Patent Application
20090139371
Aluminum metal is generally manufactured by two techniques: the traditional Hall method, where an electric current is passed between two electrodes to electrolytically reduce alumina to aluminum metal; and the carbothermic method, where aluminum oxide is chemically reduced to aluminum via chemical reaction with carbon. The overall aluminum carbothermic reduction reaction:
Al2O3+3C→2Al+3CO (1)
takes place, or can be made to take place, via a series of chemical reactions, such as:
2Al2O3+9C→Al4C3+6CO(vapor) (2)
Al4C3+Al2O3→6Al+3CO(vapor) (3)
Al2O3+2C→Al2O(vapor)+2CO(vapor) (4)
Al2O3+4Al→3Al2O(vapor) (5)
Al→Al(vapor) (6)
Reaction (2), generally known as the slag producing step, often takes place at temperatures between 1875° C. and 2000° C. Reaction (3), generally known as the aluminum producing step, often takes place at temperatures above about 2050° C. Aluminum vapor species may be formed during reactions (2) and (3), although aluminum vapor species may be formed via reactions (4), (5), and (6).
Broadly, the instant disclosure relates to systems and methods for carbothermically producing aluminum. The systems and methods may employ a top-entering electrode and a plurality of side-entering electrodes. Alternating current may be utilized in conjunction with the electrodes, which may facilitate efficient production of aluminum.
According to one aspect of the disclosure, a system for carbothermically producing aluminum is provided, the system including a carbothermic reactor and an electrical supply. The carbothermic reactor comprises a chamber adapted to contain a molten bath, the chamber being at least partially defined by an outer shell and a floor of the carbothermic aluminum production reactor. A set of side-entering electrodes penetrate the outer shell and are in communication with the chamber. A single top-entering electrode is in communication with the chamber, and the top-entering electrode is moveable in the up-down directions. In one embodiment, a cover that substantially covers the chamber is utilized. The cover includes a first port for receiving the single top-entering electrode. In one embodiment, the cover includes at least one additional port for receiving feedstock to be fed to the chamber.
The electrical supply is in electrical communication with the set of side-entering electrodes. In one approach, the electrical supply includes an electrical generator adapted to supply a different voltage phase to each electrode of the set of side-entering electrodes. In one approach, the electrical supply is adapted to impose phase shifting with respect to each electrode of the set of electrodes. In one embodiment the electrical supply is operable to supply an equal amount of each voltage phase to each electrode. In one embodiment the electrical supply is operable to supply an adjustable amount of each voltage phase to each electrode. In one embodiment, when the top-entering electrode is in a first position, and during operation of the reactor, at least some current from the electrical supply passes through the molten bath in delta configuration. In one embodiment, when the top-entering electrode is in a second position, and during operation of the reactor, at least some current passes through the molten bath in a Wye configuration.
The reactor may include an inner wall interconnected with the cover and extending toward the floor of the reactor. In one embodiment, the inner wall at least partially circumscribes a portion of the top-entering electrode. In another embodiment, the inner wall completely circumscribes a portion of the top-entering electrode. In one embodiment, the inner wall is interconnected with a cooling supply system. In one embodiment, the inner wall includes at least one passageway adapted to flow a coolant therethrough. In one embodiment, the inner wall comprises at least one aperture that completely penetrates the wall, and the at least one aperture is in fluid communication with the at least one additional port of the cover, thereby facilitating passage of off-gas from the chamber to the at least one additional port during operation of the reactor.
In one approach, a feeder is fluidly interconnected with the at least one additional port. The feeder may be operable to feed feedstock to the reactor via the at least one additional port, thereby facilitating interaction between off-gas exiting the reactor and feedstock entering the reactor. In one embodiment, the feeder comprises a moveable member located proximal the at least one additional port. The moveable member may be operable to push the feedstock into the at least one additional port. In one embodiment, the feeder comprises a heater for preheating the feed materials prior to supply to the reactor. In one embodiment, the feeder comprises a hopper.
In one approach, a plurality of electrode sets are utilized. In one embodiment, the system includes a first set of electrodes and a second set of electrodes. The relative heights and/or spacing of the electrodes may be varied, between sets or within sets. In one embodiment, the first set of electrodes is aligned with a first horizontal plane, and the second set of electrodes is aligned with a second horizontal plane. In one embodiment, the first horizontal plane is different than the second horizontal plane. In one embodiment, the electrodes are spaced equidistance about the perimeter of outer shell of the reactor. The electrical system may be configured to operate each set of electrodes independently.
