Chemical looping combustion (CLC) is potentially the technology 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 the cyclic reduction and oxidation of metal oxide particles, which act as oxygen carriers. The particles are exchanged between two reactors, usually a circulating fluidised bed and a bubbling bed reactor, where the oxidation and reduction reactions occur, respectively. Noorman et al. (2007) explored a dynamically operated packed bed for CLC technology. Successive work undertaken by the same group (Noorman et al., 2009) has shown the feasibility of the concept, and expressions for the mass and heat front velocities were determined. In this work, the oxidation of the packed bed reactor is analysed as a problem presenting discontinuities which are sustained by transport processes and are indistinguishable from phase interfaces. Travelling mass and heat fronts arise as a consequence of the reaction kinetics; a specific problem is analysed, where the oxidation is modelled similarly to an adsorption problem and the mass front velocity is calculated for some limiting transport conditions. It is shown that the mass front velocity arises naturally when the Kotchine's procedure (Astarita and Ocone, 2002) is applied to the system. An interesting feature of the analysis presented here is that some general results can be obtained without making any specific assumption about the kinetics. The results obtained are indeed amenable to be extended to other processes where the reacting material is a bed of solid particles. The treatment presented can be implemented when small perturbations occur in the bed, thus giving useful information on predicting whether the unwanted changes in the process conditions are sustained or die out.
|Number of pages||7|
|Journal||Chemical Engineering Research and Design|
|Publication status||Published - 2012|
- Packed beds
- Chemical looping combustion
- Kotchine theorem