Hydrodynamic characteristics of gas–solid fluidized beds with shroud nozzle distributors for hydrochlorination of metallurgical-grade silicon

Abstract

The hydrodynamic characteristics of a gas–solid fluidized bed for the hydrochlorination of metallurgical-grade Si were compared by analyzing the distributor configuration at similar opening area ratios, and using a superficial gas velocity (U0) ranging from 0.02 to 0.17m/s. A perforated plate with a similar opening area ratio to those of the shroud nozzle distributors was also used as a reference. Metallurgical-grade silicon (MG-Si) and air were used as the bed material and the fluidizing gas, respectively. To evaluate the stability of gas distribution, the pressure drop across each distributor was measured, and the coefficient of variation (CV) of the pressure drop was compared between distributors, according to the number of nozzles and the superficial gas velocity. The CV for distributors decreased with an increasing modified Froude number. The CV was significantly increased in 1 and 2 shroud nozzle distributors when the modified Froude number was under 50. The bed expansion ratio was also found to increase with an increasing number of nozzles in the distributors. In addition, the drop in bed pressure increased with an increasing number of nozzles. Bed pressure drops of the 1, 2, and 3-shroud nozzle distributors were lower than those of 7-shroud or the perforated plate. In the case of a 1 shroud nozzle, high dead zone occurred, causing poor gas distribution. The standard deviation of the bed pressure drop was measured to evaluate fluctuations in the drop. The fluctuation was found to be proportional to the superficial gas velocity. The CV of the distributor and the bed pressure drop fluctuation were not directly proportional; however, the pressure fluctuation of a 1 shroud nozzle distributor was higher than those of other distributors, due to a non-uniform gas distribution.