May 22-27, 2016
Autothermal Chemical Looping Reforming (CLR) is a promising technology for hydrogen production with integrated CO2 separation. Conventional CLR employs two fluidized beds (fuel and air reactors) with an oxygen carrier circulating between them. In this way, CLR supplies heat to the endothermic reforming reaction while avoiding fuel/nitrogen mixing. This configuration can achieve steady operation and low gas leakages between reactors, but has some drawbacks. The complex interconnected configuration is challenging to scale up, especially under the pressurized conditions required for high process efficiency. Moreover, the external circulation of particles through cyclones and loop seals increases reactor costs and imposes a narrow operating window.
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. This gas switching (GS) concept has been demonstrated experimentally (1) and thermodynamically (2) for chemical looping combustion (CLC) and can be extended to CLR. The primary drawbacks of the GS 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 objective of this paper is to compare the conventional CLR configuration against the GS configuration using a generic phenomenological model. This model is based on the probabilistic approach (3) which makes it applicable to the fluidization regimes used in both concepts. Steady state (looping) and transient (switching) simulations are completed and results are compared in terms of important variables such as methane conversion and CO2 separation efficiency.
1. Zaabout, A., Cloete, S., Johansen, S. T., Sint Annaland, M. van, Experimental Demonstration of a Novel Gas Switching Combustion Reactor for Power Production with Integrated CO2 Capture. Industrial & Engineering Chemistry Research, 2013. 52(39): p. 14241-14250.
2. Cloete, S., Romano, M. C., Chiesa, P., Lozza, G., Amini, S., Integration of a Gas Switching Combustion (GSC) system in integrated gasification combined cycles. International Journal of Greenhouse Gas Control, 2015. 42: p. 340-356.
3. Abba, I. A., Grace, J. R., Bi, H. T., Spanning the flow regimes: Generic fluidized-bed reactor model. AIChE Journal, 2003. 49(7): p. 1838-1848.
Joana F. Morgado, Schalk Cloete, John Morud, Thomas Gurker, and Shahriar Amini, "Modelling study of two chemical looping reforming reactor configurations: Looping vs. switching" in "Fluidization XV", Jamal Chaouki, Ecole Polytechnique de Montreal, Canada Franco Berruti, Wewstern University, Canada Xiaotao Bi, UBC, Canada Ray Cocco, PSRI Inc. USA Eds, ECI Symposium Series, (2016). https://dc.engconfintl.org/fluidization_xv/33