JPH11153544A - Gas analyzer - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a luminous type gas analyzer which simultaneously measure a substituted gas to be measured, and an unsubstituted gas obtained by displacing the nitrogen dioxides (NO2 ) of the gas to be measured with nitrogen oxides (NO), and makes the calibration of a detector unnecessary. SOLUTION: A gas to be measured in a first passage 2a which passes a converter 3 is led into a first reaction tank 4a, and a gas to be measured in a second passage 2b which does not pass the converter 3 is led into a second reaction tank 4b. Lights emitted by reaction with ozone (O3 ) in individual reaction tanks 4a, 4b are collected into a detector 8 by a condensing lens 5. Luminous intensities from individual reaction tanks 4a, 4b are inputted interchangeably by an optical chopper 6 put between the detector 8 and both reaction tanks 4a, 4b, and a nitrogen dioxide (NO2 ) concentration is found from the difference between both luminous intensities.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a chemiluminescent gas analyzer for measuring the concentration of nitrogen oxides contained in flue gas from a boiler, exhaust gas from a motor vehicle and the like.

[0002]

Although BACKGROUND ART Plant harmful nitrogen oxides to the human body caused by such combustion in combustion and in automotive engine in the combustion furnace (NO _X) becomes a problem, NOx in the atmosphere or exhaust gas One of the devices for measuring the concentration of substances is a chemiluminescent gas analyzer. In this method, a gas to be measured (sample, exhaust gas, etc. collected from the atmosphere) and an ozone (O ₃ ) gas are brought into contact with each other in a reaction tank of a measuring device. The amount of nitric oxide in the gas to be measured is quantitatively measured by detecting light generated when the light is generated by a photodetector.

In this gas analyzer, ammonia (NH
Concentration measurement can also be performed on ₃ ) and nitrogen dioxide (NO ₂ ) by previously converting them into nitric oxide in another reaction tank.

FIGS. 2 and 3 are schematic views showing the vicinity of a reaction section of a conventional chemiluminescence type gas analyzer. In FIG. 2, the gas to be measured collected by the pump 1 from the sample inlet is divided into two flow paths 2a and 2b. In one of the flow paths 2a, the gas to be measured is irradiated with ultraviolet rays in the converter 3 to perform photolysis. Nitrogen dioxide (NO ₂ ) in the gas component to be measured is converted into nitric oxide (NO) and supplied to the first reaction tank 4a. In the other flow path 2b, it is supplied to the second reaction tank 4b as it is. Ozone gas is supplied to each of the first and second reaction tanks 4a and 4b, and a chemical reaction between nitrogen monoxide (NO) and ozone in the measurement gas occurs. Then, the amount of light emitted by the chemical reaction in each of the reaction tanks 4a and 4b is measured by the first detector 8a and the second detector 8b, respectively.

[0005] Here, nitrogen dioxide (NO
₂ ) does not react with ozone and only nitric oxide (NO) reacts with ozone, so that the first detector 4a and the second detector 4
b, the nitrogen dioxide (NO
₂ ) The concentration is measured.

FIG. 3 shows another conventional example. What is different from FIG. 2 is that the reaction tank 4 for performing the reaction with ozone and the detector 8 for measuring the amount of luminescence generated by the reaction are each measured by one. In the apparatus shown in FIG. 3, the flow path of the gas to be measured collected from the sample inlet by the pump 1 is a flow path 2a having the converter 3 and a flow path 2b not passing through the converter 3.
These flow paths 2 a and 2 b are connected to a three-way cock 9 before entering the reaction tank 4. First, the three-way cock 9 is set so that the gas to be measured that has passed through the converter 3 in the flow path 2a is introduced into the reaction tank 4, and the amount of luminescence generated in the reaction tank 4 is measured by the detector 8, and then the flow path is measured. The three-way cock 9 is switched so that the gas to be measured that does not pass through the converter 3 of 2b is introduced into the reaction tank 4, and the amount of light emitted in the reaction tank 4 is detected by the detector 8.
Measure with As a result, the concentration of nitrogen dioxide (NO ₂ ) in the gas to be measured is measured from the difference between the two measured values.

