Method for monitoring VOC (Volatile Organic Compounds) unorganized emission by utilizing ultrasonic imaging technology

Abstract

The invention discloses a method for monitoring VOC (Volatile Organic Compounds) unorganized emission by utilizing an ultrasonic imaging technology, and belongs to the technical field of environment monitoring. The method comprises the following steps: acquiring ultrasonic data of a chemical industry park production device through an ultrasonic imaging module; 20-100 kHz leakage ultrasonic signals are separated, and sound pressure is read; positioning a leakage source in combination with coordinate mapping and a digital twinborn model, and marking sound pressure with a color code; a fitting coefficient is obtained through laboratory calibration, the leakage rate is calculated, the total leakage volume is calculated according to the duration, and gas density can be combined to be converted into the total mass. The method has the advantages of wide-area coverage, real-time response, accurate positioning, small monitoring deviation and the like, solves the problems of multiple blind areas and difficulty in quantification of a traditional method, and provides data support for safety and environment management of chemical industrial parks.

Description

Technical Field

[0001] This invention belongs to the field of environmental monitoring technology and relates to a method for monitoring fugitive VOC emissions using ultrasonic imaging technology. Specifically, it is a method that uses ultrasonic imaging technology combined with a digital twin model to locate fugitive VOC leakage sources, calculate leakage rates, and statistically analyze total emissions. It is applicable to monitoring fugitive VOC emissions in chemical industrial parks, such as production facilities, storage tanks, pipelines, valves, and loading and unloading facilities. Background Technology

[0002] Volatile organic compounds (VOCs) are the main characteristic pollutants in chemical industrial parks. Their unorganized leaks (such as failure of production equipment seals, storage tank breathing losses, pipeline valve leaks, etc.) can not only cause safety accidents (such as explosions and fires), but also cause air pollution (such as the formation of ozone and PM2.5), and cause long-term harm to the human respiratory and nervous systems. They are the core control targets for safety and environmental management in chemical industrial parks.

[0003] Currently, monitoring of fugitive VOC emissions in chemical industrial parks primarily relies on deploying VOC concentration monitoring facilities at fixed locations to determine the presence of leaks. This method has a limited monitoring range, is prone to creating blind spots, cannot directly pinpoint multiple emission sources, and cannot quantify whether the leakage rate meets safety production standards. It also requires significant manpower and resources for on-site investigation and verification. Chemical industrial parks also use infrared gas cloud imaging for remote monitoring of fugitive VOC emissions; however, infrared gas cloud imaging is susceptible to weather factors such as strong winds, and accurately tracing the source of moving infrared gas clouds presents technical challenges.

[0004] There is an urgent need in this field for a technical means to directly detect and locate VOC fugitive emission sources and calculate emission rates and total emissions, so as to achieve a new VOC fugitive emission monitoring solution with wide coverage, real-time response, accurate location, and controllable cost, and comprehensively improve the safety and environmental management level of chemical industrial parks. Summary of the Invention

[0005] The purpose of this invention is to provide a method for monitoring fugitive VOC emissions using ultrasonic imaging technology. Based on the principle of ultrasound, this method locates leaks in pipelines, pressure systems, and equipment within chemical industrial parks, and monitors fugitive VOC emissions by capturing the high-frequency ultrasonic signals generated by the leaks. This objective is achieved through the following specific technical solutions.

[0006] A method for monitoring fugitive VOC emissions using ultrasound imaging technology includes the following steps: S1: Monitor the production equipment in the chemical industrial park using an ultrasonic imaging module, collect ultrasonic monitoring data, and transmit the ultrasonic monitoring data to a terminal computer via a network; S2: Separate ultrasonic signal data with a frequency higher than 20kHz from the ultrasonic monitoring data, and read the sound pressure data corresponding to the ultrasonic signal data; S3: Based on the ultrasonic signal data and sound pressure data, and combined with the digital twin model, the data is superimposed to locate the source of VOC fugitive leakage emissions; S4: Based on the sound pressure data, the formula is used. v = k × f + b Calculate the leakage rate of the leakage source, where f Sound pressure level, in dB. k , b The fitting coefficients are those used in the experimental calibration. v Leakage rate, in meters (m). 3 / h; and calculate the total amount of fugitive VOC emissions from the leaking emission source based on the monitoring duration.

