Study On Quantitative Characterization And Light Radiometric Properties Of White Plume From Coal-Fired Flue Gas

Coal-fired flue gas becomes saturated wet flue gas at about 50℃ after wet desulfurization process,then it is condensed into liquid droplets by the cooling effect of air after the emission from the chimney.The scattering effect of these droplets weakens the transmission of visible light,and then forms the white plume.White plume can cause a series of problems,such as visual pollution,"chimney rain" and water waste.Consequently,some regions have introduced quantitative wet flue gas emission standards.However,the description methods for white plume mainly rely on subjective experience at present,and there is a lack of quantitative characterisation of the visual obscuration properties of white plumes.In addition,the formation process of white plume is mainly explained by the Temperature-Humidity diagram of saturated air,while the essence of the white plume formation is the scattering effect on visible light,which has not been studied in depth.Therefore,this paper used the method of combining experiment and simulation to establish the quantitative characterization index of white plume,and investigated the characteristics and radiation properties of droplet population inside the white plume.The main research elements of this paper were as follows:(1)The formation mechanism and the elimination technique of white plume were first analyzed by saturated air Temperature-Humidity diagram.The results showed that the supersaturation degree of the wet flue gas could reflect the intensity of the white plume during its diffusion process.(2)Through the Fluent numerical simulation method,the influence of environmental and flue gas conditions on the diffusion characteristics of saturated wet flue gas was investigated in this paper,taking the area of the supersaturated zone and the diffusion distance of the supersaturated flue gas as quantitative indicators.The results showed that the decrease of air temperature,the increase of relative humidity of air,the increase of exhaust velocity and the increase of initial flue gas temperature could enhance the supersaturation degree during the diffusion of saturated wet flue gas,promoting the diffusion degree of saturated wet flue gas and the formation of white plume at the same time.(3)The experimental system of white plume generation and dispersion had been set up and quantitative characterisation of white plume had been carried out.The results showed that the maximum shading degree decreased from 23.5%to 4.2%with the increase of ambient temperature from 14.5℃ to 27.6℃ when the other experimental parameters unchanged.The maximum shading degree increased from 15.2%to 28.7%with the increase of ambient relative humidity from 37.3%to 76.5%.With the exhaust velocity increases from 1 m/s to 5 m/s,the maximum shading degree increased from 9.1%to 23.5%.The maximum shading degree increased from 17.3%to 58.9%when the initial flue gas temperature increased from 40℃ to 60℃.The experimental results showed that the maximum shading degree of the white plume decreased with increasing ambient temperature and increased with increasing ambient relative humidity,exhaust velocity and initial temperature of flue gas;the experimental results of different seasonal conditions showed that the maximum shading degree of white plume was in accordance with the rule of winter>spring≈autumn>summer,which was consistent with the actual situation.It could be found that the variation of the maximum shading degree of white plume with the environmental and flue gas conditions was consistent with the variation of the saturated wet flue gas diffusion degree,which proved the scientificity of the characterization index.(4)The calculation method of droplet number density within the white plume was proposed based on the white plume formation process.The influence of environmental and flue gas conditions on the particle system characteristics and radiation properties of white plume droplet population were investigated by Mie theory and experimental data of droplet distribution.The results showed that the attenuation of white plume on visible light was mainly scattered,and the attenuation effect was affected by the scattering ability of individual droplets and the density of the particle system together.Besides,the attenuation coefficient of white plume was consistent with the variation of its maximum shading degree.This paper obtained quantitative characterization index for white plume,which was maximum shading degree,and revealed the formation mechanism of white plume from the perspective of droplet light scattering,which is important to promote the development of white plume elimination technology.