Gas concentration measuring apparatus

Abstract

To provide a gas concentration measuring apparatus which can measure the concentration of at least two different types of target gases in a multi-component gas and is less expensive.SOLUTION: A gas concentration measuring apparatus 1 according to the present invention includes: a plurality of separation membrane modules 1a, 1b configured to separate a target gas in a mixed gas; flow rate adjustment mechanisms 21a, 21b provided in inlet pipes 31a, 31b of the separation membrane modules 1a, 1b, respectively; differential pressure gauges 13a, 13b configured to measure differential pressures between permeation sides P and non-permeation sides N of the separation membrane modules 1a, 1b; and a calculation device 51 configured to calculate concentrations of a plurality of target gases on the basis of values of the differential pressure gauges 13a, 13b.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a gas concentration measuring device. [Background technology]

[0002] Methods for measuring the concentration of a target gas in a mixed gas consisting of two types of gas include measuring the thermal conductivity and speed of sound. However, when the gas contains three or more components, even if the concentration of the target gas is the same, the thermal conductivity and speed of sound change depending on the component ratio of the gases other than the target gas, reducing the accuracy of the measured target gas concentration. Measurement of the concentration of a target gas in a multi-component gas is generally performed using gas chromatography, but because concentration measurement takes time, it is not suitable for measuring the concentration of gases whose concentration fluctuates transiently. For example, Patent Document 1 describes an apparatus that can measure the concentration of a target gas in a multi-component gas in a short time.

[0003] This patent document 1 describes a gas concentration measurement device that includes a separation means for separating a measurement target gas (target gas) from a sample gas (multi-component gas) and a pressure change detection means for detecting a pressure change caused by separation of the measurement target gas by the separation means. The separation means in this device is formed of a gas permeable membrane that selectively allows the measurement target gas to pass through. Patent document 1 lists metal thin films and polymer membranes as examples of gas permeable membranes.

[0004] Patent Document 1 also describes that a measuring cell having the separation means and a comparison cell not having the separation means are provided, sample gas is supplied to both the measuring cell and the comparison cell, and after separation of the gas to be measured in the measuring cell, the pressure difference between the measuring cell and the comparison cell is detected as a pressure change amount by a pressure change amount detection means (differential pressure gauge).

[0005] That is, in the device described in Patent Document 1, a sample gas is passed through two cells: a measurement cell having a gas-permeable membrane that selectively allows the target gas to pass through, and a comparison cell having no gas-permeable membrane, and the concentration of the target gas is measured by detecting the difference in permeation-side pressure, which changes depending on the amount of gas passing through, with a differential pressure gauge. Patent Document 1 also describes that because the comparison cell does not allow gas to pass through, no pressure change occurs inside or outside the membrane, but that by making the lines of the measurement cell and the comparison cell the same shape, errors due to fluctuations in the amount of gas supplied and the like are canceled out, improving measurement accuracy. [Prior art documents] [Patent documents]

[0006] [Patent Document 1] Japanese Patent Application Laid-Open No. 2002-202235 Summary of the Invention [Problem to be solved by the invention]

[0007] In recent years, in order to promote the use of hydrogen, methods have been considered in which hydrogen is mixed with natural gas from existing gas grids, transported, and then highly purified hydrogen is extracted and used in areas where hydrogen is in demand using hydrogen separation membranes or other methods.

[0008] It is possible to measure hydrogen concentration using the device described in Patent Document 1 in this method, but when a polymer membrane is used as the gas permeable membrane, if gases other than the target gas have a high permeation rate, the accuracy of the target gas concentration measurement decreases due to the pressure changes caused by the gases other than the target gas. The target gas concentration can be accurately measured only when the target gas is hydrogen and a metal membrane such as palladium, which in principle only allows hydrogen to pass through, is used as the gas permeable membrane. However, in this case, the concentration of gases other than the target gas cannot be measured.

