Infrared gas analyzer, and infrared gas analysis method

Abstract

The present invention provides an infrared gas analyzer with which running costs are reduced by eliminating the need for a catalyst, which is a consumable, the infrared gas analyzer comprising: a measuring cell 2 into which a sample gas is introduced; an infrared light source 3 for emitting infrared light into the measuring cell 2; an infrared detector 4 for detecting infrared light that has been transmitted through the measuring cell 2; and a gas filter 5 filled with a plurality of interference components that interfere with a measurement component in the sample gas.

Description

Infrared gas analyzer and infrared gas analysis method

[0001] The present invention relates to an infrared gas analyzer and an infrared gas analysis method.

[0002] In recent years, nitrous oxide (N) has been identified as a greenhouse gas that causes global warming. ２ O) is attracting attention. ２ Reduction of O is required in various industrial sectors, such as sewage treatment plants, waste incineration plants, industrial waste treatment plants, and chemical plants.

[0003] On the other hand, as an apparatus for measuring the concentration of a target component in exhaust gas emitted in the above-mentioned industrial fields, a non-dispersive infrared absorption analyzer (NDIR analyzer) is used, as shown in Patent Document 1.

[0004] Here, using this NDIR analyzer, N in the sample gas ２ When measuring the concentration of O, in the infrared absorption wavelength range, as shown in FIG. ２ The infrared absorption wavelength range of carbon monoxide (CO) overlaps with the infrared absorption wavelength range of O, ２ CO is an interfering component with O. Therefore, CO in the sample gas is converted to carbon dioxide (CO ２ Attempts have been made to reduce the interfering effects of CO by oxidizing it to HCl.

[0005] However, CO ２ The oxidation catalyst, which oxidizes the gas, is a consumable item and requires periodic maintenance such as replacement, resulting in high running costs.

[0006] JP 2013-96889 A

[0007] The present invention has been made to solve the above-mentioned problems, and its main object is to reduce running costs by eliminating the need for a catalyst, which is a consumable item.

[0008] That is, the infrared gas analyzer according to the present invention is characterized by comprising a measurement cell into which a sample gas is introduced, an infrared light source that irradiates the measurement cell with infrared rays, an infrared detector that detects the infrared rays that have passed through the measurement cell, and a gas filter that contains a plurality of interfering components that interfere with the measurement components in the sample gas.

[0009] This type of infrared gas analyzer has a gas filter containing multiple interfering components that interfere with the measured component in the sample gas, making it possible to eliminate the need for a catalyst that oxidizes or reduces at least one of the multiple interfering components, thereby reducing running costs.In addition, because the gas filter contains the multiple interfering components, the interference effect of the multiple interfering components on the measured component can be reduced.

[0010] As a specific embodiment of the gas filter, it is desirable that the gas filter contains a plurality of interfering components that do not react with each other, or a plurality of interfering components that are stable in a state of equilibrium with each other.

[0011] The components measured by the infrared gas analyzer of the present invention include nitrous oxide (N2O), a greenhouse gas that causes global warming. ２ O). ２ By measuring the concentration of O, the infrared gas analyzer of the present invention can be suitably used in industrial fields where a reduction in environmental load is required.

[0012] In the infrared wavelength range, the measured component is N ２ In the infrared absorption wavelength range of O, carbon dioxide (CO ２ The infrared absorption wavelength range of carbon monoxide (CO) overlaps with that of N ２ CO against O ２ and CO are interfering components. In order to remove the influence of these interfering components, the gas filter ２ It is desirable that gas and CO gas are enclosed.

[0013] Furthermore, CO ２ and interference components other than CO, such as N ２If there is a component that interferes with O, the component may be sealed in the gas filter. For example, if a high concentration of methane (CH ４ ) is included, CH ４ Therefore, the gas filter is ２ In addition to CO gas and CO ４ It is desirable that a gas is further enclosed.

