Steam Turbine Inner Casing Clearance Control
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Solution Overview
Problem
In steam turbines, the clearance between rotor blades and the inner casing, as well as stator vanes and the rotor, can inadvertently narrow, leading to potential contact and reduced efficiency due to varying operational conditions and thermal expansion differences.
Innovation Solution
A steam turbine design that includes a rotor with annular rotor blades, an inner casing with a steam inlet and exhaust system, and an outer casing with adjustable steam outlet ports and valves, allowing for controlled cooling and expansion management to maintain optimal clearances and prevent contact between components.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If the inner casing is cooled by exhaust steam during rated operation, then the inner casing size is reduced and clearance between rotor blades and inner casing is reduced, but the clearance may become too small leading to contact during transition phases
Solution Approach 1:
The patent applies dynamics by making the clearance control adaptive to operating conditions. The system dynamically adjusts the cooling intensity of the inner casing based on whether the turbine is in rated operation or transition phase, using valve control to regulate exhaust steam flow. This allows the clearance to be optimized for different operational states, reducing it during rated operation while preventing contact during transition.
Solution Approach 2:
The patent changes the thermal parameter (temperature) of the inner casing dynamically. By controlling the amount of exhaust steam used for cooling, the system can adjust the inner casing temperature and size in response to operational conditions. This parameter change allows the clearance to be reduced during rated operation while maintaining safety margins during transition phases.
2Loss of energy
If the clearance between rotor blades and inner casing is reduced to minimize steam leakage, then energy conversion efficiency is improved, but the risk of contact between components increases
Solution Approach 1:
The system dynamically adjusts clearance based on operational phase. During rated operation, the clearance is reduced to minimize steam leakage and maximize energy conversion efficiency. During transition phases, the system expands the clearance to prevent component contact. This dynamic adjustment resolves the contradiction between energy efficiency and reliability.
Solution Approach 2:
The system takes preliminary action by expanding the clearance before transition phases occur. By anticipating the need for larger clearance during transition, the system proactively adjusts the inner casing temperature and size to prevent contact, while still allowing reduced clearance during stable rated operation for optimal efficiency.
3Productivity
If the inner casing is rapidly cooled to reduce size during rated operation, then energy conversion efficiency is improved, but thermal shock and uneven expansion occur during transition
Solution Approach 1:
The system uses periodic action by alternating between intensive cooling during rated operation and reduced cooling during transition phases. The valve control mechanism periodically adjusts the cooling intensity based on operational requirements, allowing rapid cooling when needed for efficiency while providing thermal stability during transition.
Solution Approach 2:
The cooling system is made dynamic, adjusting the rate of cooling based on operational conditions. During rated operation, rapid cooling is applied to maximize efficiency. During transition phases, the cooling rate is reduced to prevent thermal shock and uneven expansion, maintaining stability of the inner casing composition.
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 clearance sizes, minimizes steam leakage, and enhances energy conversion efficiency by ensuring proper clearance settings during operation and transition phases, thereby preventing contact between stator vanes, rotor blades, and the inner casing.
Implementation Method 1
when the inner casing main body and the outer casing main body are cooled by using exhaust steam which is steam lowered in temperature
Implementation Method 2
there is a possibility of contact between the stator vanes and the rotor main body and contact between the rotor blades and the inner casing main body since the inner casing main body, of which the thickness is small and the thermal capacity is low, is lowered in temperature and is reduced in size earlier than the rotor of which the thermal capacity is high
Data Source
AI summary
A steam turbine includes an outer casing (19) that is provided with a first steam outlet port (54), through which exhaust steam flowing through the entire length of a flow path (21) defined between an inner casing main body (45) and an outer casing main body (51) in a direction along an axis (O1) is discharged to the outside of the outer casing (19), and a second steam outlet port (55), which is provided in the outer casing main body (51) and through which the exhaust steam passing through a portion of the flow path (21) or the exhaust steam not passing through the flow path (21) is discharged to the outside of the outer casing (19); a first valve (28) that adjusts opening of the first steam outlet port (54); and a second valve (32) that adjusts opening of the second steam outlet port (55).