System and method for operating a liquefaction train
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Solution Overview
Problem
Natural gas liquefaction plants face challenges in dynamically responding to rapid changes in feed gas flow rates, leading to potential equipment damage and downtime due to temperature gradients and liquid refrigerant dropout in main cryogenic heat exchangers.
Innovation Solution
A method and system for operating a main cryogenic heat exchanger that involves monitoring or predicting flow rate variations and using compressor recycle valves to adjust the mixed refrigerant flow, maintaining constant pressure and temperature in the refrigerant loop to stabilize the heat exchanger during rapid flow changes.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the refrigerant loop operates without dynamic control during rapid feed gas flow rate changes, then the system structure remains simple, but temperature gradients and liquid refrigerant dropout occur causing equipment damage
Solution Approach 1:
The control scheme is activated in advance when a variation in feed gas flow rate exceeding a predetermined threshold is monitored or predicted. This preliminary activation allows the refrigerant loop to respond proactively to upcoming changes, preventing temperature gradients and liquid refrigerant dropout before they occur, thereby protecting equipment without requiring permanently complex control infrastructure
Solution Approach 2:
The system continuously monitors variations in feed gas flow rate and uses this feedback to dynamically adjust the refrigerant loop operation. When flow rate variations exceed predetermined thresholds, the control scheme automatically activates to recycle compressed mixed refrigerant, creating a closed-loop feedback mechanism that enhances reliability only when needed
2Reliability
If compressor recycle valves are used to dynamically control refrigerant flow, then the dynamic response and reliability improve, but the device complexity and initial cost increase
Solution Approach 1:
The system transitions from static operation to dynamic control by activating the control scheme only when feed gas flow rate variations exceed predetermined thresholds. Compressor recycle valves are dynamically adjusted based on real-time monitoring, allowing the system to adapt its complexity level to operational needs rather than maintaining high complexity continuously
Solution Approach 2:
The control scheme changes operational parameters (refrigerant flow rate, compression ratio) in response to feed gas flow rate variations. By adjusting these parameters dynamically through compressor recycle valve control, the system maintains heat exchanger reliability during transient conditions without requiring permanently complex valve control infrastructure
3Productivity
If the mixed refrigerant flow rate is not adjusted during rapid feed gas flow changes, then the control system remains simple, but liquid refrigerant drops out causing compressor trips and production loss
Solution Approach 1:
The control scheme is activated in advance when feed gas flow rate variations are detected, allowing the system to preemptively adjust mixed refrigerant flow rates before liquid dropout occurs. This preliminary automated action prevents compressor trips and maintains continuous LNG production without requiring permanent high-level automation infrastructure
Solution Approach 2:
The system uses automated feedback control to monitor feed gas flow rate and dynamically adjust mixed refrigerant flow accordingly. This feedback mechanism ensures productivity continuity by preventing liquid refrigerant dropout during transient conditions while maintaining simple manual operation during stable 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 enhances the dynamic response of the refrigerant loop, reducing the risk of equipment damage and downtime by maintaining stable operating conditions, even during rapid feed gas flow rate changes, thereby improving the reliability and efficiency of the LNG plant.
Implementation Method 1
passing the mixed refrigerant through the main cryogenic heat exchanger to allow the mixed refrigerant to exchange heat with the feed gas stream in the main cryogenic heat exchanger and thereby cool the feed gas stream
Implementation Method 2
a refrigerant compressor unit comprising a suction side and a discharge side, wherein cycling comprises discharging a compressed mixed refrigerant stream from the discharge side
Data Source
AI summary
A method for operating a main cryogenic heat exchanger for use in a natural gas liquefaction process, involves monitoring or predicting variations in the flow rate of a feed gas stream provided to the main cryogenic heat exchanger. When a variation of the flow rate exceeding a predetermined threshold value is monitored or predicted, a control scheme is started to control one or more compressor recycle valves in response to the monitored or predicted variation of the flow rate to recycle part of a compressed mixed refrigerant stream in a refrigerant loop.