Reverse rotation prevention in centrifugal compressor
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Solution Overview
Problem
In heat exchanger systems, particularly water-cooled chillers, centrifugal compressors experience reverse rotation after shutdown, which can be problematic for magnetic bearings, leading to potential issues and inefficiencies.
Innovation Solution
A control algorithm that positions inlet guide vanes (IGVs) of the compressor in specific positions and opens a hot gas bypass valve upon shutdown, while monitoring pressures to maintain zero compressor speed until equalization, utilizing a controller to manage these operations based on predefined conditions.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the compressor is shut down using conventional methods, then the shutdown process is simple, but the compressor experiences reverse rotation which can damage magnetic bearings
Solution Approach 1:
The control algorithm performs preliminary actions before complete shutdown by positioning inlet guide vanes in specific positions and opening hot gas bypass valves to prevent reverse rotation from occurring, thereby protecting magnetic bearings during the shutdown process
Solution Approach 2:
The system continuously monitors compressor speed and pressure differential between evaporator and condenser, using this feedback to dynamically adjust inlet guide vane positions and hot gas bypass valve openings to maintain zero compressor speed until pressure equalization
2Loss of time
If the compressor speed is reduced quickly, then the shutdown time is shortened, but reverse rotation may occur before pressure equalization
Solution Approach 1:
The control algorithm continuously monitors pressure differential between evaporator and condenser, using this feedback to determine when it is safe to remove power from the motor, ensuring pressure equalization occurs before shutdown completion to prevent reverse rotation
Solution Approach 2:
The system dynamically adjusts inlet guide vane positions and hot gas bypass valve openings based on real-time compressor speed and pressure conditions, allowing flexible control that prevents reverse rotation while minimizing shutdown time
Data Source
AI summary
A method of operating a heat exchanger system in which a compressor, which is drivable by a motor, is fluidly interposed between an evaporator and a condenser following receipt of a shutdown command is provided. The method includes positioning inlet guide vanes (IGVs) of the compressor in a first position in the event of at least one of a first precondition being in effect and the first and a second precondition both not being in effect. The method further includes positioning the IGVs in a second position in an event the first precondition is not in effect but the second precondition is in effect, ramping a speed of the compressor down until a third precondition takes effect, removing power from the motor and positioning the IGVs in the first position once power is removed from the motor.