Optimization of Retrofit and Cleaning Schedules for Heat Exchanger Networks Subject to Fouling

Retrofit of heat exchanger networks (HEN) is commonly done to increase their efficiency or respond to changing operational needs. It involves modifying the structure of the network and/or the design of individual units. Decisions are usually based on simplified, steady state models, ignoring performance decay due to fouling, the system dynamics, and possible mitigation actions during operation. However detailed dynamic simulations show all these aspects are important. Here, a mathematical formulation and solution are presented for the optimal retrofit of HEN under fouling that consider realistic exchanger models, fouling dynamics, and cleaning scheduling at the same time. A case study for a refinery preheat train demonstrates that simultaneous optimization of retrofit and cleaning schedules significantly reduces operating cost and capital investment.