Solvent-refined coal from high-ash non-coking coals and washery middlings for use in metallurgical coke making Part 1. Production, testing and characterisation

Abstract

This paper presents studies on the preparation of a potential coking additive, solvent-refined coal (SRC), from typical high-ash Indian non-coking bituminous coals, tertiary Assam coal with a high sulphur content and washery middlings in a bench-scale unit (10 kg h −1 coal throughput capacity) under hydrogen pressure. The extraction of the coal samples was conducted under moderate reaction conditions of temperature, pressure and residence time. No external catalyst was used in the process. Pre-beneficiated coal was used as the feed material and anthracene oil with a boiling range of 270–360°C was used as the solvent. Rigorous solid separation from the extract slurry by filtration was avoided by centrifugation in a super-decanter centrifuge to produce SRC with an ash content of 6–7%. The yield of SRC from non-coking Samla seam coal of the Raniganj coalfield was found to be 85% while its caking index was 44. Substantial improvement in the quality of blast furnace-grade coke was achieved by co-carbonisation of coking blends by mixing only 10% of the SRC prepared from Assam coal. The hydrogen requirement was low (1.5% wt/wt of d.a.f. coal) and recovery was of the order of 96% of the solvent used for the preparation of the coal-oil slurry. The yield of SRC and its quality as a coking agent are reported, along with the quality of the coke produced using SRC obtained from typical coal.