Electrolytic cell case, method for manufacturing electrolytic cell case, molten salt electrolysis apparatus, and method for manufacturing metal

Abstract

To provide an electrolytic bath case that can be easily carried.SOLUTION: An electrolytic bath case 10 made of steel for covering the outer surface of an electrolytic bath made of brick comprises: a cylindrical member 11 for covering the outer surface of the side wall of the electrolytic bath; and a bottom member 12 connected to the cylindrical member 11 for covering the outer surface of the bottom wall of the electrolytic bath. The cylindrical member 11 includes a pair of semi-cylindrical segments 13 and a junction 15 in which the edge faces of the pair of semi-cylindrical segments 13 are butted against each other to join in the circumferential direction. The junction 15 is formed in the height direction of the cylindrical member 11.SELECTED DRAWING: Figure 1A

Description

Technical Field

[0001] The present invention relates to an electrolytic cell case, a method for manufacturing an electrolytic cell case, a molten salt electrolysis apparatus, and a method for manufacturing a metal.

Background Art

[0002] Ingots of metallic titanium, titanium alloys, etc. are industrially manufactured using sponge titanium produced by the Kroll process. And the sponge titanium production process including this Kroll process can be roughly classified into four processes: a chlorination process, a reduction separation process, a crushing process, and an electrolysis process. Among these processes, in the reduction separation process, titanium tetrachloride is reduced with metallic magnesium to produce sponge titanium. And the electrolysis process is a process of decomposing magnesium chloride, which is a by-product of the reduction separation process, by molten salt electrolysis to obtain metallic magnesium.

[0003] In order to obtain sponge titanium, a large amount of metallic magnesium is used in the reduction separation process. In order to produce a large amount of metallic magnesium, the electrolytic cells of a number of molten salt electrolysis apparatuses may be operated simultaneously. In this case, the number of electrolytic cells may be arranged side by side, whereby effective utilization of power transmission facilities and efficient recovery and transportation of the produced metallic magnesium may be achieved. Also, in order to efficiently produce a large amount of metallic magnesium, it is preferable that the operating time of the electrolytic cell is long, and the electrolytic cell may be used for a long period of several years.

[0004] The electrolytic cell having a container shape is made of, for example, refractory bricks from the viewpoint of safety and the like. An electrolytic cell case may be arranged to cover the outer surface around the electrolytic cell made of bricks which are a porous body. For example, FIG. 1 of Patent Document 1 shows "a multipolar electrolytic cell 10 which is a steel container 11 lined with a refractory material 12 on the inside". Also, for example, Patent Document 2 describes that "the electrolytic cell 1 includes an iron outer plate 3, a heat insulating brick layer 4, and a refractory brick layer 5" (see FIG. 1 of Patent Document 2).

Prior Art Documents

Patent Documents

[0005] [Patent Document 1] Japanese Patent Publication No. 2002-520490 [Patent Document 2] Japanese Unexamined Patent Application Publication No. 2005-171354 [Summary of the Invention] [Problems to be Solved by the Invention]

[0006] The electrolytic cell case may be made of steel. The reasons are that welding is easy when the electrolytic cell case is of a member-assembled type, the electrolytic cell made of bricks can be covered without gaps to prevent liquid leakage, and the mechanical strength is high, etc. As described above, when the electrolytic cell case is of a member-assembled type, welding work is essential. When welding steel is performed in a site where a plurality of molten salt electrolytic cells are installed side by side, there is a problem that the welding is not stable due to the influence of a magnetic field or the like derived from other molten salt electrolytic cells. That is, when installing the electrolytic cell case, the operation of other molten salt electrolytic cells must be stopped. Therefore, in order to suppress the reduction of productivity as much as possible, there is a desire to shorten the welding work period. By the way, the electrolytic cell case is large and can be made by combining a plurality of structural steel materials. Therefore, it takes time to assemble the electrolytic cell case from a plurality of structural steel materials at the installation location of the molten salt electrolytic cell. In addition, since a plurality of molten salt electrolytic cells are already arranged, there is almost no space available for work such as a place to temporarily place the structural steel materials. Therefore, in a place different from the installation location of the molten salt electrolytic cell, it may be assembled to a certain extent large divided material, and then the divided material is transported to the installation location of the molten salt electrolytic cell and assembled. In such a case, for example, if the constituent members of the electrolytic cell case include a square tube-shaped divided material 213 having a shape as shown in FIG. 3B, not only does it take a lot of labor to transport it, but it is also conceivable that it cannot be properly loaded.

[0007] Therefore, an object of an embodiment of the present invention is to provide an electrolytic cell case that can be easily transported.

