Liquid level meter for liquid hydrogen and liquid level measurement method

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 with, for example, liquid hydrogen. [Background technology]

[0002] The use of hydrogen, a clean energy source, was included as one of the basic policies of the Sixth Basic Energy Plan. When transporting and storing hydrogen, it is expected to be used in a liquid state, which has a density 1 / 800 that of a gas. Accurate measurement and understanding of the volume of liquid hydrogen in a container with an insulated structure is essential for hydrogen utilization. Volume measurement is performed using a standard liquid level gauge, as with other cryogens (nitrogen, helium, etc.). For example, a simple float type is used for liquid nitrogen. Regarding hydrogen level gauges, those that utilize 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] Japanese Patent Application Laid-Open No. 2009-175034 [Patent Document 2] Japanese Patent Application Laid-Open No. 2014-098659 [Patent Document 3] WO2017-179488 publication Summary of the Invention [Problem to be solved by the invention]

[0004] However, the capacitance type requires calibration for each experiment, and in the coming hydrogen society, it is not realistic to make it compatible with individual containers ranging from large tanks for plants in the 5-ton class to small and medium-sized containers up to about 100 kg that are intended for local production and consumption. Even in methods using superconducting wires, the boiling point of hydrogen at normal pressure is 20 Kelvin, compared to helium, which has a boiling point of 4.2 Kelvin. Usable superconducting materials are limited to MgB2 and the like. Furthermore, there is currently no established method for evaluating superconducting materials under hydrogen pressure.

[0005] Additionally, challenges unique to hydrogen must be overcome. Because hydrogen itself is flammable, safety is even more important. Furthermore, the introduction of a level sensor into a liquid hydrogen container inevitably results in heat inflow, leading to the evaporation of a valuable energy source. Furthermore, the introduction of a level sensor inside the container requires consideration of hydrogen embrittlement and low-temperature embrittlement of the liquid surface materials used, while also making the container structure even more complex. Another unavoidable concern is the hydrogen embrittlement and low-temperature embrittlement of welds and connections due to the level sensor installed inside the container.

[0006] The present invention has been made to solve the above-mentioned problems of the prior art, and has as its object to provide a liquid level gauge and a liquid level measurement method that can measure the liquid level of the liquid hydrogen inside a container without contacting the liquid hydrogen. [Means for solving the problem]

[0007] [1] As shown in FIG. 1, the liquid level gauge of the present invention is a liquid level gauge comprising an X-ray irradiator 20 that irradiates X-rays of a predetermined energy in a direction parallel to the liquid surface toward the central axis of a liquid hydrogen tank 10, an X-ray detector 32 that detects backscattered X-rays generated in the vicinity of 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 detector, and a calculator 34 that calculates the liquid level at the central axis based on the detected backscattered X-rays. The X-ray irradiator 20 is moved in the vertical direction of the liquid hydrogen tank 10 to detect the backscattered X-rays. The shielding member 30 has slits arranged at regular intervals in the vertical direction of the liquid hydrogen tank 10, and X-rays that pass through the slits are incident on the X-ray detection device 32, which detects backscattered X-rays and measures the X-ray dose and energy of the backscattered X-rays. A calculation device 34 calculates 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 meter [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 the predetermined energy irradiated toward a test piece 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 calculation device 34 determines the liquid level based on the X-ray dose at the specific energy of the detected backscattered X-rays and the calibration curve data. [3] In the liquid level meter [1] or [2] of the present invention, preferably, the X-ray irradiator 20 further comprises a shielding cylinder having one end attached near the X-ray focus 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 surface, and the X-ray detection device 32 is movable in a direction perpendicular to the sliding direction of the collimator, The calculation device 34 preferably includes a scanning information generation unit that generates scanning information in a predetermined range in the vicinity of the central axis. [5] In the liquid level gauges [1] to [4] of the present invention, preferably, the beam diameter of the X-rays when incident on the vicinity of 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 may be oriented so 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, the level gauges may be used in a liquid helium tank, a liquid air tank, a liquid nitrogen tank, or other cryogen storage tank instead of the liquid hydrogen tank, and the X-ray detection device may be used to detect the boundary between the liquid phase and the gas phase occurring in liquid helium and helium gas, liquid air and air, liquid nitrogen and nitrogen gas, or other cryogen 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 includes, as shown in FIG. 1, an X-ray irradiation device 20 that irradiates X-rays of a predetermined energy in a direction parallel to the liquid surface toward the central axis of a liquid hydrogen tank 10, an X-ray detection device 32 that detects backscattered X-rays generated in the vicinity of the central axis by the X-rays, a shielding member 30 that shields part 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, and the shielding member 30 is a shielding member that shields the liquid hydrogen tank 10 from the liquid hydrogen. The X-ray irradiator 20 is configured to have slits arranged at regular intervals in the vertical direction of the liquid hydrogen tank 10, and X-rays that pass through the slits are incident on the X-ray detection device. The X-ray irradiator 20 is moved in the vertical direction of the liquid hydrogen tank 10 to irradiate X-rays toward the vicinity of the central axis, detect backscattered X-rays generated near the central axis, measure the X-ray dose and energy of the backscattered X-rays, and determine 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. [9] In the liquid level measurement method [8] of the present invention, it is preferable that the method is used in a liquid helium tank, a liquid air tank, a liquid nitrogen tank, or a tank for storing other cryogens instead of the liquid hydrogen tank, and the X-ray detection device may be used to detect the boundary between the liquid phase and the gas phase occurring in liquid helium and helium gas, liquid air and air, liquid nitrogen and nitrogen gas, or other cryogens instead of liquid hydrogen and hydrogen gas.

