 and 4.4, Figures 4.5 and
4.6). Telovitrinite is major to dominant (20.4% to 69.7%, average of 45.2%) and occurs
as thick bands (up to 0.60 mm) within a detrovitrinite groundmass. Eu-ulminite is the most
prominent component of telovitrinite followed by textinite, telocollinite and rarely texto-
ulminite.
Detrovitrinite (12.9% to 57.5%, average of 30.8%) consists predominantly of densinite and
desmocollinite; attrinite is not a significant component. Gelovitrinite (0.2% to 8.8%,
average of 3.4%), typically occurs as corpogelinite and porigelinite and is mostly
disseminated throughout the coals. Some porigelinite, however, infills cell lumens of
vitrinite.
Inertinite
Sparse to abundant inertinite (0.2% to 6.1%, average of 2.2%) is present in most Eocene
coals and mainly consists of semifusinite, sclerotinite and inertodetrinite (Tables 4.2 and
4.5, Figure 4.7). Semifusinite is rare to abundant (<0.1% to 2.8%, average of 0.8%) and
typically occurs as lenses and thin, isolated layers in telovitrinite. Sclerotinite is rare to
abundant (<0.1% to 3.2%, average of 0.8%) and comprises predominantly teleutospores and sclerotia. In some sclerotinite, the cell lumens arefilled by either resinite (Section 4.5) or 51 mineral matter (Chapter 5).
Inertodetrinite is rare to common in most samples (<0.1% to 1.6%, average of 0.6%) except in one sample (GM 24160 of Senakin coal) where it is abundant (2.2%). It is associated with semifusinite and detrovitrinite.
Fusinite, micrinite and macrinite are rare except in a few samples where fusinite is sparse
(up to 0.2%) and micrinite is common (up to 0.6%). Fusinite and macrinite are normally associated with semifusinite.
Liptinite
Liptinite ranges from common to major (1.4% to 33.3%, average of 11.6%) in all Eocene samples and comprises predominantly resinite, sporinite, suberinite, liptodetrinite and exsudatinite (Tables 4.2 and 4.6, Figure 4.8). Fluorinite and Bofryococcus-related telalginite are minor components.
Resinite averages 4.1% (0.2% to 15.6%) and has yellow to dull orange fluorescence. It typically occurs as isolated bodies which are circular or rod-shaped. Rarely, resinite is present as distinct layers within telovitrinite or infilling cell lumens of telovitrinite, semifusinite or sclerotinite.
Sporinite, comprising mainly miospores and sporangia, is sparse to abundant (0.2% to 7.5%, average of 2.4%) and has yellow to orange fluorescence (Plates 2e and 2f). It commonly is associated with other liptinite macerals, particularly resinite and liptodetrinite.
Suberinite, both thick and thin wall forms, is rare to abundant (<0.1% to 3.9%, average of
1.7%) and has yellow to dull orange or no fluorescence, particularly the thinner variety. 52
Cutinite commonly occurs as tenuicutinite, is rare to abundant «0.1% to 4.3%. average of
1.4%) and has yellow to dud orange or no fluorescence. Non-fluorescing cutinite is very
.Hn and is normally associated with telovitrinite. Rare to abundant liptodetrinite «0.1% to 3.8%. average of 1.0%) is typically found as scattered fine-grained detritus derived from other liptinite macerals; hence its fluorescence colour varies widely from greenish-yellow to orange.
Exsudatinite averages 0.7% «0.1% to 4.2%) in most samples and typically occurs as infilhngs along bedding planes and in transverse fractures/cracks and cell lumens (Section
4.5). It has bright greenish-yellow to orange fluorescence. Fluorinite is rare to common
(average of 0.1%) in these coals and has strong greenish-yellow fluorescence of very strong intensity. It occurs as isolated lenses or globular masses in association with vitrinite and resinite.
Rare to sparse Botryococcus-reMQd telalginite (maximum percentages of 0.4%) is present in Satui, Senakin and Tanjung coals and commonly has very intense yellow to orange fluorescence (Plates 2g and 2h). It is normally disseminated throughout the sample.
Common Botryococcus-rdatQd telalginite is also reported in Eocene coals from Ombilin
(Daulay, 1985; Daulay and Cook, 1988), and coals from Melawi and Ketungau Basins
(Sutjipto, 1991) and North Sumatera Basin (Hadiyanto, 1992). Stach et al. (1982) noted that alginite is not common in humic coals but typically occurs in lacustrine oil shales such as torbanite and lamosite and in sapropelic coals.
4.3 COAL RANK
In this study, vitrinite reflectance measurements were taken on all the 379 coal and shaly 53 coal samples from the various coalfields in eastern Kalimantan. Mean maximum vitrinite reflectance (Rvmax), range, standard deviation and the number of readings for each of the
379 samples are listed in Appendix 2. A summary of mean maximum vitrinite reflectance data for each of the coalfields is presented in Table 4.7. Vitrinite reflectance data support the rank assessment based on volatile matter and calorific value data (Appendix 2 and
Tables 3.3 and 3.4) that the coals range from soft brown coal through to semi-anthracite rank (Rvmax of 0.30% to 2.03%).
Figure 4.9 shows a grouping of coals based on vitrinite reflectance and vitrinite content.
This classification has regional and stratigraphic significance in that it is important in the assessment of utilisation potential for eastern Kalimantan coals (Chapter 6). Based on this classification, coals from eastern Kalimantan can be divided into four main groups (Figures
4.9, 4.10 and 4.11):
Miocene, soft brown to sub-bituminous coals subjected to regional coalification in areas with normal geothermal gradients; Rvmax values of 0.30% to 0.55%;
Miocene, sub-bituminous to low volatile bituminous coals subjected to regional coalification in high geothermal gradients areas (characterised by strongly folded strata); Rvmax values of 0.48% to 0.71%;
Miocene, semi-anthracitic coals affected by contact thermal metamorphism;
Rvmax values of 1.60% to 2.03%; and
Eocene, brown to low volatile bituminous coals subjected to regional coalification in areas with normal geothermal gradients; Rvmax values of
0.43% to 0.66%.
4.3.1 Miocene Coals
Mean maximum vitrinite reflectance values (Rvmax) for Miocene coals and shaly coal samples vary from 0.30% to 2.03% (Table 4.7). These values indicate soft brown coal to 54 semi-anthracite rank. Miocene coals can be divided into three main groups on the basis of rank.
The first group contains coal with a vitrinite reflectance in the range of 0.30% to 0.55%
(average of 0.42%). These coals have been subjected to normal regional coalification only
and are found in the following areas:
- Berau (Rvmax of 0.38% to 0.55%, average of 0.45%);
- Mahakam (^max of 0.38% to 0.55%, average of 0.47%);
- Tanjung (^max of 0.34% to 0.47%, average of 0.40%); and
- Asem Asem (Rvmax of 0.30% to 0.41%, average of 0.36%).
The second group contains coal with vitrinite reflectance ranging from 0.48% to 0.71%
(average of 0.63%). The coal mainly occurs in the Sangatta region where the strata have
been strongly folded. In this area, a marked difference between vitrinite reflectance values
for coal in the lowest seam, compared to those of the uppermost seam, is evident even
though the difference in stratigraphic level is less than 50 metres. Reflectance values for
the lower coal range from 0.58% to 0.71% (average of 0.64%), whereas for the upper
seam, Rvmax varies between 0.48% and 0.52% (average of 0.49%). The significant
difference in vitrinite reflectance is probably related to high geothermal gradients in this
region which are reported to be approximately 40°C/km (Kenyon et al, 1976; Thamrin
1987). A comparison of these coals with those in the second group does not show any
unusual or different maceral types and abundances, thus eliminating any influence of type
on rank.
Herudiyanto (pers. comm.) also observed a high vitrinite reflectance gradient in a deep well
in the Sangatta region. The high rank gradients are presumably associated with high
palaeogeothermal gradients and therefore high heat flow, which in turn, are related to the 55 above average igneous activity in the region.
The third group of coals contains Sangatta coal which has been affected by local thermal metamorphism. The rank of this group spans the low volatile bituminous to semi- anthracite range (P^max of 1.60% to 2.03%, average of 1.87%). The range in vitrinite reflectance for any single sample is very wide (Figure 4.12) compared to the range in samples from the same seam away from the intrusion and therefore, only exposed to normal coalification (Figure 4.13). The intrusion is hidden and has not been identified in outcrop or borehole intersections which were drilled adjacent to the coal seams. Miocene coals also have been affected by igneous intrusions in the Bukit Asam area of South Sumatera Basin and span semi-anthracite to anthracite ranks (Daulay, 1985; Daulay and Cook, 1988).
The average mean maximum vitrinite reflectance values for telovitrinite is slightly higher than that for detrovitrinite and gelovitrinite in most samples. As an example, for all
Mahakam samples measured, the average mean maximum vitrinite reflectance value for telovitrinite is 0.48% (range of 0.40% to 0.55%) whereas for detrovitrinite and gelovitrinite, it is 0.46% (range of 0.37% to 0.54%).
4.3.2 Eocene Coals
The rank of the Eocene coals varies between sub-bituminous and high volatile bituminous
(Table 4.7) with mean vitrinite reflectance ranging from 0.43% to 0.66% (average of
0.57%). The lowest mean vitrinite reflectance value occurs in the Satui coals (0.43% to
0.54%, average of 0.50%) whereas the highest is in the Pasir coals (0.58% to 0.66%, average of 0.62%).
Vitrinite reflectance values for Eocene coals from eastern Kalimantan are similar to the values for Eocene coals from Bone Basin of South Sulawesi (Pujobroto, 1991) but they are slightly lower than values for other Indonesian Eocene coals from areas such as Ombilin- 56
West Sumatera, Bayah-Southwest Java, Melawi, Ketungau or North Sumatera Basins
(Daulay, 1985; Daulay and Cook, 1988; Sutjipto, 1991; Hadiyanto, 1992). The difference
in vitrinite reflectance values between eastern Kalimantan and coals from other regions
probably reflects the thickness of overburden and geothermal gradients in the respective
areas.
Unlike most of the Miocene coals, all Eocene coals in eastern Kalimantan have reached a
similar level of coalification with no evidence of any of the Eocene coals having been
affected by intrusions. Lowest vitrinite reflectance is commonly associated with shaly coals
and clay partings.
Elsewhere in Indonesia, Eocene coals have been affected by igneous intrusions and have
attained semi-anthracite to anthracite rank. Examples are found in the Bayah area of the
Southwest Java Basin (Daulay, 1985), the Bone Basin of South Sulawesi (Pujobroto, 1991)
and the Melawi and Ketungau Basins of West Kalimantan (Sutjipto, 1991). Small
resources of anthracite are also present in Ombilin Coalfield where P^max values are up
to 4% (Daulay, 1985).
As for the Miocene coals, Eocene coals show only small differences in reflectance values
between different macerals. For example, in all Pasir samples, mean maximum vitrinite reflectance values for telovitrinite range from 0.58% to 0.67% (average of 0.63%) whereas for detrovitrinite and gelovitrinite, values vary from 0.57% to 0.65% (average of 0.61%).
4.4 SPATIAL AND TEMPORAL VARIATIONS IN COAL TYPE
Petrographic composition of coal is related to palaeoclimate, geological age and tectonic setting. The tectonic setting also plays an important role in any subsequent burial 57 metamorphism. As a result of these factors, spatial and temporal variations in palaeoclimate, geological age and tectonic setting cause coal type provincialism (Cook,
1975), and thus, some coals have properties that are different to the properties of other coals in different parts of the same seams, in different part of the same basins or coals in other basins.
The range of plant components preserved in the peat and the extent of alteration to these components during the diagenesis of the peat, and subsequent coalification, determines coal type variations (White, 1915; Smith, 1968). Coals from eastern Kalimantan are largely derived from ombrogenous peat mires (Tennison-Woods, 1885; Anderson, 1964) which contained peats which were analogues of.the ombrotrophic peats described by Coulter
(1957). The vegetation precursor of this type of peat is typically tropical rainforest dominated by angiosperms (many of which were herbaceous), ferns and mosses that developed in lowlands. The peat is typically low in mineral matter and high in vitrinite content.
Many papers (including Brown et al, 1964; Cook and Edwards, 1971; Cook, 1975; 1981a;
Nandi et al, 197T, Sanyal, 1983; Shibaoka et al, 1985; Jok Jan and Yan Yan, 1990; and
Keat, 1990) discussed the practical implication of type-related differences in coal properties.
The differences cover a wide range of properties and processes such as combustion of pulverised coal, suitability for liquefaction and gasification processes, and coking behaviour.
In this study, an assessment of eastern Kalimantan coals by stratigraphic age is given and in addition, depositional environment and tectonic setting are reviewed to assess variations in coal type for coals of the same age.
The maceral compositions of Tertiary coals from eastern Kalimantan are remarkably 58 consistent with those for Tertiary coals from other localities in Indonesia. The composition is similar to those for some Tertiary coals from West Germany, Victoria (Australia), New
Zealand, China, Greece and Nigeria. There are, however, slight differences in composition compared to some Tertiary Indian and Canadian coals which have much higher inertinite contents (Figure 4.14).
Overall, the coals of eastern Kalimantan are characterised by the dominance of vitrinite with subordinate liptinite and relatively low inertinite. The dominance of vitrinite in all coals is indicative of forest type vegetation in a humid tropical zone which does not have a significant dry season (Stach et al, 1982; Bustin et al, 1983). Vitrinite-rich coal in some cases (for example, Sangatta and Tanjung Miocene coals) have a very low mineral content (as shown by low ash yields). Low ash is a characteristic of many Tertiary coals and has been interpreted as indicating a high-moor origin (for example, Smith and Cook,
1984; Titheridge, 1988).
The most outstanding feature of the coals in eastern Kalimantan is the increased vitrinite and inertinite contents and decreased liptinite content in Miocene coal compared to Eocene coal. Furthermore, the proportion of mineral matter is more in Eocene coals compared to
Miocene coals; this is probably due to the relative differences in the rate of peat accumulation (Chapter 5).
Vitrinite is dominant in all Eocene and Miocene coals (Figures 4.15 and 4.16) and mostly is perhydrous telovitrinite and detrovitrinite. The perhydrous nature of some of the vitrinite
(particularly detrovitrinite) may be due to the presence of suberin-related tissues which are abundant to major in some lithotypes. The high vitrinite content of the coals indicates that they have been deposited in areas of rapid subsidence. 59
The relatively lower vitrinite composition of some of the Eocene coals compared to the
Miocene coals is probably related to differences in floral composition.
The degree of gelification (both biochemical and geochemical) controls vitrinite structure and texture. Telovitrinite in Eocene coal is mostly eu-ulminite, textinite and telocollinite whereas, in Miocene coals, the telovitrinite is textinite, texto-ulminite and eu-ulminite.
Densinite and desmocollinite are the most abundant detrovitrinite macerals in Eocene coals, whereas attrinite and densinite are abundant in Miocene coals. This suggests that the
Eocene coals have undergone more extensive coalification, a fact that is borne out by the reflectance data.
Telovitrinite is more abundant than detrovitrinite in both Eocene and Miocene coals (Figure
4.17), except for Berau and Satui coals, where it is slightly lower. However, compared with Miocene coals, the ratio of telovitrinite to detrovitrinite is higher in Eocene coals.
Ratios of telovitrinite to detrovitrinite (Figure 4.18) for Eocene coals vary between 0.93
(Satui coals) and 1.58 (Tanjung coals) whereas for Miocene coals the range is 0.77 (Berau coals) to 1.34 (Sangatta coals).
The increased detrovitrinite content in Berau and Satui coals may be due to a generally higher degree of tissue destruction under the influence of higher pH values which favour greater bacterial activity than do acid peats (Stach et al, 1982; Littke, 1987). Some detrovitrinite (mainly in the low rank coals ) has weak, dull orange to weak brown fluorescence of very low intensity; fluorescence was rarely observed in telovitrinite and gelovitrinite.
It is likely that the fluorescence in detrovitrinite is caused by hydrocarbons which were produced from the vitrinite during coalification. This is also suggested by the presence of 60 common exsudatinite (typically as much as 1.0%) and oil hazes in some samples (Section
4.5).
Taylor and Liu (1989) noted that the presence of fluorescence from some vitrinite (mainly detrovitrinite) is related to the presence of bacterial lipids that contributed to the degradation of hurnic products during peat formation. The lipid material in eastern
Kalimantan coals is thought to be abundant enough to generate hydrocarbons which may be the cause of the fluorescence from the vitrinite. Levine and Davis (1989) and A. Davis
(pers. cornm.) also noted the same phenomena in Pennsylvanian coals.
Telovitrinite typically occurs as thin layers and small lenses associated with other macerals,
particularly detrovitrinite. In Miocene coals, some telovitrinite has a layered or striated
appearance with a lower reflectance than the more massive, non-layered vitrinite. Cell
structure of vitrinite in Eocene coals is better preserved than in Miocene coals except for
Sangatta coals (Section 4.8).
Inertinite is more abundant in Miocene coals than in Eocene coals and comprises
predominantly semifusinite, sclerotinite and inertodetrinite with minor fusinite, micrinite and
macrinite. It is generally believed that inertinite is derived from strongly oxidised,
degraded wood tissue which is indicative of the comparatively dry conditions during peat
diagenesis even though the overall climate may have been wet and temperate as it was
during the Tertiary in Indonesia. Thus, the higher inertinite content in some of the
Mahakam, Sangatta and Tanjung Miocene coals may indicate that coal deposition occurred
in a shallow basin under more aerobic conditions where the peat was frequently exposed to the atmosphere.
Although it is not significant, the ratio of vitrinite to inertinite is lower for Miocene coals 61
(0.95) compared with Eocene coals (0.97). This indicates more oxidising conditions, possibly caused by a lower water table during peat formation, for the Miocene coals.
Gould and Shibaoka (1980) noted the same phenomenon in some Palaeozoic coals from
Australia and suggested that inertinite-rich coal developed in areas where slow subsidence or basin margin factors allowed intermittent aeration of the peat during its accumulation.
Cell structure in semifusinite, fusinite or sclerotinite is usually better preserved where the reflectance is higher.
Liptinite is abundant in all Eocene and Miocene coals (Figure 4.16) with the exception of the thermally-affected coals from Sangatta. In these coals the liptinite is not easy to recognise because of the high rank (approximately 2.0% Rvmax). However, cutinite and suberinite (Plates 3 a and 3b respectively) were identified in these coals and the reflectance of the macerals was 2.28% and 2.32%, respectively, which is much higher than for the associated vitrinite (1.92%) as is predicted from coalification paths of the respective macerals. Reflectance of inertinite (mainly sclerotinite and semifusinite) in the same grain was much lower (1.71%) than for associated vitrinite and liptinite. This matches the results of Smith and Cook (1980) who also noted that at vitrinite reflectances of greater than 1.4%, liptinite has a higher reflectance than vitrinite and the liptinite does not fluoresce.
Compared to the Miocene coals, liptinite content of the Eocene coals (mainly resinite and sporinite) is relatively higher. This indicates that there may have been different floral assemblages at these times. It is likely that the proportion of flowering plant types in the
Eocene coal precursors was relatively higher than in the floral assemblages that gave rise to the Miocene coals. Relatively low liptinite content in Sangatta coals (average of 5.6%) may also reflect a slight difference in floral composition. 62
Resinite is more abundant than suberinite, sporinite and liptodetrinite in both Eocene and
Miocene coal samples except in those from Berau and Asem Asem coals in which suberinite is dominant over resinite, sporinite and liptodetrinite. The fluorescence colour of resinite varies from strong greenish-yellow to dull orange even in a single sample. As a result, the distinction between fluorinite and resinite with strong greenish-yellow fluorescence is difficult, although the former is normally featureless and has a greenish tint in white light.
Highest suberinite contents are normally found in the samples with lowest vitrinite reflectance (Figure 4.19). Again, this is predictable and is related to the rapid increase in suberinite reflectance, indicating rapid coalification, that occurs over the range of subbituminous to high volatile bituminous coal stages (Cook and Kantsler, 1982;
Teichmuller, 1982). Suberinite is generally not observed in coals with a rank beyond 0.9%
Rvmax and this is thought to be related to the convergence of liptinite reflectance with that of vitrinite as described earlier. For eastern Kalimantan coals, in samples of lower rank
(Rvmax < 0.5%), suberinite has greenish-yellow to orange fluorescence whereas in the higher rank coals, Rvmax > 0.5%, it has yellow to dull orange or no fluorescence.
Sporinite content is higher in the Eocene coals than in the Miocene coals. Typically, sporinite content for Eocene coals is more than 2.0% whereas for Miocene coals it is less than 1.0%. Sporinite in Eocene coals is dominated by thin-walled miospores whereas in the Miocene coals, sporinite is mostly crassispores and pollen. The increased sporinite content in some of the Eocene coals suggests that a more herbaceous vegetation existed as these coals formed. Alternatively, this increase may reflect the higher resistance of spores as compared to woody tissue during degradation.
(particularly crassicutinite) is more abundant in the Miocene coals than in the 63
Eocene coals. In some samples, cutinite occurs in association with leaf tissue which contains abundant resinite. Some tenuicutinite in the Sangatta, Senakin, Pasir, Satui and
Tanjung (Eocene) coals has weak, dull orange to brown or no fluorescence. This may indicate that tenuicutinite probably has a lower hydrogen content than crassicutinite.
Some of the Eocene (Senakin, Satui and Tanjung) and Miocene (Berau) coals contain
Botryococcus-related telalginite which is more abundant in the Eocene coals than in
Miocene coals. The fluorescence intensity is less in Eocene coals than in Miocene coals.
Botryococcus-related telalginite in this coal indicates that the coals were deposited in a more lacustrine environment in which conditions were probably more reducing and with a lower humic acid content than the other coals of eastern Kalimantan.
Although Radke et al (1980) noted that liptinite fluorescence intensities do not vary greatly in coal of high volatile bituminous rank, where Rvmax is less than 0.60% a distinction between Eocene and Miocene coals in eastern Kalimantan can be made on the basis of liptinite fluorescence intensity. Based on visual examination only, liptinite fluorescence intensity of Miocene coals is relatively higher than Eocene coals, except for the Sangatta coals. Most of the Sangatta coals have similar fluorescence intensity to the Eocene coals which is as expected because the rank of the Sangatta coals is equal to, or higher, than that of Eocene coals. Thus, it is hypothesised, but not shown quantitatively, that liptinite fluorescence intensity for eastern Kalimantan coals is closely correlated with rank which, in turn, is a function of the age of the coals.
4.5 EXSUDATINITE IN EASTERN KALIMANTAN COALS
Exsudatinite is rare to abundant (<0.1% to 9.9%, average of 0.8%) in most eastern
Kalimantan coals. The exsudatinite content of the Miocene coals is relatively higher than 64
that of the Eocene coals. In both, exsudatinite normally occurs in association with vitrinite
and liptinite (particularly resinite, cutinite and suberinite) and therefore some, if not all of
the exsudatinite originates from these macerals. Exsudatinite fluorescence varies from
greenish-yellow to orange. Some exsudatinite shows oil smearing and oil stains.
