Investigation of reactions in a fluidized bed reactor during chemical looping combustion of coal/steam with copper oxide-iron oxide-alumina oxygen carrier

Abstract

This paper presents data on conversion of two different coals with a chemical looping oxygen carrier, CuO-Fe2O3-alumina, and over a range of conditions including steam and various levels of reduction of the oxygen carrier.Reactions of coal/steam/CuO-Fe2O3-alumina oxygen carrier and coal/steam/partially reduced CuO-Fe2O3-alumina oxygen carrier were investigated with Wyodak coal and Illinois #6 coal in a fluidized bed reactor. Temperature programmed reaction studies indicated that the oxygen carrier enhanced the steam gasification/combustion rates of both coals. Rates of gasification/combustion were higher with Wyodak coal (sub bituminous) than that with Illinois #6 coal (bituminous). In addition to the increase in reaction rates, the total moles of carbon that were gasified and combusted from coal/steam increased in the presence of the oxygen carrier. The reduced oxygen carrier promoted the water-gas shift reaction when reacted with synthesis gas in the presence of steam, but the reverse water gas shift reaction was observed when steam was not present. The partially reduced oxygen carrier enhanced the production of H2 from coal/steam, which was different from the observations with un-reduced oxygen carrier. Water splitting reaction to produce H2 was also observed with the reduced oxygen carrier. CuO-Fe2O3-alumina reacted with coal during the temperature ramp to 850°C even in the absence of steam due to the chemical-looping oxygen uncoupling (CLOU) reaction. Fourier transform infra-red (FTIR) analysis indicated the presence of volatile aromatics during the temperature ramp and these may have also contributed to the reactions with the oxygen carrier in the absence of steam. Increasing steam concentration had a negative effect on the CLOU reaction.