[0010] The liquid level gauge of the present invention eliminates the need to install sensors for measurement from outside the vessel inside the vessel. Compared to liquid level gauges that use superconducting wires inside the vessel, which can be considered an extension of conventional types, this has the following advantages: reduced heat inflow, no concerns about hydrogen embrittlement or low-temperature embrittlement, no dependency on vessel size, simplified vessel structure, improved safety when handling hydrogen, and the ability to perform precise measurements. [Brief explanation of the drawings]

[0011] [Figure 1A] 1 is an explanatory diagram of a liquid level gauge according to an embodiment of the present invention, showing the state where it is attached to the outside of a liquid hydrogen tank. FIG. [Figure 1B] 1B is an explanatory diagram of a liquid level gauge according to an embodiment of the present invention, showing the arrangement as viewed from above when attached to the liquid hydrogen tank shown in FIG. 1A. FIG. [Figure 2] FIG. 1 is an explanatory diagram of X-ray Compton scattering. DETAILED DESCRIPTION OF THE INVENTION

[0012] The present invention will be described below with reference to the drawings. Fig. 1A is an explanatory diagram of a liquid level gauge according to one embodiment of the present invention, showing the gauge attached to the outside of a liquid hydrogen tank. Fig. 1B is a top view of the level gauge attached to the liquid hydrogen tank shown in Fig. 1A. In the figure, the liquid hydrogen container 10 has a double-wall structure consisting of an outer wall 10a and an inner wall 10b, with a heat insulating layer 12 provided in the gap between the two. The outer wall 10a and the inner wall 10b are made of five types of stainless steel (304, 304L, 316, 316L, 317) that have passed hydrogen embrittlement tests. The heat insulating layer 12 is made of vacuum or pearlite material. On the inner wall 10b of the liquid hydrogen container, hydrogen gas 14 is located above the liquid surface, and liquid hydrogen 16 is located below.

