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The effects of igneous intrusion on coal are observed in various parts of the world. Thermally altered coals are known by various names, such as, geological coke, natural coke, cinder etc. The nature and intensity of coal alteration depend on the temperature of the intrusion, the duration of magmatic heating and the distance from direct contact with the igneous rock. In general, igneous intrusions cause dramatic changes in vitrinite reflectance, mineralogy and geochemistry of the coal seams. In most cases, these changes are gradual with distinct physical, chemical and microscopical properties.1,2) Three zones in the intrusion affected coal seams can be demarcated as (i) normal coal (%Romax 0.8–1.2%) (ii) slightly thermally altered coal (%Romax 1.2– 1.8%) and (iii) highly thermally altered coal (%Romax 1.8– 5.0%).3) In India, a large amount of thermally metamorphosed coal has been found in the Damodar Valley coalfields in Jharia, which is locally known as “jhama”. Jharia coalfield of Damodar Valley has a reserve of approximately 5 313 million tonne which is about 2% of total coal deposits of India. Major part of the reserve of coking coal is altered due to igneous intrusion (Fig. 1). Due to metamorphism, the pseudo carbonization takes place and coking coal is converted into natural coke or jhama. The total insitu reserve of jhama at Jharia division of Tata Steel is 154.10 million tonne wherein the extractable reserve is only 8.64 million tonne till date.4) The nature and amount of influence of the igneous intrusions seems to be quite complex and it has substantially altered the physico-chemical properties of the surrounding coal mass. Due to various difficulties very few systematic characterizations were done earlier. Hence, proper industrial utilization of heat affected coal could not be made till now. With this background a laboratory scale study has been designed to find the possibility of using moderately affected jhama coal in coke making using some specific pre-carbonization techniques, adding some additives and by combination of both. Result shows that pre-carbonization techniques like “groupwise crushing” and some binders are useful for utilization of maximum quantity of jhama coal as a component of coal blend in coke making.

Heat Altered Coal and Its Use in Metallurgical Coke Making