CN114965357A - Methyl ethyl alkane double-gas detection method and device based on TDLAS - Google Patents
Methyl ethyl alkane double-gas detection method and device based on TDLAS Download PDFInfo
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- CN114965357A CN114965357A CN202210440752.4A CN202210440752A CN114965357A CN 114965357 A CN114965357 A CN 114965357A CN 202210440752 A CN202210440752 A CN 202210440752A CN 114965357 A CN114965357 A CN 114965357A
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
- G01N21/00—Investigating or analysing materials by the use of optical means, i.e. using sub-millimetre waves, infrared, visible or ultraviolet light
- G01N21/17—Systems in which incident light is modified in accordance with the properties of the material investigated
- G01N21/25—Colour; Spectral properties, i.e. comparison of effect of material on the light at two or more different wavelengths or wavelength bands
- G01N21/31—Investigating relative effect of material at wavelengths characteristic of specific elements or molecules, e.g. atomic absorption spectrometry
- G01N21/39—Investigating relative effect of material at wavelengths characteristic of specific elements or molecules, e.g. atomic absorption spectrometry using tunable lasers
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
- G01N2201/00—Features of devices classified in G01N21/00
- G01N2201/02—Mechanical
- G01N2201/024—Modular construction
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
- G01N2201/00—Features of devices classified in G01N21/00
- G01N2201/06—Illumination; Optics
- G01N2201/061—Sources
- G01N2201/06113—Coherent sources; lasers
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
- G01N2201/00—Features of devices classified in G01N21/00
- G01N2201/12—Circuits of general importance; Signal processing
- G01N2201/123—Conversion circuit
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
- G01N2201/00—Features of devices classified in G01N21/00
- G01N2201/12—Circuits of general importance; Signal processing
- G01N2201/125—Digital circuitry
Abstract
The invention relates to a method and a device for detecting methane and ethane double gases based on TDLAS, wherein the device comprises a laser driving module, a laser, a gas chamber, a detector, a phase-locked amplifying module and a main control unit; the laser driving module receives a modulation signal input by the phase-locked amplification module, controls a laser to excite a modulation laser beam with a preset wavelength according to the modulation signal, and the beam enters a gas chamber for storing gas to be detected through an optical fiber; the gas chamber allows the laser beam to enter and exit and reflect back and forth in the inner cavity; the detector is used for converting an optical signal absorbed by gas to be detected in the gas chamber into an electric signal and transmitting the electric signal to the phase-locked amplification module; the phase-locked amplification module is used for generating a modulation signal, sending the modulation signal to the laser driving module, and generating a second harmonic signal according to the electric signal converted by the detector and the modulation signal; the main control unit identifies the components in the gas to be detected according to the position information of the second harmonic signal, and the concentration values of the components in the gas to be detected are obtained according to the information of wave crests and wave troughs of the second harmonic signal.
Description
Technical Field
The invention relates to the technical field of trace multi-component gas detection, in particular to a method and a device for identifying components and detecting concentration of methane and ethane based on a TDLAS technology.
Background
With the development of industrial internet and the requirement of urbanization safety production, the demand of natural gas as clean energy in the urbanization development is increasing. In order to prevent serious safety accidents caused by natural gas leakage, the urban inspection work of the gas pipeline is increasingly strengthened, and higher requirements on gas component identification and concentration detection are also provided. Tunable semiconductor laser absorption spectroscopy (TDLAS) is a commonly used gas detection technique, which detects the concentration of a target gas by using the change of absorption intensity when laser wavelength sweeps a gas absorption line, has the advantages of high response speed, high resolution, unique selectivity and the like, and has been widely applied to a plurality of fields such as environmental pollution detection, greenhouse gas measurement, gas leakage monitoring and the like. However, because the spectral line of laser is narrow, a laser can only detect one gas component, and most of the existing gas detection devices measure a specific gas, and cannot accurately judge whether natural gas leakage or gas and methane leakage occurs. If want accurate discernment natural gas to leak, need detect two kinds of gases of methane and ethane simultaneously, but it is less, the strong weak of absorption line at near infrared band ethane absorption peak, and detection device to ethane is mostly mid-infrared detection, and detection device has the problem such as structure complicacy, price are expensive. The CN208060383U patent develops a TDLAS-based trace methane detector which can monitor methane gas in real time, but does not find a TDLAS-based trace ethane detection related patent. Therefore, in order to accurately and quickly realize natural gas leakage detection, how to realize simultaneous detection of high-sensitivity methyl ethane double gases is a difficult point and a hot point which are relatively concerned by technicians in the field at present.