[0013] The X-ray source 20 irradiates X-rays in the direction of the liquid surface of the liquid hydrogen container 10. The irradiated X-rays propagate, spreading out over an angle of about 7-8 degrees in both the vertical and horizontal directions relative to the liquid surface. The X-ray source vertical drive mechanism 22 is a mechanism for driving 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 positioned above and below the liquid hydrogen container 10, 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 formed at intervals of, for example, 1 mm. The intervals between the slits 31 determine the resolution (approximately 1 mm) of 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 is implemented by, for example, a bar graph display. If the shielding member 30 is installed perpendicular to the X-ray irradiation direction, the X-ray detection device will be oriented so that the X-ray detection axis intersects the irradiation axis at an angle of 90°. However, this perpendicular orientation is determined for ease of installation, and the X-ray detection device may be installed at any angle that maximizes the intensity of scattered X-rays and facilitates their detection. For example, the X-ray detection device may be installed so that the X-ray detection axis intersects the irradiation axis at an angle between 30 and 165°, or, if possible, between 10 and 170°. If the X-ray detection axis intersects the irradiation axis at an angle less than 10°, it becomes difficult to separate elastically scattered X-rays from scattered X-rays required for liquid level measurement. Furthermore, if the X-ray detection axis intersects the irradiation axis at an angle greater than 170°, the X-ray irradiation source and detector may overlap.

[0015] The operation of the level gauge configured in this manner will now be described. Figure 2 is an explanatory diagram of X-ray Compton scattering, showing the scene where an X-ray photon collides with an electron in a material and is scattered. The Compton effect is a phenomenon in which photons with such high energy remain as photons even after colliding with an electron and scatter, resulting in the wavelength of the scattered X-ray becoming longer than that 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 between the incident direction and the scattering 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]. The following equation expresses this:

[0016]

number

number

number

number

number

number

[0017] In the liquid hydrogen environment inside a liquid hydrogen tank, the density of hydrogen molecules changes discontinuously at the gas-liquid interface. Therefore, by utilizing the characteristics of Compton scattering, it is possible to detect the liquid hydrogen level inside a hydrogen storage container surrounded by stainless steel or heat insulating material. 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. Because both the incident X-ray device and detector are installed outside the hydrogen container, there are no problems with hydrogen embrittlement or low-temperature embrittlement of the incident and detection devices themselves.

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

[0019] Next, the effects of the liquid level gauge of the present invention compared with a system using a superconducting wire will be listed. (1) It is not necessary to install sensors inside the vessel, and it is possible to prevent heat inflow through the sensors and hydrogen embrittlement and low-temperature embrittlement of the sensors. (2) X-ray Compton scattering can penetrate the stainless steel and insulating materials used in liquid hydrogen tanks, making it possible to determine the amount of liquid hydrogen remaining inside. (3) X-rays irradiated from the outside of the container to the inside are scattered by electrons in the hydrogen inside the tank. The scattering intensity differs between the gas and liquid phases, with the liquid phase scattering intensity being stronger due to its higher density. This difference in intensity can be used as the gas-liquid phase boundary to accurately determine the liquid level.

[0020] For light elements such as hydrogen, the intensity of Compton scattering is relatively strong compared to the fluorescent X-rays emitted at the same time. Furthermore, the use of high-energy X-rays allows for high penetration, and a major feature is that measurements can be made non-destructively and without contact.

[0021] In the above embodiment, the case where the boundary between liquid hydrogen and hydrogen gas is detected using X-ray Compton scattering has been described using a liquid hydrogen tank as an example, but the present invention is not limited to this. For example, instead of a liquid hydrogen tank, the X-ray detection device may be used in a liquid helium tank, a liquid air tank, a liquid nitrogen tank, or a tank for storing other cryogens, 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 occurring in liquid helium and helium gas, liquid air and air, liquid nitrogen and nitrogen gas, or other cryogens. [Industrial Applicability]

[0022] The liquid level meter of this invention, which is designed to utilize large amounts of clean energy, uses the X-ray Compton scattering method to measure the volume of liquid hydrogen in a container. With the X-ray Compton scattering method, X-rays are irradiated from the outside of the container to the inside, and the reflections from the liquid and gas phases of the cryogen inside can be distinguished as differences in their densities, and the position of the liquid level can be determined from the boundary between them. This method does not require the introduction of sensors or other measurement devices from outside the container into the container. Compared to liquid level gauges that use superconducting wires inside a vessel, which can be considered an extension of conventional types, this has the advantages of suppressing heat inflow, eliminating concerns about hydrogen embrittlement and low-temperature embrittlement, not being dependent on the size of the vessel, simplifying the vessel structure, and enabling precise measurements. [Explanation of symbols]

