Conceptual development of supercritical CO2 system configurations for waste heat recovery

Waste heat recovery from medium-temperature heat sources (300°C -700°C) has a great potential to increase the utilization efficiency of primary energy resources. Several configurations of supercritical CO2power systems have been recently proposed as promising alternatives to the more conventional steam Rankine cycle and Organic Rankine Cycle (ORC) systems.The goal of thispaper is to find a common thread in the conceptual developmentof sCO2systems configurations that have been specifically conceived for waste heat recovery (WHR) applications. The analysis of thebest performing WHR configurations in the literature showthat they areall created introducinga splitter after the compression process of the simple Brayton Joule cycle. Theydiffer for the location of the subsequent junction and for the components in between splitter and junction. To make then a fair comparisonof these configurations, the thermodynamic parameters of four properly-selected onesare optimized under the same boundary conditions for three heat source temperatures (300, 500 and 700°C) and their performances arediscussed analysing the thermal match in the heating and regeneration processes.Results show that, in the analysed rangeof the heat source temperature, a junction (i.e. a mixing point of the two mass flow rates generated by the splitter)in the heating zone yields higherpower output than a junction in the expansion zone. In fact, the single-split double-heating layout shows a power production that is from 1.5 to 40% higher than that of the double expansion and the simple-regenerative configurations, respectively.