Removal Of Scale Forming Substance From Circulating Cooling Water Of Power Plant By Electrocoagulation

Recycling wastewater from industrial production is the urgent need for industrial water saving and industrial wastewater reduction.During the treatment of circulating cooling water,inorganic substance such as Ca²⁺,Mg²⁺and silicon（colloidal Si O₂,molecular silicic acid and few silicate etc.）,and organic matter in the circulating cooling water are enriched and concentrated with the evaporation of water,so that Ca CO₃·Si O₂ scale and magnesium silicate scale with low heat transfer coefficient will be easily generated.Then,it is necessary to remove Ca²⁺,Mg²⁺and silicon to increase the number of cycles and concentration ratio of circulating cooling water,and to reduce the amount of replenishment water and displacement of circulating cooling water.In this paper,the removal of scale forming substance(mainly for Ca²⁺,Mg²⁺and silicon)from circulating cooling water of power plant by electrocoagulation was performed.We mainly focused on the effects of electrode type,electrochemical parameters,chemical agents addition and other factors on hardness removal by electrocoagulation and the process mechanism.First,the effect of current density,electrolysis time,stirring rate,inter-electrode distance on the removal of Ca²⁺,Mg²⁺,hardness and silicon during the electrocoagulation process by using the aluminum anodes（Al-electrode）and iron anodes（Fe-electrode）were investigated.The results showed that the removal rate of Ca²⁺,Mg²⁺,hardness and silicon by Al-electrode is higher than that by Fe-electrode under the same reaction condition.And when the current density was 60 m A·cm^-2,the electrolysis time was 60 minutes,the stirring rate was 100 rpm and the inter-electrode distance was 0.5 cm,the removal rates of Ca²⁺,Mg²⁺,hardness and silicon using Al-electrode and Al-electrode reached the maximum,which were 48.99%,89.46%,64.03%,87.71%and 26.61%,84.27%,48.03%and 81.07%,respectively.Furthermore,the removal of low hardness and high hardness circulating cooling water by electrocoagulation using Al-electrode was carried out in detail.The effect of current density,electrolysis time,initial p H and sodium carbonate addition on the removal of Ca²⁺,Mg²⁺,hardness and silicon were investigated in the process of low hardness circulating cooling water treatment.The results showed that the increased current density and extended electrolysis time were conducive to the removal of Ca²⁺,Mg²⁺,hardness and silicon.When the current density was 10 m A·cm^-2 and the electrolysis time was 90 minutes,the removal efficiencies of Ca²⁺,Mg²⁺,hardness and silicon were 73.19%,95.44%,83.88%,97.76%,respectively.Compared with neutral and acidic conditions,the alkaline condition was more benefit for the removal of Ca²⁺,Mg²⁺and silicon.At the initial p H of 10,the removal efficiencies of Ca²⁺,Mg²⁺,hardness and silicon were 85.38%,97.70%,91.30%,and 100%,respectively.The addition of sodium carbonate was benefit for the removal of Ca²⁺,Mg²⁺,hardness and silicon.To increase the removal rate for scale forming substance from high hardness circulating cooling water by electrocoagulation using Al-electrode,the effect of the addition of sodium carbonate and initial p H on Ca²⁺,Mg²⁺,hardness and silicon removal were investigated in detail.The results showed that the addition of sodium carbonate was benefit for the removal of Ca²⁺,Mg²⁺,hardness and silicon.Compared with neutral and acidic conditions,the alkaline condition was more benefit for the removal of Ca²⁺,Mg²⁺,hardness and silicon.When the initial p H is 8,the removal efficiencies of Ca²⁺,Mg²⁺,hardness and silicon reached100%,99.21%,99.71%,100%,respectively.In this paper,the scale forming substances from circulating cooling water of power plant are effectively removed by electrocoagulation.The obtained results provide valuable information for the study and application of electrocoagulation technique in the removal of scale forming substances from the wastewater.