Transient simulation and fatigue evaluation of fast gas turbine startups and shutdowns in a combined cycle plant with an innovative thermal buffer storage

In this paper a novel buffer storage for the thermal decoupling of gas turbine (GT) and heat recovery steam generator (HRSG) during startups and shutdowns is presented to the scientific public. The storage consists of a matrix of metal plates, placed in the flue gas channel between GT and HRSG, which is heated up during startup and cooled down during shutdown thus reducing the thermal gradients in the actual HRSG. The limitation to fast startups in combined cycle gas turbine (CCGT) plants is usually fatigue induced damage in critical components in the HRSG. To investigate the influence of the storage on the fatigue damage, a transient modeling strategy of both, storage and HRSG, is developed. It is found, that in the investigated plant such a storage is capable of reducing the cycling fatigue damage in the most critical part of the HRSG by up to 90% and therefore enables to act the GT as flexible as if no HRSG was connected to it.