JP7436020B2 - Gas concentration measuring device and gas concentration measuring method - Google Patents

Description

The present invention relates to a gas concentration measuring device and a gas concentration measuring method capable of non-contactly measuring the concentration of gas present in a measurement target space using ultraviolet absorption spectroscopy.

BACKGROUND ART Conventionally, a technique is known for non-contactly measuring the concentration of a gas to be measured existing in a space to be measured using ultraviolet absorption spectroscopy (for example, Non-Patent Document 1). For example, Non-Patent Document 1 discloses that the concentrations of SO ₂ gas, NO gas, and NH ₃ gas present in a measurement target space are measured in a non-contact manner using ultraviolet absorption spectroscopy.

“Development of high-temperature gas concentration measuring device using ultraviolet absorption spectroscopy”, Shikoku Electric Power, Shikoku Research Institute Research Report 102 (June 2015) 19-27 (URL: http://www.ssken.co. jp/research/pdf/102/102_04.pdf)

However, since the ultraviolet wavelength band in which NO gas absorbs ultraviolet light and the ultraviolet wavelength band in which SO ₂ gas absorbs ultraviolet light overlap, the concentration of NO gas cannot be measured in a measurement target space where SO ₂ gas is mixed. When attempting to do so, there was a problem in that the concentration of NO gas or SO ₂ gas could not be measured appropriately due to interference between SO ₂ gas and NO gas.

The present invention provides a gas concentration measuring device and a gas concentration measuring method that can appropriately measure the gas concentration without contact even when two or more gases with overlapping ultraviolet wavelength bands that absorb ultraviolet light are present. The purpose is to provide.

The gas concentration measuring device according to the present invention irradiates a measurement target space in which a first gas and a second gas that interfere with each other in a specific ultraviolet wavelength band coexist with ultraviolet light having a wavelength that includes the specific ultraviolet wavelength band. an irradiation device, a light receiving device that receives the ultraviolet light that has passed through the measurement target space, and a calculation that calculates the concentrations of the first gas and the second gas based on the light intensity of the ultraviolet light received by the light receiving device. a device, the arithmetic device is configured to calculate the light intensity in a second ultraviolet wavelength band where the second gas interferes, based on the first light intensity in the first ultraviolet wavelength band where the second gas does not interfere. Create an interpolation line for interpolating the light intensity when the second gas does not interfere , calculate the second light intensity when the second gas does not interfere in the second ultraviolet wavelength band, calculating the concentration of the second gas based on the light intensity of the first gas and the third light intensity when the second gas interferes in the second ultraviolet wavelength band ; The concentration of the first gas is calculated based on the light intensity in the second ultraviolet wavelength band of the ultraviolet light that has passed through a cell filled with a reference gas that does not interfere with the second gas, and the second light intensity. It is characterized by
In the above gas concentration measuring device, the arithmetic device may detect the second ultraviolet wavelength when the first ultraviolet wavelength band is present on both shorter wavelength side and longer wavelength side than the second ultraviolet wavelength band. The interpolation line is determined based on the light intensity in the first ultraviolet wavelength band on the shorter wavelength side than the band and the light intensity in the first ultraviolet wavelength band on the longer wavelength side than the second ultraviolet wavelength band. The light intensity on the interpolated line in the second ultraviolet wavelength band can be specified as the second light intensity.
In the above gas concentration measuring device, the arithmetic device calculates a wavelength that is shorter than the second ultraviolet wavelength band among the wavelengths in the first ultraviolet wavelength band, and that is from the second ultraviolet wavelength band. Light intensity at a wavelength separated by a certain bandwidth or more, or a wavelength on the longer wavelength side than the second ultraviolet wavelength band, which is separated by a certain bandwidth or more from the second ultraviolet wavelength band. The interpolation line may be created based on the light intensity at .
The gas concentration measuring device further includes a calibration cell that is continuously filled with a calibration gas having a predetermined concentration , and the calculation device is configured to calculate the amount of change over time in the light intensity of the ultraviolet light that has passed through the calibration cell. Accordingly, the concentration of the first gas can be calibrated.
In the gas concentration measuring device, the first gas is SO ₂ gas in the flue, the second gas is NO gas in the flue, and the second ultraviolet wavelength band has a wavelength within a range of 225 to 229 nm. It can be configured to be a band.
In the above gas concentration measuring device, the light receiving device includes a spectrometer that spectrally separates ultraviolet light in an ultraviolet wavelength band that is absorbed by the first gas and ultraviolet light in an ultraviolet wavelength band that is absorbed by the second gas. Can be configured.
The gas concentration measuring device may be configured to include a deuterium lamp that irradiates the measurement target space with ultraviolet light in an ultraviolet wavelength band.

