Study On The Atomization Characteristics Of Desulfurization Wastewater And Evaporation Release Law Of HCl

Zero emission of desulfurization wastewater is one of the tasks of flue gas management in coal-fired power plants.Direct evaporation using flue gas is a process with the lowest investment and energy consumption in the desulfurization wastewater treatment.In this process,the desulfurization wastewater is atomized into liquid droplets and sprayed into the tail flue of the boiler.The desulfurization wastewater is evaporated by the flue gas.After evaporation,residual crystal particles are captured by the dust collector and released with the ash.However,droplet evaporation is affected by multiple factors such as the flue gas temperature,the moisture content of the flue gas,the size of the droplet and the residence time of the droplet in the tail flue.If the droplets can not completely evaporate,the downstream equipment such as electrostatic precipitator will be corroded.In addition,accompanying with the evaporation of the desulfurization wastewater,part of aqueous chloride ions will hydrolysis and generate hydrogen chloride released into the flue gas,and the HCl will reenter into the desulfurization wastewater.If the proportion of the release of hydrogen chloride is too high,the amount of desulfurization waste water treatment will be significantly increased.In serious cases,the process can is out of run.Therefore,it is of great significance to study the atomization characteristics of desulfurization wastewater and the release law of hydrogen chloride in the evaporation process.In this paper,the spraying characteristics of the atomizing nozzle were studied using a phase Doppler particle analyzer(PDPA).The atomizing gas flow,liquid flow and gas-liquid ratio were studied to analyze the spray cone angle,droplet size and droplet velocity.The experimental results show that:(1)The atomized cone Angle increases with the increase of gas flow and decreases with the increase of liquid flow;(2)The Sauter mean diameter of the droplet increases with the increase of axial distance and radial distance,and decreases with the increase of the nozzle gas-liquid ratio,the Sauter mean diameter of droplet on the central axis is less than 30?m,and the Sauter mean diameter of droplet at the maximum radial distance is less than 120?m;(3)Axial droplet velocity decreases with the increase of radial distance,and increase with the increase of the gas-liquid ratio.The experimental system with the two-fluid nozzle was established for the evaporation of desulfurization wastewater.Taking into account the fact that the concentration of calcium ions and magnesium ions in desulfurization wastewater is comparable,the simulated wastewater was prepared with the same concentration of CaCl2 and MgCl2.The experimental study of HCl release during the evaporation process of desulfurization wastewater at moderate and low temperatures was conducted.The experimental results show that:(1)When temperature rises from 200?to 340?,the concentration of HCl increases from 4.82 ppm to65.65 ppm,and the evaporation release rate of Cl~-increases from 1.59%to 17.29%.(2)When the concentration of Cl~-in the wastewater decreases from 15 g/L to 10g/L,the concentration of HCl decreases significantly,the corresponding concentration of HCl at 200?is reduced to 2.88ppm,and the release rate is reduced to 1.42%;the corresponding concentration at 340?is reduced to 14.19ppm,and the release rate is reduced to 5.71%;(3)When the wastewater flow rate is increased from 12 ml/min to 24 ml/min,the hydrogen concentration in the outlet flue gas increases from 39.29 ppm to 40.67 ppm and then decreased to 30.95 ppm;but the release rate monotonously decreases from 14.69%to 5.79%.A comparative experiment was conducted using waste water formulated with calcium chloride alone.When the inlet flue gas temperature increases from 200°C to 300°C,the outlet concentration of HCl increases from3.13 ppm to 5.70 ppm,which is much lower than that of waste water with the same concentration of calcium chloride and magnesium chloride.This results show that the HCl from the actual desulfurization wastewater is mainly derived from the magnesium chloride in the wastewater.On the basis of experiments research,based on the Euler-Lagrange method,numerical studies on a biomass power plant was carried out.The effects of the temperature,velocity and moisture content of flue gas,and atomization droplet size on the evaporation process of the desulfurization wastewater were investigated.The numerical results show that:(1)The wastewater evaporation is accelerated by the increasing gas temperature and velocity,the decreasing droplet size and the gaseous moisture content.(2)The temperature of the flue gas and the droplet size of the wastewater have a great influence on the complete evaporation time,while the velocity of flue gas has a limited effect on the total evaporation time of wastewater droplet.