Fracture resistant electrodes for a carbothermic reduction furnace

Abstract

Graphite electrodes for the production of aluminum by carbothermic reduction of alumina are either submerged in the molten bath in the low temperature compartment or they are horizontally arranged in the side walls of the high temperature compartment. The electrodes are manufactured by using a mixture of coke particles covering the complete particle size range between 25 μm to 3 mm and by using an intensive mixer to effectively wet all coke particles with pitch. The electrodes have a flexural strength of at least 20 N / mm2. By using a complete range (continuum) of particle sizes in conjunction with an intensive mixer, the geometric packing of the particles is significantly improved, hence the material density is increased and thus a higher mechanical strength as well as improved electrical conductivity in comparison to conventional graphite electrodes is achieved.

Description

CROSS-REFERENCE TO RELATED APPLICATION [0001] This application claims the benefit under 35 U.S.C. § 119 (e), of copending U.S. Provisional Application No. 60 / 571,755, filed May 17, 2004.BACKGROUND OF THE INVENTION [0002] 1. Field of the Invention [0003] The present invention relates to graphite electrodes for the production of aluminum by carbothermic reduction of alumina. [0004] 2. Description of the Related Art [0005] For a century the aluminum industry has relied on the Hall-Heroult process for aluminum smelting. In comparison with processes used to produce competing materials, such as steel and plastics, the process is energy-intensive and costly. Hence, alternative aluminum production processes have been sought. [0006] One such alternative is the process referred to as direct carbothermic reduction of alumina. As described in U.S. Pat. No. 2,974,032 (Grunert et al.) the process, which can be summarized with the overall reaction Al2O3+3 C=2 Al+3 CO   (1) takes place, or can be ...

AI Technical Summary

Benefits of technology

[0032] In other words, the present invention provides for graphite electrodes for the production of aluminum by carbothermic reduction of alumina, more particularly to the graphite electrodes submerged into the molten bath in the low temperature compartment as well as to the electrodes horizontally arranged in the side walls of the high temperature compartment. The electrodes of this invention are manufactured by using a mixture of coke particles covering the complete particle size range between 25 μm to 3 mm and by using an intensive mixer to effectively wet all coke particles with pitch and said electrodes having a flexural strength of at least 20 N / mm2.

[0033] By using a complete range (continuum) of particle sizes in conjunction with an intensive mixer, the geometric packing of the particles is significantly improved, hence the material density is increased and thus a higher mechanical strength as well as improved electrical conductivity in comparison to conventional graphite electrodes is achieved.

Problems solved by technology

In comparison with processes used to produce competing materials, such as steel and plastics, the process is energy-intensive and costly.

Unless recovered, these volatile species represent a loss in the yield of aluminum.

The technical as well as economical requirements to establish and run such grinding, milling and sieving equipment are quite substantial, yet they are not in any case offset by the high quality properties of the finished graphite products.

In the context of the production of aluminum by carbothermic reduction, the requirements to the mechanical strength of the graphite electrodes submerged into the molten bath in the low temperature compartment and even more so to the electrodes horizontally arranged in the side walls of the high temperature compartment are challenging because the relatively long electrodes have to sustain the partially extensive movements of the molten bath which furthermore contains solid particles of carbon and slag a well as gas bubbles, all contributing to a mechanically demanding environment.