CN201152458Y - Urban gas pipeline leakage detection and positioning system - Google Patents

Abstract

The utility model discloses a novel urban natural gas pipeline leakage detection and location system. An infrared laser, a laser temperature current controller and a signal generator are installed in a box body. An infrared laser outlet is arranged at the front end of a laser inlet window plate of a multi-reflection absorption pool, a gas outlet of the multi-reflection absorption pool is connected with a micro getter pump, and a gas inlet is connected with a hose. The end part of the hose is connected with a sampling probe, and an exhaust port of the micro getter pump is led to the air outside the box body. Laser which enters the multi-reflection absorption pool is launched out from a laser outlet window plate, is received by a laser detector, and is carried out signal processing by signal outlet of the laser detector. Sampling probe air absorption type sampling is adopted, so the detection is more agile and convenient, and the resolution is high. The laser spectrum technology is adopted, the novel urban natural gas pipeline leakage detection and location system only has reaction on CH4 gas with the detection limit reaching a millionth (PPM) level, and can detect the small change of CH4 gas concentration at the periphery of leakage points generated by natural gas pipeline leakage.

Description

New urban natural gas pipeline leak detection and positioning system

technical field

The utility model relates to the field of environmental spectroscopy and the technical field of detection and positioning of gas pipeline leakage, in particular to a _CH4 gas concentration measurement system based on tunable laser spectrum technology (TDLAS) for detection and positioning of urban natural gas pipeline leakage .

technical background

At present, as one of the essential infrastructures of cities, gas pipelines have made great contributions to the improvement of people's living standards. However, due to the aging of pipeline equipment, the influence of geographical and climatic conditions, and man-made sabotage, leakage accidents often occur. Once the urban gas pipeline leaks, it will not only bring economic losses and environmental pollution, but also cause fires and explosions due to the many uncertain fire sources in the city, causing casualties and other catastrophic accidents, which will have a huge negative impact on society.

The current natural gas pipeline leakage detection and location methods are mainly divided into direct method and indirect method, and the direct detection of the concentration of methane (more than 95%), the main component of natural gas, is a widely used method.

Most of the gas sensors used for natural gas pipeline leak detection are semiconductor sensors, but they generally have the disadvantages of long response time, easy poisoning, and interference from other gases. Gas sensing technology based on laser spectroscopy technology can realize highly sensitive and non-contact online detection of gas, so it has broad application prospects in the field of natural gas pipeline leakage detection.

In the prior art, there is also an open natural gas leakage monitoring method based on tunable semiconductor laser absorption spectroscopy technology. Although the sensitivity of large-scale natural gas leakage monitoring is well improved, this method adopts an open optical path structure and is not suitable for Leakage detection and location of natural gas pipelines in complex urban ground environments.

Utility model content

The utility model provides a sampling type urban natural gas pipeline leakage detection and positioning system based on semiconductor tunable laser absorption spectrum technology. This system utilizes the modular system design and simple and practical optical path structure, uses the hand-held probe suction sampling and positioning method, successfully applies the highly sensitive laser spectrum gas concentration measurement technology to the detection of natural gas pipeline leakage, and combines the laser gas The high sensitivity and anti-jamming of analytical technology and the flexible and simple advantages of traditional semiconductor sensor point measurement have effectively improved the accuracy of natural gas leak detection and positioning in complex urban ground environments.

The technical scheme of the utility model is as follows:

The new urban natural gas pipeline leakage detection and positioning system is characterized in that: an infrared laser is installed in the box, the control signal of the signal controller is input to the laser temperature and current controller, and the output control signal of the laser temperature and current controller is connected to the infrared laser. The light outlet of the infrared laser is located at the front of the light entrance window of the multi-reflection absorption cell. The air inlet of the pool is connected with a hose, and the end of the hose is connected with a sampling probe. The laser light entering the multi-reflection absorption pool exits from the light-emitting window and is received by the laser detector. The signal of the laser detector is output to the lock-in amplifier, and then Through the signal acquisition module, it is connected to the signal analysis and processing module, and the output control signal of the lock-in amplifier is connected to the infrared laser.

A collimating lens is installed in front of the light entrance window and the light exit window of the multiple reflection absorption pool.

The visible light laser is installed in the box, the light outlet of which is connected with an optical fiber, and the light outlet of the infrared laser is connected with an optical fiber. Two bundles of optical fibers are coupled and positioned at the front end of the light entrance window of the multiple reflection absorption pool.