[0009] Hydrogen separation membranes are used to extract hydrogen mixed with natural gas from existing gas grids, but many separation membranes are required to process large amounts of gas. Because the aforementioned metal membranes are expensive, it is necessary to reduce costs by using relatively inexpensive membranes such as polymer membranes and molecular sieve membranes. However, natural gas contains carbon dioxide, which has a high permeability rate, in addition to its main component, methane. Therefore, as the carbon dioxide concentration increases, the amount of carbon dioxide that permeates the separation membrane increases, and the concentration of extracted hydrogen decreases. To address this, the purity of hydrogen can be maintained by controlling the gas flow rate and pressure supplied to the hydrogen separation membrane according to the carbon dioxide concentration to suppress the amount of carbon dioxide permeation. To perform this control, it is necessary to measure the carbon dioxide concentration of the supplied gas. Gas chromatography can measure the concentration of multicomponent gases, but its response time is slow, making it unsuitable for the aforementioned control.

[0010] Fast-responding devices for measuring the concentration of multi-component gases include those that use lasers or infrared rays, but these are generally expensive and large, which increases costs when measuring gas concentrations at multiple locations in an existing gas grid.

[0011] An object of the present invention is to provide a low-cost gas concentration measuring device that can measure the concentrations of two or more target gases in a multi-component gas. [Means for solving the problem]

[0012] In order to solve the above problem, the gas concentration measuring device of the present invention comprises a plurality of separation membrane modules capable of separating target gases in a mixed gas, a flow rate control mechanism provided in the inlet pipe of each of the separation membrane modules, a differential pressure gauge that measures the differential pressure between the permeate side and the non-permeate side of each of the separation membrane modules, and a calculation device that calculates the concentrations of multiple target gases from the values ​​of each of the differential pressure gauges. [Effects of the Invention]

[0013] According to the present invention, it is possible to provide a low-cost gas concentration measuring device that can measure the concentrations of two or more target gases in a multi-component gas. Problems, configurations, and effects other than those described above will become apparent from the following description of the embodiments. [Brief explanation of the drawings]

[0014] [Figure 1] 1 is a schematic diagram showing the configuration of a gas concentration measurement device according to a first embodiment. [Figure 2] FIG. 10 is a characteristic diagram showing an example of determining a gas concentration from a pressure difference when target gases are hydrogen and carbon dioxide. [Figure 3] FIG. 4 is a schematic diagram showing the configuration of a gas concentration measuring device according to a second embodiment. [Figure 4] FIG. 10 is a schematic diagram showing the configuration of a gas concentration measuring device according to a fifth embodiment during calibration. DETAILED DESCRIPTION OF THE INVENTION

[0015] DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of a gas concentration measuring device according to the present invention will be described in detail below with reference to the accompanying drawings. In the description of each embodiment, substantially the same or similar components are denoted by the same reference numerals, and if the description is redundant, the description may be omitted.

[0016] The gas concentration measurement device according to each embodiment described below is preferably used, for example, when an existing gas grid for natural gas containing methane as the main component is used to transport a target gas other than natural gas mixed with the natural gas. More specifically, for example, the gas concentration measurement device is used when measuring the concentration of a target gas in order to control the target gas concentration to the required level at the target gas user's location.

[0017] First Embodiment 1 is a schematic diagram showing the configuration of a gas concentration measurement device 1 according to a first embodiment. In this embodiment, a case will be described in which the hydrogen concentration and carbon dioxide concentration of a mixed gas in which hydrogen is mixed with natural gas are measured. Natural gas is a multi-component gas, primarily composed of methane, but also containing flammable gases such as ethane and propane, and non-flammable gases such as nitrogen and carbon dioxide. Therefore, gas concentration meters that use thermal conductivity or sonic velocity are affected by the ratio of gas components other than the target gas, resulting in significant error in concentration measurements when the gas component ratio of natural gas changes. The gas concentration measurement device 1 has the following configuration, enabling it to accurately measure the concentration of the target gas even when the gas component ratio of natural gas changes.

