Method and filling pump for filling metal container with molten sodium

Abstract

Provided is a filling pump suitable for highly accurately filling a metal container with a predetermined amount of molten sodium. The filling pump is for filling a metal container with molten sodium from a tank that stores the molten sodium. The filling pump comprises: a molten sodium accommodation chamber that has an inlet linked to the tank and an outlet linked to the metal container; and a volume control unit that has a bellows and a movable plate for closing one opening end of the bellows, and that is capable of changing the volume of the accommodation chamber through expansion and contraction of the bellows.

Description

Method and filling pump for filling molten sodium into a metal container 【0001】 The present invention relates to a method and a filling pump for filling molten sodium into a metal container. In particular, the present invention relates to a method and a filling pump for filling molten sodium into a negative electrode container of a sodium-sulfur battery that can be used as a secondary battery such as for power storage. 【0002】 A sodium-sulfur battery (hereinafter also referred to as a "NAS battery") has, for example, a bottomed cylindrical component made of a solid electrolyte such as β-alumina disposed in a metal container on the positive electrode side serving as a storage case, and sodium as a negative electrode active material is contained inside the bottomed cylindrical component, and sulfur as a positive electrode active material is contained outside. And, in the sodium-sulfur battery, when discharging, ionized sodium permeates through the solid electrolyte and reacts with sulfur to generate sodium polysulfide while generating electricity, and on the contrary, sodium and sulfur are generated by the reverse reaction to perform charging. 【0003】 Patent Document 1 describes a method of moving a predetermined amount of molten metal sodium from a sodium storage tank into a sodium metering tank, and then filling the metal sodium into a sodium solid electrolyte tube through a pipeline from the sodium metering tank. 【0004】 Japanese Patent Laid-Open No. 01-218613 【0005】 In a NAS battery, sodium as a negative electrode active material is filled in a metal container. The amount of sodium contained in the metal container is predetermined according to the required battery performance. Therefore, it is required to accurately fill a predetermined amount of sodium into the metal container. Patent Document 1 describes a method of metering sodium with a sodium metering tank and then filling molten metal sodium into a solid electrolyte tube. 【0006】However, Patent Document 1 lacks sufficient discussion from the perspective of filling a predetermined amount of molten sodium into a metal container with high precision. Therefore, in one embodiment of the present invention, the object of providing a method for filling a predetermined amount of molten sodium into a metal container with high precision. In another embodiment of the present invention, the object of providing a filling pump suitable for filling a predetermined amount of molten sodium into a metal container with high precision. 【0007】 The inventors of this invention have diligently studied and developed the present invention as illustrated below in order to solve the above problems. 【0008】[Aspect 1] A method for filling a metal container with a predetermined allowable amount of molten sodium from a tank storing molten sodium via a filling pump, wherein the filling pump comprises a molten sodium storage chamber having an inlet communicating with the tank and an outlet communicating with the metal container, and a volume control unit having a bellows and a movable plate that closes one open end of the bellows, and capable of changing the volume in the storage chamber by the expansion and contraction of the bellows, A1 of investigating the correlation between the height of the molten sodium in the tank, the stroke distance when contracting and extending the bellows, and the amount of sodium to be filled into the metal container, B1 of determining filling conditions, including the height of the molten sodium in the tank and the stroke distance when contracting and extending the bellows, that are suitable for filling the metal container with a predetermined allowable amount of molten sodium from the tank via the filling pump, A method comprising: step C1, which increases the volume of the containment chamber by contracting the bellows according to the filling conditions, and introduces molten sodium from the tank into the containment chamber of the filling pump through the inlet; and step D1, which decreases the volume of the containment chamber by extending the bellows according to the filling conditions, and fills the metal container with molten sodium from the filling pump through the outlet.[Aspect 2] A method for filling a metal container with a predetermined allowable amount of molten sodium from a tank storing molten sodium via a filling pump, wherein the filling pump comprises a molten sodium storage chamber having an inlet communicating with the tank and an outlet communicating with the metal container, and a volume control unit having a bellows and a movable plate that closes one open end of the bellows, and capable of changing the volume in the storage chamber by the expansion and contraction of the bellows, Step A2: Investigating the correlation between the height of the molten sodium in the tank, the stroke distance when the bellows is contracted and extended, and the amount of sodium to be filled into the metal container, Step B2: Determining the lower and upper limits of the height of the molten sodium in the tank based on the correlation, such that when the bellows is contracted and extended by a predetermined stroke distance, the amount of molten sodium to be filled into the metal container falls within the predetermined allowable range. A method comprising: step C2, when the height of molten sodium in the tank is within the range from the lower limit to the upper limit, contracting the bellows by a predetermined stroke distance to increase the volume of the containment chamber, and introducing molten sodium from the tank into the containment chamber of the filling pump via the inlet; and step D2, when the bellows is extended by a predetermined stroke distance to decrease the volume of the containment chamber, and filling the metal container with molten sodium from the filling pump via the outlet. [Aspect 3] The method according to aspect 1 or 2, wherein the metal container is a component of a battery that uses Na as the positive electrode and / or negative electrode. [Aspect 4] The method according to any one of aspects 1 to 3, wherein the tank is equipped with one or more liquid level sensors capable of measuring the height of molten sodium. [Aspect 5] The method according to any one of aspects 1 to 4, wherein step D1 or step D2 is performed in an inert atmosphere. [Aspect 6] The method according to any one of aspects 1 to 5, wherein the bellows is equipped with stainless steel folds. [Aspect 7] The method according to any one of aspects 1 to 6, wherein the space above the liquid level of molten sodium in the tank is filled with an inert gas. [Aspect 8] The method according to any one of aspects 1 to 7, wherein the expansion and contraction of the bellows is controlled by a linear servo motor.