[0007]

The conventional chemiluminescence type gas analyzer is constructed as described above. However, as shown in FIG. 2, two reaction tanks 4a and 4b in the first and second reaction tanks 4a and 4b are used. In a gas analyzer using a tank and installing the first and second detectors 8a and 8b in correspondence with each other, these two detectors 8a and 8b are used.
It is assumed that the detection characteristics of b completely match, but it is difficult to match the characteristics of the detectors. Therefore, there is a problem that a troublesome operation of calibrating the detection characteristics so that the detection characteristics of the two detectors 8a and 8b match is required. Furthermore, even if the calibration is performed, the first and second detectors 8a, 8b
If the respective detection characteristics fluctuate independently, there is a problem that the measurement accuracy of nitrogen dioxide (NO ₂ ) is greatly adversely affected.

Although the above-mentioned problem does not occur in a gas analyzer having one reaction vessel 4 and one detector 8 as shown in FIG. 3, the converter 3 is connected to the reaction vessel 4 by switching the three-way cock 9. After the measurement is performed by introducing the gas to be measured from the flow path 2a that has passed, the measurement is performed by introducing the gas to be measured from the flow path 2b that does not pass through the converter 3 to the reaction tank 4. It takes about ten seconds for the measured gas to be completely replaced. Therefore, the sample gas nitrogen dioxide (N
O ₂₎ If the concentration is changing temporally, the converter 3
There is a time difference between the measured value of the gas to be measured passing through the converter and the measured value of the gas to be measured not passing through the converter 3, causing a problem that an error occurs in the measured value.

The present invention has been made in view of such circumstances, and eliminates the need for the operation of calibrating the detection characteristics of a detector and accurately measures the time-varying concentration of nitrogen dioxide (NO ₂ ). It is an object of the present invention to provide a gas analyzer which can be used.

[0010]

In order to achieve the above object, a gas analyzer according to the present invention comprises: an optical path focusing means for focusing light emitted by a first reaction tank and light emitted by a second reaction tank; And light intermittent means for intermittently emitting light from the second reaction tank and alternately introducing the light into the detector.

[0011]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS One embodiment of a chemiluminescent gas analyzer according to the present invention will be described with reference to FIG. FIG. 1 is a schematic view of the vicinity of a reaction section of a chemiluminescence type gas analyzer. Reference numeral 1 denotes a pump, the output side of which is branched into a first flow path 2a and a second flow path 2b. A converter 3 is connected to the first flow path 2a,
Converter 3 is connected to first reaction tank 4a. One second flow path 2b is directly connected to the second reaction tank 4b. The first reaction tank 4a and the second reaction tank 4b have an ozone gas inlet and a gas outlet, respectively, in addition to the above-mentioned measured gas inflow connection port.

A first light beam 7a emitted from the first reaction tank 4a and a second light beam emitted from the second reaction tank 4b are provided between the two reaction tanks 4a and 4b and the detector 8 as light receiving portions for light emitted from the reaction tank. A condenser lens 5 for converging the light beam 7b,
A light chopper 6 for passing the lights a and 7b alternately is provided.

Next, the operation for measuring the concentration of nitrogen dioxide (NO ₂ ) will be described. Pump 1 from sample gas inlet
The gas to be measured sucked in is branched into one flowing into the first flow path 2a and one flowing into the second flow path 2b. First channel 2a
Is flowing through the converter 3, where nitrogen dioxide (NO ₂ ) in the gas to be measured is converted into nitrogen monoxide (N
O) and is introduced into the first reaction tank 4a. The gas to be measured flowing through one second flow path 2b is directly introduced into the second reaction tank 4b.

