Membrane crack detection system, membrane crack detection method, and hydrogen purification apparatus

Abstract

This technology enables earlier and more reliable online detection of cracks in hydrogen-permeable metal membranes used during the operation of hydrogen purification equipment, compared to conventional technologies. [Solution] During operation of a hydrogen purification apparatus having a hydrogen purification module (10) equipped with a hydrogen permeable metal membrane (11), helium gas is mixed with the raw material gas as a detection gas using a gas mixing means (30). A detection gas detection means (40) provided on the permeate side of the hydrogen purification module (10) monitors the helium gas concentration in the gas flowing on the permeate side. If a fine crack occurs in the hydrogen permeable metal membrane (11), the helium gas, which has a small molecular size, may pass through the crack and reach the permeate side before other gas components and differential pressure changes. Therefore, by detecting an increase in helium concentration with the detection gas detection means (40), the membrane crack is detected early.

Description

Technical Field

[0001] The present invention relates to a membrane crack detection system, a membrane crack detection method, and a hydrogen purification apparatus for a hydrogen permeable metal membrane in a hydrogen purification apparatus. More specifically, the present invention relates to a hydrogen purification apparatus that selectively separates and purifies hydrogen from a raw material gas using a hydrogen permeable metal membrane, and to a system, a method, and an apparatus for detecting cracks (including defects such as cracks and pinholes) in the hydrogen permeable metal membrane.

Background Art

[0002] In recent years, the demand for high-purity hydrogen has been increasing in various industrial fields such as fuel cell vehicles (FCVs) and processes for manufacturing state-of-the-art semiconductors.

[0003] As one method for producing such high-purity hydrogen, a technique using a hydrogen permeable metal membrane has attracted attention, but it has several problems including hydrogen embrittlement.

[0004] For example, metal fatigue due to the difference in pressure (differential pressure) applied on both sides of the membrane, hydrogen expansion caused by the membrane dissolving hydrogen, thermal expansion due to operation at high temperatures, and further, the membrane may become fragile by repeatedly starting and stopping the apparatus.

[0005] Furthermore, impurities contained in the raw material gas (especially hydrogen sulfide, carbon monoxide, etc.) may affect the membrane, resulting in a decrease in the hydrogen permeation performance of the membrane or deterioration of the membrane itself.

[0006] When one or a combination of these causes occur, defects such as "cracks" and small holes called "pinholes" are likely to form in the membrane.

[0007] If such defects form in the membrane, there is a problem that gases other than hydrogen pass through the membrane, resulting in a decrease in the purity of the purified hydrogen.

[0008] In addition, if the raw material gas leaks to the purified hydrogen side, purging of the ultra-high purity hydrogen line becomes necessary.

[0009] Furthermore, if the source gas leaks into the purified hydrogen side, adverse effects due to a decrease in purity are possible. For example, in the semiconductor manufacturing process, the semiconductors being manufactured at that time become defective, leading to a decrease in yield. Furthermore, when used in medical applications, there are concerns about the potential effects of impurities on the human body.

[0010] Therefore, in order to keep the hydrogen purification system running safely and stably, it is extremely important to constantly check that the hydrogen permeable metal membrane is in good condition and to find any defects as quickly as possible.

[0011] Several techniques have been proposed and investigated to date to detect cracks and abnormalities in the film.

[0012] For example, there is an "AE monitoring method" that uses sensors to detect very small sounds (elastic waves, acoustic emissions: AE) generated when a membrane breaks.

[0013] This AE method has the advantage of potentially capturing the exact moment a crack occurs, and it also has high sensitivity, allowing for real-time detection.

[0014] However, it is susceptible to ambient noise (background noise) such as vibrations while the device is running and the sound of gas flowing, which could lead to it mistakenly detecting a crack when there isn't one, or conversely, missing a crack altogether.

[0015] Another challenge is that analyzing AE signals requires specialized knowledge.

[0016] Another method known as the "differential pressure monitoring method" involves constantly monitoring the pressure difference (ΔP) between the inlet (supply side) and outlet (permeate side) of the membrane, and detecting gas leakage due to membrane damage if this pressure difference changes abnormally.