A CH ₄ standard gas calibration cell is installed between the light exit window of the multiple reflection absorption cell and the laser detector.

A displacement sensor is installed on the outer wall of the sampling probe, and the output end of the displacement sensor is connected to the signal acquisition module.

The sampling probe is composed of a handle, a metal pipe body, an interface flange and a joint, and a filter screen is built between the interface flange and the joint.

The components of the utility model except the sampling probe are all built in the box body, and the sampling probe communicates with the air inlet of the multi-reflection absorption pool in the box through a pipeline.

The sampling probe is an air intake pipe, and a filter screen is also installed at the front end.

Principle of the utility model:

The monochromatic laser with intensity I ₀ and frequency υ passes through the absorbing medium (gas) with length L, and the intensity measured at the receiving end is I, which follows Lambert-Beer's law

I(υ)＝I ₀ (υ)exp(-σ(υ)NL)

Where σ(υ) is the central absorption cross section of the gas molecule, and N is the molar concentration of the gas.

When the center frequency υ _c of the laser is modulated by a sinusoidal modulating wave with amplitude δυ and frequency ω, the laser frequency can be expressed as:

υ＝ _υc +δυcosωt

Using the cosine Fourier series of I(υ _c ) in the above formula can be written as:

$\mathrm{<span\; class="notranslate">\; I</span>}<span\; class="notranslate">\; (</span>{\mathrm{<span\; class="notranslate">\; \&upsi;</span>}}_{\mathrm{<span\; class="notranslate">\; c</span>}}<span\; class="notranslate">\; ,</span>\mathrm{<span\; class="notranslate">\; t</span>}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; =</span>\underset{\mathrm{<span\; class="notranslate">\; no</span>}<span\; class="notranslate">\; =</span>\mathrm{<span\; class="notranslate">\; 0</span>}}{\overset{<span\; class="notranslate">\; \&infin;</span>}{\mathrm{<span\; class="notranslate">\; \&Sigma;</span>}}}{\mathrm{<span\; class="notranslate">\; A</span>}}_{\mathrm{<span\; class="notranslate">\; no</span>}}<span\; class="notranslate">\; (</span>{\mathrm{<span\; class="notranslate">\; \&upsi;</span>}}_{\mathrm{<span\; class="notranslate">\; c</span>}}<span\; class="notranslate">\; )</span>\mathrm{<span\; class="notranslate">\; cos</span>}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; no</span>}\stackrel{<span\; class="notranslate">\; \&OverBar;</span>}{\mathrm{<span\; class="notranslate">\; \&omega;</span>}}\mathrm{<span\; class="notranslate">\; t</span>}<span\; class="notranslate">\; )</span>$

${\mathrm{<span\; class="notranslate">\; A</span>}}_{\mathrm{<span\; class="notranslate">\; no</span>}}<span\; class="notranslate">\; (</span>{\mathrm{<span\; class="notranslate">\; \&upsi;</span>}}_{\mathrm{<span\; class="notranslate">\; c</span>}}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; =</span>\frac{\mathrm{<span\; class="notranslate">\; 2</span>}}{\mathrm{<span\; class="notranslate">\; \&pi;</span>}}{<span\; class="notranslate">\; \&Integral;</span>}_{\mathrm{<span\; class="notranslate">\; 0</span>}}^{\mathrm{<span\; class="notranslate">\; \&pi;</span>}}{\mathrm{<span\; class="notranslate">\; I</span>}}_{\mathrm{<span\; class="notranslate">\; 0</span>}}<span\; class="notranslate">\; (</span>{\mathrm{<span\; class="notranslate">\; \&upsi;</span>}}_{\mathrm{<span\; class="notranslate">\; c</span>}}<span\; class="notranslate">\; +</span>\mathrm{<span\; class="notranslate">\; \&delta;\&upsi;</span>}\mathrm{<span\; class="notranslate">\; cos</span>}\stackrel{<span\; class="notranslate">\; \&OverBar;</span>}{\mathrm{<span\; class="notranslate">\; \&omega;</span>}}\mathrm{<span\; class="notranslate">\; t</span>}<span\; class="notranslate">\; )</span>\mathrm{<span\; class="notranslate">\; exp</span>}<span\; class="notranslate">\; [</span><span\; class="notranslate">\; -</span>\mathrm{<span\; class="notranslate">\; \&sigma;</span>}<span\; class="notranslate">\; (</span>{\mathrm{<span\; class="notranslate">\; \&upsi;</span>}}_{\mathrm{<span\; class="notranslate">\; c</span>}}<span\; class="notranslate">\; +</span>\mathrm{<span\; class="notranslate">\; \&delta;\&upsi;</span>}\mathrm{<span\; class="notranslate">\; cos</span>}\stackrel{<span\; class="notranslate">\; \&OverBar;</span>}{\mathrm{<span\; class="notranslate">\; \&omega;</span>}}\mathrm{<span\; class="notranslate">\; t</span>}<span\; class="notranslate">\; )</span>\mathrm{<span\; class="notranslate">\; NL</span>}<span\; class="notranslate">\; ]</span>\mathrm{<span\; class="notranslate">\; cos</span>}\mathrm{<span\; class="notranslate">\; n\&theta;d\&theta;</span>}$

