Synthesis of transcritical ORC-integrated heat exchanger networks for waste heat recovery

Abstract

This article aims to present a mathematical model for synthesis of a heat-exchanger network (HEN) which can be integrated with a transcritical organic Rankine cycle (T-ORC) for recovering low-grade waste heat from the heat surplus zone of the background process. This work is a direct extension of previous one where the working fluid was operated under subcritical pressure. A T-ORC integrated stagewise superstructure considering all possible match of process hot/cold streams and the recirculated working fluid is proposed. Based on this superstructure, a mathematical model for synthesizing T-ORC integrated HENs is formulated as a mixed-integer nonlinear program (MINLP), therein the objective is to maximize the net work produced from waste heat in the heat surplus zone below the process pinch. A literature example is solved to demonstrate the application of the proposed model for industrial waste heat recovery. For a given heat source, some organic fluids can be used in both subcritical and transcritical status. After a minor modification, the model can be applied for not only subcritical but also transcritical ORC. Based on the results from the modified model, it is found that the T-ORC-involved HEN can produce higher net power over the heat recovery system where the ORC is operated under subcritical state. ? 2015 Elsevier B.V.