Means for Solving the Problem

[0008] That is, in one aspect, the present invention is a steel electrolytic cell case for covering the outer surface of a brick-made electrolytic cell, comprising a cylindrical member for covering the outer surface of the side wall of the electrolytic cell, and a bottom member connected to the cylindrical member for covering the outer surface of the bottom wall of the electrolytic cell. The cylindrical member has a pair of semi-cylindrical split members and a joint portion where the end faces of the pair of semi-cylindrical split members in the circumferential direction are butted and joined, and the joint portion is formed in the height direction of the cylindrical member. This is the electrolytic cell case.

[0009] In one embodiment of the electrolytic cell case according to the present invention, the joint portion of the cylindrical member of the electrolytic cell case is located on the surface located outside the base end portion of the partition wall of the electrolytic cell.

[0010] In one embodiment of the electrolytic cell case according to the present invention, the electrolytic cell is for the electrolysis of magnesium chloride.

[0011] Further, in another aspect, the present invention is a method for manufacturing a steel electrolytic cell case for covering a brick-made electrolytic cell, comprising an arranging step of arranging a pair of semi-cylindrical split members on a bottom member for covering the outer surface of the bottom wall of the electrolytic cell, and a welding step of butting and welding the end faces of the pair of semi-cylindrical split members in the circumferential direction after the arranging step to form a cylindrical member from the pair of semi-cylindrical split members. This is the method for manufacturing the electrolytic cell case.

[0012] Further, in another aspect, the present invention is a molten salt electrolysis apparatus comprising a brick-made electrolytic cell and a steel electrolytic cell case for covering the electrolytic cell. The electrolytic cell case is the electrolytic cell case described above, and the electrolytic cell includes a bottom wall, side walls each having front and rear wall portions extending in the height direction from the bottom wall and left and right wall portions respectively connected to the front and rear wall portions, and a partition wall extending between the left and right wall portions. This is the molten salt electrolysis apparatus.

[0013] In one embodiment of the molten salt electrolysis apparatus according to the present invention, the joint portion of the cylindrical member of the electrolytic cell case is located outside the left and right wall portions.

[0014] In one embodiment of the molten salt electrolysis apparatus according to the present invention, it further includes a wall body for reinforcing the electrolytic cell case from the outside.

[0015] In one embodiment of the molten salt electrolysis apparatus according to the present invention, the wall body is made of reinforced concrete.

[0016] In one embodiment of the molten salt electrolysis apparatus according to the present invention, the reinforcing bars included in the wall body made of reinforced concrete are made of austenitic stainless steel.

[0017] Furthermore, in another aspect of the present invention, there is provided a method for producing a metal, which includes an electrolysis step of producing a metal from a metal chloride by performing molten salt electrolysis of the metal chloride using the molten salt electrolysis apparatus described above.

[0018] In one embodiment of the method for producing a metal according to the present invention, in the electrolysis step, molten salt electrolysis of magnesium chloride is performed using the molten salt electrolysis apparatus to produce magnesium metal from the magnesium chloride.

Advantages of the Invention

[0019] According to one embodiment of the present invention, it is possible to provide an electrolytic cell case that can be easily transported.

Brief Description of the Drawings

[0020]

Figure 1A

Figure 1B

Figure 1C

Figure 2A

Figure 2B

Figure 2C

Figure 3A

Figure 3B

Figure 3C

[0021] The present invention is not limited to the embodiments described below, and components can be modified and embodied without departing from the gist thereof. Also, various inventions can be formed by appropriately combining a plurality of components disclosed in each embodiment. For example, an invention may be formed by deleting some components from all the components shown in the embodiment.

[0022] [1. Electrolytic Cell Case] The electrolytic cell case 10 shown in Fig. 1 is for covering the outer surface of the brick-made electrolytic cell 20 (see Fig. 2A). The electrolytic cell case 10 has a container shape with an opening formed on the upper side, and includes a tubular member 11 and a bottom member 12, and is made of steel appropriately selected from carbon steel, stainless steel, etc. from the viewpoint of heat resistance and the like. Note that the use of the electrolytic cell case 10 for the electrolysis of magnesium chloride will be described below as an example.

[0023] (Tubular Member) The cylindrical member 11 is for covering the outer surface of the side wall 22 (see FIG. 2B) of the electrolytic cell 20. The cylindrical member 11 has a pair of semi-cylindrical split members 13 and a joint portion 15 where the end faces 14 of the pair of semi-cylindrical split members 13 in the circumferential direction are butted and joined together. This joint portion 15 is formed in the height direction of the cylindrical member 11. According to the cylindrical member 11 in which the joint portion 15 is formed in the height direction in this way, when moving the pair of semi-cylindrical split members 13 before joining, the labor of transportation is small and it can be transported appropriately. Note that the shape of the cylindrical member 11 is not particularly limited, and examples include a square tube shape, a cylindrical shape, and an elliptical tube shape. However, in many cases, the shape of the cylindrical member 11 is a square tube shape.

