An online monitoring system and control method for volatile organic compounds from stationary pollution sources

Abstract

This invention discloses an online monitoring system and control method for volatile organic compounds (VOCs) from stationary pollution sources. The system includes a multi-point sampling probe, an intelligent flow control unit, a switching valve, a sample gas pretreatment device, a gas analysis host, and a data acquisition and communication module. The multi-point sampling probe is strategically positioned according to the flow field distribution and is equipped with heating and backflushing functions. The switching valve is equipped with a cleaning module, employing a dual mechanism of vacuum extraction and nitrogen purging to prevent cross-contamination. The intelligent flow control unit is linked to the switching valve, achieving differentiated monitoring based on concentration thresholds. When the pollutant concentration in the sampling channel exceeds a preset threshold, the sampling time is automatically extended. The system uses an incremental PID control algorithm to automatically switch control parameters according to concentration changes. This system ensures stable sampling under different operating conditions through intelligent flow control, effectively solving the problem of poor adaptability of fixed flow control.

Description

Technical Field

[0001] This invention relates to the field of pollution source detection technology, specifically to an online monitoring system and control method for volatile organic compounds from stationary pollution sources. Background Technology

[0002] Online monitoring systems for volatile organic compounds (VOCs) from stationary pollution sources have adopted multi-point sampling technology, which improves monitoring coverage by setting sampling probes at different spatial locations. However, existing multi-point sampling systems have significant shortcomings in flow control: First, they use a fixed flow control mode, usually set to a fixed value (such as 1L / min, 2L / min), which cannot be dynamically adjusted according to changes in pollutant concentration. This can easily lead to analyzer overload or decreased detection accuracy when concentrations fluctuate drastically. Second, the sampling time allocation strategy is simplistic, allocating equal time for pollutant sampling in each sampling channel, ignoring the differences in pollutant concentrations at different locations, resulting in insufficient monitoring of high-concentration areas and over-sampling of low-concentration areas. Third, the flow control algorithm lacks adaptive capability and cannot automatically adjust control parameters according to different operating conditions. It exhibits lag in response to changes in operating conditions such as production plant start-up and shutdown, and raw material changes, affecting the timeliness and accuracy of monitoring data.

[0003] Therefore, existing technologies suffer from problems such as a lack of adaptive adjustment capability in flow control, insufficient targeting of sampling time allocation strategies, and poor responsiveness to changes in operating conditions, making it impossible to achieve intelligent flow control and differentiated sampling based on concentration differences. Summary of the Invention

[0004] The purpose of this invention is to provide an online monitoring system for volatile organic compounds from stationary pollution sources to solve the problems mentioned in the background art.

[0005] To achieve the above objectives, the first aspect of this application provides an online monitoring system for volatile organic compounds (VOCs) from stationary pollution sources, comprising: a multi-point sampling probe, an intelligent flow control unit, a switching valve, a sample gas pretreatment device, a gas analysis host, and a data acquisition and communication module; each sampling probe of the multi-point sampling probe is connected to the intelligent flow control unit via a sampling channel, the output of the intelligent flow control unit is connected to the input of the switching valve, the output of the switching valve is connected to the sample gas pretreatment device, the sample gas pretreatment device is connected to the gas analysis host, and the data acquisition and communication module is connected to the gas analysis host; the switching valve is equipped with a purging module, including a nitrogen purging circuit and a vacuum extraction circuit; before performing channel switching, a vacuum pump is started to extract the sampling channel through the vacuum extraction circuit, and then high-purity nitrogen is introduced. The gas is purged under positive pressure through a nitrogen purging circuit. After the channel switching is completed, the sampling operation of the new channel is delayed for a preset time. The multi-point sampling probe is used to collect the sample gas in the sampling channel. The intelligent flow control unit is linked with the switching valve and performs cyclic detection on each sampling channel based on preset polling and set concentration thresholds. When the pollutant concentration in the sampling channel exceeds the preset threshold, the switching valve is controlled to automatically extend the sampling time of the sampling channel and shorten the sampling time of other sampling channels accordingly. The sample gas pretreatment device is used to pretreatment the sample gas output by the intelligent flow control unit. The gas analysis host is used to receive the sample gas after processing by the sample gas pretreatment device and detect the pollutant concentration. The data acquisition and communication module receives the pollutant concentration data output by the gas analysis host and transmits it remotely.

[0006] Based on the first aspect, in one possible implementation, the multi-point sampling probe includes a probe body, a multi-hole sampling head disposed at the front end of the probe body, a heat tracing cable laid along the outer wall of the probe body, and a backflush air path connected to the internal sampling channel of the probe body; the heat tracing cable heats the probe body and the multi-hole sampling head; the backflush air path is connected to a high-pressure air source through a solenoid valve, and periodically blows from the end of the multi-hole sampling probe toward the sampling port, with the backflush airflow path being opposite to the sampling direction.

[0007] Based on the first aspect, in one possible implementation, the multi-point sampling probes are arranged differently according to the airflow velocity distribution field and pollutant concentration distribution field inside the sampling channel. When the cross-section of the sampling channel perpendicular to the airflow direction is circular, an equal-area ring distribution method is adopted, dividing the cross-section of the sampling channel into several equal-area rings according to the radial distance, with a sampling probe set at the center of each ring. When the longitudinal cross-section of the sampling channel perpendicular to the airflow direction is rectangular, an equal-area grid distribution method is adopted, dividing the cross-section of the sampling channel into several equal-area rectangular grids, with a sampling probe set at the geometric center of each grid. Each sampling probe is connected to the sampling channel corresponding to the intelligent flow control unit through a heated sampling pipe, and the insertion depth of each sampling probe reaches 2 / 3 of the equivalent diameter of the sampling channel.

[0008] Based on the first aspect, in one possible implementation, the intelligent flow control unit includes multiple independent flow control loops, each connected to a corresponding sampling probe. Each flow control loop is equipped with a flow sensor, an electric regulating valve, and a microprocessor control module. The flow sensor is used to monitor the sample gas flow rate of each sampling channel in real time and provide flow feedback signals to the intelligent flow control unit. The microprocessor control module, based on the real-time concentration feedback from the data acquisition and communication module, dynamically adjusts the electric regulating valve to change the sampling flow rate of the sampling channel.

