Pilot Test Study On Zero Discharge Of Desulfurization Wastewater From Coal-Fired Power Plants

Desulfurization wastewater from coal-fired power plants was recognized as one of the most difficult wastewater treatments in the world because of the high concentration of pollutants,complex types of pollutants,and high salinity.At present,its zero-emission treatment technology and engineering application were still in the initial stage in China,and the process routes were diverse,and there was no mature process route for reference.In this paper,a pilot test of wastewater softening treatment,ceramic membrane microfiltration,reverse osmosis membrane concentration and electrodialysis concentration in a zero-emission process for a domestic power plant desulfurization wastewater was carried out,and the idea of zero discharge of wastewater and resource utilization of main components of wastewater was put forward.On this basis,the engineering design concept was put forward and economic analysis was carried out.Firstly,the water quality of desulfurization wastewater in power plant was analyzed and the results showed that the suspended solids and the salt content in the waste were high,the pollutant composition was complex,and the water quality fluctuated greatly,among them,the scaling ion content such as calcium sulfate suspension crystal,sulfate ion,calcium ion and magnesium ion were high.The softening reaction comparison test showed that the sedimentation effect was better and most of the sulfate ion and fluoride ion was removed when Ca(OH)2 was used as the first-grade softener,and the optimal dosage is 21 g/L;The second softening used Na2CO3 as a softening agent,the Ca2+ removal rate reached 99.83%under the optimum dosage of 23 g/L.At the same time,the sulphur gypsum produced by the precipitation and reaction can be used together with the desulfurization gypsum of the power plant for resource utilization.Subsequently,the ceramic microfiltration membrane was used for the pilot test of the chemical softening reaction microfiltration membrane to remove hardness and remove heavy metals.It was found that the reaction was more thorough than the conventional coagulation precipitation,and the calcium ion concentration in effluent was 3.89 mg/L,the magnesium ion concentration was 3.32 mg/L,and the turbidity of the produced water was 0.13 NTU?0.15 NTU,which could basically meet the water quality requirements of the NF membrane device.The nanofiltration system was used to treat the water produced by the ceramic microfiltration membrane.Although the desalination rate of the nanofiltration membrane was low(average 35.01%),the sulfate ion removal rate was 96.48%,and the chloride ion removal rate was 23.50%.The separation of sulfate ion and chloride ion could be carried out efficiently,and the purity of NaCl in the produced water reached 99.5%,which was beneficial to the resource utilization of sodium chloride industrial salt.The electrodialysis technology was used to concentrate the high salt water under constant current,which could effectively increase the concentration efficiency and concentration limit.The concentration of TDS on the electrodialysis concentrated water side could be maintained at about 216000 mg/L,and the TDS concentration on the fresh water side was about 10000 mg/L.When the ratio of concentration to light was controlled at about 20,the water quality of electrodialysis was stable,and it had good operation.The high concentration of TDS in concentrated water was beneficial to reduce the investment and operating cost of the subsequent evaporation crystallization section.After electrodialysis fresh water side effluent treatment by RO system,the average conductivity of RO water production was 356.3?s/cm,and the concentration of TDS was about 235mg/L,which was lower than the water quality requirement of circulating water(TDS was less than 1000 mg/L).Water resources could be reused.The electrodialytic concentrate could obtain industrial grade sodium chloride salt through a crystallizer and utilize it in resources.Finally,this paper studied the operation of the pilot test and the economic budget of the zero-emission engineering of the desulfurization wastewater treatment of coal-fired power plants.It was hoped that it can provide useful reference value for the zero-emission treatment and resource utilization project of enterprise desulfurization wastewater.