[0014] Furthermore, the infrared gas analysis method according to the present invention is an infrared gas analysis method in which infrared rays are irradiated onto a measurement cell into which a sample gas has been introduced, and the infrared rays that have passed through the measurement cell are detected by an infrared detector to analyze a measurement component in the sample gas, and is characterized in that a gas filter containing a plurality of interfering components that interfere with the measurement component is used to reduce the interference effect of the plurality of interfering components on the measurement component.

[0015] The infrared gas analyzer of the present invention further includes a calculation device that calculates the concentration of a analyte in a sample gas using the output of the infrared detector. The infrared detector includes a analyte detector for measuring the concentration of the analyte and an interference detector for measuring the concentrations of interfering components that interfere with the analyte. The calculation device calculates the concentration of the analyte by subtracting the output of the interference detector multiplied by a predetermined weighting coefficient from the output of the analyte detector. In this configuration, the predetermined weighting coefficient changes depending on the concentration of the interfering component, so using a fixed weighting coefficient may result in measurement errors. Therefore, it is desirable for the calculation device to change or correct the weighting coefficient based on the concentration of the interfering component.

[0016] Furthermore, the infrared gas analyzer of the present invention comprises a measurement cell into which a sample gas is introduced, an infrared light source which irradiates the measurement cell with infrared rays, an infrared detector which detects the infrared rays which have passed through the measurement cell, and a computing device which calculates the concentration of a measurement component in the sample gas using the output of the infrared detector, wherein the infrared detector has a measurement component detector for measuring the concentration of the measurement component and an interference component detector for measuring the concentration of an interference component which interferes with the measurement component, and the computing device calculates the concentration of the measurement component by subtracting the output of the interference component detector multiplied by a predetermined weighting coefficient from the output of the measurement component detector, and changes or corrects the weighting coefficient based on the concentration of the interference component.

[0017] According to the present invention configured as described above, the catalyst, which is a consumable item, is not required, and running costs can be reduced.

[0018] It is a schematic diagram showing an infrared gas analyzer according to one embodiment of the present invention. It is a diagram showing the infrared absorption spectrum of each component. It is a schematic diagram showing an infrared gas analyzer according to a modified embodiment. It is a schematic diagram showing an infrared gas analyzer according to a modified embodiment.

[0019] An embodiment of an infrared gas analyzer according to the present invention will be described below with reference to the drawings. Note that, for ease of understanding, all of the drawings shown below are drawn in a schematic manner with appropriate omissions or exaggerations. Identical components are designated by the same reference numerals, and their description will be omitted where appropriate.

[0020] The infrared gas analyzer 100 according to this embodiment is configured to measure nitrous oxide (N ) in a sample gas such as exhaust gas (flue gas) emitted from industrial facilities such as sewage treatment plants, incineration plants, industrial waste treatment plants, and chemical plants. ２ O), nitrogen oxides (NO Ｘ ), sulfur dioxide (SO ２ ), carbon monoxide (CO), carbon dioxide (CO ２ ), methane (CH ４ ) and other component concentrations are measured by non-dispersive infrared absorption (NDIR).

[0021] Specifically, the infrared gas analyzer 100 detects N in the sample gas. ２ As shown in FIG. 1, the device comprises a measurement cell 2 into which a sample gas is introduced, an infrared light source 3 provided at one end of the measurement cell 2 to irradiate the measurement cell 2 with infrared rays, an infrared detector 4 provided at the other end of the measurement cell 2 to detect the infrared rays that have passed through the measurement cell 2, and a measurement component (N ２ The output from the gas filter 5 containing the interfering components that interfere with the measurement component (N ２ and a computing device 6 for calculating the concentration of .O.

[0022] The measurement cell 2 has, for example, a roughly cylindrical shape, and both ends thereof are sealed by cell window members 2a, 2b made of an infrared-transparent material, and an inlet port P1 for introducing sample gas into the cell and an outlet port P2 for discharging the sample gas to the outside of the cell are provided on the side wall.

