JP2002148192A - Chemiluminescence type nitrogen oxide concentration meter - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a chemiluminescence type nitrogen oxide concentration meter capable of preventing dew condensation of water in sample gas on a glass window surface interposed between a reaction vessel and a detecting part. SOLUTION: A semiconductor photoelectric converting element 41 for converting the intensity of chemiluminescence light to an electric signal is mounted through a metallic cooling bed 43 on the cooling side of an electronic cooling element 42 utilizing a Peltier effect, the radiation side of the electronic cooling element 42 is closely fixed onto a metallic detector base 44 of the electronic cooling element 42, and the reaction vessel 3 where sample gas and O3 are inserted is integrally connected to the upper part of a detector cap 45 including the glass window W connected to the detector base 44. The glass window W is formed by a double-glass window where two glass sheets W1, W2 are arranged in parallel through a spacer S.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION The present invention relates to a nitrogen oxide (N) contained in flue gas from a boiler or exhaust gas from an automobile.
O _X) chemiluminescent nitrogen oxide concentration meter which measured using chemiluminescence by reaction concentration nitric oxide (NO) and ozone (O ₃₎ of about.

[0002]

BACKGROUND ART Although harmful NO _X to the human body caused by such combustion in plants boilers and combustion and in automotive engines in incinerators is a problem to measure the concentration of nitrogen oxides in the atmosphere and the exhaust gas one of the device, chemiluminescent nitrogen oxide concentration meter by chemiluminescence method (hereinafter, referred to as NO _X meter) is. This is caused by bringing a sample gas (a sample gas collected from the atmosphere or exhaust gas or the like) into contact with O ₃ in a reaction tank in a measuring device, and causing a chemical (gas phase) reaction between NO and O ₃ in the sample gas. Using the fact that the chemiluminescence intensity is proportional to the NO concentration, the concentration of NO in the sample gas is measured by detecting the chemiluminescence intensity with a photoelectric detector.

In this case, the chemiluminescence intensity is detected by using a silicon photodiode or the like. The semiconductor photoelectric conversion element has a low ambient humidity and can obtain high sensitivity in a low temperature state, and the drift of the amplifier (substrate) is reduced by cooling. For this reason, a metal or resin detector cap with a light transmission window and a metal detector base are used to hermetically shield the semiconductor photoelectric conversion element, metal cooling stand, electronic cooling element, amplifier, etc. And cooling the electronic cooling element by contacting and arranging the semiconductor photoelectric conversion element via a metal cooling stand on the cooling side of the electronic cooling element,
The heat radiation side of the element is disposed in contact with a metal detector base to radiate heat.

The light receiving section of the semiconductor photoelectric conversion element as a sensor of the detecting section having a closed structure cooled from the inside is a glass window made of a single glass plate, and the outside of the glass window is a sample gas. And O ₃ are introduced and are in contact with a reaction tank in which both gases are contact mixed.

It should be noted that N contained in exhaust gas and ambient air
O_XIs mainly NO₂And NO, but NO₂Is O₃With
Since there is no chemiluminescence reaction, measurement with chemiluminescence
Can not be determined. So, NO_XIn total, NO₂Measure concentration
Introduce the sample gas into the reaction tank of the detection unit so that it can
Interposed a converter equipped with a catalyst in the sample gas introduction channel
Let NO₂And NO coexist in exhaust gas and ambient air
NO in sample gas is passed through converter₂To N
It is reduced to O and measured by a chemiluminescence method. here
And the measured value obtained through the converter is NO₂And N
NO combined with O _X(= NO + NO₂) For concentration,
NO by subtracting NO concentration when not passing through converter
₂Find the concentration.

[0006]

[SUMMARY OF THE INVENTION However, in the NO _X equipped with a detection unit of the sealed structure in which sensor is cooled by the electronic cooling element, the following problems. That is, the outside of the glass window is in contact with a reaction tank for causing a chemical reaction by contacting and mixing the sample gas and O _{3. In} order to increase the efficiency of detecting the chemiluminescence intensity in the reaction tank, a sensor is used. Because it is located close to the glass window, the glass window is cooled by an electronic cooling element that cools the sensor and is 10 ° C. below ambient temperature.
It is about low temperature.

Therefore, when the sample gas is introduced into the reaction tank, the moisture in the sample gas cools and condenses on the surface of the glass window at a low temperature. Impurities contained in air (air) introduced into an ozone generator that generates O ₃ by electric discharge and the like, as well as crystals generated by a chemical reaction between the sample gas and O _{3 in} the reaction tank, etc., are deposited on the surface of the glass window. It becomes easy to adhere. As described above, if impurities and the like adhere to the glass window interposed between the reaction tank and the detection unit and become contaminated, the light transmittance decreases, which causes a reduction in detection sensitivity, and as a result, measurement of the gas concentration becomes unstable. Or disable.

In view of the above, it is an object of the present invention to provide a chemiluminescent nitrogen oxide concentration meter in which water in a sample gas does not condense on the surface of a glass window interposed between a reaction tank and a detection unit. And

[0009]

In order to solve the above-mentioned problems, a chemiluminescent nitrogen oxide concentration meter according to the present invention comprises a detecting section for accommodating a photoelectric sensor cooled by an electronic cooling element.
It is characterized in that the glass window in contact with the reaction tank into which the sample gas containing nitric oxide and the ozone gas are introduced is a double glass window.

