A novel hydrogen production process integrated biomass gasification and CaCO3 decomposition in vacuum for CO2 enrichment

The novel hydrogen production process combining biomass gasification and CaCO3 decomposition in vacuum for CO2 enrichment is proposed in this paper, which can simultaneously achieve green H2 and CO2 enrichment. The proposed novel process employs excess CaO as sensible heat storage material, when carbonation temperature is higher than decomposition temperature, the heat released from CaO carbonation is stored can be utilized for CaCO3 decomposition in vacuum, thereby optimizing its energy utilization efficiency. The conventional hydrogen production process based on CaCO3 decomposition in atmospheric pressure for CO2 enrichment is taken as the benchmark, and it is compared with the newly proposed hydrogen production process. Wheat-straw and CaO were used as biomass feedstock and CO2 sorbent, respectively. The two processes were modeled using ASPEN Plus and simulated using thermodynamic equilibrium model. The effect of important parameters, such as biomass gasification condition, carbonation temperature and pressure, mass ratio of steam to biomass and CaO to biomass on gas composition, H2 concentration and yield, as well as the overall energy efficiency were discussed. For the biomass gasification process, when the mass ratio of steam to biomass is 0.1, the cold gas efficiency reaches its maximum value of 74.93%, and the corresponding H2 concentration and yield are 38.65% and 0.49 Nm3/kg, respectively. For the conventional hydrogen production process, when carbonation pressure is 0.6 MPa, the H2 concentration significantly decreases as the carbonation temperature increases to higher than 750 °C. In addition, the simulation results indicate that the mass ratio of CaO to biomass should be maintained at a value higher than 1.5 to ensure the highest CO2 capture capacity. At this condition, H2 concentration and yield reaches up to 88.56% and 0.66 Nm3/kg, respectively, and the overall energy efficiency of the conventional process is 48.41%. Moreover, under the same H2 concentration, the conventional and novel processes were compared. For the novel hydrogen production process, the simulation results shows that when CaCO3 decomposition temperature and pressure are 675 °C and 1 kPa, the mass ratio of CaO to CaCO3 should be higher than 35 to ensure the energy requirement for CaCO3 decomposition. H2 concentration and yield of the novel process reaches up to 88.69% and 0.98 Nm3/kg, respectively. The overall energy efficiency of the novel process is 58.25%, which is about 10% higher than that of the conventional process. Therefore, the proposed novel hydrogen process shows the potential to significantly improve green H2 production.