[0017] This method is relatively simple in mechanism and keeps costs low.

[0018] However, while it is effective when the membrane is significantly damaged, it is difficult to detect slight leaks from very small defects that have just begun to crack, and there are limitations to its sensitivity and detection speed.

[0019] Another method is "permeate gas composition analysis," which directly examines the components of the gas that has passed through the membrane (permeate gas) using analytical instruments (such as mass spectrometers (MS) or gas chromatographs (GC)).

[0020] This method allows for highly sensitive direct detection of membrane performance degradation (decreased selectivity) by examining whether impurities other than hydrogen have increased.

[0021] However, systems that perform real-time analysis while the equipment is running often require expensive and complex equipment.

[0022] In particular, using a gas chromatograph (GC) has the disadvantage of taking a long time to obtain analytical results.

[0023] Other research being conducted includes methods for monitoring changes in the electrical resistance of membranes, methods for analyzing vibrations, and sensors using optical fibers (such as those that detect strain or leaked hydrogen gas itself).

[0024] For example, Patent Document 1 discloses a sensor technology that uses light to detect hydrogen gas itself.

[0025] This is a hydrogen gas leak detection technology that utilizes the principle of hydrogen gas being absorbed into the sensor material. Therefore, it does not detect the occurrence of physical "cracks" in the hydrogen permeable metal film and capture the phenomenon of gases other than hydrogen leaking from there. [Prior art documents] [Patent Documents]

[0026]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0027] The above differential pressure monitoring method and permeation gas composition analysis method utilize an "indirect" phenomenon of gas leakage (leak) that occurs as a "result" of membrane rupture.

[0028] Therefore, there is inevitably a time delay until a detectable pressure change or an increase in impurity concentration occurs after a minute rupture occurs.

[0029] In addition, a general helium leak test performed during device manufacturing or regular inspections is an inspection (offline inspection) that stops the operation of the device and is not suitable for real-time monitoring (online monitoring) of the operating state.

[0030] Thus, the conventional membrane rupture detection techniques each have their own advantages and disadvantages.

[0031] Therefore, there has been a strong demand for a technique that can detect particularly the very initial stage when a rupture begins to occur in the membrane, is less affected by noise during device operation, has a relatively simple configuration, minimizes time delay, and can detect with high reliability.

[0032] In particular, it is desired to have an online detection system that can detect even in situations where detection is difficult with an AE sensor (such as a lot of noise, slow progress of rupture, etc.), functions as a backup when the AE sensor fails, and can detect membrane rupture before the change in differential pressure and the amount of leakage of the main impurities in the raw material gas become significant, and is more sensitive and reliable.

[0033] This invention has been made in view of the problems of the prior art described above, and aims to provide a novel film crack detection system and film crack detection method that can detect cracks in a hydrogen permeable metal film during the operation of a hydrogen purification apparatus, particularly in their initial stages, earlier and with greater reliability than the prior art. [Means for solving the problem]

[0034] The means for solving the problems of the present invention are as follows.

[0035] Firstly, The membrane crack detection system according to the present invention relates to a hydrogen purification apparatus using a hydrogen permeable metal membrane, A hydrogen purification module having a supply side to which raw material gas is supplied, a permeation side through which purified hydrogen permeates, and a hydrogen permeable metal membrane, A gas mixing means that contains a detection gas (0.01% to 10% by volume) in the aforementioned raw material gas, The hydrogen purification module is provided on the permeate side and is characterized by comprising a detection gas detection means for detecting a detection gas in the gas flowing through the permeate side, Film crack detection system.

[0036] Here, the gas mixing method can be any method that involves adding the detection gas to the raw gas, and is not limited to on-site mixing; it also includes cases where a gas cylinder containing a pre-mixed detection gas is used.

[0037] Furthermore, helium (He), argon (Ar), neon (Ne), and xenon (Xe) can be used as detection gases (tracer gases), but it is particularly preferable to use gases with a molecular diameter equal to or smaller than that of hydrogen molecules, such as helium.

