Liquid Level Measuring Device

Abstract

To provide a liquid level measurement device with which it is possible to measure a liquid level, even for ultra-low temperature liquids having a small specific gravity.SOLUTION: A liquid level measurement device 1 according to the present invention measures a liquid level in a storage tank 3 that stores a low-temperature liquified gas 2. The liquid level measurement device 1 comprises a wave-dissipating tube 5 that is installed in the storage tank 3 and composed of a cylindrical body, and that has a bottom hole 17 allowing a liquid fluid in the storage tank 3 and a liquid fluid in the tube to mutually move; a float 7 that is located inside the wave-dissipating tube 5 and that is composed of a hollow globe having at the top a laser reflection unit 25 capable of reflecting a laser; and a laser type liquid level gauge 9 that is provided at the top of the storage tank 3 and is located so as to be capable of irradiating the laser reflection unit 25 with a laser. The liquid level measurement device measures a liquid level in the storage tank 3 by causing the laser reflection unit 25 to reflect the laser radiated by the laser type liquid level gauge 9.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present invention relates to a liquid level measuring device for measuring the liquid level in a storage tank that stores low-temperature liquefied gas. [Background technology]

[0002] Methods for measuring the liquid level of low-temperature liquefied gas include using a superconducting level gauge or a differential pressure level gauge. A superconducting liquid level gauge calculates the position of the liquid level from changes in the electrical resistance of a superconducting wire, but as the element becomes longer, it becomes difficult to accurately determine the liquid level. In addition, when a differential pressure type level gauge is used for helium, the density difference between the saturated liquid and the saturated gas is smaller than that for other liquids, so correction for changes in the pressure inside the tank is necessary. Furthermore, all of the above methods indirectly measure the liquid level, and therefore have the problem that measurement accuracy decreases when used in a large storage tank.

[0003] On the other hand, there is a method for directly measuring the liquid level using a laser distance meter, as disclosed in, for example, Patent Documents 1 and 2. The method disclosed in Patent Document 1 is a method for measuring the liquid level using a laser level gauge, a float, and a wave dissipating tube. Moreover, the device disclosed in Patent Document 2 "includes a float that floats on the surface of a cryogenic liquid, and a sensor that is positioned vertically above the float and measures the distance to the float in a non-contact manner." [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Patent No. 5589248 [Patent Document 2] JP 2019-128200 A Summary of the Invention [Problem to be solved by the invention]

[0005] The devices disclosed in Patent Documents 1 and 2 measure the liquid level by projecting a laser onto a float placed on the liquid surface. In the device disclosed in Patent Document 1, the liquid to be treated is water, and a disk-shaped float is disclosed. However, because the specific gravity of cryogenic liquids such as helium and hydrogen is low, a large volume is required to obtain sufficient buoyancy in a float with a disk structure. This leads to the problem that the wave dissipation tube surrounding it becomes large, making it difficult to install in the cryogenic storage tank. Furthermore, a larger wave dissipation tube increases the amount of heat that enters, which causes problems such as an increase in the amount of evaporation of the cryogenic liquid.

[0006] Moreover, the float disclosed in Patent Document 2 is also a disk-shaped float, and like Patent Document 1, has the problem of not being able to obtain sufficient buoyancy. Furthermore, in Patent Document 2, a J-shaped guide member is used, which causes a problem in that the amount of evaporation of the cryogenic liquid increases due to heat entering from this guide member.

[0007] The present invention has been made to solve the above problems, and has an object to provide a liquid level measuring device capable of measuring the liquid level even of a cryogenic liquid having a low specific gravity. Another object of the present invention is to provide a liquid level measuring device capable of suppressing heat intrusion. [Means for solving the problem]

[0008] (1) The liquid level measuring device according to the present invention measures the liquid level in a tank that stores low-temperature liquefied gas, and includes a wave dissipating tube that is installed in the tank, is made of a cylindrical body, and has a hole through which the liquid in the tank and the liquid in the tube can move relative to each other; A float that is disposed in the wave dissipating tube and is made of a hollow sphere having a laser reflecting portion on an upper portion thereof that can reflect a laser; a laser type liquid level gauge provided at an upper portion of the storage tank and arranged so as to be able to irradiate a laser onto the laser reflecting portion; The laser level gauge is characterized in that the liquid level in the storage tank is measured by reflecting the laser emitted by the laser reflecting portion.

[0009] (2) In addition, in the device described in (1) above, the device is characterized in having a balance structure that balances the float so that the laser reflecting portion is always on the top.