[0009] Based on the first aspect, in one possible implementation, the microprocessor control module includes an incremental PID control algorithm processor, a parameter memory, and a concentration change rate detector. The parameter memory presets control parameters including a steady-state parameter group, a fast-response parameter group, and a damping parameter group. The steady-state parameter group is suitable for operating conditions with gradual concentration changes, the fast-response parameter group is suitable for operating conditions with rapid concentration changes, and the damping parameter group is suitable for operating conditions with drastic concentration fluctuations. The incremental PID control algorithm processor calculates the control deviation based on the real-time concentration feedback signal and the preset target value, generates flow regulation commands through proportional, integral, and derivative control algorithms, and outputs the regulation commands to the electric regulating valves of each flow control loop. The concentration change rate detector is used to continuously monitor the pollutant concentration data of each sampling channel through a sliding window algorithm, calculate the concentration change rate between continuous sampling points, and compare the calculation results with a preset change rate threshold. When the concentration change rate exceeds 20 mg / m³ / min, a parameter switching command is sent to the incremental PID control algorithm processor. The microprocessor control module also includes a flow rate adjuster, which is connected to the electric regulating valve and controls the sampling flow rate of each sampling channel by adjusting the opening of the electric regulating valve.

[0010] Based on the first aspect, in one possible implementation, the switching valve adopts a multi-channel rotary valve structure. The switching valve has an air inlet channel and an air outlet channel corresponding to the number of multi-point sampling probes. The sequential connection of each air inlet channel and the air outlet channel is achieved by rotating the valve core. The intelligent flow control unit works in conjunction with the switching valve. The intelligent flow control unit controls the flow rate of each sampling channel to stabilize, and the switching valve performs time-sequential switching of the sampling channels by rotating the multi-channel valve.

[0011] Based on the first aspect, in one possible implementation, the sample gas pretreatment device sequentially includes a coarse filtration unit, a condensation and dehumidification unit, and a pressure and flow stabilization unit along the sample gas flow direction. The inlet of the coarse filtration unit is connected to the outlet of the switching valve, the outlet of the pressure and flow stabilization unit is connected to the inlet of the gas analyzer, and the condensation and dehumidification unit is located between the coarse filtration unit and the pressure and flow stabilization unit. The coarse filtration unit is used for primary filtration of the sample gas, and the condensation and dehumidification unit is equipped with a temperature-controlled cooler and a condensation separator. The temperature-controlled cooler is used to reduce the temperature of the sample gas from the switching valve, and the condensation separator is used to condense and separate water vapor. The pressure and flow stabilization unit includes a pressure regulating valve and a buffer tank. The pressure regulating valve is used to regulate the pressure value of the sample gas after coarse filtration and dehumidification, and the buffer tank is used to control the flow fluctuation within a set value range.

[0012] The second aspect of this application provides an online monitoring and control method for volatile organic compounds (VOCs) from stationary pollution sources, applied to an online monitoring system for VOCs from stationary pollution sources. This system includes a multi-point sampling probe, an intelligent flow control unit, a switching valve, a sample gas pretreatment device, a gas analysis host, and a data acquisition and communication module. The method includes: collecting sample gas from the pollution source through multiple sampling channels of the multi-point sampling probe; cyclically detecting each sampling channel based on a preset polling strategy by linking the intelligent flow control unit and the switching valve; automatically extending the sampling time of the sampling channel and correspondingly shortening the sampling time of other sampling channels when the pollutant concentration in any sampling channel exceeds a preset threshold; before switching sampling channels, first starting a vacuum pump to extract negative pressure through a vacuum extraction circuit, then introducing high-purity nitrogen for positive pressure purging through a nitrogen purging circuit; after completing the channel switching, delaying for a preset time before starting the sampling operation of the new channel; pre-treating the collected sample gas through the sample gas pretreatment device; detecting the pollutant concentration in the pre-treated sample gas through the gas analysis host; and receiving and remotely transmitting the pollutant concentration data through the data acquisition and communication module.

[0013] Based on the second aspect, in one possible implementation, the intelligent flow control unit includes multiple independent flow control loops, each connected to a corresponding sampling probe. Each flow control loop is equipped with a flow sensor, an electric regulating valve, and a microprocessor control module. The method further includes: pre-setting a steady-state parameter group, a fast response parameter group, and a damping parameter group, and storing these groups in the microprocessor control module; monitoring the sample gas flow rate of each sampling channel in real time using the flow sensor and calculating the concentration change rate; when the concentration change rate exceeds 20 mg / m³ / min, it is determined to be a significant change, and the system automatically switches from the steady-state parameter group to the fast response parameter group; based on the real-time concentration feedback from the data acquisition and communication module, the microprocessor control module dynamically adjusts the opening of the electric regulating valve; and when the switching valve performs sampling channel switching, the flow rate adjustment achieves differentiated allocation of sampling time for each sampling channel.

[0014] Based on the second aspect, one possible implementation involves setting a primary concentration threshold and a secondary concentration threshold, and establishing a fixed polling cycle. Under standard conditions, each sampling channel is allocated an equal sampling time. The pollutant concentration in each sampling channel is monitored in real time, and the sampling time is dynamically optimized and adjusted according to the preset primary and secondary concentration thresholds. When the concentration in a sampling channel exceeds the primary concentration threshold, the sampling time of the sampling channel is extended by a first duration, and the sampling time of other channels is shortened accordingly. When the concentration in a sampling channel reaches the secondary concentration threshold, the sampling time of the sampling channel is extended by a second duration, and the sampling time of other channels is adjusted accordingly. Wherein, the primary concentration threshold is higher than the secondary concentration threshold, and the first duration is longer than the second duration.

[0015] Compared with the prior art, the beneficial effects of the present invention are:

[0016] 1. In this invention, by deploying multiple sampling probes in the sampling channel and cooperating with an automatic switching mechanism, sample gas from different spatial locations can be collected in turn, which significantly improves the coverage and spatial representativeness of the monitoring data and effectively avoids the monitoring deviation caused by traditional single-point sampling.

[0017] 2. In this invention, by introducing an intelligent flow control unit, the sampling flow rate of each channel can be adjusted according to the real-time fluctuation of the pollution source emission status, maintaining stable sampling under different concentration conditions, and avoiding measurement distortion, instrument overload, or long-term error accumulation caused by improper flow setting.

[0018] 3. In this invention, the independence of each sample gas in the multi-channel sampling process is ensured by independent control paths and pollution prevention and control mechanisms, thereby improving the accuracy and reliability of component analysis. Attached Figure Description

[0019] Figure 1This is a schematic diagram of the overall structure of an online monitoring system for volatile organic compounds from stationary pollution sources, as described in an embodiment of this application.

[0020] Figure 2 This is a schematic diagram of the structure and cross-section of the multi-point sampling probe in the embodiments of this application;

[0021] Figure 3 This is a schematic diagram of the rectangular cross-section sampling probe layout in an embodiment of this application;

[0022] Figure 4 This is a schematic diagram of the internal structure of the intelligent flow control unit in the embodiments of this application;

[0023] Figure 5 This is a schematic diagram of the switching valve in an embodiment of this application.