[0023] The infrared light source 3 is provided at one end of the measurement cell 2 facing the cell window member 2a, and irradiates the inside of the measurement cell 2 with infrared rays. An optical chopper (not shown) is provided between the infrared light source 3 and the measurement cell 2, and is configured to be rotated by, for example, a motor to chop the infrared rays generated by the infrared light source 3 at a constant cycle.

[0024] The infrared detector 4 is provided opposite the cell window member 2b at the other end of the measurement cell 2, and detects the measurement component (N ２ The detector 41 is a main detector for measuring the concentration of an interference component (CO ２ The measurement cell 2 includes an interference component detector 42 as a compensation detector for measuring the concentration of the component (a component of the measurement sample) of interest. The measurement component detector 41 and the interference component detector 42 are optically arranged in series in this order from the other end of the measurement cell 2. The detection signals obtained by the measurement component detector 41 and the interference component detector 42 are output to the calculation device 6.

[0025] The measurement component detector 41 is, for example, a pneumatic detector of a condenser microphone type. The measurement component detector 41 has a main body block made of a corrosion-resistant metal, both ends of which are sealed with window members made of an infrared-transmitting material, and a condenser microphone 41x is disposed inside the main body block. The measurement component detector 41 contains a detector for detecting the measurement component (N ２ The detector 41 detects the intensity of infrared light in a wavelength range that matches the infrared absorption spectrum of the component to be measured. The detector 41 is sensitive to both the component to be measured and the interfering components.

[0026] In this embodiment, the measurement component is N ２ Since the concentration of N is O, the measurement component detector 41 contains a predetermined concentration of N. ２ O gas is sealed in. As a result, the measurement component detector 41 detects N ２ The infrared intensity in the wavelength range that matches the infrared absorption spectrum of O is detected (see Figure 2).

[0027] The interference component detector 42 is, for example, a pneumatic detector of the condenser microphone type, similar to the measurement component detector 41. The interference component detector 42 has a main body block made of corrosion-resistant metal, both ends of which are sealed with window members made of an infrared-transparent material, and a condenser microphone 42x is disposed inside the main body block. The interference component detector 42 contains a detector for detecting interference components (CO ２ ) or an interfering gas having equivalent infrared absorption characteristics is sealed in the detector 41, and the detector 42 detects the infrared intensity in a wavelength range that matches the infrared absorption spectrum of the interfering component. ２ Since O is mostly absorbed by the measurement component detector 41, it has sensitivity to interference components.

[0028] In this embodiment, N ２ CO to O ２ In order to correct the influence of interference, the interference component detector 42 includes the N ２ Higher concentration of N than O gas ２ O gas is sealed in. This allows the interference component detector 42 to detect CO ２The infrared intensity in the wavelength range that matches the infrared absorption spectrum of the substance is detected (see Figure 2).

[0029] The gas filter 5 is provided between the measurement cell 2 and the infrared detector 4, and is used to filter the measurement component (N ２ CO ２ Specifically, the gas filter 5 is configured to filter CO ２ The gas filter 5 is configured by sealing a mixed gas of N2 gas and CO2 gas. Here, both ends of the chamber of the gas filter 5 are sealed with window members made of an infrared-transmitting material. By configuring the gas filter 5 as a single chamber in this way, the gas filter 5 can be made smaller. In addition, by passing through the infrared gas filter 5, N2 gas can be ２ This can reduce the loss of infrared intensity in the infrared absorption wavelength range of O.

[0030] The gas filter 5 of this embodiment is a filter for 60 vol % CO ２ The gas filter 5 contains a mixed gas of a plurality of interference components that do not react with each other, or a mixed gas of a plurality of interference components that are stable in equilibrium with each other.

[0031] In addition, CO ２ The interference effect of CO 2 sealed in the gas filter 5 ２ Since the effect does not change (increase) much if the amount of gas is 50 vol% or more, it is desirable that the amount of CO2 gas is 50 vol% or more. On the other hand, assuming that the CO concentration in the sample gas is estimated to be 1000 ppm at the most, it is desirable to seal 20 vol% of CO gas in the gas filter 5 in order to remove the interference effect of that CO. ２ In consideration of the amount of gas, the amount of CO gas sealed in the gas filter 5 is 50 vol % or less.