[0024] (A pair of semi-cylindrical split members) In a preferred form as a pair of semi-cylindrical split members, as shown in FIG. 1C, when the pair of semi-cylindrical split members 13 are viewed in plan, they are in a U shape with substantially right-angled corners. Therefore, by facing the inner sides of the U shapes of the pair of semi-cylindrical split members 13 and shifting them in the width direction of the U shape (the left-right direction in FIG. 1C) so that one end of the semi-cylindrical split member 13 enters the inner sides of each other, the space occupied by the pair of semi-cylindrical split members 13 can be made sufficiently small. Therefore, in one embodiment, the pair of semi-cylindrical split members 13 can be arranged on the loading platform of a truck, and the load of transportation can be appropriately reduced. In addition, to manufacture the electrolytic cell case 10 with the pair of semi-cylindrical split members 13 and the bottom member 12, in addition to joining the cylindrical member 11 and the bottom member 12 by welding or the like, the end faces of the pair of semi-cylindrical split members in the circumferential direction of the cylindrical member 11 may be butted and welded together. Here, when the total circumferential length of the electrolytic cell case 10 is longer than twice the length in the height direction of the electrolytic cell case 10, compared with those shown in FIGS. 3A and 3B, the length of the joint portion 15 that needs to be joined by welding or the like becomes shorter, so the manufacture of the electrolytic cell case 10 can be completed in a short time, and this aspect is preferable.

[0025] (Joint portion) The joining portion 15 is a portion formed between the circumferential end faces 14 of the pair of semi-cylindrical split members 13 by butting and joining them together. For example, the joining portion 15 may be located on the surface positioned outside the base end portion 25d of the partition wall 25 of the electrolytic cell 110 of the molten salt electrolysis apparatus 100 (see FIG. 2B).

[0026] Although details will be described later, in the electrolytic cell 20, a partition wall 25 is provided to divide an electrolysis chamber 23 for electrolyzing a molten salt containing magnesium chloride and a metal recovery chamber 24 for recovering metallic magnesium obtained by the electrolysis. The container-shaped electrolytic cell 20 is made of bricks, for example, having fire resistance, etc., from the viewpoint of safety surface, etc. During the operation of the molten salt electrolysis apparatus 100, the molten salt penetrates into a plurality of holes in the brick-made partition wall 25 which is a porous body, causing the partition wall 25 to expand. Along with the expansion of the partition wall 25, the electrolytic cell 20 may gradually bulge and deform outward as indicated by the arrow in FIG. 2B. At this time, in order to ensure more reliable mechanical strength so that the partition wall 25 (see FIGS. 2A and 2B) can withstand expansion in the extending direction during molten salt electrolysis, the adjacent semi-cylindrical split members 13 may be fixed to each other around the joining portion 15 by fixtures such as bolts.

[0027] (Bottom member) The bottom member 12 covers the outer surface of the bottom wall 21 (see FIG. 2A) of the electrolytic cell 20 and is disposed immediately below the bottom wall 21. Usually, the bottom member 12 is connected to the lower edge portion 16 of the cylindrical member 11 (pair of semi-cylindrical split members 13). Note that the outside of the bottom member 12 may be reinforced with a reinforcing member or the like.

[0028] [2. Manufacturing method of electrolytic cell case] The manufacturing method of the electrolytic cell case described above includes an arrangement step and a welding step. Hereinafter, an example of each step will be described, but the description of the content overlapping with the above will be omitted.

[0029] <Arrangement step> In the configuration process, as shown in FIG. 1B, a pair of semi-cylindrical split members 13 are arranged on a bottom member 12 for covering the outer surface of the bottom wall of the electrolytic cell. At this time, the end faces 14 of the pair of semi-cylindrical split members 13 in the circumferential direction are abutted against each other respectively.

[0030] <Welding Process> In the welding process, after the configuration process, the abutted end faces 14 of the pair of semi-cylindrical split members 13 in the circumferential direction are welded together. Thereby, a cylindrical member 11 is formed from the pair of semi-cylindrical split members 13. The order of performing the welding is not limited. For example, first, in order to weld the pair of semi-cylindrical split members 13 and the bottom member 12, the lower edge 16 of the pair of semi-cylindrical split members 13 and the bottom member 12 may be welded. Thereafter, in order to weld the pair of semi-cylindrical split members 13 together, the end faces 14 of the pair of semi-cylindrical split members 13 may be welded. Also, for example, the order of welding described above may be reversed. Also, for example, the welding of the pair of semi-cylindrical split members 13 together and the welding of the pair of semi-cylindrical split members 13 and the bottom member 12 may be performed simultaneously.