where θ=ωt

Ideally, I ₀ is not a function of frequency υ. When measuring trace gas, N is a minimum value, so σ(υ _c +δυcosωt)NL<<1, the above formula is approximately written as:

${\mathrm{<span\; class="notranslate">\; A</span>}}_{\mathrm{<span\; class="notranslate">\; no</span>}}<span\; class="notranslate">\; (</span>{\mathrm{<span\; class="notranslate">\; \&upsi;</span>}}_{\mathrm{<span\; class="notranslate">\; c</span>}}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; =</span>\frac{\mathrm{<span\; class="notranslate">\; 2</span>}{\mathrm{<span\; class="notranslate">\; I</span>}}_{\mathrm{<span\; class="notranslate">\; 0</span>}}\mathrm{<span\; class="notranslate">\; NL</span>}}{\mathrm{<span\; class="notranslate">\; \&pi;</span>}}$

Therefore, the nth harmonic component is directly proportional to the trace gas concentration.

That is, CH ₄ with a known concentration of N ₀ is passed into the multiple reflection absorption cell, and the second harmonic signal intensity is measured and recorded as A ₀ , then the measured CH ₄ concentration N _x can be expressed as

${\mathrm{<span\; class="notranslate">\; N</span>}}_{\mathrm{<span\; class="notranslate">\; x</span>}}<span\; class="notranslate">\; =</span>\frac{{\mathrm{<span\; class="notranslate">\; N</span>}}_{\mathrm{<span\; class="notranslate">\; 0</span>}}}{{\mathrm{<span\; class="notranslate">\; A</span>}}_{\mathrm{<span\; class="notranslate">\; 0</span>}}}{\mathrm{<span\; class="notranslate">\; A</span>}}_{\mathrm{<span\; class="notranslate">\; x</span>}}$

The beneficial effect that the utility model produces:

(1) High resolution, using laser spectroscopy technology, only reacts to CH ₄ gas, the detection limit reaches the million molecule-(PPM) level, and can detect small changes in the concentration of CH ₄ gas around the leakage point caused by natural gas pipeline leakage ;

(2) The method of probe suction sampling is adopted to make the detection more flexible and convenient;

(3) A displacement sensor is installed on the probe to obtain the position distribution information of the gas leakage;

(4) Modular design, simple installation, easy installation and disassembly maintenance and function expansion.

Description of drawings

Fig. 1 is a schematic diagram of the overall structure of the utility model

Fig. 2 is the structural diagram of the multi-reflection absorption pool of the components of the utility model

Detailed ways

Combined with Figure 1 and Figure 2, the labels in the figure: 1. Infrared laser, 2. Visible light laser, 3. Input fiber coupler, 4. Incident collimator lens, 5. Exit collimator lens, 6. Multiple reflection absorption pool, 7. Miniature suction pump, 8. Breathing sampling probe, 9. Laser temperature and current controller, 10. Signal generator, 11. Laser detector, 12. Standard gas calibration pool, 13. Display terminal, 14. Phase lock Amplifier, 15. Signal analysis and processing module, 16. Signal acquisition module, 17. Displacement sensor, 18. Primary mirror adjustment knob, 19. Light entrance window, 20. Air outlet, 21. Primary reflector, 22. Secondary reflector , 23, air inlet, 24, light-emitting window, 25, reflective corner mirror, 26, secondary reflector, 27, secondary mirror adjustment knob.