[0024] In the diagram: 1. Multi-point sampling probe; 2. Intelligent flow control unit; 3. Switching valve; 4. Sample gas pretreatment device; 5. Gas analysis host; 6. Data acquisition and communication module; 21. Flow control loop; 22. Central processing unit; 23. Human-machine interface; 24. Communication interface; 25. Power supply module; 26. Data storage unit; 211. Mass flow meter; 212. Proportional solenoid valve; 213. Pressure sensor; 214. Temperature sensor. Detailed Implementation

[0025] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0026] Exemplary System

[0027] This invention discloses an online monitoring system for volatile organic compounds (VOCs) from stationary pollution sources, comprising a multi-point sampling probe 1, an intelligent flow control unit 2, a switching valve 3, a sample gas pretreatment device 4, a gas analysis host 5, and a data acquisition and communication module 6. The multi-point sampling probe 1 is positioned at different locations within the exhaust pipe, and the intelligent flow control unit 2 is connected to the multi-point sampling probe 1. The switching valve 3 switches the gas path between different sampling channels of the multi-point sampling probe 1 and is connected to the sample gas pretreatment device. The sample gas pretreatment device 4 is connected to the gas analysis host 5. The multi-point sampling probe 1 includes at least two probes positioned at different locations within the sampling channels, and its design is optimized based on the airflow velocity distribution and pollutant concentration distribution within the sampling channels. Each sampling probe is connected to the intelligent flow control unit via an independent sampling channel and is equipped with heating and backflushing cleaning functions. The intelligent flow control unit 2 includes multiple independent flow control loops, each loop equipped with a flow sensor, an electric regulating valve, and a microprocessor control module. The intelligent flow control unit 2 continuously collects pressure, temperature, and flow data of the sampled gas in each sampling channel and dynamically adjusts the sampling flow rate of each sampling channel based on real-time sampling concentration feedback. The intelligent flow control unit 2 is linked with the switching valve 3, controlling the sampling path switching and flow regulation through a combination of preset polling and concentration threshold strategies. The sample gas pretreatment device 4 includes a coarse filtration unit, a condensation and dehumidification unit, and a pressure and flow stabilization unit. The coarse filtration unit removes large particulate impurities, the condensation and dehumidification unit reduces water vapor interference and prevents gas condensation, and the pressure and flow stabilization unit ensures the sample gas enters the analyzer at a suitable pressure and flow rate. The gas analysis host 5 is a gas chromatography-flame ionization detector combination device or a gas chromatography-mass spectrometry device, equipped with a calibration module for periodic calibration using standard gases. The gas analysis host 5 separates and quantitatively analyzes volatile organic compounds, outputting concentration values ​​and component spectra. The data acquisition and communication module 6 acquires the output data from the gas analysis host and transmits it remotely. The data acquisition and communication module 6 supports multiple communication interfaces, allowing connection to a local control system or a remote environmental protection platform for online monitoring, data storage, and over-limit alarm functions.

[0028] Figure 1 This is a schematic diagram of the overall structure of an online monitoring system for volatile organic compounds from stationary pollution sources, as described in an embodiment of this application. (See also...) Figure 1, an on-line monitoring system for volatile organic compounds from stationary sources of the present invention adopts a modular design architecture, and each module realizes system integration through standardized interfaces. The multi-point sampling probe 1 is connected to the intelligent flow control unit 2 through a stainless steel sampling pipeline. A heating cable is provided on the outer wall of the multi-point sampling probe 1, and the working temperature range is 120-180 degrees Celsius. The output end of the intelligent flow control unit 2 is connected to the switching valve 3 through a quick connector, and the output end of the switching valve 3 is connected to the sample gas pretreatment device 4 through a polytetrafluoroethylene pipeline. The clean sample gas processed by the sample gas pretreatment device 4 enters the gas analysis host 5 through a standard gas path interface. The data acquisition and communication module 6 is connected to the intelligent flow control unit 2 and the gas analysis host 5 through the RS485 bus to realize the unified control and data management of the system.

[0029] Refer to Figure 2 , the multi-point sampling probe 1 includes three core parts: a probe body, a heating system, and a backflush cleaning system. A porous sampling head is provided at the front end of the probe. The heating system uses a heating cable heating method and is equipped with a temperature sensor to achieve closed-loop temperature control, ensuring that the temperature of the sampling pipeline is stable at 150 degrees Celsius. The backflush cleaning system includes a backflush gas source, a solenoid valve, and a timing controller. The backflush program is automatically executed every 4 hours, the backflush pressure is 0.3 MPa, and the duration is 30 seconds. Figure 2 The control system supporting the multi-point sampling probe 1 is also shown. The temperature control unit and the backflush control unit in the control system are responsible for coordinating the working states and parameter settings of each probe. The flow monitoring unit in the control system monitors the flow changes in each sampling channel in real time and provides feedback signals. The installation position of the multi-point sampling probe 1 is determined according to the geometric dimensions and flow field distribution of the sampling channel. As Figure 2 shown, for a sampling channel with a circular cross-section, the first probe, the second probe, the third probe, and the fourth probe are arranged on the cross-section according to the equal-area ring division method to ensure that each sampling point represents an equal cross-sectional area. For a sampling channel with a circular cross-section, in another implementation, the first probe is located in the central area of the channel, and the second probe, the third probe, and the fourth probe are respectively located at the center positions of the annular zones with different radial distances. For a sampling channel with a rectangular longitudinal section, the sampling probes are arranged on the cross-section according to the grid method, dividing the cross-section into several equal rectangular areas, and a sampling point is set at the geometric center of each area to form a regular grid distribution pattern. Refer to Figure 3Taking a typical 4.5m × 2.0m rectangular cross-section as an example, the cross-section is divided into 3 equal segments along the long side and 2 equal segments along the short side, forming 6 rectangular grids of equal area, each grid having an area of ​​0.75 square meters. The coordinates of the first row of probes are: Probe 1' (0.33m, 0.75m) and Probe 2' (1.67m, 0.75m); the coordinates of the second row of probes are: Probe 3' (0.33m, 2.25m), Probe 4' (1.00m, 2.25m), and Probe 5' (1.67m, 2.25m); the coordinates of the third row of probes are: Probe 6' (0.33m, 3.75m) and Probe 7' (1.67m, 3.75m). The origin of the coordinate system is set at the lower left corner of the rectangular cross-section, with the X-axis along the short side and the Y-axis along the long side. Each sampling probe is located at the geometric center of its corresponding grid area, ensuring that each probe represents an equal cross-sectional area and airflow rate. The sampling probe should penetrate two-thirds of the equivalent diameter of the sampling channel to ensure that representative gas samples from the central region of the channel are collected, thus avoiding the influence of wall effects on the sampling results.

