Silica to high purity silicon production process

Abstract

An apparatus and a process for the production of high purity silicon from silica containing material such as quartz or quartzite, using a vacuum electric arc furnace, are disclosed.

1 . An apparatus for producing silicon from silica, comprising a vacuum electric arc furnace adapted to receive feedstock therein, a vacuum system for providing vacuum in the furnace, wherein a plasma arc created in the furnace is adapted to provide energy to reduce silica to silicon. 
     
     
         2 . The apparatus of  claim 1 , wherein a mixture of silica containing material, for instance quartz, and a reducing agent, for instance carbon, is adapted to be fed to the furnace. 
     
     
         3 . The apparatus of  claim 1 , wherein the furnace is adapted to operate under vacuum conditions, for instance <100 kPa, and more typically <1000 Pa. 
     
     
         4 . The apparatus of  claim 1 , wherein the plasma arc in the furnace is adapted to volatilize impurities from the silicon phase under vacuum and to provide heat for keeping the silicon in molten phase during a refining process. 
     
     
         5 . (canceled) 
     
     
         6 . The apparatus of  claim 1 , wherein the feedstock is fed to the furnace via at least one feedstock port, a crucible being provided for receiving the feedstock, and wherein the feedstock is adapted to be piled up in the crucible. 
     
     
         7 .- 8 . (canceled) 
     
     
         9 . The apparatus of  claim 1 , wherein at least one electrode is provided for carrying current to an electrically conductive plate, for instance provided at a bottom of the crucible, and wherein the electrode is hollow for allowing for the introduction of at least one of (1) arc stabilizing gases in the furnace, either inert or reactive, and (2) volatilizing chemical agents, for reacting with impurities or enhance the volatilization rate of impurities from the melt. 
     
     
         10 .- 13 . (canceled) 
     
     
         14 . The apparatus of  claim 9 , wherein the electrode is moveable to control the voltage(s). 
     
     
         15 . The apparatus of  claim 9 , wherein the electric arc is adapted to be formed directly between the electrode and the conductive plate at the beginning of the process, thereby producing a silicon melt thereafter, the melt containing silicon, and wherein an outlet is provided for tapping the melt, in liquid form, from the furnace. 
     
     
         16 . (canceled) 
     
     
         17 . The apparatus of  claim 1 , wherein the furnace environment is adapted to be controlled by introducing various gases in the furnace via a gas injection port, for carrying over the volatilized impurities and gaseous by-products and for partially oxidizing the monoxide gaseous species, such as CO(g) and SiO(g). 
     
     
         18 .- 21 . (canceled) 
     
     
         22 . The apparatus of  claim 9 , wherein the electrode is adapted to conduct current to the conductive plate placed at a bottom of the furnace through direct contact at the beginning of the process and thereafter, the plasma arc, with the plasma arc being adapted to heat up the feedstock to initiate the reduction reaction via SiO2(s,l)+C(s). 
     
     
         23 . The apparatus of  claim 1 , wherein the feedstock material contains silica, which is either quartz or quartzite or any other forms with high silica content, for instance >60-70%, the remaining being adapted to be mostly volatile impurities at the operating condition of the furnace, and with a reducing agent, typically carbon, being adapted to be fed directly into the furnace. 
     
     
         24 . (canceled) 
     
     
         25 . The apparatus of  claim 1 , wherein a low operating pressure is adapted to be provided for the volatilization of impurities having higher vapor pressure than silicon, and wherein volatized impurities are preferably adapted to be vented out of the furnace via an inert gas, such as Argon, or a reducing carrier gas, such as CO. 
     
     
         26 . (canceled) 
     
     
         27 . The apparatus of  claim 1 , wherein to enhance the volatilization rate of the impurities, various volatilizing agents, such as chlorine containing material, are adapted to be injected through the hollow electrode into the melt, and preferably wherein volatilizing agents are provided for enhancing a volatilization rate of impurities by reacting with the impurities producing new compound(s) with a greater volatility and/or by becoming volatile in the melt, for instance, by injecting chlorine (Cl2), impurities are adapted to be transformed to the metal salts, via M(l)+x/2 Cl2(g)=MClx(g), having much higher volatility than the metal form thereof. 
     
     
         28 . (canceled) 
     
     
         29 . A process for producing silicon from silica, using the apparatus of  claim 1 . 
     
     
         30 . The process of  claim 29 , comprising a reduction system and a gas cleaning system, a reduction process of silica containing materials to high purity silicon, e.g. >99%, taking place in the furnace, and wherein hot gas evolving from the furnace mixed with the carrier gas is adapted to be vented off the furnace to an oxygen-assisted refractory-lined cyclone. 
     
     
         31 .- 35 . (canceled) 
     
     
         36 . The process of claim  31 , wherein gas coming from the cyclone is adapted to pass through a gas cooler-expander, where the gas is adapted to be cooled down to reach temperatures below 80° C., and the particulates, from the condensates that are volatile in the cyclone, are adapted to settle down and to be collected in a collection box, and wherein gas coming out of the gas cooler-expander is adapted to pass through a high efficiency particulate air (HEPA) filtration system for capturing very fine particulates, e.g. <5 μm, escaping from the cyclone and the gas cooler-expander. 
     
     
         37 .- 40 . (canceled) 
     
     
         41 . The apparatus of  claim 1 , wherein the vacuum is provided by a vacuum pump in communication with the furnace, for instance via an outlet port, and wherein the operating pressure of the furnace is adapted to be regulated with the vacuum pump. 
     
     
         42 . (canceled) 
     
     
         43 . A system for reducing silica to silicon, which uses a combination of a plasma arc and vacuum, to produce high purity silicon from silica containing materials, such as quartz or quartzite; wherein a vacuum electric arc furnace is provided, such that the plasma arc produces a silicon melt from the silica containing materials; and wherein, to enhance a volatilization rate of impurities contained in the silica containing materials, volatilizing agents, such as a chlorine containing material, are provided and are adapted to be injected through at least one hollow electrode into a melt produced in the furnace. 
     
     
         44 .- 49 . (canceled) 
     
     
         50 . A process for reducing silica containing materials to silicon, comprising the steps of:
 providing a vacuum arc furnace;   feeding silica containing materials into the furnace; and   heating the silica containing materials in the furnace to produce a silicon metal.