JP3342446B2 - Gas concentration measurement device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

[0001] The present invention relates to a device that may generate or emit gas, such as all devices utilizing combustion and chemical plants, and its surroundings, or underground parking lots, tunnels, and tollgates on highways. relates to apparatus for monitoring and analyzing the gas concentration and the like are likely to gases such as from staying places, particularly NOx, CO, relates to a gas concentration measuring device for measuring the concentration of exhaust gas, such as NH _3.

[0002]

2. Description of the Related Art In order to control combustion equipment such as boilers, refuse incinerators, gas turbines, diesel engines, and gasoline engines and to evaluate the properties of exhaust gas, the concentration of nitrogen oxides (NOx) contained in the exhaust gas is required. It is important to measure For this reason, various methods are used to measure the NOx concentration.

Conventional gas concentration measurement methods for measuring NOx include a chemical analysis method (JIS K0104) and an automatic measurement method (JIS 7982). Further, the automatic measurement methods include 1) a chemiluminescence method and 2) an infrared ray. Absorption method 3) ultraviolet absorption method 4)
There are various measurement methods such as a constant potential electrolysis method. These conventional gas concentration measurement methods basically introduce a gas sampled in a continuous or batch manner into an analyzer.

[0004]

However, the conventional chemical analysis method is not suitable for continuous measurement because it takes a long time to collect a sample gas and it takes too much time to complete color development. Also, depending on the method, N
Since O cannot be measured directly, a pretreatment device for converting it to NO ₂ is required. Furthermore, both the conventional chemical analysis method and the automatic measurement method are interfered by other coexisting components such as gas, moisture, and dust, so it is necessary to remove these coexisting components or correct the measured values. In addition, there are various problems such as the need to keep the sample gas temperature and flow rate constant in order to guarantee a certain level of measurement accuracy.

Further, in the conventional method, since it is necessary to sample a fixed amount of the sample gas, it is impossible to directly measure in a boiler furnace, a flue, a road, and the like, and therefore, it is impossible to measure a distribution over a wide range.

In recent years, the performance of semiconductor lasers in the visible or near-infrared wavelength region has been improved, and the semiconductor lasers have sufficient spectral characteristics to be used as a light source for high-resolution spectroscopy. Research at the laboratory level is beginning to take place. This technique uses tunable diode laser absorption spectroscopy.
This is a technique called rption spectroscopy (hereinafter, referred to as TDLAS). Conventional TDLAS has the following (1)
Due to the various problems described in (4) to (4) above, the industry has not yet been put to practical use in actual plants.

(1) Since a sinusoidal fringe generated by an optical component such as a mirror is superimposed on a gas absorption signal and appears in a measurement signal, the size of the fringe is affected by a change in ambient temperature or the like. If it fluctuates, it affects the concentration measurement signal, and the accuracy of gas concentration measurement decreases.

(2) When solid particles coexist in the measurement area,
The laser light is absorbed or scattered, and it becomes impossible to distinguish between the noise and the absorption by the gas, and the accuracy of the gas concentration measurement is reduced. So far, gas concentration measurement using laser light has been possible for clean gas.However, since gas emitted from combustion equipment contains solid particles such as dust, the accuracy of gas concentration measurement is high. A decline is inevitable. In addition, it is necessary to remove solid particles such as dust from the sampling gas by using a pretreatment device, and it is not possible to directly measure the inside of a combustion furnace, a flue, a pipe, or the like.

(3) Absorption of gas has a very narrow line width and is absorbed only at a specific wavelength. A semiconductor laser oscillates at a substantially constant wavelength when the temperature and current are controlled to be constant. However, if the semiconductor laser oscillates for a long time, it is inevitable that the oscillation wavelength itself gradually drifts. When the oscillation wavelength from the semiconductor laser deviates slightly from the absorption peak of the gas to be measured, the measurement sensitivity is greatly reduced. Furthermore, if the oscillation wavelength deviates from the absorption line width (measurement sensitivity band) centered on the absorption peak of the gas to be measured, the laser light is not absorbed by the gas at all, and gas concentration measurement becomes impossible.

(4) In a plant installed outdoors, sunlight may enter the laser receiver, and the intensity of the received light tends to fluctuate depending on the time of day even during a day, and the measurement accuracy of the gas concentration is reduced. Low. Even if all optical components are housed in a box and installed so that sunlight does not enter, if light emission due to combustion always occurs in a furnace such as a boiler, light other than laser light is applied to the receiver. In many cases, it is unavoidable to enter as background light, and measurement accuracy is greatly reduced.

SUMMARY OF THE INVENTION The present invention has been made to solve the above-mentioned problems, and has a high sensitivity, a high sensitivity, and a gas concentration which enables in-situ observation and real-time measurement. It is an object to provide a measuring device .

