Method and apparatus for measuring concentration in each temperature zone

Abstract

To provide a method for measuring concentration in each temperature zone capable of measuring the concentration of a concentration measurement target gas for each temperature zone.SOLUTION: Along a path 11 of a laser beam passing through a measurement target gas that includes a temperature measurement target gas and a concentration measurement target gas, absorption information at two or more wavelengths A1, A2, A3 having different temperature dependency absorbed by the temperature measurement target gas and at two or more wavelengths B1, B2 having different temperature dependency absorbed by the concentration measurement target gas is acquired. The path 11 of the laser beam is divided into two or more sections, and the temperature of each section is obtained on the basis of absorption information on the temperature measurement target gas. Then, the concentration of the concentration measurement target gas for each section is obtained on the basis of the obtained temperature for each section and the absorption information on the concentration measurement target gas.SELECTED DRAWING: Figure 4

Description

[Technical Field]

[0001] The present invention relates to a concentration measurement method and apparatus for measuring the concentration of a target gas for concentration measurement in each temperature range using tunable diode laser absorption spectroscopy. [Background technology]

[0002] Tunable Diode Laser Absorption Spectroscopy (TDLAS) is a method that utilizes the property of a target gas to absorb a laser beam when the target gas is irradiated with the laser beam of a certain wavelength, and measures the temperature and concentration of the target gas from the amount of laser beam absorbed by the target gas.

[0003] This absorption spectroscopy method can determine the average temperature and concentration of the target gas along the path of the laser beam, but it has the problem that it does not determine how the temperature and concentration of the target gas are distributed, i.e., whether they are uniformly distributed or localized.

[0004] Temperature binning, which is a type of tunable diode laser absorption spectroscopy, is a method in which the path of a laser beam is divided into two or more sections and the temperature of each section is determined (see Non-Patent Document 1).

[0005] Using this temperature binning, it is possible to determine the temperature and length of each section along the path of the laser beam, and to know how long the high-temperature section is and how long the low-temperature section is.

[0006] However, even with temperature binning, it is not possible to determine the concentration of the target gas (e.g., O2, CO, etc.) for each section (each temperature zone). In other words, it is not possible to know whether the target gas is localized in a high-temperature zone or a low-temperature zone. This information is very useful for controlling combustion furnaces, combustion equipment, etc.

[0007] If a CT (Computed Tomography) technique is applied to temperature binning, it is possible to obtain the temperature for each temperature range and the concentration of the target gas for concentration measurement (see Patent Document 1). However, this method has the problem that the application of the CT technique requires many laser beam paths, which is very costly. [Prior art documents] [Non-patent literature]

[0008] [Non-Patent Document 1] Nathan A Malarich, Gregory B Rieker, Resolving nonuniform temperature distributions with single-beam absorption spectroscopy. Part I: Theoretical capabilities and limitations, Journal of Quantitative Spectroscopy and Radiative Transfer, February 2021, volume 260 [Patent documents]

[0009] [Patent Document 1] Special Publication No. 2010-528296 Summary of the Invention [Problem to be solved by the invention]

[0010] The present invention has been made in view of the above-mentioned problems, and aims to provide a method and apparatus for measuring concentration for each temperature range, which is capable of measuring the concentration of a gas to be measured for each temperature range. [Means for solving the problem]

[0011] In order to solve the above problem, one aspect of the present invention is a concentration measurement method for each temperature range, comprising the steps of: acquiring absorption information at two or more wavelengths having different temperature dependencies absorbed by a gas for temperature measurement and at two or more wavelengths having different temperature dependencies absorbed by a gas for concentration measurement along a path of a laser beam passing through a gas for measurement, the gas including a gas for temperature measurement and a gas for concentration measurement; dividing the path of the laser beam into two or more sections and determining the temperature of each section based on the absorption information regarding the gas for temperature measurement; and determining the concentration of the gas for concentration measurement for each section based on the determined temperature of each section and the absorption information regarding the gas for concentration measurement.

