The Generation And Control Mechanism Of Moist Plumes From Low Temperature Coal-fired Wet Flue Gas

At present,my country has fully implemented coal-fired power plants with ultra-low emissions.The emissions of soot particles,S02 and NOx from coal-fired power plants are below 10 mg/Nm3,35 mg/Nm3 and 50 mg/Nm3 respectively.Among them,wet desulfurization is the mainstream process of ultra-low emissions of coal-fired flue gas SO2.The flue gas after wet desulfurization is humidified and cooled to 45?55 ? and 100%relative humidity.After the flue gas is discharged,it interacts with the ambient air and is cooled by the atmosphere.Part of the water vapor is condensed into water droplets.These water droplets produce scattered reflections under the irradiation of light and the phenomenon of "white smoke" occurs.The "white smoke" phenomenon has brought about waste of resources and environmental problems,and has become the key control direction for further deep purification of flue gas.In this paper,the theory of wet air conditioning,plume up-diffusion,wet steam two-phase flow and other theories are used to make a theoretical study of the temperature and humidity changes of the plume,geometrical dimensions of the plume,the amount of condensed water in the plume,and the growth law of condensed water beads.Calculation.The change process of the water vapor content in the flue gas from the start of fuel combustion to the desulfurization is analyzed.Using the temperature and humidity chart,the changes of temperature and humidity during the process of mixing wet flue gas and air are analyzed.The condition for obtaining white smoke from evacuation of wet flue gas is whether the connection between the flue gas and the ambient air state point intersects the saturated wet air line.By fitting the humid air saturation curve to the d-T relationship,the discriminant formula for the generation of white smoke is derived.The tangent theory of white smoke is summarized and summarized,and the change rule of the maximum condensed water volume of the wet smoke plume with the ambient air temperature and humidity is solved by this theory.Using the Slawson equation,the change law of the length of the wet plume with the temperature and humidity of the environment is calculated.The calculation result shows that the length of the wet plume is between tens of meters and hundreds of meters.Use the temperature and humidity chart to analyze the mechanism of white smoke.The basis for judging whether the wet flue gas produces white smoke is whether the mixing line of the discharged flue gas and the ambient air intersects the saturated flue gas on the enthalpy humidity chart.If they intersect,white smoke occurs,and if they do not intersect,there is no white smoke.The critical condition for wet smoke to produce white smoke is that the mixed line of smoke and environment is exactly tangent to the saturated smoke line.The whitening boundary line is not uniquely determined.It changes according to different environmental conditions.Each ambient air with temperature and humidity corresponds to a whitening boundary line.The higher the ambient temperature and the smaller the moisture content of the environment,the greater and steeper the slope of the blanking boundary line.Conversely,the lower the ambient temperature and the greater the moisture content of the environment,the smaller and gentler the slope of the blanking boundary line.The control mechanism of white smoke is the process of regulating the temperature and humidity of smoke to within the whitening area.The condensation method is more suitable for cold and humid weather,and the heating method is more suitable for hot and dry weather.Taking the meteorological data of the whole year of Jinan in 2019 as an example,the working conditions required for different whitening technology routes to achieve no white smoke throughout the year are calculated.Among them,the heating method is used to achieve no white smoke throughout the year in Jinan.The flue gas needs to be heated to more than 228? in winter,the flue gas must be heated to more than 157?in spring and autumn,and the flue gas must be heated to more than 81? in summer.The condensation method is used to achieve no white smoke throughout the year in Jinan.In winter,the flue gas must be cooled to below 3?,in spring and autumn,the flue gas must be cooled to below 13?,and in summer,the flue gas must be cooled to below 24?.The condensation reheating method is used to achieve no white smoke throughout the year in Jinan.The operating parameters of the winter condensing and reheating device are:condensation temperature 20? and reheat temperature 30?.In spring and autumn,the condensation temperature is 35?,and the reheat temperature is 50?.In summer,the condensation temperature is 48?,and the reheat temperature is 60?.Finally,the simulated wet flue gas was used to conduct an experimental study on the occurrence and development of wet smoke plume.Using a laser particle size analyzer,the shading degree of the wet smoke plume,the growth rule of the droplet size,and the distribution of droplet size were measured,and the horizontal temperature,environmental moisture content,saturated flue gas temperature,and flue gas superheat were compared laterally.Effect on wet plume.Studies have shown that the shading(visibility)of wet plume plume increases first and then decreases as the plume plume height increases.The shading degree is mainly affected by the condensation strength of water vapor and the diffusion degree of smoke plume.The particle size of the wet plume is mainly concentrated in the range of 5?m?50?m,and with the increase of the smoke plume height,the droplet size undergoes rapid growth,slowly increasing and gradually decreasing until disappearing.In the cross-section of the plume,the droplet size outside the wet plume is larger than the droplet size inside the plume.The analysis shows that the lower the ambient temperature and the higher the moisture content,the greater the shading of the plume is,that is,the higher the visibility,and the droplet size within the plume will also grow to a greater level.The higher the temperature of saturated flue gas,the shade of smoke plume grows exponentially.The greater the degree of flue gas superheat,the smaller the visibility of the plume.