The gas concentration measuring method according to the present invention irradiates a measurement target space in which a first gas and a second gas that interfere with each other in a specific ultraviolet wavelength band coexist with ultraviolet light having a wavelength that includes the specific ultraviolet wavelength band. , a gas concentration measuring method comprising: receiving ultraviolet light that has passed through the measurement target space; and calculating the concentrations of the first gas and the second gas based on the light intensity of the received ultraviolet light; Based on the first light intensity in a first ultraviolet wavelength band in which the two gases do not interfere, interpolate the light intensity in a second ultraviolet wavelength band in which the second gas interferes when the second gas does not interfere. The second light intensity in the second ultraviolet wavelength band when the second gas does not interfere is calculated by creating an interpolation line for the second ultraviolet wavelength band. A gas concentration measuring method that calculates the concentration of the second gas based on the light intensity when the second gas interferes, the method comprising: filling a reference gas that does not interfere with the first gas and the second gas; The concentration of the first gas is calculated based on the light intensity in the second ultraviolet wavelength band of the ultraviolet light that has passed through the cell and the second light intensity.
In the above concentration measuring method, the first gas is SO ₂ gas in the flue, the second gas is NO gas in the flue, and the second ultraviolet wavelength band is a wavelength band within the range of 225 to 229 nm. It can be configured as follows.

According to the present invention, even when two or more gases having overlapping ultraviolet wavelength bands that absorb ultraviolet light are present, the concentration of the gases can be appropriately measured without contact.

FIG. 1 is a configuration diagram of a gas concentration measuring device according to the present embodiment. It is a graph showing the relationship between the absorption cross section (cm ² ) of NO gas, SO ₂ gas, and NH ₃ gas as a single substance and the wavelength in the ultraviolet wavelength band. It is a graph which shows an example of the measurement result of the ultraviolet spectrophotometric analysis of the mixed gas which NO gas and _SO2 gas coexist. It is a graph which shows an example of the measurement result of ultraviolet spectrophotometric analysis of _SO2 gas alone. It is a graph for explaining the measuring method of NO gas concentration. It is a graph for explaining a method of measuring SO ₂ gas concentration. It is a graph for explaining the calibration method of the gas concentration of NO gas and SO ₂ gas. 5 is a graph showing the measurement results of NO gas concentration in Example 1. FIG. 3 is a graph showing the measurement results of NO gas concentration in Example 2. 3 is a graph showing the measurement results of NO gas concentration in Example 3. 3 is a flowchart showing gas concentration measurement processing according to the present embodiment.

The gas concentration measuring device according to the present embodiment will be explained below based on the drawings. In addition, in this embodiment, a gas concentration measuring device that measures the concentration of NOx gas (for example, NO gas and NO ₂ gas) and SO ₂ gas contained in the flue gas of a thermal power plant or the like is exemplified. Although the invention will be described, the gas concentration measuring device according to the present invention is not limited to this use, and for example, it can be used to measure two or more gases that have overlapping ultraviolet wavelength bands that absorb ultraviolet light, specifically, to measure ultraviolet wavelengths. A first gas (for example, CO ₂ , O ₂ , CO, H ₂ S, NH ₃ , Cl ₂ , HCl, COS) in which the ultraviolet absorption band of the gas in the ultraviolet wavelength band is continuous, and a first gas in which the ultraviolet absorption band of the gas in the ultraviolet wavelength band is continuous. The present invention can also be applied to a gas concentration measuring device that measures the concentration of any one or more gases when a second gas (for example, NO gas) is present intermittently. Furthermore, in the present invention, the measurement target space may be, for example, an open space such as near the exhaust port of a flue, or a closed space within the flue in which an ultraviolet-transparent window is provided within the flue. Furthermore, it is not limited to the flue of a thermal power plant, but can also be used to measure exhaust gas at a garbage treatment plant, industrial process management, and exhaust gas measurement. Note that in this embodiment, NO ₂ is converted to NO using a NO ₂ /NO converter for measurement.

In addition, in the present embodiment below, SO ₂ gas is exemplified as the "first gas" and NO gas is exemplified as the "second gas" in the present invention. In the present invention, the ultraviolet wavelength band in which the second gas "does not interfere" (the "first ultraviolet wavelength band") refers to the ultraviolet wavelength band in which the second gas does not absorb any ultraviolet light; It also includes an ultraviolet wavelength band in which the absorption characteristic (absorption cross section) of the second gas is 1/10 or less of that of the ultraviolet wavelength band in which the second gas "interferes" (the "second ultraviolet wavelength band").

FIG. 1 is a configuration diagram showing a gas concentration measuring device 1 according to this embodiment. As shown in FIG. 1, the gas concentration measuring device 1 includes an irradiation device 10, a lens 11, beam splitters 12 and 13, reflectors 14 and 15, a sample cell 20, a temperature control device 30, and a calibration cell. 40, light shielding plates 51 and 52, a spectroscope 60, and an arithmetic device 70.

The irradiation device 10 has a light source that emits light including at least a wavelength in the ultraviolet wavelength band (hereinafter also referred to as ultraviolet light). A deuterium lamp can be used as such a light source. The ultraviolet light emitted from the irradiation device 10 is expanded in diameter by the lens 11 and made into parallel light, and then split into two beams by the beam splitter 12, one of which is guided to the sample cell 20 and the other to the calibration cell. Leads to 40. Note that the beam splitter 12 is not particularly limited as long as it can split ultraviolet light, but in this embodiment, a polka dot beam splitter with a transmittance of about 50% is used.