[0030] Figure 4 This is a schematic diagram of the internal structure of the intelligent flow control unit in an embodiment of this application. (See also...) Figure 4The intelligent flow control unit 2 includes a multi-channel flow control loop 21, a central processing unit 22, a human-machine interface 23, a communication interface 24, a power module 25, and a data storage unit 26. Each flow control loop 21 consists of a mass flow meter 211, a proportional solenoid valve 212, a pressure sensor 213, and a temperature sensor 214. Each sensor is connected to the central processing unit 22 via signal lines. The mass flow meter 211 uses a thermal mass flow sensor with a measurement range of 0-5 standard liters per minute and an accuracy class of 1.5, enabling real-time monitoring of gas flow changes in each sampling channel. The proportional solenoid valve 212 uses a pilot-operated structure with a response time of less than 100 milliseconds and a control accuracy of 2% of the set value, achieving precise flow regulation through a PWM signal. The pressure sensor 213 monitors pipeline pressure changes, and the temperature sensor 214 provides temperature compensation data to ensure the accuracy of flow measurement. The central processing unit 22 uses a 32-bit ARM architecture microcontroller with a main frequency of 72 MHz, a built-in floating-point arithmetic unit, runs a real-time operating system, and supports multi-task parallel processing. The processor incorporates an incremental PID control algorithm module, including adaptive adjustment functions for proportional gain, integral time, and derivative time parameters. When a significant change in the sampled concentration is detected, the system automatically switches between preset steady-state parameter groups, fast-response parameter groups, and damping parameter groups to ensure the speed and stability of flow control. The human-machine interface 23 uses a 7-inch color touchscreen to display real-time flow, pressure, and temperature data for each channel, as well as system operating status and alarm information. Operators can set sampling strategies, flow parameters, and alarm thresholds via the touchscreen, enabling flexible system configuration and convenient operation. The communication interface 24 includes an Ethernet interface, an RS485 interface, and a wireless communication module, supporting Modbus RTU, Modbus TCP, and 4G LTE communication protocols to achieve data exchange with the host computer system and remote monitoring platform. The power module 25 provides the system with a 24V DC power supply and a 5V logic power supply, and features overvoltage, undervoltage, and short-circuit protection. The data storage unit 26 uses a flash memory with a storage capacity of 32GB, capable of storing historical data, control parameters, and system configuration information.

[0031] In one specific embodiment, the incremental PID control algorithm processor of the microprocessor control module in the intelligent flow control unit 2 includes a concentration change rate detector, an incremental PID control algorithm processor, and a parameter memory. The concentration change rate detector continuously monitors the pollutant concentration data of each sampling channel using a sliding window algorithm, calculates the concentration change rate between five consecutive sampling points, and the sampling interval is 30 seconds. When the concentration change rate exceeds 20 mg / m³ / min, the concentration change rate detector sends a parameter switching command to the incremental PID control algorithm processor. The parameter memory presets three sets of control parameters: a steady-state parameter set (Kp=0.8, Ki=0.2, Kd=0.1) suitable for operating conditions with gradual concentration changes; a fast response parameter set (Kp=1.2, Ki=0.5, Kd=0.05) suitable for operating conditions with rapid concentration changes; and a damping parameter set (Kp=0.6, Ki=0.15, Kd=0.2) suitable for operating conditions with drastic concentration fluctuations. The incremental PID control algorithm processor calculates the control deviation based on the real-time concentration feedback signal and the preset target value. It generates flow regulation commands through proportional, integral, and derivative control algorithms and outputs these commands to the electric regulating valves in each flow control loop. Parameter switching employs a gradual switching process with a 10-second switching time to avoid impact on the control system. Three concentration thresholds are set: low (50 mg / m³), medium (200 mg / m³), and high (500 mg / m³). The standard polling cycle is 40 minutes, and the standard sampling time for each channel is 10 minutes. When the concentration in a sampling channel exceeds the high concentration threshold, the sampling time for that channel is extended to 15 minutes, while the sampling time for the other three channels is adjusted to 8 minutes and 20 seconds. When the concentration in a sampling channel is between the medium and high concentration thresholds, the sampling time for that channel is extended to 12 minutes, while the sampling time for the other channels is adjusted to 9 minutes and 20 seconds. This allocation strategy ensures differentiated monitoring of different concentration levels.

[0032] See Figure 5The switching valve 3 adopts a multi-channel rotary valve structure, supporting the switching of up to 8 sampling channels with a switching time of less than 5 seconds. The switching valve 3 includes a rotary valve core, a drive system, a control unit, and a position feedback device. The rotary valve core is made of precision-machined stainless steel with a chrome-plated surface to ensure good sealing and corrosion resistance. The drive system uses a stepper motor (model 57HS22-4004S4) with a step angle of 1.8 degrees and a positioning accuracy of ±0.05 degrees. The motor is connected to the valve core via a reducer with a reduction ratio of 10:1 and an output torque of 5 N·m, ensuring reliable rotation of the valve core under high-pressure conditions. The control unit uses a 32-bit ARM microprocessor (model STM32F407VGT6) with a main frequency of 168 MHz, and includes a built-in floating-point unit and a real-time clock module. The control unit receives commands from the host computer and controls the rotation angle and speed of the stepper motor to achieve precise switching between different sampling channels. The position feedback device uses an absolute encoder, model ROD426-2500, with a resolution of 2500 lines. It connects to the valve core via magnetic coupling, providing real-time feedback of the valve core's absolute position information to ensure the accuracy and repeatability of the switching position. Switching valve 3 is equipped with a dedicated cleaning system, including a nitrogen cleaning circuit and a vacuum extraction circuit. The nitrogen cleaning circuit includes a pressure regulating valve, a flow meter, and a solenoid valve. The nitrogen purity is 99.999%, and the cleaning pressure is adjustable from 0.05 to 0.2 MPa. The vacuum extraction circuit is equipped with a vacuum pump, a vacuum gauge, and control valves. The vacuum pump uses a rotary vane design, with a pumping rate of 20 liters per minute and an ultimate vacuum of -0.09 MPa. The specific timing of the cleaning procedure is as follows: At time T0, the control unit sends a shutdown command, and the solenoid valve of the current sampling channel closes; at T0+2 seconds, the vacuum pump starts, and the sampling channel is subjected to negative pressure extraction through the vacuum extraction circuit for 12 seconds to completely remove residual sample gas; at T0+14 seconds, the vacuum extraction stops, and the nitrogen positive pressure cleaning system starts, with a cleaning pressure of 0.1 MPa and a cleaning time of 18 seconds to completely replace the residual gas in the pipeline; at T0+32 seconds, the nitrogen cleaning stops, and the control unit sends a motor rotation command; at T0+37 seconds, the stepper motor drives the valve core to rotate to the target position, and the encoder feeds back a position signal to confirm that it is in place; at T0+42 seconds, the solenoid valve of the new channel opens, and the sampling operation of the new channel begins. The entire switching cleaning process takes a total of 42 seconds. Through the dual processing of vacuum extraction and nitrogen positive pressure cleaning, cross-contamination between channels is effectively prevented, ensuring the independence and accuracy of data from different sampling points.

