JP4042638B2 - 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. 9 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. 10, 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. Electronic coolers 18a and 18b using Peltier elements are provided to dehumidify the water.
[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. 10, the water vapor in the gas is removed by the electronic cooler, but due to the problem of freezing of the drain generated in the electronic cooler, the temperature of the electronic cooler is about 1 ° C. at the lowest. . 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 if 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 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 the same may be used. Nevertheless, it is difficult to make the temperature of the cooling block completely the same without temperature distribution.
[0011]
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.
Further, when water vapor is removed by an electronic cooler, water condensed from the gas comes into contact with the gas, so that there is a problem that water-soluble gas such as SO ₂ is absorbed by the condensed water and lost.
[0012]
The present invention has been made to solve the above-described problems, and aims to overcome errors and other problems caused by the cooling capacity of the electronic cooler.
[0013]
[Means for Solving the Problems]
The present invention provides a semipermeable membrane between a three-way solenoid valve for gas switching and a sample cell, instead of removing the water vapor in the reference gas and the sample gas using an electronic cooler, which is a pretreatment for gas analysis by infrared rays. We propose to reduce the water vapor concentration difference between the two gases by installing a water vapor exchange material.
[0014]
That is, the infrared gas analyzer of the present invention includes a switching valve that selectively supplies a reference gas and a sample gas to the sample cell, and a gas stream in the gas in contact with the switching valve that is installed in the middle of the introduction of the gas from the switching valve to the sample cell. A water vapor concentration adjusting means for adjusting the water vapor concentration of both gases by adsorbing and releasing the semipermeable membrane water vapor exchange material in accordance with its concentration, and allowing both the reference gas and the sample gas to pass through the semipermeable membrane water vapor exchange material 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 switching of the switching valve The measurement gas concentration in the sample gas is obtained based on the controller that performs control and the intermittent control of the intermittent means, and the detection values of the infrared light transmitted through the reference gas and the sample gas in the detector. And a signal processing unit.
[0015]
[Action]
The semipermeable membrane water vapor exchange material has a so-called humidity control function of taking water vapor in the gas into the material or conversely releasing water vapor into the gas depending on the water vapor concentration in the gas in contact therewith. Even when the water vapor concentrations in the reference gas and the sample gas are different, by alternately flowing the reference gas and the sample gas through the semipermeable membrane water exchange material, the water vapor concentrations in both gases that have passed through the semipermeable membrane water exchange material are equal. Therefore, the measurement error caused by the difference in water vapor concentration can be reduced.
In addition, when the water vapor concentration difference between the reference gas and the sample gas is large, it is less by using an electronic cooler and a semipermeable membrane water vapor exchange material together and providing a semipermeable membrane water vapor exchange material downstream of the electronic cooler. It is possible to reduce the measurement error caused by the difference in water vapor concentration with the amount of semipermeable membrane water vapor exchange material.
[0016]
DETAILED DESCRIPTION OF THE INVENTION
An embodiment of the present invention will be described below.
FIG. 1 is a flow chart of an infrared analyzer according to one embodiment, and the same reference numerals are used for the same parts as in FIG.
The sample cell 1 has a gas introduction port 1a and a gas discharge port 1b, and a sample gas or a reference gas is supplied from the introduction port 1a into the sample cell 1 through a three-way valve 7 which is a switching valve. Discharged.
[0017]
In this embodiment, in the flow path between the three-way valve 7 and the sample cell 1, a water vapor concentration adjusting means 10 containing a semipermeable membrane water vapor exchange material 11 having a function of adsorbing and releasing water vapor in the gas is installed, Both the sample gas and the reference gas supplied from the three-way valve 7 are led to the sample cell 1 via the water vapor concentration adjusting means 10.
[0018]
Since the water vapor concentration adjusting means 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. That is, in order to supply each of the sample gas and the reference gas, the pretreatment apparatus has filters 12a and 12b for removing dust, pumps 14a and 14b for sucking gas, and gas flow rates as shown in FIG. Only the needle valves 16a and 16b to be adjusted are included, and a cooler for dehumidifying the gas is omitted.