[0023] 10 Liquid hydrogen container (liquid hydrogen tank) 10a Liquid hydrogen container outer wall 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 Slit 32 Semiconductor detector (X-ray detection device) 34 Calculation device 36 X-ray intensity monitor

Claims

1. A liquid level gauge comprising an X-ray irradiator which irradiates X-rays of a predetermined energy in a direction parallel to the liquid surface toward a central axis of a liquid hydrogen tank, an X-ray detection device which detects backscattered X-rays generated in the vicinity of the central axis by the X-rays, a shielding member which blocks a portion of the backscattered X-rays in front of the X-ray detection device, and a calculation device which calculates the liquid level at the central axis based on the detected backscattered X-rays, a vertical drive means for moving the X-ray irradiator in the vertical direction of the liquid hydrogen tank to adjust the height of the irradiation axis of the X-rays in the hydrogen tank, the shielding member has slits provided at regular intervals in the up-down 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 level gauge 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. 2. The liquid level gauge according to claim 1, wherein the calculation device has calibration curve data showing the relationship between an X-ray dose at a specific energy of backscattered X-rays generated by irradiating a test piece made of the same material as the vicinity of the central axis with X-rays of the specified energy and a known liquid level of the liquid hydrogen in the liquid hydrogen tank, and the liquid level is calculated based on the X-ray dose at the specific energy of the detected backscattered X-rays and the calibration curve data.

3. 3. The liquid level gauge according to claim 1 or 2, wherein the X-ray irradiator further comprises a shielding cylinder having one end attached in the vicinity of an X-ray focal point that irradiates the X-rays and the other end located in the vicinity of a 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.

4. The collimator is slidable in a direction parallel to the liquid surface, the X-ray detection device is movable in a direction perpendicular to a sliding direction of the collimator, The liquid level gauge according to claim 3 , wherein the calculation device includes a scanning information generating section that generates scanning information in a predetermined range in the vicinity of the central axis.

5. 2. The liquid level gauge according to claim 1, wherein the X-rays have a beam diameter of 10 mm or less when incident on the vicinity of the wall surface of the liquid hydrogen tank.

6. 2. The liquid level gauge according to claim 1, wherein the X-ray detection device is oriented so that an axis of a detection direction of X-rays intersects the irradiation axis at an angle of 30 to 165 degrees.

7. Instead of the liquid hydrogen tank, the liquid hydrogen tank may be used for a liquid helium tank, a liquid air tank, a liquid nitrogen tank, or another cryogen storage tank. The X-ray detector is used to detect the boundary between liquid and gas phases 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.

2. The liquid level gauge according to claim 1.

8. A liquid level measurement method using a liquid level gauge including an X-ray irradiation device that irradiates X-rays of a predetermined energy in a direction parallel to the liquid surface toward the vicinity of the liquid surface of a liquid hydrogen tank, an X-ray detection device that detects backscattered X-rays generated in the vicinity of the central axis by the X-rays, a shielding member that blocks a portion of the backscattered X-rays in front of the X-ray detection device, and a calculation device that calculates the liquid level in the vicinity of the central axis based on the detected backscattered X-rays, the shielding member has slits provided at regular intervals in the up-down direction of the liquid hydrogen tank, and is configured so that X-rays passing through the slits are incident on the X-ray detection device, the X-ray irradiator is moved in a vertical direction of the liquid hydrogen tank to irradiate X-rays toward the vicinity of the central axis; Detecting backscattered X-rays generated in the vicinity of the central axis and measuring the X-ray dose and energy of the backscattered X-rays; A liquid level measuring method for determining 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.

9. Instead of the liquid hydrogen tank, the liquid hydrogen tank may be used for a liquid helium tank, a liquid air tank, a liquid nitrogen tank, or another cryogen storage tank. The X-ray detection device is used to detect the boundary between liquid and gas phases occurring 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 measuring method according to claim 8.

Images