[0007] This invention provides a novel method for monitoring fugitive VOC emissions. Based on the principle of ultrasound, it captures high-frequency ultrasonic signals generated by leaks to monitor fugitive VOC emissions. Matching the acoustic characteristics of "small hole leaks" in chemical industrial park production units, it can accurately locate the leak location and calculate the leak rate and total fugitive VOC emissions. This method is not easily affected by weather factors such as strong winds.

[0008] Furthermore, in step S2, the frequency range of the ultrasonic signal data is 20kHz-100kHz. This frequency range precisely matches the acoustic characteristics of "small hole leakage" in the production equipment of the chemical industrial park, eliminating environmental interference sound waves below 20kHz or above 100kHz, improving the accuracy of leakage signal identification, and reducing the impact of invalid data on subsequent calculations.

[0009] Furthermore, in step S3, when locating the source of fugitive VOC emissions, the following coordinate mapping formula is used to calculate the correspondence between the two-dimensional monitoring data of the ultrasonic imaging module and the actual location of the production unit: x = x i × ( d / r ), y = ( r - y j ) × ( d / r); in x The horizontal position within the production unit is expressed in meters (m). y The longitudinal position within the production unit, in meters (m). d The distance between the ultrasonic imaging module and the production equipment is in meters (m). r The length of the two-dimensional matrix of monitoring data from the ultrasound imaging module is dimensionless. x i For the horizontal direction of a two-dimensional matrix i One point; y j For the vertical direction of a two-dimensional matrix j One point.

[0010] By directly linking the "two-dimensional data" of ultrasonic monitoring with the "physical location" of the production unit through a quantitative coordinate formula, the problem of "fuzzy positioning and inability to accurately locate the leak point" in traditional monitoring is solved. This provides a clear spatial coordinate basis for subsequent single-point leakage rate calculation and ensures that the monitoring results can be traced back to the specific equipment location.

[0011] Furthermore, in step S3, when overlaying data using the digital twin model, a color-coded card is used to mark the sound pressure intensity corresponding to the leakage emission source. The color-coded card (e.g., red for high sound pressure intensity, yellow for low sound pressure intensity) visually displays the severity of the leak (higher sound pressure corresponds to higher leakage risk). This allows staff to quickly determine the leakage priority without interpreting complex data, improving the usability of monitoring results and the efficiency of emergency response.

[0012] Furthermore, in step S4, the fitting coefficients k , b The calibration process includes: A1: In the ventilation laboratory, a calibration device is set up. The calibration device includes a high-pressure gas cylinder, a pressure regulating valve, a flow monitor, and a valve with a leakage hole. One end of the valve with the leakage hole is connected to the flow monitor, and the other end is blocked. A2: Adjust the pressure regulating valve to stabilize the gas rate displayed on the flow monitor. V 1. The ultrasonic signal at this time is acquired by the ultrasonic imaging module and converted into sound pressure. db 1. Record data pairs ( V 1, db 1); A3: Repeat step A2 to stabilize the gas rate displayed on the flow monitor at [value missing]. V 2 to V n Corresponding sound pressure level db 2 to db n We obtained n-1 sets of data pairs (V 2, db 2)…( V n , db n ), where n is a natural number greater than or equal to 3; A4: The least squares method is used to perform linear fitting on a total of n data pairs to obtain the fitting coefficients. k , b .

[0013] By eliminating external air interference through the "ventilation laboratory" and ensuring the accuracy of linear fitting through the "leakspan method," precise parameter support is provided for the leakage rate formula, ensuring the reliability of the quantitative results.