[0033] Furthermore, the sample gas pretreatment device 4 adopts a five-stage series processing structure, with each stage having a clearly defined function and high processing efficiency. The first-stage coarse filter uses a sintered stainless steel filter element with a filtration accuracy of 50 microns, effectively removing large particulate impurities from the sample gas. The second-stage temperature-controlled cooler uses semiconductor refrigeration technology with a cooling power of 200 watts, rapidly reducing the sample gas temperature from 200 degrees Celsius to below 40 degrees Celsius. The third-stage condenser dehumidifier uses compressor refrigeration to achieve deep dehumidification of the sample gas. The refrigeration system includes a compressor, condenser, evaporator, and expansion valve, using environmentally friendly R134a refrigerant. The evaporator temperature is controlled at 5 degrees Celsius, reducing the relative humidity of the sample gas to below 10%. Condensate is discharged through an automatic drain to prevent water accumulation from affecting the system. The fourth-stage fine filter uses a PTFE membrane filter with a filtration accuracy of 0.1 microns, effectively removing oil mist and fine particles from the sample gas. The fifth-stage pressure and flow stabilizer stabilizes the sample gas pressure at 0.05 MPa and controls the flow fluctuation within 5% through a pressure regulating valve and a buffer tank, providing stable sample gas conditions for downstream analytical equipment.

[0034] The gas analyzer unit 5 is equipped with a gas chromatograph and flame ionization detector (GC-FID). The chromatographic column is a capillary column with an inner diameter of 0.25 mm and a length of 30 m. The stationary phase is dimethylpolysiloxane. The carrier gas is high-purity helium with a purity of 99.999% and a flow rate of 1 mL / min. The injector temperature is set to 250°C, and the detector temperature is set to 300°C. The analyzer unit is equipped with an automated injection system, including a six-way injection valve, a quantitative loop, and a carrier gas switching system. The quantitative loop has a volume of 1 mL and an injection accuracy of 2%. The analysis program uses a programmed temperature ramp mode, starting at 50°C, holding for 2 minutes, then ramping to 250°C at a rate of 10°C / min and holding for 5 minutes. The entire analysis cycle is 27 minutes, enabling effective separation and quantitative detection of common VOC components. The calibration module includes a standard gas storage system, a gas dilution system, and an automatic switching system. The standard gas is stored in high-pressure cylinders at a concentration of 1000 ppm. Calibration gases of different concentration gradients can be obtained through multi-stage dilution. The calibration procedure is automatically executed every 24 hours, including zero-point calibration and span calibration, to ensure the accuracy and traceability of analytical results.

[0035] The data acquisition and communication module 6 utilizes an industrial-grade embedded computer equipped with an ARM Cortex-A9 quad-core processor with a 1GHz clock speed, 2GB of memory, and 32GB of storage. Running a Linux operating system, the module offers excellent stability and real-time performance. Data acquisition is achieved through a multi-channel analog-to-digital converter with a 16-bit conversion accuracy and a 1kHz sampling frequency. The module can simultaneously acquire 32 channels of analog signals and 16 channels of digital signals, supporting various signal types including voltage, current, RTD, and thermocouple signals. Data storage employs a cyclic storage method, capable of storing historical data for the most recent 30 days. Communication functions support multiple interfaces and protocols. Wired communication includes Ethernet, RS485, and RS232 interfaces, supporting Modbus RTU, Modbus TCP, and OPC protocols. Wireless communication includes 4G LTE and Wi-Fi interfaces, supporting HTTP, MQTT, and FTP protocols. The module can simultaneously connect to a local DCS system and a remote environmental protection platform, enabling real-time data upload and remote monitoring.

[0036] Example 1:

[0037] A petrochemical plant's catalytic cracking unit has a 3-meter diameter chimney, a flue gas temperature of 180 degrees Celsius, and VOC emission concentrations ranging from 50 to 500 mg / m³. Based on the chimney's cross-sectional area, four sampling probes are deployed in an equal-area ring configuration, positioned at distances of 0.5 meters, 1.0 meter, 1.5 meters, and 2.0 meters from the chimney center. The intelligent flow control unit is set to a sampling flow rate of 1.5 liters per minute with a switching cycle of 10 minutes. When the pollutant concentration detected in a sampling channel exceeds 200 mg / m³, the system automatically extends the sampling time of that channel to 15 minutes, while the sampling time for other channels is correspondingly shortened to 8 minutes, enabling focused monitoring of high-concentration areas. A sample gas pretreatment device reduces the flue gas temperature to 35 degrees Celsius, the relative humidity to 8%, and the particulate matter concentration to below 1 mg / m³. The gas analyzer uses a GC-FID configuration with a detection limit of 0.5 mg / m³ and a linear range of 0.5-1000 mg / m³. Monitoring results showed significant differences in pollutant concentrations at the four sampling points, with the ratio of the highest to the lowest value reaching 2.3. Using a weighted average of multi-point sampling data as the emission concentration significantly improved the representativeness and accuracy of the data compared to traditional single-point sampling.

[0038] Example 2:

[0039] The exhaust gas duct of a pharmaceutical company's fermentation workshop has a rectangular cross-section, measuring 4.5 meters × 2.0 meters. The exhaust gas temperature is 60 degrees Celsius, and the main pollutants are ethanol, acetone, and ethyl acetate. Based on the duct's longitudinal cross-section, seven sampling probes are deployed using a grid method. Due to the intermittent nature of the fermentation process, VOC emission concentrations fluctuate significantly, with peak concentrations reaching 1000 mg / m³ and trough concentrations as low as 10 mg / m³. An intelligent flow control unit dynamically adjusts the sampling flow rate based on real-time concentration feedback, automatically reducing the flow rate to 0.8 L / min during high-concentration periods and increasing it to 2.2 L / min during low-concentration periods to ensure the analytical equipment operates at its optimal state. The switching valve employs an 8-channel configuration, with each sampling channel equipped with an independent purge loop. In cases of rapid concentration changes, the system automatically extends the purge time to 30 seconds to ensure no cross-contamination between sample gases at different concentration levels.

