This work details an integrative mechanical design process for combustion chambers. A major challenge in the development process of modern gas turbine combustors is to achieve low NOx emissions whilst ensuring the stability of the combustion process at all phases of the guaranteed operation regimes. The burner hardware plays a crucial role in determining emissions and maintaining a suitable aero- and thermo-acoustic performance of the combustion process. In addition, the burner hardware must be manufacturable at a reasonable cost. Efficient burner development requires a design process able to judge this behaviour at an early phase. This process must predict the combustor behaviour, the thermoacoustic mechanisms, the mechanical integrity as well as the life cycle of the burner. Based on the Alstom SEV (Sequential EnVironmental) burner for the reheat combustor of the GT24 gas turbine, this paper describes an exemplary process for the mechanical design, mechanical integrity, cooling and manufacturing. The acoustic aspects and the successful engine validation are addressed in separate papers. The improved GT24 SEV burner has been developed with the following key features: a) A Straight Mixing Zone aerodynamic design (SMZ) resulting in increased velocity and improved reactant pre-mixing b) Multi-layered and braze constructed Front Panel design integrating combined and novel cooling and high frequency damping features c) Optimised alloy selection for extended lifetime and improved manufacturability In addition to the mechanical design and manufacturing process further details will be provided on aspects of cooling and mechanical integrity.
Designing a state-of-the-art combustor requires an iterative process where mechanical design solutions in the early concept phase are continuously assessed using analytical cooling and lifetime assessments, which are later backed up with experimental investigations and validation measures. This paper describes the integrated design process in terms of design, cooling, manufacturing, aerodynamic and mechanical integrity for the transition duct of the GT13E2 combustor, which houses the flame development region of the combustor. The objective was to develop a retrofit design with reduced lifecycle costs, with no impact on the combustor-turbine interface and no impact on the overall engine performance. The major challenges were the on-site welding of the two half-shells as well as the increasing demand for cyclic operation of the engine. During the development process, the focus was on selecting reliable and robust cooling schemes on the inner and outer shell to reduce mechanical deflections and thus to reduce the overall stress distribution. Key features of the GT13E2 combustor zone 2 are the following: • Drastically reduced lifecycle cost with no performance penalty (retrofit) • Separation planes at 3 and 9 o’clock position with mechanical locking connections (bridges) and a recess weld with film cooling • Bellmouth shaped inlet of cooling channel with improved impingement and convective cooling • Unique membrane seals with great mechanical flexibility around the turbine inlet outer diameter including mitigation against hot gas ingress (bow wave effect) • Improved cooling during transient conditions to reduce mechanical deflections • Reduced reconditioning effort due to innovative manufacturing methods The cooling schemes were successfully validated against laboratory experiments and integrated into a stable manufacturing process. Increased dimensional stability was achieved through higher rigidity and led to an improved on-site welding process for the separation planes. All the aforementioned features result in a marked improvement of the cyclic lifetime with no performance penalty. This is proven by the fact that the GT13E2 with annular combustor transition duct has now accumulated more than 30,000 operating hours with 1,200 starts.
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