JP4398320B2 - Gas detector - Google Patents

Description

  The present invention relates to a gas detection device.

  In recent years, with the development of fuel cells, facilities called hydrogen stations (hydrogen stations) that handle hydrogen have been built. Since hydrogen has a risk of explosion, establishment of a disaster prevention system capable of early detection of hydrogen gas leakage in facilities such as hydrogen stations is desired. However, since hydrogen gas is lighter than air and has small molecules, if it leaks from a pipe or the like, it diffuses into the air, and it is very difficult to detect hydrogen gas. In addition, when an explosion-proof gas detector is used in preparation for an explosion, there is a problem that it takes time to detect the gas.

As means for detecting gas, there is a mass spectrometer in addition to a general-purpose gas sensor such as a semiconductor type or a catalytic combustion type. A mass spectrometer is an excellent instrument that can detect the gas to be detected in the range of one molecule to 100%, but it is a precision analytical instrument that is mainly used indoors. Not suitable for leak detection. Patent Document 1 discloses a mass spectrometry type gas leak detector that uses this mass spectrometer to test the airtightness of instruments.
JP-A-6-137986

  However, this gas leak detector has not been provided with means for removing noise when detecting gas outdoors. That is, when gas is sampled outdoors, not only the target gas but also moisture in the air is detected. Due to its extremely high sensitivity, mass spectrometers have the problem that if even a small amount of water is detected, the resulting mass spectrum peak will be blurred, making it impossible to identify what gas was detected. there were. Therefore, an object of the present invention is to detect hydrogen gas in a monitoring area at an early stage using a mass spectrometer.

The present invention has been made to solve the above-described problems. A sampling tube that samples air from a monitoring area, and a mass that is provided on the proximal end side of the sampling tube and ionizes the sampled air to perform mass analysis. In a gas detection apparatus comprising an analyzer and a membrane filter provided at the tip or in the middle of the sampling tube, the inner diameter of the sampling tube and the pore diameter of the membrane filter are formed smaller than the extinguishing distance of hydrogen gas. Thus, the mass spectrometer detects hydrogen gas in the air.

Further, the membrane filter is a filter that cuts oxygen molecules and selectively transmits only hydrogen molecules . Further, keeping the pressure of the mass spectrometer high vacuum, keeping the sampling tube to atmospheric pressure, a and the mass spectrometer the sampling tube is connected via a gas inlet tube, the gas inlet tube with a heater It is characterized by heating .

  Since the mass spectrometer detects the hydrogen gas leaked into the air, the gas can be detected significantly faster than a normal gas sensor, and the gas can be detected from a low concentration to a high concentration. Further, by using the sampling tube, the gas leaked in the monitoring area can be introduced into the mass spectrometer.

  In addition, since the membrane filter is provided at the tip of the sampling tube, the drip-proof effect is improved and water can be prevented from entering the sampling tube. In addition, since a membrane filter having a pore diameter smaller than the extinguishing distance of hydrogen gas is provided in the sampling tube, it is possible to prevent an explosion from occurring in the middle of the sampling tube.

  In addition, since the mass spectrometer is heated by the heater, the water droplet can be prevented from freezing when the water droplet adheres to the gas pipe in the mass spectrometer.

  FIG. 1 is a system block diagram for explaining a gas detector G of the present invention. The gas detection device G according to the present invention includes a mass spectrometer MS and a sampling portion including a sampling tube 10 and a dry pump.

  In the figure, MS is a mass spectrometer. The mass spectrometer MS includes an ionization unit 2, a mass separation unit 4 (also called an analysis unit), and a detection unit 6. The mass spectrometer MS is provided on the base end side of the sampling tube 10 and ionizes sampled air. Perform mass analysis.

  As the ionization unit 2 of the mass spectrometer MS, the most common electron impact ionization (EI) method is used as an example. This is a method in which accelerated electrons collide with a sample (neutral) molecule to be ionized.

For the mass separator 4, for example, the most popular quadrupole type is used. In the quadrupole type, the same voltage of the same polarity is applied to each of the two diagonal lines of the four pole-shaped electrodes, and the mass number of ions that can pass through the pole when this polarity is switched at high speed is proportional to the voltage applied to the pole. By utilizing this, only ions having a specific mass-to-charge ratio (m / z) (hydrogen ions in this embodiment) are allowed to pass through and separation is performed. Here, m is the molecular weight and z is the number of charges.

The detection unit 6 includes a photomultiplier tube and the like, and detects one separated ion. The detection unit 6 is connected to an external data analysis processing device 8 and is configured to send a detection signal to the data analysis processing device. The MS is configured to obtain an MS spectrum having a horizontal axis (ion mass number) / vertical axis (ion detection intensity) by separating and detecting ions for each mass. The data analysis processing device 8 processes the spectrum data from the mass spectrometer MS, selects only necessary peak values, and analyzes the data.

