Research On Processing Technic Of Circulating Cooling System Sewage Water In Gas Fired Power Station

The circulating cooling water system was the largest water supply part in the power plant,with a high degree of the sewage water and makeup water.The water will cause equipment corrosion and scaling problems due to the presence of Cl^-,Ca²⁺and SO₄^2-.Gas power plant was lack of desulfurization system,which result in circulating cooling sewage water can not be used for other treatment system and cause waste.Ultra-High Lime with Aluminum?UHLA?is a new kind of dechlorination method developed by lime softening method and coagulation and sedimentation method.By adding Ca?OH?₂ and Na Al O₂ and react with anions in to form hydrotalcite substances?LDH?to decrease the concentration of Cl^-,Ca²⁺and SO₄^2-.The purpose of this study was to explore the use of UHLA to process the simulated water,detect the ionic concentration and indexes and obtain the best removal efficiency and conditions;predict the reaction mechanism through the product composition and reaction kinetics;also the actual sewage water will be primarily processed,make the water quality meet the circulating cooling supply water requirements and can be reused for system.In the first part,simulated water contained 500mg/L Cl^-and 280mg/L Ca²⁺.Through the orthogonal experiment and single factor experiment,the result showed that the optimum dosage ratio was n?Ca?:n?Al?:n?Cl?=5:3:1,25?was the optimum temperature and 2 hours was the best shock time.The final concentration of Cl^-was155mg/L and the removal rate was 71.24%;while the concentration of Ca²⁺was62mg/L and the removal rate was 78.74%.The dosage radio effected the removal rate heavily.The decrease of Cl^-initial concentration could greatly inhibit Cl^-removal rate.The mathematical model of the effect of each process condition on the removal rate of Cl^-and Ca²⁺was established.With the addition of 500mg/L SO₄^2-in aqueous solution,the Cl^-removal rate was affected greatly,and with the increase of SO₄^2-concentration,the removal rate decreased rapidly,but it also promoted the Ca²⁺removal rate.The method of secondary treatment and micro-overdose can solve this problem.The removal rate of Ca²⁺and SO₄^2-can exceed 90%when the dose ratio was n?Ca?:n?Al?:n?Cl?=6.3:4.2:1,as well as the Cl^-removal rate was 72.76%.The result of product composition through XRD and analysis of Cl^-reaction kinetics showed that the removal mechanism of Cl^-and SO₄^2-was the anion in the water combined with Ca²⁺and Al³⁺produced by the hydrolysis of the chemical agent to produce Ca₄Al₂Cl₂?OH?₁₂ and Ca₆Al₂?SO₄?₃?OH?₁₂,and the free Ca²⁺in the aqueous solution caused the reaction to proceed forward.The Cl^-removal reaction was expected to be a tertiary reaction with a Cl^-reaction rate constant of 4.607×10^-4?mmol·L?^-2·min^-1.The use of this method to deal with the actual power plant circulating cooling sewage water found that the three ions removal rate were more than 72%,the effluent water's ion concentration can meet the makeup water requirements.But because of the high p H,the effluent water needed to be acidified.The final water through acidification treatment was more stable than the raw water.The low process cost and simple equipment flow indicated the industrial application prospect.But the higher conductivity and TDS in effluent water was the biggest drawback of this method,while the filtration process and solid waste treatment process should also be paid attention in the future.