Annexure D: Thar Coal Analysis

American Journal of Scientific Research ISSN 1450-223X Issue 11(2010), pp.92-102 © EuroJournals Publishing, Inc. 2010 http://www.eurojournals.com/ajsr.htm

Annexure-'D' 160

Composition, Trace Element Contents and Major
Ash Constituents of Thar Coal, Pakistan

M. Afzal Farooq Choudry

Department of Environmental Science, FUUAST, Karachi, Pakistan

E-mail: [email protected]

Yasmin Nurgis

Environmental Research Center, Bahria University, Karachi, Pakistan

Mughal Sharif

Environmental Research Center, Bahria University, Karachi, Pakistan

Amjad Ali Mahmood

Geological Survey of Pakistan, Karachi, Pakistan

Haq Nawaz Abbasi

Department of Environmental Science, FUUAST, Karachi, Pakistan

Abstract

Thar coalfield is a part of the Thar Desert of Pakistan. Pakistan has coal reserves of
185 billion tons, of this Thar coal reserves account for 175 billion tons spread over a single geographically contained area of 9100 sq km in the south eastern part of the Sindh. It is bounded in the north, east and south by India, in the west by the irrigated Indus river flood plain. The terrain is sandy and rough with sand dunes forming the topography. Various physio-chemical parameters including chemical composition of coal ashes, distribution of trace elements in them, were analyzed to understand the coal prospects and its share in the domestic energy production. In addition a preliminary study have also undertaken on the factors that effect the chemical composition of coal ashes. The apparent rank is high volatile Lignite “B” coal. Arithmetic mean values for proximate analysis of coals (as received basis; n=54) show these coals to be 6.83% Ash, 29.55% volatile matter, 19.2% fixed carbon and 44.3% moisture and have a heat of combustion of 6094 BTU/lb. Average values for ultimate analysis of the coal show these coals to be 4.96% hydrogen, 51.18% carbon, 0.31% nitrogen, 2.45% sulphur and 14.88% oxygen. The geometric mean values of these, as viewed from the analysis of coal ash samples collected from the Thar coal field region, it can be seen that coal ashes from region studied are composed of organic matter and the major chemicals are SiO₂, Al₂O₃, Fe₂O₃and CaO as well as minor amounts of SO₃,P₂O₅, Na₂O, K₂O and TiO₂. During the combustions of coal, its trace elements will be redistributed and most of them are enriched in coal ashes.The mineralogy of Sindh coal samples suggests that these coals have quartz and Kaolinite as the dominant phase and minor amount of calcite, Illite and Muuscovite. The dominant minerals of Thar coals are

Composition, Trace Element Contents and Major Ash Constituents of Thar Coal, Pakistan

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quartz. Quartz also tends to occur in the form of comparatively large particles of free mineral matter, whereas much of the pyrite is dispersed in the coal substances and clay sediments.

Keywords: Coal, Thar, Bara, Trace Elements, Ash

1. Introduction

Energy has become an important prerequisite for the economic development of a country. On one hand it is used for the industrial and agricultural purposes and on other hand it is required for domestic use of the citizens. Pakistan is presently facing an acute power shortage, with a rapidly growing population and economy, and relying heavily on thermal power generation. About half of the thermal power generation is based on imported oil or on natural gas. Oil is very expensive and rising unpredictable to unprecedented height. Where as reserves of natural gas are limited. Pakistan is presently facing a demand and supply gap of electricity approximately 5000MW and may increase in the coming years.
Out of total generation capacity of 17664MW, coal fired power generation is presently only
50MW. Whereas Pakistan has total coal reserves of 185 billion tons of these Thar coal reserves account for 175 billion tons spread over a single geographical contained area of 9100 sq km in Thar desert in South-Eastern corner of the province of Sindh, Pakistan. Coal is projected as a primary source for power generation through its combustion and could even surpass oil and natural gas in use, especially when the real costs of energy are compared to the costs of using indigenous coal resources of Pakistan. In this scenario coal presents itself as the foremost solution to country energy crises.
In the process of combustion organic and inorganic materials in it will undergo a complex variation part of them will become volatiles, together with coal smoke, enter into atmosphere in the form of solid particles and the rest will be retained in ash and slag. Coal ashes are the residues of organic and inorganic substances in coal left after coal combustion ( Abernethy et al; 1969).The concentration of trace elements are much higher than those of bottom ash ( Swaine, 1975) coal combustion not only produce heat and energy but significantly harm the environment and human health ( Hepplaston et al; 1984; Borm, 1994; Vanhee et al, 1995; Borm and Driscoll, 1996; Driscoll et al; 1996, 1997; Paul, 1997; Frinkelman et al; 1999). Under leaching action the ashes will find their way into underground water, causing underground water pollution (Mareal Pires et al; 2000; Liuguijian, 2000 a). Therefore, coal combustion and ash slag formation will lead to obvious redistribution of elements on the earth surface.
Coal quality is now generally recognized as being an impact, often significant, on coal combustion especially in many areas of power plant operation. The parameters of rank, mineral matter content (ash content) sulfur and moisture contents are regarded as determining factors in combustibility as it relates to both heating value and ease of reaction. Therefore this study is undertaken the geochemical characteristics, chemical composition and element composition of Thar coal .In addition this study is a brief effort to stimulate the already growing interest in the possibilities of raising the coal prospects and its share in the domestic energy production. Coal ashes analysis will provide the scientific basis for their comprehensive utilization and for reducing environmental pollution.

