In this paper a dynamic simulator of Brazed Plate-Fin Heat Exchangers (PFHEs) ProSec(TM) is presented. A rigorous model is used which allows one to represent the very broad range of configurations for this kind of equipment. A DAE solver (DISCo) is used with a sparse direct solver (MA38) to handle the large number of equations. Applications for control and design are highlighted through an industrial case study involving shutdown.