Turbine Casing Segments for Thermal Expansion Control
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Solution Overview
Problem
Turbine performance is compromised due to uneven thermal expansion of the casing, leading to rubbing of buckets against the casing, which increases clearance and reduces efficiency, especially during start-up and shutdown.
Innovation Solution
The turbine design features arc-shaped segments with affixing protrusions extending only part-way along the casing, creating a region with a fast and even thermal response to prevent rubbing by maintaining a consistent clearance between the buckets and the casing.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If the clearance between casing and buckets is made small to improve turbine efficiency, then fluid leakage is reduced and efficiency increases, but during start-up the slow thermal expansion of the casing causes uneven expansion leading to bucket rubbing against the casing
Solution Approach 1:
The casing is designed with different thermal response characteristics in different regions. Specifically, the region adjacent to the buckets has a faster thermal response than other parts of the casing, achieved through localized structural modifications such as reduced wall thickness or enhanced thermal conductivity in that specific area. This allows the bucket-adjacent region to expand more quickly and uniformly during start-up, preventing rubbing while maintaining small clearances for efficiency during normal operation
Solution Approach 2:
The invention changes the thermal response parameter of the casing by providing an annular region with different thermal properties compared to the rest of the casing. This is achieved through modifying the casing structure in the annular region to have faster heat transfer characteristics, thereby changing the thermal expansion behavior locally to ensure uniform expansion during transient operations while maintaining the designed clearance for efficient operation
2Ease of manufacture
If the casing is designed with uniform structure for ease of manufacture, then manufacturing is simplified, but thermal expansion becomes uneven during operation causing bucket rubbing and material loss
Solution Approach 1:
Instead of uniform structure, the casing incorporates a localized annular region with modified properties adjacent to the buckets. This region has different thermal characteristics (faster response) compared to the rest of the casing, achieved through localized structural changes such as varying wall thickness or material properties only in the necessary annular zone, while the remainder of the casing maintains its simple uniform structure for ease of manufacture
Solution Approach 2:
The casing is effectively segmented into two functional zones: a standard region for ease of manufacture and an annular region with modified thermal properties for precise clearance control. This segmentation allows the complex thermal response requirements to be localized to a specific area, while the majority of the casing retains its simple, easy-to-manufacture uniform structure
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 ensures consistent clearance and prevents material loss from bucket tips, enhancing turbine efficiency and performance by maintaining a round shape during thermal cycles.
Implementation Method 1
When the turbine is heated and cooled, the components of the turbine, including the casing, expand and contract according to their thermal response characteristics
Data Source
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Figure 5~6
AI summary
A turbine casing includes a plurality of arc-shaped segments (11) having a flange (36a,36b) at each side end (34,35) to connect to a flange of an adjacent arc-shaped segment. The flange extends outward from an outer surface of each arc-shaped segment and extends along the outer surface (31) in a front-to-rear direction. Each arc-shaped segment has a portion of the outer surface that is co-linear with the flange in a front-to-rear direction that does not include the flange.