MP-PIC simulation on CO₂ gasification of biomass in a pilot plant circulating fluidized bed gasifier

CO₂ gasification of biomass offers a potential carbon-negative solution which combines biomass-to-energy conversion with carbon capture and utilization. In this study, biomass gasification with CO₂ in a pilot plant circulating fluidized bed (CFB) gasifier is numerical investigated via a reactive multiphase particle-in-cell (MP-PIC) model. Gas-solid hydrodynamics and thermochemical characteristics under different percentages of CO₂ in gasifying agent (mixed with air from 0 to 100 wt%) are comprehensively analyzed, in terms of the biomass conversion, bed temperature, gas species distributions, chemical reaction rates, product gas yields, lower heating value of product gas (LHV_gas) and cold gas efficiency (CGE). Simulation results indicate that the CO₂ percentage in gasifying agent has insignificant influence on gas–solid distribution, while it directly affects the char conversion and product gas compositions. CO₂ gasification favors the CO production, increases the CO/H₂ ratio in product gas and mitigates the CO₂ emission. However, increasing the CO₂ percentage in gasifying agent results in a decreased char conversion rate and reduced bed temperature, which restricts the use of pure CO₂ as gasifying agent. The optimal CO₂ percentage occurs to 60 wt% where the gasifier has the best thermochemical performance, i.e., the highest compositions of combustible gases, the largest LHV_gas and CGE. This research sheds light on biomass gasification with CO₂ in a large-scale CFB facility, and would be helpful for the design and scale-up of this technology.