JP3941679B2 - Infrared gas analyzer - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to an infrared gas analyzer suitable for use in process monitors relating to gas concentrations in chemical factories and steelworks, analysis of combustion gases in boilers and combustion furnaces, air pollution monitoring, automobile exhaust gas measurement, etc. The present invention relates to an infrared gas analyzer that measures the concentration of a specific component in a gas or vapor by using an inherent infrared absorption effect.
[0002]
[Prior art]
An infrared gas analyzer is known in which a reference gas and a sample gas are switched to flow through a sample cell.
FIG. 7 is a flow chart of such an infrared gas analyzer, which was previously proposed by the present inventor (see Patent Document 1). The sample cell 1 has a gas inlet 1a and a gas outlet 1b. A sample gas or a reference gas is supplied from the gas inlet 1a into the sample cell 1 through the three-way valve 7, and is discharged from the gas outlet 1b. . A light source 5 that emits infrared light is disposed at one end of the sample cell 1, and a detector 2 for detecting infrared light transmitted through the sample cell 1 is disposed at the other end of the sample cell 1. .
[0003]
A sector 3 for interrupting infrared light is provided between the light source 5 and the end portion of the sample cell 1. Sector 3 includes a light shielding portion and a cutout portion, and rotates around a rotation axis. When the cutout portion is on the optical axis of sample cell 1, infrared light is irradiated into sample cell 1, and the light shielding portion is When the sample cell 1 is on the optical axis, it is configured to block irradiation of infrared light into the sample cell 1. The controller 6 controls the rotational position of the sector 3 via the motor 4, and controls the driving of the three-way valve 7 via the driver 8.
[0004]
The detector 2 has a measurement target gas in the sample gas sealed therein, and detects infrared light intensity at a frequency unique to the measurement target gas based on a change in internal pressure. The detection output from the detector 2 is subjected to predetermined signal processing by the signal processing circuit 9, and the measurement gas concentration in the sample gas is measured.
[0005]
In such an infrared gas analyzer, a pretreatment device for obtaining a reference gas and a sample gas supplied to the sample cell 1 via the three-way valve 7 is provided at the sample gas port and the standard gas port of the three-way valve 7, respectively. Connected. As shown in FIG. 8, these pretreatment devices include filters 12a and 12b for removing dust, pumps 14a and 14b for sucking gas, needle valves 16a and 16b for adjusting the gas flow rate, and gas. In order to dehumidify, electronic coolers 18a and 18b using Peltier elements are provided.
[0006]
As the reference gas, it is necessary that the concentration of the measurement target component contained in the reference gas does not affect the measurement, and the atmosphere or a gas obtained by removing the measurement target component by passing the atmosphere through a purifier is used.
[0007]
[Patent Document 1]
JP-A-9-49797
[Problems to be solved by the invention]
When measuring SO ₂ and NO with an infrared gas analyzer, there is an interference error due to water vapor having an absorption wavelength band overlapping with the infrared absorption wavelength bands of SO ₂ and NO. In the pretreatment apparatus as shown in FIG. 8, the water vapor in the gas is removed by the electronic cooler, but the temperature of the electronic cooler is limited to about 1 ° C. even if the temperature of the electronic cooler is low due to the problem of freezing of the drain generated in the electronic cooler. . However, at 1 ° C., about 7000 ppm of water vapor is contained in the gas at normal pressure.
[0009]
Therefore, in SO ₂ and NO measurement, the detector signal is affected by water vapor in the gas. Therefore, the temperature of each electronic cooler used in the reference gas and the sample gas is the same, and the reference gas and the sample introduced by switching to the sample cell. The water vapor error is eliminated by equalizing the amount of water vapor contained in the gas.
[0010]
However, it is difficult to control the temperature of the two electronic coolers exactly the same over a long period of time, and when the operating environment temperature of the electronic cooler rises, the temperature cannot be controlled due to the limit of the cooling capacity of the Peltier element . There was a problem that the measurement error increased due to the temperature difference of the electronic cooler. As a countermeasure, a so-called two-line electronic cooler in which two flow paths are installed in the same cooling block in order to make the temperatures of the two electronic coolers completely the same may be used.
