Liquefied gas phase change detection system and liquefied gas phase change detection method

Abstract

This liquefied gas phase change detection system comprises: an accommodation structure which accommodates a liquefied gas thereinside; an ultrasonic sensor which is configured to emit an ultrasonic beam from the outside of the accommodation structure to the liquefied gas accommodated inside the accommodation structure, and which is configured to acquire the reflection intensity and the arrival time of a reflection wave of the ultrasonic beam reflected from the liquefied gas; and a detection device which is configured to detect whether or not a phase change has occurred in the liquefied gas, by considering reflection intensities and arrival times of a plurality of reflection waves obtained by the ultrasonic sensor through repeatedly emitting the ultrasonic beam to the liquefied gas a plurality of times.

Description

Liquefied gas phase change detection system and liquefied gas phase change detection method

[0001] This disclosure relates to a liquefied gas phase change detection system and a liquefied gas phase change detection method.This application claims priority to Japanese Patent Application No. 2024-015337, filed with the Japan Patent Office on February 5, 2024, the contents of which are incorporated herein by reference.

[0002] When transporting or storing a liquefied gas such as liquid carbon dioxide in a sealed container, the liquefied gas may be kept above its triple point to prevent solid phase formation. If a solid phase forms in the liquefied gas in a pipe through which the liquefied gas is transported, the solid phase may accumulate on equipment for transporting the liquefied gas, such as pumps and valves, installed in the pipe, potentially making the transport of the liquefied gas difficult. Furthermore, if a solid phase formed in the pipe is introduced into a sealed container or if a solid phase forms in the liquefied gas in the sealed container, the solid phase may accumulate at the bottom of the sealed container and block the suction port of the pump that guides the liquefied gas from the sealed container to the outside. Furthermore, if a closed space is formed locally by the solid phase within the sealed container, heat input to the liquid phase confined in the closed space may gasify the liquid phase, resulting in local overpressurization and potentially damaging the sealed container. For this reason, it is important to detect the phase change of the liquefied gas contained in the sealed container from the liquid phase to the gas phase or the solid phase.

[0003] Japanese Unexamined Patent Publication No. 61-29722

[0004] Patent Document 1 discloses an invention that focuses on the phenomenon in which an ultrasonic beam incident from the side of a container propagates through the liquid in the container, is reflected by the opposing wall of the container, and returns to the insertion part, and detects the presence or absence of a liquid based on the presence or absence of a reflected pulse from the opposing wall. However, when the difference in acoustic impedance between the container and the liquid is large, only a small amount of the ultrasonic beam penetrates the liquid, and therefore the reflected pulse from the opposing wall is buried in noise, making detection difficult.

[0005] In view of the above circumstances, at least one embodiment of the present disclosure aims to provide a liquefied gas phase change detection system and a liquefied gas phase change detection method that can detect the phase change of a liquefied gas contained inside a storage structure from outside the storage structure.

[0006] A liquefied gas phase change detection system according to at least one embodiment of the present disclosure is a liquefied gas phase change detection system for detecting a phase change of a liquefied gas, comprising: a storage structure for storing the liquefied gas therein; an ultrasonic sensor configured to emit an ultrasonic beam from the outside of the storage structure toward the liquefied gas stored inside the storage structure, the ultrasonic sensor configured to acquire the reflection intensity and arrival time of the reflected wave of the ultrasonic beam from the liquefied gas; and a detection device configured to detect whether a phase change has occurred in the liquefied gas, taking into account the reflection intensity and arrival time of the multiple reflected waves obtained by the ultrasonic sensor repeatedly emitting the ultrasonic beam toward the liquefied gas multiple times.

[0007] A liquefied gas phase change detection method according to at least one embodiment of the present disclosure is a liquefied gas phase change detection method for detecting a phase change of a liquefied gas, and includes a reflected wave acquisition step of irradiating an ultrasonic beam from outside a storage structure that stores the liquefied gas toward the liquefied gas stored inside the storage structure, and acquiring the reflection intensity and arrival time of the ultrasonic beam reflected from the liquefied gas, and a detection step of detecting whether a phase change has occurred in the liquefied gas, taking into account the reflection intensity and arrival time of the reflected wave obtained multiple times by repeating the reflected wave acquisition step multiple times.

[0008] According to at least one embodiment of the present disclosure, a liquefied gas phase change detection system and a liquefied gas phase change detection method are provided that are capable of detecting a phase change of a liquefied gas contained inside a containment structure from outside the containment structure.

[0009] FIG. 1 is a schematic diagram of a liquefied gas phase change detection system according to an embodiment of the present disclosure. FIG. 2 is an explanatory diagram for explaining a storage structure according to an embodiment of the present disclosure. FIG. 3 is an explanatory diagram for explaining information about a reflected wave acquired by a first ultrasonic sensor according to an embodiment of the present disclosure. FIG. 4 is an explanatory diagram for explaining a method for determining whether or not a liquid surface is swaying according to an embodiment of the present disclosure. FIG. 5 is an explanatory diagram for explaining information about a reflected wave acquired by a second ultrasonic sensor according to an embodiment of the present disclosure. FIG. 6 is an explanatory diagram for explaining an attachment member according to an embodiment of the present disclosure. FIG. 7 is an explanatory diagram for explaining the surface roughness of the inner wall surface of the storage structure according to an embodiment of the present disclosure. FIG. 8 is an explanatory diagram for explaining a rod-shaped member according to an embodiment of the present disclosure. FIG. 9 is an explanatory diagram for explaining a pressure acquisition device and a temperature acquisition device according to an embodiment of the present disclosure. FIG. 10 is an explanatory diagram for explaining a pressurizing device according to an embodiment of the present disclosure. FIG. 11 is an explanatory diagram for explaining a heating device according to an embodiment of the present disclosure.

[0010] Hereinafter, several embodiments of the present disclosure will be described with reference to the accompanying drawings. However, the dimensions, materials, shapes, relative arrangements, etc. of components described as embodiments or shown in the drawings are merely illustrative examples and are not intended to limit the scope of the present disclosure.

[0011] (Liquefied Gas Phase Change Detection System) Figure 1 is a schematic diagram of a liquefied gas phase change detection system 1 according to one embodiment of the present disclosure. The liquefied gas phase change detection system 1 and the liquefied gas phase change method according to some embodiments of the present disclosure are systems (methods) for detecting a phase change of a liquefied gas contained inside a storage structure 2 that stores the liquefied gas therein, particularly a phase change from a liquid phase to a solid phase, from the outside of the storage structure 2. In some embodiments, the liquefied gas phase change detection system 1 includes a storage structure 2, at least one ultrasonic sensor 3, and a detection device 4, as shown in Figure 1.

[0012] In the following embodiments, a case where the liquefied gas is liquefied carbon dioxide will be described, but the present disclosure can also be applied to liquefied gases other than liquefied carbon dioxide, such as liquefied hydrogen and liquefied natural gas. In the present disclosure, it is preferable that the difference in ultrasonic properties between the material of the storage structure 2 and the liquefied gas is relatively small, and the transmittance of the liquefied gas is high. In one embodiment, the material of the storage structure 2 is stainless steel such as SUS304, and the liquefied gas is liquefied carbon dioxide. In this case, the difference in ultrasonic properties between the material of the storage structure 2 and the liquefied gas is relatively large, and the transmittance to the liquid is low, but the present disclosure can be suitably applied.