[0012]

Means for Solving the Problems The present inventors have conducted intensive studies on a highly sensitive gas concentration measuring device which is hardly affected by coexisting components and the measurement environment and whose measurement accuracy does not decrease over a long period of time. The present invention having the following features has been completed.

(1) As a first viewpoint, a gas concentration measuring apparatus according to the present invention comprises a light source for oscillating a laser beam having an absorption wavelength unique to a gaseous substance to be measured, and a laser oscillated from the light source. Means for modulating the oscillation wavelength of the light at at least two different frequencies; means for guiding the laser light modulated by the modulating means to a measurement area where the gaseous substance is present; and means for transmitting, reflecting or scattering in the measurement area. a first light receiving means for receiving the laser beam, the first
The signals modulated by the signals received by the light receiving means are sequentially demodulated for each frequency, and the components of the modulation frequency or
A plurality of first phase-sensitive detectors for obtaining the harmonic components ;
It is characterized by having.

(2) As a second viewpoint, the gas concentration measuring apparatus according to the present invention further comprises a light receiving means for receiving light by the first light receiving means.
And a low-frequency pass filter for obtaining a DC component from the signal .

(3) As a third viewpoint, the gas concentration measuring device according to the present invention further comprises a standard gas having a known gas concentration.
Enclosed or flowable reference cells and this reference
Means for introducing the laser beam into a reference cell, and the reference cell
Second light receiving means for receiving the laser light passing through
The modulation frequency component is selected from the signals received by the second light receiving means.
Second phase-sensitive detector for obtaining minute or harmonic components thereof
From the signals received by the second light receiving means.
Third phase sensitive detector for obtaining odd harmonic components of wave number
And the signal output from the third phase-sensitive detector
Control the oscillation wavelength of the laser light emitted from the light source
And means for performing the operation.

(4) As a fourth viewpoint, the gas concentration measuring device according to the present invention further includes a gas detector near the first light receiving means.
And receives laser light oscillated from the light source.
The second receiving only the intensity of the light emitted from the measurement area.
It is characterized by comprising three light receiving means .

Further, other gas concentration measuring devices (5) to
(8) is characterized in that two or more of the above (1) to (4) are combined as follows.

[0018]

[0019]

[0020]

[0021]

[0022]

[0023]

(5) A gas concentration measuring device comprising a combination of (1), (2) and (3).

(6) is a gas concentration measuring device comprising a combination of (1), (3) and (4).

(7) is a gas concentration measuring device comprising a combination of (1), (2) and (4) .

(8) corresponds to (1), (2), (3) and (4)
Gas concentration measuring device consisting of a combination of:

In the combustion furnace, laser light is applied to the exhaust gas passage.
A measurement window as a guiding means and a laser beam outside the exhaust gas passage
As means for guiding to the light receiving means of the gas concentration measuring device
All measurement windows are required, but two types of measurement windows can be shared by one window. Of course, a plurality of measurement windows can be provided.

In this case, two types of measurement windows can be provided in at least one of the combustion area and the flue.

The various gas concentration measuring devices of the present invention function as follows (a) to (e).

(A) The oscillation wavelength of the laser is modulated at two different frequencies, and this is sequentially demodulated using two phase-sensitive detectors.

(B) A DC component and a modulated component are separated from the modulated laser light intensity signal.

(C) A standard gas is sealed or circulated in the reference cell, and the wavelength of the laser beam received by the second light receiving means is swept.
The oscillation wavelength of the laser is stabilized by fixing the wavelength at the absorption center of the standard gas .

[0034] (e) in addition to the means for receiving the laser beam that has passed through the measurement area, by providing the third light receiving means for detecting the intensity of light emitted from the measurement area without receiving the laser beam, the measurement region It may determine the intensity of the laser light transmitted independently.

The operations (a) to (d) of the present invention will be described with reference to FIGS.

(A) Elimination of Fringe Effect Fringes appearing in an absorption spectrum due to reflection at an optical component often interfere with concentration measurement. Even after carefully removing this fringe, small amplitude fringes may remain. FIG. 4 schematically shows a spectrum in which an absorption signal due to a gaseous component in the form of a Gaussian second derivative and a fringe in the form of a sine wave overlap. In particular, the fluctuation of the amplitude occurs in accordance with the temperature fluctuation of the optical components installed near the outdoor test plant or the actual plant, and as a result, the peak intensity of the absorption fluctuates. However, we have solved this problem by using double modulation. That is, FIG.
In the example shown in ( 1 ), after the output of the second photodiode 5 (or the first photodiode 4) is amplified by the amplifier 15, it is demodulated by the phase sensitive detector 16 of the frequency 2f, and further, the phase of the frequency 2w is The signal is demodulated by the sensitive detector 17 and the high frequency noise is removed by the low frequency filter 18.

