A sootblowing system leakage detection system and method based on acoustic spectrum analysis

Abstract

The present invention discloses a leakage detection system and method for a soot blowing system based on acoustic spectrum analysis. The detection system of the present invention includes a soot blowing system and an acoustic leakage detection system. The soot blowing system includes a soot blowing medium main pipe, a lifting valve, a soot blower inner pipe, a soot blowing barrel, etc. The inlet of the lifting valve is installed on the soot blowing medium main pipe, and the outlet of the lifting valve is connected to the soot blowing barrel through the soot blower inner pipe. The soot blowing barrel is provided with a soot blowing nozzle. The acoustic leakage detection system is installed on the soot blower inner pipe between the outlet of the lifting valve and the soot blowing barrel, and includes an upper cover plate, an acoustic resonance cavity, a sound pressure collecting pipe, a sound guiding pipe, a lower cover plate and a high-frequency microphone. Generally, there are 3-6 acoustic resonance cavities with different cavity volumes and different resonant frequencies, and the resonant frequency range is 20-50 kHz. When the lifting valve leaks, the measured sound pressure level will increase, and the proportion of high-frequency sound power above 20 kHz will also increase. These indicators can help accurately identify the occurrence of leakage and improve the operation safety of the soot blower.

Description

Technical Field

[0001] The present invention relates to the technical field of boilers, and particularly relates to a soot blowing system leakage detection system and method based on acoustic spectrum analysis. Background Art

[0002] Soot blowers are important component devices in power station boilers. A large number of soot blowers are installed at positions such as the furnace water wall, superheater, reheater, economizer, and air preheater, and are regularly operated to clean the heating surface to ensure the safe and economic operation of the boiler.

[0003] Soot blowers generally use high-pressure steam or compressed air as the soot blowing medium, with a pressure generally of 0.7 - 1.5 MPa. After being accelerated by a Laval nozzle, they have a strong purging ability, but also have a certain blowing damage effect on the heating surface. Usually, the soot blower is started regularly, closed after purging for several minutes, and will not cause blowing damage to the heating surface. However, if the lift valve in the soot blower system has an internal leak, it will cause the heating surface to be continuously purged by steam or compressed air. On the one hand, a large amount of energy is wasted, and on the other hand, accidents such as pipe bursts are extremely likely to occur under long-term purging.

[0004] For a long time, factors such as improper soot blowing and internal leakage of the lift valve of the soot blower have caused many boiler pipe burst accidents, resulting in boiler shutdowns and huge economic losses. Therefore, how to effectively detect the leakage of the soot blowing system has become a major problem in the safe operation of boilers. Some manufacturers use the method of installing thermocouples at the lift valve and other places for leakage detection. However, on the one hand, the temperature change is not obvious when there is an internal leak, and on the other hand, if the soot blowing medium is compressed air, this method is ineffective. Summary of the Invention

[0005] Aiming at the technical problems existing in the prior art, the purpose of the present application is to provide a soot blowing system leakage detection system and method based on acoustic spectrum analysis.

[0006] The technical solution adopted by the present invention is as follows:

[0007] A soot blowing system leakage detection system based on acoustic spectrum analysis includes a soot blowing system and an acoustic leakage detection system; the soot blowing system includes a soot blowing medium main pipe, a lift valve, a soot blower inner pipe, and a soot blower barrel. The inlet of the lift valve is installed on the soot blowing medium main pipe, the outlet of the lift valve is connected to the soot blower barrel through the soot blower inner pipe, and the soot blower barrel is provided with a soot blowing nozzle for generating a high-speed jet.

[0008] The acoustic leakage detection system is installed on the soot blower inner pipe, that is, on the outer side of the pipe between the outlet of the lift valve and the soot blower barrel. The acoustic signal passing through the soot blower inner pipe is collected by the acoustic leakage detection system and subjected to mathematical analysis to detect the internal leakage of the lift valve.