The sample cell 20 includes an inlet 21 for introducing a mixed gas to be measured (a mixed gas containing two or more gases that interfere in at least some ultraviolet wavelength bands) into the sample cell 20, and a mixed gas to be measured. and an outlet 22 for discharging gas from the sample cell 20. One of the ultraviolet lights split by the beam splitter 12 is input into the sample cell 20 from one end of the sample cell 20, passes through an optical path 23 inside the sample cell 20, and is outputted from the other end of the sample cell 20 to the outside. be done. Note that although the sample cell 20 according to this embodiment has an optical path length of 400 mm and a window material made of synthetic quartz, the structure is not limited to this.

The temperature control device 30 controls the temperature near the inlet 21 and the outlet 22 of the sample cell 20 to a constant temperature. In this embodiment, the temperature control device 30 heats and maintains the vicinity of the inlet 21 and the outlet 22 of the sample cell 20 to about 50°C. By controlling the temperature near the inlet 21 and outlet 22 of the sample cell 20 in this way, it is possible to effectively prevent moisture contained in the mixed gas from adhering to the window and reducing the detection accuracy of gas concentration. It can be prevented. Note that the controlled temperature is not limited to 50°C, and can be set to any temperature within the range of 45 to 55°C, for example.

The ultraviolet light output from the sample cell 20 is reflected by the reflecting mirror 14 and then also reflected by the beam splitter 13, and then input to the spectrometer 60. Note that the reflecting mirror 14 is not particularly limited, but an aluminum enhanced reflection mirror having a reflectance of 80% or more can be used. In addition, in the gas concentration measuring device 1, a beam splitter 13 is used to input ultraviolet light output from the sample cell 20 and ultraviolet light output from a calibration cell 40, which will be described later, into the spectrometer 60 through the same optical path. is used. That is, by using the beam splitter 13, the ultraviolet light outputted from the sample cell 20 and reflected by the reflecting mirror 14 is also reflected by the beam splitter 13, inputted to the spectrometer 60, and outputted from the calibration cell 40. The ultraviolet light transmitted passes through the beam splitter 13 and is input to the spectrometer 60. Note that the beam splitter 13 is not particularly limited, but in this embodiment, a polka dot beam splitter with a transmittance of about 30% is used.

Furthermore, the gas concentration measuring device 1 according to the present embodiment includes a calibration cell 40 in order to detect a decrease in the amount of ultraviolet light passing through the sample cell 20 due to deterioration of the light source of the irradiation device 10. . Here, in the gas concentration measuring device 1 of this embodiment, when measuring the concentration of a mixed gas, the light shielding plate 51 is placed on the optical path and the light shielding plate 52 is placed on the optical path so that the ultraviolet light passes through the sample cell 20. By avoiding it from the road, input of ultraviolet light to the calibration cell 40 is prevented, and ultraviolet light output from the sample cell 20 is input to the spectrometer 60. On the other hand, when detecting deterioration of the light source of the irradiation device 10, by avoiding the light shielding plate 51 from the optical path and placing the light shielding plate 52 on the optical path, the ultraviolet light is allowed to pass through the calibration cell 40, and the sample cell The ultraviolet light output from 20 is prevented from being input to spectrometer 60. Thereby, only the ultraviolet light that has passed through the calibration cell 40 can be input to the spectrometer 60. Note that the light shielding plates 51 and 52 may have a configuration in which the positions are changed manually, or a configuration in which the positions are automatically changed by the user operating a button or the like.

The calibration cell 40 is continuously filled with N ₂ gas at a rate of approximately 100%, and the filling pressure is also continuously set to 1 atmosphere (1 atm). Furthermore, in this embodiment, the spectrum of the ultraviolet light that has passed through the calibration cell 40 is measured in advance before use (before the light source deteriorates), and the spectrum before use and the current calibration cell By comparing the spectrum with the spectrum of the ultraviolet light when it passes through the ultraviolet light 40, it is possible to detect the amount of decrease in the amount of ultraviolet light due to deterioration of the light source. Note that details of a method for calibrating the light intensity of the ultraviolet light measured in the sample cell 20 using the measurement results in the calibration cell 40 will be described later.

The spectrometer 60 separates the ultraviolet light into wavelengths and measures the intensity (spectrum) of each wavelength. Note that the spectrometer 60 has a lens 61, and can converge and measure the luminous flux of ultraviolet light input to the spectrometer 60. The measurement results obtained by the spectrometer 60 are then output to the arithmetic device 70.

The calculation device 70 measures the concentration of NO gas based on the measurement results obtained by the spectrometer 60. Here, FIG. 2 is a graph showing the relationship between the absorption cross section (cm ² ) and the ultraviolet wavelength band of each of NO gas, SO ₂ gas, and NH ₃ gas. As shown in Figure 2, NO gas, SO ₂ gas, and NH ₃ gas each have different wavelengths for absorbing ultraviolet light and absorption cross sections for absorbing ultraviolet light, but there are two types of gas in a specific ultraviolet wavelength band. It can be seen that the above gases are absorbed in duplicate. For example, as shown in Figure 2, _SO2 gas absorbs ultraviolet light in the entire ultraviolet wavelength band of 200-250 nm, while NO gas absorbs ultraviolet light in a part of the ultraviolet wavelength band of 200-250 nm (for example, 226 nm). 0 nm to 227.5 nm). Since SO ₂ gas absorbs ultraviolet light in the entire wavelength band of 200 to 250 nm, in the wavelength band where NO gas absorbs ultraviolet light (for example, 226.0 nm to 227.5 nm), NO gas and SO ₂ gas Both will absorb ultraviolet light, and interference will occur in the light intensity of the ultraviolet light detected by the light receiving device 60.