Disclosure of Invention
The technical problem solved by the invention is as follows: the method and the device for detecting the methane and the ethane double gas based on the TDLAS can realize the detection of the methane and the ethane double gas and solve the problems of weak characteristic absorption peak, low detection precision and easy methane interference of the ethane gas in a near infrared band.
The technical scheme of the invention is as follows: a methylethyl alkane double-gas component identification method based on TDLAS comprises the following steps:
detecting the gas to be detected by adopting a TDLAS technology, and scanning absorption peaks of methane and ethane simultaneously during detection;
and acquiring a second harmonic signal of the gas to be detected by utilizing a harmonic signal analysis processing method, and identifying the components in the gas to be detected in two stages by respectively taking the peak position information and the full width at half maximum information of the second harmonic signal as evaluation functions.
Preferably, a laser with the center wavelength of 1680nm is selected for scanning, and the laser can excite a laser beam with the wavelength range of 1679-1681 nm and cover absorption peaks of methane and ethane.
Preferably, the wavelength of 1680.81nm is selected as the characteristic absorption peak of the detection for methane, and the wavelength of 1680.19nm is selected as the characteristic absorption peak of the detection for ethane.
The second technical scheme of the invention is as follows: a method for detecting concentration of methane and ethane double-gas components based on TDLAS comprises the following steps:
identifying a component in a gas under test using the method of claim 1;
and determining concentration values of methane and ethane in the gas to be detected by taking the obtained peak-trough difference value of the second harmonic signal of the gas to be detected as an evaluation function.
The third technical scheme of the invention is as follows: a double-gas detection device for methane and ethane comprises a laser driving module, a laser, a gas chamber, a detector, a phase-locked amplifying module and a main control unit;
the laser driving module receives a modulation signal input by the phase-locked amplification module, controls a laser to excite a modulation laser beam with a preset wavelength according to the modulation signal, and the beam enters a gas chamber for storing gas to be detected through an optical fiber;
the detector is used for converting an optical signal absorbed by gas to be detected in the gas chamber into an electric signal and transmitting the electric signal to the phase-locked amplification module;
the phase-locked amplification module is used for generating a modulation signal and sending the modulation signal to the laser driving module, and generating a second harmonic signal according to the electric signal converted by the detector and the modulation signal;
the main control unit identifies the components in the gas to be detected according to the position information of the second harmonic signal, and the concentration values of the components in the gas to be detected are obtained according to the information of wave crests and wave troughs of the second harmonic signal.
Preferably, the phase-locked amplification module comprises a modulation signal excitation unit, a filtering amplification unit and a phase-sensitive detection unit;
the modulation signal excitation unit excites a sawtooth wave signal and a sine wave signal with adjustable amplitude and frequency, and the superposed modulation signals are output to the laser driving module;
the filtering and amplifying unit amplifies and filters the electric signal converted by the detector, the amplitude of the amplified electric signal meets the working voltage of the AD chip, and meanwhile, a direct current signal and a noise signal are filtered, and the obtained useful signal is used for being collected by the AD chip;
the phase-sensitive detection unit multiplies the useful signal acquired by the AD chip with the modulation signal phase-sensitive of the modulation signal excitation unit to form a second harmonic signal;
preferably, the laser driving module controls the TEC temperature and the working current to enable the laser to emit a light beam with a center wavelength of 1680nm, and controls a wavelength scanning range and frequency modulation parameters of the laser beam through a modulation signal obtained by superimposing a sawtooth wave and a sine wave.
Preferably, the amplitude and frequency of the sawtooth wave and the sine wave of the modulation signal excitation unit are adjusted by the main control unit, so that the output beam of the laser can simultaneously scan the absorption peaks of methane and ethane.
Preferably, the main control unit comprises a two-stage component identification algorithm, the first-stage component identification algorithm is used for identifying components according to set second harmonic signal intervals of methane and ethane, and the second-stage component identification algorithm is used for identifying components according to half-height widths of second harmonic signals of methane and ethane.
Preferably, the main control unit further comprises a concentration detection algorithm for calculating the concentration value of methane or ethane according to the peak-to-trough difference of the second harmonic signal after component identification and the concentration scaling factor of the corresponding gas component.
Compared with the prior art, the invention has the beneficial effects that:
(1) according to the invention, a laser scans a wider wavelength range, so that the concentration of two gases, namely methane and ethane, can be detected simultaneously, the limitation that the TDLAS technology only aims at the detection of a single gas component is solved, and an idea is provided for the detection of multiple gases;
(2) the method selects different absorption peaks aiming at methane and ethane, and adopts the position information of second harmonic as an evaluation function to identify the components of the methane and the ethane, thereby avoiding the mutual interference between the two gases.