[0011]
However, even if the temperatures of the two electronic coolers can be made exactly the same, if the atmosphere as the reference gas is dry and the gas dew point is lower than the electronic cooler temperature, the reference gas to be switched and introduced into the sample cell There was a problem that the amount of water vapor in the sample gas was different, resulting in a large measurement error.
[0012]
An object of the present invention is to provide an infrared gas analyzer that can eliminate an error caused by a difference in water vapor amount between a reference gas and a sample gas.
[0013]
[Means for Solving the Problems]
The present invention is an infrared gas analyzer for measuring a reference gas and a sample gas containing different amounts of water vapor , and is in contact with the gas between a switching valve for switching the supply of the reference gas and the sample gas and the sample cell. A common cooler that can hold moisture in the state and is set to a constant temperature between the dew points of both gases, dehumidifying one gas and humidifying the other gas to equalize the moisture content of both gases And the flow path is configured so that the reference gas and the sample gas pass through the common cooler, thereby equalizing the amounts of water vapor contained in the reference gas and the sample gas introduced alternately into the sample cell.
[0014]
That is, the infrared gas analyzer of the present invention has a switching valve for selectively supplying a reference gas and a sample gas to the sample cell, and equalizes the amount of water vapor in both gases while the gas is being introduced from the switching valve to the sample cell. A common cooler, a light source for irradiating the sample cell with infrared light, an intermittent means for interrupting infrared light from the light source, a detector for detecting infrared light transmitted through the sample cell, and A controller that performs switching control of the switching valve and the intermittent control of the intermittent means, and a measurement gas concentration in the sample gas is determined based on detection values of the infrared light transmitted through the reference gas and the sample gas in the detector. Signal processing means.
[0015]
[Action]
Since the reference gas and the sample gas pass through a common cooler with the same amount of water vapor, the water vapor of both gases is stable even in the long term and even if the temperature of the cooler is high and temperature control cannot be performed accurately. Since the amounts are always equal, water vapor errors can be eliminated.
[0016]
If the dew point of the reference gas is lower than the cooler temperature and the sample gas is higher than the cooler temperature, such as combustion exhaust gas, the drain water that is condensed when the sample gas is dehumidified by the cooler is stored in the cooler. When the reference gas passes through the cooler and is humidified by the drain water, a water vapor error can be eliminated. This is because both the reference gas and the sample gas come out of the cooler including the saturated water vapor amount at the temperature in the cooler.
[0017]
DETAILED DESCRIPTION OF THE INVENTION
FIG. 1 is a flow chart of an infrared analyzer of one embodiment, and the same reference numerals are used for the same parts as in FIG.
The sample cell 1 has a gas inlet 1a and a gas outlet 1b. A sample gas or a reference gas is supplied from the gas inlet 1a into the sample cell 1 through a three-way valve 7 which is a switching valve, and the gas outlet 1b. Discharged from.
[0018]
In this embodiment, an electronic cooler 10 using a Peltier element is installed in the flow path between the three-way valve 7 and the sample cell 1 as a common cooler for cooling and removing water vapor in the gas. Both the sample gas and the reference gas supplied from are guided to the sample cell 1 via the electronic cooler 10.
[0019]
Since the electronic cooler 10 is disposed in the flow path between the three-way valve 7 and the sample cell 1, a cooler is not required for the pretreatment device that supplies the reference gas and the sample gas to the three-way valve 7. That is, the pretreatment devices connected to the sample gas port and the standard gas port of the three-way valve 7 for supplying the sample gas and the reference gas, respectively, are for dust removal as shown in FIG. Only the filters 12a and 12b, the pumps 14a and 14b for sucking the gas, and the needle valves 16a and 16b for adjusting the gas flow rate are included, and the cooler for dehumidifying the gas is omitted.
[0020]
A light source 5 that emits infrared light is disposed at one end of the sample cell 1, and a detector 2 for detecting infrared light that has passed through the sample cell 1 is disposed at the other end of the sample cell 1.
[0021]
A sector 3 for interrupting infrared light is provided between the light source 5 and the end portion of the sample cell 1. As shown in FIG. 3, the sector 3 includes a light shielding portion 3a and a cutout portion 3b, and is configured such that the sector 3 rotates about the sector rotation shaft 3c. 1 a represents a cross section of the sample cell 1. When the sector 3 rotates and the notch 3b is on the optical axis of the sample cell 1, infrared light is irradiated into the sample cell 1, and when the light-shielding portion 3a is on the optical axis of the sample cell 1, the sample cell The infrared light irradiation into 1 is cut off.
