Thermodynamic, economic, and environmental analysis and multi-objective optimization of a dual loop organic Rankine cycle for CNG engine waste heat recovery

Abstract

• Thermodynamic, economic, and environmental analysis are presented. • Proposing a multi-model driven NSGA-III method for DORC performance optimization. • A tradeoff appears among thermal efficiency, payback period and CO 2 emission. Waste heat energy exists in the exhaust, intercooler, and coolant during the operation of the compressed natural gas (CNG) engine. The cascade utilization of the waste heat energy of the CNG engine can be realized considering the structural advantages of the dual loop organic Rankine cycle (DORC) system. Operating parameters have an important influence on DORC system performance. Traditional analysis methods have limitations in analyzing the relationship between operating parameters and system performance, and little attention is paid to the environmental impact of the system. The environmental performance of the system plays an important role in saving energy and protecting the environment. Therefore, the bilinear interpolation algorithm is introduced to analyze the waste heat sources of the CNG engine and the thermodynamic, economic, and environmental performances of the DORC system. In addition, the comprehensive operating performance of the DORC system has not been thoroughly and comprehensively optimized. Therefore, this study proposes a multi-model driven NSGA-III method for DORC comprehensive performance optimization. Results show that the optimal thermal efficiency, payback period (PB), and emissions of CO 2 equivalent (ECE) are 11.98%, 4.02 years, and 43.74 ton CO 2,eq , respectively. Moreover, decreasing the thermal efficiency of the system will significantly decrease ECE and increase PB at the same time. This research provides a reliable reference for the analysis, design, evaluation, and optimization of the comprehensive performance of the DORC system.