Therefore, in the gas concentration measurement device 1, when ultraviolet light is measured by flowing a mixed gas containing NO gas and SO ₂ gas into the sample cell 20, the ultraviolet wavelength band including the ultraviolet wavelength band where NO gas and SO ₂ gas interfere is detected. As shown in FIG. 3, in the spectrum of ultraviolet light in the range from 230 nm to 230 nm, the light intensity decreases significantly in the ultraviolet wavelength band (for example, 226.0 nm to 227.5 nm) where NO gas absorbs ultraviolet light. Note that FIG. 3 is a diagram showing an example of the results of measuring the light intensity of ultraviolet light by flowing a mixed gas of NO gas and SO ₂ gas into the sample cell 20, and shows an example where the concentration of SO ₂ gas is 100 ppm. It shows.

On the other hand, FIG. 4 is a diagram showing an example of the results of measuring the light intensity of ultraviolet light for SO ₂ gas alone, and similarly to FIG. 3, it shows a scene where the concentration of SO ₂ gas is 100 ppm. ing. As shown in FIG. 4, it can be seen that in the absence of NO gas, the light intensity does not decrease in the ultraviolet wavelength band (for example, 226.0 nm to 227.5 nm) where NO gas absorbs ultraviolet light. From this, the reason why the light intensity decreases in the ultraviolet wavelength band (for example, 226.0 nm to 227.5 nm) where NO gas absorbs ultraviolet light in Figure 3 is because NO gas absorbs ultraviolet light. It can be assumed that

In this way, the amount of change in light intensity that decreases in the ultraviolet wavelength band where NO gas absorbs ultraviolet light (hereinafter also referred to as the second ultraviolet wavelength band) is due to the change in light intensity according to the ultraviolet light absorbed by NO gas. This is assumed to be the amount of change. Therefore, in this embodiment, the calculation device 70 calculates the concentration of NO gas based on the amount of change in the light intensity decreased in the second ultraviolet wavelength band, as shown in FIG. Note that FIG. 5 is a diagram for explaining a method of measuring the concentration of NO gas.

Specifically, as shown in FIG. 5, the computing device 70 first calculates the light intensities C1 and C2 of predetermined wavelengths in the ultraviolet wavelength band (hereinafter also referred to as the first ultraviolet wavelength band W1) in which NO gas does not interfere. Identify. Note that, as shown in FIG. 5, the predetermined wavelength is preferably a wavelength that is relatively close to the second ultraviolet wavelength band W2 among the wavelengths in the first ultraviolet wavelength bands W1 and W3; It is preferable to use a wavelength separated from the ultraviolet wavelength band W2 by a predetermined bandwidth (margin). For example, in the example shown in FIG. 5, 224.5 nm and The wavelength at 229.0 nm is specified as the predetermined wavelength.

Based on the light intensities C1 and C2 of predetermined wavelengths in the first ultraviolet wavelength bands W1 and W3, the arithmetic device 70 calculates the light intensity of the ultraviolet light when NO gas does not interfere in the second ultraviolet wavelength band W2. Interpolate. For example, in the example shown in FIG. are specified as predetermined wavelengths C1 and C2, and in the spectrum of ultraviolet light, a straight line connecting light intensity C1 at 224.5 nm and light intensity C2 at 229.0 nm is defined as the second ultraviolet wavelength band W2. is created as an interpolated line showing the spectrum of ultraviolet light when NO gas does not interfere.

Furthermore, the calculation device 70 calculates the light intensity C4 on the interpolation line of the second ultraviolet wavelength band W2 (that is, the light intensity C4 when NO gas does not interfere in the second ultraviolet wavelength band W2) and the second ultraviolet wavelength. The concentration of NO gas is calculated based on the light intensity C3 actually measured in the band W2 (that is, the light intensity C3 when NO gas interferes in the second ultraviolet wavelength band W2). Note that the concentration of NO gas can be calculated using Equation 1 below.
In the above equation 1, I ₀ (λ) is the light intensity C4 on the interpolation line of the second ultraviolet wavelength band W2, I (λ) is the light intensity C3 actually measured in the second ultraviolet wavelength band W2, and n is The molecular density (concentration) of NO gas, σ (λ) is the absorption cross section, and L is the optical path length.

Further, in this embodiment, a configuration may be adopted in which the gas concentration of SO ₂ gas is measured in addition to NO gas. The gas concentration of SO ₂ gas may be calculated using the light intensity in the first ultraviolet wavelength band W1, W3 where NO gas interferes, or the light intensity in the second ultraviolet wavelength band W2 where NO gas interferes. It may be calculated based on the light intensity on the interpolation line.

