Simulation of hydrogen production from biomass gasification in interconnected fluidized beds

Abstract

Abstract Hydrogen production from biomass gasification in interconnected fluidized beds is proposed in this paper. It resembles a circulating fluidized bed with the extra bubbling fluidized bed after the cyclone. The circulating fluidized bed is designed for combustion fed with air, the bubbling fluidized bed for biomass gasification fed with steam. Direct contact between the gasification and combustion processes is avoided; the gasification-required heat is achieved by means of the circulation of bed particles. Hydrogen-rich gas is produced free of N2 dilution. The paper intends to provide some process fundamentals about hydrogen production from biomass gasification in interconnected fluidized beds. Simulation of the processes, including chemical reactions and heat/mass balance, is carried out with Aspen Plus software. The effects of gasifier temperature and steam/biomass ratio on the composition of fuel gas, hydrogen yield, carbon conversion of biomass, recirculation of bed particles, etc., are discussed. Some useful results are achieved. The results indicate that both a high hydrogen content and a relatively great hydrogen yield are obtained from biomass gasification in interconnected fluidized beds. The favorable temperature of the gasifier should be between 750 and 800 °C, the combustor temperature should be 920 °C, and the ratio of the steam/biomass should be between 0.6 and 0.7. The increment of hydrogen yield is distinct with the increase of steam/biomass ratio at the lower gasifier temperatures (below 750 °C). The steam/biomass ratio corresponding to maximal hydrogen yield declines with the increase of gasifier temperature. To maintain the gasifier temperature, the recirculation of bed particles increased exponentially with an increase in the gasifier temperature.