JPH032844Y2 - - Google Patents

Description

[Detailed explanation of the invention] (a) Industrial application field This invention relates to a chemiluminescent analyzer that measures and analyzes NOx in the atmosphere and exhaust gas.

(b) Prior Art A chemiluminescent analyzer measures the light energy emitted by reacting NO and O ₃ . This light energy is proportional to the mass flow rate of NO, so in conventional chemiluminescence analyzers, the amount of light due to chemiluminescence is detected while always collecting a predetermined flow rate of sample gas.
I have been trying to calculate the NOx concentration. Therefore, the analytical accuracy of the analyzer depends on the ability of the control mechanism to manage the sample gas sampling flow rate to a predetermined value.

Further, in the conventional chemiluminescence analyzer, there are the following problems that need to be solved. In other words, (1) Flow controllers, pressure reducing valves, back pressure valves, etc. are used to control the flow rate, but since the sample gas flow rate is easily affected by disturbances such as foreign substances in the gas, it is always controlled at a constant flow rate (e.g.
500±5ml/min) is technically not easy to collect while controlling the flow rate.

(2) Conventional control mechanisms used for constant control of the sample gas flow rate usually have a pressure loss of 0.5 to 1.0 Kg/cm ³ , so the sample gas is pressurized;
Moisture may be generated in the sample gas due to this pressurization.

(c) Purpose of the invention This invention was made in view of these circumstances, and one of its main purposes is to enable highly accurate measurement without the need for a control mechanism to control the sample gas flow rate to a constant amount. The purpose of the present invention is to provide a chemiluminescence analyzer.

(d) Structure of the idea The configuration of this invention will be explained using FIG. 1.

101 is a reaction tank for causing chemiluminescence by reacting nitrogen monoxide NO and ozone _O3 ; 102 is a sample gas supply means for supplying a gas containing nitrogen oxide to the reaction tank 101; and 103 is for supplying ozone gas to the reaction tank 101. Ozone gas supply means 104 is a flow rate measurement means 1 that measures the flow rate of the sample gas supply means 102 and outputs a first signal e1 proportional to the flow rate.
05 is a light amount detection means for detecting the amount of chemiluminescence in the reaction tank 101 and outputting a second signal e2 proportional to the amount of light, and 106 is a means for calculating and outputting the ratio e2/e1 of the second signal e2 to the first signal e1. This is a calculation means that outputs e3.

In such a configuration, if the nitrogen monoxide concentration of the sample gas supplied from the sample gas supply means 102 is [C] (ppm) and the flow rate is Q (ml/min), the output e1 of the flow rate measuring means is equal to the flow rate Q. Since it is proportional to, it is expressed as e1=K ₁・Q...(1) (where K ₁ is a constant of proportionality). In addition, in the reaction tank 101, the well-known reaction formula is NO + O ₃ → NO ₂ ^* + O ₂ ... (A) NO ₂ ^* → NO ₂ + hν ... (B) (However ^, NO _{2 2} , h is Planck's constant, ν is the frequency of the emission energy), NO and O ₃ react, and the emission energy hν
emit. Therefore, the output e of the light amount detection means 105
2 is proportional to the amount of NO present in the reaction tank 101, so it is expressed as e2=K ₂ ·[C] ·Q (2). By the way, the output e of the calculation means 106
3 is e3=e2/e1...(3), so equation (3) is calculated from equations (1) and (2), and e3=K ₂・[C]・Q/K ₁・Q = K ₂ /K ₁ ·[C] ...(4) Therefore, an output e3 proportional to the concentration [C] can be obtained regardless of the gas flow rate Q. Furthermore, it is well known that at this time, as long as the ozone gas has a concentration of a certain amount (rich condition) or more, it will not participate in the reactions of formulas (A) and (B) even if the flow rate changes.

In this manner, this invention provides a chemiluminescent analyzer that does not require control to constantly maintain the gas flow rate at a constant value by detecting the sample gas flow rate.

Note that it is preferable to use a hot wire flowmeter using a thermocouple, a thermistor, or the like as the flow rate measuring means 104. Further, as the calculation means 106, an analog calculation circuit or a digital calculation circuit configured with an integrated circuit can be used. The output e3 may be displayed by an analog or digital meter, or may be a control input to a recorder or the like.

(e) Examples This invention will be described in detail below based on examples shown in the drawings. Note that this invention is not limited to this.

In Figure 2, 1 is a sample gas inlet, 2 is a filter that removes dust in the sample gas, 3 is a calibration gas inlet, 4 is a switching solenoid valve that switches between sample gas and calibration gas, and 5 is for "NO measurement" mode. Flow path, 6 is a converter that converts NO ₂ to NO in "NOx measurement" mode, 7 is a "NO measurement" and "NOx measurement" mode.
A mode switching solenoid valve for switching between "measurement" and a pump 8 constitute a sample gas supply means A. 9 is a hot wire flow meter that measures the flow rate of the sample gas and outputs a voltage E1 proportional to the flow rate;
A reaction tank for NO and O ₃ , 11 is an exhaust port for discharging the sample gas after the reaction. 12 is an air inlet for ozone generation, 13 is a pump, 14 is a cooler passage for cooling the air and removing moisture from the air, 15
1 is a flow meter with a needle valve, and 16 is an ozone generator that generates O ₃ by performing silent discharge in the air, and these constitute ozone gas supply means B. 17 is a photomultiplier tube that detects the amount of chemiluminescence in the reaction tank 10; 18 is a light shielding plate that periodically blocks the light that the photomultiplier tube 17 receives from the reaction tank 10; and 19 is a motor that rotates the light shielding plate 18. , 23 is an optical filter for the photomultiplier tube 17, 20 is an amplifier that amplifies the output of the photomultiplier tube and outputs a voltage E2, 21
is an arithmetic unit that calculates the ratio E2/E1 of the voltage E2 to E1 and outputs the voltage E3; 22 is an arithmetic unit 21;
This is a recorder that records the output of

