The Potential of Recuperated Semiclosed CO2 Cycles

Abstract

Semi-closed cycles are characterized by firing a fuel with technically pure oxygen. The combustion gases mainly consist of CO2 and H2O. The use of the exhaust heat of the turbine in a steam bottoming cycle is the most common approach to achieve a sufficient thermal efficiency. In this paper it is shown that a semi-closed CO2 cycle with thermal recuperation avoids the complexity of a bottoming steam cycle and at the same time adds the potential of supercharging the cycle to high pressure. This allows both a very high power density and a discharge of fairly clean CO2 under sufficiently high pressure, which may be used directly or after separation of parasitic gases for enhanced oil recovery or other kind of disposal methods. We show in this paper preliminary cycle calculations, the optimization of pressure ratio, pressure level, turbine inlet temperature and recuperator assumptions. The real gas properties influence the cycle optimization and especially the temperature match within the recuperator.