Influence of Start-up Management on the Residual Life of a Large Steam Turbine Shaft

The liberalization of electricity market in Europe led to a growing competition between energy producers, making crucial the ability to optimize the management strategies of power plants. Combined Cycle Power Plants (CCPP) have to operate in a flexible way, with frequent and rapid variations of the power produced, in order to quickly adapt to the frequent changes in load imposed by the demand. Nowadays, they typically operate in cycling mode with daily start-up and shut-down. The components of the plant are subjected to great cyclical variations in temperature, which induce stresses on materials, especially during the start-up phases. The present activity concerns the assessment of life consumption -caused by these operations- on the rotor of the steam turbine of the CCPP (800 MW) inside the Tirreno Power thermal plant located in Vado Ligure, Italy. The aim is to draw a set of curves representing the percent life expended per cycle as a function of rate of steam temperature change and magnitude of the overall temperature increase. These curves are called Cyclic Life Expenditure curves (CLE). In the future, the developed methodology will be used to reduce the start-up times, keeping under control the life consumption of the rotor and optimizing the maneuvers that generate thermal transients.