(3) The invention selects the methane and ethane absorption spectra in the near infrared band to realize the high-sensitivity detection of methane and ethane, and greatly reduces the detection cost compared with the intermediate infrared detection technology.
Drawings
FIG. 1 is a schematic diagram of the present invention for identifying methane and ethane components based on second harmonic location information and full width at half maximum information;
FIG. 2 is a graph of methane second harmonic signals at different concentrations in accordance with the present invention;
FIG. 3 is a graph of the second harmonic signal of ethane at various concentrations in accordance with the present invention;
fig. 4 is a schematic view of a detection process of the apparatus for detecting a methane-ethane double-gas concentration in the present invention.
Detailed Description
The invention is further illustrated by the following examples.
By inquiring a HITRAN database and comparing gas absorption spectral lines of methane and ethane, absorption peaks of methane and ethane exist simultaneously in a 1680-1681 nm wave band interval, and mutual interference between the absorption peaks is small. Therefore, the wavelength of 1680.81nm is selected as the characteristic absorption peak of the detection for methane, and the wavelength of 1680.19nm is selected as the characteristic absorption peak of the detection for ethane. According to the characteristic absorption peaks of methane and ethane, the DFB laser with the center wavelength of 1680nm is selected, the DFB laser can excite a light beam with the wavelength range of 1679-1681 nm, the DFB laser is used for scanning a wide wavelength range, and the DFB laser can cover the absorption spectral lines of methane and ethane at the same time. The method comprises the steps of obtaining a second harmonic signal of a gas to be detected through a harmonic signal analysis processing method based on a TDLAS technology, and realizing component identification and concentration detection of methane and ethane according to the position, half-height width information and wave crest and trough difference value information of the harmonic signal.
The invention will be described in detail with reference to the drawings and specific embodiments, and the features of the invention will become more apparent and apparent as the description proceeds.
The invention provides a method for identifying components of methane and ethane and detecting the concentration of the methane and the ethane based on a TDLAS technology. Gas characteristic absorption lines of methane and ethane were studied according to the HITRAN database. According to the characteristic absorption spectral line, four absorption peaks of ethane in near infrared exist, wherein an ethane absorption peak of 1680.19nm and a methane absorption peak of 1680.81nm exist at the same time near 1680nm, and mutual interference between the two absorption peaks is small, so that the invention selects a DFB laser beam of 1680nm to scan a wider wavelength range, and the range can simultaneously cover the absorption spectral lines of methane and ethane, thereby realizing the simultaneous detection of two gases.
In the invention, the TDLAS technology is adopted to detect the gas to be detected, the light beam emitted by the laser is set by using the modulation signal during detection, so that the absorption peaks of methane and ethane can be scanned simultaneously, and the second harmonic signal of the gas to be detected is obtained by the phase-locked amplification module. The second harmonic signals of the gas to be detected simultaneously contain methane and ethane second harmonic signals, and the second harmonic signals are different in position and half-height width value. As shown in fig. 1, which is a waveform diagram of a second harmonic signal of a gas to be measured, it can be known that the second harmonic of the signal to be measured is composed of 250 points, wherein the second harmonic signal of ethane is located between 10-140 points, and the peak value thereof is located at 79 points; the second harmonic signal of methane is between 150 and 250 points, and the wave peak value is at 202 points. The positions of the second harmonics of methane and ethane correspond to the wavelength position information selected in the present invention, and thus methane and ethane can be distinguished according to the positions.
However, under the influence of factors such as unstable power of the laser, change of ambient temperature and the like, when the wavelength changes greatly, the wave peak value of the second harmonic signal exceeds the originally set position judgment range, so that the methane and ethane components are inaccurately identified, and the concentration detection value is abnormal. Therefore, the method performs a secondary component identification method, and further identifies the components of methane and ethane by taking the half-height width information of the second harmonic signal as an evaluation function. As can be seen from the waveform diagram of the second harmonic signal of the gas to be measured shown in fig. 1, the full width at half maximum of methane accounts for 26 points, the full width at half maximum of ethane accounts for 40 points, and the full widths at half maximum of the two points are consistent with the theoretical full widths at half maximum of the absorption spectral lines of 1680.81 methane and 1680.19nm ethane in the HITRAN database, so that methane and ethane in the gas to be measured can be effectively identified.