Next, the operation of this configuration will be explained. The sample gas is introduced from the sample gas inlet 1 by the pump 8, and after dust of approximately 5 micrometers or more is removed by the filter 2, it is converted to "NO" or "NOx".
The measurement mode is switched to one of the measurement modes by the mode switching solenoid valve, and the measurement mode is supplied to the reaction tank 10 via the hot wire flow meter 9. At this time, the hot wire flow meter 9 outputs a voltage E1 proportional to the flow rate.

On the other hand, air introduced from the air inlet 12 by the pump 13 is cooled down to 5°C or less in the cooler passage 14 and dehumidified, and is measured at 0.8% by flow meter with a needle valve.
The flow rate is adjusted to about min and then supplied to the ozone generator 16. The ozone generator 16 generates ozone in an amount of about 1% of the supplied air, and the ozone is introduced into the reaction tank 10. In the reaction tank 10, NO in the sample gas reacts with O ₃ to emit light, and the wavelength of the light has a spectrum (0.6 to 3 micrometers) specific to NO, so it is a photoelectron increaser that can measure relatively long wavelengths. It is detected by the multiplier tube 17. The intensity of the light is
Since it is proportional to the mass flow rate of NO, the photomultiplier tube 1
7 outputs a signal proportional to NO concentration. In addition to NO and O ₃ , the light emitted in the reaction tank also contains O 3 and O ₃ .
Since it contains light emitted by coexisting components contained in the sample gas such as C ₂ H ₄ and sulfur compounds, an optical filter 2 is used to remove this unnecessary light.
3 will be installed. In addition, since the light generated by the reaction between NO and O ₃ is weak light, in order to improve its stability, the light entering the photomultiplier tube 17 is made into an intermittent light by a light shielding plate 18 and the output signal of the photomultiplier tube 17 is is used as an AC signal.

The output signal of the photomultiplier tube 17 is amplified to a voltage E2 by an amplifier 20, and is input to a computing unit 21 together with the output voltage E1 of the hot wire flowmeter 9. Arithmetic unit 2
1 calculates E2/E1 and outputs a voltage E3, and the voltage E3 is recorded on the recorder 22. By the way, in FIG. 2, even if the flow rate of the sample gas introduced by the pump 8 fluctuates, the flow rate is not changed by the hot wire flowmeter 9.
At the same time, in the reaction tank 17, the intensity of light proportional to the NO mass flow rate is measured and detected as a voltage E2, and the ratio E2/E1 is calculated to determine the voltage. Since it is output as E3, the NO concentration can be detected by the above-mentioned equation (4) regardless of the sample gas flow rate.

FIG. 3 shows an example of recording of each output voltage and detected concentration during a performance test of this embodiment. That is, these are the measurement results when two types of standard gases containing 100 ppm NO and 200 ppm NO were introduced as sample gases while switching between them.

100 ppm NO gas for the first minute, 200 ppm NO gas for the next minute, and the flow rate was artificially increased to 300.
〜800ml/min, voltage E1,
Examples of recording the detected density converted by voltage E2 and voltage E3 are shown in FIGS. 3a, b, and c, respectively. The change in voltage E1 in FIG. It shows that the temporal change in the amount is outputted faithfully, and Figure 3c shows that the concentration of the sample gas can be detected with high accuracy by the calculation result of E2/E1, regardless of the change in the sample flow rate. There is.

In this way, this example shows that it is no longer necessary to keep the flow rate constant, which has been done in the past, and that highly accurate analysis becomes possible.

(f) Effect of the device According to this device, by detecting the change in the sample gas flow rate and taking the ratio between the detected value and the intensity of chemiluminescence light, the change in the sample gas flow rate can be detected, regardless of the sample gas flow rate.
The NO concentration is detected with high precision, eliminating the need for a conventional control mechanism to maintain a constant sample gas.

[Brief explanation of the drawing]

FIG. 1 is a block diagram showing the configuration of this invention, FIG. 2 is a block diagram showing an embodiment of this invention, and FIG. 3 is a graph showing an example of the performance of FIG. 2. 1...Sample gas inlet, 9...Hot wire flowmeter,
10...Reaction tank, 16...Ozone generator, 17...
...Photomultiplier tube, 20...Amplifier, 21...Arithmetic unit, 22...Recorder.

Claims (1)

[Claims for Utility Model Registration] (a) A reaction tank for reacting nitrogen monoxide and ozone to produce chemiluminescence, (b) Sample gas supply means for supplying a gas containing nitrogen oxides to the reaction tank, (c) ozone gas supply means for supplying ozone gas to the reaction tank; (d) measuring the flow rate of the sample gas supply means;
a flow rate measuring means for outputting a first signal proportional to the flow rate; (e) a light amount detection means for detecting the amount of chemiluminescence in the reaction tank and outputting a second signal proportional to the amount of light; (f) the second signal. A chemiluminescent analyzer comprising: a calculation means for calculating and outputting a ratio of a signal to the first signal.