Online Laser Detection Device and Method for Water Content of Natural Gas with Continuous Multiple Reflection Absorption

Abstract

The present invention discloses a continuous multi-reflection absorption type on-line laser detection device and method for natural gas water content. Natural gas in a natural gas pipeline enters an absorption chamber. A computer controls a distributed feedback laser to emit laser light to a first fiber collimator. The first fiber collimator injects the laser light onto a fourth reflector. After the laser light is injected, it reflects along a predetermined reflection path in the absorption chamber for several cycles. A second fiber collimator emits the laser light carrying the absorption spectral signal after reflecting along the predetermined reflection path for several cycles. A photomultiplier tube receives the laser signal carrying the absorption spectral signal reflected by the second fiber collimator, and amplifies and performs photoelectric conversion on the laser signal carrying the absorption spectral signal. The computer performs reverse deduction on the laser signal carrying the absorption spectral signal according to the Beer-Lambert law to obtain the water vapor concentration in the natural gas to be measured. The present invention realizes on-line laser detection of natural gas water content, and has the characteristics of small volume, long optical path, and high detection accuracy.

Description

Technical Field

[0001] The present invention belongs to the technical field of concentration detection devices, and particularly relates to an on-line laser detection device and method for the water content of natural gas with continuous multi-reflection absorption type. Background Art

[0002] In the process of exploitation and utilization of natural gas, the pipeline transportation process is an extremely important link. Since water vapor in natural gas often causes internal corrosion of pipelines, it is often necessary to measure the water content during the pipeline transportation of natural gas, and non-contact laser detection is one of the ways to detect the water content.

[0003] In recent years, a detection technology for detecting gas concentration by making a detection device using the infrared spectral absorption principle has gradually developed. When detecting trace gases, the direct application of TDLAS technology often fails to obtain an ideal absorption signal due to the too low concentration of the gas to be detected, making it difficult to complete the measurement. To detect the spectral absorption of such low-concentration gases, the method of increasing the optical path of the gas cell is often adopted in the TDLAS system to enhance the absorption signal and improve the detection performance.

[0004] In the current detection technologies, the absorption gas cells adopted are mostly of two modes, namely the White type gas cell and the Herriott type gas cell, and their derivative type gas cells. However, considering the actual device, in order to increase the optical path within a certain volume, such gas cells often use reflectors such as multi-faceted concave mirrors and plane mirrors to adjust the incident angle of the laser, change the number of reflections, and thus increase the optical path. Therefore, the above gas cells mostly have problems such as large external dimensions, low space utilization rate, and inconvenient installation and layout. Summary of the Invention

[0005] Aiming at the problems existing in the prior art, the present invention provides an on-line laser detection device and method for the water content of natural gas with continuous multi-reflection absorption type. Based on the principle of light reflection and tunable diode laser absorption spectroscopy technology, on-line laser detection of the water content of natural gas is realized, which has the characteristics of small volume, long optical path, high detection accuracy, and improves the detection efficiency.

[0006] In order to solve the above technical problems, the present invention is realized through the following technical solutions:

[0007] A continuous multi-reflection absorption type on-line laser detection device for natural gas water content, comprising two bypass pipes, a gas chamber box body, a first fiber collimator, a second fiber collimator, and a first mirror, a second mirror, a third mirror and a fourth mirror arranged in the gas chamber box body. The first mirror, the second mirror, the third mirror and the fourth mirror are connected end to end in sequence to form a column with a parallelogram cross-section, and two ports of the column are closely attached to the two side walls of the gas chamber box body to form an absorption chamber. An air inlet and an air outlet are arranged on the absorption chamber; one end of one bypass pipe is communicated with a natural gas pipeline, and the other end is communicated with the air inlet. One end of the other bypass pipe is communicated with the air outlet, and the other end is communicated with the natural gas pipeline; one ends of the first fiber collimator and the second fiber collimator pass through the first mirror and extend into the absorption chamber. The first fiber collimator is used to emit laser onto the fourth mirror, and the second fiber collimator is used to emit the laser carrying the absorption spectral signal after being reflected for a number of cycles along a predetermined reflection path. One cycle of the reflection path is from the fourth mirror to the second mirror, then from the second mirror to the third mirror, and finally from the third mirror to the first mirror; the other end of the first fiber collimator is connected with a distributed feedback laser, the distributed feedback laser is connected with a computer, the computer is connected with a data acquisition card, the data acquisition card is connected with a photomultiplier tube, and the photomultiplier tube is connected to the other end of the second fiber collimator;

