Liquid level gauge and liquid level measurement method for liquid hydrogen

Abstract

To provide a liquid level meter capable of measuring a liquid level so as to be in non-contact with liquid hydrogen inside a container.SOLUTION: A liquid level meter comprises: an X-ray irradiation device 20 that irradiates X-rays toward a central axis of a liquid hydrogen tank 10 in a direction parallel to a liquid level; an X-ray detection device 32 that detects backscattered X-rays generated near the central axis by X-rays; a shielding member 30 that shields a part of the backscattered X-rays in front of the X-ray detection device 32; and a calculation device 34 that calculates a liquid level at the central axis based on the detected backscattered X-rays. The liquid level meter has a vertical drive mechanism 22 that moves the X-ray irradiation device 20 in a vertical direction of the liquid hydrogen tank 10 to adjust a height of an X-ray irradiation axis in the liquid hydrogen tank 10. The shielding member 30 allows X-rays having passed through slits provided at regular intervals in the vertical direction of the liquid hydrogen tank 10 to enter the X-ray detection device 32. The X-ray detection device 32 detects backscattered X-rays. The calculation device 34 determines the liquid level at an interface between liquid hydrogen and hydrogen gas in the liquid hydrogen tank 10.SELECTED DRAWING: Figure 1A

Description

Technical Field

[0001] The present invention relates to a liquid level gauge and a liquid level measurement method suitable for use, for example, in liquid hydrogen.

Background Art

[0002] The use of hydrogen, which is a clean energy, has been incorporated as one of the basic policies of the Sixth Energy Basic Plan. When transporting and storing hydrogen, it is assumed that it will be used in a liquid state with a density 1 / 800 that of a gas. At that time, precisely measuring and grasping the volume of liquid hydrogen in a container having a heat insulation structure is essential for hydrogen utilization. For volume measurement, a general liquid level gauge is used, similar to other refrigerants (such as nitrogen and helium). For example, a simple float type is used for liquid nitrogen. Regarding hydrogen liquid level gauges, those applying superconductivity have been proposed (see, for example, Patent Documents 1 to 3), and a capacitance type is also known.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Patent Document 2

Patent Document 3

Summary of the Invention

Problems to be Solved by the Invention

[0004] However, in the capacitance type, calibration for each experiment is required, and in the upcoming hydrogen society, it is not realistic to accommodate individual containers from large tanks for 5-ton-class plants to small and medium-sized containers of about 100 kg assuming local production and local consumption. Even in methods using superconducting wires, the available superconducting materials are limited to MgB2 and similar materials, compared to hydrogen, which has a boiling point of 20 Kelvin at atmospheric pressure, compared to helium, which has a boiling point of 4.2 Kelvin. Furthermore, evaluation methods under hydrogen conditions have not yet been established.

[0005] Furthermore, challenges unique to hydrogen must be overcome. Since hydrogen itself is flammable, safety is paramount. Additionally, introducing a liquid level sensor into a liquid hydrogen container inevitably leads to heat inflow, resulting in the evaporation of this valuable energy source. Moreover, introducing a liquid level sensor into the container requires consideration of hydrogen embrittlement and low-temperature embrittlement of the liquid level system materials used, while simultaneously complicating the container's structure. Hydrogen embrittlement and low-temperature embrittlement of welds and connections due to the liquid level sensor inside the container are also unavoidable concerns.

[0006] The present invention solves the problems of the prior art described above and aims to provide a liquid level gauge and a liquid level measurement method that can measure the liquid level of the liquid hydrogen inside the container without contact with it. [Means for solving the problem]

[0007] [1] The liquid level gauge of the present invention, as shown in Figure 1 for example, comprises an X-ray irradiation device 20 that irradiates a liquid hydrogen tank 10 with X-rays of a predetermined energy in a direction parallel to the liquid surface toward the central axis, an X-ray detection device 32 that detects backscattered X-rays generated near the central axis by the X-rays, a shielding member 30 that shields a portion of the backscattered X-rays in front of the X-ray detection device, and a calculation device 34 that calculates the liquid level at the central axis based on the detected backscattered X-rays, wherein the X-ray irradiation device 20 is moved in the vertical direction of the liquid hydrogen tank 10, and the X-rays The system has a vertical drive mechanism 22 for adjusting the height of the irradiation axis in the liquid hydrogen tank 10. The shielding member 30 has slits provided at regular intervals in the vertical direction of the liquid hydrogen tank 10. X-rays passing through the slits are incident on the X-ray detection device 32, which detects the backscattered X-rays and measures the X-ray dose and energy of the backscattered X-rays. The calculation device 34 determines the liquid level at the interface between liquid hydrogen and hydrogen gas in the liquid hydrogen tank 10 based on the X-ray dose at a specific energy of the detected backscattered X-rays.

