Enhancing sustainable energy conversion: Comparative study of superheated and recuperative ORC systems for waste heat recovery and geothermal applications, with focus on 4E performance

Abstract

This study investigates the 4E performance of small-scale (<100 kW), low-temperature (<179 °C) Organic Rankine Cycle (ORC) technology, comparing two distinct configurations using different working fluids and heat sources. The work utilizes experimental methods to analyse the efficiency of the ORC systems, focusing on variables such as evaporation temperature and pressure drop across the heat exchanger. Various working fluids and heat sources are tested to evaluate their impact on performance using CoolProp libraries.The results reveal that the ideal evaporation temperature for maximizing overall performance and efficiency is between 140 and 150 °C. Higher pressure drop across the heat exchanger improves heat transfer, thermal efficiency, and power output, but increases pumping requirements and reduces overall effectiveness. Among the tested heat sources, the Dynalene SF exhibits the best performance, followed by therminol T72, T66, geothermal water, and Paratherm HE. The most suitable working fluids for commercial ORC units are R245fa and hexamethyldisiloxane (MM), providing excellent thermodynamic properties and low environmental impact. Comparatively, the superheated ORC system using R245fa outperforms the MM, achieving higher net efficiency (7.29%), greater network generation (20.29%), and improved exergy efficiency (20.54%). The economic viability of the recuperative system is evident from the Levelized Cost of Electricity (LCOE) range of 12.4–14.5 (cents/kWh), with an average Total Installed Cost (TIC) of 354.5 k$. These results showcase the system's competitiveness in providing cost-effective electricity generation, reaffirming its potential as a financially viable option for sustainable energy solutions.The objective is to explore the use of Organic Rankine Cycle (ORC) technology as an alternative to steam Rankine cycle for low-power and lower-temperature applications. Specifically, the study focuses on ORC systems with external heat sources, including geothermal, solid fuels and waste heat recovery (WHR).The novelty of this article lies in its updated analysis of the techno-economic-environmental feasibility of ORC systems for different applications, which goes beyond previous studies. It provides a systematic evaluation and comparison specifically tailored to small-scale and low-temperature operating conditions. The aim is to promote the integration of these two systems in various sectors, particularly for countries undergoing an energy transition. This emphasis on the technical aspects and the specific focus on small-scale and low-temperature conditions make this study unique and valuable in advancing the understanding and application of ORC technology.