In the invention, after second harmonic signals of methane and ethane are respectively found according to a component identification method, concentration values of the second harmonic signals can be calculated according to peak and trough information of the second harmonic signals. As shown in fig. 2, by filling N into the air chambers respectively 2 、8ppmCH 4 、50ppmCH 4 、100ppmCH 4 、500ppmCH 4 And then obtaining methane second harmonic signals with different concentrations. As shown in fig. 3, N2 and 10ppm C were charged into the air chamber respectively 2 H 6 、100ppmC 2 H 6 、500ppmC 2 H 6 The second harmonic signals of ethane with different concentrations are obtained. The concentration value is deduced according to the peak-trough difference value of the second harmonic signal under different concentrations of methane or ethane, the specific deduction mode can be carried out by referring to the method in the prior art in the field, and a methane concentration calibration curve and an ethane concentration calibration curve can be respectively obtained, so that the concentration values of corresponding components are obtained.
Example 1
According to the detection method, the invention provides a device for identifying components of methane and ethane and detecting the concentration of methane and ethane based on TDLAS technology. The device is developed according to the TDLAS technical principle, has a two-stage component identification algorithm and a concentration detection algorithm, and comprises a laser driving module, a laser, an air chamber, a detector, a phase-locked amplification module, a main control unit and the like. The device utilizes a laser driving module to control the central wavelength of a laser; exciting a modulation signal formed by superposing sawtooth waves and sine waves by using a phase-locked amplification module to control the wavelength scanning width, amplitude and frequency of a laser beam; storing gas to be measured by using a gas chamber, and allowing a laser beam to enter and exit and reflect back and forth in an inner cavity of the gas chamber; the detector can be used for converting an optical signal carrying concentration information into an electric signal, and the lock-in amplifier module can amplify and filter the electric signal and extract a second harmonic signal of the gas to be detected; the main control unit is responsible for completing component identification, concentration calculation and the like. As shown in fig. 4, a schematic diagram of the detection process of the device is shown, and the specific operation steps are as follows:
(1) the laser driving module can control the central wavelength output by the laser by controlling the temperature and the working current of the TEC, the module parameter is adjusted to enable the output wavelength of the laser to be 1680nm, and a spectrum analyzer is used for detecting the output wavelength of the laser;
(2) the modulation signal excitation unit in the phase-locked amplification module can excite sawtooth waves and sine waves with controllable amplitude and frequency, the modulation signals obtained by superposing the sawtooth waves and the sine waves can control the wavelength scanning range, amplitude and frequency of the laser beams, and the amplitude and frequency of the sawtooth waves and the sine waves of the module are adjusted, so that the laser output beams can scan the absorption peaks of methane and ethane at the same time;
(3) filling gas to be detected into the gas chamber, and connecting one end of the gas chamber with a laser through an optical fiber to enable a laser beam to be connected into the gas chamber; the other end of the air chamber is connected with a detector through an optical fiber, and an optical signal is converted into an electric signal through the detector;
(4) the filtering and amplifying unit in the phase-locked amplifying module can amplify and filter the converted electric signal, so that the amplitude of the electric signal meets the working voltage of the AD chip, and meanwhile, direct-current components and noise signals in the electric signal can be filtered, and useful signals are acquired and collected by the AD chip;
(5) the phase-sensitive detection unit in the phase-locked amplification module can multiply the useful signal acquired by the AD chip with the modulation signal phase-sensitive of the modulation signal excitation unit to form a second harmonic signal related to the gas concentration;
(6) the main control unit comprises a two-stage component identification algorithm and a concentration detection algorithm, the first-stage component identification algorithm is used for identifying components according to set second harmonic signal intervals of methane and ethane, and the second-stage component identification algorithm is used for identifying components according to half-height widths of the second harmonic signals of methane and ethane. The concentration detection algorithm calculates the concentration value of methane or ethane according to the peak-trough difference value of the second harmonic signal after component identification and the concentration scale factor of the corresponding gas component.
The invention has been described in detail with reference to specific embodiments and illustrative examples, but the description is not intended to be construed in a limiting sense. Various equivalent substitutions, modifications or improvements may be made on the technical solution of the present invention and the embodiments thereof by those skilled in the art without departing from the spirit and scope of the present invention, which fall within the scope of the present invention.
Those skilled in the art will appreciate that those matters not described in detail in the present specification are well known in the art.
Claims (10)
1. A methylethyl methane double-gas component identification method based on TDLAS is characterized by comprising the following steps:
detecting the gas to be detected by adopting a TDLAS technology, and scanning absorption peaks of methane and ethane simultaneously during detection;
and acquiring a second harmonic signal of the gas to be detected by utilizing a harmonic signal analysis processing method, and identifying the components in the gas to be detected in two stages by respectively taking the peak position information and the full width at half maximum information of the second harmonic signal as evaluation functions.
