A two-layer optimization framework for combined heat and power with an enhanced organic rankine cycle

Abstract

Integration of Organic Rankine Cycle (ORC) and chemical process is conductive to raise energy efficiency and mitigate carbon emissions. Current studies chiefly consider combination of ORC and heat exchanger network to recover low-temperature waste heat, which neglects power-heat interaction for process streams with pressure and temperature variations. To address this issue, this paper proposes a two-layer optimization framework to achieve the integration of an enhanced ORC and process streams with pressure/temperature variation. The presented framework aims to optimize the pressure-temperature path of process streams through the network for optimal combined heat and power generation. The outer layer focuses on optimizing the configurations and operating parameters of the ORC, while the inner layer utilizes an extended Duran-Grossmann model (D-G model) to reduce utility consumption by determining the optimal inlet temperature of the pressure-change sub-streams. The objective function is to minimize the exergy consumption. Case studies with six schemes are performed to assess the effectiveness of the presented method, where the amount of total heat recovery increased by 82.7 % compared to the approach without using ORC. The main contributions of the proposed framework are of significant aid in providing guidelines for the further development of low-temperature waste heat recovery combined with a power/heat-integrated system.