Chemical looping gasification and hydrogen (CLGH) process from solid biomass in a dual fluidized-bed system
Jimin Zeng, Rui Xiao*, Yihong Wang, Shanshan Shao and Dewang Zeng
Key Laboratory of Energy Thermal Conversion and Control, Ministry of Education, School of Energy and Environment, Southeast University, Nanjing, 210096, P.R. China
Chemical looping gasification (CLG) process is one of CO2 capture technologies for producing syngas with high system conversion efficiency and inherent separation of CO2. Chemical looping hydrogen (CLH) process with renewable energy sources is the other promising technology for producing H2 and decreasing emission of greenhouse gas. Chemical looping gasification and hydrogen (CLGH) process from solid biomass is a promotion of the existing steam-iron process by combining CLG process and CLH process in one step (Fig. 1).
This process in a dual fluidized-bed system can not only avoid highly concentrated CO2 gas but also generate hydrogen with no direct efficiency loss. Meanwhile, the system offers two separate fluidized-bed reactors for biomass gasification and H2 production. Iron-based oxygen carrier is used as bed material in the two fluidized beds to provide with lattice oxygen for gasification in the gasifier and to create a reduced environment for H2 production in the reducer. In this study, the experiment for CLGH process with pine sawdust was conducted in a dual fluidized-bed system, aiming to a suitable H2/CO-ratio syngas and the best H2 yield for the whole system. The effects of gasifier temperature, reducer temperature, steam preheating temperature and steam-to-biomass ratio (S/B) on the process were investigated. The optimum operating conditions concluded in the experiment were: gasifier temperature at 760 °C, reducer temperature at 780 °C, steam preheating temperature at 500 °C and S/B at 1.0 kg/kg. At this condition, the H2/CO-ratio syngas of 1.22 mol/mol and H2 yield in the reducer of 0.735 Nm3/kg were obtained. And the results enhance understanding of CLGH process and facilitate commercial utilization of solid biomass.
Key words: Chemical looping gasification and hydrogen; A dual fluidized-bed system; Biomass
Fig. 1 Principle of chemical looping gasification and hydrogen production in a dual fluidized-bed system