JP5349996B2 - Gas concentration measuring device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To continuously measure the concentration of a gas in real time. <P>SOLUTION: An apparatus includes: the probe 3 inserted in a flow channel 1 of a measuring target gas and having a first reflecting mirror 2 reflecting the signal light, which is allowed to irradiate the measuring target gas, to reciprocate the same; a light source 5 which emits the laser beam 4 of a wavelength band absorbed by the sulfur oxide (target gas) in the measuring target gas and can scan the wavelength of the laser beam; a light path changeover device 6 for changing over the light path of the laser beam 4 to alternately generate the signal light and reference light; a photodetector 7 for measuring the intensities of the signal light and reference light passed through the measuring target gas; and an arithmetic part 8 for calculating the concentration of the sulfur oxide in the measuring target gas on the basis of the intensities of both of the signal light and the reference light measured by the photodetector 7. <P>COPYRIGHT: (C)2010,JPO&amp;INPIT

Description

The present invention relates to a gas concentration measuring apparatus. More specifically, the present invention relates to a gas concentration measuring apparatus for measuring a concentration distribution of a target gas in a measurement target gas based on absorption characteristics obtained by irradiating the measurement target gas with laser light and scanning the wavelength thereof. Is.

As an apparatus for measuring the concentration of SO ₃ contained in combustion exhaust gas discharged from a thermal power plant, for example, there is one described in Japanese Patent Application Laid-Open No. 2003-232758. In this SO ₃ concentration measuring apparatus, as shown in FIG. 9, the combustion exhaust gas in the flue 101 is taken into the spiral tube 102 and cooled by the cooling unit 103, and the SO ₃ in the combustion exhaust gas is spirally converted to H ₂ SO _4. Condensation is caused on the inner wall of the tube 102. Then, H ₂ SO ₄ is washed and recovered, and the electrical conductivity of the recovered H ₂ SO ₄ aqueous solution is measured by the conductivity meter 105 in the conductivity measuring tank 104 to calculate the H ₂ SO ₄ concentration. Thereafter, SO ₃ in the combustion exhaust gas is calculated based on the calculated H ₂ SO ₄ concentration.

JP 2003-232758 A

However, the above measuring device, after condensation the SO ₃ in the combustion exhaust gas as H ₂ SO _4, since measuring the electrical conductivity and washed with water recovered as aqueous H ₂ SO _4, and flows into the flue 101 The SO ₃ concentration in the flue gas cannot be measured in real time and continuously.

An object of the present invention is to provide a gas concentration measuring device capable of continuously measuring a concentration distribution of a target gas contained in a measurement target gas such as a concentration distribution of sulfur oxide in combustion exhaust gas in real time. .

In order to achieve this object, the gas concentration measuring device according to claim 1 is inserted into the flow path of the measurement target gas, and reflects and reciprocates the signal light irradiated in the measurement target gas. And a probe having driving means for moving the first reflecting mirror along the optical path of the signal light, and a light source capable of irradiating laser light in a wavelength band absorbed by the target gas in the measurement target gas and scanning the wavelength An optical path switch that alternately generates a signal light and a reference light by switching an optical path of the laser light, a photodetector that measures the intensity of the signal light and the reference light that has passed through the measurement target gas, and a photodetector target gas based on a difference in concentration of the target gas obtained by changing the position of the first reflecting mirror together determine the concentration of target gas in the gas as the object of measurement based on the signal light intensity and reference light intensity measured by the Those comprising a calculation unit for obtaining a concentration distribution along the optical path of the signal light.

Therefore, the laser light emitted from the light source becomes signal light or reference light by switching the optical path of the optical path switch. The signal light is irradiated toward the probe inserted in the flow path of the measurement target gas, passes through the measurement target gas flowing in the flow path, is reflected by the first reflecting mirror, and returns. The intensity of this return light is measured with a photodetector. Further, the reference light is incident on the photodetector without touching the measurement target gas in the flow path. The photodetector measures the intensity of this incident light. Since the optical path switch alternately generates the signal light and the reference light, it is possible to measure the intensity of the signal light that has been absorbed by the target gas in the measurement target gas and the reference light that has not received such absorption. it can. The light source scans the wavelength of the laser light, and the signal light intensity and the reference light intensity are measured for each wavelength. Based on the measurement result, the calculation unit obtains the concentration of the target gas. The probe includes driving means for moving the first reflecting mirror along the optical path of the signal light, and when the driving means moves the first reflecting mirror, the optical path length of the signal light in the measurement target gas. Increases or decreases. If the absorption of the signal light is measured while changing the optical path length, it becomes a function of the integrated value of the concentration. Therefore, the concentration distribution can be obtained by performing a differential operation on the optical path length.

