INDIAN COALS FOR SPONGE IRON PROCESS s. BAGCH1, K. K. RAYCHAUDHURI K. RAJA Central Fuel Research Institute, P.O. FRI. Dist. Dhanbad, Bihar
Abstract IN CONTRAST to conventional two stage process of steel making via blast furnace, direct steel making with pre-reduced iron ores or agglomerates have attra cted attention in recent times. This is particularly so for dev?loping countries where there is availability of other raw mate- rials for iron making but there is dearth of or limited resources of coking coal and abundant supply of other type of non coking coals. In terms of energy equivalent, availability of . solid fuel is many hundred times more than that of natural gas. Extensive attempts have therefore been made to utilise non coking coals to produce iron by non conventional methods such as direct reduction processes. The solid iron produced by reduction technique known as 'sponge' can then be transformed into steel by melting.
An attempt has been made in the paper to indicate the available resources of Indian coals, their nature and property which may be considered suitable for the production of sponge i ron either as such or after beneficiation. Indications have also been given for the possibility of utilising char from the fluid bed car- bonisation of non coking coal where such material can be obtained from an integrated formed coke plant.
Introduction temperature, oxygen content of the blast, humidification of the blast and by high The Conventional two-stages process top pressure of the blast furnace. of steel making via blast furnace has been in vogue over a century. In recent times, for iii) By utilising alternate fuels prepared reason of economy and productivity, large sized from non coking coals in the form of blast furnaces have been installed, which calls `formed coke.' for stringent specifications for the raw materials, particularly the coke. For coke with superior iv) Lastly, attempts are being made to by- pass the blast furnace technique alto- physical properties, good quality coking coals gether by adopting direct reduction tech- have to be used. The shortage of such coking coals nique for the production of iron- (sponge the world over, therefore, becomes the chief iron) followed by melting in electric fur- bottleneck in the expansion of iron and steel nace. industry. Attempts are being made to conserve this valuable raw material in the following The idea to produce iron without the use of ways: the blast furnace has been a favoured objective of the metallurgist during the past several de- i) By reducing intake of good quality cok- cades. Numerous processes1,7 have been sug- ing blend by incorporating medium and gested and reviewed which aim at producing pre-determined blends, followed by im- iron in the soild form and not in the liquid state proved techniques of coal preparation as in tne blast furnace practice. and carbonisation. In a recent analysis Miller (3) has forecast ii) By injecting auxiliary fuels like coal, oil, that while steel production in the world would coal-oil slurry, gas etc. at the tuyeres of reach a twat of 735 million tons in 1975 and 915 the blast furnaces with improvethent in million tons by 1980, the production and consum- operation such as by raising the blast ption of pre-reduced ore would equal to 11 mil-
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lion and 62 million tons respectively in those carried out in an inclined rotary kiln, fired by years. pulverised coal, and coke is used as the solid re- ductant. Though this process is adopted in sever- Direct Reduction Processes al countries, the consumption of fuel is high. It Directly reduced iron ore is neither iron nor is stated that about 150-250 kg of coke per to of ore as one normally understand either of the 'luppen' produced is required for which about 350 components. It is nothing more than the redu- kg of coal dust is also fired in the kiln. ction of oxygen in the ore below the melting and fusion point of the ores, pellets or agglomerates. The SL/RN process'', for which also an in- For a given mass of ore, the total iron weight re- clined rotary kiln is employed for reduction, has mains unchanged even though metallic iron is been adopted in many countries. Almost any increased by a reduction in the oxygen combined solid carbonaceous material may be used as heat- with it. With oxygen removal a honeycombed ing and reducing agent. Low rank high volatile microstructure remains which is called 'sponge coals having low strength and with fusion tem- iron.' The term is used inter-changeably with perature of ash above 1150°C may be used with pre-reduced agglomerates and directly reduced advantage for the reduction. It has, also been iron ores. mentioned that heat requirement varies from 2.37x10 6 to 3.5x10 6 K. cal per ton of sponge iron. It is possible to use reducing agents (solid or gaseous reductants) other than coke, which are Considering this, it may be pointed out that also cheaper in most of the cases. In this context, the large reserves of non coking coal (about 