The signal waveform shown in FIG. 4 is an absorption signal accompanied by fringes. This is a frequency 2f which is twice the first frequency f.
Corresponds to the demodulated signal. Here, FIG. 3 shows a simplified waveform to make it easier to understand the effects of double modulation and demodulation.
The demodulated spectral absorption signal for each dimension will be described with reference to FIGS. FIG. 3A shows a waveform measured without modulation, FIG. 3B shows a waveform demodulated at a frequency of 1 × (odd order) , FIG. 3C shows a waveform demodulated at a frequency of 2 × twice, d) shows a waveform demodulated at a frequency of 2f + w (odd order) , and (e) shows a waveform demodulated at a frequency of 2f + 2w.

In the apparatus of the present invention, the absorption signal with fringe shown in FIG. 4 (the second derivative absorption spectrum of FIG.
4 in Figure by a signal) fringe is superimposed, and further demodulated at twice the frequency 2w of the second frequency w 3 (e)
The fourth derivative signal is obtained, and the maximum peak of this fourth derivative signal is
This corresponds to observing the difference in intensity between the peaks of the second derivative signal. Therefore, irrespective of the presence or absence of the fringe, the intensity between the peaks is observed. Such double modulation and demodulation enable high-sensitivity and stable measurement for a long time. First phase sensitive detector
Output is a harmonic component 2f that is twice the first modulation frequency f.
This corresponds to the demodulated signal (the signal shown in FIG. 3 (c)).
The output of the second phase-sensitive detector is equal to the output of the first phase-sensitive detector.
Of the signals that have passed through the
The signal demodulated with the double harmonic component 2w (shown in (e) of FIG. 3)
Signal). Here, the significance of double modulation is a single
Modulation at frequency requires multiple reflections of the measurement laser (Flint).
The drift of the measurement value caused by the
Is to suppress.

(B) Simultaneous Measurement of Gas and Solid Particle Concentrations Absorption of gaseous molecules depends on the wavelength of laser light.
Scattering and absorption by solid particles do not depend much on the wavelength of the laser light. In FIG. 2, the second photodiode 5
The output of (PD2) is divided into two. One is a component modulated by the amplifier 15 and the phase-sensitive detector 16, and the other is a DC component detected by the low-pass filter 18. As a result, since both the modulated component and the DC component of the intensity of the laser beam transmitted through the measurement area can be measured, simultaneous measurement of the gas concentration and the solid particle concentration becomes possible.

(C) Stabilization of wavelength In order to realize stable measurement for a long period of time , a wavelength sweep is performed as shown in FIG.
As a result, the oscillation wavelength of the laser light was locked to the absorption peak of the gas in the reference cell. Specifically, in the example shown in FIG. 2, after the output of the first photodiode 4 (PD1) is amplified by the amplifier 15, the output is demodulated by the phase-sensitive detector 16 of the frequency 2f, and further, the phase-sensitive detection of the frequency w is performed. Demodulated by the unit 19,
After passing through the low-pass filter and the amplifier 20, the third derivative of the absorption signal by the gas in the reference cell 3 is obtained. This third-order differential signal is proportional to the difference between the absorption center wavelength of the gas and the oscillation wavelength of the laser light near the absorption center, as shown in FIG. By utilizing this relationship and adding to the adder 14 such that the wavelength difference between the two becomes zero, feedback control is applied, and as a result, the oscillation wavelength of the laser light is stabilized.

(D) Elimination of the influence of background light Since the output of the phase sensitive detector is proportional to the gas concentration and the laser intensity, it must be divided by the laser intensity to calculate the gas concentration.

In the example shown in FIG.
The intensity of the light received by (PD2) includes both the transmitted laser light and the emission of light such as flame (background light).
Therefore, the photodiode 6 (PD3) for receiving only the background light is installed at a position off the optical axis of the laser,
By subtracting the output (light reception intensity) of the photodiode 6 (PD3) from the output (light reception intensity) of the photodiode 5 (PD2), the influence of the background light can be removed.

As described above, according to the gas concentration measuring apparatus of the present invention, the gas concentration in a furnace such as a boiler or a refuse incinerator, in a plant such as smoke, around the plant, or in the atmosphere can be directly measured in real time. Can be.

[0044]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Various preferred embodiments of the present invention will be described below with reference to the accompanying drawings.

As shown in FIG. 1, two optical windows 7 are provided at appropriate positions in a plant 7 where a gas to be measured exists or passes therethrough.
a, 7b are attached. The plant 7 is a combustion furnace such as a boiler or a refuse incinerator, and a laser beam L is directed from one optical window 7a to the other optical window 7b so as to cross an exhaust path through which combustion exhaust gas generated therein flows. Is incident on the measurement area. This measurement area is
It corresponds to a part of the combustion space of the plant 7 and is located in a range where the flame reaches.