[0008] The computer is used to control the distributed feedback laser to emit laser to the first fiber collimator; the photomultiplier tube is used to receive the laser signal carrying the absorption spectral signal reflected by the second fiber collimator, and amplify and perform photoelectric conversion on the laser signal carrying the absorption spectral signal; the data acquisition card is used to collect the laser signal carrying the absorption spectral signal after amplification and photoelectric conversion; the computer is also used to perform reverse deduction on the laser signal carrying the absorption spectral signal according to the Beer-Lambert law to obtain the water vapor concentration in the natural gas to be measured.

[0009] Further, the first fiber collimator is located at a position close to the air inlet, and the second fiber collimator is located at a position far from the first fiber collimator.

[0010] Further, a blower and a natural gas pipeline filtering device are arranged on the bypass pipe communicated with the air inlet, and the natural gas pipeline filtering device is located between the blower and the air inlet.

[0011] Further, stop valves are also arranged on the two bypass pipes.

[0012] Further, the first fiber collimator is connected with the distributed feedback laser through an optical fiber, and the second fiber collimator is connected with the photomultiplier tube through an optical fiber.

[0013] Further, the included angle between the first reflector and the fourth reflector is 60°, the included angle between the second reflector and the third reflector is 60°, and the length ratio of the first reflector, the second reflector, the third reflector, and the fourth reflector is 7:6:7:6 in sequence.

[0014] Further, a first small hole and a second small hole are formed in the first reflector. The first small hole is arranged on the first reflector near the acute-angle end, and the distance between the first small hole and the acute-angle vertex is 1 / 7 of the length of the first reflector. The second small hole is arranged on the first reflector near the obtuse-angle end, and the distance between the second small hole and the obtuse-angle vertex is 1 / 7 of the length of the first reflector. The first fiber collimator is installed in the first small hole, the second fiber collimator is installed in the second small hole, the first fiber collimator is horizontally arranged, and the second fiber collimator is parallel to the second reflector.

[0015] Further, a protective housing is arranged in the first small hole and the second small hole, and the first fiber collimator and the second fiber collimator are connected to the first reflector through the protective housing.

[0016] Further, the central wavelength of the distributed feedback laser is 1370±2 nm.

[0017] A continuous multi-reflection absorption type on-line laser detection method for natural gas water content, applying the detection device, specifically:

[0018] The natural gas in the natural gas pipeline enters the absorption chamber through the bypass pipe; the computer controls the distributed feedback laser to emit laser light to the first fiber collimator; the first fiber collimator emits laser light onto the fourth reflector. After the laser light is emitted, it reflects along a predetermined reflection path in the absorption chamber for several cycles. The second fiber collimator emits the laser light carrying the absorption spectrum signal after reflecting along the predetermined reflection path for several cycles. The reflection path of one cycle is from the fourth reflector to the second reflector, then from the second reflector to the third reflector, and finally from the third reflector to the first reflector; the photomultiplier tube receives the laser signal carrying the absorption spectrum signal reflected by the second fiber collimator, and amplifies and performs photoelectric conversion on the laser signal carrying the absorption spectrum signal; the data acquisition card acquires the laser signal carrying the absorption spectrum signal after amplification and photoelectric conversion; the computer performs reverse deduction on the laser signal carrying the absorption spectrum signal according to the Beer-Lambert law to obtain the water vapor concentration in the natural gas to be measured.

