A Simple Strategy for Optimal Operation of Heat Exchanger Networks

The objective of this work is to propose a systematic procedure to find a control structure for optimal operation of heat exchanger networks. Optimal operation in this context requires that 1) all controlled temperatures are kept at their targets and 2) utility cost is minimized. The degrees of freedom of heat exchanger networks are analyzed and used to identify if the operation is structurally feasible and if the utility cost can be optimized. The LP problem formulation for optimal operation of HENs implies that optimal operation is always at active constraints in terms of target temperatures and zero or maximum heat transfer (such as fully open or fully closed bypass valves). The information from an offline optimization is used to identify the set of nominally active constraints, and then split-range and selective controls are used to track the active constraints during operation for optimality