[0009] Further, the acoustic leakage detection system includes an upper cover plate, an acoustic resonance cavity, a sound pressure collecting pipe, a sound guiding pipe, a lower cover plate, and a high-frequency microphone. There are a plurality of acoustic resonance cavities arranged in a row on the upper cover plate. All the acoustic resonance cavities are respectively connected to the sound pressure collecting pipe through pipes. The sound pressure collecting pipe is communicated with the sound guiding pipe. The high-frequency microphone is arranged at one end of the sound guiding pipe far away from the sound pressure collecting pipe. The upper cover plate and the lower cover plate are spliced and fixed together and sleeved on the outer side of the side part of the inner pipe of the soot blower, and are in contact connection with the inner pipe of the soot blower.

[0010] Further, both the upper cover plate and the lower cover plate are in a semi-circular tubular shape. After the upper cover plate and the lower cover plate are spliced, they form a sleeve structure and are cooperatively sleeved on the outer wall of the side part of the inner pipe of the soot blower. The upper cover plate and the lower cover plate are connected to the inner pipe of the soot blower by welding or a hoop.

[0011] Further, the number of acoustic resonance cavities is generally 3 - 6. Their cavity volumes are different, so they have different resonance frequencies, and the resonance frequency range is 20 - 50 kHz.

[0012] Further, the sound guiding pipe is made of stainless steel, with a diameter not greater than 20 mm and a length not less than 1000 mm. The surface has no heat insulation to prevent the adverse effect of the high temperature generated when the soot blowing medium is high-temperature steam on the high-frequency microphone. The frequency response range of the high-frequency microphone is 200 - 50000 Hz.

[0013] The leakage detection system of the soot blowing system based on acoustic spectrum analysis is applicable regardless of whether the soot blowing medium is steam or compressed air.

[0014] The present invention provides a method for detecting leakage of a soot blowing system based on acoustic spectrum analysis. Its principle and detection method are as follows: (1) An acoustic leakage detection system is installed on the inner pipe of the soot blower between the outlet of the lift valve and the soot blowing gun barrel. If there is an internal leakage in the lift valve, the generated airflow will produce a significant high-frequency acoustic signal at this position, which can be detected.

[0015] (2) There are 3 - 6 acoustic resonance cavities with different volumes on the upper cover plate of the leakage detection device, and the resonance frequency range is 20 - 50 kHz, which is used to amplify the high-frequency part of the audio.

[0016] (3) Through the sound pressure collecting pipe, the audio signals of several acoustic resonance cavities are summarized, and then connected to the high-frequency microphone through the sound guiding pipe. When the soot blowing medium is high-temperature steam, the inner pipe of the soot blower can reach more than two hundred degrees Celsius. At this time, due to the good heat dissipation of the slender stainless steel sound guiding pipe, it can ensure that the temperature at the high-frequency microphone has been reduced to 50 - 60 °C.

[0017] (4)Analyze the sound signals obtained by the high-frequency microphone to obtain indicators such as waveform, sound pressure level, and spectral distribution. Determine whether there is internal leakage in the lift valve through a mathematical model. The processing steps of the mathematical model include: ① Apply a Hanning window to the time-domain signal; ② Perform a fast Fourier transform (FFT); ③ Identify the peak value of the sound signal above 20 kHz and calculate the proportion of the sound power above 20 kHz; ④ When there is an obvious peak value in the sound signal above 20 kHz and the proportion of the high-frequency sound power > 5%, it is determined that there is leakage; otherwise, there is no leakage.

[0018] The beneficial effects of the present invention are as follows:

[0019] 1. Using acoustic signals as a method for detecting internal leakage of valves in the soot blowing system has the advantages of high sensitivity and accurate determination.

[0020] 2. The system and method are applicable to soot blowing media such as steam or compressed air.

[0021] 3. The system has a simple structure, requires little modification work, and is easy to implement. Brief Description of the Drawings

[0022] Figure 1 It is a schematic diagram of a soot blowing system leakage detection system based on acoustic spectrum analysis according to the present invention;

[0023] In the figure, 1 - soot blowing gun barrel; 2 - soot blowing nozzle; 3 - inner pipe of the soot blower; 4 - acoustic leakage detection system; 5 - lift valve; 6 - main pipe of the soot blowing medium.

