Take care to avoid interactions between oil and acids, if present, as these could saponify. Finalize all cleaning treatment by passivation.
In extreme cases, usually when the exchanger is operated at high temperatures, build-ups may not be easily removed by chemical treatment — re-tubing may be the only good option. As a rule of thumb, if more than 30% carbon by weight is present in a sample of the oil deposit, chemical treatment will not be successful.
Dirk Willard, consultant
A safety expert from headquarters surveyed our refinery's pressure relief system and took issue with a number of practices, including use of a check valve for thermal relief, connecting blowdown lines to the discharge of a pressure safety valve, and having several relief devices share a common discharge (Figure 1). Operations dismiss the expert's comments as quibbling to justify the survey and maintain nothing is wrong with the current solutions to these pressure relief problems. Please help me convince them these really are problems.
Send us your comments, suggestions or solutions for this question by March 9, 2012. We'll include as many of them as possible in the April 2012 issue and all on ChemicalProcessing.com. Send visuals — a sketch is fine. E-mail us at ProcessPuzzler@putman.net or mail to Process Puzzler, Chemical Processing, 555 W. Pierce Road, Suite 301, Itasca, IL 60143. Fax: (630) 467-1120. Please include your name, title, location and company affiliation in the response.
And, of course, if you have a process problem you'd like to pose to our readers, send it along and we'll be pleased to consider it for publication.