[0031] (Welding Means) The welding means is not particularly limited. For example, as the welding means, arc welding for joining metals together is suitable. Examples of the arc welding include MIG (Metal Inert Gas) welding and TIG (Tungsten Inert Gas) welding, etc. However, from the viewpoint of avoiding the possibility of tungsten being mixed into the metal magnesium produced by electrolysis, MIG welding is more suitable. During the operation of the molten salt electrolysis device, since a large current is passed between the electrodes in the electrolytic cell, a strong magnetic field (magnetic field) is generated. If a large number of electrolytic cells in operation around are not stopped, it is considered that the arc will be affected by the strong magnetic field and the directionality of the arc will become indeterminate. Therefore, in order to suppress the occurrence of welding defects due to the influence of the magnetic field, when welding the members of the electrolytic cell case by arc welding, it is preferable to stop other electrolytic cells in operation around. Welding defects may cause various problems such as liquid leakage to the outside of the electrolytic cell case due to the occurrence of holes, etc., and poor mechanical strength of the welded part.

[0032] [3. Molten Salt Electrolysis Device] The molten salt electrolysis device 100 shown in Fig. 2A includes a brick electrolytic cell 20, the electrolytic cell case 10 described above, and an upper lid 30.

[0033] (Electrolytic Cell) The electrolytic cell 20 has a container shape with an opening formed on the upper side, and includes a bottom wall 21, side walls 22 (see Fig. 2B), and a partition wall 25 for partitioning an electrolysis chamber 23 and a metal recovery chamber 24. The side walls 22 have front and rear wall portions 22a extending in the height direction from the bottom wall 21 and left and right wall portions 22b respectively connected to the front and rear wall portions 22a. The partition wall 25 extends between the left and right wall portions 22b and includes a first partition wall 25a and a second partition wall 25b. Note that the material of the electrolytic cell 20 is, for example, brick mainly composed of aluminum oxide, silicon oxide, etc. from the viewpoints of fire resistance and hot strength.

[0034] In this electrolytic cell 20, a molten salt bath Bf composed of a molten salt containing a metal chloride supplied therein is stored. The metal magnesium generated by electrolysis of magnesium chloride in the electrolysis chamber 23 is sent to the metal recovery chamber 24, and the molten salt is sent from the metal recovery chamber 24 to the electrolysis chamber 23 to circulate the molten salt bath Bf. Therefore, the first partition wall 25a and the second partition wall 25b are arranged. Here, the molten salt electrolysis device 100 forms a circulation port 25c between the first partition wall 25a and the second partition wall 25b, thereby ensuring the flow of the molten salt bath (flow from the electrolysis chamber 23 to the metal recovery chamber 24) shown by the arrow A. Also, a passage through which the molten salt bath Bf can flow is formed on the lower surface side of the second partition wall 25b, and the flow (flow from the metal recovery chamber 24 to the electrolysis chamber 23) shown by the arrow B can be ensured.

[0035] (Molten Salt) By electrolysis of magnesium chloride, magnesium (Mg) is generated as a molten metal, and chlorine gas (Cl 2 ) is generated as a gas. In addition to the above-mentioned magnesium chloride (MgCl 2 ), the molten salt contains sodium chloride (NaCl) and calcium chloride (CaCl 2) Potassium chloride (KCl) and / or calcium fluoride (CaF 2 ) etc. may be included. As the component used as the supporting salt, it is preferable to use one with a higher electrolysis voltage than magnesium chloride. Metallic magnesium can be used for the reduction of titanium tetrachloride in the Kroll process for producing metallic titanium, and chlorine gas can be used for the chlorination of titanium ore, respectively. As the magnesium chloride used as the raw material for this electrolysis, that produced as a by-product in the Kroll process can be used.

[0036] (Electrolytic cell case) During the molten salt electrolysis, when the molten salt penetrates into a plurality of holes in the brick partition wall 25 which is a porous body, the partition wall 25 expands in the extending direction. Therefore, when the electrolytic cell case 10 has appropriate strength, due to the expansion of the brick, the left and right wall portions 22b of the electrolytic cell 20 are deformed in the direction of bulging outward, and the life of the electrolytic cell 20 is prolonged without the left and right wall portions 22b and the partition wall 25 being damaged. Therefore, as shown in FIG. 2B, the joint portion 15 of the cylindrical member 11 of the electrolytic cell case 10 is preferably positioned outside the left and right wall portions 22b. In this case, it is more preferable that the joint portion 15 is not positioned in the extending direction (arrow C) of the partition wall 25, that is, it is shifted from the extension line of the partition wall 25 on the outside of the electrolytic cell 20.

