Series Cryogenic Compressor Speed Control Against Surge And Choke
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Solution Overview
Problem
Controlling the speed of compressors in series, particularly in cryogenic helium compression systems, is challenging due to temperature and pressure fluctuations, which affect the efficiency and stability of the compressor system, leading to undesirable operating states like choke and surge characteristics, and requires a method to maintain stable and economical operation across the compressor series.
Innovation Solution
A method that involves specifying a target inlet pressure, detecting actual pressures, calculating a proportional-integral value, determining a capacity factor, and using a model total pressure ratio to set reduced target speeds for each compressor, ensuring stable operation by damping pressure fluctuations and maintaining compressors within their design points.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Use of energy by moving object
If compressors in series are controlled to operate at high efficiency points, then energy efficiency is improved, but the system becomes highly sensitive to temperature and pressure fluctuations
Solution Approach 1:
The control method continuously monitors actual pressures at compressor inlets and outlets, compares them with target values, and adjusts compressor speeds in real-time using feedback control. This maintains stable operation despite temperature and pressure fluctuations in the cryogenic system.
Solution Approach 2:
The control system dynamically adjusts the operating points of compressors based on real-time system conditions. Instead of fixed speed control, the method adapts compressor speeds to maintain optimal operation while responding to changing thermal and pressure conditions in the helium cooling system.
2Productivity
If compressor speed is increased to handle higher mass flow, then productivity is improved, but the compressor may enter undesirable operating states like choke or surge
Solution Approach 1:
The control method uses feedback from actual pressure measurements to continuously adjust compressor speeds, ensuring operation remains within the stable region of the compressor characteristic map and avoiding choke and surge conditions while maximizing mass flow.
Solution Approach 2:
The method changes operating parameters (compressor speeds) to maintain operation within the optimal region of the compressor characteristic map. By adjusting speeds based on actual system conditions, the system maximizes mass flow while preventing entry into unstable operating regions.
3Use of energy by moving object
If multiple compressors are controlled independently to maintain their own design points, then individual compressor efficiency is improved, but the overall system becomes complex to coordinate
Solution Approach 1:
The control method merges the control of multiple compressors into a coordinated system. By considering the series connection and using coupled control equations that account for inter-compressor influences, the system achieves efficient operation of all compressors through a unified control strategy rather than independent controls.
Solution Approach 2:
The control method segments the overall control problem into individual compressor control equations while maintaining coordination. Each compressor has its own control characteristics and design points, but these are integrated through the series connection model to achieve system-wide optimization.
Data Source
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AI summary
The invention relates to a method for regulating rotational speeds of compressors which are arranged in series, for compressing a fluid, in particular cryogenic helium, wherein a setpoint inlet pressure which the fluid is supposed to be at at an inlet of the compressor which is arranged furthest upstream is predefined, an actual inlet pressure of the fluid at that inlet is detected, an actual outlet pressure of the fluid at an outlet of the compressor which is arranged furthest downstream is detected, an actual overall pressure ratio is detected, wherein the actual overall pressure ratio corresponds to the quotient of the actual outlet pressure and the actual inlet pressure, a proportional integral value is determined from the deviation of the actual inlet pressure from the setpoint inlet pressure, a capacity factor is determined from the proportional integral value and the actual overall pressure ratio, a model overall pressure ratio is determined from the actual overall pressure ratio and the capacity factor, a reduced setpoint rotational speed is determined for each compressor, wherein the respective reduced setpoint rotational speed is determined as a functional value of a regulating function which is assigned to the respective compressor and assigns a reduced setpoint rotational speed to each value pair comprising capacity factor and model overall pressure ratio, and the rotational speed of each compressor is set using the reduced setpoint rotational speed which is determined for it.