Exsudatinite is a "secondary maceral (Murchison, 1976; Stach et al, 1982) that typically
infills veins, cell lumens, bedding planes and wedge-shaped fractures. It is also a binding
agent for some gelovitrinite and normally originates from lipid-rich liptinite constituents
(fats, waxes and oils) and is exuded from this organic matter during coalification but may
also be derived from vitrinite macerals, and in some cases, is probably mistaken for migrated hydrocarbons. From a review of early studies, Stach et al. (1982) noted that exsudatinite is mainly found in liptinite-rich coals of subbituminous to high volatile bituminous rank. However, later studies extended the range and exsudatinite is known to occur in coals of varying rank ranging from soft brown coal to bituminous rank. This study shows that exsudatinite can be generated during the very early stages of coalification, that is in the earliest soft brown coal stage, (approximately 0.35% Rvmax) as can be seen in Plates 3c and 3d which show coals from Asem Asem.
Exsudatinite occurrence may be directly related to the formation of hydrocarbons (Cook and
Struckmeyer, 1986; Teichmuller, 1989). The abundant exsudatinite in most eastern
Kalimantan coals, for example, Asem Asem and Berau coals, is thought to be indicative of in situ hydrocarbon genesis and migration although most samples do not appear to have anomalous vitrinite reflectance values.
Murchison (1976) and Shibaoka (1978) suggested that vein-filling secondary macerals
(including exsudatinite) are found in bituminous coals because they form as expulsions from other macerals, and subsequently migrate, during the subbituminous stage. 65
In the past, it has been difficult to distinguish between exsudatinite and material referred to by the term migrabitumen (terminology which was adopted by Jacob, 1989) as both have similar properties. However, Stach et al. (1982) and ICCP (1990 Annual Meeting) defined migrabitumen as natural solid bitumen occurring in sedimentary rocks, particularly in carbonates where it infills intergranular porosity and fractures. Exsudatinite is not found as dispersed organic matter (DOM) except where present in very large vitrinite phytoclasts.
Using the above definitions, the term migrabitumen is not used for any organic matter observed in this study because all 'exsudatinite-migrabitumen' is in coal even though some is thought to have undergone migration.
4.5.1 Types of Exsudatinite
Five types of exsudatinite, based on morphology and occurrence, have been distinguished in the coals from eastern Kalimantan (Table 4.8).
Type I exsudatinite has bright greenish-yellow to yellow fluorescence and infills long thin veins and fractures as can be seen in samples GM 24258 and GM 24138 from Sangatta and Satui, respectively (Plates 4a to 4d). This type normally occurs in cross-cutting veins, perpendicular to bedding, or rarely in veins parallel to bedding. It is found mainly in association with telovitrinite. This is probably related to the tendency of telovitrinite to fracture more than detrovitrinite and gelovitrinite. The telovitrinite-Type I association is also a function of origin as it is probable that Type I originates from telovitrinite and associated resinite.
Type II exsudatinite infills larger and longer fractures than Type I exsudatinite (Plates 4e to 4h) and is probably derived from detrovitrinite and resinite. This is shown in Plates 4e to 4h where exsudatinite is closely associated with resinite in samples from Sangatta (GM
24235) and Senakin (GM 23906). It commonly occurs in fractures parallel to bedding and 66 has yellow to orange fluorescence although some detrovitrinite-associated exsudatinite has dull orange to weak brown fluorescence of very low intensity. In reflected white light,
Type JI exsudatinite is normally reddish-brown or opaque. Many of the fractures in which
Type II exsudatinite is found, commonly have smaller fractures on both sides of the larger fractures.
Type m exsudatinite occurs as infillings in cell lumens, both in vitrinite (telovitrinite) and inertinite (particularly semifusinite and sclerotinite). It is probably derived from vitrinite as well as resinite and has strong greenish-yellow to orange fluorescence (Plates 5a to 5d, samples GM 24401, Mahakam coal and GM 24268, Sengatta coal). The distinction between Type IE andfluorinite, wher e both occur in the same coal, is not always easy although the latter has a more intense green fluorescence and has a weak greenish-blue colour in reflected white light.
Type TV exsudatinite infills irregular cavities of different sizes and shapes and is normally associated with the detrovitrinite groundmass (Plates 5e to 5h, samples GM 23716,
Mahakam coal and GM 23913, Senakin coal). It typically has internal fractures which are more abundant than in other types of exsudatinite. It has a greenish-yellow to yellow fluorescence colour. Type IV is unquestionably generated from detrovitrinite (particularly perhydrous detrovitrinite) as well as liptinite and is trapped in the fine pore structure of detrovitrinite.
Type V exsudatinite infills short cleats or fractures (wedge-shaped fractures) and normally
has yellow to orange fluorescence. This type of exsudatinite is normally exuded from
liptinite macerals, particularly resinite, cutinite and suberinite as shown in samples GM
24327, Sangatta coal and GM 24381, Berau coal (Plates 6a to 6d). Therefore, the origin
of this type of exsudatinite is mainly from liptinite macerals. Generally, this exsudatinite 67 has more intense fluorescence than the parent liptinite.
Type IV exsudatinite is the most common form in eastern Kalimantan coals followed by
Type U, Type I, Type UI and Type V respectively. This is probably a function of origin as Types IV and II are mostly associated with detrovitrinite and liptinite which are the dominant maceral assemblage in the coals. In addition, detrovitrinite is also more heterogeneous and porous than telovitrinite and gelovitrinite, therefore expulsion of generated exsudatinite is easier.
With reference to the literature, many authors, including Struckmeyer (1988, her plate 6e),
Panggabean (1991, his plate 4g) and Sutrisman (1991, his plates 4a to 4d) have described migrabitumen in dispersed organic matter (DOM) and this organic matter is referrable to
Type IV exsudatinite. From the occurrence and association of Type IV „ exsudatinite in eastern Kalimantan coals, it appears to be related to oil generation rather than to oil degradation as has been suggested by others.
Type JJJ exsudatinite has the most intense fluorescence and this is probably a function of its greater mobility relative to other types of exsudatinite. A mobile origin is inferred from the presence of this type of exsudatinite in cell lumens of semifusinite and sclerotinite; macerals that could not themselves generate or expel large amounts of secondary material.
Meta-exsudatinite is present in some of the Sangatta semi-anthracite (Plates 6e and 6f).
Meta-exsudatinite is exsudatinite that has been thermally altered due to the proximity of the coal to intrusions, resulting in the loss of volatile hydrocarbons. In reflected white light, it has a brighter colour than associated macerals (mainly vitrinite) and does not fluoresce which is assumed to indicate the chemical degradation, or the loss of hydrogen during a rapid coalification jump, that is needed to change the fluorescence properties. 68
Reflectance of meta-exsudatinite (2.70%) is greater than that of the associated vitrinite
(1.74%), inertinite (1.58%) and liptinite (2.11%).
Meta-exsudatinite has also been recognised in anthracite, formed by thermal alteration adjacent to an intrusion, from Bukit Asam, South Sumatera where its reflectance is also higher than that of the associated vitrinite and inertinite. Liptinite (especially cutinite and suberinite) is recognisable in both Bukit Asam and Bayah thermally-affected coals (Daulay,
1985). However, liptinite macerals are more abundant in the Sangatta coals than in Bukit
Asam and Bayah coals which is probably a function of rank. Thermally-affected coals from Sangatta have a lower vitrinite reflectance than that for Bukit Asam anthracite but higher reflectance than that for thermally-affected coals from Bayah.
Kantsler (1980) and Stach et al. (1982) also noted that beyond the high volatile bituminous stage, the reflectance of meta-exsudatinite is generally greater than that of vitrinite. This is probably due to higher plasticity and greater condensation of the aliphatic molecular complexes compared to the more rigid ring structure of vitrinite.
4.6 RANK VARIATIONS
The coals from eastern Kalimantan span the rank range from soft brown coal to high volatile bituminous coal with a few from the Sangatta area in the semi-anthracite rank. A map of eastern Kalimantan, showing vitrinite reflectances at the surface, is presented in Figure 4.20.
The Eocene coals were originally at greater depths and therefore have a higher vitrinite reflectance than the younger Miocene coals, except in the Sangatta area. The higher vitrinite reflectance for most of the Sangatta coals is probably related to the regional 69 geology which is characterised by strongly folded units and a relatively higher geothermal gradient.
Vitrinite reflectance values for Eocene coals are higher in the Pasir and Tanjung Coalfields of the Barito Basin (average of 0.62% and 0.60% respectively) compared to the Satui and
Senakin Coalfields of the Asem Asem Basin (average of 0.50% and 0.56% respectively).
Vitrinite reflectance of Miocene coals is higher in the Mahakam Coalfield of the Kutei
Basin and the Berau Coalfield of the Tarakan Basin (average of 0.48% and 0.45%, respectively) compared to the Asem Asem Coalfield of the Asem Asem Basin (average of
0.36%). Differences in vitrinite reflectance values for the basins largely reflect the thickness of cover at the time of coalification although some influence from variations in vertical rank gradients may also have had a minor effect.
Vitrinite reflectance of both Eocene and Miocene coals in the Kutei, Asem Asem and
Barito Basins increases from east to west toward the Meratus Range and Kuching Highs.
This variation in rank probably reflects an increase in depth of burial during coalification.
Higher rank gradients may be more significant near the Meratus Range in the western part of the Kutei Basin (Panggabean, 1991).
The higher vitrinite reflectance values in the western part of the Kutei Basin are complicated in the Sangatta area in the northwest part of the basin, because of the local increases due to the intrusions. Elsewhere, the coals do not appear to have been affected by any known igneous body. The gradually increasing vitrinite reflectance values from east to west, not including the Sangatta data, probably supports this hypothesis. The deposition of the coals in these areas is likely to have been controlled, in part, by the activation of the South Kutei Boundary Fault at the time of, and immediately after, formation. This fault may have caused tilting of the basement under the Kutei Basin with the western part 70 of the coalfield subsiding more than the eastern part.
Increasing rank with increasing depth of burial occurs in the Mahakam and Sangatta areas of the Kutei Basin, Tanjung and Pasir areas of the Barito Basin, the SatuL Senakin and
Asem Asem areas of the Asem Asem Basin and the Berau area of the Tarakan Basin as already shown by many workers (for example, Durand and Oudin, 1979; Samuel, 1980;
Oudin and Picard, 1982; Panggabean, 1991; Herudiyanto, pers. comm.; and numerous confidential reports).
The low vitrinite reflectance (average of less than 0.33%) in some of the coals, particularly
Asem Asem and Berau coals, is thought to be due to the influence of maceral associations, mineral matter and type differences within the vitrinite. For example, extremely fine grained liptinite such as resinite or secondary liptinite (exsudatinite) and mineral matter infill the lumens in vitrinite and this would give an apparent vitrinite reflectance rather than the true reflectance.
Hutton and Cook (1980), Cook et al. (1981a) and Cook (1987) noted that vitrinite which is associated with abundant telalginite, tends to have a much lower reflectance compared to vitrinite in coal which does not contain abundant alginite. -Hutton and Cook argued that the decreased vitrinite reflectance was probably related to the adsorption of low molecular weight hydrocarbons by the vitrinite but no evidence was given for this. Senakin and
Berau coals contain up to 0.4% Botryococcus-TQlatQd telalginite but the presence of this volume of the maceral in the coals does not appear to influence the vitrinite reflectance.
It is assumed that these coals contain far too little telalginite to affect the vitrinite reflectance, something that can be interpreted from the Hutton and Cook data.
For most of the eastern Kalimantan coal seams, differences in vitrinite reflectance between 71 the seams is insignificant except in the Tanjung area where vitrinite reflectance for Eocene coals ranges from 0.55% to 0.64% (average of 0.60%) and for the Miocene coals, the range is 0.34% to 0.47% (average of 0.40%).
There is also no significant vertical variation in vitrinite reflectance for any single coal seam (Figure 4.21) except for the Berau and Senakin coals where reflectance increased slightly from top to the bottom of the coal seam (Figure 4.22). For example, the value increase from 0.43% to 0.47% in one Berau seam and from 0.48% to 0.54% in a Satui seam.
4.7 COAL FACIES AND DEPOSITIONAL ENVIRONMENTS
Maceral assemblage data can be used to assess depositional environments during the accumulation of the peat (Teichmuller, 1962; Diesel, 1982; 1986; Navale and Misra, 1984;
Mukhopadhyay, 1986; Kalkreuth and Leckie, 1989; Kalkreuth et al, 1991). Teichmuller
(1962) noted that the precursor peat for coals rich in well-preserved humotelinite
(telovitrinite under the Australian nomenclature) accumulated in forest-type swamps whereas coals rich in humodetrinite (detrovitrinite under the Australian nomenclature) and spores are thought to have accumulated in a reed-marsh environment. Sub-aquatic conditions are indicated by an association of detrovitrinite, sporinite and clay minerals.
By applying the facies-critical maceral association of Mukhopadhyay (1986), the ratio of telovitrinite to detrovitrinite (Figure 4.23) can be used to outline relative differences in depositional environments for the samples studied. The Mukhopadhyay facies model was selected for this study because it was designed mostly for low rank coals whereas the methods for higher rank coals, such as that of Diessel, do not work for Tertiary Indonesian coals. 72
Figure 4.23 shows that, generally, for eastern Kalimantan coals maceral assemblages indicate that the level of the water table in the swamps was high enough to prevent accumulation of large amounts of oxidised components such as semifusinite and fusinite.
Inertinite contents of the coals do not exceed 5%, except for some samples from Mahakam and Sangatta and a few samples from Berau and Tanjung (Miocene) coals. The relatively high inertinite in these coals suggests that, locally, peat was exposed to the atmosphere, particularly if deposited at the edge of the basin.
The relative narrow range for the distribution of telovitrinite and detrovitrinite, suggests that most of the coals from eastern Kalimantan were deposited in a wet forest-type swamp.
The remainder of the samples accumulated under conditions more representative of reed marsh conditions.
4.8 COALIFICATION AND THERMAL HISTORY
The rank or level of organic metamorphism has been related to temperature during coalification and time (Francis, 1961; Bostick, 1973; Hood et al, 1975; Mathews et al,
1975; Kantsler et al, 1978a; 1978b; Bostick, 1979; Teichmuller and Teichmuller, 1968;
1982). It is generally accepted that an increase in depth of cover results in increased temperature and therefore a higher rank. For any given cover, rank will be a function of the geothermal gradient and the thermal conductivity of the rocks (Dow, 1977; Cook and
Kantsler, 1980). The general increase in coal rank with depth is generally referred to as "Hilt's Law" (Hilt, 1873).
Igneous activity locally increases the available heat and causes an increase in rank, as for example, the Sangatta coals. This phenomenon was also discussed by Kisch and Taylor
(1966), Daulay (1985), Daulay and Cook (1988), Pujobroto (1991) and Sutjipto (1991). 73
4.8.1 Geothermal Gradient
A review of the literature including Schwartz et al. (1973), Kenyon et al. (1976) and
Thamrin (1987) shows that all reported geothermal gradients for Asem Asem (average of
32.8°C/km), Barito (average of 34.6°C/km), Kutei (average of 31.3°C/km) and Tarakan
(average of 34.0°C/km) Basins were in the moderately high range. A relatively high geothermal gradient/heat flow, however, was reported for the northwestern flank of the
Meratus Range and in the southern part of the Asem Asem Basin. Both were thought to be related to the Meratus Uplift events. A high geothermal gradient was also reported in the northwestern part of the Kutei Basin (Pinang Dome). Thus heat flow data for the four basins studied here was considered to be similar to the those for other basins in Indonesia.
Schwartz et al. (1973) and Thamrin (1987) stated there were no cases of high heat flow values in the basins along the east coast of Kalimantan and interpreted this to indicate no shallow heat sources. Furthermore, the low heat flow values in the basins were considered to be typical of those for stable lithospheric plates lacking volcanic activity (Katili, 1975;
Thamrin, 1987). However, the presence of thermally-affected coal in the Sangatta area suggests that, locally, a high geothermal gradient, associated with an igneous intrusion, should exist in this area and that previously published data should be reviewed to account for the Sangatta data. This is supported by the higher vitrinite reflectance values for
Sangatta coals (Miocene) compared to all other coals (Miocene and Eocene) in eastern
Kalimantan.
Indirect evidence for this also comes from the literature. The highest geothermal gradient in an Indonesian Tertiary basin is reported from the Central Sumatera Basin, where the average value is 67.6°C/km; the lowest gradient is from the Sibolga Basin (North
Sumatera), where the average is 21.4°C/km (Thamrin et al, 1980; 1981; 1982; Thamrin,
1987). The high geothermal gradient/heat flow in the Central Sumatera Basin is associated 74 with a shallow heat source underneath the basin and is interpreted to be the result of magma injection accompanying tectonic movements.
4.8.2 Palaeotemperatures Karweil's nomogram (as modified by Bostick, 1973) has been widely used to correlate temperature, duration of heating and coalification level (Karweil, 1956; Bostick, 1973;
Kantsler et al, 1978b). Karweil used volatile matter yield as a measure of coal rank and
Bostick (1973) provided data whereby the nomogram could be calibrated for vitrinite reflectance.
Smith (1981) and Smith and Cook (1984) described a procedure for calculating isothermal and gradthermal temperatures from vitrinite reflectance and basin history data. These calculations were also carried out by Bostick (1973) and similar work was undertaken by
Cook and Johnston (unpublished data, 1974). Comparing the isothermal (TjJ and gradthermal (T^J model temperatures with present temperatures, shows the relative palaeothermal history of a formation. The Tiso temperature model corresponds with coalification at a constant temperature over the entire period after deposition of the peat.
T^ is obtained from the Tiso value and assumes that the sequence underwent continuous burial with temperature rising at a steady rate to a present day maximum.
Calculation of isothermal and gradthermal models for some Indonesian Tertiary basins, including the present study area, were carried out by Daulay (1985) and Panggabean (1991) who calculated temperature models from twelve drill hole sections in southeastern
Kalimantan basins. The modelled temperature calculations, including a plot of the relationship between T^^ and T,^ for basins along the east coast of Kalimantan and for some other Indonesian Tertiary basins, are shown in Figure 4.24 which was modified from Daulay (1985) and Panggabean (1991). 75
The modelled temperature calculations indicate that the present formation temperatures are significantly lower than those in the past for all basins. Therefore, the present geothermal gradient (31.3°C/km to 34.6°C/km) is probably lower than that operating during the main period of coalification which was probably during Middle Miocene. The model indicates that relatively rapid coalification may have occurred during Eocene and Miocene in all basins.
4.8.3 Estimation of Maximum Cover
Using modelled temperatures, geothermal gradients and surface temperatures, Daulay (1985) concluded that most Indonesian Tertiary coals, including the eastern Kalimantan basins, had a maximum cover of more than 1000 metres. Petrographic data for this study shows that in some samples from the Asem Asem Coalfield, vitrinite has relatively well-preserved cellular structure with cell lumens that are partially open (Plate 6g). In contrast, vitrinite cell structure in other Miocene coals from the Sangatta, Mahakam, Tanjung and Berau areas are largely gelified with only a few cell lumens still open (Plate 6h). This indicates that some coals from the Asem Asem area have not undergone coalification to the same degree as coals from the Sangatta, Mahakam, Tanjung and Berau areas. Therefore the rank of the
Miocene coals in the latter areas, as indicated by the reflectance data (average Rvmax of
0.40% to 0.63%), is slightly higher than for the coals in the Asem Asem areas (average
Rvmax of 0.36%).
Smith (1981) applied changes in textural properties of vitrinite to correlate the increase in coal rank with depth of burial. He reported that in the Tertiary sequences of the Gippsland
Basin (Australia), telovitrinite (at approximately 1250 m depth and with Rvmax of 0.30%) showed remnants of cell lumens; cell walls and cell contents were aligned parallel to bedding. With increased depth, Smith recognised that the major process of vitrinite coalification appeared to be conversion of textinite and well-preserved texto-ulminite to eu- 76 ulminite. At a depth of approximately 1265 m. he found that telovitrinite showed a slightly more advanced stage of coalification (R,max of 0.33%). A, 1742 m, almost all cell lumens had completely gelified.
Assuming that the data relating to vitrinite structure for the Tertiary sequence of the
Gippsland Basin can be applied to eastern Kalimantan coals, the textural and reflectance properties of Tertiary coal sequences in eastern Kalimantan indicate that the coals have been buried to depths of 1000 m to 1500 m in the Asem Asem area, 1250 m to 1750 m in the Berau and Tanjung areas, 1500 m to 2000 m in the Mahakam area and 2000 m to
2500 m in the Sangatta, Tanjung, Pasir, Satui and Senakin areas.
4.9 SUMMARY AND CONCLUSIONS
Macroscopically, the coals from eastern Kalimantan are characterised by clarain and vitrain bands with only rare inertinite-rich dull layers which may have been derived from peat that had been more exposed to an oxidising atmosphere above the water table. The vitrinite- rich, brighter layers were derived from peat that accumulated under water, in more reducing conditions.
Small variations in coal type are present in the samples studied. Differences in type can be caused by interaction of tectonic, sedimentary, climatic factors and floral composition.
For eastern Kalimantan coals, the most important of these is probably differences in floral composition. However, because of the relatively short period over which peat accumulation took place and the probable similarity in climates during peat formation, slight differences in tectonic and sedimentary settings during both the Eocene and Miocene periods also have to be considered. 77
Beside the petrographic similarities, many of the eastern Kalimantan coals are characterised by the development of very thick seams (for example, up to 10 metres thick in the Kutei
Basin) and many have a remarkably low ash content (for example, some of the Sangatta and Tanjung (Miocene) coals contain less than 2.0% mineral matter). It is assumed that during peat accumulation the water table rose at a similar rate as plant debris accumulation, effectively eliminating an environment conducive to the input of mineral matter.
Overall, vitrinite reflectance for the older Eocene coals, associated with a greater depth of burial and geothermal gradient, is higher than for the Miocene coals. Coals in the Sangatta area were affected by an intrusion which resulted in a higher regional rank and metamorphism to anthracite rank near the intrusion. 78 79
CHAPTER FIVE MINERAL MATTER
5.1 NATURE AND OCCURRENCE OF MINERAL MATTER IN COAL
Inorganic constituents of coals are either "inherent" or "adventitious" mineral matter
(Edgecombe and Manning, 1952; ICCP, 1963; Rao and Gluskoter, 1973; Mackowsky,
1982a; Clymo, 1987). The term inherent mineral matter is commonly applied to those inorganic constituents that are derived from the original plant material. Because of the small grain size, identification of this mineral matter is mostly only possible by scanning electron microscopy and chemical analyses rather than optical methods.
Adventitious mineral matter is commonly subdivided into "primary" (syngenetic) and
"secondary" (epigenetic) mineral matter. Syngenetic mineral matter is formed as the peat is being deposited and/or during early coalification. The syngenetic mineral matter is commonly of smaller grain size than epigenetic mineral matter and is intimately dispersed throughout the coal (Reyes-Navarro and Davis, 1976; Renton, 1979). Epigenetic mineral matter, by contrast, is incorporated into the coal at a later stage, after compaction or partial consolidation. The epigenetic mineral matter normally fills fractures, cleats and cavities or pseudomorphs primary minerals (Renton, 1979; 1982; Mackowsky, 1982b; Clymo, 1987).
