中水的侵蚀性因子对发电厂凝汽器不锈钢管材的影响

Effect of Corrosive Factors in the Regenerated Water on Stainless Steels of Condenser Tube in Power Plant

以污水处理厂的二级排放水经膜生物反应器、弱酸离子交换树脂处理后回用于电厂循环冷却水系统为背景，研究了其水质中氨氮、化学需氧量（chemlcal oxygen demand，COD）在蒸发浓缩过程中的转化规律；采用电化学方法、正交实验方法、表面成像分析技术（扫描电镜）研究了氨氮浓度、COD浓度和介质pH值对凝汽器管材316L不锈钢表面耐蚀性的影响。结果表明，蒸发浓缩过程中氨氮约80％以上被硝化和解吸，COD在浓缩初期以线性趋势上升，当水样倍率达到4倍时，COD增长到3．0倍；在试验条件下，氨氮浓度≥18mg／L时，316L不锈钢电极的点蚀电位有明显下降，电极表面达到击穿电位后，表面形成大块黑色腐蚀斑，说明对316L不锈钢耐蚀性能影响显著；介质pH值在8．3～8．5范围内，COD〈300mg／L，氨氮浓度〈5mg／L对316L不锈钢管的耐蚀性基本无影响。

This paper demonstrated the reuse of secondary drainage water treated by the membrane bioreactor and weak acid ion exchange resin from sewage treatment plants in circulating cooling water systems of power plants. For the water quality characteristics, the methods of electrochemistry, orthogonal experiment, and surface image analysis technique （scanning electron microscope, SEM） were employed to study the erosion of the main factor in medium, including ammonia concentration, chemical oxygen demand （COD） concentration, and medium pH on 316L stainless steels of condenser tubes. The results show that under the test conditions, when the ammonia concentration grows above 18 mg/L, a significant impact on the corrosion resistance of 316L stainless steels electrode surface will occur, and the electrode pitting potential of 316L stainless steels will decrease significantly. At the same time, the SEM observation reveales that after the electrode surface reaching the breakdown potential, the electrode surface will form large pieces of black corrosion spot. As the medium pH ranges from 8.3 to 8.5, values of COD〈300 mg/L and NH^＋4-N〈5 mg/L have no significant effect on the corrosion resistance of 316L stainless steels.