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In-situ CO gas measuring device and method based on wavelength modulation spectrum technology

A technology of wavelength modulation spectrum and gas measurement, which is applied in measuring devices, color/spectral characteristic measurement, material analysis through optical means, etc. It can solve the problems that the measurement method cannot respond quickly to CO, change the composition, and the sampling path is long, etc., to achieve Reduce the amount of daily maintenance, prolong the service life and save resources

Inactive Publication Date: 2020-10-09
TSINGHUA UNIV
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AI Technical Summary

Problems solved by technology

[0003] 1. TDLAS technology includes two methods: direct absorption spectroscopy and wavelength modulation spectroscopy. Direct absorption spectroscopy obtains the absorptivity function by fitting the transmitted light intensity and then obtains the gas parameters. The physical concept of this method is clear, but it is susceptible to environmental vibrations, laser intensity Influenced by fluctuations and baseline fitting errors, it is not suitable for complex industrial field measurements
Wavelength modulation spectroscopy has the advantages of high signal-to-noise ratio and high sensitivity by performing high-frequency modulation on the target signal, and the non-target signal is removed in the subsequent harmonic detection process without modulation. However, this method cannot effectively absorb The rate function is generally used in conjunction with the second harmonic peak method combined with complex calibration experiments
[0004] 2. At present, the existing CO on-line monitoring instruments generally use non-dispersive infrared technology (NDIR) combined with traditional extraction methods to achieve measurement. The traditional multi-stage filtration extraction method is complex, and due to temperature changes and the physical and chemical characteristics of the gas during the sampling process Adsorption or chemical reaction will occur, which will change the composition of the sample gas, resulting in distortion of the measurement results, and cannot achieve high-fidelity online measurement. In addition, non-dispersive infrared technology (NDIR) is easily affected by other gas molecules due to the use of a wide-spectrum light source for measurement.
[0005] 3. The extraction sampling scheme is used for measurement, the sampling path is long, the measurement lags (about 1-2 minutes), and the CO fluctuates violently in the flue. During the sampling process, the CO concentration in the flue has changed dramatically. This measurement method Cannot respond quickly to CO changes

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  • In-situ CO gas measuring device and method based on wavelength modulation spectrum technology

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Embodiment 1

[0057] The in-situ CO gas measurement method based on wavelength modulation spectroscopy technology of the present invention uses tunable diode laser absorption spectroscopy (TDLAS) technology with high sensitivity and strong anti-interference ability, and adopts wavelength modulation-direct absorption spectroscopy (wavelength modulation —direct absorption spectroscopy, WM-DAS) algorithm.

[0058] Traditional scanning-wavelength modulation spectroscopy generally uses high-frequency sinusoidal signals and low-frequency triangular signals to achieve wavelength scanning and modulation. The WM-DAS method includes the following steps:

[0059] S1: Use a high-frequency sinusoidal signal with a frequency of ωt to realize wavelength scanning and modulation at the same time. Considering the nonlinear influence of the laser frequency, the instantaneous laser frequency v(t) is described by the following formula:

[0060]

[0061] In the formula is the center frequency of the spectra...

Embodiment 2

[0092] Such as figure 2 As shown, the in-situ CO gas detection device for the boiler flue of a power plant includes a measuring chamber 7 and a signal transmitting and receiving device. Among them, a through hole is used for the signal generated by the signal transmitting and receiving device to enter and exit the measuring cavity 7, and the inner top of the measuring cavity 7 is provided with a corner mirror 5, and the corner mirror 5 is used to reflect the signal emitted by the signal transmitting and receiving device .

[0093] When in use, the device is installed in the boiler flue of the power plant and is heated by flue gas without condensation.

[0094] Specifically, the through holes include a flue gas through hole 18 and a signal through hole 20. The inner diameters of the signal through hole 20 and the flue gas through hole 18 are smaller than the inner diameter of the measuring chamber 7, and the inner diameter of the flue gas through hole 18 is smaller than the s...

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Abstract

The invention discloses an in-situ CO gas measuring device and method based on a wavelength modulation spectrum technology, which belong to the technical field of tunable laser diode absorption spectra. The measuring device aims at the characteristic that CO in flue gas fluctuates violently; in-situ sampling type measurement is innovatively provided; a measuring cavity is arranged in the flue; thesmoke temperature and components are ensured not to be changed during measurement; according to the WM-DAS method, wavelength scanning and modulation are carried out by using a high-frequency sinusoidal signal with a frequency of omega t; defining is carried out according to the Fourier series; the Lambert-Beer law is combined; Fourier series expansion is carried out on the absorbed transmissionlight intensity signal It; a gas absorptivity function can be obtained by establishing a relationship between a laser instantaneous frequency and a transmission light intensity signal and combining synchronous fitting; and the CO gas concentration in gas is acquired. According to the method, in the light intensity signal reconstruction process, only the frequency spectrum at the frequency multiplication position of the modulation frequency is adopted, noise signals irrelevant to the modulation frequency are filtered out, the reconstructed light intensity signals have a higher signal-to-noise ratio, and high-precision CO in-situ online monitoring is achieved.

Description

technical field [0001] The invention relates to an in-situ CO gas measurement method and device based on wavelength modulation spectroscopy technology. Background technique [0002] Energy conservation and emission reduction has become the mainstream direction of energy development. Improving boiler efficiency and power plant economy becomes inevitable. Power plants generally use the oxygen in the flue gas as an adjustment parameter for boiler efficiency. However, oxygen data can only obtain the excess air coefficient of the boiler, which cannot well reflect the specific conditions of burner combustion and wind-coal mixing. CO is an incomplete combustion product in the combustion process, and its content directly reflects the unburned condition of the fuel, which can better explain the combustion efficiency. Therefore, the high-precision online monitoring of the total amount of CO in the flue gas, combining the CO monitoring value with the oxygen value, provides a data bas...

Claims

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Application Information

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Patent Type & Authority Applications(China)
IPC IPC(8): G01N21/39G01N21/01G01N21/15
CPCG01N21/01G01N21/15G01N21/39G01N2021/0112G01N2021/151G01N2021/152
Inventor 彭志敏杜艳君丁艳军
Owner TSINGHUA UNIV
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