Chemical looping gasification of biomass with Fe2O3/CaO as the oxygen carrier for hydrogen-enriched syngas production

Abstract

Biomass-derived chemical looping gasification is a novel technology to convert biomass into renewable hydrogen-enriched syngas. In this study, bimetallic Fe-Ca oxides were synthesized to be used as oxygen carriers to promote the hydrogen production from the chemical looping gasification of rice straw. The effects of Fe/Ca ratio, temperature together with the cyclic performance of oxygen carrier were studies in terms of produced syngas distribution, solid structure evolution and the durability of oxygen carrier. Results found that two types of calcium ferrites (Ca2Fe2O5 and CaFe2O4) were formed with different Fe/Ca ratios, and Fe and Ca were uniformly distributed within oxygen carriers by wet impregnation method. Compared with pyrolysis or steam gasification, the hydrogen production was largely promoted during the steam chemical looping gasification process due to the iron re-oxidation by steam. When the ratio of Fe:Ca was1:1, the formed oxygen carrier (Ca2Fe2O5) produced the highest hydrogen yield (23.07 mmol/g biomass) at 800 °C, which benefited from one step reduction and oxidation properties of Ca2Fe2O5. A temperature of no less than 800 °C was needed for the completed redox of Ca2Fe2O5 during chemical looping gasification with steam. The cyclic stability test for Ca2Fe2O5 showed that the continuously accumulated Si from biomass ash would destroy the bimetallic Fe-Ca structure to generate CaSiO3 and Fe2O3 after 3 times of cycle, and this led to the decreased hydrogen production during chemical looping gasification cycle. The great hydrogen selectivity of Fe:Ca = 1:1 (Ca2Fe2O5) makes it a suitable candidate of oxygen carrier, but the cyclic durability should be enhanced to enable a better application for chemical looping gasification conversion of biomass.