WO2023233196A1

WO2023233196A1 - Lining design of electrolytic cell in an aluminum smelter

Info

Publication number: WO2023233196A1
Application number: PCT/IB2022/095002
Authority: WO
Inventors: Bibhudatta MOHANTY; Swapnil Hirave; Kuwar Anant Vikram Singh
Original assignee: Vedanta Limited (Aluminium & Power)
Priority date: 2022-06-03
Filing date: 2022-11-03
Publication date: 2023-12-07

Abstract

The present disclosure relates to an electrolytic cell (100) for aluminum smelting, comprising a graphitized cathode having a collector bar (106) disposed of therewithin. The collector bar (106) is made of mild steel with copper (108) inserted therewithin through a window, which leads to lower cathode voltage drop, and stable and low power consumption, resulting in savings and improved efficiency and providing higher amperage creep. Further, the window is sealed with a thermally insulative seal box (110), to restrict air to enter the cell (100) through the collector bar (106), thereby preventing any air oxidation chances. Further, thermally insulative materials (114-1 to 114-7) are provided in the bottom lining (102-2), and side linings (102-1) of the electrolytic cell (100), along with additional insulation in the slope area of the electrolytic cell (100), thereby making the electrolytic cell (100) thermally balanced and thermally insulated, with longer operating life.

Description

LINING DESIGN OF ELECTROLYTIC CELL IN AN ALUMINUM SMELTER

TECHNICAL FIELD

[0001] The present disclosure, in general, relates to the field of aluminum smelters. More particularly, the present disclosure relates to a robust, cost-effective, and efficient electrolytic cell for aluminum smelting, which consumes less electrical power and is operable at low voltage, with lower cathode voltage drop and higher current creepage options, and which is also thermally balanced with long operating life.

BACKGROUND

[0002] Background description includes information that may be useful in understanding the present invention. It is not an admission that any of the information provided herein is prior art or relevant to the presently claimed invention, or that any publication specifically or implicitly referenced is prior art.

[0003] Aluminum smelting is the process of extracting aluminum from its oxide, alumina, generally by the Hall-Heroult process, which is an electrolysis process. An aluminum smelter consists of a large number of electrolytic cells (pots) in which the electrolysis takes place, each of which is capable of producing aluminum. Conventional electrolytic cells are made of a steel shell with a series of insulating linings of refractory materials. The cell consists of a brick-lined outer steel shell as a container and support. Inside the shell, cathode blocks are cemented together by ramming paste. The top lining of the cathode block remains in contact with the molten metal and acts as the cathode. The molten electrolyte is maintained at a high temperature inside the cell. Further, prebaked anode made of carbon in the form of large sintered blocks is suspended in the electrolyte. The electrolyte is generally a molten bath of cryolite (NaaAIFf,) and dissolved alumina. Upon energization of the cathode and anode, the electrolysis reduction takes place, wherein aluminum is produced by the electrolytic reduction of aluminum oxide dissolved in the molten cryolite. At the same time, the carbon electrode is oxidized, initially to carbon monoxide. Although the formation of carbon monoxide (CO) is thermodynamically favored at the reaction temperature, the presence of considerable overvoltage changes the thermodynamic equilibrium, and a mixture of CO and CO2 is produced.

[0004] Existing electrolytic cells or aluminum smelters are capable of producing a large amount of aluminum in a batch, however, the inefficient design and materials used in the existing cells, require them to be operated at higher voltage, which results in a large amount of electrical power consumption, high cathode voltage drop, and power losses, making them electrically inefficient and costlier to operate. In addition, existing cells also have lower current creepage options. Besides, the existing cells have thermal insulation issues and thermal balancing issues due to the inefficient choice of materials used in the cell, which significantly lowers the cell’s life over time. Further, the lack of proper air sealing in existing cells, causes air to enter the cells, which leads to air oxidation within the cell and degradation of the cell.

[0005] There is, therefore, a need to overcome the above drawback, limitations, and shortcomings associated with the existing electrolytic cells and aluminum smelters, and provide a robust, cost-effective, and efficient electrolytic cell that consumes less electrical power and is operable at low voltage, with lower cathode voltage drop and higher current creepage options, which is also thermally balanced and has long operating life.

SUMMARY

[0006] The present disclosure relates to a robust, cost-effective, and efficient electrolytic cell for aluminum smelting, which consumes less electrical power and is operable at low voltage, with lower cathode voltage drop and higher current creepage options, and which is also thermally balanced with long operating life.

[0007] The proposed electrolytic cell may comprise a housing defining the shape of the electrolytic cell. The housing may comprise a bottom lining, and side linings such that a pot shell is created within the housing. Further, the pot shell may comprise a slope at the comers of the housing connecting the bottom lining with the side linings. The electrolytic cell may be adapted to receive, in the pot shell, a mixture of aluminum ore dissolved in an electrolytic bath.

