Centrifugal Compressor Recirculation for Part-Load Surge Control
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Solution Overview
Problem
Refrigerant compressors face challenges in efficiently managing capacity control during part-load operating conditions, particularly in maintaining flow angles and velocities similar to full-load design conditions without the complexity and maintenance requirements of variable-geometry diffusers and inlet guide vanes.
Innovation Solution
A centrifugal compressor design featuring a recirculation flow path between specific locations along the main refrigerant flow path, utilizing a recirculation volute and nozzles to recirculate refrigerant, which is regulated by a flow regulator controlled by a controller to inject refrigerant back into the main flow path, thereby maintaining stable operation without the need for inlet guide vanes or variable geometry diffusers.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If variable-geometry diffusers are used to improve capacity control during part-load conditions, then flow angles and velocities can be maintained similar to full-load design conditions, but device complexity and maintenance requirements increase
Solution Approach 1:
The patent removes the variable-geometry diffuser component from the system entirely. Instead of using a diffuser with adjustable geometry to control capacity, the invention uses a fixed diffuser in combination with a recirculation system that extracts excess refrigerant from the discharge side and returns it to the suction side, thereby achieving capacity control without the complex moving parts of a variable-geometry diffuser.
Solution Approach 2:
The patent introduces a recirculation system as an intermediary mechanism between the discharge and suction sides of the compressor. This recirculation system acts as a mediator to control capacity by recirculating a portion of the discharged refrigerant back to the inlet, allowing capacity modulation without requiring complex variable-geometry components in the main flow path.
2Adaptability or versatility
If inlet guide vanes are used to regulate capacity during various operating conditions, then capacity control is improved, but reliability decreases due to maintenance requirements
Solution Approach 1:
The patent eliminates the inlet guide vane assembly from the compressor design. Instead of using adjustable inlet guide vanes to control the direction and amount of refrigerant entering the impeller, the invention uses a fixed inlet geometry combined with a recirculation system that controls capacity by recirculating refrigerant from discharge to suction, thereby removing the reliability issues associated with moving parts at the inlet.
3Productivity
If recirculation is used to improve capacity control, then efficient operation at part-load conditions is extended, but device complexity increases
Solution Approach 1:
The recirculation system serves multiple functions: it controls capacity during part-load operation, prevents surge conditions by maintaining minimum flow through the impeller, and works with a fixed diffuser and fixed inlet geometry to achieve stable operation across a wide range of loads. This multi-functionality is achieved through a relatively simple recirculation line with a control valve, avoiding the need for complex variable-geometry 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
This design enhances the compressor's stability and extends its efficient operating range to lower part-load conditions, reducing the likelihood of surge conditions and eliminating the need for maintenance-prone mechanical parts like inlet guide vanes and variable geometry diffusers, thus increasing reliability.
Implementation Method 1
a recirculation flow path provided between a first location and a second location along the main refrigerant flow path. The first location is downstream of the second location
Implementation Method 2
the recirculation flow path includes a recirculation volute
Data Source
AI summary
This disclosure relates to a centrifugal compressor. In a first example, the compressor includes a first impeller provided in a main refrigerant flow path, a second impeller provided in the main refrigerant flow path downstream of the first impeller, and a recirculation flow path. In the first example, the recirculation flow path is provided between a first location and a second location along the main refrigerant flow path. The first location is downstream of the second location, and the second location is downstream of the first impeller. In a second example, the compressor includes an impeller provided in a main refrigerant flow path, and a recirculation flow path provided between a first location and a second location along the main refrigerant flow path. In the second example, the recirculation flow path includes a recirculation volute. Further disclosed is a method for operating a centrifugal compressor.