Gas turbine combined cycle start-up and stress evaluation: A simplified dynamic approach

•A simplified dynamic model of a GTCC bottoming cycle for plant start-up is presented.•Particular emphasis is placed on determining thermal stress on Steam Turbine rotor.•To enhance accessibility, the model is developed within Microsoft Excel environment.•The target system is the 390 MW Tirreno Power GTCC of Napoli Levante (Italy).•Model validation is pursued against field measurement data (mean error of 5%).

The main topic of this work is the development and validation of a simplified approach for the dynamic analysis of a Gas Turbine Combined Cycle (GTCC), with a particular focus on start-up procedure and associated mechanical stresses on the steam turbine (ST). The currently deregulated energy market led GTCC to undergo frequent startups, a condition often not considered during plant design. Moreover, the time required for the start-up is crucial under an economical viewpoint, though it is constrained by mechanical stresses imposed to thick components by thermal gradients. The framework proposed in this work aims to improve the accessibility to simulation software by applying commonly used office suite - Microsoft Excel/Visual Basic - with acceptable reduction in accuracy. Simplicity of model allow fast computation and its exploitation can be pursued by non-qualified plant operators. The obtained tool can be than adopted to support decision process during plant operations. The developed tool has been validated for a hot start-up against field measurements supplied by Tirreno Power S.p.A. Italy. Data are recorded through control and monitoring sensors of a 390 MW multi-shaft combined cycle based on the GT AEN94.3 A4 frame, but the results can be easily generalized to other layouts. Simulation result and stress evaluations around the steam turbine (ST) rotor show good agreement with experimental data.