[0008] The electrolytic cell may comprise a cathode assembly comprising a graphitized cathode having a collector bar disposed of therewithin such that the collector bar is oriented parallel to the bottom lining and a bottom surface of the anode assembly. The collector bar may be made of mild steel and may have a window. Further, copper may be inserted within the mild steel collector bar through the window using plugs, and the window of the collector bar may be sealed with a seal box or sealant made of thermally insulative material, to restrict air to enter the electrolytic cell through the collector bar, thereby preventing any air oxidation chances within the electrolytic cell.

[0009] The pot shell may be adapted to receive an anode assembly therewithin through an opening provided over the pot shell, such that a gap is present between the anode assembly and the cathode assembly. The volume created by the gap may receive the mixture of the aluminum ore and electrolytic bath such that the cathode remains in contact with the mixture. Further, the cathode and anode may be connected to a power source, which may energize the cathode and anode to initiate an electrolytic reaction in the mixture, which facilitates aluminum smelting and converts the mixture of aluminum ore and electrolytic bath into aluminum.

[0010] In an aspect, the bottom lining of the electrolytic cell may be made of a material selected from any or a combination of Calcium Silicate, vermiculate, insulation brick, and dry impervious material. Further, the side linings of the electrolytic cell may be configured with a material selected from any or a combination of vermiculate, monolithic castable, Silicon Nitride, Nitride bonded Carbide blocks and bricks. Furthermore, the slope of the pot shell may be configured with a thermally insulative material comprising calcium silicate.

[0011] Accordingly, the use of mild steel with copper insert in the cathode may help in reducing the current resistance of the cathode, which may lead to lower cathode voltage drop, stable and low power consumption, resulting in savings and improved efficiency compared to existing electrolytic cells, and providing higher amperage creep.

[0012] Besides, the use above-mentioned thermally insulative materials in the bottom lining, and side linings of the pot shell, along with additional insulation in the slope area of the pot shell and at the window of the collector bar, makes the proposed electrolytic cell thermally balanced and thermally insulated, leading to a longer operating life compared to existing electrolytic cells.

[0013] Various objects, features, aspects and advantages of the inventive subject matter will become more apparent from the following detailed description of preferred embodiments, along with the accompanying drawing figures in which like numerals represent like components.

BRIEF DESCRIPTION OF DRAWINGS

[0014] The accompanying drawings are included to provide a further understanding of the present disclosure, and are incorporated in and constitute a part of this specification. The drawings illustrate exemplary embodiments of the present disclosure and, together with the description, serve to explain the principles of the present disclosure. The diagrams are for illustration only, which thus is not a limitation of the present disclosure. [0015] In the figures, similar components and/or features may have the same reference label. Further, various components of the same type may be distinguished by following the reference label with a second label that distinguishes among the similar components. If only the first reference label is used in the specification, the description is applicable to any one of the similar components having the same first reference label irrespective of the second reference label.

[0016] FIG. 1 illustrates an exemplary cross-sectional view of the proposed electrolytic cell, in accordance with an embodiment of the present disclosure;

[0017] FIG. 2 illustrates an exemplary view of the cathode assembly of the proposed electrolytic cell, in accordance with an embodiment of the present disclosure; and

[0018] FIG. 3 illustrates an exemplary view depicting a 3D thermal model of the proposed electrolytic cell, in accordance with an embodiment of the present disclosure

DETAILED DESCRIPTION

[0019] The following is a detailed description of embodiments of the disclosure depicted in the accompanying drawings. The embodiments are in such detail as to clearly communicate the disclosure. However, the amount of detail offered is not intended to limit the anticipated variations of embodiments; on the contrary, the intention is to cover all modifications, equivalents, and alternatives falling within the spirit and scope of the present disclosure as defined by the appended claims.

[0020] In the following description, numerous specific details are set forth in order to provide a thorough understanding of embodiments of the present invention. It will be apparent to one skilled in the art that embodiments of the present invention may be practiced without some

[0021] Embodiments of the present disclosure relate to a robust, cost-effective, and efficient electrolytic cell for aluminum smelting, which consumes less electrical power and is operable at low voltage, with lower cathode voltage drop and higher current creepage options, and which is also thermally balanced with long operating life.

[0022] Referring to FIG. 1, the proposed electrolytic cell 100 can include a housing 102 defining the shape of the electrolytic cell 100. The housing 102 can include a bottom lining 102-2, and side linings 102-1 extending from the sides of the bottom lining 101-2 in an upward direction such that a pot shell or pot cavity 102-3 is created within the housing 102. Further, the pot shell 102-3 can comprise a slope at the bottom comers of the housing connecting the bottom lining 102-2 with the side linings 102-1. The electrolytic cell 100 can be adapted to receive, in the pot shell 102-3, a mixture of aluminum ore dissolved in an electrolytic bath. The size or dimension of the electrolytic cell 100 can be based on the amount of alumina ore to be smelted or the amount of aluminum to be produced. In an exemplary embodiment, the aluminum ore can be alumina, but not limited to the like, and the electrolytic bath can be molten bath of cryolite (NasAlFe), but not limited to the like.