A laser oscillator is arranged near one optical window 7a. Laser oscillator is LD module 1
A mirror 1a for reflecting the laser light oscillated from the LD module 1, a half mirror 1b for reflecting a part of the laser light reflected by the mirror 1a toward the optical window 7a and transmitting a part, and a half. A mirror 1c for reflecting the laser beam transmitted through the mirror 1b toward the reference cell 3,
It has.

A semiconductor laser device as a light source is an LD together with a Peltier device for controlling the temperature of the laser device.
It is provided in the module 1. The semiconductor laser device is connected to a control circuit of the LD driver 2 so that its temperature and current are controlled. In the present embodiment, a case where a semiconductor laser element is employed as a light source is described as an example. However, the light source of the present invention is not limited to a semiconductor laser element, and a laser capable of performing other wavelength modulation. The present invention can be applied to all oscillators, and can be applied to all types of light and electromagnetic waves other than lasers if wavelength modulation is possible.

Two photodiodes 5, 6 (PD2, PD3) as light receiving means are provided near the other window 7b. One of the photodiodes 5 is arranged on the laser optical axis, and receives the laser light L passing through the measurement area. The other photodiode 6 is arranged at a position deviated from the laser optical axis, and receives light emitted from the flame in the measurement area as background light. These two photodiodes 5 and 6 are connected so as to send a light receiving signal to the AD converter 9 via the measuring unit 8. The AD converter 9 is a computer 1
0, and the computer 10 is further connected to a display device (not shown) having a display.

The laser light oscillated from the LD module 1 is split into two by the half mirror 1b. The transmitted light passes through the reference cell 3 and passes through the first photodiode 4
The light is received by (PDl) and used for gas concentration verification and wavelength stabilization. On the other hand, the reflected light is introduced into the inside of the combustion furnace 7 through the optical window 7a, and after passing through the measurement region, goes out of the combustion furnace 7 through the optical window 7b, and is reflected by the second photodiode 5 (PD2). ).

Further, light (flame light) emitted from the measurement area is received by the third photodiode 6 (PD3) arranged at a position off the optical axis of the laser light. The electric signals from the three photodiodes 4, 5, 6 are processed by the measuring unit 8. The measurement unit 8 sends the processed analog data to the AD converter 9, which converts the analog data into digital data, and converts this into digital data.
Send to 0. The computer 10 stores the transmitted data in a memory, digitizes or graphs the data, and displays the data on a screen of a display device (not shown). further,
The computer 10 has a second photodiode 5 (PD
The intensity of the light (laser light + background light) received in 2) and the light (background light) received by the third photodiode 6 (PD3)
Is calculated by calculation, and this difference is also displayed on the screen of the display device.

The verification of the gas concentration is performed as follows.

First, a known gas concentration in the reference cell 3 and
The known optical length of the reference cell 3 and the known optical length of the measurement area are input to the computer 10 as data. The computer 10 calls a predetermined mathematical expression from the memory and substitutes the three input data into the corresponding parameters of the mathematical expression,
A gas concentration value is obtained by calculation. The reference cell 3 is filled with a standard gas having a known gas concentration at a constant pressure or is allowed to flow therethrough.

FIG. 2 is a block circuit diagram showing a main part of the gas concentration measuring device according to the embodiment of the present invention.

The measuring unit 8 which is a main part of the apparatus of the present invention
Are ramp wave generator 11, two sine wave generators 12,
13, an adder 14, two amplifiers 15, three phase-sensitive detectors 16, 17, 19, five low-pass filters 1
8. Built-in amplifier / low-pass filter 20.

The ramp generator 11 is shown in FIG.
In order to slowly sweep the laser oscillation wavelength at the absorption spectrum specific to the gas to be measured, for example, a ramp wave having a frequency of 0.5 Hz or 0.01 Hz is applied to the injection current of the semiconductor laser element. I have.
When the change in gas concentration is measured for a long time, the sweep of the laser oscillation wavelength by the ramp generator 11 is stopped, and the laser oscillation wavelength is locked at a predetermined wavelength.

The two sine wave generators 12 and 13 apply sine waves of different frequencies to the injection current of the semiconductor laser element in order to modulate the laser oscillation wavelength. For example, one sine wave generator 1
2, a 10 kHz sine wave (f = 10 kHz) is applied to the LD drive 2 via the adder 14 as a first modulation frequency f, and the other sine wave generator 13 generates a second modulation frequency w. 500 Hz sine wave (w = 5
00 Hz = 0.5 kHz) through the adder 14
The drive 2 is applied.

The adder 14 includes a sweep signal from the ramp generator 11, modulation signals of different frequencies f and w from the two sine wave generators 12 and 13, and a third order of the frequency 2 f + w from the phase sensitive detector 19. The differential demodulation signal is superimposed and applied to the injection current of the semiconductor laser device.

