| For the reduction of SOx and secondary condensable PM,limestone gypsum wet desulfurization technology(WFGD)has been widely used in coal-fired power plants.Cl element from coal,limestone and water is enriched in the circulating slurry of WFGD.To prevent corrosion of the equipment,a certain amount of desulfurization slurry is let out to control the concentration of Cl-in the desulfurization slurry within 10g/L-20g/L.Due to its complex compounds component,low pH nature and relative high heavy metal concentration,it would harm the local environment and water resources if desulfurization wastewater was discharged directly.The conventional desulfurization wastewater treatment technology is not effective in the mitigation of Cl-.This paper presents a novel technical routine,which is to extract a portion of the flue gas from the inlet of the electrostastic precipitator(ESP),and concentrate the wastewater in a circulating evaporation tower to reduce the wastewater amount and then evaporate the wastewater in the flue duct with the high-temperature gas.In this paper,Cl elelment migration properties during the concentration and evaporation process are studied;the evaporation time and residence distance for complete evaporation of sparyed wastewater was investigated with numerical simulation method,which provides support for the further application in coal-fired power plants.First of all,the material content,pH and conductivity variation was studied with the laboratory desulfurization wastewater evaporation circulating tower.Energy balance and water mass balance calculation was conducted theretically;influence of pH,concentration and salute type of salt solution on the enrichment ratio of Cl-in the saline water were investigated,of which the results showed that the promotion effect of Ca2+、Mg2+ is larger than NH4+,while Cl-escape phenomenon was not detected in NaCl and KCl solution.With pH decreasing from 5.5 to 1,Cl enrichment ratio decreased from 96%to 88%.Evaporation tower method can effectively reduce the amount of the desulfurization wastewater,with the concentration of the total salt content increased progressively with the increase of concentration ratio;the pH decreased gradually.The concentration of Cl-increased linearly with the concentration ratio.The undissolved material fraction increased with the concentration ratio.S and Ca element fraction in the precipitate is higher in the concentrated wastewater than in the original wastewater.Secondly,numerical simulation on the evaporation time and residence distance was carried out for the evaporation of the sprayed wastewater in a simplified flue gas duct.The influence of flue gas properties and operation parameters on droplet evaporation time and residence distance were studied with a DPM model.The results show that the increase of gas temperature,smaller droplet size,lower humidity and lower injection flowrate would lead to shorter droplet evaporation time and residence distance,higher jet velocity and increasing wastewater temperature help to reduce water evaporation time and residence distance,but the influence is smaller.Finally,a twin-fluid atomization optical detection platform was built,and atomization properties of saline water and WFGD wastewater were investigated on this platform.Results showed that air-liquid mass ratio has a dominating effect on the droplet diameter.The atomization diameter of saline water is larger than water,and increased slightly with the solute concentration.As the temperature of the solution increases,the atomization droplet size decreases gradually;the mean diameter increased as the distance from the nozzle exit increased,but the diameter span decreases.The thermogravimetric characteristics of different wastewater were compared from 50 to 400 ℃.A pilot-test platform for the desulphurization wastewater evaporation was developed,on which the temperature distribution and Cl escape ratio were studied.The results showed that the concentration of HCl in the flue gas increases with the flue gas temperature.With the increase of flue gas temperature,the proportion of larger particles in the evaporation product of WFGD wastewater increased,and a increased gas liquid mass ratio could significantly reduce the particle size.The morphology of evaporated wastewater changed obviously,and the boundary became more clear. |
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