[0023] The electrolytic cell 100 can include a cathode assembly comprising a graphitized cathode 104 having a collector bar 106 disposed of therewithin as shown in FIG. 2. In an embodiment, the collector bar 106 can be in form of a longitudinal hollow member having an opening window and a chamber therewithin. The collector bar 106 can be made of mild steel. Further, copper 108 can be inserted within the mild steel collector bar 106 through the window using plugs such that the collector bar 106 is oriented parallel to the bottom lining 102-2 as shown in FIG. 1. Furthermore, the window of the collector bar 106 can be sealed with a seal box or sealant 110 made of thermally insulative material, to restrict air to enter the electrolytic cell 100 through the collector bar 106. This can help prevent any air oxidation chances within the electrolytic cell 100.

[0024] The electrolytic cell 100 can include an anode assembly including a graphitized anode 112, wherein the pot shell 102-3 can be adapted to receive the anode 112 therewithin through an opening provided over the pot shell 102-3, such that a gap is present between the anode and the cathode assembly. The volume created by the gap between the cathode and the anode assembly can receive the mixture of the aluminum ore and electrolytic bath such that the cathode 104 remains in contact with the mixture. In an exemplary embodiment, the anode 112 can have a dimension of 1600 x 700 mm and the cathode assembly can include the cathode 104 of dimension 3420 x 515 x 450 mm with the mild steel having copper insert, with the pot shell or cavity of 620 mm.

[0025] Further, the cathode and anode assemblies can be connected to a power source, which can energize the cathode 104 and anode 112 to initiate an electrolytic reaction in the mixture present in the pot shell 102-3, which can facilitate aluminum smelting, leading to the conversion of the mixture of aluminum ore into aluminum.

[0026] Those skilled in the art would appreciate that the use of mild steel with copper insert in the collector bar 106 can help in reducing the current resistance of the cathode 104, which can lead to lower cathode voltage drop, stable and low power consumption, resulting in savings and improved efficiency compared to existing electrolytic cells, and providing higher amperage creep. As a result, the proposed electrolytic cell 100 can be operated at a lower voltage. [0027] In an embodiment, the bottom lining 102-2 of the electrolytic cell 100 can be provided with a first set of materials (114-4 to 114-7) selected from any or a combination of Calcium Silicate, vermiculate, insulation brick, and dry impervious material, but not limited to the like. Further, the side linings 102-1 of the electrolytic cell 100 can be configured with a second set of materials (114-1 to 114-2) selected from any or a combination of vermiculate, monolithic castable, Silicon Nitride, Nitride bonded Carbide blocks and bricks, but not limited to the like. Furthermore, the slope of the pot shell can additionally be configured with a thermally insulative material 114-3 such as calcium silicate, but not limited to the like.

[0028] Those skilled in the art would further appreciate that the use of above- mentioned thermally insulative materials (114-1 to 114-7) in the bottom lining, and side linings of the pot shell, along with additional insulation in the slope area of the pot shell and at the window of the collector bar 106, makes the proposed electrolytic cell 100 thermally balanced and thermally insulated, leading to a longer operating life compared to existing electrolytic cells. FIG. 3 illustrates an exemplary view depicting a 3D thermal model of the proposed electrolytic cell.

[0029] A comparative experimental difference between the proposed electrolytic cell and the existing electrolytic cell is shown in Table- 1 below.

TABLE-1

[0030] The proposed electrolytic cell required a pot voltage of 4.07 Volts with a gain of 9 mV over existing electrolytic cells. The cathode voltage drop was measured to be 187 mV with a gain of 50-70 mV over existing electrolytic cells. The current efficiency of the proposed electrolytic cell was calculated to be 95% with a gain of 0.5% over existing cells), which can be further improved with a magnetic loop. The energy consumption by the proposed electrolytic cell was calculated to be 12.81 KWh/KgAl with a gain of 200 units over existing electrolytic cells). Further, Aluminum production achieved in the proposed electrolytic cell was 2602 Kg Al/Pot/Day with a gain of 14 Kg over existing cells). Furthermore, the current feasibility was measured to be 15Ka, 4.27% Vol for Plant 1: 345 KA, and 10KA, 2.5% Vol for Plant 2: 350 KA.