The first, second and third phase-sensitive detectors 16,
Reference numerals 17 and 19 are connected to the photodetector 4 (PD1) of the reference cell 3 via the amplifier 15. Of these, the first and second
The circuit composed of the phase sensitive detectors 16 and 17 is connected to an external AD converter 9 via a low-pass filter 18. On the other hand, a circuit including the first and third phase-sensitive detectors 16 and 19 is connected to the adder 14 via the amplifier / low-pass filter 20. Such a phase sensitive detector is disclosed, for example, in the specification of Japanese Patent Application No. 9-96046.

The laser light receiver 5 (PD2)
Is connected to an AD converter 9 via a series circuit including an amplifier 15, two phase-sensitive detectors 16 and 17, and a low-pass filter 18, and another low-pass filter 1
8 and is bypass-connected to an AD converter 9.
The light receiver 6 (PD3) for background light is connected to the AD converter 9 via the low-pass filter 18.

The low-pass filter 18 removes high-frequency components from the received light signal and allows only low-frequency signals to pass.

When a ramp wave having a sweep wavelength is applied from the ramp generator 11 to the injection current, and sine waves having different frequencies f and w are applied to the injection current from the sine wave generators 12 and 13, respectively. As a result, the laser oscillation wavelength is doubly modulated at two different frequencies f and w. As a result, the modulation frequency f, w
And its higher harmonics, the signal is doubled by the first phase sensitive detector 16 to a frequency of 20 kHz (2 kHz).
f), and then demodulated by the second phase-sensitive detector 17 at twice the frequency of 1 kHz (2w), and a superimposed fourth-order differential signal (2f + 2w) is passed through the low-pass filter 18 to the AD converter. 9

Further, the first phase-sensitive detector 16
The signal demodulated at the double frequency of 20 kHz (2f) is demodulated at the third phase-sensitive detector 19 at the frequency w. The superimposed third-order differential signal (2f + w) is sent to the adder 14 through the amplifier / low-pass filter 20, and based on this signal, the laser oscillation wavelength is feedback-controlled to the absorption center wavelength of the gas to be measured.

Next, the results of measuring the gas concentration using the apparatus of the present invention under various conditions will be described.

Example 1 Analysis of Atmospheric Water Vapor Concentration The characteristics of a 1.8 μm distributed feedback (DFB) semiconductor laser are as follows: injection current: 100 mA; element temperature: 25 ° C .; output power: 4 mW; spectrum width: 2 MHz or less. It is. The oscillation wavelength of the laser is set roughly at the element temperature, and the injection current is set precisely.

The laser oscillation wavelength was calibrated with a Michelson interferometer. The transmitted laser beam is an indium gallium arsenide pin-coupled photodiode (InGaAs PINP).
D) was received.

In our system, one of two measurement methods can be selected.

To measure the absorption spectrum, a ramp wave of 0.5 Hz or 0.01 Hz is applied to the injection current by the ramp generator 11, and the laser wavelength is slowly swept. The laser wavelength is locked to measure a long-term concentration change. Modulation of two sine waves (f = 10 kHz
When (z, w = 500 Hz) is superimposed on the injection current, the laser wavelength is modulated at frequencies of 10 kHz and 500 Hz. The intensity signal of the received light is sequentially demodulated by the phase-sensitive detectors 16 and 17 to 20 kHz and 1 kHz which are twice the modulation frequency.

FIG. 5 is a characteristic diagram showing an absorption spectrum of atmospheric water vapor obtained by measuring indoor air using the apparatus of the present invention. This is an absorption spectrum obtained by detecting atmospheric water vapor on the optical axis in a room. The spectrum in this figure shows the fourth derivative of the absorption line obtained by double modulation, the amplitude of which is proportional to the concentration of water vapor in the atmosphere.

Example 2 Analysis of NO in Sample Cell To detect nitric oxide NO, sample gas was placed in a stainless steel single optical path absorption cell having an effective optical path length of 150 mm and a wedge substrate as a window plate. Was charged. Commercial gas mixture NO
(2.93%) was used as the sample gas. 1.79 wavelength
FIG. 6 shows the measurement results of the absorption spectrum of NO of 67 μm.
(A). 1,796.673nm (5565.843cm- ¹ ) and 1,79
Absorption line of 6.712nm (5565.721cm ^-1), the electronic state ² [pi _1/2 and ² [pi _3/2 of NO molecules, rotation structure R of the third harmonic of the vibration
(6.5).

Next, the result of measurement with the laser wavelength fixed at 1,796.673 nm is shown in FIG. 6B. From the resulting signal strength and noise level,
Was determined to be 1.3 ppm-m / Hz1 / ² .

Example 3 Analysis of CO Gas in Sample Cell A CO absorption spectrum near a wavelength of 1,565.6 nm was measured. In the experiment, C
A standard gas having an O concentration of 5.01% (N ₂ balance) was sealed and used. Measurement cell is 150mm long and 22mm inside diameter
A single optical path cell made of stainless steel with windows for laser transmission at both ends.