[0012] Another aspect of the present invention is a concentration measurement device for each temperature range, comprising: means for acquiring absorption information at two or more wavelengths having different temperature dependencies absorbed by a gas for temperature measurement and at two or more wavelengths having different temperature dependencies absorbed by a gas for concentration measurement, along a path of a laser beam passing through a gas for measurement, including a gas for temperature measurement and a gas for concentration measurement; means for dividing the path of the laser beam into two or more sections and calculating the temperature of each section based on the absorption information regarding the gas for temperature measurement; and means for calculating the concentration of a gas for concentration measurement for each section based on the calculated temperature of each section and the absorption information regarding the gas for concentration measurement. [Effects of the Invention]

[0013] In the present invention, the path of the laser beam is divided into two or more sections, and the temperature of each section (each temperature zone) is determined. Then, the concentration of the target gas for concentration measurement is determined for each section (each temperature zone) based on the determined temperature of each section (each temperature zone) and absorption information at two or more wavelengths with different temperature dependencies at which the target gas absorbs. According to the present invention, the concentration of the target gas for concentration measurement for each section (each temperature zone) can be determined even without providing multiple laser beam paths, for example, even with a single laser beam path. Note that in the present invention, two or more laser beam paths may be provided. [Brief explanation of the drawings]

[0014] [Figure 1] FIG. 1 is a schematic diagram of absorption spectroscopy. [Figure 2] 1 is a schematic diagram of the absorption spectrum of a laser beam. [Figure 3] FIG. 1 is a schematic diagram illustrating an example of using temperature binning to divide the path of a laser beam into two sections (a cold section and a hot section). [Figure 4] FIG. 2 is a configuration diagram of a concentration measuring device for each temperature range according to the present embodiment. [Figure 5] FIG. 5(a) is a diagram showing the absorption spectrum of water vapor at a temperature of 800K, and FIG. 5(b) is a diagram showing the absorption spectrum of water vapor at a temperature of 300K. [Figure 6] 1 is a schematic diagram showing absorbances B1 and B2 when laser beams of wavelengths B1 and B2 pass through two sections (a low-temperature section and a high-temperature section). [Figure 7] FIG. 2 is a schematic diagram showing the correspondence relationship between the temperature of each section (each temperature zone) and the concentration of a gas whose concentration is to be measured. DETAILED DESCRIPTION OF THE INVENTION

[0015] Hereinafter, a method and apparatus for measuring concentration for each temperature range according to an embodiment of the present invention will be described in detail with reference to the accompanying drawings. However, the method and apparatus for measuring concentration for each temperature range according to the present invention can be embodied in various forms and is not limited to the embodiments described herein. The present embodiment is provided with the intention that those skilled in the art will be able to fully understand the invention by fully disclosing the specification. (Lambert-Beer law)

[0016] The basic principle of absorption spectroscopy is the Lambert-Beer law. First, let us explain the Lambert-Beer law. As shown in Figure 1, when a laser beam with an initial intensity I0 is sent into a gas to be measured with a path length L, part of the laser beam is absorbed by the gas to be measured, and the transmitted laser intensity I is detected.

[0017] The Lambert-Beer law can be expressed as follows using the ratio of the initial intensity I0 to the transmitted laser intensity I: (Formula 1) TIFF2025161195000002.tif21123where α v is the absorbance, K v is the spectral absorption coefficient, p (bar) is the total pressure of the gas being measured, L (cm) is the path length, and X abs is the mole fraction of the absorbing species of interest, i is the transition (absorption line), S i (T)(cm -2 bar -1 ) is the line strength of the transition i (absorption line i) at temperature T, and Φ(v) is the lineshape function.

[0018] Absorbance A in absorption spectroscopy i is the α in Eq. v It can be simply expressed using the following equation 2, which is the integral of the absorbance A in the frequency direction. iis the partial pressure (concentration) of the absorbing species pX abs , path length L, absorption line intensity S i It is represented by the product of (T). (Formula 2) TIFF2025161195000003.tif26123 (Temperature and concentration in a system with uniform temperature distribution)

[0019] Figure 2 shows the absorption spectrum of a laser beam. The horizontal axis of Figure 2 is the frequency of the laser beam, and the vertical axis is the absorbance α v In Figure 2, #1 and #2 indicate transition i (absorption line i). The ratio of the integral areas A1 and A2 of the two absorption lines i = #1 and #2 in Figure 2 can be simplified to the ratio of the line intensities, since they are measured simultaneously at the same pressure, mole fraction, and path length. Therefore, the temperature T can be calculated using equation 3 from the ratio of the line intensities of two appropriately selected absorption lines #1 and #2. (Formula 3) TIFF2025161195000004.tif26158Here, S1(T0) is the line intensity of absorption line #1 at the reference temperature T0 (296K), S2(T0) is the line intensity of absorption line #2 at the reference temperature T0 (296K), c (cm / s) is the speed of light, h (J·s) is Planck's constant, k (J / K) is the Boltzmann constant, and E1´´ and E2´´ are the low-lying state energies of absorption lines #1 and #2. These parameters at the reference temperature T0 (296K) can be obtained from the HITRAN database, so the temperature T can be calculated from equation 3.

