JP2526263Y2 - NO gas analyzer - Google Patents

Description

[Detailed description of the invention]

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a NO gas analyzer for measuring the concentration of NO gas in various kinds of exhaust gas, which is used, for example, in the analysis of NO gas in flue gas led to a flue.

[0002]

2. Description of the Related Art NO in exhaust gas led to a flue or the like
When analyzing the concentration of gas, it has been practiced to improve the measurement accuracy of NO gas by compensating for the influence of interference components coexisting in the exhaust gas, for example, CO ₂ . As an NO gas analyzer that compensates for the influence of CO ₂ , for example, an infrared gas analyzer shown in FIG. 6 is known.

In FIG. 6, reference numerals 31a and 31b denote a first cell and a second cell which are configured to transmit infrared rays, and these are provided with gas inlets 32a and 32b and gas outlets 33a and 33b. . Reference numeral 34 denotes a four-way switching valve connected to the gas inlets 32a and 32b, to which a sample gas 35 and a zero gas 36 are supplied. 37a and 37b are a first light source and a second light source which emit infrared light arranged on one side of the first and second cells 31a and 31b, and 38 are first and second light sources.
An optical filter disposed on the other side of the cells 31a and 31b, which is configured to transmit the absorption wavelength band of NO gas and block transmission of the absorption wavelength band of other interference components.

Numeral 39 denotes a pneumatic main detector using a condenser microphone into which infrared light transmitted through the optical filter 38 is incident, and detects a NO gas as a measurement component and CO _{2 as an} interference component. It is possible. Numeral 40 denotes a pneumatic sub-detector into which the infrared light transmitted through the main detector 39 is incident, which is capable of detecting CO ₂ . 41a and 41b are preamplifiers to which detection signals of the main detector 39 and the sub detector 40 are input, and 42 is a preamplifier 41a
Is an arithmetic unit that subtracts the output signal of the preamplifier 41b from the output of the preamplifier 41b or performs a ratio operation or other arithmetic processing on both output signals to output a signal in which the influence of CO ₂ is compensated.

The infrared gas analyzer comprises a first light source 37 and a second light source 37.
Infrared rays enter the first and second cells 31a and 31b from a and 37b, and the sample gas 35 and the zero gas 36 are alternately introduced into the first and second cells 31a and 31b by operating the four-way switching valve 34. I do. In this way, when the infrared rays are transmitted through the first and second cells 31a and 31b and the optical filter 38 and enter the main detector 39 and the sub-detector 40, the main detector 39 and the sub-detector Since each of the devices 40 outputs each detection signal, the arithmetic unit 42 performs an arithmetic process such as subtraction or ratio operation on each of the detection signals to correspond to the concentration of the NO gas in which the influence of the interference component CO ₂ is compensated. Since a signal is output, the NO gas concentration is measured based on the output.

[0006]

As described above, in the conventional NO gas analyzer, the main detector 39 and the sub-detector 40 compensate for the influence of the interference component. However, in order to accurately compensate for the influence of the interference component CO ₂ by the main detector 39 and the sub-detector 40, the gas to be filled in each of the main detector 39 and the sub-detector 40 is appropriately selected, and When H ₂ O is introduced into the first and second cells 31a and 31b to adjust the interference value of H ₂ O in each output signal of the main detector 39 and the sub-detector 40 to zero,
The optical filter 38 is required to have a spectral characteristic capable of reducing CO _{2 and} other interference components to a certain value or less. However, it is very difficult to accurately manufacture an optical filter 38 having a spectral characteristic capable of reducing the interference component to a certain value or less, and it is more difficult to reduce the CO ₂ to a certain value or less. . Therefore, even if the main detector 39 and the sub-detector 40 are used, the influence of the interference component CO ₂ can be accurately compensated, and NO
There is a problem that the measurement of gas is limited.

SUMMARY OF THE INVENTION The present invention solves the above-mentioned problems, and an object of the present invention is to provide a NO gas analyzer capable of measuring the NO gas by accurately compensating for the influence of the interference component CO _2. Aim.

