Refining Process for Producing Solar Silicon, Silicon Carbide, High-Purity Graphite, and Hollow Silica Microspheres

Abstract

A process for producing solar grade silicon from silica sand employs a plurality of plasma furnaces to perform a sequence of chemical reactions together with other process steps to produce solar grade silicon. The plasma furnace generates a stable dirty air, donutshaped plasma into which particulate matter can be introduced. The plasma in the first two stages is formed by gases from the chemical reactions and in the third from inert gasses. Cyclone separators are used to extract particulates from the plasma in an inert gas that prevents reverse reactions as the particular cools.

1 . A process, comprising:
 a. charging impurity containing silica into a rotary heat exchanger in the presence of methane to produce carbon-coated silica, carbon-coated silicon, and carbon;   b. charging the output of step a to first JHQ plasma together with a getter, the plasma comprising gaseous silicon monoxide and carbon monoxide; the plasma being produced in a JHQ furnace that produces rotatable, stable dirty-air plasma whose rotation, shape and temperature are controllable;   c. heating the material in the plasma to 2300° C. to volatize impurities in the silica, dissolve these volatized impurities in the getter, and produce silicon carbide and a getter that with dissolved impurities; wherein silicon carbide and the getter with dissolved impurities fall through the plasma into a cyclone separator;   d. charging the cyclone separator of step c with nitrogen to allow cooling of the silicon carbide and getter to a temperature below 1800° C. without a reverse reaction;   e. ball and/or rod milling the output from step d to separate the getter from the silicon carbide;   f. removing the getter from the silicon carbide;   g. milling the silicon carbide output from step f with substantially pure silicon dioxide to produce an output of silicon carbide and silicon dioxide;   h. charging the silicon carbide and silicon dioxide output from step g into a second JHQ plasma, the plasma comprising gaseous silicon monoxide and carbon monoxide;   i. heating the silicon carbide and silicon dioxide in the plasma to temperatures above 1880° C. whereby silicon and carbon monoxide are produced, the silicon falling out of the plasma into a cyclone separator;   j. charging the cyclone separator of step i with nitrogen or argon to allow cooling of the silicon to a temperature below 1800° C. without a reverse reaction;   h. charging the output of step j into third JHQ plasma furnace with plasma, the plasma comprising argon;   l. heating the output of step h to a temperature above 1830° C. to decompose silicon nitride, and react the silicon and silicon dioxide to produce silicon monoxide that reacts with residual silicon carbide producing silicon and carbon monoxide, the latter drawn off in a cyclone separator, leaving silicon in form of chunks and/or granules;   n. processing the silicon chunks or granules from step I through a unidirectional solidification or continuous unidirectional solidification casting process to produce solar silicon.   
     
     
         2 . The process of  claim 1  wherein step a further comprises charging recycled silicon unidirectional solidification (“UDS”) waste from step n into the rotary heat exchanger. 
     
     
         3 . A process of according to  claim 1 , wherein the cyclone separators of steps c and i are replaced with a counter current feed system whereby solids enter the respective plasma furnace through gas exiting the furnace. 
     
     
         4 . The process of  claim 1 , further comprising charging gas exiting the second JHQ plasma furnace at step i to a JHQ-2 combustion chamber further charged with air to produce solid and high purity silicon dioxide and gaseous carbon monoxide and nitrogen. 
     
     
         5 . The process of  claim 4 , further comprising charging the gas exiting the JHQ-2 combustion chamber to a turbine combustion chamber to drive a turbine producing electrical energy. 
     
     
         6 . The process of  claim 1 , further comprising charging gas exiting the first JHQ plasma furnace at step c to the turbine combustion chamber. 
     
     
         7 . The process of  claim 1 , further comprising charging gas exiting the rotary heat exchanger at step a to the turbine combustion chamber. 
     
     
         8 . The process of  claim 1 , wherein the getter comprises iron or an oxide of iron, copper or an oxide of copper. 
     
     
         9 . The process of  claim 1 , wherein the step f of removing the getter comprises using the use of a magnetic filter, an electrostatic separator and/or a shaker table. 
     
