Reverse circulation fluidized bed reactor for granular polysilicon production

A method for producing a silicon product from polysilicon, comprising:

• providing an internally recirculating fluidized bed reactor having at least one vertical separator that creates within the reactor a pre-reaction heating zone, a reaction zone, and a dehydrogenation zone, said zones being in particle communication with each other;
• introducing polysilicon particles into the reactor;
• introducing a pre-reaction fluidizing gas into the pre-reaction heating zone, a reaction gas comprising silane (SiH4) into the reaction zone, and a dehydrogenation gas into the dehydrogenation zone, each of said gases being introduced at a velocity that is at least equal to a minimum fluidizing velocity for the polysilicon particles;
• controlling the velocities of the gases so as to cause the polysilicon particles to circulate upward through the pre-reaction heating zone, downward through the reaction zone, and through the dehydrogenation zone, whereby:
• the polysilicon particles are heated in the pre-reaction heating zone to a reaction temperature that is above a minimum reaction temperature for the reaction gas;
• silicon is deposited from the reaction gas onto the polysilicon particles in the reaction zone;
• and
• the polysilicon particles are heated in the dehydrogenation zone to a temperature that is sufficient to remove hydrogen gas from the polysilicon particles,
• said circulation causing the polysilicon particles to be converted to silicon product;
• and
• removing the silicon product from the reactor.