[0014] Furthermore, in step S4, when calculating the total fugitive VOC emissions, the formula is used. Q = v × t ,in Q Total emissions, in cubic meters (m³) 3 ; v Leakage rate, in meters (m). 3 / h; t The monitoring duration is measured in hours (h). A clear quantitative relationship for total emission calculation is established, combining "instantaneous rate" with the "time dimension" to achieve the transformation from "single-point rate" to "cumulative total," thus meeting the core requirements of VOC emission accounting in environmental management.

[0015] Furthermore, it also includes step S5: combining the gaseous composition of the VOCs emitted by the production device, querying the density of the gaseous composition, and using the formula... m = Q × ρ Total volume of VOC emissions Q Convert to total mass m ,in ρ VOC gas density, unit: kg / m³ 3 This enables the conversion from "total volume" to "total mass," aligning with the national environmental emission standards that use "mass concentration / total mass as the control indicator" (such as GB 31571-2015 "Emission Standard for Pollutants from Petrochemical Industry"), thereby enhancing the practicality of monitoring results.

[0016] Furthermore, in step S1, the monitoring data from the ultrasound imaging module is two-dimensional planar data. N [ r , r The two-dimensional planar data N [ r , rThe square region corresponding to the receiving surface of the ultrasound imaging module, wherein the side length of the square region is... L By defining the correspondence between the "two-dimensional matrix structure" and the "physical receiving surface" of the monitoring data, the data format is ensured to match the hardware characteristics of the ultrasound module, providing a unified data foundation for the coordinate mapping in step S3 and avoiding positioning calculation errors caused by chaotic data structure.

[0017] Furthermore, the method also includes an accuracy verification step: using a portable VOC measuring device to conduct on-site detection of the located leakage emission source, obtaining the leakage rate detected manually, calculating the deviation between the leakage rate monitored by this method and the manually detected rate, and controlling the deviation to be within 15%.

[0018] Furthermore, in step A1, the ventilation rate of the exhaust chamber is controlled at 0.5-1 m / s to eliminate interference from airflow within the chamber on ultrasonic signal acquisition. By quantitatively controlling the ventilation rate, the disturbance of airflow within the chamber to the ultrasonic signal (such as airflow noise superimposed on leakage sound waves) is further reduced, ensuring the stability of sound pressure data during calibration. k , b The accurate fitting provides environmental protection.

[0019] Compared with the prior art, the present invention has the following beneficial technical effects: (1) Wide coverage: The coverage range of the ultrasonic imaging module can reach 100-200m (far exceeding the traditional concentration monitoring instrument), with no monitoring blind spots; (2) Precise positioning: Through coordinate mapping + digital twin model superposition, the positioning accuracy of the leakage source can be controlled within ±0.5m, without the need for manual investigation; (3) Quantitative calculation: Through the linear formula calibrated in the laboratory, the leakage rate and total emission can be accurately calculated, and can also be converted into total mass; (4) High accuracy: Deviation ≤15%; (5) Low cost: Reduces the cost of manual investigation, and the equipment maintenance cost is lower than that of the traditional online monitoring system. Attached Figure Description

[0020] Figure 1 is a schematic diagram of data transmission for ultrasound module monitoring. In the figure, 1 is the ultrasound monitoring module (collecting ultrasound distribution data), 2 is the 4G / 5G wireless network (transmitting data), and 3 is the terminal computer (installing data processing software).

[0021] Figure 2 shows the correspondence between the monitoring data of the acoustic module and the target location.

[0022] Figure 3 is an overlay of the acoustic module monitoring data and the twin model.

[0023] Figure 4 shows the calibration parameter fitting process.

[0024] Figure 5 shows the results of a certain monitoring session. Detailed Implementation

[0025] The technical solution of the present invention will now be clearly and completely described with reference to the accompanying drawings. Obviously, the described embodiments are only a part of the embodiments of the present invention, and not all of them. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention without creative effort are within the protection scope of the present invention.

