Mini Heat Shield for Gas Turbine Combustion Chamber Transition
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Solution Overview
Problem
The transition region between the combustion chamber and the turbine in gas turbines faces challenges due to large gaps caused by differing thermal expansion and pressure differences, leading to leakage, overheating, and oxidation issues, which existing solutions struggle to address effectively.
Innovation Solution
The introduction of mini heat shields attached to the turbine support upstream of the first row of guide blades creates a new gap location further away from the critical leading edge, allowing for a smaller gap size that compensates for thermal expansion differences and reduces the impact of pressure peaks, with the mini heat shields forming a flow wall adapted to the gap area.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the gap between the combustion chamber heat shield and the turbine blade platform is reduced to minimize leakage and hot gas exposure, then the sealing performance improves, but the gap cannot accommodate thermal expansion differences and pressure variations
Solution Approach 1:
A purge cavity is introduced as an intermediary space between the combustion chamber heat shield and the turbine blade platform. This cavity acts as a buffer zone that can accommodate thermal expansion and pressure variations while preventing hot gas leakage into the turbine components through controlled purging with cooler gas.
Solution Approach 2:
The transition region is segmented into distinct zones: the combustion chamber heat shield, the purge cavity, and the turbine blade platform. This segmentation allows each component to move independently due to thermal expansion while maintaining functional separation and preventing hot gas intrusion.
2Adaptability or versatility
If a large gap is maintained to accommodate thermal expansion and pressure differences, then the adaptability to transient conditions improves, but hot gas leakage and overheating of turbine components increase
Solution Approach 1:
The purge cavity serves as a protective intermediary between the hot combustion gases and the turbine components. It allows a larger gap for thermal expansion while preventing hot gas exposure to turbine parts through active purging with cooler gas from the combustion chamber.
Solution Approach 2:
A pneumatic purging system is implemented where cooler gas is actively supplied into the purge cavity to counterbalance hot gas pressure and prevent hot gas leakage into the turbine blade platform, utilizing pressure differential control.
3Reliability
If the gap width is reduced at the base load point, then the sealing performance improves, but the gap becomes insufficient during transient conditions such as hot restart
Solution Approach 1:
The purge cavity system is designed to dynamically adjust its purging capacity based on operating conditions. During transient conditions like hot restart, the system can increase purging flow to accommodate larger thermal expansion gaps, while at base load it maintains effective sealing with reduced purging requirements.
4Adaptability or versatility
If the gap is made larger to ensure sufficient clearance throughout all transient courses, then the adaptability to thermal expansion improves, but leakage and RTDF emissions increase
Solution Approach 1:
The purge cavity acts as an intermediary that decouples the gap size from leakage consequences. The larger gap accommodates thermal expansion while the purging mechanism prevents hot gas and combustion products from leaking into the turbine components.
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 design effectively shifts the critical gap to a less stressful area, reducing leakage and overheating, requiring less cooling air and pressure for purge, while allowing for a more compact turbine design and improved pressure distribution.
Implementation Method 1
A so-called bow wave forms at the leading edge of the guide vanes, which causes hot combustion air in the wall area to be pressed under pressure into this cavity
Implementation Method 2
an outer wall which consists of a heat-resistant material or is coated accordingly
Data Source
Figure 1~2
Figure 3~4
AI summary
The turbine has a blade (2) arranged downstream to a combustion chamber (9). A mini-heat shield (13) is fastened to a turbine carrier (4) and arranged at an upstream extension (4') of the turbine carrier or over a turbine carrier element at the turbine carrier upstream to the blade. The shield is arranged adjacent to a vane platform (3) in a flow direction (10) of hot gas between a heat shield and the platform. The mini-heat shield forms a flow wall between the heat shield and the platform. An upstream small gap (17) is formed between the mini-heat shield and the heat shield.