The origin of particular minerals can be inferred from texture, grain shape, morphology and composition in some samples. In the present study, it has been found that the association of mineral matter with particular macerals is also species related for many of the minerals.
This has significant practical applications as sophisticated techniques such as SEM and X- 80 ray diffraction techniques can be bypassed and mineral identification can be concurrent with maceral analysis.
Based on modes of occurrence, mineral matter in eastern Kalimantan coals can be grouped as follows:
1) Mineral matter in clay partings
This mineral matter constitutes a significant proportion of the total mineral content of the coal and therefore is important in coal utilisation studies. Most of the eastern Kalimantan coal seams, particularly the Eocene Satui and Senakin coals, have clay partings of varying thickness (ranging from a few millimetres up to 10 cms).
For Eocene coals, the number of clay partings ranges from three (as in Pasir and Tanjung coal seams) up to six (Satui and Senakin coal seams) in a single seam whereas the number
of partings in the Miocene coals is typically less than four (ranging in thickness from a few millimetres up to 5 cms). The partings occur in any part of the coal seam but most commonly in the middle or upper parts and only rarely near the base.
The proportion of the seam section occupied by clay partings in the Eocene coals varies
from 4 percent to more than 10 percent. In Miocene coals, clay partings comprise typically less than 5 percent, except for several Sangatta and Tanjung seams where it is less than
one percent.
The clay partings are formed as a result of sudden influxes of sediment-laden water into the peat swamp and the conditions under which they form, are similar to those under which coal is formed. It has been suggested by previous workers (for example, Brown et al,
1965; Jenkins and Walker, 1978; Ward, 1986) that the organic and mineral composition of 81 the partings should, therefore, be the same as those in the coal and should reflect processes active during formation of the coal. For eastern Kalimantan coals this is the case. Coal directly below clay partings or roof strata normally have the same macerals (Chapter 4) and are normally only enriched in mineral matter.
As clay partings are relatively free of organic matter, identification of these minerals in the plies is much easier than identifying the mineral matter in the coal plies.
2) Syngenetic and Epigenetic Minerals in Coal Plies
Syngenetic and epigenetic minerals in eastern Kalimantan coal plies are typically finely- divided mineral matter and represent sediment or wind-blown dust that was deposited with the original plant material, inorganic constituents of plants and mineral matter later introduced during coalification by percolating water. Silicate minerals, such as quartz and clay minerals, are generally syngenetic whereas carbonates are generally epigenetic.
5.2 ANALYTICAL PROCEDURES
In the present study, three analytical methods were employed to identify and quantify mineral matter in the samples:
- optical microscopy, both reflected white light and fluorescence mode, was used to identify and point count the mineral matter in coal samples;
- X-ray diffraction techniques were used to identify the minerals in clay partings and shaly coals; and
- scanning electron microscopy (SEM) was used to observe the morphological and textural features of the minerals. 82
5.2.1 Optical Microscopy Optical methods are very useful for describing the types and occurrence of mineral matter i„ coals. Information can be gathered on various mineral types and mineral-macerals
associations. The normal point count method was used to determine the mineral
abundances.
Minerals were identified by properties such as morphology, reflectance and anisotropy. The
mineral under the point of the cross hair was examined under reflected white light and
fluorescence mode as some minerals (for example, carbonate and some clay minerals)
fluoresce with reasonably distinctive colours and intensities. Mineral content is expressed
as the percentage by volume of the whole rock.
Three hundred and twenty six coals and fifty three shale and shaly coals were analysed
from the various coalfields in eastern Kalimantan. Point counts for clay partings were only
conducted if organic content of the sample was greater than 10%, otherwise a visual
estimate was taken. In this study three main mineral groups were identified:
- silicates, including clay minerals and quartz;
- sulphides, predominantly pyrite; and
- carbonates, mainly calcite.
5.2.2 X-ray Diffraction
X-ray diffraction has been used extensively by a number of workers (Gluskoter, 1965;
1967; Hardy and Tucker, 1988) to identify mineral matter in coals and other rocks. It is
considered to be a better method for mineral identification in coals and shaly coals than
optical and scanning electron microscopy. However, quantitative results are difficult to
obtain. For most samples a relative abundance, relative to the sample with the greatest
abundance of any mineral, rather than the exact content, is obtained. X-ray diffraction 83 methods are not accurate for quantification of minor mineral components, that is, minerals that constitute less than 5%.
In the present study, twenty two coal and shaly coal samples were selected for X-ray diffraction analysis. The mineral content of these samples was high enough for X-ray diffraction methods to be used directly without applying separation techniques such as combustion of the organic matter. Separation techniques are only required if the mineral abundance in the coals is low and the mineral matter is dispersed throughout the sample
(Gluskoter, 1965; 1967).
5.2.3 Scanning Electron Microscopy (SEM)
Scanning electron microscopy (SEM) techniques have been widely used by many workers
(Kieke and Hartman, 1973; Sutherland, 1975; Augustyne et al, 1976; Harris, et al, 1981;
Trewin, 1988) to study morphology, shape, grain size and organic-mineral interrelationships in coals and other rocks. In addition, Hamilton and Salehi (1986) applied SEM methods to coal petrography to identify types of macerals. However, the application of this method for maceral identification has not been developed as well as optical microscopy, partly because liptinite macerals are much easier to observe and identify in fluorescence mode.
In this study, fifteen selected samples were examined by SEM techniques. Both secondary electron (SE) and backscattered electron (BS) images were employed. Backscattered electron mode is the most useful procedure for identifying minerals in the coal as the response of the beam to density is more accurate. The secondary electron (SE) mode is best to determine relief or morphology of either macerals or mineral matter in coals.
In this study, morphology was compared with elemental compositions determined by energy dispersive X-ray (EDX) methods to aid identification. 84
With back scattered electron images, grey levels (brightness) of the organic and inorganic concentrations are used to identify the various components. Mineral matter shows the brightest phase, followed by inertinite, vitrinite and liptinite respectively.
5.3 MINERAL COMPOSITION
Total mineral contents of the bulk samples range from 0.2% to 27.9% with an average of
5.2% (Figure 5.1; Table 5.1). The lowest mean is for Sangatta coals (range of 0.2% to
27.9%, average of 3.7%) and the Miocene Tanjung coals (range of 2.2% to 5.9%, average of 3.7%) whereas the highest means are for Senakin coals (range of 1.6% to 22.2%, average of 8.3%). The Sangatta coals which contain up to 27.9% of mineral matter, are commonly associated with clay partings and are generally from the top or the bottom plies of the seam. Most Sangatta coals have less than 2.0% mineral matter.
Megascopically, clay minerals (including kaolinite, illite, smectite, montmorillonite, sericite and halloysite) and quartz are the most common minerals in samples from eastern
Kalimantan. These minerals normally occur in partings, veins and nodules of different sizes or are disseminated throughout the coal seams. Silicate mineral contents for the coals
(Figures 5.2 and 5.3) range from 0.7% to 24.8% (average of 4.5%).
Pyrite is the most abundant sulphide and is also the most ubiquitous of all minerals despite its relatively low abundance. Pyrite content ranges from 0% to 9.9% (average of 0.5%).
Pyrite is most abundant in the Sangatta, Pasir and Berau coals where it mostly fills cleavage partings, joints (cleats) and bedding planes. Small isolated grains and small aggregates are also present in coals such as those from the upper part of Q seams at Berau.
The pyrite is brittle and friable on the polished surface of blocks. 85
Calcite is the most common carbonate mineral and contents range from 0% to 1.5%
(average of 0.2%). Calcite occurs mainly as veinlike fracture fillings, both parallel and perpendicular to bedding, and as nodules scattered throughout the coal.
Silicates, sulphides and carbonates comprise up to 99.0% of the mineral matter in some coals. Figure 5.4 and Table 5.1 show the mean proportions of mineral matter in each coal.
Apart from the most common minerals listed above, gypsum, feldspar, jarosite, muscovite, goethite, anhydrite and marcasite were also recognised in some samples, predominantly by
X-ray diffraction and scanning electron microscopy.
Mean silicates content (including clay minerals and quartz) of Eocene coals, ranging from
4.6% (Satui coals) to 7.8% (Senakin coals), is higher than that for Miocene coals where the range is 3.0% (Berau coals) to 3.5% (Tanjung and Asem Asem coals).
Mean sulphide content (mostly pyrite) for Eocene coals ranges from 0.2% (Satui coals) to
1.7% (Pasir coals), whereas for Miocene coals the range is 0.1% (Tanjung coals) to 1.0%
(Berau coals).
Mean carbonate content for Eocene coals ranges from 0.1% (Tanjung, Pasir and Satui coals) to 0.2% (Senakin coals), whereas for Miocene coals the carbonate content ranges from
0.1% (Sangatta, Tanjung and Asem Asem coals) to 0.4% (Mahakam coals).
5.3.1 Clay Minerals
Optical microscopy, scanning electron microscopy and X-ray diffraction techniques confirm that most of the coal samples contain a wide variety of clay minerals with the differences between samples being very obvious in most cases when using the X-ray diffraction and 86
SEM techniques. Both epigenetic and syngenetic clay minerals can be identified. Some of the clay minerals show fluorescence colours ranging from yellowish-orange to dull orange with intensities in the low to medium range. Fluorescence colour is thought to result from the absorption of hydrogen-rich compounds by the clay structure.
The types and relative abundances of clay minerals should reflect the chemistry of the original swamp waters or the immediate post-burial environment when most of these minerals were incorporated into the peat. The major component of clay minerals in the samples from eastern Kalimantan is kaolinite with illite and sericite the next most abundant species.
Figure 5.5 is an X-ray diffraction pattern for an Eocene coal from Senakin. This figure shows the monomineralic character of the clay mineral component. It is composed entirely of kaolinite with only traces of muscovite and quartz. The kaolinite is well-crystallised as shown by narrow diffraction peaks and the well-defined prism reflections indicate a syngenetic origin for this mineral. Gluskoter (1965; 1967) also noted that kaolinite was the most abundant clay mineral in the shales and claystones immediately overlying the coals he studied.
Illite and halloysite (Figure 5.6) are also present in some samples although the abundance of these clay minerals is much less than that of kaolinite. Small amounts of montmorillonite, smectite and sericite are also present in some samples.
In Eocene coals, the clay minerals typically occur as thin layers or lenses within vitrinite
(Plate 7a) and normally show very weak fluorescence to no fluorescence. Some of the clay minerals replace the organic matter, particularly vitrinite (Plate 7b). In Miocene coals, on the other hand, clay minerals commonly occur as grains and isolated lenses disseminated 87 throughout the samples and normally show weak to moderate fluorescence (Plates 7c and
7d).
Some of the clay minerals in both Eocene and Miocene coals infill cell lumens of both vitrinite (mainly telovitrinite) and inertinite, particularly semifusinite and sclerotinite. Clay minerals are associated with all maceral groups but are most commonly associated with vitrinite followed by inertinite and Uptinite.
5.3.2 Quartz
Quartz is the second most abundant mineral in eastern Kalimantan coals and commonly occurs in the partings, suggesting a detrital origin as for most of the clay minerals. It is only rarely found in relatively clean coal layers and normally occurs as discrete syngenetic grains or isolated lenses disseminated throughout the samples. Most detrital grains are generally angular to subhedral and range from 50 to 160 microns diameter. Some of the quartz is epigenetic and was formed as a chemical precipitate, infilling fractures or cleats and cell lumens in either vitrinite or inertinite. Quartz normally does not fluoresce.
X-ray diffraction analysis shows that all coal samples contain quartz and most have associated kaolinite.
Quartz has been identified in some modem swamp plants (Renton and Cecil, 1979). The solution of this inherent quartz when the plant tissues undergo chemical reaction during peat formation could be the source of some of the epigenetic quartz in coals.
5.3.3 Pyrite and Related Minerals
Total sulphur content of potentially minable eastern Kalimantan coals ranges from 0.1% to
10.1% with an average of 0.4% (Tables 3.3 and 5.2). Highest total sulphur contents occur 88 in the Pasir and Berau coals (average of 3.0% and 1.3% respectively) whereas the lowest is in the Satui and Senakin coals (average of 0.2% and 0.4% respectively). Extremely high total sulphur contents of up to 10.0% were also reported from subsurface coal samples
(Sahminan et al, 1988; Strauss, 1988).
Most of the sulphur is in pyrite (both syngenetic and epigenetic forms) with the remainder probably as organic sulphur incorporated within the coal-forming plant material. Small amounts of sulphur occur as hydrous ferrous sulphate, derived from the weathering of pyrite, and as other sulphates. The percentage of pyritic sulphur in all samples ranges between 0% and 9.9% (average of 0.5%).
Tables 5.1 and 5.2 show mean pyrite content of the samples for each coal. The highest pyrite content is in Pasir coals (average of 1.7%) whereas the lowest is in Miocene Tanjung coals (average of 0.1%).
Microscopically, pyrite occurs as fine grains disseminated throughout the coal, massive nodules (up to 2.0 millimetres in diameter), veins, dendritic masses, framboidal nodules and also replaces organic matter. Plate 7e shows a common type of finely-disseminated, discrete grains (bright grains), 1.0 to 2.0 microns diameter, in vitrite. Where this assemblage occurs in other samples, crystalline fibre bundles and small crystal aggregates of pyrite are also present in the vitrite. In other samples pyrite infills cell lumens in telovitrinite, semifusinite and/or sclerotinite.
Framboidal pyrite is rounded (Plate 7f) and commonly shows the several-sided outlines inherited from the constituent grains. Spears (1987) and Casagrande (1987) reported that framboidal pyrite is commonly formed during the early pre-compaction stage. At a later stage, pyrite forms as non-framboidal granular to massive aggregates and may replace plant 89 tissue. Less commonly, pyrite occurs as lenses or grains of variable shape and size but generally flattened and elongate in cross-section, ranging from 2.0 to 30.0 microns diameter and also as dendritic masses (Plate 7g).
Veins of epigenetic pyrite (Plate 7h) are particularly common in coals with a comparatively high pyrite content (for example, Berau, Sangatta and Pasir coals). The veins are commonly associated with vitrite because it is the vitrinite-rich layers (particularly telovitrinite) that are more susceptible to cleat fracturing than liptinite- and inertinite-rich lithotypes (Ting, 1977; Spears and Caswell, 1986). Most veins are either parallel or subparallel to the bedding planes of the coal. In many cases, pyrite infills pre-existing or formerly incipient cleats. The veins are commonly only 5.0 to 10.0 microns in width with large crystals in some of the veins having well-developed crystal faces.
Vein pyrite is of post-compaction origin (Spears, 1987; Casagrande, 1987) and the formation of this epigenetic pyrite is dependent primarily on the availability of reduced sulphur, dissolved cations (commonly ferrous iron) and suitable locii for precipitation, generally, cleats, fractures or cell lumen.
Pyrite grains occur sporadically in all microlithotypes, especially vitrite and clay-rich layers.
In the Pasir coals, pyrite was also found in the vitrinite-rich vitrinertite. Renton (1982) also noted that the most common associate maceral for pyrite was vitrinite macerals followed by inertinite macerals. The least frequent association is with liptinite macerals although some cavity infillings in sporinite are found. In coals from eastern Kalimantan, the normal pyrite-vitrinite association is accentuated by the dominance of vitrinite in the coals.
The vertical distribution of pyritic sulphur in some coal seams is distinctive. For example, in the Berau coals, the highest concentration of pyritic sulphur is commonly localised at 90
the top of the coal seam (Figure 5.7), although less commonly, high pyrite levels may be
present in the lower or middle parts of the seam. The higher pyritic sulphur content in the
upper portion of the seam, rather than in the lower and middle parts as in the Berau coals,
implies that the sulphur content of the coal is influenced by marine roof strata. The same
feature was also found by Williams and Keith (1963), Gluskoter and Simon (1968) and
Gluskoter (1977).
In some Pasir and Sangatta coals, the highest pyritic sulphur content is in the lowermost
benches of the seam (Figure 5.8). The lowermost parts of the seam, and sometimes the
uppermost parts, contain high clay minerals and quartz contents as well. High pyritic
sulphur in these coals is probably associated with the ombrogenous peat environment rather
than a marine influence.
No definite lateral trend for any mineral was found.
5.3.4 Carbonate Minerals
Calcite is the dominant carbonate mineral although dolomite is also found. Most of the
calcite is epigenetic with a small proportion of syngenetic calcite. Both forms are easily
identified using optical microscopy (especially fluorescence mode), scanning electron
microscopy or X-ray diffraction techniques.
The carbonate content of samples ranges from 0% to 1.5% (average of 0.2%) with the
exception of one sample from Mahakam area (GM 24412) which contains up to 9.9% carbonate (Appendix 1). Generally, Mahakam coals contain the highest carbonate content
(average of 0.4%) followed by Berau and Senakin coals (average of 0.2%).
Carbonates occur mainly as veins (Plates 8a and 8b), lenses (Plates 8c and 8d), nodules 91
(either singly or in aggregates) and infillings in cell lumen. Individual nodules are commonly 50 to 400 microns in diameter and are roughly spherical. Veins are the dominant form of calcite; veins are commonly perpendicular to the bedding plane although some veins parallel to bedding were observed. Because such veins commonly follow cleat directions, they are typically exposed when the coal is broken.
The occurrence of calcite in fractures and cleats in the coal indicates that it is epigenetic and formed after the initial stages of coalification, probably after the coal seams had been uplifted sufficiently close to the surface to allow the development of cleats and fractures which allowed percolation of groundwater through the fractures. At least two periods of calcite deposition may have occurred in some of the coals from eastern Kalimantan - syngenetic precipitation of nodular calcite and epigenetic precipitation of vein fillings.
Multiple stages of calcite precipitation in coal is not uncommon. Hatch et al. (1976) observed as many as five distinct generations of veinlets of calcite filling a single cleat in
Illinois coals.
The presence of carbonates in cell lumens of telovitrinite, semifusinite and sclerotinite has been observed in many coals from eastern Kalimantan (Daulay, 1985). Calcite is commonly well crystallised and has a granular texture exhibiting greenish-yellow to orange fluorescence of medium to high intensity.
Some carbonate occurs in association with exsudatinite (Plates 8e and 8f)-
Distinguishing fluorescing carbonate from liptinite (particularly resinite, fluorinite and exsudatinite) is very difficult. However, in reflected white light, carbonate is anisotropic.
Carbonate fluorescence may result from the presence of interstitial oil-related substances or 92 the presence of organic entities such as animal fats and proteins that are bound in the carbonate structure.
5.4 FACTORS CONTROLLING MINERAL CONTENT
As for the Tertiary coals from other parts of the world, coals from eastern Kalimantan and other basins in Indonesia contain very little mineral matter compared to many of the older coals such as the Permian coals of Australia and India. Typically, the mineral content of
Tertiary coals is <5.0%, whereas in Permian coals it is >7.0% (Cook, 1975; Mishra, 1986;
Queensland Coal Board, 1986). An exception to the higher mineral content of post-
Tertiary coals is the data for a large group of Carboniferous coals which contain <5.0% mineral matter (Lapo, 1978; Stach et al, 1982).
The distribution of mineral matter in coal depends on its geological history and the environment of the peat mires. Such factors as the surrounding geological setting and the nature of the ground water are a great influence on the proportion of mineral matter added to a peat swamp.
In the Sangatta area of the northwestern Kutei Basin, many of the seams have <2.0% mineral matter and in the Adaro area of southeastern Kutei Basin, the coal presently mined from some thick seams has ash yields of <1.0% (Perusahaan Umum Tambang Batubara,
1986; Sahminan et al, 1988). The extremely low mineral matter/ash yield for the coals in these areas is a consequence of the elevated topography of the peat with respect to floodwaters, the acidity associated with high moor development and the increased solubility of mineral matter under conditions of low pH.
average mean mineral content of Eocene coals (average of 6.7%, Figure 5.9) is higher 93 than that for the Miocene coals (average of 3.9%) although the range of the means is greater for the Miocene coals, 1.6% to 22.2% compared to 0.2% to 27.9% respectively.
The low mineral content in some of the Miocene coals indicates that the balance between the rate of subsidence and the rate of accumulation of peat during the Miocene was significantly different from those during the Eocene and this influenced the mineral input to the respective peats.
Clay minerals and quartz (silicates) are the most common mineral components in the coals from eastern Kalimantan (Figure 5.10) although a small proportion of coals contain relatively high proportions of pyrite and calcite. Elsewhere, this phenomenon has been reported by Renton (1979; 1982), Mackowsky (1968; 1982a) and Bustin et al. (1983). In eastern Kalimantan coals, the silicates occur in a variety of modes ranging from thick interbeds and veins to micron-sized inclusions, selectively associated with specific organic entities.
Clay minerals, quartz, pyrite and carbonates show a preferential association with vitrinite as it is the most susceptible maceral for replacement (Cook, 1981b; Stach et al, 1982;
Roberts, 1988).
It is noteworthy that clay partings in eastern Kalimantan coals do not differ compositionally from those in the associated sediments (Panggabean, 1991); suggesting uniformity of the pore fluid composition with respect to clay stability fields. There is no evidence of volcanic products in the constituents of the clay partings.
Kaolinite is the dominant clay mineral in clay partings in the seams although sericite, illite, montmorillonite and halloysite are also present. Miller and Given (1978) postulated that the kaolinite in Tertiary lignites may be of detrital (or allochthonous) origin as well derived 94 from pre-diagenetic transformation of K-rich clay minerals in the original peat swamp.
Either mode of formation could be applicable to the eastern Kalimantan coals.
Pyrite, especially framboidal pyrite, is most abundant in coal seams that are directly overlain by marine strata (Williams and Keith, 1963; Chandra et al, 1983; Lyons et al,
1989) and for this reason pyrite is thought to develop mainly in areas where a marine or brackish environment transgressed the swamp shortly after peat accumulation. This has also been observed in recent peat deposits (Cohen et al, 1984; Casagrande, 1987). However, this is not the mode of pyrite formation in most, if not all, eastern Kalimantan coals (for example, coals in the Pasir and Sangatta areas) because there is no evidence of a marine succession directly above the coal seams. It is postulated that vitrinite formed where the water table and pH of peat environments were high and Eh was low. These conditions
2+ promoted bacterial sulphate reduction and the resulting H2S reacted with Fe and organic peat components to form pyrite and sulphur-bearing organic compounds. Inertinite precursors formed where the water table was lower and the Eh higher; aerobic conditions prevailed and little H2S was formed.
It should be noted that for eastern Kalimantan coals, there is no clear correlation between pyritic sulphur and vitrinite abundance although an inverse correlation between pyritic sulphur and inertinite was noted (Figures 5.11 and 5.12 respectively).
Figure 5.13 is a plot of mineral matter versus vitrinite content and shows that vitrinite- rich coals generally have lower mineral contents than vitrinite-poor coals. In other words, the proportion of mineral matter increases in clarite and duroclarite compared to that in vitrite. Furthermore, the data suggest a wide range of mineral abundances for the high- vitrinite coals. Correspondingly, inertinite-rich coals have lower mineral contents compared to inertinite-poor coals (Figure 5.14) as would be expected if the liptinite content was the 95 same in both.
