| Multi-effect evaporation desalination technology is an important way to solve the shortage of fresh water resource.During the actual operation,seawater will foul on the surface of the heat transfer tube of the evaporator,affecting the heat exchange efficiency,limiting the top temperature of the brine and reducing the fresh water production.This paper conducts scale inhibition experiments about the scaling problem in multi-effect evaporation desalination technology.In this paper,the experimental platform is improved for the horizontal tube falling film evaporation of seawater scale inhibition.The special scale inhibitor is selected for desalination,which is developed by the Water Treatment Research Institute of Nanjing University of Technology.The local seawater of Dalian is used as the working medium,spraying and falling film process of multi-effect evaporation seawater desalination of evaporator is simulated on surface of the titanium tube.The scale inhibition experiment was carried out according to the changes of seawater salinity,spray seawater temperature,scale inhibitor dosage and spray seawater density.The selected spray seawater temperature is 70 °C,80 °C,90 °C,seawater salinity is 3%,6%,8%,spray seawater density is 0.03kg/(m·s),0.06kg/(m·s),0.08kg/(m·s),and the dosage of the scale inhibitor is 4mg/ l,6mg / l,8mg / l,10 mg / l,12 mg / l.After adding the scale inhibitor,the effect of different parameters change on the scaling regular pattern is studied,and compared with the experiment without the scale inhibitor,studying the scale inhibition effect and scale inhibition mechanism.Research has shown that the addition of the scale inhibitor at different spray seawater temperatures significantly reduces the amount of scale.As spray seawater temperature increases,the asymptotic value of scale increases and the scale inhibition efficiency decreases.After adding the scale inhibitor under different seawater salinity,the amount of scale is obviously reduced.As the seawater salinity increases,the asymptotic value of scale increases and the scale inhibition efficiency decreases.The effect of adding the scale inhibitor is very good under different spray seawater density.As spray seawater density increases,the asymptotic value of scale increases first and then decreases,when spray seawater density is 0.06kg/(m·s)reaches the maximum.The scale inhibition efficiency first drops and then rises.When seawater salinity is 8%,heat transfer temperature difference is 3°C,spray seawater density is 0.03kg/(m·s),spray seawater temperature is 90°C,experiment is carried out under different dosages of the scale inhibitor.When the dosage is 6mg/l,the scale inhibition efficiency reaches the maximum,54%,indicating that the threshold is 6mg/l.Through the field emission electron microscopy and EDX test analysis,it can be inferred that the special scale inhibitor developed by the Institute of Water Treatment of Nanjing University of Technology has a good scale inhibition effect,whinch through lattice distortion and chelation solubilization.The functional group of the scale inhibitor combines with the sulfate ion to form a water-soluble chelate,which prevents the formation of scale by the sulfate ion and the calcium ion.The addition of the scale inhibitor changes the morphology and properties of the scale,and the magnesium hydroxide scale changes from a sharply shaped rod to a layered staggered agglomerate,the particle size of the scale becomes small,the scale layer is loose and not dense.It is not easy to attach to the surface of the heat transfer tube,so achieves the aim of scale inhibition. |
