Research On Calcium Sulphate Fouling In Heat Exchanger Of Feicheng Well Mineral Salt Brine And Cleaning Processs

During the preheating process in heat exchanger of the plaster brine that produces vacuum salt,it can produce a large amount of calcium sulfate scaling,which results in damages to the production in two ways.One is the loss in heat transfer efficiency.According to the relevant data,a 30%decrease in the heat transfer coefficient with 0.5 mm of scaling,and heat transfer coefficient decreased by 50%when the scaling accumulates into 1 mm,resulting in the loss of heat energy and reduction in production,and it also affect the continuity of the whole process.The other is the pipeline local corrosion induced by the scaling.Therefore,it is necessary to prevent the formation of scaling and to timely clear calcium sulfate scale in the production process of vacuum salt used plaster brine to improve the heat transfer efficiency and reduce the operating cost,which leads to great practical significance and economic benefits.Firstly,the phase equilibria of the four-componet systems of Na+,Ca2+//Cl-,SO42-—H2O at 55℃ was experimentally determined,which lays the foundation for the polymorphic determination of the plaster brine.It can be concluded that the brine is supersaturated with calcium sulfate dihydrate according to the thermodynamic phase and the brine composition of Shandong Feicheng.It provides basis for the prevention of scale.Secondly,the scaling formation process of the plaster brine was investigated using the coupon test.The effects of temperature and seeding on the formation of scaling were investigated.Without seeding,the quantity of calcium sulfate scale formed in 60 days were 1.28 mg/cm2 at 35℃,1.31 mg/cm2 at 45℃ 1.71 mg/cm2 at 55 ℃,0.63 mg/cm2 at 65 ℃,respectively,while with seeding of 10.3 g/L,the scaling amount at the corresponding conditions were 0.86 mg/cm2,0.83 mg/cm2,1.38 mg/cm2,0.63 mg/cm2,respectively.The results showed that adding seed can inhibit scaling at 35℃,at 45℃,at 55℃,respectively,while adding seed has no effect on scaling at 65 ℃.Finally,continuous pilot scale test was designed and created according to the preheating process of the industrial production of the plaster brine.The results showed that the heat transfer coefficient of the high temperature area(103℃-119.4℃)during the continuous pilot scale test decreased by more than 40%after 50 days compared to the low temperature area(53.1℃-103℃).The effect of 2%hydrochloric acid on the elimination of calcium sulfate scale at room temperature was remarkable and caused no corrosion to the equipment,and the heat transfer coefficient after cleaning turned out to be the same with that before the formation of scaling.