[0019] Compared with the prior art, the present invention has at least the following beneficial effects: For an on-line laser detection device for continuously multi-reflection absorption type natural gas water content provided by the present invention, during use, natural gas in the natural gas pipeline enters the absorption chamber through a bypass pipe; a computer controls a distributed feedback laser to emit laser light to a first fiber collimator; the first fiber collimator injects laser light onto a fourth mirror, and after the laser light is injected, it reflects along a predetermined reflection path in the absorption chamber for several cycles. A second fiber collimator emits the laser light carrying the absorption spectrum signal after reflecting along the predetermined reflection path for several cycles. The reflection path for one cycle is from the fourth mirror reflecting to the second mirror, then from the second mirror reflecting to the third mirror, and finally from the third mirror reflecting to the first mirror; a photomultiplier tube receives the laser signal carrying the absorption spectrum signal reflected by the second fiber collimator, and amplifies and performs photoelectric conversion on the laser signal carrying the absorption spectrum signal; a data acquisition card acquires the laser signal carrying the absorption spectrum signal after amplification and photoelectric conversion; the computer performs reverse deduction on the laser signal carrying the absorption spectrum signal according to the Beer-Lambert law to obtain the water vapor concentration in the natural gas to be measured. The absorption chamber part of the present invention is different from the design method of a common reflective gas chamber. The reflection optical path is arranged on the same reflection plane, so that a maximum optical path is obtained within a limited space, the device structure is more compact, the work is more efficient, and the detection performance is improved. The present invention provides an on-line laser detection device with a small volume, a compact structure, flexible application, strong practicability, rapid response and capable of continuous measurement, which can detect the water content of natural gas in the natural gas pipeline during the gas transportation process. The entire detection link is completed within a closed device, eliminating the possibility of leakage and reducing the interference of external environmental factors at the same time. At the same time, the present invention adopts a non-contact measurement method, and the problem of the pressure of the gas to be measured will not interfere with the measurement result, and the detection device will not pollute the gas to be measured, reducing the possibility of two-way interference.

[0020] Further, the first fiber collimator of the present invention is located at a position near the air inlet at the bottom of the first mirror, and the second fiber collimator is located at a position away from the first fiber collimator at the top of the first mirror. This design arranges the second fiber collimator on the predetermined emission path of the laser, so that after the laser reflects the maximum number of times along the predetermined path, it finally carries the absorption spectrum signal and just emits from the second fiber collimator.

[0021] Further, the present invention is provided with a blower and a natural gas transportation filtering device on the bypass pipe communicated with the air inlet, and the natural gas transportation filtering device is located between the blower and the air inlet. During use, by using the suction of the blower, the natural gas to be measured flows into the bypass pipe, and after being sieved by the filter screen of the natural gas transportation filtering device, the solid impurities mixed in the long-distance transportation process can be removed, reducing the interference to the test result.

[0022] Further, stop valves are also provided on the two bypass pipes to cut off and connect the gas to be measured through the stop valves, so as to regulate the flow rate.

[0023] Further, the included angle between the first mirror and the fourth mirror is 60°, the included angle between the second mirror and the third mirror is 60°, and the length ratio of the first mirror, the second mirror, the third mirror, and the fourth mirror is 7:6:7:6 in sequence. After repeated verification, there is a specific geometric relationship when the mirrors are arranged alternately at this angle and ratio. When the laser is incident at a specific angle, equilateral triangles will be formed multiple times at the acute-angled vertices where the two mirrors intersect. After multiple reflections, a fixed outgoing path is formed. The laser reflects in the absorption chamber along this path for several cycles, which can effectively increase the optical path and achieve the purpose of improving the detection accuracy.

[0024] Further, a first small hole and a second small hole are opened on the first mirror. The first small hole is arranged on the first mirror near the acute end, and the distance between the first small hole and the acute vertex is 1 / 7 of the length of the first mirror. The second small hole is arranged on the first mirror near the obtuse end, and the distance between the second small hole and the obtuse vertex is 1 / 7 of the length of the first mirror. The above positions are the optimal incoming and outgoing positions in the verified laser periodic reflection path. When the laser is horizontally incident here through the first small hole, an equilateral triangle can be formed with the first mirror and the second mirror, and subsequent reflections will start along the predetermined path and finally exit at the position of the second small hole. The first fiber collimator is installed in the first small hole, and the second fiber collimator is installed in the second small hole. The first fiber collimator is horizontally arranged, and the second fiber collimator is parallel to the second mirror, which can well realize the injection and emission of the laser.