  Further, the gas concentration measuring apparatus according to claim 2, wherein the optical path switch includes a first position where the laser beam emitted from the light source is incident on the photodetector via the probe, and the laser beam emitted from the light source is probed. The optical chopper has a second position that is incident on the photodetector without passing through the first chopper, and moves alternately to the first position and the second position.

  Therefore, when the optical path switch, which is an optical chopper, moves to the first position, the laser light emitted from the light source becomes signal light, passes through the measurement target gas, and is incident on the photodetector. When the optical path switch is moved to the second position, the laser light emitted from the light source becomes reference light and enters the photodetector without passing through the measurement target gas. Since the optical chopper is rotating and alternately moves to the first position and the second position, the signal light and the reference light are alternately generated, and their intensity is measured by the photodetector.

  According to a third aspect of the present invention, there is provided the gas concentration measuring apparatus according to the third aspect, wherein the optical path switching unit divides the laser light emitted from the light source into signal light and reference light, and the first disposed on the optical path of the signal light. An optical modulator and a second optical modulator disposed on the optical path of the reference light are provided, and the first optical modulator and the second optical modulator are alternately opened and closed.

  Therefore, the laser light emitted from the light source is split into signal light and reference light by the splitter. When the first optical modulator on the optical path of the signal light is opened and the second optical modulator on the optical path of the reference light is closed, only the signal light reaches the photodetector. On the other hand, when the first optical modulator is closed and the second optical modulator is opened, only the reference light reaches the photodetector. Since the first optical modulator and the second optical modulator are alternately opened and closed, the optical path of the laser light reaching the photodetector is switched, and the intensity of the optical signal and the reference light are measured alternately.

  Further, the gas concentration measuring apparatus according to claim 4 forms a space surrounded by a wall in front of the first reflecting mirror and supplies a cleaning gas to the space to reduce the pressure in the space. Higher than the pressure. Therefore, the measurement target gas can be prevented from flowing into the space in front of the first reflecting mirror from the periphery, and soot and dust in the gas can be prevented from adhering to the first reflecting mirror.

Further, in the gas concentration measuring apparatus according to claim 5, the drive means is a guide rail provided in parallel with the optical path of the signal light, and is guided and moved by the guide rail, and the first reflector is attached. A mirror holder and a screw for moving the reflector holder along the guide rail are provided.

  In the gas concentration measuring apparatus according to claim 6, the target gas is sulfur oxide. Therefore, the concentration of sulfur oxide in the measurement object gas can be measured.

In the gas concentration measuring apparatus according to the first aspect, the concentration of the target gas in the measurement target gas can be measured continuously in real time, and the concentration distribution of the target gas in the flow path can be obtained.

  In the gas concentration measuring apparatus according to the second aspect, since the optical chopper is an optical path switch, the laser light can be converted into signal light and reference light with a mechanical configuration. Further, since the laser light is switched to the signal light or the reference light and used, the generated laser light can be used effectively.

  In the gas concentration measuring apparatus according to the third aspect, the laser beam can be converted into the signal beam and the reference beam electro-optically, and the control thereof is easy.

  In the gas concentration measuring apparatus according to claim 4, the surface of the first reflecting mirror can be maintained in a clean state. Therefore, it is possible to prevent the signal light intensity from decreasing other than the absorption by the target gas in the measurement target gas, and the concentration of the target gas can be measured more accurately.

Further, as in the gas concentration measuring apparatus according to claim 5 , the driving means is guided by the guide rail provided parallel to the optical path of the signal light, and is moved by being guided by the guide rail, and the first reflecting mirror is attached. It is preferable to include a reflecting mirror holder and a screw that moves the reflecting mirror holder along the guide rail.

  In the gas concentration measuring apparatus according to the sixth aspect, since the target gas is sulfur oxide, the concentration of sulfur oxide in the measurement target gas can be measured.

It is sectional drawing which shows an example of embodiment of the gas concentration measuring apparatus of this invention. The state of measurement by the measurement apparatus is shown, (A) is a conceptual diagram in a state where signal light is irradiated, and (B) is a conceptual diagram in a state where reference light is irradiated. It is sectional drawing which expands and shows the stain | pollution | contamination prevention mechanism of a 1st reflective mirror. It is sectional drawing which expands and shows an inflow prevention mechanism. The light shielding plate of the optical chopper as an optical path switch is shown, (A) is a front view of the state which moved to the 1st position, (B) is a front view of the state which moved to the 2nd position. It is explanatory drawing of the procedure which produces | generates a trigger signal from a chopper synchronizing signal, (A) is a chopper synchronizing signal, (B) is a signal light gate signal, (C) is a reference light gate signal, (D) is a laser synchronization. (E) is a signal light trigger signal, and (F) is a reference light trigger signal. The other embodiment of the gas concentration measuring apparatus of this invention is shown, (A) is a conceptual diagram of the state which irradiates signal light, (B) is a conceptual diagram of the state which irradiates reference light. FIG. 6 is a cross-sectional view of a driving means for moving the first reflecting mirror, showing still another embodiment of the gas concentration measuring apparatus of the present invention. It is a conceptual diagram illustrating a conventional SO ₃ concentration measuring apparatus.