[0018] As shown in FIG. 1, the gas concentration measuring device 1 includes a plurality of separation membrane modules 1a and 1b capable of separating a target gas from a mixed gas. The gas concentration measuring device 1 includes flow rate adjusting mechanisms 21a and 21b provided on the inlet pipes 31a and 31b of the separation membrane modules 1a and 1b, respectively. The gas concentration measuring device 1 is equipped with differential pressure gauges 13a and 13b that measure the differential pressure between the permeate side P and the non-permeate side N of each separation membrane module 1a and 1b. The gas concentration measuring device 1 includes a calculation device 51 that calculates the concentrations of a plurality of target gases from the values ​​of the differential pressure gauges 13a and 13b. In addition, the gas concentration measuring device 1 is preferably provided in the outlet piping (non-permeation side outlet piping 32a, 32b) of the non-permeation side N of each separation membrane module 1a, 1b, and is equipped with non-permeation side pressure adjustment mechanisms 22a, 22b that adjust the pressure of the non-permeation gas that does not permeate the separation membranes Ma, Mb in the separation membrane modules 1a, 1b and discharge the non-permeation gas. In addition, the gas concentration measuring device 1 is preferably provided in the outlet piping (permeation side outlet piping 33a, 33b) of the permeation side P of each separation membrane module 1a, 1b, and is equipped with a permeation side pressure adjustment mechanism 23 that adjusts the pressure of the permeation gas that has permeated the separation membranes Ma, Mb in the separation membrane modules 1a, 1b and discharges the permeation gas.

[0019] As described above, the gas concentration measurement device 1 according to this embodiment uses hydrogen and carbon dioxide as the target gases, and therefore uses polymer membranes for the separation membranes Ma and Mb. Examples of polymer membranes that can be used include, but are not limited to, polyimide membranes and polyamide membranes, and any membrane that can transmit the target gases can be used. The polymer membranes described above have the property of easily transmitting hydrogen and carbon dioxide, among the mixed gases targeted in this embodiment, but being difficult to transmit hydrocarbon gases such as methane and nitrogen.

[0020] The separation performance of separation membranes Ma and Mb is expressed as the ratio of the permeation rates between gas species. Taking hydrogen, which is the most permeable, as the standard, the ratio of the permeation rates of hydrogen to carbon dioxide is H2 / CO2 = 2.5 to 10, although this varies depending on the composition of the polymer membrane. This indicates that under the same conditions, hydrogen permeates 2.5 to 10 times more than carbon dioxide. The ratio of the permeation rates of hydrogen to other gases is 100 or more. A molecular sieve membrane can also be used as a separation membrane that, like a polymer membrane, allows hydrogen and carbon dioxide to permeate easily but is impermeable to other gases. For example, a carbon-based or ceramic non-porous membrane with a pore size of approximately 0.1 to 0.3 nm can be used as the molecular sieve membrane.

[0021] The sample gas used for measurement is introduced into the gas concentration measuring device 1 through a single inlet pipe 30. The sample gas is supplied to the separation membrane modules 1a and 1b through inlet pipes 31a and 31b branching from the inlet pipe 30. The permeation flow rate of each gas permeating the separation membranes Ma and Mb is determined by the partial pressure difference between the permeate side P and non-permeate side N of each gas, the permeation rate, and the membrane area. The amount of gas permeating through the separation membrane modules 1a and 1b is affected by the supplied gas flow rate and the pressures on the permeate side P and non-permeate side N. The gas flow rate is adjusted by flow rate adjustment mechanisms 21a and 21b, and the flow rate is measured by gas flow meters 10a and 10b installed on the inlet pipes 31a and 31b. Valves are used as the flow rate adjustment mechanisms 21a and 21b, and the flow rate is adjusted by their opening. The flow rate adjustment mechanisms 21a and 21b need not be valves as long as they can adjust the flow rate. The non-permeate side pressure is adjusted by non-permeate side pressure adjustment mechanisms 22a and 22b. The permeate side pressure is adjusted by the permeate side pressure adjustment mechanism 23. Valves are used as the non-permeate side pressure adjustment mechanisms 22a, 22b and the permeate side pressure adjustment mechanism 23, and the pressure is adjusted by changing the opening degree of the valves. The non-permeate side pressure adjustment mechanisms 22a, 22b and the permeate side pressure adjustment mechanism 23 need not be valves as long as they can adjust the pressure.

