Study On The Key Technologies Of Particulate Matter Continuous Ultra-low Emission Monitoring System For Coal-fired Power Plants

With the increasingly stricter environmental protection policies in China,the Ministry of Environmental Protection and the National Development and Reform Commission jointly proposed that all coal-fired power plants with ultra-low emission reform conditions in the country strive to achieve ultra-low emissions by 2020.Therefore,real-time accurate monitoring of flue gas emissions from coal-fired power plants is bound to become the main means to assess whether flue gas emissions are up to standard.For the ultra-low emission reform of coal-fired power plants,the flue gas has the characteristics of high temperature,high humidity and low concentration of particulate matter.In order to solve the problem,the existing conventional detection technology can’t achieve long-term continuous online precision of the concentration of particulate matter in the flue gas under ultra-low emission environment.On the basis of the national key R&D plan “Ultra-low emission monitoring instrument for coal-fired power plants”(2016YFF0102800),based on the analysis and summary of the advantages and disadvantages of particulate matter concentration detection technology,this paper has carried out in-depth research on real-time continuous on-line detection technology of ultra-low emission particulate matter mass concentration in coal-fired power plants,and an overall monitoring plan is developed.Firstly,based on the basic theories such as Mie scattering theory and β-ray absorption law,the principles of laser scattering method and β-ray absorption particle mass concentration detection technology are analyzed in detail,and the mass concentration inversion model of non-spherical particles based on optical equivalent diameter is established.According to the correlation between the two detection techniques,a new particle concentration detection technology based on laser scattering and β-ray absorption fusion detection method is proposed,which is to establish an algorithm based on the fusion of laser scattering and β-ray absorption detection data to improve the accuracy of on-line monitoring of particulate matter concentration,overcomes the technical difficulties of automatic calibration of on-line monitoring of particulate matter,and provide a new method and idea for on-line monitoring of ultra-low emission particulate matter in coal-fired power plants.Secondly,in order to further improve the measurement accuracy of the β-ray absorption detection unit,theoretical and experimental analysis methods are used.Based on the analysis of the influence of high temperature and high humidity flue gas and membrane deformation on the measurement accuracy,an additive dynamic heating device is proposed.And the method of calculating the formula correction compensates the instrument.Studies have shown that the condensation of liquid water and water vapor in the flue gas and the deformation of the membrane have a great influence on the measurement results of the instrument,while the temperature of the flue gas has less influence on the measurement results and the compensated instrument has a higher measurement accuracy than before.Then,the optical detection unit,β-ray detection mechanism,A/D conversion unit,signal conditioning unit,power supply and other hardware circuits of the system were designed,and the selection of the key components of the detection unit and the flue gas parameter monitoring sensor was completed.In addition,the main parameters of the data acquisition instrument,the CPU core board,the communication module and other hardware circuits and software are designed in accordance with the requirements of the relevant national environmental monitoring standards for the function of the data acquisition instrument in the continuous monitoring system of flue gas emission.Finally,the accuracy and adaptability of the system prototype are verified by laboratory and field experiments.The results show that the measurement accuracy of the prototype of the particulate matter monitoring system is less than 10%,which meets the requirement of the measurement accuracy of the particulate matter concentration of the project,and preliminarily verifies the adaptability of the system.