Depositional conditions influence both lithotype and mineral composition of coals. Miocene coals contain fewer clay partings than Eocene coals and tend to be characterised by bright lithotypes with abundant vitrinite and low mineral contents. This is interpreted as indicating variations in subsidence rates with rapid burial of plant material encouraging preservation of the organic matter and producing coals rich in vitrinite with fewer clay partings.
5.4 SUMMARY AND CONCLUSIONS
Coal from eastern Kalimantan contains predominantly clay minerals, quartz, pyrite and carbonate. The mineral contents are much higher in the Eocene coals than in the Miocene coals.
Well-crystallised kaolinite is the dominant clay mineral and the presence of this mineral indicates a freshwater environment during peat formation. Only a small proportion of the clay minerals are considered to be epigenetic in origin; these clays are in veins.
Quartz, the second most abundant mineral, is mostly syngenetic although epigenetic quartz is present. Detrital quartz was introduced into the peat mire as overbank deposits from streams or by wind action.
Pyrite is most abundant in the Pasir coals (average of 1.7%) and the Berau coals (average of 1.0). Pyrite occurs mostly as grains, framboids, massive nodules, veins and a replacement mineral in organic matter. 96
Calcite is the dominant carbonate in eastern Kalimantan coals and is particularly abundant in Mahakam coals. The calcite is mostly epigenetic, occurring in fractures and fissures.
From a utilisation viewpoint, the most important feature of the eastern Kalimantan coals is the relatively low mineral contents, especially pyrite, which suggests that the coals will have a ready market both for domestic use and for export, when production is increased in the near future. 97
CHAPTER SIX COAL QUALITY AND UTILISATION
6.1 COAL QUALITY
Coal quality is a function of the interaction of a wide variety of parameters and the needs of the users. A high quality coal for one application may be an inferior coal for another, especially if one or more parameters do not fall in the desired range specified for the second application. Coal itself is an heterogenous organic material, formed largely from partially decomposed and metamorphosed plant material mixed with inorganic components.
Organic components of plants consist principally of cellulose, tannin and lignin with tannin and lignin more important because cellulose is more readily biochemically degraded to carbon dioxide and water during the accumulation and peat stages (Francis, 1961; van
Krevelen, 1981; Stach et al, 1982).
Differences in plant materials, such as tissue type and plant type, and differences in the extent of decay influence the type of organic components in coals. The organic components in coal are best described using maceral terminology. From a coal quahty/utihsation viewpoint, each maceral group and each maceral has a set of properties where the variation for each property is bounded by well-defined end points. For some properties the variation is a function of coal type whereas for others, variation is a function of rank. In this study, vitrinite reflectance is used as the rank indicator when assessing the effect of coal rank on utilisation. 98 In a particular coal, vitrinite contains relatively less hydrogen but relatively more oxygen than hptinite whereas inertinite tends to have relatively higher carbon and lower hydrogen than vitrinite but similar oxygen. In addition, some Hptinite is soluble and dissolves in selected organic solvents whereas inertinite is mostly insoluble (Davis et al, 1976).
Vitrinite is partly soluble in weak solvents and the degree of solubility depends largely on rank. In brown coals, vitrinite (huminite in ICCP terminology) is soluble in alkalis.
Maceral density increases in the order liptinite < vitrinite < inertinite.
Each maceral behaves differently under extraction conditions so that it is possible for two coals to have the same chemical analysis (proximate and ultimate analyses) but to give significantly different conversion yields under extraction (Given et al, 1975a; 1975b).
Chemical, physical and technological properties of a coal depend largely on both rank and type. Technological properties of eastern Kalimantan coals, including those important in
relation to combustion, gasification, liquefaction (hydrogenation and pyrolysis) and
carbonisation (low- and high-temperature processes) can be related to petrographic data
(coal rank, coal type and mineral matter) as well as to chemical analyses which generally
include both proximate analyses (volatile matter and moisture) and ultimate analyses. With
respect to ultimate analyses, sulphur content and ash yield (the residue left after combustion
of the coals) are particularly important. Several miscellaneous analyses, such as specific
energy, free swelling index and Hardgrove Grindability Index (HGI) are also useful tests
for evaluating coal utilisation.
Coal petrology/petrography has an important role when explaining the anomalous behaviour
during combustion although the coals have similar chemical analyses and therefore should
have similar predictable combustion performance. On the other hand, two coals with
different mean maximum vitrinite reflectances (R.max) may show identical volatile contents, 99 for example, Mahakam coal of Miocene age and Pasir coal of Eocene age (Table 6.1) but their chemical properties are different. Both coals also have identical vitrinite and liptinite contents but have different inertinite and mineral contents and the latter differences are the cause of the chemical differences. Titheridge (1988) also noted that coals with identical volatile matter and therefore identical hydrogen/carbon (H/C) ratio can have different vitrinite reflectance and aromaticities, that will in part be related to the forms and amount of organic sulphur. Thus for a study relating to coal quality and coal utilisation, organic petrography should be an integral part of the study.
Coals from eastern Kalimantan invariably contain inorganic, ash-forming constituents, particularly the Eocene coals, and these components may cause problems in relation to coal utilisation. Information on the nature of mineral matter in coal is important as it is needed to predict ash values. Improvements that reduce ash levels can be expected when coal is washed. For this purpose it is desirable to know the types of mineral matter, the range of phyteral, grain and/or crystal sizes and distribution patterns of the mineral matter in the coal.
Kaolinite and quartz are the main inorganic constituents together with minor other clay minerals (including illite and sericite), pyrite and carbonates. Some mineral components, particularly pyrite, act as catalysts in some reactions, for example, liquefaction or gasification processes. In carbonisation processes, mineral matter together with inertinite are inert materials.
Table 6.2 gives the ash analysis of eastern Kalimantan coals. The major components of the ash are Si02 and A1203 together with minor amounts of Fe203, CaO, MgO, K20, Na^,
P205, Ti02 and S03. As expected, the higher the mineral content of the coal (for example, as in the Senakin and Pasir coals), the higher the ash and therefore the greater the amount 100
of Si02 and Al2Os which clearly shows that the ash is derived predominantly from quartz
and kaolinite in the coals. This is supported by X-ray diffraction and scanning electron
microscopy studies. The exception to this is Asem Asem coal which has a high
percentage of Fe203 in the ash (average of 35.2%). The main source of Fe203 in this ash
is probably from pyrite which constitutes up to 4.0% of the bulk rock in some samples and
accounts for more than half of the total sulphur in most coals. High FejOj is also a feature
of the ash from Berau coal (average of 16.4%) and Sangatta coal (average of 17.1%). The
lowest of Fe^ in the ash is for Senakin coals (average of 3.5%).
The Miocene coals normally have lower vitrinite reflectance, ash fusion temperature,
mineral matter and liptinite contents, but higher inherent moisture, Hardgrove Grindability
Index (HGI), vitrinite and inertinite contents than Eocene coals. The Miocene Sangatta
coal occurs in an area with a high geothermal gradient and has the highest vitrinite
reflectance and the lowest hptinite content, of all the coals in eastern Kalimantan. It is
noteworthy that the Sangatta coal, together with the Miocene Tanjung coal, have the lowest ash yields.
6.2 COAL UTILISATION
Coal remains a_major Indonesian and worldwide energy resource even with the rapid growth in crude oil and natural gas production (Chapter 7). It is used as a solid fuel and as a reducing agent (either as coal or as refined products such as coke) and also as feedstock for the chemical industry.
The government policy requiring the substitution of coals for oil and gas in most
Indonesian industries that, up to now, have been based largely on crude oil and natural gas, requires the introduction of new technologies for coal utilisation to provide operating 101 conditions equivalent to crude oil and natural gas. These technologies may require the conversion of coals into oil and gas and thus processes such as liquefaction (hydrogenation and pyrolysis), gasification and carbonisation may become important in the future. For these conversion processes to be economically and technically viable, a data bank on coal quality is required. Thus data, such as provided by this study, is urgently needed to facilitate evaluation of eastern Kalimantan coals for these processes.
The quality characteristics of coal, to some extent, dictate how coal will be utilised. If coals with undesirable characteristics are to be used, coal preparation can, in some cases, produce significant economic benefits for the coal. The impact of coal preparation on coal utilisation, includes: blending (to get a more uniform quality product); minimising moisture content (to improve handling characteristics); reducing inertinite and mineral contents (particularly for combustion and liquefaction processes); and optimising inertinite content (to improve coke strength).
After direct combustion, the conversion of coals to liquid and gaseous products is likely to become the second priority for use of eastern Kalimantan coals. The rank, type and chemical composition of the eastern Kalimantan coals are generally favourable for both processes, but liquefaction and gasification have not been considered an economically attractive processes in the past owing to the low cost of crude oil and natural gas. It has been predicted that these processes could be economical if the residue from the processes
(40% to 60% of the raw coal) can be reused as feedstocks for such combustion technologies as electricity generation. 102
According to Davis et al. (1976) and Cudmore (1977), the highest conversion rates of coal to liquids and gases are obtained from coals with the following characteristics: mean maximum vitrinite reflectance (Rvmax) of less than 0.8%; reactive maceral contents, vitrinite plus liptinite, greater than 60%; volatile matter (dry air free basis) greater than 35%; and hydrogen to carbon atomic ratios (dry air free basis) greater than 0.75.
Comparison of these variables with typical properties of coals from eastern Kalimantan is shown in Table 6.3. In general, all eastern Kalimantan coals (except for Sangatta thermally affected coals) are suitable as raw materials in the conversion process and will be discussed in more detail in Section 6.2.2.
6.2.1 Combustion
6.2.1.1 General
Direct combustion of coal currently is the largest consumer of coal in Indonesia and this will probably continue to be the case for many years. The primary use of coal combustion is for steam generation used directly or indirectly for electricity generation, industrial processes (including cement, bricks and tiles manufactures) and domestic consumption. In direct combustion, coal is burned and the carbon and hydrogen are oxidised to carbon dioxide and water; potential chemical energy of the coal is converted to thermal energy.
Eastern Kalimantan coals have calorific values ranging between 4344 and 7650 kcal/kg which are comparable to those of coals from Sumatera (4500 to 8050 kcal/kg) which are the major feedstocks for combustion in Indonesia at present.
The combustion of coal particles involves several steps including heat-up, devolatilisation, volatiles combustion and char burn-out (Tsai, 1982; Smoot and Smith, 1985; Crelling et al,
1992). These steps are controlled by many factors including the interaction between the rate of oxygen diffusion to the reacting surface and the inherent chemical kinetics of char 103 oxidation. For any given heating rate, char morphology depends largely on coal type and coal rank.
The three commonly-used processes for the direct combustion of coal, based on coal particle size or temperature of combustion, are pulverised coal, fluidised bed and fixed bed combustors (Lowry, 1963; Elliot, 1981; Merrick, 1984). The pulverised coal combustor technique is in widest use amongst utilities in Indonesia and represents the most modern design and highest combustion efficiency for this application.
Coal that is burned in pulverised-coal plants is typically ground to a nominal average particle size of -200 mesh (75 |im) and, together with air, is blown into the furnace cavity in suspension firing. The coal burns at a high temperature (typically 1500°C) transferring heat by radiation to water-filled tubes in the walls of the combustion chamber. Residence time required for a constant combustion efficiency is affected by both volatile content and the coal particle size.
Slagging and fouling are two of the greatest problems associated with high-temperature combustion processes. Slagging problems are defined as those in the actual furnace itself, that is, in that part of the furnace that houses the flame. Fouling, on the other hand, occurs as a result of the mineral matter or ash being carried into the convection passages, away from the flame. Slagging is the result of fusion to form liquids whereas fouling is the result of vaporisation-recondensation processes.
Eastern Kalimantan coals are well suited for pulverised coal combustors because the high vitrinite contents which range from 61.9% to 98.0% and average of 81.4%) lead to rapid burnout. 104
6.2.1.2 The Influence of Coal Rank and Type Traditionally, Indonesian combustion industries selected coals for use in pulverised coal- fired boilers largely on the basis of chemical analysis (including calorific value, volatile matter, ash yield and ash fusion characteristics) and physical tests (particularly HGI), as these factors were known to affect combustion characteristics. With the increase in use of coals from diverse sources rather than from a single supplier, it was found, in many instances, that coals tested and grouped in the traditional way behaved differently to expectations during boiler combustion, especially when in full-scale operation mode.
It appeared that some traditional tests were no longer adequate. Many combustion industries in the world have adopted coal petrology as a major testing technique. After some speculation, there is an acknowledgment that maceral composition should contribute to the ranking and classification of coals for the international market and many users are quickly appreciating the influence of macerals on combustion characteristics of coal.
However, this technique is not widely adopted in the Indonesian combustion industry due to a lack of understanding of coal type and coal rank, and the lack of experienced organic petrographers. In the future, it is expected that coal petrography (maceral composition, vitrinite reflectance and mineral matter) will become an important analysis technique that will be used when evaluating coals for a specific uses.
Lithotypes, microlithotypes, macerals, mineral matter and maximum vitrinite reflectance can be used on a comparative basis for boiler design purposes. The differences in the combustion characteristics of the coals are influenced by the nature of variations in the organic constituents, that is the maceral and microlithotype compositions, and mineral constituents, although other factors, such as chemical structure, coal microstructure, inter-
and intra-maceral porosity and rate of heating also have to be considered. These factors will affect plasticity and the release of volatile decomposition products. 105
Coals from eastern Kalimantan are dominated by vitrite and resinite-rich and/or suberinite- rich clarite (Chapter 4). Vitrite is brittle and therefore it normally concentrates in the fines during preparation whereas clarite is less brittle and does not. Stach et al (1982) and
Bustin et al. (1983) showed that the strength of microlithotypes increase from vitrite --> clarite --> durite --> mudrocks. Multimaceral microlithotypes are stronger than monomaceral one.
Eastern Kalimantan coals are composed mostly of the reactive macerals vitrinite and liptinite, which contain relatively more hydrogen than inertinite which is less reactive. The reactivity characteristics of macerals observed during carbonisation can be extrapolated equally to combustion (Nandi et al, 1977). Therefore, the high proportion of reactive components in the coals from eastern Kalimantan is an advantage in combustion. On the other hand, this is a problem for some coals because of the tendency for spontaneous combustion during mining, transport or storage.
Particle size, flame length and boiler design critically influence aspects of combustion and thus, a power station equipped with a specific boiler type can be operated optimally only with coal suited for that boiler type.
Nandi et al (1977), Lee and Whaley (1983) and Sanyal (1983) noted that the proportion of unburnt carbon during combustion is directly related to the inertinite content of the coal.
The higher the inertinite content, the lower the combustion efficiency. In addition, combustion of coals with lower inertinite contents is completed earlier compared to coals with higher inertinite contents. Further investigations by Sanyal (1983), Hough and Sanyal
(1987) and Crelling et al. (1992) noted that vitrinite-rich vitrain and vitrinite-poor clarain tend to form thin-walled cenospheres whereas clarain (inertinite-rich) tend to form thick- walled cenospheres with higher carbon contents. 106
Inertinite content controls the flame length during combustion.
In the case of eastern Kalimantan coals the influence of the inertinite on combustion
process can largely be ehminated, because:
inertinite content of the coal is very low typically <5% for Miocene coals and
<3% for Eocene coals, except for a small number of Miocene Mahakam,
Sangatta and Berau coals where inertinite is more abundant. Thus, the
combustion efficiency of these coals, which contain up to 31% inertinite, may
be lower than for the other Miocene coals due to their very low inertinite
content.
reflectance of inertinite in all samples is typically very low and close to the
reflectance of vitrinite. For example, in sample GM 24163 from Senakin coal,
reflectance of inertinite is 0.71%, compared with a vitrinite reflectance of
0.51% within the same grain. Thus most, if not all, of the inertinite is
reactive inertinite.
This phenomenon is also supported by Hardgrove Grindability Index (HGI) values of the
coals (Table 3.7). The average HGI of eastern Kalimantan coals ranges from 34 to 58 and
thus they are classified into very hard (<40), hard (40-55) and medium (>55). The mean
HGI values for Eocene coals varies from 34 to 40 whereas for the Miocene coals, the mean
HGI values ranges between 46 and 58. Based on the HGI values, Eocene coals which
contain lower inertinite contents than Miocene coals, are nevertheless tougher and therefore,
combustion times for Eocene coals are longer because of larger particle size for any given
level of grinding.
The HGI values of Miocene coals from eastern Kalimantan are generally identical with 107 values for other Miocene coals in Indonesia. However, the HGI values for the Eocene coals are typically lower (that is, the coals are tougher) than for other Indonesian Eocene coals. This is partly related to eastern Kalimantan coals having higher hptinite and mineral contents than other Indonesian Eocene coals (for example Ombilin coals; Daulay, 1985) and it is these components that lower the HGI of coals (Hower et al, 1987; Hower and Wild,
1988)
Figure 6.1 shows the general relationship between HGI and rank as indicated by vitrinite reflectance for eastern Kalimantan coals. The data agree with the results of Hower et al.
(1987) and Harrison (1963) who noted that for Kentucky (USA) coals and Illinois coals, respectively, that HGI increases with an increase in rank. The authors attributed the relationship to petrographic composition and mineral content.
Based on Figure 6.1, coals having vitrinite reflectance values of less than 0.50% or greater than 0.60% (mostly Miocene coals) are easier to grind than coals with vitrinite reflectance in the range of 0.50% to 0.60% (mostly Eocene coals). Specifically, Asem Asem coal
(average ^max = 0.36%) is the easiest to grind followed by Miocene Tanjung coal
(average Rvmax = 0.40%), Berau (average ^max = 0.45%), Sangatta (average Rvmax =
0.63%) and Mahakam (average Rvmax = 0.47%). The Eocene Tanjung (average Rvmax =
0.60%), Pasir (average Rvmax = 0.62%), Satui (average Rvmax = 0.50%) and Senakin
(average Rvmax = 0.56%) coals are harder to grind.
Petrographic examination also suggests that selective crushing and grinding procedures may yield a better product for pulverised coal burners. Each maceral group behaves differently during grinding and this is related to the properties of the maceral group. Liptinite, for example, is very difficult to grind and normally concentrates in the coarse fraction whereas vitrinite and inertinite concentrate in the fines during coal preparation (Nandi et al, 1977; 108
Hower et al, 1987).
Eocene coals (Satui, Senakin, Tanjung and Pasir) typically contain more liptinite than
Miocene coals (Berau, Mahakam, Tanjung, Sangatta and Asem Asem) and are more difficult to grind and therefore the duration of combustion needed is much longer for
Eocene coals because of the higher proportion of larger grain sizes.
Mineral matter is the cause of most problems associated with burning eastern Kalimantan
(particularly Eocene) coals. Mineral matter may result in stack emissions that contravene environmental regulations. Therefore, ash characteristics are the major obstacle in efforts to improve the thermal efficiency of combustion processes.
Mineral matter in eastern Kalimantan coals influences the HGI (Figure 6.2) and ash fusion temperature. The high mineral content of Eocene coals (typically 8.0% to 10.0%) compared to that of Miocene coals (typically 2.0% to 5.0%) tends to result in lower HGI values for the former and therefore, larger grain sizes. Thus, for the Eocene coals burnout is more difficult. The low HGI values for Satui coals, although mineral matter content of the coals is relatively low compared with other Eocene coals (Figure 6.2), is a result of the high Hptinite content of the coals which is as high as 33% in some samples. Thus, for eastern Kalimantan coals, several variables influence HGI.
Lowry (1963) and Sanyal (1983) reported that the duration of combustion processes commonly increases with increasing rank of the coal. Applying this to eastern Kalimantan coals, longer combustion times are needed to avoid high residual carbon levels in the fly ash produced from combustion of the Eocene coals, which normally have a higher vitrinite reflectance than Miocene coals. Consequently, Miocene coal burnout is relatively more complete than for Eocene coals, because the average particle size of Miocene coals tend to be finer for any given grinding circuit. 109
Ash composition also affects ash fusion temperatures and causes chancering, slagging and fouling in the gasifier and seriously affects the design of the ash removal system employed.
The fusion characteristics of the ash from various coalfields in eastern Kalimantan are shown in Table 6.4. The low ash fusion temperatures for Miocene coals compared with that for Eocene coals is probably related to relatively high carbonate contents in the
Miocene coals (>1% and up to 10% in several Sangatta, Mahakam and Berau coals).
Shibaoka et al. (1985) found that during combustion, slagging behaviour of low rank coals is greatly influenced by the volume of mineral matter. At a temperature of 1500°C +
200°C, all of the inorganic material is transformed to ash. On collection this is largely glassy material rather than crystalline. As well as a dilutent effect, which lowers the calorific value of the fuel, the mineral constituents may produce large quantities of fly ash, the composition of which varies from one mineral assemblage to another and varies according to the physical interrelationships of the minerals to each other and to the organic matter.
The composition of fly ash also depends on the combustion temperature, the residence time at high temperatures and possibly on the oxidising or reducing conditions in the immediate environment of each ash particle. Therefore, fly ash is a mixture of particles of complex chemical composition and physical state.
Since coal ash is a complex mixture of compounds, it melts over a range of temperatures instead of at a unique melting point. According to Watt (1969), clays begin to dehydrate below 300°C, pyrite rapidly decomposes at 600°C, carbonates and sulphates evolve C02 and
S02 above 500°C and silica volatilises at temperatures higher than 1600°C. These changes commence during the rapid heating of the coal on injection into the furnace. 110
The high silica content of the mineral matter in most eastern Kalimantan coals is a negative aspect of the coal as the silica promotes rapid deterioration of fabric filters and result in hard, massive deposits on the boiler heat transfer surfaces, thus reducing thermal efficiency.
Coals from Berau and Pasir have a high sulphur content, particularly pyritic sulphur, and this may cause numerous problems with respect to combustion applications. The sulphur and related components could cause corrosion in the boilers and a build up of fouling on the boiler tubes. Corrosion is normally accompanied by plugging of the gas passages with fly ash which adheres to the wetted metal surfaces. This causes problems with atmospheric pollution, especially acid rain, as large amounts of S02 are released with the stack gases.
During combustion, most of the sulphur is oxidised to S02, of which 0% to 7% is further oxidised to S03; the balance of the sulphur remains in the coal ash or slag (Tsai, 1982).
The concentration of S02 in the flue gas vented to the atmosphere is now regulated by the
Indonesian Environmental Protection Agency and greater care will be needed in future when selecting coals for combustion. Coarse-grained pyrite in the high-gravity fractions will formation low-melting species not detected by conventional analyses of coal ash (Reyes-
Navarro and Davis, 1976). The behaviour of pyrite during combustion varies widely and is influenced by the ignition mechanism and kinds of defects in the crystal surfaces caused by impurities (Miller et al, 1979). Thus the high sulphur coals from Pasir should not be placed high on the priority list of coals to be used for combustion.
Other coal properties that affect design and operation of a boiler include calorific value, volatile content and moisture content. The calorific value of coals determines the amount
of steam that can be generated per unit of coal in a boiler. Coals with higher calorific
values normally generate more steam per unit of coal. Miocene coals from Mahakam,
Sangatta and all Eocene coals (with average calorific values of 6300 kcai/kg to 7100 Ill kcal/kg) generate more steam per unit of coal than Miocene coals from Berau, Tanjung and
Asem Asem coals which have lower calorific values.
