Study On "Zero Emission" Technology Of Desulfurization Wastewater From Coal-fired Power Plants

The desulfurization system of coal-fired power plants has low drainage volume,but the water quality is complex and difficult to deal with.Under the requirements of current environmental protection policies,power plants are required to realize zero discharge of wastewater,and the desulfurization system,as the end of the water system of power plants,makes the "zero emission" of desulfurization wastewater become the key technology to realize the "zero emission" of coal-fired power plant wastewater.In this paper,a coal-fired power plant in north China is taken as the research object.The water network model of coal power plant is established by water pinch technology.The changes of water quality and quantity of desulfurization system were studied when the water quality of power plant changed.And the whole power plant wastewater discharge to the desulfurization system,for the realization of the bypass flue evaporation process to provide a guarantee.Through experiments,the feasibility and optimum reaction condition of calcium carbide slag replacing lime in traditional double alkali process were studied,so as to improve the pretreatment process of desulfurization wastewater.The mathematical model of the bypass flue evaporation system was established by combining computational fluid dynamics and Fluent software,and the feasibility of the bypass flue evaporation process was analyzed under actual working conditions.The study shows that when the fresh water source of the power plant is changed from groundwater to sewage treatment,the concentration ratio of the circulating cooling water and the desulfurization system of the power plant is adjusted through the analysis of the whole plant water use model,and the water use process of the power plant is adjusted,so that the water inflow of the desulfurization wastewater becomes the water produced by the wastewater treatment system.The concentration of chloride ions in the water of the desulfurization system was 351 mg/L,and the concentration of chloride ions in the drainage system was 9886 mg/L.The discharge amount of wastewater in the whole plant decreased from 120 t/h to 14t/h,which reduced by 88.3%.And the desulfurization system is responsible for all the wastewater discharge.So that the total discharge of wastewater can meet the requirements of zero discharge process.By XRD quantitative analysis,it is determined that the main components of calcium carbide slag samples include Ca(OH)2,CaCO3,SiO2,Fe2O3,Fe and Mg/Al hydrotalcite impurities.Among them,Ca(OH)2 accounted for 83.14%of the total mass of the sample,and the analysis of the active components showed that calcium carbide slag could replace lime to re1ove Mg2+in the desulfurization wastewater.The optimal conditions of calcium carbide slag-sodium carbonate pretreatment for desulfurization wastewater were determined by experiments.The mixing time was 15min at room temperature and the mixing rate was 500r/min.Under this condition,when the removal rate of Mg2+reached more than 99%,the dosage of calcium carbide slag-calcium carbide was 10.5 g/L,and when the removal rate of Ca2+reached more than 99%,the dosage of sodium carbonate was 9 g/L.The average particle size of the reaction solution of calcium carbide slag treating desulfurization wastewater was 25.4?m,which was 39.3%higher than that of the solid particles formed by lime-sodium carbonate method.The settling rate of suspended solids was increased by 3 times.The results show that the treatment effect of calcium carbide slag-sodium carbonate method is equivalent to that of traditional method,and the direct treatment cost is reduced by 15.7%,and the area of clarifying pond is reduced by 40%.Build the mathematical model of evaporation flue by computational fluid dynamics,using Fluent software to carry on the numerical simulation,the evaporation of droplet trajectories under different flue gas flow rate,outlet temperature of the flue cloud,analyses the effect of evaporation,determine the design parameters of the bypass flue evaporator is:bypass evaporator inlet flue gas before the air preheater,exports in front of the electric dust catcher.Evaporation flue gas extraction from air preheater before the high temperature flue gas,flue gas temperature is 330? The height of the main evaporation section is 11m,and the diameter is D=2.8m.Three spray guns are arranged in the evaporator,equilateral triangle.The distance between the spray guns and the center of the circle is 0.55m.The spray parameters of the spray gun are:the flow rate of the spray gun is 1000L/h,the spray pipe diameter is D32,the average atomized particle size is 52?m,and the maximum atomized particle size is 120?m.The optimal velocity of flue gas was 3?4m/s.It is proved that the flue evaporation effect is good under this design parameter by bringing in different boiler operating parameters,thus realizing the "zero emission" of desulfurization wastewater.