Research On Measurement Method Of Particle Concentration And Development Of Measuring Device

A large amount of particulate matter is generated during the combustion process,which is the main cause of atmospheric pollution.Realizing accurate monitoring of particulate matter emission concentration is of great significance to environmental protection.In order to promote the clean use of fossil energy and improve the quality of the atmospheric environment,the government requires the full implementation of ultra-low emissions and energy saving transformation of coal-fired units,strict implementation of energy efficiency and environmental protection standards,and enhanced monitoring of pollutant emissions from coal-fired power plants.Higher requirements.In coal-fired power plants,the particulate matter concentration emission value is an important monitoring parameter of the Continuous Emission Monitoring System(CEMS),which is of great significance for the statistics of total pollutant emissions and the monitoring of equipment operating conditions.At present,although the filter weighing method,ray absorption method,and oscillatory balance method have high measurement accuracy for the measurement of particulate matter concentration,they need to extract the flue gas and measure the particulate matter offline.The process is tedious,and the particulate matter concentration cannot be achieved Real-time monitoring.As an online measurement method,the light transmission method is often used for the measurement of high-concentration particles.The light transmission method has a small attenuation of light intensity and a low signal-to-noise measurement for low-concentration particles.As a high-precision,non-invasive,real-time online measurement method,light scattering method has been widely used in the field of particle measurement.However,when measuring the concentration of low-concentration particles,the method is susceptible to interference from external noise due to the weak scattered light intensity.In this paper,based on the light scattering technology of Mie scattering theory,the measurement and study of the particle concentration and particle size parameters of coal-fired power plants are carried out.The main work and innovations are as follows:1.Aiming at the problem that the measurement signal is easily affected by external noise when the scattered light intensity is weak,the high-frequency modulation signal is superimposed on the original signal,and the scattered light signal is digitally phase-locked and low-pass filtered,thereby effectively improving the signal-to-noise ratio of the measurement.The traditional light scattering uses a constant light intensity light source,which is susceptible to interference from external light intensity fluctuations and detector noise.This paper uses light emphasis technology and digital phase-locked-low-pass filtering technology to effectively avoid the impact of low-frequency noise on the measurement.The experiments compared the measurement results with and without the modulation signal.The experimental results show that the measured value obtained by using the light emphasis technology has a higher linearity with the dust meter measurement value.2.Combined with the light emphasis system technology,a particle concentration measurement device was developed,and its mechanical structure and light path structure were optimized.During the long-term operation of the particulate matter concentration measuring device,the laser light intensity is slowly attenuated,thereby affecting the accuracy of the particulate matter concentration measurement.To this end,a light intensity calibration light path is added to the light path structure to achieve a regular calibration of the original light intensity.In addition,in order to prevent particles from affecting the measurement,a protective air flow channel was added to the mechanical structure.Simulation and experimental results verified the feasibility of the flow channel.An online processing program for particle concentration measurement device was written using Labview software.Finally,the reliability and accuracy of the particle concentration measurement device were verified in laboratories and industrial sites.3.A simultaneous measurement method of particulate matter and gas concentration is proposed to realize the coupling of the two measuring optical paths,and a corresponding signal processing algorithm is proposed.A mathematical model of scattered light signals under wavelength modulation is established.Theoretical analysis and simulation results show that the gas concentration is directly proportional to the height of the normalized second harmonic peak,and the particle concentration is directly proportional to the first harmonic of the scattered light signal after gas absorption is deducted.A simultaneous measurement system for the concentration of particulate matter and gas was set up.The nearinfrared laser at 1392 nm was used to measure the concentration of water vapor and particulate matter produced by the combustion of mosquito coils,and the experimental verification of the accuracy of the method was completed.4.In the process of particle size measurement,the traditional measurement method based on Mie scattering theory is not applicable to the inversion of the particle size of nonspherical particles.A particle size measurement method based on optical coherence tomography is proposed.Experiments are performed on the particles in the aqueous solution on the established optical coherence tomography experimental bench,and for the problem of noisy images,the threshold denoising and binarization are used to obtain the edges of each particle.The online measurement of the particle size of non-spherical particles is realized.