Crude Overhead System Design Considerations
SUMMARY
Proper crude unit overhead system is important when building a new unit or revamping an existing one to process different crudes. Overhead condenser designs should meet the specific processing objectives, such as distillate yield, run length and energy recovery.
TEXT
Process flow schemes and equipment design play a major role in atmospheric crude column and condenser system corrosion and fouling. There are two major types of overhead systems- single- and two-drum - but there are many different process flow schemes and several exchanger configurations. Some overhead systems experience severe corrosion and fouling that increase the atmospheric column operation pressure, reduce the distillate yield or require exchanger bundle changes at intervals less than the normal four- to six-year turnarounds. Some crude columns have to be shut down to remove salts deposited on the internals.
The atmospheric crude column and overhead system are exposed to a number of corrosive species, depending on the crude type, slop oil processing and desalter operation. Desalter operation is an integral part of overhead system corrosion and the two cannot be separated. Calcium and magnesium chloride salts hydrolyse in the atmospheric heater, creating HCl. When processing difficult-to-desalt crudes such as Venezuelan extra-heavy, diluted bitumen blends and conventional crudes such as Doba, salt content entering the heater can be high...