(143e) Transport Phenomena in Packed Bed Reactors for Chemical Looping Combustion

Chemical looping combustion (CLC) is potentially one of the technologies best suited for capturing CO2 at low cost and efficiently providing a low energy option for the separation of CO2 from flue gases. The process consists in cyclic reduction and oxidation of a metal oxygen carrier (in the form of particulates) which is exchanged between two reactors, usually a circulating fluidised bed (the oxidation reactor) and a bubbling bed reactor (the combustor). The oxygen carrier transfers oxygen from the air to the fuel, hence a direct contact between air and fuel is avoided. Consequently, the outlet gas from the combustor contains only CO2 and H2O: the latter is easily removed by condensation and the CO2 is readily captured for storage and/or utilisation.

Noorman et al (2007) have proposed a novel reactor concept for CLC consisting of dynamically operated packed beds where the metal particles remain stationary and the gas flow is periodically switched. This process consists in alternating the oxidation and reduction cycles, avoiding gas?solid separation. In this work, the behaviour of the fixed bed reactor is analysed as a problem presenting discontinuities which are sustained by transport process and are indistinguishable from phase interfaces. It is shown that the model presented by Noorman et al (2007) arises naturally when the Kotchine's procedure is applied to the system in exam (Astarita and Ocone, 2002). A generalisation of the model by Noorman (2007) is then proposed and that is based on a previous model (Ocone and Astarita, 1987) for heat and mass transfer in polymers. It is shown that when the relaxation phenomena are coupled to the transport, a more precise interpretation of the maximum temperature rise and front velocities is obtained thus resolving some inaccuracies reported by Noorman et al., (2010).

References

Noorman, S., van Sint Annaland, M., Kuipers, J.A.M., Industrial Engineering and Chemistry Research 46, 4212?4220, 2007 Ocone, R., Astarita, G., "Special Topics in Transport Phenomena", Elsevier, Amsterdam, 2002 Ocone, R. Astarita, G., AIChE J., 33, 423-435, 1987 Noorman, S., van Sint Annaland, M., Kuipers, J.A.M., Chemical Engineering Science, 65, Issue 1, 92-97, 2010