The working principle of CEMS (Continuous Emission Monitoring System) is based on physical and chemical sensor technology, as well as data acquisition and transmission technology. Through sampling, preprocessing, analysis, data acquisition and transmission, it achieves continuous monitoring of flue gas emissions. The following is a detailed introduction to its working principle:
1、 Sampling and preprocessing
Sampling: The CEMS system extracts flue gas samples from the flue through sampling probes. Sampling probes are usually equipped with ceramic or stainless steel filters to filter out dust in flue gas, preventing it from entering subsequent equipment and causing blockage and damage.
Preprocessing: The extracted flue gas samples need to undergo pretreatment, including heating, transportation, filtration, and condensation steps. Heating and conveying are used to prevent condensation of water vapor in flue gas and avoid interference with subsequent analysis; Filtering is to further remove particulate matter from the flue gas; Condensation is used to lower the temperature of the flue gas for subsequent analysis.
2、 Gas analysis
The preprocessed flue gas sample is sent to a gas analyzer for various component analyses, such as SO ₂, NOx, O ₂, etc. Gas analyzers use various technologies, including but not limited to:
Optical technology: such as ultraviolet spectroscopy, infrared spectroscopy, and fluorescence spectroscopy. These technologies utilize the absorption characteristics of different gases towards specific wavelengths of light, and determine the concentration of the gas by measuring the degree of light absorption.
Electrochemical technology: measuring the concentration of a gas by utilizing the changes in current or potential generated by chemical reactions that occur on an electrode.
3、 Particle monitoring
The CEMS system is also equipped with a particulate matter monitor to monitor the concentration and total emissions of smoke and dust. The particulate matter monitoring instrument adopts various principles, such as laser forward scattering, light scattering method, etc., to obtain the mass concentration of particulate matter by measuring the intensity of scattered light energy.
4、 Smoke parameter monitoring
The CEMS system also measures other parameters of flue gas, such as flow rate, temperature, pressure, humidity, etc. These parameters are crucial for the accumulation of total emissions and the conversion of related concentrations. For example, measuring the velocity of flue gas can help calculate the total emissions of flue gas; The measurement of flue gas temperature and pressure can be used to correct the readings of gas analyzers, ensuring the accuracy of measurement results.
5、 Data collection and transmission
Data collection: The CEMS system collects various parameters in real-time through a data collector, including gas concentration, particulate matter concentration, flue gas parameters, etc.
Data processing: The data collector processes the collected data to generate dry basis, wet basis, and converted concentrations corresponding to each concentration value, as well as cumulative emissions for days, months, and years.
Data transmission: The processed data is transmitted in real-time to the environmental protection department and relevant monitoring centers through communication devices such as environmental data acquisition equipment or VPN. In this way, the environmental protection department can timely understand the emission situation of enterprises and take corresponding regulatory measures.