[0008] [2] In the liquid level gauge [1] of the present invention, preferably, the calculation device 34 has calibration curve data showing the relationship between the X-ray dose at a specific energy of backscattered X-rays generated by X-rays of a predetermined energy irradiated toward a test specimen made of the same material as the vicinity of the central axis and the known liquid level of liquid hydrogen in the liquid hydrogen tank, and the liquid level is determined based on the detected X-ray dose at a specific energy of backscattered X-rays and the calibration curve data. [3] In the liquid level gauge [1] or [2] of the present invention, preferably the X-ray irradiation device 20 further comprises a shielding cylinder, one end of which is attached near the X-ray focal point that irradiates the X-rays and the other end located near the wall surface of the liquid hydrogen tank 10, and a collimator provided at the other end of the shielding cylinder and having an opening at one location. [4] In the liquid level gauge [3] of the present invention, preferably, the collimator is slidable in a direction parallel to the liquid level, and the X-ray detection device 32 is movable in a direction perpendicular to the sliding direction of the collimator. The calculation device 34 may have a scanning information generation unit that generates scanning information in a predetermined range near the central axis. [5] In the liquid level gauges [1] to [4] of the present invention, preferably, the beam diameter of the X-ray when incident near the wall surface of the liquid hydrogen tank 10 is 10 mm or less. [6] In the liquid level gauges [1] to [5] of the present invention, for example, the X-ray detection device 32 is preferably oriented such that the X-ray detection direction axis intersects the irradiation axis at an angle of 30 to 165°. [7] In the liquid level gauges [1] to [6] of the present invention, instead of the liquid hydrogen tank, the X-ray detection device may be used to detect the boundary between the liquid phase and the gas phase that occurs with liquid helium and helium gas, liquid air and air, liquid nitrogen and nitrogen gas, or other cryogens, instead of liquid hydrogen and hydrogen gas.

[0009] [8] The liquid level measurement method of the present invention is a liquid level measurement method using a liquid level gauge, which comprises, for example as shown in Figure 1, an X-ray irradiation device 20 that irradiates a liquid hydrogen tank 10 with X-rays of a predetermined energy in a direction parallel to the liquid surface toward the central axis, an X-ray detection device 32 that detects backscattered X-rays generated near the central axis by the X-rays, a shielding member 30 that shields a portion of the backscattered X-rays in front of the X-ray detection device, and a calculation device 34 that calculates the liquid level at the central axis based on the detected backscattered X-rays, wherein the shielding member 30 is a liquid hydrogen tank The X-ray irradiation device 20 has slits provided at regular intervals in the vertical direction of the tank 10, and is configured such that X-rays passing through the slits are incident on the X-ray detection device. The X-ray irradiation device 20 is moved vertically in the liquid hydrogen tank 10, and X-rays are irradiated toward the vicinity of the central axis. The backscattered X-rays generated near the central axis are detected, and the X-ray dose and energy of the backscattered X-rays are measured. Based on the X-ray dose at a specific energy of the detected backscattered X-rays, the liquid level at the interface between liquid hydrogen and hydrogen gas in the liquid hydrogen tank 10 is determined. [9] In the liquid level measurement method [8] of the present invention, preferably, instead of the liquid hydrogen tank, a liquid helium tank, a liquid air tank, a liquid nitrogen tank, or a tank for storing other cryogens may be used, and instead of liquid hydrogen and hydrogen gas, the X-ray detection device may be used to detect the boundary between the liquid phase and the gas phase that occurs with liquid helium and helium gas, liquid air and air, liquid nitrogen and nitrogen gas, or other cryogens.

