We have a batch ethoxylation / propoxylation process. Temperatures range from 85° F during changeover to 350° F during reaction periods. Pressure ranges from full vacuum to 100 psig. Currently we use a welded plate and frame heat exchanger with a diathermic fluid medium for cooling applications. This heat exchanger has failed three times in six years. We have two schools of thought here: One believes that the temperature swings inherent to our process are the cause of the equipment failure, while the other feels that it is something else. Should we go to a shell and tube solution? If not a shell and tube, then what? Some of our concerns are maintaining current cooling capabilities, changeover, and sheer available space for installation.
--from May 2004 CONTROL
I would never use a plate and frame heat exchanger for an application with temperature swings. Are they approach temperature limited? Probably. It is hard to get very tight approach temper-atures with a shell-and-tube since true counter current is almost impossible. If they don't have room for shell-and-tube they would never have room for double pipe.
Maybe they need a shell and tube exchanger with a refrigerant loop so they can minimize surface area and still fit a U-tube in place.
How about this? Stand a U-tube straight up! In my experience we had a few like this.
They can't be in a fouling service. But I don't think this is true as they currently have a welded plate and frame.