[0013] (Storage Structure) As shown in FIG. 1, the storage structure 2 includes a main body portion (thick portion) of the storage structure 2 having an outer wall surface 21 and an inner wall surface 22. The storage structure 2 has an internal space 23 that is sealed inside the storage structure 2 by the inner wall surface 22. The internal space 23 contains liquefied gas that is mainly in a liquid phase. The liquefied gas stored inside the storage structure 2 has a liquid level LS. In the embodiment shown in FIG. 1, the main body portion of the storage structure 2, which has the outer wall surface 21 and the inner wall surface 22, is formed in a cylindrical shape extending along the vertical direction. Note that the main body portion may also be formed in a rectangular tubular shape extending along the vertical direction.

[0014] 2 is an explanatory diagram illustrating a storage structure 2 according to an embodiment of the present disclosure. In FIG. 2, a first storage device (a storage tank in the illustrated example) 101, a second storage device (a storage tank in the illustrated example) 103, a pump 105, a pipe 106, and a valve 107 are shown.

[0015] The first storage device 101 is a sealed container having an internal space 102 for storing liquefied gas in liquid phase. The second storage device 103 is a sealed container having an internal space 104 for storing liquefied gas in liquid phase. The piping 106 forms a flow path for guiding the liquefied gas in liquid phase from the first storage device 101 to the second storage device 103, and one end of the piping 106 is connected to the first storage device 101 and the other end of the piping 106 is connected to the second storage device 103. In one embodiment, the first storage device 101 is located on land, and the second storage device 103 is installed on a ship. In another embodiment, the first storage device 101 is installed on a ship, and the second storage device 103 is located on land.

[0016] Pump 105 is disposed inside second storage device 103 (internal space 104), and is configured to pump liquid-phase liquefied gas from the inside to the outside of second storage device 103. Valve 107 is provided in pipe 106, and is configured to be able to adjust the flow rate of the liquid-phase liquefied gas flowing through pipe 106.

[0017] When transporting or storing liquefied gas in a sealed container such as the first storage device 101 or the second storage device 103, the liquefied gas may be kept at a temperature above its triple point to prevent the formation of a solid phase. If a solid phase were to form in the liquefied gas in the pipe 106 through which the liquefied gas is transported, the solid phase may accumulate on equipment for transporting the liquefied gas, such as a pump (not shown) or a valve 107, provided in the pipe 106, making it difficult to transport the liquefied gas. Furthermore, if the solid phase formed in the pipe 106 is introduced into the sealed container (the second storage device 103) or if a solid phase were to form in the liquefied gas in the sealed container, the solid phase may accumulate at the bottom of the sealed container and clog the suction port of the pump 105 that guides the liquefied gas from the sealed container to the outside. Furthermore, if a closed space is formed locally by the solid phase within the sealed container, heat input to the liquid phase trapped in the closed space may cause the liquid phase to gasify, resulting in local overpressure and damaging the sealed container. For this reason, it is important to detect the phase change of a liquefied gas contained in a sealed container from the liquid phase to the gas phase or solid phase.

[0018] In the embodiment shown in Fig. 1, the storage structure 2 is a sealed container such as a first storage device 101 or a second storage device 103. For the liquefied gas in the sealed container to generate a solid phase, the pressure inside the sealed container must be reduced to a pressure equal to or lower than the triple point pressure. This reduction in pressure causes the liquefied gas in the sealed container to boil, generating bubbles that cause the liquid level LS to fluctuate. In the embodiment shown in Fig. 1, the liquefied gas phase change detection system 1 can detect the fluctuation of the liquid level LS due to the decompression boiling of the liquefied gas, which is a precursor to the generation of the solid phase, thereby enabling advance detection of the generation of the solid phase before it occurs.

[0019] (Ultrasonic Sensor) The ultrasonic sensor 3 is disposed outside the storage structure 2, and is configured to emit an ultrasonic beam from outside the storage structure 2 toward the liquefied gas stored inside the storage structure 2. The ultrasonic sensor 3 is also configured to acquire the reflection intensity and arrival time of the reflected wave from the liquefied gas of the ultrasonic beam emitted by the ultrasonic sensor 3. The reflected wave acquired by the ultrasonic sensor 3 is a wave reflected by the liquefied gas in the vicinity of the inner wall surface 22 on the side where the ultrasonic sensor 3 is disposed, through which the ultrasonic beam passes (for example, within a range where the delay in the arrival time of the reflected wave is 5 μsec or less).

[0020] 1 , the ultrasonic sensor 3 includes a first ultrasonic sensor 3A provided at a predetermined height position at which the liquid level LS of the liquefied gas contained inside the storage structure 2 can be detected. When the liquid level LS of the liquefied gas fluctuates, the predetermined height position at which the liquid level LS of the liquefied gas can be detected means a height position between an upper limit position and a lower limit position of the liquid level LS within the measurement range of the first ultrasonic sensor 3A. Also, the predetermined height position at which the liquid level LS of the liquefied gas can be detected means a height position at which the liquid level LS is included in the measurement range of the first ultrasonic sensor 3A.

[0021] The first ultrasonic sensor 3A is attached to the outer wall surface 21 of the housing structure 2, and emits an ultrasonic beam along the thickness direction of the main body of the housing structure 2. In the embodiment shown in Fig. 1 , the incident direction of the ultrasonic beam from the first ultrasonic sensor 3A is a direction along the horizontal direction and toward the inside in the radial direction of the housing structure 2 (to the right in Fig. 1 ).

[0022] The ultrasonic beam emitted by the first ultrasonic sensor 3A from outside the containing structure 2 toward the inside of the containing structure 2 passes through the main body of the containing structure 2 and is mostly reflected at the metal interface (inner wall surface 22) of the main body, but a portion passes through the metal interface and the liquid phase of the liquefied gas in contact with the metal interface and is reflected at the liquid level LS. The reflected wave emitted by the first ultrasonic sensor 3A and reflected at the liquid level LS has a delay in arrival compared to the reflected wave emitted by the first ultrasonic sensor 3A and reflected at the inner wall surface 22. When the liquid level LS (LS1, LS2, LS3) is fluctuating, the delay in arrival time of the reflected wave varies.

[0023] FIG. 3 is an explanatory diagram illustrating information related to the reflected wave acquired by the first ultrasonic sensor 3A according to an embodiment of the present disclosure. FIG. 3 illustrates a distribution of the reflection intensity RI of the reflected wave from the first ultrasonic sensor 3A versus the arrival time AT. In FIG. 3, the arrival time of the reflected wave incident on the first ultrasonic sensor 3A and reflected by the inner wall surface 22 is denoted as AT1, and the period from the arrival time AT1 to the arrival time AT2, which takes into account the delay in the arrival time of the reflected wave reflected by the liquid surface LS, is denoted as T1. During this period T1, the reflected wave incident on the first ultrasonic sensor 3A and reflected by the liquid surface LS reaches the first ultrasonic sensor 3A. As shown in FIG. 3, because the transmittance of an ultrasonic beam through a liquid-phase liquefied gas is relatively low, the reflection intensity RI of the reflected wave reflected by the liquid surface LS is smaller than the reflection intensity of the reflected wave reflected by the inner wall surface 22 and is therefore difficult to detect due to being buried in the noise level.

