JP2000206041A - Detecting method for concentration of content in sample by using laser spectroscopy - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a detecting method in which the concentration of a content in a sample can be detected precisely even when a change in the temperature of the sample is large. SOLUTION: A light absorption spectrum is measured by laser spectroscopy (S100). A plurality of energy levels are selected on the basis of the light absorption spectrum (S20). Light absorption intensities at the energy levels are found respectively (S22). On the basis of the ratio of the obtained light absorption intensities, the temperature of an exhausts gas is found by referring to a reference table (S21). Then, an optical absorption coefficient is corrected by the temperature of the exhaust gas (S31). Light absorption intensities at the energy levels whose absorption coefficient is corrected are found (S32). By using the corrected optical absorption coefficient and the light absorption intensities, the concentration of carbon monoxide in the exhaust gas is found (S 33). In this manner, since the optical absorption coefficient is corrected by the temperature of the exhaust gas, the concentration can be detected precisely even when a change in the temperature of a sample is large.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for detecting the concentration of a substance contained in a sample using laser spectroscopy, and more particularly, to a method for detecting the concentration of a substance contained in exhaust gas generated during incineration of dust.

[0002]

2. Description of the Related Art It has been reported that exhaust gas generated during incineration of garbage contains substances harmful to the human body. Among such harmful substances, dioxins are highly toxic, so it is urgently necessary to suppress the generation of dioxins. In recent years, it has become clear that there is a correlation between the concentration of carbon monoxide in exhaust gas and dioxin. In order to suppress the generation of dioxins, it has become necessary to monitor the concentration of carbon monoxide in the exhaust gas at the time of incineration of garbage and to suppress the concentration of carbon monoxide to a certain value or less.

[0003] An infrared spectrometer is widely used as a combustion monitor for monitoring the concentration of carbon monoxide during incineration of refuse. FIG. 8 shows the configuration of the infrared spectrometer.

The infrared light emitted from the infrared light source 70 is
Optical path A and optical path B are divided into two optical paths. The infrared rays divided into two optical paths are exhaust gas, that is, a sample cell 71 containing a sample and a reference cell 7 containing an inert gas.
2 respectively. Exhaust gas is taken into the sample cell 71 from the gas inlet 73 and discharged from the gas outlet 74.

[0005] The infrared light that has entered the sample cell 71 is absorbed by a substance contained in the sample (hereinafter, referred to as a substance), the intensity thereof is reduced, and the intensity of the infrared light is reduced.
It is incident inside. In addition, the infrared light that has entered the reference cell enters the other room 76 of the detection unit without absorption and without changing its intensity. A detection gas is sealed in the rooms 75 and 76, and a special sensor 77 is provided between the rooms 75 and 76. Due to the difference in the intensity of the incident infrared rays, a pressure difference occurs between the rooms 75 and 76. This pressure difference is detected by the special sensor 77, and the concentration of the substance contained in the sample in the sample cell 71 is obtained from the pressure difference.

[0006]

However, when the refuse is burned, the temperature of the exhaust gas is reduced from about 0 degrees Celsius to about 1000 degrees Celsius.
The degree and change are very large. Since the intensity of infrared rays has temperature dependence, the intensity may fluctuate due to a change in exhaust gas temperature, that is, a change in sample temperature, and a concentration detection error may occur.

SUMMARY OF THE INVENTION The present invention has been made to solve such a problem, and provides a concentration detecting method for accurately detecting the concentration of a substance contained in a sample to be detected even when the sample temperature change is large. With the goal.

[0008]

A first aspect of the present invention is a method for detecting the concentration of a substance contained in a sample using laser spectroscopy,
First step of measuring the light absorption spectrum of the sample by laser spectrometry, from among the energy levels of the contents of the sample, at least two energy levels are selected and measured in the first step From the obtained light absorption spectrum, light absorption intensity at the selected energy level is obtained, a second step of obtaining a sample temperature using a reference table from the ratio of the light absorption intensity, and corrected at the sample temperature. A third step of obtaining the concentration of the inclusion using the light absorption coefficient obtained.

Therefore, in the method of detecting the concentration of a substance contained in a sample using laser spectroscopy according to the first invention, a selected energy level (from an optical absorption spectrum of the sample measured by laser spectroscopy) is used. Using the light absorption intensity in the vibration / rotation spectrum) and the light absorption coefficient at the energy level, the concentration of the substance contained in the sample is detected. However, the light absorption coefficient changes with the sample temperature. Therefore, in the second step, the sample temperature is determined from the light absorption intensity at the selected energy level. Then, in the third step, the concentration of the inclusion is determined from the light absorption coefficient corrected at the sample temperature. The sample temperature is prepared in advance in the second step from the ratio of the light absorption intensity at at least two energy levels selected from among the known energy levels of the contents of the sample whose concentration is to be detected. Required by a lookup table. As described above, since the light absorption coefficient is corrected at the sample temperature, and the concentration of the contained substance is obtained using the corrected light absorption coefficient, accurate concentration detection is possible even when the range of the change in the sample temperature is large.

