Active Retractable Seal for Turbo Machinery Rub Prevention
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Solution Overview
Problem
Existing rotary machine seals, such as those in steam turbines and gas turbines, face inefficiencies due to transient events causing rubbing and heat generation, leading to rotordynamic instabilities, and current variable clearance positive-pressure arrangements are not effective in preventing rubs during steady-state operation.
Innovation Solution
An active retractable seal assembly is introduced, utilizing a fluid bypass circuit to reduce pressure drop across seal segments, allowing them to be opened by springs or low-force actuators at any operating condition, including full load and thermal transients, enabling optimal sealing.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If variable clearance positive-pressure arrangement is used to hold seal segments open during transient events, then rubbing between seal segments and rotor is reduced, but seal segments remain closed during steady-state operation preventing optimal sealing
Solution Approach 1:
The seal segments are designed to dynamically adjust their position between open and closed states based on operating conditions. During transient events, they remain open to prevent rubbing, while during steady-state operation, they close to optimize sealing efficiency. This dynamic adaptability resolves the contradiction between reliability during transients and productivity during steady-state operation.
Solution Approach 2:
The system incorporates feedback mechanisms through pressure sensors and control systems that monitor operating conditions in real-time. When transient conditions are detected, the control system activates to hold seal segments open. When steady-state conditions are detected, the system deactivates allowing segments to close for optimal sealing. This feedback loop enables the system to automatically adapt to changing operating conditions.
2Productivity
If seal segments are held closed by ambient fluid pressure during steady-state operation, then optimal sealing is achieved, but seal segments become susceptible to rubbing during rotor vibrations
Solution Approach 1:
The system applies preliminary anti-action by maintaining a readiness state where seal segments can be quickly opened in response to detected rotor vibrations. The control system continuously monitors vibration levels and pre-positions seal segments in an open state when vibrations are detected, preventing rubbing before it occurs. This preliminary protective action maintains both sealing efficiency and reliability.
Solution Approach 2:
The seal segments transition from a static closed position to a dynamic state where they can rapidly open and close in response to rotor vibrations. This dynamic capability allows the segments to maintain optimal sealing during normal operation while providing protection during vibration events, resolving the contradiction between productivity and reliability.
3Adaptability or versatility
If high force capacity pneumatic actuators are used to actively open seal segments, then seal segments can be opened under any operating condition, but device complexity and external high-pressure gas supply system are required
Solution Approach 1:
The seal segments utilize the existing ambient fluid pressure within the turbo-machine as the actuating force to open the segments, eliminating the need for external high-pressure gas supply systems. The control system selectively allows or blocks the ambient pressure from acting on the seal segments, enabling active positioning control without adding complex external pressurization infrastructure. This self-service approach reduces device complexity while maintaining adaptability.
Solution Approach 2:
The ambient fluid pressure system serves multiple functions: it provides the actuating force to open seal segments, maintains the sealing environment, and eliminates the need for separate pneumatic actuator systems. By utilizing this existing universal resource, the invention achieves adaptability in seal positioning while significantly reducing device complexity compared to dedicated pneumatic actuator systems.
4Reliability
If seal segments are opened during no- or low-flow transient conditions, then rubbing is prevented, but sealing efficiency decreases during these conditions
Solution Approach 1:
The seal segments dynamically adjust their position based on real-time detection of transient conditions. During no- or low-flow conditions, the segments remain open to prevent rubbing, accepting reduced sealing efficiency as necessary. When flow conditions improve and transient events subside, the segments transition to a closed position to optimize sealing efficiency. This dynamic response resolves the contradiction by prioritizing reliability during transients and productivity during normal operation.
Solution Approach 2:
The system employs periodic monitoring of operating conditions and adjusts seal segment position accordingly. During transient events, segments are held open; during steady-state operation, segments close for optimal sealing. This periodic adjustment cycle ensures that the system prioritizes rubbing prevention during transients while maintaining high sealing efficiency during normal operation, resolving the productivity-reliability contradiction.
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
The active retractable seal assembly effectively reduces pressure drop across seal segments, allowing them to remain open during transient events and maintain optimal sealing during steady-state operation, reducing the risk of rubbing and enhancing machine performance and reliability.
Implementation Method 1
A retractable seal assembly for use between a stationary turbine stator and a turbine rotor component of a turbine... comprising: a plurality of seal rings fixed to the turbine stator, each ring having at least two arcuate seal segments movable toward and away from the turbine rotor between respective closed and open positions as a function of pressure drop in a fluid flowing axially along the rotor
Implementation Method 2
By eliminating or reducing this pressure drop, the radially inward force on the seal segments due to ambient fluid pressure is effectively reduced and the seal segments are then retracted open by springs or other suitable low-force capacity actuators
Data Source
AI summary
An active retractable seal assembly for use between rotating and non-rotating turbo machinery components including: a plurality of seal rings mounted to the non-rotating component, the seal rings movable toward and away from the rotating component between respective closed and open positions as a function of pressure drop across the seal rings, wherein the seal rings are normally in the open position; and a fluid bypass circuit for directing fluid around one or more of the plurality of seal rings to reduce the pressure drop across the one or more of the seal rings, thereby causing the one or more seal rings to move towards the open position under the action of spring(s) or actuator(s).