Study On The Effect Of Compound Phosphorus On Scaling Of Reclaimed Water Circulating Cooling System

The reuse of reclaimed water to power plant circulating cooling water system is an effective way to solve the problem of urban water shortage.Reclaimed water has the advantages of large amount of water,stable water quality,etc.;however,the nutrients such as nitrogen and phosphorus that are rich in it can cause problems such as scaling,corrosion and microbial growth in the system.At present,there is no uniform conclusion about the change of morphology and content of phosphorus in the circulating cooling water system of the power plant and its influence on the scaling and corrosion of the system.In this paper,a small-scale simulated circulating cooling system was set up with formulated reclaimed water as the system feed water,and the organic phosphor in the reclaimed water and the scale inhibitor defined as the complex phosphorus.The extraction method of granular organic phosphorus was optimized.The migration and transformation of complex phosphorus,as well as its impact on system water quality,scaling and corrosion,were studied under different conditions.The results of the continuous extraction of granular organic phosphorus showed that the extraction rate of active organic phosphorus was up to 96.3%with 0.5 mol/L KHCO₃ and medium-active organic phosphorus with 0.3 mol/L HCl.The results showed that the higher the conversion rate of dissolved organic phosphorus in the system,the greater the tendency of scaling corrosion.Among them,the higher the conversion rate was,the larger the scaling amount would be,and the more severe pitting corrosion of stainless steel 304 would be.The higher the conversion rate was,the lower dissolved organic phosphorus concentration was and meanwhile the scale structure was more loose.?1?Temperature,concentration ratio?COC?and total hardness?TH?were positively correlated with the conversion rate of organophosphorus in the system,and the minimum sum of migration and conversion rates were 59.1%and 64.37%respectively at 40?and TH2,while the COC4 and COC5 were 77.4%<80.0%and80.0%<84.2%.Hence,the highest concentration rate of the system is up to 4.?2?When the flow rate was 0.7m/s and the dosage of organic phosphorus was10ppm,the minimum sum of migration and conversion rates was 77.3%and 73.8%,respectively.?3?The amount of inorganic phosphorus had little effect on the conversion rate,and the minimum sum of the conversion rates was 68.4%at 2ppm.?4?Complex phosphorous promoted the crystal structure of CaCO₃ crystals from calcite to vaterite and arago nite,and meanwhile the self-corrosion potential moved forward,and the absolute value of anodic and cathodic Tafel slope?b_c,b_a?as well as corrosion current density decreased.Hence,complex phosphorous showed a good scale-corrosion inhibition performance.In conclusion,the minimum amount of scaling is at a temperature of 40?,a flow rate of 0.7m/s,a hardness of TH2,and a concentration of 10 ppm of organophosphorus pesticide and 2 ppm of inorganic phosphorus.The corrosion rate is far less than the national standard of 0.005 mm/a.The maximum concentration ratio up to 4.0.The above is the best operating conditions.The research results provide experimental basis and theoretical reference for actual operation and other research of power plant,and its promotion will have important economic benefits and social values.