Steam gasification of biomass with subsequent syngas adjustment using shift reaction for syngas production: An Aspen Plus model

A simulation model of biomass gasification for syngas production with steam as gasifying agent and subsequent syngas adjustment has been developed using Aspen Plus. The developed model is based on Gibbs free energy minimization applying the restricted equilibrium method. The objective is to study the effect of important parameters such as gasification temperature, steam to biomass ratio and shift reaction temperature on hydrogen concentration, CO concentration, CO conversion, CO2 conversion and H2/CO ratio in the syngas. Simulations were performed for different biomass feedstocks to predict their syngas composition. The hydrogen and CO concentrations were altered such that the H2/CO molar ratio in the syngas composition gets adjusted close to a value of 2.15 as required for FT synthesis by the shift reaction. The present model has been validated with experimental data from literature on steam biomass gasification conducted in a research scale fluidized bed gasifier. The product gas obtained from steam gasification of food wastes resulted in a composition with a H2/CO molar ratio close to 2.15 which can be directly fed to a Fischer-Tropsch synthesis plant whereas remaining feedstocks requires a syngas adjustment either by WGS or RWGS reactions to achieve H2/CO molar ratio close to 2.15.