80% it will be worthwhile to consider the quantum of the total reserve) available in the country and of "available" reductants in the worlds against even char made of low temperature by fluid bed the "total" reserve in India (expressed in terms carbonisation may be used as reductants for the of 1015 K. cals). production of sponge iron. Ghosh and Lahiri2 have also suggested suitability of the solid redu- Reductants World India ction technique in India. Recently Miller and Koring7 have reiterated that direct reduction Coal 47000 461.7 technique can make a good impact for the ambi- Lignite 11000 5.6 Oil 730 1.7 tious iron and steel plans India is drawing up. In Natural Gas 0.8 the direct reduction process, for the manufacture of spcnge iron, high volatile, non coking coals From the above it is seen that the reserves of with relatively high ash fusion point particularly coal are about several hundred times larger than the initial deformation (I.D.) temperature that of natural gas. Due to this and also in view (> 1150°C) appear to be most desirable. In addi- of the ability of the processes utilising solid re- tion the coals should be low to medium in ash, ductants to handle a variety of raw materials, with relatively low sulphur ( < 1.0%) and phos- many plants4,5 are in operation in various coun- phorus ( < 0.1%) tries as may be seen in Table 1. Resources of Indian Coals Available for Direct The limited resources of coking coal in India Reduction are well known. The imbalance between the A detailed study of the available information availabilityl,8,9 of quality iron ore and good on the nature and composition of coals occurring quality coking coal has been emphasised many a in India shows that unlike coking coals, non cak- time. In Fig. 1 is given the distribution of the ing coals are well distributed all over the Lower iron ore and coal resources of .India. In the years Gondwana coal basins of the peninsular India to come it is also likely that pig iron plants may (Figure 1). In Table II are compiled the nature, be installed in locations away from the coking composition and resoure potentialities11.12 of coal areas. In this context, two points of great the solid minerals fuels ranging from lignite to significance emerge. They are (1) the production bituminous coals which are likely to conform to and utilisation of formed cokel0 from non coking the specifications of solid fuels suitable for the coals as an alternate fuel for blast furnaces and (ii) manufacture of sponge iron by the direct redu- consideration of the increasing application of ction process. non conventional techniques for the reduction of iron oxide, by passing the standard blast furnace Non coking coals with ash ranging normally route. between 11% and 24% (on air dried basis), and volatile matter between 25% and 35%1 (on air dried In the Krupp-Renn process,4 reduction is basis) have been largely selected. Moreover, due
118
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consideration is necessary for lower contents of i) Raniganj coalfield total sulphur, phosphorus and relatively higher initial deformation temperature of the ash in The Central and Eastern part of Raniganj mildly reducing atmosphere ( > 150°C). The coalfield accounts for a total reserve of non cok- areas of occurrence of coal seams containing ing coals of over 2300 million tonnes available coals of the specifications are restricted to cen- from 7 to 8 working coal horizons. Thickness of tral and eastern sectors of the Raniganj Mea- the seams generally varies between 1.2 and 9 sures coals of Raniganj coalfield in the East, metres. The coals are high in volatile (31 to 35% Sone Mahanadi valley coalfields of Madhya Pra- air dried) with ash mostly below 20%, The I.D. desh and Orissa, and the Pench Valley coalfields temperatures of the coal ash are often somewhat in the West. The coals also are found to under- lower, ranging between 1100°-1210° C. line in the South in the Kamptee, Wardha valley coalfields of Maharashtra and the Godavari val- ii) North sad Swath Karanpura Coalfields ley coalfields of Andhra Pradesh. In further South, there occurs the lignite deposit of Ney- The total reserves of the working coal hori- veli in Tamil Nadu. The proved reserves of such zons of these two coalfields amount over 1000 coals from seams under exploitation total to million tonnes. In north Karanpura coalfield, 3 over 5600 million tonnes excluding 600 million to 9 coal horizons (viz—Bachra, Karkata, Bisram- tonnes of proved reserves of Neyveli lignite. This pur, Bukbuka, Dakra, etc.) generally ranging in estimate excludes all coking, medium coking, thickness between 1.5 and 6 metres are being ex- semi to weekly coking coals of „Maria. Raniganj, ploited. The ash in these coals vary widely—even East and West Bokaro, Rarngarh, Jhilm.ili and from the same coal horizon, which at times ex- Kanhan valley coalfields and the semi to weakly- ceeds 28%. The T.D. temperature of the coal ash coking, high sulphur tertiary coals of Assam. is, however, high (above .1250°C).