[0020] If the temperature T is known, the gas concentration of the absorbing species can be determined from Equation 2 above. (Temperature Binning)

[0021] In many practical systems, the temperature varies along the path of the laser beam. Temperature binning involves dividing the path of the laser beam into two or more sections (also called temperature bins) and determining the temperature for each section. Here, we define a uniform temperature T i , uniform mole fraction X abs , i , pressure Pi Assume that:

[0022] When m absorption lines are selected, Equation 2 leads to Equation 4 below: The absorbance vector Ai is the measurand. (Formula 4) TIFF2025161195000005.tif45158If the number of absorption lines m is greater than the number of sections n (if the number of sections n is 2 or greater, and the number of absorption lines m is 3 or greater), S is calculated by the algorithm that minimizes the following equation 5. i (t j ), pX abs L i The temperature and length for each section (each temperature zone) can be determined uniquely. (Formula 5) TIFF2025161195000006.tif38153

[0023] As described above, temperature binning can be used to determine the frequency distribution of temperatures for each section (each temperature zone). However, temperature binning does not necessarily provide positional information (temperature distribution) for each temperature zone. In other words, if section 21 (low temperature area) and section 22 (high temperature area) in Figure 3 are reversed or nested, temperature binning cannot distinguish them. (Method and device for measuring concentration for each temperature range according to this embodiment)

[0024] FIG. 4 shows a configuration diagram of a concentration measurement device for each temperature range according to this embodiment. The concentration measurement device of this embodiment includes three or more laser light sources 1a to 1c for temperature measurement, two or more laser light sources 2a and 2b for concentration measurement, laser control devices 3 and 4, a multiplexer 5, and a collimator 6. The concentration measurement device of this embodiment further includes a photoreceiver 7, an amplifier 8 that amplifies the signal from the photoreceiver 7, and an analyzer 9. Gases to be measured in a furnace 10 include a gas for temperature measurement and a gas for concentration measurement. The gas for temperature measurement is, for example, water vapor. The gas for concentration measurement is, for example, at least one of O2, CO, N2, NH3, NO, and NOx.

[0025] The laser light sources 1a to 1c are light sources capable of outputting laser beams of three or more wavelengths A1, A2, and A3 that have different temperature dependencies and are absorbed by the gas whose concentration is to be measured. In this embodiment, the laser light sources 1a to 1c are DFB lasers. Similarly, the laser light sources 2a and 2b are light sources capable of outputting laser beams of two or more wavelengths B1 and B2 that have different temperature dependencies and are absorbed by the gas whose concentration is to be measured.

[0026] The laser control device 3 controls the laser light sources 1a to 1c, and irradiates the measurement target gas with the laser beams output from the laser light sources 1a to 1c while scanning (changing) the wavelengths A1, A2, and A3 of the laser beams in their respective wavelength bands. Similarly, the laser control device 4 controls the laser light sources 2a and 2b, and irradiates the measurement target gas with the laser beams output from the laser light sources 2a and 2b while scanning (changing) the wavelengths B1 and B2 of the laser beams in their respective wavelength bands. The wavelength of the laser beam can be changed by changing the value of the current input to the laser light sources 1a to 1c, 2a, and 2b.

[0027] The multiplexer 5 mixes three or more laser beams output from the laser light sources 1a to 1c and two or more laser beams output from the laser light sources 2a and 2b. The collimator 6 collimates the mixed light from the multiplexer 5 and irradiates the gas to be measured in the furnace 10. The path 11 of the laser beam irradiating the gas to be measured is a single path.

[0028] When the mixed light passes through the gas to be measured, the laser beams with wavelengths A1 to A3 are absorbed by the gas to be measured for temperature. The laser beams with wavelengths B1 and B2 are absorbed by the gas to be measured for concentration. The mixed light that has passed through the gas to be measured is received by the photoreceiver 7.

[0029] The photodetector 7 receives the laser beam that has passed through the gas whose temperature and concentration are to be measured, and outputs an electrical signal corresponding to the intensity of the received laser beam. The amplifier 8 amplifies the electrical signal and converts the analog signal from the photodetector 7 into a digital signal.

[0030] The analysis device 9 is a computer that includes a processor such as a CPU (Central Processing Unit), a main memory such as a RAM (Random Access Memory) or a ROM (Read Only Memory), and a memory that stores a predetermined program, such as a volatile memory, a non-volatile memory, an EPROM (Erasable Programmable ROM), a hard disk drive, or a solid state drive. The analysis device 9 executes the predetermined program stored in the memory to perform the following steps.