[Aspect 9] The method according to any one of aspects 1 to 8, wherein step D1 or D2 includes the flow of molten sodium into the metal container from a supply port communicating with the outlet of the filling pump, the vertical distance between the supply port and the inner bottom surface of the metal container when the molten sodium is first supplied into the metal container is 20 mm or less, and thereafter, after the liquid level of the molten sodium rises and the supply port is submerged in the molten sodium, the supply of molten sodium into the metal container is continued with the supply port submerged in the molten sodium. [Aspect 10] The method according to any one of aspects 1 to 9, wherein after carrying out step D1 or D2, degassing is performed to remove any remaining air bubbles in the molten sodium filled in the metal container. [Aspect 11] A filling pump for filling a metal container with molten sodium from a tank for storing molten sodium, the filling pump comprising: a molten sodium storage chamber having an inlet communicating with the tank and an outlet communicating with the metal container; and a volume control unit having a bellows and a movable plate that closes one open end of the bellows, and capable of changing the volume in the storage chamber by the expansion and contraction of the bellows. [Aspect 12] The filling pump according to aspect 11, wherein the bellows is made of metal pleats. [Aspect 13] The filling pump according to aspect 11, wherein the bellows is made of stainless steel pleats. [Aspect 14] The filling pump according to any one of aspects 11 to 13, wherein the expansion and contraction of the bellows is controlled by a linear servo motor. 【0009】 According to one embodiment of the present invention, a method for filling a metal container with molten sodium can be used to fill a predetermined amount of molten sodium into the metal container with high precision. Furthermore, a filling pump for filling a metal container with molten sodium according to one embodiment of the present invention can be suitably used to fill a metal container with a predetermined amount of molten sodium with high precision. 【0010】This is a schematic diagram of a filling system suitable for carrying out a method for filling a metal container with molten sodium according to one embodiment of the present invention. This is a schematic diagram showing the internal structure of a filling pump. This is a schematic diagram showing an example of the configuration of a sealed chamber suitable for carrying out the process of filling a metal container with molten sodium. 【0011】 Next, embodiments of the present invention will be described in detail with reference to the drawings. The present invention is not limited to the following embodiments, and it should be understood that appropriate design changes, improvements, etc., can be made based on the ordinary knowledge of those skilled in the art, without departing from the spirit of the invention. 【0012】 <1. Filling System> Figure 1 shows a schematic diagram of a filling system 100 useful for carrying out a method for filling a metal container with molten sodium according to one embodiment of the present invention. The filling system 100 comprises a tank 110 for storing molten sodium, a filling pump 120, and a metal container 130. 【0013】 (1-1. Tank) Tank 110 has an inlet 111 for molten sodium that communicates with a receiving tank (not shown), and an outlet 112 for molten sodium that communicates with a filling pump 120. The inlet 111 can communicate with the receiving tank via piping 141. A valve 161 can be provided in the middle of piping 141 (typically outside and near tank 110) to control the inflow of molten sodium into tank 110. The outlet 112 can communicate with the filling pump 120 via piping 142. A valve 162 can be provided in the middle of piping 142 (typically outside and near tank 110) to control the outflow of molten sodium from tank 110. 【0014】 The body of the tank 110 can be made of a metal such as stainless steel (e.g., SUS304, SUS316). The molten sodium pipes 141 and 142 can be made of a metal such as stainless steel. 【0015】 The height of molten sodium in tank 110 has a lower limit (H min ) and upper limit (H maxA limit is set. It is preferable that the outlet 112 is located below the lower limit and the inlet 111 is located above the upper limit. It is desirable to install one or more liquid level sensors (e.g., continuous level meter, level switch, etc.) capable of measuring the height of molten sodium in the tank 110 and to monitor the liquid level of molten sodium in the tank 110. In the illustrated embodiment, a liquid level sensor 115a for detecting the upper limit and a liquid level sensor 115b for detecting the lower limit are provided. 【0016】 To ensure safety, it is preferable to fill the space above the liquid level of molten sodium in the tank 110 with an inert gas. Examples of inert gases include nitrogen, argon, and helium. One type of inert gas may be used alone, or two or more types may be mixed. The inert gas is supplied from the inlet 113 via a pipe 151 that is connected to a gas cylinder (not shown). A valve 163 capable of controlling the inflow of the inert gas into the tank 110 can be provided in the middle of the pipe 151. The pressure of the inert gas in the tank 110 can be set to, for example, 40 to 60 kPa (e.g., 45 kPa) (gauge pressure) when the height of the molten sodium in the tank 110 is at its upper limit. Setting the internal pressure within this range has the advantage of preventing oxidation of the sodium. 【0017】 Although not shown in the diagram, the tank 110 is covered with insulating material for heat retention and is equipped with a heater. A suitable heater is, for example, a jacket-type heater through which a heat transfer oil circulates. In a jacket-type heater, a jacket, piping, and a pump are circulated to an electric heater (not shown), and the heat transfer oil circulates between the electric heater and the jacket to maintain the temperature of the molten sodium in the tank 110. The temperature of the molten sodium in the tank 110 is maintained at, for example, 120 to 150°C. The piping through which the molten sodium flows is also covered with insulating material for heat retention. 