水平管降膜蒸发器中铝制管的腐蚀特性研究

发布时间：2018-04-04 01:42

本文选题：水平管降膜蒸发器　切入点：铝管　出处：《大连理工大学》2014年硕士论文

【摘要】：由于低温多效蒸发海水淡化技术有着产品水的水质好、可靠性高、传热温差小等诸多优点,现已得到非常广泛的应用。但此方法的一次投资成本较高,严重制约了其进一步发展。采用铝管来代替蒸发器中的铜管可以有效地降低成本,但铝管在海水环境中的腐蚀问题一直以来都在困扰着它在实际工程中的应用,对其腐蚀机理进行深入研究是解决铝管在海水中腐蚀问题的首要条件。本论文设计和搭建了水平管降膜蒸发实验台,首先使用天然海水作为腐蚀介质,在水平管降膜蒸发器中对铝管进行了腐蚀实验,总结了铝管表面腐蚀形貌变化规律并确定了对铝管的腐蚀影响较大的因素；为了探究盐度对铝管在水平管降膜蒸发器中腐蚀的影响,使用蒸发浓缩后的海水作为腐蚀介质,在水平管降膜蒸发器中对铝管进行了腐蚀实验,总结了铝管表面腐蚀形貌变化规律并与之前的海水腐蚀实验进行了对比。实验结果表明,在水平管降膜蒸发器中,由于其特殊的温度和压力环境,使得铝管容易遭受空泡腐蚀。铝管在蒸发器中使用一段时间后会被腐蚀,腐蚀的主要形态为孔蚀。在本实验工况下,选用盐度为2.9%的天然海水作为腐蚀介质时,铝管开始发生孔蚀的时间为腐蚀实验进行的第38个小时左右,铝管在水平管降膜蒸发器中开始发生孔蚀时,其初期的腐蚀速率较大,随着腐蚀的进行和腐蚀产物的积累,其腐蚀速率逐渐减小,腐蚀产物在初期对铝管的腐蚀起到了促进作用,在后期对腐蚀的发展起到了抑制作用；当选用蒸发浓缩后的海水作为腐蚀介质,海水的盐度为6%,铝管开始发生孔蚀的时间为实验进行的第6个小时左右,铝管发生孔蚀时,相对于天然海水冲刷腐蚀作用下的铝管来说,其表面的腐蚀孔直径更大,腐蚀孔直径增大使得腐蚀产物难以完全覆盖整个腐蚀孔,故腐蚀产物对铝管的保护作用被削弱,这就使蒸发浓缩后的海水对铝管表面有着持续的破坏能力。将铝管应用于水平管降膜蒸发器中时,应尽量通过减少蒸发器中气泡的产生、降低海水盐度等方法来抑制铝管表面的腐蚀,根据铝管发生孔蚀的具体时间做好相应的准备工作。
[Abstract]:Due to the advantages of low temperature and multi-effect evaporation desalination, such as good water quality, high reliability, low heat transfer temperature difference and so on, it has been widely used.However, the primary investment cost of this method is high, which seriously restricts its further development.Using aluminum tube instead of copper tube in evaporator can reduce the cost effectively, but the corrosion problem of aluminum tube in seawater environment has been puzzling its application in practical engineering.It is the most important condition to study the corrosion mechanism of aluminum pipe in seawater.In this paper, a horizontal tube falling film evaporator is designed and built. Firstly, using natural seawater as corrosion medium, the corrosion experiment of aluminum tube is carried out in the horizontal tube falling film evaporator.In order to explore the effect of salinity on corrosion of aluminum tube in horizontal tube falling film evaporator, the evaporated concentrated seawater is used as corrosion medium.The corrosion experiments of aluminum tubes were carried out in a horizontal tube falling film evaporator. The surface corrosion morphology of aluminum tubes was summarized and compared with the previous seawater corrosion experiments.The experimental results show that aluminum tubes are vulnerable to cavitation corrosion due to their special temperature and pressure environment in the horizontal tube falling film evaporator.Aluminum tubes will be corroded after being used in evaporator for a period of time, the main form of corrosion is pitting.Under the experimental condition, when the natural seawater with a salinity of 2.9% is selected as the corrosion medium, the time when the pitting corrosion of the aluminum tube begins is about 38 hours of the corrosion experiment, and the pitting corrosion of the aluminum tube begins in the horizontal tube falling film evaporator.The corrosion rate decreases gradually with the development of corrosion and the accumulation of corrosion products. The corrosion products promote the corrosion of aluminum tubes in the initial stage and inhibit the development of corrosion in the later stage.When the evaporated and concentrated seawater is used as the corrosion medium, the salinity of seawater is 6 and the time when the pitting corrosion of the aluminum tube begins is about 6 hours after the experiment, when the pitting corrosion of the aluminum tube occurs,Compared with the aluminum tube subjected to natural seawater erosion, the diameter of corrosion hole on the surface of aluminum pipe is larger, and the corrosion product is difficult to cover the whole corrosion hole completely, so the protective effect of corrosion product on aluminum tube is weakened.This makes evaporated and concentrated seawater to the surface of the aluminum tube has continued damage.When the aluminum tube is applied to the horizontal tube falling film evaporator, the corrosion of the aluminum tube surface should be restrained by reducing the bubble in the evaporator and reducing the salinity of the seawater, and the corresponding preparation work should be made according to the specific time of the pitting corrosion of the aluminum tube.
【学位授予单位】：大连理工大学
【学位级别】：硕士
【学位授予年份】：2014
【分类号】：P747

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