Method using single furnace carbothermic reduction with temperature control within the furnace

Abstract

A start-up process of making aluminum using a single carbothermic reactor/furnace ( 11 ) having a single hollow reactor compartment with bottom resistance heating electrodes ( 16 ) ( 13 ) in the side of the reactor, involves adding Al 2 O 3 and C (carbon) for start-up and melting the mixture to provide a (Al 2 O 3 —Al 4 C 3 ) slag having a temperature between about 1875° C. and 2000° C.; and then adding Al 4 C 3 to the slag and raising the temperature of the furnace ( 11 ) to form a top Al phase with 6 to 8 wt % C ( 21 ) and a bottom slag phase ( 22 ); and then adding Al 2 O 3 is added to the Al—C/slag ( 21, 22 ) to produce an Al 2 O 3 rich slag lower the reactant temperature and produce a decarbonization reaction (step 30 ) providing a top Al phase with less than 5 wt % C ( 23 ) which is then tapped after step ( 40 ). The remaining slag is the starting material.

1 . A method of using a single carbothermic reactor to produce aluminum with low carbon content, comprising: 
 (a) providing a single furnace having a single hollow, interior reactor compartment with a plurality of bottom resistance heating electrodes in the furnace walls and one or more optional vertical electrodes;    (b) adding Al 2 O 3  and C for start-up of the process to the inside of the furnace and melting their mixture, to provide a (Al 2 O 3 —Al 4 C 3 ) and excess Al 4 C 3  slag having a temperature between about 1875° C. and 2000° C.;    (c) adding Al 4 C 3  to the slag, and raising the temperature of the furnace to form a top Al phase with about 6 wt % to 8 wt % C and a bottom slag phase having a temperature between about 2050° C. and 2100° C.;    (d) adding Al 2 O 3  to the Al—C/slag which Al 2 O 3  addition results in producing an Al 2 O 3  rich slag and in lowering the temperature to between about 1800° C. and 1900° C., to produce a decarbonization reaction within the single reactor compartment, providing a top Al phase with less than <5 wt % C and a bottom (Al 2 O 3  rich-Al 4 C 3 ) slag having a temperature between about 1800° C. and 1900° C.; and    (e) tapping the top Al<5 wt % C phase; and    (f) repeating steps (b) to (e).    
   
   
       2 . The method of  claim 1 , wherein at least one vertical top electrode is used to provide arc heating in step (b).  
   
   
       3 . The method of  claim 1 , wherein, in step (d) addition of Al 2 O 3  changes the slag composition, transferring C from Al to the slag, and where in step (d) the top Al phase has <3 wt % C, which is tapped in step (e).  
   
   
       4 . The method of  claim 1 , wherein off-gas comprising Al 2 O, CO from step (b) and step (c) Al result are fed to a reactor to produce Al 4 C 3  and Al 2 O 3  or Al 4 C 3 —Al 2 O 3  slag which is added to the slag in step (c).  
   
   
       5 . The method of  claim 1 , wherein, in step (d) the top Al phase has <3 wt % C, which is tapped in step (e).  
   
   
       6 . The method of  claim 1 , wherein after step (e) the temperature is increased to from about 1875° C. to 2000° C. and Al 2 O 3  and C are added to begin step (a).  
   
   
       7 . The method of  claim 1 , wherein, in step (d) during decarbonization C is transferred form the Al phase to the slag.  
   
   
       8 . The method of  claim 1 , wherein, Al 2 O, CO, and gaseous Al are passed to an off gas reactor, where C is added to produce solid Al 4 C 3  and Al 2 O 3  and Al 4 C 3 —Al 2 O 3  slag which is returned to the furnace.  
   
   
       9 . The method of  claim 8 , wherein the Al 4 C 3  is returned during step (c).  
   
   
       10 . The method of  claim 1 , wherein the bottom resistance heating electrodes are disposed in the side of the furnace adjacent the bottom slag phase and are of a material selected form the group consisting of carbon, graphite or non-consumable inert anode material comprising ceramic.  
   
   
       11 . The method of  claim 1 , wherein the slag from step (d) is used as a starting material for the next cycle, along with additional Al 2 O 3  and C.