[0025] Further, protective shells are arranged in the first small hole and the second small hole. The first fiber collimator and the second fiber collimator are hermetically connected to the first mirror through the protective shells, ensuring the airtightness of the absorption chamber.

[0026] Further, the central wavelength of the distributed feedback laser is 1370 ± 2 nm. The spectral absorption of water molecules is relatively strong within this range, the laser is easy to obtain, and there are no other strong background absorption lines near the spectral line. Considering the above factors, the spectral line in the range of 1370 ± 2 nm is selected, and the water vapor content is measured based on its absorption spectrum.

[0027] To make the above objects, features, and advantages of the present invention more obvious and understandable, the following specifically enumerates preferred embodiments and, in conjunction with the accompanying drawings, makes a detailed description as follows. Description of the Drawings

[0028] To more clearly illustrate the technical solutions in the specific embodiments of the present invention, the following will briefly introduce the drawings required for use in the description of the specific embodiments. Obviously, the drawings in the following description are some embodiments of the present invention. For those of ordinary skill in the art, without creative efforts, other drawings can also be obtained based on these drawings.

[0029] Figure 1 Schematic diagram of an actual detection device for applying a continuous multi-reflection absorption type natural gas water content on-line laser detection device of the present invention to a natural gas pipeline;

[0030] Figure 2 Structural diagram of the gas chamber device part of a continuous multi-reflection absorption type natural gas water content on-line laser detection device of the present invention;

[0031] Figure 3 Schematic diagram of the connection position structure of the bypass pipe and the absorption chamber part of the present invention.

[0032] In the figure: 1. Bypass pipe, 2. Stop valve, 3. Gas chamber box body, 4. Absorption chamber, 5. Photomultiplier tube, 6. Optical fiber, 7. Computer, 8. Distributed feedback laser, 9. Natural gas transmission and filtration device, 10. Blower, 11. First small hole, 12. Second small hole, 13. Protection shell, 14. Circuit, 15. Data acquisition card, 16. First optical fiber collimator, 17. Second optical fiber collimator, 401. First reflector, 402. Second reflector, 403. Third reflector, 404. Fourth reflector. Specific embodiments

[0033] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the following will clearly and completely describe the technical solutions of the present invention with reference to the accompanying drawings. Obviously, the described embodiments are some, but not all, of the embodiments of the present invention. All other embodiments obtained by those of ordinary skill in the art based on the embodiments of the present invention without creative efforts fall within the scope of protection of the present invention.

[0034] As Figure 1 shown, a continuous multi-reflection absorption type natural gas water content on-line laser detection device provided by the present invention is applied to the actual detection of a natural gas pipeline.

[0035] As a specific embodiment of the present invention, as Figure 1 shown, a continuous multi-reflection absorption type natural gas water content on-line laser detection device includes two bypass pipes 1, a gas chamber box body 3, a first optical fiber collimator 16, a second optical fiber collimator 17, and a first reflector 401, a second reflector 402, a third reflector 403, and a fourth reflector 404 arranged in the gas chamber box body 3. CombiningFigure 2 As shown in the figure, the first reflector 401, the second reflector 402, the third reflector 403 and the fourth reflector 404 are connected end to end in sequence to form a column with a parallelogram cross-section. The two ports of the column are closely attached to the two side walls of the gas chamber box body 3 to form an absorption chamber 4. An air inlet and an air outlet are provided on the absorption chamber 4. That is to say, the absorption chamber 4 and the gas chamber box body 3 form a gas chamber device in a nested form of two parts. The absorption chamber 4 is mainly composed of four reflectors and has the same width as the gas chamber box body 3. In this embodiment, the outer part of the gas chamber device is a cuboid semi-hollow groove gas chamber box body 3, and the inner part is the absorption chamber 4 for actual reaction and detection. Since the laser reflection path in the present invention is in the same plane, the width design of the gas chamber device does not need to be too wide and is set to 50 mm. The length and height of the gas chamber device can be determined according to actual detection requirements. The gas chamber box body 3 mainly plays a role in protecting and fixing the internal absorption chamber 4, and at the same time can also play a secondary protection role in preventing the natural gas to be measured from leaking. The absorption chamber 4 as a whole has a columnar structure with a parallelogram cross-section. In this embodiment, the included angle between the first reflector 401 and the fourth reflector 404 is 60°, the included angle between the second reflector 402 and the third reflector 403 is 60°, and the length ratio of the first reflector 401, the second reflector 402, the third reflector 403 and the fourth reflector 404 is 7:6:7:6 in sequence.

