Thermo-economic Comparison of Organic Rankine and CO2 Cycle Systems for Low-to-medium Temperature Applications

orc2019 Tracking Number 108

Organic Rankine cycle (ORC) power systems are a well-established technology for low-to-medium temperature heat-conversion applications. Recently, CO2-cycle power systems have emerged as another promising heat-to-power conversion technology and have been receiving increased interest due to certain advantages offered by the working fluid (e.g., non-flammable, high-temperature stability) and system compactness. However, it remains a challenge to select the appropriate technology between ORC and CO2 power-cycle systems for different applications, as these can span a wide range of scales and heat-source conditions, particularly from an integrated thermodynamic and economic perspective. This paper presents a comprehensive thermo-economic comparison of ORC and CO2 power systems with various architectures (i.e., with or without recuperation) in the specific context of power generation from two representative low- and medium-temperature heat sources, namely, brine in geothermal heat applications, and exhaust gases in waste-heat recovery from internal combustion engine applications. Expansion devices suitable for the given power scales, i.e., reciprocating-piston expanders and radial-inflow turbines, are considered and compared using comprehensive component-level models. Based on thermodynamic and economic performance analyses, technology selection maps for power generation from the pre-defined low- and medium-temperature heat sources are generated using the net power output and specific investment cost as key performance indicators. These performance selection maps allow for quick and effective decision making in choosing the optimal power cycles and system designs for geothermal exploitation, engine waste-heat recovery and other relevant heat-to-power applications.