  Hereinafter, the configuration of the present invention will be described in detail based on the best mode shown in the drawings.

  FIGS. 1-6 shows an example of embodiment of the gas concentration measuring apparatus of this invention. The gas concentration measuring device is inserted into the flow path 1 of the measurement target gas, and includes a probe 3 having a first reflecting mirror 2 that reflects and reciprocates the signal light irradiated in the measurement target gas, and the measurement target gas. A light source 5 capable of irradiating a laser beam 4 in a wavelength band absorbed by the target gas and scanning the wavelength; and an optical path switch 6 for alternately generating a signal light and a reference light by switching an optical path of the laser light 4; The photodetector 7 that measures the intensity of the signal light and the reference light that has passed through the measurement target gas, and the target gas in the measurement target gas based on the signal light intensity and the reference light intensity measured by the photodetector 7. A calculation unit 8 for obtaining the concentration is provided. The light source 5 is installed toward the probe 3. The optical path switch 6 is installed between the light source 5 and the probe 3. The photodetector 7 is installed so as to face the optical path switch 6 from a direction orthogonal to the optical axis of the light source 5. A second reflecting mirror 9 is installed on the opposite side of the photodetector 7 with the optical path switch 6 interposed therebetween. The light source 5, the optical path switch 6, the photodetector 7, and the second reflecting mirror 9 are accommodated in the casing 10.

  The gas concentration measuring device of this embodiment is a sulfur oxide measuring device, and the target gas is sulfur oxide.

  The probe 3 has, for example, an elongated cylindrical shape, and the first reflecting mirror 2 is accommodated at the distal end 3 a of the probe 3 toward the base end 3 b, in other words, toward the light source 5. A flange 3c for attachment to the flow path 1 is provided on the outer peripheral surface in the vicinity of the base end 3b of the probe 3, and the distal end 3a side of the flange 3c is inserted into the flow path 1. In the insertion portion of the probe 3 into the flow path 1, a long hole 3 d serving as a gas passage 33 through which the measurement target gas flows in the radial direction, more specifically in the direction in which the measurement target gas flows, flows. Is formed. The long hole 3d is formed at a position away from the both ends 3a and 3b of the probe 3 to some extent. Accordingly, spaces 11 and 12 surrounded by the peripheral wall 3e are formed on both sides of the gas passage 33 in the probe 3. The proximal end 3 b of the probe 3 is attached at a position facing the light source 5 on the wall 10 a of the casing 10. A window 10b is provided at a position where the probe 3 is attached to the wall 10a, and the laser light 4 emitted from the light source 5 enters the probe 3 through the window 10b and returns from the probe 3 into the casing 10.

  The light source 5 is a wavelength tunable infrared laser, such as a quantum cascade laser, which generates laser light 4 in the wavelength band absorbed by sulfur oxide, which is a target gas, for example, an infrared region having a wavelength of 7.0 to 7.5 μm. The light source 5 emits laser light 4 toward the probe 3.

  The optical path switching device 6 of the present embodiment is irradiated from the light source 5 with a first position 13 (FIG. 5A) where the laser light 4 irradiated from the light source 5 is incident on the photodetector 7 via the probe 3. The second position 14 (FIG. 5B) where the laser beam 4 is incident on the photodetector 7 without passing through the probe 3 is alternately provided at the first position 13 and the second position 14. A moving chopper. In the present embodiment, the first reflecting mirror 2 and the first reflecting mirror 2 allow the laser light 4 irradiated from the light source 5 to the light shielding plate to pass as signal light toward the first reflecting mirror 2 in the probe 3. A first reflecting portion 16 that reflects the reflected signal light toward the photodetector 7 is provided, and a position where these portions coincide with the optical axis of the laser light 4 is a first position 13. Further, the second reflecting portion 17 that reflects the laser light 4 irradiated from the light source 5 onto the light shielding plate toward the second reflecting mirror 9 as reference light, and the reference light reflected by the second reflecting mirror 9 A second hole 18 that is passed toward the photodetector 7 is provided, and a position where these holes coincide with the optical axis of the laser light 4 is a second position 14. As shown by a broken-line circle in FIG. 5, the first hole 15 and the second reflecting portion 17 are provided on the same circumference, and the first reflecting portion 16 and the second hole 18 are on the same circumference. Is provided. In the present embodiment, the first hole 15 and the second reflecting portion 17 are formed inside the first reflecting portion 16 and the second hole 18, but the first hole 15 and the second reflecting portion are formed. The portion 17 may be formed outside the first reflecting portion 16 and the second hole 18.

