JPH0566200A - Method and device for measuring iodine concentration in gas - Google Patents

Abstract

PURPOSE:To provide a method and a device for measuring the iodine concentration of gas by which precise iodine concentrations can be measured by correcting the influence of the fluorescence of a coexisting fluorescent material gas which overlaps the fluorescence of iodine, and correcting the influence of the fluorescence extinction phenomenon of the iodine due to the coexisting gas. CONSTITUTION:Laser light 20 from a light source 1 is split by a beam splitter 2 and one of the rays is transmitted to a cell 4 and the other to a power monitor 9. The light output monitored by the power monitor 9 is fed to a box car integrator 10. The fluorescence of sample gas in the cell 4 is detected by a photomultiplier tube 7 through filters 5, 6. The filters 5, 6 cut the scattered laser light 20 and the filter 5 for iodine allows more transmission of the fluorescence of iodine therethrough than the filter 6, while the filter 6 for NO2 allows more transmission of the fluorescence of NO2 than the filter 5. The box car integrator 10 integrates fluorescence signals. A device controlling and data processing unit 13 controls a pulse generator 11 and a wavelength sweep controller 12 and reads data about measurements from the box car integrator 10 and performs arithmetic processing to find the iodine concentration.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method and an apparatus for measuring the concentration of iodine in a gas, for example, a measuring method and an apparatus suitable for in-line measurement of the concentration of iodine in off gas of a nuclear fuel reprocessing plant.

[0002]

2. Description of the Related Art As a fluorescence analysis method for iodine in gas, a collection of proceedings (19 Autumn Meeting) of the Atomic Energy Society of Japan (19
89, H24). In this conventional technique, application of a fluorescence analysis method using a He-Ne laser for the measurement of iodine in gas in a nuclear fuel reprocessing plant is being studied.

[0003]

However, in the above-mentioned prior art, the fact that the coexisting NOx gas quenches the fluorescence of iodine and that the coexisting NO ₂ fluoresces interferes with the measurement of the fluorescence of iodine. No consideration has been given to this point, and there is a problem that it is difficult to measure the iodine concentration in the presence of NOx.

An object of the present invention is to accurately measure the iodine concentration by correcting the influence of the fluorescence of the coexisting gas that overlaps with the fluorescence of iodine, and further by correcting the influence of the fluorescence quenching phenomenon of iodine by the coexisting gas. Another object of the present invention is to provide a method and a device for measuring the iodine concentration in various gases.

[0005]

In the method for measuring the concentration of iodine in a gas according to the present invention, the fluorescence intensity from the gas measured at an excitation light wavelength and a fluorescence wavelength with high sensitivity for measuring the fluorescence of iodine (hereinafter referred to as F1 And the fluorescence intensity from the gas measured at the excitation light wavelength and the fluorescence wavelength with high sensitivity to the fluorescent substance coexisting in the gas (hereinafter referred to as F2).
By using the two fluorescence intensities, which are represented by, and solving the two equations expressing the above two fluorescence intensities by the iodine concentration and the concentration of the fluorescent substance coexisting therewith,
The iodine concentration in the gas is determined. That is, the sensitivity of iodine fluorescence at the excitation light wavelength (λe1) and the fluorescence wavelength (λf1), which have high iodine fluorescence measurement sensitivity, is α1, the fluorescence sensitivity of the coexisting fluorescent substance is β1, and the coexisting fluorescent substance is The sensitivity of iodine fluorescence at the excitation light wavelength (λe2) and the fluorescence wavelength (λf2) having high sensitivity to α2 is α2, the fluorescence sensitivity of the coexisting fluorescent substance is β2, and the iodine concentration is I,
When the concentration of the coexisting fluorescent substance is C, the fluorescence intensity F
1, F2 becomes F1 = α1 · I + β1 · C (1) F2 = α2 · I + β2 · C (2), and when this simultaneous equation is solved, I becomes

[0006]

[Equation 1]

From this equation, the iodine concentration in the gas in which the fluorescent substance coexists can be determined.

