Modelling study of two chemical looping reforming reactor configurations: looping vs. switching

Autothermal Chemical Looping Reforming (CLR) is a promising technology for hydrogen production with integrated CO₂ separation. However, the interconnected CLR reactor configuration is expected to present significant scale up challenges, especially under the pressurized conditions required for high process efficiency. These challenges can be circumvented by carrying out the reduction/oxidation reactions in a single bubbling/turbulent fluidized bed alternatively fed with fuel and air, henceforth called gas switching reforming (GSR). The primary drawbacks of the GSR concept are the undesired mixing between fuel and nitrogen after the gas feed switch and the need for high temperature valves at the reactor outlet. The performance of the CLR and GSR concepts are compared using a generic phenomenological model, applicable over different fluidization regimes. Results showed that the GSR process is best operated by separating the reduction and reforming reactions, whereas these reactions occur simultaneously in the CLR fuel reactor. This fundamental difference led to lower fuel conversion, but a higher heating value syngas in the GSR process. Separation of reduction and reforming steps in the GSR concept also allows for the efficient utilization of the off-gas fuel from a PSA unit for high purity pressurized hydrogen production. This makes the GSR process more applicable to hydrogen production with integrated CO₂ capture, whereas the CLR concept is better suited to power production with pre-combustion CO₂ capture.