Patent Application
20090236233
Aluminum is generally produced via the Hall process, which entails passing current through an electrolytic bath comprising alumina and cryolite to reduce the alumina to aluminum metal. An electrolysis cell generally holds the electrolytic bath and includes a plurality of anodes that pass current through the bath to a cathode. Conventional anodes are made of carbon and are thus consumed during the electrolysis process. Efforts have been made to utilize non-consumable anodes for use in electrolysis cells. Such anodes are typically metal or metal-oxide based and are referred to as “inert anodes” since they are both dimensionally stable, compared to carbon anodes, and electrically conductive at normal electrolysis temperatures.
Broadly, the instant disclosure relates to systems and methods for containing the electrolytic bath within an aluminum electrolysis cell. During conventional aluminum production processes, a crust generally develops over the electrolytic bath. Crust that develops on the sidewall is called a ledge. The ledge may protect the sidewall and may prevent the electrolytic bath from leaking out of the cell via cracks between sidewall members. Maintenance of the ledge results in significant heat loss, and attempts to insulate the system to conserve this heat loss generally result in loss of the ledge (e.g., via melting). Thus, it is desirable to eliminate reliance on the ledge for bath containment purposes, especially with the use of inert anodes, which may facilitate operation of electrolysis cells at lower temperatures.
In one approach, an aluminum electrolysis cell is provided. The aluminum electrolysis cell may include an outer shell, a bottom (e.g., a cathode), and a plurality of bath resistant blocks defining a surrounding wall. The bottom and the plurality of bath resistant blocks may define a chamber adapted for holding a molten salt electrolyte. The cell may further include at least one spring member coupled to at least one of the plurality of bath resistant blocks and the outer shell. In one embodiment, a spring member is maintained at least some of the bath resistant blocks in a substantially leak-tight configuration. For example, a spring-member may be used to accommodate the differential expansion that may be realized between one or more bath resistant blocks and the steel shell as a result of differential coefficients of thermal expansion. In one embodiment, a spring member is adapted to expand and/or contract during operation of the aluminum electrolysis cell. In one embodiment, the plurality of bath resistant blocks includes a corner block, and at least one spring member is coupled to the corner block (e.g., via the outer shell).
In one embodiment, the plurality of bath resistant blocks includes both corner blocks and side blocks, where at least one corner block is located between adjacent side blocks. In one embodiment, a first set of side blocks defines a first inner sidewall. In a related embodiment, a second set of side blocks defines a second inner sidewall. In one embodiment, the first sidewall is parallel the second sidewall. In one embodiment, the first sidewall is transverse (e.g., orthogonal) the second sidewall. In one embodiment, a corner block joins the first sidewall to the second sidewall.
In one embodiment, at least some of the plurality of bath resistant blocks define an inner row and an outer row. In one embodiment, a spring member assists in maintaining the inner row in a substantially leak-tight configuration. In one embodiment, a spring member assists in maintaining the outer row in a substantially leak-tight configuration. In one embodiment, at least some of the plurality of bath resistant blocks define an upper row and a lower row. In one embodiment, a spring member assists in maintaining the upper row in a substantially leak-tight configuration. In one embodiment, a spring member assists in maintaining the lower row in a substantially leak-tight configuration.
In one embodiment, at least two spring members are coupled to a corner block and the outer shell. In one embodiment, the spring members are restrictively coupled to the outer shell (e.g., via mechanical restraints, such as bolts). In one embodiment, the spring members are coupled to the corner block via simple physical contact (e.g., not via mechanical restraints). The physical contact may be facilitated, for example, via a head of the spring member, which is interconnected to a spring. Thus, the spring members may remain coupled to the corner block over various operating temperatures, and may expand and/or contract, as necessary to maintain physical contact with the corner block. In one embodiment, a corner block may include a first surface and a second surface. In one embodiment, a first spring member is coupled to the first surface of the corner block, and a second spring member is coupled to the second surface of the corner block. Thus, application of a responsive force in at least two directions may be facilitated. In one embodiment, an axis of the first surface of the corner block is transverse (e.g., non-parallel to, such as orthogonal to) an axis of the second surface of the corner block.
