New Classification Scheme for Microtextures of Natural Cokes:A Case Study from Heat Affected Coking Coalsof Jharia Coalfield,India

摘要

In Jharia coalfield,approx.1250 Mt of coking coal has been devolatilized due to igneousintrusives (dolerite dykes & mica peridotite sills) and mine fires.An effort has been madeto investigate the effect of carbonization vertically and laterally in two severely heataffected coal seams in Ena & Alkusa collieries.Through micropetrographic studies,characterisation of components of normal & heat affected coals have been done,enablingto deduce the level of changes leading to carbonization and subsequent enhancement ofrank,etc.The microstructures and microtextures deduced through the above study of heataltered maceral products in-situ,have revealed the nature & extent of heat effect,direction of heating source,quality and quantity of natural coke produced.Based on thisapproach and survey of existing literature,an effort has been made to classify themicrotexture of natural cokes generated due to carbonisation in the coal seams.Changes,due to heat effect on coking coals,whether in-situ or laboratory carbonizationare almost similar,barring the effect of pressure.Organic and inorganic constituentsundergoing changes at particular temperature and pressure are almost similar in both theabove conditions.Several studies have been made on microtextures in coke,but for thenatural cokes very scanty effort has been made.As a result still a universally acceptableclassification system for classifying the microtextures generated in the coking coal seamsdue to in-situ carbonization is lacking.Through this work an effort has been made to study the microtextures of natural cokesand devise a new acceptable classification system.Three broad categories I.e.isotropic,semi-isotropic and anisotropic,encompassing several sub-classes have been taken intoaccount.Organic and inorganic inerts,different forms (mosaic & flow) of anisotropicnatural coke components,pyrolytic carbon,domains (isochromatic & isometric) andintermediate stage (mesophase spheres) have also been taken into account.Most of thecomponents and microtextures produced in heat affected coking coals due totransformation have been covered under this classification system.