Chemical Looping Combustion (CLC) and Chemical Looping with Oxygen Uncoupling (CLOU) are carbon-capture technologies that utilize a metal oxide as an oxygen carrier to selectively separate oxygen from air, for combustion. These technologies typically accomplish this separation using two reactors: an air reactor (AR) where the oxidation of metal is performed using ambient air, and a fuel reactor (FR) where the reduction of metal is accomplished and the combustion of fuels occurs. For optimal CLC and CLOU operation both reactors need to be exothermic to maintain the reactor temperature. For CLC and CLOU the oxidation of metal particles is an exothermic reaction resulting in an exothermic AR.
In CLC, gaseous fuel reacts with the metal oxide directly to form CO2 and H2O. The reaction in the fuel reactor is slightly endothermic. When utilizing a solid fuel in CLC the fuel needs to be gasified before reacting the fuel with the metal oxide. Gasification is a highly endothermic reaction which results in an overall endothermic FR. To run the FR as an exothermic reactor, energy needs to be provided. The optimal way to provide energy is through the hot oxygen carrier particles. To achieve this energy transfer the air reactor needs to operate at a higher temperature then the fuel reactor.
In CLOU, the metal oxides reduce by spontanously releasing oxygen which is directly used in the combustion of fuel. The reduction of metal oxides is an endothermic reaction, but the combustion of fuel with oxygen is highly exothermic. These reactions can result in an overall exothermic reaction, with both reactors being exothermic.
Using ASPEN Plus process modeling, temperature ranges were explored for when both reactors can be run exothermically. The process models took into account particle transfering energy, preheating of the air and steam, recycling flue gas, oxidation/reduction reaction, and the combustion of the fuel. ΔT is the temperature the AR is above the FR. For CLC, the FR temperature was 975 oC and it was 950 oC for CLOU. It was determined that in CLC the autothermal temperature range is ΔT = 75 – 125 oC. In CLOU the autothermal temperature range is ΔT = 0 – 25 oC.
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