[0024] The first ultrasonic sensor 3A repeatedly emits an ultrasonic beam toward the liquefied gas multiple times, thereby obtaining the reflection intensity RI and arrival time AT of the reflected wave reflected multiple times by the liquid surface LS. The reflection intensity RI and arrival time AT of the reflected wave reflected multiple times by the liquid surface LS obtained by the first ultrasonic sensor 3A are sent to the detection device 4.

[0025] The detection device 4 is configured to detect whether a phase change is occurring in the liquefied gas, taking into consideration the reflection intensity RI and arrival time AT of multiple reflected waves obtained by the first ultrasonic sensor 3A (ultrasonic sensor 3) repeatedly irradiating an ultrasonic beam toward the liquefied gas multiple times. The first ultrasonic sensor 3A (ultrasonic sensor 3) can acquire the reflection intensity RI and arrival time AT of the ultrasonic beam reflected from the liquefied gas from outside the containment structure 2. As will be described in detail later, when a phase change occurs in the liquefied gas contained inside the containment structure 2, changes occur in the reflection intensity RI and arrival time AT of the ultrasonic beam reflected from the liquefied gas. Therefore, by monitoring the reflection intensity RI and arrival time AT of the ultrasonic beam reflected from the liquefied gas, the detection device 4 can detect a phase change of the liquefied gas contained inside the containment structure 2.

[0026] The detection device 4 may be configured by a computer such as an electronic control device. This computer includes a processor such as a CPU or GPU, memories such as ROM and RAM, and an I / O interface (not shown). The detection device 4 configured by a computer realizes each of the functional units described below by the processor operating (calculating, etc.) according to instructions of a program loaded into the memory. The detection device 4 includes a memory unit 41. The memory unit 41 stores the reflection intensity RI and arrival time AT of the reflected wave from the liquefied gas acquired multiple times by the first ultrasonic sensor 3A.

[0027] In the embodiment shown in FIG. 1 , the detection device 4 includes a sway determination unit 42. The sway determination unit 42 is configured to determine whether or not the liquid level LS of the liquefied gas is swaying, taking into account statistical variability in the reflection intensity RI obtained by statistically processing the reflection intensity RI and arrival time AT of the reflected wave from the liquefied gas over multiple times acquired by the first ultrasonic sensor 3A. The statistical variability in the reflection intensity RI obtained by statistically processing the reflection intensity RI and arrival time AT of the reflected wave has a relatively high S / N ratio, which is the ratio of signal to noise, and therefore can suitably determine whether or not the liquid level LS of the liquefied gas is swaying. Note that, when the sway determination unit 42 determines that the liquid level LS of the liquefied gas is swaying, the detection device 4 may consider that the liquefied gas is undergoing a phase change from liquid to solid.

[0028] FIG. 4 is an explanatory diagram illustrating a method for determining whether or not the liquid level LS is fluctuating according to an embodiment of the present disclosure. FIG. 4 shows the distribution of the standard deviation SD of the reflection intensity RI versus the arrival time AT. Reference line L1 in FIG. 4 indicates the change in the standard deviation SD of the reflection intensity RI versus the arrival time AT when the liquid level LS of the liquefied gas is fluctuating. Reference line L2 in FIG. 4 indicates the change in the standard deviation SD of the reflection intensity RI versus the arrival time AT when the liquid level LS of the liquefied gas is not fluctuating. As shown in FIG. 4 , during a period T1 that takes into account the delay in the arrival time AT of the reflected wave, if the liquid level LS of the liquefied gas is fluctuating, the standard deviation SD of the reflection intensity RI is relatively large. However, if the liquid level LS of the liquefied gas is not fluctuating, the standard deviation SD of the reflection intensity RI is relatively small. In other words, the magnitude of the standard deviation SD of the reflection intensity RI during period T1 can be used to determine whether or not the liquid level LS of the liquefied gas is fluctuating.

[0029] In some embodiments, the statistical variation of the reflection intensity RI is the standard deviation SD of the reflection intensity RI. The fluctuation determination unit 42 is configured to determine that the liquid level LS of the liquefied gas is fluctuating when the standard deviation SD of the reflection intensity RI is greater than a threshold value TSD of the standard deviation SD (see FIG. 4).

[0030] (Second Ultrasonic Sensor) In some embodiments, the ultrasonic sensor 3 includes a second ultrasonic sensor 3B provided at a predetermined height position capable of detecting the liquid phase of the liquefied gas contained inside the storage structure 2, as shown in Fig. 2. The second ultrasonic sensor 3B preferably has a measurement range that includes locations where a solid phase is likely to occur. Examples of locations where a solid phase is likely to occur include bends 106A and 106B of the pipe 106 shown in Fig. 2, connections of the pipe 106 with the valve 107 and the pump, and the bottom of the first storage device 101 or the second storage device 103 (particularly the suction port of the pump 105).

[0031] The second ultrasonic sensor 3B is attached to the outer wall surface 21 of the storage structure 2, such as the first storage device 101, the second storage device 103, and the piping 106, and emits an ultrasonic beam along the thickness direction of the main body of the storage structure 2. The incident direction of the ultrasonic beam of the second ultrasonic sensor 3B may be either horizontal or vertical.

[0032] The second ultrasonic sensor 3B is configured to acquire the reflection intensity RI and arrival time AT of the reflected wave from the liquefied gas of the ultrasonic beam emitted by the second ultrasonic sensor 3B. The reflected wave acquired by the second ultrasonic sensor 3B is not reflected by the liquid surface LS of the liquefied gas, but is reflected by the liquid phase or solid phase of the liquefied gas.

[0033] The second ultrasonic sensor 3B repeatedly emits an ultrasonic beam toward the liquefied gas a plurality of times, thereby obtaining the reflection intensities RI and arrival times AT of the waves reflected by the liquefied gas a plurality of times. The reflection intensities RI and arrival times AT of the waves reflected by the liquefied gas a plurality of times, obtained by the second ultrasonic sensor 3B, are sent to the detection device 4. The memory unit 41 stores the reflection intensities RI and arrival times AT of the waves reflected by the liquefied gas a plurality of times, obtained by the second ultrasonic sensor 3B.

[0034] 1, the detection device 4 includes a phase state determination unit 43. The phase state determination unit 43 is configured to determine the phase state of the liquefied gas in consideration of at least one of the peak value PV of the reflection intensity RI or the arrival time AT corresponding to the peak value PV, which are obtained from the reflection intensity RI and the arrival time AT of the reflected wave acquired multiple times from the second ultrasonic sensor 3B (ultrasonic sensor 3).

