Patent Application
20080016984
a is a schematic side-view of one embodiment of a carbothermic aluminum production system of the present invention.
b is a schematic side-view of the carbothermic production system of
Reference will now be made in detail to the accompanying drawings, which at least assist in illustrating various pertinent embodiments of the present invention.
The depth of the reactor 10 is such that when the reactor 10 is operated, the molten liquid (e.g., molten Al2O3, Al4C3 and mixtures thereof) creates a significant hydrostatic pressure within the reactor as measured proximal the bottom 12 of the reactor. More particularly, the reactor 10 has a depth D such that when the reactor 10 contains molten liquid 60, the hydrostatic pressure created by the molten liquid is at least about 0.5 atm, such as at least about 0.75 atm, or even at least about 1.0 atm. Thus, the total pressure at the bottom of the reactor (hydrostatic pressure+atmospheric pressure) is at least about 1.5 atm, such as at least about 1.75 atm, or even at least about 2 atm. These increased pressures decrease the thermodynamic favorability of the vapor forming reactions, thereby restricting vapor formation with increased aluminum production.
The depth D of the reactor 10 is dependent on the approximate density of the molten liquid within the reactor. For example, the slag produced during carbothermic aluminum production processes generally has a density of about 3.5 g/cm3. To achieve a hydrostatic pressure of about 0.5 atm proximal the bottom 12 of the reactor 10 due to the slag, the reactor should have a depth of at least about 1.48 meters. To achieve a hydrostatic pressure of about 0.75 atm proximal the bottom 12 of the reactor 10 due to the slag, the reactor 10 should have a depth of at least about 2.2 meters. To achieve a hydrostatic pressure of about 1 atm proximal the bottom 12 of the reactor 10 due to the slag, the reactor 10 should have a depth of at least about 2.95 meters.
Despite the foregoing, some aluminum-containing gases will be produced during the carbothermic production operations. In this regard, the system 1 generally includes a vapor recovery unit 30 to recover aluminum in the gases. However, with the present invention, the load on the vapor recovery unit 30 may be substantially decreased, thereby increasing the efficiency of carbothermic aluminum production processes. Suitable vapor recover units are described in, for instance, U.S. Pat. No. 6,530,970 to Lindstad, which is incorporated herein by reference in its entirety.
As noted, the reactor 10 includes a plurality of substantially horizontal heating electrodes 20. The electrodes 20 may be spaced from one another in a vertical and/or a horizontal direction. The heating electrodes 20 may be consumable graphite electrodes or non-consumable inert electrodes. Each of the electrodes 20 is individually supplied with electric current. By using a plurality of electrodes 20 in the sidewall 16 of the reactor 10 and a variable current supply for each of the electrodes 20, a selective temperature profile may be achieved within the reaction chamber. Due to the depth of the reactor 10, the heating electrodes 20 may be spaced at various depths within the reactor 10 to facilitate selective heating of molten liquid. For example, a first set of heating electrodes 20a may be disposed above a second set of electrodes 20b, wherein the first set of electrodes 20a may be operable to heat the molten liquid at a first heating rate and the second set of electrodes may be operable to heat the molten liquid at a second heating rate. The first set of electrodes 20a may be operable to heat the molten liquid to temperatures that facilitate the reduction of aluminum oxide to aluminum carbide (e.g., temperatures of from about 1900° C. to temperature of about 2000° C.), and the second set of electrodes 20b may be operable to heat the molten liquid to temperatures that facilitate the reduction of aluminum carbide to aluminum metal (e.g., temperatures of at least about 2060° C.). Thus, a selective temperature gradient may be achieved within the reactor and molten liquid, thereby increasing the efficiency of carbothermic processes. Moreover, higher heating rates may be achieved proximal the bottom 12 of the reactor 10, where the hydrostatic pressure is high, thereby suppressing aluminum vapor producing reactions that may accompany the reduction of aluminum carbide to aluminum. Any number of heating electrodes 20 may be used to achieve the desired heating rates and heating gradients.
