CN218512299U

CN218512299U - Methane gas detection device based on photoacoustic spectroscopy

Info

Publication number: CN218512299U
Application number: CN202222067747.1U
Authority: CN
Inventors: 乐继修; 钟文波; 杨正华; 李浩文
Original assignee: Shenzhen Micro Optical Instruments Technology Co ltd
Current assignee: Shenzhen Micro Optical Instruments Technology Co ltd
Priority date: 2022-08-04
Filing date: 2022-08-04
Publication date: 2023-02-21
Anticipated expiration: 2032-08-04

Abstract

The utility model discloses a methane gas detection device based on photoacoustic spectroscopy, including degasification module, the photoacoustic cell that is provided with the collection module, the light source module of the luminous beam to the photoacoustic cell, the rotatable filter disc that sets up between photoacoustic cell and light source module, and the control processing module who is connected with the collection module communication, wherein, the control processing module is used for handling the signal that the collection module gathered and obtains gas composition and gas content in the photoacoustic cell; the degassing module comprises a degassing chamber connected with the transformer channel, a gas channel connected with the degassing chamber, and the degassing chamber is connected with the photoacoustic cell channel based on the gas channel; the filter disc comprises a disc bottom and a plurality of optical filters arranged on the disc bottom, wherein the optical filters comprise a first optical filter with the center wavelength of 3300nm and a second optical filter with the center wavelength of 7974 nm. The utility model discloses can improve accuracy and efficiency to methane gas measurement.

Description

Methane gas detection device based on photoacoustic spectroscopy

Technical Field

The utility model relates to a gaseous detection, in particular to methane gas detection device based on optoacoustic spectrum.

Background

Once a power transformer fails, power interruption can be caused, even fire can be caused in serious conditions, and serious consequences are brought to social life and economic development. The state and fault diagnosis of the power transformer can be analyzed accurately and comprehensively by analyzing the content of the dissolved gas in the oil of the transformer. In the method for analyzing the gas content, the photoacoustic spectroscopy detection technology based on the photoacoustic effect is a novel application mode, the gas in the oil is decomposed in an oil-gas separation mode, and after the photoacoustic effect is formed by different gases and mid-infrared light with different wavelengths, the photoacoustic effect is collected through a microphone and data processing is carried out to judge the type and the content of the gas.

When gas is detected by photoacoustic spectroscopy, 3300nm is generally used as the characteristic peak of methane, and 3365nm is used as the characteristic peak of ethane. And ethane has a partial absorption band at 3300nm, and a significant overlap exists with a characteristic peak of methane, so that for a mixed gas, the measurement of methane is often interfered by ethane, and the measurement accuracy of the methane concentration based on photoacoustic spectroscopy is low.

SUMMERY OF THE UTILITY MODEL

The to-be-solved technical problem of the utility model lies in that the measuring accuracy to methane concentration is lower based on the optoacoustic spectrum, to prior art not enough, provides a methane gas detection device based on optoacoustic spectrum.

In order to solve the technical problem, the utility model discloses the technical scheme who adopts as follows:

a methane gas detecting apparatus based on photoacoustic spectroscopy, the apparatus comprising:

the device comprises a degassing module, a photoacoustic cell provided with an acquisition module, a light source module emitting light beams to the photoacoustic cell, a rotatable filter disc arranged between the photoacoustic cell and the light source module, and a control processing module in communication connection with the acquisition module, wherein the control processing module is used for processing signals acquired by the acquisition module to obtain gas components and gas content in the photoacoustic cell;

the degassing module comprises a degassing chamber connected with the transformer channel, a gas channel connected with the degassing chamber, and the degassing chamber is connected with the photoacoustic cell channel based on the gas channel;

the filter disc comprises a disc bottom and a plurality of optical filters arranged on the disc bottom, wherein the optical filters comprise a first optical filter with the central wavelength of 3300nm and a second optical filter with the central wavelength of 7974 nm.

