The process plant layout problem consists in defining the
optimal spatial arrangement of a set of facilities and the required
connections among them within a plant site. The location of process
units and plant facilities is chosen in order to reduce land use
and the costs of the piping interconnecting each units pair, as well
as to organize more efficiently the production and increase the
plant safety. Such requirements frequently give rise to conflicting
goals. If, on the one hand, material transfer cost and occupied area
are reduced by placing interrelated units at a short distance, on the
other hand safety concerns ask for minimum safety distances between
process units to be maintained. Process plant layout design is
an activity usually carried out by human designers (Mecklenburgh,
1985). Computer-aided layout planning methods were instead
scarcely adopted in the past in this sector owing to the difficulty in
minimizing a number of different objective functions simultaneously
in a realistic manner. Nevertheless, there is a growing need
to develop computer-aided methods to support process plant engineers
in the rapid generation of alternative chemical plants