[0036] As Figure 1 and Figure 3 shown, one end of a bypass pipe 1 is connected to the natural gas delivery pipe, and the other end is connected to the air inlet. One end of another bypass pipe 1 is connected to the air outlet, and the other end is connected to the natural gas delivery pipe. Preferably, a blower 10 and a natural gas delivery filtering device 9 are provided on the bypass pipe 1 connected to the air inlet, and the natural gas delivery filtering device 9 is located between the blower 10 and the air inlet. And stop valves 2 are also provided on the two bypass pipes 1. During operation, when the natural gas to be measured flows through the bypass pipe 1, it is sucked into the bypass pipe 1 by the blower 10, and after passing through the sieving action of the filter screen of the natural gas delivery filtering device 9, the solid impurities mixed in the long-distance transportation process are removed. Subsequently, the gas to be measured flows into the absorption chamber 4 from the air inlet, undergoes an absorption reaction with the laser of a specific wavelength in the absorption chamber 4, and the components of the gas to be measured are detected. The natural gas after the absorption reaction flows into the bypass pipe 1 again from the air outlet and finally flows back to the natural gas delivery pipeline for continuous transportation. Among them, the stop valve 2 is used to cut off and connect the gas to be measured and plays a role in regulating the flow rate.

[0037] As Figure 2As shown in the figure, one end of the first fiber collimator 16 and the second fiber collimator 17 passes through the first mirror 401 and extends into the absorption chamber 4. Preferably, the first fiber collimator 16 is located near the air inlet, and the second fiber collimator 17 is located away from the first fiber collimator 16. The first fiber collimator 16 is used to inject laser light onto the fourth mirror 404, and the second fiber collimator 17 is used to emit the laser light carrying the absorption spectrum signal after being reflected along a predetermined reflection path for several cycles. The reflection path for one cycle is from the fourth mirror 404 to the second mirror 402, then from the second mirror 402 to the third mirror 403, and finally from the third mirror 403 to the first mirror 401.

[0038] As a preferred embodiment, a first small hole 11 and a second small hole 12 are provided on the first mirror 401. The first small hole 11 is provided near the acute angle end of the first mirror 401, and the distance between the first small hole 11 and the acute angle vertex is 1 / 7 of the length of the first mirror 401. The second small hole 12 is provided near the obtuse angle end of the first mirror 401, and the distance between the second small hole 12 and the obtuse angle vertex is 1 / 7 of the length of the first mirror 401. The first fiber collimator 16 is installed in the first small hole 11, and the second fiber collimator 17 is installed in the second small hole 12. The first fiber collimator 16 is horizontally arranged, and the second fiber collimator 17 is parallel to the second mirror 402. Preferably, to ensure the airtightness of the absorption chamber 4, a protective housing 13 should be provided around the first fiber collimator 16 and the second fiber collimator 17 and be hermetically connected to the first mirror 401. More preferably, the first fiber collimator 16, the second fiber collimator 17 and the protective housing 13 can be designed to be threadedly detachable for easy replacement of parts.

[0039] In this embodiment, the laser light emitted by the first fiber collimator 16 is directed towards the fourth mirror 404, and the emitted laser light forms an angle of 60° with the first mirror 401, that is, the emitted laser light forms an equilateral triangle with the first mirror 401 and the fourth mirror 404 at the acute angle vertex. After repeated verification, when the laser light is injected into the absorption chamber 4 by the first fiber collimator 16 and undergoes multiple reflections among the four mirrors, its final emission path is fixed. The emitted laser light will be directed from the third mirror 403 towards the first mirror 401, and the emitted laser light is parallel to the second mirror 402, and the emission position is the second small hole 12. Therefore, the straight line where the receiving direction of the second fiber collimator 17 is located forms a 60° angle with the first mirror 401, and the straight line is parallel to the second mirror 402.