The methane gas detection device based on photoacoustic spectroscopy, wherein the light source module comprises an emission unit, and the emission unit comprises an infrared blackbody light source and a condenser lens.

The methane gas detection device based on the photoacoustic spectrum is characterized in that the inner curved surface of the condenser is a paraboloid; the cavity formed by the paraboloid faces the photoacoustic cell, and the infrared black body light source is located in the cavity.

The methane gas detection device based on the photoacoustic spectroscopy is characterized in that the infrared black body light source is made of nickel iron ceramic rods.

The methane gas detection device based on photoacoustic spectroscopy comprises an acquisition module, a photoacoustic cell and a control module, wherein the acquisition module comprises at least two microphones which are uniformly arranged relative to the photoacoustic cell.

The methane gas detection device based on photoacoustic spectroscopy, wherein the degassing module further comprises a two-way electromagnetic valve arranged on the gas channel.

The methane gas detection device based on photoacoustic spectroscopy comprises a filter disc, wherein the filter disc further comprises a third optical filter for detecting acetylene, a fourth optical filter for detecting ethylene, a fifth optical filter for detecting ethane, a sixth optical filter for detecting carbon monoxide, a seventh optical filter for detecting carbon dioxide and/or an eighth optical filter for detecting water vapor.

The methane gas detection device based on photoacoustic spectroscopy, wherein the light source module comprises a modulation disc arranged between the emission unit and the filter disc, and the modulation disc rotates according to a preset rotation frequency.

The methane gas detection device based on the photoacoustic spectrum comprises a control processing module and a phase-locked amplifier, wherein the control processing module comprises a phase-locked amplifier and a control processing unit, the phase-locked amplifier is respectively in communication connection with the modulation panel and the acquisition module, and the control processing unit is in communication connection with the acquisition module.

The methane gas detection device based on photoacoustic spectroscopy further comprises a shell, wherein the photoacoustic cell, the light source module and the filter disc are located in the shell.

Has the advantages that: compared with the prior art, the utility model provides a gaseous detection device of methane based on optoacoustic spectrum, this gaseous detection device include degasification module, light source module, be equipped with the optoacoustic pond of collection module, be equipped with the central wavelength for the filter disc of 3300nm and 7974nm light filter. The light source module emits light to the photoacoustic cell, when light enters the photoacoustic cell through the filters of 3300nm and 7974nm, methane gas can generate strong mechanical motion under the light of the two wavelengths, and ethane cannot generate mechanical motion at the position of 7974nm, so that the concentration of the methane gas is accurately determined by combining the oscillation conditions of the gas under the irradiation of the light with the two different wavelengths of 7974nm and 3300 nm. Meanwhile, the central wavelength of incident light is adjusted by adopting a filter disc mode, so that wavelength switching can be reduced, the simplicity and convenience of operation are improved, and light with different wavelengths can enter conveniently.

Drawings

Fig. 1 is a spectrum obtained by detecting ethane by photoacoustic spectroscopy.

Fig. 2 is a spectrum obtained by detecting methane by using photoacoustic spectroscopy.

Fig. 3 is a spectral diagram obtained by detecting methane and ethane by photoacoustic spectroscopy, in which the dark line is ethane gas and the light line is methane gas.

FIG. 4 shows the results of photoacoustic spectroscopy for methane and ethane at 3300nm and 3365 nm.

Fig. 5 is a schematic diagram of a methane gas detection device based on photoacoustic spectroscopy according to the present invention.

Fig. 6 is a schematic structural diagram of a filter disk in the methane gas detecting device based on photoacoustic spectroscopy according to the present invention.

Fig. 7 is a test chart of voltage and light intensity of the black body light source of the methane gas detecting device based on photoacoustic spectroscopy.

