Layer thickness estimation method of molten material, and production method of titanium sponge

Abstract

To provide a layer thickness estimation method, which can make a good estimate of the layer thickness of at least one type of molten materials among multiple types of molten materials separated in layers in a container, and a production method of a titanium sponge.SOLUTION: A layer thickness estimation method of the present invention is a method of estimating the layer thickness TL1 or TL2 of at least one type of molten materials M1 and M2 in a container 11, in which multiple types of molten materials M1 and M2 with different densities are stored in layers. The layer thicknesses TL1 and TL2 of the molten materials M1 and M2 are estimated on the basis of the difference of between a measurement value of the surface height Ls of the molten materials M1 and M2 measured by a contact-type level meter 22 in consideration of the densities of the molten materials M1 and M2 under an assumption that the molten materials M1 and M2 stored in the container 11 are less than the multiple types, and a measurement value of the surface height Ls of the molten materials M1 and M2 measured by a non-contact-type level meter 23.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present invention relates to a method for estimating the layer thickness of at least one type of melt in a container in which multiple types of melts having different densities are stored in layers, and a method for producing titanium sponge. [Background technology]

[0002] In the Kroll process, which is widely used as a method for industrially producing titanium, the reduction reaction in which titanium tetrachloride is reduced with magnesium produces magnesium chloride as a by-product in addition to titanium. The magnesium chloride produced in the reduction reaction can be decomposed into magnesium and chlorine by molten salt electrolysis, and the magnesium obtained is used in the reduction reaction of titanium tetrachloride.

[0003] In the above-mentioned molten salt electrolysis, molten salt is stored in an electrolytic cell of an electrolytic device to form a molten bath, and a voltage is applied between the anode and cathode of the electrodes. Then, magnesium chloride in the molten bath is decomposed into magnesium and chlorine. This magnesium floats up in the molten bath in the electrolytic cell due to the density difference with the molten salt containing magnesium chloride, and accumulates at the upper side.

[0004] During molten salt electrolysis, magnesium chloride in the molten bath is consumed by electrolysis, and the bath surface height of the molten bath may fluctuate due to the supply of magnesium chloride to the molten bath, etc. Regarding the bath surface height of the molten bath, Patent Document 1 describes "a steel tubular level gauge that is immersed in the molten salt bath and measures the liquid level from the pressure value of argon or the like supplied inside."

[0005] Furthermore, Patent Document 2 describes "a molten salt electrolytic cell equipped with a bath surface adjustment device that adjusts the bath surface level by supplying an inert gas into a container-like structure installed below the bath surface in order to maintain the bath surface level and discharging the inert gas from within the structure, the molten salt electrolytic cell comprising, as an inert gas supply system for supplying inert gas into the structure, a precision control system that suppresses fluctuations in the bath surface level by controlling the amount of inert gas supplied when compensating for a drop in the bath surface level due to electrolytic consumption of molten salt during normal operation, and a high-speed control system that rapidly increases the amount of inert gas supplied to restore the bath surface level when there is an abnormal drop in the bath surface level due to the pumping out of electrolytically produced metal." [Prior art documents] [Patent documents]

[0006] [Patent Document 1] JP 2019-065355 A [Patent Document 2] JP 2015-140459 A Summary of the Invention [Problem to be solved by the invention]

[0007] For example, in molten salt electrolysis, the molten magnesium that is generated in the molten bath in the electrolytic cell and accumulates in a layer above the molten salt may be pumped out of the electrolytic cell. In that case, it is desirable to know how much of the layer of molten magnesium has accumulated in the upper part of the electrolytic cell.

[0008] In addition, the molten magnesium chloride and the multiple types of melts including molten magnesium recovered after the reduction reaction may be stored in a storage container or transported in a transport container in a state of being stored therein. In this case, the multiple types of melts may be separated into layers in the container, and it may be necessary to know the layer thickness of at least one of the types of melts.

[0009] In electrolytic cells and containers that may be made of bricks or steel, it is difficult to visually confirm the layer thickness of the molten material from the outside. It is also necessary to obtain information on the layer thickness in the container for melts other than molten magnesium chloride and molten magnesium.

