The Plume Diffusion Measurement Test And Numerical Simulation Study Of Wet Desulfurization Tail Gas Emissions

With the increasing of China's energy demand,the installation of wet flue gas desulfurization(WFGD)systems developed rapidly and the problem of wet flue gas plumes received more and more public attentions.Since the flue gas after the WFGD is in the saturated condition,the direct discharge of wet flue gas will form wet plumes,causing environmental and visual pollution.In order to achieve ultra-low emissions in coal-fired power plant,Shanghai and many other local governments have issued the "Emission Standard for Air Pollutants from Coal-Fired Power Plants." The treatment of the wet flue gas plume has become a hot research issue.In this paper,a novel method for the measurement of wet flue gas plume was proposed,and two typical coal-fired power plants with power capacity of 200 MW and 300 MW were selected for flue gas plume field measurement testing.Furthermore,the Computational Fluid Dynamics(CFD)method was applied to establish a 3-dimensional numerical model and the diffusion of wet flue gas plume in atmosphere were simulated for two pulverized-coal fired boiler with 670 t/h and 960 t/h capacity respectively.The effect of different atmospheric conditions and operating conditions on the dilution of wet flue gas plume was obtained.Furthermore,the cause of the formation of the wet flue gas plume and diffusion mechanism was investigated by the analysis of simulation results and field testing data.When the flue gas temperature is 348K and the ambient temperature drops from 283K to 253K,the wet flue gas plume diffusion distance increases from 452.5m to 822m,with the decreasing of the ambient temperature,the length of the wet flue gas plume increased exponentially.When the operating conditions are the same and the ambient wind speed increases from 3.8m/s to 6m/s,the spread of smoke plume increases from 510m to 822m,the higher the ambient wind velocity,the farther the wet flue gas plume is drifting.When the ambient temperature is 253K and the temperature of the flue gas is reduced from 384K to 315K in a cooling mode,the diffusion distance is reduced from 822m to 542.5m,the decreasing of the flue gas temperature,the moisture vapor in the flue gas converted to the state of oversaturation and then easy to be precipitated and the length of the wet plume became shorter.In the same atmospheric environment,the flue gas temperature is 348K.When the boiler's capacity increases to 960t/h,and the flue gas flow rate is increased from lOm/s to 20m/s,the diffusion distance increases from 822m to 940m.the flow rate of flue gas increases,the moisture vapor content increases,and the wet flue gas plume becomes longer.This indicates that the load of the coal-fired unit is an important factor affecting the wet plume diffusion.At the same time,when the relative humidity of the environment is relatively high,the length of the wet plume increases exponentially,indicating that it is difficult for the moisture in the wet plume to diffuse when the humidity of atmosphere is high,and the wet plume to be difficult to be treated.Through the gas cooling method,saturated moisture in wet flue gas can be precipitated,the better effect of treatment for wet flue gas plume can be achieved.If direct flue gas heating method is applied,the temperature of the wet flue gas will be increased.During this process,the absolute moisture content of the flue gas will not change and the relative moisture content will decrease.wet flue gas can reach an unsaturated state,combine with flue gas cooling and reheating method,the better effect of treatment for wet flue gas plume can be achieved.In addition,the effect of eight different chimney configurations on the process of droplets adhering on inner wall was discussed to optimize the new design of the chimney.By comparing the effects of the adsorption of small droplets on the inner wall of chimneys of different configurations,it can be seen that increasing the vortex strength at the same flow rate of flue gas is beneficial to the adsorption of droplets.When there is no baffle on one side,the flue gas in the chimney will form two vortices and the droplets are easy to be captured on the surface.Bilateral symmetrical inlet can be without baffles.Bilateral misalignment configuration lowed position of the baffle and made it easier to form the larger vortex,resulting in the centrifugal force to make droplets more easily attached on the wall.The shrink of the chimney outlet will lead to the tearing of the liquid film by the high-speed airflow and thus the secondary carrying content of tiny droplets are increased.