【0018】(1-2. Filling Pump) Figure 2 schematically shows the internal structure of the filling pump 120. The filling pump 120 includes a molten sodium storage chamber 124 having an inlet 121 communicating with the tank 110 and an outlet 122 communicating with the metal container 130, and a volume control unit 126 having a bellows 127 and a movable plate 128 that closes one open end of the bellows 127, which can change the volume of molten sodium stored in the storage chamber 124 by expanding and contracting the bellows 127. 【0019】 In the illustrated embodiment, the inlet 121 and outlet 122 are installed on the ceiling 124b of the containment chamber 124. The inlet 121 is provided with a valve 166 capable of controlling the inflow of molten sodium from the piping 142 to the filling pump 120. The outlet 122 is provided with a valve 167 capable of controlling the outflow of molten sodium from the filling pump 120 to the piping 143. 【0020】 The bellows 127 preferably has multiple metal folds to provide a highly reliable sealing method to prevent leakage of molten sodium to the outside and inflow of air from the outside. Furthermore, it is preferable that the multiple folds are connected by welding. The bellows 127 comprises multiple folds made of stainless steel, for example. In addition, a movable plate 128 is joined to one open end (upper end in Figure 2) of the bellows 127 in a liquid-tight manner by welding or the like so as to close it. The other open end (lower end in Figure 2) of the bellows 127 is fixed to the floor 124a of the containment chamber 124. A through hole 124c is provided in the floor 124a, making it possible to place the inside of the volume control unit 126 under atmospheric pressure. 【0021】The movable plate 128 has a surface 128a that contacts the molten sodium and a back surface 128b that is shielded from the molten sodium. The back surface 128b is connected to a rod 125a of a motor 125 capable of controlling linear motion, such as a linear servo motor, a linear stepping motor, and a linear motor, thereby enabling the movable plate 128 to move to a predetermined position at a predetermined speed. The bellows 127 expands and contracts as the movable plate 128 moves. In the illustrated embodiment, the movable plate 128 is configured to move vertically to prevent the bellows from deforming unevenly due to its own weight, but it is not necessarily required to move in the vertical direction. For example, the movable plate 128 may be moved horizontally or in other directions. 【0022】 The volume inside the containment chamber 124 changes as the bellows 127 expands and contracts. More specifically, as the bellows 127 contracts as the movable plate 128 moves, the volume of the volume control unit 126 decreases, while the volume that can accommodate molten sodium inside the containment chamber 124 increases. Therefore, when the bellows 127 contracts with valves 162 and 166 open and valve 167 closed, it is possible to take in an amount of sodium corresponding to the change in the volume of the containment chamber 124 from the inlet 121 into the containment chamber 124. 【0023】 Conversely, as the movable plate 128 moves, the bellows 127 extends, increasing the volume of the volume control unit 126, while decreasing the volume of molten sodium that can be contained within the containment chamber 124. Therefore, with valve 166 closed and valves 167 and 168 open, when the bellows 127 extends, it is possible to discharge an amount of sodium corresponding to the volume change of the containment chamber 124 from the supply port 131. 【0024】It is desirable that the metal container 130 be filled with an amount of molten sodium within a predetermined allowable range. When sodium is used as the negative electrode active material of a NAS battery, the amount of sodium filled into the metal container 130 must be strictly controlled, as even a slight error can affect the battery performance, such as the voltage characteristics and discharge capacity, as well as the internal pressure characteristics of the NAS battery. For example, if the target amount of sodium to be filled into one metal container 130 is 1000g, it is necessary to control the error to within approximately 10g. In this respect, the filling pump 120 is advantageous in safely and accurately carrying out the process of filling the metal container 130 with molten sodium. 【0025】 If sodium leaks from the containment chamber 124 into the volume control unit 126, it reacts with moisture in the atmospheric gas to generate hydrogen. Therefore, a hydrogen sensor 129 may be installed to detect sodium leakage into the volume control unit 126. 【0026】 The floor 124a, ceiling 124b, and walls 124d of the containment chamber 124 can be made of metal such as stainless steel (e.g., SUS304, SUS316). The molten sodium piping 143 can be made of metal such as stainless steel (e.g., SUS304, SUS316). 【0027】 (1-3. Metal Container) Molten sodium discharged from the filling pump 120 is filled into the metal container 130. The material of the metal container 130 can be high-chromium steel, stainless steel (SUS304, etc.), aluminum alloy, SPCC (cold-rolled steel sheet), etc. The shape of the metal container 130 can be, for example, a bottomed cylindrical shape (typically a bottomed cylindrical shape). In one embodiment, the metal container 130 can be used as a component of a battery in which Na is used as the positive electrode and / or negative electrode. In a typical embodiment, the metal container 130 contains sodium as the negative electrode active material. 【0028】The metal container 130 has a molten sodium supply port 131 that communicates with the filling pump 120. To suppress the generation of bubbles, it is preferable to attach a heater-type nozzle 132 to the supply port 131. The nozzle 132 is preferably oriented so that the molten sodium flows out vertically downward from the supply port 131. The supply port 131 can communicate with the filling pump 120 via piping 143. A valve 168 capable of controlling the inflow of molten sodium can be provided in the middle of piping 143. 【0029】 To prevent oxidation, the filling process of the metal container 130 with molten sodium is preferably carried out under an inert atmosphere. Examples of inert gases include nitrogen, argon, and helium. One type of inert gas may be used alone, or two or more types may be used in mixture. Furthermore, to prevent reaction with moisture in the inert gas, the filling process is preferably carried out under low humidity conditions, for example, a dew point of -30°C or lower is preferred, and more preferably -60°C or lower. For this reason, the filling process of the metal container 130 with molten sodium is preferably carried out in a sealed chamber 180 (e.g., a glove box) under a dehumidified inert gas atmosphere. 