Methods of operating aluminum electrolysis cells are also provided. In one embodiment, a method includes the steps of passing electricity through a molten salt electrolyte comprising alumina via an anode and cathode of an electrolysis cell, maintaining a plurality of bath resistant blocks in a substantially leak-tight configuration, thereby at least assisting in containing the molten salt electrolyte within the electrolysis cell, and producing alumina in the electrolysis cell in the absence of a ledge. In one embodiment, the maintaining step includes the step of applying a force to at least one of the plurality of blocks via a spring member. In one embodiment, during the maintaining step, the spring member is responsive to fluctuating operating conditions of the electrolysis cell.
These and other aspects, advantages, and novel features of the invention 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 invention.
a is a top, schematic view illustrating one embodiment of an aluminum electrolysis in accordance with the instant disclosure.
b is a side, cross-sectional view of the aluminum electrolysis of
a is a top, view illustrating one embodiment of a corner of an aluminum electrolysis cell.
b is a side, cross-sectional view of the corner of
Reference is now made to the accompanying drawings, which at least assist in illustrating various pertinent features of the instant disclosure.
As noted above, the instant disclosure relates to systems and methods for containing an electrolytic bath in an aluminum electrolysis cell in the absence of a ledge. Conventional aluminum electrolysis cells generally include anodes, a cathode and a plurality of blocks. The arrangement of the plurality of blocks defines a sidewall. During conventional aluminum production processes, a crust generally develops over the electrolytic bath. Crust that develops on the sidewall is often referred to as a ledge. The ledge may protect the sidewall and may prevent the electrolytic bath from leaking out of the cell via cracks between the blocks.
One embodiment of a conventional aluminum electrolysis cell is illustrated in
It may be useful to operate an aluminum electrolysis cell in the absence of a ledge. In such an embodiment, it is important that the sidewall have a leak-tight configuration. In this regard, improved aluminum electrolysis cells are disclosed herein. One embodiment of an aluminum electrolysis in accordance with the instant disclosure is illustrated in
As used herein, “ledge” means a solid phase form of the salt electrolyte that is generally located between the molten salt electrolyte (also sometimes referred to as “bath”) and one or more portions of the inner sidewall of an aluminum electrolysis cell. In this regard, the ledge is sometimes referred to as “frozen electrolyte”. As used herein, “molten salt electrolyte” means an electrolyte comprising alumina (Al2O3) and cryolite (Na3AlF6), and which is in a liquid/molten phase. The aluminum may be in dissolved form. The molten salt electrolyte may include other additives. As used herein, “spring member” means any apparatus capable of applying a force to at least one of the plurality of blocks to at least assist in maintaining at least some of the blocks in a substantially leak-tight configuration.
In one embodiment, the cell 2 is operated in the absence of a ledge and produces aluminum at commercial viable rates (e.g., from about 100,000 to 300,000 amperes and at a current efficiency of at least about 90%]. In one embodiment, the cell 2 produces commercial purity aluminum. As used herein, “commercial purity aluminum” means aluminum produced by an electrolytic process that meets generally accepted commercial purity standards. In one embodiment, the commercial purity aluminum includes not greater than of 0.2 wt. % Fe, such as not greater than 0.15 wt. % Fe, or even not greater than 0.13 wt. % Fe. In one embodiment, the commercial purity aluminum includes not greater than 0.1 wt. % Cu, such as not greater than 0.034 wt. % Cu, or even not greater than 0.03 wt. % Cu. In one embodiment, the commercial purity aluminum includes not greater than 0.034 wt. % Ni, such as not greater than 0.03 wt. % Ni. In one embodiment, the commercial purity aluminum includes not greater than 0.2 wt. % Si, such as not greater than 0.15 wt. % Si, or even not greater than 0.10 wt. % Si. In one embodiment, the commercial purity aluminum includes a not greater than 0.03 wt. % Zn and/or and not greater than 0.03 wt. % Co. In one embodiment, the cell 2 is operated in the absence of a ledge and at reduced temperatures relative to conventional electrolysis cells. In one embodiment, the temperature of the molten salt electrolyte is not greater than 900° C., such as from about 700° C. to 900° C.