[0032] Furthermore, in this embodiment, SO in the sample gas ２ and CH ４In order to reduce the influence of interference from components such as the above, an optical filter 9 is provided to narrow the wavelength of the infrared light detected by the infrared detector 4. This optical filter 9 is made of N ２ Specifically, the optical filter 9 transmits, for example, a wavelength range of 4 μm to 5 μm. The optical filter 9 in this embodiment is provided between the measurement cell 2 and the infrared detector 4, specifically, between the gas filter 5 and the infrared detector 4.

[0033] The calculation device 6 calculates N based on the difference between the output signal of the measurement component detector 41 and the output signal of the interference component detector . ２ The calculation device 6 calculates the concentration of N. ２ The measurement results such as the O concentration can be displayed on a display unit 60 such as a display.

[0034] Specifically, the arithmetic unit 6 includes a measurement preamplifier 61 that amplifies and outputs the output signal of the measurement component detector 41, an interference preamplifier 62 that amplifies and outputs the output signal of the interference component detector 42, an amplifier 63 that multiplies the output from the interference preamplifier 62 by a predetermined weighting coefficient k and amplifies it, and a subtractor 64 that subtracts the output signal of the amplifier 63 from the output signal from the measurement preamplifier 61.

[0035] Here, the predetermined weighting coefficient k is the ２ ) is measured. This weighting coefficient k is adjusted to be close to 1, that is, so that the output signal of the measurement component detector 41 and the output signal of the interference component detector 42 are approximately the same. Specifically, it is possible to adjust the resistance value built into the interference preamplifier 62 to bring the coefficient k closer to 1. Alternatively, it is possible to adjust the concentration of the measurement fill gas or the interference fill gas to bring the coefficient k closer to 1.

[0036] The weighting coefficient k is CO ２Since the weighting coefficient k varies depending on the concentration, there is a risk of measurement errors occurring when a fixed weighting coefficient k is used. ２ Measure the concentration of CO ２ The measuring unit 7 is further provided, and ２ CO obtained by the measurement unit 7 ２ The concentration is used to modify or correct the weighting coefficient k.

[0037] This CO ２ The measuring unit 7 is a CO ２ A measuring cell 71 and a CO ２ an infrared ray irradiating unit 72 that irradiates infrared rays onto the measurement cell 71; ２ CO that detects infrared rays that have passed through the measurement cell 71 ２ The CO detector 73 of this embodiment ２ The sample gas that has passed through the measuring cell 71 is introduced into the measuring cell 2, but the opposite may also be true.

[0038] CO ２ The measuring cell 71 has the same configuration as the measuring cell 2 described above, but its cell length is CO ２ The cell length is shorter than that of the measuring cell 2 in accordance with the concentration. ２ The detector 73 is, for example, a pneumatic detector of a condenser microphone type, similar to the above-mentioned measurement component detector 41 .

[0039] Here, the infrared irradiating unit 72 is configured using the above-mentioned infrared light source 3 and a condensing member 8 provided between the infrared light source 3 and the measurement cell 2. The condensing member 8 has a first optical path 8a formed of a tapered inner wall surface that condenses the infrared light. By passing through this first optical path 8a, the infrared light from the infrared light source 3 is condensed and irradiated onto the measurement cell 2. In addition, the inner wall surface that forms the first optical path 8a has a CO ２ A second optical path 8b is connected to irradiate the measurement cell 71 with infrared light. The infrared light reflected from the tapered inner wall surface passes through the second optical path 8b, and the infrared light passing through the second optical path 8b is converted into CO ２ The measurement cell 71 is irradiated.