     
         10 . The process of  claim 9 , further comprising slowing the cooling of the output of the first JHQ furnace to allow austenitic iron to transform into ferric iron. 
     
     
         11 . The process of  claim 1 , further comprising charging pure carbon to the second JHQ furnace at step h. 
     
     
         12 . A process according to  claim 1 , comprising combining steps h through I by heating the solids charged to the first JHQ plasma furnace to a temperature higher than 1880° C., cooling the exiting gases and solid output to 1900° C., and diluting the concentration of silicon monoxide gas in this output with argon gas of the same temperature. 
     
     
         13 . A process, comprising:
 a. charging impurity containing silica into a rotary heat exchanger in the presence of methane to produce carbon-coated silica, and carbon;   b. charging the output of step a to first JHQ plasma together with a getter, the plasma comprising gaseous silicon monoxide and carbon monoxide; the plasma being produced in a JHQ furnace that produces rotatable, stable dirty-air plasma whose rotation, shape and temperature are controllable;   c. heating the material in the plasma to 2300° C. to volatize impurities in the silica, dissolve these volatized impurities in the getter, and produce silicon carbide and a getter that with dissolved impurities; wherein silicon carbide and the getter with dissolved impurities fall through the plasma into a cyclone separator;   d. charging the cyclone separator of step c with nitrogen to allow cooling of the silicon carbide and getter to a temperature below 1800° C. without a reverse reaction;   e. ball and/or rod milling the output from step d to separate the getter from the silicon carbide;   f. removing the getter from the silicon carbide;   h. charging argon gas and the output from step f into a fourth JHQ plasma furnace and there heating the particulate to above 1830° C. to remove silicon nitride, and volatile impurities.   
     
     
         14 . The process of  claim 14 , further including a withdrawing particulate matter from the fourth JHQ plasma furnace through a cyclone separator that is charged with argon gas. 
     
     
         15 . The process of  claim 14 , wherein the getter comprises iron, copper, tin, nickel or cobalt, or oxides thereof. 
     
     
         16 . A process according to  claim 13 , wherein the cyclone separator of step c is replaced with a counter current feed system whereby solids enter the respective plasma furnace through the gas exiting the furnace. 
     
     
         17 . (canceled) 
     
     
         18 . (canceled) 
     
     
         19 . A process, comprising:
 a. charging impurity containing silica into a rotary heat exchanger in the presence of methane to produce carbon-coated silica, and carbon;   b. charging the output of step a to first JHQ plasma together with a getter, the plasma comprising gaseous silicon monoxide and carbon monoxide; the plasma being produced in a JHQ furnace that produces rotatable, stable dirty-air plasma whose rotation, shape and temperature are controllable;   c. heating the material in the plasma to 2300° C. to volatize impurities in the silica, dissolve these volatized impurities in the getter, and produce silicon carbide and a getter that with dissolved impurities; wherein silicon carbide and the getter with dissolved impurities fall through the plasma in to a cyclone separator;   d. charging the cyclone separator of step c with nitrogen to allow cooling of the silicon carbide and getter to a temperature below 1800° C. without a reverse reaction;   e. ball and/or rod milling the output from step d to separate the getter from the silicon carbide;   f. removing the getter from the silicon carbide;   h. sizing of the silicon carbide and separating the different size particles with diameters of between 0.04 to 200/−1 m.   i. charging air and the output of step F 2  a rotary kiln to produce an oxide layer on the exterior surface of the sized silicon carbide particles;   j. charging air and the output from step i into a sixth JHQ plasma furnace and there heating the particulate to above 1816° C. to produce hollow silica sphere;   k. rapidly quenching the hollow silica spheres in a cyclone separator as the particles emerge from the sixth JHQ plasma furnace.   
     
     
         20 . The process of  claim 19 , further comprising operating a sixth JHQ plasma furnace at pressures greater than one atmosphere. 
     
     
         21 . A process according to  claim 19 , wherein the cyclone separator of step c is replaced with a counter current feed system whereby solids enter the respective plasma furnace through the gas exiting the furnace. 
     
     
         22 . The process of  claim 19 , further comprising the use of silicon instead of silicon carbide.