[0008]

According to the NO gas analyzer of the present invention, a light source for irradiating an infrared ray into the cell on one side of a cell through which a sample gas flows and an infrared ray transmitted through the cell on the other side are detected. In the NO gas analyzer in which the pneumatic measurement detectors are respectively arranged, an infrared detecting element is arranged in the cell at a position perpendicular to the optical axis of the infrared light passing through the cell, and the light beam of the infrared detecting element On the incident side, a wide band pass type optical filter that rises at about 4 μm and falls at about 5 μm is arranged so that the infrared light incident on the cell passes through the optical filter and also enters the infrared detecting element. The detection signal of the measurement detector and the detection signal of the infrared detection element are arithmetically processed to compensate for the influence of the interference component and measure the NO gas.

The measuring detector is, as in the conventional example,
Two detectors, a main detector to which the infrared light transmitted through the cell is incident and a sub-detector to which the infrared light transmitted through the main detector is incident, or only one detector to detect NO gas It is possible to make it arbitrary. And the introduction of the cell and the sample gas to it,
As in the conventional example, using a pair of cells, sample gas and zero gas are alternately introduced into them, or sample gas and zero gas are alternately introduced into one cell,
Furthermore, it is possible to use a pair of cells, introduce a sample gas into one of them, and introduce a zero gas into the other, and make the infrared rays incident on them into intermittent light with a chopper. . Further, the infrared detection element,
The optical filter, which can be composed of an arbitrary infrared detecting element such as PbSe, PbS or other quantum type, pyroelectric type or thermopile, and which is disposed on the light incident side of the infrared detecting element, is a multilayer interference filter. And so on. The arithmetic processing of each output signal of the measurement detector and the infrared detection element by the arithmetic unit is performed by subtracting the output signal of the infrared detection element from the output signal of the measurement detector, or calculating the ratio of both output signals. , It is possible to select an arbitrary calculation process capable of compensating for the influence of the interference component in the sample gas and outputting a detection signal corresponding to the NO gas concentration.

[0010]

In the NO gas analyzer of the present invention, a sample gas is introduced into the cell, and the infrared light emitted from the light source is incident on the cell. In this way, the measurement detector outputs a detection signal corresponding to the concentration of the NO gas based on the infrared light transmitted through the sample gas and incident on the measurement detector. On the other hand, the infrared light that has entered the cell and has passed through the sample gas has passed through the optical filter and has also entered the infrared detection element, where the infrared detection element detects the infrared light. It is a wide band-pass type that rises and falls near about 5 μm, and its theoretical spectral characteristic is shown as 0 degree incidence in FIG. 5, and allows both the CO ₂ and CO absorption wavelength ranges to pass.

However, since the light incident surface of the optical filter and the optical axis of the infrared light are parallel to each other, the infrared light incident into the cell from the light source is converted into an optical light at an angle of about 60 degrees in parallel light conversion. It is considered to be incident on the filter.
The theoretical spectral characteristics of the optical filter at that time are as follows:
This is shown in FIG. 5 as a 60 degree incidence. On the other hand, CO
The experimental results in the absorption wavelength ranges of ₂ and CO are as shown in FIG. Therefore, as is apparent from FIG. 5, when the infrared light is incident at an angle of about 60 degrees in parallel light conversion, the optical filter transmits the CO ₂ absorption wavelength range.
It greatly reduces the transmission of CO in the absorption wavelength range. For this reason, since the infrared detection element outputs a detection signal corresponding to the concentration of almost only CO ₂ , arithmetic processing such as electrically subtracting the output signal of the infrared detection element from the output signal of the measurement detector is performed. Then, the NO gas is measured while compensating for the influence of CO ₂ .