[0035] FIG. 5 is an explanatory diagram illustrating information related to the reflected wave acquired by the second ultrasonic sensor 3B according to an embodiment of the present disclosure. FIG. 5 shows the distribution of the reflection intensity RI versus the arrival time AT of the reflected wave from the second ultrasonic sensor 3B. Reference line L3 in FIG. 5 indicates the change in the reflection intensity RI versus the arrival time AT of the reflected wave from the liquid-phase liquefied gas. Reference line L4 in FIG. 5 indicates the change in the reflection intensity RI versus the arrival time AT of the reflected wave from the two-phase liquefied gas (liquid and solid). Reference line L5 in FIG. 5 indicates the change in the reflection intensity RI versus the arrival time AT of the reflected wave from the solid-phase liquefied gas.

[0036] 5 , the peak value PV4 of the reflection intensity RI of reference line L4 (waves reflected from two phases) is lower than the peak value PV3 of the reflection intensity RI of reference line L3 (waves reflected from the liquid phase) and higher than the peak value PV5 of the reflection intensity RI of reference line L5 (waves reflected from the solid phase). That is, as the proportion of the solid phase of the liquefied gas in the measurement range of the second ultrasonic sensor 3B increases, the peak value PV of the reflection intensity RI of the reflected wave decreases. The phase state determination unit 43 obtains the peak value PV of the reflection intensity RI from the reflection intensity RI and arrival time AT of multiple reflected waves obtained from the second ultrasonic sensor 3B, and can obtain the phase state of the liquefied gas corresponding to the obtained peak value PV by utilizing the relationship between the peak value PV and the phase state.

[0037] 5 , the arrival time AT4 corresponding to the peak value PV4 of the reference line L4 (the wave reflected from two phases) is later than the arrival time AT3 corresponding to the peak value PV3 of the reference line L3 (the wave reflected from the liquid phase) and earlier than the arrival time AT5 corresponding to the peak value PV5 of the reference line L5 (the wave reflected from the solid phase). That is, as the proportion of the solid phase of the liquefied gas in the measurement range of the second ultrasonic sensor 3B increases, the arrival time AT corresponding to the peak value PV of the reflection intensity RI of the reflected wave becomes later. The phase state determination unit 43 obtains the arrival time AT corresponding to the peak value PV of the reflection intensity RI from the reflection intensity RI and arrival time AT of the reflected wave obtained multiple times by the second ultrasonic sensor 3B, and can obtain the phase state of the liquefied gas corresponding to the arrival time AT corresponding to the obtained peak value PV by utilizing the relationship between the arrival time AT and the phase state.

[0038] The peak value PV of the reflection intensity RI of the second ultrasonic sensor 3B (ultrasonic sensor 3) and the arrival time AT corresponding to this peak value PV change depending on the phase state of the liquefied gas, so the phase state of the liquefied gas can be determined from the peak value PV of the reflection intensity RI and the arrival time AT corresponding to this peak value PV.

[0039] In some embodiments, the phase state determination unit 43 is configured to determine that a phase change from liquid to solid has occurred in the liquefied gas when the peak value PV of the reflection intensity RI, obtained from the reflection intensity RI and the arrival time AT of multiple reflected waves acquired from the second ultrasonic sensor 3B (ultrasonic sensor 3), becomes smaller than a threshold value TPV of the peak value PV (see FIG. 5 ). As the proportion of the solid phase in the liquefied gas within the measurement range of the ultrasonic sensor 3 increases, the peak value PV becomes smaller. Therefore, when the peak value PV becomes smaller than the threshold value TPV of the peak value PV, it can be determined that a phase change from liquid to solid has occurred.

[0040] In some embodiments, the phase state determination unit 43 is configured to determine that a phase change from liquid to solid has occurred in the liquefied gas when the arrival time AT corresponding to the peak value PV of the reflection intensity RI, obtained from the reflection intensity RI and arrival time AT of multiple reflected waves acquired from the second ultrasonic sensor 3B (ultrasonic sensor 3), is delayed compared to the threshold value TAT of the arrival time AT. As the proportion of the solid phase in the liquefied gas within the measurement range of the ultrasonic sensor 3 increases, a delay occurs in the arrival time AT corresponding to the peak value PV. Therefore, when the arrival time AT corresponding to the peak value PV is delayed compared to the threshold value TAT of the arrival time AT, it can be determined that a phase change from liquid to solid has occurred.

[0041] In some embodiments, the phase state determination unit 43 is configured to obtain the ratio of the solid phase to the liquid phase of the liquefied gas from at least one of the peak value PV of the reflection intensity RI or the arrival time AT corresponding to the peak value PV, which are obtained from the reflection intensity RI and the arrival time AT of the reflected wave obtained multiple times from the second ultrasonic sensor 3B (ultrasonic sensor 3), based on association information that associates at least one of the peak value PV of the reflection intensity RI or the arrival time AT of the reflected wave corresponding to the peak value PV, which has been prepared in advance, with the ratio of the solid phase to the liquid phase of the liquefied gas.The peak value PV of the reflection intensity RI and the arrival time AT corresponding to the peak value PV correspond to the ratio of the solid phase to the liquid phase of the liquefied gas, so by utilizing this correspondence, the ratio of the solid phase to the liquid phase of the liquefied gas can be obtained from the peak value PV of the reflection intensity RI and the arrival time AT corresponding to the peak value PV.

[0042] The association information indicates a correspondence relationship between at least one of the peak value PV of the reflection intensity RI or the arrival time AT corresponding to the peak value PV and the solid / liquid phase ratio of the liquefied gas. When at least one of the peak value PV or the arrival time AT corresponding to the peak value PV is used as input information, the solid / liquid phase ratio of the liquefied gas corresponding to the input information can be obtained as output information. The association information includes a list, table, map, function, machine learning model, strength analysis model, etc., indicating the correspondence relationship between the input information and the output information. The association information may be created based on steady-state test data, or may be created based on past actual values, experimental values, numerical analysis results, etc. other than steady-state test data. The phase state determination unit 43 may refer to the association information stored in the memory unit 41.

[0043] 1, the liquefied gas phase change detection system 1 includes a first ultrasonic sensor 3A, a second ultrasonic sensor 3B, and a detection device 4 including a sway determination unit 42 and a phase state determination unit 43. However, the liquefied gas phase change detection system 1 may be configured to include the first ultrasonic sensor 3A and a detection device 4 including the sway determination unit 42 (but not the phase state determination unit 43) (without the second ultrasonic sensor 3B). Alternatively, the liquefied gas phase change detection system 1 may be configured to include the second ultrasonic sensor 3B and a detection device 4 including the phase state determination unit 43 (but not the sway determination unit 42) (without the first ultrasonic sensor 3A).

[0044] 6 is an explanatory diagram illustrating the mounting member 5 according to an embodiment of the present disclosure. In some embodiments, the liquefied gas phase change detection system 1 described above includes the mounting member 5, which is disposed between the outer wall surface 21 of the storage structure 2 and the ultrasonic sensor 3 (3A or 3B), and has heat dissipation fins 52. The mounting member 5 includes a main body 51 having one end surface abutting the outer wall surface 21 and the other end surface abutting the ultrasonic sensor 3, and a plurality of heat dissipation fins 52 extending from the outer peripheral surface of the main body 51 in a direction intersecting the extension direction of the main body 51 (the left-right direction in the figure).

