Method and system for controlling refrigerant composition in case of gas tube leaks in a heat exchanger
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Solution Overview
Problem
Conventional leak management strategies in LNG facilities result in significant collateral loss of refrigerant components like ethane and nitrogen due to continuous bleeding and make-up, leading to increased downtime, reduced production, and higher costs, especially when ethane supply is limited.
Innovation Solution
A heat exchanger system and method that reduces refrigerant make-up requirements by using a refrigerant bleed vessel with selective methane bleed streams, allowing for precise control of refrigerant composition and minimizing ethane and nitrogen demand, featuring a skid-mounted kit for efficient operation across multiple LNG trains.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Stability of the object's composition
If conventional leak management strategies are used to maintain refrigerant composition by continuous bleeding and make-up, then the predetermined temperature profile across the MCHE is maintained, but significant collateral loss of refrigerant components (ethane and nitrogen) occurs
Solution Approach 1:
The patent changes the operating parameters of the bleed system by introducing a controlled heating phase followed by a cooling phase. During the heating phase, the bleed stream is heated to a temperature where methane is preferentially vaporized and removed. During the cooling phase, the bleed stream is cooled to condense heavier refrigerant components. This parameter change enables selective methane removal while minimizing loss of ethane and nitrogen.
Solution Approach 2:
The patent utilizes phase transitions (vaporization and condensation) to achieve selective separation of refrigerant components. By heating the bleed stream, methane transitions to vapor phase and is removed. By subsequently cooling the stream, heavier components transition to liquid phase and are retained. This phase transition mechanism enables the system to maintain refrigerant composition stability while minimizing collateral loss of valuable refrigerant components.
2Stability of the object's composition
If continuous bleed and make-up of refrigerant is performed to compensate for leaks, then the refrigerant composition is maintained, but refrigerant make-up requirements increase significantly
Solution Approach 1:
The patent implements periodic parameter changes in the bleed system operation, alternating between heating and cooling phases. This enables the system to selectively remove methane during the heating phase while retaining valuable refrigerant components during the cooling phase. As a result, the quantity of refrigerant make-up required is significantly reduced compared to conventional continuous bleed strategies, as the system minimizes collateral loss of ethane and nitrogen.
3Stability of the object's composition
If the MCHE is shut down for maintenance to repair gas tube leaks, then the refrigerant composition can be restored, but production downtime increases
Solution Approach 1:
The patent implements a self-service mechanism where the bleed system automatically performs composition control by selectively removing leaked methane during normal operation. The controlled heating and cooling cycles enable the system to self-regulate the refrigerant composition without requiring external intervention or shutdown. This extends the operational life of the MCHE between maintenance periods, reducing production downtime while maintaining stable refrigerant composition.
4Loss of substance
If selective methane bleed is implemented to reduce refrigerant make-up requirements, then ethane and nitrogen loss is minimized, but the system complexity increases
Solution Approach 1:
The patent segments the bleed stream processing into distinct functional phases: a heating phase for methane vaporization and a cooling phase for heavier component condensation. By dividing the continuous bleed process into these discrete temporal segments, the system achieves selective separation without requiring complex continuous separation equipment. This segmentation approach minimizes device complexity while effectively reducing refrigerant component loss.
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
The system achieves a significant reduction in refrigerant make-up needs, up to a factor of 2 or 3, with methane selectivity exceeding 80%, minimizing downtime and production losses, and enabling longer operation between scheduled maintenance periods.
Implementation Method 1
The mixed refrigerant bleed stream is heated in a vaporizer to a temperature of above the dew point of the mixed refrigerant bleed stream, thereby obtaining a vaporized mixed refrigerant bleed stream
Implementation Method 2
The vaporized mixed refrigerant bleed stream is cooled in a condenser to a temperature of below the bubble point of the mixed refrigerant bleed stream, thereby obtaining a partially condensed mixed refrigerant bleed stream
Implementation Method 3
The section for liquefaction typically includes one or more heat exchangers to cool the (natural) gas by heat exchange with a refrigerant
Implementation Method 4
at least one expansion device arranged to receive at least part of the cooled mixed refrigerant stream and discharge a further cooled mixed refrigerant stream
Data Source
AI summary
A heat exchanger unit that comprises a heat exchanger vessel comprising a plurality of process stream conduits to receive the gaseous process stream and discharge a cooled process stream, and a plurality of refrigerant conduits to receive a pre-cooled mixed refrigerant stream and discharge a cooled mixed refrigerant stream; an expansion device to receive the cooled mixed refrigerant stream and discharge a further cooled mixed refrigerant stream, which is connected to a third and/or fourth refrigerant inlets to provide cooling to the process stream conduits and the refrigerant conduits; a refrigerant bleed vessel to receive a first refrigerant split-off stream from the cooled mixed refrigerant stream and a second refrigerant split-off stream from the pre-cooled mixed refrigerant stream; the refrigerant bleed vessel comprising a bleed outlet to discharge a bleed stream and a recycle outlet fluidly connected to the third and/or fourth refrigerant inlets.