[0010] According to the liquid level gauge of the present invention, there is no need to introduce sensors or other devices for measurement into the container from outside. Compared to conventional liquid level gauges that use superconducting wires introduced into the container, this has the advantages of suppressing heat inflow, eliminating concerns about hydrogen embrittlement and low-temperature embrittlement, being independent of container size, simplifying the container structure, improving safety when handling hydrogen, and enabling precise measurement. [Brief explanation of the drawing]

[0011] [Figure 1A] This is an explanatory diagram of a liquid level gauge showing one embodiment of the present invention, illustrating it in a state where it is mounted on the outside of a liquid hydrogen tank. [Figure 1B] This is an explanatory diagram of a liquid level gauge showing one embodiment of the present invention, and shows a top view of the gauge installed in the liquid hydrogen tank shown in Figure 1A. [Figure 2] This is an explanatory diagram of X-ray Compton scattering. [Modes for carrying out the invention]

[0012] The present invention will be explained below with reference to the drawings. Figure 1A is an explanatory diagram of a liquid level gauge showing one embodiment of the present invention, in which it is mounted on the outside of a liquid hydrogen tank. Figure 1B is a top view of the configuration shown in Figure 1A, mounted on the liquid hydrogen tank. In the diagram, the liquid hydrogen container 10 has a double-wall structure consisting of an outer wall 10a and an inner wall 10b, with an insulating layer 12 provided in the gap between them. Five types of SUS (304, 304L, 316, 316L, 317), which overcome hydrogen embrittlement and other issues, are used as structural materials for the outer wall 10a and inner wall 10b of the liquid hydrogen container. Vacuum or perlite material is used for the insulating layer 12. In the inner wall 10b of the liquid hydrogen container, the upper side is hydrogen gas 14, and the lower side is liquid hydrogen 16.

[0013] The X-ray source 20 irradiates the liquid hydrogen container 10 with X-rays in the direction of the liquid surface. The irradiated X-rays propagate by spreading out in the vertical direction of approximately 7-8 degrees relative to the liquid surface. The X-ray source vertical drive mechanism 22 is a mechanism that drives the X-ray source 20 in the vertical direction of the liquid hydrogen container 10, and a general-purpose lifting mechanism is used.

[0014] The shielding member 30 is located in the vertical direction of the liquid hydrogen container 10, and is provided, for example, in a direction perpendicular to the direction of X-ray irradiation. The shielding member 30 is made of a tantalum or tungsten plate material and has slits 31 provided at intervals of, for example, 1 mm. The spacing of the slits 31 determines the resolution (approximately 1 mm) for liquid level measurement. The semiconductor detector 32 detects the parallel beam of X-rays that has passed through the slit 31. The calculation device 34 calculates the liquid level at the central axis based on the detected backscattered X-rays. The X-ray intensity monitor 36 visualizes the X-ray intensity detected by the semiconductor detector 32, and a bar graph display is used, for example. Incidentally, when the shielding member 30 is provided in a direction orthogonal to the X-ray irradiation direction, the X-ray detection device will be oriented such that the X-ray detection direction axis intersects the irradiation axis at 90°. However, the orthogonal direction is determined for the convenience of installation work, and it may be installed at an angle where the intensity of scattered X-rays is high and detection is easy. For example, the X-ray detection device may install the shielding member 30 such that the X-ray detection direction axis intersects the irradiation axis between 30° and 165°, and if possible, the shielding member 30 may be installed such that they intersect at 10° to 170°. When the X-ray detection direction axis intersects the irradiation axis at an angle less than 10°, there is a disadvantage that it becomes difficult to separate the elastically scattered X-rays from the scattered X-rays necessary for liquid surface measurement. Also, when the X-ray detection direction axis intersects the irradiation axis at an angle exceeding 170°, there is a disadvantage that the installation of the X-ray irradiation source and the detector overlaps.

