Optimisation for the retrofit of large scale heat exchanger networks with different intensified heat transfer techniques

Intensified heat transfer (IHT) techniques have recently been used for retrofit in the process industry, leading to significant energy saving in heat exchanger network (HEN) by facilitating heat transfer intensification without network topology modification. In this paper, an optimisation method has been developed for dealing with the retrofit of large scale HENs in which the location of intensified heat transfer within the network and its degree of intensification are systematically identified, given the objective function and design constraints, including topological limitation in the existing heat recovery systems. The optimisation framework developed is based on iterative optimisation of a relatively simple mixed integer linear programming (MILP), which can effectively deal with computational difficulties associated with nonlinearity. In the retrofitted HENs, several conventional intensified heat transfer techniques are available, including tube-side intensification (twisted-tape inserts, coiled-wire inserts and internal fins), and shell-side intensification (external fins and helical baffles). Suitable exchangers can be selected for enhancement by implementing one or more intensification techniques to increase the whole network energy recovery within very low retrofit cost. A large-size industrial case study is considered to demonstrate the validity and efficiency of the proposed optimisation approach.