Abstract

The operating conditions of steam turbine used in combined cycle (GTCC) power plants have significantly changed in last years. Traditional power plants are moving to work as peaker plants to support electrical grid during drop of production of renewable ones. This operative condition means steam turbines have to start-up often and quickly.

High fuel costs are driving power producer to seek high efficiency. In this way, Ansaldo Energia is offering combined cycles with his H class gas turbines GT-36. Gas exhaust of these turbines are at higher temperature compared to F class ones, allowing combine steam turbines to operate at higher inlet temperatures and so increasing their efficiency.

Both the presented change in operative condition could affect the component life of some parts of steam turbine, but the true challenge is to satisfy both requests together.

This paper shows studies carried out on a three-pressure level steam turbine operating in combining with a H class GT-36, focusing on rotors, turbine casings and valve casings lifetime. Different typologies of start-up after different cooling times have been considered, reaching a super-heater and re-heater base load inlet temperature of 600°C. Fatigue damage due to each start-up and creep damage due to high temperature base load have been calculated separately, and the summed up as Ansaldo practice to verify each component lifetime.