When the fluorescent substance coexisting with iodine in the gas is a substance that quenches the fluorescence of iodine, in order to obtain the iodine concentration corrected for the influence of the quenching, the fluorescent substance coexisting with iodine can be obtained. The concentration of is determined from the simultaneous equations, the ratio at which the fluorescent substance quenches the fluorescence of iodine at that fluorescent substance concentration (quenching rate) is determined in advance from other measured values, and the fluorescence value of iodine is corrected by the quenching rate. Then, the iodine concentration can be obtained. That is, the formula of the fluorescence intensity considering the fluorescence quenching of iodine by the coexisting fluorescent substance is as follows: F1 = α1 · S · I + β1 · C (4) F2 = α2 · S · I + β2 · C (5) S = 1 / ( 1 + k · C) (6) Here, S represents the quenching rate, and k represents the quenching constant for the fluorescence of iodine due to the coexisting substance. In equation (5), if α2 is sufficiently small and can be ignored,
C can be obtained from the equation (5). Therefore, if the value of S in this value of C is obtained in advance by measurement, (4),
According to the equation (6), I becomes I = (1 / α1) (1 + k · F2 / β2) {F1- (β1 / β2) · F2} (7). From this equation, fluorescence quenching is also corrected and iodine concentration is corrected. Can be asked.

The coexisting fluorescent substance is nitrogen dioxide (which is also a substance that quenches the fluorescence of iodine), and at the same time nitric oxide (which is not a fluorescent substance but a substance that quenches the fluorescence of iodine). ) Also coexist,
By preliminarily oxidizing coexisting nitric oxide with oxygen gas or a metal catalyst to chemically change it to nitrogen dioxide, the influence of quenching of fluorescence of iodine by nitric oxide can be removed.

In the apparatus for measuring the concentration of iodine in gas according to the present invention which carries out the above measuring method, the light source which emits the excitation light is
It is possible to generate light having an excitation light wavelength having a high sensitivity for measurement of iodine fluorescence and an excitation light wavelength having a high sensitivity for a fluorescent substance coexisting in a gas. This excitation light is
The fluorescence emitted by the sample gas irradiated with the sample cell containing the sample gas containing iodine is detected by the photodetector.
The photodetector measures a fluorescence intensity F1 at a fluorescence wavelength having a high measurement sensitivity to iodine fluorescence and a fluorescence intensity F2 at a fluorescence wavelength having a high sensitivity to a fluorescent substance coexisting in the gas. Two fluorescence intensities F1 measured by the photodetector
F2 is sent to a data processing device, and the data processing device solves the above simultaneous equations that represent the above two fluorescence intensities F1 and F2 by the iodine concentration I and the fluorescent substance concentration C coexisting with the iodine concentration I. The calculation for obtaining the concentration I is performed.

When the coexisting fluorescent substance is a substance that quenches the fluorescence of iodine, when the fluorescence quenching of iodine due to the coexisting fluorescent substance is corrected, the iodine is processed by the data processor as described above. The concentration C of the fluorescent substance coexisting with is obtained from simultaneous equations, and the ratio at which the fluorescent substance quenches the fluorescence of iodine at the obtained fluorescent substance concentration C is obtained in advance from other measured values, and the above-mentioned equation is used. The iodine concentration is calculated by correcting the fluorescence value of iodine by the extinction rate.

When the coexisting fluorescent substance is nitrogen dioxide and, at the same time, nitric oxide also coexists, a converter that chemically oxidizes the coexisting nitric oxide by oxygen gas or a metal catalyst into nitrogen dioxide is used. Installed in front of the measuring cell,
By introducing the gas that has passed through this converter into the measurement cell, the fluorescence quenching of iodine by nitric oxide is removed.

[0013]

EXAMPLES In each of the following examples shown in FIGS. 1, 6, 7 and 8, the coexisting substance that interferes with the fluorescence of iodine is a fluorescent substance and also has the effect of quenching the fluorescence of iodine. It is assumed to be NO ₂ .