1,19 In South Karanpura coalfield 10 to 12 upper pared to other coals, it is important to note that coal horizons (Argada 'A' and above) are being the productions in both the coalfields come from exploited whose thickness ranges generally bet- a single seam i.e. from Pasang seam in Bisram- ween 2 and 7 metres. Argada seam is a thick pur coalfield and Ghordewa (G-III) seam in coal horizon (11 to 54 metres). The ash of the coals Korba coalfield. Furthermore, the production from the seams also varies widely and often potentialities of this coalfield are high. The pre- tends to go quite high. The initial deformation sent annual production target of coals are 2.7 temperature of the coal ash is at times lower million tonnes from Pasang seam (from 3 col- which ranges between 1100° to 1280°C. lieries) of Bisrampur coalfield and a little over 2 million tonnes from Ghordeva seam (3 collieries) iii) Sohagpur Coalfield of Korba coalfield. In Sohagpur coalfield of Madhya Pradesh, Burhar, Kotma and Jhagrakhand are the three vi) Rampur Coalfield potential areas which account for a total reserve Rampur coalfield of Orissa working Rampur of over 260 million tonnes of coals. These are and Ib seams has a total reserve of about 40 mil- available from 1 to 3 working coal horizons lion tonnes of low to medium ash coals. The whose thickness range between 2 to 8 metres. seams are generally 2 to 3 metres in thickness. The coals there from are fair to medium in qua- The coals from lb seam is relatively low in ash lity, the percentage ash being mostly below 20%. (below 16%) but is also somewhat low in vola- The coals are high in volatiles (24 to 31% air tile matter (23 to 25% air dried). The coals from dried) and low in sulphur (below 0.8%) and pho- both the seams are low in sulphur (0.2 to 0.5%) sphorus (below 0.01%). The initial deformation and phosphorus (0.005%). However, the I.D. tem- temperature of the coal ash is b, tween 112.)'C to perature of the coal ash sometime shows a 1350°C. lower trend of 1130°C or so.
Of the three, Burhar area appears to be pro- vii) Talcher Coalfield mising as the coals can be had from a single source (i.e. Dhanpuri Seam) of a composite unit. The Bottom seam (2 to 7.5 m) worked in 3 In the single unit there is a reserve of over 100 collieries of Talcher coalfield of Orissa has a million tonnes of coal. The volatiles and fusion total proved reserve of about .110 million tonnes. temperatuhe (I.D.) of the coals are also on the The coals are comparatively low in ash (13 to higher side. 18%), high in volatiles (33 to 35%, air dried) and low in sulphur (0.4 to 0.7%) and phosphorus (be- iv) Chirimiri Coalfield low 0.01%). The L.D. temperature of the coal ash is also fairly high (above 1150°C). The present This coalfield accounts for a total reserve of production target of this seam, from the 3 col- over 430 million tonnes of non coking coals from lieries is over 1.4 million tonnes per year. 1 to 3 working coal horizons (viz. Korankohi Bijora/Gorghela/Main, 3A, Sonawani etc.) whose viii) Pench Valley Coalfield thickness generally range between 1.5 and 8 metres. The coals are low to moderate in ash, Situated in the western part of Madhya Pra- being mostly below 20% and high in volatiles desh, the Pench Valley coalfield accounts for a (25 to 33% air dried). The I.D. temperature of total reserve of about 190 million tonnes of fair the coal ash is above 1200°C. The coals are low to medium quality (ash 14 to 24%) coals, produ- in sulphur (below 0.7%.) and phosphorus (below ced from 3 to 4 working coal horizons. The coals 0.01%). The coal resources of Chirimiri coal- are fairly high in volatiles (27 to 33%, air dried) field thus appear to be quite promising. with I.D. temperature of the coal ash always above 1200°C. The sulphur content of the coals