The meanings marked in the figures are as follows:

11, a degassing chamber; 12, an oil inlet channel; 13, an oil outlet channel; 14, an intake passage; 15, an exhaust passage; 15, an electromagnetic valve; 210, a left channel microphone; 220, a right channel microphone; 31, an infrared blackbody light source; 32, a condenser lens; 33, a chopper wheel; 40, a filter wheel; 41, a first filter; 42, a second filter; 43, a third filter; 44, a fourth filter; 45, a fifth filter; 46, a sixth filter; 47, a seventh filter; 48, an eighth filter; 51, a lock-in amplifier; 52, a control processing unit; 60, a housing.

Detailed Description

The utility model provides a gaseous detection device of methane based on optoacoustic spectrum, for making the utility model discloses a purpose, technical scheme and effect are clearer, make clear and definite, and it is right to refer to the figure below and to lift the embodiment the utility model discloses further detailed description. It should be understood that the specific embodiments described herein are for purposes of illustration only and are not intended to limit the invention.

According to research, 3300nm is generally used as a characteristic peak of methane, and 3365nm is used as a characteristic peak of ethane. And ethane has a partial absorption band at 3300nm, and a significant overlap exists with a characteristic peak of methane, so that for a mixed gas, the measurement of methane is often interfered by ethane, and the measurement accuracy of the methane concentration based on photoacoustic spectroscopy is low. As shown in fig. 3 and 4, the ethane gas measurement results gave about 8% cross interference with the methane gas. In addition, the most common photoacoustic spectroscopy detection at present adopts laser detection, and multiple lasers are required to be switched for use when multiple gases are detected, so that the detection difficulty is increased.

The following description of the embodiments will further explain the present invention by referring to the accompanying drawings.

As shown in fig. 5, the present embodiment provides a methane gas detecting apparatus based on photoacoustic spectroscopy, in which a dotted line formed by short and horizontal lines is a communication connection and a dotted line formed by dots is an optical path, the apparatus comprising:

the gas detection device comprises a degassing module, a photoacoustic cell provided with an acquisition module, a light source module emitting a light beam to the photoacoustic cell, a control processing module and a filter disk 40 arranged between the photoacoustic cell and the light source module.

The degassing module is used for obtaining transformer oil in the transformer and extracting gas to be detected in the oil sample in a dynamic headspace mode so as to be used for subsequent detection. The degassing apparatus includes a degassing chamber 11, a transformer oil passage, and a gas passage, the transformer oil passage including an oil inlet passage 12 for sucking the transformer oil in the transformer into the degassing chamber 11, and an oil outlet passage 13 for discharging the transformer oil in the transformer back into the transformer. The degassing chamber 11 can separate oil and gas of the transformer oil, and the degassing chamber 11 can be provided with an oil-gas separation membrane, a vacuum degassing device and the like. Based on the gas channel, the degassing module is connected with the photoacoustic cell channel. The gas passage includes a gas inlet passage 14 for inputting the gas of the degassing chamber 11 into the photoacoustic cell and a gas outlet passage 15 for discharging the gas of the photoacoustic cell to the degassing chamber 11. An electromagnetic valve 16 can be arranged on the gas channel, the electromagnetic valve 16 is opened, and gas freely flows; the electromagnetic valve 16 is closed, gas cannot flow between the degassing chamber 11 and the photoacoustic cell, and a closed chamber with problems of gas concentration and gas type is formed in the photoacoustic cell. The solenoid valve 16 may be replaced with a valve that opens and closes automatically according to a parameter such as air pressure, such as a flow valve. The solenoid valve 16 may be a two-way solenoid valve 16.

The photoacoustic cell is a reaction environment for photoacoustic spectrometry detection, is used for accommodating gas to be detected for subsequent gas detection, and can be in various shapes such as a cylinder, a T shape and an ellipse. The present embodiment takes a cylindrical photoacoustic cell as an example, the photoacoustic cell includes two cylinders with the same diameter as the first chamber and the second chamber, respectively, a third chamber with a larger diameter than the first chamber is disposed between the two cylinders, and an acquisition module for acquiring a mechanical signal is disposed on an outer wall of the third chamber. The gas of photoacoustic cell absorbs light energy under the irradiation of light to be demagnetized in a mode of releasing thermal energy, and the acquisition module can convert mechanical waves generated by the demagnetization into electric signals to be transmitted to the control processing module for data processing and analysis.

