Flue gas torrefaction integrated with gasification based on the circulation of Mg-additive

Abstract

Flue gas torrefaction (FGT) is a feasible way to improve fuel properties and enhance gasification performance. Torrefaction inevitably causes CO2 emissions. In this study, FGT integrated with gasification based on the circulation of Mg-additive (MgO-FGT-GS) was developed to capture CO2 released during FGT and transferred it to gasification to achieve a higher effective carbon conversion efficiency (ECC). Firstly, FGT with Mg-additive (MgO-FGT) was conducted on distilled spirits lees (DSL) and the effect of different Mg-additive (MgO) ratios was explored. Based on the characterizations of DSL and Mg-additive before and after MgO-FGT, the mechanism of MgO-FGT was revealed, and the looping property of Mg-additive was investigated. A fixed-bed gasification experiment was finally performed to validate the MgO-FGT-GS process. The results show that the optimal MgO-FGT was obtained as the MgO: DSL ratio was 1:1. Under this condition, the torrefied DSL had the highest HHV of 16.20 MJ/kg and the lowest O/C ratio. In MgO-FGT, the MgO absorbed 15.75 % of CO2 and changed into basic magnesium carbonate. Then in gasification, CO2 was released by Mg-additive at 800 ℃, and the Mg-additive largely returned to MgO. The LHV of syngas of the MgO-FGT-GS was 9.22 MJ/Nm3, which was 1.3 times higher than raw DSL. Meanwhile, the tar yield decreased by 68.99 %, and the ECC increased by 1.5 times. Therefore, the MgO-FGT-GS process shows a great improvement in gasification and better utilization of CO2. This study provides a technological breakthrough for the full-component utilization and low-carbon conversion of biomass.