[0019]
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.
[0020]
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 s represents the end face 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.
[0021]
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.
The three-way valve 7 is switched by the controller 6 at a constant period of about 2 to 10 seconds, and the reference gas and the sample gas are alternately introduced into the sample cell 1. The detector 2 measures the infrared absorbance of the gas in the sample cell 1 when each gas replaces the sample cell 1.
[0022]
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, the detector output with the sample gas is corrected with the detector output with the reference gas, and the concentration is calculated from the absorbance.
[0023]
The semipermeable membrane water vapor exchange material 11 is a water retention material such as a water vapor exchange material in which a hydrophilic functional group such as a sulfone group is modified with respect to PTFE (polytetrafluoroethylene), polystyrene, or the like as a polymer of a base material. It is a substance that can be released and is made into small pieces of about several millimeters, an appropriate amount is put in a container, and is installed as a water vapor concentration adjusting means 10 between the flow path between the three-way valve 7 and the sample cell 1.
[0024]
The function of the semipermeable membrane water exchange material 11 will be described below.
Assuming that the water vapor concentration in the sample gas is higher than that of the reference gas, the inlet gas of the water vapor concentration adjusting means 10 when the sample gas and the reference gas are switched to each other at a long cycle and introduced into the semipermeable membrane water vapor exchange material 11 The time change of the water vapor concentration in the outlet gas is shown in FIGS. 4 (A) and 4 (B).
The semipermeable membrane water vapor exchange material 11 takes in and discharges water vapor and serves as a condenser for water vapor. For this reason, the inlet gas has a rectangular shape as shown in FIG. 4A due to gas switching, but the water vapor concentration in the outlet gas is rectangular as shown in FIG. It will start to change as if it has been lost.
[0025]
FIGS. 5A and 5B show a case where the switching cycle of introduction of the reference gas and the sample gas in FIG. 4 is shortened.
When the gas switching cycle is shortened, the water vapor concentration in the inlet gas is rectangular, but in the outlet gas, as shown in FIG. 5B, the change in the water vapor concentration in the outlet gas disappears, and the reference gas and the sample The water vapor concentration in the gas becomes equal.
[0026]
The capacity of the water vapor condenser is determined by the amount of the semipermeable membrane water vapor exchange material 11 to be used, and the capacity increases as the amount increases. Therefore, if the amount of the semipermeable membrane water vapor exchange material 11 is increased, the outlet gas can be increased even if the gas switching period is longer, the gas flow rate is increased, or the difference in the water vapor concentration between the reference gas and the sample gas is increased. The water vapor concentration difference in the inside can be made constant. Accordingly, the difference in water vapor concentration between the reference gas and the sample gas is determined by determining the amount of the semipermeable membrane water vapor exchange material 11 in consideration of the actually required switching period, flow rate, water vapor concentration difference between the reference gas and the sample gas, and the like. Can be the same.
[0027]
As described above, by using the semipermeable membrane water vapor exchange material 11 and making the difference in water vapor concentration of the reference gas and the sample gas the same, the measurement of SO ₂ or NO that is affected by water vapor is not affected by water vapor. Can be implemented.
The shape of the semipermeable membrane water exchange material 11 may be a tube shape that is generally available, or a shape obtained by cutting it short, and the shape is not particularly limited.
The semipermeable membrane water exchange material 11 can be used not only for an infrared gas analyzer but also for a gas analyzer based on the principle of being affected by water vapor.
[0028]
Also, when a large amount of semipermeable membrane water exchange material 11 is required, such as when the difference in water vapor concentration between the reference gas and the sample gas is large, an electronic cooler is provided upstream of the semipermeable membrane water vapor exchange material, and It is also possible to make the installation amount of the semipermeable membrane water vapor exchange material 11 small by reducing the difference in water vapor concentration. By doing so, the volume from the switching valve to the sample cell can be reduced, and the analyzer main body can be downsized.
[0029]
FIG. 6 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.
[0030]
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.
[0031]
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.
[0032]
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.