Methods of operating carbothermic aluminum production reactors are also provided. In one aspect, the method includes the steps of generating a molten bath and off-gas within the carbothermic reactor, supplying feedstock to the carbothermic production reactor via a feedstock supply path, flowing off-gas into the feedstock supply path, and removing at least a portion of the aluminum species from the off-gas phase via interaction of the off-gas and the feedstock. The molten bath may include at least one of aluminum metal, aluminum carbide and slag. The off-gas may include aluminum vapor species and carbon monoxide. The feedstock supply path may be defined by a port in a cover of the carbothermic aluminum production reactor, a top-entering electrode communicable with the molten bath, and an inner wall circumscribing the top-entering electrode.
In one approach, the molten bath is generated/maintained by flowing multiphase current therethrough. In one embodiment, the molten bath is generated/maintained by passing multiphase current between a plurality of side-entering electrodes in communication with the molten bath. In one embodiment, the molten bath is generated/maintained by flowing alternating current from at least one of the side-entering electrodes to the top-entering electrode. In one embodiment, the method includes positioning the top-entering electrode in a first vertical position, where a first amount of alternating current may flow into to the top-entering electrode. In turn, the method may include moving, concomitant to the generating step, the top-entering to a second vertical position, where a second amount of alternating current may flow to the top-entering electrode.
In one approach, the supplying feedstock step comprises pre-conditioning the feedstock prior to supplying the feedstock to the molten bath. In one embodiment, the supplying step includes pre-heating the feedstock in a pre-heating zone located external to the feedstock supply path. For example, the feedstock may be heated to a temperature of at least about 100° C. prior to entering the feedstock supply path, such as via the above-described feeder. The feedstock may also be heated/conditioned while the feedstock is in the reactor, but before the feedstock is supplied to the molten bath (e.g., via the feedstock supply path). In one embodiment, the method includes heating the feedstock to a temperature of at least about 600° C. while the feedstock is located within the feedstock supply path. In one embodiment, the method includes heating the feedstock to a temperature below the melting point of the feedstock materials (e.g., not greater than about 1900° C.) while the feedstock is located within the feedstock supply path. In one embodiment, aluminum oxide and a carbonaceous material of the feedstock may react to create aluminum carbide while the feedstock is located within the feedstock supply path.
As noted, the method may include generating off-gas during operation of the reactor. In one embodiment, the method includes generating a first portion of off-gas outside the perimeter of the inner wall that circumscribes a portion of the top-entering electrode. In turn, the method may include flowing at least some of the first portion of the off-gas into the feedstock supply path via an aperture located in the inner wall.
As noted, the method may include removing at least some aluminum species from the generated off-gas. In one embodiment, the removing step includes reacting at least some aluminum species with carbonaceous material of the feedstock. In a related embodiment, the removing step includes condensing at least some aluminum species on a surface of the feedstock. In one approach, the method includes cooling the inner wall via an external coolant supply, such as via flowing coolant through at least one passageway located within the inner wall. In turn, the removing aluminum-containing vapors step may include condensing aluminum vapor species on a surface of the inner wall.
As may be appreciated, various ones of the inventive aspects noted hereinabove may be combined to yield various carbothermic reactors and associated systems. These and other aspects, advantages, and novel features of the disclosure are set forth in part in the description that follows and will become apparent to those skilled in the art upon examination of the following description and figures, or may be learned by practicing the disclosure.
a is a flow diagram illustrating one embodiment of a method for operating a carbothermic reactor.
b is a flow diagram illustrating one embodiment of a method for operating a carbothermic reactor.
c is a flow diagram illustrating one embodiment of a method for operating a carbothermic reactor.
d is a flow diagram illustrating one embodiment of a method for operating a carbothermic reactor.
Reference will now be made in detail to the accompanying drawings, which at least assist in illustrating various pertinent embodiments of the present disclosure.