  The first hole 15 and the first reflecting portion 16 that are the first position 13 and the second reflecting portion 17 and the second hole 18 that are the second position 14 are alternately arranged at equal intervals in the circumferential direction. Is provided. In the present embodiment, these are alternately provided at six locations at intervals of 30 degrees. However, the number is not necessarily limited to six, and other numbers may be used. The optical path switch 6 is provided in a state inclined by, for example, 45 degrees with respect to the optical axis of the light source 5.

The photodetector 7 measures the intensity of the laser beam 4 and supplies the measurement signal to the arithmetic unit 8. The calculation unit 8 is constituted by a microcomputer, for example. The calculation unit 8 calculates the SO ₂ concentration and the SO ₃ concentration in the measurement target gas, for example, by the following procedure. The calculation unit 8 stores a program indicating a calculation procedure, data such as absorption amounts a and a ′ per unit concentration of the target gas measured in advance in a storage device, and refers to the data while referring to the data. Run the program to calculate the concentration.

Assuming that the substances that absorb the laser beam 4 in the optical path are only SO ₂ and SO ₃ , the relationship of Equation 1 is established.
<Equation 1>
I = I ₀ exp [−anL−a′n′L]
Here, I: signal light intensity obtained by measuring the laser beam reflected by the first reflecting mirror 2 by the photodetector 7, I ₀ : laser beam reflected by the second reflecting mirror 9 by the photodetector 7 Measured reference light intensity, L: optical path length of signal light, n: SO ₂ concentration in the optical path, n ′: SO ₃ concentration, a: absorption amount per unit concentration of SO ₂ , a ′: unit concentration of SO ₃ The amount absorbed per unit. Note that a and a ′ do not depend on the concentration or the optical path length.

Absorption a, to determine a 'is measured before the measurement of the gas signal light is transmitted through the gas cell of known SO ₂ concentration n length was placed _a L _a, the signal light intensity I _a, the reference beam The intensity I _0a is measured. Then, a is obtained from Equation 2. When the wavelength of the laser beam 4 is scanned, a coefficient a for each wavelength is obtained.
<Equation 2>
I _a = I _0a exp [-an _a L _a ]

Equation 3 is obtained from Equation 2.
<Equation 3>
_{a = (1 / n a L} a) log e (I 0a / I a)

Similarly, a known SO ₃ concentration n _a ′ is put in the cell, and the signal light intensity I _a ′ and the reference light intensity I _0a ′ are measured. Then, a ′ is obtained from Equation 4. When the wavelength of the laser beam 4 is scanned, a coefficient a ′ for each wavelength is obtained.
<Equation 4>
_{I a '= I 0a' exp} [-a'n a 'L a]

Equation 5 is obtained from Equation 4.
<Equation 5>
a ′ = (1 / n _a ′ L _a ) log _e (I _0a ′ / I _a ′)

Next, Formula 1 at the time of measurement of the measurement target gas is rewritten to Formula 6.
<Equation 6>
na + n′a ′ = (1 / L) log _e (I ₀ / I)
The left side of Equation 6 is a linear function of the result obtained by the measurement using the gas cell, and the right side is the result obtained by the measurement in the measurement target gas.

The wavelength w of the laser beam 4 is scanned, and I ₀ and I are measured for each wavelength. Then, Expression 6 becomes a matrix arithmetic expression nA + n′A ′ = B. Here, A and A ′ are vectors in which a and a ′ for each wavelength obtained by Equations 2 and 4 are arranged, and B is a vector in which the right side of Equation 6 is arranged for each wavelength. Therefore, the coefficients n and n ′ can be determined by an optimization operation such as a least square method, and the SO ₂ concentration n and the SO ₃ concentration n ′ are determined. In the case of the optimization operation of the least square method, the values of n and n ′ that minimize Equation 7 are obtained. Here, E is a deviation between the linear function of the result obtained by the measurement using the gas cell and the result obtained by the measurement in the measurement target gas.
<Equation 7>
E = ‖nA + n'A'-B‖ ²