[0022]
The controller 6 controls the rotational position of the sector 3 via the motor 4, and controls the driving of the three-way valve 7 via the driver 8.
[0023]
The detector 2 has a measurement target gas in the sample gas sealed therein, and detects infrared light intensity at a frequency unique to the measurement target gas based on a change in internal pressure. The detection output from the detector 2 is subjected to predetermined signal processing by the signal processing circuit 9, and the measurement gas concentration in the sample gas is measured.
[0024]
FIG. 4 shows an embodiment of the signal processing circuit 9. The comparator 9b outputs a signal proportional to the difference between the predetermined voltage Vr determined in advance and the comparison signal that is the detection output of the infrared light that has passed through the reference gas, and the amplifier 9a gains due to the output of the comparator 9b. It is configured to be adjusted. Therefore, the gain of the amplifier 9a is adjusted so that the amplified output of the reference gas is held at a constant value Vr, and the measurement signal that is the detection output of the sample gas is multiplied by the gain here. As a result, an output ratio with respect to the reference gas is obtained.
[0025]
The output of the amplifier 9a is appropriately switched to the measurement input or comparison input of the subtractor 9c by the controller 6 according to the supply state of the sample gas or reference gas, and the subtractor 9c takes the difference between the two and outputs it. Here, when the comparison signal of the detector 2 is R and the measurement signal is M, the amplification factor of the amplifier 9a is Vr / R so that the comparison signal R is set to a constant value Vr. Therefore, the output V of the subtractor 9c Is
V = (Vr / R) · (R−M)
= Vr (1-M / R)
Thus, an output corresponding to the ratio between the measurement signal M and the comparison signal R can be obtained.
[0026]
As described above, since the infrared light transmitted through the sample gas and the reference gas is separately detected and the detection output ratio between them is obtained, the change in the light amount due to the applied voltage of the light source, the ambient temperature, or the deterioration of the light source itself, the sample Even if there is a cell transmission window, dirt inside the cell, or a change in sensitivity of the detector, the problem of a decrease in detection accuracy can be solved.
[0027]
Next, the operation of the controller 6 will be described based on the flowchart of FIG. First, in a state where the sector 3 is rotated via the motor 4 and infrared light is blocked (step S1), the three-way valve 7 is set via the driver 8 so as to supply a gas different from the gas previously supplied. Switching (steps S2, S3, S4). Then, after waiting for a time for the supplied gas to completely replace the previously supplied gas and be filled in the sample cell 1 (step S5), the sector 3 is rotated again via the motor 4 to emit infrared light. Is irradiated into the sample cell 1 (step S6). Then, after waiting for a time for infrared light to be detected by the detector 2, the sector 3 is rotated again via the motor 4 to shut off the infrared light, and the operations in steps S1 to S7 are repeated.
[0028]
FIG. 6 is a timing chart showing the opening / closing operation of the sector 3 when the controller 6 operates as described above and the state of filling the sample gas in the sample cell 1. This figure shows an example in which the inner diameter of the sample cell 1 is 8 mm, the length is 50 mm, the internal volume is 2.51 cm ³ , the gas flow rate is 1 liter / min, and the three-way valve 7 is switched every 0.5 seconds. ing. In this case, the time for completely replacing the gas is 0.15 seconds, and the state of the sample gas in the sample cell is as shown in the upper diagram of FIG. Here, the portion where the sample gas does not exist indicates that the reference gas is filled.
[0029]
As shown in the lower diagram of FIG. 6, the timing at which the sector 6 is driven by the controller 6 is the time from switching the three-way valve 7 to driving the sector 3 and irradiating the sample cell 1 with infrared light. If it is about 0.3 seconds, which is about twice the time until the gas is completely replaced, infrared light is incident with the gas completely replaced, so that more accurate measurement is possible. At the same time, even if the gas flow rate is reduced to about 0.5 liter / min, the measurement accuracy is not affected.
