At present, there are many kinds of flue gas online monitoring and measurement principles and methods. The following is an introduction to the measurement principles of several common gaseous pollutant components in China.
1 Direct extraction method + infrared absorption or ultraviolet absorption measurement
The extracted flue gas is heated and insulated through the sampling probe and heating pipeline to keep the flue gas from condensing, and then sent to the condensation drying device for dehumidification and then sent to the analysis unit or non-condensing Directly sent to the analysis unit, the analyzer analyzes the data as a dry basis value or a wet basis value. This method has a large amount of system maintenance, is easy to be blocked and easily corroded and leaks, and has a slow response time. It is not suitable for occasions with high dust concentration. At present, this measurement method is commonly used in my country.
2 Dilution pumping method + UV fluorescence method
The dilution gas is diluted and mixed with the flue gas in a certain proportion in the sampling probe, and the diluted flue gas enters the analysis system for measurement. This method has a small amount of system maintenance, and the measured value is a wet base value. This method has complex technology, slow response, high price, and stable operation. It can be adapted even in places with high dust concentrations. This measurement method is very used in the United States. universal.
3 Infrared or ultraviolet light direct measurement
A beam of infrared light or ultraviolet light is emitted inside the flue to directly illuminate the flue gas, and the characteristic absorption spectrum of sulfur dioxide is used for measurement. The method is simple, does not require heating pipelines, has a fast response time, and the measured value is a wet base value. The analysis system cannot be calibrated online, is easy to be blocked and easily polluted, has poor accuracy, and has fewer applications. It can be used in better working conditions.
In addition, the current principles of particle determination methods mainly include turbidity method, back light scattering method, ray absorption method, light scintillation method and charge method. Commonly used flow rate measurement methods mainly include pitot tube pressure difference method, heat balance method, ultrasonic method, and target flowmeter method. The temperature measurement mainly includes thermal resistance and thermocouple methods. Absolute humidity measurement mainly includes capacitance method and wet and dry oxygen method. Most oxygen measurement uses zirconia sensor and oxygen cell. Since the oxygen content in the flue gas online monitoring system is a very critical parameter, it will directly affect the converted concentration of the final pollutant, and then affect the calculation of emissions, so the oxygen content measurement should have an automatic online calibration function.