FIG. 7A shows the result. The spectrum in the figure is the result of measurement by the double modulation method, and is a fourth-order derivative with respect to the wavelength of the gas absorption spectrum. The spectral peak position coincides with the CO absorption center wavelength, and the peak height is proportional to the CO concentration.

Next, FIG. 7B shows the result of measurement with the laser length fixed at the CO absorption wavelength. From the signal strength and noise level of the result, the lower limit of the CO measurement by this method was evaluated as 5 ppm · m / Hz ^1/2 .

[Example 4] Measurement of CO and dust in a refuse incinerator FIG. 8 shows a system diagram of an experimental apparatus. The large-scale test furnace 30 for waste incineration used in the experiment has a size of 2.2 m in width × 2.2 m in height × 19 m in height. The gas concentration measuring device of the present invention used for the measurement was installed downstream of the secondary air inflow port 31. That is, on the downstream side of the secondary air inflow port 31, two measurement windows 33a and 33b are mounted so as to face each other at an appropriate position in the combustion area of the furnace 30, and the laser beam L from the laser oscillator 21 is passed through one measurement window 33a. Enters the furnace, passes through the measurement area, and the other measurement window 33b
The laser light L that has passed through the light receiving device 22 is received by the light receiver 22. The laser oscillator 21 and the light receiver 22 are connected to a signal processor 23, respectively. An LD control signal is sent from the signal processing device 23 to the laser oscillator 21, whereby the built-in semiconductor laser device oscillates a laser beam having a specific absorption spectrum wavelength of the gas to be measured (CO). The LD signal and the reference signal are sent from the laser oscillator 21 to the signal processing device 23, and the signal processing device 23 changes the LD control signal based on the light receiving signal from the light receiver 22 and the LD signal / reference signal. Thus, the laser oscillation wavelength is feedback-controlled to an optimum one.

The thermometer 2 is located immediately downstream of the measurement area.
4 is inserted so that the temperature of the measurement area is detected. Further, a sampling pipe of the sampling / pretreatment device 25 is inserted into the exhaust gas port 35 so that the exhaust gas is sampled.
A CO concentration meter 26 is connected to the sampling / pretreatment device 25 via a pump.

In the experiment, CO and dust concentration in the furnace were
The temperature inside the furnace was measured with a thermocouple installed at the same position. Furthermore,
At the position of the downstream exhaust boat, the CO at the furnace outlet was measured by a non-dispersive infrared CO concentration meter. In this case, a pretreatment for removing moisture and dust from the sampling gas is performed.

FIG. 9 shows the experimental results. FIG. 9A shows the measurement time on the horizontal axis, and the measurement results by TDLAS and the conventional CO meter on the vertical axis. FIG. 9B shows that T
The measurement result of the dust concentration by DLAS and the measurement result of the furnace temperature by the thermocouple are shown.

When combustion fluctuations occur, CO in the TDLAS
The measurements and the dust measurements are changing simultaneously. On the other hand, the conventional measurement method is delayed by about 100 seconds. From this result, it was demonstrated that the CO concentration in the combustion furnace can be measured in real time by using the apparatus of the present invention.

Example 5 Measurement of CO and Dust in Boiler Furnace FIG. 10 shows a system diagram of an experimental apparatus. The large test furnace 40 for boilers used in the experiment has a size of 2.2 m in width × 2.2 m in height × 19 m in height. The gas concentration measuring device of the present invention used for the measurement was installed downstream of the secondary air inflow port 41. That is, on the downstream side of the secondary air inflow port 41, two measurement windows 43a and 43b are mounted to face each other at an appropriate position in the combustion area of the furnace 40, and the laser light L from the light source unit 63 is passed through one measurement window 43a. Is incident on the furnace, and the laser beam L passing through the measurement area and passing through the other measurement window 43b is received by the light receiving unit 64. The light source unit 63 is connected to the modulation unit 61 of the central control room 60. The light receiving unit 64 is connected to the analyzing unit 62. An LD control signal is sent from the modulation section 61 to the light source section 63, whereby the built-in semiconductor laser element oscillates a laser beam having an absorption spectrum wavelength specific to the gas to be measured (CO). Further, the LD signal and the reference signal are sent from the modulation unit 61 to the analysis unit 62, and the analysis unit 62 changes the LD control signal based on the light reception signal from the light reception unit 64 and the LD signal / reference signal. The oscillation wavelength is feedback-controlled to an optimum one.

A superheater 45 and a reheater 46 are provided downstream of the measurement area. In the flue 47, a denitration device 48, a dust collection device 49, a desulfurization device 50, a chimney 51
Are sequentially provided.