Specifically, before introducing the mixed gas to be measured into the sample cell 20, the calculation device 70 introduces a reference gas such as _N2 gas that does not absorb ultraviolet light in an ultraviolet wavelength band of 200 nm or more into the sample cell 20. Then, as shown in FIG. 6, the light intensity of the ultraviolet light in the sample cell 20 in the presence of _N2 gas is measured as the reference light intensity. Thereafter, the computing device 70 introduces the mixed gas to be measured into the sample cell 20 and measures the light intensity of the ultraviolet light when the mixed gas is present. The reference light intensity of ultraviolet light in the presence of _N2 gas can be regarded as the light intensity of ultraviolet light when it is not absorbed by other gases, and as shown in Figure ₆ , the reference light intensity of ultraviolet light in the presence of N2 gas The difference between the reference light intensity C5 and the light intensity C4 on the interpolation line in the second ultraviolet wavelength band W2 can be considered to be the amount of change in the light intensity reduced by the SO ₂ gas absorbing the ultraviolet light. Therefore, in the above equation 1, the calculation device 70 substitutes the reference light intensity C5 of ultraviolet light (light intensity C5 when NO gas and SO ₂ gas are not present) to I ₀ (λ), and calculates the value to I (λ). By substituting the light intensity C4 on the interpolation line of the second ultraviolet wavelength band W2 (light intensity C4 when NO gas does not interfere), the concentration n of SO ₂ gas can be calculated. Note that FIG. 6 is a graph in which the spectrum of ultraviolet light when N ₂ is introduced into the sample cell 20 is superimposed on the graph shown in FIG.

Further, in this embodiment, a configuration may be adopted in which the concentration of SO ₂ gas is calibrated using the calibration cell 40. Here, FIG. 7 is a graph for explaining a method of calibrating the gas concentration of SO ₂ gas using the calibration cell 40. Since the calibration cell 40 is filled with _N2 gas at a constant concentration, the calculation device 70 calculates the amount of ultraviolet light in the calibration cell 40 measured when measuring the gas concentration of the mixed gas to be measured (current measurement). By comparing the spectrum with the spectrum of ultraviolet light measured before use (before the light source of the irradiation device 10 deteriorates), it is determined whether the light source has deteriorated. For example, the calculation device 70 uses the calibration cell 40 to compare the light intensity C7 of the spectrum measured this time with the light intensity C6 of the spectrum before use, as shown in FIG. Reference light intensity C6/reference light intensity C7 at the time of current measurement) is calculated as a calibration rate (change rate) α. Then, as shown in FIG. 6, the calculation device 70 calibrates the reference light intensity C5 by multiplying the reference light intensity C5 of the ultraviolet light in the presence of _N2 gas by the calibration rate α. The difference between the calibrated reference light intensity C5' and the light intensity C4 on the interpolated line in the second ultraviolet wavelength band W2 is the difference between the light intensity reduced by SO ₂ gas absorbing ultraviolet light, taking into account the deterioration of the light source. This is considered to be based on the amount of change (C5'-C4), and the calculation device 70 calculates SO ₂ gas based on the calibrated reference light intensity C5' and the light intensity C4 on the interpolation line, taking into account the deterioration of the light source. The gas concentration of can be calculated. For example, if the reference light intensity C7 of the ultraviolet light spectrum measured this time in the calibration cell 40 is 10% lower than the reference light intensity C6 of the spectrum before use (if the calibration rate α is 1.1, ), assuming that the amount of ultraviolet light emitted from the light source has decreased by 10%, by performing calibration to increase the light intensity C5 of the ultraviolet light that has passed through the sample cell 20 by 10%, using the light intensity after calibration. , an appropriate concentration of SO ₂ gas can be determined.

(Example 1)
In Example 1, by using the gas concentration measuring device 1 according to the present embodiment, NO gas at a predetermined concentration is continuously introduced into the sample cell 20, and the concentration of NO gas is measured. We verified whether it could be measured. Further, in Example 1, the concentration of NO gas was adjusted to increase from 0 ppm by 100 ppm every 5 minutes, and the concentration of NO gas was measured. The measurement results of NO gas concentration in Example 1 are shown in FIG. As shown in FIG. 8, the measurement result of the concentration of NO gas in the mixed gas by the gas concentration measuring device 1 and the concentration of NO gas actually introduced into the sample cell 20 almost match, indicating that the measurement was good. It turns out that results can be obtained.

(Example 2)
Furthermore, in Example 2, the concentration of NO gas was measured while fixing the concentration of NO gas while changing the concentration of SO ₂ gas. Further, in Example 2, the concentrations of NO gas were fixed at 200 ppm, 400 ppm, and 600 ppm, respectively, and measurements were performed for each concentration with and without using the NO ₂ /NO converter. As a result, as shown in FIG. 9, it was found that even if the concentration of SO ₂ gas was changed, the concentration of NO gas could be appropriately measured. Furthermore, it was found that the concentration of NO gas can be appropriately measured both when the NO ₂ /NO converter is used and when it is not used. Note that FIG. 9 is a graph showing the measurement results of the concentration of NO gas in Example 2.

