Turbine Clearance Control via Axial Casing Movement
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Solution Overview
Problem
Steam and gas turbines face inefficiencies due to inconsistent axial clearance between the rotor and stator, which changes with centrifugal forces, vibration, and thermal growth, leading to potential damage and leakage, and existing solutions fail to maintain optimal clearance across varying operating conditions.
Innovation Solution
A hydraulic or pneumatic actuator system is used to axially move the inner turbine casing, allowing for dynamic adjustment of clearance between the rotor and stator, enabling better alignment and reduced leakage through dual overlap and tapered rotor designs.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the axial clearance between rotor and stator is increased to prevent contact during acceleration and thermal growth, then reliability is improved, but cooling air leakage increases and efficiency decreases
Solution Approach 1:
The patent applies dynamics by making the axial clearance adjustable rather than fixed. The inner turbine casing is movable relative to the outer casing, allowing the clearance to be dynamically optimized. During normal operation, the casing can be positioned to minimize leakage, while during acceleration or thermal growth, it can be adjusted to prevent contact, thus resolving the contradiction between reliability and energy loss.
Solution Approach 2:
The patent changes the clearance parameter from a static value to a variable one. By using movable inner casing and adjustable positioning mechanisms, the axial clearance can be changed based on operating conditions. This allows the system to maintain small clearance for efficiency during steady state, while increasing it when needed to prevent damage, thereby addressing both reliability and energy loss concerns.
2Manufacturing precision
If a fixed positional relationship between stator and rotor is maintained, then manufacturing precision is improved, but clearance changes during acceleration and thermal growth cause rubbing and damage
Solution Approach 1:
The system transitions from a fixed positional relationship to a dynamic one. The inner turbine casing can move axially relative to the outer casing, allowing the clearance to be adjusted in response to changing operating conditions. This dynamic adjustment prevents rubbing and damage during acceleration and thermal growth while maintaining precision during steady state operation.
Solution Approach 2:
The patent incorporates feedback mechanisms to monitor and control the clearance. Position sensors detect the actual clearance and feed this information back to the control system, which then adjusts the inner casing position accordingly. This feedback loop ensures that the clearance remains optimal under varying conditions, preventing contact while maintaining manufacturing precision.
3Adaptability or versatility
If the inner turbine casing is made movable to adjust clearance, then adaptability to operating conditions is improved, but device complexity increases
Solution Approach 1:
The patent uses pneumatic or hydraulic actuators to provide the necessary force for moving the inner turbine casing. These actuators are compact and can be integrated into the existing turbine structure. The pneumatic/hydraulic system provides smooth, controlled movement with relatively simple mechanics, achieving adaptability without excessive complexity compared to alternative solutions like complex mechanical linkages or multiple motors.
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 solution maintains optimal clearance between the rotor and stator across varying operating conditions, reducing damage and inefficiencies by dynamically adjusting the axial gap, thereby enhancing turbine performance and efficiency.
Implementation Method 1
a hydraulic or pneumatic controller to directly drive a shaft connected to two actuators disposed at horizontal joints on the inner turbine casing
Implementation Method 2
a hydraulic or pneumatic controller to directly drive a shaft connected to two actuators disposed at horizontal joints on the inner turbine casing
Implementation Method 3
the components of the turbine can thermally expand (or contract) at varying rates due to high operating temperatures in excess of 1093°C (2,000 degrees Fahrenheit)
Implementation Method 4
clearance changes during periods of acceleration or deceleration due to changing centrifugal forces on the buckets
Data Source
AI summary
A clearance control system for a turbine (10) having a stator assembly and a rotor assembly includes a hydraulic or pneumatic controller (26,28) that axially drives, through a shaft (34), one or more actuators (36,38) connected to the stator assembly casing (30,32). The controller (26,28) causes relative movement between the stator and rotor assemblies to adjust the clearances between portions of the stator and rotor in accordance with the varying operating conditions of the turbine. More particularly, the controller (26,28) moves the stator relative to the rotor in first and second axial directions to compensate for thermal expansion and contraction during the operating conditions of the turbine (10).