Chlorine speciation and migration pathways during pyrolysis of coking coals

This paper systematically investigates the occurrence forms of chlorine in typical coking coals and its migration behaviour during pyrolysis under simulated industrial coking conditions. Nine representative coking coals (including gas-fat coal, fat coal, 1/3 coking coal, prime coking coal, and lean coal) from a specific steel plant were selected. A 5 kg laboratory coke oven experimental device was utilised to simulate the heating environment of an industrial coke oven. Using X-ray photoelectron spectroscopy and microcoulometric chlorine analysis (JF-WK-2000A), the chlorine content and speciation in raw coal and pyrolysis products (coke, tar, and gas) were quantitatively analysed. Organic chlorine was identified as the dominant form in both raw coal and coke. The results reveal significant differences in chlorine conversion rates among coal types: 0.02% to 0.35% of chlorine migrated into gas, 2.27% to 39.27% into tar, and 8.08% to 86.55% remained in coke. These findings indicate that chlorine undergoes complex chemical transformation reactions throughout coking processes involving these coals. In this study – conducted under conditions closely resembling those found in industrial settings – the systematic quantification of chloride migration and distribution throughout all stages of coking has been achieved. It provides critical theoretical data support for steel enterprises aiming to optimise their blending strategies for coals while enhancing coke quality alongside improving treatment methods for condensate water containing elevated levels of chlorides – an endeavour crucial for advancing cleaner production practices within the industry.