A measuring end of a thermometer (not shown) is inserted to detect the temperature of the measuring area.
Further, a sampling pipe of a sampling / pre-processing device (not shown) is inserted at an appropriate position of the flue 47 so that the exhaust gas is sampled. A CO concentration meter (not shown) is connected to the sampling / pretreatment device via a pump.

In the present embodiment, if a combustion fluctuation occurs,
The CO measurement value and the dust measurement value in TDLAS are simultaneously changing. From this result, it was demonstrated that the CO concentration in the combustion furnace can be measured in real time by using the apparatus of the present invention.

[0083]

According to the present invention, high sensitivity and stable measurement can be performed for a long time regardless of the presence or absence of a fringe.

Further, according to the present invention, since both the modulated component and the DC component of the transmitted laser beam intensity can be measured, it is possible to simultaneously measure the concentrations of gas and solid particles.

Further, according to the present invention, since the oscillation wavelength of the laser is locked to the absorption peak of the gas in the reference cell, stable measurement for a long period can be realized.

Further, according to the present invention, the means for receiving the background light is installed at a position off the optical axis of the laser, and the light receiving output of the background light is subtracted from the light receiving output of the laser light, whereby the influence of the background light is reduced. Can be removed.

As described above, according to the present invention, it is possible to directly measure the gas concentration in a furnace such as a boiler or a refuse incinerator, inside a plant such as smoke, around the plant, or in the atmosphere in real time.

[Brief description of the drawings]

FIG. 1 is an overall configuration diagram of a gas concentration measurement device according to an embodiment of the present invention.

FIG. 2 is a block circuit diagram showing a main part of the gas concentration measuring device according to the embodiment of the present invention.

FIG. 3 (a) is an absorption spectrum diagram when gas concentration is measured without modulation, (b) is a first-order differential absorption spectrum diagram when demodulated at a frequency f of 1 ×, and (c) is 2 × (D) is the tertiary differential absorption spectrum when demodulated at frequency 2f + w, and (e) is the quadratic differential absorption spectrum when demodulated at frequency 2f + 2w. Next-order differential absorption spectrum diagram.

FIG. 4 is an absorption spectrum diagram of an absorption signal accompanied by fringes.

FIG. 5 is an absorption spectrum diagram of atmospheric water vapor.

FIG. 6 (a) is a wavelength tunable semiconductor laser absorption spectroscopy (T
FIG. 4B is a characteristic diagram showing a measurement result of NO spectrum in standard gas by DLAS), and FIG. 4B is a characteristic diagram showing a measurement result of NO concentration by TDLAS.

FIG. 7A is a characteristic diagram showing a measurement result of a CO spectrum in a standard gas by TDLAS, and FIG. 7B is a characteristic diagram showing a measurement result of a CO concentration by TDLAS.

FIG. 8 is a schematic configuration diagram showing a large-scale waste incineration test furnace to which a gas concentration measurement device according to an embodiment of the present invention is attached.

9 (a) is a characteristic diagram showing the time change of the CO concentration measurement value in the large test furnace of FIG. 8, and FIG. 9 (b) shows the time change of the dust concentration and the furnace temperature in the large test furnace of FIG. 8, respectively. FIG.

FIG. 10 is a schematic configuration diagram showing a boiler facility to which the gas concentration measurement device according to the embodiment of the present invention is attached.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... LD module (light source), 2 ... LD driver unit, 3 ... Reference cell, 4,5,6 ... Photodiode (light receiving means; PD1, PD2, PD3), 7 ... Measurement target plant (boiler, combustion furnace), 8 Measurement unit, 9 AD
Converter, 10 ... computer, 11 ... ramp generator,
12, 13 ... sine wave generator (modulation means), 14 ... adder, 15 ... amplifier, 16, 17, 19 ... phase sensitive detector (demodulation means), 18 ... low-pass filter (low frequency pass filter), 20 ... Amplifier / low-pass filter, 21 laser oscillator (LD module / LD driver unit /
Optical system), 22 photodetector, 23 signal processing device (measuring unit / AD converter / computer), 24 thermocouple thermometer, 25 sampling and pre-processing device, 26 non-dispersive infrared CO concentration meter , 30 ... Large test furnace for refuse incineration, 21 ... Laser oscillator, 22 ... Receiver, 23 ... Signal processing device, 24 ... Temperature meter, 25 ... Sampling / pre-processing device, 26 ... CO concentration meter, 40 ... Boiler furnace, Reference numeral 61 denotes a modulator, 62 denotes an analyzer, 63 denotes a light source, and 64 denotes a light receiver.