[0037] (Upper lid) The upper lid 30 serves as heat insulation for the outside of the electrolytic cell 20 because the molten salt bath Bf is at a high temperature. Also, the upper lid 30 is arranged to make the electrolytic cell 20 a closed space, and the inside of the electrolytic cell 20 is made negative pressure with respect to the outside to prevent the leakage of chlorine gas generated from the anode 26 during the molten salt electrolysis. Also, the material of the upper lid 30 is not particularly limited, but from the viewpoint of preventing a short circuit occurring between the upper lid 30 and the anode 26 during the molten salt electrolysis, it is sufficient that the back surface 31 side of the lid on the molten salt bath Bf side of the upper lid 30 is an insulating material, and a ceramic material may be arranged on the back surface 31 side of the lid on the molten salt bath Bf side of the upper lid 30, and a castable refractory may also be constructed. The method of providing this castable refractory may be a known method. For example, the castable refractory may be constructed on the back surface 31 side by dry spraying or wet spraying, etc.

[0038] The upper lid 30 may be provided with a first gas recovery port 32, a second gas recovery port 33, and a supply / discharge port 34. Each of these ports may be one or a plurality. The first gas recovery port 32 is used to recover the chlorine gas generated by the electrolysis of magnesium chloride in the electrolysis chamber 23. The first gas recovery port 32 is provided in the region where the electrolysis chamber 23 is located. Also, in the second gas recovery port 33, the gas generated by the electrolysis of magnesium chloride in the electrolysis chamber 23 may be recovered. The second gas recovery port 33 is provided in the region where the metal recovery chamber 24 is located. The second gas recovery port 33 may be used to recover the remaining gas that has flowed into the metal recovery chamber 24 without being recovered by the first gas recovery port 32 among the gases generated by electrolysis. Also, the supply / discharge port 34 is used for recovering the molten metal magnesium generated by the electrolysis of magnesium chloride in the electrolysis chamber 23 and for supplying the molten salt into the electrolytic cell 20. The supply / discharge port 34 is provided in the region where the metal recovery chamber 24 is located.

[0039] (Electrolysis chamber) In the electrolysis chamber 23, magnesium chloride is electrolyzed to generate molten metal magnesium and chlorine gas by the electrolysis. Inside the electrolysis chamber 23, as shown in FIGS. 2A and 2C, an anode 26, bipolar electrodes 27a, 27b, and a cathode 28 having an electrolysis surface substantially parallel to the depth direction of the molten salt bath Bf (vertical direction in FIG. 2A) are arranged. In the illustrated electrolysis chamber 23, two bipolar electrodes 27a, 27b are arranged, but at least one bipolar electrode may be arranged. Also, electrolysis can be carried out even when there is no bipolar electrode.

[0040] The anode 26 is inserted through the upper lid 30 and extends downward, and is arranged so that a part of it is immersed in the molten salt bath Bf. The shape of the anode 26 is not particularly limited, and examples include a plate shape, a cylindrical shape, and a prismatic shape. From the viewpoint of the production efficiency of molten metal magnesium, the molten salt electrolysis apparatus 100 may be provided with a plurality of anodes 26 and cathodes 28 respectively. The material of the anode 26 is not particularly limited, and examples thereof include graphite. The material of the cathode 28 is not particularly limited, and examples thereof include graphite, carbon steel, and the like.

[0041] The anode 26 and the cathode 28 are connected to a power source via a bus bar, a conductive wire, or the like. In molten salt electrolysis, magnesium chloride is decomposed into chlorine and metallic magnesium at the anode 26 and the cathode 28 based on a predetermined reaction such as the following chemical formula (1). MgCl 2 →Mg + Cl 2 ···Chemical formula (1)

[0042] As shown in FIG. 2A, the cathode 28 has an extension portion 28a that extends outward, and this extension portion 28a is arranged so as to penetrate the side wall 22 and the electrolytic cell case 10 and protrude to the outside thereof. The shape of the cathode 28 may be plate-shaped, but can be appropriately changed in consideration of the shape of the anode 26 and the like, and may be rectangular tubular, cylindrical, or the like. Even in this case, the cathode 28 has the extension portion 28a.

[0043] Note that the inter-pole distances between the anode 26 and the bipolar electrode 27a, the cathode 28 and the bipolar electrode 27a, and the bipolar electrode 27a and the bipolar electrode 27b may be the same as or different from each other.

