High H2/CO ratio syngas production from chemical looping co-gasification of biomass and polyethylene with CaO/Fe2O3 oxygen carrier

Abstract

Chemical looping co-gasification of pine wood and polyethylene with CaO/Fe2O3 oxygen carrier was preliminarily conducted in a fixed bed reactor and thermogravimetric analyzer (TGA). The effects of Fe2O3 /biomass mass ratio, temperature and steam/biomass mass ratio on the product distribution (syngas yield, H2/CO ratio and cold gas efficiency) during the pine wood chemical looping gasification were investigated. Results showed that the optimal product distribution was obtained at the gasification temperature of 850 °C with the Fe2O3/feedstock ratio of 0.25 and steam/biomass mass ratio of 0.25. The interactions of pine wood and polyethylene were further studied. It was found that the positive or even the synergetic effects existed, which resulted in the enhancement of syngas and hydrogen yield. The optimal addition of 75% polyethylene increased H2 yield from 0.62 Nm3/kg to 1.59 Nm3/kg compared to the pine wood chemical looping mono-gasification. Chemical looping co-gasification also improved the cold gas efficiency from 77.22% to 89.30% and H2/CO ratio from 1.54 to 1.88. The CaO/Fe2O3 mass ratio of 1.0 was sufficient to elevate the H2/CO ratio above 2. The maximum H2 yield of 1.73 Nm3/kg, cold gas efficiency of 92.23% and H2/CO ratio of 2.09 were finally obtained to meet the demand for the Fischer-Tropsch synthesis. The presence of synergetic effects on syngas and hydrogen yield from the fixed bed data but their absence from the TGA data revealed the interaction mechanism could be attributed to gas phase reformation and cracking reactions.