A case study of cascade supercritical CO2 power cycle for waste heat recovery from a small gas turbine

Among the technological solutions that can be applied to waste heat recovery, the supercritical CO2 (sCO(2)) cycle represents an innovative option. This work studies the performance of the single heated cascade sCO(2) cycle as the bottomer power system of a 5 MW-class gas turbine and follows a former study of the authors about the partial heating cycle. A number of parametric analyses has been carried out with attention paid to the selection of (i) minimum and maximum CO2 pressures, based on a compressor Mach number selected to avoid highly loaded turbomachinery, (ii) maximum CO2 temperature, and (iii) specific design parameters such as temperature dif-ference at the cold side of the primary heater, recuperator effectiveness and single-stage radial-type turbine efficiency, the latter calculated according to Aungier's correlations by taking actual size and running conditions into account. The results of this study suggest that around 1500 kW of net electric power can be recovered by the single heated cascade sCO(2) cycle. This figure is not so different from the power output previously calculated for the partial heating cycle as well as the specific cost of the technology, which is around 2000 $/kW, lower than a possible competing technology for waste heat recovery applications as the organic Rankine cycle. Nevertheless, the architecture investigated in this study needs two turbines which can rotate on the same shaft, but driving the compressor at the same rotational speed of the two turbines is not possible, as emerges from preliminary con-siderations about the size of the turbomachinery impellers.