v) Korba and Bisrampur Coalfields at times higher (unto 1.9%). These two coalfields account for a total re- serve of over 130 million tonnes of fair to me- ix) Umer and Kamptee Coalfield dium quality non coking coals. The coals are Situated in the state of Maharashtra, these relatively low in ash (below 18%), sulphur (be- two areas near Nagpur account for a total re- low 0.6%) and phosphorus (below 0.01% ). The serve of about 120 million tonnes of medium I.D. temperature of the coal ash is also high quality (ash 14 to 21%) coals worked in two col- (over 1200°C). Although the coals are slightly lieries viz. Umrer and Silewara (Kamptee) lower in volatiles (25 to 28% air dried) as corn- mines. The coalash generally shows somewhat
120
lower range of fusion temperature, although the from Sohagpur (Jhagrakhand and Kotma areas), I.D. temperature is always over 1100°C. Bisrampur. Chirimiri and bench Valley coalfields x) Wardha Valley Coalfields of Madhya Pradesh, Talcher and Rampur coal- The 7 working collieries of Wardha coalfield, fields of Orissa and Raniganj coalfield of West working different sections of a thick composite Bengal. These coals are mostly low in sulphur seam, account for a total reserve of over 140 mil- (below 0.7%) and phosphorus (below 0.01%). lion tonnes of coal. Although the coals contain The phosphorus contents of Ranigani coals are ash below 20%, the sulphur content of the coals comparatively high (around 0.1%). The I.D. tem- is generally on the higher side (0.8 to 1.8%). The perature of the coal ash is also generally high coal ash shows somewhat lower range of fusion (above 1150°C), except those of Raniganj, temperature, although the temperature is al- Kotma and Rampur coals where it is generally ways above 1150°C. between 1100° and 1200 C. The total re- serves of such low ash coals (ash below 16%) xi) Godavari Valley Coalfields would be well over 1200 million tonnes. Of these, Situated in Andhra Pradesh, the Kothagu- Bisrampur, Talcher, and Jhagrakhand areas dium Tandur and Ramagundam areas of Goda- appear to be attractive. vari Valley coalfields are the other potential re- gions having coals suitable for sponge iron indu- Use of medium ash coals after beneficiation stry. Studies on the available data on cleaning Of these, Kothagudium area, working Queen characteristics of coals of medium ash group (ash and King seams, with a reserve of about 220 mil- 17 to 25%) indicate that these are amenable to lion tonnes appears to be important. The ash in washing with reasonably good yield of cleans.. the coals lies between 15 and 24% with sulphur A broad generalisation of the cleaning pos- mostly below 1% and phosphorus below (0.01%). sibilities such modium ash coals are given in The I.D. temperature of the coal ash is high Table IV: (above 1340°C). Table IV The other two areas working Seam No. I Cleaning possibilities of medium ash coals. to IV have a total reserve of over 578 million ton- Cleans Sinks Sp Gr. nes. Although the coals of these two areas are Particulars Ash% cut around Wt% Ash% Wt% Ash% also similar in quality the sulphur content of Ross Seam (i.e. Seam II) in Tandur area is gene- Overall 17 1.50 60 13 20 30 rally high (upto 2%). In Ramagundam area, the raw coal to to to to to 25 RO 15 40 45 I.D. temperature of coal ash sometimes shows the tendency to be on the lower side (below It is possible to have 60-80% yield of cleans 1100°C). with ash 15% or below at a specific gravity of separation around 1.50. The corresponding sinks xii) Neyveli (South Arcot) Lignite Field with 30-45% ash may be considered suitable for Situated further south in Tamil Nadu, the pulverised fuel firing in large boilers. At times Lignite deposit of Neyveli has a proved mineab- when the coals contain distinct shale bands the ble reserve of over 600 million tonnes which also ash of the sinks may be still higher (50-55%) appears to be attractive. The lignites at a mois- with consequent increased recovery of cleans. ture level of 15 to 20% (air dried) has ash of 4 The clean coals can thus be used after dewater- to 6%. They are low in sulphur (generally below ing to a reasonable moisture content. 