Experimental study on biomass steam-oxygen enriched air gasification in a two-stage fixed bed gasifier

The experiments on the gasification of corncob chips with steam-oxygen enriched air was carried out in an atmospheric two-stage fixed bed gasifier. The effects of equivalence ratio (ER), oxygen concentration (OC) and steam to biomass ratio (S/B) on the gasification temperature, gas compositions, lower heating value, gas yield, carbon conversion and cold gas efficiency were investigated, and the gasification characteristics between conventional downdraft fixed bed and two-stage fixed bed was compared. The results show that under the operating conditions of ER=0.27, H₂ content, CO content and cold gas efficiency reach their maximums; Enhancing oxygen concentration can optimize the gasification performance, but it is less to further improve the fuel gas quality as the OC exceeds 90%. By increasing S/B, the H₂ content, CO₂ content and gas yield are increased, but the CO content, cold gas efficiency and carbon conversion are decreased. H₂ content reachs maximum of 33.3% at the S/B of 0.6, while H₂/CO ratio reachs 1.32. Compared with conventional downdraft fixed bed, the two-stage fixed bed has a higher gasification temperature, H₂ content, carbon conversion, cold gas efficiency and a lower tar content.