Volatile matter is important as it controls smoke emissions and ignition properties. Figure
6.3 shows a positive correlation between volatile matter and ash fusion temperatures of selected coals from eastern Kalimantan. Asem Asem and Berau coals which have low volatile matter (average of 37.6% and 38.1% respectively) burn slowly with a short flame and are normally best used for domestic heating where the heat is dominantly transferred from the fuel bed. Miocene coals from Sangatta and Eocene coal from Senakin, Satui,
Pasir and Tanjung, have high volatile contents (typically >40.0%) and burn with long hot flames. They are suitable for use in kilns. However, coals with high volatile contents tend to produce more smoke (Lowry, 1963; Tsai, 1982). Provided temperatures are high and with sufficient residence time, smoke can be reduced and even prevented by sufficient mixing of the correct volume of air for the volume of hydrocarbons released from the coal.
This should be taken into account when new Indonesian combustion facilities are designed.
Moisture content normally lowers the flame temperature causing loss of sensible heat with the flue gases, affects the grindability of the coal and causes clogging of pulverised coal systems. The average inherent moisture content of each coal from eastern Kalimantan is plotted against the average HGI (Figure 6.4) which range from 34 to 58.
The high moisture content of Asem Asem and Tanjung Miocene coals, (average of 27.7% and 22.1% respectively) is probably related to a high unit surface area of the coal (a feature discussed by Merrick, 1984), especially for retained moisture after drying. Coals also become harder to grind as the percentage of volatiles decreases. Merrick (1984) also noted that approximately 8.0% moisture is necessary for the prevention of combustion loss from a chain-grate stoker. Moisture content is most important for fines less than 0.5 mm 112
diameter and affects handling characteristics.
The HGI values of Sangatta coals are higher than those of all Eocene coals from eastern
Kalimantan, although the average moisture contents are identical (Figure 6.4). This is
probably related to higher contents of vitrinite and inertinite (typically >90%) and the
corresponding lower liptinite plus mineral contents (typically <10%) of Sangatta coals
compared to those in the Eocene coals.
Overall, maceral composition (especially hptinite), mineral matter (ash yield and sulphur content) and vitrinite reflectance represent the main controls over combustion behaviour of eastern Kalimantan coals. For the lower rank coals, the influence of inherent moisture and volatile matter are also significant. Thus, in general, combustion time for Eocene coals is much longer than for Miocene coals because of the higher proportion of larger particles in the Eocene coals, a phenomenon that is controlled by the higher liptinite and mineral contents in these coals.
6.2.2 Liquefaction
6.2.2.1 General
Production of liquid fuels from coal is one of the potential uses for eastern Kalimantan coals. Until now, preliminary research has been conducted only on Banko coals from
South Sumatera Basin but in the future it is anticipated that this research will be continued on coals from other big mines such as those in eastern Kalimantan. Development of successful liquefaction processes would maximise the use of the coal and also decrease the negative impact on the environment.
Liquefaction processes can be conducted directly or indirectly. Direct coal liquefaction produces liquids which normally require upgrading prior to cracking in a conventional 113 petroleum refinery, whereas indirect coal liquefaction yields clean liquid products from processes such as gasification or Fisher-Tropsch synthesis.
Direct coal liquefaction involves hydrogenation of coal in a solvent slurry at an elevated temperature of 370°C to 480°C. Pyrolysis involves heating coal in the absence of air to drive off the volatile components, which are condensed to liquids, leaving a solid residue
(Lowry, 1963; Berkowitz, 1979; Ward, 1984).
Elevated temperatures are required for the thermal breakdown of coal in order to produce reactive fragments (free radicals). The solvent slurry is needed for coal solvation and transfer of reactive hydrogen to stabilise the coal-derived free radicals. As a result of thermal cracking or hydrogenation, liquids of relatively low molecular weights and gases are produced. Liquid coal liquefaction products are normally divided into three fractions: oils, asphaltenes and pre-asphaltenes which have molecular weights of 400 or less, 300 to
1000 and 1000 to 3000, respectively. Liquid products are normally separated from solids either by distillation or by filtration.
The aim of coal liquefaction is to break down the molecular structure of the coal and increase the hydrogen to carbon ratio of the products thus forming hydrocarbon liquids.
As the major components of natural crude oil are dominated by alkanes, to produce synthetic oil substitutes, a high make of product alkanes is required.
Coals consist of solid material dominated by aromatic structures with aliphatic side-chains.
At low rank, the hydrogen atoms are equally divided between aliphatic and aromatic structures. This contrasts with the carbon atoms where approximately 80% of the atoms are in aromatic groups (van Krevelen, 1981). 114
The hydrogen content of most coals must be virtually doubled in order to produce alkanes.
A much smaller increase could produce aromatic compounds but many of these are toxic.
Thus, efficient utilisation of hydrogen is an important aspect of coal liquefaction from the standpoint of reaction mechanism and chemistry.
6.2.2.2 The Influence of Coal Rank and Type
The liquefaction behaviour of coals varies markedly depending on chemical composition, coal type, coal rank and mineral matter characteristics. The behaviour of coal macerals during liquefaction has been linked to the degree of gelification of the original plant material and to the type of solvent used (Shibaoka, 1981). Poorly-gelified vitrinite expands readily and becomes vesicular, liquefying at relatively low temperatures. In contrast, highly-gelified vitrinite, expands only moderately to form relatively coarse vitroplast particles and thus liquefying at relatively high temperatures.
Given et al. (1975a; 1975b), Davis et al. (1976) and Machnikowska and Jasienko (1985) showed that petrographic composition of coals strongly influences liquefaction behaviour.
Further investigations by Machnikowska and Jasienko (1985) and Mackay (1985) noted that hptinite macerals are completely depolymerised to liquid and gaseous products at a temperature of approximately 380°C. Saxby and Shibaoka (1986) suggested a ratio of
40:5:1 for the maximum specific yield of oil that could be released from hptinite, vitrinite and inertinite respectively.
On an elemental basis, the atomic hydrogen to carbon (H/C) ratio ranges from 1.2 to 1.5 for crude oil whereas this ratio is 0.4 to 1.0 for most coals. H/C ratios of coal depend on maceral composition as well as coal rank (Durie, 1982). The H/C ratio of coal is very similar to that of benzene. Thus, direct production of liquid fuels from coal, requires the breakdown of the chemical structures to lower molecular weight fragments which are fluid 115 under ambient conditions, with the simultaneous elimination of oxygen and an increase in the hydrogen to carbon ratio so as to effect saturation of some of the aromatic structures in the coals.
Typically H/C ratios of selected eastern Kalimantan coals range from 0.76 (Asem Asem) to 0.96 (Senakin); the H/C ratio of Eocene Tanjung coal is 0.89 (Table 6.3). The H/C ratios correlate with high hptinite and volatile contents. Liptinite macerals are the main sources of both volatile matter and hydrogen in the coals. Vitrinite and hptinite are the main components of eastern Kalimantan coals thus, using the data of Saxby and Shibaoka
(1986), eastern Kalimantan coals are likely to produce significant amounts of liquid hydrocarbons in liquefaction reactions.
Fischer Assay Yields
In an attempt to understand the yield of liquid products under pyrolysis conditions, twenty two coal samples from eastern Kalimantan were pyrolysed by The Australian Coal Industry
Research Laboratories Ltd. (ACIRL), Brisbane. A modified Fischer assay technique was used and the results are shown in Table 6.5. Fischer assays provide data on the yields of coke, tar, light-oil, gas and water when coal is heated at a temperature of 500°C to 600°C.
The samples were selected on the basis of rank (ranging from brown coal to high-volatile bituminous coal rank) and type (liptinite-rich to liptinite-poor).
Fisher assay values provide direct information about liquid yields under pyrolysis conditions and this information can be related to liquefaction, and hydrogen demand for hquefaction, during hydrogenation.
Oil yield (water-free basis) of the samples ranges from 55 litres/tonne to 279 litres/tonne with an average of 136.0 litres/tonne (Table 6.5). On the hmited data available, the lowest 116
oil yielding coal is Berau coal from the Tarakan Basin (55 litres/tonne to 97 litres/tonne,
average of 78.5 litres/tonne), whereas the highest oil yielding coal is Satui coals from the
Asem Asem Basin (198 litres/tonne to 241 litres/tonne, average of 219.5 litres/tonne).
Compared with Miocene coals where the oil yields are 55 litres/tonne to 279 litres/tonne
(average of 120.6 litres/tonne), the oil yield from Eocene coals is 161 litres/tonne to 241
litres/tonne, average of 188.0 litres/tonne which is significantly higher (Figure 6.5). The
variations in the oil yield mostly appear to be related to maceral composition. For
example, Figure 6.6 shows a positive correlation between oil yield and reactive maceral
content (vitrinite plus hptinite) where the combined percentage of the two is normally
greater than 85% of any bulk sample.
R-mode cluster analysis was carried out to show interrelationships between oil yield and
various organic components, mineral matter and vitrinite reflectance for the twenty two
samples analysed (Table 6.6). The data set, using Pearson product moment correlation
coefficient as a measure of similarity, and the equally weighted pair-grouping method of
clustering, shows five cluster groups (Figure 6.7):
Cluster A vitrinite reflectance, telovitrinite, silicate minerals
Cluster B semifusinite, inertodetrinite and fusinite
Cluster C micrinite, carbonate and pyrite
Cluster D sporinite, cutinite, resinite, oil yield, exsudatinite, hptodetrinite,
suberinite and fluorinite
Cluster E : detrovitrinite, sclerotinite and gelovitrinite
Oil yield is including in cluster group D in which the only other members are hptinite
macerals. The group has a moderate to strong positive correlations (r of 0.40 to 0.89).
Oil yield is moderately to strongly linked with total liptinite (Figure 6.8). 117
The highest oil yield (279 litres/tonne) is for GM 24402, a Mahakam coal with 16.1%
liptinite (Figure 6.8). A high oil yield (241 litres/tonne) was also obtained from a Satui
coal (GM 24146; hptinite content of 22.0%, predominantly resinite, sporinite and cutinite).
These two coals illustrate the strong correlation between hptinite content and oil yield. In
contrast, Berau coal (GM 24335) with 3.0% hptinite produced only 64 litres/tonne oil yield.
This small but significant oil yield appears to be higher than that predicted from the
liptinite content and it is assumed that some of the oil is derived from vitrinite during pyrolysis.
The correlation coefficients for oil yields with resinite, exsudatinite, suberinite, fluorinite,
sporinite, liptodetrinite and cutinite are 0.89, 0.79, 0.64, 0.61, 0.56, 0.54 and 0.50
respectively (Table 6.7). From these data, resinite appears to be the dominant source of
Fischer assay oil in eastern Kalimantan coals with suberinite and exsudatinite also
significant sources. To test this hypothesis, oil yield was plotted against each of the
hptinite macerals (Figures 6.9, 6.10 and 6.11 respectively) and all groups showed a good positive correlation for the line of best fit.
Sample GM 24311, a Sangatta coal with a low hptinite content (2.5%, Figure 6.8) had a high oil yield of 139 litres/tonne. This is much greater than that amount predicted from the Hptinite content. Some of the vitrinite in this sample had anomalous colour and reflectance and it is believed that this vitrinite may have been intimately mixed with suberinite (although only 0.40% suberinite, Figure 6.10, was recorded). Difficulty was experienced in distinguishing suberinite from vitrinite at high levels of rank. Suberinite appearance changes rapidly with small changes in rank from subbituminous to bituminous coals (Section 4.4).
Liptinite macerals normally are characterised by high hydrogen content, high atomic H/C 118 ratio, high volatile yields, low decomposition temperatures and high fluidity during conversion (Murchison and MMais, 1969; van Krevelen, 1981). Hydrogen content of eastern KaHmantan coals ranges from 5.1% to 6.3%. hi general, the higher the hydrogen content of coal, the greater the ability of a coal to generate oil and gas. Berau coals, for example, have an average hydrogen content of 5.1%, and an average oil yield (water free basis) of 78.5 Htres/tonne. In contrast, Senakin coals have an average hydrogen content of 6.3% and an average oil yield of 167.0 Htres/tonne.
Inertinite (typicaUy <5% in most samples) contributes Httle toward the liquefaction products.
In some of the Mahakam coals, however, the percentage of inertinite is moderately high, up to 31%. These coal have low yields of Hquids under normal Hquefaction conditions and it is assumed that this is a function of numerous condensed aromatic nuclei. For the high- inertinite Mahakam coals to be Hquefaction feedstocks they would have to be beneficiated to increase the reactive macerals before use although removal of inertinite from the coal
Hquefaction feed typicaUy results in a higher percent solvation, higher distiUate yield and reduced hydrogen consumption.
Plots of oil yield against vitrinite reflectance (Figure 6.12) show considerable scatter. In general, for eastern Kalimantan coals, oil yield decreases at higher ranks. The highest oH yields were found for coals with Rvmax of 0.34% to 0.55%. This section of the plot
(Figure 6.12) includes most of the Miocene coals (except for some of the higher rank
Sangatta coals) and some of the Eocene coals. It can be concluded that the less mature coals (^max less than 0.6%) give higher Fisher assay yields than the more mature coals
(Rvmax more than 0.6%) for any given maceral composition. This effect is beHeved to be related to the lower abundance of condensed rings and the higher hydrogen content of the younger coals which renders them more amenable to compositional change and breaking of C-C bonds. 119
Abdel-Baset et al. (1978), Huttinger and Krauss (1981) and Merrick (1984) noted that a high pyrite content is advantageous for liquefaction because pyrite acts as a catalyst for the reactions involving hydrogen. Pyrite is transformed into pyrrhotite (Fe,.x S) and it is this mineral that has the catalytic influence. The studies cited above suggest that selected coals from Berau, Sangatta and Pasir which have relatively abundant pyrite (up to 9.9%, Table
5.2) are the coals that would show maximum catalytic enhancement. For catalytic enhancement to occur, however, elemental iron must be formed during heat-treatment and gasification, especially from iron sulphides.
It is concluded that on the basis of the Fischer assay data, coals from eastern KaHmantan have a high potential for hydrocarbon production. The hydrogen-rich and more ahphatic nature of the coals with abundant Hptinite are the best feedstocks for Hquefaction.
It is interesting to note that the coals which showed direct evidence of the presence of hydrocarbons under microscopic examination, in the form of oh haze, oil drops and abundant exsudatinite (Section 4,7) are the same samples that gave high Fischer assays.
This suggests that these coals are exceUent natural source rocks as well.
6.2.3 Gasification
6.2.3.1 General
Gasification of coal is, essentially, the conversion of coal to combustible gases by heating it under pressure. This is achieved by maximising the volume of methane that can be generated. Gasification reactions take place at temperatures between 600°C and 1100°C
(van Heek et al, 1973). At a temperature of approximately 900°C, reactions form hydrogen, C02, CO and small quantities of methane. Below 600°C devolatUisation and reaction with the water vapour take place simultaneously. Potential uses of the gaseous hydrocarbons are as substitutes for natural gas or fuel oil in equipment such as utility 120 boHers, industrial boilers and gas turbines to generate power.
Based on the methods of reagents and the condition of the residue after reaction, processes for conversion of coals into gas can be divided into four types (Hebden and Stroud, 1981;
Johnson, 1981):
- entrained-flow (particles <0.12 mm);
- molten bath (particles 0.12 mm or larger);
- fluidised bed (particles <3.0 mm); and
- fixed-bed (particle ranges from 6.0 mm to 50 mm).
Most gasification reactions are mainly directed towards producing either synthetic gas, a mixture of CO and H2, or synthetic natural gas consisting mostly of methane. The main gasification reactions include:
* C + 2H20 > C02 + 2H2
* 2C + 02 > 2CO
* 2CO + 02 > 2C02
* CO + H20 > C02 + H2
By converting coal to gaseous fuel, environmental problems can be reduced because the gas is made sulphur-free, eliminating acid rain, and burns without producing particulate soHds.
According to Fung (1982) there are three stages in the gasification reaction: devolatilisation, gasification and combustion stages. DevolatiHsation is the first reaction and terminates when all the volatile matter has evolved or when there is no further evolution of methane to the product gas. Gasification is foUowed by combustion. Fung (1982) noted that the commencement of combustion process is defined as the time when the oxygen concentration 121 exceeds 1% in the product gas.
6.2.3.2 The Influence of Coal Rank and Type
Compared to combustion, gasification and Hquefaction occur at lower temperatures, take place under more reducing conditions and have longer residence times. The main coal properties influencing gasification are coal rank and type together with reactivity, mineral matter, moisture, volatile matter, fixed carbon and size distribution.
As with liquefaction, high gasification rates are largely dependant on the abundance of reactive macerals (vitrinite plus Hptinite) and the reactivity of the char. Experiments involving gasification of coal char in air or C02 show that the reactivity of char increases as the rank of the feed coal decreases (Jenkins et al, 1975; Beesting et al, 1977; Bend et al, 1992). Neaval (1981) suggested that coals used for feedstock in gasification reactions should have a high reactive macerals content (typicaUy >80%) and have a vitrinite reflectance ranging from 0.5% to 0.8%.
Eastern Kalimantan coals have high reactive macerals contents (typicaUy ranging from
89.6% to 92.8%) and low vitrinite reflectance (typically ranging from 0.40% to 0.63%) and are considered to be good quality feedstocks for gasification.
Under non-slagging conditions, reactive coals are preferred as feedstocks in gasification reactions in order to maximise the conversion and throughput. In particular, reactivity is an important factor for hydrogasifiers, both because the reaction rates are slow and equUibrium considerations favour low operating temperature. The increased reactivity of char obtained from low rank coals has been attributed to higher porosity and calcium content (Tsai, 1982). In oxidising atmospheres, such as air and C02, calcium improves the char reactivity (Ningrum, 1990). 122
Mineral matter (particularly pyrite) interacts with the catalysts in the gasification process.
Abdel-Baset et al (1978) noted that mineral matter extracted from coals promotes the gasification of less reactive coals. In addition, Hippo et al (1979) found that mineral matter can act as an active catalyst when low rank coals are gasified.
Rank influences the volume of product gas. For example, Fung (1982) noted that under the same gasification conditions, low rank coals lost more weight and generated more product gas than high rank coals. Van Heek et al (1973) plotted the rate of carbon conversion, as a function of temperature (Figure 6.13) and showed, in general, that high rank coals have lower reactivity than low rank coals, so that gasification temperatures have to be higher to achieve the same reaction rates. For example, in the case of brown coal,
a rate of 20% conversion (Figure 6.13) is reached at a temperature of approximately 760°C whereas in the case of anthracite, this conversion rate is reached at a temperature of approximately 1000°C.
Based on Figure 6.13, 20% conversion for eastern Kalimantan coals can be reached at three different temperatures:
760°C, for Miocene coals from Asem Asem and Tanjung and some coals from
Berau and Mahakam; vitrinite reflectance is 0.40% or less;
910°C, for several coals from Mahakam, Berau, Sangatta and Satui, and
selected coals from Senakin; vitrinite reflectance ranges between 0.40% and 0.60%.
1000°C, for most of the Miocene coals from Sangatta, the Eocene coals from
Tanjung and Pasir and selected coals from Senakin; vitrinite reflectance is 0.60% or more. 123
6.2.4 Carbonisation
6.2.4.1 General
Carbonisation is the process where a carbon-rich residue (char or coke) is produced by thermal decomposition, with simultaneous removal of volatUe substances by destructive distiUation. During carbonisation reactions (without the addition of chemical agents) three important stages determine the properties of the final product. These are softening, swelhng and stiffening (Cook and Wilson, 1969; Cook, 1982).
The products of carbonisation can be divided into char and coke based on their physical structures, which in turn is related to molecular structures. Chars are formed where the parent coal (especially low rank coals) shows no viscosity during carbonisation. However, if the coals soften, fuse and resolidify during decomposition, then the vesicular structure of coke is formed.
Gas, ammonia, tar and tight oil are produced as volatiles. These products vary with coal rank, coal type, mineral content and carbonisation conditions such as temperature, heating rate and residence time. Coal carbonisation reactions are commonly regarded as low- temperature, medium-temperature and high-temperature reactions where the temperature of the reaction ranges from 500°C to 700°C, 700°C to 900°C and 900°C to 1050°C, respectively
(Jasienko, 1978; EUiott, 1981).
Low-temperature carbonisation is developed mainly as a process to provide a "smokeless"
(devolatUised) solid fuel for domestic consumption and industrial boUers. EUiott (1981) and
Tsai (1982) noted that the ultrafine pore structure of the parent coal is substantiaUy retained within chars until pyrolysis has been carried out between 650°C and 700°C. Therefore, the char produced in low-temperature carbonisation is substantiaUy as reactive as the parent coal. With continued heating at temperatures in excess 700°C, low temperature chars lose 124 their reactivity through devolatiUsation and also suffer a decrease in porosity.
High-temperature carbonisation is employed for the production of coke. Coal is heated for several hours in ovens, in the absence of air, at a temperature of approximately 1000°C to remove the volatUe components by destructive distillation (a form of pyrolytic decomposition).
MetaUurgical coke is used mainly in iron-making blast furnaces as:
- an energy source;
- a chemical reducing agent, particularly after partial combustion to CO; and
- to provide permeabihty within, and support for, the furnace load.
6.2.4.2 The Influence of Coal Rank and Type
Carbonisation of coal involves the interaction of a wide range of chemical and physical properties of the coal. The most important factors controlling the suitabiHty of coal for making coke are related to those properties of the coal that impart strength characteristics to the coke, either alone, or when blended.
Coke strength is normaUy assessed by a set of empirical tests and the most commonly used indices measure the tendency of the coke to break along major fissures and the abiHty of the coke to withstand abrasion (Schapiro et al, 1961; Schapiro and Gray, 1964). Prediction of coke stabUity is largely related to coal rank (vitrinite reflectance, calorific value, fixed carbon or other rank parameters) and coal type (maceral, lithotype or microtithotype compositions).
Rank strongly influences the temperature of minimum fluidity, maximum fluidity and the temperature of resolidification. These properties are directly related to the thermal 125 decomposition of the coal and thus are determined more by the maceral composition than by the chemical structure of the coal. Effective fluidity is largely related to vitrinite content. Liptinite is very fluid but distils rapidly. Inertinite has low fluidity properties.
The coals normaUy used in low-temperature carbonisation are low rank coals, ranging from brown coals to high volatile bituminous coals with Rvmax of <1.0% (Berkowitz, 1979).
Low rank coals, when pyrolysed at temperatures of 600°C to 700°C, yield porous chars or semi-cokes that are smokeless and are as reactive as the parent coals. However, low rank coals can be briquetted (typically with a binder) and carbonised at temperatures of 900°C to 1000°C to produce formed coke. Char yield is also dependent on coal type. Inertinite- derived char is less porous than vitrinite-derived char but the difference decreases with increasing rank.
On the other hand, the coals used in high-temperature carbonisation are higher rank coals ranging from medium volatUe bituminous to high volatile bituminous coals with R^max of
1.00% to 1.40%. Coal of lower and higher ranks may be blended to minimise cost and maximise quahty.