[0024] Figure 2 It is a schematic diagram of the connection structure between the acoustic leakage detection system, the inner pipe of the soot blower, the lift valve, and the main pipe of the soot blowing medium, where 401 is the upper cover plate, 402 is the acoustic resonance cavity, 403 is the sound pressure collecting pipe; 404 is the sound guiding pipe; 405 is the lower cover plate.

[0025] Figure 3 It is a schematic diagram of the structure of the acoustic leakage detection system, where 406 is the high-frequency microphone.

[0026] Figure 4 It is a schematic diagram of the connection structure between the upper cover plate, the acoustic resonance cavity, the sound pressure collecting pipe, and the sound guiding pipe in the acoustic leakage detection system.

[0027] Figure 5 It is a schematic diagram of the structure of the lower cover plate.

[0028] Figure 6 It is a schematic diagram of the structure of the upper cover plate and the acoustic resonance cavity.

[0029] Figure 7 It is a cross-sectional view of the connection structure between the upper cover plate and the acoustic resonance cavity.

[0030] Figure 8 Schematic structural diagram of the end of the sound guide tube and the high-frequency microphone, where 4061 is the microphone and the preamplifier; 4062 is the power supply and signal pin.

[0031] Figure 9 Sound pressure waveforms in the cases of no leakage and leakage.

[0032] Figure 10 Spectrum distribution of the acoustic signal in the case of no leakage.

[0033] Figure 11 Spectrum distribution of the acoustic signal in the case of leakage. Detailed implementation manners

[0034] The present invention will be further described in detail below with reference to the accompanying drawings and embodiments. It should be noted that the following embodiments are intended to facilitate the understanding of the present invention and do not impose any limitations on it.

[0035] As Figure 1 shown, the soot blowing system is composed of a soot blowing medium main pipe 6, a lifting valve 5, a soot blowing inner pipe 3, a soot blowing gun barrel 1, etc. A soot blowing nozzle 2 is provided on the soot blowing gun barrel 1 for generating a high-speed jet. The acoustic leakage detection system 4 is installed on the soot blowing inner pipe 3, that is, on the outer side of the pipe between the outlet of the lifting valve 5 and the soot blowing gun barrel 1. Acoustic signals are collected by this device and subjected to mathematical analysis for detecting the internal leakage of the lifting valve 5. The inlet of the lifting valve 5 is installed on the soot blowing medium main pipe 6.

[0036] As Figure 2 shown, the acoustic leakage detection system 4 is composed of an upper cover plate 401, an acoustic resonance cavity 402, a sound pressure collecting pipe 403, a sound guide tube 404, a lower cover plate 405, a high-frequency microphone 406, etc. A row of multiple acoustic resonance cavities 402 are provided on the upper cover plate 401. All the acoustic resonance cavities 402 are respectively connected to the sound pressure collecting pipe 403 through pipes. The sound pressure collecting pipe 403 is communicated with the sound guide tube 404. The high-frequency microphone 406 is arranged at the end of the sound guide tube 404 far from the sound pressure collecting pipe 403.

[0037] In contrast Figures 1-5 , both the upper cover plate 401 and the lower cover plate 405 are in a semi-circular tubular shape and are tightly sleeved on the outer wall of the side part of the soot blowing inner pipe 3 in cooperation with each other. The upper cover plate 401 and the lower cover plate 405 can be connected to the soot blowing inner pipe 3 by welding or hoop. After the upper cover plate 401 and the lower cover plate 405 are spliced, a sleeve structure is formed and tightly sleeved on the outer side of the side wall of the soot blowing inner pipe 3.

[0038] As Figure 3 , Figure 8As shown, the sound guiding tube 404 is made of stainless steel, with a diameter not greater than 20 mm and a length not less than 1000 mm. There is no need for heat preservation on the surface to prevent the adverse effects of high temperature generated when the soot blowing medium is high-temperature steam on the high-frequency microphone 406. The frequency response range of the high-frequency microphone 406 is 200 - 50000 Hz.

