Research On The Effect Of Particle Characteristics On Concentration Measurement With Laser Scattering Method

In recent years,the air pollution problems of China become increasingly serious,and the dust emitted from coal-fired power plants is an important cause of air pollution,for this our country has launched more stringent standards to limit the dust emissions from coal-fired power plants and the dust emissions can not exceed 10mg/Nm~3 in the ultra-clean emission standards.Because the conventional measurement methods are difficult to accurately monitor soot concentrations at such low concentrations,it is important to make accurate measurements of the particle concentration under the new standards.with the development of optical technology,the application of optical method for dust concentration measurement has become a hot spot,but the complex particle characteristics still have a great impact on the measurement accuracy.In this paper,the light extinction method was used to do the measurement,firstly,the relational parameters such as the extinction coefficient are deduced and analyzed,and a self-designed measuring device has been built,Then,the effect of particle size and sphericity on the concentration measurement was investigated by using silica samples with different particle size distribution and shape.In this paper,a MATLAB program was developed based on light scattering theory to analyze the characteristics of the light scattering method,and the key parameters of measuring unit such as optical path,circuit and gas path in the system are determined.Then a concentration measuring device was built and calibrated with two standard particle samples.In order to investigate the effect of size distribution on the particle concentration measurement via the light extinction method,four kinds of spherical silicon dioxide particles with different particle size distributions were selected in the experiment.The experimental results showed that the larger the sample particle size was,the larger the experimental error was.As the dimensionless dimension factor?increases,the intensity of the scattered light will enhance and the scattered signal tends to move forward.When the intensity of the scattered light near zero is large enough,which will inevitably affect the collection of transmitted light.As the proportion of particle with the dimensionless size factor?>30 in the sample increases,this part of the particles will inevitably produce errors using the average algorithm,which will result in the increase of the measurement deviation.Three kinds of silicon dioxide powders of different shapes were used in the experiments to investigate the impact of sphericity on the concentration measurement.The results demonstrated that the scattering properties of the non-spherical particles are anisotropic,the difference of the scattering cross section and extinction cross section between the spherical particles and the non-spherical particles in different angles will increase with the shape of the particles deviates from the sphere.With the increase of the incident wavelength,the distribution of the scattering function tends to be gentle,the scattering deviation caused by the shape will decrease,and the scattered light is closer to the spherical particles,which will lead to the effect of the particle shape on the scattering gradually decrease.