Methane Combustion in a 500 Wth Chemical-Looping Combustion System Using an Impregnated Ni-Based Oxygen Carrier

Chemical-looping combustion (CLC) is a promising method for the combustion of fuel gas with CO2 capture and sequestration (CCS). This paper presents the methane combustion results obtained in a continuous CLC prototype using an oxygen carrier containing 18 wt % NiO impregnated on alumina. The design of the CLC prototype was a circulating fluidized bed reactor, consisting of two interconnected fluidized bed reactors, the fuel reactor (FR) and the air reactor (AR). The main operating conditions affecting combustion, such as fuel gas flow, solids circulation rate, and FR temperature, were analyzed. The CLC operation was carried out using methane as fuel gas in the FR with a thermal power between 500 and 850 W-th. The prototype was successfully operated during 100 h, of which 70 h was at combustion conditions. No methane was detected at the FR exit, with CO and H-2 being the unconverted gases. Increasing the temperature in the FR or the solids circulation rates increased the combustion efficiency, reaching efficiency values as high as 99% at temperatures in the range of 1073-1153 K, and a solid inventory in the FR of 600 kg per MWth. The effect of operating conditions on the performance of the oxygen carrier in the CLC prototype was analyzed. During operation of the CLC prototype, no signs of agglomeration or carbon formation were detected and the main properties of particles did not vary. The two different phases in the oxygen carrier, NiO and NiAl2O4, were active to transfer oxygen to the fuel gas. The NiO/NiAl2O4 ratio increased with a decrease in the solids circulation rate, which affected to the reactivity of the oxygen carrier.