Modeling and Simulation of Calcium Oxide Enhanced H2 Production from Steam Gasification of Biomass

The hydrogen concentration produced from conventional steam gasification of biomass is currently less than 60%, the gas products still contain large amount of carbonaceous gases such as CO, CO2 and CH4, etc. However, adding absorbents (CaO, etc.) for in-situ CO2 removal during the steam gasification process could break the chemical equilibrium of water gas shift reaction (WGSR), and promote the gasification process to produce more Hydrogen. To study the promotion effect of in-situ CO2 removal on hydrogen production from steam gasification of biomass, a model of calcium oxide enhanced steam gasification of biomass for H-2 production was built using ASPEN PLUS software based on Gibbs free energy minimization via chemical equilibrium and phase equilibrium, and the effects of various factors on gasification characteristics were analyzed. The results showed that, as carbon conversion rate increasing, the H-2 concentration changed slightly, but the H-2 production and gas yield increased greatly. As the molar ratio of calcium to carbon increasing, the H-2 concentration and production increased largely, and the concentration of CO and CO2 decreased rapidly. The suitable condition for H-2 production is at gasification temperature of 600-700 degrees C, with atmospheric pressure or slight pressurization (<= 0.6 MPa), and the mass ratio of steam to biomass of 1.6 and the molar ratio of calcium to carbon of >= carbon conversion rate, the H-2 concentration could reach to 94.92%. And it is also found that as gasification pressure >1.8 MPa, calcium oxide reacting with steam generating calcium hydroxide caused that the CO2 absorption efficiency and gasification ratio of steam decreased rapidly, and the H2 concentration and production decreased rapidly.