In the photoacoustic cell, since the microphone is susceptible to environmental noise, in this embodiment, the collection module includes at least two microphones, the mechanical wave passes through the microphones, and the microphones can make the current change correspondingly with the change of the mechanical wave and generate an electrical signal. The signals collected by the two microphones are combined, so that the electric signals can be denoised, and the noise influence is reduced. Two microphones can be placed evenly with respect to the photoacoustic cell, one microphone being located above the third chamber and the other microphone being located below the third chamber, as shown in fig. 1. These two microphones may also be referred to as a "left channel microphone" and a "right channel microphone". Still be equipped with the window piece in the optoacoustic pond, the window piece is located one side that the optoacoustic pond is close to light source module to in throwing into the optoacoustic pond with light source module's light beam. In addition, different temperature conditions can also produce the influence to the motion of the gas that awaits measuring, and the higher the temperature, the gas motion is faster, and the mechanical wave that produces is also stronger, for the accuracy that improves gas detection result, and the photoacoustic cell is inside still to be equipped with the constant temperature refrigeration piece to keep the temperature of first cavity, second cavity and third cavity at a invariable temperature. The constant temperature refrigeration piece can adopt a TEC constant temperature refrigeration piece.

The light source module is used for providing a light source for the photoacoustic cell. In this embodiment, the light source module may employ a broadband tunable laser, multiple lasers, or other types of light sources. Since the blackbody can not only fully absorb the electromagnetic radiation from the outside, but also scatter the electromagnetic radiation more strongly than any other object at the same temperature, the light source module includes an emission module, and the emission module can use a blackbody light source. For the wavelength range of gas detection, the blackbody light source may be an infrared blackbody light source 31. In order to concentrate the light from the infrared black body light source 31 into the photoacoustic cell, the light source module may further include a light collecting mirror 32, and the light collecting mirror 32 may converge the light from the infrared black body light source 31 to form a thinner light beam to be emitted into the photoacoustic cell. The material of the infrared blackbody light source 31 can be nickel iron ceramic rod to improve the stability of the blackbody light source.

Further, in a manner of disposing the collecting mirror 32, the collecting mirror 32 is disposed between the infrared black body light source 31 and the photoacoustic cell, and the infrared black body light source 31 collects light beams after passing through the collecting mirror 32 and then emits the light beams into the photoacoustic cell. In this way, only a part of the light rays of the infrared blackbody light source 31 can be collected, and the light rays which do not pass through the condenser lens 32 cannot be collected, which is the majority of the light rays and causes resource waste. Therefore, in another way of disposing the light collecting mirror 32, the inner curved surface of the light collecting mirror 32 is a paraboloid, and the cavity formed by the paraboloid faces the photoacoustic cell, and the infrared blackbody light source 31 is located in the cavity. As shown in fig. 5, most of the light beams emitted by the infrared blackbody light source 31 irradiate the collecting mirror 32, and the paraboloid of the collecting mirror 32 reflects the light beams and emits the reflected light beams to the photoacoustic cell, so that most of the light beams emitted by the infrared combined light source are effectively utilized, and the resource utilization rate is improved.

Furthermore, the light source module further includes a modulation wheel 33 disposed between the emission unit and the filter wheel 40, the modulation wheel 33 is capable of chopping the light signal to add pulse modulation, and the modulation wheel 33 can rotate according to a preset rotation frequency to achieve synchronization between the incidence of the light beam and the time when the single optical filter is located on the window.

