Automated design method for heat exchanger network using block decomposition and heuristic rules

Abstract

The research in HEN synthesis has achieved significant progress over the last two decades, particularly through the discovery of the pinch concept and the research in targeting energy and capital. Normally, the HEN synthesis is carried out with two stages, targeting and design. In the past, many researchers mainly focused on developing manual design methods. Having realised the significance of saving engineering time and the possibility of using mathematical optimisation techniques to enhance the search for good designs, much research has been carried out to develop automated HEN design methods and significant progress has been achieved. However, there is still no design methods available which can fulfil the task of automated synthesis for practical applications. In the present paper, a simple method for automated synthesis of HEN is presented, which is based on the block concept proposed by Zhu et al. (1995a). The basic idea is to simplify a design problem by decomposing it into a number of blocks. In each block, piece-wise stream composites present similar profiles and hot streams are in energy balance with cold streams. After the block decomposition, design is carried out using area targeting principles and a number of newly developed heuristic rules. An MILP model and a simple MINLP model are used for selecting a best set of matches and determining the optimal split ratios, respectively. The initial designs produced by such a method can approach the energy and area targets closely coupling with a small number of units. Such good initial solutions are then provided for subsequent cost optimisation. The main advantage of this design strategy is that designs with good quality can be achieved efficiently and effectively. In addition, the block concept can be easily extended to handle problems with different film coefficients by combining the current method with the diverse pinch approach proposed by Rev and Fonyo (1991) [( Chem. Eng. Sci. 46, 1623–1634 (1991)] and thus the above strategy for HEN synthesis can be applied for such problems.