Theoretical Study of Particulate Flows Formation in Circulating Fluidized Bed

Background: The research works on circulating fluidized bed are mostly devoted to investigation of the process in separate parts of a circulating fluidized bed reactor, and practically never to investigation of the entire circulating loop. The interference between the processes in the riser, separator and downer remains practically unexamined. Objective: The objective of the study is to develop a simple yet informative model to investigate the features of a particulate flows forming in a circulating gas-solid fluidized bed reactor. Method: The method of mathematical modeling is used. The proposed model is based on the theory of Markov chains. The transformation of a raw particulate material into an end product in the riser is taken into account. The return flow in a downer is described with a time delay between the inflow and outflow from it. Results: The proposed model allowed performing numerical experiments on the influence of the process parameters on its main technological characteristics both for the transient and steady state. Conclusion: It is found that the batch circulating fluidization has advantages in comparison to the dense bed only at 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 its blockage. Optimal positioning of the return flow input allows increasing this maximum feed flow rate.