Chemical looping combustion process in fixed-bed reactors using ilmenite as oxygen carrier: Conceptual design and operation strategy

• The feasibility of fixed-bed CLC with methane and ilmenite as carrier is assessed.
• A conceptual design has determined operating windows for each stage of the system.
• Suitable recycles allow the advance of the fronts along the beds to be controlled.
• A steam reforming stage enhances the reduction of the carrier and the combustion efficiency.
• Results show technical viability of fixed-bed CLC and its potential for further development.

A process scheme based on 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 operation at high pressure permits the use of highly efficient power cycles. However, complex heat management strategies and switching valves able to function at very high temperatures are required. 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 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 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 conceptual 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 min 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.