Thermodynamics of combinedcycle electric （热力学combinedcycle电气）.pdf

Thermodynamics of combined-cycle electric power plants Harvey S. Leffa) Department of Physics, Reed College, Portland, Oregon 97202 (Received 7 October 2011; accepted 27 February 2012) Published data imply an average thermal efficiency of about 0.34 for U.S. electricity generating plants. With clever use of thermodynamics and technology, modern gas and steam turbines can be coupled, to effect dramatic efficiency increases. These combined-cycle power plants now reach thermal efficiencies in excess of 0.60. It is shown how the laws of thermodynamics make this possi- C ble. V 2012 American Association of Physics Teachers. [/10.1119/1.3694034] I. INTRODUCTION Perhaps fortuitously, gnca is a rough guide to the efficien- cies of many existing fossil fuel, nuclear, and geothermal It is common in the study of thermodynamics to examine electric power plants. For example, a plant with combustion reversible heat engine models. One learns that the maximum temperature 838 K and ambient temperature 298 K has an efficiency of a heat engine operating between colder (Tc ) and actual plant efficiency of 0.36,4 which compares reasonably hotter (Th ) constant-temperature reservoirs is gcarnot well with g ¼ 0:40. In contrast, g ¼ 0:64, consistent nca carnot ¼ 1 T =T , that of a reversible Carnot cycle. Of course, c h with inequality (2). there are no such reversible cycles