Low-Carbon Hydrogen Production from Biomass via Staged Sorption-Enhanced Gasification and Reforming: Process Modelling and Techno-Economic Assessment

This research introduces a staged sorption-enhanced gasification and reforming process for converting biomass into hydrogen with an accompanying CO2-capture pathway, using wheat straw as feedstock. Renewable hydrogen from biomass gasification is already established as a route to low- and potentially negative-emission hydrogen production when combined with CO2 storage, but conventional SEG systems typically rely on continuous sorbent circulation between interconnected carbonation and regeneration stages. This study instead investigates a staged configuration in which CO2 removal is carried out in dedicated carbonation reactors before and after reforming, while sorbent regeneration is performed separately. In the proposed process, carbonation and calcination take place in separate reactor units, allowing each stage to be independently controlled and optimised. The process model included submodels for pyrolysis and gasification, dual-stage carbonation, steam reforming, CaO regeneration, and hydrogen purification. Sensitivity analysis was carried out across gasifier temperature (500–1000 °C), air-to-feed ratio (0.5–3.0), steam-to-feed ratio (0.5–3.0), and CaO-to-feed ratio (0.3–1.5). The proposed staged route consistently outperformed the no-sorbent conventional route, delivering syngas with a hydrogen content approximately 1.6–1.7 times that of the conventional route under the common baseline conditions, while showing greater resistance to hydrogen loss under excess-air gasification conditions. For the proposed configuration, CO2 capture reached a plateau at a CaO-to-feed ratio of approximately 0.65 kg/kg, with no further increase observed at higher sorbent loadings. Mass-flow analysis confirmed that the proposed configuration produces more hydrogen from wheat straw and creates a pathway for CO2 capture. The economic assessment further showed that the levelised cost of hydrogen (LCOH) for the proposed configuration was approximately 18% lower than that of the conventional configuration. These findings provide an initial assessment of whether staged CO2 sorption integrated with biomass gasification and reforming can improve hydrogen production and the techno-economic performance of biomass-to-hydrogen systems.