【0030】 (1-4. Sealed Chamber) Figure 3 schematically shows an example of the configuration of a sealed chamber 180 suitable for carrying out the process of filling a metal container 130 with molten sodium. The sealed chamber 180 comprises a front chamber 181 and a filling chamber 182 adjacent to the front chamber 181. A gate 183 is provided at the boundary between the front chamber 181 and the outside for removing the metal container 130 from the sealed chamber 180 or for introducing the metal container 130 into the sealed chamber 180. A shutter or other fitting 191a is attached to the gate 183, and the opening and closing state of the gate 183 can be controlled. A shutter or other fitting 191b can also be attached at the boundary between the front chamber 181 and the filling chamber 182. This makes it possible to seal the filling chamber 182 even when the front chamber 181 is open to the atmosphere. 【0031】The front chamber 181 is connected to the vacuum pump 192a via piping 192b, allowing for reduced pressure inside the front chamber 181 and further inside the filling chamber 182. In addition, the front chamber 181 is connected to an inert gas supply source 193a, such as a cylinder, via piping 193b, allowing for the filling chamber 182 and further inside to be filled with inert gas. 【0032】 The movements of the door 191a of the anteroom 181 and the door 191b of the filling chamber 182 are described below illustratively, along with the movement of the metal container 130. • First, with the door 191b of the filling chamber 182 closed, the door 191a of the anteroom 181 is opened (opening to the atmosphere). • Next, the metal container 130 filled with sodium is taken out of the anteroom 181, and an empty metal container 130 is placed into the anteroom 181 from the outside. • Next, the door 191a of the anteroom 181 is closed. • Next, the anteroom 181 is depressurized to expel the air. The vacuum level in the anteroom 181 after depressurization is preferably 1 to 10 Pa (absolute pressure), and more preferably 1 to 3 Pa (absolute pressure). • Next, an inert gas such as nitrogen gas is supplied to the anteroom 181. • Next, the door 191b of the filling chamber 182 is opened. Next, the metal container 130 filled with sodium is moved from the filling chamber 182 to the anteroom 181, and the empty metal container 130 is moved from the anteroom 181 to the filling chamber 182. Next, the door 191b of the filling chamber 182 is closed. Next, molten sodium is filled into the empty metal container 130 that has been moved to the filling chamber 182. 【0033】 The filling chamber 182 is preferably connected to the cooler 194a via the circulation pipe 194b. This allows the inert gas in the filling chamber 182 to be extracted through the circulation pipe 194b, cooled in the cooler 194a, and then returned to the filling chamber 182 through the circulation pipe 194b. By circulating the inert gas between the filling chamber 182 and the cooler 194a, the inert gas in the filling chamber 182 can be maintained within a predetermined temperature range. The temperature of the filling chamber 182 during the filling process is preferably 10 to 35°C, and more preferably 15 to 25°C. 【0034】The filling chamber 182 is preferably connected to the gas purification device 195a via the circulation piping 195b. This allows the inert gas in the filling chamber 182 to be extracted through the circulation piping 195b, and after impurities such as oxygen and moisture are removed in the gas purification device 195a, it can be returned to the filling chamber 182 through the circulation piping 195b. By circulating the inert gas between the filling chamber 182 and the gas purification device 195a, the impurity concentration of the inert gas in the filling chamber 182 can be reduced. For example, from a safety viewpoint, the oxygen concentration in the filling chamber 182 is preferably 1 ppm by mass or less, and more preferably 0.3 ppm by mass or less. There are no particular restrictions on the type of gas purification device 195a, but examples include adsorption type, getter type, and catalytic type. The gas purification device 195a may be a combination of two or more of these types. 【0035】 The following series of steps can be performed on the empty metal container 130 that has been moved from the anteroom 181 to the filling chamber 182: (1) A step to measure the weight of the empty metal container 130 (empty container weight measurement) (2) A step to fill the metal container 130 with molten sodium (Na filling) (3) A degassing step to remove any remaining air bubbles in the molten sodium (degassing) (4) A step to measure the weight of the metal container 130 that has been filled with sodium (filled container weight measurement) (5) A step to cool the metal container 130 that has been filled with sodium (cooling) (6) A step to attach the lid 136 to the metal container 130 that has been filled with sodium (lid attachment) 【0036】 (1) The empty container weight measurement is a process of measuring the weight of an empty metal container 130, and can be carried out using a weighing scale 197a such as a load cell. By measuring the weight of the empty metal container 130 in advance, it becomes possible to calculate the weight of only the sodium that is later filled in. 【0037】(2) Na filling is the process of filling the metal container 130 with molten sodium discharged from the filling pump 120 as described above. A predetermined amount of molten sodium discharged from the filling pump 120 is sent into the filling chamber 182 through the piping 143. The supply port 131, which is the outlet of the piping 143 extending into the filling chamber 182, is inserted into the metal container 130, and the molten sodium is supplied into the metal container 130. As described above, it is preferable to attach a heater-type nozzle 132 to the supply port 131. Furthermore, it is preferable to set the orientation of the nozzle 132 so that the molten sodium flows out vertically downward from the supply port 131. 【0038】 The pipe 143 extending into the filling chamber 182 is suitable for maintaining the molten sodium flowing through it at a predetermined temperature (e.g., 120-140°C), considering that the melting point of sodium is approximately 100°C. This is appropriate from the standpoint of reducing the risk of temperature fluctuations causing solidification and minimizing unnecessary energy loss associated with high temperatures. One method for maintaining the pipe 143 at a predetermined temperature is to wrap it with insulating material. However, from the viewpoint of improving temperature control, it is preferable to heat the pipe 143 extending into the filling chamber 182 with a heater 146 equipped with a temperature control function (e.g., a jacketed heater). 