[0010] (3) Furthermore, in the item (1) above, the upper part of the wave dissipating pipe is removably attached to the upper part of the tank so as to be removable from the upper part of the tank.

[0011] (4) Furthermore, in the above-mentioned (3), the wave dissipating tube is characterized in having a float holding structure that holds the float when it is removed.

[0012] (5) Furthermore, in the above-mentioned (1), the wave dissipating pipe is fixed to the lower part of the tank, and its upper part is not in contact with the tank.

[0013] (6) Furthermore, in the device described in any one of (1) to (5) above, a baffle is provided within the wave dissipating tube.

[0014] (7) Furthermore, in the above-mentioned (6), the wave dissipating pipe has a gas vent hole for venting gas vaporized within the wave dissipating pipe, and the gas vent hole is located above the mounting position of the baffle.

[0015] (8) In addition, in the device described in any one of (1) to (7) above, the low-temperature liquefied gas in the storage tank is liquid hydrogen or liquid helium. Effect of the Invention

[0016] According to the liquid level measuring device of the present invention, it is possible to measure the liquid level even for a cryogenic liquid having a low specific gravity. [Brief description of the drawings]

[0017] [Figure 1] 1 is an explanatory diagram of a liquid level measuring device according to an embodiment of the present invention; [Diagram 2] 2 is an explanatory diagram of a wave dissipation tube and its internal structure in the liquid level measuring device according to the present embodiment. FIG. [Diagram 3] 5 is an explanatory diagram of another aspect of the liquid level measuring device according to the present embodiment. FIG. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0018] [Embodiment 1] The liquid level measuring device 1 of this embodiment measures the liquid level in a storage tank 3 that stores low-temperature liquefied gas 2, and as shown in Figure 1, is equipped with a wave dissipating tube 5 installed in the storage tank 3, a float 7, and a laser type liquid level gauge 9. Each component will be described in detail below.

[0019] <Storage tank> The storage tank 3 is for storing the low-temperature liquefied gas 2, and as shown in FIG. 1, is provided with a supply pipe 11 for supplying the low-temperature liquefied gas 2, such as liquid helium liquefied by a helium liquefaction device not shown, to the storage tank 3, and an extraction pipe 13 for extracting the low-temperature liquefied gas 2 stored in the storage tank 3. A lid 15 is provided on the top of the storage tank 3, and the wave-dissipating tube 5 can be removed by opening the lid 15.

[0020] <Wave dissipation tube> The wave dissipating pipe 5 is made of a cylindrical body and has a bottom hole 17 through which the liquid in the storage tank 3 and the liquid in the cylinder can move between each other. In this embodiment, the bottom hole 17 is provided in the bottom of the wave dissipating pipe 5, as shown in Fig. 2. By providing the bottom hole 17 in the wave dissipating pipe 5, the liquid levels inside and outside the wave dissipating pipe 5 can be kept at the same height.

[0021] The upper part of the wave dissipating pipe 5 is removably attached to the upper part of the storage tank 3 (for example, the lid 15 of the storage tank 3) so as to be removable from the upper part of the storage tank 3.

[0022] In addition, the diameter of the bottom hole 17 is set to be smaller than the outer diameter of the float 7. This prevents the float 7 from falling off the wave dissipating pipe 5 when the liquid level in the storage tank 3 falls below a predetermined level. Furthermore, with this structure, when the wave dissipating tube 5 is removed from the tank 3 for maintenance or the like, the float 7 can be removed while being held at the bottom of the wave dissipating tube 5, without being left behind in the tank 3. In this manner, the bottom of the wave dissipating tube 5, which has the bottom hole 17 with a diameter smaller than the outer diameter of the float 7, functions as a float holding structure that holds the float 7 when the wave dissipating tube 5 is removed. In addition, by making the bottom of the wave dissipating tube 5 removable, the float 7 can be easily removed during maintenance. However, the position of the hole provided for moving the liquid flow between the inside and outside of the wave-dissipating pipe 5 is not limited to the bottom of the wave-dissipating pipe 5.

[0023] 2, the wave dissipating tube 5 is preferably provided with a baffle plate 19 for reducing radiation. By providing the baffle plate 19, the heat entering the cryogenic liquid due to radiation from the upper part of the storage tank 3 can be reduced. Furthermore, by cooling the baffle plate 19 in the wave dissipating tube 5 using the sensible heat of the evaporated gas of the low-temperature liquefied gas 2, the evaporation of the cryogenic liquid due to radiant heat from the upper part of the storage tank 3 can be further reduced. In addition, it is preferable to provide the wave dissipating tube 5 with an exhaust port 21 for exhausting evaporative gases, and in order to efficiently cool the baffle plate 19, it is preferable to locate the exhaust port 21 above the baffle plate 19. Furthermore, in order to prevent the intrusion of radiant heat, it is more preferable to form the baffle plate 19 in multiple layers as shown in FIG. The baffle plate 19 of the present invention is not limited to a plate shape, and may have any shape that can effectively prevent the intrusion of radiant heat.