[0031] First, in the process of acquiring absorption information, the analyzer 9 acquires absorption information (absorption spectra) at three or more wavelengths A1, A2, and A3, which have different temperature dependencies and are absorbed by the gas whose temperature is to be measured. Figure 5(a) shows the absorption spectrum of water vapor at a temperature of 800 K as a reference example of an absorption spectrum. Figure 5(b) shows the absorption spectrum of water vapor at a temperature of 300 K as a reference example of an absorption spectrum. These Figures 5(a) and 5(b) were created using the HITRAN database. #1, #2, and #3 in Figures 5(a) and 5(b) represent three absorption lines at wavelengths A1, A2, and A3. Comparing Figures 5(a) and 5(b), it can be seen that the absorbance of each of the three absorption lines #1, #2, and #3 at wavelengths A1, A2, and A3 changes depending on the temperature, i.e., they have different temperature dependencies.

[0032] In the next step, the analyzer 9 divides the laser beam path 11 into two or more sections and calculates the temperature of each section based on the absorption information (absorption spectrum at wavelengths A1, A2, and A3) of the gas whose temperature is to be measured. For example, as shown in Figure 6, the analyzer 9 calculates the temperature of section 21, the temperature of section 22, the length L1 of section 21, and the length L2 (=L-L1) of section 22. Using the temperature binning described above, the temperature of each of sections 21 and 22 can be calculated.

[0033] The method for determining the temperature for each section 21, 22 is not limited to the above-mentioned temperature binning, and the profile fitting method can also be used. The profile fitting method assumes a temperature distribution, calculates the absorbance from it, calculates the deviation between the calculated absorbance and the actual absorbance, corrects the temperature distribution so that the deviation is small, and repeats this process to determine the correct temperature distribution.

[0034] In the next step, the analysis device 9 determines the concentration of the gas for which concentration is to be measured for each of the sections 21 and 22 based on the determined temperatures for each of the sections 21 and 22 and the absorption information (absorption spectrum at wavelengths B1 and B2) relating to the gas for which concentration is to be measured.

[0035] For example, if the temperature of section 21 shown in Figure 6 is T1, the temperature of section 22 is T2, the length of section 21 is L1, the length of section 22 is L2, the concentration of the gas whose concentration is to be measured in section 21 is X1, the concentration of the gas whose concentration is to be measured in section 22 is X2, the absorbance of wavelength B1 in section 21 is B11, the absorbance of wavelength B1 in section 22 is B12, the absorbance of wavelength B2 in section 21 is B21, and the absorbance of wavelength B2 in section 22 is B22, then the following equation 6 holds for the absorbance B1 of wavelength B1 and the absorbance B2 of wavelength B2. (Formula 6) Absorbance B1 (measured value) = B11 x X1 x L1 + B12 x X2 x L2 Absorbance B2 (measured value) = B21 x X1 x L1 + B22 x X2 x L2

[0036] Because the temperatures T1, T2, lengths L1, and L2 are known from the temperature binning described above, the absorbances B11, B12, B21, and B22 at the temperatures T1 and T2 can be obtained from the HITRAN database.

[0037] The unknowns are the concentrations X1 and X2 of the gases whose concentrations are to be measured. Ultimately, by solving the simultaneous linear equations with two unknowns in Equation 6, X1 and X2 can be found as shown in Equation 7 below. (Formula 7) X1=(B22×L2×B1-B12×L2×B2) / (B11×L1×B22×L2-B12×L1×B21×L2) X2=(B11×L1×B2-B21×L1×B1) / (B11×L1×B22×L2-B12×L1×B21×L2)

[0038] Concentrations X1 and X2 of the target gas can be found only when the number of wavelengths B1 and B2 absorbed by the target gas is greater than the number of sections 21 and 22. The concentration of the target gas for concentration measurement for each of sections 21 and 22 may be found using Equation 6, or the concentration may be found using an algorithm that minimizes the actual absorbance value and the measured absorbance value.

