Modelling the Transient Behavior of Combined Cycle Plants

Abstract

The last decade has seen remarkable improvement in industrial gas turbine unit size and performances. The coming years and decades hold the promise of even more progress in these fields. Simultaneously, the fuel utilization achieved by combined cycles has been steadily increased, which is a combination of improvements both in the gas turbine technology and in the new combined cycle schemes with multiple pressure levels. These combined cycles quite often have to operate on a load cycling duty or in the intermediate load range, so that not only the design point performances but even the off design are sufficient to ensure the plant profitability. Its transient behaviour, its ability to start quickly and reliably, are key parameters when selecting the plant. This paper describes a method developed for the calculation of the transient performances of combined cycles, from no load situations, including cold conditions, to full load. The method is then applied and illustrated with a recently commissioned plant, for which some transient measurements are available.