[0040] Example 3:

[0041] A chemical industrial park has set up a centralized monitoring station to monitor the combined emissions of multiple enterprises. The main emission channel of the park has a diameter of 5 meters and is equipped with 8 sampling probes arranged in an equal-area ring pattern. Due to differences in the production processes of different enterprises, the emission concentration varies drastically in time and space, ranging from 10 to 2000 mg / m³. The system uses a three-level concentration threshold setting: 50 mg / m³, 300 mg / m³, and 800 mg / m³. On a certain day, two of the eight probes continuously detected high concentrations of emissions. The system automatically extended the sampling time of these two channels from the standard 6 minutes to 9 minutes, and adjusted the sampling time of the remaining 6 channels to 4 minutes and 30 seconds. The intelligent flow control unit automatically switches PID parameters according to the concentration changes. During the phase of a sharp increase in concentration, the system switches to the fast response parameter group, shortening the flow regulation response time from 3 minutes to 1 minute. During the phase of drastic concentration fluctuations, the system switches to the damping parameter group, effectively suppressing the oscillation phenomenon of flow control. Compared with traditional single nitrogen purging, the method of vacuum extraction plus positive pressure purging reduces the cross-contamination rate between channels from 15% to below 3%, which is particularly effective when treating high-boiling-point organic matter.

[0042] Example 4:

[0043] A pharmaceutical company's fermentation workshop employs a batch production process, resulting in distinct periodic VOC emissions. Peak emissions last for 30 minutes, reaching a concentration of 1500 mg / m³, while during intermittent periods, concentrations drop below 20 mg / m³. To address this emission pattern, the system was configured with an intermittent emission monitoring mode. During peak emissions, all sampling channels operate simultaneously, reducing sampling time to 3 minutes for rapid acquisition of high-concentration data at each location. During intermittent periods, the system switches to a regular polling mode, restoring the sampling time to 10 minutes. In the initial emission phase, the concentration rapidly rises from 20 mg / m³ to 1500 mg / m³. When the system detects a concentration change rate exceeding 100 mg / m³ / min, it immediately switches to the fast-response parameter group. In the stable phase after reaching the peak, the system switches to the steady-state parameter group. During the rapid decline phase after emissions cease, the system switches back to the fast-response parameter group. Throughout the entire process, flow control remains stable, ensuring the reliability of the analyzed data.

[0044] Exemplary methods

[0045] This invention also provides an online monitoring and control method for volatile organic compounds (VOCs) from stationary pollution sources. The method involves collecting sample gas from the pollution source through multiple sampling channels of a multi-point sampling probe. An intelligent flow control unit, linked with a switching valve, performs cyclical monitoring of each sampling channel based on a preset polling strategy. When the pollutant concentration in any sampling channel exceeds a preset threshold, the sampling time of that channel is automatically extended, while the sampling time of other channels is correspondingly shortened. Before switching sampling channels, a vacuum pump is started to extract negative pressure through a vacuum extraction circuit, followed by positive pressure purging through a nitrogen purging circuit using high-purity nitrogen. After channel switching, the sampling operation of the new channel is started after a preset delay. The collected sample gas is pre-treated using a sample gas pre-treatment device. The pre-treated sample gas is then analyzed for pollutant concentration using a gas analysis host. Pollutant concentration data is received and remotely transmitted via a data acquisition and communication module.

[0046] The online monitoring and control method for volatile organic compounds (VOCs) from stationary pollution sources provided in this application achieves effective monitoring of the entire cross-section of the pollution source emission channel through coordinated control of multi-point sampling probes. An intelligent polling strategy combined with a concentration threshold judgment mechanism ensures that the system can promptly identify and focus on high-concentration emission areas, avoiding monitoring omissions caused by flow field inhomogeneity or instantaneous fluctuations, and significantly improving the spatial representativeness and detection accuracy of emission data. This method achieves intelligent dynamic allocation of monitoring resources, automatically adjusting the sampling time ratio according to the real-time concentration level of each sampling channel. For high-concentration areas exceeding a preset threshold, the system automatically extends the sampling time to obtain more detailed concentration change information; for areas with relatively stable concentrations, the system correspondingly shortens the sampling time to avoid resource waste. This differentiated monitoring strategy significantly improves overall monitoring efficiency and equipment utilization while ensuring the monitoring quality of key areas. A dual cleaning mechanism effectively solves the problem of cross-contamination in multi-channel monitoring systems. Residual sample gas is thoroughly removed through vacuum negative pressure extraction, and then the pipeline gas is completely replaced by high-purity nitrogen positive pressure purging, ensuring the independence and authenticity of data from each sampling channel. The delayed sampling mechanism further ensures data stability after channel switching, avoiding data jumps and abnormal fluctuations common in traditional systems.

[0047] In other embodiments of this application, the control method further includes pre-setting a steady-state parameter group, a fast response parameter group, and a damping parameter group, and storing these parameter groups in a microprocessor control module; monitoring the sample gas flow rate of each sampling channel in real time using a flow sensor and calculating the concentration change rate; when the concentration change rate exceeds 20 mg / m³ / min, it is determined to be a significant change, and the system automatically switches from the steady-state parameter group to the fast response parameter group; based on the real-time concentration feedback from the data acquisition and communication module, the opening of the electric regulating valve is dynamically adjusted by the microprocessor control module; when the switching valve performs sampling channel switching, the sampling time of each sampling channel is differentiated by adjusting the flow rate.

[0048] The online monitoring and control method for volatile organic compounds (VOCs) from stationary pollution sources provided in this application effectively solves the technical challenge of significant performance differences in response under different operating conditions by pre-setting multiple sets of PID control parameters and achieving intelligent switching. The steady-state parameter set ensures the system's control stability during periods of stable concentration, the fast-response parameter set guarantees the system's rapid tracking capability during rapid concentration changes, and the damping parameter set effectively suppresses system oscillations during drastic concentration fluctuations. This adaptive parameter switching mechanism significantly improves flow control accuracy and ensures the consistency and reliability of sampling conditions under various operating conditions. An intelligent judgment mechanism based on the rate of concentration change is established, achieving automatic optimization of the control strategy by setting a change rate threshold of 20 mg / m³ / min. When the system detects a significant change in pollutant concentration, it can complete parameter switching within seconds, ensuring the control system is always in optimal operating condition. This rapid response capability is particularly suitable for industrial pollution source monitoring scenarios with frequent changes in production processes and unstable emission states, effectively avoiding control failures or response lags caused by improper parameter settings in traditional systems. Through real-time flow monitoring and dynamic valve adjustment, precise control of the sampling flow rate and intelligent allocation of sampling time for each channel are achieved. The microprocessor control module dynamically adjusts the opening of the electric regulating valve based on real-time concentration feedback information to ensure that the optimal sampling flow rate is maintained at different concentration levels. Combined with the coordinated control of the switching valve, the system can allocate sampling time according to the importance and concentration level differences of each channel, maximizing overall monitoring efficiency while ensuring the monitoring quality of key areas.