[0026] A method for monitoring fugitive VOC emissions using ultrasound imaging technology, comprising the following steps: Step S1: Acquisition and transmission of ultrasound monitoring data As shown in Figure 1, the ultrasonic imaging module 1 is installed at the monitoring point of the production equipment (such as storage tanks and pipelines) in the chemical industrial park to ensure that the module's monitoring range covers the target equipment; the ultrasonic imaging module collects ultrasonic monitoring data (including ultrasonic signal distribution, sound pressure intensity, etc.) of the target equipment, which is two-dimensional planar data. N [ r , r ], corresponding to the square area of ​​the receiving surface of the module (side length is L The ultrasound monitoring data is transmitted in real time to the terminal computer 3 via the 4G / 5G wireless network 2. The terminal computer is pre-installed with ultrasound data processing software for subsequent data analysis.

[0027] Step S2: Ultrasonic signal separation and sound pressure reading VOC fugitive leaks from production facilities in chemical industrial parks are mostly "small hole leaks," which typically generate sound waves with frequencies above 20kHz (within the ultrasonic range) and are significantly different from the low-to-medium frequency noise (<20kHz) generated during normal equipment operation. Based on this characteristic, the terminal computer software separates ultrasonic signal data with frequencies between 20kHz and 100kHz (this frequency band is the main frequency band of the leak signal) from the ultrasonic monitoring data collected in step S1, and simultaneously reads the corresponding sound pressure data (unit: dB).

[0028] Step S3: Locate the leak source (using a digital twin model) As shown in Figure 2, the coordinate mapping relationship between ultrasonic monitoring data and the actual location of the production device is first established: the distance between the ultrasonic imaging module and the target device is... d (Unit: m), the length of the two-dimensional matrix of monitoring data is r (Dimensionless), for any point in a two-dimensional matrix ( x i , y j The actual location of the corresponding production unit is: x = xi × ( d / r (Horizontal position, unit: m) y = ( r - y j )×( d / r (Vertical position, unit: m); Subsequently, the ultrasonic signal data and sound pressure data after the above coordinate mapping are superimposed with the digital twin model of the production device (such as the three-dimensional model of the storage tank and the three-dimensional model of the pipeline) (as shown in Figure 3), and the sound pressure intensity of each leakage point is marked with a color code card (such as red indicating sound pressure ≥60dB, orange indicating 50-60dB, and yellow indicating <50dB), and finally the source of VOC fugitive leakage emission is located.

[0029] Step S4: Calculation of Leakage Rate and Total Emissions (1) Leakage rate calculation: using a linear formula v = k × f + b ,in f The sound pressure data (dB) read in step S2. v Leakage rate (m 3 / h), k , b (2) Fit coefficients for experimental calibration; k , b Calibration: such as Figure 4 As shown, a calibration setup is constructed in a ventilation laboratory (ventilation rate 0.5-1 m / s, eliminating airflow interference): high-pressure gas cylinder (stores simulated VOC gas) → pressure regulating valve → flow monitor → valve with a leak hole (the other end sealed); adjust the pressure valve to stabilize the flow rate displayed on the flow monitor sequentially at... V 1- V 10 (Total of 10 groups, such as 0.1-1.0 m) 3 / h), synchronously collecting the sound pressure corresponding to each rate. db 1- db 10 The least squares method was used to analyze 10 sets of data ( V 1, db 1)…( V 10 , db 10 Perform linear fitting to obtain k , b (3) Calculation of total emissions: using the formula Q =v × t ,in t For monitoring duration (h), Q Total volumetric emissions of VOCs (m³) 3 ).

[0030] Step S5: Convert total volume to total mass (optional) Based on the specific components of the VOCs emitted by the production unit (such as methane, benzene, and toluene), find the density of that component. ρ (kg / m 3 ), using formula m = Q × ρ Total volume Q Convert to total mass m (kg).

[0031] Step S6: Accuracy Verification Portable VOC measuring equipment (such as a photoionization detector) is used to manually detect the leakage source located in step S3 on-site to obtain the leakage rate detected manually; the deviation between the monitoring rate of this method and the manual detection rate is calculated.