In relation to carbonisation, coal macerals are broadly divided into reactive (binder) and inert (filler) macerals depending on their behaviour during carbonisation. The reactive macerals soften on heating, become plastic, serve as a bonding medium and yield varying amounts of coke residue and by-products depending on the rank and specific maceral types.
The reactive macerals are vitrinite, Hptinite and some semifusinite. Ammosov et al. (1957) and Schapiro et al. (1961) suggested that one third of the semifusinite is reactive.
Inert macerals, on the other hand, degasify but remain almost structurally unchanged during carbonisation. Included in this group are all inertinite macerals, except for reactive 126 semifusinite, and mineral matter.
A simple method for displaying the relationship between coke strength, coal rank and coal type was used by Cook and Edwards (1971). They showed contours for coke strength on an orthogonal plot with vitrinite reflectance and vitrinite content as the axes. Unfortunately the range of rank studied by these authors was Hrnited.
Another method, that of Schapiro and Gray (1964), is based on that published by Ammosov
et al (1957). The coals used to cahbrate the method had a large range of ranks but very
little type variation. The Schapiro and Gray (1964) method has become widely used but
has serious Umitations in relation to the basic data used. Brown et al. (1964) gave a
detaUed critique of the method.
In order to produce the best coke, the reactive to inert maceral ratio is critical. Schapiro
et al. (1961) and Schapiro and Gray (1964) gave a series of curves, based on vitrinite
types, which show that the maximum coke strength index depends on the ratio of reactives
to inerts and rank (Figure 6.14). The figure shows the vitrinite types range from 3 to 21
as the vitrinite reflectance increases from 0.3% to 2.2%. Each reactive type has an
optimum ratio of reactives to inerts that produces maximum coke strength. Vitrinite type
13, for example, requires five parts of reactives to bond one part of inerts to achieve
maximum coke strength. Coals containing vitrinite types 9 through 13 (Figure 6.14) which
have coke strength increasing rapidly as vitrinite reflectance increases, are the best coals for making cokes.
Figure 6.14 shows that eastern Kalimantan coals He in the range of vitrinite types 3 through
7 and have a very low coke strength. The inert contents are low and therefore coke strengths are also low. 127
The petrographic composition of coals can be used to calculate the coke stabihty index
(Ammosov et al, 1957; Schapiro et al, 1961; Brown et al, 1964; Cook and WUson,
1969). The calculation method assumes that coke strength can be plotted in "rank/type"
spaces where there is a rank factor caUed the strength index and a type factor caUed the
composition balance index.
Strength index is based on the specific famUy of reactives present and their composite
response to the available inerts. The composition balance index shows the relationship of the available inerts to the individual reactive types. Different types, however, show
different capacities for assimUation and, therefore, ultimate strength differences relative to
rank.
Coking coals have been subdivided into:
low-rank coking coals, including those below high volatile A bituminous rank;
medium-rank coking coals, including the high volatUe A bituminous through
most of the medium-volatUe bituminous coals; and
high-rank coking coals, including the uppermost range of the medium-volatUe
bituminous coals and the low-volatile bituminous coals.
Based on the graphs of Ammosov et al. (1957) and Schapiro et al. (1961), the best coking coals are those having coke stabihties in the range of 45 to 65.
Coke stabUities for eight selected coal samples from Senakin (GM 24160, GM 24173 and
GM 24175), Pasir (GM 24834) and Sangatta (GM 24229, GM 24233, GM 24303 and GM
24309) were calculated and the results are plotted on the iso-stabUity graph of Schapiro et al (Figure 6.15 and Table 6.8). The coke stabihty indices for three samples (GM 24160,
GM 24173 and GM 24229) are 18, 11 and 14 respectively and the values for the other five 128 samples are 0. Eastern Kalimantan coals are composed mostly of vitrinite (typically >80%) and do not have sufficient inert macerals (typically <10%) to stabUise and strengthen the coke structure and vesicle walls; hence the low coke stabUities.
Edwards and Cook (1972) analysed AustraHan coals and suggested that the strongest cokes are made from coals having a relatively restricted range of rank (Rvmax of 1.2% to 1.4%) and type (vitrinite content of 45.0% to 55.0%). Later, using elemental data for non-
Australian coals, Jasienko (1978) proposed that coals with 84.0% to 91.0% carbon, 4.0% to 5.5% hydrogen, 4.0% to 8.0% oxygen, 1.1% to 1.5% nitrogen and 0.6% to 0.9% sulphur are the best coking coals.
Selected Miocene (mainly Sangatta) and Eocene (Senakin, Pasir and Tanjung) coals He in domain A of the Edwards and Cook curve (Figure 6.16a). In this domain, where vitrinite reflectance is <0.8%, vitrinite produces isotropic vesicular coke. With respect to vitrinite content, the coals that He in domain A' (Figure 6.16b) produce cokes that are weU fused but are frothy cokes and have thin vesicle walls and extensive Assuring.
Mineral content (ash yield) and the composition of the mineral matter also play a part in determining the suitabUity of coal for coke production. For example, mineral contents in excess of 12% by weight, may dUute the coal to such an extent that the coking properties of the coal are markedly diminished (Edwards and Cook, 1972).
From the above results it can be concluded that none of the eastern Kalimantan coals can be used as a single component coke feedstock for high temperature carbonisation.
However, selected Eocene coals from Senakin, Tanjung and Pasir and Miocene coals, mostly from Sangatta), can be used as a blend component with better quality coking coals to produce strong coke. In addition, Eocene coals from Senakin and Pasir, and Tanjung 129 and Miocene coals from Pasir and Sangatta are suitable as feedstocks for low-temperature carbonisation process over a temperature range 600°C to 700°C. Speight (1983) noted that coals with P^max higher than 0.8% are less suitable for low-temperature coking because of the tendency of these coals to adhere to the waUs of the carbonisation chamber.
None of the eastern KaUmantan coals have mineral contents that are deleterious for coke manufacture if used as single feedstocks. The Eocene Senakin coals contain the highest mineral matter (average of 8.3%) but have the highest predicted coke stabHity index (18, sample GM 24160, Table 6.8). Sangatta coal, which has the highest vitrinite reflectance of eastern Kalimantan coals, does not have a good predicted coke stabihty because its mineral content is typically less than 2.0%. However, blending high mineral coals would not be desirable and the Miocene coals (particularly Sangatta coals) are more likely to be suitable for use in blending or for a low-temperature carbonisation than the Eocene coals.
6.3 SUMMARY AND CONCLUSIONS
Proper evaluation of the quaHty of coals must include many variables. Some of the variables are rank related, such as maximum vitrinite reflectance, calorific value and fixed carbon; other parameters are only partly related to rank, for example, Hardgrove
GrindabUity Index (which does vary with rank but is highly dependent on maceral composition and mineral content) and moisture content. Some variables such as coal type are, however, essentially unrelated to rank. Table 6.9 summarises coal quaHty and utUisation potential of coals from eastern KaUmantan.
Coal rank, coal type and mineral matter, together with chemical characteristics, are of a great commercial significance in assessing combustion, liquefaction (hydrogenation and pyrolysis), gasification, low-carbonisation and high-carbonisation properties of eastern 130
KaUmantan coals. Vitrain and clarain, the main lithotypes in these coals, are relatively easy to mine and grind and are more likely to produce excessive fines. Selected Eocene coals from Satui and Senakin, however, have high Hptinite and mineral contents that make them tougher than Miocene coals and normaUy produce coarser particle sizes during preparation.
Combustion is the most economic and technologically easy use of eastern KaUmantan coals because of the lower rank, the high vitrinite and Hptinite contents and the relatively low mineral and sulphur contents. Sangatta, Mahakam and Berau coals have the highest priority for use in combustion followed by Tanjung and Pasir coals (Table 6.9). The lowest priority coals for combustion are those from Asem Asem, Satui and Senakin areas; these have high moisture, liptinite and mineral matter (ash yield) respectively. High moisture, liptinite and mineral content in the coal lower the flame temperatures, affect the grindabiHty and produce fouling during the combustion process.
Eastern KaUmantan coals, with ranks ranging from brown coal to high volatUe bituminous coal (average Rvmax values of 0.38% to 0.62%), are potential feedstocks for Hquefaction and gasification reactions, but of the coals in this rank range, only the coals that consist predominantly of vitrinite and Hptinite wiU prove to be commercially attractive. Fischer assay analyses of eastern Kalimantan coals show the yield of oU products on pyrolysis decreases with increasing rank. The highest yields are obtained from coals of high volatUe bituminous rank.
Petrographic composition of coal is less significant for gasification than for Hquefaction.
Coal gasification reactivity is normally determined by char reactivity. Char reactivity varies with rank and chars produced from low rank coals are more reactive than chars from high rank coals. Thus, aU Miocene coals and the Eocene Satui coals have the highest priority 131 as feedstock in liquefaction and gasification reactions.
The reactives to inerts ratio and rank of eastern KaUmantan coals are negative factors in relation to use as high-temperature carbonisation feedstocks. These coals are of low rank, have few fine-grained inerts and wiU, at best, produce a weak spongy coke. Therefore, to produce an acceptable coke from eastern Kalimantan, the coals have to be blended with higher quaHty coking coal of higher rank. Selected Miocene coals from Sangatta and
Eocene coals from Senakin, Pasir and Tanjung, could be used as a single component coal for low temperature carbonisation that produces char.
Eastern Kalimantan coals can be economicaUy utUised for both gasification and liquefaction if the residue from the processes (approximately 40% to 60%) can be used for combustion.
However, in order to use the residue for feedstocks in combustion processes, new, specificaUy designed char-fired plants would have to be buUt. 132 133
CHAPTER SEVEN COAL PRODUCTION AND CONSUMPTION
7.1 COAL PRODUCTION
7.1.1 General
Coal deposits are widely distributed throughout the world with total resources amounting of 1.1 x 1012 tonnes (Figure 7.1; Joint Coal Board and Queensland Coal Board, 1990;
USA/OECD, 1991). Indonesia's coal resources amount to 36.3 bilHon tonnes (Perusahaan
Umum Tambang Batubara, 1990; SoeHstijo, 1990; Directorate of Coal, 1993), representing
3.2% of the world total coal resources. Eastern Kalimantan has 24.5% of the Indonesian total coal resources.
At present, the bulk of the mining in Indonesia is in Sumatera and KaUmantan. The potential for additional development on the island of Sumatera exists but is not significantly large. On the other hand the potential for KaUmantan is extremely high given the supply capabUities that are rapidly emerging in Indonesia, and especiaUy those in KaUmantan.
This is especiaUy true in eastern Kalimantan where investments by large multinational corporations in recent years has been a significant impetus for growth.
As a result of massive exploration carried out in eastern Kalimantan since the early 1980s
(Chapter 3), Indonesia has a proven a coal resource base sufficient to support energy requirements for the country's development.
Development of eastern KaUmantan coal is essential because it is recognised that the projected production from other coal mines in the country wUl not be sufficient to service domestic coal demand (particularly for the electricity sector and cement industry) or to 134 increase coal exports. Coal is expected to become the second most important domestic energy source, next to oU and natural gas, in the near future due the large potential resources that can be developed.
Comparison of Indonesia's resources with those of other countries shows the potential for
Indonesian coal. Indonesia's share of the Asian coal resources is 13.4% and this rates third after China (61.7%) and India (23.0%) respectively (Figure 7.2). On a world basis, India and China have 5.6% and 14.9%, respectively, of the world total coal resources. China is third after the Commonwealth Independent States, formaUy USSR (21.4%) and the
United States (25.6%). Asian countries account for 24.2% (270.5 biUion tonnes) of the world total coal resources.
Within ASEAN member countries (Association of Southeast Asia Nations) which include
Malaysia, Singapore, Thailand, Phihppines, Indonesia and Brunei Darussalam, Indonesia has the most extensive coal resources foUowed by ThaUand with 2,506 million tonnes,
Phihppines with 1,558 million tonnes and Malaysia with 971 milHon tonnes (Figure 7.3;
Johannas, 1989; Proudfoot, 1990). Although coal resources data for Brunei Darussalam and
Singapore are not avaUable it is clear that Indonesia has the most significant proportion of coal resources - a maximum of 88% of the known ASEAN coal resources which totals 41.3 biUion tonnes.
7.1.2 Indonesian Coal Production
Table 7.1 and Figure 7.4 show the trend in Indonesia's coal production from 1939 to 1992.
UntU the early 1980s coal production was erratic with the highest production of 2.0 mUHon tonnes attained in 1941. The dechne of the coal industry reached a critical point in the early 1970s when the lowest coal production (148,826 tonnes) was recorded in 1973. In
1971 aU the major coal mines in eastern Kalimantan stopped production altogether. Coal 135 production from both Bukit Asam (South Sumatera) and OmbiHn (West Sumatera) mines continued but only with government subsidies.
The fluctuation in Indonesia's coal production up to the end of 1970s, was due to Hmited markets; coal could not compete with the relatively low price of oU. In this period, oU became the most favoured fuel in Indonesia and also worldwide. The pressure of low oil prices has decreased since the "1973 energy crisis". However, subsidies for domestic oU since the early 1970s has acted as the disincentive for increased coal production in
Indonesia. The oil crises in 1973 and 1978 led to a re-evaluation of the potential of coal and subsequent domestic energy policy developments in Indonesia have placed increased emphasis on coal utUisation.
From the late 1970s to the early 1980s, Indonesia's coal production increased shghtly but between 1985 and 1988, the production increased significantly. Indonesia's total coal production rose sharply during the last five years as indicated in Table 7.1 and Figure 7.4.
Production expanded in eastern KaUmantan coal mines by 100% from 1991 to 1992 with a 1992 production of approximately 14 milHon tonnes. This reflected increased output from the Sangatta, Senakin, Satui, Mahakam and Tanjung coal mines (currently the five big coal producing areas in eastern Kalimantan) which all commenced production in 1988/1989 using open cut methods.
Production from the Pasir coal mine commenced in 1990 and from the Berau coal mine in 1992. The development of Asem Asem coals is stiU dependent on finding additional consumers. Thus, since 1992 eastern Kalimantan has become the biggest coal producing island in Indonesia and has replaced Sumatera from this position.
Sangatta mine, Indonesia's biggest contracted coal area and jointly owned by CRA Ltd. of 136
Australia and British Petroleum, is the largest suppher of eastern KaUmantan coal with a production of 7.4 mUHon tonnes (52.5% of eastern Kalimantan production or 31.3% of
Indonesia's total coal production) in 1992. Production in 1993-1994 is expected to increase by 35% to approximately 10 mUHon tonnes.
The next largest coal producer is P.T. Arutmin (partly owned by Broken HiU Pty of
Australia) who developed the Senakin and Satui coal mines. These operations accounted for 27.7% (3.9 milHon tonnes) of eastern KaUmantan production or 16.5 % of Indonesia's total coal production in 1992. Thus, in 1992 production from eastern Kalimantan coal mines contributed approximately 59.7% of Indonesia's total coal production, compared to
42.7% in 1991 (Figure 7.5).
Figure 7.6 shows the actual growth rate in Indonesia's coal production from 1977 and the predicted growth rate to 2000. The highest growth rate occurred in 1984 (126.2%) and this was partly the result of increased production capacity from Bukit Asam (South Sumatera) coal mine. Growth decreased during 1985 to 1987 by 26.5% but again increased in 1989 by 83.1% due to the commencement of production from eastern Kalimantan coal mines, especiaUy Mahakam and Senakin, and also the expansion of Bukit Asam and OmbUin coal mines. Total Indonesian output was 9.5 mtilion tonnes in 1989. However, by 1992, the growth rate was 42.7%, compared to 53.1% in 1991.
Future production levels wiU continue to depend heavUy on domestic demand from electric utiHties, cement manufacturers and export markets. Absolute coal production from
Indonesia wUl rise considerably in the period 1993 to 2000 and during this time Indonesia is expected to move from being a modest producer of coal to join the ranks of the middle level producers and exporters. 137
Projections of coal production for eastern Kalimantan and other coal mines in Indonesia can be seen in Table 7.1 and Figure 7.7 (Perusahaan Umum Tambang Batubara, 1990;
Soehstijo, 1990; Directorate of Coal, 1993). The growth rate is expected to decrease from
1992 to 1994 by 10.3%, reaching a low of 6.3% in 2000 (Figure 7.6). This trend wiU happen because the supply of coal wiU meet the level of coal consumption and export market projections.
The contribution of eastern KaUmantan coal to the Indonesia's total production, however, increases markedly. By 1995, for example, coal production from eastern Kalimantan coal mines is expected to increase to 25.3 mUHon tonnes or by 79.3% over 1992 figures; this wiU be 68.9% of Indonesia's total production. In 2000, eastern Kalimantan's share of the
Indonesian total production of 50 mUHon tonnes wUl be 72.4% or 36.2 mUHon tonnes
(Figure 7.5). Clearly, with these rapid growth rates, there is a great need for a review of coal quality and an assessment of each coal so that market opportunities can be optimised.
7.1.3 Comparison Between Production in Indonesia and Other Countries
Table 7.2 and Figure 7.8 show coal production for some countries including Organisation for Economic Co-operation and Development (OECD) countries, such as Australia, Canada,
Germany, United Kingdom and the United States and non-OECD members including
Indonesia, China, other Asian countries, USSR, Latin America and some European countries.
Coal production in many countries outside Europe increased steadily over the last 10 years.
The increased coal production in these countries is the result of increased oU price, domestic consumption for electricity and cement manufacture as weU increases in exports.
However, worldwide total coal production feU sHghtly by 1.3% from 1989 to 1990 to approximately 4,740 miUion tonnes. This is partly due to the lower demand for steaming 138 coal production in some regions, for example, Germany, Czechoslovakia and Romania.
Coal production in China and other Asian regions in 1990 recorded substantial increases of 1.2% and 9.6% respectively. The increased coal production in the Asian region is due to new mines and expansion of existing coal mines in countries such as Indonesia and
China. India also recorded a significant increase of 13.3% and produced approximately 238 mUHon tonnes coal in 1990, consisting predominantly of hard coals, mostly steaming coals.
Total Indonesian coal production amounted to 10.8 miUion tonnes in 1990, representing only 0.2% of world total coal production. Compared to coal production in China, the world's largest coal producer with an output of 1,066 miUion tonnes (22.5% of world total coal production) in 1990, or in AustraHa, 209.5 milHon tonnes (4.4% of world total coal production), Indonesia's coal production is very low. However, given these initial production figures, the production growth rate in 1990 in Indonesia (14.1%) was much higher (Figure 7.6) compared to production growth rates in AustraHa (6.8%) or China
(1.2%). This is because energy consumption growth rates in both the former countries are lower than in Indonesia. Energy consumption growth rates in Indonesia are projected to be 10% to 17% between 1990 and 2000.
Among the ASEAN member countries, Indonesia has the highest coal production, hi 2000, for example, Indonesia wUl account for 62.5% of total ASEAN coal production compared to 30% (3.5 milHon tonnes) in 1987. ASEAN countries wUl produce approximately 80 mUHon tonnes of coal in 2000. As with Indonesia, they try to maximise use of their coals both for local uses (mainly for electricity and cement industries) and exports so as to conserve their oil reserves for exports. OU is a better foreign exchange earner than coal.
Worldwide coal production is forecast to grow steadUy. For example, AustraHa will produce approximately 265 mUHon tonnes in 2000, an increase of 26% on 1990 production. 139
Indonesia's coal production wUl grow 117% between 1992 and 2000 to approximately 50 mUHon tonnes or one fifth of AustraHa's production.
Eastern Kalimantan coal mines are largely worked by open cut methods and are located close to the sea or have easy access to inland waterways for relatively short transport to ocean loading terminals. Much of the world's coal has traditionally been mined by underground methods, with the deep-seated seams of Western Europe being worked largely by longwaU techniques. The shallow-lying beds of the United States were exploited by open cut or by underground bord and piUar methods. In recent years, however, large- scale mining by high productivity open cut techniques has also become estabhshed in many countries, including West Germany (brown coals) and AustraHa (both brown coals and bituminous coals).
The 1990 Clean Air Act Amendment (IEA/OECD, 1991) introduced more constraining regulations and this may have some impact on the structure of coal production, as lower sulphur coal may become a prime fuel for electricity generation. Eastern KaUmantan coals
(with rare exceptions) have low sulphur contents and are acceptable as feedstocks in electricity generation and cement industries when and where the more strict emission standards set in the revised Clean Air Act are in force.
The return of coal as the major energy source is not only necessary but also inevitable, both for the coal-rich nations and the not so coal-rich nations of the world. However, coal must become "new-coal", that is, uses wiU have to adapt to suite the specific features of secondary energy requirements which may mean liquid and gaseous fuels. Thus, to be used strategically during the period of dwindling fossil resources, especiaUy crude oU, coal must serve as the raw material for the production of synthetic liquids, gases, briquettes or coking fuels (Chapter 6). 140
The utiHty industries that turn to oil, gas, briquettes and coke as their energy mainstays,
wiU do so because of the higher specific energy contents and easier transportation and
handling. In 1993, with crude oU spot prices under US $18 per barrel at times, there is
concern that coal may not be able to compete with oU in the short term and there is apathy
towards developing new coal technologies.
7.2 COAL CONSUMPTION AND PROJECTIONS
Coal quaHty studies of eastern KaUmantan coals (Chapters 4, 5 and 6) showed that most
of the coals can be utUised for electricity generation, cement and general industrial uses.
Low mineral contents (average of 3.7% for Miocene coals and 8.3% for Eocene coals) and
sulphur contents (0.1% to 5.4%, typicaUy <1%) of eastern KaUmantan coal, are seen as a
great benefit to Indonesia's environmentally sensitive consumers.
The avaUable coal reserves are sufficient to have a significant impact on Indonesia's energy
needs during the next decade. With the advances in coal conversion technologies and the
likely production of simUar products to crude oil and natural gas, eastern Kalimantan coals
are prime feedstocks and should satisfy a great diversity of markets.
In the 1940s and 1950s, Indonesia's coal was consumed mainly by raUways, steam ships,
factories, city gas and exports to southeast Asia. Coal was first used in the cement
industry in the early 1970s. Use of coal in transportation industry, especiaUy trains,
declined dramaticaUy in 1980s.
Currently, domestic consumption in Indonesia is largely dependent on the progress made on the construction of new coal-fired plants and the expansion programs in the cement 141 industries. A third area for potential growth is small-scale industry and the household sector but the necessary infrastructure to distribute the coal has to be established. Another alternative potential use is to replace the oU in refineries.
In 1992, coal used for electricity generation (Figure 7.9) amounted of 22.4% of total coal production (63.6% of total coal consumption within Indonesia), while the cement industry consumed 11.2% (31.6% of total coal consumption within Indonesia); other industries accounted for only 1.7% (4.8% of total coal consumption within Indonesia). Thus, most of the 1992 coal production was for exports, particularly that produced from eastern
Kalimantan.
In comparison, over 60% of the world total coal production in 1990 was consumed for electricity generation with a further 25% used for metaUurgical coke manufacture.
Industrial, residential (households) and commercial consumers (including the cement industry) consumed the remainder.