[0049] In other embodiments of this application, the control method further includes setting a primary concentration threshold and a secondary concentration threshold and setting a fixed polling period; allocating equal sampling time to each sampling channel under standard conditions; monitoring the pollutant concentration in each sampling channel in real time and dynamically optimizing and adjusting the sampling time according to the preset primary and secondary concentration thresholds; when the concentration in a sampling channel exceeds the primary concentration threshold, extending the sampling time of that channel by a first duration and correspondingly shortening the sampling time of other channels; when the concentration in a sampling channel reaches the secondary concentration threshold, extending the sampling time of that channel by a second duration and correspondingly adjusting the sampling time of other channels. Wherein, the primary concentration threshold is higher than the secondary concentration threshold, and the first duration is greater than the second duration.

[0050] For example, the primary concentration threshold is set to 500 mg / m³, the secondary concentration threshold is set to 200 mg / m³, the fixed polling period is set to 40 minutes, and the standard sampling time is 10 minutes. The first duration is set to 5 minutes, meaning that when the concentration in a sampling channel exceeds the primary concentration threshold, the sampling time for that channel is extended to 15 minutes, and the sampling times for the other three channels are adjusted accordingly to 8 minutes and 20 seconds. The second duration is set to 2 minutes, meaning that when the concentration in a sampling channel exceeds the secondary concentration threshold but does not reach the primary concentration threshold, the sampling time for that channel is extended to 12 minutes, and the sampling times for the other channels are adjusted accordingly to 9 minutes and 20 seconds.

[0051] The online monitoring and control method for volatile organic compounds (VOCs) from stationary pollution sources provided in this application establishes a graded monitoring mechanism based on dual-threshold judgment, which can automatically adjust the monitoring intensity according to different pollutant concentration levels. By setting reasonable primary and secondary concentration thresholds, the system can accurately identify different levels of pollution emissions and adjust the allocation of monitoring resources accordingly. The graded monitoring strategy ensures focused attention on high-risk emission areas while avoiding over-monitoring of low-concentration areas, achieving an optimal balance between monitoring accuracy and efficiency. By setting different duration extension parameters, a gradient allocation of sampling time is achieved. When extremely high concentration emissions are detected, the system significantly extends the monitoring time of key channels through the first duration parameter to ensure sufficient high-concentration data samples are obtained. When moderate concentration emissions are detected, the system moderately extends the monitoring time through the second duration parameter to maintain overall monitoring efficiency while ensuring data quality. This differentiated time allocation mechanism effectively improves the utilization efficiency of monitoring resources.

[0052] It will be apparent to those skilled in the art that the present invention is not limited to the details of the exemplary embodiments described above, and that the invention can be implemented in other specific forms without departing from its spirit or essential characteristics. Therefore, the embodiments should be considered in all respects as exemplary and non-limiting, and the scope of the invention is defined by the appended claims rather than the foregoing description. Thus, all variations falling within the meaning and scope of equivalents of the claims are intended to be included within the present invention. No reference numerals in the claims should be construed as limiting the scope of the claims.

Claims

1. An online monitoring system for volatile organic compounds from stationary pollution sources, characterized in that, include: Multi-point sampling probe (1), intelligent flow control unit (2), switching valve (3), sample gas pretreatment device (4), gas analysis host (5), and data acquisition and communication module (6); Each sampling probe of the multi-point sampling probe (1) is connected to the intelligent flow control unit (2) through a sampling channel. The output end of the intelligent flow control unit (2) is connected to the input end of the switching valve (3). The output end of the switching valve (3) is connected to the sample gas pretreatment device (4). The sample gas pretreatment device (4) is connected to the gas analysis host (5). The data acquisition and communication module (6) is connected to the gas analysis host (5). The switching valve (3) is equipped with a cleaning module, which includes a nitrogen cleaning circuit and a vacuum extraction circuit. Before the channel switching is performed, the vacuum pump is started to extract the sampling channel through the vacuum extraction circuit. Then, high-purity nitrogen is introduced and positive pressure cleaning is performed through the nitrogen cleaning circuit. After the channel switching is completed, the sampling operation of the new channel is started after a preset time. The multi-point sampling probe (1) is used to collect sample gas in the sampling channel. The intelligent flow control unit (2) is linked with the switching valve (3) to perform cyclic detection on each sampling channel based on preset polling and set concentration threshold. When the pollutant concentration of the sampling channel is detected to exceed the preset threshold, the switching valve (3) is controlled to automatically extend the sampling time of the sampling channel and shorten the sampling time of other sampling channels accordingly. The sample gas pretreatment device (4) is used to pretreatment the sample gas output by the intelligent flow control unit (2). The gas analysis host (5) is used to receive the sample gas processed by the sample gas pretreatment device (4) and perform pollutant concentration detection. The data acquisition and communication module (6) receives the pollutant concentration data output by the gas analysis host (5) and performs remote transmission. The intelligent flow control unit (2) includes multiple independent flow control loops, which are connected one-to-one with each of the sampling probes. Each flow control loop is equipped with a flow sensor, an electric regulating valve, and a microprocessor control module. The flow sensor is used to monitor the sample gas flow rate of each sampling channel in real time and provide flow feedback signal to the intelligent flow control unit (2); the microprocessor control module changes the sampling flow rate of the sampling channel by dynamically adjusting the electric regulating valve based on the real-time concentration feedback of the data acquisition and communication module (6); The microprocessor control module includes an incremental PID control algorithm processor, a parameter memory, and a concentration change rate detector; The preset control parameters in the parameter memory include a steady-state parameter group, a fast-response parameter group, and a damping parameter group. The steady-state parameter group is suitable for operating conditions with gradual concentration changes, the fast-response parameter group is suitable for operating conditions with rapid concentration changes, and the damping parameter group is suitable for operating conditions with drastic concentration fluctuations. The incremental PID control algorithm processor calculates the control deviation based on the real-time concentration feedback signal and the preset target value, generates flow regulation commands through proportional, integral, and derivative control algorithms, and outputs the regulation commands to the electric regulating valves of each flow control loop. The concentration change rate detector is used to continuously monitor the pollutant concentration data of each sampling channel through a sliding window algorithm, calculate the concentration change rate between continuous sampling points, and compare the calculation results with a preset change rate threshold. When the concentration change rate exceeds 20 mg / m³ / min, a parameter switching command is sent to the incremental PID control algorithm processor. The microprocessor control module also includes a flow rate adjuster, which is connected to the electric regulating valve and controls the sampling flow rate of each sampling channel by adjusting the opening of the electric regulating valve.