[0022] In this embodiment, the flow rate adjusting mechanisms 21a and 21b are adjusted to supply the sample gas to the separation membrane modules 1a and 1b at the same flow rate. The two separation membrane modules 1a and 1b have different permeation rate ratios of H2 / CO2. For example, the separation membrane module 1a has a permeation rate ratio of H2 / CO2 = 2.5, and the separation membrane module 1b has a permeation rate ratio of H2 / CO2 = 10.

[0023] The sample gas is supplied to the separation membrane modules 1a and 1b at the same flow rate by flow rate adjustment mechanisms 21a and 21b. The pressure on the non-permeate side N, to which the sample gas is supplied in the separation membrane modules 1a and 1b, is adjusted by non-permeate side pressure adjustment mechanisms 22a and 22b to a pressure somewhat higher than that on the permeate side P. The pressure on the permeate side P is adjusted by the permeate side pressure adjustment mechanism 23, and it is preferable to adjust the aperture by choking the permeate side pressure adjustment mechanism 23 so that the effect of the downstream pressure of the permeate side pressure adjustment mechanism 23 is eliminated. The apertures of the non-permeate side pressure adjustment mechanisms 22a and 22b and the permeate side pressure adjustment mechanism 23 are determined when the gas concentration measurement device 1 is calibrated and are not changed during measurement.

[0024] When sample gas is supplied to separation membrane modules 1a and 1b at the same flow rate, more carbon dioxide in the sample gas permeates through the separation membrane Ma in separation membrane module 1a, which is more permeable to carbon dioxide, than in separation membrane module 1b. Therefore, the amount of non-permeate gas discharged from non-permeate side outlet pipe 32a through non-permeate side pressure adjustment mechanism 22a is less than the amount of non-permeate gas discharged from non-permeate side outlet pipe 32b of separation membrane module 1b through non-permeate side pressure adjustment mechanism 22b. Therefore, the non-permeate side pressure of separation membrane module 1a is lower than the non-permeate side pressure of separation membrane module 1b. Meanwhile, permeate gas is discharged from permeate side outlet pipes 33a and 33b through permeate side pressure adjustment mechanism 23. By merging the permeate side outlet pipes 33a and 33b, the permeate side pressures of separation membrane modules 1a and 1b are made the same. Therefore, there is a difference between the readings of differential pressure gauge 13a, which measures the differential pressure between the non-permeate side and the permeate side of separation membrane module 1a, and differential pressure gauge 13b, which measures the differential pressure between the non-permeate side and the permeate side of separation membrane module 1b. The readings of differential pressure gauges 13a and 13b change depending on the hydrogen concentration and carbon dioxide concentration. When the hydrogen concentration and carbon dioxide concentration are low, the permeation amount decreases (particularly because the permeation amount in separation membrane module 1b is less than that in separation membrane module 1a), and the differential pressure increases. On the other hand, when the hydrogen concentration and carbon dioxide concentration are high, the permeation amount increases (because the permeation amount in both separation membrane modules 1a and 1b is high), and the differential pressure decreases.

