Air–steam gasification of biomass in fluidized bed with CO2 absorption: A kinetic model for performance prediction

Abstract

Significance of decarbonized energy production in the context of a foreseeable hydrogen economy has called for the need of extensive research in biomass gasification-carbon dioxide capture technique. The feasibility of calcium oxide as a sorbent for CO2 in syngas is studied for air–steam fluidized bed (FB) gasification through a reaction kinetic modeling approach. Arrhenius rate equations are employed for primary and secondary pyrolysis, gasification and carbonation reactions. Devolatilization product yields are predicted using available correlations for FB gasification and cracking of tar is incorporated. Parametric performance analysis is carried out highlighting the significance of equivalence ratio (ER), gasification temperature, steam to biomass ratio (SBR) and sorbent to biomass ratio (SOBR). The effects of various gasifying media on H2 concentration and performance indicators such as heating value and efficiencies are analyzed. The simulation results are validated with the reported experimental results. The kinetic study reveals that air–steam gasification significantly reduces the unreacted steam but at a lower H2 concentration than steam gasification. A maximum of 53% hydrogen rich gas mixture is predicted at ER = 0.25, SBR = 1.5, SOBR = 2.7 and 1000 K. Against fossil fuel expended steam gasification, pure oxygen gasification is suggested by the study.