Pan Peiyuan, Zhou Weijian, Chen Heng, Zhang Naiqiang
National Thermal Power Engineering & Technology Research Center, North China Electric Power University, Beijing 102206, China.
ACS Omega. 2020 Dec 10;5(50):32551-32563. doi: 10.1021/acsomega.0c04838. eCollection 2020 Dec 22.
Sulfuric acid condensation has long been considered as the major cause of the corrosion issues at the cold-end of coal-fired boilers. However, in a flue gas cooler, where flue gas is cooled to around 90 °C for heat recovery, the influence of chlorides might be underestimated. In this article, some elbows of the heat transfer tubes in the flue gas cooler of a coal-fired power plant were found to be badly corroded, after a 5-year operation. The corroded elbows, coupled with the corrosion products and deposits on the tube wall, were sampled and analyzed by scanning electron microscopy, energy dispersive spectrometry, X-ray diffraction, X-ray fluorescence spectroscopy, and ion chromatography. The results indicated that chlorides, unexpectedly, formed in flue gas before the dew point for hydrochloric acid was met. The corrosion layer on the steel surface was mainly composed of FeO, FeO, and FeO(OH), while showing an oxidation gradient in depth. The sulfates in the corrosion products were rather limited. Instead, Cl from the deposits gradually accumulated deep inside the corrosion layer, resulting in a considerable generation of Cl-containing compounds. The enrichment of Cl induced cracking and spalling of the corrosion products, and greatly accelerated the failure of the tube wall.
长期以来，硫酸凝结一直被认为是燃煤锅炉冷端腐蚀问题的主要原因。然而，在烟气冷却器中，烟气被冷却至约90°C以进行热回收，氯化物的影响可能被低估了。在本文中，一座燃煤电厂的烟气冷却器中，一些传热管弯头在运行5年后被发现严重腐蚀。对腐蚀的弯头以及管壁上的腐蚀产物和沉积物进行了采样，并通过扫描电子显微镜、能谱分析、X射线衍射、X射线荧光光谱和离子色谱进行了分析。结果表明，出乎意料的是，在达到盐酸露点之前，烟气中就形成了氯化物。钢表面的腐蚀层主要由FeO、FeO和FeO(OH)组成，且在深度上呈现氧化梯度。腐蚀产物中的硫酸盐相当有限。相反，沉积物中的Cl逐渐在腐蚀层深处积累，导致大量含Cl化合物的生成。Cl的富集导致腐蚀产物开裂和剥落，并极大地加速了管壁的失效。