[0025] Due to the difference in the permeation rate ratio between hydrogen and carbon dioxide, the behavior of the change in differential pressure due to changes in the hydrogen and carbon dioxide concentrations of the sample gas differs between separation membrane module 1a and separation membrane module 1b. Figure 2 is a characteristic diagram showing an example of calculating gas concentration from the differential pressure when the target gases are hydrogen and carbon dioxide. Figure 2 shows an example of a differential pressure map in which the differential pressure generated in the separation membrane module was calculated in a simulation using hydrogen and carbon dioxide concentrations as parameters for a certain sample gas flow rate, and the differential pressure (DP1) of separation membrane module 1a is plotted on the horizontal axis and the differential pressure (DP2) of separation membrane module 1b is plotted on the vertical axis. The hydrogen concentration produces different straight lines along the vertical axis, and the plot position along the horizontal axis changes depending on the carbon dioxide concentration. The dashed-dotted line indicates a hydrogen concentration of 8%, the solid line indicates a hydrogen concentration of 10%, and the dashed line indicates a hydrogen concentration of 12%. The right end of each line corresponds to a carbon dioxide concentration of 0%, and the left end corresponds to a carbon dioxide concentration of 6%. For example, if the value of differential pressure gauge 13a is a1 and the value of differential pressure gauge 13b is b1, the hydrogen concentration is 8% and the carbon dioxide concentration is 3% according to the graph (differential pressure map) in Figure 2. If the value of differential pressure gauge 13a is a2 and the value of differential pressure gauge 13b is b2, the hydrogen concentration is 12% and the carbon dioxide concentration is 5% according to the graph (differential pressure map) in Figure 2. This differential pressure map differs depending on the sample gas flow rate, so a differential pressure map is prepared for each sample gas flow rate.

[0026] In this embodiment, data related to the differential pressure map of FIG. 2 is incorporated into the arithmetic unit 51. The values ​​of gas flow meters 10a and 10b are converted into electrical signals and sent to the arithmetic unit 51 via cables 110a and 110b. Similarly, electrical signals from differential pressure meters 13a and 13b are sent to the arithmetic unit 51 via cables 113a and 113b. The arithmetic unit 51 calculates the sample gas flow rate and differential pressure from the electrical signals sent via cables 110a, 110b, 113a, and 113b, and determines the hydrogen concentration and carbon dioxide concentration by referring to the differential pressure map of FIG. 2 and displays them on the screen.

[0027] The permeation rates of hydrocarbon gases such as methane contained in natural gas and nitrogen are less than 1 / 100 of that of hydrogen. Therefore, even if the concentration of these gases changes, the change in the gas flow rate permeating the separation membranes Ma and Mb is small, so the effect on the differential pressure is small, and the effect on the measurement accuracy of hydrogen and carbon dioxide concentrations is also small.

[0028] In this embodiment, two separation membrane modules 1a and 1b are used to measure the concentrations of two target gases, hydrogen and carbon dioxide, in natural gas mixed with hydrogen, but it is also possible to use three or more separation membrane modules to measure three or more target gases using the same principle. The higher the permeation rate of the target gas, the more accurate the measurement, but if a differential pressure meter that can measure minute changes in differential pressure is used, the concentration of gases with low permeation rates can be measured.

[0029] As described above, the gas concentration measuring device 1 is provided with separation membrane modules capable of separating target gases, the number of which is equal to the number of target gases, and calculates the concentrations of two or more target gases in a multi-component gas from the differential pressure between the non-permeation side and the permeation side of each separation membrane module. Therefore, the gas concentration measuring device 1 can measure gas concentrations more quickly than conventional methods that use gas chromatography. Furthermore, the gas concentration measuring device 1 is low-cost because it does not use expensive equipment that uses lasers or infrared rays.

[0030] As shown in FIG. 1 , the hardware configuration of the arithmetic device 51 includes, for example, a central processing unit (CPU) 1001, a random access memory (RAM) 1002, a read-only memory (ROM) 1003, an interface (I / F) 1004, and a bus 1005. The CPU 1001, RAM 1002, ROM 1003, and I / F 1004 are connected via, for example, the bus 1005. The functions of the arithmetic device 51 are realized by loading predetermined programs, differential pressure maps, etc. stored in the ROM 1003 or an external storage device (not shown) into the RAM 1002 and executing the programs by the CPU 1001. Signals and information are exchanged between the arithmetic device 51 and various devices, external networks, etc. via the I / F 1004. The arithmetic device 51 may be a mobile device such as a smartphone.