[0045] The temperature of the outer wall surface 21 of the accommodation structure 2 on which the ultrasonic sensor 3 is attached may drop to a temperature below the triple point temperature of the liquefied gas (-56.6°C for liquefied carbon dioxide). The mounting member 5 having the heat dissipation fins 52 promotes heat input from the outside to the mounting member 5, thereby suppressing the cold energy transferred from the outer wall surface 21 of the accommodation structure 2 to the ultrasonic sensor 3 and protecting the ultrasonic sensor 3 from the cold energy.

[0046] (Starting point of phase change) Fig. 7 is an explanatory diagram for explaining the surface roughness of the inner wall surface 22 of the storage structure 2 according to an embodiment of the present disclosure. Fig. 8 is an explanatory diagram for explaining the rod-shaped member 6 according to an embodiment of the present disclosure. In some embodiments, as shown in Fig. 7 , a portion 22A included in the measurement range of the ultrasonic sensor 3 on the inner wall surface 22 of the above-described storage structure 2 has a smaller arithmetic mean roughness than another portion 22B on the inner wall surface 22.

[0047] For a phase change to start, a group of molecules of the liquefied gas, which is the target substance, must exceed a certain size (critical nucleus radius). If the phase change starts within the measurement range of the ultrasonic sensor 3, the phase change can be easily detected. By polishing or the like at a location 22A on the inner wall surface 22 that is within the measurement range of the ultrasonic sensor 3, and making the arithmetic mean roughness of the location 22A smaller than that of other locations 22B on the inner wall surface 22, the location 22A can be used as the phase change start point.

[0048] 8 , the liquefied gas phase change detection system 1 includes a rod-shaped member 6 that is disposed opposite, with a gap therebetween, the inner wall surface 22 of the storage structure 2 that is within the measurement range of the ultrasonic sensor 3, and that has a longitudinal direction that intersects with the direction of the ultrasonic beam that is incident along the thickness direction of the main body of the storage structure 2. The outer surface 61 of the rod-shaped member 6 has a smaller arithmetic mean roughness than the inner wall surface 22. By polishing the outer surface 61 of the rod-shaped member 6 or the like to make the arithmetic mean roughness of the outer surface 61 smaller than that of the inner wall surface 22, the outer surface 61 can be used as the starting point of a phase change.

[0049] (Pressure Acquisition Device) Fig. 9 is an explanatory diagram illustrating the pressure acquisition device 7 and the temperature acquisition device 8 according to an embodiment of the present disclosure. In some embodiments, the above-described liquefied gas phase change detection system 1 includes a pressure acquisition device (a pressure sensor in the illustrated example) 7 configured to acquire the pressure inside the storage structure 2, as shown in Fig. 9. The pressure inside the storage structure 2 acquired by the pressure acquisition device 7 is sent to the detection device 4.

[0050] The detection device 4 is configured to detect whether a phase change is occurring in the liquefied gas by further taking into consideration the pressure inside the storage structure 2 acquired by the pressure acquisition device 7. In one embodiment, the detection device 4 is configured to make a determination in the fluctuation determination unit 42 or the phase state determination unit 43 described above when a prerequisite is met that the pressure inside the storage structure 2 acquired by the pressure acquisition device 7 is equal to or less than a pressure threshold value that has a margin on the higher side of the triple point pressure of the liquefied gas. When the pressure inside the storage structure 2 acquired by the pressure acquisition device 7 is a pressure that does not cause a phase change in the liquefied gas, it can be determined early on that a phase change is not occurring in the liquefied gas.

[0051] (Temperature Acquisition Device) In some embodiments, the liquefied gas phase change detection system 1 described above includes a temperature acquisition device (a temperature sensor in the illustrated example) 8 configured to acquire the temperature inside the storage structure 2 or the temperature of the outer wall surface 21 of the storage structure 2, as shown in Fig. 9. The temperature acquisition device 8 may be a temperature sensor 8A configured to acquire the temperature inside the storage structure 2, or a temperature sensor 8B configured to acquire the temperature of the outer wall surface 21 of the storage structure 2. The liquefied gas phase change detection system 1 may include both the temperature sensor 8A and the temperature sensor 8B.

[0052] The detection device 4 is configured to detect whether a phase change has occurred in the liquefied gas by further considering the temperature acquired by the temperature acquisition device 8. In one embodiment, the detection device 4 is configured to make a determination in the fluctuation determination unit 42 or the phase state determination unit 43 described above when a prerequisite is satisfied that the temperature acquired by the temperature acquisition device 8 is equal to or lower than a temperature threshold value that has a margin on the higher side of the triple point temperature of the liquefied gas. When the temperature acquired by the temperature acquisition device 8 is a temperature that does not cause a phase change in the liquefied gas, it can be determined early that a phase change has not occurred in the liquefied gas.

[0053] (Pressurizing Device) Fig. 10 is an explanatory diagram illustrating a pressurizing device 70 according to an embodiment of the present disclosure. In some embodiments, the liquefied gas phase change detection system 1 described above includes a pressurizing device 70 configured to pressurize the interior of the storage structure 2, as shown in Fig. 10. The pressurizing device 70 includes a communication space forming member 71 that forms a communication space 72 that communicates with the internal space 23 of the storage structure 2, and a piston 73 that is disposed in the communication space 72 and pressurizes the communication space 72. The piston 73 can increase or decrease the volume of the space that communicates with the internal space 23 inside the communication space forming member 71 by driving an actuator 74 attached to the piston 73. The internal space 23 can be pressurized by reducing the volume of the space that communicates with the internal space 23 inside the communication space forming member 71.

[0054] The detection device 4 may include a control unit 44 that controls the driving of the pressurizing device 70. The control unit 44 may control the driving of the pressurizing device 70 in accordance with the determination results of the oscillation determination unit 42 and the phase state determination unit 43 described above, or the pressure inside the storage structure 2 acquired by the pressure acquisition device 7. Specifically, the control unit 44 may be configured to drive the pressurizing device 70 when it is determined that the liquid level LS is oscillating, when it is determined that a phase change from the liquid phase to the solid phase is occurring, or when the pressure acquired by the pressure acquisition device 7 is equal to or lower than the triple point pressure of the liquefied gas.

[0055] By applying pressure using the pressure device 70, the pressure inside the storage structure 2 can be increased to a pressure higher than the triple point pressure, thereby preventing the generation of a solid phase inside the storage structure 2 and liquefying any solid phase that has been generated inside the storage structure 2.

[0056] (Heating Device) Fig. 11 is an explanatory diagram illustrating a heating device 80 according to an embodiment of the present disclosure. In some embodiments, the above-described liquefied gas phase change detection system 1 includes a heating device 80 configured to heat the interior of the storage structure 2, as shown in Fig. 11. The heating device 80 includes a heating unit 81 disposed in the internal space 62 formed inside the rod-shaped member 6. Heat generated in the heating unit 81 is transferred to the liquefied gas via the rod-shaped member 6, thereby heating the liquefied gas.

