Study on calcium looping biomass sorption enhanced gasification in 1 MWth compact-fast dual fluidized bed pilot plant

Biomass gasification, particularly when integrated with calcium looping sorption-enhanced hydrogen production technology, offers a promising pathway to convert biomass into high-value syngas while significantly enhancing hydrogen yield and enabling in-situ CO2 capture, thereby delivering substantial environmental and economic benefits. This study presents an experimental investigation into hydrogen production and CO2 capture via calcium-looping sorption-enhanced biomass gasification, conducted in a novel 1 MWth compact-fast dual fluidized bed pilot system. The reactor configuration comprises a lower bubbling fluidized bed (BFB) gasifier coupled with an upper riser reactor, utilizing dolomite as a calcium-based CO2 sorbent. This stacked design enables effective integration of two distinct fluidization regimes—bubbling and fast fluidization—under individually adjustable temperature zones, thereby offering remarkable operational flexibility and strong potential for industrial scalability. The system's ability to decouple gasification and regeneration processes, while maintaining continuous solids circulation, represents a significant advancement in reactor design for sorption-enhanced gasification (SEG). The experimental campaign focused particularly on the impacts of two critical operational parameters—riser temperature and solid circulation flux—on key performance indicators including product gas composition, hydrogen yield, cold gas efficiency, carbon conversion efficiency, and CO2 capture rate. Under thermal operation, the system demonstrated notable stability, with the pressure differential established by the static bed height in the BFB serving as the primary driving mechanism for solid circulation between the two reactors. This auto-generated pressure balance effectively sustained the solid transfer without requiring additional mechanical assistance. The results indicated that riser temperature exerted a profound influence on hydrogen production. Operating at an elevated temperature of 850 °C resulted in a peak hydrogen yield of 0.38 Nm3·kg-1 (on a biomass basis), with a hydrogen volume fraction of 59.14% in the product gas. Under these conditions, the cold gas efficiency reached 50.03%, the carbon conversion efficiency was 60.75%, and the CO2 capture efficiency attained 78.84%. These findings clearly demonstrate that higher riser temperatures significantly promote endothermic reforming reactions, notably methane reforming and tar cracking, while simultaneously enhancing the in-situ CO2 adsorption capacity of dolomite. The elevated temperature also improves kinetics of heterogeneous reactions, contributing to increased gas quality and overall process efficiency. Furthermore, increasing the solid circulation flux was found to positively affect both hydrogen concentration and total yield, as well as the CO2 capture performance. Higher circulation rates facilitate greater transport of active CaO-based sorbent between the gasifier and the regenerator, thereby increasing the availability of adsorption sites and improving the efficiency of the calcium looping cycle. However, it was also observed that reactor geometry constraints, operating conditions, and sorbent characteristics collectively impose significant influences on the overall capture efficiency and active space-time utilization. In particular, the interaction between solid circulation rate, reaction temperature, and sorbent activity dictates the system’s ability to maintain high purity hydrogen production over extended durations. This research provides comprehensive experimental insights and a solid theoretical foundation for the scale-up and industrial implementation of calcium-based sorption-enhanced gasification coupled with efficient tar cracking. The findings affirm the viability of the proposed stacked dual fluidized bed system as a sustainable and efficient route for high-purity hydrogen generation from biomass with inherent carbon capture, thereby supporting the transition toward advanced bioenergy systems with negative emissions potential.