[0040] As Figure 1As shown, the other end of the first fiber collimator 16 is connected to a distributed feedback laser 8 through an optical fiber 6. The distributed feedback laser 8 is connected to a computer 7 through a circuit 14. The computer 7 is connected to a data acquisition card 15 through the circuit 14. The data acquisition card 15 is connected to a photomultiplier tube 5 through the circuit 14. The photomultiplier tube 5 is connected to the other end of the second fiber collimator 17 through the optical fiber 6. The computer 7 is used to control the distributed feedback laser 8 to emit laser light towards the first fiber collimator 16. The photomultiplier tube 5 is used to receive the laser signal carrying the absorption spectrum signal reflected by the second fiber collimator 17, and amplify and perform photoelectric conversion on the laser signal carrying the absorption spectrum signal. The data acquisition card 15 is used to collect the laser signal carrying the absorption spectrum signal after amplification and photoelectric conversion. The computer 7 is also used to perform reverse deduction on the laser signal carrying the absorption spectrum signal according to the Beer-Lambert law to obtain the water vapor concentration in the natural gas to be measured. That is to say, during operation, the computer 7 outputs a specific sawtooth current to modulate the output laser wavelength of the distributed feedback laser 8. In this embodiment, the distributed feedback laser 8 selects a semiconductor DFB laser, and the output center wavelength is maintained at 1370 ± 2 nm. The laser is emitted from the distributed feedback laser 8, transmitted through the optical fiber 6 to the first fiber collimator 16 and enters the absorption chamber 4. During the process that the detection laser is reflected multiple times by the four-sided mirrors in the absorption chamber 4, it makes full contact with the natural gas to be measured. Part of the laser with a wavelength consistent with the absorption peak wavelength of the gas to be measured is absorbed by the gas to be measured inside the absorption chamber 4, and the remaining laser is emitted along a specific route after the reaction, received by the second fiber collimator 17 and coupled into the optical fiber 6 and transmitted to the photomultiplier tube 5. The laser after being absorbed by the gas to be measured contains water vapor concentration information. After a series of signal amplifications and photoelectric conversions when passing through the photomultiplier tube 5, the concentration signal is collected by the data acquisition card 15. The data acquisition card 15 uploads the concentration signal to the computer 7, and the computer performs post-processing on the concentration signal to obtain the water vapor concentration in the natural gas to be measured.

[0041] A continuous multi-reflection absorption type on-line laser detection method for the water content of natural gas, specifically:

[0042] Open the stop valve 2, start the blower 10 and the natural gas transportation and filtration device 9, and transport the natural gas to be measured in the natural gas pipeline through the bypass pipe 1 into the absorption chamber 4;

[0043] The computer 7 controls the distributed feedback laser 8 to emit laser light towards the first fiber collimator 16. Specifically, start the computer 7 to emit a sawtooth current to drive the distributed feedback laser 8 to emit laser light with a center wavelength of 1370 ± 2 nm. The wavelength of the laser is near the optimal absorption wavelength of the gas to be measured;

[0044] The first fiber collimator 16 emits laser light onto the fourth mirror 404. After the laser light is incident, it reflects several cycles along a predetermined reflection path within the absorption chamber 4. The second fiber collimator 17 emits the laser light that has carried the absorption spectrum signal after reflecting several cycles along the predetermined reflection path. One cycle of the reflection path is from the fourth mirror 404 to the second mirror 402, then from the second mirror 402 to the third mirror 403, and finally from the third mirror 403 to the first mirror 401. That is to say, the laser light reflects multiple times between the four mirrors along a specific path within the absorption chamber 4, makes full contact with the gas to be measured during the reflection process, and part of the laser light with wavelengths consistent with the absorption peak wavelengths of the gas to be measured is absorbed. The remaining laser light carries the concentration information and exits the absorption chamber 4. After being received by the second fiber collimator 17, it is coupled into the optical fiber.

