Effect of temperature on reduction reactivity of oxygen carrier particles in a fixed bed chemical-looping combustor

Abstract

In a chemical-looping combustor (CLC), gaseous fuel is oxidized by metal oxide particle, e.g. oxygen carrier, in a reduction reactor (combustor), and the greenhouse gas CO2 is separated from the exhaust gases during the combustion. In this study, NiO/bentonite particle was examined on the basis of reduction reactivity, carbon deposition during reduction, and NOx formation during oxidation. Reactivity data for NiO/bentonite particle with methane and air were presented and discussed. During the reduction period, most of the CH4 are converted to CO2 with small formation of CO. Reduction reactivity (duration of reduction) of the NiO/bentonite particle increased with temperature, but at higher temperature, it is somewhat decreased. The NiO/bentonite particle tested showed no agglomeration or breakage up to 900 ‡C, but at 1,000 ‡C, sintering took place and lumps of particles were formed. Solid carbon was deposited on the oxygen carrier during high conversion region of reduction, i.e., during the end of reduction. It was found that the appropriate temperature for the NiO/bentonite particle is 900 ‡C for carbon deposition, reaction rate, and duration of reduction. We observed experimentally that NO, NO2, and N2O gases are not generated during oxidation.