Specifically, a glass tank is used to measure the intensity of the chemiluminescence produced by the chemical reaction between nitric oxide and ozone in the reaction vessel into which a sample gas containing nitric oxide and ozone gas are introduced. A chemiluminescent nitrogen oxide densitometer comprising a photoelectric sensor and an electronic cooling element for cooling the photoelectric sensor, wherein the glass window has two gaps. Characterized in that it is a double glass window in which glass plates are arranged in parallel. Note that the photoelectric sensor is preferably a semiconductor photoelectric conversion element such as a silicon semiconductor.

As described above, with the configuration in which the glass window in contact with the reaction tank of the detection unit interposed between the reaction tank and the detection unit is a double glass window, the glass plate of the glass window on the detection unit cools the sensor. Although it is cooled to a low temperature by the electronic cooling element, the glass plate of the glass window on the reaction tank side faces with a gap. The heat of the glass plate of the glass window cooled to the temperature is shut off, and the glass plate of the glass window on the reaction tank side is not cooled. Thereby, even if the sample gas introduced into the reaction tank comes into contact with the glass window plate, it is possible to prevent the moisture in the sample gas from condensing on the surface of the glass window.

Therefore, the glass window becomes fogged,
Impurities contained in the sample gas and air introduced into the ozone generator that generates O ₃ , as well as crystals generated by the chemical reaction between the sample gas and O ₃ , do not stain the glass window due to adhesion. Can maintain high sensitivity over
Stable measurement can be performed. If the photoelectric sensor is a semiconductor photoelectric conversion element, the detection unit can be made compact.

[0013]

DETAILED DESCRIPTION OF THE INVENTION Hereinafter, will be described with reference to the drawings NO _X analyzer of the present invention, a schematic configuration of the present invention embodiment apparatus shown in Fig. In FIG. 1, a gas introduction unit 1 for introducing a sample gas, a reaction tank 3 and a photoelectric detector 4
The flow path 2 is connected to the detection unit 5 to which is coupled. A pre-processing unit 6 including an electronic cooler and a filter, a converter 7 for converting NO ₂ to NO, and a flow meter 8 are connected to the flow path line 2. Further, a switching cock 9 is provided at an inlet of the converter 7, and a bypass passage 10 which leads to an outlet of the converter 7 without passing through the converter 7 is connected to the switching cock 9 by piping.

An O ₃ gas supply line 12 connected to an ozone generator 11 for generating O ₃ by silent discharge or the like is connected to the reaction tank 3 by piping. Reference numeral 13 denotes an indicator for indicating the NO gas concentration obtained by processing the chemiluminescence intensity measured by the photoelectric detector 4 of the detection unit 5 by an arithmetic processing unit (not shown), and 14 denotes an unreacted gas in the exhaust gas. Is an ozone killer (ozone decomposer) of a thermal decomposition type or the like that decomposes excess O ₃ .

[0015] In the apparatus having such a configuration, the sample gas NO ₂ gas and NO gas introduced through the gas inlet 1 coexist, the NO ₂ to NO through _NO 2 -NO converter 7 the reduction catalyst is provided Convert to N in the gas
The O concentration is detected by the detection unit 5 and the sample gas is
The NO concentration in the gas can be detected by the detection unit 5 without passing through the O ₂ -NO converter 7, and the NO ₂ gas concentration can be calculated from the difference between the NO gas concentrations.

FIG. 2 shows the structure of the detection unit 5 in which the reaction tank 3 and the photoelectric detector 4 are combined. In the figure, a photoelectric detector 4 is a semiconductor photoelectric conversion element 4 composed of a silicon semiconductor or the like and converting the intensity of chemiluminescent light into an electric signal.
1 is attached to the cooling side of the electronic cooling element 42 utilizing the Peltier effect via a metal cooling stand 43,
The heat radiation side of No. 2 is tightly fixed on a detector base 44 made of metal.

The detector cap 45 is made of a heat-insulating polymer resin, and is provided at a position facing the semiconductor photoelectric conversion element 41 by a chemical reaction between NO and O ₃ in the sample gas in the reaction tank 3. A glass window W for transmitting emitted light is provided, and a metal plate 46 is attached on the inside,
The detector base 44 is hermetically fastened to the detector base 44 via an O-ring by screws.
4 and a lead wire (not shown). The resin detector cap 45 and the metal detector base 4
4, the semiconductor photoelectric conversion element 41, the electronic cooling element 4
2. The metal cooling stand 43, the amplifier board 47 and the like are hermetically shielded.

The glass window W formed in the detector cap 45 has two glass plates W1 and W as shown in FIG.
2 are arranged in parallel via a spacer S, and both glass plates W
1, a double-glazed window having an air layer formed between W2 and a heat insulating layer, which is hermetically attached to the flange of the opening of the cap 45. In the embodiment, the thickness of the glass plate W1 on the semiconductor photoelectric conversion element 41 side is smaller than the thickness of the glass plate W2 on the outer side (reaction tank 3 side).

