From time to time one hears of objections to the implementation of CAPE OPEN proptocols because it is said that the overhead due to the interaction between, for example, a unit operation model and a thermodynamic properties package is considered excessive. To the best of our knowledge, however, there are no published measures of this added overhead.

Distillation simulation is perhaps that aspect of chemical process simulation that makes the greatest demands on thermodynamic properties packages.

In order to determine the overhead incurred by the CapeOpen protocol calculations were performed for thermodynamic and physical property calculations in column simulations using the ChemSep column simulator and the CapeOpen flowsheet environment COCO. Because COCO includes a re-implementation of the ChemSep property routines, the overhead of the CapeOpen protocol could be computed as function of the number of components and the type of property calls. Several industrial test cases are used to illustrate the overhead of CapeOpen technology.