Thermodynamic analysis of a biomass anaerobic gasification process for hydrogen production with sufficient CaO

Based on CO2 acceptor gasification technology, a biomass anaerobic gasification technology for H2 production was proposed. Utilizing thermodynamic equilibrium calculation software FactSage 5.2, the rules of biomass/CaO/H2O and C/CaCO3/air reaction system involved in this H2 production technology were studied. The results show that the increase of CaO can obviously increase H2 mole fraction in C/H2O reaction products. When the mole ratio of CaO to carbon ([Ca]/[C]) is 1, H2 concentration may achieve the maximum value. The H2 amount obviously increases, and H2 mole fraction decreases slightly with increasing reaction pressure in a specific range. Higher reaction temperature obviously decreases the amount and mole fraction of H2. There are different maximum temperatures which are suitable for H2 production under various pressures. Increasing of the mole ratio of H2O to carbon of biomass ([H2O]/[C]) is helpful for H2 production. But the H2 mole fraction is reduced with the increasing of [H2O]/[C] when it exceeds 1.5. The calculations of linear sensitivity coefficient show that [H2O]/[C] has the greatest influence on H2 production efficiency, the influence of reaction pressure and temperature are also obvious. Compared with the coal gasification for H2 production, the excess of H2O in biomass anaerobic gasification system is relatively obvious. Lower reaction pressure is helpful for CaO regeneration in the C/CaCO3/air reaction system, and there are different minimum temperatures which CaO regeneration needs under various reaction pressures.