【0039】 When filling the metal container 130 with molten sodium, it is desirable to prevent air bubbles from entering as much as possible from the viewpoint of quality stability. In this regard, the vertical distance between the supply port 131 and the inner bottom surface 133 of the metal container 130 when the molten sodium is first supplied into the metal container 130, and the distance between the liquid surface of the molten sodium in the metal container 130 and the supply port 131 thereafter, should be as close as possible to prevent air bubbles from entering. 【0040】Therefore, in one embodiment, when molten sodium is first supplied into the metal container 130, the vertical distance between the supply port 131 and the inner bottom surface 133 of the metal container 130 is within 20 mm, preferably within 10 mm. Thereafter, as the liquid level of the molten sodium in the metal container 130 rises, the supply port 131 is positioned below the liquid level of the molten sodium, and the supply port 131 is immersed in the molten sodium, thereby suppressing the entrainment of bubbles. While the supply port 131 is immersed in the molten sodium, by maintaining the vertical distance between the liquid level of the molten sodium and the supply port 131 within 20 mm, preferably within 10 mm, for example within 7 - 10 mm, and continuing to supply the molten sodium into the metal container 130, the entrainment of bubbles is suppressed. 【0041】 The above conditions can be achieved by moving the metal container 130 relatively downward with respect to the supply port 131 as the molten sodium is filled into the metal container 130, for example, by supplying the molten sodium while moving the metal container 130 vertically downward, or by supplying the molten sodium while moving the supply port 131 vertically upward. 【0042】 However, when supplying molten sodium into the metal container 130, it is preferable that the supply port 131 and the inner bottom surface 133 of the metal container 130 do not contact each other for the reason of not blocking the supply path of sodium. 【0043】 The supply rate of the molten sodium from the supply port 131 is preferably high for higher production efficiency, but if it is too high, bubbles are likely to occur. Therefore, from the perspective of both suppressing bubbles and achieving high production efficiency, the supply rate of the molten sodium from the supply port 131 is preferably 2 - 3 mm / s, and more preferably 1 - 2 mm / s. 【0044】(2) When the Na filling is completed, the supply port 131 is withdrawn from the metal container 130, and (3) degassing is performed. (3) Degassing is a process for removing bubbles remaining in the molten sodium filled in the metal container 130. As described above, although the molten sodium is supplied into the metal container 130 so that bubbles are generated as little as possible, it is difficult to completely eliminate them. Therefore, it is preferable to remove the bubbles remaining in the molten sodium after (2) Na filling. 【0045】 The removal of bubbles can be carried out by reducing the pressure inside the metal container 130. When the pressure inside the metal container 130 is reduced, the bubbles remaining in the molten sodium grow and float to be discharged. For example, an airtight cap 196c is attached to the upper end opening of the metal container 130 except for the degassing through-hole 196d, and the inside of the metal container 130 is connected to a vacuum pump 196a via the through-hole 196d and a pipe 196b connected to the through-hole 196d, so that a method of reducing the pressure inside the metal container 130 can be mentioned. 【0046】 (3) Degassing can be carried out until the inside of the metal container 130 reaches a predetermined degree of vacuum (for example, 200 kPa or less (absolute pressure), preferably 100 kPa or less (absolute pressure)). 【0047】 The molten sodium filled in the metal container 130 gradually decreases in temperature to the freezing point over time, and solidification gradually progresses. Since it becomes difficult to remove bubbles as solidification progresses, it is preferable to quickly perform (2) Na filling and complete (3) degassing. Specifically, it is preferable to set it to 1 to 5 minutes, preferably 2 to 3 minutes, from the start of (2) Na filling until (3) degassing is completed (for example, until the inside of the metal container 130 reaches a predetermined degree of vacuum). If the predetermined degree of vacuum is not reached even after a predetermined time has elapsed, it is also possible to determine it as a defective product. 【0048】(3) Once degassing is complete, (4) the weight of the filled container is measured. (4) The weight of the filled container is measured in the process of measuring the weight of the metal container 130 that has been filled with sodium, and can be performed using a weighing scale 197b such as a load cell, similar to (1) the weight measurement of the empty container. (4) By performing the weight measurement of the filled container, it is possible to check whether or not a predetermined amount of sodium has been filled into the metal container 130. 【0049】 (4) After measuring the weight of the filled container, (5) cooling is performed. (5) Cooling is a process of cooling the metal container 130 filled with sodium, and here the sodium inside the metal container 130 is cooled sufficiently and solidified. The cooling method is not limited to this, but one example is to blow air of inert gas from a blower 198 such as a fan installed in the filling chamber 182 toward the metal container 130. 【0050】 (5) After cooling, (6) the lid is attached. (6) The lid attachment is the process of attaching the lid 136 to the metal container 130 that has been filled with sodium. The lid 136 can be made of metal such as stainless steel. There are no particular restrictions on the method of attaching the lid 136 to the metal container 130, but one example is to press-fit it into the upper opening of the metal container 130. When press-fitting, a press-fitting device 199 such as a hydraulic cylinder type or an air cylinder type can be used. 【0051】 (6) After attaching the lid, remove the metal container 130 filled with sodium from the sealed chamber 180. Then, if necessary, the contact area between the lid 136 and the metal container 130 can be welded by laser welding or the like to prevent leakage of sodium. The temperature of the filled metal container 130 when removed from the sealed chamber 180 is preferably 50°C or lower, and more preferably 40°C or lower (e.g., 20-40°C). 