[0045] The photomultiplier tube 5 receives the laser signal carrying the absorption spectrum signal reflected by the second fiber collimator 17, and amplifies and performs photoelectric conversion on the laser signal carrying the absorption spectrum signal. The data acquisition card 15 acquires the laser signal carrying the absorption spectrum signal after amplification and photoelectric conversion. The computer 7 performs reverse deduction on the laser signal carrying the absorption spectrum signal according to the Beer-Lambert law to obtain the water vapor concentration in the natural gas to be measured. In other words, the laser light carrying the concentration information is transmitted along the optical fiber 6 to the photomultiplier tube 5. After signal amplification and photoelectric conversion, the signal is transmitted to the data acquisition card 15. The data acquisition card 15 collects and transfers the data to the computer 7. The computer 7 performs reverse deduction on the absorption spectrum signal according to the Beer-Lambert law to obtain the water vapor concentration in the gas to be measured.

[0046] Finally, it should be noted that the above-described embodiments are only specific embodiments of the present invention, used to illustrate the technical solutions of the present invention, rather than limiting it. The protection scope of the present invention is not limited thereto. Although the present invention has been described in detail with reference to the foregoing embodiments, those of ordinary skill in the art should understand that any person skilled in the art within the technical scope disclosed by the present invention can still modify the technical solutions described in the foregoing embodiments or can easily think of changes, or perform equivalent replacements on some of the technical features; and these modifications, changes or replacements do not cause the essence of the corresponding technical solutions to deviate from the spirit and scope of the technical solutions of the embodiments of the present invention, and should all be covered within the protection scope of the present invention. Therefore, the protection scope of the present invention should be subject to the protection scope of the claims.

Claims

1. A continuous multi-reflection absorption type on-line laser detection device for natural gas water content, characterized in that: It includes two bypass pipes (1), a gas chamber box body (3), a first fiber optic collimator (16), a second fiber optic collimator (17), and a first reflector (401), a second reflector (402), a third reflector (403), and a fourth reflector (404) arranged inside the gas chamber box body (3). The first reflector (401), the second reflector (402), the third reflector (403), and the fourth reflector (404) are connected end to end in sequence to form a column with a parallelogram cross-section, and the two ports of the column are closely attached to the two side walls of the gas chamber box body (3) to form an absorption chamber (4). An air inlet and an air outlet are arranged on the absorption chamber (4); one end of one bypass pipe (1) is communicated with a natural gas delivery pipe, and the other end is communicated with the air inlet. The other end of the other bypass pipe (1) is communicated with the air outlet, and the other end is communicated with the natural gas delivery pipe; one ends of the first fiber optic collimator (16) and the second fiber optic collimator (17) pass through the first reflector (401) and extend into the absorption chamber (4). The first fiber optic collimator (16) is used to emit laser light onto the fourth reflector (404). The second fiber optic collimator (17) is used to emit the laser light carrying the absorption spectrum signal after being reflected along a predetermined reflection path for several cycles. The reflection path for one cycle is from the fourth reflector (404) to the second reflector (402), then from the second reflector (402) to the third reflector (403), and finally from the third reflector (403) to the first reflector (401); the other end of the first fiber optic collimator (16) is connected to a distributed feedback laser (8). The distributed feedback laser (8) is connected to a computer (7). The computer (7) is connected to a data acquisition card (15). The data acquisition card (15) is connected to a photomultiplier tube (5). The photomultiplier tube (5) is connected to the other end of the second fiber optic collimator (17). The computer (7) is used to control the distributed feedback laser (8) to emit laser light to the first fiber optic collimator (16); the photomultiplier tube (5) is used to receive the laser signal carrying the absorption spectrum signal reflected by the second fiber optic collimator (17), and amplify and perform photoelectric conversion on the laser signal carrying the absorption spectrum signal; the data acquisition card (15) is used to acquire the laser signal carrying the absorption spectrum signal after amplification and photoelectric conversion; the computer (7) is also used to perform reverse deduction on the laser signal carrying the absorption spectrum signal according to the Beer-Lambert law to obtain the water vapor concentration in the natural gas to be measured.

