Theoretical Study of Particulate Flows Formation in Circulating Fluidized Bed (E-pub Ahead of Print)
The objective of the study is to develop a simple yet informative model to investigate the features of a particulate flow forming process that takes place in a circulating gas-solid fluidized bed reactor. The proposed model is based on the theory of Markov chains. The riser is presented as a chain of perfectly mixed cells. The transformation of particles of a raw material into particles of an end product occurs in these cells due to this or that chemical or thermo-physical process. The transportation of material over the chain is controlled by a matrix of transition probabilities. This matrix is different for particles of the raw material and particles of the end product. The separator is presented as an imperfect classifier. The return flow that comes from it is routed to the downer which is described as a plug flow apparatus that has a time delay between the inflow and outflow coming from it. The outflow is routed back into the riser. The numerical experiments were carried out for the batch and continuous fluidization. It is found that the batch circulating fluidization only has advantages in comparison to the dense bed under a small time delay in the downer and a relatively high gas flow velocity in the riser. It is also found that the maximum feed flow rate exists in a continuous circulating fluidization that ensures the stable operation of the circuit. This threshold crossing leads to the overfilling of the riser and blockage of the process. Optimal positioning of the return flow input allows increasing this maximum feed flow rate.
Keywords: Circulating fluidized bed, cell model, Markov chain, rate of reaction, time delay, gas flow velocity, return flow positioning
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