| As the main form of thermal power generation,coal fired power plant make a difference in China's energy,economy,environment and many other areas?The official implementation of the "Water Pollution Prevention and Control Action Plan",which was promulgated in April 2015,marked that the policy of environmental protection in the power industry will change from a single focus of smoke treatment to a dual focus of water and gas treatment.Firstly,the related literatures of electrochemical wastewater treatment technology were reviewed.In recent years,electrochemical oxidation technology has been greatly developed,and it has been widely used in wastewater treatment field.It is an efficient and inexpensive wastewater treatment process.In this paper,the water balance of a large coal-fired power plant and the treatment capacity of the existing wastewater treatment system are comprehensively and systematically sorted out.It is found that the key factors affecting the wastewater reuse rate of the power plant are:high-salt ammonia-nitrogen wastewater represented by desulfurization wastewater and regenerated wastewater from refined treatment,which is difficult to meet the treatment standard and reuse stably by conventional process means.This is also a representative problem in wastewater treatment of coal-fired power plants.If ammonia nitrogen and chemical oxygen demand(COD)in these two wastewater can be eliminated,they can be accepted by coal yard or industrial water system and reused.Due to the dual pressures of environmental protection and management,it is urgent to explore an economical and efficient new ammonia nitrogen wastewater treatment process.Taking desulfurization wastewater and regeneration wastewater from a large coal-fired power plant as research objects,a pilot-scale process of ammonia nitrogen removal by electrochemical oxidation was designed after fully analyzing its water quality characteristics.By changing the water temperature,current density,residence time,total soluble solids(TDS),initial chloride concentration and electrode surface cleanliness,the factors affecting ammonia nitrogen degradation were studied comprehensively.The results showed that current density,residence time,initial chloride concentration and cleanliness of electrodes had great influence on the degradation of ammonia nitrogen in water samples,while TDS had little effect on the degradation of ammonia nitrogen.The higher the current density,residence time and initial chloride concentration,the higher the cleanliness of the electrode surface,the better the removal effect of ammonia nitrogen.Specifically,the following conclusions can be drawn:(1)The higher the current density,the higher the degradation concentration of ammonia nitrogen(120-480 A/m2),and the better linear relationship between them,R2=0.9699,when the initial concentration of ammonia nitrogen(121 mg/L)remains unchanged for a constant residence time(1.2 minutes)through the electrolytic device(2)Under the same current density,the removal efficiency of ammonia nitrogen from wastewater with the same composition is significantly affected by the residence time When the initial concentration of ammonia nitrogen is 121 mg/L,the outlet water temperature is about 25?,and the current density remains unchanged(120-480 A-m2),the longer the residence time of wastewater in the electrolysis unit,the higher the removal rate of ammonia nitrogen(3)When a certain concentration of ammonia-nitrogen wastewater passes through the electrolysis device under constant current density(120-480 A/m2),the removal effect of ammonia-nitrogen is significantly affected by the initial chloride concentration When the initial concentration of ammonia nitrogen is about 120 mg/L and the temperature of effluent is about 25?,the higher the initial chlorine radical of wastewater is,the higher the removal rate of ammonia nitrogen is(4)Under the same current density(120-480 A/m2)and different TDS(22520-32066 mg/L),the degradation capacity of ammonia nitrogen was basically the same.It was found that the upper limit of adjustable current of electrolysis increased significantly with the increase of TDS.In addition,with the rise of TDS,the voltage is gradually decreasing,so increasing the initial TDS of ammonia nitrogen wastewater is helpful to reduce the energy consumption of ammonia nitrogen degradation(5)When the water sample passes through the electrolysis device with the same residence time(1.2 minutes),when the current density remains unchanged(240.0 A/m2),the voltage rises slowly with the rise of the inlet temperature;the outlet pH decreases gradually with the rise of the inlet temperature;when the temperature approaches 3 5?,the pH drops rapidly,and the outlet Cl-concentration root rises and falls gradually with the rise of the inlet temperature,and when the temperature rises,the outlet Cl-concentration root decreases gradually.The concentration of Cl-in effluent rises rapidly when the temperature is close to 38?.(6)When the residence time is 2 minutes and the initial chloride ion is 8947 mg/L,there is an upper limit for the ammonia nitrogen treatment capacity of the electrolysis system,which should be about 150.0 mg/L.(7)As long as there is a certain concentration of ammonia nitrogen in the water sample,the chlorine produced by electrolysis will be mainly consumed by ammonia nitrogen.In the process of ammonia nitrogen removal by electrolysis,the proportion of free chlorine to total chlorine is about 20%under different current densities(120-378 A/m2).When ammonia nitrogen is removed,the proportion of free chlorine is rapidly increased to more than 70%after a short time of electrolysis.This is in line with the indirect electrochemical oxidation pathway of ammonia nitrogen in the presence of chloride ions.The electrochemical oxidation of ammonia nitrogen first produces chloramine,and then further oxidizes ammonia nitrogen to produce nitrogen.(8)In the process of ammonia nitrogen degradation with the same residence time(1-2 minutes),the energy consumption of high current density(with the average energy consumption of removing ammonia nitrogen per unit mass,the same below)is higher than that of low current density(120-480 A/m2);while in the process of ammonia nitrogen degradation with the same current density(120-480 A/m2),the energy consumption of high residence time is higher than that of low residence time(1-2 minutes).When the concentration of ammonia nitrogen in wastewater is close to zero,the energy consumption increases slightly.Increasing the initial TDS of ammonia-nitrogen wastewater and the cleanliness of the electrode surface are helpful to reduce the energy consumption of ammonia-nitrogen degradation.(9)Electrolysis can not reduce the role of heavy metals;after electrolysis,the cationic concentration of Ca,Mg and other metals increases by about 5%,which may be due to the production of free chlorine and the increase of acidity in water during electrolysis,resulting in the dissolution of precipitation mixtures containing metal elements in small parts of wastewater;the increase of sulfate is about 23%,which may be due to the oxidation of reducing sulfides.Sulfate is formed under acidic conditions.The removal rate of CODCr by electrolysis was 91.1%.(10)Pollution and scaling on the surface of the plate will reduce the activity of the electrode and the removal efficiency of ammonia nitrogen.The average energy consumption of electrolysis after plate cleaning is lower than that before cleaning.With the same current density(120-480 A/m2),the wastewater with initial ammonia nitrogen concentration of 149.8 mg/L was electrolyzed.The average energy consumption of electrolysis after plate cleaning was lower than that before cleaning.Before plate cleaning,the average energy consumption of electrolysis was 0.294 kW.h/g.After plate cleaning,the average energy consumption of electrolysis was 0.264 kW.h/g,which decreased by 10.2%.Based on the experimental conclusion,the paper compares electrochemical oxidation with the current breakpoint chlorination method in the coal-fired power plant from the aspects of process characteristics,investment cost,operation economy,environmental protection benefit and ammonia nitrogen degradation ability.The feasibility of replacing the breakpoint chlorination method with electrochemical oxidation method is discussed in depth,and the application of electrochemical process in the thermal power industry is analyzed.Jing.According to the characteristics of water quality and quantity of ammonia-nitrogen wastewater after reduction,the industrial application of electrolysis to treat ammonia-nitrogen wastewater in power plant was studied.Based on the analysis of water balance in the plant,the reuse direction of qualified wastewater after electrolysis treatment was planned,and the reuse route for spraying in coal yard,sterilization of circulating water and pavement washing was determined. |
PDF Full Text Request