碱金属氯化物对金属材料的高温腐蚀特性研究

准东煤及生物质燃料中由于富含碱金属如Na、K等元素,在燃烧过程中会产生灰相关问题,易形成烟气侧受热面的积灰结渣以及金属管壁的高温腐蚀,影响金属管束的换热效率和使用安全,严重时会导致爆管,威胁锅炉的正常安全运行。通过模拟烟气气氛对金属材料15CrMoG和T91进行高温腐蚀试验,并采用KCl涂抹方法模拟受热面表面碱金属盐的沉积腐蚀现象,利用SEM、EDS和XRD等检测方法分析腐蚀产物的形貌与组成,研究金属材料、腐蚀时间和反应温度对碱金属氯化物高温腐蚀的影响。结果表明:金属表面的KCl涂层加剧了金属腐蚀,碱金属氯化物可有效加剧对金属材料的高温腐蚀程度。在不同腐蚀时间和反应温度下,金属材料15CrMoG的腐蚀增重与腐蚀层厚度均大于T91,表明T91的抗腐蚀性能优于15CrMoG。随着反应时间的增加,腐蚀增重与腐蚀增厚逐渐增大,而腐蚀速率逐渐降低,在腐蚀时间低于20 h时,腐蚀速率较快;处于20～48 h时,腐蚀速率明显降低,总体上腐蚀曲线符合抛物线规律。导致腐蚀后期腐蚀速率降低的主要原因是由于碱金属腐蚀会导致形成致密氧化膜覆盖在金属基体表面,对金属有一定的保护作用,减缓了腐蚀的发生。随着反应温度的增加,腐蚀加剧,在温度低于500℃时,腐蚀增重曲线斜率较小,腐蚀速率较低;温度高于500℃时,曲线斜率明显增加,腐蚀速率加快。腐蚀增厚曲线与增重曲线趋势基本一致,腐蚀曲线符合抛物线规律。随着温度的升高,碱金属腐蚀的化学反应速率与温度呈指数关系,温度升高,参加腐蚀反应的活化分子数增多,腐蚀反应速率得以迅速加快。由腐蚀微观形貌图可看到腐蚀前金属基体结构完整,表面较平滑,腐蚀后金属与腐蚀层的接触表面出现凹凸不平的结构,随着腐蚀时间的增加,腐蚀层的厚度逐渐增大。综合分析样品的SEM-EDS检测结果可以得到2种金属材料腐蚀产物的主要组成元素是Fe和O,结合XRD物相峰谱识别分析得到金属材料的腐蚀产物主要以Fe2O3的形式存在。 Due to high content of alkali metals such as Na and K in Zhundong coal and biomass,there will be related problems of ash in the combustion process,and it is easy to slag and deposit on the heating surfaces in the combustion process,resulting in high-temperature corrosion of metal tube,which will affect the heat exchange efficiency and use safety of metal tube bundles.In serious cases,it can lead to tube explosion and threaten the normal and safe operation of the boiler.In this paper,the high-temperature corrosion test under simulated flue gas was conducted on metal materials of 15 CrMoG and T91 and the deposition corrosion of alkali metal salt on the surface of heating surface was simulated by KCl coating method. The morphology and composition of corrosion products were analyzed by SEM,EDS and XRD,and the effects of metal materials,corrosion time and reaction temperature on the high temperature corrosion of alkali metal chloride were studied.The results show that the KCl coating on the metal surface aggravates the high-temperature corrosion,and the alkali metal chloride can effectively intensify the high-temperature corrosion of the metal materials.Under various corrosion time and reaction temperature,the weight gain and thickness of corrosion layer of metal material 15 CrMoG are greater than that of T91,indicating that the corrosion resistance of T91 is greater than that of 15 CrMoG.With the increase of reaction time,the weight and thickness of corrosion increase gradually,while the corrosion rate decreases gradually. Compared with the corrosion time between 20-48 h,the corrosion rate is faster when the corrosion time is less than 20 h and the corrosion curve generally conformes to the parabolic law. The main reason for the decrease of corrosion rate in