Utilization of a Thermo-Mechanical Model Coupled With Multi-Objective Optimization to Enhance the Start-Up Process of Solar Steam Turbines

Abstract

The need to mitigate the climate change has brought in the last years to a fast rise of renewable technologies. The inherent fluctuations of the solar resource make concentrating solar power technologies an application that demands full flexibility of the steam turbine component. A key aspect of this sought steam turbine flexibility is the capability for fast starts, in order to harvest the solar energy as soon as it is available. However, turbine start-up time is constrained by the risk of low cycle fatigue damage due to thermal stress, which may bring the machine to failure. Given that the thermal limitations related to fatigue are temperature dependent, a transient thermal analysis of the steam turbine during start process is thus necessary in order to improve the start-up operation. This work focuses on the calculation of turbine thermo-mechanical properties and the optimization of different start-up cases in order to identify the best solution in terms of guaranteeing reliable and fast start-ups. In order to achieve this, a finite element thermal model of a turbine installed in a concentrating solar power plant was developed and validated against measured data. Results showed relative errors of temperature evolutions below 2%, making valid the assumptions and simplifications made. Since there is trade-off between start-up speed and turbine lifetime consumption, the model was then implemented within a multi-objective optimization scheme in order to test and design faster start-ups while ensuring safe operation of the machine. Significant improvements came up in terms of start-up time reduction up to 30% less than the standard start-up process.