Zero-Emission Combined Power Cycle Using LNG Cold

A potential zero emission combined power generation plant fired by liquefied natural gas (LNG) has been investigated. A mixture of carbon dioxide (CO_2)-steam is used as the working fluid of a gas turbine cycle, which replaces the normal combustion-in-air products and air, notably as the thermal ballast for the control of flame temperature. Oxygen (O_2) is used as the fuel oxidant and is obtained from an air separation unit (ASU). The excess CO_2 due to combustion is extracted by a simple flow separator and liquefied ready to be reused and/or sequestered. The plant configuration and thermodynamics of the cycle are discussed first and then the optimised overall efficiency of the plant is calculated with a comparison of 100% and 120% stoichiometric combustion. The overall net efficiency, optimised to pressure and temperature levels complying with the material and cooling techniques currently available, is around 56% (LHV basis), including the energy penalty of the ASU and the CO_2 separation.