[0033]
FIG. 8 is a timing chart showing the opening / closing operation of the sector 3 when the controller 6 is operated as described above, and the filling state of the sample gas in the sample cell 1. In this figure, the inner diameter of the sample cell 1 8 mm, 50 mm length, internal volume 2.51Cm ^3, a gas flow rate of 1 l / min, an example in which switching the three-way valve 7 every 0.5 seconds shown 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.
[0034]
As shown in the lower diagram of FIG. 8, 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.
[0035]
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.
[0036]
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.
[0037]
【The invention's effect】
The infrared gas analyzer of the present invention, it was established a water vapor concentration adjusting means incorporating a semi-permeable membrane steam exchange material between the switching valve and the sample cell for switching the supply of the reference gas and the sample gas, water, such as SO ₂ It is possible to realize a gas analyzer with no loss of property gas and quick response.
In addition, when water vapor was removed by an electronic cooler in a situation where the operating environment temperature was high, there was a problem that the cooling capacity of the electronic cooler was insufficient and temperature control became impossible, but instead a semipermeable membrane water vapor exchange material was used. For example, measurement can be performed without being affected by the temperature of the use environment.
[0038]
When an electronic cooler is used, the error due to water vapor increases when the reference gas dries and the dew point is lower than the electronic cooler temperature. Even in such a dry reference gas, a semipermeable membrane water exchange material should be used. Thus, measurement errors due to the influence of water vapor can be reduced.
In addition, since the water vapor concentration adjusting means incorporating the semipermeable membrane water vapor exchange material does not require power supply and is small in size, it is possible to construct a gas analyzer that is smaller and less expensive than when an electronic cooler is used. it can.
[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 diagram for explaining the function of a semipermeable membrane water vapor exchange material when a long period is switched between a reference gas and a sample gas, (A) is a water vapor concentration in the gas at the inlet of the water vapor concentration adjusting means; B) is a graph showing the water vapor concentration in the gas at the outlet of the water vapor concentration adjusting means.
FIG. 5 is a diagram for explaining the function of the semipermeable membrane water vapor exchange material when switching between the reference gas and the sample gas in a short period, (A) is the water vapor concentration in the gas at the inlet of the water vapor concentration adjusting means; B) is a graph showing the water vapor concentration in the gas at the outlet of the water vapor concentration adjusting means.
FIG. 6 is a circuit diagram showing a signal processing circuit in the same example;
FIG. 7 is a flowchart showing the operation of the embodiment.
FIG. 8 is a timing chart showing the operation of the embodiment.
FIG. 9 is a flow chart showing a conventional infrared analyzer.
FIG. 10 is a flow chart showing a pretreatment device for gas supplied in the conventional example.
[Explanation of symbols]
DESCRIPTION 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 Water vapor concentration control means 11 Semipermeable membrane water vapor exchange material

Claims (4)

A switching valve for selectively supplying a reference gas and a sample gas to the sample cell;
A semipermeable membrane water vapor exchange material is provided in the flow path through which gas is introduced from the switching valve to the sample cell, and adsorbs and releases the water vapor in the gas in contact with its concentration. Both the reference gas and the sample gas are contained in the semipermeable membrane. Water vapor concentration adjusting means for adjusting the water vapor concentration of both gases by passing through the membrane water vapor exchange material;
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, and a measurement gas concentration in the sample gas based on a detection value in the detector of each infrared light transmitted through the reference gas and the sample gas An infrared gas analyzer comprising: a signal processing means to be obtained. In the flow path provided with the water vapor concentration adjusting means,
The infrared gas analyzer according to claim 1, wherein an electronic cooler is provided upstream of the water vapor concentration adjusting means.   The controller supplies a reference gas or sample gas to the sample cell, and after the inside of the sample cell is completely replaced with 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 or 2, which controls the intermittent means.   4. The signal processing unit according to claim 1, wherein the signal processing unit performs a process of obtaining a measurement gas concentration based on a ratio of detection values of the infrared light transmitted through the reference gas and the sample gas in the detector. An infrared gas analyzer as described in 1.

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