(Example 3)
Furthermore, in Example 3, the concentration of NO gas was measured in the gas concentration measuring device 1 according to the present embodiment by changing the light intensity of the light source of the irradiation device 10 while keeping the concentration of NO gas fixed. Specifically, in Example 3, an interpolation line is created based on the spectrum of ultraviolet light detected in the sample cell 20 filled with a mixed gas of NO gas and SO ₂ gas, and the ultraviolet light in the sample cell 20 is The concentration of NO gas was calculated based on the light intensity C3 and the light intensity C4 on the interpolation line. FIG. 10 shows the measurement results of NO gas concentration in Example 3. As shown in FIG. 10, in the gas concentration measuring device 1 according to the present embodiment, an interpolation line is created based on the spectrum of the ultraviolet light in the sample cell 20, and the light intensity C3 of the ultraviolet light in the sample cell 20 and the interpolation line are It has been found that because the NO gas concentration is calculated based on the difference from the light intensity C4, the NO gas concentration can be appropriately measured even when the light intensity of the light source changes.

In this way, the gas concentration measuring device 1 according to the present embodiment can increase NO gas to a high level even when SO ₂ gas and NO gas coexist, or when the amount of ultraviolet light decreases due to deterioration of the light source. It was possible to measure with precision.

Next, the measurement processing of the gas concentration measuring device 1 according to this embodiment will be explained. FIG. 11 is a flowchart showing the measurement process of the gas concentration measuring device 1 according to this embodiment. In this embodiment, a method of repeatedly measuring the concentrations of NO gas and SO ₂ gas will be described as an example, but it is also possible to adopt a configuration in which only the concentration of NO gas is repeatedly measured, and in this case, step S112 Processing can be omitted. Furthermore, in the example shown in FIG. 11, the spectrum of ultraviolet light is measured and stored with a reference gas ( _N2 gas) introduced into the calibration cell 40 before use (before the light source of the irradiation device 10 deteriorates). It is assumed that there is

First, in step S101, the reference light intensity C6 of the ultraviolet light passing through the calibration cell 40 during the current measurement is detected. Specifically, the irradiation device 10 irradiates the calibration cell 40 with ultraviolet light, the ultraviolet light that has passed through the calibration cell 40 is received by the spectrometer 60, and the spectrum of the ultraviolet light that has passed through the calibration cell 40 is measured. Note that the arithmetic device 70 detects the light intensity C6 at a frequency (for example, 226.7 nm) at which the concentration of the gas to be measured is measured, for example, out of the spectrum. Further, in step S101, the light shielding plate 51 is avoided from the optical path and the light shielding plate 52 is placed on the optical path to prevent ultraviolet light from entering the sample cell 20 and to prevent the ultraviolet light from entering the calibration cell 40. is input so that the ultraviolet light that has passed through the calibration cell 40 is input to the spectrometer 60.

In step S102, the calculation device 70 calculates the calibration rate α. Specifically, the arithmetic device 70 determines the frequency ( For example, the light intensity at 226.7 nm) is detected as the reference light intensity C7 before use. Then, the calculation device 70 calculates the ratio (C6/C7) of the reference light intensity C6 of the ultraviolet light in the calibration cell 40 at the present time obtained in step S101 to the reference light intensity C7 of the ultraviolet light before use, as the calibration rate. Calculated as α.

In step S103, a reference gas (such as N ₂ gas) is introduced into the sample cell 20. Then, in step S104, the arithmetic unit 70 detects the reference light intensity C5 of the ultraviolet light when the reference gas is present in the sample cell 20. Specifically, the irradiation device 10 irradiates the sample cell 20 into which the reference gas has been introduced with ultraviolet light, and the spectrometer 60 measures the spectrum of the ultraviolet light when the reference gas is present. The computing device 70 detects the light intensity at a frequency (for example, 226.7 nm) for measuring the concentration of the gas to be measured in the measured spectrum as the reference light intensity C5 of the ultraviolet light when the reference gas is present in the sample cell 20. Note that from step S104 onward, the light shielding plate 51 is placed on the optical path and the light shielding plate 52 is avoided from the optical path to prevent ultraviolet light from entering the calibration cell 40 and to prevent ultraviolet light from being output from the sample cell 20. The ultraviolet light is input to a spectrometer 60.

In step S105, a mixed gas to be measured is introduced into the sample cell 20. Then, in step S106, the arithmetic unit 70 detects the reference light intensity C3 of the ultraviolet light when the gas to be measured is present in the sample cell 20. Note that the computing device 70 calculates the light intensity at the frequency (for example, 226.7 nm) at which the light intensities C6 and C5 are detected in step S101 and step S104 out of the spectrum of the measured ultraviolet light, based on the presence of the gas to be measured in the sample cell 20. It is detected as the light intensity C3 of the ultraviolet light at the time.

In step S107, the arithmetic device 70 specifies light intensities C1 and C2 at predetermined wavelengths in the first ultraviolet wavelength bands W1 and W3 in which NO gas does not interfere. In the example shown in FIG. 5, the light intensities C1 and C2 at wavelengths of 224.5 nm and 229.0 nm, which are separated by a bandwidth of 1.5 nm from the second ultraviolet wavelength band (226.0 nm to 227.5 m), are , specified as the light intensity at a predetermined wavelength. Then, in step S108, the arithmetic unit 70 creates, as an interpolation line, a straight line connecting the light intensities C1 and C2 of the wavelengths extracted in step S107 in the spectrum of the ultraviolet light that has passed through the sample cell 20.

