Engineers are continually being asked to improve processes and increase efficiency. These requests may arise as a result of the need to increase process throughput, increase profitability, or accommodate capital limitations. Processes which use heat transfer equipment must frequently be improved for these reasons. This paper provides some methods for increasing shell-and-tube exchanger performance. The methods consider whether the exchanger is performing correctly to begin with, excess pressure drop capacity in existing exchangers, the re-evaluation of fouling factors and their effect on exchanger calculations, and the use of augmented surfaces and enhanced heat transfer. Three examples are provided to show how commercial process simulation programs and shell-and-tube exchanger rating programs may be used to evaluate these exchanger performance issues. The last example shows how novel heat transfer enhancement can be evaluated using basic shell-and-tube exchanger rating calculations along with vendor supplied enhancement factors.

Scott Fulton, Costal Corporation, USA, and Jay Collie, Bryan Research and Engineering, Inc., USA, discuss the use of process simulators to analyse the performance of heat transfer equipment, focusing particularly on brazed aluminium heat exchangers

Brazed aluminum heat exchangers have superior heat transfer capabilities and can be cost effective for non-corrosive gases and liquids as compared with traditional shell-and-tube exchangers. Even so, brazed aluminum exchangers are often not considered because of complicated design equations and complex stacking arrangements. The simpler yet less efficient shell-and-tube exchangers or networks of shell-and-tubes are employed instead. Recently, the design equations for multistream brazed aluminum heat exchangers for both single and multiphase flow have been added to the Heat Exchanger Rating package of the process simulator PROSIM® . This paper presents guidelines for designing a brazed exchanger, and the brazed exchanger is compared with traditional shell-and-tube exchangers and networks of exchangers in several examples.

Since complex brazed aluminum plate exchangers can include as many as 8-10 process streams within a single exchanger, the process design calculations become quite involved and must include incremental duty versus temperature calculations to check for temperature pinch points. The capability to perform the process design for complex plate exchangers has recently been added to a process simulation program called PROSIM. Three case studies involving the simulation and optimization of cryogenic operations for liquids recovery from gases using complex plate exchangers are presented. Due to their low cost and superior heat transfer capabilities, complex plate exchangers can be very useful in reducing costs and optimizing cryogenic operations.