HYDRODYNAMIC BEHAVIOR OF AN INTERNAL CIRCULATION FLUIDIZED BED FOR PREPARING POLYSILICON GRANULES

摘要

The production of polysilicon granules using a fluidized bed reactor (FBR) is a promising alternative to the Siemens process for its low cost and high efficiency.The silicon deposition on the heated wall is a big issue for normal operation of FBR.An Internal Circulation Fluidized Bed (ICFB) reactor was designed to prevent silicon deposition on the heated wall by dividing the reactor into a heating zone (annulus) and a reaction zone (draft tube).In this reactor, particles are heated in the heating zone, and then circulated to the reaction zone.As the reactant gas is fed only to the reaction zone and little reactant gas flows to the heating zone, the silicon deposition on the heating wall is well suppressed.This paper aimed to experimentally study the fluidization behavior of wide-size-distribution (WSD) particles in an ICFB.The segregation of WSD particles was effectively suppressed by the circulation of particles in the ICFB.The solids holdup εs, solids circulation rate Gs, and gas bypassing fraction γRD (gas bypassing from the draft tube to annulus) and γDR (from the annulus to draft tube) were studied.When UD/Umf was 2.5～3.2 and UR/Umf was 2.2～2.7, γRD was smaller than 4％, indicating that the bypassing of reactant gas to the heating zone was well controlled.Meanwhile, the experimental and calculated results showed that the ICFB could meet the need of heat supply and effectively reduce silicon deposition on the heated wall.