  The gas concentration measuring apparatus of the present embodiment includes a contamination preventing mechanism for the first reflecting mirror 2. The dirt prevention mechanism forms, for example, a space 11 surrounded by a wall in front of the first reflecting mirror 2 and supplies a cleaning gas to the space 11 so that the pressure in the space 11 is higher than the surrounding pressure. To do. In this embodiment, as shown in FIG. 3, a space 11 surrounded by the peripheral wall 3 e of the probe 3 is formed in front of the first reflecting mirror 2. A plurality of air holes 19 are formed in the circumferential wall 3e at a position surrounding the space 11 along the circumferential direction. An annular passage 20 is attached around each air hole 19. A blower pipe 21 is connected to the annular passage 20, and the blower pipe 21 is connected to a compressor 22 provided outside the flow path 1. When the compressor 22 is operated to supply air from the blower pipe 21 into the space 11 and the pressure in the space 11 is made higher than the surrounding pressure, it is possible to prevent the measurement target gas from flowing into the space 11. It is possible to prevent soot and dust contained in the measurement target gas from adhering to the first reflecting mirror 2 and contaminating it.

  In addition, the gas concentration measurement device of the present embodiment includes an inflow prevention mechanism that prevents the measurement target gas from flowing into the casing 10. The inflow prevention mechanism forms, for example, a space 12 surrounded by a wall at the base end 3b of the probe 3 and supplies a cleaning gas to the space 12 to make the pressure in the space 12 higher than the surrounding pressure. It is. In the present embodiment, as shown in FIG. 4, a space 12 surrounded by the peripheral wall 3 e of the probe 3 is formed in front of the window 10 b of the casing 10. A plurality of air holes 23 are formed in the circumferential wall 3e at a position surrounding the space 12 along the circumferential direction. An annular passage 24 is attached around each air hole 23. A branch pipe 25 branched from the middle of the blower pipe 21 is connected to the annular passage 24. When the compressor 22 is operated to supply air from the branch pipe 25 to the space 12 via the blower pipe 21 and the pressure in the space 12 is made higher than the surrounding pressure, the measurement target gas flows into the space 12. It is possible to prevent the measurement target gas from flowing into the casing 10 from the window 10b.

  The contamination prevention mechanism of the first reflecting mirror 2 and the inflow prevention mechanism of the measurement target gas into the casing 10 in the gas concentration measurement apparatus of the present embodiment prevent the measurement target gas from flowing into the spaces 11 and 12. Thus, since the region where the gas exists is limited to the space of the gas passage 33, it is determined that the optical path length L in the measurement target gas of the signal light is twice the length of the gas passage 33. The double is because the signal light reciprocates in the gas passage 33.

The gas concentration measuring device is used, for example, to measure the concentration of sulfur oxides, specifically SO ₂ and SO ₃ contained in combustion exhaust gas generated by thermal power generation. That is, the measurement target gas is, for example, combustion exhaust gas, and the flow path 1 is, for example, a flue from a boiler. For example, a cylindrical fixing portion 26 is provided at the measurement position of the flow path 1, and a hole 1 a for inserting the probe 3 is formed in the back of the fixing portion 26. The probe 3 is inserted into the fixed portion 26, and further inserted into the flow path 1 through the hole 1a, and the flange 3c of the gas concentration measuring device is fixed to the flange 26a of the fixed portion 26, so that the measurement target gas from the measurement position A gas concentration measuring device can be attached in a state in which leakage of gas is prevented. When the gas concentration measuring device is attached, the long hole 3d is located in the flow path 1. For example, the probe 3 is inserted so as to be orthogonal to the flow of the measurement target gas.

  Next, measurement by the gas concentration measuring device will be described.

  In a state where the probe 3 is inserted into the flow channel 1, the measurement target gas passes through the gas passage 33 of the long hole 3d. In this state, the compressor 22 and the optical path switch 6 are operated, and the laser light 4 is emitted from the light source 5. The laser beam 4 is emitted in a pulse shape.

  The laser beam 4 emitted from the light source 5 while the optical path switch 6 is moved to the first position 13 passes through the first hole 15 and enters the probe 3 and is reflected by the first reflecting mirror 2. It returns to the inside of the casing 10 (FIG. 2 (A)). At this time, the laser beam 4 passes through the measurement target gas passing through the gas passage 33. That is, the laser beam 4 reciprocates in the probe 3 as signal light. Since the optical axis of the signal light is slightly shifted when reflected by the first reflecting mirror 2, the signal light returning into the casing 10 hits the first reflecting portion 16 of the optical path switch 6 and strikes the photodetector 7. Reflected towards.