2. Location and Topography of the Area

Pakistan lies along the contact between the Indian and Eurasian Plates. It is situated in the northwestern corner of the Indian Plate, to its south-east is Indian Plate and to the north the Asian/Karakorum continental Plate.
The province of Sindh is situated in the Lower Indus Basin.Lower Indus Basin has a number of coal basins. These basins extend westward from Thar coalfield, through Badin to Lakhra-Sonda-Thatta area. The western part of Sindh falls in the folded belt zone where as most of the eastern part covers the

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Amjad Ali Mahmood and Haq Nawaz Abbasi

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platform slope. Shelf platform and carbonate deposits ranging in age from Triassic to recent overlie the basement slope (Kazmi and Jan, 1995).
The Thar coalfield is located between latitudes 24o15'N and 25o 45'N and longitudes 69o45'E and in the south-eastern part of Sindh. The Thar desert lies in the south-eastern part of Pakistan on the stable western margin of the Indian plate (Kazmi and Jan, 1995).

3. Geology of Thar

The Thar coalfield is covered by dunes with an average depth varying from 14-93 meters and is located on the Indus platform in the eastern part of the desert. This structural platform is underlain by relatively shallow granitic basement. This granite complex dips down abruptly beneath the western part of the Thar Desert and is highly faulted (Fasset and Durrani, 1994).
An unconformity at the base of underlying sedimentary sequence east ward to the point where the Paleocene/Eocene rocks rest directly on the basement granite is present. The maceral components indicate less maturity of coal formed herbaceous plants in warm climate with rapid rise and fall in water level and environment of raised bogs (Fasset and Durrani, 1994). The quality of coal is liginite ‘B’, Clay stone forms the roof as well as floor of coal benches (Jaleel et. al., 2002). Thar coals are Paleocene to Eocene in age and may be deposited in raised bog environment (Jaleel et. al., 2002). The geological studies shows that coal bearing strata of palocene-Eocene sediments unconformabaly overlie the pre-cambrian basement igneous rocks exposed al-Nagar Parkar ( Fasset and Durrani, 1994) and this is only out crop bed rock in the region.
At the depth of 110 to 277 meters the basement rock is generally granite and granodiorite. The granite is of white, pinkish grey to very light grey in colour and coarse grained having feldspar to highly altered Kaolinite (Jaffery, 1994).
The Paleocene-Ecocene coal bearing horizons of clay stone, carbonaceous clay stone, sand stone and silt stone with inter-laminated coal beds. Sand stone is very fine to coarse grained and consists of ferro –magnesium mineral grains.
The metabasalts are medium to coarse grained volcanic and plutonic rocks that have metamorphosed to epidote amphibolites and contain acidic dykes of rhyolite to quartz trachyte composition (Jan et al., 1997). The coal bearing horizon of the Paleocene-Eocene sediments above the basement complex is designated as Bara formation is highly altered Kaolinite (Jaffery, 1994). The granite is white, pinkish grey. The stratigraphic sequence in the Thar coal test holes is generally the same (Table 1)

4. Sample Collection and Analytical Methods

The coal reserves spread over a large area and the potential area is divided into four blocks. Coal seam is persistent over most of the area in all the blocks. The seam attains a maximum thickness of 36 meters. The commutative thickness of the coal beds range from 0.2 to 3.6 meters. Coal samples were systematically collected from coal seam of the Bara formation from the Thar coal bore holes. Vertically each sample was taken at the interval of one meter.

A total of 270 representative samples of Thar coal from all four blocks have been investigated for
Proximate and ultimate parameters including combustion properties. Among these 13 each from block I & block II and 14 each from block III & IV. Sample collection and preparation, analytical procedures including proximate, ultimate, Atomic Absorption Spectroscopy and Spectra photometry were all conducted according to ASTM procedures and US Geological Survey (USGS) guidelines. (Flow chart) At the same time 22 representative Coal-Ash samples from all four blocks were analyzed for heavy trace elements including Pb, Zn, Cd, Cu, Co, Ni, Cr, Fe, Mn and As as per ASTM methods. The main mineral components were also determined in this study are Silicon dioxide, aluminum oxide, ferric oxide, titanium dioxide, phosphorus pentaoxide, calcium oxide, magnesium oxide, sodium oxide, and potassium oxide.

