Work-heat exchanger network synthesis (WHENS)

Research on heat integration has made significant advances in reducing utility consumption in chemical plants. However, the idea of work exchange between high and low-pressure process streams to reduce the consumption of the relatively expensive electricity has received limited attention. In this article, we present a more efficient mixed-integer nonlinear programming (MINLP) formulation to synthesize work-heat exchanger networks (WHENs). We propose a superstructure that explicitly considers constant-pressure streams for heat integration and enables an optimized selection of end-heaters and end-coolers to meet the desired temperature targets. Using a few examples, we demonstrate that simultaneous integration of work and heat in a chemical plant can offer significant savings in total annualized cost. In a case study from the literature, our approach yields a network with 3.1% lower total annualized cost, 10.6% more work exchange, and 81.0% more heat exchange than the best solution obtained from the existing literature approach. Furthermore, our approach successfully solves two case studies that previous literature approaches fail to solve.