[0024] By using a resin with low thermal conductivity for part or all of the wave-dissipating tube 5, it is possible to reduce heat intrusion due to conduction. The baffle plate 19 is provided with a laser passage hole 23 having a size corresponding to the light projecting portion and light receiving portion of the laser level gauge 9 (laser range finder), so that the passage of the laser is not impeded.

[0025] <Float> The float 7 is disposed inside the wave dissipating tube 5 and is made of a hollow sphere having a laser reflector 25 on its upper portion. In order to reduce the weight of the float 7, it is desirable to manufacture the float 7 from a metal such as aluminum that has a low density and high toughness even at extremely low temperatures. As the material of the float 7, magnesium can be used in addition to aluminum.

[0026] The float 7 is a hollow sphere. The gas sealed inside during manufacture condenses and solidifies in the cryogenic environment in which it is used, lowering the internal pressure and subjecting it to external pressure that crushes it due to atmospheric pressure. For this reason, the float 7 needs to be strong enough to withstand external pressure, but the spherical structure makes it possible to minimize the plate thickness required to maintain the required strength. In addition, since the float 7 is spherical, it does not get caught on the wave dissipating tube 5 and can move up and down smoothly in accordance with the liquid level.

[0027] A laser reflector 25 is provided on the top of the float 7, and as long as the laser reflector 25 can reflect the laser, a reflector plate may be provided, or the top surface of the float 7 may be processed to be flat. Also, as long as the laser oscillator and receiver function, the structure that reflects the laser may be flat or may be another structure, such as a concave structure.

[0028] It is desirable to provide a balancing structure that balances the float 7 so that the laser reflecting portion 25 is always at the top. As a balancing structure, as shown in Fig. 2, a weight 27 may be provided at the bottom of the float 7, or at least a part of the bottom of the float 7 may be made thick. Furthermore, air or a small amount of water vapor (hereinafter, referred to as residual gas) may remain inside the float 7 during the manufacturing process. Therefore, when the float 7 is used to measure the level of liquid hydrogen or liquid helium, the residual gas may liquefy or solidify at the bottom inside the float 7, and this liquid or solid may be used as the weight 27 of the float 7. In this manner, the weight 27 at the bottom of the float 7, the thickening of the bottom of the float 7, the presence of liquid and solid residual gas, etc., provide a balanced structure for the present invention.

[0029] Table 1 shows the liquid densities and latent heats of vaporization of representative industrial gases.

[0030] [Table 1]

[0031] The buoyancy force acting on the float 7 is proportional to the density of the liquefied gas, so when measuring liquid hydrogen or liquid helium, which have low liquid densities, the buoyancy force acting on the float 7 is small. In this regard, the float 7 of the present invention is a hollow sphere and can float even with a small buoyancy, so it is also applicable to liquefied gases with low liquid densities.

[0032] As shown in FIG. 2, when a laser reflector 25 (reflector) is provided on the top of the float 7 and a weight 27 is provided on the bottom, and the float 7 body is made of aluminum, it was confirmed that a diameter of about 100 mm and a wall thickness of 0.5 mm provides sufficient buoyancy for liquid helium, and the liquid level can actually be measured.

[0033] <Laser type liquid level gauge> The laser level gauge 9 is provided on the top of the storage tank 3 and is arranged so as to be able to irradiate a laser onto the laser reflector 25 of the float 7. The laser emitted by the laser level gauge 9 is reflected by the laser reflector 25 to measure the liquid level in the storage tank 3. Since the laser rangefinder is assumed to function at room temperature, the laser rangefinder is separated from the inside of storage tank 3 by a transparent plate that allows laser light to pass through. In this way, the laser level gauge 9 can be a commercially available general level gauge.

[0034] In the liquid level measuring device 1 according to the present embodiment configured as described above, the float 7 is formed as a hollow sphere, so that it is possible to measure the liquid level even for a cryogenic liquid having a low specific gravity. In addition, by providing a bottom hole 17 in the bottom surface of the wave-dissipating tube 5, the liquid inside and outside the wave-dissipating tube 5 can move between each other, and the liquid level inside and outside the wave-dissipating tube 5 can be maintained at the same height. Furthermore, by setting this bottom hole 17 to a diameter smaller than the outer diameter of the float 7, the bottom surface functions as a float holding means when the wave-dissipating tube 5 is removed from the storage tank 3.

