Today’s and future electric power generation is characterized by a large diversification using all kind of sources, including renewables resulting in noncoherent fluctuations of power supply and power usage. In this context, gas turbines offer a high operational flexibility and a good turn down ratio. In order to guide the design and down select promising solutions for improving partload emissions, a new combustion model based on the assumption of two separate timescales for the fast premixed flame stabilization and the slow post flame burnout zone is developed within the commercial computational fluid dynamics (CFD) code ANSYS CFX. This model enables the prediction of CO emissions generally limiting the turn down ratio of gas turbines equipped with modern low NOx combustion systems. The model is explained and validated at lab scale conditions. Finally, the application of the model for a full scale analysis of a gas turbine combustion system is demonstrated.
From the very first beginning of the V64.3A development the HR3 burner was selected as standard design for this frame. The HR3 burner was originally developed for the Vx4.2 and Vx4.3 fleet featuring silo combustors in order to mitigate the risk of flashback and to improve the NOx-emissions (Prade, Streb, 1996). Due to its favourable performance characteristics in the Vx4.3 family the advanced HR3 burner was adapted to the Vx4.3A series with annular combustor (hybrid burner ring – HBR). This paper reports about the burner development for V64.3A gas turbines to reach NOx emissions below 25 ppmvd and CO emissions below 10 ppmvd. It is described how performance and NOx emissions have been optimised by implementation of fuel system and burner modifications. The development approach, emission results and commercial operation experiences as well are described. The modifications of the combustion system were successfully and reliably demonstrated on commercially running units. NOx emissions considerably below 25ppmvd were achieved at and above design baseload. An outlook to further steps of V64.3A burner development in the near future will be given in this paper.
Todays and future electric power generation is characterized by a large diversification using all kind of sources including renewables resulting in non coherent fluctuations of power supply and power usage. In this context, gas turbines offer a high operational flexibility and a good turn down ratio. In order to guide design and down select promising solutions for improving part load emissions a new combustion model based on the assumption of two separate time scales for the fast premixed flame stabilization and the slow post flame burnout zone has been developed within the commercial CFD code ANSYS CFX. This model enables the prediction of CO emissions generally limiting the turn down ratio of gas turbines equipped with modern low NOx combustion systems. The model will be explained and validated at lab scale conditions. Finally application of the model for a full scale analysis of a gas turbine combustion system is demonstrated.
The lean premixed combustion system was scaled from Siemens 60Hz engine application and optimized for implementation in the new SGT5-8000H 50Hz engine. The Siemens H-class engine is air cooled, uses a pressure ratio of 19:1 and is designed to achieve an efficiency of >60% efficiency in combined cycle operation. This improved dry low NOx system is of can annular type and consists of 16 cans in the SGT5-8000H. It was developed and tested in a full scale, high pressure rig test program. The single can high pressure rig simulates closely the flow conditions upstream of the combustor in the SGT5-8000H midframe and downstream of the combustor at the turbine inlet. The combustion system uses 5 fuel stages which allow flexible tuning over the whole range of engine operation conditions (ignition, idling, part- and base load). The system is designed to operate over a wide range of fuel quality and preheat temperatures. The test program is carried out over multiple years and encompasses rig / engine tests. This paper describes the combustion system in more details and the testing methodology. The test rig results showed that the performance targets are fully achieved in terms of emissions and operational requirements. Furthermore, the development / validation program will continue to reduce emissions through extended programs for future engines.
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