Steam Nozzle Flow Restrictor With Movable Orifice Plate
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Solution Overview
Problem
Nuclear steam generators face inefficiencies due to high pressure drops in existing steam nozzle flow limiters, which also lead to increased moisture carryover, affecting turbine longevity and plant efficiency.
Innovation Solution
A steam nozzle flow restrictor design featuring a support web with a central opening and an axially movable shaft, an orifice plate with openings that restrict steam flow during a steam line break, and a biasing mechanism to maintain open position during normal operation, reducing pressure drop and moisture carryover.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a flow limiter is installed in the steam exit nozzle to limit steam exhaust during a line break, then safety is improved, but pressure drop increases significantly (nearly 138 kPa or 20 psi)
Solution Approach 1:
The flow limiter transitions from a static component to a dynamic system that can change its flow restriction characteristics. The limiter includes a movable disc that responds to pressure differential changes, automatically adjusting the flow area to maintain optimal pressure drop under different operating conditions (normal operation vs. line break).
Solution Approach 2:
The flow limiter operates autonomously without external control systems. The movable disc is actuated automatically by the pressure differential across the limiter itself, eliminating the need for external actuators, control valves, or power sources while still providing effective flow limitation during line breaks.
2Reliability
If a flow limiter is installed in the steam exit nozzle to limit steam exhaust during a line break, then safety is improved, but plant efficiency decreases due to increased pressure drop
Solution Approach 1:
The dynamic adjustment of flow area allows the system to maintain high efficiency during normal operation while providing safety limitation during line breaks. The movable disc remains in a position that minimizes pressure drop under normal conditions, preserving plant efficiency and productivity.
3Reliability
If a flow limiter is installed in the steam exit nozzle to limit steam exhaust during a line break, then safety is improved, but moisture carryover increases by up to 0.05 percent, affecting turbine longevity
Solution Approach 1:
The flow limiter modifies the steam flow parameters (velocity, pressure, flow area) in a controlled manner. By dynamically adjusting the flow area, the system maintains optimal steam quality and minimizes moisture carryover while still providing effective flow limitation during line breaks.
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 design achieves a significant reduction in pressure drop and moisture carryover, enhancing plant efficiency and turbine longevity by limiting steam escape during a steam line break while maintaining normal operation efficiency.
Implementation Method 1
The full power pressure drop in the steam nozzle flow limiter of some steam generators can be nearly 138 kPa (20 psi). A pressure drop reduction to 35kPa (5 psi) or less in the steam nozzle flow limiter can have a significant benefit to the outlet steam pressure
Implementation Method 2
A biasing mechanism maintains the shaft in an open position during normal steam generator operation, but its force is overcome by the increase flow of steam experienced upon a steam line break
Implementation Method 3
its force is overcome by the increase flow of steam experienced upon a steam line break
Data Source
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AI summary
A steam nozzle flow restrictor for a steam generator that restricts steam exit flow during a steam line break, but has a low pressure drop during normal operation. The flow restrictor has a support web suspended from the steam outlet nozzle with the web having a central opening concentric with the central axis of the nozzle. A shaft is slidably supported within the central opening of the web and has an orifice plate that is suspended within the steam generator at one end of the shaft, spaced from the steam nozzle. The orifice plate closes against the underside of the nozzle upon encountering increased steam exit flow as a result of a steam line break.