[0010] An object of the present invention is to provide a layer thickness estimation method capable of accurately estimating the layer thickness of at least one type of melt among multiple types of melt separated into layers in a container, and a method for producing titanium sponge. [Means for solving the problem]

[0011] After much research, the inventors noticed that the multiple types of melt in the container have different densities, and discovered that the melt layer thickness can be estimated by using a contact level gauge, which measures the surface height of the melt while taking into account the melt density, in combination with a non-contact level gauge.

[0012] The layer thickness estimation method of the present invention is a method for estimating the layer thickness of at least one type of melt in a container in which multiple types of melt with different densities are stored in layers, and estimates the layer thickness of the melt based on the difference between the measured value of the surface height of the melt measured using a contact level meter, taking into account the density of the melt under the assumption that the amount of melt stored in the container is less than the multiple types of melt, and the measured value of the surface height of the melt measured using a non-contact level meter.

[0013] When measuring the measured value using the contact type level meter, it can be assumed that the molten material stored in the container is of two or less types.

[0014] The non-contact level meter may be a radar level meter or an ultrasonic level meter.

[0015] The plurality of melts may include a first melt and a second melt.

[0016] In this case, the contact type level meter is a pressure type level meter that measures the surface height of the melt based on the pressure of the second melt that is present at a position deeper than the first melt in the container, and the density ρ1 (g / cm 3 ), the density ρ2 (g / cm 3 ), gravitational acceleration g(m / s 2 ), the measurement value MVn (cm) of the non-contact level meter, and the measurement value MVc (cm) of the contact level meter, it is preferable to estimate the layer thickness TL1 (cm) of the first melt and / or the layer thickness TL2 (cm) of the second melt from the following equations (1) and (2). TL1+TL2=MVn (1) ρ1×TL1+ρ2×TL2=MVc×g×ρ2 (2)

[0017] The pressure type level gauge may be a back pressure type level gauge that uses an inert gas.

[0018] The vessel may be an electrolytic cell, a storage vessel or a transfer vessel.

[0019] The multiple melts may include molten magnesium and molten magnesium chloride.

[0020] The method for producing titanium sponge of the present invention involves referring to the layer thickness of the molten magnesium and / or the layer thickness of the molten magnesium chloride estimated by the above-mentioned layer thickness estimation method, removing the molten magnesium from the container, and using the molten magnesium to produce titanium sponge. Effect of the Invention

[0021] According to the layer thickness estimation method of the present invention, it is possible to accurately estimate the layer thickness of at least one type of melt among a plurality of types of melt separated into layers in a container. [Brief description of the drawings]

[0022] [Figure 1]1 is a cross-sectional view along the depth direction of a molten bath, showing a molten body that can be the subject of layer thickness estimation by a layer thickness estimation method of one embodiment of the present invention, together with a container in which the molten body is stored. FIG. [Diagram 2] 1 is a cross-sectional view taken along the depth direction of a molten bath, showing an example of a molten salt electrolysis apparatus to which a layer thickness estimation method according to an embodiment of the present invention can be applied. [Diagram 3] FIG. 3 is a cross-sectional view taken along line III-III in FIG. [Figure 4] FIG. 3 is a partial cross-sectional view similar to FIG. 2, showing another example of a molten salt electrolysis apparatus. [Diagram 5] 1 is a schematic diagram and photographs showing a method for verifying estimated values ​​of layer thickness in an embodiment. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0023] Hereinafter, an embodiment of the present invention will be described in detail.

[0024] (Layer thickness estimation method) A layer thickness estimation method according to one embodiment of the present invention estimates layer thicknesses TL1, TL2 of at least one type of melt M1, M2 in a container 21 storing multiple types of melts M1, M2 as illustrated in FIG.

[0025] The multiple types of melts M1 and M2 constitute at least a part of the molten bath Bm in the container 21, and in the illustrated example, the majority or almost the entirety of the molten bath Bm. The melts M1 and M2 are stored in layers in the container 21 due to their different densities. As shown in FIG. 1, the melts M1 and M2 are stored in layers in the container 21, separated via an interface Si. The melt M1, which has a relatively low density, floats vertically upward relative to the melt M2, which has a relatively high density, and forms a layer on the melt M2, which has a high density. On the other hand, the melt M2, which has a high density, sinks vertically downward relative to the melt M1, and exists in a layer below the melt M1, which has a low density. Here, the melt M1, which has a low density and is located on the upper side, is also called the first melt M1, and the melt M2, which has a high density and is located on the lower side, is also called the second melt M2.