Table 7.3, Figures 7.10 and 7.11 show the existing and predicted coal consumption in
Indonesia from 1971 untU 2000.
7.2.1 Electricity Generation
Installed electricity generation capacity in Indonesia was 6,420 MW in 1987 and it is expected to reach 24,880 MW by 2000 (Perusahaan Umum Listrik Negara/State Electricity
Corporation, 1992). Of the total electricity capacity, coal-fired plants accounted only for
865 MW (13.5%) in 1987 and it is planned that accumulated instaUed coal-fired capacity at the end of 1995 wUl be 4,665 MW (18.8%) with a sharp increase to 12,890 MW by
2000 (Table 7.4) or 51.8% of total electricity generation capacity. This is 1.7% of the total predicted 700,000 MW from coal-fired plants across the world in 2000. Electricity 142 generation accounts for the largest share of coal consumption in Indonesia (63.6%) and rose
15.2% from 1989 to 1992 to 5.3 miUion tonnes (Table 7.3, Figure 7.10). Of the coal- fired plants, currently the biggest user is the Suralaya plant (West Java) which consumes
4.9 miUion tonnes coal per annum (92.4% of total coal for electricity plants) or 58.8% of
Indonesia's total coal consumption in 1992.
In 1989, electricity plants consumed approximately 4.6 miUion tonnes coal which is only
0.3% of the world total consumption of 1,658.2 mUHon tonnes (coal-fired plants only). The
United States consumed the highest amount of coal for electricity generation, 624.6 million tonnes (37.7% of world total consumption in coal-fired plants). This was foUowed by
China with 252.0 milHon tonnes and the USSR with 193.9 miUion tonnes.
Consumption of coal in electricity plants wiU increase sharply in Indonesia in the next five years (Table 7.3, Figure 7.11) mainly due to new coal-fired plants coming on stream.
Examples include an extension to the Suralaya plant (West Java), and new plants at Paiton
(East Java), Central Java, OmbUin (West Sumatera) and Bukit Asam (South Sumatera).
Paiton coal-fired plant wiU become the biggest plant in the country after 1998 with 4000
MW generation capacity (Table 7.4).
According to the plan estabhshed by the State Electricity Corporation/Perusahaan Umum
Listrik Negara (PLN) in 1992, the estimated consumption of coal for a 4,665 MW generation capacity in 1995 wUl be 8.3 miUion tonnes (low estimate) and 12.1 nulhon tonnes (high estimate) corresponding to 54.2% (low estimate) and 63.5% (high estimate) of Indonesia's total coal consumption.
In 2000, the projected consumption of coal for a 12,890 MW generation capacity is estimated to be between 15.4 mUHon tonnes (low estimate) and 28.9 mUHon tonnes (high 143 estimate) per annum (Table 7.3, Figure 7.11). This wiU account for 54.9% (low estimate) and 69.5% (high estimate) of Indonesia's total coal consumption or 30.8% (low estimate) and 57.8 (high estimate) of total coal production in 2000. Estimates are based largely on the assumption that to produce 1 MW electricity per year, approximately 2,100 tonnes of coal are required (State Electricity Corporation, 1992).
The rank (average of 0.36% to 0.63% P^max) and coal type (typically high vitrinite and low inertinite and mineral contents) of eastern Kalimantan coals are generally favourable for use in pulverised plants (Chapter 6). Typical characteristics of coals used in some coal- fired plants in Indonesia are shown in Table 7.5.
Comparisons between the existing and planned additions to coal-fired generation capacity in non-OECD countries, OECD member countries and Indonesia is shown in Figure 7.12.
According to these plans, the newly industrialised countries, particularly in Asia, wUl account for an increasing share of coal-fired capacity. Electricity demand is expected to increase more rapidly than total energy demand in aU major regions.
World electricity demand increased at an average rate 4.5% per annum between 1970 and
1980, more than doubting over this period (Eden, 1993). Electricity use, per capita, in
1988 averaged 0.4 MWh per year in developing countries. This is very low if compared to the 7.3 MWh per year average in the OECD member countries.
7.2.2 Cement Plants
The second largest consumer of coal in Indonesia is the cement industry. The most common plants are horizontal rotary kilns, with the raw materials for chnker formation being mixed and added either in a dry state or as a slurry with water. Fuel costs generaUy represent a high proportion of the total cost of cement clinker manufacture. 144
Since the early 1970s the old cement plants that used crude oU and natural gas for energy, were graduaUy converted to use coal as a fuel and 100% conversion was reached in the early 1990s. Coal was found to be more competitive compared to crude oti and natural gas and this complied with the pohcy of the Indonesian Government to seek diversification of energy resources.
Low mineral contents of some eastern Kalimantan coals (particularly Miocene coals) are a positive feature for these coals to be used as fuel for cement plants. Typical properties of coal used in some cement plants are shown in Table 7.5. Some coal ash is used in the cement clinker during the firing process and for this reason the mineral content of coal must be kept relatively constant.
Coal demand for the cement industry has grown rapidly because of the switch from oU or natural gas to coal and the growth in demand for cement. The environmental problems associated with coal are normally less in the cement industry compared to the problems in other types of coal-fired plants, because coal ash from the combustors is fixed in the chnker. In contrast, ash from other coal-fired plants reports as fly ash and bottom ashes
(Chapter 6).
Current capacity of the Indonesia's cement industry which comprises 10 companies, is a total of 18.46 miUion tonnes cement in 1992 compared to 13.3 mUHon tonnes in 1990
(Table 7.6, Figure 7.13). This figure wiU grow remarkably reaching 36.89 miUion tonnes in 2000 (Wardijasa, 1990). Wardijasa (1990) also noted that by using coal as a fuel, production cost of cement decreases 20% compared to the use of crude oU or natural gas fuels.
Coal consumption in the cement sector accounted of 2.6 mUHon tonnes in 1992 compared 145 to 1.9 milHon tonnes in 1990 (Tables 7.3 and 7.6, Figure 7.13). With an average annual growth rate being maintained at between 6.0% and 7.5% during the period 1993 to 2000, it is expected that coal demand wUl be 4.6 miUion tonnes in 1998 and 5.3 miUion tonnes in 2000. Thus, by 2000, the cement industry wtil consume 12.7% (low estimate) and
18.8% (high estimate) of the Indonesia's total coal consumption or 10.5% of the total coal production. This calculation is based on an estimate that one tonne of cement requires approximately 0.143 tonnes coal with specifications of average Rvmax of 0.45% and calorific value of 5500 kcal/kg.
Unlike the Indonesian case, the world scenario for the cement industries is that of a small but highly significant user of coal. The share of coal in the world cement industry in 1990 amounted of 13.4 miUion tonnes, representing only 0.5% of total world coal consumption
(IEA/OECD, 1991). However, coal consumption in this sector is expected to grow graduaUy because of changes in fuel type from crude oU or natural gas to coal and the increasing demand for cement in some countries, particularly in OECD member countries and developing countries.
7.2.3 Small Industries
In the small industries sector (for example, lime burning, brick and the making) wood is normaUy used as the principal fuel source and conversion to coal firing has been under review as a means of protecting the remaining forest areas. These industries have significant potential if conversion from other fuel types to coal is achieved.
The Mineral Technology Development Centre (MTDC, 1989) estimated the potential coal demand to be 7.1 milHon tonnes coal equivalent (TCE) per year by 1995 increasing sHghtly to 8.1 mUHon TCE in 2000. However, before coal can be allocated to this use some constraints have to be clarified among other coal users so as to encourage the industries 146 to use coal instead of wood and ensure continuity of coal supply at a competitive price.
Small-scale mining (for example, mines located in West Java, South Sumatera and South
Sulawesi) have commenced supplying a portion of this demand.
7.2.4 Residential Consumption
The use of coal as briquette fuel to substitute for kerosene and wood in domestic cooking apptiances in rural areas, particularly in the most densely populated regions such as Java,
Madura and Bali, has been extensively researched and developed by a number of Institutes,
The use of coal should also lessen the pressure on some forest resources in the more densely populated areas if briquettes are used.
The use of briquettes in Indonesia was commerciaUy introduced early in 1993. However, developing coal use in this sector requires the continuation of briquette research and a possible need to subsidise coal use. Subsidies may be required because briquettes wiU be replacing a non-commercial energy source (for example, wood) that is often avaUable at no cost.
MTDC (1989) estimated the potential coal demand for this sector to be in the range of 22 to 37 miUion TCE by 1995 and this should remain the same up to the year 2000,
However, this estimate is not included in the consumption forecasts in Table 7.6 and Figure
7.11 because the development of a briquette industry and educating people to use this fuel in households has a lead time of 5 to 10 years. It may also require the development and distribution of cooking apptiances suitable for using briquettes.
7.2.5 Exports
The international market for Indonesia's steaming coal has experienced substantial growth 147 in the last few years and it is expected to continue to grow in the next decade. Growth has been significant in the Asian region, as well as other parts of the world, with the foUowing trends apparent:
increased use of coal in electricity generation;
increased acceptance of coal as a fuel in cement, pulp and paper industries
and industrial boUers;
an increased level of economic activity resulting in growing energy
requirements; and
closing down of coal mines in many countries because of the cheaper price
of imported coal compared to local coal, for example, in Japan, Thailand,
Malaysia and most countries in Europe.
The ultimate decision to import coal from any particular source is governed by several considerations such as cost, quality, security of supplies and preferences by the nation concerned. MetaUurgical/coking coal export markets have been more widespread and longstanding because coking coal has a smaUer, less-widely distributed resource base.
Steaming coal, on the other hand, has a much larger and more widely-distributed resource base and the markets have tended to be newer and more geographicaUy limited. Steaming coal also seUs at prices lower than coking coals.
7.2.5.1 Indonesia
For commercial purposes, eastern Kalimantan coals are divided in two broad categories, hard coal and brown coal. Hard coal has a mean maximum vitrinite reflectance of >0.50% and a gross calorific value >5,500 kcal/kg on an ash free basis. Most of the Miocene
Sangatta coal, some of the Miocene Mahakam coal and the Eocene Tanjung, Pasir, Satui and Senakin coals are included in this category. Brown coal, on the other hand is a non- agglomerating coal with a gross calorific value <5,500 kcal/kg (average P^max of <0.50%) 148 containing >10% of inherent moisture and >30% of volatUe matter on a dry mineral matter free basis. Included in this category are aU Miocene coals from Berau, Tanjung, Asem
Asem and some from Mahakam.
Based on quaHty (rank and type), aU eastern Kalimantan coals are normaUy used as
steaming coals although some coals can be used as a blending component in metaUurgical
coke making, particularly the low-ash Sangatta coals and some Eocene coals (Chapter 6).
The most probable metaUurgical use is for direct injection but some coals could be used
as a minor component of coking blends. Many of the coals would also be suitable for
direct reduction processes now under development by a number of countries.
In 1939 Indonesia started to export its coal with shipments amounting to 0.7 miUion tonnes
to neighbouring countries such as Malaysia, ThaUand and Singapore and continued to do
so at a similar level in 1940. From 1941 until 1975, however, there were no coal exports,
Indonesia again exported its hard coal production in 1976 at a rate of 0.7 million tonnes.
UntU the end of 1980s, coal exports increased steadUy and reached 2.982 miUion tonnes in 1989 or 31.5% of total production (Figures 7.14 and 7.15). However, the percentage of Indonesia's total coal production, as coal exports, decreased from 1984 and reached a minimum of 28.6% in 1987 (Figure 7.15) although this was an increase in actual tonnage.
This was mainly due to an increase in domestic consumption, particularly coal-fired electricity generation.
Coal exports rose sharply by 96% from 1991 to 1992 to a record of 17.1 milHon tonnes with a free on board value of US$677.6 mUHon. Exports are expected to grow at an even higher average rate of 13.4% per year to fulfil the expanding markets in Europe, Japan and
ASEAN member countries. Coal prices range from US $37 to $60 per tonne. Indonesia's 149 coal exports in 1992 accounted for 72.2% of Indonesia's total coal production (Figure 7.16).
Most of the Indonesia's coal exports came from eastern Kalimantan mines. These mines recorded an increase in export coal production of 350%, or 12.1 milHon tonnes, from 1990 to 1992. Sangatta, Satui and Senakin coal mines exported approximate 9.0 miUion tonnes of coal in 1992. Significant increases in coal shipments were made to neighbouring countries, including Japan, South Korea, Taiwan, Malaysia and PhUippines. Shipments to
Europe (including Holland and Belgium) were slightly up in 1992. Prospects for future exports of Indonesia's coal are promising, but in order to compete with exports from other countries, for example, Australia and China, production efficiency must increase to retain low production costs.
As is the case for Austrahan steaming coal export patterns, Japan remains the major market for Indonesian steaming coals. Japan took approximately half of Indonesia's coal exports for the year 1992. The number of coal-fired plants in Japan should double in the next 10 years as coal is expected to continue to be the major source of energy. The growth in demand for coal in the Japanese industrial market is projected to be 3 to 5% per year
(IEA/OECD, 1991).
The jump in Indonesia's coal exports in the period 1991 to 1992 was due to both price and quaHty competitiveness on the World markets. The location of Indonesia's coal, in relation to the Asian market, ensures much shorter transport distances than any alternative supptier other than China.
It has been proposed by Japan (New Energy Industrial Technology Development
Organisation, 1989) that only coal sufficiently high in rank (I^max of 0.50% to 0.70%) with a moisture content (air dried basis) of less than 9.0%, and preferably less than 6.0%, 150 is suitable for import into Japan and it is considered that similar constraints could apply to other markets in the future. This would restrict the sources of Indonesia's export coal to areas such as Sangatta (average Rvmax of 0.63%, inherent moisture content of 5.0%),
Senakin (average Rvmax of 0.56%, inherent moisture content of 3.5%), and Eocene coals from Tanjung (average P^max of 0.60%, inherent moisture content of 6.6%), Pasir (average
R.max of 0.62%, inherent moisture content of 4.4%) and Satui (average Rvmax of 0.50%, inherent moisture content of 7.0%).
Some coals from Senakin, Pasir and Satui have a wide range of properties with relatively high mineral matter in the raw coal but with generally low sulphur levels. The low sulphur and inertinite contents of most eastern Kalimantan coals offer a considerable quaHty advantage in the market place because a feature of future steaming coal markets wUl be environmental considerations particularly in Europe, Japan and the United States.
To increase coal exports from Indonesia requires some changes including: securing sufficient long term buyer commitment at prices which justify investment in mines and infrastructure; acceleration of the development of infrastructure, particularly rati and port facitities, to ensure timely and retiable export timetables and capabUity; and reduction in the lead times in securing mining leases, environmental impact approval and other interactions between developers and government agencies.
7.2.5.2 Outlook for Exports from Other Countries
UntU now, the Pacific Basin coal market has been dominated by Australia and the United
States but with its abundant coal resources now developing, Indonesia is certainly well situated, and has the potential, to become a significant coal supplier to countries in southeast and eastern Asia. Among the ASEAN countries, only Indonesia has a substantial 151 coal export capacity whereas other ASEAN member countries, for example, Thailand,
Phihppines, Singapore and Malaysia are expected to be potential coal importers.
In 1990, a total of 91.6% of the World total coal production was consumed in the country of origin and only 8.4% (3.9% of coking coal and 4.5% of steaming coal) was traded internationally. This is sUghtly higher than in 1989 (7.9%) or in 1985 (7.6%) but it is much higher than the 3.6% of 1973 (Figure 7.16).
IEA/OECD (1991) forecast an expansion in worldwide coal exports from 400 miUion tonnes in 1990 (5.0% more than in 1989) to 527 mUHon tonnes in 2000 (Figure 7.17). Growth in world coal trade wUl occur primarily in the steaming coal sector (68.1% of the total in
2000, compared to 53.7% in 1990 and 35.4% in 1977). This is in response to increased demand by electricity utilities and industrial users in Western Europe and Asia.
The growth rates in demand, however, vary from country to country as each country has its own special considerations relating to industrialisation, external trade, balance of payments, standards of living and the energy resources at its command. Total international trade in steaming coal is expected to reach 359 mUHon tonnes in 2000, compared to 215 mUHon tonnes in 1990. In contrast, world coking coal trade (particularly in the European market) is predicted to dechne from 185 miUion tonnes in 1990 to 168 milHon tonnes in
2000 (Figure 7.17). This is largely due to increased efficiencies in the production of iron and steel and competition from steel substitutes.
In 2000, Indonesia is expected to export approximately 24.0 miUion tonnes of steaming coals (4.5% of the World's total coal trade or 6.7% of the World's steaming coal trade), compared to 1.2% of the world total coal trade or 2.2% of the World steaming coal trade in 1990. Total world coal consumption wUl be approximately 8.0 bUHon tonnes in 2000 152
(calculated using an annual growth rate of 4.0%).
Australia is projected to remain the largest steaming coal exporter with 89 miUion tonnes of steaming coal exports in 2000, compared to 49.5 mfflion tonnes in 1990 (Joint Coal
Board and Queensland Coal Board, 1990; IEA/OECD, 1991). Australia is also the largest suppher of coking coals in the Asian region and forecasts are that this country will maintain its dominance in that market and to increase exports to Europe. Total coking coal exports from Australia in 2000 wUl be 60.8 miUion tonnes compared to 57.1 mUHon tonnes in 1990.
China is expected to export 25 mUHon tonnes of steaming coal by 2000 compared to 20.1 mUHon tonnes in 1990. AU China's coal exports are projected for the Asian region and it becomes a strong competitor for Indonesia's coal exports. However, it should be noted that most of China's coal resources are a great distance from ports and that the rati system is currently under considerable strain to carry existing levels of coal production let alone increased levels. Additionally, the effects of restructuring within the Chinese coal industry are difficult to predict.
The United States is also forecast to increase its share of the steaming coal market, from
18% in 1990 to 27% in 2000 (amounting to 45.8 mtilion tonnes) but concentrating mostly on Western European markets.
Strong market growth is forecast for electricity generation in the developing countries that have high economic growth rates but do not have potential unexploited hydro-electricity resources, for example, Japan, South Korea, Taiwan, Philippines and some countries in
Latin America. 153
Future world-wide export supplies wUl consist of the existing capacity base augmented by newly-created production capacity. More than half the current world-wide supply of coal is accounted for by a generation of mines that have been in service for no more than 10 years and experience shows that most mines have a useful Hfe of 20 to 30 years. It can thus be assumed that most of the existing capacity base in exporting countries wUl be maintained. That is, the base wUl be Httle affected by the depletion of reserves and closure of individual mines in the short term. This applies especially to steaming coal. Major additions to capacity are planned by AustraHa, South Africa and China (IEA/OECD, 1991).
7.3 COAL'S SHARE OF PRIMARY ENERGY CONSUMPTION
Coal is the largest energy resource in Indonesia foUowed by natural gas, hydropower, crude oil and geothermal respectively (Table 7.7, Figure 7.18). However, oU and natural gas are currently sttil the main primary energy source in the country and this pattern is expected to remain until the year 2000 (Figure 7.19). Energy demand in Indonesia wUl increase by
89.2% between 1988 and 2000 to 548.6 miUion barrels oil equivalent (BOE) as is shown in Figure 7.19.
Although the ratio of Indonesia's crude oil to primary energy supply is decreasing (although the absolute amount is increasing), the share of this energy source in year 2000 wiU be sttil high, accounting for 51.3% (279.6 miUion BOE) of total energy consumed compared to
64.9% in 1988/1989 and 82.5% in 1978/1979 (Figure 7.19). The share of natural gas as a primary energy source increased from 14.6% in 1978/1979 to 20.8% in 1988/1989 and is predicted to increase to 32.4% in 2000 (176.4 miUion BOE).
Coal's share of Indonesia's total primary energy was only 0.5% in 1978/1979 but it had grown to 7.1% in 1988/1989 and wiU increase slightly to 8.8% in 1993 (Figure 7.19). 154
Nevertheless coal's share, even in 1993, wUl be sttil far behind that of crude oil (58.0%) and that of natural gas (25.2%). The contribution of coal to the primary energy supply in
2000 wtil decrease slightly in percentage terms to 8.0% (43.7 miUion BOE) of the total primary energy supply. This is partly due to the increased coal exports and maximisation of the use of natural gas. The contribution of hydropower to the primary energy base will be 6.8% (37.1 mtilion BOE) in 2000 .
The percentage share of primary energy contributed by coal, crude oU and natural gas in
1990, and the predictions for 2000, for Indonesia and some other countries can be seen in Table 7.8 and Figure 7.20. In general, the main primary energy source for most countries (including Indonesia) is crude oil, except for AustraHa where the primary energy supply is coal due to the large coal resource base (Figure 7.1 and Table 7.8).
The percentage of Indonesia's primary energy supply contributed by oil and natural gas is stightly higher, whereas the contribution of coal is shghtly lower compared with those of most other countries (Figure 7.20). This is probably due to the development of oti reserves and the later development of coal, both for the electricity sector and the cement industry.
As for Indonesia, the share of oil in primary energy supply in most countries wtil show a stight decrease by 2000 whtie the contribution of natural gas wiU increase stightly.
Plans exist for the installation of one or more nuclear power stations in Indonesia. Nuclear power stations are a significant component in Japan and the United States and this is likely to continue.
The proportion of hydropower in primary energy supply is much higher in Indonesia compared with most other countries. 155
The primary energy growth rate between 1990 and 2000 is much higher in developing countries compared with developed countries. For example, Indonesia has an expected growth rate of 78.6% whereas AustraHa has a growth rate of 24.2%, Japan, a growth rate of 22.4% and the United States a growth rate of 14.6%. Consumption of coal in Indonesia is expected to rise at a faster rate than the growth rate of primary energy consumption.
Coal's Share in Electricity Sector
Currently, coal, gas and hydropower play an important role Indonesia's electricity sector and these energy sources are predicted to continue to increase in the next decade. Figure
7.21 shows the forecast Indonesian electricity generation figures for different primary energy sources. The figure indicates a dramatically increased share for coal from 23.5% of the total in 1993/1994 to 55.4% in 1998/1999 and to 65.7% in 2008/2009.
In tine with the effort towards diversification of the energy sources, the share of crude oti to electricity generation capacity wiU decrease from 37.5% in 1993/1994 to approximately
5.2% in 1998/1999 and 5.0% in 2008/2009 (State Electricity Corporation/PLN, 1992; Figure
7.21). OU reserves are decreasing and oti is now allocated for exports to increase the national income and alternative energy sources within Indonesia are becoming more important. Thus, the projections of electricity generation show that by 2003/2004 oil will be replaced to a greater extent by alternative energy sources, mostly coal (65.7% of production), natural gas (15.3%), hydropower (11.3%) and geothermal energy (2.5%).
7.4 THE FUTURE OF COAL CONVERSION
Coal is an inhomogeneous mixture of aromatic, cycloaliphatic and aliphatic compounds.
The ratio of aliphatic to aromatic moieties decreases with increasing rank and the H/C ratio also decreases with coalification from approximately 1 for low rank brown coals to 0.5 for 156 anthracite. Coal can be liquified in two ways - disruption of the bonds by hydrogenation cracking to produce liquid hydrocarbons or oxidative breaking of the bonds by gasification to form the CO fragments and then reconstitution with H2 to form the liquid hydrocarbons in a process generaUy known as gasoline synthesis. There are two methods for gasoline synthesis, Fischer-Tropsch synthesis in which the gases are converted directly to Hquids and the 'Mobti' process whereby the gases are converted to liquids via methanol.