In operation, multiphase current from an electrical supply (not illustrated) may be supplied to the electrodes 12, 13 and passed through the molten bath 16 to produce aluminum metal. In particular, multiphase current may be utilized to resistively heat the molten bath 16 to temperatures within the range of from about 1875° C. to about 2200° C. to facilitate production of aluminum metal. In one embodiment, the reactor 1 may be operated within the temperature range of from about 1875° C. to 2000° C. to produce aluminum-carbide and aluminum-carbide containing slag. The reactor 1 may be operated within the temperature range of from about 2050° C. to 2200° C. to produce aluminum metal from the aluminum-carbide and aluminum-carbide containing slag. The reactor 1 may be operated within the temperature range of from about 1900° C. to 1950° C. to extract carbon from the produced aluminum metal. Various off-gas and various species (e.g., Al2O, Al, CO) may be produced during operation of the reactor 1.
In one mode of operation, multiphase current is passed through the molten bath 16 in a delta configuration. As illustrated in
In the illustrated embodiment, a third set of electrodes 32 and a fourth set of electrodes 33 are included with the reactor 1, the third set of electrodes 32 being horizontally aligned with the first set of electrodes 12, and the fourth set of electrodes 33 being horizontally aligned with the second set of electrodes 13. One or more of these electrode sets 33, 34, and/or additional sets of electrodes, may optionally be utilized to further facilitate electrical current distribution in the molten bath 16, thereby facilitating more uniform and efficient heating of the molten bath 16. Moreover, various electrode sets may be aligned in horizontal and/or vertical directions to facilitate varying current distribution through the molten bath 16.
In the illustrated embodiments, three electrodes per set are utilized, and the electrodes are equally spaced about the perimeter of the reactor 1. In turn, three differing voltage phases may be supplied to each electrode of the set of electrodes. Phase shifting may also be employed. Other configurations may also be utilized. For instance, six electrodes per set may be utilized and six differing voltage phases may be supplied to each electrode of the set of electrodes. The amount of electrodes per set is generally application dependent. Each set of electrodes may be operated independently of the other sets of electrodes.
In the illustrated embodiment, a plurality of side entering electrode sets are employed. However a single set of side entering electrodes may be employed.
As noted, the electrodes may be arranged in any suitable manner to facilitate operation of the carbothermic reactor. In the illustrated embodiment of
Use of multiphase current in conjunction with the side-entering electrodes 12, 13 provides advantages over previous carbothermic reactor designs. For example, the use of multiphase current, as opposed to direct current, allows utilization of higher current loads within the reactor 1, which facilitates higher wattage intensities. In turn, fewer electrodes may be required for a given reactor size, thereby reducing capital costs and complexity of the reactor.
The amount of current provided to the reactor 1 may also be tailored relative to the particular processing step. For example, a plurality of the sets of side-entering electrodes (e.g., 12, 13, 32, and/or 33) may be utilized during start-up of the reactor 1. If the reactor is operated in batch mode (e.g., production of aluminum-carbide and slag, followed by production of metal, optionally followed by carbon extraction from the aluminum metal, followed by removal of the aluminum metal from the reactor), during slag making, multiple sets of the side-entering electrodes may be utilized to further facilitate uniform production of aluminum carbide within the molten bath 16. Alternatively, lower and/or middle oriented sets of side-entering electrodes may be predominantly utilized during operations so as to lower the amount of current passed through, and hence lower the temperature of, the upper portion of the molten bath 16. In turn, lower vapor production rates may be realized. Similarly, multiple sets of side-entering electrodes may be utilized during metal making to facilitate temperatures suitable for reduction of aluminum carbide to aluminum metal and carbon, but, as with slag making, lower and/or middle oriented sets of side-entering electrodes may be predominantly utilized so as to control heating of the upper portion of the molten bath 16. Likewise, multiple sets of side-entering electrodes may be utilized during carbon extraction to facilitate temperatures suitable for extraction of carbon from the metal phase to the slag phase, but, as with slag and metal making, lower and/or middle oriented sets of side-entering electrodes may be predominantly utilized so as to control heating of the upper portion of the molten bath 16. Middle and/or upper side-entering electrodes may be intermittently utilized during these steps to achieve desired temperatures and/or temperature gradients within the molten bath 16. If the reactor 1 is operating in a continuous mode, discussed in further detail below, one or more sets of the side-entering electrodes may be operated as appropriate to achieve the desired conditions within the reactor. Hence, use of a plurality of sets of side-entering electrodes and multiphase current facilitates tailored operation of the reactor so as to create the desired temperature and/or temperature gradients within the molten bath.
