Thermodynamic features of the regenerative system of direct fired sCO2 power cycles with oxygen combustion of methane

•The share of heat recycling in the sCO2 power cycle exceeds 50%.•The contribution of steam to heat fluxes is 3–5 times higher than its mass fraction.•The regenerative system is able to heat CO2 to 2/3 level of turbine inlet temperature.•The theoretical heat flux to the regenerative system is 800–1000 kJ/kg of CO2. The article presents an analysis of the thermodynamic features of the operation of a regenerative system of sCO2 power cycles. The cycle with a two-stage pressure increase configuration is taken as a basis for calculation. The supply of energy to the working fluid is provided by the operation of the regenerative system and by oxy-fuel combustion. Methane is used as fuel. The issues of theoretically achievable heating temperatures of the working fluid in the cycle regenerative system are considered. The influence of thermodynamic parameters on the heat fluxes of the regenerative system is estimated. For the first time, an assessment was made of the relative and absolute contribution of water vapor, formed during fuel combustion, to heat flows. This study makes it possible to establish the physical quantities pressure, temperature and heat fluxes, which are necessary for further design calculations of heat exchangers to be used in industrial installations. As a result of multi-variant calculations of the cycle (when varying the temperature at the turbine inlet in the range of 500–1500 °C and pressure - from 100 to 400 bar), it was found that the temperature of the working fluid supply to the combustion chamber can be taken at the level of 2/3 of the temperature at its outlet. At operating temperatures of the working fluid at the level of 1000–1200 °C, the contribution of water vapor to regenerative heating will be 3–17%, depending on their mass content. The total theoretical heat flow to the cycle regenerative system will be 800–1000 kJ/kg CO2. The energy supply to the working fluid due to fuel combustion does not exceed 50% of the total energy supplied in the operating temperature and pressure ranges.