Combustor Cap Assembly Cooling and Mixing
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Solution Overview
Problem
Existing combustor designs face challenges in efficiently cooling the cap plate without exacerbating NOx and CO2 generation, as compressed air used for cooling enters the combustion chamber unmixed with fuel, potentially decreasing turbine efficiency.
Innovation Solution
The combustor cap assembly incorporates an impingement plate with cooling holes and a cooling flow return passage, creating an impingement air plenum that allows for mixed compressed air to impinge on the cap plate, providing convective cooling and routing heated air back into the combustion chamber to mix with fuel, reducing emissions.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Temperature
If compressed air is routed through cooling holes in the cap plate, then the cap plate is cooled effectively, but the compressed air enters the combustion chamber unmixed with fuel, exacerbating NOx and CO2 generation and decreasing turbine efficiency
Solution Approach 1:
An intermediary mixing region is introduced between the cooling holes and the combustion chamber. The cap plate includes cooling holes that allow compressed air to pass through, but the air is directed into a mixing region where it combines with fuel vapor before entering the combustion chamber. This intermediary zone ensures that the cooling air does not enter the combustion chamber unmixed, thereby reducing NOx and CO2 generation while still providing effective cooling to the cap plate.
Solution Approach 2:
The cap plate design incorporates localized cooling regions with cooling holes in specific areas where thermal stress is highest, while maintaining fuel-air mixing in other regions. The cooling holes are strategically positioned to provide targeted cooling to the cap plate without compromising the overall fuel-air mixing quality in the combustion chamber, thus addressing both cooling requirements and emission reduction.
2Strength
If compressed air is used to cool the cap plate, then thermal stresses on the cap plate are reduced, but turbine efficiency decreases due to unmixed air entering the combustion chamber
Solution Approach 1:
A mixing region serves as an intermediary between the cooling holes and the combustion chamber. Compressed air passing through the cooling holes enters this mixing region where it combines with fuel vapor, ensuring proper fuel-air mixing before combustion. This eliminates the energy loss associated with unmixed air entering the combustion chamber while maintaining the cooling function that reduces thermal stress on the cap plate, thereby preserving turbine efficiency.
Solution Approach 2:
The design performs preliminary mixing of compressed air with fuel vapor in a dedicated mixing region before the air enters the combustion chamber. This preliminary action ensures that the cooling air is properly integrated into the fuel-air mixture, preventing energy loss and maintaining turbine efficiency while the cap plate continues to benefit from the cooling effect that reduces thermal stress.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
This solution effectively cools the cap plate while minimizing NOx emissions by ensuring that the compressed air is premixed with fuel before ignition, enhancing turbine efficiency and reducing thermal stresses on mechanical components.
Implementation Method 1
The compressed air is then routed through multiple cooling holes which extend through the cap plate. This method is known in the industry as effusion cooling.
Implementation Method 2
The compressed air flowing through the multiple cooling holes enters the combustion chamber generally unmixed with the fuel.
Implementation Method 3
The impingement plate includes a first side portion, a second side portion and an outer band portion. The impingement plate at least partially defines a plurality of impingement cooling holes and a cooling flow return passage.
Implementation Method 4
allows for mixed compressed air to impinge on the cap plate, providing convective cooling and routing heated air back into the combustion chamber to mix with fuel
Data Source
AI summary
A combustor cap assembly includes an annular shroud and an impingement plate coupled to the shroud. The impingement plate at least partially defines a plurality of impingement cooling holes and a cooling flow return passage. A cap plate is coupled to the impingement plate. The cap plate includes an impingement side which faces a second side portion of the impingement plate where the impingement side is axially spaced from the second side portion to define an impingement air plenum therebetween. The cooling flow return passage is in fluid communication with the impingement air plenum. A fluid conduit extends from a first side portion of the impingement plate towards a first end portion of the shroud. The fluid conduit is in fluid communication with the cooling flow return passage and provides for fluid communication out of the impingement air plenum.