常压塔顶塔盘腐蚀原因分析及对策

Corrosion Analysis and Countermeasures of Atmospheric Tower Top Tray

某炼油厂10 Mt/a常减压蒸馏装置2009年建成投产,2019年大检修发现,常顶第1层塔盘、浮阀及常顶回流管等内件均有腐蚀现象.通过对比分析2015年大修前后装置工艺条件发现:2015年大修后原油性质变化,常顶油气HCl含量上升,同时,2015年大修开工后蒸馏装置加工负荷下降,常顶回流对塔内油气的局部降温作用更加明显,第1层塔盘靠近常顶回流出口的区域存在常顶回流的急冷作用,局部产生了液相水,在该区域塔盘及浮阀附近形成H2S-HCl-H2O型腐蚀环境.因常顶回流管线温度低,管外壁低于铵盐结晶温度,在管外壁形成NH4Cl盐沉积,导致该部位发生垢下腐蚀.为减轻常顶部位腐蚀,建议将常顶回流温度提升至90 ~95 ℃,研究将常顶回流并入顶循回流进塔的可行性,增加常压拔出率,提高常顶温度.同时,应开展原油有机氯分析攻关,掌握原油有机氯变化趋势.

The 10 Mt/a atmospheric and vacuum distillation unit of a refinery was completed and put into operation in 2009.During the overhaul in 2019,corrosion was found in the first layer of tray,float valve and reflux pipe.Through comparative analysis of process conditions before and after 2015 overhaul,it is found that the change of crude oil properties after 2015 overhaul led to the increase of HCl content.In the meantime,processing load of distillation unit decreased,local cooling effect on oil and gas of tower became more obvious which caused by overhead reflux.Shock chilling phenomenon presented near reflux outlet of the first layer tray and liquid phase water emerged locally,forming H2 S HCl H2O type corrosion environment around tray and float valve of the area.Due to low temperature in reflux pipelines,NH4Cl salt deposited on outer wall,resulting in under deposit corrosion.Several proposals were provided,such as raising reflux temperature from 90℃to 95℃,studying the feasibility of making overhead reflux incorporate with overhead circulating reflux,increasing extraction rate,launching analysis on organic chlorine content in crude oil so as to grasp its tendency.