Centrifugal Compressor Recirculation Structure for Surge Stability
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Solution Overview
Problem
Conventional centrifugal compressors in chiller systems face instability due to surge phenomena, which can lead to mechanical damage and efficiency losses, particularly during startup and part-load operations, as the operating point approaches the surge line, causing flow recirculation and pressure fluctuations.
Innovation Solution
A centrifugal compressor with a recirculation structure that includes a recirculation path and discharge cavity, featuring rotatable recirculation discharge guide vanes and an annular groove, which imparts a swirl to the refrigerant flow, allowing for controlled recirculation and reduced efficiency losses, thereby preventing surge without complex construction or performance reduction.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If conventional centrifugal compressors operate near the surge line during startup and part-load conditions, then the compressor can maintain higher flow rates, but surge phenomena occur causing flow recirculation, pressure fluctuations, and system instability
Solution Approach 1:
The harmful recirculating flow is extracted from the compression system through a dedicated recirculation path that bypasses the impeller, allowing the main flow to remain stable while managing the excess flow separately. This prevents surge by removing the recirculating portion of the flow that would otherwise cause instability.
Solution Approach 2:
A recirculation valve acts as an intermediary component that controls and regulates the recirculating flow, mediating between the high-flow requirement and the stability requirement. The valve allows precise control of the recirculation amount to maintain stable operation near the surge line.
2Device complexity
If the recirculation path is integrated within the compressor casing, then the construction remains compact and simple, but the recirculation flow path length is limited
Solution Approach 1:
The recirculation path is nested within the compressor casing, with the recirculation pipe routed through the existing internal space of the compressor housing. This allows the recirculation system to be integrated without adding external complexity, while the pipe can extend sufficiently to provide adequate path length for flow stabilization.
3Reliability
If surge control mechanisms are added to prevent flow recirculation, then system stability improves, but the compressor operation range is limited and performance is reduced
Solution Approach 1:
The recirculation valve is made dynamically controllable, allowing its opening degree to be adjusted in real-time based on operating conditions. This enables the system to adapt to different load conditions and maintain stable operation across a wide range of flows, from startup through part-load to full-load conditions.
Solution Approach 2:
The system changes the flow distribution parameter by varying the recirculation valve opening degree, which redirects the appropriate amount of flow through the recirculation path. This parameter adjustment allows the compressor to operate stably across different operating points without limiting the overall operation range.
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 recirculation structure effectively stabilizes the compressor operation by managing refrigerant flow, preventing surge and maintaining performance across a wider range of operating conditions, reducing mechanical stress and efficiency penalties.
Implementation Method 1
The recirculation structure is configured to impart a swirl to a flow of refrigerant into the inlet portion
Implementation Method 2
The diffuser works to transform the velocity of refrigerant gas (dynamic pressure), given by the impeller, into (static) pressure
Implementation Method 3
The impeller increases the velocity of refrigerant gas
Implementation Method 4
refrigerant is compressed in the centrifugal compressor
Data Source
AI summary
A centrifugal compressor for a chiller system includes a casing having an inlet portion and an outlet portion, a recirculation structure including a recirculation path and a recirculation discharge cavity, an impeller disposed downstream of the recirculation discharge cavity, a plurality of recirculation discharge guide vanes disposed to surround the recirculation discharge cavity, and a diffuser disposed in the outlet portion downstream of the impeller. The recirculation structure is configured to impart a swirl to a flow of refrigerant into the inlet portion. The recirculation path supplies the refrigerant from the diffuser to the recirculation discharge cavity. The recirculation path includes a recirculation pipe that introduces the refrigerant toward the plurality of recirculation discharge guide vanes. An annular groove is disposed between the recirculation pipe and the plurality of recirculation discharge guide vanes. An annular plate is disposed between the annular groove and the recirculation discharge cavity.