Advanced Combined Cycle Alternatives With the Latest Gas Turbines

Abstract

The last decade has seen remarkable improvements in industrial gas turbine size and performances. There is no doubt that the coming years are holding the promise of even more progress in these fields. As a consequence, the fuel utilization achieved by combined cycle power plants has been steadily increased. This is, however, also because of the developments in the heat recovery technology. Advances on the gas turbine side justify the development of new combined cycle schemes, with more advanced heat recovery capabilities. Hence, the system performance is spiraling upward. In this paper, we look at some of the heat recovery possibilities with the newly available gas turbine engines, characterized by a high exhaust temperature, a high specific work, and the integration of some gas turbine cooling with the boiler. The schemes range from classical dual pressure systems, to triple pressure systems with reheat in supercritical steam conditions. For each system, an optimum set of variables (steam pressures, etc.) is proposed. The effect of some changes on the steam cycle parameters, like increasing the steam temperatures above 570°C are also considered. Emphasis is also put on the influence of some special features or arrangements of the heat recovery steam generators, not only from a thermodynamic point of view.