Supercritical carbon dioxide (sCO2) power cycles, such as the Allam Cycle, operate in a manner similar to other turbine cycles but with CO2 as the working fluid. The cycles operate above the critical point of CO2, so that very high changes density occur for relatively small changes in temperature and pressure. This allows a large amount of energy to be extracted at high temperature from equipment that is relatively small in size. Supercritical CO2 turbines will have a nominal gas path diameter an order of magnitude smaller than both utility scale gas turbines and steam turbines.
The Advanced Turbines Program at NETL conducts R&D for directly and indirectly heated sCO2-based power cycles for fossil fuel applications. The focus is on components for indirectly heated fossil fuel power cycles with turbine inlet temperatures in the range of 1300 - 1400ºF (700 - 760ºC) and oxy-fuel combustion for directly heated supercritical CO2 based power cycles.
The turbomachinery R&D focuses on advancing technologies and designs of turbomachinery to be used in supercritical CO2 power cycles. Operating power cycles with supercritical CO2 offers potential for further improvements in power cycle efficiencies and lower costs. 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 supercritical CO2 turbomachinery. Current and future 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.