[0044] (Metal recovery chamber) In the metal recovery chamber 24, the molten metal generated by electrolysis in the electrolysis chamber 23 is recovered. The metal recovery chamber 24 communicates with the electrolysis chamber 23 and may have a heat exchanger (not shown). The heat exchanger can adjust the temperature of the molten salt bath Bf in the electrolytic cell 20. The heat exchanger may be configured to include an inlet through which a fluid flows, an outlet through which the fluid is discharged, and a pipe connecting the inlet and the outlet. The pipe may be made of steel such as carbon steel and stainless steel.

[0045] Furthermore, the molten salt electrolysis apparatus 100 may further include a wall body (not shown) that reinforces the electrolytic cell case 10 from the outside. The wall body may be made of reinforced concrete in terms of strength. The reinforcing bars included in the reinforced concrete include, for example, austenitic stainless steel and ferritic stainless steel, and among them, austenitic stainless steel that is non-magnetic is preferable. The reason for this is that during the operation of the molten salt electrolysis apparatus, a magnetic field is generated in the system by energizing between the electrodes. Therefore, if the wall body includes reinforcing bars made of austenitic stainless steel, it is hardly affected by the magnetic field. On the other hand, since ferritic stainless steel is affected by the magnetic field and receives stress, the life of the reinforced concrete tends to be relatively short.

[0046] As another embodiment, the molten salt electrolysis apparatus may further include a heat exchange chamber (not shown) having a heat exchanger (not shown) in addition to the electrolysis chamber and the metal recovery chamber arranged side by side in the horizontal direction. For example, the molten metal can be recovered using the supply and discharge ports of the metal recovery chamber, and the molten salt such as molten magnesium chloride can be replenished to the heat exchange chamber. As a result, the molten metal can be stored more stably in the metal recovery chamber. In addition to these, the heat exchange chamber may further include a stirrer (not shown) for stirring the molten salt bath.

[0047] [4. Method for manufacturing metal] One embodiment of the method for manufacturing a metal according to the present invention includes an electrolysis step of electrolyzing magnesium chloride using the molten salt electrolysis apparatus 100 described above to produce metallic magnesium. Hereinafter, a preferred embodiment will be described by taking the case of using the molten salt electrolysis apparatus 100 shown in FIGS. 2A to 2C as an example. In a further embodiment, molten salt electrolysis of metal chlorides other than magnesium chloride can also be performed.

[0048] <Electrolysis step> In the electrolysis process, electrolysis of magnesium chloride contained in the molten salt bath Bf is carried out. The molten salt bath Bf flows from the electrolysis chamber 23 through the circulation port 25c into the metal recovery chamber 24 as shown by the arrow A in Fig. 2A, and flows from the metal recovery chamber 24 through the lower side of the second partition wall 25b into the electrolysis chamber 23 as shown by the arrow B in Fig. 2A. In the electrolysis chamber 23, magnesium chloride in the molten salt bath Bf is electrolyzed to produce molten magnesium metal. Then, this molten magnesium metal flows into the metal recovery chamber 24 by the flow of the molten salt bath Bf. Thereafter, the molten magnesium metal, which has a smaller specific gravity than the molten salt, floats to a shallow portion of the metal recovery chamber 24 and accumulates there. The molten magnesium metal floating in the metal recovery chamber 24 can be recovered by inserting a recovery pipe or the like into the supply and discharge port 34.

Example

[0049] The present invention will be specifically described based on examples and comparative examples. The following descriptions of the examples and comparative examples are merely test specific examples for facilitating the understanding of the technical content of the present invention, and the technical scope of the present invention is not limited by these specific examples.

[0050] [Test Example 1] (Examination of welding method) When welding a pair of semi-cylindrical split members 13 described later to fabricate the electrolytic cell case 10 shown in Fig. 1A by MIG welding, after stopping other operating electrolytic cells around it, the pair of semi-cylindrical split members 13 and the bottom member 12 were welded respectively. As a result, no fluctuation was confirmed in the direction of the arc of MIG welding.

[0051] [Test Example 2] An attempt was made to weld the pair of semi-cylindrical split members 13 and the bottom member 12 respectively in the same manner as in Test Example 1, except that other operating electrolytic cells around the fabrication of the electrolytic cell case 10 were not stopped. However, since the direction of the arc of MIG welding could not be determined, the welding was abandoned. The reasons for abandoning the welding include concerns about leakage of the molten salt bath and a decrease in the mechanical strength of the electrolytic cell case. Next, the assembly and operation of the molten salt electrolysis apparatus will be described.

