EXERGETIC EVALUATION OF GAS TURBINE COGENERATION SYSTEMS FOR DISTRICT HEATING AND COOLING

Abstract

A cogeneration system (CGS) generating both power and heat for district heating and cooling is required to be able to cope efficiently with its heat demand change. In this paper, two types of gas turbine CGSs were investigated: (1) a CGS using a dual fluid cycle; and (2) a CGS using a combined cycle. Exergy flows at various points of each CGS have been evaluated when its heat demand is changed. The following have been shown through simulation studies: (a) the higher the heat supply ratio, the higher the exergetic efficiency of the dual fluid cycle CGS; (b) the lower the heat supply ratio, the higher the exergetic efficiency of the combined cycle CGS; and (c) the highest exergetic efficiency of the dual fluid cycle CGS at the maximum heat supply operation is higher than that of the combined cycle CGS; and the exergetic efficiency of the combined cycle CGS at the minimum heat supply operation is higher than that of the dual fluid cycle CGS. A simple criterion has also been derived for determining which type of CGS has higher average exergetic efficiency for a specific district when its heat demand characteristics are known. © 1997 by John Wiley & Sons, Ltd.