[0015] Next, the operation of the liquid level gauge configured as described above will be explained. FIG. 2 is an explanatory diagram of X-ray Compton scattering, showing a scene where one X-ray photon collides with one electron in a substance and is scattered. The Compton effect is a phenomenon in which even after a photon with high energy collides with an electron, it remains as a photon and is scattered, and the wavelength of the scattered X-ray becomes longer than the wavelength of the incident X-ray. Let the frequency of the irradiated X-ray be ωi [Hz], the frequency of the scattered X-ray be ωf [Hz], the angle formed by the incident direction and the scattered direction (scattering angle) be θ, the mass of the electron be m [kg], the potential energy of the electron before the collision be Vi [J], the potential energy of the scattered electron be Vf [J], the momentum of the electron before the collision be pi [kg·m / s], the momentum of the scattered electron be pf [kg·m / s], and the Planck constant be h [J·s]. Then, it is expressed by the following formula.

[0016]

Equation

Equation

Equation

Equation

number

number

[0017] In the environment beneath liquid hydrogen in a liquid hydrogen tank, the hydrogen molecule density changes discontinuously at the gas-liquid interface. By utilizing the characteristics of Compton scattering, the liquid level of hydrogen in a container enclosed by stainless steel or insulating material, which serves as a hydrogen storage vessel, can be detected. The geometric arrangement of the incident X-ray and reflected X-ray detectors is arbitrary, and an appropriate scattering angle (θ) can be set depending on the situation. Since both the incident X-ray device and the detector are installed outside the hydrogen container, problems of hydrogen embrittlement and low-temperature embrittlement of the incident and detection devices themselves do not occur.

[0018] Furthermore, since existing commercially available semiconductor elements can be used to detect scattered X-rays, measurement costs are low. Although the accuracy of liquid level detection depends on the arrangement of elements and slits inside the detector, an accuracy of less than 1 mm can be achieved. This accuracy is higher than that of liquid level gauges currently used in cryogenic containers.

[0019] Next, the advantages of the liquid level gauge of the present invention compared to a method using superconducting wires are listed. (1) This eliminates the need to introduce sensors into the container, preventing heat inflow through sensors and preventing hydrogen embrittlement and low-temperature embrittlement of sensors. (2) X-ray Compton scattering allows us to determine the amount of liquid hydrogen remaining inside a liquid hydrogen tank by passing through stainless steel and insulating materials used in the tank. (3) X-rays irradiated from the outside of the container toward the inside are scattered by electrons in the hydrogen inside the tank. The scattering intensity differs between the gas phase and the liquid phase, with the scattering intensity being stronger in the denser liquid phase. This difference in intensity can be used as the gas-liquid phase boundary to precisely determine the liquid level.

[0020] For light elements such as hydrogen, the Compton scattering intensity is relatively strong compared to the simultaneously emitted fluorescent X-rays. Furthermore, because high-energy X-rays are used, they have high penetration power, and the ability to perform measurements non-destructively and non-contact is a major advantage.

[0021] In the above embodiment, a case is described in which the interface between liquid hydrogen and hydrogen gas is detected using X-ray Compton scattering, using a liquid hydrogen tank as an example. However, the present invention is not limited to this. For example, instead of a liquid hydrogen tank, it may be used in a liquid helium tank, a liquid air tank, a liquid nitrogen tank, or a tank for storing other cryogens, and the X-ray detection device may be used to detect the interface between the liquid phase and the gas phase that occurs with liquid helium and helium gas, liquid air and air, liquid nitrogen and nitrogen gas, or other cryogens, instead of liquid hydrogen and hydrogen gas. [Industrial applicability]

[0022] The liquid level gauge of the present invention uses X-ray Compton scattering to determine the volume of liquid hydrogen in a container, which is a clean energy source, for large-scale utilization of hydrogen. In X-ray Compton scattering, X-rays incident from outside the container into the interior are reflected from the liquid and gas phases of the cryogenic agent inside, and the difference in density between them can be distinguished, allowing the liquid level to be determined from the boundary between them. This method does not require introducing sensors or other devices for measurement into the container from the outside. Compared to conventional liquid level gauges that use superconducting wires introduced into a container, this method offers several advantages: suppression of heat inflow, no concerns about hydrogen embrittlement or low-temperature embrittlement, independence from container size, simplified container structure, and the ability to perform precise measurements. [Explanation of symbols]

[0023] 10. Liquid hydrogen container (liquid hydrogen tank) 10a Outer wall of liquid hydrogen container 10b Inner wall of liquid hydrogen container 12. Insulation layer 14. Hydrogen gas 16. Liquid Hydrogen 20 X-ray source (X-ray irradiation device) 22 X-ray source vertical drive mechanism 30 Shielding member 31 slits 32. Semiconductor detectors (X-ray detection devices) 34 Calculation device 36 X-ray intensity monitor

