Heat exchangers "close loop" to resolve cooling constraints

Heat exchangers "close loop" to resolve cooling constraints

The Customer Challenge

When refinery temperatures are too warm its products produce vapors that can ignite, thus it’s essential that every product in an oil refinery be adequately cooled from process conditions to near ambient temperatures, and can be safely stored.  Often the final cooling process is accomplished through a series of heat exchangers with the last exchanger usually being against cooling water.

Aggreko was contacted because a refinery’s diesel product from the crude unit was not being adequately cooled and presented a possible safety hazard. The assumption was that the cooling water exchanger was fouled; however, the refinery didn’t want to shut down the entire plant to fix the exchanger, nor did the plant operator want to reduce crude rates enough so that the available cooling in that exchanger would reduce diesel temperatures enough to be able to send it to storage.  The plant ordered a 400-ton closed-loop chiller system which they calculated would solve the problem.

The Aggreko Solution

Aggreko delivered and installed the 400-ton chiller; however, the technicians observed even after initial system start-up, that the diesel temperature wouldn’t reduce enough to safely send the crude to storage.  They assessed that the cooling water exchanger was more fouled than initially estimated. The chiller’s return temperature was actually much higher than it should have been and was causing mechanical issues with the chiller. The technicians knew this was likely due to a severe restriction on the cooling water side of the diesel/cooling water exchanger.  The customer wanted to order another 200-ton chiller; however, Aggreko suggested involving Aggreko Process Service (APS),  a team of experienced chemical, mechanical and electrical engineers that can be called in to evaluate process cooling issues and provide expert recommendations.
The APS team reviewed process data and recommended that the client change the closed-loop chiller configuration to a ‘once through’ configuration using only the 400-ton chiller.

In this arrangement, instead of the chiller cooling water discharge being routed directly back to the chiller it was routed to the cooling water tower as it had been before the temporary chiller was installed. This was contrary to normal procedure, since 95% of the time a closed-loop chiller configuration is the most efficient.  However, APS conducted thorough calculations that showed a different option was needed.

Upon recommendations, the diesel to storage temperature dropped below the safety limit and the client didn’t need the additional 200-ton chiller, which provided a cost savings.

The Benefit to the Customer

Aggreko has more than 50 years’ experience providing turn-key solutions to industries that require strategic temporary power and temperature control planning.
Aggreko was chosen because of its technical expertise and advanced services such as the onsite scoping study that is provided by its unique team, Aggreko Process Services (APS). APS is highly credentialed chemical, mechanical, and electrical engineers that design complete, packaged engineering solutions for emergency, process improvement, or debottlenecking purposes.