Chemical looping gasification of biomass: Part I. screening Cu-Fe metal oxides as oxygen carrier and optimizing experimental conditions

Abstract

Fe2O3 and CuO are commonly used as oxygen carrier (OC) for chemical looping gasification (CLG) of biomass. However, Fe2O3 shows relatively low reactivity even though it is cheap, whilst CuO presents too high reactivity to react with the produced syngas and suffers from sintering problem at high temperatures. This paper is the first part of a two-part series work, where synthetic OCs of bimetallic Cu-Fe oxides prepared by the sol-gel combustion synthesis (SGCS) method were proposed for the biomass-derived CLG process. The reforming reactivity of Cu-Fe OCs with sawdust was first investigated in a thermogravimetric analyzer (TGA). The result indicated that Cu-Fe OCs with higher Cu loading ratio demonstrated better reactivity towards sawdust. Subsequently, the performances of five kinds of Cu-Fe OCs in biomass-derived CLG process were evaluated in a batch fluidized-bed reactor. By comparing the product gas components, gas yield, tar yield and carbon conversion, Cu5Fe5 OC (50 mol.% CuO + 50 mol.% Fe2O3) was found to demonstrate the best comprehensive CLG performance. The effects of steam to biomass ratio (S/B), temperature and oxygen carrier to biomass ratio (O/B) on the performance of Cu5Fe5 were further investigated. The optimum operation state can be attained when the S/B was 0.75, the temperature was 800 °C and the O/B was 0.2. The results of XRD and ESEM characterization showed that the addition of Fe2O3 into CuO-based OC significantly improved the sintering resistance, and the existence of CuO component in Fe2O3 was conductive to improving the porous structure of OC.