  On the other hand, the laser light 4 emitted from the light source 5 in a state where the optical path switch 6 is moved to the second position 14 hits the second reflecting portion 17 of the optical path switch 6 and is used as a reference light for the second reflecting mirror. It is reflected toward 9 (FIG. 2B). Then, the reference light is reflected by the second reflecting mirror 9 and returned. Since the optical axis of the reference light is slightly shifted when reflected by the second reflecting mirror 9, the returned reference light passes through the second hole 18 and enters the photodetector 7. Since the optical path switch 6 rotates and alternately moves to the first position 13 and the second position 14, the signal light and the reference light are alternately generated in synchronization with the switching cycle of the positions 13 and 14. Then, the light detector 7 measures the intensity of the signal light and the reference light.

  At the start end and the end end of each position 13, 14 of the optical path switch 6, a part of the laser beam 4 hits the edge of each hole 15, 18 and the intensity decreases. In order to suppress such fluctuations in the intensity of the laser beam 4, intensity measurement is not performed at the start and end ends of the positions 13 and 14. The concept is shown in FIG. FIG. 2A shows a chopper synchronization signal generated by the optical path switch 6 or supplied from an external signal generator (not shown). Further, the optical path switch 6 has a signal light gate signal (FIG. 5B) in which the rise and fall of the first position 13 of the chopper synchronization signal are shortened by time t, and the rise and rise of the second position 14 respectively. A reference light gate signal (FIG. 5C) in which the decrease is shortened by time t is generated and supplied to the arithmetic unit 8.

  The light source 5 generates a laser synchronization signal that is a reference for the irradiation of the laser beam 4 ((D) in the figure). The frequency of the laser synchronization signal is sufficiently larger than the frequency of the chopper synchronization signal. The calculation unit 8 performs a logical AND operation of the laser synchronization signal and the signal light gate signal to generate a signal light trigger signal (FIG. 5E), and also calculates the laser synchronization signal and the reference light gate signal. A logical AND operation is performed to generate a reference light trigger signal ((F) in the figure). Further, the calculation unit 8 records the output signal of the photodetector 7 in synchronization with the signal light trigger signal and the reference light trigger signal. As a result, the output signal of the photodetector 7 corresponding to the laser beam 4 irradiated at the start and end ends of the positions 13 and 14 of the optical path switch 6 and attenuated by the optical path switch 6 is recorded by the arithmetic unit 8. It is possible to prevent the signal light signal and the reference light signal from being used. For example, the chopper synchronization signal is 20 to 25 Hz, the laser synchronization signal is 100 kHz, and the time t is 2 ms.

The intensity measurement of the signal light and the reference light is performed for each wavelength by scanning the wavelength of the laser light 4. The calculation unit 8 calculates the SO ₂ concentration and the SO ₃ concentration based on the measured values for each wavelength. In the present invention, only the signal light is transmitted through the measurement target gas and the light intensity is measured, and the measurement can be performed in an extremely short time. Therefore, the SO ₂ concentration and the SO ₃ concentration in the measurement target gas can be measured in real time. It can be measured continuously. In particular, real-time and continuous measurement is effective when the SO ₂ concentration and the SO ₃ concentration in the flowing measurement target gas constantly fluctuate.

Moreover, since highly corrosive H ₂ SO ₄ is not generated during the measurement, the measurement can be performed easily. Furthermore, automatic measurement is possible, and measurement at a remote place is possible via a network.

Furthermore, since the gas concentration measuring apparatus of the present invention can perform continuous measurement and can perform unmanned operation, it is effective in reducing labor costs. Also, to calibrate the SO ₂ concentration by matching the SO ₂ concentration measurement results measured on the basis of the SO ₂ concentration measurements and JIS standards by the gas concentration measuring apparatus, determining the conversion of _SO 3 / SO ₂ based on this Is possible. The conversion rate is theoretically obtained by calculation based on the thermal equilibrium of the chemical reaction SO ₂ + 1 / 2O ₂ ⇔SO ₃ representing the oxidation of SO ₂ , but besides the direct oxidation reaction, Fe ₂ O ₃ , V ₂ O ₅ , Since there is also a conversion reaction due to the catalytic action of a metal oxide such as Cr ₂ O ₃ , conventionally the conversion rate has not been accurately determined. Therefore, the present invention in which the conversion rate can be determined by measuring the SO ₃ concentration is useful.

