Research On Seawater Falling Film Evaporator Tube Corrosion Experiment System

Low-temperature multi-effect distillation technology is the first distillation technology to enter the commercial application. Nowadays with the high-speed development of desalination industry, low-temperature multi-effect distillation technology has hold a lead in the distillation-technology market because of its low pretreatment requirement, low power consumption, can take advantage of the low grade industrial preheating temperature. However, the problem of high initial investment is restricting the further development. Compare with the copper tube heat exchanger, the aluminium one has great advantages both in the heat transfer performance and the economy, but the aluminium heat exchanger mainly exists the corrosion problem. Therefore, it has important and far-reaching significance on the LT-MED technology to carry out the aluminium corrosion characteristic of heat exchanger tube.An evaporation-corrosion experiment system of Horizontal Tube Falling Film Evaporator was designed according to the actual operation of LT-MED desalination device. Took the 3FL aluminium alloy tube as the experimental object, choose fresh seawater as raw materials experimental fluid. During the experiment process, first deoxidate the fresh seawater use of the experimental system, then simulating actual operation LT-MED device for the corrosion experiment. through macroscopic observation, microscopic detection method to research the corrosion characteristics of the aluminium alloy during or after the experiment process to define the type and characteristic of corrosion for the aluminium tube in deoxidize seawater.Experiments were carried out in the condition of evaporation pressure of 19.94 kPa, the evaporation temperature of 60℃, oxygen content of seawater for 0.3 mg/L. Time use 150h. During the experiment process, macro morphology real-time observation of experimental tube, after the experiment of the experiment, used SEM scanning electron microscope of aluminium alloy tube.The experimental results show that, in the deoxidation environment, the aluminium alloy heat changer mainly reacted impact erosion, pitting and general corrosion during the process of Horizontal Tube Falling Film Evaporator. In the dual role of the two factors of the impact erosion and residual dissolved oxygen,The tube surface can be observed corrosion phenomenon obviously in the experiment after 70 hours, mainly for the tube surface appears black spots,along with the experiment, the rate of corrosion became lower in the later stage of the experiment, which result from the depleted residual oxygen and the protection covering action for the tube from the process of corrosion. After the experiment. The pitting corrosion number of the spray side surface is more than the non spray side, and the pitting diameter of the spray side is greater than that of the non spray side through macro observation, micro detection and other means.Because of the impact erosion, the surface layer of the spray side of the experimental tube can be peeled off, and some aluminum matrix is bare. Compared with the experimental tube, the bottom of the experimental tube is covered with clear dirt layer.