[0038] Secondly, The hydrogen purification module is further equipped with an acoustic emission sensor that detects elastic waves (specifically 200 to 400 kHz, more specifically 200 to 250 kHz during metal fracture) generated when cracks occur in the hydrogen permeable metal film. The present invention is characterized by determining whether or not there is a crack in the hydrogen permeable metal film based on the detection result from the detection gas detection means and the detection result from the acoustic emission sensor. The film crack detection system described in the first above.

[0039] Thirdly, The gas mixing means is characterized by mixing the raw material gas so that the detection gas concentration in the raw material gas is in the range of 0.01% to 10% by volume. The film crack detection system according to the first or second above.

[0040] Fourth, A method for detecting membrane cracking during operation of a hydrogen purification apparatus that purifies hydrogen from a raw material gas using a hydrogen purification module equipped with a hydrogen permeable metal membrane, A detection gas mixing step in which a detection gas is added to the aforementioned raw material gas, A supply step of supplying the raw material gas mixed with the detection gas to the supply side of the hydrogen purification module, During the operation of the hydrogen purification apparatus, a concentration monitoring step is performed to monitor the concentration of a detection gas in the gas that has permeated from the permeate side of the hydrogen purification module, The method is characterized by including a determination step of determining whether or not there is a crack in the hydrogen permeable metal film based on the monitoring detection gas concentration. A method for detecting film cracks.

[0041] Fifth, The process further includes an elastic wave monitoring step in which elastic waves generated when cracks occur in the hydrogen permeable metal film are monitored by an acoustic emission sensor, The determination step is characterized by determining whether or not there is a crack in the hydrogen permeable metal film based on the monitoring concentration of the detection gas and the monitoring result from the acoustic emission sensor. The film crack detection method described in Section 4 above.

[0042] Sixth, A film crack detection system as described in the first or second above, characterized by comprising the above, Hydrogen purification device.

[0043] In the present invention, the gas mixing means is preferably a static mixer or a dynamic mixer capable of uniformly mixing the raw material gas and the detection gas before they reach the membrane surface.

[0044] The concentration of the detection gas mixed with the raw material gas can be set, for example, in the range of 0.01 to 10 volume percent.

[0045] This increases the probability that the detection gas will effectively reach the crack location and leak to the permeable side, regardless of where a crack occurs on the membrane surface.

[0046] The aforementioned detection means is preferably a sensor (for example, a thermal conduction type or a mass spectrometry type) capable of selectively and sensitively detecting trace amounts (e.g., on the order of ppm, specifically 0.01 volume% or more) of the detection gas that may leak out in a high-concentration hydrogen gas atmosphere, which is the main component of the permeating side.

[0047] The present invention is not limited to a specific sensor structure, but includes any means for detecting a detection gas in a permeate gas online.

[0048] Furthermore, the system of the present invention may further include an acoustic emission (AE) sensor that detects elastic waves generated when a film crack occurs, and a control unit (determination means) that combines the detection result from the detection gas detection means and the detection result from the AE sensor to determine whether a film crack has occurred.

[0049] The control unit can also be configured to execute a hierarchical decision logic, for example, by determining that a serious crack has occurred and emergency stopping the device if the output of the AE sensor exceeds a first threshold, or by determining that it is in the initial stage of a fine crack and issuing a warning or taking preventive measures such as depressurization measures if the output of the detection gas detection means exceeds a second threshold, even if the output of the AE sensor is below the first threshold.

[0050] This allows for the integration of information from multiple detection methods that capture different physical phenomena (sensor fusion), complementing anomalies that might be missed by a single method, and enabling more reliable film crack detection and appropriate responses based on the situation.

[0051] The present invention is widely applicable to hydrogen purification apparatuses that use self-supporting membranes made of various types of hydrogen-permeable metal membranes, such as vanadium (V), niobium (Nb), tantalum (Ta), vanadium alloys, palladium (Pd), palladium alloys (e.g., Pd-Ag, Pd-Cu, Pd-Au, etc.), or supporting membranes (composite membranes) formed by forming these metal thin films on a porous support (ceramics, metal, etc.).