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5. The Basic Characteristics of Raw Coal

The coal samples from the coal seams are mainly lignite coal. In the raw coal ashes accounts for 2.34 to 20.31% Ash, 34.52 to 51.65 % Moisture, 6.96 to 22.95% Fixed Carbon, 25.82 to 33.43 % Volatile Matter, Heat yield is 48.44 to 66.27 BTU/ Lb, .The sulfur contents in Bara formation Coal seams of Thar is 0.46 to 9.94% .The major minerals in coal are Silicon dioxide, aluminum oxide, ferric oxide, titanium dioxide, phosphorus pentaoxide, calcium oxide, magnesium oxide, sodium oxide, and potassium oxide (Table 2).

6. The Basic Characteristics of Coal Ash

Ash content of coal in the non combustible residue left after coal is burnt. It represents the bulk mineral matter after carbon, oxygen, sulphur and water including (from Clays) has been driven off during combustion. The yield of coal ashes and their geochemical properties determine the quality of coal and its forming conditions. It is found from the analytical results of raw coal ashes that the ash yield of coal seam of the Bara Formation ranges from 2.34 % to 20.31%. According to the standards for the classification of coal ashes in Pakistan, coal ashes from this region belong to be “B” type. (Table 2)

6.1. Chemical Composition of Coal Ashes

The analysis of coal ash may be carried out to determine not only the composition of coal ash but also levels at which trace elements occur in ash. Such data is useful for environmental impact modeling.
The chemical composition of coal ashes depends on the composition of inorganic minerals and organic matter in coal. In the process of coal combustion organic and inorganic matter will be liberated and changed. A part of them will be released as volatiles together with coal smoke into atmosphere and another parts of them , which are present in flying ash, dust and micro grains, will find their way as solid particles into atmosphere and another part of them will remain in ashes slag. Some chemical components in the inorganic matter of ashes are derived from organic matter in the coal and will be present as a new phase and mineral components in the ashes. (Table 2)
The chemical analysis of raw coal ash contents of various minerals are listed in Table 2. From the analysis it is found that the region are characterized as being high in Al₂O₃and SiO₂but low in Fe₂O₃and CaO contents , with minor amount of SO₃and MnO.
Ash is calculated with the formula

CaO + MgO
MO=
Sio₂+ Al₂O₃

The minimum Value obtained is 4.84 and the maximum value is 40.37. MO is less then unity indicative of acidic coal ashes.
The mean, minimum, maximum and standard deviations are shown in Table 4 and 5 for proximate analysis (as determined and as received). Descriptive statistical analysis for ultimate analysis (as determined and as received) is tabulated in Table 6 and 7 and comparative study of all the four blocks as received is indicated in Table 8.

7. Correlation Analyses

Correlation analysis is applied to the multivariate data set to investigate the degree of similarities and probable interrelations among the chemical and physical parameters (Nurken, 1997).
Correlation coefficient between the variables for proximate and ultimate (as determined, as received) were calculated and listed in Table 9-12. Statistical analysis for the determination of correlation coefficient has been calculated. An overall view of the correlation mean results reveals that the numbers of parameters are not correlating with each other and which are correlated indicated by bold faces in the Table 9-12, suggesting that they are dependent on each other.

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The values obtained in proximate analyses (as determined and as received) suggesting that those variables which are correlating are similar in both types of analysis, indicating that energy values are dependent on volatile matter whereas the ash contents depend on % of sulfur in coal.
The strong correlation existing between carbon: hydrogen and ash: sulfur in ultimate analyses
(as determined and as received), pointing out that these variables are dependent on each other.

Table 1: Stratigraphic Sequence in the Thar Coal Field (Jaleel et al.,1999)

Formation

Dune sand

Age

Recent

Thickness

14 to 93m

Lithology

Sand, silt, clay

UN CONFORMITY

Sandstone, siltstone, claystone, mottled

Alluvial deposit

Sub recent

11 to 209m

0 to 185m -

UN CONFORMITY

Claystone, shale, coal, sandstone, carbonaceous claystone
Middle Paleocene to Early Eocene
Bara formation, Ranikot group

UN CONFORMITY

Nagar Parkar Granite (Basement complex)

Pre-cambrian

Granite, Gabbro and Diorite,

Table 2: Coal ash analysis of Thar coal

N o

12345678

SiO₂

57.78 10.50 51.95 15.75 4.60

TiO₂

0.16 0.01 0.45 0.08 0.15 0.08 0.11 0.50 0.75 0.60 0.53 1.10 0.20 0.15 0.24 0.40 0.40 0.41 0.02 0.01 0.41 0.33

