Among the technologies which allow to reduce greenhouse gas emissions, mainly of carbon dioxide, special attention deserves the idea of 'zero-emission' technology based on boilers working in oxy-combustion technology. In the paper a thermodynamic analysis of supercritical power plant fed by lignite was made. Power plant consists of: 600 MW steam power unit with live steam parameters of 650°C/30 MPa and reheated steam parameters of 670°C/6 MPa; circulating fluidized bed boiler working in oxy-combustion technology; air separation unit and installation of the carbon dioxide compression. Air separation unit is based on high temperature membrane working in three-end technology. Models of steam cycle, circulation fluidized bed boiler, air separation unit and carbon capture installation were made using commercial software. After integration of these models the net electricity generation efficiency as a function of the degree of oxygen recovery in high temperature membrane was analyzed.