[0026] Here, two types of melts M1 and M2 are stored in two layers in a container 21. Although not shown, in a container storing three or more types of melts each having a different density, the melts may be separated into three or more layers. However, in the case of three or more types of melts, it is sufficient that at least one of them has a different density from the remaining melts, and the remaining two or more melts may have substantially the same density. In other words, it is not necessary that all of the three or more melts have different densities. In addition to the melts M1 and M2, the molten bath Bm may contain a relatively small amount of melt such as a molten salt that does not form a layer.

[0027] In this embodiment, two types of level gauges are used to estimate the layer thicknesses TL1 and TL2 of the melts M1 and M2: a contact level gauge 22 that measures the height Ls of the surface Sm of the melts M1 and M2 while in contact with the melts M1 and M2, and a non-contact level gauge 23 that measures the surface height Ls of the melts M1 and M2 without contacting the melts M1 and M2. Note that although the layer thicknesses TL1 and TL2 can be grasped in a cross-sectional view such as that shown in Fig. 1, in reality, a container 21 made of brick, steel, or the like often does not have a transparent window in its side wall, making it difficult to visually confirm the layer thicknesses TL1 and TL2 from the outside.

[0028] Here, various types of contact type level gauges can be used as long as they take into consideration the densities of the melts M1 and M2 when measuring the surface height Ls and use the densities in the process of calculating the surface height Ls. As the contact type level gauge 22, a pressure type level gauge such as a differential pressure type level gauge or a back pressure type level gauge (a purge type level gauge) can be suitably used. The contact type level gauge 22 as a pressure type level gauge has a pipe 22a, at least a part of which is immersed in the molten bath Bm, and the immersed end 22b of the pipe 22a may be positioned at a depth that reaches at least the second melt M2 on the lower side.

[0029] In particular, in the contact type level gauge 22 of the back pressure type level gauge, as shown in FIG. 1, an inert gas such as argon gas or helium gas is supplied into the pipe 22a and released from the immersed end 22b to perform bubbling, and the pressure applied to the inside of the pipe 22a at that time is measured. The pressure is due to the melts M1 and M2 located vertically above the immersed end 22b of the pipe 22a, and is therefore equal to the product of the surface height Ls from the immersed end 22b, the density of the molten bath Bm, and the gravitational acceleration. According to the contact type level gauge 22 of the back pressure type level gauge, the surface height Ls is obtained in this manner. Here, the position of the immersed end 22b of the contact type level gauge 22 in the molten bath Bm becomes the reference height SL, and the surface height Ls means the height relative to the reference height SL.

[0030] Specific examples of the non-contact level meter 23 include radar level meters and ultrasonic level meters. In particular, radar level meters using electromagnetic waves are preferred because they allow measurement without being affected by the atmosphere inside the container 21, which may be an electrolytic cell. Of the electromagnetic waves, radar level meters that irradiate and detect microwaves are preferably usable.

[0031] The non-contact level meter 23, which is a radar type level meter or an ultrasonic level meter, irradiates electromagnetic waves or ultrasonic waves toward the surface Sm of the melts M1 and M2, and detects the reflected waves caused by the electromagnetic waves or ultrasonic waves being reflected by the surface Sm. In the TOF (Time of Flight) method, the distance between the non-contact level meter 23 and the surface Sm may be calculated from the time taken from when the non-contact level meter 23 irradiates electromagnetic waves or ultrasonic waves to when the non-contact level meter 23 detects the reflected waves. Specifically, the distance between the non-contact level meter 23 and the surface Sm is calculated by multiplying half the time (propagation time) from irradiation to detection by the speed of the electromagnetic waves or ultrasonic waves. Alternatively, in the case of a phase difference detection method, the distance between the surface Sm is calculated from the phase difference between the irradiated wave and the reflected wave. Alternatively, the distance between the surface Sm may be calculated using a triangulation method. When the distance between the non-contact level meter 23 and the surface Sm is obtained in this manner, the surface height Ls is calculated by subtracting this distance from the height of the non-contact level meter 23. When used in conjunction with the contact level meter 22, when the surface height Ls is measured with the non-contact level meter 23, the height of the non-contact level meter 23 is taken as the height from the reference height SL at which the immersed end 22b of the contact level meter 22 is located.