[0031] Second Embodiment Fig. 3 is a schematic diagram showing the configuration of a gas concentration measurement device 2 according to a second embodiment. As shown in Fig. 3, the gas concentration measurement device 2 according to the second embodiment differs from the gas concentration measurement device 1 according to the first embodiment in that flow rate adjustment mechanisms 21a and 21b attached to inlet pipes 31a and 31b of the gas concentration measurement device 2 are orifices, gas flow meters 10a and 10b are eliminated, and a pressure gauge 11 and a thermometer 12 are attached to the inlet pipe 30.

[0032] The orifice opening diameter (i.e., the opening of the flow rate control mechanisms 21a and 21b) is set to an opening diameter that causes choking at the orifice portion. When choked, the gas flow rate passing through the orifice is determined by the pressure and gas density upstream of the orifice and is not affected by pressure changes associated with gas permeation through the separation membrane modules 1a and 1b. Therefore, if the upstream conditions are constant, the sample gas can always be supplied to the separation membrane modules 1a and 1b at a constant flow rate.

[0033] The flow rate at the orifice can be calculated from the upstream pressure and gas density. The pressure is measured by pressure gauge 11, and the temperature, which affects the gas density, is measured by thermometer 12. These measurements are converted into electrical signals and sent to arithmetic unit 51 via cables 111 and 112, respectively. Arithmetic unit 51 calculates the sample gas flow rate and differential pressure based on the electrical signals sent via cables 111, 112, 113a, and 113b, and determines (calculates) the hydrogen concentration and carbon dioxide concentration by referring to the differential pressure map in FIG. 2, and displays them on the screen. In the second embodiment, as in the first embodiment, the graph (differential pressure map) in FIG. 2 is prepared for each sample gas flow rate and referenced. The hardware configuration of arithmetic unit 51 in FIG. 3 and FIG. 4, described later, is the same as that shown in FIG. 1.

[0034] In this embodiment, operation of the flow rate adjustment mechanisms 21a and 21b is not required, simplifying operation, and since pressure gauges and thermometers are generally cheaper than flow meters, a lower cost gas concentration measurement device 2 can be constructed.

[0035] <Third embodiment> In the first and second embodiments, separation membrane modules 1a and 1b with different permeation rate ratios are used, but in the third embodiment, separation membrane modules (not shown) with the same separation performance (same permeation rate ratio) are used. In the case of separation membrane modules with the same separation performance, the flow rate of the sample gas introduced into each separation membrane module is made different so that the measured values ​​of differential pressure gauge 13a and differential pressure gauge 13b differ depending on the gas component ratio.

[0036] A separation membrane module with a high sample gas flow rate has a small drop in hydrogen partial pressure within the separation membrane module, resulting in a large amount of hydrogen permeation, and a small increase in carbon dioxide partial pressure associated with hydrogen permeation, resulting in a small amount of carbon dioxide permeation. On the other hand, in a separation membrane module with a low sample gas flow rate, the hydrogen partial pressure drops significantly within the separation membrane module, resulting in a low amount of hydrogen permeation, and the carbon dioxide partial pressure increases significantly as hydrogen permeates, resulting in a high amount of carbon dioxide permeation.

[0037] In this way, by varying the sample gas flow rate supplied to each separation membrane module, the permeation rates of hydrogen and carbon dioxide differ, resulting in the same differential pressure behavior as in the first and second embodiments, which use separation membrane modules with different permeation rate ratios. Therefore, the differential pressure map shown in Figure 2 can be created. This differential pressure map is incorporated into the computing device 51, which then calculates the hydrogen concentration and carbon dioxide concentration from the electrical signals from each instrument and displays them on the screen. The sample gas flow rates can be varied by varying the openings of the flow rate adjusting mechanisms 21a and 21b, specifically by varying the valve openings or the orifice opening diameters.