FIG. 1 shows a device configuration of an embodiment.
By using a laser as the light source 1, the sensitivity of fluorescence analysis can be increased. In this embodiment, the light source 1
A tunable pulsed laser is used for. As the wavelength variable pulse laser, a dye laser using a pulse YAG laser, a nitrogen laser, an excimer laser, or the like is used as an excitation laser. The excitation light wavelength used is 630 to 640 nm for the analysis of iodine fluorescence, as will be described later.
Range of 400 to 640 for analysis of NO ₂ fluorescence.
The range of nm is used. Usually, the wavelength range that can be changed by using one type of dye is in the range of 20 to 100 nm. Therefore, it is not necessary to change the dye between the wavelength used for the iodine fluorescence analysis and the wavelength used for the NO ₂ fluorescence analysis. It is more advantageous in terms of maintenance. When the wavelength is changed with the same dye, the angle of the diffraction grating in the dye laser is changed. This wavelength sweep is performed by the wavelength sweep controller 12.
When it is necessary to change the dye depending on the wavelength used for iodine fluorescence analysis and the wavelength used for NO ₂ fluorescence analysis, a system that automates dye conversion is used, or two lasers are used for one excitation laser. This can be dealt with by using a stage dye laser. Other specifications regarding the wavelength tunable pulse laser of the light source 1 include an optical output of 0.1 to 10 m.
J / pulse. The higher the light output, the higher the sensitivity of fluorescence analysis.

A laser beam 20 emitted from a light source 1 is split by a beam splitter 2, one of which is sent to a cell 4 containing a sample gas and the other of which is sent to a power monitor 9. The power monitor 9 monitors the optical output of the laser light 20.
The monitored light output is sent to the boxcar integrator 10. The laser light 20 sent to the cell 4 is condensed by the lens 3 and irradiated into the cell 4. When the laser light 20 is sent from the light source 1 to the cell 4, an optical fiber is used and
It is also possible to separate it from. The method using the optical fiber is particularly effective in terms of maintenance when the sample gas contains a radioactive substance.

In the cell 4, the incident surface of the laser light 20 and the surface for detecting the fluorescence of the sample are optical windows made of, for example, quartz. The fluorescence of the sample is usually taken out in the direction perpendicular to the incident direction of the laser light 20. The sample gas is sent into the cell 4. In the case of in-line analysis, it is possible to measure even if the sample gas is continuously flowed.

The fluorescence of the sample passes through the filter 5 on the one hand and the filter 6 on the other hand, respectively.
It is detected by the photomultiplier tube 7. Filter 5 for iodine
Is used to cut off the scattered light of the laser light 20 and to transmit the fluorescence wavelength range where the fluorescence intensity of iodine is high and the fluorescence intensity of NO ₂ is low. On the other hand, N
The intensity of the fluorescence of iodine is weak in the O ₂ filter 6,
A material having a characteristic of transmitting a fluorescence wavelength range in which the fluorescence intensity of NO ₂ is strong is used. The details of each fluorescence wavelength range will be described later. The signal from each photomultiplier tube 7 is amplified by the preamplifier 8 and sent to the boxcar integrator 10. The beam stopper 14 uses the laser light 2 emitted from the cell 4.
It is used to prevent 0 from returning to cell 4 and increasing the scattered light intensity.

In this embodiment, since the light source 1 is a pulsed laser, the fluorescence detected is also pulsed. The boxcar integrator 10 is effective for detecting such a pulse signal. The timing at which the boxcar integrator 10 detects a signal is adjusted by the pulse generator 11. That is, a trigger signal is sent from the pulse generator 11 to the light source 1 to generate a laser, and at the same time, a trigger signal is also sent to the boxcar integrator 10 to give a timing for taking a fluorescence signal in the boxcar integrator 10. The boxcar integrator 10 integrates the fluorescence signals generated for each shot to reduce fluctuations and the like due to variations in pulse laser shots. Further, by taking the ratio of the fluorescence signal obtained by the photomultiplier tube 7 and the light output detected by the power monitor 9, it is possible to correct the fluctuation of the light source 1 over a long range.

