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Computational Particle-Fluid Dynamics Simulations of a Commercial-Scale Turbulent Fluidized Bed Reactor

Paul Zhao, Dale Snider, and Ken Williams. CPFD Software, LLC, 10899 Montgomery Blvd. NE, Suite B, Albuquerque, NM 87111

            The three-dimensional gas-solid flows inside a dense-phase fluidized bed with a diameter  close to 5 meters, and running in the turbulent to fast fluidization mode, is numerically simulated and analyzed. The solids are FCC-type material, the superficial gas velocity is 43 cm/s, and all key internals are modeled, such as ganged cyclones, spargers, and air injectors. The commercial Barracuda-CPFDTM software package was used to simulate the reactor's behavior for over 187 s in order to obtain meaningful time-averages for solids concentrations, gas and solids velocities, and pressures. The new Barracuda commercial software is an advanced math-based computational particle-fluid dynamics (CPFDTM) tool developed for efficient simulation of dense-phase fluidization in industry-scale units. The software's numerical methodology uses a direct element method wherein solids are modeled as discrete particles with proper size and density distributions, and the fluid is modeled as a continuum. The actual solid particles numbering on the order of 1013 are modeled with 5x105 ~ 5x106 numerical particles, each of which groups the physical particles with the same properties (size, shape, density, etc.) as a single entity. The fluid (gas) flow is compressible and isothermal. The model includes complex internal structures such as cyclones and diplegs inside the bed. The elutriated particles exit the bed through the cyclones, and then particles feed back into the bed through the diplegs in various elevations. The simulation is the first of its kind in terms of efficiency, accuracy, run-time, and the geometrical scale (commercial size bed) of the model.

            The deep turbulent fluidized bed does not behave as an idealized plug flow fluidized-unit, and its complex solids-fluid dynamics differ from the traditional bubbling fluidized bed. Specifically, gas streaming occurs in certain regions, resulting in poor gas-solids contact and reduced product yields. The occurrence of gas streaming behavior in large, deep beds is supported by experimental data. The fluidization properties such as solid concentration distribution, particle size distribution (PSD), particle species distribution, particle residence time distribution(RTD), pressure distribution, and gas and solid flow patterns are analyzed. The simulation provides a unique insight into the complex behavior of a commercial-scale turbulent fluidized bed reactor with internals.