【0052】In carrying out the above series of processes, the metal container 130 in the sealed chamber 180 may be manually moved by using a glove box as the sealed chamber 180, or the metal container 130 may be placed on a pallet and automatically transported on a roller conveyor using an air cylinder, or automatically transported by a belt conveyor or the like. 【0053】 <2. Method for filling with molten sodium> A method for filling a metal container with molten sodium according to one embodiment of the present invention will be described with reference to the drawings, using the filling system 100 described above. 【0054】 As mentioned above, it is desirable that the metal container 130 be filled with an amount of molten sodium within a predetermined allowable range. The filling pump 120 is advantageous in safely and accurately carrying out the process of filling the metal container 130 with molten sodium. In principle, if the travel distance (stroke distance) of the movable plate 128 in the volume control unit 126 of the filling pump 120 is the same, and other conditions are also the same, it is possible to take in and discharge the same amount of molten sodium. 【0055】 However, for industrial production, the tank 110 is enlarged to lower the limit of molten sodium (H) inside the tank 110. min ) and upper limit (H max As the height difference between the two increases, the pressure applied to the outlet 112 of the tank 110 when the molten sodium is at its lower limit becomes significantly smaller compared to the pressure applied to the outlet 112 of the tank 110 when the molten sodium is at its upper limit. Therefore, the pressure applied to the bellows 127 also changes according to the height of the molten sodium in the tank 110. As a result, the amount of deformation of the bellows 127 changes, so even if the stroke distance of the filling pump 120 is constant, changes occur in the intake and discharge rates. 【0056】Therefore, in a method for filling a metal container with molten sodium according to one embodiment of the present invention, the correlation between the height of the molten sodium in the tank 110, the stroke distance when contracting and extending the bellows 127, and the amount of sodium to be filled into the metal container 130 is investigated. When investigating, it is preferable not to intentionally change other conditions in order to obtain the correct correlation. 【0057】 For example, the necessary correlation can be obtained by investigating the change in the amount of sodium filled into the metal container 130 when the height of molten sodium in the tank 110 is changed while keeping the stroke distance constant. When obtaining the correlation, it is preferable to keep the starting and ending points of the movable plate 128 when contracting and extending the bellows 127 the same, in addition to the stroke distance, as this increases reproducibility. Furthermore, when obtaining the correlation, it is preferable to keep the moving speed of the movable plate 128 when contracting and extending the bellows 127 the same, in addition to the stroke distance, as this increases reproducibility. 【0058】 The correlation can be expressed by an approximation formula. For example, the correlation can be expressed by the relationship between the liquid level h of molten sodium in tank 110 and the amount m of sodium filled into metal container 130, when the stroke distance is fixed. Alternatively, the correlation may be obtained by machine learning using the height of the molten sodium in tank 110, the stroke distance when contracting and extending the bellows 127, and the amount of sodium filled into metal container 130 as training data. Other factors may be added to the training data as needed. Known learning models such as neural networks and support vector machines can be used for machine learning. Deep learning may be used when training the neural network. 【0059】 Once a correlation is obtained, filling conditions can be determined, including the height of molten sodium in the tank 110 and the stroke distance when contracting and extending the bellows 127, which are suitable for filling the metal container 130 with a predetermined allowable amount of molten sodium from the tank 110 via the filling pump 120. 【0060】 Regarding the filling conditions for the height of molten sodium in the tank 110, the lower and upper limits of the height of molten sodium in the tank 110 are mentioned. Furthermore, it is preferable that the filling conditions include the stroke distance when contracting and extending the bellows 127, as well as the starting and ending points of the movable plate 128 when contracting and extending the bellows 127. It is even more preferable that the filling conditions include the moving speed of the movable plate 128 when contracting and extending the bellows 127. 【0061】 Subsequently, by sequentially performing the following steps: first, contracting the bellows 127 according to the determined filling conditions to increase the volume in the containment chamber 124 and introducing molten sodium from the tank 110 into the containment chamber 124 of the filling pump 120 via the inlet 121; and second, extending the bellows 127 according to the aforementioned filling conditions to decrease the volume in the containment chamber 124 and filling the metal container 130 with molten sodium from the filling pump 120 via the outlet 122, an amount of molten sodium within a predetermined allowable range can be filled into the metal container. 【0062】Accordingly, according to one embodiment of the present invention, a method for filling a metal container 130 with a predetermined allowable amount of molten sodium from a tank 110 for storing molten sodium via a filling pump 120, comprising: Step A1: Investigating the correlation between the height of the molten sodium in the tank 110, the stroke distance when contracting and extending the bellows 127, and the amount of sodium to be filled into the metal container 139; Step B1: Based on the correlation, determining filling conditions including the height of the molten sodium in the tank 110 and the stroke distance when contracting and extending the bellows 127, which are suitable for filling a metal container 130 with a predetermined allowable amount of molten sodium from the tank 110 via the filling pump 120; Step C1: In accordance with the filling conditions, increasing the volume in the containment chamber 124 by contracting the bellows 127, and introducing molten sodium from the tank 110 into the containment chamber 124 of the filling pump 120 via the inlet 121. A method is provided which includes step D1 of filling molten sodium into a metal container 130 via an outlet 122 from a filling pump 120, by extending the bellows 127 according to the aforementioned filling conditions to reduce the volume in the containment chamber 124. 