Steam Turbine Inner Casing Cooling via Diaphragm Outer Ring Passage
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Solution Overview
Problem
Steam turbines operating with high-temperature steam (650 to 750°C) face challenges in material strength and production costs due to the limited availability and high cost of heat-resistant alloys, and existing cooling methods are inadequate for efficiently cooling the inner casing and diaphragm outer ring in double-structure casings.
Innovation Solution
A steam turbine design with a double-structure casing featuring a cooling medium passage between the inner casing and diaphragm outer ring, utilizing a cooling medium supplied through a supply pipe to flow between these components, and an exhaust passage to guide working fluid, along with a heat insulating structure to prevent heat transfer from the diaphragm outer ring to the inner casing.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If heat-resistant alloy is used for component parts to maintain material strength at high temperatures, then material strength is improved, but production cost increases and fabrication difficulty increases
Solution Approach 1:
The patent applies local quality by implementing a cooling passage system specifically in the diaphragm outer ring where high temperatures occur, rather than using heat-resistant alloys throughout the entire component. The cooling passages are strategically positioned to cool the stationary blade supporting portion, allowing conventional materials to be used while maintaining local strength where needed.
Solution Approach 2:
The patent segments the diaphragm outer ring into distinct functional zones: a stationary blade supporting portion with cooling passages for high-temperature areas, and other portions that can use conventional materials. This segmentation allows differential material and cooling strategies applied only where thermally critical.
2Ease of manufacture
If conventional heat-resistant steel is used for the inner casing to reduce production cost, then production cost is reduced, but the inner casing cannot be sufficiently cooled with existing cooling methods
Solution Approach 1:
The patent introduces a diaphragm outer ring as an intermediary cooling structure between the high-temperature steam environment and the inner casing. The cooling passages in the diaphragm outer ring act as a thermal barrier, cooling the inner casing indirectly through this intermediate component rather than directly cooling the inner casing itself.
3Productivity
If steam temperature is increased to 650-750°C to improve turbine efficiency, then turbine efficiency is improved, but material strength decreases due to high temperature
Solution Approach 1:
The patent applies preliminary action by cooling the diaphragm outer ring before the high-temperature steam reaches critical components. The cooling passages are designed to receive cooling steam in advance, establishing a protective thermal environment that allows the main steam to operate at 650-750°C without compromising material strength in critical areas.
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 cools the inner casing and diaphragm outer ring, allowing the use of conventional heat-resistant steel materials even at high temperatures, reducing production costs and improving turbine efficiency while preventing heat transfer and thermal stress.
Implementation Method 1
a cooling medium passage formed between the inner casing and the diaphragm outer ring to flow a cooling medium
Implementation Method 2
heat tends to be conducted from the diaphragm outer ring to the inner casing
Implementation Method 3
a heat insulating structure to prevent heat transfer from the diaphragm outer ring to the inner casing
Data Source
AI summary
A steam turbine 10 is provided with a double-structure comprising an inner casing 20 and an outer casing 21. A turbine rotor 22, in which plural stages of moving blades 24 are circumferentially implanted, is operatively disposed in inner casing 20. A diaphragm outer ring 25 and a diaphragm inner ring are disposed along the circumferential direction in inner casing 20. Stationary blades 27 are circumferentially provided between diaphragm outer ring 25 and the diaphragm inner ring, so that diaphragm outer ring 25, the diaphragm inner ring and stationary blades 27 form a stage of stationary blades. The stages of the stationary blades are arranged alternately with the stages of moving blades 24 in the axial direction of turbine rotor 22. A cooling medium passage 40 for passing a cooling medium CM which is supplied through a supply pipe 45 is formed between inner casing 20 and diaphragm outer ring 25.