Chemical looping with oxygen uncoupling (CLOU) and chemical looping combustion (CLC) using copper-enriched oxygen carriers supported on fly ash

An experimental investigation on chemical activity and stability of innovative CuO-based oxygen carriers (OC) supported on coal fly ash, towards Chemical Looping Combustion (CLC) and Chemical Looping Oxygen Uncoupling (CLOU) is presented. The materials were prepared by granulation of fine powders of CuO and fly ash (FA), with 40-60-80 wt% CuO loading (Cu40FA, Cu60FA and Cu80FA), using a high shear granulator. CLC and CLOU activities were investigated in a thermogravimetric analyzer (TGA) in the presence of a reactive fuel or an inert atmosphere, respectively. A rather stable CLOU capacity (Ro-CLOU) in the range of 4-8 g O2/100 g OC was found over 42 redox cycles, in agreement with the stoichiometry of the prepared samples. CLC oxygen carrying capacity (Ro-CLC) with gaseous fuel, on the other hand, has evidenced a quick decline for the material with higher copper loading (80 wt% CuO). Furthermore, both oxygen carriers with 40-60 wt% CuO were tested for combustion of coal in a macro-TGA rig using CO2 as carrier gas and different OC:fuel ratios. First, a blank test in the absence of the OC was carried out to characterize the fast devolatilization and slow gasification reactions taking place due to the exposure of the fuel to high temperature and CO2-rich atmosphere. The comparison of the weight loss curve evolution with and without oxygen carrier, and the measured residual carbon after test, enabled to extract the CLOU effect for each combination of material/solid fuel.