Al₂O₃

23.17
5.44
28.69 13.36
8.34 9.43
31.57
9.14
40.34 36.70 36.72 18.01 12.10
1.50

Fe₂O₃

8.59 53.64 6.38 13.53
8.57 16.73 2.47 6.07 1.08 6.93 8.10 0.51 23.00 47.00 39.74 34.36 16.40 20.02 11.40 75.42 5.03

MnO

0.07 0.01 0.06 0.14 0.23 0.16 0.08 0.23 Traces Traces
0.04 0.48 0.08. 0.08 0.08 0.07 0.05 0.13 0.24 0.11 0.32 0.23

MgO

1.89 3.07 2.57 8.78 13.84 11.34 2.86 10.61
0.01 0.01 0.85 0.01 6.40 2.80 4.43 2.80 0.40 8.80 2.40 2.80 0.40 1.20

CaO

4.00 7.80

Na₂O

1.07 2.97 2.67 4.24 5.48 4.06 1.89 7.02 0.32 1.06 1.10 1.21 3.35 2.69 3.26 2.20 1.15 2.70 1.60 4.00 4.10 4.04

K₂O

0.20 0.15 0.17 0.28 0.35 0.24 0.32 0.57 0.24 0.09 0.11 0.96 0.42 0.26 0.44 0.30 0.13 0.25 0.48 0.11 0.54 0.45

SO₃

2.46 14.24 0.39 21.87 27.40 29.85 6.68
20.03 Traces Traces Traces Traces
0.10 16.54 Traces Traces Traces Traces Traces Traces Traces Traces Traces Traces

P₂O₅

Moisture

0.82 1.44 0.05 3.66 0.46 0.30 4.32 3.51 0.41 0.49 0.67 0.20 0.50 0.35 0.45 0.50 0.50 0.35 0.50 0.52 0.42 0.45
Traces Traces Traces Traces Traces Traces Traces Traces
6.58
18.01 29.62 21.09 7.52
27.04
0.97 0.70
6.33 41.75 15.20 55.76 54.61 51.05 12.06 20.40 23.04 13.78 31.40 47.28 25.46 20.08 1.32
910 11 12 13 14 15 16 17 18 19 20 21 22

0.70

Traces

Traces 16.29 10.01 20.00
6.86
48.95 17.30 12.33 16.80 8.90
0.80
12.90 30.05
8.80

3.30

0.25

14.02 28.00
9.50
35.80 18.30
19.57 22.80 5.83
30.58 13.00
11.80
0.52
16.01 29.02
5.94

31.22

2.65

Table 3: Average Thar Coal analysis

Coal Quality

Moisture (AR) Ash (AR)

Lignite A-B %

43.24 - 49.01%
5.18 - 6.56%
Volatile Matter (AR) Fixed Carbon (AR) Sulphur (AR) Heating Value (Btu/Lb.)
As Received
26.50 - 3.04% 19.35 - 22.00%
0.92 - 1.34%

5780 - 6398

10723 - 11353

Dry

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Table 4: Descriptive statistic of proximate analysis (as determinant)

Variable

Moisture Ash% Volatile Fixed Ca Sulphur% Energy V

N

Mean

15.830 10.228 44.668 29.107 2.4860 09216

Min

Max

St. Dev

4.787 6.681 3.501 3.919 2.966 00760
54 54 54 54 54 54
2.4700 4.0000 38.560 10.050 0.6500 07670
25.660 29.340 53.500 35.080 13.850 010850

Table 5: Descriptive statistic of proximate analysis (as receive)

Variable

Moisture Ash%

N

Mean

44.301 6.8270 29.549 19.206 1.6830 6094.2

Min

Max

St. Dev

4.287 4.639 2.638 2.408 2.087 480.8
54 54 54 54 54 54
32.120 2.3400 24.570 6.9600 0.4400 4844.0
51.650 20.310 36.230 23.020 9.9400 7063.0
Volatile Fixed Ca Sulphur% Energy V

Table 6: Descriptive statistic of ultimate analysis (as determent)

Variable

Carbon Hydrogen Nitrogen Sulfur Ash Moisture Oxygen

N

Mean

51.186 4.9681 0.3094 2.4530 10.238 15.922 14.880

Min

Max

St. Dev

6.4940 0.7218 0.1311 2.9460 6.6810 4.8400 5.9590
54 54 54 54 54 54 54
34.880 3.1100 0.1200 0.6400 4.0000 2.4700 5.6400
62.210 5.8800 0.8700 13.870 29.340 25.660 35.950