The filter disk 40 includes a disk bottom and a plurality of filters disposed on the disk body, as shown in fig. 6, the filters can be dispersed uniformly to cover the filter disk 40, and the filters are used for controlling the wavelength of the light beam passing through the filters. The filter disk 40 of fig. 6 is provided with eight filters, namely a first filter 41 (corresponding to a center wavelength of 3300 nm), a second filter 42 (corresponding to a center wavelength of 7974 nm), a third filter 43 (corresponding to a center wavelength of 3050 nm), a fourth filter 44 (corresponding to a center wavelength of 10500 nm), a fifth filter 45 (corresponding to a center wavelength of 3365 nm), a sixth filter 46 (corresponding to a center wavelength of 4350 nm), a seventh filter 47 (corresponding to a center wavelength of 4640 nm), and an eighth filter 48 (corresponding to a center wavelength of 5600 nm). The corresponding detection gases are methane, acetylene, ethylene, ethane, carbon monoxide, carbon dioxide and water vapor respectively. Currently, single wavelength is used for detecting single gas, and methane at 3300nm and ethane at 3365nm have peak cross. As shown in fig. 1, 2 and 3, when the detection is performed using only ethane or methane, not only the methane peak but also the ethane peak is visible around 3300nm, and therefore, the methane cannot be effectively detected only by a filter for 3300 nm. The experimental results of fig. 4 show that the cross interference caused by the measurement result of ethane gas to methane gas is about 8%.

Therefore, the present embodiment is provided with a second filter 42 for detecting methane with a center wavelength of 7974nm in addition to the first filter 41 for detecting methane. As shown in FIG. 3, ethane does not have a peak at a wavelength around 7974nm, whereas methane has a relatively single peak in this region. Therefore, the present embodiment uses the first filter 41 and the second filter 42 to obtain two independent signals to distinguish methane gas. In addition to the filters described above, the filter wheel 40 may also be provided with filters for other wavelengths. Further, as shown in fig. 7, the system adopts a black body light source, and the radiation intensity of a 3300nm black body is about 3 times stronger at the absorption peaks with wavelengths of 3300nm and 7974nm, and the photoacoustic effect is relatively stronger when the optical power is stronger, so that the detection lower limit and the resolution can be improved by selecting a narrow-band optical filter with the central wavelength of 3300 nm.

The filter wheel 40 is rotatable, and in one manner, when the user selects the gas to be detected, e.g., ethane, the filter wheel 40 rotates the filter corresponding to ethane to a position opposite to the window of the photoacoustic cell at a predetermined rotation speed. In another rotation mode, the gas to be detected selected by the user is multiple gases or multiple filters are needed to assist the detection, for example, for the gas methane, a rotation frequency is preset, the filter wheel 40 rotates around the center of the filter wheel 40 according to the rotation frequency, and during the rotation process, the light source module sequentially passes through the first filter 41 and the second filter 42. The rotation frequency can be rotating according to a stable angular speed, and when a certain optical filter is positioned in front of a window sheet of the photoacoustic cell, the optical filter stays for a period of time and continues to rotate, so that the condition that the certain optical filter has a period of time corresponding to the same wavelength is ensured, and the detection accuracy is improved.

The control processing module is in communication connection with the acquisition module and can collect and process signals acquired by the acquisition module so as to obtain the absorption intensity within a certain time range or at a certain moment. According to the rotation frequency of the filter disk 40, the position where the optical filter is set, and the time when the filter disk 40 starts to rotate, the wavelength of the light beam entering the photoacoustic cell at each time can be determined, and further, the wavelength corresponding to the signal acquired by the acquisition module at that time can be determined. After the filter disk 40 rotates for a circle, the collecting module can collect the gas content corresponding to the wavelength screened by all the optical filters, thereby realizing the measurement of the gas. The control module comprises a phase-locked amplifier 51 and a control processing unit 52, wherein the phase-locked amplifier 51 is respectively in communication connection with the modulation panel 33 and the acquisition module to obtain a chopping signal of the modulation panel 33 and an electric signal acquired by the acquisition module, and performs noise reduction processing to realize amplification of a weak signal. The signal processed by the chopper wheel 33 is transmitted to the control processing unit 52, and the control processing unit 52 determines the signal intensity corresponding to each central wavelength according to the intensity of the acquired signal, the acquisition time and the optical filter corresponding to the time, and then determines the concentration of the gas. For ethane gas, the concentration can be determined from the signal peak at 3365nm, for methane gas, the presence or absence of methane can be determined from the signal peak at 7700nm, the interference intensity for methane gas is confirmed from the signal peak intensity of ethane, typically 8%, and finally the concentration of methane gas is determined from the signal peak and interference intensity at 3300 nm.