[0010] A second aspect of the present invention is a method for detecting the concentration of a substance contained in a sample using laser spectroscopy, comprising: a first step of measuring a light absorption spectrum of the sample by laser spectroscopy; From the energy levels of the inclusions, at least two energy levels are selected, and the light absorption intensity at the selected energy level is determined from the light absorption spectrum measured in the first step. A second step of obtaining the sample temperature from the ratio of the light absorption intensity using a reference table, and using the light absorption coefficient corrected at the sample temperature, to obtain the measured concentration of the content, respectively, A third step of setting an average value of the measured concentration values to the concentration of the content.

Therefore, in the method for detecting the concentration of a substance contained in a sample using laser spectrometry according to the second invention, in the third step, the light absorption coefficient is corrected based on the sample temperature obtained in the second step. This correction is performed at at least two energy levels. A plurality of density measurement values are obtained from the corrected plurality of light absorption coefficients. Then, the average value of each measured concentration value is defined as the concentration of the contained substance. As described above, by using the average of the measured concentration values obtained from the plurality of light absorption coefficients as the substance concentration, the concentration detection error can be further reduced, and accurate concentration detection is possible.

[0013] In a third aspect of the present invention, in the method for detecting the concentration of a substance contained in a sample using laser spectroscopy according to the first aspect or the second aspect, the second step comprises at least two steps. The energy level is selected from energy levels in which the temperature dependence of the light absorption coefficient is high and the sign of the rate of change of the light absorption coefficient with respect to temperature is opposite.

Therefore, in the method for detecting the concentration of a substance contained in a sample using laser spectroscopy according to the third invention, in the second step, the temperature dependence of the light absorption coefficient is high, and the light absorption coefficient of the light absorption coefficient with respect to temperature is high. Select from energy levels with opposite signs of rate of change. Since the light absorption coefficient at such an energy level changes greatly with a change in the sample temperature, the detection error of the sample temperature decreases.

[0014]

Embodiments of the present invention (hereinafter referred to as embodiments) will be described below with reference to the drawings.

FIG. 1 shows the steps of a method for detecting the concentration of a substance contained in a sample according to the present embodiment, for example, a method of detecting the concentration of carbon monoxide in exhaust gas generated during incineration of refuse by a combustion monitor. I have. Hereinafter, the description of the concentration detection method for each step will be described in detail.

In the combustion monitor of this embodiment, first, the light absorption spectrum of the exhaust gas is measured by laser spectroscopy (S
100).

FIG. 2 is a configuration diagram of a known semiconductor laser spectrometer 100 used in the method for detecting the concentration of a substance according to the present embodiment. Laser light 14 emitted from the semiconductor laser 10 is incident on the sample cell 12, and the light absorption intensity of the laser light 14 transmitted through the sample cell 12 is measured by the photodetector 16. In the sample cell 12, a sample whose concentration is to be detected, that is, exhaust gas is injected from a gas inlet 11 and discharged from a gas outlet 13. The laser light 14 incident on the sample cell 12 is absorbed by the contents of the exhaust gas in the sample cell 12, and the absorbed and reduced intensity laser light 14 is incident on the photodetector 16, and the light intensity is measured. . Then, by changing the oscillation frequency of the semiconductor laser 10, the light absorption spectrum of the substance contained in the exhaust gas is measured.
FIG. 3 shows a conceptual diagram of the measured light absorption spectrum. The horizontal axis is the frequency of the laser, and the vertical axis is the light intensity of the laser light measured by the photodetector 16. Due to the absorption of the laser beam by the contents of the exhaust gas, the light intensity at the frequency corresponding to each energy level decreases.

In the semiconductor laser spectrometer 100, the temperature controller 18 and the current controller 20
Since the operating temperature and the driving current of the semiconductor laser 10 are changed, the oscillation frequency of the semiconductor laser 10 is swept. The frequency sweep of a wide range is performed by changing the temperature by the temperature control device 18, and the frequency sweep of the narrow range is performed by changing the current by the current control device 20.

The driving current of the semiconductor laser 10 is modulated by the oscillator 22. Therefore, the laser light 14
Is frequency-modulated (FM) by current modulation. The signal detected by the photodetector 16 is
Lock-in amplifier 24 which uses the signal from 2 as a reference signal
Thus, synchronous detection is performed at the modulation frequency or a frequency twice the modulation frequency, and noise is reduced. The detected signal is input from the lock-in amplifier 24 to a computer or the like (not shown).