The device control and data processing device 13 controls the pulse generator 11 and the wavelength sweeping control device 12, reads out the measurement data from the boxcar integrator 10, and calculates the fluorescence of iodine by the formula 3 or NO _2. To correct the effect of extinction and obtain a more accurate result, Equation 7,
It is used for data processing for calculating iodine concentration by performing calculation using.

As described above, according to this embodiment, iodine and NO are obtained for each of the excitation light wavelength and the fluorescence wavelength.
Fluorescence measurement can be performed with the optimum setting for ₂ , and the iodine concentration can be measured by correcting the interference caused by coexisting NO ₂ gas.

Next, the wavelength bands of excitation light and fluorescence suitable for iodine analysis will be described with reference to FIGS. 2 and 3.

FIG. 2 shows fluorescence spectra of iodine (I ₂ ) and NO ₂ (excitation light wavelength: 632.8 nm). From this figure, it can be seen that the wavelength band of λf1 has a higher ratio of the fluorescence intensity of iodine to the fluorescence intensity of NO ₂ than that of λf2, and is suitable as a wavelength band for detecting the fluorescence of iodine. The wavelength band for detecting the fluorescence of NO ₂ is λ
It can be seen that the wavelength band of λf2 is more suitable than f1, or the wavelength band of 750 nm or more where fluorescence of iodine is scarce.

FIG. 3 shows the excitation spectra of iodine and NO ₂ (fluorescence wavelength: 680 to 720 nm). From this figure, it can be seen that the ratio of the fluorescence intensity of iodine to the fluorescence intensity of NO ₂ at the wavelength of λe1 becomes high, and this wavelength is suitable as the excitation light wavelength for detecting the fluorescence of iodine. The wavelength for exciting the fluorescence of NO ₂ is, for example, λe
It turns out that a wavelength of 2 is suitable.

Next, FIG. 4 shows a calibration curve for iodine and NO ₂ . In this figure, the excitation light wavelength and the fluorescence wavelength are the same for iodine and NO ₂ . Α1, α2, β1, β2 in the equations 1 and 2 or the equations 4 and 5 correspond to the slope of the calibration curve. Therefore, it is necessary to obtain α1, α2, β1, β2 in advance by measuring a calibration curve at an excitation light wavelength and a fluorescence wavelength suitable for iodine, and at an excitation light wavelength and a fluorescence wavelength suitable for NO _2. is there.

FIG. 5 shows the fluorescence quenching rate (S) of iodine by NO and NO ₂ . From this figure, it can be seen that the fluorescence of iodine is quenched by NO and NO ₂ . Also, from this figure, the extinction constant k due to NO ₂ in the equation 6 used in the above-mentioned embodiment can be obtained. Therefore,
By using the quenching constant k due to NO ₂ obtained from this figure in Equation 7, the iodine concentration corrected for the fluorescence quenching of iodine by NO ₂ can be obtained.

FIG. 6 shows another embodiment of the present invention. The light source 1 of this embodiment is a pulse laser alone, and its wavelength cannot be changed. Therefore, the excitation light wavelengths are iodine and NO ₂
This is the same in the measurement of 1., and the influence of the fluorescence of NO ₂ is corrected by changing the fluorescence wavelength to be detected. According to this embodiment, since the dye laser for changing the excitation light wavelength and the wavelength sweep control device 12 are not required, the system is inexpensive and the maintenance is easy.

FIG. 7 shows still another embodiment of the present invention. In this embodiment, the light source 1 is a tunable pulse laser, but the photomultiplier tube 7 for detecting fluorescence is only one system. Therefore, although the fluorescence wavelengths to be detected are the same, the influence of the fluorescence of NO ₂ is corrected by changing the excitation light wavelength in the measurement of iodine and NO ₂ . According to this embodiment, since one system of the photomultiplier tube 7 for detecting fluorescence is not required, there is an advantage that the system is inexpensive and the maintenance is easy.

