Fluidization of Silicon Powder

Silicon powder is reacted with hydrogen chloride (HCl) in a fluidized bed reactor to produce trichlorosilane (TCS or HSiCl3). This reaction produces a lot of heat (ΔH° = -219 kJ/mol TCS), and it is important to avoid high temperature areas in the reactor since increased temperature will promote formation of silicon tetrachloride (STC or SiCl4). Good fluidization is important for the heat transport and temperature control in the reactor. In this paper, the principles of fluidization is discussed. The theory is demonstrated with a laboratory test equipment. A one-dimensional model has been developed to calculate the fluidization conditions as a function of the vertical position in the reactor. The fluidization conditions will change along the reactor due to changes in gas composition, stoichiometry, pressure drop, etc. Laboratory results are applied in this model to simulate Si powder fluidization in an industrial reactor. It was found that the fluidization is weaker in the middle of the bed which may cause poor temperature control in the reactor.