The structure of the semiconductor laser spectrometer 100 is not limited to the semiconductor laser spectrometer having the structure shown in FIG. 2 as long as it can measure the light absorption spectrum of the substance contained in the sample.

The material of the semiconductor laser 10 is InG
It may be appropriately selected according to the characteristics such as the oscillation frequency such as aAsP and AlGaAs.

As described above, the temperature of the exhaust gas generated during the combustion of dust usually varies greatly from about 0 degrees Celsius to about 1000 degrees Celsius. When the concentration of carbon monoxide is determined from the light absorption spectrum, the concentration of carbon monoxide is determined using the light absorption coefficient of carbon monoxide at a specific energy level.

For deriving the carbon monoxide concentration, for example, the well-known Lambert-Beer law may be used. The incident light intensity of the semiconductor laser incident on the sample cell 12 is I ₀ , the light intensity measured by the photodetector 16 is I, the light absorption coefficient is α,
Assuming that the concentration of the substance contained in the sample cell 12 is n and the length of the sample cell, that is, the optical path length is L, a relationship of I = I ₀ · exp (−αnL) is established. If αnL is sufficiently small, the above equation can be expressed as I = I ₀ (1−αnL). Therefore, (I ₀ -I) / I ₀ = αnL, and (I ₀ -I) / I ₀ is the light absorption intensity. Therefore, based on the light absorption intensity, light absorption coefficient, and optical path length, the sample cell 1
2 can be determined.

However, the light absorption coefficient has temperature dependence. Therefore, a correct carbon monoxide concentration cannot be obtained unless the light absorption coefficient is corrected for the temperature. In the present embodiment, the sample temperature, that is, the exhaust gas temperature is obtained from the light absorption spectrum, the light absorption coefficient is corrected with the obtained exhaust gas temperature, and the carbon monoxide concentration is obtained using this correction value.

Next, a method for obtaining the sample temperature, that is, the exhaust gas temperature from the light absorption spectrum shown in FIG. 3 will be described (S200).

When obtaining the concentration of carbon monoxide in the exhaust gas,
First, at least two energy levels are selected from among known energy levels of carbon monoxide (S2).
1). FIG. 4 shows, among the energy levels of carbon monoxide in the 1.57 μm band, an energy level having a relatively high light absorption coefficient and a wave number (cm ⁻¹ ) causing absorption. In the present embodiment, two energy levels are selected from these energy levels, but the selection may be made from an arbitrary energy level of carbon monoxide. Further, two or more energy levels may be selected. In the present embodiment, the light absorption coefficient has a high temperature dependency, and the sign of the rate of change of the light absorption coefficient with respect to temperature is selected from different energy levels. Such an energy level selection method will be described with reference to FIG.

FIG. 5 is a schematic diagram showing the temperature dependence of the light absorption coefficient at the energy levels shown in FIG. The horizontal axis in FIG. 5 is the energy level, and the vertical axis is the light absorption coefficient. From FIG. 5, the temperature dependence of the light absorption coefficient is high, and the sign of the rate of change of the light absorption coefficient with respect to temperature,
That is, energy levels with different rates of change are selected. For example, the energy levels R4 and R13 satisfy the conditions described above and are energy levels suitable for selection.

It should be noted that the exhaust gas usually contains substances other than carbon monoxide, such as water. With such an energy level of carbon monoxide overlapping with the energy level of the inclusions other than carbon monoxide, accurate light absorption intensity is not required. Therefore, an energy level that does not overlap with the energy level of such inclusions may be selected.

After two energy levels are selected in S21, the light absorption intensity at the selected energy level is determined for each energy level from the light absorption spectrum measured in S100 (S22).

FIG. 6 shows the energy level R in FIG.
An enlarged view of a portion 30 corresponding to 4 is shown. As described above, the light absorption intensity is obtained from the incident light intensity of the semiconductor laser and the light intensity measured by the photodetector 16. Since the light absorption spectrum has a certain spread, there are various methods for obtaining the light absorption intensity. Energy level R
4 may be obtained from the peak value Ipeak of the light intensity corresponding to the energy level R4 and the incident light intensity, or may be obtained by using various other spectrum analysis methods.

Next, the exhaust gas temperature is determined from the intensity ratio of the light absorption intensity determined in S22 (S23). The exhaust gas temperature at the light absorption intensity ratio can be prepared in advance as a reference table by a known calculation method. In FIG.
The exhaust gas temperature and the light absorption intensity ratio of R13 and R4 are shown. For example, the ratio between the light absorption intensities of R13 and R4 is 0.523 when the exhaust gas temperature is 900 degrees Celsius and 1.23 when the exhaust gas temperature is 0 degrees Celsius.
842. The exhaust gas temperature is determined using such a reference table.

Next, the light absorption coefficient is corrected based on the exhaust gas temperature determined in S200, and the concentration of carbon monoxide in the exhaust gas is determined using the corrected light absorption coefficient (S300).

