Bled Diffuser Secondary Combustion Gas Turbine
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Solution Overview
Problem
Gas turbines face efficiency and performance issues due to non-uniform airflow velocity profiles and flow losses caused by boundary layer separation in diffusers, which are exacerbated by bleeding air to reduce boundary layer size, leading to reduced compressed air availability for cooling and pressure increase.
Innovation Solution
A system that includes a bled diffuser with a bleed duct directing bleed air from the compressor section to a secondary combustion system, where it is mixed with fuel, enhancing static pressure recovery and reducing emissions by utilizing the bleed air effectively without compromising overall efficiency.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of energy
If a bled diffuser is used to reduce boundary layer size and improve static pressure recovery, then flow losses are reduced, but the overall efficiency and performance of the gas turbine are reduced due to bleeding pressurized air from the main airflow
Solution Approach 1:
The patent extracts the boundary layer air from the main airflow through the bled diffuser, separating it into a distinct bleed stream. This extracted air is then directed to a secondary combustion system rather than being wasted, allowing the main airflow to maintain its efficiency while the extracted air is utilized for additional combustion purposes.
Solution Approach 2:
The bleed air that would otherwise be wasted is given a new function by directing it to a secondary combustion system. This multi-functional approach allows the same air to serve both as boundary layer removal (reducing flow losses) and as fuel support air (enabling secondary combustion), thereby resolving the efficiency penalty.
2Stress or pressure
If a diffuser is made longer to obtain necessary static pressure recovery without boundary layer separation, then static pressure recovery is improved, but the device complexity and space requirements increase
Solution Approach 1:
By extracting the boundary layer air through the bled diffuser, the patent reduces the effective length of the diffuser needed to achieve the same static pressure recovery. The boundary layer removal prevents separation, allowing shorter diffuser lengths while maintaining pressure recovery performance.
Solution Approach 2:
The bled diffuser creates a localized region of controlled flow by extracting boundary layer air at specific locations. This local modification allows the diffuser to achieve better pressure recovery characteristics without requiring the entire diffuser to be longer, thus reducing overall complexity.
3Reliability
If bleed air is removed from the main airflow to reduce boundary layer size, then boundary layer separation is reduced, but the amount of compressed air available for cooling and pressure increase is reduced
Solution Approach 1:
The patent converts the harmful effect of boundary layer air (which causes separation and losses) into a beneficial resource by directing it to a secondary combustion system. The same air that would be wasted is now utilized to support additional combustion, turning a loss into a gain while maintaining reliable boundary layer control.
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 approach improves gas turbine efficiency and performance by maintaining static pressure recovery while minimizing flow losses and emissions, allowing for increased turbine inlet pressure and reduced cooling requirements, and enabling higher firing temperatures with lower NOx formation.
Implementation Method 1
A diffuser may generally comprise at least one diverging diffuser wall, which allows the pressurized airflow to spread or diffuse over the length of the diffuser
Implementation Method 2
friction along the diffuser wall(s) creates a boundary layer, wherein the velocity of the airflow is significantly lower than the velocity of the main airflow
Implementation Method 3
The bleed duct may be configured to direct bleed air from the pressurized airflow exiting the compressor section to a secondary combustion system located downstream from the main combustion system in a combustor
Implementation Method 4
The bleed air flowing into the secondary combustion system may be mixed with fuel to form an air/fuel mixture
Data Source
AI summary
The present subject matter provides a system for modifying static pressure recoveries and emissions formation within a gas turbine. The system includes a bled diffuser positioned downstream from a compressor section of the gas turbine and a bleed duct extending from the bled diffuser. The bleed duct may be configured to direct bleed air from the pressurized airflow exiting the compressor section to a secondary combustion system located downstream from the main combustion system in a combustor. The bleed air flowing into the secondary combustion system may be mixed with fuel to form an air/fuel mixture.