In step S109, the arithmetic unit 70 detects the light intensity C4 on the interpolation line created in step S108. For example, the calculation device 70 detects the light intensity on the interpolation line created in step S108 at a frequency (for example, 226.7 nm) at which the concentration of the gas to be measured is measured as the light intensity C4 on the interpolation line. .

In step S110, the calculation device 70 calculates the concentration of NO gas. Specifically, the arithmetic device 70 performs a calculation on the sample cell 20 based on the light intensity C4 on the interpolation line and the actual light intensity C3 of the ultraviolet light in the second ultraviolet wavelength band W2, based on the above equation 1. The concentration of NO gas in the introduced mixed gas can be calculated.

In step S111, the arithmetic unit 70 performs a process of calibrating the reference light intensity C5 of the ultraviolet light in the sample cell 20 detected in step S104 when the reference gas _N2 is present, based on the calibration rate α. Note that in the following description, the calibrated light intensity C5 will be referred to as C5'.

In step S112, the calculation device 70 calculates the concentration of SO ₂ gas. Specifically, the calculation device 70 substitutes the reference light intensity C5' of the ultraviolet light in the second ultraviolet wavelength band W2 calibrated in step S111 to I ₀ (λ) in the above equation 1, and calculates I(λ ) by substituting the light intensity C4 on the interpolation line of the second ultraviolet wavelength band W2, the concentration n of SO ₂ gas can be calculated.

Then, in step S113, the arithmetic unit 70 determines whether or not to end the measurement of the gas to be measured. Until the user instructs to end the measurement of the target gas, the gas concentration measuring device 1 periodically repeats the measurement of the concentration of the target gas by repeating steps S106 to S113, and monitors the target gas. It can be performed. Then, when the user instructs to end the measurement of the gas to be measured, the gas concentration measurement process shown in FIG. 11 is ended.

As described above, the gas concentration measuring device 1 according to the present embodiment detects NO in the second ultraviolet wavelength band where NO gas interferes based on the light intensity in the first ultraviolet wavelength band where NO gas does not interfere. The light intensity when there is no interference is interpolated, and based on the light intensity when NO gas does not interfere in the second ultraviolet wavelength band and the light intensity when NO gas interferes in the second ultraviolet wavelength band, NO Calculate the concentration of gas. Thereby, even when NO gas and SO ₂ gas that interfere with each other coexist, the concentration of NO gas can be appropriately calculated.

In addition, in this embodiment, by creating a straight line connecting the light intensities C1 and C2 of wavelengths in the first ultraviolet wavelength band in which NO gas does not interfere, as an interpolation line, NO gas does not interfere in the second ultraviolet wavelength band. The light intensity in the case can be easily interpolated. Furthermore, in this embodiment, the light intensities C1 and C2 of wavelengths in the first ultraviolet wavelength band where NO gas does not interfere, and the light intensity of wavelengths separated by a predetermined bandwidth (margin) from the second ultraviolet wavelength band. By doing so, it is possible to appropriately specify the light intensity when NO gas does not interfere in the second ultraviolet wavelength band.

Furthermore, in this embodiment, the SO ₂ gas concentration n can be calculated based not only on the NO gas concentration but also on the light intensity of the ultraviolet light that has passed through the calibration cell 40. That is, the calibration cell 40 is filled with approximately 100% _N2 gas that does not absorb ultraviolet light in the ultraviolet wavelength band of 200 nm or more, and the intensity of the ultraviolet light that has passed through the calibration cell 40 is different from that of other ultraviolet light. It can be considered as the light intensity of ultraviolet light when it is not absorbed by the gas. Therefore, in the above equation 1, the arithmetic device 70 substitutes the light intensity C5 of the ultraviolet light that has passed through the calibration cell 40 for I ₀ (λ), and substitutes the light intensity C5 of the ultraviolet light that has passed through the calibration cell 40 for I (λ) on the interpolated line of the second ultraviolet wavelength band W2. By substituting the light intensity C4, the concentration n of SO ₂ gas can be calculated.

In addition, in the gas concentration measuring device 1 according to the present embodiment, an interpolation line is created based on the spectrum of the ultraviolet light in the sample cell 20, and the light intensity C3 of the ultraviolet light in the sample cell 20 and the light intensity C4 on the interpolation line are Since the NO gas concentration is calculated based on the difference (C4-C3), even if the light source of the irradiation device 10 deteriorates, the NO gas concentration can be appropriately measured. Further, the configuration is such that the spectrum of the ultraviolet light that has passed through the sample cell 20 or the calibration cell 40 is calibrated based on the comparison result between the spectrum of the ultraviolet light before use in the calibration cell 40 and the current spectrum of ultraviolet light. Even if the light source of the irradiation device 10 deteriorates, the concentration of SO ₂ gas can also be appropriately measured.

Although preferred embodiments of the present invention have been described above, the technical scope of the present invention is not limited to the description of the above embodiments. Various changes and improvements can be made to the embodiments described above, and forms with such changes and improvements are also included within the technical scope of the present invention.

