Reaction performance and mechanism of a NiO/Ca2Fe2O5 oxygen carrier in Chemical looping gasification of cellulose

Abstract

Chemical looping gasification (CLG) is a novel technology created to realize the clean and efficient utilization of solid fuels, where the syngas product avoids dilution by N2 and the pollutants are inhibited by using metal oxide as oxygen carrier (OC) instead of molecular oxygen. Cellulose, as the main component of biomass-based solid waste, was evaluated in the CLG process with NiO/Ca2Fe2O5 prepared by the impregnation method. Reaction mechanism and morphology evolution of the OC as well as the influence of key reaction parameters were investigated by fixed-bed reactor and thermogravimetric analysis experiments coupled with various characterization techniques. The results indicated that the addition of Ni not only improved the oxygen release performance of Ca2Fe2O5 but also helped tar cracking and carbon conversion. On the other hand, the excellent activity in the solid–solid reaction of Ca2Fe2O5 promoted the performance of the Ni-based OC. The test results revealed that Ca2Fe2O5 was a better base than CaFe2O4, and the carbon conversion efficiency reached 98% with the OC sample at 850 °C. NiO markedly improved the reactivity of Ca2Fe2O5 after 10 cyclic reactions. The temperature notably affected activity below temperatures of 850 °C and slightly above. Due to the limited reduction of Ca2Fe2O5 below 800 °C and the redox behavior improvement being minor above 850 °C, the temperature of 850 °C was marked as the optimum for the studied process Addition of water inhibited OC inactivation in cyclic reactions, which was mainly attributed to the crystal separation and agglomeration of OC particles. However, water inhibited the deep reduction of metal on the surface, which reduced the activity on tar cracking and carbon conversion to a certain extent.