Development of New Coal Blend Preparation Methodologies for Improvement in Coke Quality

Abstract

Coal preparation has become a very important technique for preparation of high-quality metallurgical coke, the quality characteristics of which play a major role in the performance and economics of blast furnaces. Since availability of good quality metallurgical coals are meager in India, coal charge blends for carbonization in slot-type coke ovens are prepared from blending of various indigenous and imported sources of diverse characteristics. Preparation of coal blends for carbonization assumes paramount importance in terms of cost, quality, and resource utilization. Judicious coal-blending techniques based on intrinsic quality parameters coupled with various precarbonization steps to maintain blend homogeneity, granulometry, caking and coking properties of the blend are practiced under Indian conditions. The quality of metallurgical coke depends on type of coal, its physico-chemical properties including its granulometry, and its thermochemical behavior. Quality parameters of coke produced from a particular coal blend can be significantly influenced by the coal preparation technique adopted particularly when the blend comprises several sources of diverse quality parameters. Groupwise crushing of coal was developed with the aim to reduce the heterogeneity of different size fractions in terms of distribution of inerts and reactive contents. The groupings were based on their grindability indices, caking/coking properties, and dilation properties of individual size fractions. This article discusses in detail new coal preparation methodologies for improvement in coal charge blend granulometry and flowability, reduction in microfines content, and improvement in blast furnace coke quality.