[0040] Then, the calculation device 6 calculates the CO ２ A CO amplifier amplifies the output signal of the detector 73 and outputs it. ２ A detection amplifier 65 is provided. ２ The output signal of the detection amplifier 65 is ２ The concentration is calculated where CO ２ The output signal of the detection amplifier 65 or the CO determined therefrom ２ The concentration is input to the amplifier 63 of the computing device 6 .

[0041] The amplifier 63 multiplies the output signal of the interference component detector 42 by a weighting coefficient k, ２ The output signal of the detection amplifier 65 or the CO determined therefrom ２ The weighting coefficient is changed or corrected depending on the concentration of a plurality of CO ２ The weighting coefficient k is calculated in advance using the gas and stored in the calculation device 6. Then, at the time of measurement, ２ The output signal of the detection amplifier 65 or the CO determined therefrom ２ The weighting coefficient k is changed or corrected depending on the density.

[0042] In the infrared gas analyzer 100 of the present embodiment described above, the gas filter 5 is used to remove the interference effect of CO. ２ In addition, in the infrared gas analyzer 100, the influence of interference from N ２ O and CO ２ a measurement component detector 41 for detecting CO ２ The CO added to the output signal of the measurement component detector 41 is calculated by electrical calculation of "output of the measurement component detector 41" - "output of the interference component detector 42 x k" using the interference component detector 42 that detects the CO ２ The interference effect is eliminated.

[0043] <Effects of this embodiment> According to the infrared gas analyzer 100 of this embodiment configured as described above, the measurement component (N ２ Multiple interfering components (CO ２Since the gas filter 5 contains interfering components (CO and CO), an oxidation catalyst for oxidizing at least one of the interfering components (CO in this case) is not required, thereby reducing running costs. Furthermore, since the gas filter 5 contains the interfering components, the influence of the interfering components on the measured component can be reduced.

[0044] In this embodiment, N ２ The weighting coefficient k used to calculate the O concentration is ２ CO obtained by the measurement unit 7 ２ Since the CO concentration is used to change or correct the ２ Regardless of concentration, N ２ The O concentration can be determined with high accuracy.

[0045] <Other Embodiments> For example, the gas filter 5 of the above embodiment can detect CO as an interfering component. ２ The gas and CO gas were sealed in, but there was also an interference component, CH ４ It may be filled with gas.

[0046] Furthermore, although the gas filter 5 in the above embodiment is provided between the measurement cell 2 and the infrared detector 4, it may be provided between the infrared light source 3 and the measurement cell 2 (between the light collecting member 8 and the measurement cell 2 if a light collecting member 8 is provided), as shown in FIG. 2 . Here, when an optical filter 9 is provided, the optical filter 9 may also be provided between the infrared light source 3 and the measurement cell 2 (between the light collecting member 8 and the measurement cell 2 if a light collecting member 8 is provided, or between the infrared light source 3 and the light collecting member 8). Alternatively, the gas filter 5 may be built into the infrared light source 3 or the measurement cell 2.

[0047] Moreover, in the above embodiment, SO ２ and CH ４ In order to reduce the influence of interference from components such as those mentioned above, an optical filter 9 is used to narrow the wavelength of the infrared light detected by the infrared detector 4, but the optical filter 9 may not be used.

[0048] The infrared gas analyzer of the above embodiment is an optical chopping type that uses an optical chopper to chop the infrared light from the infrared light source 3 at regular intervals, but it may also be a fluid modulation type that introduces a sample gas and a reference gas alternately into the measurement cell 2 at regular intervals.

[0049] Furthermore, the infrared gas analyzer of the embodiment is ２ It was designed to measure the concentration of NO Ｘ , S.O. ２ , CO, CO ２ , C.H. ４ The concentration of other components such as the above may be measured, or the concentration of two or more of these components may be measured.

[0050] An example of the configuration of an infrared gas analyzer 100 for measuring the concentrations of, for example, four components is shown in FIG. 4. The infrared gas analyzer 100 shown in FIG. 4 measures, for example, N ２ O, SO ２ , CO ２ In addition to the configuration of the above embodiment, the concentration of each of the four components of SO ２ It is equipped with a measuring unit 10 and an NO measuring unit 11 .

