(551b) Multiphase-PBM Model and Its Application in the Simulation of an Industrial F-T Reactor

The gas-liquid-solid slurry bubble columns are widely used in the Coal-to-Liquid and Gas-to-Liquid processes.  A systematic study of the multiphase hydrodynamics of the slurry bubble columns is of great importance for an optimal design and operation of the F-T reactors.  In recent years, computational fluid dynamics (CFD) approach is becoming increasingly popular for the descriptions of the multiphase reactors.  Among different CFD techniques, the Euler-Euler multiphase model coupled with population balance model (PBM) has been used in the simulations bubble size evolutions, and in the computations of gas holdup, liquid velocity, and other hydrodynamic parameters. 

In this presentation, three-dimensional Eulerian simulations of gas–liquid-solid transient flows were performed using a multiphase flow algorithm based on the finite-volume method by means of the commercial software FLUENT 14.0, and discussed in connection with an industrial scale slurry bubble column F-T reactor.  A pseudo gas-slurry closure model was proposed and validated.  The effects of turbulence model and the interphase momentum closure model on the simulation results were examined. Of particular interest, simulations were performed with and without internal cooling tubes.

The results showed that the various bubble size models had significant impacts on the predictions of the overall gas holdup in slurry bubble column and the multispecies mass transport, and affected the syngas conversion rate and the gas phase shrinkage significantly.  The following results were obtained based on an industrial F-T reactor: (1) For a slurry reactor without internals, large-scale vortex structures were formed in the near-wall zone, while for a reactor with internals, large-scale vortex structures were replaced by small-scale vortex; (2) The distributions of gas holdup, liquid velocity, and bubble size were more complex with internals than without; (3) The existence of internals played a positive role in slowing down the particle settling.