1%) and phosphorus (below 0.01%). The I.D. temperature of the coal ash is relatively high Use of low temperature char as solid reductant (1184°-1220°C), although the ash fusion As indicated earlier, use of formed cokelO range is somewhat law (1180°-1380° C). prcduced from chars of non coking coals as alter- nate fuel for blast furnaces can be effective Availability of low ash coals means of conserving coking coals whose availa- It is apparent from Table II that the ash limits bility is limited. In an integrated scheme, formed of coals suitable for sponge iron manufacture coke may be used as substitute of coke in the have been considered generally upto 24%. How- conventional blast furnace and sufficient 'char' ever, if it is desired that the ash in the raw coals may be manufactured for use as solid reductant should be low, say, upto 16% or so, the poten- in sponge iron plant. The 'char' from a typical tialities of the areas containing such coals, along Indian nen. coking coal by fluid bed carbonis with their properties, are given in Table III. ation at 500-550°C has the properties given in Thus. relatively low ash coals are available Table V below:
121 Table V 4. Altekar, VA., Chatterjee A.B., Gupta K.N., Mathur G.P., and Kapoor A.N., 'Some ex- Properties of L.T. char from a typical non coking periences on direct reduction with non cok- Indian coal ing coals in a rotary kiln, (Ibid). 1.64.8 g/ c.e. M 3-5% Real density : 5. Janke W., The SL/RN process—Develop- A 20.24% Bulk density: 365-415 kg/m' ment and Experience (Ibid). VM 10-12% Reactivity to CO2-180-185. 6. Ray P. Litton and Gunther H. Miller `DeVe- lopment and Growth of the HYL process, The char being a reactive solid, may be suit- (Ibid). able for the purpose of reduction of iron ores, where the heat required for the process can be 7. KOnig H., Problems of prereduction of supplied by fixing pulverised coal of the type iron ores and their economic aspects (Ibid). from which char ic," produced. 8. Baneriee N.G., Sarkar G.G., and Lahiri, A., India in Industries, 2 (1957) 36. Conclusion 9. Banerjee N.G., Moitra A.K., Paper present- In view of the attempts that are being made ed at the symposium on Coal Mining Indu- to by-pass the conventional blast furnace route •of stry at CFRI, Jan. (1970). steel making and the increasing importance of the direct reduction technique for the produc- 10. Raja K., Moitra A.K., and Lahiri A., Alter- tion of sponge iron, it is thought worthwhile to nate fuels for blast furnaces Paper present- assess the quality and quantity of solid reductants ed at the Silver Jubilee Symposium, Indian available in India suitable for the purpose. It is Instt. of Metals, New Delhi, Feb. (1972). felt that the coals from Talcher, Bisrampur and 11. Report of task force on Coal and lignite, Jhagrakhand coalfield may be eminently suit- April (1972), Planning Commission, Govt. able for the process because cf their superior of India. quality. The coals from Kothagudium area of Godavari Valley coalfield and the lignites from 12. Report of the Committee on Assessment of Neyveli also deserve attention because of their Resources, volume H, Ranigani coalfield geographical positions. Char obtained from inte- (1963). grated 'formed coke' plant produced by carbonis- 13. Report on the utilisation of South Arcot ing non coking coals in fluid bed at low tempera- lignite, CFRI (1954). ture may also be utilised with advantage. 