Biomass steam gasification for hydrogen-rich syngas production over fly ash-based catalyst pretreated by coupling of washing and calcination

Abstract

Biomass gasification to produce syngas is promising, but the limited hydrogen content of the syngas restricts its potential applications. This study proposed an efficient thermochemical approach that used cost-effective fly ash pretreated with washing and calcination (WCFA) as a catalyst to enhance hydrogen-rich syngas production from biomass steam gasification. Catalyst characterizations indicated that washing removed most chloride salts in raw fly ash by dissolution, and subsequent calcination decomposed Ca-containing compounds into CaO, resulting in smaller catalyst grains, more developed pore structure, and greater capability and reaction rate of CO2 sorption. With WCFA, the H2 release during gasification was prolonged by ∼10 min and its release peak increased by over 1.5 times, compared to no catalyst. Consequently, the cold gas efficiency, syngas yield, and H2/CO ratio increased from 53%, 792 mL/gbiomass, and 0.39 for no catalyst to 72%, 1132 mL/gbiomass, and 1.05 for WCFA. The WCFA catalyst calcined at 800 °C for 60 min was optimal for H2 formation, due to its enriched CaO composition and improved porosity, which effectively catalyzed volatiles cracking/reforming and absorbed CO2 to lead the chemical equilibrium of water gas shift reaction move foward.