As noted, the system 1 may include a feed tube 40 for feeding supply materials to the reactor 10 (e.g., aluminum oxide and pet coke or aluminum carbide containing feed materials). The feed tube 40 may be fixedly positioned relative to a depth of the reactor, or the feed tube 40 may be selectively positionable to facilitate feeding of supply materials at a desired depth. In one approach, the feed tube 40 is positioned or positionable such that its outlet is proximal the bottom of the reactor to further restrict the aluminum vapor forming reactions as such feed materials will be subjected to increased pressure upon entry to the reactor 10. In the illustrated embodiment, the feed tube 40 is substantially vertically oriented and adapted for vertical movement. In this embodiment, the feed tube 40 extends through the top of the reactor 10 toward the bottom 12 of the reactor 10. A motor or other mechanical means may be utilized to raise or lower the feed tube as necessary to facilitate feeding of the feed material at a desired vertical location within the reaction chamber 18. It is preferred that the feed tube 40 forms a seal with the top 14 so that off-gases do not escape at the interface between the top 14 and the feed tube 40.
In another embodiment (not illustrated), the feed tube may be substantially horizontally oriented and fixedly interconnected to a sidewall of the reactor for feeding of the feed materials. In this embodiment, the sidewall may include a port for receiving the feed tube and the feed tube outlet may extend therethrough. The outlet of the feed tube may terminate proximal the bottom of the reactor. In this regard, the port within the sidewall should be located just above the bottom of the reactor.
The system 1 may include one or more vertically oriented electrodes 22 extending through the top 14 of the reactor 10. The electrodes 22 are generally used in addition to the plurality of horizontally disposed electrodes 20. The electrodes 22 may be consumable graphite electrodes or inert electrodes (e.g., see U.S. Pat. No. 6,818,106, which is incorporated herein by reference in its entirety). During certain phases of operation of the reactor 10, the electrodes 22 pass through the bath and are submerged in the molten liquid to supply energy by resistance heating. For instance, in
The reactor 10 may include a top 14. The top 14 is generally utilized to cover the reactor so as to restrict heat and vapor loss. As may be appreciated, the use of the top 14 will also facilitate a slightly increased vapor pressures within the reactor 10, thereby assisting in suppressing the aluminum vapor producing reactions.
Another carbothermic production system useful in accordance with the present invention is illustrated in
Similar to the batch reactor 10 of
The baffle 117 may be fixedly positioned relative to the reactor, or the baffle 117 may be moveable so as to facilitate selection of a suitable passageway P height. The baffle 117 may be positioned such that its terminal end T terminates proximal the bottom 112 of the reactor 110. Thus, as molten liquid flows from the first zone 113 to the second zone 115, the molten liquid will be subjected to an increased pressure, thereby suppressing aluminum vapor forming reactions. One or more of the horizontally disposed electrodes 22 may be located proximal the second zone 115 side of the passageway P, thus facilitating the reduction of aluminum carbide to aluminum at increased pressures.
The system 100 may also include the feed tube 40, which, may be fixedly positioned or positionable such that its outlet is proximal the bottom 112 of the reactor 110. The feed tube 40 may be utilized on either side of the baffle 117. For example, if the feed material comprises alumina and/or pet coke, the feed tube 40 is utilized in the first zone 113 of the reactor 110, as illustrated. If the feed material comprises aluminum carbide, such as aluminum carbide recovered from the vapor unit 30, the feed tube 40 would be utilized in the second zone 115 of the reactor 110 (not illustrated). As may be appreciated, the feed tube 40 and baffle 117 may be integrated as a unitary structure wherein a single device is utilized to serve as both a baffle and a feed tube.
A computerized program (FACTSAGE, Thermfact/CRCT, Montreal, Canada and GTT-Technologies, Herzogenrath, Germany) was utilized to simulate the effect of increased pressures in the operation of the carbothermic reactor. The results from the simulation are given below in Table 1.
While various embodiments of the present invention have been described in detail, it is apparent that modifications and adaptations of those embodiments will occur to those skilled in the art. However, it is to be expressly understood that such modifications and adaptations are within the spirit and scope of the present invention.