[0039] Note that when B11 × B22 = B12 × B21, Equation 6 cannot be solved. However, this is limited to highly fortuitous cases, such as when absorbances B1 and B2 change in exactly the same way with respect to temperature. In practice, it is sufficient to select a combination of wavelengths that does not cause such a change in absorbance in the expected sections 21 and 22. Furthermore, if there are three or more sections, the simultaneous equations of Equation 6 cannot be solved using only the two wavelengths B1 and B2. Therefore, it is possible to determine the concentration for each section by using three or more wavelengths, or by selecting the most likely combination of concentrations X1, X2, X3, etc. based on the gas diffusion phenomenon. (Example of use)

[0040] By using the concentration measurement method for each temperature zone of this embodiment, it is possible to know the correspondence between the temperature of each section (each temperature zone) along the path of the laser beam and the concentration of the gas whose concentration is to be measured, as shown in Figure 7.

[0041] For example, if the gas to be measured for concentration is CO, and a high CO concentration coincides with a low temperature area, there is concern about insufficient combustion temperature, so measures such as combustion support can be taken in the combustion furnace or combustion equipment.

[0042] For example, if the gas to be measured for concentration is O2, there is a concern that NOx may be generated if a high O2 concentration coincides with a high temperature area, so the combustion furnace, combustion equipment, etc. should be controlled so that a high O2 concentration does not coincide with a high temperature area.

[0043] For example, if the gases to be measured for concentration are N2 and O2, the amount of NOx generated can be predicted by knowing their concentrations at each temperature range.

[0044] For example, if the gases to be measured for concentration are NO and NH3, the denitrification rate can be estimated by knowing their temperature ranges. (Effects of the concentration measurement method for each temperature range according to this embodiment)

[0045] According to this embodiment, even if a large number of laser beam paths 11 are not provided, for example, even if the laser beam path 11 is a single path, the concentrations X1 and X2 of the gas to be measured for each section 21 and 22 (each temperature zone) can be obtained.

[0046] Temperature binning is used to determine the temperature for each section 21, 22 (each temperature zone), so the temperature for each section 21, 22 (each temperature zone) can be determined without providing multiple laser beam paths 11, for example, even if the laser beam path 11 is a single path.

[0047] Since the laser beam path 11 is a single path, the openings required for the combustion furnace and combustion device can be minimized, thereby reducing costs.

[0048] Since the gas whose temperature is to be measured is water vapor, the temperature of each of the sections 21 and 22 (each temperature zone) can be obtained efficiently.

[0049] Gases to be measured for concentration are O2, CO, N2, NH3, NO, and NO 2、 Since at least one of the gases is N2O, the correspondence between the temperature of each section 21, 22 (each temperature zone) and the concentration of the gas whose concentration is to be measured can be known, and this can be used for control. [Explanation of symbols]

[0050] 1a to 1c...Laser light source for gas for temperature measurement, 2a to 2b...Laser light source for gas for concentration measurement, 3 to 4...Laser control device, 5...Multiplexer, 6...Collimator, 7...Photodetector, 8...Amplifier, 9...Analysis device, 10...Furnace, 11...Laser beam path

Claims

1. Acquiring absorption information at two or more wavelengths having different temperature dependencies absorbed by the temperature measurement target gas and at two or more wavelengths having different temperature dependencies absorbed by the concentration measurement target gas along a path of a laser beam passing through the measurement target gas including the temperature measurement target gas and the concentration measurement target gas; Dividing the path of the laser beam into two or more sections and determining the temperature of each section based on absorption information about the gas whose temperature is to be measured; and calculating the concentration of the gas to be measured for each section based on the calculated temperature for each section and absorption information related to the gas to be measured for each section.

2. Acquire absorption information at three or more wavelengths having different temperature dependencies absorbed by the gas to be measured for temperature; 2. The method for measuring a concentration in each temperature zone according to claim 1, wherein the temperature of each section is determined using temperature binning.

3. 3. The method for measuring a concentration in each temperature range according to claim 2, wherein the path of the laser beam is a single path.

4. 3. The method for measuring concentration in each temperature range according to claim 1, wherein the gas whose temperature is to be measured is water vapor.

5. The gas to be measured is O ２ , CO, N ２ , N.H. ３ 3. The method for measuring the concentration of at least one of NO, NOx, and NOH in each temperature range according to claim 1 or 2.

6. a means for acquiring, along a path of a laser beam passing through a measurement target gas including a temperature measurement target gas and a concentration measurement target gas, absorption information at two or more wavelengths having different temperature dependencies and absorbed by the temperature measurement target gas, and at two or more wavelengths having different temperature dependencies and absorbed by the concentration measurement target gas; means for dividing the path of the laser beam into two or more sections and determining the temperature of each section based on absorption information about the gas whose temperature is to be measured; and means for determining the concentration of the gas to be measured for each section based on the determined temperature for each section and absorption information relating to the gas to be measured for each temperature zone.

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