First, the light absorption coefficient is corrected based on the exhaust gas temperature (S31). The energy level for correcting the light absorption coefficient is
Although it may be the energy level selected in S21,
A completely arbitrary level may be selected. The light absorption coefficient with respect to the exhaust gas temperature is obtained in advance by an experiment. Or
It may be calculated.

Then, the light absorption intensity at the energy level whose light absorption coefficient has been corrected is obtained from the light absorption spectrum measured in S100 (S32). The light absorption intensity is S
As in the case where the light absorption intensity is obtained in step 21, it can be obtained by various spectrum analysis methods.

Then, using the corrected light absorption coefficient, light absorption intensity, and length of the sample cell, the concentration of carbon monoxide is determined by the method described above (S33).

As described above, in the present embodiment, the concentration of carbon monoxide is obtained by using the light absorption coefficient corrected with the temperature of the exhaust gas, so that accurate detection of the concentration of carbon monoxide is possible even when the change in the sample temperature is large. It is.

The correction of the light absorption coefficient is performed at several energy levels, the measured value of the concentration of carbon monoxide at each energy level is obtained, and the average of the measured values of the concentration is calculated as the true concentration of carbon monoxide. It may be. As described above, by obtaining the concentration at a plurality of energy levels, it is possible to detect the concentration with higher accuracy.

The concentration detecting method according to the present embodiment can be used for various concentration detecting devices other than the combustion monitor for detecting the concentration of carbon monoxide in exhaust gas generated during incineration of refuse. Therefore, in the present embodiment, the exhaust gas is used as a sample. However, the material is not limited to the exhaust gas as long as it is a substance capable of spectroscopic measurement.

In this embodiment, the concentration of carbon monoxide contained in the sample is detected. However, the concentration may be detected as long as it is a substance capable of spectroscopic measurement. May be measured.

[0040]

As described above, in the method for detecting the concentration of a substance contained in a sample according to the present invention, since the light absorption coefficient is corrected with the sample temperature, even if the sample temperature change is large, the sample to be detected can be accurately detected. It is possible to provide a concentration detection method for detecting the concentration of a substance.

[Brief description of the drawings]

FIG. 1 is a flowchart illustrating a method for detecting a concentration of a substance contained in a sample according to an embodiment.

FIG. 2 is a block diagram of a semiconductor laser spectrometer used in the method for detecting a concentration of a substance according to the present embodiment.

FIG. 3 is a schematic diagram of a light absorption spectrum measured by spectrometry of the present embodiment.

FIG. 4 is a table showing the energy levels of carbon monoxide in the 1.57 μm band.

FIG. 5 is a graph showing the temperature dependence of the light absorption coefficient at the energy level of carbon monoxide in the 1.57 μm band.

6 is an enlarged view of a light absorption spectrum corresponding to the energy level R4 shown in FIG.

FIG. 7 is a table showing the ratio between the exhaust gas temperature and the light absorption intensity of R13 and R4.

FIG. 8 is a block diagram of a combustion monitor conventionally used.

[Explanation of symbols]

Reference Signs List 10 semiconductor laser, 12 sample cell, 14 laser light, 16 photodetector, 22 oscillator, 24 lock-in amplifier, 100 semiconductor laser spectrometer.

Claims (3)

[Claims] A first step of measuring a light absorption spectrum of a sample by laser spectroscopy; and selecting at least two energy levels from among energy levels of inclusions in the sample; From the light absorption spectrum measured in the step, the light absorption intensity at each of the selected energy levels is determined, a second step of obtaining a sample temperature using a reference table from the ratio of the light absorption intensity, A third step of obtaining the concentration of the inclusion using a light absorption coefficient corrected at the sample temperature. A method for detecting the concentration of an inclusion in a sample using laser spectroscopy. 2. A first step of measuring a light absorption spectrum of a sample by laser spectroscopy; and selecting at least two energy levels from among energy levels of inclusions of the sample, From the light absorption spectrum measured in the step, the light absorption intensity at each of the selected energy levels is determined, a second step of obtaining a sample temperature using a reference table from the ratio of the light absorption intensity, Using a light absorption coefficient corrected at the sample temperature, each of the measured concentration values of the inclusions, and a third step of setting the average value of the respective concentration measurement values to the concentration of the inclusions, A method for detecting the concentration of a substance contained in a sample using laser spectroscopy. 3. The method for detecting the concentration of a substance contained in a sample using laser spectroscopy according to claim 1 or 2, wherein the second step includes: determining at least two energy levels of a light absorption coefficient; A method for detecting a concentration of a substance contained in a sample using laser spectroscopy, wherein the method is selected from energy levels having high temperature dependence and having the opposite sign of the rate of change of the light absorption coefficient with respect to temperature.