Modeling of a Slurry Bubble Column Reactor Using a Two-Phase Two-Bubble Class Approach-A Hydrodynamics Study

The slurry bubble column reactor (SBCR) is of particular interest in Fischer-Tropsch (FT) reactor modeling because of its importance to gas-to-liquids processes and the technical challenges it poses. Being one of the more important and complex FTS systems in use today, the current knowledge and understanding of the SBCR at a fundamental level, the hydrodynamics in particular, has to improve in order to improve its efficiency. Accordingly, a mathematical model of a SBCR has been developed in this work. The model is based on mass balances into which hydrodynamic, mass transfer, and kinetic parameters have been incorporated. The hydrodynamic model considers two distinct phases in the SBCR, namely the gas and slurry phases with the liquid and solid treated as a single pseudohomogenous phase. The gas phase in the reactor was assumed to exist in the form of distinctly large and small bubbles with each bubble class moving predominantly upward through the center of the reactor and down near the wall, respectively. Material balances were accordingly performed over three compartments including the slurry, large bubbles, and small bubbles compartments. Axial dispersion was assumed in both the slurry and gas phases. The overall superficial gas velocity decrease along the axial direction was taken into account using an overall gas balance. Species material balances, hydrodynamics, kinetics, and gas/liquid physicochemical property models were all coupled into a single SBCR model. The model was able to produce simulations capable of tracking the fate of the reactant species, in the axial direction, in all three phases. Notably, the CO and H-2 concentrations dropped by 62.01% and 64.13%, respectively, in the large bubble phase. A sensitivity study revealed the negative dependence of syngas conversion on the superficial gas velocity. A positive effect on the syngas conversion was evident with a change in reactor diameter; that is, an increase in diameter between 6 and 7.8 m resulted in an increase in the syngas conversion between 38.3% and 90.78%. An increase in catalyst loading (0.28 to 0.38) resulted in a decrease in the syngas conversion (93.57% to 0.704%) due mainly to the overall decrease in the bubble hold-up.