Simulation of a Multistage Compressor at Low Load Operation with Additional Bleed Air Extraction for Minimum Environmental Load Reduction

The need for more flexible operation of gas-fired power plants has led manufacturers to exploit possibilities to retrofit existing systems and increase turndown capabilities, lowering the minimum environmental load (MEL) - the lowest output at which the unit can operate and still meet environmental emissions limits. A possible measure for the compressor to enable a reduced MEL is to extract significant mass flow rates through the bleed ports in operation with a closed IGV to lower the mass flow entering the combustor, enabling a further load reduction while maintaining emissions. For this measure to be implemented, a stable operation of the compressor has to be ensured at the reduced MEL conditions. It is well known that bleed-air offtake at full speed shifts the loading towards the rear stages of the compressor. At MEL, the rear stages already operate at an increased loading compared to base-load. Therefore, to confirm the viability of bleed offtake as a turndown strategy, the effects on performance and stability have to be quantified for operation at MEL. Of particular interest is how an increase in air extraction through the bleed ports influences the stability of the compressor at MEL, especially when the offtake is from low pressure. Information on the degradation of the stability margin due to the additional bleed-air extraction at MEL is gained through numerical simulations. Full-compressor CFD simulations of an F-class gas turbine at reduced MEL conditions are performed. The influence of several geometrical and numerical modeling details is studied, and the model is validated against a comprehensive set of experimental data. The numerical results show good agreement with the experimental data, even with increased bleed air extraction. It can be concluded that bleed-air extraction is a capable method of reducing the compressor discharge mass flow rate significantly. The extraction rate is limited by the stability of the last compressor stages. To verify the integrity of the whole GT at operation under such conditions, e.g., the thermal state of hot parts, further analysis should be performed

Ottimizzazione delle VIGV nei propulsori aeronautici civili moderni

Questa tesi si propone di analizzare una delle possibili idee per aumentare le performance off-design dei propulsori aeronautici civili. In particolare si concentra sul design, lo sviluppo e la valutazione delle performance di una nuova ed avanzata configurazione per Variable Inlet Guide Vane (VIGV) in propulsori Turbofan ad alto rapporto di bypass. Lo scopo è di ridurre le perdite di pressione totale comunemente associate con le VIGV convenzionali operanti in condizioni off-desig

Predicting the Impact of Compressor Flexibility Improvements on Heavy-Duty Gas Turbines for Minimum and Base Load Conditions

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. In order to improve existing power plants’ flexibility in facing energy surplus or deficit, retrofittable solutions for gas turbine compressors are proposed. 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. 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. 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. 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

Predicting the Impact of Compressor Flexibility Improvements on Heavy-Duty Gas Turbines for Minimum and Base Load Conditions

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. In order to improve existing power plants’ flexibility in facing energy surplus or deficit, retrofittable solutions for gas turbine compressors are proposed. 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. 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. 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. 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

Retrofittable Solutions Capability for Gas Turbine Compressors

The increasing introduction of renewable energy capacity has changed the perspective on the operation of conventional power plants, introducing the necessity of reaching extreme off-design conditions. There is a strong interest in the development and optimization of technologies that can be retrofitted to an existing power plant to enhance flexibility as well as increase performance and lower emissions. Under the framework of the European project TURBO-REFLEX, a typical F-class gas turbine compressor designed and manufactured by Ansaldo Energia has been studied. Numerical analyses were performed using the TRAF code, which is a state-of-the-art 3D CFD RANS/URANS flow solver. In order to assess the feasibility of lower minimum environmental load operation, by utilizing a reduction in the compressor outlet mass-flow rate, with a safe stability margin, two different solutions have been analyzed: blow-off extractions and extra-closure of Variable Inlet Guide Vanes. The numerical steady-state results are compared and discussed in relation to an experimental campaign, which was performed by Ansaldo Energia. The purpose is to identify the feasibility of the technologies and implementation opportunity in the existing thermal power plant fleet

Compressor Retrofittable Solutions in Heavy-Duty Gas Turbines for Minimum Environmental Load Reduction

International policies aiming at keeping global warming within safety limits will strongly impact gas-fired power plants. Flexibility is going to be the key-word, hence this paper focuses on possible strategies to increase turndown capability (i.e. lowering Minimum Environmental Load (MEL)) of open and combined cycle power plants (CCPP) through retrofittable compressor service packages. In particular, the following three options have been analyzed: extra-closure of Variable Inlet Guide Vanes (IGVs), Blow-Off (BO) lines opening and inlet bleed heating. All these solutions aim at reducing the compressor outlet mass-flow rate while keeping a safe stability margin. The effect of lowering the minimum load capability by opening the BO lines has been numerically investigated through full compressor 2D throughflow analyses. Moreover, the impact on compressor performance and stability of the extra-closure of IGVs has been analyzed with the support of 3D steady-state CFD modelling. Finally, the overall performance of the power-plant has been included and discussed in order to provide plant managers with a solid starting point for a techno-economic analysis