[0057] The detection device 4 may include a control unit 45 that controls the driving of the heating device 80. The control unit 45 may control the driving of the heating device 80 in accordance with the determination results of the fluctuation determination unit 42 and the phase state determination unit 43 described above, or the temperature acquired by the temperature acquisition device 8. Specifically, the control unit 45 may be configured to drive the heating device 80 when it is determined that the liquid level LS is fluctuating, when it is determined that a phase change from the liquid phase to the solid phase is occurring, or when the temperature acquired by the temperature acquisition device 8 is equal to or lower than the triple point temperature of the liquefied gas.

[0058] By heating using the heating device 80, the inside of the storage structure 2 can be heated to a temperature above the triple point temperature, thereby suppressing the generation of a solid phase inside the storage structure 2 and liquefying any solid phase that has generated inside the storage structure 2.

[0059] A liquefied gas phase change detection method according to some embodiments includes a reflected wave acquisition step and a detection step. In the reflected wave acquisition step, an ultrasonic beam is irradiated from the outside of the containment structure 2 that contains the liquefied gas toward the liquefied gas contained inside the containment structure 2, and the reflection intensity RI and arrival time AT of the ultrasonic beam reflected from the liquefied gas are acquired. The reflected wave acquisition step is preferably performed by the ultrasonic sensor 3 described above.

[0060] In the detection step, whether or not a phase change has occurred in the liquefied gas is detected in consideration of the reflection intensities RI and arrival times AT of the multiple reflected waves obtained by repeating the reflected wave acquisition step multiple times. The detection step may be performed by a device other than the detection device 4 described above.

[0061] In the reflected wave acquisition step, the reflection intensity RI and arrival time AT of the reflected wave of the ultrasonic beam from the liquefied gas can be acquired from outside the containment structure 2. When a phase change occurs in the liquefied gas contained inside the containment structure 2, changes occur in the reflection intensity RI and arrival time AT of the reflected wave of the ultrasonic beam from the liquefied gas. Therefore, in the detection step, by monitoring the reflection intensity RI and arrival time AT of the reflected wave of the ultrasonic beam from the liquefied gas, it is possible to detect a phase change of the liquefied gas contained inside the containment structure 2.

[0062] In this specification, expressions expressing relative or absolute arrangements, such as "in a certain direction," "along a certain direction," "parallel," "orthogonal," "center," "concentric," or "coaxial," not only strictly express such arrangements, but also express a state in which there is a relative displacement with a tolerance or an angle or distance to the extent that the same function is obtained. For example, expressions expressing that things are in an equal state, such as "identical," "equal," and "homogeneous," not only express a state in which there is a strict equivalence, but also express a state in which there is a tolerance or a difference to the extent that the same function is obtained. Furthermore, in this specification, expressions expressing shapes such as a rectangular shape or a cylindrical shape not only express shapes such as a rectangular shape or a cylindrical shape in the strict geometric sense, but also express shapes including concave and convex portions, chamfered portions, etc., to the extent that the same effect is obtained. Furthermore, in this specification, the expressions "comprise," "include," or "have" a component are not exclusive expressions that exclude the presence of other components.

[0063] The present disclosure is not limited to the above-described embodiments, but also includes modifications to the above-described embodiments and appropriate combinations of these modifications.

[0064] The contents of the above-described embodiments can be understood, for example, as follows.

[0065] 1) A liquefied gas phase change detection system (1) according to at least one embodiment of the present disclosure is a liquefied gas phase change detection system (1) for detecting a phase change of a liquefied gas, comprising: a storage structure (2) for storing the liquefied gas therein; an ultrasonic sensor (3) configured to emit an ultrasonic beam from the outside of the storage structure (2) toward the liquefied gas stored inside the storage structure (2), the ultrasonic sensor (3) configured to acquire the reflection intensity and arrival time of a wave of the ultrasonic beam reflected from the liquefied gas; and a detection device (4) configured to detect whether a phase change has occurred in the liquefied gas, taking into account the reflection intensity and arrival time of the multiple reflected waves obtained by the ultrasonic sensor (3) repeatedly emitting the ultrasonic beam toward the liquefied gas multiple times.

[0066] According to the configuration 1) above, the ultrasonic sensor (3) can acquire the reflection intensity and arrival time of the ultrasonic beam reflected from the liquefied gas from outside the containment structure (2). When a phase change occurs in the liquefied gas contained inside the containment structure (2), the reflection intensity and arrival time of the ultrasonic beam reflected from the liquefied gas change. Therefore, by monitoring the reflection intensity and arrival time of the ultrasonic beam reflected from the liquefied gas using the detection device (4), it is possible to detect the phase change of the liquefied gas contained inside the containment structure (2).

[0067] 2) In some embodiments, in the liquefied gas phase change detection system (1) described in 1) above, the ultrasonic sensor (3) is provided at a predetermined height position where the liquid level of the liquefied gas can be detected, and the detection device (4) includes a fluctuation determination unit (42) configured to determine whether or not the liquid level of the liquefied gas is fluctuating, taking into account the statistical variation in the reflection intensity obtained by statistically processing the reflection intensity and the arrival time of the reflected wave obtained from the ultrasonic sensor (3) over multiple times.

[0068] According to the configuration 2) above, the statistical variation in reflection intensity obtained by statistically processing the reflection intensity and arrival time of the reflected wave has a relatively high S / N ratio, which is the ratio of signal to noise, so that it is possible to suitably determine whether or not the liquid surface of the liquefied gas is fluctuating.

[0069] 3) In some embodiments, in the liquefied gas phase change detection system (1) described in 2) above, the statistical variation of the reflection intensity is a standard deviation of the reflection intensity, and the fluctuation determination unit (42) is configured to determine that the liquid surface of the liquefied gas is fluctuating when the standard deviation of the reflection intensity becomes larger than a threshold value of the standard deviation.

[0070] According to the configuration 3), when the liquid level of the liquefied gas is fluctuating, the standard deviation of the reflection intensity becomes relatively large. Therefore, when the standard deviation of the reflection intensity becomes larger than the threshold value of the standard deviation, it can be determined that the liquid level of the liquefied gas is fluctuating.

[0071] 4) In some embodiments, in the liquefied gas phase change detection system (1) described in 1) above, the ultrasonic sensor (3) is provided at a predetermined height position where the liquid phase of the liquefied gas can be detected, and the detection device (4) includes a phase state determination unit (43) configured to determine the phase state of the liquefied gas by taking into account at least one of the peak value of the reflection intensity or the arrival time corresponding to the peak value, which are obtained from the reflection intensity and the arrival time of the reflected wave acquired multiple times from the ultrasonic sensor (3).

[0072] According to the configuration of 4) above, the peak value of the reflection intensity and the arrival time corresponding to the peak value change depending on the phase state of the liquefied gas, so the phase state of the liquefied gas can be determined from the peak value of the reflection intensity and the arrival time corresponding to the peak value.

[0073] 5) In some embodiments, in the liquefied gas phase change detection system (1) described in 4) above, the phase state determination unit (43) is configured to determine that a phase change from liquid to solid has occurred in the liquefied gas when the peak value (PV) of the reflection intensity obtained from the reflection intensities and arrival times of the reflected waves acquired multiple times from the ultrasonic sensor (3) becomes smaller than a threshold value (TPV) of the peak value (PV).