Ozone gas (O ₃ ) is supplied to each of the reaction tanks 4a and 4b, and chemiluminescence is caused by a chemical reaction between nitrogen monoxide (NO) and ozone in the gas to be measured introduced into each of the reaction tanks. Occurs. These emitted lights are incident on the detector 8 by the condenser lens 5 as the first light flux 7a and the second light flux 7b. An optical chopper 6 is provided between the two reaction vessels 4a and 4b and the detector 8, and the light of the first light beam 7a and the light of the second light beam 7b is
At the timing determined by the rotation speed of the laser beam and the size of the opening of the sector, the light enters the detector 8 and the output signal of the detector 8 alternately emits the light emission intensity I1 from the reaction tank 4a and the light emission from the reaction tank 4b at a fixed time width. The intensity I2 is shown. These signals are discriminated by using a synchronizing signal synchronized with the rotation of the optical chopper 6, and the cycle time can be sufficiently fast within the limits of the time constant and sensitivity of the detector. Good. The intensity I1 represents the sum of the amounts of nitrogen dioxide (NO ₂ ) and nitric oxide (NO) in the gas to be measured, and I2 represents the amount of nitric oxide (NO) in the gas to be measured. Nitrogen dioxide (NO ₂ ) concentration Y is represented by Y = F, where F is a calibration curve function.
It is obtained as (I1-I2).

By performing the measurement using the two reaction tanks 4a and 4b and the single detector 8, it is possible to eliminate the gas replacement time and the calibration of the detector.

In the above embodiment, the condenser lens 5 is used as the optical path focusing means. However, due to the limited space between the reaction tanks 4a and 4b and the detector 8, the optical path can be focused by a prism or a Fresnel lens. When the distance between the tanks 4a and 4b and the detector 8 is large, the reaction tank 4 is separately provided for focusing the optical path.
By installing lenses in the first light flux 7a and the second light flux 7b that make the detectors 8a and 4b conjugate, weak light can be efficiently condensed on the detector 8.

Further, in the above-described embodiment, the optical chopper 6 of the type in which the sector is rotated is used as the optical intermittent means, but it may be of the type in which the light shielding plate is reciprocated in a sliding manner due to space limitations.

Although the optical chopper is provided behind the condenser lens in the above embodiment, the same effect can be obtained by providing an optical chopper before the condenser lens.

[0019]

The gas analyzer according to the present invention is constructed as described above. The gas analyzer for the reaction of the gas to be measured in which nitrogen dioxide (NO ₂ ) is replaced by nitrogen monoxide (NO) is used in the reaction tank. Since they are arranged separately for the reaction of the gas to be measured which is not performed, both can be measured at the same time, and the measurement accuracy can be improved.

Further, since one detector can be used in spite of two reactors, the work of calibrating the detection characteristics between the detectors is unnecessary as compared with the system in which two detectors are arranged. At the same time, the problem of the detection characteristic fluctuation disappears, whereby the measurement accuracy can be improved.

[Brief description of the drawings]

FIG. 1 is a diagram showing one embodiment of a gas analyzer of the present invention.

FIG. 2 is a diagram showing a conventional gas analyzer.

FIG. 3 is a diagram showing another conventional gas analyzer.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 ... Pump 2a ... First flow path 2b ... Second flow path 3 ... Converter 4 ... Reaction tank 4a ... First reaction tank 4b ... Second reaction tank 5 ... Condensing lens 6 ... Optical chopper 7 ... Light flux 7a First light flux 7b Second light flux 8 Detector 8a First detector 8b Second detector 9 Three-way cock

Claims (1)

[Claims] 1. A first reaction tank for reacting ozone with a gas to be measured supplied through a first channel having a converter for converting nitrogen dioxide to nitric oxide, and a second channel having no converter. A second reaction tank for causing ozone to react with the gas to be measured supplied in the above manner, and the amount of luminescence generated in these reaction tanks due to the reaction with ozone is measured by a detector, and the measured value from the first reaction tank is measured. In a chemiluminescence gas analyzer that measures the concentration of nitrogen dioxide from the difference between the measured value from the second reaction tank and the light path focusing means for focusing the light emission by the first reaction tank and the light emission by the second reaction tank, A gas analyzer comprising: light intermittent means for intermittently emitting light from a first reaction tank and a second reaction tank and introducing the light to a detector alternately.