2. The on-line laser detection device for the water content of natural gas with continuous multi-reflection absorption type according to claim 1, characterized in that: The first fiber optic collimator (16) is located at a position close to the air inlet, and the second fiber optic collimator (17) is located at a position far from the first fiber optic collimator (16).

3. The on-line laser moisture content detection device for continuous multi-reflection absorption type natural gas according to claim 1, wherein: A blower (10) and a natural gas delivery filtering device (9) are arranged on the bypass pipe (1) communicated with the air inlet, and the natural gas delivery filtering device (9) is located between the blower (10) and the air inlet.

4. The on-line laser moisture detection device for continuous multi-reflection absorption type natural gas according to claim 3, wherein: Cut-off valves (2) are also arranged on the two bypass pipes (1).

5. The on-line laser detection device for the water content of natural gas with continuous multi-reflection absorption according to claim 1, characterized in that: The first fiber collimator (16) is connected to the distributed feedback laser (8) through an optical fiber (6), and the second fiber collimator (17) is connected to the photomultiplier tube (5) through an optical fiber (6).

6. The on-line laser moisture detection device for continuous multi-reflection absorption type natural gas according to claim 1, characterized in that: The included angle between the first mirror (401) and the fourth mirror (404) is 60°, the included angle between the second mirror (402) and the third mirror (403) is 60°, and the length ratio of the first mirror (401), the second mirror (402), the third mirror (403), and the fourth mirror (404) is 7:6:7:6 in sequence.

7. The on-line laser detection device for the water content of natural gas with continuous multi-reflection absorption according to claim 6, characterized in that: A first small hole (11) and a second small hole (12) are formed in the first mirror (401). The first small hole (11) is arranged near the acute end on the first mirror (401), and the distance between the first small hole (11) and the acute vertex is 1 / 7 of the length of the first mirror (401). The second small hole (12) is arranged near the obtuse end on the first mirror (401), and the distance between the second small hole (12) and the obtuse vertex is 1 / 7 of the length of the first mirror (401). The first fiber collimator (16) is installed in the first small hole (11), the second fiber collimator (17) is installed in the second small hole (12), the first fiber collimator (16) is horizontally arranged, and the second fiber collimator (17) is parallel to the second mirror (402).

8. The on-line laser detection device for the water content of natural gas with continuous multi-reflection absorption according to claim 7, characterized in that: A protective housing (13) is arranged in the first small hole (11) and the second small hole (12), and the first fiber collimator (16) and the second fiber collimator (17) are connected to the first mirror (401) through the protective housing (13).

9. The on-line laser detection device for the water content of natural gas of a continuous multi-reflection absorption type according to claim 1, characterized in that: The central wavelength of the distributed feedback laser (8) is 1370 ± 2 nm.

10. An on-line laser detection method for the water content of natural gas with continuous multi-reflection absorption type, characterized in that: Applying the detection device according to any one of claims 1 to 9, specifically: Natural gas in the natural gas transmission pipe enters the absorption chamber (4) through the bypass pipe (1); the computer (7) controls the distributed feedback laser (8) to emit laser light to the first fiber collimator (16); the first fiber collimator (16) injects the laser light onto the fourth mirror (404). After the laser light is injected, it reflects along a predetermined reflection path in the absorption chamber (4) for several cycles. The second fiber collimator (17) emits the laser light carrying the absorption spectrum signal after reflecting along the predetermined reflection path for several cycles. The reflection path of one cycle is from the fourth mirror (404) reflecting to the second mirror (402), then from the second mirror (402) reflecting to the third mirror (403), and finally from the third mirror (403) reflecting to the first mirror (401); the photomultiplier tube (5) receives the laser signal carrying the absorption spectrum signal reflected by the second fiber collimator (17), and amplifies and performs photoelectric conversion on the laser signal carrying the absorption spectrum signal; the data acquisition card (15) acquires the laser signal carrying the absorption spectrum signal after amplification and photoelectric conversion; the computer (7) performs reverse deduction on the laser signal carrying the absorption spectrum signal according to the Beer-Lambert law to obtain the water vapor concentration in the natural gas to be measured.

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