Completed Research
Computational Fluid Dynamics Modeling With Experimental Validation
of
the Complex Spatio-Temporal Phenomena in Slurry Bubble Column
Reactors for Fischer-Tropsch Synthesis
Omar M. Basha, PhD, 2016
(Thesis: University of Pittsburgh ETD)
A multiphase Eulerian, three-dimensional, computational fluid dynamics (CFD) model was developed and implemented in ANSYS, Fluent to predict the local hydrodynamics and overall performance of Slurry Bubble Column Reactors (SBCRs) for Fischer Tropsch (F-T) synthesis. The model predictions were validated against the gas holdup profiles obtained under ambient conditions by Yu and Kim (1988) and by Chen et al. (1999) and against overall gas holdup data obtained under typical F-T process conditions in our pilot-scale SBCR (0.3-m ID, 3-m height). These validations showed that the inclusion of the RNG k-ε turbulence model, coupled with the gas-liquid drag model by Wen-Yu (1966), the liquid-solid drag model by Schiller-Naumann (1935) and the lift coefficient by Tomiyama et al. (2002), along with our empirical mass transfer coefficients correlation in the CFD model, led to the most accurate predictions of the experimental data used.
The CFD model was first used to predict the effects of internals and spargers design on the local hydrodynamics in our pilot-scale SBCR and the effects of internals on the local hydrodynamics in a conceptual SBCR (1-m ID, 10-m height). The simulations showed that the internals increased the gas holdup and turbulence intensities and led to even gas holdup radial distribution in the pilot-scale reactor. Also, the liquid recirculations were stronger when using 1-bundled or 3-bundled internals than those when using a 4- or 5- bundled internals in the conceptual SBCR.
Furthermore, F-T and WGS kinetics for iron catalyst provided by NICE, China were incorporated into the model. The CFD model was then used to predict the local hydrodynamics and performance of our pilot-scale SBCR and the commercial-scale SBCR (5.8-m, 30-m height) by NICE. The gas holdup profiles in the pilot-scale SBCR with F-T reactions were different from those without reactions; and this reactor can produce a maximum yield of 1.87 tons/day of C5+ products using a H2/CO ratio of 2/1 and a catalyst concentration of 15 vol%. Also, the CFD model predicted CO conversion of 58%, H2 conversion of 56% and C5+ products yield of 627 tons/day at a superficial gas velocity of 0.3 m/s in the commercial-scale SBCR.