Experimental Study on Herb Residue Gasification in an Air-Blown Circulating Fluidized Bed Gasifier

The gasification characteristics of herb residue for producing syngas in a pilot-scale circulating fluidized bed were investigated experimentally in this paper. The results indicated that the gas composition and tar yield were affected by the parameters including the equivalence ratio (ER), biomass feeding rate (FR), and steam-to-biomass mass ratio (S/B). The concentrations of combustible gases (H-2, CO, CH4, and CnHm) showed a decreasing trend with increasing ER, while the lower heating value (LHV) exceeded 4.0 MJ/N.m(3) in all cases when the ER was lower than 0.4. An increase in the ER can improve the reaction temperature, facilitate carbon conversion, and decrease the tar yield. The LHV increased gradually from 4.2 to 5.7 MJ/N.m(3) with an increase in the FR from 210 to 352 kg/h. The cold gas efficiency and carbon conversion efficiency reached their maximum values of approximately 68% and 93% at a feeding rate of 352 kg/h, whereas both of them decreased with a further increase in the feeding rate. The supplement of steam into the gasifier improved the LHV of the product gas, which reached a maximum value of about 6.0 MJ/N.m(3) when S/B was 0.23-0.43 and the cold gas efficiency and carbon conversion efficiency were within 62-73% and 87-94%, respectively.