[0052] [Example 1] (Operation Preparation of the Electrolytic Cell) In Example 1, in order to assemble the molten salt electrolysis apparatus 100 having the configuration shown in FIGS. 2A to 2C, the following was carried out. First, the electrolytic cell case 10 having the configuration shown in FIG. 1A was assembled on the reinforced concrete. At this time, as shown in Table 1, a pair of semi-cylindrical split members (size: width W2000 m × depth D750 m × height 1500 mm (see FIG. 1C)) 13 and the bottom member 12 were joined by MIG welding as shown in Table 1, respectively. Next, the outer periphery of the electrolytic cell case 10 was reinforced with reinforced concrete. The reinforcing bars contained in the reinforced concrete were made of austenitic stainless steel. Regarding the pair of semi-cylindrical split members 13, at a location different from the installation location of the molten salt electrolysis apparatus 100, a plurality of structural steel materials were combined into an assembly, and further, the inner surface side of the assembly was joined with a steel plate material to produce them. All materials were made of carbon steel. After production, the pair of semi-cylindrical split members 13 shown in FIG. 1C were placed on the truck bed and then transported to the installation location of the molten salt electrolysis apparatus 100 in one go as shown in Table 2.

[0053] Next, side walls 22, a bottom wall 21, a first partition wall 25a, and a second partition wall 25b were made of a shaped refractory (brick) containing aluminum oxide, and the electrolytic cell 20 was made. Next, the anode 26, the cathode 28, and two bipolar electrodes 27a, 27b were arranged in the electrolysis chamber 23. All of these electrodes were in the shape of plates. In order to close the opening on the upper side of the electrolytic cell 20, a carbon steel upper lid 30 was placed on the electrolytic cell 20. A layer of castable refractory, which is insulating, was applied to the lid back surface 31 of this upper lid 30.

[0054] Next, molten salt was introduced into the molten salt electrolysis apparatus 100, and the temperature of the molten salt was adjusted to 650 to 700°C. The composition of the molten salt was a ternary bath of magnesium chloride - calcium chloride - sodium chloride, and magnesium chloride was within the range of 10 to 25% by mass. The material of the anode 26 was graphite, and the material of the cathode 28 was carbon steel. The materials of the bipolar electrodes 27a and 27b were graphite. Also, the interelectrode distance was adjusted as follows. <Interelectrode distance> Interelectrode distance between the anode 26 and the bipolar electrode 27a: 10 mm Interelectrode distance between the bipolar electrode 27a and the bipolar electrode 27b: 10 mm Interelectrode distance between the bipolar electrode 27b and the cathode 28: 10 mm

[0055] (Production of metallic magnesium) The electrolysis process was carried out by supplying an electric current between the anode 26 and the cathode 28 through a conductive wire from a power source. After 36 months had passed since the start of electrolysis, the supply of the current was stopped.

[0056] [Evaluation] (Construction period) The construction period from when the electrolysis cell case was fabricated by MIG welding from a pair of semi-cylindrical split members and a bottom member was confirmed. Next, the relative value of the construction period of Example 1 was calculated when the construction period of Comparative Example 1 described later was taken as 100%.

[0057] (Maximum expansion distance of the left and right wall portions) The maximum expansion distance of the left and right wall portions 22b in a plan view was measured before the start of operation of the molten salt electrolysis apparatus 100 and after the stop of operation of the molten salt electrolysis apparatus 100. The expansion direction was along the arrow C shown in Fig. 2B. When the expansion distances were different between the left wall portion (the lower side of the left and right wall portions shown in Fig. 2B) and the right wall portion (the upper side of the left and right wall portions shown in Fig. 2B) of the left and right wall portions 22b, the larger expansion distance was taken as the maximum expansion distance.

[0058] (Damage to the partition wall) When the molten salt electrolysis apparatus was disassembled, the damage to the first partition wall and the second partition wall was visually confirmed.

[0059] [Comparative Example 1] In Comparative Example 1, an electrolytic cell case 210 having the configuration shown in FIG. 3A was assembled on reinforced concrete made of austenitic stainless steel. At this time, as shown in FIG. 3B, a pair of square tubular split members (size: width W2000m × depth D1500m × height 750m (see FIG. 3C)) 213 were arranged on the bottom member 212 and joined by MIG welding as shown in Table 1. Regarding the pair of square tubular split members 213, they were fabricated by combining a plurality of structural steel materials at a location different from the installation location of the molten salt electrolysis apparatus to form an assembly, and further joining the inner surface side of the assembly with steel plates. All materials were carbon steel. After fabrication, as shown in FIG. 3C, the square tubular split members 213 were placed on the truck bed and then transported to the installation location of the molten salt electrolysis apparatus in two separate trips. That is, only one square tubular split member 213 could be loaded on the truck bed.

[0060] Next, the outer periphery of the electrolytic cell case 210 was reinforced with reinforced concrete made of austenitic stainless steel. Except for this, a molten salt electrolysis apparatus was installed in the same manner as in Example 1. An electrolysis process was carried out by supplying an electric current between the anode and the cathode from a power source via a conductive wire. After 36 months had passed since the start of electrolysis, the supply of the electric current was stopped. Note that Table 2 shows the results of each evaluation.