Adjust the laser temperature and current controller 9 so that the output wavelength of the laser 1 is located at the center of a certain absorption line of the _CH4 gas, and the signal generator 10 generates a low-frequency sawtooth wave signal and inputs it to the laser temperature and current controller 9, so that the output wavelength of the laser 1 slowly sweeps Through the absorption line of CH ₄ gas, at the same time, the high-frequency sinusoidal signal output by the lock-in amplifier 14 is directly input to the laser 1 to modulate the output light. The modulated laser light generated by the laser 1 is transmitted to the input fiber coupler 3 through the optical fiber, passes through the collimating lens 5, and enters the multiple reflection absorption pool 5 through the light incident window 19, and the air inlet of the multiple reflection absorption pool 5 The suction sampling probe 8 is connected through the pipeline, and the air outlet is connected to the micro suction pump 7. After the micro suction pump 7 works, it exhausts to the atmosphere, the sampling probe 8 sucks the sample gas to be measured from the outside, and the multiple reflection absorption cell 5 The medium is filled with the sample gas that needs to be measured. The incident laser light is reflected back and forth between the primary mirror 21 and the secondary mirrors 22 and 26 for many times, and then emerges from the light-emitting window 24. The light is focused on the On the photosensitive surface of the laser detector 11, the detector 11 converts the optical signal into an electrical signal and outputs it to the lock-in amplifier 14, and demodulates to obtain the second harmonic amplitude. The generated calibration signal is linearly fitted to obtain the CH gas concentration to be detected, and the displacement _signal generated by the displacement sensor 17 is also input into the signal analysis and processing module 15 by the signal acquisition module 16 to obtain the _CH gas concentration position distribution information .

In this example:

1. Laser 1 uses a near-infrared tunable single-mode distributed feedback diode laser (NTTElectronics), with a typical wavelength of 1653.74nm and a wavelength tunable range of 2nm.

2. The frequency of the low-frequency sawtooth wave generated by the signal generator 10 is 50 Hz.

3. The multi-reflection absorption cell is a white cell, the maximum number of reflections is 100 times, the total optical path can reach 20 meters, and the volume is 0.0015 cubic meters.

4. The flow range of the micro suction pump is 0.014-0.017 cubic meters per minute.

5. Visible light laser 2 is an indicating laser, which is used to adjust the optical path of the multiple reflection pool before testing.

6. The standard gas calibration cell 12 is filled with standard CH ₄ gas of known concentration, which is used for system calibration.

Claims (6)

1, new city gas pipeline leakage detection and location system, it is characterized in that: infrared laser is installed in casing, the control signal of signal controller is input to the laser temperature current controller, swash musical instrument temperature current controller output control signal and be linked into infrared laser, the infrared laser light output port is positioned at the light inlet window front end of multiple reflectance cell, the air outlet of multiple reflectance cell connects miniature suction pump, the relief opening of miniature suction pump leads to the outer atmosphere of casing, the suction port of multiple reflectance cell connects flexible pipe, hose end is connected to sampling probe, the laser that enters multiple reflectance cell is from the outgoing of bright dipping window, receive by laser detector, the signal of laser detector outputs to lock-in amplifier, pass through signal acquisition module again, be linked into the signal analysis and processing module, lock-in amplifier output control signal is linked into infrared laser.

2, new city gas pipeline leakage detection and location according to claim 1 system is characterized in that before the light inlet window, bright dipping window of described multiple reflectance cell collimation lens being installed all.

3, new city gas pipeline leakage detection and location according to claim 1 system, it is characterized in that in the described casing visible laser being installed, its light output port is connected with optical fiber, the infrared laser light output port is connected with optical fiber, two bundle optical fiber are coupled, and are positioned the light inlet window front end of multiple reflectance cell.

4, new city gas pipeline leakage detection and location according to claim 1 system is characterized in that between the bright dipping window of described multiple reflectance cell and the laser detector CH being installed ₄The calibrating gas calibration pool.

5, new city gas pipeline leakage detection and location according to claim 1 system is characterized in that on the sampling probe outer wall displacement transducer being installed, and the output terminal of displacement transducer connects signal acquisition module.

6, new city gas pipeline leakage detection and location according to claim 1 system is characterized in that described sampling probe is made up of handle, metal tube body, flange, joint, is built-in with filter screen between flange and the joint.

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