Patent ID: 9533279
Date: 2017-01-03
CPC Classifications: B01J,C01B,Y02P

Claim:
1. A method for manufacturing polycrystalline silicon, comprising the steps of: a) reacting a metallurgical grade silicon and hydrogen chloride in a chlorination reactor to produce chlorosilanes, including crude trichlorosilane, and polymer containing high boiling chlorosilane compounds which have boiling points higher than a boiling point of silicon tetrachloride; b) distilling the chlorosilanes and the polymer in a first distillation column to obtain a purified trichlorosilane from and a distillation residue including the polymer; c) mixing, in an evaporator, the purified trichlorosilane from the first distillation column, with hydrogen, trichlorosilane, and silicon tetrachloride, which are recovered from downstream steps, to produce a raw material gas; d) introducing the raw material gas into a reactor, in which silicon rods are heated to a temperature of 900° C. to 1200° C., to deposit polycrystalline silicon on the silicon rods; e) cooling an exhaust gas from the reactor of step d) in a condenser to obtain liquefied chlorosilanes and a gas including hydrogen and hydrogen chloride; f) separating the hydrogen from the hydrogen chloride and feeding the hydrogen back to the evaporator of step c); g) distilling the liquefied chlorosilanes from the condenser of step e) to obtain a residue containing polymers and distilled chlorosilanes containing trichlorosilane and silicon tetrachloride; h) introducing a first portion of the distilled chlorosilanes obtained in step g) into a trichlorosilane conversion step via a second evaporator; i) reacting silicon tetrachloride in the first portion of the distilled chlorosilanes with hydrogen in the trichlorosilane conversion step at a high temperature of 800° C. or more and 1300° C. or less to produce trichlorosilane; j) introducing a gas including the produced trichlorosilane in step i) into a condenser to obtain a liquefied stream; k) returning the liquefied stream obtained in step j) to the distilling of step g); l) supplying a second portion of the distilled chlorosilanes obtained from the distilling of step g) to the evaporator of step c); m) supplying the polymers from the distilling the liquefied chlorosilanes of step g) and the polymer from the first distillation column of step b) to a decomposition furnace through a first supply pipe which extends from a top to a bottom of the decomposition furnace by meandering in a spiral shape while preheating the polymer in the first supply pipe; n) supplying hydrogen chloride to the decomposition furnace through a second supply pipe which extends from the top to the bottom of the decomposition furnace in a straight pipe while preheating the hydrogen chloride in the second supply pipe; o) mixing the preheated polymers supplied through the first supply pipe and the preheated hydrogen chloride supplied through the second supply pipe in the decomposition furnace to react the polymer and the hydrogen chloride at a temperature of 450° C. to 700° C. in the decomposition furnace to obtain products including trichlorosilane and silicon tetrachloride; and p) introducing the products obtained in step o) into the chlorination reactor of step a), wherein the polymers and the hydrogen chloride are not mixed during the preheating steps and do not react with each other during the preheating step so that reactants adhering to and obstructing an inside of the first and second supply pipes will not occur.