A new modeling approach for HEN retrofit design is discussed; The design ta
sk consists of a sear ch for topology changes, called the diagnostic stage,
followed by an evaluation stage and a cost optimization stage. Promising m
odifications are selected from the diagnosis stage and assessed in terms of
the impacts on implementation case, operability, and safety. The options d
eemed impractical are removed and the remaining ones are optimized together
with the existing HEN to give the final WEN retrofit design. The new appro
ach combines mathematical optimization techniques with a better understandi
ng of the retrofit problem, based on thermodynamic analysis and practical e
ngineering to produce a systematic procedure capable of efficiently solving
industrial-size retrofit problems. The network pinch concept provides new
insights to the HEN retrofit problem and plays an important role in selecti
ng promising modifications, forming the foundation of the new method. This
concept, when applied to mathematical formulation, significantly, simplifie
d the mathematical models while maintaining good quality of solutions. This
approach allows the design tasks to be automated with user interactions.