The report discloses thermodynamic studies of the semi-closed oxy-fuel combustion combined cycle. The computer simulation and parametric optimization approaches are described in details. The oxy-fuel cycle net efficiency in relationship to the carbon dioxide turbine exhaust pressure and the steam turbine inlet pressure is shown. The power production efficiency reduction is related to the turbine cooling losses is described. It is shown that the semi-closed oxy-fuel combustion cycle maximal net efficiency of 52.5% occurs at the initial temperature and pressure 1400°C and 60 bar at the carbon dioxide turbine exhaust pressure 0.5 bar and the steam turbine inlet pressure 90 bar. The cooling losses consideration leads to the net efficiency of 47.76% that is reached at the carbon dioxide turbine exhaust pressure 1 bar and the steam turbine inlet pressure 90 bar.

The paper presents results for chemical kinetics of combustion process in the combustor of oxy-fuel cycle super-critical carbon dioxide gas turbine based on the Allam thermodynamic cycle. The work shows deviation of the normal flame propagation velocity for the case of transition from the traditional natural gas combustion in the N2 diluent environment to the combustion at super-high pressure up to 300 bar in CO2 diluent. The chemical kinetics parametric study involved the Chemkin code with the GRI-Mesh 3.0 kinetic mechanism. This mechanism provides good correspondence between calculation results and test data. The CO2 and N2 diluents temperature, pressure and contents influence the flame propagation velocity and the chemical kinetics parameters in the two gas turbine types. It is demonstrated that the CO2 diluent slows down chemical reactions stronger than the N2 one. The flame propagation velocity in carbon dioxide is four time smaller than in the N2 one. In the oxy-fuel cycle combustor a pressure increase reduces the flame propagation velocity. Increase of the CO2 content from 60 to 79% reduces the flame propagation velocity for 65% at atmospheric pressure and for 94% at super-critical pressure. An increase of the combustor inlet mixture temperature from 300 to 1100 K at super-critical pressure causes the flame propagation velocity increase for 94%. The flame propagation velocities compatible with the traditional gas turbines may be reached at the CO2 diluent content of the O2 + CO2 mixture in the active combustion zone must be below 50%.

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Mitigation of harmful and greenhouse gas emissions produced by the coal combustion in thermal power plant is a topic goal. Reduction of the nitrogen oxides, sulfur and ash emissions makes remarkable progress but the carbon dioxide emission still meets considerable difficulties mostly caused by the low greenhouse gas content in the flue gas. A prospective solution to this problem may be the fuel combustion in oxygen-enriched air, which increases the flue gas carbon dioxide content. In this technology, the carbon dioxide content in flue gas is higher and this results in its easier capture. This paper presents the thermodynamic analysis results of a steam turbine power production facility that burns coal in the air with high oxygen content. The computer simulation shows that the oxygen content increase from 21 to 95.6% increases the carbon dioxide content in flue gas by a factor of 3.3 and lowers the power consumption for carbon dioxide capture by 11%. On the other side, the power consumption for pure oxygen production reduces the facility’s net efficiency from 28.54 to 21.59%.