[0032] In particular, when the vessel 21 is an electrolytic cell 2 described below, the TOF type non-contact level meter 23 is preferable. In the electrolytic cell 2 (see FIG. 2), for example, it is necessary to ensure high airtightness inside in order to suppress leakage of chlorine generated inside, and the TOF type non-contact level meter 23 allows measurement even through a narrow gap. Furthermore, the TOF type non-contact level meter 23 can measure the surface height Ls with relatively high accuracy even if waves occur on the bath surface of the molten bath Bm.

[0033] The measurement of the surface height Ls by the contact level meter 22 is performed under the assumption that the number of types of melt stored in the container 21 is less than two. For example, in the container 21 storing two types of melts M1 and M2 as illustrated in FIG. 1, it can be assumed that the container 21 contains only one type of second melt M2. In this case, the measurement value of the surface height Ls by the contact level meter 22 is a value in the absence of the first melt M1, and a difference occurs between the measurement value by the non-contact level meter 23. Based on this difference, the layer thickness TL1 of the first melt M1 can be estimated.

[0034] More specifically, for example, when the contact-type level gauge 22 is the pressure-type level gauge described above, the density ρ1 (g / cm 3 ), density of the second melt ρ2 (g / cm 3 ), gravitational acceleration g(m / s 2 ), the measurement value MVn (cm) of the non-contact level meter, and the measurement value MVc (cm) of the contact level meter, the layer thickness TL1 (cm) of the first melt M1 can be obtained by solving the simultaneous equations of formula (1): TL1 + TL2 = MVn and formula (2): ρ1 × TL1 + ρ2 × TL2 = MVc × g × ρ2. Once the layer thickness TL1 of the first melt M1 is obtained, the layer thickness TL2 (cm) of the second melt M2 can also be obtained by subtracting the layer thickness TL1 from the surface height Ls.

[0035] The above formula (1) holds true for the measurement value of the non-contact level meter 23. Regarding the above formula (2), the pressure at the actual immersed end 22b on the left side is equal to the pressure found from the measurement value of the contact level meter 22 under the assumption of only the second melt M2 on the right side, and therefore formula (2) holds true.

[0036] To reiterate, here, the surface height Ls of the melt, and the layer thickness TL1 of the first melt and the layer thickness TL2 of the second melt refer to the height or layer thickness based on the reference height SL (i.e., the reference height SL is set as zero height, and the height is above the reference height SL).

[0037] In this embodiment, as described above, the layer thicknesses of the melts M1 and M2 can be accurately estimated by using the measurement values ​​of the contact-type level gauge 22 and the non-contact-type level gauge 23 under certain assumptions.

[0038] (Method of manufacturing titanium sponge) As mentioned above, to produce titanium by the Kroll process, titanium tetrachloride is reduced with magnesium by, for example, dropping titanium tetrachloride into molten magnesium. During this process, titanium sponge mass is produced and magnesium chloride is generated as a by-product.

[0039] Magnesium chloride can be used to reduce titanium tetrachloride by performing molten salt electrolysis using a molten salt electrolysis apparatus 1 as shown in Fig. 2. During this process, magnesium chloride is decomposed to generate chlorine gas in addition to magnesium. Details of this type of molten salt electrolysis will be described below.

[0040] The illustrated molten salt electrolysis apparatus 1 comprises a container-shaped electrolytic cell 2 made of firebricks with a molten bath Bm inside, electrodes 3 including an anode 3a and a cathode 3b that are partially immersed in the molten bath Bm in the electrolytic cell 2, and a lid 5 that covers the upper opening of the electrolytic cell 2.

