The integration of biomass torrefaction with coal gasification: Performance study and process simulation

Abstract

Conventional biomass torrefaction process in a N2 atmosphere presents economic and environmental challenges, including the necessity for N2 separation from air, additional fuel consumption for heat supply, and the post-treatment of low-calorific gaseous by-products. Hence, the concept of process integration, which includes heat integration and the effective utilization of by-products, is highly desirable. This study proposed a novel concept of integrating biomass torrefaction with coal gasification to achieve both heat integration and the co-processing of gaseous by-products from biomass torrefaction and raw syngas (RS) from coal gasification. To this end, torrefaction tests were comparatively conducted on pine sawdust (PS) in a simulated RS atmosphere and its mono- or bi-component atmosphere at 280 and 320 °C. The results revealed that a marked improvement in the grindability and energy densification of the solid products when torrefaction was performed in the RS atmosphere compared with the N2 atmosphere. This improvement in the RS atmosphere was attributed to the promoting effects of the CO2 and H2O components in RS on the degradation of PS during torrefaction. The process simulation results indicated that, when utilizing RS at 600 °C as a heat carrier, the gas-solid feed ratios of 0.36 and 1.18 Nm3 kg-1 were required to achieve the torrefaction of PS at 280 and 320 °C, respectively. These findings offer valuable insights into the potential integration of biomass torrefaction with coal gasification.