Design and Simulation of a New Micro Fluidized Bed Reactor By Computational Fluid Dynamics

New applications are emerging for fluidized bed reactors such as baking and thermal cracking of ores, chemical vapor deposition, waste valorization, fluidization of nanoparticles, and catalytic reactions for feedstocks that are unconventional with a low grade of the desired elements etc.

Such reactors are usually endothermic and should operate at a high temperature with a desired gas residence time. Micro fluidized bed reactors are promising reactors to save time and cost of experimental investigations when especially designed to mimic an operation at commercial scale and to screen operating conditions, feedstock formulations, and bed material physicochemical properties in terms of feed conversion, product selectivity and gas-solid interactions, e.g. agglomeration and attrition.

Authors have designed and developed a micro fluidized bed reactor where both gas and solid phases operate in batch mode, and an induction heating mechanism supplies the required heat with a high heating rate to stay at the setpoint temperature, i.e. up to 1200 ^oC. A centrifugal impeller takes in the outlet gas from the bed and returns it to the bed though internal tubes immersed into the reactor, i.e. gas sparger. The tubes are also heating elements; that is, the generated heat on the external surface of the tubes by the induction heating is transferred to the bed.

Computational fluid dynamics was employed to optimize dimensions of the reactor and the gas circulation system so that the impeller rotates at a speed below 5000 rpm enabling fluidization of Geldart’s group B particles with negligible wall effect.

The sliding mesh technique was used for numerical simulation of the impeller rotation. Prediction of the turbulence in the system was done by using the K-omega turbulent model and the hydrodynamics of the fluidized bed reactor was simulated by the Eulerian multiphase approach. The SIMPLE algorithm was used for pressure-velocity coupling and the second order upwind was utilized to obtain precise results. The results show that the gas flow rate is proportional to the impeller diameter, however, the shape of the blades does not have a considerable effect. Based on the numerical results, the design of the impeller and the reactor was optimized.