[0041] In this example, a partition wall 4 is provided inside the electrolytic cell 2, and is disposed substantially along the depth direction (the vertical direction in FIG. 2). The partition wall 4 divides the inside of the electrolytic cell 2 into an electrolysis chamber 2a located on the right side of FIG. 2, where electrolysis takes place, and a recovery chamber 2b located on the left side of FIG. 2, into which magnesium obtained by electrolysis in the electrolysis chamber 2a flows and which accumulates at the upper side due to the density difference with the molten salt. Note that the lid 5 may be divided into a portion covering the opening on the electrolysis chamber 2a side of the electrolytic cell 2 and a portion covering the opening on the recovery chamber 2b side, for example, as shown in FIG. 2.

[0042] In the illustrated example, the partition wall 4 is disposed on the upper side close to the lid body 5. As a result, a molten salt circulation path 4a that enables the movement of the molten bath Bm from the recovery chamber 2b to the electrolysis chamber 2a is formed between the partition wall 4 and the bottom surface inside the electrolysis cell 2. In addition, a molten metal flow path 4b provided in a portion of the partition wall 4 above the molten salt circulation path 4a enables magnesium to flow from the electrolysis chamber 2a to the recovery chamber 2b. Although the partition wall 4 is installed in two separate locations, left and right, in FIG. 2, the configuration, such as the shape and number, can be appropriately changed as long as the molten salt circulation path 4a and the molten metal flow path 4b can be provided.

[0043] The electrodes 3 are disposed on the electrolysis chamber 2a side inside the electrolysis cell 2, and have portions arranged side by side in a direction parallel to the depth direction of the molten bath Bm. The electrodes 3 include an anode 3a and a cathode 3b that are connected to a power source or the like (not shown).

[0044] As long as the electrodes 3 have at least an anode 3a and a cathode 3b, they can electrolyze magnesium chloride in the molten bath Bm. On the other hand, from the viewpoint of improving the efficiency of magnesium production by electrolysis, it is preferable to further have one or more, for example two, bipolar electrodes 3c between the anode 3a and the cathode 3b that are not connected to a power source and are polarized by application of a voltage between the anode 3a and the cathode 3b, as can be seen from Fig. 3. However, such a bipolar electrode 3c is not necessarily required.

[0045] The molten salt electrolysis apparatus 1 in FIG. 2 and FIG. 3 has a plate-shaped anode 3a, a cathode 3b, and a bipolar electrode 3c arranged side by side, but the molten salt electrolysis apparatus 11 may have an anode 13a, a cathode 13b, and a bipolar electrode 13c with the shape and arrangement shown in FIG. 4. The molten salt electrolysis apparatus 11 has a columnar or plate-shaped anode 13a such as a square column extending inside and outside the electrolysis cell 12 along the depth direction of the molten bath Bm, a rectangular cylindrical cathode 13b such as a square cylindrical cathode arranged at a distance from the anode 13a to surround the periphery of the anode 13a, and a rectangular cylindrical bipolar electrode 13c arranged between the anode 13a and the cathode 13b. Although not shown in the figure, the electrodes may have a cylindrical anode and a cylindrical cathode and bipolar electrode. The rectangular cylindrical bipolar electrode 13c and the cylindrical bipolar electrode may be omitted. The configuration of the molten salt electrolysis apparatus 11 in Fig. 4 other than the anode 13a, the cathode 13b, and the bipolar electrode 13c can be substantially similar to that of the molten salt electrolysis apparatus 1 in Fig. 2 and Fig. 3, and detailed description thereof will be omitted. In the molten salt electrolysis apparatus 11 in Fig. 4, a partition wall 14 that separates the electrolysis chamber 12a in which the anode 13a, the cathode 13b, and the bipolar electrode 13c are arranged from a recovery chamber (not shown) is provided perpendicular to the portion of the cathode 13b that passes through the electrolysis cell 12 and extends to the outside.

[0046] The molten salt electrolysis apparatus 1 may further include a temperature adjustment tube or the like (not shown) arranged in the recovery chamber 2b or the like as a heat exchanger for adjusting the temperature of the molten bath Bm.