Further, there is provided a driving means for moving the first reflecting mirror 2 to the optical path of the signal light to the probe 3. An example of this is shown in Figure 8. The driving means includes a guide rail 30 provided parallel to the optical path of the signal light, a reflector holder 31 that moves while being guided by the guide rail 30, and a screw 32 that moves the reflector holder 31 along the guide rail 30. I have. The screw 32 is provided in parallel with the guide rail 30. The first reflecting mirror 2 is attached to the reflecting mirror holder 31. The reflector holder 31 is provided with a slide portion 31 a that slides along the guide rail 30 and a female screw portion 31 b that meshes with the screw 32. Therefore, when the screw 32 is rotated by a motor (not shown), the reflector holder 31 moves along the guide rail 30, and the optical path length that passes through the measurement target gas changes. In this embodiment, the slide part 31a and the female thread part 31b are provided at both front and rear ends of the reflector holder 31 so that the orientation of the reflector holder 31 is not easily changed. Instead of using the screw 32, the reflector holder 31 may be moved by pulling with a wire or the like.

By providing a driving means for the probe 3 and moving the first reflecting mirror 2, the concentration distribution of sulfur oxide can be measured. That is, when the distance from the position where the signal light enters the measurement target gas to the first reflecting mirror 2 (reflecting mirror holder 31) is x, the optical path length in the measurement target gas is L = 2x. In this configuration, when the first reflecting mirror 2 is moved in the depth direction of the probe 3, the concentration distribution of sulfur oxide can be measured. As an example, a case will be described in which measurement is performed with the position of the first reflecting mirror 2 set to x = x ₁ and then measured with x = x ₂ . For x = x _1, signal light intensity will reflect the absorption of the signal light by the sulfur oxide present between x = 0 and x = x _1. Similarly, for x = x _2, the signal intensity will reflect the absorption of the signal light by the sulfur oxide present between x = 0 and x = x _2. Therefore, the difference in these two measurements is due to the absorption of the signal light due to sulfur oxides during the x = x ₁ and x = x _2. That is, when the sulfur oxide concentration is spatially non-uniform (when a concentration distribution exists), the sulfur oxide concentration in an arbitrary section can be obtained by moving the first reflecting mirror 2.

The above is expressed as follows: The position of the first reflecting mirror 2 (reflecting mirror holder 31) is x, the position where the signal light enters the measurement target gas is x = 0, and the concentration distribution of SO ₂ and SO ₃ is n (x), n ′ (x ). In this case, Equation 1 becomes Equation 8.

Intensities I (x ₁ ) and I (x ₂ ) of the signal light obtained at the positions x = x ₁ and x = x ₂ of the first reflecting mirror 2 are as shown in Equations 9 and 10.

Therefore, the difference is obtained by Equation 11.

Here, when the average density between x = x ₁ and x = x ₂ is n ₁ and n ₁ ′, Expression 12 is obtained.

  Since the position x of the first reflecting mirror 2 can be arbitrarily set, the average density between any two positions can be obtained. When the concentration distribution of sulfur oxide exists, the concentration distribution of sulfur oxide can be obtained by shifting the position of the first reflecting mirror 2 stepwise.

  In this case, it is preferable that the space in front of the first reflecting mirror 2 in the reflecting mirror holder 31 is the space 11 to which the cleaning gas is supplied from the compressor 22. That is, an air hole (not shown) is provided in the peripheral wall of the reflector holder 31, and a cleaning gas is supplied to the air hole through an annular passage and a blower pipe (both not shown) so that the measurement target gas enters the reflector holder 31. It is preferable to prevent the inflow to prevent the first reflecting mirror 2 from being contaminated and to determine the optical path length L in the signal light measurement gas.