Electromagnetic stirring of the molten bath 16 may also be facilitated. In one approach, a first set of electrodes may flow current through the bath in a first path (e.g., clockwise). In turn, a second set of electrodes may flow current through the bath coincidental to the first path (e.g., similarly clockwise) or in a different path (e.g., counterclockwise). Due to the electromagnetic effects of supplying alternating current via differing electrodes, tailored stirring of the molten bath may be facilitated. In one approach, stirring of the molten bath is effected via cooperative current flow paths. In a related approach, motion of the molten bath (e.g., agitation, stirring) may be reduced by non-cooperative current flow paths that are countercurrent to the direction of flow of the molten bath via one or more of the set(s) of side-entering electrodes. Thus, tailored molten bath mixing intensities and flow directions may be achieved.
Multiphase current may be supplied to the side-entering electrodes 12, 13 and/or top-entering electrode 14 to facilitate production of the molten bath 16, such as heating the molten bath 16 to appropriate temperatures. Electrical current generally flows through the molten bath 16 in the delta configurations of
The top-entering electrode 14 may be used to facilitate start-up of the reactor 1. In particular, the top-entering electrode may be moved in the up-down directions to facilitate mechanical massaging of the charge. The top-entering electrode may also be positioned to receive electrical current from one or more side-entering electrodes, thereby allowing current to flow through the start-up charge (e.g., alumina and/or carbon starting materials) of the reactor 1 in various directions and provide more uniform heating. In one embodiment, the resultant electrical flow can shift from a delta resistive load to a Wye/delta combination. The closer the tip of the top-entering electrode is to the floor 15, the more the load shifts toward a Wye resistive load, which generates more heat at the top-entering electrode. In addition, the phase currents can be adjusted to facilitate additional current flow through the top-entering electrode. In one embodiment, the tip of the top-entering electrode may be resistively heated via receipt of the current, which may further assist in heating the start-up charge. When the charge reaches a suitable temperature, the top-entering electrode may be moved to another position (e.g., higher relative to the bath, or removed from the bath). The up-down movement functionality of the top-entering electrode 14 may be utilized concomitant with the electrical receipt functionality of the top-entering electrode 14. Thus, the top-entering electrode 14 may physically massage the initial charge/molten bath 16 while facilitating current flow therethrough.
One embodiment of an electrical supply for facilitating current supply/distribution is illustrated in
Aside from the current distribution benefits of using a top-entering electrode, other advantages may also be realized. For instance, since the top-entering electrode 14 is moveable in the up-down directions (e.g., via exterior mechanical means), the top-entering electrode 14 may be used to further facilitate mixing of the molten bath 16 due to its physical interaction with the molten bath 16. In one embodiment, the top-entering electrode 14 may be submerged in the molten bath 16, thereby displacing and raising the level of the molten bath 16 within the reactor 1, such as during tapping operations. In this embodiment, a metal exit (not illustrated) may be disposed within an upper portion of the outer shell 10. When the level of the molten bath 16 raises (e.g., via submersion of the top-entering electrode 14), molten metal disposed near the top of the molten bath 16 may flow out of the reactor 1 via the metal exit.
Referring back to
The reactor 1 may also include an inner wall 26 that at least partially circumscribes, and often completely circumscribes, a portion of the top-entering electrode 14, thereby providing an annular space between an outer surface of top-entering electrode 14 and the inner wall 26. The inner wall 26 may be interconnected with the cover 18 and may extend towards the floor 15 of the reactor 1. The inner wall may extend a distance such that a bottom portion of the inner wall 26 is submerged in the molten bath 16. Thus, the inner wall 26 may at least partially segregate the top-entering electrode 14 from molten aluminum metal phase 2 produced during operation of the reactor 1. In turn, reduced current flow to the aluminum metal phase 2 may be realized, thereby restricting production of off-gas G during operation of the reactor 1. More aluminum metal may thus be produced during operations without short circuiting. In one embodiment, continuous metal production is facilitated via an overflow methodology, wherein feedstock 22 is continuously supplied to the reactor 1, aluminum carbide and slag phase 3 and aluminum metal phase 2 are continuously produced therefrom, via the above-described reactions, and the produced aluminum metal flows out of the reactor 1 via a metal exit (not illustrated) located in an upper portion of the outer shell 10. In this regard, lower/middle electrodes may be operated at a first wattage to heat the lower/middle portions of the aluminum carbide-slag 3 to appropriate slag making temperatures, while middle/upper electrodes may be operated at a second wattage to heat the middle/upper portions of the aluminum carbide-slag to appropriate metal making temperatures.