Claims

1. A liquid level gauge comprising: an X-ray irradiation device that irradiates a liquid hydrogen tank with X-rays of predetermined energy in a direction parallel to the liquid surface toward the central axis; an X-ray detection device that detects backscattered X-rays generated near the central axis by the X-rays; a shielding member that shields a portion of the backscattered X-rays in front of the X-ray detection device; and a calculation device that calculates the liquid level at the central axis based on the detected backscattered X-rays, The X-ray irradiation device has a vertical drive means for moving it vertically in the vertical direction of the liquid hydrogen tank to adjust the height of the X-ray irradiation axis in the liquid hydrogen tank, The shielding member has slits provided at regular intervals in the vertical direction of the liquid hydrogen tank, and X-rays passing through the slits are incident on the X-ray detection device. The X-ray detection device detects backscattered X-rays and measures the X-ray dose and energy of the backscattered X-rays. The calculation device is a liquid level meter that determines the liquid level at the interface between liquid hydrogen and hydrogen gas in the liquid hydrogen tank based on the X-ray dose at a specific energy of the detected backscattered X-rays.

2. The liquid level gauge according to claim 1, further comprising: an X-ray irradiation device having one end attached near the X-ray focal point that irradiates the X-rays and the other end located near the wall surface of the liquid hydrogen tank; and a collimator provided at the other end of the shielding cylinder and having an opening at one location.

3. The collimator is slidable in a direction parallel to the liquid surface, The X-ray detection device is movable in a direction perpendicular to the sliding direction of the collimator, The liquid level gauge according to claim 2, wherein the calculation device has a scanning information generation unit that generates scanning information in a predetermined range near the central axis.

4. The liquid level gauge according to claim 1, wherein the beam diameter of the X-ray when incident near the wall surface of the liquid hydrogen tank is 10 mm or less.

5. The liquid level gauge according to claim 1, wherein the X-ray detection device is oriented such that the X-ray detection direction axis intersects the irradiation axis at an angle of 30 to 165°.

6. Instead of the aforementioned liquid hydrogen tank, it is used as a liquid helium tank, liquid air tank, liquid nitrogen tank, or other refrigerant storage tank. The X-ray detection device is used to detect the boundary between the liquid phase and the gas phase that occurs with liquid helium and helium gas, liquid air and air, liquid nitrogen and nitrogen gas, or other cryogens, instead of liquid hydrogen and hydrogen gas. The liquid level gauge according to claim 1.

7. A liquid level measurement method using a liquid level gauge comprising: an X-ray irradiation device that irradiates a liquid hydrogen tank with X-rays of a predetermined energy in a direction parallel to the liquid surface toward the central axis; an X-ray detection device that detects backscattered X-rays generated near the central axis by the X-rays; a shielding member that shields a portion of the backscattered X-rays in front of the X-ray detection device; and a calculation device that calculates the liquid level near the central axis based on the detected backscattered X-rays, wherein The shielding member has slits provided at regular intervals in the vertical direction of the liquid hydrogen tank, and is configured such that X-rays passing through the slits are incident on the X-ray detection device. The X-ray irradiation device is moved vertically in the direction of the liquid hydrogen tank, and X-rays are irradiated toward the vicinity of the central axis. The system detects the backscattered X-rays generated near the central axis and measures the X-ray dose and energy of the backscattered X-rays. A method for measuring liquid level to determine the liquid level at the interface between liquid hydrogen and hydrogen gas in a liquid hydrogen tank based on the X-ray dose at a specific energy of the detected backscattered X-rays.

8. Instead of the aforementioned liquid hydrogen tank, it is used as a liquid helium tank, liquid air tank, liquid nitrogen tank, or other refrigerant storage tank. The aforementioned X-ray detection device is used to detect the boundary between a liquid phase and a gas phase that occurs with liquid helium and helium gas, liquid air and air, liquid nitrogen and nitrogen gas, or other cryogens, instead of liquid hydrogen and hydrogen gas. The liquid level measurement method according to claim 7.

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