Boil-Off Gas Condensing Assembly for Stable LNG Pressure Control
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Solution Overview
Problem
Existing LNG systems face inefficiencies and environmental issues due to the venting or flaring of boil-off gas, which can be addressed by condensing it into a send-out stream, but they struggle with pressure fluctuations in the condenser, leading to operational challenges and inefficiencies in the booster pump system.
Innovation Solution
A boil-off gas condensing assembly that actively controls the flow of condensing liquid based on the liquid level in the condenser, using a level control valve and differential pressure transmitters to maintain optimal pressure without venting or adding make-up gas, ensuring continuous operation and efficient condensation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If the flow of condensing liquid is increased to maintain condenser pressure, then condensation efficiency is improved, but system complexity and control difficulty increase
Solution Approach 1:
The patent implements a feedback control system where a differential pressure transmitter continuously monitors the pressure difference across the condenser and automatically adjusts the condensing liquid flow rate. This closed-loop feedback mechanism maintains optimal condensation efficiency while eliminating the need for complex manual control systems and multiple valves, thereby resolving the contradiction between productivity and device complexity.
2Reliability
If pressure control valves are added to maintain constant condenser pressure, then operational stability is improved, but device complexity increases
Solution Approach 1:
The patent extracts and eliminates unnecessary pressure control valves and complex control systems from the conventional BOG condensing arrangement. By using the existing differential pressure between suction and discharge lines of the send-out pump, the system achieves pressure control without adding complex valve assemblies, thereby improving operational stability while reducing device complexity.
Solution Approach 2:
The system utilizes the inherent differential pressure generated by the send-out pump's operation to automatically control condenser pressure. This self-service mechanism eliminates the need for external pressure control valves and complex control systems, as the system automatically maintains optimal pressure conditions through its own operational characteristics.
3Ease of operation
If BOG is vented to atmosphere or flared to maintain pressure balance, then pressure control is simplified, but environmental harm and substance loss increase
Solution Approach 1:
The patent converts the previously harmful BOG venting or flaring operation into a beneficial condensation process. By using the cold send-out liquid to condense BOG and return it to the liquid stream, the system eliminates environmental pollution and substance loss while maintaining pressure balance, thereby converting a harmful operation into a beneficial one without sacrificing operational simplicity.
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 solution allows for efficient condensation of boil-off gas into a liquid send-out stream, reducing pressure fluctuations and maintaining system stability, thereby enhancing the reliability and efficiency of the LNG pumping and vaporization process while eliminating the need for venting or adding make-up gas.
Implementation Method 1
the cold LNG send-out is used to condense BOG at an inter-stage pressure
Implementation Method 2
Condensing the BOG into a liquid send-out stream is more efficient
Data Source
AI summary
The assembly includes a boil-off gas line that carries storage tank boil-off gas to a condenser that uses condensing liquid from the liquid send-out line to condense the gas. A level control valve on the condensing liquid line actively controls the flow of condensing liquid based on the liquid level in the condenser. A check valve prevents liquid from the send-out line from flowing into the condenser through the condensate line that discharges condensate from the condenser to the send-out line.