【0063】A preferred embodiment of the present invention provides a method for filling a metal container 130 with a predetermined allowable amount of molten sodium from a tank 110 for storing molten sodium via a filling pump 120, comprising: step A2 investigating the correlation between the height of the molten sodium in the tank 110, the stroke distance when contracting and extending the bellows 127, and the amount of sodium to be filled into the metal container 130; step B2 determining the lower and upper limits of the height of the molten sodium in the tank 110 based on the correlation, such that when the bellows 127 is contracted and extended by a predetermined stroke distance, the amount of molten sodium to be filled into the metal container 130 falls within a predetermined allowable range; and step C2 increasing the volume of the containment chamber 124 by contracting the bellows 127 by the predetermined stroke distance when the height of the molten sodium in the tank 110 is within the range from the lower limit to the upper limit, thereby introducing the molten sodium from the tank 110 into the containment chamber 124 of the filling pump 120 via the inlet 121. A method is provided which includes step D2 of reducing the volume in the containment chamber 124 by extending the bellows 127 by a predetermined stroke distance, and filling the metal container 130 with molten sodium from the filling pump 120 through the outlet 122. 【0064】 Examples of the present invention are shown below, provided to better understand the present invention and its advantages, and are not intended to limit the present invention. 【0065】 A filling system with the structure shown in Figures 1 to 3 was constructed, and a test was repeated approximately 250 times under the following conditions in which molten sodium was filled from a tank 110 storing molten sodium into a metal container 130 via a filling pump 120. As the number of tests increased, the liquid level of molten sodium in the tank 110 decreased, and consequently, the internal pressure of the tank 110 decreased. 【0066】<Test Conditions> (1) Tank 110 Main body material: SUS316 Temperature of molten sodium in the tank: 135℃ Volume: Diameter 1.2m x Height 1.8m Internal pressure (nitrogen): 145kPa (gauge pressure) when the height from the inner bottom surface of the molten sodium is 1050mm (at the start of the test) (2) Filling pump 120 Bellows material: Stainless steel Movable plate material: SUS316 Material of the floor, ceiling and walls of the containment chamber: SUS316 Internal pressure of the volume control unit: Atmospheric pressure Stroke distance: 40mm (contracted and extended positions are constant) Stroke speed: 2.7mm / s Movable plate dimensions: 180mm diameter disc (3) Metal container 130 Metal container material: SUS304 Volume: Diameter 32mm x Height 470mm (4) Glove box atmosphere gas: Inert gas (mixture of nitrogen and He) Humidity (dew point): -60℃ Oxygen concentration: 0.3 ppm by mass Temperature in the filling chamber: 28°C (5) Piping 141, 151, 142, 143 Piping material: SUS316 Inner diameter: 8 to 22 mm (6) Filling conditions Vertical distance between the supply port 131 and the inner bottom surface 133 of the metal container 130 when molten sodium is first supplied into the metal container 130: 10 mm Subsequently, when the liquid level of molten sodium rises and the supply port 131 is submerged in the molten sodium, the distance between the liquid level of molten sodium in the metal container 130 and the supply port 131: 10 mm Molten sodium supply rate: 1.6 mm / s (7) Degassing conditions The vacuum inside the metal container 130 during degassing reaches 200 kPa or less (absolute pressure) within 160 seconds from the start of filling (8) Calculation of filling amount The difference between the empty metal container 130 and the metal container 130 filled with sodium was defined as the filling amount. 【0067】 The relationship between the mass of sodium filled into the metal container 130 in each filling cycle and the liquid level in tank 110 immediately before the sodium filling operation in each cycle was investigated. As a result, it was confirmed that the amount filled gradually decreased as the number of filling cycles increased, with the maximum filling amount being 777 g and the minimum being 775 g, a difference of 2 g. In addition, the liquid level of molten sodium in tank 110 at the end of the test decreased from 1050 mm at the start of the test to 750 mm at the end of the test. 【0068】 Therefore, when filling the metal container 130 with molten sodium under the test conditions, the relationship between the liquid level height h (mm) of the molten sodium in the tank 110 and the mass m (g) of sodium filled into the metal container 130 can be linearly approximated by, for example, the following equation: m = 2 / (1050 - 750) × (h - 750) + 775 = 2 / 300 × h + 770 Thus, for example, if the allowable range is set to 770 ≤ m ≤ 780, it is sufficient to satisfy 0 ≤ h ≤ 1500. In this way, by using the filling pump according to the embodiment of the present invention, it is possible to widen the range of liquid level heights over which molten sodium can be filled into the metal container with high precision. Furthermore, if a narrower range is set as the allowable range, such as 774 ≤ m ≤ 778, it is sufficient to satisfy 600 ≤ h ≤ 1200. In other words, by adopting the filling method according to the embodiment of the present invention, it is possible to set the filling conditions according to the required precision. 【0069】100: Filling system 110: Tank 111: Inlet 112: Outlet 113: Inlet 115a: Liquid level sensor 115b: Liquid level sensor 120: Filling pump 121: Inlet 122: Outlet 124: Containment chamber 124a: Floor 124b: Ceiling 124c: Through hole 124d: Wall 125: Motor 125a: Rod 126: Volume control unit 127: Bellows 128: Movable plate 128a: Surface 128b: Back surface 129: Hydrogen sensor 130: Metal container 131: Supply port 132: Nozzle 133: Inner bottom surface 136: Lid 139: Metal container 141: Piping 142: Piping 143: Piping 146: Heater 151: Piping 161: Valve 162: Valve 163: Valve 166: Valve 167: Valve 168: Valve 180: Sealed Chamber 181: Antechamber 182: Filling Chamber 183: Gate 191a: Joinery 191b: Joinery 192a: Vacuum Pump 192b: Piping 193a: Supply Source 193b: Piping 194a: Cooler 194b: Circulation Piping 195a: Gas Purification Device 195b: Circulation Piping 196b: Piping 196c: Cap 196d: Through Hole 197a: Weighing Scale 197b: Weighing Scale 198: Blower 199: Press-Fitting Device