[0047] The molten salt that mainly constitutes the molten bath Bm may include a supporting salt in addition to magnesium chloride (MgCl2). The supporting salt means an electrolyte that lowers the crystallization temperature and reduces the viscosity when mixed with magnesium chloride. Specifically, the supporting salt may be at least one selected from the group consisting of sodium chloride (NaCl), calcium chloride (CaCl2), potassium chloride (KCl), magnesium fluoride (MgF2) and calcium fluoride (CaF2). The crystallization temperature refers to the temperature at which a phenomenon called crystallization occurs, in which one electrolyte component begins to precipitate as a solid, when the temperature of a molten salt consisting of two or more electrolytes is lowered from a liquid state. If there is only one type of molten salt, the entire salt becomes solid at the freezing point when the temperature is lowered from a liquid state, so the crystallization temperature corresponds to the freezing point, i.e., the melting point. In addition, in order to preferentially decompose magnesium chloride by electrolysis, it is common to use an electrolyte with a higher decomposition voltage than magnesium chloride as the supporting salt.

[0048] In molten salt electrolysis performed using the molten salt electrolysis apparatus 1, magnesium chloride is electrolyzed in the electrolysis chamber 2a, and based on the reaction MgCl2→Mg+Cl2, molten metal magnesium (Mg) is produced by a reduction reaction on the surface of the cathode 3b, and chlorine (Cl2) gas is generated by an oxidation reaction on the surface of the anode 3a.

[0049] More specifically, due to convection of the molten bath Bm, as shown in FIG. 2, the molten salt flows from the recovery chamber 2b through the molten salt circulation path 4a on the bottom side to the electrolysis chamber 2a. In the electrolysis chamber 2a, magnesium chloride in the molten salt is electrolyzed to generate magnesium. This magnesium flows into the recovery chamber 2b through the molten metal flow path 4b on the surface Sm side of the partition wall 4. Thereafter, the magnesium, which has a smaller specific gravity than the molten salt, floats to a shallow portion of the recovery chamber 2b and accumulates there. The magnesium that floats in the recovery chamber 2b can be collected by a pump or the like (not shown). Therefore, such molten salt electrolysis can produce magnesium. In addition, chlorine gas is also obtained.

[0050] The magnesium produced by molten salt electrolysis can be used to reduce titanium tetrachloride in the Kroll process for producing titanium, and the chlorine gas can be used to chlorinate titanium ore. Magnesium chloride, which is a by-product of the Kroll process, can be used as the raw material for molten salt electrolysis.

[0051] The above-mentioned molten salt electrolysis apparatus 1 can produce not only magnesium but also aluminum and zinc. In addition, the metal produced in the electrolytic cell 2 using the molten salt electrolysis apparatus 1 can be used for the reduction of metal chlorides, not limited to titanium tetrachloride, and can be used to produce zirconium, hafnium, or metallic silicon in addition to titanium.

[0052] Incidentally, the molten magnesium that accumulates at the upper side in the recovery chamber 2b of the electrolytic cell 2 is pumped out and recovered, and it is desirable to grasp the thickness of this molten magnesium layer. If the thickness of the molten magnesium layer is not known, the amount of molten magnesium pumped out will be insufficient, and there is a concern that the molten magnesium remaining in the electrolytic cell 2 will be oxidized to produce magnesium oxide, which will reduce the current efficiency. Furthermore, if the thickness of the molten magnesium layer is not known, the molten salt will be pumped out together with the molten magnesium, and the composition of the molten salt may change when the molten salt is returned to the electrolytic cell. Furthermore, electrolytic cells 2 made of bricks or the like generally have no windows in the side walls, making it difficult to visually check the thickness of the molten magnesium layer from the outside.

[0053] In such a case, the layer thickness estimation method described above can be suitably used. In this case, the container 21 described above (see FIG. 1) is used as the electrolytic cell 2, the first melt M1 is used as the molten metal (molten magnesium), the second melt M2 is used as the molten salt, and the contact level gauge 22 and the non-contact level gauge 23 provided in the electrolytic cell 2 can be used. The molten salt as the second melt M2 includes magnesium chloride, and in some cases may also include a supporting salt. In this case, the molten metal and the molten salt are regarded as different types, and the magnesium chloride and the supporting salt are regarded as the same type, since they are both salts or compounds. Therefore, the molten bath Bm in the electrolytic cell 2 can be considered to be mainly composed of two types of materials, molten metal and molten salt. The specific layer thickness estimation method is the same as that described above, and therefore will not be described again.