[0031] Thus, the present invention overcomes the above drawback, limitations, and shortcomings associated with the existing electrolytic cell and aluminum smelter, by providing a robust, cost-effective, and efficient electrolytic cell for aluminum smelting, which consumes less electrical power and is operable at low voltage, with lower cathode voltage drop and higher current creepage options, and which is also thermally balanced with long operating life. In addition, the seal box made of thermally insulative material being used for sealing the window of the collector bar restricts entry of air within the electrolytic cell, which restricts any chances of air oxidation within the electrolytic cell.

[0032] It is to be appreciated by a person skilled in the art that while various embodiments and drawings of the present disclosure have been elaborated for a single electrolytic cell for the sake of simplicity, however, the multiple numbers of proposed electrolytic cells can be implemented together and connected to a single power source to form an aluminum smelter based on the amount of aluminum to be produced, and all such embodiments related to the aluminum smelter are well within the scope of the present disclosure, without any limitations.

[0033] Moreover, in interpreting the specification, all terms should be interpreted in the broadest possible manner consistent with the context. In particular, the terms “comprises” and “comprising” should be interpreted as referring to elements, components, or steps in a non-exclusive manner, indicating that the referenced elements, components, or steps may be present, or utilized, or combined with other elements, components, or steps that are not expressly referenced.

[0034] While the foregoing describes various embodiments of the invention, other and further embodiments of the invention may be devised without departing from the basic scope thereof. The scope of the invention is determined by the claims that follow. The invention is not limited to the described embodiments, versions or examples, which are included to enable a person having ordinary skill in the art to make and use the invention when combined with information and knowledge available to the person having ordinary skill in the art.

ADVANTAGES OF THE INVENTION

[0035] The proposed invention overcomes the above drawback, limitations, and shortcomings associated with the existing electrolytic cells used for aluminum smelting.

[0036] The proposed invention lowers the electrical power requirement and cathode voltage drop in existing electrolytic cells and improves the efficiency of existing electrolytic cells.

[0037] The proposed invention improves the thermal balancing and operating life of existing electrolytic cells.

[0038] The proposed invention restricts air entry and air oxidation within existing electrolytic cells

[0039] The proposed invention provides a robust, cost-effective, and efficient electrolytic cell for aluminum smelting.

[0040] The proposed invention provides an electrolytic cell for aluminum smelting, which consumes less electrical power and is operable at low voltage with lower cathode voltage drop.

[0041] The proposed invention provides an electrolytic cell for aluminum smelting, which provides higher current creepage options.

[0042] The proposed invention provides an electrolytic cell for aluminum smelting, which is thermally balanced and thermally insulated, and also has long operating life.

Claims

We Claim:

1. An electrolytic cell comprising: a housing, wherein the housing comprises: a bottom lining; and side linings extending from the sides of the bottom linings in an upward direction to create a pot shell within the housing, wherein the pot shell comprises a . slope at the bottom comers of the housing to connect the bottom lining with the side linings.

2. The electrolytic cell as claimed in claim 1, wherein the housing is to define the shape of the electrolytic cell.

3. The electrolytic cell as claimed in claim 1, wherein the pot shell is adapted to receive a mixture of aluminium ore dissolved in an electrolytic bath.

4. The electrolytic cell as claimed in claim 1, further comprising a cathode assembly, wherein the cathode assembly comprises a graphitized cathode having a collector bar disposed of therein.

5. The electrolytic cell as claimed in claim 4, wherein the collector bar is a longitudinal hollow member having an opening window and a chamber therewithin.

6. The electrolytic cell as claimed in claim 4, wherein the collector bar further comprises copper inserted through the window such that the collector bar is oriented parallel to the bottom lining.

7. The electrolytic cell as claimed in claim 5, wherein the window of the collector bar is sealed with a sealant made of thermally insulative material.

8. The electrolytic cell as claimed in claim 4, wherein the collector bar is made of material comprising mild steel.

9. The electrolytic cell as claimed in claim 4, wherein the graphitized cathode has dimensions of about 3420 x 515 x 450 mm.

10. The electrolytic cell as claimed in claim 1, further comprising an anode assembly, wherein the anode assembly comprises a graphitized anode.

11. The electrolytic cell as claimed in claim 10, wherein the graphitized anode has dimensions of about 1600 x 700 mm.

12. The electrolytic cell as claimed in claim 1, wherein the bottom lining further comprises a first set of materials selected from at least one of a Calcium Silicate, vermiculate, insulation brick, dry impervious material, or a combination thereof.

13. The electrolytic cell as claimed in claim 1, wherein the side linings comprise a second set of materials selected from at least one of a vermiculate, monolithic castable, silicon nitride, nitride bonded carbide blocks, bricks, or a combination thereof.

14. The electrolytic cell as claimed in claim 1, wherein the slope of the pot shell comprises a thermally insulative material, and whererein the thermally insulative material is calcium silicate.

15. The electrolytic cell assembly as claimed in claim 1, wherein the electrolytic cell assembly is a part of an aluminium smelting apparatus.