CFD simulation of the hydrodynamic behavior in an internally circulating fluidized bed reactor for producing polysilicon granules

- An ICFB with a draft tube was studied for producing polysilicon granules.
- Hydrodynamics were better predicted by the Syamlal and O'Brien drag model.
- Two types of solids circulation patterns were found and discussed.
- Solids circulation rate and gas bypass fraction were analyzed in detail.
- Optimized reactor configuration and operating conditions were determined.

An internally circulating fluidized bed (ICFB) reactor with a central draft tube that was used for producing polysilicon granules was studied, with the focus on the inhibition of silicon deposition on the wall. The effects of gas velocity, particle diameter and reactor configuration on the solid circulation rate (Gs) and gas bypass fraction (γDA and γAD) were studied by two-dimensional CFD simulation. Among the commonly used drag models, the Syamlal and O'Brien drag model gave the best prediction. For the best heat transfer performance and inhibition of silicon deposition on the heated wall, the optimum gas velocities for the ICFB were UD/Umf = 1.0-1.7 and UA/Umf = 1.5-2.3. When UD/Umf < 0.65 and UA/Umf > 1.75, a reverse circulation pattern appeared and γDA increased significantly. The effects of particle diameter, orifice size and the parameters of the draft tube were studied. For good fluidization in the ICFB, the position and size of the orifices, area ratio of annulus to draft tube and height of draft tube should satisfy so < 0.02 m2, Ho < 320 mm, 1.5 < sA/sD < 3.2 and 700 < Hd < 900 mm, respectively.

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