2. The online monitoring system for volatile organic compounds from stationary pollution sources according to claim 1, characterized in that, Each sampling probe of the multi-point sampling probe (1) includes a probe body, a multi-hole sampling head disposed at the front end of the probe body, a heat tracing cable laid along the outer wall of the probe body, and a backflush air passage connected to the internal sampling channel of the probe body. The heating cable heats the probe body and the multi-hole sampling head; The backflush air path is connected to a high-pressure air source via a solenoid valve, and periodically blows air from the end of the multi-hole sampling head toward the sampling port. The backflush airflow path is opposite to the sampling direction.

3. The online monitoring system for volatile organic compounds from stationary pollution sources according to claim 1, characterized in that, The multi-point sampling probe (1) is deployed differently according to the airflow velocity distribution field and pollutant concentration distribution field inside the sampling channel. When the cross-section of the sampling channel perpendicular to the airflow direction is circular, an equal-area ring distribution method is adopted, which divides the cross-section of the sampling channel into several equal-area rings according to the radial distance, and a sampling probe is set at the center of each ring. When the longitudinal section of the sampling channel perpendicular to the airflow direction is rectangular, an equal-area grid layout method is adopted to divide the longitudinal section of the sampling channel into several equal-area rectangular grids, and a sampling probe is set at the geometric center of each grid. Each sampling probe is connected to the sampling channel corresponding to the intelligent flow control unit (2) through a heated sampling pipeline, and the insertion depth of each sampling probe reaches 2 / 3 of the equivalent diameter of the sampling channel.

4. The online monitoring system for volatile organic compounds from stationary pollution sources according to claim 1, characterized in that, The switching valve (3) adopts a multi-channel rotary valve structure. The switching valve (3) is provided with an air inlet channel and an air outlet channel corresponding to the number of multi-point sampling probes (1). The air inlet channel and the air outlet channel are connected sequentially by rotating the valve core. The intelligent flow control unit (2) works in conjunction with the switching valve (3), wherein the intelligent flow control unit (2) controls the flow stability of each sampling channel, and the switching valve (3) performs time-series switching of the sampling channels through multi-channel rotation.

5. The online monitoring system for volatile organic compounds from stationary pollution sources according to claim 1, characterized in that, The sample gas pretreatment device (4) includes a coarse filtration unit, a condensation and dehumidification unit and a pressure and flow stabilization unit in sequence along the sample gas flow direction. The inlet of the coarse filtration unit is connected to the outlet of the switching valve, the outlet of the pressure and flow stabilization unit is connected to the sample inlet of the gas analyzer, and the condensation and dehumidification unit is located between the coarse filtration unit and the pressure and flow stabilization unit. The coarse filtration unit is used for primary filtration of the sample gas. The condensation and dehumidification unit is equipped with a temperature-controlled cooler and a condensation separator. The temperature-controlled cooler is used to reduce the temperature of the sample gas from the switching valve, and the condensation separator is used to condense and separate water vapor. The pressure and flow stabilization unit includes a pressure regulating valve and a buffer tank. The pressure regulating valve is used to regulate the pressure value of the sample gas after coarse filtration and dehumidification treatment, and the buffer tank is used to control the flow fluctuation within a set range.

6. A method for online monitoring and control of volatile organic compounds (VOCs) from stationary pollution sources, applied to the online monitoring system for VOCs from stationary pollution sources as described in any one of claims 1 to 5, wherein the system comprises a multi-point sampling probe (1), an intelligent flow control unit (2), a switching valve (3), a sample gas pretreatment device (4), a gas analysis host (5), and a data acquisition and communication module (6), characterized in that, The method includes: Pollution source gas samples are collected through multiple sampling channels of the multi-point sampling probe (1); The intelligent flow control unit (2) is linked with the switching valve (3) to perform cyclic detection on each sampling channel based on a preset polling strategy. When the pollutant concentration of any sampling channel exceeds the preset threshold, the sampling time of the sampling channel is automatically extended and the sampling time of other sampling channels is shortened accordingly. Before switching the sampling channel, the vacuum pump is started to extract the sampling channel under negative pressure through the vacuum extraction circuit, and then high-purity nitrogen is introduced to purge under positive pressure through the nitrogen purging circuit. After the channel switching is completed, the sampling operation of the new channel is started after a preset time. The collected sample gas is pretreated by the sample gas pretreatment device (4); The pretreated sample gas is tested for pollutant concentration using a gas analysis unit (5); The data acquisition and communication module (6) receives pollutant concentration data and transmits it remotely.

7. The method for online monitoring and control of volatile organic compounds from stationary pollution sources according to claim 6, characterized in that, The intelligent flow control unit (2) includes multiple independent flow control loops, each of which is connected to a sampling probe of the multi-point sampling probe (1). Each flow control loop is equipped with a flow sensor, an electric regulating valve, and a microprocessor control module. The method further includes: A set of steady-state parameters, a set of fast-response parameters, and a set of damping parameters are preset and stored in the microprocessor control module. The flow rate of the sample gas in each sampling channel is monitored in real time by the flow sensor, and the concentration change rate is calculated. When the concentration change rate exceeds 20 mg / m³ / min, it is determined to be a significant change, and the system automatically switches from the steady-state parameter group to the fast response parameter group. Based on the real-time concentration feedback from the data acquisition and communication module, the opening of the electric regulating valve is dynamically adjusted by the microprocessor control module. When the switching valve performs sampling channel switching, the sampling time of each sampling channel is differentiated by adjusting the flow rate.

8. The method for online monitoring and control of volatile organic compounds from stationary pollution sources according to claim 7, characterized in that, Set a primary concentration threshold and a secondary concentration threshold, and set a fixed polling period. Under standard conditions, allocate equal sampling time to each sampling channel. The concentration of pollutants in each sampling channel is monitored in real time, and the sampling time is dynamically optimized and adjusted according to the preset primary concentration threshold and the secondary concentration threshold. When the concentration in the sampling channel exceeds the first-level concentration threshold, the sampling time of the sampling channel is extended by the first duration, and the sampling time of other channels is shortened accordingly. When the concentration in the sampling channel reaches the secondary concentration threshold, the sampling time of the sampling channel is extended according to the second duration, and the sampling time of other channels is adjusted accordingly. Wherein, the first-level concentration threshold is higher than the second-level concentration threshold, and the first duration is greater than the second duration.

Images