LNG Refrigerant Compressor Power Control Using Automated Flow Override
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Solution Overview
Problem
Existing methods for controlling the production of liquefied natural gas (LNG) product streams in mixed refrigerant cycles do not reliably optimize the available power to drive compressors, particularly in gas turbine systems where maximum power varies with operating conditions, requiring operator intervention and knowledge of power usage.
Innovation Solution
A control method that utilizes an electric motor-driven centrifugal compressor, implementing a control loop to determine and adjust the flow rates of heavy and light mixed refrigerants based on real-time power consumption, allowing for override set points to maximize power utilization without operator intervention.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Power
If gas turbine systems are used to drive compressors, then high power output is achieved, but the maximum available power varies with operating conditions requiring operator intervention
Solution Approach 1:
The control system automatically adjusts refrigerant flow rates based on real-time power consumption measurements without requiring operator knowledge or intervention. The system self-regulates by comparing actual power consumption against available power and autonomously modifying operational parameters to maximize power utilization.
Solution Approach 2:
The system implements continuous feedback by measuring actual power consumption of the compressor and using this information to dynamically adjust refrigerant flow rates. This closed-loop control ensures the system adapts to varying operating conditions and maintains optimal power utilization automatically.
2Loss of energy
If operator knowledge of power conditions is required, then power optimization can be achieved, but system complexity and operational difficulty increase
Solution Approach 1:
The system replaces the need for human operator decision-making with an automated control system that uses sensors and controllers to measure and adjust parameters. This substitution of mechanical/physical measurement and control mechanisms eliminates the need for operator knowledge while maintaining optimization capability.
Solution Approach 2:
The control system performs self-optimization by automatically measuring power consumption and adjusting refrigerant flow rates without external intervention, thereby simplifying operation while achieving energy optimization.
3Adaptability or versatility
If manual control of refrigerant flow rates is used, then flexibility is maintained, but maximum power utilization is not achieved
Solution Approach 1:
The system transitions from static manual control to dynamic automated control that continuously adapts refrigerant flow rates based on real-time power consumption measurements. This dynamic adjustment enables the system to respond instantly to changing operating conditions and maximize power utilization while maintaining flexibility.
Solution Approach 2:
The control system automatically modifies operational parameters (refrigerant flow rates) based on measured power consumption and available power conditions. This automatic parameter adjustment enables optimal power utilization without sacrificing operational flexibility, as the system adapts parameters in response to changing conditions.
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 ensures continuous optimization of compressor power usage by automatically adjusting refrigerant flow rates, eliminating the need for operator knowledge of power conditions and maximizing the use of available power, thereby improving the efficiency and reliability of LNG production.
Implementation Method 1
a centrifugal compressor (15) driven by an electric motor (16)
Implementation Method 2
removing heat from natural gas in a main heat exchanger in which the natural gas is in indirect heat exchange with expanded heavy mixed refrigerant and expanded light mixed refrigerant
Implementation Method 3
In the shell side of the main heat exchanger, the expanded heavy mixed refrigerant and the expanded light mixed refrigerants are allowed to evaporate so as to remove heat from the natural gas
Implementation Method 4
a centrifugal compressor (15) driven by an electric motor (16)
Data Source
AI summary
The present invention relates to a method of controlling the production of a liquefied natural gas product stream (31) obtained by removing heat from natural gas by indirect heat exchange with an expanded heavy mixed refrigerant and an expanded light mixed refrigerant. The method comprises executing a control loop comprising maintaining the flow rate of the liquefied natural gas product stream (31) at a dependent set point and maintaining the flow rates of the heavy mixed refrigerant (60a) and the light mixed refrigerant (65) at operator manipulated set points (80, 81). The method further comprises executing an override control loop comprising: determining an override set point (95′) for the flow rate of the liquefied natural gas and computing an override set point (80′) for the flow rate of the heavy mixed refrigerant and an override set point (81′) to reduce residual available power of the electric motor.