sCO2 Key Technologies

Turbomachinery: The turbomachinery R&D focuses on advancing technologies and designs of turbomachinery to be used in the supercritical CO₂ power cycle. Operating power cycles, either directly or indirectly, with supercritical CO₂ offers potential for further improvements in power cycle efficiencies and lower costs. However, the utilization of supercritical CO₂ as the working fluid must be considered when designing the turbines. Extremely compact turbine sizes are possible for use in the supercritical CO₂-based power cycles. These turbines will have high power density, lower peripheral speeds, high blade loading, and high shaft speeds, all of which will factor into the final turbine designs. The high pressure, relatively high temperature, uncertainty of the CO₂ state near the critical point, and high power density create design challenges for the supercritical CO₂ turbomachinery. The R&D will consider all aspects of the turbomachinery, including the turbo-expander, compressors, pumps, airfoils, turbine coupling with the motor/generator, seals, casings, bearings, shafts, and valves.

Recuperators: The supercritical CO₂-based power cycle utilizes high and low temperature recuperators to recover heat in the process and increase cycle efficiency. The recuperator projects focus on the advancement of technologies and designs, along with the fabrication of recuperative heat exchangers. Work includes development and testing of innovative compact, high surface area density (>700 m2/m3) recuperator designs and identification of compatible materials to allow for highly efficient heat transfer under operation at high inlet temperatures and large pressure differentials typical of the supercritical CO₂ power cycles. Multiple compact heat exchanger concepts will be identified, developed, and evaluated. Achieving recuperator cost and performance targets is vital to enabling commercial implementation of the sCO₂ power cycle.

Advanced Concepts for Direct-Fired Cycles: In directly-fired supercritical CO₂ power cycles, oxygen and fuel (either syngas or natural gas) are combusted, forming a stream of primarily supercritical CO₂ and steam which is used as the working fluid in the power cycle. The higher temperature and pressure conditions of these cycles give the potential for even higher cycle efficiencies, while the process produces CO₂ for either sequestration or reuse purposes. The R&D within this key technology aims to develop high-pressure and high-temperature oxy-fuel combustors to be used with CO₂ as the diluent, as well as the integration of the combustors with the turbomachinery, for use in directly fired sCO₂ power cycles. The challenges associated with this R&D include understanding combustion kinetics and dynamics under these conditions, combustion stability, flow path design, thermal management, pressure containment, and definition of turbine inlet conditions.

Systems Integration & Optimization: The supercritical CO₂ power cycle can be integrated with the fossil energy heat source in various configurations. Optimal integration and process operating conditions must be identified to achieve high efficiency and lower cost electricity generation. Systems integration and optimization work focuses on overall system analyses, modeling, and engineering to integrate and design the sCO₂ power cycle for optimized performance (efficiency), cost, and operability.