[0054] The non-contact level gauge 23 can be installed at any location that does not contact the molten bath Bm, as long as it is possible to irradiate the surface Sm of the molten bath Bm with electromagnetic waves or ultrasonic waves and detect the reflected waves from the surface Sm. It is preferable to install the non-contact level gauge 23 on the cover body 5 located above the surface Sm, since it is easy to handle and can perform high-precision measurements. As shown in FIG. 2, the non-contact level gauge 23 is installed on the part of the cover body 5 that covers the opening on the recovery chamber 2b side. More specifically, for example, when the non-contact level gauge 23 is a radar type level gauge, a through hole can be formed in the cover body 5, and the through hole can be sealed with a glass plate 7 such as Vycor through which electromagnetic waves and reflected waves can pass. However, the material provided in the through hole is not limited to the glass plate 7, and may be any material that can transmit the electromagnetic waves or ultrasonic waves of the non-contact level gauge 23, does not allow chlorine gas to pass, and has appropriate thermal insulation. The non-contact level meter 23 can be attached to a mounting stand 8 provided on the glass plate 7 so that electromagnetic waves or ultrasonic waves can be irradiated toward the surface Sm through the glass plate 7. By sealing the through hole of the lid 5 with the glass plate 7, it is possible to suppress leakage of chlorine gas from the electrolytic cell 2, and also to obtain a thermal insulation effect against the heat of the molten bath Bm.

[0055] The contact level gauge 22 may be disposed, for example, near the non-contact level gauge 23, through a through hole provided in the lid 5. However, the non-contact level gauge 23 and the contact level gauge 22 may be disposed at any place where magnesium in the molten bath Bm in the electrolytic cell 2 is present, and may be disposed at any place other than the above, as appropriate. During molten salt electrolysis, the convection of the molten bath Bm described above causes the molten salt to circulate through the recovery chamber 2b and the electrolytic chamber 2a, and the magnesium that has risen to the surface and accumulated in the recovery chamber 2b may be affected by this flow. For this reason, the interface Si may actually fluctuate slightly up and down, but in FIG. 2, the interface Si is shown as a straight line parallel to the horizontal direction for convenience of explanation. According to this embodiment, it may be possible to estimate the layer thickness even in the electrolytic cell 2 during molten salt electrolysis where such interface Si may fluctuate slightly.

[0056] The thickness of the molten magnesium layer can be estimated by using the measured values ​​of the contact level gauge 22 and the non-contact level gauge 23. If necessary, the thickness of the molten magnesium chloride layer can be estimated. In response to this, the molten magnesium can be taken out of the electrolytic cell 2 and used to produce titanium sponge.

[0057] Although not shown, when producing titanium sponge, in addition to the above-mentioned electrolytic cell 2, a transfer container used for transferring a melt containing molten magnesium chloride and / or molten magnesium between the reduction container and the electrolytic cell 2, and a storage container used for storing the melt may be used. The layer thickness estimation method of the above-mentioned embodiment can be applied not only to the case where the container 21 is the electrolytic cell 2, but also to the case where the transfer container or storage container is made of steel or the like. EXAMPLES

[0058] Next, the layer thickness estimation method of the present invention was experimentally implemented to confirm its effectiveness, which will be described below. However, the description here is merely for illustrative purposes and is not intended to be limiting.

[0059] As shown in FIG. 1, a back pressure level gauge was used as the contact level gauge 22, and a radar level gauge was used as the non-contact level gauge 23, to estimate the layer thickness of the molten magnesium for each of Sample 1 and Sample 2, which are molten baths containing molten magnesium and molten salt (MgCl2-NaCl-CaCl2) in an electrolytic cell as a vessel 21. The layer thicknesses for Sample 1 and Sample 2 were estimated using the above-mentioned formulas (1) and (2). More specifically, the simultaneous equations of formulas (1) and (2) were solved to calculate the layer thickness of the molten magnesium from the measured values ​​of the back pressure level gauge and the radar level gauge, and the densities of the molten magnesium and molten salt. For the calculation, a density of magnesium when molten (at about 660°C) of 1.6 g / cm was used. 3 The density of molten salt (MgCl2-NaCl-CaCl2, about 660°C) is 1.8 g / cm 3 , the acceleration of gravity is 9.8m / s 2 was used.

