Today’s power generation markets require considerable flexibility in terms of type and quality of fuels. However, this must be with low emissions, high reliability and high efficiency. In more than 100 installations worldwide the Alstom GT13E2 is in use with a wide variety of fuels. Fuel flexibility is the ability to burn natural gas fuels with a wide Wobbe index range which also allows the use of fuel preheaters (to increase efficiency) as well as the ability to use fuel oil as back up or main fuel. The paper will show the allowable Wobbe index range and higher hydrocarbon effects on gas turbine combustion and the field experience gained. Specific design features implemented in the GT13E2 ensure reliable and environmental friendly operation with varying fuels. Those are: 1.) an almost entirely convectively cooled combustor with only a small amount of film cooling. 2.) the use of premix burners which are stabilized by an aerodynamically induced recirculation at the centerline and a separately controlled pilot fuel injection. 3.) an adaptive fuel staging that monitors the flame stability by pulsation measurements and adjusts the fuel staging in the combustor such that the flame is always stable but not overly rich. This results in better NOx control under varying operating conditions due to the closed-loop controlled flame stability.

In recent years, market trends towards higher power generation flexibility are driving gas turbine requirements of operation at stable conditions and below environmental emission guarantees over a wide range of operating conditions, such as load, and for changing fuels. In order to achieve these targets, engine components and operation concept need to be optimized to minimise emissions (e.g. CO, NOx) and combustion instabilities, as well as to maximize component lifetime. Therefore the combination of field experience, experimental studies and theoretical modelling of flames with state of the art tools play a key role in enabling the development of such solutions. For many applications the relative changes of reactivity due to changes in operation conditions are important thus in this report a few examples are shown, where chemical kinetics simulations are used to determine the reactivity and to predict engine behaviour. The predicted trends are validated by correlating them to validation data from high pressure test rigs and real gas turbine operational data. With this approach the full operational range from highest reactivity (flashback) to lowest reactivity (blow out or CO emission increase) are covered. The study is focused on the sequential combustor (SEV) of reheat engines and addresses both the safety margins with respect to highly reactive fuels and achievable load flexibility with respect to part load CO emissions. The analysis shows that it is necessary to utilize updated kinetic mechanisms since older schemes have proved to be inaccurate. A version of the mechanism developed at NUI Galway in cooperation with Alstom and Texas A&M was used and the results are encouraging, since they are well in line with experimental test data and can be matched to GT conditions to determine, predict, and optimize their operational range. This example demonstrates nicely how a development over several years starting from fundamental basic research over experimental validation finally delivers a product for power plants. This report therefore validates the kinetic model in combination with the approach to use modelling for guidance of the GT development and extending it fuel capabilities. The GT24 / GT26 can not only be operated with H2 containing fuels, but also at very low part load conditions and with the integration of H2 from electrolysis (∼power to gas ∼PTG) the turndown capability can even be further improved. In this way the energy converted at low electricity prices can be stored and utilised at later times when it is advantageous to run the GT at lower loads increasing the overall flexibility. This development is well suited to integrate renewable energy at highly fluctuating availability and price to the energy provisioning by co-firing with conventional fuels.

Reducing gas turbine emissions and increasing their operational flexibility are key targets in today’s gas turbine market. In order to further reduce emissions and increase the operational flexibility of its GT24, Alstom has introduced an internally staged premix system into the GT24’s EV combustor. This system features a rich premix mode for GT start-up and a lean premix mode for GT loading and baseload operation. The fuel gas is injected through two premix stages, one injecting fuel into the burner air slots and one injecting fuel into the centre of the burner cone. Both premix stages are in continuous operation throughout the entire operating range, i.e. from ignition to baseload, thus eliminating the previously used pilot operation during start-up with its diffusion-type flame and high levels of NOx formation. The staged EV combustion concept is today a standard on the current GT26 and GT24. The EV burners of the GT26 are identical to the GT24 and fully retrofittable into existing GT24 engines. Furthermore, engines operating only on fuel gas (i.e. no fuel oil operation) no longer require a nitrogen purge and blocking air system so that this system can be disconnected from the GT. Only minor changes to the existing GT24 EV combustor and fuel distribution system are required. This paper presents validation results for the staged EV burner obtained in a single burner test rig at full engine pressure, and in a GT24 field engine, which had been upgraded with the staged EV burner technology in order to reduce emissions and extend the combustor’s operational behavior.

Premixed gas turbine combustors operated at very lean conditions are prone to thermoacoustic instabilities. Thermoacoustic instabilities have negative effects on the operability of the combustion chamber. The prevention of thermoacoustic instabilities is a major design goal of the gas turbine combustor system as well as its control system. An appropriate real-time model helps the design of effective control algorithms for the prevention of thermoacoustic instabilities. This paper presents a black-box real-time modelling approach for thermoacoustic instabilities simulation using a Gaussian-Process. A Gaussian Process is a stochastic process that can approximate arbitrary functions, similar to Neural Networks, but with the advantage that it can be implemented and tuned in a more straightforward manner since a theoretical framework exists for the optimization of the hyperparameters influencing the process. The Gaussian Process can be trained in a fast and straight-forward manner. The trained Gaussian Process has been proven to be very efficient numerically, which enables it to be used in a real-time simulation environment. The real-time gas turbine model is to be used in the development of control algorithms that allow for low-NOx and robust operation of the gas turbine in conjunction with low acoustic pulsation levels. Verification on a gas turbine demonstrated the high accuracy of this modeling approach for a wide range of operating conditions. Moreover, it was shown that a Gaussian Process trained with data of one engine correctly reproduced acoustic pulsation behaviour of another engine.