Application of stage condensation of tar during pyrolysis of high ash semi-bituminous-Morupule mine coal

Abstract

Botswana high-ash semi-bituminous coal produced by Morupule mine is under-utilized due to a lack of knowledge in possible applications of derivative products such as tar, syngas, and charcoal. This study is aimed to determine the possibility of producing tar as the main product via stage condensation in a semi-batch pyrolysis plant. A conventional process that incorporates fractional distillation to refine tar makes the low-quality coal uneconomical for coal to tar application because of high energy requirement. Raw and washed peas density medium separated at 50 % yield (DMS 50 %) Morupule coal was used for pyrolysis at 500 ˚C and connected to 3 condensers set to 150 ˚C, 80 ˚C, and 25 ˚C, respectively. The average tar yield from raw coal was about 1% and about 2.4-2.6 % in washed peas coal. Washed coal had the highest oil yield of about 2.5% as compared to the average of about 1% in raw coal. Both yields are extremely low to be considered for commercial pyrolysis (targeting tar as the main product), however, no pyrolysis product goes to waste. If all products (syngas, charcoal, and tar/oils) were marketed, the process would have the potential to become profitable.