Claims

1. A method for filling a metal container with a predetermined allowable amount of molten sodium from a tank for storing molten sodium via a filling pump, wherein the filling pump comprises a molten sodium storage chamber having an inlet communicating with the tank and an outlet communicating with the metal container, and a volume control unit having a bellows and a movable plate that closes one open end of the bellows, and capable of changing the volume in the storage chamber by the expansion and contraction of the bellows, A1 of investigating the correlation between the height of the molten sodium in the tank, the stroke distance when contracting and extending the bellows, and the amount of sodium to be filled into the metal container, B1 of determining filling conditions, including the height of the molten sodium in the tank and the stroke distance when contracting and extending the bellows, that are suitable for filling the metal container with a predetermined allowable amount of molten sodium from the tank via the filling pump based on the correlation, C1 of increasing the volume in the storage chamber by contracting the bellows according to the filling conditions, and introducing molten sodium from the tank into the storage chamber of the filling pump via the inlet. A method comprising step D1 of reducing the volume inside the containment chamber by extending the bellows according to the filling conditions, and filling the metal container with molten sodium from the filling pump through the outlet.

2. A method for filling a metal container with a predetermined allowable amount of molten sodium from a tank storing molten sodium via a filling pump, wherein the filling pump comprises a molten sodium storage chamber having an inlet communicating with the tank and an outlet communicating with the metal container, and a volume control unit having a bellows and a movable plate that closes one open end of the bellows, and capable of changing the volume in the storage chamber by the expansion and contraction of the bellows, A2 of investigating the correlation between the height of the molten sodium in the tank, the stroke distance when the bellows is contracted and extended, and the amount of sodium to be filled into the metal container, B2 of determining, based on the correlation, the lower and upper limits of the height of the molten sodium in the tank so that the amount of molten sodium to be filled into the metal container falls within the predetermined allowable range when the bellows is contracted and extended by a predetermined stroke distance. A method comprising: step C2, when the height of molten sodium in the tank is within the range from the lower limit to the upper limit, contracting the bellows by a predetermined stroke distance to increase the volume of the containment chamber, and introducing molten sodium from the tank into the containment chamber of the filling pump via the inlet; and step D2, extending the bellows by a predetermined stroke distance to decrease the volume of the containment chamber, and filling the metal container with molten sodium from the filling pump via the outlet.

3. The method according to claim 1 or 2, wherein the metal container is a component of a battery that uses Na as the positive electrode and / or negative electrode.

4. The method according to claim 1 or 2, wherein the tank is equipped with one or more liquid level sensors capable of measuring the height of molten sodium.

5. The method according to claim 1 or 2, wherein step D1 or step D2 is performed in an inert atmosphere.

6. The method according to claim 1 or 2, wherein the bellows comprises folds made of stainless steel.

7. The method according to claim 1 or 2, wherein the space above the liquid level of molten sodium in the tank is filled with an inert gas.

8. The method according to claim 1 or 2, wherein the extension and retraction of the bellows is controlled by a linear servo motor.

9. The method according to claim 1 or 2, wherein step D1 or D2 includes the flow of molten sodium into the metal container from a supply port communicating with the outlet of the filling pump, the vertical distance between the supply port and the inner bottom surface of the metal container when the molten sodium is first supplied into the metal container is 20 mm or less, and thereafter, after the liquid level of the molten sodium rises and the supply port is submerged in the molten sodium, the supply of molten sodium into the metal container is continued with the supply port submerged in the molten sodium.

10. The method according to claim 1 or 2, wherein after carrying out step D1 or D2, degassing is performed to remove any remaining air bubbles from the molten sodium filled in the metal container.

11. A filling pump for filling a metal container with molten sodium from a tank for storing molten sodium, the filling pump comprising: a molten sodium storage chamber having an inlet communicating with the tank and an outlet communicating with the metal container; and a volume control unit having a bellows and a movable plate that closes one open end of the bellows, and capable of changing the volume in the storage chamber by the expansion and contraction of the bellows.

12. The filling pump according to claim 11, wherein the bellows comprises metal folds.

13. The filling pump according to claim 11, wherein the bellows comprises folds made of stainless steel.

14. The filling pump according to claim 11 or 12, wherein the extension and retraction of the bellows is controlled by a linear servo motor.

Images