Transformation Of Inorganic Phosphorus In Circulating Cooling System Using Reclaimed Water As Makeup Water

In recent years,with the increasingly prominent problem of water resources,reclaimed water has become an important source of water for circulating cooling water system power plant.Reclaimed water has the characteristics of stable water quality,reliable source and no need of long-distance water diversion.However,the complex water quality condition of reclaimed water causes the circulating cooling water system to face more severe operational problems.The content of phosphorus in reclaimed water is high and there are various forms,which is one of the important factors that influence the scaling,corrosion and microbial growth in circulating cooling water system.In present work,inorganic phosphorus in simulated reclaimed water was studied as the object,and the effects of operating and water quality conditions on the transformation of inorganic phosphorus were investigated.The M-SMT method of quantitative and qualitative analysis of inorganic phosphorus in scale was established by using SMT continuous extraction method of inorganic phosphorus in river bed sediments.In this paper,the inorganic phosphorus in solutions and scales were measured separately,and the scale and corrosion conditions in the system were analyzed.Further,the transformation of inorganic phosphor us in the circulating cooling water system and its effects on scale and corrosion were summarized.The results showed that the M-SMT method was able to extract the inorganic phosphorus in the scale completely,the recovery rate was close to 100%,and the different forms of inorganic phosphorus could be completely separated.The transport of dissolved inorganic phosphorus into scale was mainly affected by scale-forming ions and the solubility product of corresponding insoluble matter.In the operating conditions,the temperature was the main factor affecting the transport of inorganic phosphorus in the liquid-solid phases.With the rise of temperature,the solubility product reduced.As a contrast,the transport velocity,transport amount and transport rate of the dissolved inorganic phosphorus were obviously increased.Under the conditions of water quality,the addition of inorganic phosphorus or total hardness increased the scale-forming ions significantly.Therefore,the transport velocity and transport amount of inorganic phosphorus raised,but the transport rate decreased because of the concentration of scale-forming cations.Phosphate deposits are one of the major components of scale in system,and the amount of scale is proportional to the amount of inorganic phosphorus transported to a certain extent.When the concentration ratio range from 2 to 6,the transport amount of the dissolved inorganic phosphorus rose by 920 mg,at the same time,the amount of scale increased obviously from 2.85 g to 9.35 g.Under different conditions,the effects on inorganic phosphorus in scales were different.Under the operating conditions,the content of weakly adsorbed phosphorus decreased with the increase of flow velocity,while the content of aluminum-bound phosphorus gradually increased.The raised temperature promoted the aluminum-bound phosphorus into iron-bound phosphorus and calcium-bound phosphorus.And the effect of concentration ratio on inorganic phosphorus in scales was the same.With the increase of concentration ratio,the content of all forms of inorganic phosphorus in scales increased,however,the proportion of them in total inorganic phosphorus in scales were not change.In water quality conditions,with the add of inorganic phosphorus concentration,the amount of inorganic phosphorus transport into the solid phase increased,and the formation of weakly adsorbed phosphorus and calcium-bound phosphorus were dominant;and the added total hardness in the system is favorable calcium-bound phosphorus formation.The corrosion rate of the coupons in the system was influenced by the scale amount,as well as the content of weakly adsorbed phosphorus and the aluminum-bound phosphorus.