Turboexpander Speed Control to Avoid Critical Shaft Vibration
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
The operation characteristics of the expansion unit in raw material gas liquefying devices vary over time due to component deterioration and impurity adhesion, leading to unpredictable rotation speed changes, which can result in excessive shaft vibrations and potential damage during start-up and stop processes.
Innovation Solution
Direct control of the rotation speed of the expansion unit at start-up and stop to prevent it from entering the critical speed zone, using a controller to manage valve opening rates and ensure stable operation, thereby suppressing shaft vibrations and preventing damage such as bearing seizure.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If valve opening rate schedules are used to control start-up and stop of the expansion unit, then the load to heat exchangers is reduced and shaft vibration is reduced, but the rotation speed may unexpectedly fall into the critical speed zone due to changing operation characteristics over time
Solution Approach 1:
The control system continuously monitors the actual rotation speed of the expansion unit and compares it with the target rotation speed. Based on this feedback, the controller dynamically adjusts the valve opening rates to maintain accurate rotation speed control, compensating for changes in operation characteristics over time such as component deterioration and impurity adhesion.
Solution Approach 2:
The control method transitions from static pre-set valve opening rate schedules to dynamic rotation speed control. The controller continuously adapts the valve opening rates based on real-time rotation speed measurements, making the control system flexible and responsive to changing operational conditions, thereby preventing the rotation speed from falling into the critical speed zone.
2Device complexity
If pre-set valve opening rate schedules are used, then the control process is simple, but it cannot account for deterioration of components and adhesion of impurities that change operation characteristics
Solution Approach 1:
The control system incorporates continuous feedback from rotation speed sensors to monitor actual operational characteristics. This feedback mechanism enables the controller to detect and compensate for changes caused by component deterioration and impurity adhesion, maintaining reliable operation without requiring complex predictive models or frequent manual adjustments.
Solution Approach 2:
The control system performs self-adjustment by automatically modifying valve opening rates based on real-time rotation speed measurements. This self-service capability allows the system to adapt to changing operation characteristics without external intervention, maintaining reliability while keeping the control architecture relatively simple.
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 approach effectively avoids unexpected rotation speed drops into critical zones, reducing the risk of excessive shaft vibrations and associated damages, ensuring stable and efficient operation of the expansion units during start-up and stop processes.
Implementation Method 1
The refrigerant flowing through the refrigerant circulation line is compressed by the compressor, is decreased in temperature by adiabatic expansion in the expansion unit
Implementation Method 2
heat exchangers which exchange heat between the raw material gas and the refrigerant
Implementation Method 3
The refrigerant flowing through the refrigerant circulation line is compressed by the compressor
Data Source
Figure 1
Figure 2
Figure 3
AI summary
A raw material gas liquefying device includes a feed line which feeds a raw material gas, a refrigerant circulation line which circulates a refrigerant, the refrigerant circulation line including an expansion unit of a turbine type which expands the refrigerant to generate cryogenic energy, and an expansion unit entrance valve provided at an entrance side of the expansion unit, a heat exchanger which exchanges heat between the raw material gas and the refrigerant, a cooler which performs initial cooling of the raw material gas and the refrigerant by heat exchange with liquid nitrogen, and a controller which manipulates the opening rate of the expansion unit entrance value and performs a feedback control so that the rotation speed of the expansion unit reaches a predetermined target value, and outputs the opening rate command to the expansion unit entrance valve, at start-up and stop of the expansion unit.