FIG. 8 shows still another embodiment of the present invention. The light source 1 of this embodiment is a wavelength tunable CW laser. Therefore, the detected fluorescence is also continuously emitted, and the detection system is different from the above-mentioned system. That is, the laser light 2
0 is a chopper 1 controlled by a chopper controller 17
At 6, chopping at a constant frequency. Thereby, fluorescence is also generated at a constant frequency. Lock-in amplifier 18 for detecting only the signal component in which this fluorescence is tuned to the chopper 16
By measuring with, it becomes possible to measure with low noise. Since the CW laser is superior in optical output stability to the pulse laser, this embodiment has an advantage that a signal with a good S / N can be detected. Also, as in the above-mentioned embodiment,
It is also possible to simplify the system by using a CW laser that is not variable in wavelength or by using a single photomultiplier tube 7 for detecting fluorescence.

Next, in addition to NO ₂ which is a fluorescent substance and also a substance which quenches the fluorescence of iodine, NO which is a substance having only the effect of quenching the fluorescence of iodine coexists with iodine in the gas. An embodiment of the present invention will be described with reference to FIG. In this example, first the gas 21 from the process
To the chemical reaction tower 19. In the chemical reaction tower 19, NO in the process gas 21 is changed to NO ₂ by using a platinum metal catalyst or blowing oxygen.
When the gas after this is subjected to the measurement according to each of the above-described examples, the iodine concentration corrected for the fluorescence due to NO ₂ and the fluorescence quenching can be obtained. As described above, according to this embodiment, there is an advantage that the influence of the fluorescence quenching of iodine by NO can be eliminated.

[0030]

The iodine concentration can be measured by correcting the influence of the fluorescence of the coexisting gas overlapping the fluorescence of iodine. Further, the iodine concentration can be measured by correcting the fluorescence quenching phenomenon of iodine due to the coexisting fluorescent substance gas. Further, when the coexisting fluorescent substance is nitrogen dioxide and at the same time nitric oxide also coexists, by chemically changing the coexisting nitric oxide to nitrogen dioxide, the quenching of the fluorescence of iodine by nitric oxide can be suppressed. The effect can be removed and the iodine concentration measured.

[Brief description of drawings]

FIG. 1 is a device configuration diagram of an embodiment of the present invention.

FIG. 2 is a diagram showing fluorescence spectra of iodine (I ₂ ) and NO ₂ .

FIG. 3 is a diagram showing excitation spectra of iodine and NO ₂ .

FIG. 4 is a diagram showing calibration curves for iodine and NO ₂ .

FIG. 5 is a graph showing fluorescence quenching rates of iodine by NO and NO ₂ .

FIG. 6 is a device configuration diagram of another embodiment of the present invention.

FIG. 7 is a device configuration diagram of another embodiment of the present invention.

FIG. 8 is a device configuration diagram of another embodiment of the present invention.

FIG. 9 is a device configuration diagram of still another embodiment of the present invention.

[Explanation of symbols]

1 ... Light source 2 ... Beam splitter 3 ... Lens 4 ... Cell 5 ... Filter 6 ... Filter 7 ... Photomultiplier tube 8 ... Preamplifier 9 ... Power monitor 10 ... Boxcar integrator 11 ... Pulse generator 12 ... Wavelength sweep controller 13 ... Device control and data processing device 14 ... Beam stopper 15 ... Mirror 16 Chopper 17 ... Chopper controller 18 ... Lock-in amplifier 19 ... Chemical reaction tower 20 ... Laser light

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Haruo Fujimori, Inventor Haruo Fujimori, 1168 Moriyama-cho, Hitachi, Ibaraki, Institute of Energy Research, Hiritsu Seisakusho Co., Ltd. (72) Yoshinori Takimoto 6-9, Takara-cho, Kure, Hiroshima Babkotsu Hitachi Co., Ltd. Within

Claims (11)

