Generation features and kinetics of gas products in bio-tar catalytic cracking by char for biomass gasification

Abstract

This research focused on the reaction features and kinetics of tar catalytic conversion by char based on the generation and evolution of gas products. To probe the roles of heat and catalysis in tar conversion, a micro fluidized bed reaction analyzer (MFBRA) was used to assess tar thermal cracking (TC) and catalytic cracking (CC) by char at 1073, 1123, 1173, and 1223 K. The tar cracking behavior of the individual gas components (H2, CO, CO2, and CH4), generation rates, and reaction kinetics were thoroughly investigated. The results show that TC and CC included a fast (Stage-1) and slow (Stage-2) conversion stage, in which Stage-1 contributed more than 80% of the total conversion. Compared to TC, tar CC required a longer reaction time but obtained higher conversions to individual gas components and the total gas products. The final conversion ratios (XCC/TC) of H2, CO, CO2, and CH4 were kept above 1 at the tested temperature. The char catalytic action was very remarkable, especially at low temperatures. In tar CC, the generation rate of individual gas components slowly declined after quickly reaching the peak, forming a relatively stable zone. The volume reaction model (VRM) well described the tar conversion behavior with and without char. Compared to TC, char lowered the activation energy (Ea) of gas generation. For individual gas components (H2, CO, CO2, CH4) and the total gas products, the corresponding reduction degree of Ea was 25.56%, 24.18%, 22.14%, 4.75%, and 21.71%, respectively, further displaying the promoting impact of char. The evaluated generation features and kinetics of individual components in the gas products will benefit the in-situ tar removal in the biomass gasification process.