The Effect Of Hardness Ions In Seawater On The Desalination And Concentration Of Seawater

For the purpose of the comprehensive utilization of water resources,this article has been systematically studied on the water enrichment.According to the present situation and mechanism analysis of seawater desalination engineering,the main factors influencing the deep concentration of seawater are the fouling problem,and the hardness ion is calcium ion.Therefore,this paper makes a thorough research on the pretreatment of the decalcification and decarbonization process.And then,taking humic acid as an example,the effect of organic matter in seawater on the reverse osmosis membrane fouling in the presence of Ca2+ was investigated.Based on the experimental data of six-effect evaporator,the mathematical optimization model of high-temperature multi-effect evaporator is established,a reasonable distribution of the effective heat transfer temperature difference,so that the total heat transfer loss of the entire system is minimal,finally,the optimal operating parameters and equipment parameters of the system are obtained.The seawater is concentrated after demineralization by simulated power plant cooling tower,to investigate the feasibility of the cooling tower to replace the evaporator.Calcium and magnesium ions were removed by chemical precipitation method.The amount of Na2CO3 was 1.3 times of the theoretical amount and NaOH was 1.1 times of the theoretical amount.The hollow fiber microfiltration membrane and ceramic membrane were used for solid-liquid separation.Calcium and magnesium ions content can reach less than 15 mg/L.The effect of different pre-treated water on the flux and pollution of reverse osmosis membrane was compared.It was found that decalcification and de-hardening pretreatment could delay the decay of membrane flux,and through the characterization analysis,the insoluble salt formed by seawater could lead to reverse osmosis membrane pollution,calcium ions and humic acid synergies will accelerate the reverse osmosis membrane pollution.By comparing the falling film evaporation of the horizontal tube,it was found that the heat transfer coefficient of de-hardened seawater was significantly larger than that of seawater when the boiling point of the material was higher than 70?.The difference of boiling point between de-hardened seawater and seawater was studied.Based on the experimental data,a tower six-effect high-temperature multi-effect evaporation system was optimized.The effects of the effective number,the ratio of water production and the heating temperature on the operation performance of the evaporator system were analyzed.Through the pilot test to low-temperature multi-effect desalination of salt water as raw material,the nanofiltration,reverse osmosis concentration separation,with reverse osmosis concentrated water as a cooling tower cooling circulating water technology.The results show that the heat removal efficiency of desalted brine is higher than that of concentrated seawater,and it can save water consumption and increase seawater concentration ratio,which is beneficial to industrial salt production of concentrated brine.