去丁烷塔頂之腐蝕防治研究

Corrosion Inhibition of Debutanizer Overhead System in Refinery Unit

本研究中所探討之煉製工場主要是將輕質原油經過去丁烷塔及輕油精餾塔的分餾作用取出輕餾份及LPG後，再進入下游設備中進行精煉反應。此煉製工場之去丁烷塔塔頂系統空氣冷卻器E-1因有機酸腐蝕而造成設備時有破損問題，此現象主要是因進料油中夾帶過多的醋酸，促使塔頂系統之pH值偏低（pH~4.0）引起酸性腐蝕，期間雖添加中和胺控制系統之pH值，但因未考量防蝕劑於輕質油料中的溶解度，以致系統不僅因防蝕劑中有效成份沉澱而生成黑色凝膠物使得熱交換管堵塞外，更因防蝕劑分散不均無法全面保護管壁，而導致熱交換管再度破損。為了解決此問題，本研究所採取之防治對策，除於塔頂系統實施水洗作業及添加適量中和胺以控制系統之pH值外，並就輕質油料中溶解度之考量選擇適當的防蝕劑，經長期之持續改善，並經工場歲修時之驗證檢視，可確知系統之腐蝕問題已明顯降低。

The objective of this research is to study the failure reasons and preventive methods for debutanizer overhead air cooler in refinery. The possible corrosion mechanism in overhead system includes hydrogen chloride acid corrosion, salt deposit corrosion, wet hydrogen sulfide cracking and erosion-corrosion. Overhead system failure is very dependent on feed sources. In this study, acid corrosion is the main reason for this case and the source of acid corrosion comes from organic acids. The amount of acetic acid in feed was too high and reduced the pH value (pH ~ 4.0) of the overhead system. Neutralizing amine was added to control pH value. Corrosion inhibitor was applied to provide tube protection. However, inhibitor caused the following problems, most corrosion inhibitor polymerized to form black gel and caused heat exchanger to block up. The black localized gel could not provide good protection for tube but induced localized corrosion. After further studying, we find the main reason is neglecting the solubility of the corrosion inhibitor. Process stream is very light hydrocarbon in this case. If the solubility of inhibitor could not compatible with light process stream, inhibitor would loss its performance and caused negative effect for the system. The effective solutions are to choose suitable corrosion inhibitor and to control the pH value of the system by adding neutralizing amine. If water wash of overhead system is applied, the corrosion rate will be effectively reduced and controlled.