[0039] As Figures 4-7 shown, there are generally 3 - 6 acoustic resonance cavities 402, and the cavity volumes are different from each other, so they have different resonant frequencies, and the resonant frequency range is 20 - 50 kHz. In comparison Figures 6-7 in, along the direction from left to right, the cavity volume of the acoustic resonance cavity 402 gradually decreases. The bottom of the acoustic resonance cavity 402 communicates with the upper cover plate 401.

[0040] In comparison Figure 8 , the high-frequency microphone 406 mainly includes two parts. The front end is the microphone and preamplifier 4061, and the rear end is the power supply and signal pins 4062.

[0041] The soot blowing system leakage detection system based on acoustic spectrum analysis is applicable regardless of whether the soot blowing medium is steam or compressed air.

[0042] Specifically, a soot blowing system leakage detection system and method based on acoustic spectrum analysis, taking the soot blowing leakage detection of the low-temperature superheater of a 660 MW boiler as an example, includes the following steps:

[0043] (1) Install the acoustic leakage detection system 4 on the inner tube 3 of the soot blower between the outlet of the lift valve 5 and the soot blowing barrel 1. If there is an internal leakage in the lift valve 5, the generated air flow will generate significant high-frequency acoustic signals at this position, which can be detected.

[0044] (2) The length of the inner tube 3 of the soot blower suitable for installing the acoustic leakage detection system 4 is about 310 mm, and the outer diameter is 65 mm. Therefore, the inner diameter of the upper cover plate of the leakage detection device is 65 mm, and there are 5 acoustic resonance cavities with different cavity volumes on the upper cover plate. Their cavity shapes are all cylindrical, with diameters of 35, 30, 25, 15, and 10 mm respectively, and the cavity height is 47.6 mm. The resonant frequency range is 20 - 50 kHz, which is used to amplify the high-frequency part of the audio. Without these resonance cavities, the acoustic signals transmitted to the high-frequency microphone 406 will become weak, and the acoustic signals above 20 kHz will attenuate more severely.

[0045] (3) Through the sound pressure collecting pipe 403 with a diameter of Φ6mm, the audio signals of several acoustic resonance cavities are aggregated, and then through the sound guiding pipe 404 with a diameter of Φ6mm, it is connected to the high-frequency microphone 406. When the soot blowing medium is high-temperature steam, the temperature of the inner pipe of the soot blower can reach 195 °C. At this time, due to the good heat dissipation of the slender stainless-steel sound guiding pipe 404, it can ensure that the temperature at the high-frequency microphone 406 has dropped to a safe temperature, and it can be measured that it can be reduced to about 45 °C.

[0046] (4) Analyze the sound signals obtained by the high-frequency microphone 406 to obtain indicators such as waveform, sound pressure level, and frequency spectrum distribution.

[0047] Figure 9 It is the comparison of the sound pressure waveforms in the case of no leakage and leakage. The soot blowing medium is steam (pressure 1.02 MPa, temperature 195 °C, flow rate 4 t / h per unit). The leakage situation refers to manually opening the lifting valve 5 (opening degree about 10%) to simulate leakage. As can be seen from the figure, the sound pressure is lower when there is no leakage, and the sound pressure increases significantly and the waveform burrs become more after leakage. According to the calculation, the sound pressure levels before and after leakage are 87.9 dB and 98.1 dB (both are linearly weighted).

[0048] Figure 10 and Figure 11 are the frequency spectrum distributions of the acoustic signals in the case of no leakage and leakage respectively, which are the frequency domain data obtained after performing Fourier transform on Figure 9 As can be seen from the figure, when there is no leakage, the sound waves are mainly distributed in the low frequency within 10 kHz; after leakage occurs, the high-speed jet flow in the pipe generated by the leakage produces obvious high-frequency acoustic signals, with a frequency of 30 - 40 kHz. According to the calculation, the proportions of the sound power above 20 kHz before and after leakage are 1.07% and 8.25% respectively, showing a significant increase.

