(614b) Computational Particle-Fluid Dynamics Simulations of a Commercial-Scale Turbulent Fluidized Bed Reactor

            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-CPFD^TM
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 (CPFD^TM)
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.