[0012]

1 shows a first embodiment of the NO gas analyzer of the present invention.
2 will be described. In FIGS. 1 and 2, reference numerals 1a and 1b denote a first cell and a second cell arranged in parallel, which are configured to allow transmission of infrared light and gas inlets 2a and 2b.
b and gas outlets 3a and 3b are provided. Reference numeral 4 denotes a four-way switching valve connected to each of the gas inlets 2a and 2b. The sample gas 5 and the zero gas 6 supplied thereto are switched by operating the four-way switching valve 4, and the first and second cells 1a, 1b can be introduced alternately. 7
a, 7b are arranged on one side of the first and second cells 1a, 1b, and a first light source and a second light source for emitting infrared rays to them, and 8 is a first light source and a second light source.
This is an optical filter for measurement arranged on the other side of the two cells 1a and 1b, and is configured to transmit the absorption wavelength range of the NO gas and block transmission of the absorption wavelength range of other interference components.

Reference numeral 9 denotes a pneumatic main detector using a condenser microphone into which the infrared light transmitted through the measuring optical filter 8 is incident. This detector detects NO gas as a measurement component and CO _{2 as an} interference component. It is configured to be able to detect. Numeral 10 denotes a pneumatic sub-detector into which the infrared light transmitted through the main detector 9 is incident, which is configured to be capable of detecting CO ₂ . 11a and 11b are preamplifiers to which the detection signals of the main detector 9 and the sub detector 10 are input, and 12 is a preamplifier based on the output signal of the preamplifier 11a.
11b is a first subtractor that subtracts the output signal of 11b and outputs a measurement signal.

Reference numerals 13a and 13b denote infrared detectors mounted at the first and second cells 1a and 1b, respectively, at positions perpendicular to the optical axes of the infrared rays passing through the first and second cells 1a and 1b. FIG.
As shown in (1), a detection hole 14 is provided in each of the peripheral walls of the first and second cells 1a and 1b, and is disposed outside a detection window 15 in which the detection hole 14 is closed. Reference numeral 16 denotes an optical filter disposed between the infrared detectors 13a and 13b and the detection window 15, which is a wide band pass type multilayer interference filter that rises at about 4 μm and falls at about 5 μm. I have. Reference numeral 17 denotes a pyroelectric infrared detecting element provided in the infrared detectors 13a and 13b, which is transmitted through the detection window 15 and the optical filter 16 from the detection hole 14 and is incident on the infrared detectors 13a and 13b. And outputs the signal. Reference numeral 18 denotes a packing made of rubber or the like holding the infrared detectors 13a and 13b. Reference numeral 19 denotes a supporting portion for supporting the packing 18, which is fixed to each outer surface of the first and second cells 1a and 1b. 20a and 20b are preamplifiers to which the output signals of the infrared detectors 13a and 13b are input, and 21 is a second subtracter for subtracting the output signal of the preamplifier 20a or 20b from the output signal of the first subtractor 12. It is. The inner surfaces of the first and second cells 1a and 1b and the peripheral surface of the detection hole 14 are plated with gold.

The optical filter 16 is a multilayer interference filter formed by laminating a plurality of thin films of Ge and SiO on a substrate (not shown) made of Si, which is an arbitrary material for realizing the above-mentioned spectral characteristics. It is possible to use an optical filter having the above configuration. Then, the first and second cells 1a, 1
As shown in FIG. 1, the infrared detectors 13a and 13b provided for the first and second light sources 7a and 7b of the first and second cells 1a and 1b are arranged at positions relatively close to the calibration curve. Although it is suitable for reducing the bending of the infrared detectors, the positions of the infrared detectors 13a and 13b can be set arbitrarily.

In the NO gas analyzer configured as described above, the sample gas 5 and the zero gas 6 as the exhaust gas are alternately introduced into the first and second cells 1a and 1b by switching the four-way switching valve 4. Then, the first and second light sources 7a and 7b emit infrared rays to the first and second cells 1a and 1b, respectively. Then
Since each infrared ray that has passed through the gas introduced into each of the first and second cells 1a and 1b passes through the optical filter for measurement 8 and enters the main detector 9, the main detector 9 is connected to the optical filter for measurement. A detection signal corresponding to the infrared light transmitted through the detector 8 is output, and the detection signal is input to the first subtractor 12 via the preamplifier 11a. The infrared light incident on the main detector 9 is transmitted through the main detector 9 and is incident on the sub-detector 10, which detects it, and outputs the signal via the preamplifier 11b to the first subtractor.
As a result, the first subtracter 12 subtracts the detection signal of the sub-detector 10 from the detection signal of the main detector 9 to measure the NO gas concentration that compensates for the influence of the interference component CO _2. The signal is input to the second subtractor 21.

