Corrosion Assessment And Analysis On Fractionation System Of FCC

As an important secondary processing units,the long period operation of fluidized-bed catalytic cracking（FCC）unit has a great influence on the safe operation of the whole plant.With the feedstocks are heavier、low-quality and high-sulfur,the corrosion of equipment and pipes has become a major problem affecting the safety、stability and long period operation of the FCC.In view of the corrosion status and problems of fractionation system in FCC of SINOPEC Hainan Petrochemical Co.Ltd.,through corrosion mechanism analysis,operation parameter discussion,corrosion rate prediction、device material evaluation、corrosion monitoring and test evaluation、conduct overall corrosion evaluation of the unit,and some improvement measures are put forward for the main corrosion problems from the aspects of process corrosion prevention、process modification、material upgrading and corrosion monitoring.The main work and results of this paper are as follows:（1）The feedstock composition、feedstock properties、distribution of corrosion medium in each fraction、distribution of corrosive medium in sulfur bearing wastewater were analyzed to show that the NH₄Cl corrosion、NH₄HS corrosion、high temperature sulfur corrosion、catalyst abrasion and external damage are the main corrosion mechanism of FCC fractionation system.（2）Through the calculation of corrosion rate,it is found that the corrosion rate of 11 heat exchanger tubes、8 oil refining pipelines、15 oil slurry pipelines of high temperature system,the tower wall and internals above 29 layer tray of the fractionation tower、16 heat exchanger tubes、9 overhead gas pipelines、13 top cycle pipelines of cryogenic system is too high.The material upgrading proposal is propose of above problems.（3）Through analysis of operation parameters and corrosion scale,it is found that the corrosion problem of fractionation system occurs mainly at the top of the tower and the main reason is the NH₄Cl corrosion.Except optimizing electric desalting、fractionating tower top temperature、ensure top water injection effect and on-line washing after the salt-out,new scheme of top down dehydration and desalting system is needed,injection inhibitor scheme will be considered.（4）The fundamental cause of corrosion problem in FCC fractionation system is that the operating parameters of the unit are not up to the design value and the feedstock properties and design deviations are greater.A scheme for reforming RDS and adding 2 reactors per column was proposed.The sulfur and nitrogen content of the feedstock will be reduced from0.55%to 0.265%at present to 0.3%and 0.18%respectively,the sulfur content of diesel and gasoline decreased from 0.45%to 0.032%and to 0.27%and 0.018%respectively.This study provides a direction for solving the existing corrosion problems of the FCC fractionation system,it has practical application value for improve the operation cycle and ensure the safety production of the unit.