[0035] Furthermore, by providing the baffle plate 19 in the wave dissipating tube 5, the heat that enters the cryogenic liquid due to radiation from the upper part of the storage tank 3 can be reduced. Furthermore, by providing the exhaust port 21 for evaporated gas in the wave dissipation tube 5 above the baffle plate 19, the baffle plate 19 can be cooled efficiently, and the intrusion of radiant heat from the upper part of the storage tank 3 can be effectively prevented. In this manner, in this embodiment, by making efforts to minimize heat intrusion from the top of the storage tank 3, it is also suitable for measuring the liquid level in a storage tank 3 that stores liquid helium (see Table 1), which has a small latent heat of vaporization.

[0036] [Embodiment 2] A liquid level measuring device 1 according to a second embodiment of the present invention is shown in Fig. 3. In Fig. 3, parts that are the same as or correspond to those shown in Fig. 1 are given the same reference numerals. The liquid level measuring device 1 shown in Figure 3 is a configuration in which there is no need to remove the wave-dissipating tube 5 from the tank 3, and the lower end of the wave-dissipating tube 5 is fixed to the bottom of the tank 3, while the upper end of the wave-dissipating tube 5 does not come into contact with the top of the tank 3. In this way, the heat entering from the upper part of the wave-dissipating tube 5 can be further reduced.

[0037] The upper end surface of the wave dissipating pipe 5 is provided with an upper end surface hole 29 through which the laser passes and which functions as an exhaust port 21 for evaporated gas. The diameter of the upper end surface hole 29 is made smaller than the outer diameter of the float 7. This makes it possible to prevent the float 7 from coming out of the wave dissipating pipe 5 even if the liquid level in the storage tank 3 rises more than expected. In addition, holes 31 are provided on the lower side surface of the wave dissipating pipe 5 for allowing liquid flow to move between the inside and outside of the wave dissipating pipe 5. [Explanation of symbols]

[0038] 1. Liquid level measuring device 2. Low-temperature liquefied gas 3 storage tank 5 Wave dissipation tube 7. Float 9 Laser level gauge 11 Supply piping 13 Extraction piping 15 Lid 17 Bottom hole 19 Baffle plate 21 Exhaust port 23 Laser passage hole 25 Laser reflector 27 Weight 29 Top hole 31 holes

Claims

1. A liquid level measuring device for measuring a liquid level in a storage tank for storing a low-temperature liquefied gas, comprising: a wave dissipating tube disposed in the storage tank, the wave dissipating tube being made of a cylindrical body and having a hole through which the liquid in the storage tank and the liquid in the tube can move relative to each other; a float that is disposed in the wave dissipating tube and is made of a hollow metal sphere having a laser reflecting portion at its upper portion that can reflect a laser, and has residual gas therein; a laser type liquid level gauge provided on an upper portion of the storage tank and arranged so as to be able to irradiate a laser onto the laser reflecting portion; A balance structure that balances the float so that the laser reflector is always on the top, The balance structure is constituted by the residual gas being liquefied at the bottom inside the float, and the liquid or solid that is solidified becomes the weight of the float, A liquid level measuring device, characterized in that the liquid level in the storage tank is measured by reflecting a laser emitted by the laser type liquid level gauge by the laser reflecting portion.

2. 2. A liquid level measuring device according to claim 1, wherein an upper portion of the wave dissipating pipe is removably attached to an upper portion of the storage tank so as to be removable from the upper portion of the storage tank.

3. 3. The liquid level measuring device according to claim 2, wherein the wave dissipating tube has a float holding structure for holding the float when the float is removed.

4. 2. The liquid level measuring device according to claim 1, wherein the wave dissipating pipe is fixed to the lower part of the storage tank and the upper part is not in contact with the storage tank.

5. 5. A liquid level measuring device according to claim 1, further comprising a baffle disposed within the wave dissipation pipe.

6. 6. A liquid level measuring device according to claim 5, characterized in that the wave dissipating pipe has a gas vent hole for venting gas evaporated within the wave dissipating pipe, and the gas vent hole is provided above the mounting position of the baffle.

7. 5. The liquid level measuring device according to claim 1, wherein the low-temperature liquefied gas in the storage tank is liquid hydrogen or liquid helium.

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