[0061]

Table 1

[0062]

Table 2

[0063] (Consideration according to the example) Comparing Example 1 with Comparative Example 1, the pair of semi-cylindrical split members used in the electrolytic cell case in Example 1 was able to reduce the number of transports. Furthermore, in Example 1, the construction period of welding could be shortened. For this reason, it is presumed that it was useful that the joint part of the electrolytic cell case was formed at the butting part of the end faces of the pair of semi-cylindrical split members, and thus the joint part was formed in the height direction of the cylindrical member. During the operation of the molten salt electrolysis apparatus for 36 months in Example 1, molten salt invaded into a plurality of holes in the brick partition wall which is a porous body, and the brick partition walls expanded to the same extent in the extending direction respectively. Here, it is presumed that the expansion of the partition wall was buffered by the deformation of the electrolytic cell case to the outside in Example 1, and the occurrence of short circuits, such as the contact between the electrodes due to the expansion of the partition wall, was appropriately avoided.

Explanation of Reference Numerals

[0064] 10, 210 Electrolytic cell case 11 Cylindrical member 12, 212 Bottom member 13 Semi-cylindrical split member 14 End face 15 Joint part 16 Edge part 20 Electrolytic cell 21 Bottom wall 22 Side wall 22a Front and rear wall parts 22b Left and right wall parts 23 Electrolysis chamber 24 Metal recovery chamber 25 Partition wall 25a First partition wall 25b Second partition wall 25c Flow-through port 25d Base end part 26 Anode 27a, 27b Bipolar electrode 28 Cathode 28a Extension part 30 Upper lid 31 Inner surface of the lid 32 First gas recovery port 33 Second gas recovery port 34 Feed and drain port 100 Molten salt electrolysis device 213 Angular cylindrical dividing member Bf Molten salt bath

Claims

1. A steel electrolytic cell case for covering the outer surface of a brick-made electrolytic cell, comprising: a cylindrical member for covering the outer surface of the side wall of the electrolytic cell; and a bottom member connected to the cylindrical member for covering the outer surface of the bottom wall of the electrolytic cell, wherein the cylindrical member has a pair of semi-cylindrical split members and a joint portion where end faces of the pair of semi-cylindrical split members in the circumferential direction are butted and joined; the electrolytic cell case, wherein the joint portion is formed in the height direction of the cylindrical member.

2. The electrolytic cell case according to claim 1, wherein the joint portion of the cylindrical member of the electrolytic cell case is located on a surface positioned outside the base end portion of the partition wall of the electrolytic cell.

3. The electrolytic cell case according to claim 1 or 2, wherein the electrolytic cell is for electrolyzing magnesium chloride.

4. A method for manufacturing a steel electrolytic cell case for covering a brick-made electrolytic cell, comprising: an arranging step of arranging a pair of semi-cylindrical split members on a bottom member for covering the outer surface of the bottom wall of the electrolytic cell; and a welding step of forming a cylindrical member from the pair of semi-cylindrical split members by butting and welding end faces of the pair of semi-cylindrical split members in the circumferential direction after the arranging step.

5. A molten salt electrolysis apparatus comprising a brick-made electrolytic cell and a steel electrolytic cell case for covering the electrolytic cell, wherein the electrolytic cell case is the electrolytic cell case according to any one of claims 1 to 3; the electrolytic cell includes a bottom wall, side walls having front and rear wall portions respectively extending in the height direction from the bottom wall and left and right wall portions respectively connected to the front and rear wall portions, and a partition wall extending between the left and right wall portions.

6. The molten salt electrolysis apparatus according to claim 5, wherein the joint portion of the cylindrical member of the electrolytic cell case is located outside the left and right wall portions.

7. The molten salt electrolysis apparatus according to claim 5 or 6, further comprising a wall body for reinforcing the electrolytic cell case from the outside.

8. The molten salt electrolysis apparatus according to claim 7, wherein the wall body is made of reinforced concrete.

9. The molten salt electrolysis apparatus according to claim 8, wherein the reinforcing bars included in the reinforced concrete wall body are made of austenitic stainless steel.

10. A method for manufacturing a metal, comprising an electrolysis step of generating a metal from a metal chloride by performing molten salt electrolysis of the metal chloride using the molten salt electrolysis apparatus according to any one of claims 5 to 9.

11. The method for producing a metal according to claim 10, wherein in the electrolysis step, molten salt electrolysis of magnesium chloride is performed using the molten salt electrolysis apparatus to produce metallic magnesium from the magnesium chloride.

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