──────────────────────────────────────────────────続 き Continuation of the front page (72) Inventor Ichiro Yamashita 1-8-1 Koura, Kanazawa-ku, Yokohama-shi, Kanagawa 1 Yokohama Research Institute, Mitsubishi Heavy Industries, Ltd. (56) References JP-A-4-326604 (JP, A) JP-A-7-280729 (JP, A) JP-A-10-185814 (JP, A) JP-A-58-68647 (JP, A) JP-A-2000-275173 (JP, A) JP-A-10-142148 (JP, A) JP-A-5-26804 (JP, A) JP-A-10-148613 (JP, A) JP-A-5-196502 (JP, A) Japanese Utility Model Laid-Open No. 58-6258 (JP, U) (58) Field surveyed (Int. Cl. ⁷ , DB name) G01N 21/00-21/61 JOIS WPI / L EPAT PATOLIS

Claims (8)

(57) [Claims] 1. A light source that oscillates a laser beam having an absorption wavelength specific to a gaseous substance to be measured, means for modulating an oscillation wavelength of a laser beam oscillated from the light source at at least two different frequencies, Means for guiding the laser light modulated by the modulating means to a measurement area where the gaseous substance is present; first light receiving means for receiving laser light transmitted, reflected or scattered in the measurement area ; Signals modulated from the signals received by the light receiving means are sequentially demodulated for each frequency, and the modulation frequency
And a plurality of first phase-sensitive detectors for obtaining a component or a harmonic component thereof . 2. The method according to claim 1, further comprising the step of receiving light by said first light receiving means.
Equipped with low-pass filter to obtain DC component from signal
The gas concentration measuring device according to claim 1, wherein
Place. 3. A standard gas having a known gas concentration is sealed.
A reference cell inserted or allowed to flow therethrough, means for introducing the laser light into the reference cell, and a second light receiving means for receiving the laser light passing through the reference cell
Means and a modulation frequency from signals received by the second light receiving means.
Second phase-sensitive detection for obtaining the component of
And a modulation frequency from signals received by the second light receiving means.
Using a third phase-sensitive detector that obtains an odd-order harmonic component, and a signal output from the third phase-sensitive detector
Controlling the oscillation wavelength of laser light emitted from the light source
2. The gas generator according to claim 1, further comprising:
Concentration measuring device. 4. The apparatus according to claim 1, further comprising :
Laser light emitted from the light source is not received,
A third type that receives only the intensity of light emitted from the measurement area
The gas sensor according to claim 1, further comprising light receiving means.
Concentration measuring device. 5. The apparatus according to claim 1 , wherein said first light receiving means receives light.
A low-frequency pass filter that obtains a DC component from the signal, and a standard gas with a known gas concentration is enclosed or can flow
And the laser light is guided to this reference cell.
Means for receiving a laser beam having passed through the reference cell.
Means and a modulation frequency from signals received by the second light receiving means.
Second phase-sensitive detection for obtaining the component of
And a modulation frequency from signals received by the second light receiving means.
Using a third phase-sensitive detector that obtains an odd-order harmonic component, and a signal output from the third phase-sensitive detector
Controlling the oscillation wavelength of laser light emitted from the light source
2. The gas generator according to claim 1, further comprising:
Concentration measuring device. 6. A standard gas having a known gas concentration is sealed.
A reference cell inserted or allowed to flow therethrough, means for introducing the laser light into the reference cell, and a second light receiving means for receiving the laser light passing through the reference cell
Means and a modulation frequency from signals received by the second light receiving means.
Second phase-sensitive detection for obtaining the component of
And a modulation frequency from signals received by the second light receiving means.
Using a third phase-sensitive detector that obtains an odd-order harmonic component, and a signal output from the third phase-sensitive detector
Controlling the oscillation wavelength of laser light emitted from the light source
Means for receiving light from the light source provided near the first light receiving means.
The vibrated laser light did not receive and was emitted from the measurement area
And a third light receiving unit that receives only light intensity.
The gas concentration measurement device according to claim 1, wherein: 7. A light receiving means for receiving light by said first light receiving means.
A low-frequency pass filter that obtains a DC component from a signal; and a low-pass filter that is provided near the first light receiving unit and emits light from the light source.
The vibrated laser light did not receive and was emitted from the measurement area
And a third light receiving unit that receives only light intensity.
The gas concentration measurement device according to claim 1, wherein: 8. A light receiving means for receiving light by said first light receiving means.
A low-frequency pass filter that obtains a DC component from the signal, and a standard gas with a known gas concentration is enclosed or can flow
And the laser light is guided to this reference cell.
Means for receiving a laser beam having passed through the reference cell.
Means and a modulation frequency from signals received by the second light receiving means.
Second phase-sensitive detection for obtaining the component of
And a modulation frequency from signals received by the second light receiving means.
Using a third phase-sensitive detector that obtains an odd-order harmonic component, and a signal output from the third phase-sensitive detector
Controlling the oscillation wavelength of laser light emitted from the light source
Means for receiving light from the light source provided near the first light receiving means.
The vibrated laser light did not receive and was emitted from the measurement area
And a third light receiving unit that receives only light intensity.
The gas concentration measurement device according to claim 1, wherein: