Leakage detection method and system for compressed air storage

Abstract

The invention discloses a compressed air storage reservoir leakage detection method and system, and relates to the field of compressed air energy storage power generation, and the method comprises the steps: laying a sensing optical cable used for detecting the gas leakage at any position of a compressed air storage reservoir in the compressed air storage reservoir; in the process of using the compressed air storage, the monitoring host sends a continuous optical signal to the sensing optical cable and receives a returned continuous optical signal, so that the sensing optical cable is used for detecting vibration in an ultrasonic wave range caused by gas leakage of the compressed air storage; and the monitoring host determines whether the compressed air storage has gas leakage or not by utilizing the continuous optical signals transmitted back by the sensing optical cable. According to the invention, gas leakage of the compressed air storage can be effectively detected.

Description

Technical Field

[0001] The present invention relates to the field of compressed air energy storage power generation, and in particular to a compressed air storage reservoir leakage detection method and system. Background Art

[0002] Compressed air energy storage power generation is one of the many energy storage power generation methods. It uses high-pressure air as a form of energy storage and generates electricity by expanding high-pressure air when needed. It has become a large-scale, long-term energy storage technology with development potential in addition to pumped storage. Its working principle is as follows: Energy storage period - using excess or non-peak electricity, wind / photovoltaic or valley electricity to drive the compressor to compress air, converting electrical energy into air pressure energy, and the generated high-pressure air is injected underground and stored in salt caverns, abandoned mines / oil wells or steel gas tanks for later use; Energy release period - releasing high-pressure air from the gas storage (caves / chambers), and after preheating and heating, it drives the expander to work, converting the air pressure energy into electrical energy, thereby transmitting the generated electrical energy back to the power grid. Compressed air energy storage power generation has the advantages of high energy storage density, high comprehensive efficiency, long service life, low cost, and environmental friendliness.

[0003] As the scale of compressed air energy storage power generation increases, the working pressure of the gas storage reservoir (cavern / chamber) will reach 15MPa. The working pressure of the gas storage reservoir (cavern / chamber) directly affects the working efficiency of the energy storage system. Therefore, leakage monitoring becomes a rigid requirement for the entire compressed air energy storage power generation system.

[0004] The gas storage reservoir (cave / chamber) in the compressed air energy storage power generation system can usually use an underground cave about 15m from the surface and transform it for gas storage. The structural diagram is as follows Figure 1 and Figure 2 As shown, the internal diameter of the gas storage (cave / chamber) 1 is 10m, the length is 200m, the inner wall is covered by a 20mm thick metal plate (such as a steel plate) 2, and the outside is poured with 500mm thick concrete 3 to increase its strength. The internal environment of the gas storage is very harsh, the working temperature ranges from -20℃ to +65℃, and the maximum working pressure ranges from 7.5MPa to 15MPa. Based on the special structure of the gas storage (cave / chamber), the harsh working environment and the actual conditions on site, conventional leak detection technology cannot meet the leak detection needs and it is difficult to detect it. The reasons are as follows:

[0005] First, conventional ultrasonic detection equipment based on point vibration sensors uses a single sensor with a limited detection range. Leakage in large caverns requires the deployment of a large number of sensors, which makes it difficult to cover all locations in the cavern / chamber, and the detection is not continuous.

[0006] Second, it is necessary to install power supply equipment, lay a large number of copper cables, and consider the signal transmission problem of each sensor. The leakage detection system has a complex structure;

[0007] Third, the working conditions in the gas storage facility are harsh, with large temperature changes and high working pressure. Under harsh working conditions, the reliability and stability of active equipment are very poor, failures often occur, the operation and maintenance workload is heavy, and the detection equipment cannot work properly at all. Summary of the invention

[0008] The present invention provides a compressed air storage reservoir leakage detection method and system, aiming to detect gas leakage in the compressed air storage reservoir.

[0009] The present invention provides a method for detecting leakage of a compressed air storage reservoir, the method comprising: laying a sensor optical cable inside the compressed air storage reservoir for detecting gas leakage at any position of the compressed air storage reservoir; during the use of the compressed air storage reservoir, a monitoring host sends a continuous optical signal to the sensor optical cable and receives the returned continuous optical signal, so as to use the sensor optical cable to detect vibrations within an ultrasonic range caused by gas leakage in the compressed air storage reservoir; the monitoring host uses the continuous optical signal returned by the sensor optical cable to determine whether gas leakage occurs in the compressed air storage reservoir.

[0010] Preferably, the compressed air storage reservoir comprises one or more independent air storage holes or air storage chambers, and the laying of a sensor optical cable inside the compressed air storage reservoir for detecting gas leakage at any position of the compressed air storage reservoir is specifically as follows: the sensor optical cable is looped on the inner wall of each air storage hole or air storage chamber with the direction from the entrance to the outlet of the air storage hole or air storage chamber as the laying direction; the sensor optical cables looped in each air storage hole or air storage chamber are connected in series to form a sensor optical cable capable of quickly detecting gas leakage at any position of the compressed air storage reservoir.

[0011] Preferably, a fiber optic flange made of high-pressure resistant material is used to connect the sensing optical cable to the gas storage hole or gas storage chamber from the entrance of each gas storage hole or gas storage chamber and to connect the sensing optical cable to the gas storage hole or gas storage chamber from the outlet of the gas storage hole or gas storage chamber; in the gas storage hole or gas storage chamber, a fiber optic splicing box made of high-pressure resistant material is used to realize the optical fiber splicing in the sensing optical cable.

[0012] Preferably, the sensing optical cable has optical fiber A, optical fiber B and optical fiber C; the monitoring host sends a continuous optical signal to the optical fiber A and the optical fiber B, and transmits the continuous optical signal back via the optical fiber C, wherein when the optical fiber A and the optical fiber B are subjected to vibration disturbance within the ultrasonic range caused by gas leakage from the compressed air storage reservoir, the continuous optical signals in the optical fiber A and the optical fiber B are modulated, and the modulated continuous optical signals are transmitted back to the monitoring host via the optical fiber C.

[0013] Preferably, the monitoring host uses the continuous light signal returned by the sensor optical cable to determine whether a gas leakage occurs in the compressed air storage reservoir, including: the monitoring host collects, demodulates and analyzes the continuous light signal returned by the sensor optical cable to obtain the phase difference of the continuous light signal returned by the sensor optical cable; and determines whether a gas leakage occurs in the compressed air storage reservoir based on the phase difference of the continuous light signal returned by the sensor optical cable.

[0014] Preferably, the method further includes: when the monitoring host collects, demodulates and analyzes the continuous optical signal transmitted back by the sensor optical cable, and obtains the phase difference of the continuous optical signal transmitted back by the sensor optical cable, the envelope of the carrier signal used for signal modulation is also obtained; according to the envelope of the carrier signal, the frequency of the vibration in the ultrasonic range caused by the gas leakage of the compressed air storage reservoir is determined; according to the rate of change of the phase difference of the continuous optical signal transmitted back by the sensor optical cable, the amplitude of the vibration in the ultrasonic range caused by the gas leakage of the compressed air storage reservoir is determined; according to the frequency and amplitude of the vibration in the ultrasonic range caused by the gas leakage of the compressed air storage reservoir, the gas leakage situation of the compressed air storage reservoir is determined.

[0015] Preferably, the gas leakage situation includes the size of the leakage hole and the amount of gas leakage; determining the gas leakage situation of the compressed air storage reservoir according to the frequency and amplitude of the vibration within the ultrasonic range caused by the gas leakage of the compressed air storage reservoir includes: obtaining the internal pressure of the compressed air storage reservoir monitored by the pressure sensor of the compressed air storage reservoir; determining whether the compressed air storage reservoir is full of compressed gas according to the internal pressure of the compressed air storage reservoir; if the compressed air storage reservoir is full of compressed gas, determining the size of the leakage hole of the compressed air storage reservoir according to the frequency and amplitude of the vibration within the ultrasonic range caused by the gas leakage of the compressed air storage reservoir; determining the amount of gas leakage of the compressed air storage reservoir according to the information on the change of the internal pressure of the compressed air storage reservoir and the frequency of the vibration within the ultrasonic range caused by the gas leakage of the compressed air storage reservoir with the gas leakage time.

[0016] Preferably, the method further includes: before maintaining the leaking compressed air storage reservoir, recording the frequency and amplitude of vibrations in the ultrasonic range caused by gas leakage each time the compressed air storage reservoir is filled with compressed gas; determining, based on the frequency and amplitude of vibrations in the ultrasonic range caused by gas leakage each time the compressed air storage reservoir is filled with compressed gas, a changing trend of the frequency and amplitude of vibrations in the ultrasonic range caused by gas leakage when the compressed air storage reservoir is filled with compressed gas; determining, based on the changing trend of the frequency and amplitude of vibrations in the ultrasonic range caused by gas leakage when the compressed air storage reservoir is filled with compressed gas, whether the leakage hole has increased.

[0017] Preferably, the method further comprises: the monitoring host locates the gas leakage position of the compressed air storage according to the time difference between the continuous optical signals transmitted by the optical fiber A and the optical fiber B arriving at the monitoring host.

[0018] The present invention also provides a compressed air storage reservoir leakage detection system, the system comprising: a sensor optical cable laid inside the compressed air storage reservoir, for detecting gas leakage at any position of the compressed air storage reservoir; a monitoring host, for sending a continuous optical signal to the sensor optical cable and receiving the returned continuous optical signal during the use of the compressed air storage reservoir, so as to use the sensor optical cable to detect the vibration within the ultrasonic range caused by the gas leakage in the compressed air storage reservoir, and then use the continuous optical signal returned by the sensor optical cable to determine whether gas leakage occurs in the compressed air storage reservoir.

[0019] A compressed air storage reservoir leakage detection method and system provided by the present invention lays a sensor optical cable inside the compressed air storage reservoir for detecting gas leakage at any position of the compressed air storage reservoir, and detects gas leakage in the compressed air storage reservoir based on the continuous light signal transmitted back from the sensor optical cable. Under the harsh working conditions of the compressed air storage reservoir, the system can continuously detect gas leakage at any position of the compressed air storage reservoir in real time. In addition, since passive devices are used at the detection site, there is no need to install power supply equipment, the system structure is simple and the reliability is very good. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] Figure 1 and Figure 2 It is a schematic diagram of the structure of a gas storage (cave / chamber);

[0021] Figure 3 It is a flow chart of a compressed air storage leak detection method;

[0022] Figure 4 and Figure 5 It is a schematic diagram of the structure of laying sensor optical cables in the gas storage reservoir (cavern / chamber);

[0023] Figure 6 This is a schematic diagram of a compressed air storage facility consisting of five caverns, A, B, C, D, and E, located 15 meters underground;

[0024] Figure 7 It is a schematic diagram of the interferometer principle adopted by the present invention;

[0025] Figure 8 It is a schematic diagram of the system configuration of the interferometric distributed optical fiber vibration sensor adopted by the present invention;

[0026] Fig. 9 It is a schematic diagram of the architecture of the compressed air storage leakage detection system provided by the present invention;

[0027] Fig.10 It is a schematic diagram of the configuration of the compressed air storage leakage detection system provided by the present invention;

[0028] Fig.11a and Fig.11b It is a schematic diagram of a high-voltage resistant optical fiber flange used in the present invention;

[0029] Fig.12 It is a schematic diagram of the structure of the sensing optical cable used in the present invention. DETAILED DESCRIPTION

[0030] It should be understood that the specific embodiments described herein are only used to explain the present invention, and are not used to limit the present invention.

[0031] See also Figure 3 The compressed air storage leakage detection method provided by the present invention may include:

[0032] Step S101: laying a sensor optical cable inside a compressed air storage reservoir for detecting gas leakage at any position of the compressed air storage reservoir.

[0033] The compressed air storage reservoir includes one or more independent air storage caverns or air storage chambers. If the compressed air storage reservoir has only one air storage cavern or air storage chamber, the direction from the entrance to the exit of the air storage cavern or air storage chamber is used as the laying direction, and the sensing optical cable is looped on the inner wall of the air storage cavern or air storage chamber. If the compressed air storage reservoir includes multiple independent air storage caverns or air storage chambers, for each air storage cavern or air storage chamber, the direction from the entrance to the exit of the air storage cavern or air storage chamber is used as the laying direction, and the sensing optical cable is looped on the inner wall of the air storage cavern or air storage chamber, and then the sensing optical cables looped on each air storage cavern or air storage chamber are connected in series to form a sensing optical cable that can quickly detect gas leakage at any position of the compressed air storage reservoir.

[0034] In the present invention, the sensor optical cable is laid out along the inner wall of the compressed air storage reservoir, which can be specifically: Figure 4 The sensing optical cable 4 is arranged on the inner wall of the gas storage hole or the gas storage chamber 1, and is closely attached to the inner wall of the gas storage hole or the gas storage chamber 1 to ensure high-sensitivity detection; see Figure 5 , the sensing optical cable 4 is arranged in a spiral or wavy shape, covering the entire range of the gas storage cave or gas storage chamber 1. The arrangement of the sensing optical cable 4 in the gas storage cave or gas storage chamber 1 can more effectively sense the ultrasonic signal generated when a leak occurs, and the arrangement of the sensing optical cable 4 in a spiral or wavy shape on the inner wall of the gas storage cave or gas storage chamber 1 can fully detect gas leaks at any point in the gas storage cave or gas storage chamber 1 without missing any reports; in addition, the leakage point of the gas storage cave or gas storage chamber 1 can be accurately located.

[0035] The present invention uses an optical fiber flange made of high-pressure resistant material to connect the sensing optical cable to the gas storage hole or gas storage chamber from the entrance of each gas storage hole or gas storage chamber and to connect the sensing optical cable from the outlet of the gas storage hole or gas storage chamber. The present invention uses an optical fiber splicing box made of high-pressure resistant material in the gas storage hole or gas storage chamber to realize the optical fiber splicing in the sensing optical cable. The high-pressure resistant material can be selected from aluminum alloy material.

[0036] Step S102: During the use of the compressed air storage reservoir, the monitoring host sends a continuous optical signal to the sensing optical cable and receives a returned continuous optical signal, so as to use the sensing optical cable to detect vibrations within the ultrasonic range caused by gas leakage in the compressed air storage reservoir.

[0037] The sensing optical cable comprises optical fiber A, optical fiber B and optical fiber C; the monitoring host sends continuous optical signals to the optical fiber A and the optical fiber B, and transmits the continuous optical signals back through the optical fiber C.

[0038] When the optical fiber A and the optical fiber B are subjected to vibration disturbances within the ultrasonic range caused by gas leakage from the compressed air storage tank, the continuous light signals in the optical fiber A and the optical fiber B interfere with each other and their phases are modulated. The modulated continuous light signals are transmitted back to the monitoring host via the optical fiber C.

[0039] Step S103: The monitoring host determines whether a gas leak occurs in the compressed air storage using the continuous optical signal transmitted back by the sensor optical cable.

[0040] The monitoring host of the present invention collects, demodulates and analyzes the continuous optical signal transmitted back by the sensor optical cable, obtains the phase difference of the continuous optical signal transmitted back by the sensor optical cable, and determines whether a gas leakage occurs in the compressed air storage reservoir based on the phase difference of the continuous optical signal transmitted back by the sensor optical cable. Generally, if there is a phase difference or the phase difference is greater than a preset value, it is considered that a gas leakage occurs in the compressed air storage reservoir.

[0041] In addition, the present invention can also determine the location of gas leakage when a gas leakage occurs in a compressed air storage reservoir. For example, the monitoring host locates the gas leakage position of the compressed air storage reservoir based on the time difference between the continuous light signals transmitted by the optical fiber A and the optical fiber B arriving at the monitoring host.

[0042] In addition, the present invention can also determine the gas leakage situation including the size of the leakage hole and the gas leakage amount and the trend of the leakage hole increasing when determining that a gas leakage occurs in the compressed air storage reservoir.

[0043] Specifically, the present invention collects, demodulates and analyzes the continuous optical signal transmitted back by the sensor optical cable in the monitoring host, obtains the phase difference of the continuous optical signal transmitted back by the sensor optical cable, and also obtains the envelope of the carrier signal used for signal modulation, so that the frequency of the vibration in the ultrasonic range caused by the gas leakage of the compressed air storage reservoir can be determined according to the envelope of the carrier signal. As the gas leaks, the present invention determines the amplitude of the vibration in the ultrasonic range caused by the gas leakage of the compressed air storage reservoir according to the rate of change of the phase difference of the continuous optical signal transmitted back by the sensor optical cable. The gas leakage of the compressed air storage reservoir is determined according to the amplitude and frequency of the vibration in the ultrasonic range caused by the gas leakage of the compressed air storage reservoir obtained in real time.

[0044] Among them, the internal pressure of the compressed air storage reservoir monitored by the pressure sensor of the compressed air storage reservoir is obtained, and when it is determined that the compressed air storage reservoir is full of compressed gas based on the internal pressure of the compressed air storage reservoir, the size of the leakage hole of the compressed air storage reservoir is determined according to the frequency and amplitude of vibration within the ultrasonic range caused by gas leakage of the compressed air storage reservoir.

[0045] Wherein, before performing maintenance on the compressed air storage reservoir that has leaked, the frequency and amplitude of vibrations in the ultrasonic range caused by gas leakage when the compressed air storage reservoir is filled with compressed gas are recorded, and based on the frequency and amplitude of vibrations in the ultrasonic range caused by gas leakage when the compressed air storage reservoir is filled with compressed gas, the changing trend of the frequency and amplitude of vibrations in the ultrasonic range caused by gas leakage when the compressed air storage reservoir is filled with compressed gas is determined, and based on the changing trend of the frequency and amplitude of vibrations in the ultrasonic range caused by gas leakage when the compressed air storage reservoir is filled with compressed gas, it is determined whether the leakage hole has increased.

[0046] The gas leakage amount of the compressed air storage reservoir is determined according to the internal pressure of the compressed air storage reservoir and the frequency of vibration in the ultrasonic range caused by the gas leakage of the compressed air storage reservoir changing with the gas leakage time.

[0047] In order to implement the above method, the present invention also provides a compressed air storage leakage detection system, the system includes a sensor optical cable and a monitoring host, wherein:

[0048] A sensor optical cable is laid inside a compressed air storage reservoir and is used to detect gas leakage at any position of the compressed air storage reservoir. If the compressed air storage reservoir has only one gas storage cave or chamber, the sensor optical cable is looped on the inner wall of the gas storage cave or chamber with the direction from the entrance to the exit of the gas storage cave or chamber as the laying direction. If the compressed air storage reservoir includes multiple independent gas storage caves or chambers, for each gas storage cave or chamber, the sensor optical cable is looped on the inner wall of the gas storage cave or chamber with the direction from the entrance to the exit of the gas storage cave or chamber as the laying direction, and then the sensor optical cables looped on each gas storage cave or chamber are connected in series to form a sensor optical cable that can quickly detect gas leakage at any position of the compressed air storage reservoir. Among them, the sensor optical cable is laid in a loop along the inner wall of the compressed air storage reservoir, which can be seen in Figure 4 and Figure 5 .

[0049] The monitoring host is used to send a continuous optical signal to the sensing optical cable and receive the returned continuous optical signal during the use of the compressed air storage reservoir, so as to use the sensing optical cable to detect the vibration within the ultrasonic range caused by the gas leakage of the compressed air storage reservoir, and then use the continuous optical signal returned by the sensing optical cable to determine whether the compressed air storage reservoir has a gas leakage. The sensing optical cable of the present invention has an optical fiber A, an optical fiber B and an optical fiber C, and the monitoring host sends a continuous optical signal to the optical fiber A and the optical fiber B, and returns the continuous optical signal via the optical fiber C. In particular, when the optical fiber A and the optical fiber B are subjected to vibration disturbances within the ultrasonic range caused by gas leakage from the compressed air storage reservoir, the continuous optical signals in the optical fiber A and the optical fiber B produce interference, and the phase is modulated. The modulated continuous optical signal is transmitted back to the monitoring host via the optical fiber C. The monitoring host collects, demodulates and analyzes the continuous optical signal transmitted back by the sensing optical cable, obtains the phase difference of the continuous optical signal transmitted back by the sensing optical cable, and determines whether a gas leakage occurs in the compressed air storage reservoir based on the phase difference of the continuous optical signal transmitted back by the sensing optical cable. Generally, if there is a phase difference or the phase difference is greater than a preset value, it is considered that a gas leakage occurs in the compressed air storage reservoir. In addition, the monitoring host of the present invention can also determine the gas leakage location when determining that a gas leakage occurs in the compressed air storage reservoir. For example, the monitoring host locates the gas leakage location of the compressed air storage reservoir based on the time difference between the continuous optical signals transmitted by the optical fiber A and the optical fiber B and arriving at the monitoring host. In addition, the monitoring host of the present invention can also determine the gas leakage situation including the size of the leakage hole and the gas leakage amount and the trend of the leakage hole increasing when determining that a gas leakage occurs in the compressed air storage.

[0050] The method and system of the present invention lay out the sensing optical cable on the inner wall of the gas storage hole or the gas storage chamber, in close contact with the inner wall of the gas storage hole or the gas storage chamber, to ensure detection sensitivity; the sensing optical cable is laid out in a spiral or wavy shape, to cover the entire range of the gas storage hole or the gas storage chamber, and can continuously detect leakage at any position of the gas storage hole or the gas storage chamber without missing any reports, and with more accurate positioning; in addition, the present invention utilizes the interference principle to achieve effective detection of vibrations within the ultrasonic range caused by gas leakage in the gas storage hole or the gas storage chamber.

[0051] The following is a detailed description from aspects such as the working environment of the compressed air storage reservoir, the special structure of the compressed air storage reservoir, and the leakage detection principle and system of the present invention.

[0052] 1. Working environment of compressed air storage

[0053] The compressed air energy storage system can store a lot of energy. When the compressed air pressure is 100 times the atmospheric pressure and the temperature is the ambient temperature, the energy inside 1 cubic meter of air (which can be converted into electrical energy) is 12.9 kWh; when the compressed air pressure increases to 200 times the atmospheric pressure, the energy inside 1 cubic meter of air is 28.3 kWh. Normally, when the compressed air energy storage system is working, the environment inside the compressed air storage reservoir is very harsh, with temperatures ranging from -20°C to +65°C, and working pressures up to 15MPa, which can work continuously for hours or even days.

[0054] It can be seen that the working efficiency of the compressed air energy storage system is closely related to the working pressure. Therefore, it is very necessary to detect the leakage of the compressed air storage in real time and effectively monitor the operation of the compressed air energy storage system. However, the working environment of the compressed air storage is very harsh, and conventional detection methods cannot meet the actual needs. Even if they are used reluctantly, the detection effect is very poor and the reliability and stability cannot be guaranteed.

[0055] 2. Special structure of compressed air storage

[0056] Generally, compressed air storage is composed of multiple independent underground caverns (also called gas storage caverns or gas storage rooms, gas storage caverns, or caverns for short). Figure 6 It consists of five caverns, A, B, C, D, and E, located 15 meters underground. The structure of the caverns is quite special. Figure 1 and 2 Each cavern is shaped like a huge cylinder, with an internal diameter of 10m and a length of 200m. Figure 1 It is made of 20mm thick steel plates 2 welded together, and the outside is poured with 500mm thick concrete 3 to increase its strength. Therefore, from the structural point of view of the cave, it can be regarded as a huge cavity.

[0057] When each cavern is working, there is compressed air inside, and the maximum working pressure can reach 15MPa. When a leak hole appears on the cavern wall, the gas in the cavern leaks out from the leak hole, which will cause friction with the metal wall of the cavern and cause cavity vibration. According to engineering experience, the vibration frequency during gas leakage is usually relatively high, generally in the ultrasonic range, and can even reach more than 100KHz, which is mainly related to factors such as working pressure and the size of the leak hole. In addition, the compressed air will also produce temperature changes when the cavern is working. When a leak occurs, the temperature in the cavern will also change with the change in pressure. The above two physical phenomena can be detected by sensing optical cables and distributed optical fiber sensors can be used for detection and positioning. However, the huge structure of the cavern, the large working pressure and the large range of temperature changes are a great challenge for leak detection.

[0058] 3. Leakage detection principle of the present invention

[0059] Distributed optical fiber sensors have the characteristics of high sensitivity, distributed sensing, no need for power supply, long life and high reliability. In addition, as mentioned above, distributed optical fiber sensors can detect gas storage temperature changes and ultrasonic waves to determine gas storage leakage. At present, distributed optical fiber sensors based on the scattering principle are used to detect gas leakage, as follows:

[0060] (1) Scattering Distributed Optical Fiber Vibration Sensor (Φ-OTDR)

[0061] Optical time domain reflectometry (Φ-OTDR) based on coherent Rayleigh scattering is used to detect external vibrations using a sensing optical cable. The working principle is that the optical time domain reflectometry (Φ-OTDR) based on coherent Rayleigh scattering uses a strongly coherent narrowband light source to detect the coherent results of the backscattered light of the optical pulse in the sensing optical fiber, thereby achieving highly sensitive detection and high-precision positioning of disturbance information on the sensing optical fiber.

[0062] The characteristics of Φ-OTDR are: a) it uses a single-core single-mode optical fiber and a pulse wave working system; b) the positioning accuracy is related to the distance resolution, which can be determined according to the needs of the site, ranging from 1m to 10m; c) the backscattered signal has a very low signal-to-noise ratio. After demodulation by the detector, a lot of important information is lost. In addition, the signal analysis method is relatively simple and cannot effectively identify the type of external events, so the false alarm rate is high; d) the energy of light decays exponentially over distance during propagation, so the performance on the optical link is uneven, the near-end detection signal-to-noise ratio is high, and false alarms are easy to occur; the far-end signal-to-noise ratio is very poor, and it is easy to miss alarms; e) due to the use of a narrow linewidth light source, it is greatly affected by interference fading noise, which will cause the Rayleigh scattering intensity in some areas of the optical fiber to approach zero. In these areas, the phase demodulation results are prone to a sharp deterioration of the signal-to-noise ratio, resulting in distortion of the reconstructed external vibration signal, resulting in frequent false alarms, and seriously affecting the authenticity of the detection; f) according to the sampling law, as long as the sampling frequency is greater than or equal to twice the highest frequency of the effective signal, the sampling value can contain all the information of the original signal, and the sampled signal can be restored to the original signal without distortion. However, the laser pulse repetition frequency of this sensor is contradictory to the detection distance of the system. The longer the detection distance, the lower the laser pulse repetition frequency. Therefore, the frequency response range is relatively narrow. Usually, the response range is between 1Hz and 10KHz.

[0063] The optical time domain reflectometry technology (Φ-OTDR) based on coherent Rayleigh scattering is used to detect external vibrations using a sensor optical cable. It has high detection sensitivity and relatively accurate positioning accuracy. However, due to the limitations of its working system, it is not suitable for compressed space-time gas storage leakage detection. The reasons are as follows: First, the system adopts a pulse wave system and uses one optical fiber for detection. Its measurement dynamic range is small, and large signals cause overload saturation, which has a great risk of missed reports. Second, the system is sensitive to low-frequency vibration signals, and most of the external environmental interference signals are low-frequency signals. However, the system's signal recognition method is simple, which will cause a lot of false alarms and even fail to work properly. Third, the system's frequency response range is very narrow, and it cannot detect high-frequency signals, let alone ultrasonic signals generated when gas storage leaks.

[0064] (2) Dispersive OTDR (R-OTDR)

[0065] The scattering of light with a change in frequency caused by the interaction between the incident light and the molecular motion when it passes through a medium is also called the Raman effect. Since scattering changes the frequency of light, when the laser propagates in the optical fiber, the photons collide inelastically with the microscopic particles in the sensing optical fiber. The scattered light with an increased frequency due to the absorption of phonons is Raman anti-Stokes light; the scattered light with a decreased frequency due to the emission of phonons is Raman Stokes light. The former of the Raman scattered light has a large correlation coefficient with temperature and carries the temperature information of the sensing optical fiber; the latter has a very small correlation coefficient with temperature and can be used as a reference for demodulation. The system measures the temperature by detecting the intensity of the Raman scattered light propagating in the direction of the laser.

[0066] The working principle is that the pulse light emitted by the laser is injected into the sensing fiber. When the pulse light propagates in the sensing fiber, each position in the fiber will generate backscattered Raman light, which propagates in the opposite direction of the detection pulse light, and is received by a detector that can detect weak light after passing through the wavelength division multiplexer again. In the Raman scattered light, the intensity of the Stokes component light has almost nothing to do with the axial temperature change of the optical fiber, so it can be used as the reference intensity for measuring temperature, while the intensity of the anti-Stokes component light changes with temperature, which can be used as the index intensity of the axial temperature of the optical fiber. The index intensity is compared with the reference intensity, and then the temperature information at each point of the optical fiber can be obtained based on the corresponding relationship between the intensity change and the temperature. Using OTDR technology, the position of the scattering point is calculated by measuring the time delay between the injected pulse light and the received scattered signal.

[0067] The characteristics of R-OTDR are: a) It uses a single-core single-mode or multi-mode optical fiber and a pulse wave working system; b) Distributed - the temperature distribution field of the spatial curve where the sensing optical fiber is located can be obtained. Different from the traditional point temperature sensor that obtains the temperature distribution through data processing, the temperature value of each point measured by ROTDR is real; c) Positioning - According to the principle of ROTDR, the temperature change along the optical fiber is determined by the reflection and scattering of light, so the position of abnormal temperature can be simply and quickly located; d) Singleness of measurement - The temperature result is independent of stress, pressure, loss and other parameters, and it can still work normally under harsh working conditions; e) Long distance - up to 20km. It can be applied to large-scale and multi-measurement point applications, and the layout is simple. Whether using single-mode or multi-mode optical fiber, according to the specific project situation, you can find a suitable optical fiber and layout plan; f) Large temperature measurement range - using the latest technology and special temperature measurement optical fiber, the temperature measurement range can be -100 ~ 500℃;

[0068] The optical time domain reflectometry (R-OTDR) technology based on Raman scattering is used. The intensity of the anti-Stokes component in the Raman scattered light changes with temperature, which can be used as the indicator intensity of the axial temperature of the optical fiber. The indicator intensity is compared with the reference intensity, and the temperature information at each point of the optical fiber can be obtained according to the corresponding relationship between the intensity change and the temperature. Using the OTDR technology, the position of the disturbance is calculated by measuring the time delay between the injected pulse light and the received scattered signal. This technology will cause many problems when detecting leaks in compressed air storage tanks, and even cannot accurately and timely detect leaks in practical applications. The reasons include: First, the R-OTDR technology measures temperature when detecting leaks in gas storage tanks, and the laying method of the sensor optical cable is to lay the optical cable outside the metal plate and then pour concrete. At the same time, due to the huge structure of the gas storage tank and the fact that most of the caverns are underground, the laying of the sensor optical cable is very difficult and can only be laid in a straight line in the shape of a "one". Second, the detection result is greatly affected by the leakage point and the position of the optical cable. It cannot be detected at the far end of the sensor optical cable, and the risk of missing reports is very high. Third, the detection speed is relatively slow, and it usually takes a long time to sense temperature changes. For leaks far away from the sensor cable, the transmission distance is long, the temperature dissipation is serious, and the detection time may even take several hours. Fourth, for small leaks far away from the sensor cable, the temperature change is small and the temperature is quickly dissipated during the transmission process, so the sensor cable cannot detect it. Fifth, during the operation of the gas storage, the pressure inside the cave changes, and the range of change is relatively large, which will cause the temperature of the gas in the cave to change. The detection system cannot know whether the temperature change is caused by the normal operation of the gas storage or by a leak. The false alarm is relatively high, which will cause the system to misjudge or even fail to work properly.

[0069] In order to effectively detect the leakage of compressed air storage, the present invention adopts an interferometric distributed optical fiber vibration sensor. Figure 7 , system configuration see Figure 8 .like Figure 7 and Figure 8 As shown in the figure, the system includes a monitoring host, a guide optical cable, a headend module, a sensor optical cable and a terminal module. The laser in the monitoring host emits continuous light waves to the optical fiber, in which two core optical fibers (A and B) serve as the sensing arm, and the third core optical fiber (C) transmits the signal back. When the optical fiber is subjected to external disturbance (vibration), the light in the two core optical fibers (A and B) of the sensing arm interferes, the phase is modulated, and the light is transmitted back to the monitoring host through the third core optical fiber (C). The detector in the monitoring host collects, demodulates and analyzes the light, and uses the time difference between the two core optical fibers AB reaching the detector for positioning, and finally issues an alarm and positioning information. The measurement distance is 50km (maximum effective optical cable distance), the positioning accuracy is less than 20m (optical cable distance), the measurement time is less than 1s, and the full link performance remains consistent. In addition, since continuous light waves are used for detection, the frequency response bandwidth of the system is only related to the operating frequency of the device, so the frequency response range is very wide, from 10Hz to 500KHz, which can cover the frequency range of infrasound, sound and ultrasound, and can effectively detect the vibration caused by gas leakage in compressed air storage. In addition, since the external disturbance causes interference between the light in the two-core optical fibers (A and B), the phase of the optical signal in the two-core optical fibers (A and B) is modulated. After detection by the detector, the true information of the external disturbance event signal including the amplitude and frequency of the signal can be obtained at the same time, which can be used to determine the gas leakage situation in the compressed air storage.

[0070] The following is a detailed description with reference to the accompanying drawings.

[0071] See also Fig. 9 The compressed air storage (cavity / chamber) leakage detection method may include: using optical cable as a sensing medium, using a distributed optical fiber vibration sensor based on the interference principle as a monitoring host, and detecting the ultrasonic wave generated during leakage. The architecture of the compressed air storage (cavity / chamber) leakage detection system may include a distributed optical fiber sensor, a guide optical cable, a head end module, a sensing optical cable, a terminal module, and a customer terminal.

[0072] In the specific implementation, considering that the underground compressed air storage is composed of multiple caverns, the sensor optical cables are laid on the inner wall of each gas storage cavern / chamber, and then connected in series with optical cables, so that a set of detection equipment can be used to detect leaks in all caverns of the entire compressed air storage. For this purpose, see Fig.10, the head-end module is installed in front of the entrance of the first cavern A. The entrance of the head-end module is connected to the monitoring host through a guide optical cable, and the outlet of the head-end module is connected to the sensor optical cable 4, and connected to the first cavern A through a high-pressure resistant flange 5. The sensor optical cable 4 enters the cavern through the high-pressure resistant flange 5 from the entrance of each cavern. After being laid in the cavern, it is connected from the outlet of each cavern through the high-pressure resistant flange 5, and then connected to the entrance of the next cavern, and this cycle continues until the last cavern, that is, all the caverns are connected in series. The terminal module is installed behind the outlet of the last cavern, and the entrance of the terminal module is connected to the sensor optical cable 4, and is connected to the sensor optical cable 4 in the last cavern through the high-pressure resistant flange 5 of the last cavern, and the outlet optical fiber of the terminal module is connected to the optical fiber returning to the monitoring host. Among them, the sensor optical cable 4 of the present invention is laid on the inner wall of the cavern and is close to the cavern wall, see Figure 4 , to ensure detection sensitivity; the sensor optical cable 4 is laid in a spiral or wavy shape in the cavern, covering the entire range of the cavern, see Figure 5 , to achieve continuous detection of gas leakage at any position in the cave, without missing any reports, and more accurate positioning. Among them, the optical fiber flange is used for the sensor cable entering and exiting the cave. The material used is high-pressure resistant material, with a high-pressure side 51 connected to the sensor cable in the cave and a normal-pressure side 52 connected to the sensor cable outside the cave. Fig.11a and Fig.11b , this structure can achieve the lowest insertion loss under high pressure difference conditions. Among them, the fiber optic splicing of the present invention uses a customized fiber optic splicing box. The manufacturing material adopts high pressure resistant material, and aluminum alloy material is selected to improve its compressive strength. In addition, in order to cope with the harsh working environment and effectively detect gas storage leaks, the present invention adopts customized optical cables. Specifically, since the internal working pressure of the gas storage is relatively high, up to 15MPa, conventional communication optical cables cannot work normally under such a high pressure. In order to cope with the harsh working environment and effectively detect gas storage leaks, the present invention adopts such Fig.12 The high-voltage resistant customized optical cable shown in the figure has a cable core including a central reinforcing rib 40, a filling rope 46 and a stainless steel bundle tube 49 surrounding the central reinforcing rib 40, and a cable paste 45 filling the remaining space. Among them, the stainless steel bundle tube 49 wraps the single-mode optical fiber 48 and is filled with fiber paste 47. The cable core is wrapped with a waterproof insulation layer 44, a plastic-coated aluminum tape 43, a sheath 42 and an antistatic layer 41 in sequence. The optical cable structure adopts a layer-twisted structure, which can improve the temperature adaptability of the optical cable. The central bundle tube 49 is made of stainless steel, which can improve the high-voltage resistance and tensile strength. The bare fiber 48 adopts products from well-known manufacturers to ensure the sensing performance of the optical cable.

[0073] In the present invention, the monitoring host, the head end module, and the end module are connected together to form an optical path. When it is necessary to detect the leakage of the compressed air storage reservoir, the system is started. The monitoring host sends a continuous optical signal to the sensing optical cable via the head end module, and receives the continuous optical signal transmitted back by the sensing optical cable via the head end module. Specifically, the laser of the monitoring host sends a continuous optical signal (such as a sine wave) to the optical fiber A and the optical fiber B of the sensing optical cable via the guide optical cable and the head end module. The continuous optical signals in the optical fiber A and the optical fiber B are coupled after reaching the end module, and finally transmitted back to the monitoring host via the optical fiber C. Since the sensing optical cable of the present invention is arranged in a wavy shape along the inner wall of the compressed air storage reservoir, any vibration caused by gas leakage will be sensed by the sensing optical cable. Therefore, after using the detector to collect, demodulate and analyze the signal, the phase difference of the return signal can be obtained. According to the value of the phase difference, it can be determined whether the compressed air storage reservoir leaks. In addition, based on the feedback signal, multiple characteristics of the vibration caused by the leakage of the compressed air storage reservoir can be obtained, such as amplitude, frequency, duration, continuity, etc. These characteristics can be used to filter out various external interferences, effectively identify vibration events caused by the leakage of the compressed air storage reservoir, and reduce the false alarm rate.

[0074] When the compressed air storage tank leaks, the monitoring host can locate the gas leakage position of the compressed air storage tank according to the time difference between the continuous optical signals transmitted by the optical fiber A and the optical fiber B reaching the monitoring host. When the diameter of the cavern is 10m and the length of one circle of the sensing optical cable is about 31.4m, if the positioning accuracy of the detection system is 20m (cable length), the actual positioning error of the leakage point along the cavern wall will not exceed the distance of one circle of optical cable, and the positioning error along the axial direction of the cavern is within one cable pitch.

[0075] In addition to detecting leaks and locating leaks, the present invention can also determine leak change trends. Specifically, the degree and changes of compressed air storage leaks can be determined by monitoring the frequency and signal amplitude detected by the host. Normally, the dimensions of a compressed air storage are fixed, the material remains unchanged, and the vibration frequency generated during a leak is only related to two factors: the size of the leak hole and the pressure inside the storage. Therefore, by detecting the frequency and amplitude of the ultrasonic wave generated by the leak, the leak can be quantified and the leak change trend can be determined. It can be divided into the following two situations:

[0076] 1) Determine the size of the leak hole

[0077] If the compressed air storage reservoir (hole / chamber) is filled with compressed air (15MPa), when a leak just occurs, the vibration frequency is the highest at this time. Normally, the size of the leak hole will not change in a short time, so the size of the leak hole can be judged based on the initial vibration frequency and amplitude detected by the optical fiber sensor. If the initial vibration frequency is very high and the amplitude is relatively small, it can be judged that the size of the leak hole is relatively small; if the initial vibration frequency is relatively low and the amplitude is relatively high, it can be judged that the size of the leak hole is relatively large. As the working time goes by, generally within a few hours, since the size of the leak hole does not change in a short time, the pressure in the compressed air storage reservoir (hole / chamber) gradually decreases, and the vibration frequency caused by the leak detected by the detector will also decrease, and the amplitude will basically not change. At the same time, combined with the data monitored by the pressure sensor of the compressed air storage reservoir (hole / chamber) itself, the leakage of the compressed air storage reservoir (hole / chamber) can be judged from the change trend of the vibration frequency, including the leakage amount and the size of the leak hole.

[0078] 2) Determine the changing trend of the leakage hole

[0079] If a leak has just been discovered in the gas storage, the system operation and maintenance personnel will submit an application for maintenance of the compressed air storage (cave / chamber) to the relevant department. During this period, the system operation and maintenance personnel need to closely observe the changes in the leakage of the compressed air storage (cave / chamber), which may take several days or weeks. Since the working characteristics of the compressed air storage (cave / chamber) are regular, the internal pressure of the compressed air storage (cave / chamber) changes periodically. Whenever the compressed air storage (cave / chamber) is full of pressure, under the same pressure, the vibration frequency generated by the leak detected by the detector is recorded, and the frequency value detected each time is compared, and the amplitude data is referred to at the same time. If the frequency value decreases and the amplitude increases, it means that the leakage hole has increased. At the same time, observe and analyze the change speed of the frequency detected in each working cycle or multiple working cycles to determine the leakage situation and change trend of the gas storage.

[0080] Among them, the distributed optical fiber vibration sensor based on the interference principle of the present invention detects external disturbance events through two optical fibers on the sensing arm. When there is external disturbance, the detector detects the interference signal, and judges the amplitude of the vibration signal generated by the external disturbance event by the rate of change of the phase difference of the interference signal, and obtains the frequency of the vibration signal generated by the external disturbance event by detecting the envelope of the carrier signal.

[0081] In summary, the method and system of the present invention have the advantages of large measurement dynamic range, wide frequency response range, precise positioning and fast response speed. They can effectively detect and locate leakage of compressed air storage reservoirs (caves / chambers). In addition, by analyzing and determining the amplitude and frequency of vibrations caused by leakage of compressed air storage reservoirs (caves / chambers), the leakage situation of compressed air storage reservoirs (caves / chambers) can be judged.

[0082] The preferred embodiments of the present invention are described above with reference to the accompanying drawings, but the scope of the present invention is not limited thereby. Any modification, equivalent substitution and improvement made by those skilled in the art without departing from the scope and essence of the present invention shall be within the scope of the present invention.

Claims

1. A method for detecting leakage of a compressed air storage reservoir, characterized in that: The method comprises: Laying a sensing optical cable inside the compressed air storage reservoir for detecting gas leakage at any position of the compressed air storage reservoir; During the use of the compressed air storage reservoir, the monitoring host sends a continuous optical signal to the sensing optical cable and receives the returned continuous optical signal, so as to use the sensing optical cable to detect vibrations within the ultrasonic range caused by gas leakage in the compressed air storage reservoir; The monitoring host uses the continuous optical signal transmitted back by the sensor optical cable to determine whether a gas leak occurs in the compressed air storage.

2. The method according to claim 1, characterized in that The compressed air storage reservoir comprises one or more independent air storage holes or air storage chambers, and the sensor optical cable for detecting gas leakage at any position of the compressed air storage reservoir is laid inside the compressed air storage reservoir as follows: The sensor optical cable is looped on the inner wall of each gas storage hole or gas storage room, with the direction from the entrance to the exit of the gas storage hole or gas storage room as the laying direction; The sensing optical cables arranged in each gas storage hole or gas storage chamber are connected in series to form a sensing optical cable capable of quickly detecting gas leakage at any position of the compressed air storage reservoir.

3. The method according to claim 2, characterized in that Using an optical fiber flange made of high-pressure resistant material, the sensing optical cable is connected to the gas storage hole or gas storage chamber from the entrance of each gas storage hole or gas storage chamber and is connected to the gas storage hole or gas storage chamber from the outlet of the gas storage hole or gas storage chamber; In the gas storage cave or gas storage room, an optical fiber splicing box made of high-pressure resistant material is used to realize the optical fiber splicing in the sensor optical cable.

4. The method according to claim 1, characterized in that: The sensing optical cable comprises optical fiber A, optical fiber B and optical fiber C; the monitoring host sends a continuous optical signal to the optical fiber A and the optical fiber B, and transmits the continuous optical signal back via the optical fiber C, wherein when the optical fiber A and the optical fiber B are subjected to vibration disturbance within the ultrasonic range caused by gas leakage from the compressed air storage reservoir, the continuous optical signals in the optical fiber A and the optical fiber B are modulated, and the modulated continuous optical signals are transmitted back to the monitoring host via the optical fiber C.

5. The method according to any one of claims 1 to 4, characterized in that: The monitoring host determines whether a gas leak occurs in the compressed air storage by using the continuous optical signal returned by the sensor optical cable, including: The monitoring host collects, demodulates and analyzes the continuous optical signal returned by the sensor optical cable to obtain the phase difference of the continuous optical signal returned by the sensor optical cable; Whether a gas leak occurs in the compressed air storage is determined based on the phase difference of the continuous optical signal transmitted back by the sensing optical cable.

6. The method according to claim 5, characterized in that The method further comprises: The monitoring host collects, demodulates and analyzes the continuous optical signal returned by the sensor optical cable, obtains the phase difference of the continuous optical signal returned by the sensor optical cable, and also obtains the envelope of the carrier signal used for signal modulation; determining the frequency of vibration in the ultrasonic range caused by gas leakage of the compressed air storage reservoir according to the envelope of the carrier signal; Determining the amplitude of the vibration within the ultrasonic range caused by the gas leakage of the compressed air storage reservoir according to the rate of change of the phase difference of the continuous optical signal transmitted back by the sensing optical cable; The gas leakage of the compressed air storage reservoir is determined based on the frequency and amplitude of the vibration within the ultrasonic range caused by the gas leakage of the compressed air storage reservoir.

7. The method according to claim 6, characterized in that The gas leakage condition includes the size of the leakage hole and the amount of gas leakage; the gas leakage condition of the compressed air storage reservoir is determined according to the frequency and amplitude of the vibration in the ultrasonic range caused by the gas leakage of the compressed air storage reservoir, including: Obtaining the internal pressure of the compressed air storage reservoir monitored by a pressure sensor of the compressed air storage reservoir; determining whether the compressed air storage reservoir is full of compressed gas according to the internal pressure of the compressed air storage reservoir; If the compressed air storage reservoir is full of compressed gas, determining the size of the leakage hole of the compressed air storage reservoir according to the frequency and amplitude of the vibration in the ultrasonic range caused by the gas leakage of the compressed air storage reservoir; The gas leakage amount of the compressed air storage reservoir is determined based on the internal pressure of the compressed air storage reservoir and the frequency of vibration in the ultrasonic range caused by the gas leakage of the compressed air storage reservoir changing with the gas leakage time.

8. The method according to claim 7, characterized in that The method further comprises: Before maintaining the leaking compressed air storage tank, recording the frequency and amplitude of the vibration in the ultrasonic range caused by the gas leakage of the compressed air storage tank each time it is filled with compressed gas; Determine a change trend of the frequency and amplitude of the vibration in the ultrasonic range caused by gas leakage when the compressed air storage reservoir is filled with compressed gas, according to the frequency and amplitude of the vibration in the ultrasonic range caused by gas leakage when the compressed air storage reservoir is filled with compressed gas each time; Whether the leakage hole is enlarged is determined based on the change trend of the frequency and amplitude of the vibration in the ultrasonic range caused by gas leakage when the compressed air storage is filled with compressed gas.

9. The method according to claim 4, characterized in that The method further comprises: The monitoring host locates the gas leakage position of the compressed air storage according to the time difference between the continuous optical signals transmitted by the optical fiber A and the optical fiber B arriving at the monitoring host.

10. A compressed air storage leak detection system, characterized in that: The system comprises: a sensing optical cable, laid inside the compressed air storage reservoir, for detecting gas leakage at any position of the compressed air storage reservoir; The monitoring host is used to send a continuous light signal to the sensing optical cable and receive the returned continuous light signal during the use of the compressed air storage reservoir, so as to use the sensing optical cable to detect the vibration within the ultrasonic range caused by the gas leakage in the compressed air storage reservoir, and then use the continuous light signal returned by the sensing optical cable to determine whether the compressed air storage reservoir has a gas leakage.

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