[0051] SO ２ The measurement unit 10 detects infrared rays transmitted through the measurement cell 2. ２ The NO measurement unit 11 has an NO detector 111 that detects infrared rays transmitted through the measurement cell 2. ２ The detector 101 and the NO detector 111 are, for example, pneumatic detectors of the condenser microphone type, similar to the above-mentioned measurement component detector 41.

[0052] In this configuration example, the infrared light transmitted through the measuring cell 2 is incident on an infrared detector 4 (N ２ O detector), SO ２ The infrared light is split between the detector 101 and the NO detector 111 .

[0053] As shown in FIG. 4, the beam splitter 12 and the infrared detector 4 (N ２In this embodiment, a gas filter 5 similar to that of the previous embodiment is provided between the beam splitter 12 and the infrared detector 4 (N O detector). ２ An optical filter 9 is also provided between the beam splitter 12 and the SO ２ Optical filters 13 and 14 are also provided between the detector 101 and the NO detector 111. Furthermore, the beam splitter 12 and the SO ２ A gas filter may be provided between the detector 101 and the NO detector 111 to remove the influence of interfering components on the components to be measured. Although Fig. 4 shows an example of a configuration for measuring the concentrations of four components, it is also possible to configure the detector to measure the concentrations of three components or five or more components by changing the configuration of the beam splitter, for example.

[0054] In the above embodiment, exhaust gas emitted from an external combustion engine is analyzed, but exhaust gas emitted from an internal combustion engine of a vehicle, ship, or the like may also be analyzed.

[0055] In addition, various modifications and combinations of the embodiments may be made as long as they do not go against the spirit of the present invention.

[0056] According to the present invention, the catalyst, which is a consumable item, is not required, and running costs can be reduced.

[0057] 100: Infrared gas analyzer 2: Measuring cell 3: Infrared light source 4: Infrared detector 41: Measuring component detector 42: Interference component detector 5: Gas filter 6: Calculating device 7: CO ２ Measuring unit 8: Light collecting member 9: Optical filter

Claims

1. a measurement cell into which a sample gas is introduced; an infrared light source that irradiates the measurement cell with infrared rays; an infrared detector that detects infrared rays transmitted through the measurement cell; a gas filter containing a plurality of interfering components that interfere with the measured components in the sample gas.

2. 2. The infrared gas analyzer according to claim 1, wherein the gas filter contains a plurality of interference components that do not react with each other or a plurality of interference components that are stable in an equilibrium state with each other.

3. The component to be measured is nitrous oxide (N ２ 3. The infrared gas analyzer according to claim 1 or 2, wherein

4. The multiple interference components are carbon dioxide (CO ２ 3. The infrared gas analyzer of claim 1 or 2, wherein the infrared gas analyzer comprises a first inlet (120) and a second inlet (140) and a second outlet (160).

5. The multiple interference components are methane (CH ４ 5. The infrared gas analyzer of claim 4, further comprising:

6. A calculation device is further provided for calculating a concentration of a measurement component in a sample gas using an output from the infrared detector, The infrared detector has a measurement component detector for measuring the concentration of the measurement component, and an interference component detector for measuring the concentration of an interference component that interferes with the measurement component, 3. The infrared gas analyzer according to claim 1, wherein the calculation device calculates the concentration of the measurement component by subtracting the output of the interference component detector multiplied by a predetermined weighting coefficient from the output of the measurement component detector, and changes or corrects the weighting coefficient based on the concentration of the interference component.

7. 1. An infrared gas analysis method for analyzing a measurement component in a sample gas by irradiating an infrared ray onto a measurement cell into which a sample gas has been introduced and detecting the infrared ray transmitted through the measurement cell with an infrared detector, comprising: An infrared gas analysis method comprising: using a gas filter containing a plurality of interfering components that interfere with the measured component, the method reduces the interference effect of the plurality of interfering components on the measured component.