Effect of the Fe content on the behavior of synthetic oxygen carriers in a 1.5 kW biomass chemical looping gasification unit

Abstract

Biomass Chemical Looping Gasification (BCLG) is a promising technology that enables the production of high-purity and N2-free renewable syngas under autothermal operating conditions. In this work, the effect of the Fe-content (10, 20, and 25 wt% as Fe2O3) of three synthetic oxygen carriers supported on alumina was studied in a 1.5 kWth BCLG continuous unit. Similar syngas compositions and gasification parameters, biomass conversion, syngas yield, cold gas efficiency, etc., were obtained for the three oxygen carriers when analyzing the effect of oxygen-to-fuel ratio (λ) and fuel reactor (FR) temperature. Tars were also unaffected by the Fe-content, the increase in the FR temperature being the only parameter that allowed their reduction. A deep characterization of the oxygen carriers showed that the increase of Fe-content in the oxygen carrier promoted the migration of iron to the outer layer of particles, being detached of them. Lifetimes of 900, 350 and 100 h (corresponding to approximately 4500, 1750 and 500 cycles) were found for the oxygen carriers with 10 wt%, 20 wt% and 25 wt% of iron oxide, respectively. Therefore, among the three oxygen carrier tested, the one composed by a 10% of Fe2O3 was shown to be the most suitable for BCLG, providing the longest lifetime whereas the same syngas composition and tar removal could be obtained regardless of the Fe-content.