On the other hand, the infrared light introduced into each of the first and second cells 1a and 1b and transmitted through the sample gas 5 passes through the detection window 15 and the optical filter 16 through the detection hole 14 and passes through the infrared detector 13a or 13a. 13b, which is detected by the infrared detection element 17, and the detection signal is sent to the preamplifier 20a or
20b, the signal is input to the second subtractor 21.
Subtracts the detection signal input from the infrared detector 13a or 13b from the measurement signal input from the first subtractor 12, and outputs a signal. The NO gas concentration of the sample gas 5 is measured based on the output signal of the second subtractor 21.

As described above, this NO gas analyzer compensates for the influence of the interference component CO _{2 on} the detection signal of the main detector 9 with each detection signal of the sub detector 10 and the infrared detector 13a or 13b. Then, the concentration of the NO gas in the sample gas 5 is measured. Then, from the first and second light sources 7a and 7b, the first and second cells 1
It is considered that the infrared rays incident on the optical filters 16a and 1b enter the optical filter 16 at an angle of about 60 degrees in parallel light conversion as described above. In addition, the theoretical spectral characteristics of the optical filter 16 at 60 degrees incidence shown in FIG. 5 clearly show that the transmission through the absorption wavelength range of CO ₂ is greatly reduced, while the transmission through the absorption wavelength range of CO ₂ is greatly reduced. Therefore, since the optical filter 16 almost transmits only the absorption wavelength range of the interference component CO ₂ and makes it incident on the infrared detection element 17, the infrared detection element 17 accurately detects the concentration of the interference component CO ₂ of the sample gas 5. Can be detected. Therefore, it is possible to more accurately compensate for the influence of the interference component CO2 in the sample gas 5 and measure the NO gas concentration.

The detection of the infrared light transmitted through the first and second cells 1a and 1b can be performed without providing the sub-detector 10 and the main detector 9
It is also possible to perform only with. In this case, the main detector 9
From the detection signal by subtracting a detection signal of the infrared detector 13a or 13b of compensating for the effect of interfering components CO _2.

FIG. 3 shows a second embodiment. In this NO gas analyzer, one cell 1 is provided with a gas inlet 2 and a gas outlet 3. Reference numeral 4a denotes a three-way switching valve connected to the gas inlet 2 and the sample gas 5 supplied thereto.
And the zero gas 6 are switched by the operation of the three-way switching valve 4a, and are alternately introduced into the cell 1. Reference numeral 7 denotes a light source which is arranged on one side of the cell 1 and emits infrared rays thereto. Reference numeral 8 denotes a measurement optical filter which is arranged on the other side of the cell 1 and transmits an NO gas absorption wavelength region and transmits another light. It is configured to prevent transmission of the interference component in the absorption wavelength range. Reference numeral 13 denotes an infrared detector attached to the cell 1, and reference numeral 20 denotes a preamplifier to which an output signal of the infrared detector 13 is input. The other configuration is the same as that of the first embodiment, and is therefore denoted by the same reference numerals.

In the measurement of the NO gas of the sample gas 5 by the NO gas analyzer of the second embodiment, the sample gas 5 and the zero gas 6 are alternately supplied to the cell 1 by operating the three-way switching valve 4a, and the gas is transmitted therethrough. The detected infrared rays are detected by the main detector 9 and the sub-detector 10, respectively, and the interference component CO of the sample gas 5 is detected.
₂ is detected by the infrared detector 13. The compensation of the influence of the interference component CO ₂ by each detection signal thus obtained is the same as in the first embodiment.

