Centrifugal Compressor Return Vane Prewhirl Optimization
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Solution Overview
Problem
Multistage centrifugal compressors face challenges in securing sufficient surge and choke margins, leading to a reduced operation range due to inadequate fluid flow distribution across stages.
Innovation Solution
The design includes a rotary shaft with multiple impeller stages and a return flow path with inclined return vanes, where the exit angle of the return vane decreases towards the rear stage, optimizing fluid prewhirl and flow rate distribution to enhance both surge and choke margins.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Temperature
If the exit angle of the return vane is increased toward the rear stage side, then the prewhirl of the fluid increases, but the choke margin excessively decreases
Solution Approach 1:
The exit angle of the return vane is made different for each stage, with front stage return vanes having larger exit angles and rear stage return vanes having smaller exit angles. This local differentiation optimizes the prewhirl generation at each stage, ensuring that each impeller receives appropriate prewhirl corresponding to its design flow rate, thereby maintaining adequate choke margin across all stages.
2Quantity of substance
If the exit angle of the return vane is increased toward the rear stage side, then the fluid having large volume flow rate is supplied to the impeller, but the surge margin decreases
Solution Approach 1:
The exit angle of the return vane is differentiated by stage position, with front stage return vanes having larger exit angles that generate higher prewhirl and redirect more fluid to the front stage impeller. This ensures that the front stage impeller, which has smaller surge margin, receives adequate fluid flow to maintain sufficient surge margin, while rear stage impellers receive appropriate prewhirl corresponding to their lower design flow rates.
3Temperature
If the exit angle of the return vane is decreased toward the rear stage side, then the prewhirl generated by the return vane decreases, but the fluid having small volume flow rate is supplied to the impeller
Solution Approach 1:
The exit angle of the return vane is optimized for each stage, with rear stage return vanes having smaller exit angles that generate lower prewhirl. This matches the design flow rate characteristics of rear stage impellers, which operate at lower flow rates, ensuring that each impeller receives prewhirl appropriate to its stage while maintaining proper fluid distribution.
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 configuration broadens the operational range of the centrifugal compressor by ensuring adequate fluid supply to each stage, thereby securing both surge and choke margins.
Implementation Method 1
the fluid provided with a larger prewhirl is introduced to the impeller subsequent to the return vane
Implementation Method 2
The multistage centrifugal compressor provides gas with pressure energy and velocity energy by rotating the impeller
Data Source
AI summary
A casing surrounds a rotary shaft and impellers (4), and includes a return flow path through which a fluid discharged from the impeller (4) on a front stage side between the impellers (4) adjacent to each other is guided inward in a radial direction so as to be introduced to the impeller (4) on a rear stage side, and a plurality of return vanes (50) disposed at an interval in a circumferential direction inside the return flow path. An exit angle of the return vane (50) is inclined forward in a rotation direction of the impeller (4), according to the radial direction, and the exit angle of the return vane (50) decreases toward the return vane (50) on the rear stage side.