Chemical looping combustion process in fixed - bed reactors using ilmenite as oxygen carrier

A process scheme based on a series of fixed-bed reactors is presented as a possible alternative for carrying out the chemical looping combustion of methane at high pressure with ilmenite as oxygen carrier. The oxygen carrier is stationary and it is alternately exposed to reducing and oxidizing atmospheres by means of the periodic switching of the gas feeds (i.e., methane and air, respectively). Cyclones and filters for the separation of gases and solids are not needed in fixed-beds, which allows a more compact reactor design. Moreover, the operation at high pressure permits the use of highly efficient power cycles. However, more complex heat management strategies and switching valves able to function at very high temperatures are required in these systems. The continuous cyclic operation of a packed-bed chemical looping combustion process is described using a basic reactor model. A sequence of four stages: reduction, steam reforming, oxidation and heat removal ensures the production of a continuous high temperature and high pressure gas stream able to efficiently drive a gas turbine for power generation in combination with a steam cycle. At the same time, a concentrated stream of CO2 suitable for transport and storage is also produced. The use of suitable recycles of the product gases makes it possible to control the progression of the reaction and the heat exchange fronts, which improves the heat management of the CLC process. The inclusion of steam methane reforming in the process allows the conversion of the ingoing methane to syngas, which enhances the reduction kinetics of the ilmenite and the overall combustion efficiency of the process. A preliminary design for an inlet flow of 10 kg/s of methane (500 MWt) has shown that a minimum of five reactors, 10 m long, with an inner diameter of 6.7 m, would be required to fulfil the overall process assuming cycles of 10 minutes with maximum pressure drops per stage of less than 6 %. These results demonstrate the potential of this novel technology for power generation in combination with CO2 capture.