Hydrogen production through two-stage sorption-enhanced biomass gasification: process design and thermodynamic analysis

This study presents process design and thermodynamic analysis of hydrogen production through a novel two-stage sorption-enhanced gasification (SEG) process. The SEG process integrates decoupled gasification with calcium looping to convert solid fuels such as biomass. The proposed two-stage SEG process employs a fluidized bed gasifier and a countercurrent moving bed reformer. The first stage involves high-temperature sorption-enhanced gasification in a fluidized bed. Then the product gas from the first stage undergoes sorption-enhanced reforming at relatively lower temperatures to further improve the hydrogen purity. This study employs an autothermal multistage model based on Gibbs free energy minimization to analyze and optimize the calcium looping ratio, steam-to-carbon ratio and feed temperatures of the moving bed reformer. The product gas distribution and temperature profile along the moving bed are discussed. Under optimal conditions, the two-stage SEG process can directly produce 99% H₂ (dry basis), and the overall energy efficiency of the two-stage SEG is 58.7%, which is nearly 10% higher than the conventional process. Therefore, two-stage sorption-enhanced biomass gasification shows the potential to significantly improve green hydrogen production.