Method and system for producing low carbon ferroalloy from chromite ore

A method of producing a metal or metal alloy from feed materials located within a chamber in a plasma arc furnace, said feed materials comprising aluminum granules and chromite ore, said method comprising:

• providing three individual and electrically isolated DC arc graphite cathode electrodes in said furnace above said feed materials in said chamber;
• providing a controlled and controllable constant DC output current to each of said electrically isolated DC arc graphite cathode electrodes from plasma power supplies to initiate a respective plasma arc from each of said DC arc graphite cathode electrodes to heat said feed materials in said chamber to produce a molten material bath in said chamber;
• individually establishing the height of each of said DC arc graphite cathode electrodes with respect to said feed materials until a desired voltage is established to produce said molten material bath in said chamber, said voltage varying as a function of the sum of the resistance of the plasma arc above said molten bath, and the resistance of the plasma arc in said molten material bath;
• and
• stirring of said molten material bath, said stirring resulting from current flowing through said molten material bath producing Joule heating coupled with a magnetic effect of current flow through said molten bath to cause a local ripple effect or stirring motion in said molten material bath.

A system for recovering a high yield of a low carbon ferroalloy from chromite ore, said system comprising:

• a blender configured for receiving chromite ore and aluminum granules, said chromite ore including chromium oxide and an iron oxide;
• a plasma arc furnace, comprising an internal chamber, a plurality of graphite plasma transferred arc cathode electrodes, a plurality of anode electrodes, and a plurality of individually controlled DC power supplies, said plurality of graphite plasma transferred arc cathode electrodes extending into said internal chamber from above said internal chamber, said plural anode electrodes extending into said internal chamber from below said internal chamber, said chamber having a first outlet port and a second outlet port, said plurality of individually controlled DC power supplies being connected to said plurality of graphite plasma transferred arc cathode electrodes and configured for applying DC power to said plurality of graphite plasma transferred arc cathode electrodes to cause said plurality of graphite plasma transferred arc cathode electrodes to arc and heat said internal chamber;
• and
• a feed hopper configured to feed said chromite, lime and aluminum granules to said internal chamber at a controlled rate with said internal chamber being heated to a temperature in the range of approximately 1,650° C. to 1850° C., whereupon said aluminum granules act as a reducing agent to produce an exothermic reaction reducing oxygen in said chromium oxide and said iron oxide to produce a bath of a molten low carbon ferroalloy with molten slag floating on top of said molten low carbon ferroalloy within said internal chamber, said first outlet port being configured to receive said molten low carbon ferroalloy, whereupon said molten low carbon ferroalloy flows out of said first outlet, said second outlet port being configured to receive said molten slag, whereupon said molten slag flows out of said second outlet.

A system for producing a metal or metal alloy from feed materials, the feed materials comprising aluminum granules and chromite ore, the chromite ore including chromium oxide and an iron oxide, said system comprising:

• a plasma arc furnace comprising:
• an internal chamber for receipt of the feed materials;
• a plurality of anode electrodes;
• a plurality of individual electrically isolated DC arc graphite cathode electrodes;
• a plurality of individually controlled DC power supplies connected to said plural individual electrically isolated DC arc graphite cathode electrodes for applying a controlled and controllable constant DC output current to each of said electrically isolated DC arc graphite cathode electrodes to initiate a respective plasma arc from each of said DC arc graphite cathode electrodes to heat said internal chamber to a temperature in the range of approximately 1,650° C. to 1850° C., wherein said aluminum granules act as a reducing agent to produce an exothermic reaction reducing said chromium oxide and iron oxide in said chromite ore to produce a molten bath of molten low carbon ferroalloy with molten slag floating on top of said molten low carbon ferroalloy, said plurality of anode electrodes extending into said internal chamber from below said internal chamber, said plurality of individual electrically isolated DC arc graphite cathode electrodes extending into said internal chamber from above said internal chamber and being adjustable in height so that the height of each of said DC arc graphite cathode electrodes with respect to said feed materials can be adjusted until a desired voltage is established to produce said molten bath in said internal chamber and stirring of said molten bath, said voltage varying as a function of the sum of the resistance of a plasma arc produced above said molten bath, and the resistance of the plasma arc in said molten bath, said stirring resulting from current flowing through said molten bath producing joule heating coupled with a magnetic effect of current flow through said molten bath to cause a local ripple effect or stirring motion in said molten bath;
• a first outlet port in communication with said internal chamber;
• and
• a second outlet port in communication with said internal chamber.