The working process is as follows:

based on the oil inlet channel 12, the degassing module sucks transformer oil from the transformer, the transformer oil is subjected to oil-gas separation in the degassing chamber 11 to obtain gas to be detected, and the gas to be detected enters the photoacoustic cell through the air inlet channel 14. The light source module emits light beams to the photoacoustic cell, and gases in the photoacoustic cell generate photoacoustic spectrum effect and are collected by the collecting module and transmitted to the control processing module. And controlling a processing module to determine the components and the concentration in the gas to be detected according to the strength of the mechanical signals caused by the collected laser with different wavelengths.

In addition, the gas detection apparatus may further include a housing 60, the photoacoustic cell, the light source module and the filter wheel 40 are located in the housing, and the control processing module may be disposed on a surface of the housing 60, so as to facilitate obtaining or viewing of a subsequent processing result. For example, the processing result is transmitted to a computer subsequently, and is positioned on the surface of the shell to be more easily transmitted; or the control processing unit 52 comprises a display, the processing result is directly displayed on the display, and the result can be directly viewed when the control processing unit is arranged outside the shell.

Claims

1. A methane gas detection device based on photoacoustic spectroscopy, the gas detection device is connected with a transformer pipeline, includes:

2. The photoacoustic spectroscopy-based methane gas detecting apparatus according to claim 1, wherein the light source module comprises an emitting unit, and the emitting unit comprises an infrared black body light source and a condenser.

3. The photoacoustic spectroscopy-based methane gas detecting apparatus according to claim 2, wherein the inner curved surface of the condenser is a paraboloid; the cavity formed by the paraboloid faces the photoacoustic cell, and the infrared black body light source is positioned in the cavity.

4. The photoacoustic spectroscopy-based methane gas detecting apparatus according to claim 2, wherein the infrared blackbody light source is made of a nickel iron ceramic rod.

5. The photoacoustic spectroscopy-based methane gas detecting apparatus according to claim 1, wherein the collecting means comprises at least two microphones uniformly arranged with respect to the photoacoustic cell.

6. The photoacoustic spectroscopy-based methane gas detecting apparatus according to claim 1, wherein the degassing module further comprises a two-way solenoid valve disposed in the gas passage.

7. The photoacoustic spectroscopy-based methane gas detecting apparatus according to claim 1, wherein the filter wheel further comprises a third filter for detecting acetylene, a fourth filter for detecting ethylene, a fifth filter for detecting ethane, a sixth filter for detecting carbon monoxide, a seventh filter for detecting carbon dioxide, and/or an eighth filter for detecting water vapor.

8. The photoacoustic spectroscopy-based methane gas detecting apparatus according to claim 2, wherein the light source module comprises a reticle disposed between the emitting unit and the filter wheel, wherein the reticle rotates according to a preset rotation frequency.

9. The photoacoustic spectroscopy-based methane gas detecting apparatus according to claim 8, wherein the control processing module comprises a lock-in amplifier and a control processing unit, the lock-in amplifier is respectively connected with the chopper wheel and the collecting module in a communication manner, and the control processing unit is connected with the collecting module in a communication manner.

10. The methane gas detecting apparatus according to any one of claims 1 to 9, further comprising a housing, wherein the photoacoustic cell, the light source module, and the filter wheel are located in the housing.