The power generation and energy market scenarios are requiring the power generation plants to fulfill more flexible operations respect to the recent past. One of the main concerns of plant operators is the lowering of minimum load at which the machines can be exercised while respecting the pollution limits. A strategy to improve minimum turndown capability by reducing the minimum environmental load of heavy duty axial gas turbines is here presented: it is based on the use of the compressor air bleeding lines (blow-off lines). The described technical development activities are based on the numerical modeling of blow-off lines and bleeding compressor sections; these preliminary tasks have been followed by on-field plant testing. The blow-off lines modeling reserves a particular regard, due to the somehow non-usual fluid dynamics involved. A Fanno flow 1D approach has been adopted to properly model the bleeding lines fluid flow whereas full 3D numerical solutions have been developed to get a better insight of the bleeding plenums and of the line sector including the valve. In addition, the gas turbine components off-design behavior and the overall performances are computed by the Ansaldo modular simulation code. Numerical analysis and performed field tests are here presented and results are compared, showing a good agreement, in accord to the simplified model adopted. Additional comparisons with different alternative strategies are finally presented in terms of gas turbine power and excess air variation. The described technique by blow-off lines opening shows to be able to fulfill the required task by incrementing the plant operative flexibility and guaranteeing safe plant operation. The technique drawbacks are a gas turbine slightly lower efficiency and the lower output flue gas temperature, whose relative importance have to evaluate by the plant operators. At present the long term sustainability of the new operative condition is the object of a deeper and longer field testing phase.

The high share of non-dispatchable renewable energy source generators in the electrical grid has increased the need for flexibility of Gas Turbine Combined Cycles (GTCC) already installed. To maximize not only the maximum power produced, via Power Augmentation Technologies (PATs), but also to reduce the Minimum Environmental Load (MEL), both OEMs and GTCC owners have adopted several technical solutions. This kind of flexibility has become, year-by-year, ever more crucial to guarantee GTCC economical sustainability. Amongst the solutions which can be adapted to guarantee GTCC flexibility, the Inlet Conditioning System is a particularly interesting technical solution, which can be installed without restrictions related to the different GT design. In this paper, an evaluation of the compressor inlet temperature effect over the Combined Cycle performance is presented, with a focus on the bottoming Cycle impact. Different Inlet Conditioning Strategies are then compared considering the energy, and the environmental impact on GTCC behavior. The performance of a layout including a Thermal Energy Storage (TES) and a Heat Pump (HP) is then evaluated and compared to other technical solutions.

This paper presents a flexible and effective optimization approach to design an axial compressor transonic blade for heavy duty gas turbines. The design goals are to improve design efficiency, choke margin and off-design performance while maintaining mass flow in design point as well as structural integrity. The new blade has to provide a wide operating range and to satisfy tight geometrical constraints. A database of aero-mechanical calculation results is obtained for three operating conditions. A number of 3D flow simulations are performed using a CFD solver with endwall boundary layer simplified model (thin layer) to reduce computational costs. The optimization process adopts a set of artificial neural networks (ANN) trained for each operating condition and a random walking search algorithm to determine the multi-objective Pareto Front. ANN enables speed up of the optimization process and allows high flexibility in choosing criteria for optimum member selection. Random walking algorithm gives a fast and effective method to predict the multi-dimensional Pareto Front.

The operation of a gas turbine is the result of the aero-thermodynamic matching of several components which necessarily experience aging and degradation over time. An approach to treat degradation phenomena of the axial compressor is provided, with an insight into the impact they have on compressor operation and on overall GT performances. The analysis is focused on the surface fouling of compressor blades and on rotor tip clearances variation. A modular model is used to simulate the gas turbine operation in design and off-design conditions and the aerodynamic impact of fouling and rotor tip clearances increase is assessed by means of dedicated loss and deviation correlations implemented in the 1D mid-streamline code of the compressor modules. The two different degradation sources are individually considered and besides the overall GT performance parameters, the analysis includes an evaluation of the compressor degradation impact on the secondary air system.

In order to improve performance of heavy-duty gas turbines, in terms of power, efficiency and reliability, accurate calculation tools are required. During conceptual design phase, an effective integration of main GT components design into a single modular simulation tool can significantly reduce design iterations and improve the results. Thanks to an innovative modular-structured program for the simulation of air-cooled gas turbines, the one-dimensional design of compressor and turbine flow paths is used to create a complete gas turbine model including a detailed secondary air system and a simplified heat transfer model. This zero-dimensional heat transfer model is applied to each turbine row in order to calculate the cooling flow required to keep turbine blades and vanes metal temperatures below a prescribed threshold. After a description of the air cooled gas turbine modular model, the integrated design approach adopted by Ansaldo Energia is described. The knowledge of technical risks that the designers have to withstand developing advanced technologies during conceptual engine design is fundamental. The inter-disciplinary influence of some disciplines is analyzed and finally it is shown how Ansaldo Energia approach can track expected performance results and provide recovery plans during the conceptual design phase.