[0049] Therefore, for this case, the following conditions can be used as the detection indicators for leakage, and both need to be met simultaneously: (1) The sound pressure level has increased by more than 5 dB; (2) The proportion of the sound power above 20 kHz has increased by more than 5%. For other different power plants and soot blower systems, similar detection and determination indicators can be obtained through experiments, and the principle is the same.

Claims

1. A sootblowing system leakage detection system based on acoustic spectrum analysis, characterized in that: It includes a soot blowing system and an acoustic leakage detection system; The soot blowing system includes a soot blowing medium main pipe (6), a lifting valve (5), a soot blower inner pipe (3) and a soot blower barrel (1). The inlet of the lifting valve (5) is installed on the soot blowing medium main pipe (6). The outlet of the lifting valve (5) is connected to the soot blower barrel (1) through the soot blower inner pipe (3). A soot blowing nozzle (2) is provided on the soot blower barrel (1) for generating a high-speed jet; The acoustic leakage detection system is installed on the soot blower inner pipe (3), that is, on the outer side of the pipe between the outlet of the lifting valve (5) and the soot blower barrel (1). The acoustic signal passing through the soot blower inner pipe (3) is collected by the acoustic leakage detection system and subjected to mathematical analysis for detecting internal leakage of the lifting valve; The acoustic leakage detection system includes an upper cover plate (401), an acoustic resonance cavity (402), a sound pressure collecting pipe (403), a sound guiding pipe (404), a lower cover plate (405) and a high-frequency microphone (406). A row of multiple acoustic resonance cavities (402) are provided on the upper cover plate (401). All the acoustic resonance cavities (402) are respectively connected to the sound pressure collecting pipe (403) through pipes. The sound pressure collecting pipe (403) is communicated with the sound guiding pipe (404). The high-frequency microphone (406) is arranged at one end of the sound guiding pipe (404) far from the sound pressure collecting pipe (403); The upper cover plate (401) and the lower cover plate (405) are spliced and fixed together and sleeved on the outer side of the side part of the soot blower inner pipe (3), and are in close contact connection with the soot blower inner pipe (3); Both the upper cover plate (401) and the lower cover plate (405) are in a semi-circular tubular shape, and the two are tightly sleeved on the outer wall of the side part of the soot blower inner pipe (3) in cooperation; the upper cover plate (401) and the lower cover plate (405) are connected to the soot blower inner pipe (3) by welding or a hoop; The number of the acoustic resonance cavities (402) is 3 - 6, and their cavity volumes are different, so they have different resonance frequencies, and the resonance frequency range is 20 - 50 kHz; The sound guiding pipe (404) is made of stainless steel, with a diameter not greater than 20 mm and a length not less than 1000 mm, and there is no thermal insulation on the surface.

2. The leakage detection system of the soot blowing system based on acoustic spectrum analysis according to claim 1, characterized in that: The frequency response range of the high-frequency microphone is 200 - 50000 Hz.

3. A method for detecting leaks in a sootblowing system based on acoustic spectrum analysis, characterized in that, When using the soot blowing system leakage detection system based on acoustic spectrum analysis according to any one of claims 1 - 2, its principle and detection method are as follows: S1: The acoustic leakage detection system is installed on the soot blower inner pipe between the outlet of the lifting valve and the soot blower barrel. If internal leakage occurs in the lifting valve, the generated airflow generates a significant high-frequency acoustic signal at the position of the soot blower inner pipe, which can be detected; S2: The acoustic leakage detection system is provided with 3 - 6 acoustic resonance cavities with different volumes, and the resonance frequency range is 20 - 50 kHz, which is used to amplify the high-frequency part in the audio; S3: Through the sound pressure collecting pipe, the audio signals of several acoustic resonance cavities are aggregated, and then transmitted to the high-frequency microphone through the sound guiding pipe. The sound signals obtained by the high-frequency microphone are analyzed to obtain a series of indexes such as waveform, sound pressure level and frequency spectrum distribution. Through a mathematical model, it is determined whether internal leakage has occurred in the lifting valve of the soot blowing system.

4. The leakage detection method of the soot blowing system based on acoustic spectrum analysis according to claim 3, characterized in that, The sootblowing medium of the sootblowing system is steam or compressed air.

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