Selection of minimum temperature difference (dTmin) for heat exchanger network synthesis based on trade-off plot

Abstract

This paper presents a systematic technique to select the optimal design target for the heat exchanger network (HEN) synthesis by using a new trade-off plot which considers aspects of design, controllability in terms of steady state flexibility and sensitivity analysis, and cost. By selecting the HEN design target according to this guideline, the designer is able to predict the design, operability, and controllability of the designed HEN at the beginning of the synthesis stage. In this study, the HEN design target that needs to be optimized is the value of the minimum temperature difference (δTmin). In traditional HEN synthesis, designers only consider the trade-off between capital and operating costs in selecting the best δTmin. As a result, the HEN design at the selected δTmin may not be optimum in terms of steady state controllability. In addition to considering the capital and operating costs, the proposed new method provides additional design insights in terms of energy recovery, operability, controllability (steady state) through the flexibility and sensitivity. The proposed trade-off plot allows designers to choose the most suitable design target either for the purpose of improving a network's energy recovery and/or controllability. A case study has been applied to test the capability of the new proposed trade-off plot. The results show that δTmin = 40 °C is the optimal design target to synthesize flexible and operable HEN.