  Since the ionization unit 2, the mass separation unit 4, and the detection unit 6 constituting the mass spectrometer MS require a high degree of vacuum for gas analysis, two turbo molecular pumps TMP and two dry pumps 9 are used as vacuum pumps. Directly connected to each other, the pressure inside the mass spectrometer MS is set to about 10 ↑ -5 Torr. This pressure is adjusted in the range of 10 ↑ -4 to 10 ↑ -6 Torr, and a preferable value is 10 ↑ -5 Torr. In addition, the number of pumps may be increased to configure a differential exhaust system that sequentially decreases the pressure in the chambers of the ionization unit 2, the mass separation unit 4, and the detection unit 6.

  The part related to the mass spectrometer MS described above can be replaced with another already known mass spectrometer MS. For example, other mass spectrometers such as a soft ionization method, an ion trap type, a magnetic field type, and a TOF type, which have different ionization and mass separation principles, may be used.

  Next, the sampling part will be described. Reference numeral 10 denotes a sampling pipe, the tip of which is installed in the monitoring area, and the dry pump 12 is connected to the base end to sample air from the monitoring area. Here, the monitoring area is, for example, a facility storing hydrogen such as a hydrogen station.

  In this embodiment, the “dry pump” that does not use the oil working liquid is used as the vacuum pump, without using the “wet pump” that uses the oil working liquid. This is because when the “wet pump” is used, oil, which is the working fluid necessary to perform the exhaust operation, causes oil contamination in the mass spectrometer MS, causing interference peaks due to oil components in the spectrum. This is because. There is also a problem that the sample gas is dissolved in the oil and the sample peak does not disappear as a residual peak indefinitely.

  It is desirable to make the inner diameter of the sampling tube 10 as thin as possible so that the flow rate does not decrease. The inner diameter is adjusted according to the distance from the monitoring area to the dry pump 12. For example, if the distance is about 1 m, a sampling tube having an inner diameter of about 0.3 mm or less is used. If the distance is about 10 m, the inner diameter of the sampling tube is adjusted to about 0.52 mm, and the tube diameter is adjusted so that a constant flow rate of air can be sampled within a predetermined time.

  A first membrane filter 13 is provided at the tip of the sampling tube 10, and a second membrane filter 15 is provided in the middle of the sampling tube 10. As the membrane filter, a polymer film such as rubber, a ceramic porous body, a metal sintered body, a liquid film, or the like is used. The first membrane filter 13 is formed of, for example, a polymer film and has a pore diameter of 0.01 to 1 μm, preferably 0.05 μm. The pore diameter of the second membrane filter 15 is 1 μm to 0.3 mm, preferably about 0.5 μm. As the second membrane filter 15, a metal sintered body or a wire mesh is used in particular.

  The membrane filters 13 and 15 have three functions (effects) depending on the pore diameters: “drip-proof”, “hydrogen selectivity”, and “extinguishing (preventing explosion by hydrogen gas)”. If the hole diameter is less than 0.6 mm, there is an effect of extinguishing the flame, and if it is 50 μm or less, there is an effect of drip-proofing. When the pore size is 10 μm or less, a membrane (filter) that cuts oxygen molecules and efficiently selects and transmits only hydrogen molecules having a small molecular diameter.

  In the sampling tube 10, the primary side of the dry pump 12 and the mass spectrometer MS are connected by a gas introduction tube 20 having a thin tube diameter. A needle valve 22 for controlling the flow rate is provided in the middle of the gas introduction pipe 20 to restrict the flow path of the gas introduction pipe 20. An orifice may be used instead of the needle valve 22. Here, the pressure on the dry pump side 12 of the sampling tube 10 is 760 torr (approximately 10 ↑ 3 torr), the pressure of the mass spectrometer MS is 10 ↑ −5 torr, and is in a high vacuum state, and the pressure difference between the two is large. . For this reason, the sampling tube 10 and the mass spectrometer MS are connected via the gas introduction tube 20, and the flow path is restricted by the needle valve 22. By doing so, it becomes possible to maintain the vacuum state of the mass spectrometer MS and allow gas components to pass therethrough, and a so-called differential exhaust system is configured. Since sampled air is introduced into the mass spectrometer MS through such a differential exhaust system, impurities are unlikely to enter the mass spectrometer MS, and long-term monitoring is possible.

  In the figure, reference numeral 30 denotes a heater as a heating means. The heater 30 heats the entire mass spectrometer MS and the gas introduction tube 20 at 100 ° C. This is because the pressure inside the mass spectrometer MS is low, and if water drops adhere to the gas pipe (capillary) in the mass spectrometer MS, it is more likely to freeze than under atmospheric pressure. It is for preventing. In particular, since the portion narrowed and narrowed by the needle valve 22 in the gas introduction pipe 20 has a high possibility of freezing, heating by the heater 30 is desired.

