Pressure gain combustion (PGC) is widely considered to improve gas turbine thermal efficiency substantially. However, there is no consensus on the modelling in gas turbine performance simulation. Even though it remains the main tool for design studies, the steady-state 0D representation has difficulties in modelling the inherently intermittent behaviour of pressure gain combustion. Selecting the optimal gas turbine design is therefore difficult as common PGC models tend to under-or overestimate performance. In this paper, an algebraic combustor model is inferred from published CFD data and varied to have an optimistic and pessimistic representation. These models among others will be used in an optimisation to identify the best gas turbine design with respect to thermal efficiency. The consideration of the secondary air system and blade metal temperatures ensure a realistic case study. At the end of this paper, sensitivity studies shed light on cycle design at uncertain combustor performance. The selected PGC models achieve an improvement in thermal efficiency between 3.8-6.6 percentage points compared to conventional isobaric combustion. However, this is less than half the 13.3 percentage points gain promised by ideal isochoric combustion.
The design of new stationary gas turbines and development of upgrades for existing respectively is facing challenges regarding part load operation. The demands for high overall efficiency and compliance with legal requirements depend on the design of cooling air circuits among others. The design of an optimized secondary air distribution at both base load and part load as well as the consideration of different ambient conditions requires conceptual studies and hence appropriate models. This paper introduces the holistic model of a literature based generic stationary gas turbine, which essentially couples a gas turbine performance synthesis model with a more detailed secondary air system (SAS) network model. Extended with additional models such as evaluation of blade and vane material temperatures T mat , it allows for comparative off design studies with uncontrolled and controlled turbine cooling air circuits. The presented studies here first focus on margins of T mat with base load condition as benchmark. The subsequent exploitation of these margins is limited by the fundamental requirements of hot gas ingestion at common rim seal configurations. Either way, the reduction of cooling air at part load is beneficial in terms of fuel flow reduction: vane cooling air control results in up to 0.12% of fuel flow reduction at part load operation.
The demand for flexible part load operation of stationary gas turbines requires the simultaneous design for sufficient efficiency and life time. Both can be addressed by the secondary air system. This paper presents investigations on concepts of modulated cooling air in off-design, aiming for trade-offs between fuel burn and turbine blade life. The considered life time mechanisms are creep and oxidation. In addition, the effects on emissions from the combustion are outlined. The reference gas turbine is a generic gas turbine in the 300 MW power output segment. The focus is on the first two stages of the four-stage turbine. All simulations are performed by application of a coupled model that essentially connects gas turbine performance with a secondary air system network model. This coupled model is now extended with blade life evaluation and emission models. The results contain trade-offs for operating points at base and part load. For example, the combined cooling air control of stage 1 rotor blade and stage 2 vane offers savings up to 0.5 % fuel flow at 60 % of base load in a combined cycle application. This saving is at the expense of creep life. However, some operating points could even operate at higher blade temperatures in order to improve life regarding hot corrosion. Furthermore, generic sensitivities of controlled secondary air supply to cooling layers and hot gas ingestion are discussed. Overall, the presented trades mark promising potentials of modulated secondary air system concepts from a technical point of view.
The demand for flexible operation of stationary gas turbines, especially at part load, requires the simultaneous design for sufficient efficiency and life time. Both can be addressed by the secondary air system. The here applied concept modulates cooling air supply in off-design. Typically, a reduction of cooling air leads to higher efficiency but shorter turbine life time. This paper presents investigations on such concepts, aiming for trade-offs between fuel burn and turbine blade life. The considered life time mechanisms are creep, which is dominant in rotor blades, and oxidation. In addition, the effects on emissions from the combustion are outlined. The reference gas turbine is a literature-based, generic gas turbine in the 300 MWpower output segment. Regarding cooling air control, the focus is on the first two stages of the four-stage turbine. All simulations are performed by application of component zooming with an appropriate in-house tool: a previously introduced coupled model of the reference gas turbine that essentially connects gas turbine performance with a secondary air system network model. This coupled model is now extended with blade life evaluation and emission models. The results contain trade-offs for different operating points at base and part load. For example, the combined cooling air control of stage 1 rotor blade and stage 2 vane offers several benefits regarding fuel consumption: saving up to Δwfuel,rel = 0.5% in the heat recovery’s kink point operation at 60 % of base load of a combined cycle application. This saving is at the expense of creep life. However, some operating points could even operate at higher blade temperatures in order to improve life regarding hot corrosion. Furthermore, generic sensitivities of controlled secondary air supply to cooling layers and hot gas ingestion at rim seals are discussed. Overall, the presented trades mark promising potentials of modulated secondary air system concepts from a technical point of view.
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