Methodology for developing flexible, controllable and cost-effective heat exchanger network

Overview & Synopsis

This thesis pioneers to consider the time response in the heat exchanger network (HEN) multi-period design problem. We define the transition time (TT) as an indicator to measure the dynamic performance when HEN gets an operational period changeover. The thesis aims to solve two problems: how to measure the TT of a given HEN; and how to carry out synthesis work to optimize the HEN cost, allowing us to obtain a trade-off between the cost and TT. Relying on the Laplace transform, we develop a mathematical formulation to reach TT, leading to two dynamic models. The basic one requires the inverse Laplace transform process during the calculation. The improved dynamic model follows the analytic way, and free of the concern of the numerical difficulty of the inverse Laplace transform. The synthesis methods follow the sequential approach to iterate various structures and then TT can be calculated for each cost-optimized HEN. We propose two iteration methods: BINLP for the small case and IINLP for medium-large scale problems. The synthesis methods and HEN dynamic models were applied successfully in five case studies through different chapters, and found that TT varied hugely for different designs in each case. It is important to consider the time response in the HEN design problem, and our proposed methods can act as a pre-selection tool to help sort out those designs in terms of the cost and dynamic performances.