FIG. 4 shows a third embodiment. This example is
The sample gas 5 is supplied to the first cell 1a, and the zero gas 6 is supplied to the second cell 1b. The first and second light sources 7a and 7b and the first and second light sources 7a and 7b
A chopper 22 is disposed between the first and second cells 1a and 1b, and the chopper 22 uses the infrared rays emitted from the first and second light sources 7a and 7b as intermittent light to form first and second cells 1a and 1b. It is incident. The infrared detector 13 is attached to the first cell 1a to which the sample gas 5 is supplied, and the detection signal is input to the second subtracter 21 via the preamplifier 20.
The other configuration is the same as that of the first embodiment, and is therefore denoted by the same reference numerals.

In the measurement of the NO gas of the sample gas 5 by the NO gas analyzer of this embodiment, the sample gas 5 is supplied to the first cell 1a, the zero gas 6 is supplied to the second cell 1b, and the first and second cells are supplied. 1a, the infrared light transmitted through the 1b detected by each of the main detector 9 and the sub-detector 10, and the interference component CO ₂ in the sample gas 5 of the first cell 1a is detected by the infrared detector 13. The interference component CO due to each detection signal thus obtained
The effect compensation of ₂ is the same as in the first embodiment.

[0024]

As described above, the NO gas analyzer of the present invention introduces a sample gas into a cell, makes the cell incident on the cell, detects the transmitted infrared light with a measurement detector, and detects the infrared light. At a position perpendicular to the optical axis, even by an infrared detecting element arranged in the cell, the infrared light was detected by transmitting through an optical filter, and the output signal of the infrared detecting element was subtracted from the detection signal of the measurement detector. Based on the signal
It measures NO gas.

The optical filter is of a wide band pass type that rises at about 4 μm and falls at about 5 μm, and has a spectral characteristic that allows transmission in the absorption wavelength range of CO ₂ and CO. However, this optical filter, infrared rays incident on the cell from the light source is considered to be incident at an angle of about 60 degrees parallel light converted, and the absorption wavelength region of the optical filter is CO ₂ at an incident angle of the light beam While transmitting, from the transmission of the absorption wavelength region of the CO to the effective well blocking, infrared detector is substantially CO ₂ is an interference component
A detection signal corresponding to only the density is output. Therefore, it is possible to accurately compensate for the influence of the interference component CO ₂ in the sample gas and measure the NO gas.
Moreover, since the optical filter disposed on the light incident side of the infrared detection element can be manufactured accurately and at low cost due to its spectral characteristics, it is possible to easily obtain an analyzer capable of measuring NO gas with high accuracy. is there.

[Brief description of the drawings]

FIG. 1 is a configuration diagram in which a part of a first embodiment is sectioned;

FIG. 2 is an enlarged sectional view of a main part of the first embodiment.

FIG. 3 is a configuration diagram in which a part of the second embodiment is sectioned;

FIG. 4 is a configuration diagram in which a part of a third embodiment is sectioned.

FIG. 5 is a theoretical spectral characteristic diagram of an optical filter.

FIG. 6 is a configuration diagram in which a part of a conventional example is sectioned.

[Description of References] 1a / 1b: First and second cells, 7a / 7b: First and second light sources, 8: Measurement filter, 9: Main detector, 10: Sub detector, 13a / 13
b: infrared detector, 16: optical filter, 17: infrared detection element, 12.21: first and second subtractors.

Claims (1)

(57) [Scope of request for utility model registration] 1. A light source for irradiating an infrared ray into the cell and a pneumatic measurement detector for detecting an infrared ray transmitted through the cell are arranged on one side of the cell through which the sample gas flows, and on the other side. In the NO gas analyzer, at a position perpendicular to the optical axis of the infrared light transmitted through the cell,
An infrared detecting element is disposed in the cell, and rises at about 4 μm on the light incident side of the infrared detecting element, and about 5 μm
A wide band-pass type optical filter that falls near μm is arranged, and infrared light incident on the cell is configured to pass through the optical filter and also enter the infrared detecting element, and the detection signal of the measurement detector and The detection signal of the infrared detection element is arithmetically processed to compensate for the influence of the interference component, and NO
A NO gas analyzer characterized by measuring gas.