Techno-economic assessment of Joule-Brayton cycle architectures for heat to power conversion from high-grade heat sources using CO2 in the supercritical state

Abstract

Bottoming thermodynamic power cycles using supercritical carbon dioxide (sCO2) are a promising technology to exploit high temperature waste heat sources. CO2 is a non-flammable and thermally stable compound, and due to its favourable thermophysical properties in the supercritical state, it can achieve high cycle efficiencies and a substantial reduction in size and cost compared to alternative heat to power conversion technologies. Eight variants of the sCO2 Joule-Brayton cycle have been investigated. Cycle modelling and sensitivity analysis identified the Turbine Inlet Temperature (TIT) as the most influencing variable on cycle performance, with reference to a heat source gas flow rate of 1.0 kg/s and 650°C. Energy, exergy and costs metrics for different cycle layouts have been are compared for varying TIT in the range between 250°C and 600°C. The analysis has shown that the most complex sCO2 cycle configurations lead to higher overall efficiency and net power output but also to higher investment costs. Conversely, more basic architectures, such as the simple regenerative cycle, with a TIT of 425°C, would be able to achieve an overall efficiency of 25.2%, power output of 93.7 kWe and a payback period of less than two years.