The VOCs online monitoring system usually consists of a sampling unit, a preprocessing unit, a gas analysis unit, a data acquisition and transmission unit, an auxiliary unit, and monitoring software. Each unit works together to achieve real-time monitoring and data management of VOCs. The following is a detailed introduction to each component:
1. Sampling unit:
Sampling probe: responsible for collecting gas samples from flue gas or air, usually made of high temperature and corrosion-resistant materials such as stainless steel to ensure normal operation in harsh environments. The sampling probe has a filtering function, which can preliminarily filter the particles in the flue gas to prevent them from entering the subsequent equipment and causing blockage and damage.
Heat tracing pipeline: Due to the tendency of VOCs to condense into liquid form or adsorb on the inner wall of the pipeline at room temperature, the function of the heat tracing pipeline is to maintain the temperature of the gas, keeping it in a gaseous state for easy transmission and measurement. Heat tracing pipelines generally use heating wires or heat tracing pipes to maintain a constant temperature through a temperature control system.
2. Preprocessing unit:
Dust removal device: removes impurities such as particulate matter and dust from the gas to avoid contamination and interference with subsequent analytical instruments, which may affect the accuracy of measurement results. Common dust removal devices include filter cartridge dust collectors, cyclone dust collectors, etc.
Water removal device: The moisture in the gas can interfere with the measurement of VOCs, so it is necessary to use water removal devices such as dehumidifiers and drying tubes to remove the moisture.
Oil removal device: If the gas contains impurities such as oil stains, it also needs to be removed by an oil removal device to prevent damage to the analytical instrument caused by oil stains.
Flow calibration device: used for precise control and measurement of gas flow, ensuring stable gas flow entering the analytical instrument, and improving measurement accuracy and repeatability.
3. Gas analysis unit:
Chromatography: It is one of the commonly used analytical instruments in VOCs online monitoring equipment. It uses the difference in distribution coefficients between different substances in the stationary phase and the mobile phase to separate the components in the mixed gas and detect them through a detector. For example, gas chromatography-mass spectrometry (GC-MS) can perform qualitative and quantitative analysis of various VOCs components.
Sensors: including photoionization sensors (PID), metal oxide sensors (MOS), etc. PID sensors respond to most organic compounds and have the characteristics of fast response and high accuracy; MOS sensors have high sensitivity and selectivity towards certain specific VOCs.
4. Data collection and transmission unit:
Data collector: responsible for collecting analog or digital signals generated by analytical instruments and converting them into data formats that computers can recognize and process. The performance of data collectors directly affects the speed and accuracy of data collection.
Industrial computer or controller: As the core device for data processing, it analyzes, processes, and stores the collected data. It can run specialized monitoring software to achieve real-time display, alarm, historical data query and other functions of data, and perform statistical analysis and evaluation of data according to preset programs and algorithms.
Communication module: used to transmit monitoring data to remote monitoring centers or cloud platforms, so that users can view monitoring data anytime and anywhere through terminal devices such as mobile phones and computers. The communication module generally supports multiple communication methods such as Ethernet, GPRS, 4G/5G, etc.
5. Auxiliary unit:
Standard gas supply system: provides standard gas for analytical instruments, used for instrument calibration and performance verification. The concentration and accuracy of the standard gas directly affect the accuracy and reliability of the measurement results.
Hydrogen generator: In some analytical methods, such as hydrogen flame ionization detector (FID), hydrogen gas is required as the combustion gas, and the hydrogen generator can provide stable and pure hydrogen gas for FID.
Zero gas generator: used to generate pure zero air as the zero calibration gas for instruments, ensuring measurement accuracy.
Air compressor: provides compressed air for the blowback device, used to regularly clean dust and impurities in the sampling probe and pipeline, and maintain the normal operation of the equipment.
6. Monitoring software:
Monitoring software is an important component of the VOCs online monitoring system, responsible for analyzing, processing, and displaying the collected data. Users can view monitoring data, historical data, alarm information, etc. in real time through monitoring software, and can generate various reports and charts for data analysis and decision-making.