Steam Turbine Inner Casing Segmentation for Thermal Load Distribution
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Solution Overview
Problem
Steam turbines with resuperheating face challenges due to extreme temperature and pressure loads on the outer casing, which can lead to damage and inefficiencies, especially at low exhaust steam pressures, requiring measures like additional resuperheating and drying to manage wet steam content and prevent condensation-induced damage.
Innovation Solution
A steam turbine design featuring two inner casings with separate blading regions and a sealing shell, where fresh steam is expanded in one casing and superheated steam in another, minimizing temperature and pressure loads on the outer casing by distributing steam flows and pressures, and optimizing the sealing system to reduce leakage and thermal stresses.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If resuperheating is implemented to manage wet steam content and prevent condensation damage, then reliability is improved, but the outer casing experiences extreme temperature and pressure loads that can lead to damage
Solution Approach 1:
The turbine is divided into multiple independent casings (first casing for high-pressure fresh steam, second casing for low-pressure resuperheated steam, third casing for low-pressure wet steam). This segmentation isolates the extreme temperature and pressure loads to specific casing sections rather than exposing the entire outer casing to combined extreme conditions, thereby maintaining reliability while protecting overall casing strength.
2Strength
If the casing wall is thickened to withstand high pressures, then strength is improved, but thermally induced stresses become impermissibly high
Solution Approach 1:
By segmenting the turbine into separate casings for different pressure and temperature ranges, each casing can be optimized with appropriate wall thickness. The high-pressure casing has sufficient thickness for pressure resistance, while the low-pressure casing has reduced thickness, avoiding excessive thermal stresses. This eliminates the need for a uniformly thick casing that would experience impermissible thermal stresses.
Solution Approach 2:
Each casing is designed with local quality appropriate to its operating conditions. The high-pressure casing has greater wall thickness and material properties suited for high stress, while the low-pressure casing has thinner walls appropriate for lower pressures. This localized optimization allows each section to withstand its specific loads without generating impermissible thermal stresses.
3Device complexity
If a single-casing design is used to simplify the structure, then device complexity is reduced, but the outer casing becomes overloaded thermally at two points by temperatures and pressures
Solution Approach 1:
The single overloaded casing is segmented into multiple casings, each handling a specific temperature and pressure range. The first casing handles high-temperature fresh steam, the second casing handles resuperheated steam at moderate temperatures, and the third casing handles low-temperature wet steam. This segmentation distributes the thermal loading across multiple components rather than concentrating it on a single outer casing.
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 reduces the loading on the turbine outer casing, minimizes leakage, and allows for efficient operation at high steam parameters, enabling continuous operation without damage from condensation and maintaining efficiency by distributing temperature and pressure loads across multiple casings.
Implementation Method 1
an additional sealing shell, also referred to as partition, is arranged in the turbine casing, in particular on the inner side of the turbine outer casing. The sealing shell is sealed toward the turbine shaft via sealing elements
Implementation Method 2
the previously absorbed energy of the working medium is converted into kinetic energy. The kinetic energy is used, for example, to operate a generator which converts the mechanical power generated into electrical energy
Implementation Method 3
The expanded and cooled steam then flows into a condenser where the steam condenses by heat transfer in a heat exchanger
Implementation Method 4
is fed again as liquid water by a pump to the steam boiler for heating, evaporating and subsequent superheating
Data Source
AI summary
A steam turbine has a single-shell turbine casing and specific inner casings arranged inside the turbine casing. The steam turbine has a turbine casing with an outer wall, a turbine shaft mounted rotatably about a turbine axis in the turbine casing, a first turbine part, and at least one second turbine part which is arranged downstream of the first turbine part in the axial direction of the turbine shaft, wherein the expansion direction for steam conducted through the steam turbine runs from the first turbine part to the second turbine part, wherein between the first turbine part and the second turbine part, a sealing shell is arranged on the turbine casing, in particular on the inner side of the outer wall for rotation therewith, the sealing shell being formed in a sealing manner with respect to the turbine shaft via sealing elements.