Wet Hydrocarbon Stream Cooling to Prevent Heat Exchanger Pinching
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Solution Overview
Problem
Existing methods for liquefying natural gas, such as those described in GB 1,572,900, face issues with high temperature differences between refrigerant streams and dried natural gas, leading to thermal stresses and internal pinching in heat exchangers, which can result in unstable cooling processes and damage.
Innovation Solution
A method and apparatus that involves passing a wet hydrocarbon stream through a wet feed ambient heat exchanger to cool it, followed by a water removal device, and then using a refrigerant stream in a compressed condition to indirectly heat exchange with the effluent stream in a further heat exchanger, maintaining temperatures within a narrow range to minimize temperature differences and prevent thermal stresses.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Quantity of substance
If a conventional drier is used to remove water from natural gas, then water removal is achieved, but a high temperature difference is created between the dried gas and refrigerant stream entering the heat exchanger
Solution Approach 1:
The water removal process is segmented into two distinct stages: first, a conventional drier removes the bulk of water content; second, a heat exchanger recovers heat from the cold refrigerant stream to pre-cool the dried gas. This segmentation allows each stage to optimize its function while managing temperature differences.
Solution Approach 2:
A heat exchanger is introduced as an intermediary device between the conventional drier and the refrigerant stream. This intermediary recovers heat from the cold refrigerant stream to pre-cool the dried gas, thereby reducing the temperature difference that would otherwise cause thermal stresses in the heat exchanger.
2Productivity
If a high temperature difference exists between streams in the heat exchanger, then cooling efficiency may be improved, but thermal stresses and internal pinching occur causing unstable behavior and damage
Solution Approach 1:
The system performs preliminary cooling of the dried gas stream using heat recovered from the refrigerant stream before the gas enters the main heat exchanger. This preliminary action reduces the temperature difference at the heat exchanger inlet, preventing thermal stresses while maintaining overall cooling efficiency.
Solution Approach 2:
The system uses the cold refrigerant stream as a feedback mechanism to pre-cool the dried gas. The heat exchanger captures heat from the refrigerant stream and transfers it to the gas stream, creating a self-regulating system that maintains appropriate temperature differences without causing thermal shock.
3Device complexity
If the natural gas is cooled directly without pre-cooling, then the cooling process is simpler, but thermal stresses damage the heat exchanger
Solution Approach 1:
The system merges the water removal function and the pre-cooling function into an integrated process. The heat exchanger serves dual purposes: it recovers heat from the refrigerant stream and uses this heat to pre-cool the dried gas, combining multiple functions in a single device.
Solution Approach 2:
The system utilizes phase transition heat transfer in the heat exchanger, where the refrigerant stream undergoes phase change to transfer heat efficiently to the gas stream. This enables effective pre-cooling without requiring complex mechanical systems.
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 stabilizes the cooling process, reduces the risk of thermal stress and internal pinching in heat exchangers, and ensures efficient cooling of the hydrocarbon stream while maintaining the integrity of the equipment.
Implementation Method 1
passing said wet hydrocarbon stream through a wet feed ambient heat exchanger thereby heat exchanging said wet hydrocarbon stream against ambient
Implementation Method 2
passing a refrigerant stream in a compressed condition through an ambient heat exchanger thereby providing a source refrigerant stream at a refrigerant temperature equal to a third temperature
Implementation Method 3
cooling both the effluent stream and the at least the part of the refrigerant stream in the further heat exchanger by indirect heat exchanging against an evaporating refrigerant fraction
Implementation Method 4
cooling both the effluent stream and the at least the part of the refrigerant stream in the further heat exchanger by indirect heat exchanging against an evaporating refrigerant fraction
Data Source
AI summary
A wet hydrocarbon stream having at least methane and water, provided at a temperature equal to a first temperature, is cooled thereby lowering the temperature to a second temperature. In a water removal device a wet disposal stream having water is withdrawn from the wet hydrocarbon stream, at the second temperature. An effluent stream having the wet hydrocarbon stream from which the wet disposal stream has been removed, is discharged from the water removal device and passed to a further heat exchanger. A refrigerant stream is also passed to the further heat exchanger, and both the effluent stream and the refrigerant stream are cooled in the further heat exchanger by indirect heat exchanging against an evaporating refrigerant fraction. The effluent stream is heated by indirectly heat exchanging against the wet hydrocarbon stream. The cooling of the wet hydrocarbon stream includes this indirectly heat exchanging.