Variable Geometry Diffuser Ring for Centrifugal Compressor Flow Control
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Solution Overview
Problem
Centrifugal compressors face challenges with stall, surge, and transient loads during startup and shutdown, which existing variable geometry diffusers do not adequately address, limiting their usage and reliability.
Innovation Solution
A variable geometry diffuser mechanism with an L-shaped diffuser ring that extends fully across the diffuser gap to control gas flow, reducing axial forces through reduced radial thickness and incorporating a controller-actuated mechanism for precise positioning, allowing for enhanced control during startup, shutdown, and capacity control.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the diffuser ring is extended across the diffuser gap to stabilize flow during stall, then stall mitigation is improved, but the mechanism cannot sufficiently block flow during shutdown to prevent backspin and transient loads
Solution Approach 1:
The diffuser ring is designed to be dynamically adjustable between multiple positions: a first extended position for stall mitigation during operation, and a second fully extended position for blocking flow during shutdown. The drive mechanism enables continuous adjustment of the diffuser ring position based on real-time compressor operating conditions, allowing the system to adaptively switch between different functional requirements.
2Force
If the diffuser ring radial thickness is reduced to minimize axial forces, then the load on the diffuser mechanism is reduced, but the structural strength and ability to withstand pressure differential may be compromised
Solution Approach 1:
The diffuser ring is constructed using composite materials that provide high strength-to-weight ratio and exceptional mechanical properties. This allows the ring to have reduced radial thickness for minimizing axial forces while maintaining sufficient structural strength to withstand the pressure differential across the ring during operation.
Solution Approach 2:
Instead of increasing radial thickness to strengthen the diffuser ring, the design reinforces the ring in other dimensions - through optimized cross-sectional geometry, strategic rib reinforcement, and enhanced support from the drive mechanism bearings. This dimensional redistribution of strength allows thickness reduction without compromising structural integrity.
3Object-affected harmful factors
If the diffuser ring is positioned to fully block the diffuser gap during shutdown, then compressor backspin and transient loads are minimized, but the mechanism experiences increased wear and tear affecting reliability
Solution Approach 1:
The controller predicts impending shutdown conditions and begins positioning the diffuser ring toward the blocking position in advance. This preliminary action allows the ring to be in the optimal position when shutdown occurs, minimizing backspin and transient loads without requiring the mechanism to make abrupt, high-stress movements during the actual shutdown event.
Solution Approach 2:
The patent replaces traditional mechanical wear-prone components with magnetic bearing technology that supports the diffuser ring and drive mechanism. This substitution eliminates direct mechanical contact and friction, dramatically reducing wear and tear while enabling precise control of the diffuser ring position during shutdown operations.
4Reliability
If existing variable geometry diffusers are used, then stall can be mitigated during operation, but they cannot eliminate the need for pre-rotation vanes and cannot provide adequate control during startup and shutdown
Solution Approach 1:
The diffuser ring mechanism is designed as a multi-functional device that can perform multiple roles: (1) stall mitigation during normal operation by adjusting flow distribution, (2) surge prevention during startup by controlling initial flow, (3) backspin prevention during shutdown by blocking reverse flow, and (4) capacity control during part-load operation. This universal design eliminates the need for separate pre-rotation vanes and other auxiliary components.
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 mechanism effectively minimizes compressor backspin, transient loads, and surge during shutdown, and eliminates the need for pre-rotation vanes by providing precise control over gas flow, enhancing compressor reliability and longevity.
Implementation Method 1
a diffuser ring extending into a diffuser gap that mitigates stall
Implementation Method 2
an L-shaped diffuser ring that extends fully across the diffuser gap to control gas flow, reducing axial forces through reduced radial thickness
Implementation Method 3
incorporating a controller-actuated mechanism for precise positioning, allowing for enhanced control during startup, shutdown, and capacity control
Data Source
AI summary
An improved variable geometry diffuser (VGD) mechanism for use with a centrifugal compressor. This VGD mechanism extends substantially completely into the diffuser gap so that the VGD mechanism may be used more fully to control other operational functions. The VGD mechanism may be used to minimize compressor backspin and associated transient loads during compressor shut down by preventing a reverse flow of refrigerant gas through the diffuser gap during compressor shutdown, which is prevented because the diffuser gap is substantially blocked by the full extension of the diffuser ring. During start-up, transient surge and stall also can be effectively eliminated as gas flow through the diffuser gap can be impeded as load and impeller speed increase, thereby alleviating the problems caused by startup loads at low speeds. The VGD mechanism can be used for capacity control as well so as to achieve more effective turndown at low loads.