  Next, a case where hydrogen leaks from a cracked part such as a pipe in a facility such as a hydrogen station (not shown) in an outdoor monitoring area will be described. Although hydrogen gas is diffused into the air, a part of the hydrogen gas is sampled through a membrane filter at the tip of the sampling tube 10.

  At this time, since the membrane filter 13 is provided at the tip of the sampling tube 10, raindrops do not enter the sampling tube 10, and only gas is allowed to pass into the sampling tube 10, so that moisture in the air (liquid ) Can be prevented from entering. In other words, the size of water droplets such as raindrops is 20-50 μm larger than the membrane filter 13, so that the drip-proof effect is improved by providing the membrane filter 13, and even if the gas detection device G is installed outdoors. There is no hindrance.

  Further, by using a membrane filter 13 having a small pore diameter of 0.05 μm, it is possible to prevent only oxygen molecules having a small molecular diameter to be detected from permeating and flowing oxygen molecules into the sampling tube 10. By selecting only hydrogen molecules in this way, the hydrogen gas entering the sampling tube 10 can be concentrated.

  Most of the hydrogen gas sucked in by the sampling pipe 10 is led to the dry pump 12 side, exhausted and released into the atmosphere, and part of the hydrogen gas passes through the gas introduction pipe 20 and the needle valve 22, Introduced into the mass spectrometer MS.

  By the way, “the inner diameter of the sampling tube 10 is desirably as thin as possible so that the flow velocity does not decrease”. One reason is that the flow rate is not reduced, and at the time of gas leakage, the gas is detected at an early stage, but there is another reason. This is because the use of a large diameter tube may cause an explosion when sampling hydrogen gas.

  The flame extinguishing distance of hydrogen gas, that is, the minimum distance necessary for generating a flame by explosion is 0.6 mm. That is, if the inner diameter of the sampling tube 10 is less than 0.6 mm, it is possible to prevent an explosion from occurring in the middle of the sampling tube 10 even if the distance of the sampling tube 10 is increased. In this embodiment, since the sampling tube 10 having an inner diameter of less than 0.6 mm is used, there is no particular problem of explosion, but the second membrane filter (metal) having a pore diameter smaller than the flame extinguishing distance of hydrogen gas. By providing the (manufactured filter) 15, it becomes possible to more reliably prevent explosion due to the sucked hydrogen gas.

  When the tube diameter is small and the pressure in the tube is lower, the flow of gas molecules flowing through the sampling tube 10 changes from a viscous flow to a molecular flow, and the mean free path in which molecules do not collide with each other increases. Becomes a concentrated state.

  When the air containing the sampled hydrogen gas is introduced into the mass spectrometer MS, it is ionized by the ionization unit 2, and the mass separation unit 4 performs separation by passing only hydrogen ions having a specific mass-to-charge ratio. The detection unit 6 detects the separated ions. Then, the detection unit 6 sends a detection signal to the data analysis processing device 8. Here, since a mass spectrum having a peak at a mass to charge ratio of 2 is obtained, the peak is recognized as a hydrogen molecule and detected. In this manner, the hydrogen gas leaked into the air is detected outdoors (monitoring area) by the mass spectrometer MS. The data analysis processing device 8 may determine that a fire has occurred when hydrogen gas (hydrogen molecules) is detected, and operate a fire alarm unit (not shown).

It is a system block diagram for demonstrating the gas detection apparatus G of this invention.

Explanation of symbols

2 ionization section, 4 mass separation section, 6 detection section,
8 data analysis processing equipment, 10 sampling pipe, 12 dry pump, 13 membrane filter, 15 membrane filter, 20 gas introduction pipe,
22 needle valve, 30 heater,
MS mass spectrometer, TMP turbo molecular pump,

Claims (3)

A sampling tube that samples air from a monitoring area, a mass spectrometer that is provided on the base end side of the sampling tube and ionizes the sampled air to perform mass analysis , and is provided at the distal end or in the middle of the sampling tube In a gas detection device equipped with a membrane filter ,
The gas detector according to claim 1, wherein an inner diameter of the sampling tube and a pore diameter of the membrane filter are formed to be smaller than a quenching distance of hydrogen gas, and the hydrogen gas in the air is detected by the mass spectrometer. The membrane filter is to cut the oxygen molecules, gas detection device according to claim 1 characterized in that it is a filter that transmits only select hydrogen molecules. The pressure of the mass spectrometer is kept in a high vacuum state, the inside of the sampling tube is kept at atmospheric pressure, the mass spectrometer and the sampling tube are connected via a gas introduction tube, and the gas introduction tube is heated by a heater. The gas detection device according to claim 1 or 2, wherein

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