(213e) Application of a Modified CFD-PBM Method to the Simulation of a Slurry Bed Reactor

Slurry bed reactors, which own many advantages such as high gas-liquid interfacial area and good mass/heat transfer performance between gas and liquid phase, are widely adopted to oxidation and hydrogenation reactions, fermentation, especially Fischer–Tropsch synthesis and so on. In this work, a CFD-PBM method was used to study the hydrodynamics in a slurry bed reactor. In previous work, numerous studies on PBM had been performed to achieve better prediction of bubble characteristics. However, those works were all based on air-water system and had not taken the solid phase into account. In previous experiments, it was found that small amounts of particles can enhance bubble coalescence process, and the average bubble size generally increased with the increase of solid concentration within a certain range, which resulted in the decrease of gas holdup. Therefore, it was proposed that the previous PBM could not be extended to the simulation of slurry bed reactor. However, there are few reports on the modification of PBM for considering the effect of the solid phase. In fact, the main influence of solid concentration lies in the change of liquid apparent properties, including viscosity, density, etc.. There are many reports about the effect of particles on the apparent liquid viscosity and density in slurry bed reactors However, few reports have focused on the apparent liquid surface tension which also has significant effect on bubbles breakup and coalescence. Therefore, the aim of this work is to develop a modified PBM by considering the effect of particles on the liquid surface tension to the application in the simulation of slurry bed reactors.

Methods

Due to the small size (<100 μm) and homogeneous dispersibility of particles in the reactor, the liquid phase and the solid phase was simplified to a pseudo-homogenous phase. Then the two-fluid model (TFM) method based on the Eulerian-Eulerian scheme was applied. It was reported that the addition of small amounts of particles can lead to a higher liquid apparent viscosity and surface tension. So by taking the influence of particles into account, a modified apparent surface tension of the liquid phase was used to modify the PBM. Then Ojima’s and Prashka’s experiment dates was used to validate the model, and the simulation study was following their experimental equipment and operating conditions.

Results and Discussion

Simulation results that employed the modified and non-modified surface tension were compared to the experiment data, respectively. From the results, it was demonstrated that the modified PBM was suitable to describe the bubbles behaviors in the slurry bed reactor. In addition, it was found that the effect of particles had significant difference under low and higher gas superficial velocity, which may lie on the significant turbulent characteristics between cases under low and higher gas superficial velocity in the slurry bed reactor.

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