[0052] The inventors focused on the principle that when microscopic cracks (cracks or pinholes) occur in a hydrogen-permeable metal film, the gas with the smallest molecular (atomic) size is more likely to pass through these tiny gaps than other larger gas molecules.

[0053] Helium (He), as a detection gas, is an inert gas and has a smaller effective size than other major components in the source gas containing hydrogen molecules (H2) (e.g., CO, CO2, N2, CH4, etc.).

[0054] Therefore, in this invention, during the normal operation of the hydrogen purification apparatus, a small amount of helium gas is intentionally mixed into the raw material gas as a detection gas, and a membrane crack is determined to have occurred when helium gas is detected on the membrane permeation side.

[0055] This configuration has technical characteristics that clearly differentiate it from conventional technology in the following respects.

[0056] Firstly, it involves "proactive use of tracer gases."

[0057] While conventional differential pressure monitoring and permeate gas composition analysis (when targeting existing impurity components in the source gas) detect pressure changes and unintended component leaks that occur "passively" as a result of membrane cracking, the present invention is characterized by "actively" adding the smallest amount of inert gas (e.g., helium), which is considered optimal for early detection of membrane cracking, as a tracer and monitoring its leakage.

[0058] Secondly, there is the "possibility of early detection."

[0059] For example, helium is a monatomic molecule and is extremely small in size. Therefore, if a microscopic crack occurs in the membrane, it is more likely that helium will pass through that crack and reach the permeate side before other larger molecular-sized source gas components leak to the permeate side in significant amounts.

[0060] Therefore, by detecting the presence or absence of helium gas on the transmission side with high sensitivity, it is expected that the occurrence of membrane cracking can be detected at a very early stage.

[0061] This has the advantage of enabling a faster response compared to conventional indirect detection methods.

[0062] Thirdly, there is the "complementarity of detection principles."

[0063] This invention is based on a different principle (transmission of minute-sized gas components) than the AE method, which captures physical phenomena (elastic waves) at the time of crack initiation. It has the potential to detect film cracks even in noisy environments where the AE method is not effective, in cases of slow crack propagation that does not emit an AE signal, or when the AE sensor malfunctions. By combining it with the AE method, the weaknesses of each can be complemented, improving the reliability of the entire detection system.

[0064] Fourthly, it involves "online surveillance."

[0065] While typical gas leak detection tests are offline inspections, this invention enables real-time monitoring of the membrane state during the operation of a hydrogen purification system. [Effects of the Invention]

[0066] The present invention can achieve the following effects.

[0067] According to the present invention, when minute cracks occur in a hydrogen-permeable metal film, the principle that helium gas, for example, which is intentionally mixed into the raw material gas as a detection gas, can pass through the cracks earlier than other gas components due to the small size of its monatomic molecules is utilized, making it possible to detect the occurrence of film cracks very early and with high sensitivity.

[0068] This minimizes the degradation of product hydrogen purity, prevents impacts on downstream processes, and allows for countermeasures such as alarm activation and equipment shutdown before membrane damage escalates, significantly contributing to the safe operation and improved reliability of the hydrogen purification plant.

[0069] Furthermore, because it is based on a detection principle different from conventional AE methods and differential pressure monitoring methods, combining it with these methods can compensate for each other's shortcomings and further enhance the reliability of the entire detection system. [Brief explanation of the drawing]

[0070] [Figure 1] This is a schematic diagram of a membrane crack detection system for a hydrogen purification apparatus according to one embodiment of the present invention. [Modes for carrying out the invention]

[0071] Hereinafter, embodiments for carrying out the present invention will be specifically described with reference to the drawings. The description herein represents only one embodiment of the present invention, and therefore the present invention is not limited to this embodiment.

[0072] As shown in Figure 1, the membrane crack detection system 1 of the hydrogen purification apparatus according to this embodiment mainly comprises a hydrogen purification module 10, a helium supply means 20 as a detection gas, a mixer 30 as a gas mixing means, and a helium detection sensor 40 as a detection gas detection means, and further comprises an AE sensor 50 and a determination means (not shown) as a control unit.

