高压锅炉水冷壁管碱腐蚀诊断与机理研究

AN INVESTIGATION ON THE MECHANISM OF CAUSTIC GOUGING FAILURE IN WATER-WALL-TUBES FOR A HIGH-PRESSURE DRUM BOILER

从高压汽包锅炉水冷壁管频繁爆漏的实例出发,系统阐述了炉管碱腐蚀判断方法、发生机理及防止对策。提出了炉水中游离碱含量的精确算法并定量分析了一级除盐水电导率与其中游离氢氧化钠含量之间的关系及其对炉水游离碱的影响。炉水中存在过量游离氢氧化钠和水冷壁管存在局部过热是造成炉管碱腐蚀的两个基本原因。一级除盐系统在运行后期(特别是在失效前)会释放出大量氢氧化钠,这是炉水中游离氢氧化钠的一个主要来源。努力提高锅炉补给水品质并适当调整炉水工况,把游离碱控制在安全范围以内,才能有效防止碱腐蚀。

This paper describes the characteristics, the mechanism and the root cause of crater corrosion caused by caustic gouging that appeared at a high-pressure drum boiler. A new method has been devised to determine the non-captive hydroxyl in boiler water. The relationship between conductivity and concentration of sodium hydroxide at simple makeup demineralizer effluent was proposed. It is found that the tube failure is caused by both the superfluous non-captive hydroxyl in boiler water and the local overheat caused by deposition in boiler tubes. Sodium hydroxide at simple makeup demineralizer effluent is the root cause of the non-captive hydroxyl in boiler water, so the quality of the makeup water should be improved and the non-captive hydroxyl in boiler water should be controlled under a safe limit in order to protect boiler tubes against crater corrosion.