In one embodiment, a cooling system (not illustrated) may be fluidly interconnected with the inner wall 26 to cool the inner wall 26 so as to further restrict production of off-gas G in contact therewith. In particular, passageways, or other suitable apparatus (not illustrated), may be included within the inner wall 26 to facilitate flow of coolant therethrough. Such passageways or other apparatus may be disposed proximal the outer perimeter OP of the inner wall 26 (e.g., away from inner perimeter IP) so as to facilitate cooling of the molten aluminum metal phase with restricted cooling of feedstock 22 located proximal the inner perimeter IP of the inner wall 26.
The inner wall 26, port 21 and outer surface of the top-entering electrode 14 may define a feedstock supply path for supplying feedstock 22 to the molten bath 16 of the reactor 1. Thus, the feedstock supply path may be changeable (e.g., via movement of the top-entering electrode 14), and its length may be tailored to fit its application. The feedstock supply path may be segregated from at least a portion of the molten aluminum metal via the inner wall 26. In turn, restricted interaction between the feedstock 22 and aluminum metal phase 2 may be realized, thereby decreasing the amount of aluminum metal that, due to thermodynamics, returns to aluminum carbide. Hence, increased metal production efficiency may be realized. The top-entering electrode 14 may be moved in the up-down directions to massage feedstock 22 in the feedstock supply path to restrict agglomeration of the feedstock 22 and bridging of the feedstock 22. Use of the feedstock supply path is also useful in that the feedstock 22 in the feedstock supply path provides a place for in-situ heating of the feedstock 22 and may reduce radiant heat losses to the cover 18, thereby providing further reactor operating efficiencies.
As illustrated in
Off-gas G may be in fluid communication with at least a portion of the feedstock supply path. Thus, off-gas G generated during operation of the reactor 1 may flow into the feedstock supply path and may interact with feedstock 22 contained therein. In particular, aluminum species (e.g., Al2O, Al) of the off-gas may physically interact with the feedstock 22, such as via condensation on the surface of the feedstock 22, thereby removing at least a portion of the aluminum species from the off-gas G. The aluminum species may also chemically interact with the feedstock 22, such as reaction with carbonaceous materials to produce aluminum carbide/slag, thereby removing at least a portion of the aluminum species from the off-gas G. Aluminum species of the off-gas G may also condense on the outer perimeter OP of the inner wall 26. In turn, inefficiencies due to aluminum vapor losses may be reduced.
As illustrated, the top-entering electrode 14 is of a cylindrical construction. In other embodiments, other configurations may be utilized (e.g., rectangular-solid). In a particular embodiment (not illustrated), the top-entering electrode is tubular. In this embodiment, electrical current may pass through the solid portion of the tubular top-entering electrode, and feedstock 22 may pass into the reactor 1 via the hollow inner portion of the tubular top-entering electrode. In this embodiment, the diameter of the tube could be tailored so as to achieve a desired feed rate of feedstock 22 to the reactor 1. Feedstock exiting the tip of the tubular top-entering electrode may thus be pre-heated and may readily liquefy upon entering the molten bath 16.
Methods of operating a carbothermic aluminum production reactor are also provided, one embodiment of which is illustrated in
As illustrated in
As noted, the method may include the step of supplying feedstock to the carbothermic reactor via a feedstock supply path. The feedstock supply path may be at least partially defined by a port of a cover of the carbothermic reactor, a top-entering electrode communicable with the molten bath, and an inner wall circumscribing the top-entering electrode. As illustrated in
As illustrated in
The step of removing aluminum species from the off-gas (840) may be accomplished in various manners. In one embodiment, at least some of the aluminum species are reacted with carbonaceous material in the feedstock (842), thereby producing recyclable material (e.g., aluminum carbide, slag) for resupply to the carbothermic reactor. In another embodiment, at least some of the aluminum species may be condensed on a surface of the feedstock (844). Hence, aluminum vapor losses may be restricted.
While various embodiments of the present disclosure 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 disclosure.