The Fischer-Tropsch method was successfuUy used in Germany during World War U and is presently the backbone of the synthetic gasoline production from coal in South Africa where 12,500 tonnes of coal are converted to a variety of liquids per day. In South Africa, two processes are used, the fixed bed ARGE method and the fluidised-bed Synthol method,
The parent coal for the process is a high-ash coal (34% d.b.) with 22% volatiles, 0.5% sulphur, 11% total moisture and a specific energy of 20 MJkg"1 (Ward, 1984).
After coal-fired generation, coal conversion, Hquefaction and gasification processes are potential uses for eastern Kalimantan coals that rate as having the second priority. Despite abundant natural crude oil, liquid and gaseous fuels are sttil a prime necessity in Indonesia, and in the modern world in general, because of the Indonesian governments poUcy. Liquid hydrocarbons be more easily and efficiently transported, stored and used, than other energy resources. However, despite successful production of synthetic liquid hydrocarbons in
South Africa, the liquefaction of coal is sttil generaUy uneconomic, even the peak of oil prices over the last 15 year. Conversion of the coal to a Hquid or a gas, with a typically medium to high specific energy, provides a means of obtaining a clean Hquid or gaseous fuel for combustion. However, the costs associated with the processes are very high, and the overall thermal efficiency is lower than for direct firing of the coal in a pulverised state. 157
The properties of eastern Kalimantan coals, salient to liquefaction, include:
- maceral composition: reactive macerals (vitrinite plus liptinite) >85% and commonly greater than 90%;
- Rvmax: typically 0.42% for Miocene coals of normal regional coalification, 0.63% for Miocene coals occurred in areas of high geothermal gradient and 0.57% for all Eocene coals;
- H/C ratio: 0.76 - 0.96; and
- VolatUe matter: 37.6% - 41.5% (dry ash free basis).
Thus, eastern Kalimantan coals are excellent feedstocks for conversion, both liquefaction and gasification processes when compared to the South African coals presently used for conversion to Hquids. One important property is the very low sulphur for most of the coals except those from Berau, Pasir and Asem Asem coals which have relatively high pyritic sulphur (up to 1% in some bulk samples). There is some evidence to suggest that pyrite acts as catalyst but the product oti wtil contain more sulphur.
Using coals from Morwell and Denman-Scone (Australia) with properties simtiar in the range of those for eastern Kalimantan coals, Staker and Kelvin (1985) reported that the oil yield derived from the MorweU and Denman-Scone coals during Hquefaction ranges from
45% to 48% (dry ash free basis). The catalysts added to the coal in their process were red mud (3%) and sulphur (1%).
Davis et al (1976) stated that for coals with ranks between 0.49% and 1.02% vitrinite reflectance, the Hquefaction behaviour of a coal was determined by the proportion of reactive macerals, namely vitrinite, pseudovitrinite and Hptinite. For coals with a high proportion of reactive macerals, it was not unreasonable to expect that conversions of 70%. 158
Maledi (cited in Stach et al, 1982) gave the following formula for calculating a conversion factor for each maceral in coal Hquefaction:
K(p) = 1 Vitrinite(t) - Vitrinite(r)1 / 100 Vitrinite(t) where K(p) = conversion factor vitrinite(t) = total vitrinite vitrinite(r) = vitrinite remaining as a residue after liquefaction.
The amount of solid residue remaining generally ranges between 3% and 15%.
Using the above equation, substituting the high and low residues figures and assuming a total reactive maceral content of 80% for a typical eastern Kalimantan coal, conversion factors of 81% to 96% are obtained. These figures reinforce the potential of eastern
Kalimantan as a feedstock for liquid conversion.
Asem Asem coal is currently not mined because of its high moisture content and low vitrinite reflectance compared to other coals in eastern Kalimantan. Large resources of this coal exist near the surface and these can easily be developed. This coal, however, is too expensive to transport out of eastern KaUmantan. Thus, to maximise the use of eastern
Kalimantan coals, particularly those coals of high moisture content, such as the Asem Asem coal, it would be desirable to establish coal liquefaction and gasification plants adjacent to coal mines.
Residues from both Hquefaction and gasification processes could be reused as a feedstock in electricity plants that could be set up directly adjacent to liquefaction and gasification plants. This would save transport costs and also provide a power supply for industrial and regional development in eastern Kahmantan. Clearly, use of eastern Kalimantan coals in 159
Kalimantan depends on a suitable market and at present, this is stumbhng block as the population is relatively smati, as is the population density and industries are poorly developed as a consequence. A factor that might change the Kalimantan scenario is the government's policy of moving people from densely populated regions, such as Java, to
Kalimantan as part of the transmigration policy. This poUcy could have a snowbalhng effect in that if it is partly successful, it may encourage other people to move thus increasing the population and increasing the demand for industry. This would enhance the possibtiity of using Kalimantan coal locally.
Currently all large capacity coal-fired plants and big industries are located in Java and
Sumatera. It may be economic to transport the energy product from conversion and power generation to consumers, mainly in Java, using a sub-sea transport system. The technical developments required to make long sub-sea commodity transport are probably similar in their order of difficulty to those required to make coal liquefaction or gasification economic.
The estabhshment of the liquefaction, gasification and char-fired plants in eastern
Kalimantan also would reduce the environment impact of fuel use in Java which is the most densely populated island in Indonesia. Associated with this dense population are the highest levels (for Indonesia) of industriaHsation and environmental degradation.
In the next 15 years, it is predicted that coal wtil be the main energy source for industrial development in Indonesia because the current oti reserves are only sufficient for 15 to 20 years and the Indonesian Government takes a consideration view of undiscovered oti reserves. On the other hand, large coal resources are widely distributed in eastern
Kalimantan and Sumatera and can be developed readily. The priority then becomes the transport of a high proportion of this energy to Java. Direct transport of coal, transport of 160 coal products such as briquettes, coal-derived liquids and synthetic natural gas, and transmission of electricity generated in mine site power stations are all possible and likely to participate in the future mix of energy supply to Java.
7.5 SUMMARY AND CONCLUSIONS
The Indonesian Governmental Development Planning (REPELITA) strategy requires coal play a steadily increasing role in domestic supply and exports in the period from 1988 to
2000. The first part of these plans has been implemented and the share of coal on domestic consumption scenario, in 2000, is estimated to be in the range of 28.1 to 41.6 million tonnes per annum. Of this, 15.4 to 28.9 mtilion tonnes will be for electricity generation, 5.3 million tonnes for cement industry and 7.4 miUion tonnes for other uses.
By the year 2000, annual coal production is expected to reach approximately 50 miUion tonnes and exports wiU be 20 to 25 miUion tonnes.
The increased dependence on coal in the future is predicted because crude oti and natural gas reserves are only sufficient for 20 to 50 years at current production rates whereas coal will last over 300 years at current production rates. In addition, alternative uses of coal within Indonesia's industries are becoming more important. However, the effects of energy production and utilisation on the environment have become very important and there is an ever increasing public awareness in favour of protecting the environment. To reduce these environmental problems, alternative coal combustion techniques and the use of clean coal technology have to be developed and established.
The prospect of increasing coal exports each year, to maintain a foreign exchange earner for the country, requires a high degree of cooperation from all parties, including buyers, seUers, communities and government. Recognition of the national and international 161 importance for increasing coal exports is also required.
Interest in producing liquid and gas transport fuels from coal in selected countries elsewhere in the world is growing and the Indonesia's Government is currently supporting research and development related to coal conversions (gasification, liquefaction and low- temperature carbonisation through various research departments. The lead times for planning, design, construction and commissioning of commercial plants are expected to be very long. However, the major constraints to the early implementation of coal liquefaction and gasification projects are posed by uncertainties about the most appropriate technology and the high capital and operating costs.
Currently, there is also a growing interest also in the conversion of coal to briquettes with the product intended for household use in rural areas as a substitute for wood.
If coal is to significantly contribute to the liquid, gas and briquette fuels demand in
Indonesia, coal production must be on a large scale - production from Kalimantan mines must double and perhaps triple the estimate of 32 million tonnes that is required just to accommodate for present styles of domestic coal use and increased export demand. 162 163
CHAPTER EIGHT SUMMARY AND CONCLUSIONS
Second only to Bukit Asam and Ombtiin Coalfields of Sumatera, eastern KaUmantan has the second largest coal resources in Indonesia but currently has the highest annual coal production and it expected that the production wtil increase dramaticaUy over the next few years. One drawback to this expected increase in production could be the lack of an understanding of the suitability of the coals for domestic use, such as electricity generation, for export to neighbouring Asian countries such as Japan.
Economic coal deposits in eastern Kahmantan occur in the Tertiary Tarakan, Kutei, Barito and Asem Asem Tertiary Basins which formed as a result of rifting along, or close to, the eastern edge of the Kalimantan continental block. Barito and Asem Asem Basins were deposited in retro-arc settings close to the foreland whereas the Kutei and Tarakan Basins formed along the rifted border of eastern KaUmantan. The coal measures sequences were deposited in environments ranging from fluvial to deltaic.
Eastern Kalimantan coals are largely derived from lowland, ombrogenous (analogous with ombrotrophic) peat mires for which the detrital vegetation precursors were typicaUy tropical rainforest species, dominated by angiosperms (many of which were herbaceous), ferns and mosses, which grew in a humid tropical zone lacking a significant dry season.
The major objective of this study was to evaluate the variations in coal quality so as to provide a better understanding of the eastern Kalimantan coals by collecting new data and evaluate existing published and unpubhshed data. Interpretations based on these data will 164 provide a better understanding of coal quaHty variations thus providing valuable input for short term and long term plans for uttiisation of the coals.
Data coUected specificaUy for this study comprised organic petrographic data for 379 samples, including coal and dirt band samples, obtained through the microscopic examination of the samples in white Hght and fluorescence mode. For each sample, the maceral composition was determined by point counting techniques, with an average of 500 points per sample, and the mean maximum reflectance (Rvmax) was measured as set out in the AustraHan Standard. Routine analysis using X-ray diffraction and scanning electron microscopic techniques were carried out on selected samples.
8.1 CONCLUSIONS
This thesis has made a significant contribution to the understanding of the organic petrography of eastern Kalimantan coals and this forms the basis for a critical appraisal of the future utilisation for Kalimantan coals. Specific conclusions are listed below.
1. The thickness of the coal seams varies from a few centimetres to 40 metres with dips ranging between 5° and 25° near the surface. Typically the Miocene coals are thicker than the Eocene coals. Variations in thickness are associated with sphtting (particularly in
Eocene coals), wash-outs and wedge-outs. Sphtting was probably caused by channel activity at the time of peat accumulation.
2. In hand specimen, coals from eastern KaUmantan are composed dominantly of clarain and vitrain. Inertinite-rich dull layers are very rare but are more common in Miocene coals, particularly those from Mahakam and Sangatta, than in the Eocene coals. The vitrinite-rich bright layers were derived from peat that accumulated under water, in more 165 reducing conditions than were present for the inertinite-rich, dull layers which were probably derived from peat that was exposed to an oxidising atmosphere above the water table.
The rank of coals from eastern Kalimantan ranges from soft brown coal to high volatUe bituminous with thermaUy altered coals at Sangatta reaching semi-anthracite rank. Average mean maximum reflectance values range from 0.30% to 2.03%. Using rank as the main criterion, eastern Kalimantan coals can be divided into four groups:
Miocene, soft brown to sub-bituminous coals subjected to regional coalification in areas with normal geothermal gradients; Rvmax values of 0.30% to 0.55%;
Miocene, sub-bituminous to low volatUe bituminous coals subjected to regional coalification in high geothermal gradients areas (characterised by strongly folded strata); Rvmax values of 0.48% to 0.71%; these coals are restricted to the Sangatta area where there is a relatively high geothermal gradient, related to intrusions, that has not previously been reported;
Miocene, semi-anthracitic coals affected by contact thermal metamorphism;
Rvmax values of 1.60% to 2.03%; and
Eocene, brown to low volatile bituminous coals subjected to regional coalification in areas with normal geothermal gradients; Rvmax values of
0.43% to 0.66%; these coals were buried to greater depths than the Miocene coals.
Vitrinite reflectance of eastern KaUmantan coals shows significant increases with depth.
However, no significant vertical differences in vitrinite reflectance values were found within any single coal seam section, except for some of the Berau and Senakin coals where vitrinite reflectance exhibits an increase from the top to the bottom of the seam. The 166 changes within a single seam section are assumed to be related to differences in vitrinite type.
PetrographicaUy, vitrinite is the dominant maceral in both Miocene and Eocene coals with the vitrinite content of Miocene coals (range of 63.5 to 98.0%, average of 82.9%) higher than for Eocene coals (range of 61.9 to 93.9%, average of 79.4%). Average vitrinite content for aU samples was 81.4%. Vitrinite consists predominantly of telovitrinite and detrovitrinite with gelovitrinite content invariably low. Eu-ulminite is the dominant telovitrinite maceral whereas densinite and desmocolhnite are the dominant detrovitrinite macerals.
Inertinite content is generally very low and is more abundant in Miocene coals (average of 4.2%) compared with Eocene coals (average of 2.2%). Dominant macerals are semifusinite, sclerotinite and inertodetrinite with minor fusinite, micrinite and macrinite.
Several Miocene Mahakam coals have above average inertinite contents of up to 31.3%,
These coals probably formed in areas with more oxidising conditions, possibly caused by a lowering of the water table during peat formation, resulting in more frequent exposure to the atmosphere.
Liptinite is abundant in aU coals with the exceptions of thermaUy-affected coals from
Sangatta in which Hptinite is not easy to recognise because of the high rank. Liptinite contents of Eocene coals averages 11.6% which is typicaUy higher in Miocene coals where the average of 9.0%. The data indicate that there were stight differences in the floral assemblages at the time of peat formation of the respective coals. Resinite, suberinite, cutinite, sporinite and Hptodetrinite are the most common liptinite macerals in both Eocene and Miocene coals; fluorinite, exsudatinite and Botryococcus-related telalginite are minor components. Suberinite is more abundant in Miocene coals, particularly in coals with lower 167 vitrinite reflectance. Sporinite is less abundant in Miocene coals than in Eocene coals.
Exsudatinite content ranges from <0.1% to 9.9%, average of 0.8%. Five types of exsudatinite, based on morphology and occurrence, have been distinguished:
Type I exsudatinite has bright greenish-yeUow to yeUow fluorescence and infills long thin veins and fractures in, and is derived from, telovitrinite.
Type n exsudatinite inftils larger and longer fractures than Type I exsudatinite and is associated with, and derived from, detrovitrinite and resinite; it has yeUow to orange fluorescence although some detrovitrinite-associated exsudatinite has dull orange to weak brown fluorescence of very low intensity.
Type DI exsudatinite infills ceU lumens, both in vitrinite (telovitrinite) and inertinite (particularly semifusinite and sclerotinite). It is derived from vitrinite and resinite and has strong greenish-yeUow to orange fluorescence.
Type IV exsudatinite infills irregular cavities of different sizes and shapes, normally in the detrovitrinite groundmass; it has greenish-yellow to yellow fluorescence.
Type V exsudatinite infills short cleats or fractures (wedge-shaped fractures) and normally has yellow to orange fluorescence and is exuded from liptinite macerals, particularly resinite, cutinite and suberinite.
Type rv exsudatinite is the most common type.
3. The Tertiary coals from eastern Kahmantan have maceral compositions that are remarkably similar to that of coals from other Tertiary Indonesian basins. Similarities with
Tertiary coals in most other parts of the world are also apparent.
Small differences in coal type are seen when comparing Miocene coals with the Eocene 168 coals. These differences can be attributed to the interaction of tectonic, sedimentary, palaeoclimate and plant evolutionary factors.
4. ModeUed palaeotemperatures indicate that the present formation temperatures are significantly lower than those in the past for all basins in eastern Kalimantan. Therefore, the present geothermal gradient (31.3°C/km to 34.6°C/km) is probably lower than that operating during the main period of coahfication which was probably during Middle
Miocene. The model indicates that relatively rapid coalification may have occurred during the Eocene and Miocene in aU basins.
Textural and reflectance properties of eastern KaUmantan coals indicate that the Miocene
coals have been buried to depths of 1000 to 2000 m whereas Eocene coals have been
buried to depths of 2000 to 2500 m.
5. The mineral content of coals from eastern Kalimantan is typicaUy low with the
average in Eocene coals (6.7%) slightly higher than in the Miocene coals (3.9%). The low
mineral content is a function of the environment of deposition of the peat. Clay minerals,
especially kaolinite, and quartz are the most abundant minerals. Calcite is a minor
component and generally infills fractures. Pyrite occurs in most coals but in areas currently
being mined levels are low. Some Berau coals have moderate to high sulphur contents in
some plies and this indicates some marine influence. High sulphur in some Pasir coals
may be associated with the ombrogenous peat environments.
6. Currently, eastern Kalimantan coals are generaUy used for combustion, the traditional
use of Indonesian coals. However, understanding of the differences in coal type and coal
rank, together with an appreciation of the variation in chemical properties, permits a
reappraisal of the utilisation of eastern Kalimantan coals. 169
Eastern Kalimantan coals typicaUy have a low rank, high vitrinite content, moderate Hptinite and relatively low mineral matter and sulphur, properties that are needed in coals that are to be used in liquefaction, gasification or low-carbonisation. Considering all coals and their properties, it is proposed that:
(i) Mahakam, Sangatta, Berau, Tanjung and Pasir coals are the best coals for pulverised fuel boiler feed; Asem Asem, Satui and Senakin coals are less suitable because of higher contents of moisture, liptinite and mineral matter respectively. The high liptinite and mineral matter affect the grindability of the coals and the burn out time is longer for these coals because of the higher proportion of larger sizes formed when crushed. High moisture lowers the flame temperature.
(ti) The petrographic studies show that coals from eastern Kalimantan typically have a high reactive macerals content and this indicates that the coals are potentiaUy suitable for tiquefaction and gasification processes. Compared with liquefaction process, petrographic composition of the coal is of less significance in relation to the gasification process. Rank strongly influences the volume of product gas; a high yield of synthetic gas is obtained from coals having a rank in the range of brown coals to high volatUe bituminous coals.
(iii) The yield of oti products from eastern Kalimantan coals, on the basis of
Fischer Assay analyses, ranges from 55 Htres/tonne to 279 litres/tonne. For any given maceral composition, lower rank coals give a higher Fischer Assay yield than higher rank coals.
All Miocene coals and the Eocene Satui coals are suitable as feedstocks for liquefaction 170 and gasification processes.
(iv) The petrography of eastern Kalimantan coals also indicates that the coals are probably a significant source of naturaUy-formed crude oils where conditions are suitable.
The presence of oti haze, oil drops and abundant exsudatinite within the coals suggest that the coals produce oti at ranks as low as 0.35% vitrinite equivalent.
(v) The rank and inertinite content of the eastern Kalimantan coals are too low for use as a single component charge in high-temperature coal carbonisation processes.
However, selected Miocene coals from Sangatta, Pasir, Senakin and the Eocene coal from
Tanjung could be used as a component in some blends for low-temperature coal carbonisation processes that produce char.
(vi) Most eastern Kahmantan coals, except those with high sulphur, have exceUent potential for use as Hquefaction feeedstocks and, besides their use in coal-fired power stations, this should be the second highest priority for the eastern Kalimantan coals..
7. On a country wide basis, Indonesian coal is split between export and domestic consumption which includes electricity generation, which is the main domestic use, cement production and other combustion-based industries. In the last five years export tonnages have outstripped domestic use. However, this trend may not continue indefinitely, as
Indonesia is expected to dramatically increase electricity generation capacity by the year
2000 to fulfil domestic needs. Thus although the total tonnage of coal exported will increase, the proportion of the total supply wtil decrease relative to domestic consumption.
With regard to Kalimantan, a high proportion of present production is exported. Predictions are that exports wtil continue to be a major destination for eastern Kalimantan coal, but 171 in line with increased domestic consumption, much of expected production increase by the year 2000 wtil be directed towards domestic consumption, especially coal-fired electricity generation. The share of coal to the domestic energy consumption by the year 2000 is expected to increase to somewhere between 28 miUion (low estimation) to 42 miUion (high estimation) tonnes per year. This reflects the government pohcies to use currently known oil and natural gas reserves, which are only sufficient for domestic consumption for 20 to
50 years at current production rates, as an export commodity.
8. Indonesian coal production increased significantly during the last five years and it is predicted to increase to 50 million tonnes by 2000. These projections reflect increased output from eastern Kalimantan coal mines, estimated to be 36.2 million tonnes per year by 2000.
The present forecast coal supply of 50 mUHon tonnes in 2000 has to be increased to a minimum of 60 miUion tonnes in order to meet the domestic consumption and exports.
This figure can only be achieved by completing large projects through production share contracts in eastern KaUmantan and further expansion of the Sumatera coal mine.
Known Indonesian resources of coal wtil last over 300 years at current production rates.
8.2 FURTHER WORK
The Indonesian Government intends to increase coal production from eastern Kahmantan in the next few years. However, of total coal resources in this area, amounting to 8.94 biUion tonnes, only 22.2% can be categorised as measured reserves. Thus, detailed exploration followed by feasibihty studies incorporating detatied petrographic and chemical analysis of the coal should be carried out in the bigger coalfields of eastern KaUmantan. 172
These data are needed if forecast coal production levels are to be met. Because eastern
Kalimantan is located far from major coal consumption areas, which are mostly in Java, substantial construction, expansion and maintenance of roads and seaports wiU be required to achieve a smooth flow of coal.
This study confirmed that eastern Kahmantan coals, which are currently being mined or explored, are comparable in quality to existing steaming coal used in Indonesian coal- fired plants and is also suitable for export to the Asian markets. However, some variations in quality exist within and between the Miocene and Eocene coals. In order to supply a continuous quality product from eastern Kalimantan it may be necessary to develop
"blending facilities" at the export ports.
Technically, the type and rank of eastern Kalimantan coals indicates that the coals are suitable as feedstocks for Hquefaction and gasification processes. To know the economic potential of these processes it is suggested that a "ptiot project" study the most suitable coals, for example, any of the Miocene coals or the Eocene Satui coal. These coals have a higher proportion of reactive components compared with other coals of eastern
Kalimantan.
In the year 2000, it is expected that 50 to 60 mtilion tonnes wtil be produced from various mines in Indonesia and about half of this, 30 miUion tonnes, will be consumed locaUy.
Thus, environmental protection plans need to be implemented for coal mines, transport facilities and consumer outlets, particularly in Java.
Coal conversion technologies should be investigated because coal conversion has a large and important role to play in the reduction of environmental problems through the use of clean coals. 173
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FIGURE 1.1 LOCATION MAP OF STUDY AREA 192
FIGURE 1.2 COAL CONTRACTOR AGREEMENT AREAS IN EASTERN KALIMANTAN FIGURES FOR CHAPTER TWO 193