CPFD simulation and optimization of a 50 kWth dual circulating fluidized bed reactor for chemical looping combustion of coal

Abstract

A 50 kWth dual circulating fluidized bed reactor for chemical looping combustion (CLC) of coal, which has been designed, constructed and operated at Huazhong University of Science & Technology (HUST), was simulated using the Computational Particle Fluid Dynamics (CPFD) method in this work. The reliability of CPFD simulation was first validated by comparing fuel reactor (FR) outlet gases concentration and FR pressure profiles of experimental measurements with the corresponding simulation results. Then, the gas-solid reactive flow in the full-scale reactor was simulated in detail, and the results can help to rationalize reactor design and optimize operation. The evolution of bed inventory and solid circulation rate were carefully analyzed to understand the bed material rebalance phenomenon observed in simulation. The self-adjustment ability among different parts within the whole unit demonstrated the feasibility and stability of the 50 kWth CLC reactor. In addition, to have a better understanding on the relationships among the complex factors of hydrodynamics and reactions, the residence time distributions of oxygen carrier (OC) and char were attained. Based on these results, a higher FR was proposed as an optimization to improve the residence time of char in FR, so as to extend reaction path of both homogeneous and heterogeneous reactions therein. Finally, according to the simulation results of the combustible gases distribution and coal conversion trail within the reactor, the coal feeding location was optimized. It was found that the combustible gases in volatile plume cannot diffuse effectively throughout FR with only one coal feeding point, which was not conductive to the good mixing among OC and combustible gases. As an optimization, well mixed gas-solid contact was achieved with two oppositely-collocated coal feeding points. In summary, the CPFD simulation conducted in this work can help to optimize the reactor configuration and operation, which eventually achieved reliable prediction of the performance of the 50 kWth CLC reactor in an effective and economical way.