[0073] The hydrogen purification module 10, shown schematically in the drawing, is equipped with a hydrogen permeable metal membrane 11 inside.

[0074] The hydrogen purification module 10 is connected to a supply-side pipe 12 (primary side) to which raw material gas G (a gas mixed with other gas components containing hydrogen) is supplied, a permeate-side pipe 13 (secondary side) through which purified hydrogen that has permeated the hydrogen permeable metal membrane 11 is discharged, and a bleed pipe 14 through which gas that has not permeated (bleed gas) is discharged.

[0075] The helium supply means 20 is for storing helium as a detection gas and supplying it at a controlled flow rate.

[0076] The mixer 30 is located upstream of the hydrogen purification module 10 and mixes the raw material gas G and the helium gas supplied from the helium supply means 20 so that they are uniformly distributed across the entire membrane surface.

[0077] The concentration of helium gas mixed here is set to a range that allows the helium detection sensor 40 on the permeation side to reliably detect film cracking, does not substantially adversely affect the permeation performance of the hydrogen permeable metal film 11, and is economically acceptable (for example, about 0.05 to 5 volume%).

[0078] The helium detection sensor 40 is installed on the permeation side piping 13 and continuously or intermittently monitors the presence and concentration of helium gas in the purified hydrogen gas that has permeated through the system during the operation of the hydrogen purification apparatus.

[0079] The helium detection sensor 40 may be, for example, a thermal conduction sensor or a mass spectrometry sensor capable of detecting helium at a concentration of 0.001 volume percent or more in a hydrogen atmosphere.

[0080] The AE sensor 50 is mounted in a location that can efficiently detect elastic waves generated when cracks occur in the membrane, such as on the casing of the hydrogen purification module 10 or on structural members near the membrane.

[0081] The detection signals from the helium detection sensor 40 and the AE sensor 50 are input to the control unit (not shown in the figure).

[0082] The control unit determines, based on the signal from the helium detection sensor 40, that there is a high probability that a crack has occurred in the hydrogen permeable metal film 11 when the helium gas concentration exceeds a preset threshold (e.g., T2). However, it can also be treated as if a crack occurred at the moment the helium gas is detected.

[0083] Furthermore, if the signal from the AE sensor 50 (for example, energy or event frequency in a specific frequency band) exceeds a threshold (for example, T1), it is determined that there is a possibility of film cracking occurring, but it can also be treated as if cracking occurred at the time the signal was received.

[0084] The control unit comprehensively evaluates these judgment results (He detection result, AE detection result) individually or in combination (for example, immediately stopping if both exceed the threshold or if the AE signal exceeds T1, or issuing a warning or taking depressurization measures if only the He signal exceeds T2), and finally determines whether a film crack has occurred (determination step).

[0085] If a membrane crack is detected, the control unit will issue an alarm and automatically take safety measures such as shutting off the supply gas to the hydrogen purification unit, isolating the permeate side line, or changing the operating mode (for example, bypassing the primary side raw material gas and purging the secondary side).

[0086] Next, the operation of the film crack detection method of this embodiment will be described.

[0087] During the operation of the hydrogen purification apparatus, first, a predetermined amount of helium gas is supplied from the helium supply means 20 to the mixer 30 and mixed with the raw material gas G passing through the supply side piping 12 (mixing step).

[0088] The raw material gas G, which is mixed with helium gas, is supplied to the supply side of the hydrogen purification module 10 (supply process).

[0089] Within the hydrogen purification module 10, hydrogen from the raw material gas is selectively permeated by the hydrogen permeable metal membrane 11 and discharged as purified hydrogen into the permeate side piping 13.

[0090] The helium detection sensor 40 continuously monitors the helium gas concentration in the purified hydrogen gas flowing through the permeation pipe 13 (monitoring process).

[0091] At the same time, the AE sensor 50 also monitors the elastic waves from the membrane.

