Design of Heat Exchangers in Complex Arrangements for Use in Preheat Trains

Abstract

Welded plate heat exchangers such as compabloc units, have found wide application in heat recovery systems, particularly in crude preheat trains. Due to their construction features, these types of exchangers present a complex multipass arrangement with an overall counter-flow arrangement and a cross-flow arrangement between passes. In design, the number of passes is a degree of freedom that is used in order to increase the velocity and the pressure drop of the streams involved, with the number of passes per stream being equal or unequal. An important step in the design of heat exchangers is the determination of the correction factor of the logarithmic-temperature difference. In this paper the correction factor is calculated using the thermal effectiveness model and a general expression for the complex arrangements exhibited by this type of exchangers is developed and applied to design.