Correcting Design Errors Can Prevent Coking in Main Fractionators
SUMMARY
Coking in petroleum refinery main fractionators causes unscheduled shutdowns and significant production losses. Coking, however, is not inevitable. It is a function of the process and equipment design and operating errors. If the equipment is not designed properly, the unit will coke, regardless of how it is operated.
TEXT
Coking in petroleum refinery main fractionators causes unscheduled shutdowns and significant production losses (Photo 1). High temperatures and excessive residence time are the primary causes of coking in these units – which include crude and lube vacuum columns, fluid catalytic cracking (FCC) and delayed coker main fractionators, and visbreaker and hydrocracker vacuum columns.
Coking, however, is not inevitable. It is a function of the process and equipment design and operating errors. If the equipment is not designed properly, the unit will coke, regardless of how it is operated.
As operating severities of refinery primary fractionators increase to improve economics, the incidence of coking also increases. If the consequences of more severe operation are ignored, the units will coke up and have to be shutdown or very poor product quality must be accepted. But higher distillate yields can be achieved through better design practices, and unit reliability can be improved while meeting higher distillate recoveries.