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With the research program ECOFLEX-Turbo the turbine research creates the bases to develop conventional power stations for a grid with 80% of renewable energy.
© Siemens AG
Conventional power plants
Projektinfo 07/2017

Since 1975, the efficiency (η ), start times and the maximum cycle durability have improved considerably in power plants with gas and steam turbines (CCPP).
© AG Turbo

Computer model of a turbine blade with the temperature distribution (blue = low temperature, red = high temperature).
© Rolls-Royce Deutschland Ltd. & Co. KG

Gas turbine with the compression, combustion and expansion sections.
© Siemens AG
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Flexible turbomachines stabilise the power grid

In future, conventional power plants will need to become more flexible in order to compensate for the fluctuating power generation by renewables. This requires modified gas and steam turbines. These will have to work more frequently under partial load, with more start-up and shut-down cycles and function with changing fuels. AG Turbo has compiled the research and development objectives for these new framework conditions in the ECOFLEX-turbo programme.

In thermal power plants, steam turbines extract energy from hot vapour and gas turbines extract energy from hot gas. They form the heart of the power plants and their technical performance is crucial for the energy efficiency, application profile and emissions of the entire plant. Turbines convert the energy absorbed into electricity using generators. Until now, gas and steam turbines have been designed so that they operate as much as possible under full load without sudden switch-on and switch-off processes. This limits the material wear. In the future power gridconventional power plants will perform new tasks. They will primarily offset the fluctuating electricity generated by wind power and photovoltaic systems in order to ensure a stable grid. To achieve this goal gas and steam turbines require further development. They must be more robust and adapted to deal with partial load operation, greater frequency fluctuations in the grid and fuel flexibility. Nevertheless, there should not be any reduction in the current standards regarding efficiency and emissions must be maintained.

The current ECOFLEX-turbo research programme run by AG Turbo compiles, in regard to the new framework requirements in the grid, the research objectives for turbomachinery until 2022 in more than 100 projects. For more than 30 years, leading German turbomachine manufacturers and more than 20 university institutes, which account for more than two thirds of the subsidised turbine projects, have been working together in the AG Turbo alliance in order to conduct jointly pre-competitive research. These aspects concern both new plants and the retrofitting of existing turbines. German manufacturers are among the leading suppliers of turbomachines on the global market with a market share of approx. 30%.

Igniting the turbo

Turbomachines are installed in power plants, airplanes and in pipelines for transporting gases. Their design can be described in a simplified manner using the example of a gas turbine. There are three sections: the compressor (compresses the sucked-in air), the combustion chambers (where the mixture of fuel and air is ignited) and the expansion, also referred to as the turbine (here the hot, over-pressurised gas expands). The gas flows through the consecutively arranged blades, reduces the pressure in doing so and transfers power from the hot gas to the rotating turbomachine. Part of this power (approx. 40-50%) is required to drive the compressor and the rest is used, for example, in power stations to drive electricity generators. The efficiency of turbines increases with higher pressure in the compressor and a higher temperature when the gas enters the expansion section. Figure 1 shows the development of the performance data since 1985.


Partial loading places different demands on turbines

When turbines previously had to work for prolonged periods under partial load or under-frequency conditions, they would have been operating at the limits of or even exceeding their design parameter boundaries during certain phases. Each of these events shortens the service life of the components. Problems that can occur include, for example, undesirable oscillations and vibrations of the blades, thermo-acoustic phenomena and disturbances in the compressor. In addition, the efficiency of the plant decreases under partial load.

In future, turbines will be working more frequently under partial load conditions, will start up and shut down more quickly and, in the case of grid frequency drops, have to compensate for the power deficit in fractions of seconds, as required by the power grid. Nevertheless, they will still have to run economically in spite of this mode of operation. They will then be running permanently in operating conditions that they previously speeded through as quickly as possible during the start-up and shut-down phases. To achieve this, the compressors and combustion chambers must be more robust in order to cope with the growing number of start processes, load changes and operating cycles. New computer software will be required for analyses, design purposes and dynamic simulations, whereby the researchers want to calculate the real operating behaviour more precisely. The models should also help to improve the design of the components and the design procedures. This will reduce the need for time-consuming and expensive experiments and prototypes, and will enable more targeted work on the test rigs. The aim is that the turbines achieve the same efficiency with partial loads under 50% and with cyclic operation as when operating under full load.

Surplus electricity from wind farms and photovoltaic systems can be used to produce hydrogen in order, for example, to mix it with natural gas. The turbines must therefore be able to cope with natural gas with a hydrogen content of at least 10%.

The ECOFLEX-turbo programme is divided into four disciplines: compression, combustion, cooling and expansion (turbines).

The compressor applies the pressure

In future, compressors will not only have to provide high efficiencies at peak load but also provide stable operation over a wide operational range. To enable turbines to perform a higher number of cycles in future, the damage mechanisms for individual components need to be investigated in more detail. Data forms the basis for better modelling and more powerful simulation programs that enable life-prolonging measures. The goals are shorter development times and more complex geometries, whereby the probabilistic approach is becoming more important. Using this approach, components will be specifically designed for a minimum number of, for example, load and temperature changes based on validated data from models and experiments.

In addition, the researchers would like to predict the actual flow behaviour and increased vibration amplitudes in partial load operation more reliably and also test new possibilities for configuring the flow and vibration damping. This would then enable them to determine and reduce the losses. ECOFLEX-turbo comprises 30 projects in the “Compression” discipline.


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