Development and Introduction of New Coal Preparation Technologies for Improvement in Coke Quality in SAIL Plants

摘要

Indian steel plants normally use 7-9 sources of coals, including low ash imported coals for carbonization and these coals differ widely in terms of caking and coking properties. Indigenous coals are much inferior to imported ones in terms of inorganic and organic inert contents, reactive content as well as rank. Conventional blend crushing of these coals for carbonization makes the coal blend heterogeneous with concentration of inerts in the coarser size fraction of the charge blend leading to heterogeneity in the properties of different size fractions in terms of reactive and inert content. More over, the content of micro-fines increases with the increase in usage of imported coals and lowers bulk density of coal charge. Differential crushing of coal charge technology was developed to make the coal blend more homogeneous and with lesser content of micro-fines. Carbonization in slot type ovens is practiced under SAIL and normally coal blend moisture is kept 7.5-8.5% so as to minimize emission of fines during charging into ovens. Content of micro-fines increases further where selective crushing technology is employed. Higher content of fines coupled with higher moisture range in the blend pose the dual problems of coal blend flow-ability including jamming of chutes etc. as well as reduction in the blend compactness, thus bulk density of the charge. This problem further aggravates particularly during monsoon when moisture content shoots up to 10-12% and sometimes even more. In order to improve coal charge blend homogeneity, reduction in fines content, improvement in charge coal bulk density as well as coal flow-ability, the technologies of differential crushing of coals and oil-water emulsion addition system with coal charge were developed and introduced wherein benefits including improvement in coke quality realized.