Energy-Efficient Calcium Looping with Vacuum-Assisted CaCO3 Decomposition for Biomass-Derived Hydrogen Production

The aim of this study is to propose and evaluate a novel hydrogen production process that integrates biomass gasification and calcium looping with vacuum-assisted low-temperature CaCO3 decomposition. To achieve this objective, excess CaO is utilized as a sensible heat storage medium, allowing the heat released during CaO carbonation to be recovered to drive CaCO3 decomposition in a vacuum. This internal heat recovery strategy reduces the external heat requirement for CaCO3 decomposition and thereby improves the overall energy efficiency of the novel process. The proposed process is simulated in Aspen Plus using thermodynamic equilibrium models and compared with the conventional process employing atmospheric-pressure CaCO3 decomposition. Wheat straw is selected as the biomass feedstock, and CaO is used as the CO2 sorbent. Systematic parametric analyses are conducted to investigate the effects of key operating parameters on gas composition, H2 concentration and yield, and overall energy efficiency. The results indicate that the optimal overall energy efficiency is achieved at a CaCO3 decomposition pressure of 1 kPa and a temperature of 675 °C. Under the optimized conditions, compared with the conventional process at a comparable H2 concentration, the novel proposed process increases the H2 yield from 0.66 to 0.98 Nm3/kg and improves the overall energy efficiency from 48.41% to 58.25%, corresponding to enhancements of 0.32 Nm3/kg and 9.84 percentage points, respectively. These results demonstrate that vacuum-assisted CaCO3 decomposition coupled with sensible heat recovery from excess CaO can substantially enhance H2 production and energy utilization, highlighting the potential of the proposed process for energy-efficient hydrogen production.