Controlling Crude Unit Overhead Corrosion – Rules of Thumb for Better Crude Desalting

摘要

Various rules of thumb, operating parameters, and benchmark values are presented that help crude unit operating personnel determine how well a crude desalter is operating. Topics covered include setting realistic salt and BS&W (bottom sediment and water) limits for incoming raw crudes, establishing specific desalting goals, ensuring desalter vessels are of sufficient size, monitoring desalter performance, avoiding desalter upsets, and ensuring that desalters are properly maintained. All refineries depend on proper crude desalting and want their desalter to operate reliably most, if not all the time. Yet, many desalters end up the “stepchild” of crude unit operations and, for various reasons, continue to suffer from the same problems year after year. Many desalter vessels are too small and have outdated electrical systems, many have insufficient instrumentation to allow on-going monitoring of critical operation variables, many receive a minimum of maintenance, and regular cleaning is not a critical item on many units. Untreated slops and various rerun streams are often added to incoming raw crude on an irregular schedule, waste streams are often added for disposal, and the type of desalter water used to extract salts is not always the best choice from both a process and corrosion point of view. These tend contribute to desalter upsets that, in turn, are often the primary cause of overhead corrosion problems on many units.