This paper presents a thermodynamic analysis of a natural gas zero-atmospheric emissions power plant with a net electrical output of 400 MW. In this power plant, methane is combusted with oxygen in a gas generator to produce the working fluid for the turbines. The combustion produces a gas mixture composed of steam and carbon dioxide. These gases drive multiple turbines to produce electricity. The turbine discharge gases pass to a condenser where water is captured as liquid and gaseous carbon dioxide is pumped from the system. The carbon dioxide can be economically conditioned for enhanced recovery of oil, or coal-bed methane, or for sequestration in a subterranean formation. The analysis considers a complete power plant layout, including an air separation unit, compressors and intercoolers for oxygen and methane compression, a gas generator, three steam turbines, a reheater, a preheater, a condenser, and a carbon dioxide pumping system to pump the carbon dioxide to the pressure required for sequestration. The computer code is a powerful tool for estimating the efficiency of the plant, given different configurations and technologies. The efficiency of the power plant has been calculated over a wide range of conditions as a function of the two important power plant parameters of turbine inlet temperature and turbine isentropic efficiency. This simulation is based on a 400 MW electric power generating plant that uses turbines that are currently under development by a U.S. turbine manufacturer. The high-pressure turbine would operate at a temperature of 1089 K (1500 °F) with uncooled blades, the intermediate-pressure turbine would operate at 1478 K (2200 °F) with cooled blades and the low-pressure turbine would operate at 998 K (1336 °F). The corresponding turbine isentropic efficiencies for these three turbines were taken as 90, 91 and 93 percent. With these operating conditions, the zero-atmospheric emissions electric power plant has a net thermal efficiency of 46.5%. This net thermal efficiency is based on the lower heating value of methane, and includes the energy necessary for air separation and for carbon dioxide separation and sequestration.
Comparative thermodynamic analysis and integration issues of CCS steam power plants based on oxy-combustion with cryogenic or membrane based air separation
