![]() For large-scale industrial calculations, such as the ones discussed here that cover an entire 15-stage compressor with (with IGV and OGV), affordable CPU times represent a mandatory requirement. The last stage stator and the OGV, which are both stationary components, share the same blade number and thus a local matching interface was employed solely for the interface between these two blade rows, as in. Here, a non-reflecting mixing-plane treatment based on the method proposed by Giles has been selected. The CFD results discussed in the paper come from RANS analyses carried out with the mixing-plane approach, which allows a steady coupling between fixed and rotating blade rows. Several advection schemes are available in the code, and the one adopted in the present work is a 2nd-order central scheme with the scalar-valued artificial dissipation proposed by Jameson, Schmidt, and Turkel. The 3D Reynolds-averaged Navier–Stokes equations are written in conservative form in a curvilinear coordinate system and solved for density, absolute momentum components, and total energy. In the present work, a state-of-the-art, in-house-developed, RANS/URANS flow solver (TRAF code ) has been used. ![]() The second solution opens one or more blow-off valves at the core of the compressor in order to bypass part of the compressed air directly in the exhaust diffuser and save the fuel needed to heat it. The first solution consists of the variation of the IGV stagger angle (a practice that is generally used to change load condition), to decrease the inlet compressor mass flow below the standard MEL value. This allows conventional power plants to be more flexible, reliable, and resilient, while ensuring full compliance with the restrictive environmental regulations imposed by several countries. ![]() These two strategies allow for a reduction in the minimum environmental load (MEL) that the power plant can be operated at, thus avoiding shutdown when the power demand from the grid is low. Among these, as a part of the European project, two different operational strategies have been investigated, including variable inlet guide vanes (IGVs) and blow-off extraction (BO). On the compressor side, the possible actions for reducing the load of a gas turbine without negatively impacting the carbon dioxide emissions, include blow-off extraction, inlet guide vane extra-closure, and bleed heating, also known as anti-icing. Within the project, a dedicated session has been reserved for retrofittable features for compressors that play a key role in the flexibility of power plants. In this scenario, thanks to European Union’s Horizon 2020 research and innovation program, the Turbo-Reflex project (TURBOmachinery REtrofits enabling FLEXible back-up capacity for the transition of the European energy system) was launched with the aim of developing and optimizing technologies that can be used to retrofit existing power plants in order to enable more flexible operation. It will be shown how the combined strategies can reduce gas turbine mass flow rate and power plant output, without significantly penalizing efficiency, and how such off-design performance figures can be reliably predicted by employing state-of-the-art CFD models. The results of an extensive 3D, steady, CFD analysis are compared with the measurements coming from an experimental campaign carried out in the framework of the European Turbo-Reflex project. A typical 15-stage F-class gas turbine compressor is chosen as a test case and some energy demand scenarios are selected to validate the adopted solutions. In this paper, two different operation strategies, variable inlet guide vanes (IGVs) and blow-off extraction (BO), are considered for enabling partial load and minimum environmental load operation, and thus to identify implementation opportunities in existing thermal power plants. In order to improve existing power plants’ flexibility in facing energy surplus or deficit, retrofittable solutions for gas turbine compressors are proposed. The increasing importance of renewable energy capacity in the power generation scenario, together with the fluctuating consumer energy demand, forces conventional fossil fuel power generation systems to promptly respond to relevant and rapid load variations and to operate under off-design conditions during a major fraction of their lives.
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