Abstract
Abstract An open-source CFD software OpenFOAM® is used to simulate two multiphase stirred-tank reactors relevant to industrial processes such as slurry polymerization and fuel production. Gas-liquid simulations are first performed in a single-impeller stirred-tank reactor, studied experimentally by Ford, J. J., T. J. Heindel, T. C. Jensen, and J. B. Drake. 2008. “X-Ray Computed Tomography of a Gas-Sparged Stirred-Tank Reactor.” Chemical Engineering Science 63: 2075–85. Three impeller rotation speeds (200, 350 and 700 rpm) with three different bubble diameters (0.5, 1.5 and 2.5 mm) are investigated. Flow patterns compared qualitatively to those from experiments. Compared to the experimental data, the simulations are in relatively good agreement for gas holdup in the reactor. The second multiphase system is a multi-impeller stirred-tank reactor, studied experimentally by Shewale, S. D., and A. B. Pandit. 2006. “Studies in Multiple Impeller Agitated Gas-Liquid Contractors.” Chemical Engineering Science 61: 486–504. Gas-liquid simulations are performed at two impeller rotation speeds (3.75 and 5.08 RPS). The simulated flow patterns agree with published pictures from the experiments. Gas-liquid-solid simulations of the multi-impeller stirred-tank reactor are also carried out at impeller rotation speed 5.08 RPS. The addition of solid particles with a volume fraction characteristic of slurry reactors changes the flow pattern significantly. The bottom Rushton turbine becomes flooded, while the upper pitched-blade downflow turbines present a radial-pumping flow pattern instead of down-pumping. Nonetheless, the solid phase has a similar flow pattern to the liquid phase, indicating that the particles modify the effective density of the fluid.
Highlights
IntroductionShewale and Pandit 2006; You et al 2014). the complexity of the flow in STRs with multiple impellers increases with increasing number of impellers as any change in the reactor parameters, such as tank aspect ratio, number, type, size, location and configuration of impellers and operating conditions, may influence the reactor operating characteristics significantly
Stirred-tank reactors (STRs) are widely used in industrial processes, such as in the chemical, biological, pharmaceutical, as well as many other industries
In (Ford et al 2008), X-ray computed tomography (CT) images of the local gas holdup obtained at different planes are presented
Summary
Shewale and Pandit 2006; You et al 2014). the complexity of the flow in STRs with multiple impellers increases with increasing number of impellers as any change in the reactor parameters, such as tank aspect ratio, number, type, size, location and configuration of impellers and operating conditions, may influence the reactor operating characteristics significantly. Many researchers have studied multiple-impeller STRs experimentally (Kasat and Pandit 2004; Shewale and Pandit 2006; Vr’abel et al, 1999, 2000; You et al 2014) for gas-liquid two-phase flows. For gas-liquid-solid systems, very few studies are reported for single-impeller STRs (Murthy, Ghadge, and Joshi 2007; Panneerselvam, Savithri, and Surender 2009) while for multi-impeller STRs, works found in the literature are very limited and almost all of these studies are performed using commercial CFD software, such as ANSYS FLUENT® and CFX®. A multi-impeller STR, studied experimentally by (Shewale and Pandit 2006), is simulated for both gas-liquid and gas-liquid-solid systems.
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