A pressurized Gas Switching Combustion reactor: Autothermal operation with a CaMnO3−δ-based oxygen carrier

Abstract

Gas Switching Combustion (GSC) promises greatly simplified scale-up of highly efficient gas-fuelled chemical looping combustion (CLC) technology. The GSC uses a single reactor alternating fuel and air feeds into a bed of oxygen carrier. Such a simple standalone reactor will be much easier to scale up and pressurize than the conventional interconnected CLC configuration. This paper presents results from autothermal GSC operation completed in a pressurized lab-scale reactor using a CaMnO3−δ-based oxygen carrier which are especially suited to GSC because they greatly reduce the temperature variation across the transient GSC cycle. The reactor showed perfect performance when H2 was used as fuel, but significant fuel slip occurs with CO after the oxygen carrier was only half way reduced. Higher temperatures improved fuel conversion, while higher pressures had a negative effect. It can be expected, however, that more oxygen carrier utilization would be possible in a full-scale reactor where the gas residence time would be much higher. In addition, 2–7% CO2 release was observed in the oxidation stage (from the total molar carbon fed in the fuel stage), increasing with the degree of oxygen carrier reduction. CH4 as fuel performs well only if the reduction stage is started on a fully oxidized CaMnO3−δ-based oxygen carrier. In summary, if the CO2 release in the oxidation stage can be efficiently dealt with, CaMnO3−δ-based materials appear to be very promising for use in future GSC-IGCC power plants.