[0074] According to the configuration of 5) above, the peak value (PV) decreases as the proportion of the solid phase in the liquefied gas in the measurement range of the ultrasonic sensor (3) increases. Therefore, when the peak value (PV) becomes smaller than the peak value (PV) threshold value (TPV), it can be determined that a phase change from liquid to solid has occurred.

[0075] 6) In some embodiments, in the liquefied gas phase change detection system (1) described in 4) above, the phase state determination unit (43) is configured to determine that a phase change from liquid to solid has occurred in the liquefied gas when the arrival time (AT) corresponding to the peak value of the reflection intensity, obtained from the reflection intensity and the arrival time of the reflected wave acquired multiple times from the ultrasonic sensor (3), is later than a threshold arrival time (TAT).

[0076] According to the configuration of 6) above, when the proportion of the solid phase in the liquefied gas in the measurement range of the ultrasonic sensor 3 increases, a delay occurs in the arrival time (AT) corresponding to the peak value. Therefore, when the arrival time (AT) corresponding to the peak value becomes slower than the arrival time (AT) threshold value (TAT), it can be determined that a phase change from liquid to solid has occurred.

[0077] 7) In some embodiments, in the liquefied gas phase change detection system (1) described in 4) above, the phase state determination unit (43) is configured to obtain the ratio of solid to liquid phases of the liquefied gas from at least one of the peak value of the reflection intensity or the arrival time corresponding to the peak value, which is obtained from the reflection intensity and the arrival time of the reflected wave acquired multiple times from the ultrasonic sensor (3), based on association information that associates at least one of the peak value of the reflection intensity or the arrival time of the reflected wave corresponding to the peak value with the ratio of solid to liquid phases of the liquefied gas.

[0078] According to the configuration of 7) above, the peak value of the reflection intensity and the arrival time corresponding to the peak value correspond to the ratio of the solid phase to the liquid phase of the liquefied gas, and by utilizing this correspondence, the ratio of the solid phase to the liquid phase of the liquefied gas can be obtained from the peak value of the reflection intensity and the arrival time corresponding to the peak value.

[0079] 8) In some embodiments, the liquefied gas phase change detection system (1) described in any of 1) to 7) above includes a mounting member (5) disposed between the outer wall surface (21) of the storage structure (2) and the ultrasonic sensor (3), the mounting member (5) having heat dissipation fins (52).

[0080] According to the configuration of 8) above, the mounting member (5) having the heat dissipation fins (52) encourages heat input from the outside to the mounting member (5), thereby suppressing the cold energy transmitted from the outer wall surface (21) of the housing structure (2) to the ultrasonic sensor (3), and protecting the ultrasonic sensor (3) from the cold energy.

[0081] 9) In some embodiments, in the liquefied gas phase change detection system (1) described in any of 1) to 7) above, the arithmetic mean roughness of a portion of the inner wall surface (22) of the storage structure (2) that is included in the measurement range of the ultrasonic sensor (3) is smaller than that of other portions of the inner wall surface (22).

[0082] According to the configuration 9) above, the starting point of a phase change requires a collection of molecules of the liquefied gas, which is the target substance, to exceed a predetermined size (critical nucleus radius). If the starting point of a phase change occurs within the measurement range of the ultrasonic sensor (3), the phase change can be easily detected. By polishing or otherwise treating a portion of the inner wall surface (22) that is within the measurement range of the ultrasonic sensor (3) and making the arithmetic mean roughness of that portion smaller than that of other portions of the inner wall surface (22), the portion can be used as the starting point of a phase change.

[0083] 10) In some embodiments, the liquefied gas phase change detection system (1) described in any of 1) to 7) above includes a rod-shaped member (6) arranged to face the inner wall surface (22) of the storage structure (2) present within the measurement range of the ultrasonic sensor (3) with a gap therebetween, and having a longitudinal direction along a direction intersecting the ultrasonic beam, and the outer surface (61) of the rod-shaped member (6) has a smaller arithmetic mean roughness than the inner wall surface (22).

[0084] According to the above configuration 10), the outer surface (61) of the rod-shaped member (6) is polished or the like, and the portion of the inner wall surface (22) of the outer surface (61) that is included in the outer surface (61) is polished or the like, and the arithmetic mean roughness of the portion is made smaller than that of the inner wall surface (22), whereby the outer surface (61) can be used as the starting point for the phase change.

[0085] 11) In some embodiments, the liquefied gas phase change detection system (1) described in any of 1) to 10) above includes a pressure acquisition device (7) configured to acquire the pressure inside the storage structure (2), and the detection device (4) is configured to detect whether a phase change has occurred in the liquefied gas, further taking into account the pressure inside the storage structure (2) acquired by the pressure acquisition device (7).

[0086] According to the configuration of 11) above, if the pressure inside the storage structure (2) acquired by the pressure acquisition device (7) is a pressure that does not cause a phase change in the liquefied gas, it can be determined early that a phase change has not occurred in the liquefied gas.

[0087] 12) In some embodiments, the liquefied gas phase change detection system (1) described in any of 1) to 11) above includes a temperature acquisition device (8) configured to acquire the temperature inside the storage structure (2) or the temperature of the outer wall surface (21) of the storage structure (2), and the detection device (4) is configured to detect whether a phase change has occurred in the liquefied gas, further taking into account the temperature acquired by the temperature acquisition device (8).

[0088] According to the configuration of 12) above, when the temperature acquired by the temperature acquisition device (8) is a temperature that does not cause a phase change in the liquefied gas, it can be determined early that a phase change has not occurred in the liquefied gas.

[0089] 13) In some embodiments, the liquefied gas phase change detection system (1) described in any of 1) to 12) above comprises a pressurizing device (70) configured to pressurize the interior of the storage structure (2), the pressurizing device (70) including: a communication space forming member (71) that forms a communication space (72) that communicates with the internal space (23) of the storage structure (2); and a piston (73) that is arranged in the communication space (72) and pressurizes the communication space (72).

[0090] According to the configuration of 13) above, the pressure inside the storage structure (2) can be increased to a pressure equal to or higher than the triple point pressure by pressurizing the storage structure (70), thereby suppressing the generation of a solid phase inside the storage structure (2) and liquefying the solid phase generated inside the storage structure (2).

[0091] 14) In some embodiments, the liquefied gas phase change detection system (1) described in 10) above includes a heating device (80) configured to heat the interior of the storage structure (2), the heating device (80) including a heating portion (81) arranged inside the rod-shaped member (6).

[0092] According to the configuration of 14) above, the inside of the storage structure (2) can be heated to a temperature equal to or higher than the triple point temperature by heating with the heating device (80), thereby making it possible to suppress the generation of a solid phase inside the storage structure (2) and to liquefy the solid phase generated inside the storage structure (2).

[0093] 15) A liquefied gas phase change detection method according to at least one embodiment of the present disclosure is a liquefied gas phase change detection method for detecting a phase change of a liquefied gas, comprising: a reflected wave acquisition step of irradiating an ultrasonic beam from the outside of a storage structure (2) that stores the liquefied gas toward the liquefied gas stored inside the storage structure (2) and acquiring the reflection intensity and arrival time of the reflected wave of the ultrasonic beam from the liquefied gas; and a detection step of detecting whether a phase change has occurred in the liquefied gas, taking into account the reflection intensity and arrival time of the reflected wave obtained multiple times by repeating the reflected wave acquisition step multiple times.