[0032] Taking the monitoring of fugitive VOC emissions from a storage tank area in a petrochemical industrial park as an example, this paper details the implementation process of this method.

[0033] 1. Equipment Preparation Ultrasonic imaging module: side length of receiving surface L =0.15m, length of the two-dimensional matrix r =300, monitoring frequency range 20-100kHz; Terminal computer: equipped with data processing software and supports 5G network connectivity; Calibration equipment: high-pressure gas cylinder (stores methane, typical VOC components), pressure regulating valve (accuracy ±0.01MPa), flow monitor (range 0-2). m 3 / h, accuracy ±0.01 m 3 / h), valves with leakage holes (orifice diameter 1mm); Portable detector: Model PGM-7340 (detection range 0-2000ppm, accuracy ±5%).

[0034] 2. On-site deployment The ultrasonic imaging module was installed on a bracket 8 meters away from the storage tank (10m in diameter and 15m in height), with the module lens aimed at the lower part of the tank (the area prone to leakage). The terminal computer was placed in the park's monitoring center and connected to the ultrasonic module via a 5G network.

[0035] 3. Calibration coefficient k , b Get Inside the exhaust-equipped laboratory (ventilation rate 0.8 m / s): Adjust the pressure valve to stabilize the flow rate monitored sequentially at... V 1 = 0.1 V 2 = 0.2… V 10 = 1.0 m 3 / h; Simultaneously collect the sound pressure corresponding to each rate: db 1=48、 db 2=53… db 10 =93 dB; The least squares fitting yields: k = 0.02, b = -0.86 (fitting formula: v = 0.02 f - 0.86).

[0036] 4. Monitoring and Calculation Data acquisition: The ultrasound module continuously monitors for 24 hours, transmitting two-dimensional data to the terminal. N [300, 300]; Signal separation: Separate the 20-100kHz signal and read the sound pressure at 3 leakage points: f 1=67 dB f 2=62 dB f 3 = 58 dB; Leakage rate calculation: v 1 = 0.02 × 67 - 0.86 = 0.48 m 3 / h; v 2 = 0.02 × 62 - 0.86 = 0.38 m 3 / h; v 3 = 0.02 × 58 - 0.86 = 0.30 m 3 / h; Total emissions calculation (24h): Q 1 = 0.48 × 24 = 11.52 m 3 ; Q 2 = 0.38 × 24 = 9.12 m 3 ; Q3 = 0.30 × 24 = 7.20 m 3 ; Mass conversion (methane density) ρ = 0.717 kg / m 3 ): m 1 = 11.52×0.717 ≈ 8.26 kg; m 2 = 9.12×0.717 ≈ 6.54 kg; m 3 = 7.20×0.717 ≈ 5.16 kg.

[0037] Manual inspection: Three leak points were detected using a PGM-7340, and the leak rates were obtained. v 1′ = 0.52、 v 2′ = 0.41、 v 3′ = 0.32 m 3 / h; Deviation calculation: Deviation 1 = (0.48 - 0.52) / 0.52 ≈ 7.7%; Deviation 2 = (0.38-0.41) / 0.41 ≈ 7.3%; Deviation 3 = (0.30-0.32) / 0.32 ≈ 6.2%; All values ​​are ≤15%, meeting the monitoring requirements.

[0038] Although embodiments of the present invention have been shown and described above, it is understood that these embodiments are exemplary and should not be construed as limiting the present invention. Those skilled in the art can make changes, modifications, substitutions, and alterations to the above embodiments within the scope of the present invention without departing from its principles and spirit. The scope of protection of the present invention is defined by the claims and their equivalents.

