煉油廠裂解單元的腐蝕問題及防制

Corrosion Problem and Prevention of Cracking Unit in Refinery

煉油工業中的重要製程之一是將重油（heavy oil）轉化成高經濟效益的輕油（light oil）。由於製程中含有硫化氫，氰化物等腐蝕因子，對設備的安全性是一嚴苛的威脅。本研究以現場實際發生的案例為主要討論點，由破損原因診斷分析到防蝕對策的提出，均有一系列報告。根據分析結果顯示，造成第二冷卻器破損的主要原因是停爐期間過多的硫酸基生成造成的酸性腐蝕及流體沖蝕。有效的解決對策包括(1)緩衝板施以熔射處理，以避免流體直接對冷卻管沖蝕(2)添加水洗設備，以免腐蝕因子的濃縮效益（condensation）造成嚴重腐蝕(3)增加中和胺劑量，有效調整系統pH值以保護冷卻器管束，並調整pH值在7.5~8.0之間。

It is the key unit in refinery to convert heavy oil into more valuable lighter products. Equipments in this unit are in the crucible of corrosive agents like hydrogen sulfide, chloride and cyanide. However, low pH value corrosion was the main cause for the performance failure in this case. In the period of emergency shutdown, the formation of excess sulfuric acid includes the decreasing of pH value of overhead system. When acids are involved, the effect of flow velocity on erosion-corrosion problem is often pronounced and extensive. Several strategies, including suitable surface treatment to protect the baffle, using water wash to cancel the concentration of corrosive agents and injecting enough neutralizer to control pH value in the range of 7.5~8.0 of overhead system, are suggested to minimize the corrosion problem.