[0092] It is desirable for the control unit to acquire and analyze the signals from the helium detection sensor 40 and the AE sensor 50 in a synchronized manner.

[0093] During normal operation (when the membrane is in good condition), helium gas does not permeate the hydrogen-permeable metal membrane 11 at all, so the helium detection sensor 40 does not detect helium gas.

[0094] Furthermore, the AE sensor 50 also does not detect any significant signal.

[0095] However, if microscopic cracks occur in the hydrogen permeable metal film 11, the smaller helium gas will pass through the cracks before other gas components and leak out to the permeable side.

[0096] The helium detection sensor 40 detects the leaked helium gas, and if its concentration exceeds a predetermined threshold, the control unit recognizes the possibility of membrane rupture.

[0097] Furthermore, if an AE signal is generated due to the occurrence of a crack, the AE sensor 50 detects it and sends a signal to the control unit.

[0098] The control unit ultimately determines, based on this information (or either of these), that a film crack has occurred (determination step).

[0099] Based on the assessment, necessary alarms will be issued and safety measures will be taken.

[0100] In this way, by actively utilizing a detection gas and monitoring its leakage, the limitations of conventional membrane crack detection methods can be overcome, enabling safer and more reliable operation of the hydrogen purification plant.

[0101] While it is theoretically possible to recover the detection gas in the bleed gas discharged from the bleed pipe 14, pressurize it, and then return it to the raw material gas line, this would complicate the system and increase costs, and therefore is not an essential component of the present invention. [Explanation of symbols]

[0102] 1. Film crack detection system 10 Hydrogen purification modules 11. Hydrogen-permeable metal film 12. Supply side piping 13 Permeate side piping 14. Bleed piping 20. Helium supply means (detection gas supply means) 30. Mixer (gas mixing means) 40. Helium detection sensor (gas detection means for detection) 50 AE Sensor (Acoustic Emission Sensor) G Raw material gas Helium gas

Claims

1. A hydrogen purification module having a supply side to which raw material gas is supplied, a permeation side through which purified hydrogen permeates, and a hydrogen permeable metal membrane, A gas mixing means for introducing a detection gas into the aforementioned raw material gas, The hydrogen purification module is provided on the permeate side and is characterized by comprising a detection gas detection means for detecting a detection gas in the gas flowing through the permeate side, Film crack detection system.

2. The hydrogen purification module is further equipped with an acoustic emission sensor that detects elastic waves generated when cracks occur in the hydrogen permeable metal film, The present invention is characterized by determining whether or not there is a crack in the hydrogen permeable metal film based on the detection result from the detection gas detection means and the detection result from the acoustic emission sensor. The film crack detection system according to claim 1.

3. The gas mixing means is characterized by mixing the raw material gas so that the detection gas concentration in the raw material gas is in the range of 0.01% by volume to 10% by volume. A film crack detection system according to claim 1 or 2.

4. A method for detecting membrane cracking during operation of a hydrogen purification apparatus that purifies hydrogen from a raw material gas using a hydrogen purification module equipped with a hydrogen permeable metal membrane, A detection gas mixing step in which a detection gas is added to the aforementioned raw material gas, A supply step of supplying the raw material gas mixed with the detection gas to the supply side of the hydrogen purification module, During the operation of the hydrogen purification apparatus, a concentration monitoring step is performed to monitor the concentration of a detection gas in the gas that has permeated from the permeate side of the hydrogen purification module, The method is characterized by including a determination step of determining whether or not there is a crack in the hydrogen permeable metal film based on the monitoring detection gas concentration. A method for detecting film cracks.

5. The process further includes an elastic wave monitoring step in which elastic waves generated when cracks occur in the hydrogen permeable metal film are monitored by an acoustic emission sensor, The determination step is characterized by determining whether or not there is a crack in the hydrogen permeable metal film based on the monitoring concentration of the detection gas and the monitoring result from the acoustic emission sensor. The film crack detection method according to claim 4.

6. A film crack detection system characterized by comprising the film crack detection system described in claim 1 or 2, Hydrogen purification device.

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