[0060] The estimated layer thickness (theoretical Mg layer thickness) of Sample 1 and Sample 2 was verified by inserting a tube into the molten bath (electrolytic bath) in an electrolytic cell as shown in Figure 5, and after the molten bath had entered the tube, the tube was removed from the molten bath with the upper end blocked, and the length of the solidified magnesium part in the tube was measured. This length of the solidified magnesium part was the value at room temperature, so it was assumed that the density of magnesium at room temperature (1.5 g / cm 3 ) and the density of magnesium when molten (about 660℃) (1.6g / cm 3 ) was used to correct the result and use it as the magnesium layer thickness (Mg layer thickness). Note that it is assumed here that the volume of the tube does not change when magnesium is collected through the tube. The results are shown in Table 1. Note that "Ar type" in Table 1 refers to a "back pressure type level meter" and "radar type" refers to a "radar type level meter."

[0061] [Table 1]

[0062] As can be seen from Table 1, the errors between the estimated layer thicknesses of Sample 1 and Sample 2 and the magnesium layer thickness were relatively small. This suggests that the present invention may enable good estimation of the layer thickness of at least one type of melt among multiple types of melts separated into layers in a container. [Explanation of symbols]

[0063] 1, 11 Molten salt electrolysis equipment 2, 12 Electrolytic cell 2a Electrolysis room 2b Recovery Room 3 electrodes 3a, 13a anode 3b, 13b cathode 3c, 13c bipolar 4, 14 Bulkhead 4a Molten salt circulation path 4b Molten metal flow path 5 Lid 7 Glass Plate 8 Installation stand 21 Container 22 Contact type level gauge 22a Pipe 22b Immersed end 23 Non-contact level gauge Bm molten bath Ls Surface height of melt M1 First molten body (molten body) M2 Second molten body (molten body) MVc contact level gauge measurement value MVn non-contact level meter measurement value SL Reference height Silicon melt interface Surface of Sm melt TL1 Thickness of the first melt layer (layer thickness) TL2 Layer thickness of the second melt (layer thickness)

Claims

1. A method for estimating a layer thickness of at least one type of melt in a container in which multiple types of melts having different densities are stored in layers, comprising the steps of: A layer thickness estimation method for estimating a melt layer thickness based on the difference between a measured value of the melt surface height measured by a contact level meter, taking into account the melt density under the assumption that the amount of melt stored in the container is less than the multiple types of melt, and a measured value of the melt surface height measured by a non-contact level meter.

2. The layer thickness estimation method according to claim 1 , wherein when the measured value is measured by the contact type level meter, it is assumed that the molten material stored in the container is of two or less types.

3. The layer thickness estimating method according to claim 1 or 2, wherein the non-contact level meter is a radar level meter or an ultrasonic level meter.

4. The layer thickness estimation method according to claim 1 , wherein the plurality of types of melts include a first melt and a second melt.

5. the contact type level meter is a pressure type level meter that measures a surface height of the melt based on a pressure of the second melt that is present at a position deeper than the first melt in the container, The density ρ1 (g / cm 3 ), the density ρ2 (g / cm 3 ), gravitational acceleration g (m / s 2 5. The layer thickness estimation method according to claim 4, wherein the layer thickness TL1 (cm) of the first melt and / or the layer thickness TL2 (cm) of the second melt are estimated from the measurement values ​​MVn (cm) of the non-contact level meter and MVc (cm) of the contact level meter according to the following formulas (1) and (2): TL1+TL2=MVn (1) ρ1×TL1+ρ2×TL2=MVc×g×ρ2 (2)

6. The layer thickness estimation method according to claim 5 , wherein the pressure type level gauge is a back pressure type level gauge that uses an inert gas.

7. The layer thickness estimation method according to claim 1 or 2, wherein the container is an electrolytic cell, a storage container, or a transfer container.

8. The layer thickness estimation method according to claim 1 or 2, wherein the plurality of types of melts include molten magnesium and molten magnesium chloride.

9. A method for producing titanium sponge, comprising the steps of: referring to a layer thickness of the molten magnesium and / or a layer thickness of the molten magnesium chloride estimated by the layer thickness estimation method according to claim 8; removing the molten magnesium from the container; and producing titanium sponge using the molten magnesium.

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