The reaction tank 3 is connected to the upper portion of the detector cap 45 by screwing. As shown in FIG. 2, the reaction tank 3 is provided with a capillary 32 for introducing a sample gas and an O ₃ gas introduction passage 33 in a reaction chamber 31 therein. An exhaust path 34 for discharging the gas is formed. In addition, in the reaction tank 3,
Temperature control means such as a heater for causing NO and O ₃ in the sample gas to react at a constant temperature in the reaction chamber 31 may be provided. Further, NO and O ₃ in the sample gas chemically react at the upper part of the glass window W of the detector cap 45, and the chemiluminescent light caused by the chemical reaction passes through the glass window W, and its intensity is reduced by the semiconductor photoelectric conversion element 41. Is detected.

As described above, since the glass window of the detection unit 5 is a double glass window, even if the temperature of the glass plate W1 on the side of the semiconductor photoelectric conversion element 41 is cooled by the electronic cooling element 42 and the temperature thereof becomes low, the reaction tank is cooled. The glass plate W2 on the third side is blocked from heat due to the heat insulating effect of the air layer interposed between the two glasses, and it is difficult for the heat of the glass plate W1 to reach the glass plate W2 on the reaction tank 3 side.

Therefore, the glass plate W2 on the reaction tank 3 side
Can be maintained at a constant temperature above the dew point without being cooled to a low temperature below the dew point of water. Even if the sample gas supplied into the reaction tank 3 comes into contact with the glass plate W2, Moisture in the gas does not condense on the surface of the glass window W.
As a result, the glass window does not become cloudy, the sample gas and air introduced into the ozone generator that generates O ₃ , impurities contained in the sample gas, and crystals formed by a chemical reaction between the sample gas and O ₃ , etc. Since the glass window does not become dirty due to the adhesion, high sensitivity can be maintained for a long time, and stable measurement can be performed.

In the above-described embodiment, the glass plates W1 and W2 constituting the double glass window are opposed to each other via the air layer. By enclosing a highly effective gas, the heat insulation effect can be further enhanced.

In the embodiment, the capillary for supplying the sample gas provided in the reaction tank and both outlet openings of the O ₃ introduction path are horizontally opposed in the reaction chamber. The outside is a double tube (double capillary) for introducing O ₃ gas, or a capillary for introducing sample gas and O ₃
The introduction path is arranged obliquely in the reaction chamber, and the sample gas and the O ₃ gas flow supplied from the capillary flow through the semiconductor photoelectric conversion element 4.
It may be made to cross on the light receiving surface of one. further,
In the embodiment, the semiconductor photoelectric conversion element is used as a sensor for detecting the chemiluminescence intensity in the reaction tank. However, the sensor may be a photomultiplier tube. Even when a photomultiplier tube is used, the detection sensitivity can be improved by cooling to 0 ° C. or less.

[0024]

According to the chemiluminescent nitrogen oxide concentration meter of the present invention, since the glass window interposed between the photoelectric detector of the detecting section and the reaction tank is a double glass window, the glass window cools the sensor. Even if the glass plate of the glass window on the sensor side is cooled to a low temperature by the electronic cooling element, the heat is insulated and cut off and is not transmitted to the glass plate of the glass window on the reaction tank side. Of the sample gas supplied to the glass window can be prevented from forming on the glass window.

As a result, air introduced into the ozone generator for generating O ₃ , impurities contained in the sample gas, and crystals formed by a chemical reaction between the sample gas and O ₃ adhere to the glass window. Since there is no contamination, high sensitivity can be maintained for a long time, and stable measurement can be performed.

[Brief description of the drawings]

FIG. 1 is a block diagram showing a schematic configuration of an apparatus according to an embodiment of the present invention.

FIG. 2 is a vertical cross-sectional view of a detection unit in FIG.

FIG. 3 is an enlarged vertical sectional view showing a schematic configuration of a main part of FIG. 2;

[Explanation of symbols]

3: Reaction vessel 31: reaction chamber 32: sample gas introducing capillary 33 ... _{O 3} gas introducing passage 34 ... exhaust passage 4: photoelectric detector 41 ... semiconductor photoelectric conversion element (photoelectric sensor) 42 ... electronic cooling device 43 ... metal Cooling stand 44 Detector base 45 Detector cap 46 Metal plate 47 Amplifier board W: glass window W1, W2 glass plate S spacer

Claims (2)

[Claims] 1. A nitrogen oxide concentration detected by a photoelectric sensor cooled by an electronic cooling element of a detection unit, the intensity of chemiluminescence generated by a chemical reaction between nitrogen oxide and ozone in a sample gas in a reaction tank. Is a chemiluminescent nitrogen oxide concentration meter for measuring a glass window interposed between the reaction tank and the detection unit,
A chemiluminescent nitrogen oxide densitometer characterized by being a double glass window in which two glass plates are arranged with a gap. 2. The chemiluminescent nitrogen oxide densitometer according to claim 1, wherein the sensor is a semiconductor photoelectric conversion element.