[0038] In this embodiment, by using separation membrane modules with the same separation performance, the procurement cost of the separation membrane modules can be reduced, and therefore a gas concentration measurement device can be provided at a lower cost.

[0039] <Fourth embodiment> In the fourth embodiment, the separation membrane modules 1a and 1b (see FIG. 1) have the same permeation rate (same separation performance) for each gas, but the areas of the separation membranes Ma and Mb in the separation membrane modules 1a and 1b are different. In the fourth embodiment, the same flow rate adjustment mechanisms 21a and 21b are used, and the flow rates of the sample gas supplied to the separation membrane modules 1a and 1b are the same.

[0040] When the separation membranes Ma and Mb in the separation membrane modules 1a and 1b have larger areas, the amount of hydrogen permeated increases, resulting in a larger drop in hydrogen partial pressure within the separation membrane module and a larger increase in carbon dioxide partial pressure associated with hydrogen permeation, resulting in a larger amount of carbon dioxide permeation.When the separation membrane areas are smaller, the amount of hydrogen permeated decreases, resulting in a smaller drop in hydrogen partial pressure within the separation membrane module and a smaller increase in carbon dioxide partial pressure associated with hydrogen permeation, resulting in a smaller amount of carbon dioxide permeation.

[0041] In this way, in the fourth embodiment, the permeation rates of hydrogen and carbon dioxide are different by changing the areas of the separation membranes Ma and Mb of the separation membrane module 1a and separation membrane module 1b. Therefore, the differential pressure behavior is similar to that of the first and second embodiments, which use separation membrane modules 1a and 1b with different permeation rate ratios. For this reason, the differential pressure map shown in FIG. 2 can be created. This differential pressure map is incorporated into the calculation device 51, which calculates the hydrogen concentration and carbon dioxide concentration from the electrical signals from each instrument and displays them on the screen.

[0042] In this embodiment, by using separation membrane modules with the same separation performance and the same flow rate adjusting mechanisms, the procurement costs of the separation membrane modules and the flow rate adjusting mechanisms can be reduced, thereby providing a lower-cost gas concentration measuring device.

[0043] Fifth Embodiment In the fifth embodiment, a method for calibrating a gas concentration measurement device using hydrogen and carbon dioxide as target gases will be described. Fig. 4 is a schematic diagram showing the configuration of a gas concentration measurement device 5 according to the fifth embodiment during calibration. As shown in FIG. 4, in the gas concentration measurement device 5, the shutoff valve 24 of the inlet pipe 30 that supplies the sample gas to the gas concentration measurement device 5 is closed, and a reference gas for calibration is supplied from a reference gas supply facility 61, such as a cylinder, connected via a calibration gas pipe 34 downstream of the shutoff valve 24. A reference gas with known hydrogen and carbon dioxide concentrations is used, and a predetermined flow rate is passed through the separation membrane modules 1a and 1b to measure the differential pressure using the differential pressure gauges 13a and 13b. The calculation device 51 compares the differential pressure measured during calibration with the differential pressure map shown in FIG. 2 and the differential pressure calculated from the hydrogen and carbon dioxide concentrations of the reference gas. If there is an error greater than the reference value, the zero point and span (i.e., the range that the differential pressure gauges 13a and 13b can measure) of the differential pressure gauges 13a and 13b are adjusted. If the error is still significant after adjusting the differential pressure gauges 13a and 13b, it is determined that the separation membranes Ma and Mb have deteriorated, and the separation membrane modules 1a and 1b are replaced.