14. Raychaudhuri K.K. & Deshmukh, B.S. Chi- rimiri Coals', CFRI (1964). Acknowledgement The opinion expressed in this paper is of 15. Raniganj Coal Survey Laboratory, Annual the authors' and not necessarily of the Central Reports (1957 to 1970). Fuel Research Institute. 16. Ranchi Coal Survey Laboratory Annual Re- The authors are grateful to the Director, ports (1965, 1968 and 1969). C.F.R.I. for permission to present this paper. 17. Bilaspur Coal Survey Laboratory, Annual The authors are particularly thankful to Sri Reports (1956, 1957, 1962 to 1971) and Tech- A.K. Moitra, Assistant Director, Central Fuel nical Reports Nos B/2/65, B/3/65, 27, 38 to Research Institute for his invaluable assistance 42, 47, 48, 50, 55 and 56). in the compilation of this paper. 18. Nagpur Coal Survey Laboratory, Annual reports (1957 to 1971) and Technical report Reference Nos N/1, 2 & 3/65, N/4/165, N 7, 8 & 9165 1. Lahiri A. FRI News, 18, 4 (1968), 118. N/65 N/1/1A67).
2. Ghosh P.C. and. Lahiri, A., (Reprint) • 19. Nagpur Coal Survey Laboratory, Report on Min, Met. Fuel 18, 11 & 12 (1970) 1. the Rapid survey of Kothagudium Yellandu .7.nd Tandur Coalfields, (1953-1957) 3. Miller J.R., 'The production and use of directly reduced iron ore' Paper presented 20. Report of the washability studies of Non at the Silver Jubilee Symposium, Indian coking coals from Wardha Valley, Kamptee Instt. of Metals, New Delhi, Feb. (1972'.. and Godavari Valley coalfields, CFRI (1961).
122 Discussion cision is taken for installing such plant and necessary action is initiated. Mr. A. N. Naik (Tata Iron & Steel Co. Ltd., Jamshedpur). i) What is the crushing strength of Mr. T.V.S. Ratnam (M.N. Dastur & Co. P. Ltd., formed coke and its cost of production as com- Calcutta). You have mentioned about large blast pared to the conventional blast furnace coke that furnaces and the quality of the new materials is now produced in integrated iron and steel required. Will the coke produced from the plants, ii) How long will it take to instal new Indian coals have adequate strength for use in coke ovens for the production of formed coke large blast furnaces? What are your views in if it is more economical than B.F. coke as none regard to the strength of the coke for large blast is at present existing? furnaces? Mr. K. K. Raychaudhuri (Author) (i) The Mr. T.V. S. Ratnam (M.N. Dastur & Co. P. crushing strength of formed coke is not fixed. It Ltd., Calcutta). Coke produced from 100% depends on the type of formed coke and its use, washed Jharia coals (Prime caking) conform to i.e. whether for domestic, industrial or metallur- the stringent international specification of Physi- gical purposes. For example the point crushing cal characteristics of coke required for large strength of formed coke prepared from non-cok- blast furnaces. Although we do not have much ing Indian coals has been found to be 275 kg, experience of using cokes produced from Indian which is suitable for metallurgical purpose. coals for large blast furnaces, cokes produced from blend of 50% prime coking coals (Jharia) The cost of production is also dependent on and 50% medium coking coals (Kargali) both the process or scheme followed for the prepara- washed, are successfully being used in 2000 tion of formed coke and the capacity of the cu.m. blast furnace of Bokaro Steel. The Russian plant. However, the cost of production of form- specification for cokes to be used in such furna- ed coke by adopting a particular process may be ce is Micum, M40 -79 to 80 and M10-10 of less. comparable to that of the commercial coke price How these cokes would behave in blast furnaces as at present. (ii). A commercial formed coke of larger capacity cannot be envisaged at the plant can be set up at least 3 years after final de- moment.
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