2. The component identification method according to claim 1, characterized in that: a laser with the center wavelength of 1680nm is selected for scanning, the laser can excite a laser beam with the wavelength range of 1679-1681 nm, and meanwhile absorption peaks of methane and ethane are covered.
3. The component identification method according to claim 1, characterized in that: the wavelength of 1680.81nm is selected as the characteristic absorption peak of methane, and the wavelength of 1680.19nm is selected as the characteristic absorption peak of ethane.
4. A method for detecting concentration of methane and ethane double-gas components based on TDLAS is characterized by comprising the following steps:
identifying a component in a gas under test using the method of claim 1;
and determining the concentration values of methane and ethane in the gas to be detected by taking the obtained peak-trough difference value of the second harmonic signal of the gas to be detected as an evaluation function.
5. A double-gas detection device for methane and ethane is characterized by comprising a laser driving module, a laser, a gas chamber, a detector, a phase-locked amplification module and a main control unit;
the laser driving module receives a modulation signal input by the phase-locked amplification module, controls a laser to excite a modulation laser beam with a preset wavelength according to the modulation signal, and the beam enters a gas chamber for storing gas to be detected through an optical fiber;
the detector is used for converting an optical signal absorbed by gas to be detected in the gas chamber into an electric signal and transmitting the electric signal to the phase-locked amplification module;
the phase-locked amplification module is used for generating a modulation signal, sending the modulation signal to the laser driving module, and generating a second harmonic signal according to the electric signal converted by the detector and the modulation signal;
the main control unit identifies the components in the gas to be detected according to the position information of the second harmonic signal, and the concentration values of the components in the gas to be detected are obtained according to the information of wave crests and wave troughs of the second harmonic signal.
6. The apparatus of claim 5, wherein: the phase-locked amplification module comprises a modulation signal excitation unit, a filtering amplification unit and a phase-sensitive detection unit;
the modulation signal excitation unit excites a sawtooth wave signal and a sine wave signal with adjustable amplitude and frequency, and the superposed modulation signals are output to the laser driving module;
the filtering and amplifying unit amplifies and filters the electric signal converted by the detector, the amplitude of the amplified electric signal meets the working voltage of the AD chip, and meanwhile, a direct current signal and a noise signal are filtered, and the obtained useful signal is used for being collected by the AD chip;
and the phase-sensitive detection unit multiplies the useful signal acquired by the AD chip by the modulation signal of the modulation signal excitation unit in a phase-sensitive manner to form a second harmonic signal.
7. The apparatus of claim 6, wherein: the laser driving module enables the laser to emit a light beam with the center wavelength of 1680nm by controlling the temperature and the working current of the TEC, and controls the wavelength scanning range and the frequency modulation parameter of the laser light beam through a modulation signal obtained by superposing the sawtooth wave and the sine wave.
8. The apparatus of claim 6, wherein: the amplitude and frequency of the sawtooth wave and the sine wave of the modulation signal excitation unit are adjusted through the main control unit, so that the laser output beam can scan the absorption peaks of methane and ethane at the same time.
9. The apparatus of claim 5, wherein: the main control unit comprises two-stage component identification algorithms, the first-stage component identification algorithm is used for identifying components according to set second harmonic signal intervals of methane and ethane, and the second-stage component identification algorithm is used for identifying components according to half-height widths of the second harmonic signals of methane and ethane.
10. The apparatus of claim 9, wherein: the main control unit also comprises a concentration detection algorithm, and the concentration value of methane or ethane is calculated according to the peak-trough difference value of the second harmonic signal after component identification and the concentration scale factor of the corresponding gas component.
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Cited By (2)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN105092527A (en) * | 2014-05-19 | 2015-11-25 | 中国石油化工集团公司 | Gas detector for logging and method thereof |
| CN115265927A (en) * | 2022-09-26 | 2022-11-01 | 南京旭奥科技有限公司 | Container sealing detection method and detection device |
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2022
- 2022-04-25 CN CN202210440752.4A patent/CN114965357A/en active Pending
Cited By (3)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN105092527A (en) * | 2014-05-19 | 2015-11-25 | 中国石油化工集团公司 | Gas detector for logging and method thereof |
| CN115265927A (en) * | 2022-09-26 | 2022-11-01 | 南京旭奥科技有限公司 | Container sealing detection method and detection device |
| CN115265927B (en) * | 2022-09-26 | 2022-12-23 | 南京旭奥科技有限公司 | Container sealing detection method and detection device |
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