[0030]
In this way, the time during which the gas in the sample cell 1 is completely replaced is obtained in advance, and the sector 3 is driven by waiting for the time after switching the three-way valve 7 or with a margin, and the infrared light. If the sample cell 1 is irradiated, the influence on the detection accuracy due to the flow rate change when the gas is replaced can be reduced.
[0031]
In the embodiment described above, the sample cell 1 is intermittently irradiated with infrared light by rotationally driving the sector 3, but the power supply to the light source is intermittently provided instead of providing the sector. In this way, the infrared light irradiation may be interrupted.
[0032]
Moreover, although the case where one kind of sample gas was analyzed was shown in the above-mentioned embodiment, it is also possible to analyze a plurality of kinds of sample gases. An example of analyzing two types of sample gases is also described in Patent Document 1 cited above. In the infrared gas analyzer configured to analyze such a plurality of types of sample gases, the present invention provides a switching valve and a sample cell for selectively supplying a reference gas and a plurality of types of sample gases to the sample cell. The same application can be made by arranging one steam cooling / cooling cooler so that all the gases pass in common in the flow path between the two.
[0033]
In the embodiment, an electronic cooler using a Peltier element is used as a cooler that cools and removes water vapor in the gas, but the cooler is not limited to an electronic cooler, and gas cooling using cooling by adiabatic expansion of gas. Any device having a function of continuously cooling gas, such as a cooler, can be used as the cooler of the present invention.
[0034]
【The invention's effect】
In the infrared gas analyzer of the present invention, a common cooler is installed between the switching valve for switching the supply of the reference gas and the sample gas and the sample cell so that the water vapor amounts of both gases are equal. Since the flow path is configured to pass through the common cooler, the measurement can be performed without being subjected to interference error due to water vapor in the gas even for a long period of time and when the operating environment temperature of the cooler is high.
Even when the reference gas is dried to a dew point lower than the cooler temperature, it can be measured without receiving an interference error due to water vapor.
Further, when the coolers are provided in the pretreatment device electronics for supplying the sample gas and the reference gas to the switching valve as in the prior art, as many coolers as the number of types of gas are required. Since only one cooler is required, the apparatus can be realized in a small size and at low cost.
[Brief description of the drawings]
FIG. 1 is a flow chart showing an infrared analyzer according to one embodiment.
FIG. 2 is a flow chart showing a pretreatment device for gas supplied in the same embodiment.
FIG. 3 is a plan view showing a sector in the embodiment;
FIG. 4 is a circuit diagram showing a signal processing circuit in the same embodiment;
FIG. 5 is a flowchart showing the operation of the embodiment.
FIG. 6 is a timing chart showing the operation of the embodiment.
FIG. 7 is a flow chart showing a conventional infrared analyzer.
FIG. 8 is a flow chart showing a pretreatment device for gas supplied in the conventional example.
[Explanation of symbols]
1 Sample cell 1a Gas inlet 1b Gas outlet 2 Detector 3 Sector 5 Light source 6 Controller 7 Three-way valve 8 Driver 10 Electronic cooler

Claims (3)

An infrared gas analyzer for measuring a reference gas and a sample gas having different amounts of water vapor,
A switching valve for selectively supplying a reference gas and a sample gas to the sample cell;
It is arranged in the middle of gas introduction from the switching valve to the sample cell, can hold moisture in contact with the gas, is set at a constant temperature between the dew points of both gases, dehumidifies one gas and the other A common cooler that humidifies the gas and equalizes the water vapor of both gases ,
A light source for irradiating the sample cell with infrared light;
Intermittent means for interrupting infrared light from the light source;
A detector for detecting infrared light transmitted through the sample cell;
A controller that performs switching control of the switching valve and intermittent control of the intermittent means;
An infrared gas analyzer comprising: signal processing means for obtaining a measurement gas concentration in a sample gas based on detection values of the infrared light transmitted through the reference gas and the sample gas in the detector.   The controller supplies a reference gas or sample gas to the sample cell, and after the inside of the sample cell is completely replaced by the reference gas or sample gas, the sample cell is irradiated with infrared light from the light source. The infrared gas analyzer according to claim 1, wherein the infrared gas analyzer controls the intermittent means.   The said signal processing means performs the process which calculates | requires measurement gas concentration based on ratio of the detected value in the said detector of each infrared light which permeate | transmitted reference gas and sample gas. Infrared gas analyzer.

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