[0094] According to the method of 15) above, in the reflected wave acquisition step, the reflection intensity and arrival time of the reflected wave of the ultrasonic beam from the liquefied gas can be acquired from outside the containment structure (2). When a phase change occurs in the liquefied gas contained inside the containment structure (2), changes occur in the reflection intensity and arrival time of the reflected wave of the ultrasonic beam from the liquefied gas. Therefore, in the detection step, by monitoring the reflection intensity and arrival time of the reflected wave of the ultrasonic beam from the liquefied gas, it is possible to detect the phase change of the liquefied gas contained inside the containment structure (2).

[0095] REFERENCE SIGNS LIST 1 Liquefied gas phase change detection system 2 Storage structure 3 Ultrasonic sensor 3A First ultrasonic sensor 3B Second ultrasonic sensor 4 Detection device 5 Mounting member 6 Rod-shaped member 7 Pressure acquisition device 8 Temperature acquisition device 21 Outer wall surface 22 Inner wall surface 23 Internal space 41 Memory unit 42 Oscillation determination unit 43 Phase state determination unit 44, 45 Control unit 52 Heat dissipation fin 70 Pressurizing device 72 Communication space 73 Piston 74 Actuator 80 Heating device 101 First storage device 103 Second storage device 105 Pump 106 Piping 107 Valve

Claims

1. A liquefied gas phase change detection system for detecting a phase change of a liquefied gas, comprising: a storage structure that stores the liquefied gas inside; an ultrasonic sensor configured to emit an ultrasonic beam from outside the storage structure toward the liquefied gas stored inside the storage structure, the ultrasonic sensor configured to obtain the reflection intensity and arrival time of the reflected wave of the ultrasonic beam from the liquefied gas; and a detection device configured to detect whether a phase change has occurred in the liquefied gas, taking into account the reflection intensity and arrival time of the reflected wave obtained by the ultrasonic sensor repeatedly emitting the ultrasonic beam toward the liquefied gas a plurality of times.

2. The liquefied gas phase change detection system of claim 1, wherein the ultrasonic sensor is provided at a predetermined height position where the liquid level of the liquefied gas can be detected, and the detection device includes a fluctuation determination unit configured to determine whether or not the liquid level of the liquefied gas is fluctuating, taking into account the statistical variation in the reflection intensity obtained by statistically processing the reflection intensity and arrival time of the reflected wave obtained from the ultrasonic sensor over multiple times.

3. A liquefied gas phase change detection system as described in claim 2, wherein the statistical variation of the reflection intensity is the standard deviation of the reflection intensity, and the fluctuation determination unit is configured to determine that the liquid surface of the liquefied gas is fluctuating when the standard deviation of the reflection intensity becomes larger than a threshold value of the standard deviation.

4. The liquefied gas phase change detection system of claim 1, wherein the ultrasonic sensor is provided at a predetermined height position where the liquid phase of the liquefied gas can be detected, and the detection device includes a phase state determination unit configured to determine the phase state of the liquefied gas by taking into account at least one of the peak value of the reflection intensity or the arrival time corresponding to the peak value, obtained from the reflection intensity and arrival time of the reflected wave acquired multiple times from the ultrasonic sensor.

5. A liquefied gas phase change detection system as described in claim 4, wherein the phase state determination unit is configured to determine that a phase change from liquid to solid has occurred in the liquefied gas when the peak value of the reflection intensity obtained from the reflection intensity and arrival time of the reflected wave obtained multiple times from the ultrasonic sensor becomes smaller than a peak value threshold value.

6. A liquefied gas phase change detection system as described in claim 4, wherein the phase state determination unit is configured to determine that a phase change from liquid to solid has occurred in the liquefied gas when the arrival time corresponding to the peak value of the reflection intensity, obtained from the reflection intensity and the arrival time of the reflected wave acquired multiple times from the ultrasonic sensor, is later than a threshold arrival time.

7. The liquefied gas phase change detection system of claim 4, wherein the phase state determination unit is configured to obtain the ratio of solid to liquid phases of the liquefied gas from at least one of the peak value of the reflection intensity or the arrival time corresponding to the peak value, which is obtained from the reflection intensity and the arrival time of the reflected wave acquired multiple times from the ultrasonic sensor, based on association information that associates at least one of the peak value of the reflection intensity or the arrival time of the reflected wave corresponding to the peak value with the ratio of solid to liquid phases of the liquefied gas.

8. A liquefied gas phase change detection system as claimed in any one of claims 1 to 7, comprising a mounting member disposed between the outer wall surface of the storage structure and the ultrasonic sensor, the mounting member having heat dissipation fins.

9. A liquefied gas phase change detection system as claimed in any one of claims 1 to 7, wherein the arithmetic mean roughness of the inner wall surface of the storage structure at a location included in the measurement range of the ultrasonic sensor is smaller than that of other locations on the inner wall surface.

10. A liquefied gas phase change detection system as described in any one of claims 1 to 7, comprising a rod-shaped member arranged opposite to, with a gap between, the inner wall surface of the containing structure within the measurement range of the ultrasonic sensor, and having a longitudinal direction along a direction intersecting the ultrasonic beam, wherein the outer surface of the rod-shaped member has a smaller arithmetic mean roughness than the inner wall surface.

11. A liquefied gas phase change detection system as claimed in any one of claims 1 to 7, comprising a pressure acquisition device configured to acquire the pressure inside the storage structure, and the detection device configured to detect whether a phase change has occurred in the liquefied gas, further taking into consideration the pressure inside the storage structure acquired by the pressure acquisition device.

12. A liquefied gas phase change detection system as claimed in any one of claims 1 to 7, comprising a temperature acquisition device configured to acquire the temperature inside the storage structure or the temperature of the outer wall surface of the storage structure, and the detection device configured to detect whether a phase change has occurred in the liquefied gas, further taking into consideration the temperature acquired by the temperature acquisition device.

13. A liquefied gas phase change detection system as claimed in any one of claims 1 to 7, comprising a pressurizing device configured to pressurize the interior of the storage structure, the pressurizing device including: a communication space forming member that forms a communication space that communicates with the internal space of the storage structure; and a piston that is disposed in the communication space and pressurizes the communication space.

14. The liquefied gas phase change detection system of claim 10, further comprising a heating device configured to heat the interior of the containment structure, the heating device including a heating portion disposed within the rod-shaped member.

15. A liquefied gas phase change detection method for detecting a phase change of a liquefied gas, comprising: a reflected wave acquisition step of irradiating an ultrasonic beam from the outside of a storage structure that stores the liquefied gas toward the liquefied gas stored inside the storage structure, and acquiring the reflection intensity and arrival time of the ultrasonic beam reflected from the liquefied gas; and a detection step of detecting whether a phase change has occurred in the liquefied gas, taking into account the reflection intensity and arrival time of the reflected wave obtained multiple times by repeating the reflected wave acquisition step multiple times.

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