Control system for vessel reliquefaction system
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Solution Overview
Problem
Existing reliquefaction systems for boil-off gas in LNG storage tanks on ships lack effective load adjustment mechanisms, leading to inefficiencies and potential destabilization due to changes in boil-off gas generation and composition.
Innovation Solution
A control system for the reliquefaction system that includes a load controller, flow rate regulator, and temperature regulator, operating in a master-slave mode, to adjust the flow rate and refrigerant mass flow rate, ensuring rapid and accurate load balancing through a combination of flow rate and temperature control.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a conventional reliquefaction system operates without a load adjustment mechanism, then the system structure remains simple, but the system cannot respond effectively to load changes, leading to potential destabilization and emergency shutdowns
Solution Approach 1:
The patent implements dynamic load adjustment by making the control valve opening degree variable based on real-time boil-off gas flow rate changes. The load adjustment mechanism dynamically modifies the control valve opening degree in response to load variations, enabling the system to adapt to changing conditions and maintain stable operation without requiring an overly complex control architecture.
Solution Approach 2:
The patent employs a feedback control mechanism where the actual boil-off gas flow rate is continuously measured and compared with the target flow rate. Based on this comparison, the control system automatically adjusts the control valve opening degree to minimize the deviation between actual and target flow rates, thereby maintaining system stability through closed-loop feedback control.
2Manufacturing precision
If the control valve opening degree is fixed, then the control system is simple, but the system cannot adapt to load changes, resulting in poor control accuracy and potential system destabilization
Solution Approach 1:
The patent transforms the static control valve opening degree into a dynamic parameter that automatically adjusts with load changes. The control valve opening degree is modified in real-time based on the ratio of actual to target boil-off gas flow rates, enabling the system to maintain high control accuracy across varying load conditions without requiring multiple fixed control settings.
Solution Approach 2:
The patent changes the control parameter from a fixed valve opening degree to a variable one that depends on the load condition. By introducing a load-dependent adjustment factor that modifies the control valve opening degree based on the ratio of actual to target flow rates, the system achieves adaptive control accuracy across different operating conditions.
3Speed
If the system responds slowly to load changes, then the control mechanism is simple, but the system cannot rapidly adjust to load variations, leading to inefficiency and potential emergency situations
Solution Approach 1:
The patent prepares the system for rapid response by pre-establishing the control valve opening degree adjustment strategy based on expected load changes. The control system is designed to immediately calculate and implement the required valve opening adjustment when load changes are detected, eliminating delays associated with complex multi-stage control sequences or manual interventions.
Solution Approach 2:
The patent replaces complex mechanical control mechanisms with a more responsive control approach that uses real-time flow rate measurements and automated valve positioning. By substituting manual or mechanically-delayed control with an automated system that directly links flow rate sensing to valve actuation, the system achieves faster response times to load variations.
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
Enhances reliquefaction efficiency by 35% responsiveness and control accuracy, stabilizing the process and preventing emergency shutdowns by adapting to load changes effectively.
Implementation Method 1
the compressed gas is cooled and reliquefied through a heat exchanger
Implementation Method 2
cooled and reliquefied through a heat exchanger
Implementation Method 3
a refrigerant that undergoes phase change to supply cold heat
Implementation Method 4
boil-off gas generated from liquefied gas in an onboard storage tank is compressed in a compressor
Implementation Method 5
cool compressed boil-off gas through heat exchange with uncompressed boil-off gas and reliquefy the cooled boil-off gas by adiabatic expansion
Data Source
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AI summary
Disclosed herein is a control system for a reliquefaction system for ships, in which boil-off gas generated from liquefied gas in an onboard storage tank is compressed by a compressor and the compressed boil-off gas is cooled and reliquefied through a heat exchanger. The control system includes: a reliquefaction line connecting the compressor to the storage tank; a control valve disposed downstream of the heat exchanger on the reliquefaction line to adjust a flow rate of boil-off gas flowing through the reliquefaction line; a flow rate regulator configured to control a degree of opening of the control valve; and a load controller configured to send a signal for adjusting a load of the reliquefaction system to the flow rate regulator, wherein, in the event of changes in load of the reliquefaction system, the load controller sends a predetermined set point indicative of a boil-off gas flow rate at a corresponding load to the flow rate regulator to adjust the load of the reliquefaction system.