Syngas production from biomass in chemical looping using metal ferrites as oxygen carrying materials

Abstract

Chemical looping gasification (CLG) is a promising technology that can possibly be used as a replacement to produce hydrogen as a source of renewable energy for the future. Through transferring oxygen by oxygen carriers, N2-free syngas can be produced without the use of air separation unit. Oxygen carriers play an important role in CLG as they can determine the reactivity and stability of the reactions. Iron oxides are promising oxygen carriers due to their low economic cost and environmental impacts. The use of alkaline earth metal (Mg, Ca, Sr and Ba) ferrites have also been proven to improve the syngas production during CLG. Therefore, this study aims to utilise four metal ferrites, MgFe2O4, CaFe2O4, SrFe2O4 and BaFe2O4, with wood as biomass fuel, to compare their effects as viable oxygen carriers during the CLG process. Their reactivity, stability and resistance to agglomeration will be studied over 20 cycles of CLG using a fixed bed reactor. To further study these effects, thermogravimetric analysis (TGA) was conducted for the selected four oxygen carriers before and after 20 cycles of CLG. X-ray powder diffraction (XRD) and scanning electron microscopy (SEM) were used to monitor the physical characteristics and surface morphology of the selected four oxygen carriers before and after 20 cycles of CLG. This was to analyse their resistance to agglomeration. The results suggests that BaFe2O4 as the oxygen carrier had the best performance as it had the highest reactivity to carbon, highest stability in the fixed bed reactor (highest gas yield, carbon conversion, syngas selectivity and H2/CO ratio) and highest resistance to agglomeration as there were still gaps/spaces observed after 20 cycles of CLG.