CFD Modeling with Experimental Validation of the Internal Hydrodynamics in a Pilot Scale Slurry Bubble Column Reactor
Abstract A multiphase Eulerian, three dimensional (3 D) computational fluid dynamics (CFD) model was built to investigate the local hydrodynamics of a pilot scale (0.29 m ID, 3 m height) Slurry Bubble Column Reactor (SBCR) The model was first validated against the gas holdup radial profiles in an air water glass beads system obtained in a 0.254 m ID and 2.5 m height column under ambient conditions at various superficial gas velocities by Yu and Kim (Bubble characteristics in the radial direction of three phase fluidized beds. AIChE Journal 34, 2069 2072, 1988) The model was next validated against the gas holdup radial profile data for N2 Drakeol glass beads system obtained in a 0.44 m ID and 2.44 m height reactor, including internals, operating under ambient conditions at various superficial gas velocities by Chen et al. (Fluid dynamic parameters in bubble columns with internals. Chemical Engineering Science 54, 2187 2197, 1999) The model was also validated against experimental data obtained in our lab for N2 Fischer Tropsch (F T) reactor wax Fe catalyst system obtained in a pilot scale, Slurry Bubble column Reactor, SBCR (0.29 m ID, 3 m height) under pressures and temperatures up to 25.9 bar and 490 K, respectively. These three validations led to the selection of the turbulence and interphase drag coefficient models, and the optimization of the solution method, mesh size and structure and the step size. Moreover, the inclusion of RNG k e turbulence model coupled with the Wen Yu (Mechanics of Fluidization. Chemical Engineering Progress Symposium Series 62, 100 111, 1966) Schiller Naumann (A drag coefficient correlation. Zeitung Ver. Deutsch. Ing 77, 318 320, 1935) drag correlations, and the mass transfer coefficients were found to provide the most accurate predictions of the experimental data. The CFD model was then used to investigate local gas holdup, liquid recirculation, local turbulence intensities, bubble diameters, and solids distribution throughout our pilot scale SBCR, operating under typical F T process conditions. The model predictions showed strong liquid recirculation and backmixing near the walls of the reactor, and the solid phase velocity vectors closely followed those of the liquid phase. A relatively high liquid turbulence intensities were observed in the vicinity of the sparger upon startup, however, after reaching a steady state, the liquid turbulence intensities became more evenly distributed throughout the reactor. The liquid turbulence intensities were slightly higher near the center of the reactor, and closely resembled the velocity vectors. Also, the Sauter mean bubble diameters increased, whereas the solids distribution decreased with reactor height above the gas distributor.