[0044] In the first to fifth embodiments described so far, hydrogen and carbon dioxide in a mixed gas of natural gas and hydrogen have been described as target gases, but the concentrations of other gas components can also be measured accurately as long as the gas has a high permeation rate. Because the polymer membrane has a high ammonia permeation rate, gas concentration measurement devices 1, 2, and 5 using such a membrane are suitable for, for example, chemical plants that produce hydrogen from ammonia. Furthermore, because the polymer membrane also has a high helium permeation rate, gas concentration measurement devices 1, 2, and 5 using such a membrane are also suitable for, for example, measuring the helium concentration during helium purification. Although the above description has been given for two types of target gases, it is possible to measure three or more types of target gases by increasing the number of separation membrane modules. In particular, gases with high permeation rates can be measured with high accuracy.

[0045] Although the gas concentration measurement device according to the present invention has been described in detail above using embodiments, the present invention is not limited to the above-described embodiments and includes various modifications. For example, the above-described embodiments have been described in detail to clearly explain the present invention, and the present invention is not necessarily limited to an embodiment including all of the described configurations. Furthermore, it is possible to replace part of the configuration of one embodiment with the configuration of another embodiment, or to add the configuration of another embodiment to the configuration of one embodiment. Furthermore, it is possible to add, delete, or replace part of the configuration of each embodiment with other configurations. [Explanation of symbols]

[0046] 1, 2, 5 Gas concentration measuring device 1a, 1b Separation membrane module 10a, 10b Gas flow meter 11 Pressure gauge 12 Thermometer 13a, 13b Differential pressure gauge 21a, 21b Flow rate adjustment mechanism 22a, 22b Non-permeation side pressure adjustment mechanism 23 Permeation side pressure adjustment mechanism 24 Shut-off valve 30 Inlet piping 31a, 31b inlet piping 32a, 32b Non-permeate side outlet piping 33a, 33b Permeate side outlet piping 34 Calibration gas piping 51 Arithmetic unit 61 Reference gas supply equipment 110a, 110b, 111, 112, 113a, 113b cables Ma, Mb separation membrane N Non-transparent side P transmission side

Claims

1. a plurality of separation membrane modules capable of separating a target gas from a mixed gas; a flow rate adjusting mechanism provided in the inlet pipe of each of the separation membrane modules; a differential pressure gauge for measuring the differential pressure between the permeate side and the non-permeate side of each of the separation membrane modules; a computing device that calculates concentrations of a plurality of target gases from the values ​​of each of the differential pressure gauges; A gas concentration measuring device comprising:

2. 2. The gas concentration measurement device according to claim 1, A gas concentration measuring device, wherein the flow rate adjusting mechanism is an orifice.

3. 2. The gas concentration measurement device according to claim 1, a pressure gauge and a thermometer provided upstream of the flow rate adjusting mechanism; A gas concentration measuring device characterized in that the values ​​of the pressure gauge and the thermometer are input into the calculation device to calculate the concentration of the target gas.

4. The gas concentration measurement device according to any one of claims 1 to 3, The gas concentration measuring device is characterized in that there are two separation membrane modules and two types of target gases.

5. 5. The gas concentration measurement device according to claim 4, A gas concentration measuring device, wherein the ratio of the permeation rates of the target gas through the two separation membrane modules is different.

6. 5. The gas concentration measurement device according to claim 4, A gas concentration measuring device, wherein the flow rate adjusting mechanisms provided on the inlet pipes of the two separation membrane modules have different opening degrees.

7. 5. The gas concentration measurement device according to claim 4, A gas concentration measuring device, characterized in that the areas of the separation membranes of the two separation membrane modules are different.

8. 2. The gas concentration measurement device according to claim 1, A gas concentration measuring device, characterized in that outlet pipes on the permeation side of each of the separation membrane modules are joined together.

9. 2. The gas concentration measurement device according to claim 1, A gas concentration measuring device characterized in that the pressure on each of the non-permeation sides is set higher than the pressure on each of the permeation sides.

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