For example, in the embodiment described above, when measuring the concentration of NO gas, as shown in FIG. Although the configuration in which the interpolation line is created based on C1 and the light intensity C2 of the wavelength of the first ultraviolet wavelength band W3 on the longer wavelength side than the second ultraviolet wavelength band W2 has been illustrated, the present invention is not limited to this configuration. First, for example, an interpolation line is calculated based on the light intensities C1 and C2 of two wavelengths in the first ultraviolet wavelength band W1, or based on the light intensities C1 and C2 of two wavelengths in the first ultraviolet wavelength band W3. It is also possible to create a configuration.

1... Gas concentration measuring device 10... Irradiation device 11... Lens 12, 13... Beam splitter 14, 15... Reflector 20... Sample cell 21... Inlet 22... Outlet 23... Optical path 30... Temperature control device 40... Calibration cell 51 , 52... Light shielding plate 60... Spectrometer 61... Lens 70... Arithmetic device

Claims (9)

an irradiation device that irradiates ultraviolet light with a wavelength that includes the specific ultraviolet wavelength band to a measurement target space in which a first gas and a second gas that interfere with each other in a specific ultraviolet wavelength band coexist;
a light receiving device that receives the ultraviolet light that has passed through the measurement target space;
an arithmetic device that calculates the concentrations of the first gas and the second gas based on the light intensity of the ultraviolet light received by the light receiving device,
The arithmetic device is configured to determine, based on the first light intensity in a first ultraviolet wavelength band in which the second gas does not interfere, the second gas does not interfere in a second ultraviolet wavelength band in which the second gas interferes. Create an interpolation line to interpolate the light intensity in the case , calculate the second light intensity in the second ultraviolet wavelength band when the second gas does not interfere, and calculate the second light intensity and the calculating the concentration of the second gas based on a third light intensity when the second gas interferes in a second ultraviolet wavelength band ;
Based on the light intensity in the second ultraviolet wavelength band of the ultraviolet light that has passed through a cell filled with a reference gas that does not interfere with the first gas and the second gas, and the second light intensity, A gas concentration measuring device characterized by calculating the concentration of one gas . When the first ultraviolet wavelength band exists on both the shorter wavelength side and the longer wavelength side than the second ultraviolet wavelength band, the calculation device The interpolation line is created based on the light intensity in the first ultraviolet wavelength band and the light intensity in the first ultraviolet wavelength band on the longer wavelength side than the second ultraviolet wavelength band, and The gas concentration measuring device according to claim 1, wherein the light intensity on the interpolation line in an ultraviolet wavelength band is specified as the second light intensity. The arithmetic device operates at a wavelength in the first ultraviolet wavelength band that is shorter than the second ultraviolet wavelength band, and is separated from the second ultraviolet wavelength band by a certain bandwidth or more. Based on the light intensity at a wavelength that is longer than the second ultraviolet wavelength band, or the light intensity at a wavelength that is longer than the second ultraviolet wavelength band and separated from the second ultraviolet wavelength band by a certain bandwidth or more, The gas concentration measuring device according to claim 1 or 2, wherein the interpolation line is created . Furthermore, it has a calibration cell that is continuously filled with a calibration gas of a predetermined concentration,
4. The gas concentration measuring device according to claim 1, wherein the arithmetic device calibrates the concentration of the first gas based on the amount of change over time in the light intensity of the ultraviolet light that has passed through the calibration cell. The first gas is _SO2 gas in the flue,
The second gas is NO gas in the flue,
The gas concentration measuring device according to any one of claims 1 to 4 , wherein the second ultraviolet wavelength band is a wavelength band within a range of 225 to 229 nm. Any one of claims 1 to 5 , wherein the light receiving device has a spectrometer that spectrally spectra the ultraviolet light in the ultraviolet wavelength band absorbed by the first gas and the ultraviolet light in the ultraviolet wavelength band absorbed by the second gas. The gas concentration measuring device described in . 7. The gas concentration measuring device according to claim 1, wherein the irradiation device includes a deuterium lamp that irradiates the measurement target space with ultraviolet light in an ultraviolet wavelength band. irradiating a measurement target space in which a first gas and a second gas that interfere with each other in a specific ultraviolet wavelength band coexist with ultraviolet light having a wavelength that includes the specific ultraviolet wavelength band;
receiving ultraviolet light that has passed through the measurement target space;
A gas concentration measuring method for calculating the concentrations of the first gas and the second gas based on the light intensity of the received ultraviolet light,
Based on the first light intensity in the first ultraviolet wavelength band in which the second gas does not interfere, calculate the light intensity in the second ultraviolet wavelength band in which the second gas does not interfere, when the second gas does not interfere. Create an interpolation line for interpolation, calculate the second light intensity in the second ultraviolet wavelength band when the second gas does not interfere, and calculate the second light intensity and the second ultraviolet wavelength. A gas concentration measuring method that calculates the concentration of the second gas based on the light intensity when the second gas interferes in a band,
Based on the light intensity in the second ultraviolet wavelength band of the ultraviolet light that has passed through a cell filled with a reference gas that does not interfere with the first gas and the second gas, and the second light intensity, A gas concentration measuring method characterized by calculating the concentration of one gas . The first gas is _SO2 gas in the flue,
The second gas is NO gas in the flue,
The gas concentration measuring method according to claim 8 , wherein the second ultraviolet wavelength band is a wavelength band within a range of 225 to 229 nm.