In the illustrated embodiment, the inner blocks 40 are in the form of rows, but may be configured in any suitable orientation (e.g., elliptical/circular). The outer blocks 50 may be used to support the inner blocks 40 and are generally configured coincidental to the configuration of the inner blocks 40. In the illustrated embodiment, the cell 2 includes first and second layers of blocks 40, 50, respectively. In other embodiments, an electrolysis cell 2 may include only a single layer of blocks. In other embodiments, an electrolysis cell 2 may include more than two layers of blocks. In one embodiment, each corner block 30 is located between adjacent rows of inner blocks 40. That is, a first row of inner blocks 40 may be adjoined to another row of inner blocks 40 via a corner block 30.
The bath resistant blocks 30, 40, 50 generally comprise materials that are suited for use in the electrolysis cell 2. In one approach, at least some of the blocks 30, 40, and/or 50 comprise a material that is resistant to degradation when exposed to the bath of the electrolysis cell 2 (the bath generally comprising alumina, cryolite, and metal aluminum). In one embodiment, at least some of the bath resistant blocks comprise a refractory material. In one embodiment, at least some of the blocks comprise metal oxides and/or metal nitrides. In one embodiment, at least some of the bath resistant blocks comprise graphite.
The cell 2 generally includes at least one anode assembly, but may include many anode assemblies, such as the plurality of anode assemblies 80 illustrated in
The inert anodes 81 are fastened to conductors 82 (e.g., metal conductors rods) which may pass through a protective cover 83 (e.g., a ceramic cover) and/or insulation 84. The conductors 82 may be attached to a distribution plate 85. The distribution plate 85 may be supported by a support beam 86, which can be used to raise or lower the anode assemblies 80. The distribution plate 85 may provide a current path between the support beam 86 and the conductors 82. The protective cover 83 and insulation 84 may provide environmental and thermal protection. For example, the protective cover 83 may be made from a highly corrosion resistant ceramic material capable of being exposed to the corrosive environment of the molten salt electrolyte 15.
The electrolysis cell 2 may include any number of spring members 20 necessary to maintain the plurality of blocks in a substantially leak-tight configuration. In the illustrated embodiment, the electrolysis cell 2 includes two spring members 20 per corner, with a first spring members applying a force in a first vector, and a second spring member applying a force in a second vector, which is different than the first vector. In the illustrated embodiment, the first vector is coincidental to a first sidewall (e.g., a first row of blocks) and the second vector is coincidental to a second sidewall (e.g., a second row of blocks). In one embodiment, the first and second force vectors are transverse, such as orthogonal. In one embodiment, the first and second force vectors are parallel (e.g., via two spring members located coincidental to one another, such as on the same side of a corner block). In one embodiment, at least one spring member per corner of the electrolysis cell is utilized. Other configurations may be employed. Thus, the spring members may be located at a plurality of locations within/relative to electrolysis cell 2, and surfaces of the spring members 20 may compressively engage surfaces of one or more blocks to facilitate compression of at least some of the blocks into a substantially leak-tight configuration.
One particular spring member arrangement is illustrated in
The corner block 30 may be designed to engage spring member(s) 20 and at least two inner blocks 40, 42 of an electrolysis cell 2. Thus, the corner block 30 may include surfaces that facilitate mating engagement with spring member(s) 20 and inner blocks 40, 42. The corner block 30 may also engage additional blocks, such as outer blocks 50, 52, and/or additional spring members. In the illustrated embodiment, the corner block 30 is offset from inner blocks 40, 42 and outer blocks 50, 52 and includes planar surfaces for mating with corresponding planar surfaces of the inner and outer blocks. The corner block 30 also includes a first surface 31 configured for engagement with the first spring members 20a and a second surface 33 configured for engagement with the second spring members 20b. In the illustrated embodiment, the first spring members 20a are offset from the second spring members 20b, and the first and second surfaces 31, 33 may be correspondingly offset from one another so as to facilitate engagement with the spring members 20a, 20b. In the illustrated embodiment, the first surface 31 is offset from the second surface 33 via a joining surface 35. In one embodiment, the first surface 31 has an axis that is transverse to an axis of the second surface 33. In the illustrated embodiment, the intersection of the axis of the first surface 31 with the axis of the second surface 33 is orthogonal. However, the intersection of the axis may define any non-parallel configuration so long as they provide surfaces that facilitate engagement with spring members. In one embodiment, the first and/or second surfaces 31, 33 are oriented orthogonal to the force vector produced by its corresponding spring member.