[Claims] 1. A method for measuring the concentration of iodine in a gas in which a fluorescent substance coexists by a fluorescence analysis method, wherein the measurement is carried out at a first excitation light wavelength and a first fluorescence wavelength, which are highly sensitive to measurement of iodine fluorescence. Two fluorescence intensities of the fluorescence intensity from the gas and the fluorescence intensity from the gas measured at the second excitation light wavelength and the second fluorescence wavelength having high sensitivity to the fluorescent substance coexisting in the gas are shown. A method for measuring the concentration of iodine in a gas, characterized in that the concentration of iodine is obtained by solving a simultaneous equation using the above two fluorescence intensities depending on the concentration of iodine and the concentration of a coexisting fluorescent substance. 2. The method for measuring the concentration of iodine in a gas according to claim 1, wherein the concentration of the fluorescent substance coexisting in the gas together with iodine is obtained by a simultaneous equation, and the fluorescent substance at the concentration of the fluorescent substance is obtained. A method for measuring the iodine concentration in a gas, wherein the ratio of quenching the fluorescence of iodine is obtained from a previously measured value, and the iodine concentration is obtained by correcting the value of the fluorescence of iodine by the ratio. 3. The method for measuring the iodine concentration in a gas according to claim 1 or 2, wherein when the fluorescent substance is nitrogen dioxide and nitric oxide also coexists, the coexisting nitric oxide is oxygen. A method for measuring the concentration of iodine in gas, which comprises removing the influence of quenching of fluorescence of iodine due to nitric oxide by oxidizing with gas or a metal catalyst and chemically changing to nitrogen dioxide in advance. 4. The method for measuring the iodine concentration in gas according to claim 1, 2 or 3, wherein the first excitation light wavelength is in the range of 630 to 640 nm. Measuring method. 5. The method for measuring the iodine concentration in gas according to claim 1, 2 or 3, wherein the first fluorescence wavelength is 680 to 720 nm. 6. The method for measuring the iodine concentration in gas according to claim 1, 2 or 3, wherein the first fluorescence wavelength is in the range of 640 to 660 nm. Method. 7. The method of measuring the iodine concentration in a gas according to claim 3, wherein the second excitation light wavelength is 620 to 620.
A method for measuring the concentration of iodine in gas, which is in the range of 630 nm. 8. The method for measuring the concentration of iodine in gas according to claim 3, wherein the second fluorescence wavelength is 750 nm.
The above is the method for measuring the iodine concentration in gas. 9. An apparatus for measuring the concentration of iodine in a gas in which a fluorescent substance coexists by a fluorescence analysis method, and a measuring cell in which the gas is contained, and a first excitation light wavelength and gas having high sensitivity for measuring iodine fluorescence. A light source for generating light having a second excitation light wavelength having high sensitivity to a fluorescent substance coexisting therein and irradiating the gas in the measurement cell, and a first fluorescence wavelength having high measurement sensitivity to fluorescence of iodine. And a photodetector for measuring the fluorescence intensity from the gas at the second fluorescence wavelength, which is highly sensitive to the fluorescent substance coexisting in the gas, and the photodetector. A data processing device that uses two fluorescence intensities and performs a calculation for obtaining the iodine concentration by solving a simultaneous equation that expresses the above two fluorescence intensities based on the iodine concentration and the coexisting fluorescent substance concentration. Featuring Measuring device for iodine concentration in gas. 10. The device for measuring the concentration of iodine in gas according to claim 9, wherein the data processing device obtains the concentration of the fluorescent substance coexisting with iodine from a simultaneous equation and A device for measuring an iodine concentration in a gas, wherein a ratio of quenching the fluorescence of iodine by the fluorescent substance is obtained from a previously measured value, and the iodine concentration is obtained by correcting the value of the fluorescence of iodine by the ratio. 11. The apparatus for measuring the concentration of iodine in gas according to claim 9 or 10, wherein the fluorescent substance coexisting in the gas is nitrogen dioxide, and when nitric oxide is also present, the coexisting one is present. A converter for oxidizing nitrogen oxide with oxygen gas or a metal catalyst to chemically change it to nitrogen dioxide is installed in front of the measuring cell, and the gas passing through the converter is introduced into the measuring cell. Measuring device for iodine concentration in gas.