The above-described embodiment is an example of a preferred embodiment of the present invention, but is not limited thereto, and various modifications can be made without departing from the scope of the present invention. For example, in the above description, the combustion exhaust gas flowing through the flue from the boiler of the thermal power generation is used as the measurement target gas, but a gas other than the combustion exhaust gas may be used as the measurement target gas.
In the above description, the light source 5 and the probe 3 are disposed opposite to each other, and the second reflecting mirror 9 and the photodetector 7 are disposed opposite to each other. However, the configuration is not necessarily limited to this. For example, the light source 5 and the photodetector 7 may be disposed opposite to each other, and the probe 3 and the second reflecting mirror 9 may be disposed to face each other, or the light source 5 and the second reflecting mirror 9 may be disposed to face each other. In addition, the probe 3 and the photodetector 7 may be arranged to face each other.
In the above description, the optical path switch 6 is an optical chopper and the optical path is mechanically switched. Alternatively, the optical path may be switched electro-optically. An example of this case is shown in FIG. The optical path switch 6 includes a splitter 27 that divides the laser light 4 emitted from the light source 5 into signal light and reference light, a first light modulator 28 disposed on the optical path of the signal light, and a reference light The second optical modulator 29 is disposed on the optical path, and the first optical modulator 28 and the second optical modulator 29 are alternately opened and closed. When the optical modulators 28 and 29 are simultaneously “opened”, the optical modulators 28 and 29 are arranged so that both the signal light and the reference light are simultaneously incident on the photodetector 7. As shown in FIG. 7A, when the first optical modulator 28 is electrically “open” and the second optical modulator 29 is “closed”, only the signal light is incident on the photodetector 7. The On the other hand, as shown in FIG. 7B, when the first optical modulator 28 is “closed” and the second optical modulator 29 is “open”, only the reference light is incident on the photodetector 7. . In this example, since the input light to the optical modulator in the “closed” state is blocked, a part of the output of the light source 5 is discarded, but the control is performed to switch the optical path by electrical operation. Is easy and convenient. In addition to performing optical intensity modulation using an AOM (acousto-optic modulator) as the optical modulators 28 and 29, it is also conceivable to perform spatial modulation of the optical axis using an AOD (acousto-optic deflector). It is done.
In the above description, the measurement target gas is prevented from flowing into the space 11 by increasing the pressure in the space 11, but the present invention is not necessarily limited to this, and the first reflection is performed by another method. The mirror 2 may be prevented from being soiled.
Further, in the above description, the measurement target gas is prevented from flowing into the space 12 by increasing the pressure in the space 12, but the present invention is not necessarily limited to this, and the measurement target gas is not limited to this. You may make it prevent inflow.
This measuring apparatus can be applied to a target gas other than sulfur oxide by replacing the light source 5. For example, the ammonia (NH ₃ ) concentration in the measurement target gas can be measured by setting the light source 5 to a wavelength tunable laser having a wavelength of 1.54 μm. Further, the nitric oxide (NO) concentration is measured by using a light source 5 as a wavelength variable laser having a wavelength of 5.33 μm, and the nitrogen dioxide (NO ₂ ) concentration is measured by using a light source 5 as a wavelength variable laser having a wavelength of 6.25 μm. can do. Moreover, simultaneous measurement of multiple components (for example, SO _x and NO _x ) can be performed by using the light source 5 in which a plurality of lasers are combined.

DESCRIPTION OF SYMBOLS 1 Flow path 2 1st reflective mirror 3 Probe 4 Laser light 5 Light source 6 Optical path switch 7 Photo detector 8 Calculation part 11 Space 13 1st position 14 2nd position 27 Divider 28 1st light modulator 29 Second optical modulator 30 Guide rail (driving means)
31 Reflector holder (drive means)
32 screw (driving means)

Claims (6)

The first reflecting mirror that is inserted into the flow path of the measurement target gas and reflects and reciprocates the signal light irradiated in the measurement target gas and the first reflection mirror are moved along the optical path of the signal light. A probe having a driving unit , a light source capable of irradiating laser light in a wavelength band absorbed by the target gas in the measurement target gas and scanning the wavelength, and switching the optical path of the laser light to reference the signal light An optical path switch that alternately generates light, a photodetector that measures the intensity of the signal light and the reference light that have passed through the measurement target gas, and the signal light intensity and reference measured by the photodetector wherein the target gas based on a difference in concentration of the target gas obtained by changing the position of the first reflecting mirror together determine the concentration of target gas in the measurement object gas based on the light intensity Gas concentration measuring apparatus comprising: a calculation unit for obtaining a concentration distribution along the optical path of the issue light.   The optical path switch includes a first position where the laser beam emitted from the light source is incident on the photodetector via the probe, and the laser beam emitted from the light source without passing through the probe. The gas concentration measuring device according to claim 1, wherein the gas concentration measuring device is a light chopper that has a second position to be incident on a photodetector and moves alternately to the first position and the second position.   The optical path switch includes a splitter that splits the laser light emitted from the light source into the signal light and the reference light, a first optical modulator disposed on the optical path of the signal light, and the reference 2. A second optical modulator disposed on an optical path of light, wherein the first optical modulator and the second optical modulator are alternately opened and closed. The gas concentration measuring device described.   A space surrounded by a wall is formed in front of the first reflecting mirror, and a cleaning gas is supplied to the space to make the pressure in the space higher than the surrounding pressure. Item 2. A gas concentration measuring apparatus according to Item 1. The drive means includes a guide rail provided in parallel with the optical path of the signal light, a reflector holder that is guided by the guide rail and moves, and the first reflector is attached, and the reflector holder. The gas concentration measuring apparatus according to claim 1, further comprising a screw that moves along the guide rail .   The gas concentration measuring apparatus according to claim 1, wherein the target gas is sulfur oxide.