The Continuous Emissions Monitoring System (CEMS) is a system used for real-time monitoring of harmful gas emissions from industrial boilers, exhaust gases, and other sources. Its main purpose is to ensure that emissions comply with environmental protection standards, and to monitor, record, and report pollutants. Common monitoring techniques include the following:
1. Chemical absorption method (chemical analysis method)
Principle: Absorb or react pollutants in flue gas through chemical reactions to produce detectable changes. Usually, absorption tubes or reaction tanks are used to measure changes in gas concentration.
Applicable gases: sulfur dioxide (SO ₂), nitrogen oxides (NO ₓ), carbon monoxide (CO), etc.
2. Infrared spectroscopy (FTIR)
Principle: Measure the absorption of infrared light of different wavelengths by gases through infrared spectroscopy technology. Each gas absorbs specific infrared light within a specific wavelength range, and the instrument identifies and determines the type and concentration of the gas by analyzing these absorption peaks.
Applicable gases: carbon dioxide (CO ₂), sulfur dioxide (SO ₂), carbon monoxide (CO), nitrogen oxides (NO ₓ), etc.
3. Chemiluminescence method
Principle: When a gas reacts with a chemical reagent, it releases light energy, which is measured by a photodetector to determine the concentration of the gas.
Applicable gases: nitrogen oxides (NO ₓ), especially NO and NO ₂.
4. Ultraviolet absorption method
Principle: The ultraviolet spectrometer determines the concentration of a gas by measuring its absorption of ultraviolet light. This method is highly suitable for determining pollutants such as sulfides and nitrogen oxides.
Applicable gases: sulfur dioxide (SO ₂), nitrogen oxides (NO ₓ).
5. Electrochemical method
Principle: Gas undergoes an oxidation-reduction reaction through an electrochemical sensor, and the current generated by the reaction is proportional to the gas concentration. This method has high sensitivity and a simple device structure, making it suitable for small-scale monitoring.
Applicable gases: nitrogen dioxide (NO ₂), carbon monoxide (CO), etc.
6. Microwave oven technology (photoacoustic spectroscopy)
Principle: When a gas absorbs microwave or spectral energy at a specific frequency, it undergoes physical changes (such as expansion) that affect the propagation of sound waves. By analyzing these changes, the gas concentration can be determined.
Applicable gases: commonly used for measuring trace gases such as nitrogen dioxide (NO ₂) and carbon monoxide (CO).
7. Laser Spectroscopy (DOAS)
Principle: Analyze the absorption characteristics of gas molecules towards specific wavelengths of light. Laser spectroscopy has high accuracy and selectivity, making it suitable for monitoring low concentration gases.
Applicable gases: sulfur dioxide (SO ₂), nitrogen oxides (NO ₓ), ozone (O3), etc.
Summary:
There are various monitoring technologies for the continuous emission online monitoring system of flue gas. Choosing the appropriate technology should consider factors such as gas type, concentration range, accuracy requirements, and operating environment. Each technology has its own advantages and limitations, and based on specific needs, a combination of multiple technologies is usually used to ensure the accuracy and reliability of monitoring.