Optimising entire lifetime economy of heat exchanger networks

This contribution presents an optimisation methodology for a Heat Exchanger Network (HEN) design over its entire lifespan. Consideration of fluctuating energy prices is essential for achieving an optimal HEN design. The objective function presents a trade-off between investment and operating costs. Accounting for higher energy prices supports greater investments compared to solutions obtained with current prices. However, due to the uncertainty of utility prices' forecasts, retrofit with the extension of HEN regarding the lifespan, will usually be the future strategy. As there can be various designs featuring similar initial investments, the objective is to identify one design that will be the most suitable for effective future extensions, preferably with low sensitivity to energy price fluctuations. These observations resulted in development of a stochastic multi-period mixed-integer nonlinear programming (MINLP) model for the synthesis of HEN designs, with extensions accounting for future energy prices. The objective of this work was to maximise both the Expected Net Present Value with no risk assessment performed, and the Certainty Equivalent with risk assessment regarding future utility prices and investment. The results obtained indicate that when applying the proposed approach, a design with improved economic performance could be obtained, especially when compared with Total Annual Cost.