Claims

1. A method for monitoring fugitive VOC emissions using ultrasonic imaging technology, characterized in that, Includes the following steps: S1: Monitor the production equipment in the chemical industrial park using an ultrasonic imaging module, collect ultrasonic monitoring data, and transmit the ultrasonic monitoring data to a terminal computer via a network; S2: Separate ultrasonic signal data with a frequency higher than 20kHz from the ultrasonic monitoring data, and read the sound pressure data corresponding to the ultrasonic signal data; S3: Based on the ultrasonic signal data and sound pressure data, and combined with the digital twin model, the data is superimposed to locate the source of VOC fugitive leakage emissions; S4: Based on the sound pressure data, the formula is used. v = k × f + b Calculate the leakage rate of the leakage source, where f Sound pressure level, in dB. k , b The fitting coefficients are those used in the experimental calibration. v Leakage rate, in meters (m). 3 / h; and calculate the total amount of fugitive VOC emissions from the leaking emission source based on the monitoring duration.

2. The method according to claim 1, characterized in that, In step S2, the frequency range of the ultrasonic signal data is 20kHz-100kHz.

3. The method according to claim 1, characterized in that, In step S3, when locating the source of fugitive VOC emissions, the following coordinate mapping formula is used to calculate the correspondence between the two-dimensional monitoring data of the ultrasonic imaging module and the actual location of the production unit: x = x i × ( d / r )， y = ( r - y j ) × ( d / r )； in x The horizontal position within the production unit is expressed in meters (m). y The longitudinal position within the production unit, in meters (m). d The distance between the ultrasonic imaging module and the production equipment is in meters (m). r The length of the two-dimensional matrix of monitoring data from the ultrasound imaging module is dimensionless. x i For the horizontal direction of a two-dimensional matrix i One point; y j For the vertical direction of a two-dimensional matrix j One point.

4. The method according to claim 1, characterized in that, In step S3, when combining the digital twin model for data overlay, a color code is used to mark the sound pressure intensity corresponding to the leakage emission source.

5. The method according to claim 1, characterized in that, In step S4, the fitting coefficients k , b The calibration process includes: A1: In the ventilation laboratory, a calibration device is set up. The calibration device includes a high-pressure gas cylinder, a pressure regulating valve, a flow monitor, and a valve with a leakage hole. One end of the valve with the leakage hole is connected to the flow monitor, and the other end is blocked. A2: Adjust the pressure regulating valve to stabilize the gas rate displayed on the flow monitor. V 1. The ultrasonic signal at this time is acquired by the ultrasonic imaging module and converted into sound pressure. db 1. Record data pairs ( V 1, db 1); A3: Repeat step A2 to stabilize the gas rate displayed on the flow monitor at [value missing]. V 2 to V n Corresponding sound pressure level to be collected db 2 to db n We obtained n-1 sets of data pairs ( V 2, db 2)…( V n , db n ), where n is a natural number greater than or equal to 3; A4: The least squares method is used to perform linear fitting on a total of n data pairs to obtain the fitting coefficients. k , b .

6. The method according to claim 1, characterized in that, In step S4, the formula is used to calculate the total fugitive emissions of VOCs. Q = v × t ,in Q Total emissions, in cubic meters (m³) 3 ; v Leakage rate, in meters (m). 3 / h; t The monitoring duration is expressed in hours (h).

7. The method according to claim 1, characterized in that, It also includes step S5: combining the gas composition of the VOCs emitted by the production device, querying the density of the gas composition, and using the formula m = Q × ρ Total volume of VOC emissions Q Convert to total mass m ,in ρ VOC gas density, unit: kg / m³ 3 .

8. The method according to claim 1, characterized in that, In step S1, the monitoring data from the ultrasound imaging module is two-dimensional planar data. N [ r , r The two-dimensional planar data N [ r , r The square region corresponding to the receiving surface of the ultrasound imaging module, wherein the side length of the square region is... L .

9. The method according to claim 1, characterized in that, The method also includes an accuracy verification step: using a portable VOC measuring device to conduct on-site detection of the located leakage emission source, obtaining the leakage rate detected manually, and calculating the deviation between the leakage rate monitored by this method and the manually detected rate, wherein the deviation is controlled within 15%.

10. The method according to claim 5, characterized in that, In step A1, the ventilation rate of the exhaust laboratory is controlled at 0.5-1 m / s.

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