The inner blocks 40, 42 are configured in conjunction with the corner block 30 to facilitate containment of the molten salt electrolyte 15 within the electrolysis cell 2. Thus, the inner blocks 40, 42, in conjunction with other inner blocks and corner blocks 30, may define a surrounding perimeter. In conjunction with a cathode, the surrounding perimeter may define a substantially leak-tight container adapted to contain the molten salt electrolyte 15. The inner blocks may be of any shape. In one embodiment, the inner blocks are of a rectangular-solid shape.
The inner blocks 40, 42 and/or outer blocks 50, 52 may expand and contract due to heat fluctuations within the electrolysis cell, such as during the transition from startup to production conditions, and vice-versa. Thus, some of the blocks may expand from a first size to a second size, or may shrink from a first size to a second size. Likewise, the spring members 20 may apply various forces and/or be oriented in various states depending on the operating conditions of electrolysis cell 2. For example, during startup the spring members 20 may apply a first force and/or be in a first compressive state, such as no or little compression. During production conditions, the spring members 20 may apply a second force or be in a second compressive state, such as a moderate to full compressive state due to expansion of the inner blocks 40, 42 and/or outer blocks 50, 52.
Expansion of the inner blocks 40, 42 and/or outer blocks 50, 52 may also be realized in directions not coincidental to the compression of the spring members 20. For example, one or more of the blocks may expand in a direction towards or away from the bath 15 and/or towards or away from the outer shell 60. To facilitate such expansion, a gap 75 may be provided between the outer shell 60 and one or more of the blocks.
Like the inner blocks 40, 42, the outer blocks 50, 52 may be of any shape. The outer blocks 50, 52 may provide a second layer of containment and/or support one or more inner blocks. The outer blocks 50, 52 may be coupled to the outer shell 60. The outer blocks 50, 52 may comprise any suitable material. The outer blocks 50, 52 may be compressed via one or more spring members 20, or may be free of compression from the spring members.
The inner sidewalls 40, outer sidewalls 50 and/or corner blocks 30, may be at least partially supported by an outer shell 60. The outer shell 60 generally surrounds and supports at least some of the blocks, and may be made of any material suited to hold and support at least some of the blocks. In one embodiment, the outer shell 60 comprises a steel material. In the illustrated embodiment, the outer shell 60 surrounds the outer blocks 50, 52, which surround the inner blocks 40, 42. The outer shell 60 may also facilitate engagement of the spring members 20 with one or more blocks. For example, and as illustrated, the spring members 20a, 20b may be interconnected with the outer shell 60, such as restrictively coupled to the outer shell 60, to facilitate engagement of the spring members 20a, 20b with the corner blocks, inner blocks and/or outer blocks of the electrolysis cell 2. In this regard, the outer shell 60 may include a corner portion 62 adapted to restrictively hold the spring members 20a, 20b in position during operation of electrolysis cell 2. A top 64 may also be included to assist in vapor/heat control.
The spring members 20 may be suitably adapted to provide the force(s) that maintain the substantially leak-tight arrangement of the plurality of bath resistant blocks. One embodiment of a spring member 20 is illustrated in
As noted above, a variety of bath resistant block arrangements may be utilized in conjunction with spring members to facilitate production of a substantially leak-tight perimeter. Various ones of those arrangements are now described with reference to
In another arrangement, and with reference to
In other arrangements, more than two sidewall layers may be utilized. For example, and with reference to
As noted above, various spring member arrangements may be utilized to force the blocks into the substantially leak-tight configuration. One alternative arrangement is illustrated in
Another spring member arrangement is illustrated in
Methods of operating aluminum electrolysis cells are also provided. In one embodiment, and with reference to
Various ones of the above features may be combined to yield various electrolysis cell, and systems and methods for operating an electrolysis cell in the absence of a ledge. Additionally, while the present invention has been described in terms of aluminum electrolysis cells, it will be appreciated that other metal electrolysis cells may utilize the sidewall configuration of the instant disclosure. Moreover, 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.
