Cryogenic Exchange Line Cooling With Parallel Start-Up Expansion
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Solution Overview
Problem
The existing methods for cryogenic separation and liquefaction using free expansion for cooling are inefficient, resulting in low cooling power and prolonged cooling times, which can lead to thermal shocks and mechanical issues in cryogenic gas separation units.
Innovation Solution
The introduction of a large-capacity cooling expansion valve, which operates during start-ups and can bypass the standard expansion valves, allowing a higher gas flow to be expanded and introduced into the liquid fraction passages, thereby increasing cooling capacity and reducing thermal stresses.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If free expansion is used for cooling during start-up, then the cooling process can be initiated without external equipment, but the cooling power is insufficient and cooling time is excessively long
Solution Approach 1:
The patent introduces a preliminary cooling phase using a dedicated cooling expansion valve before normal operation begins. This preliminary action allows the exchange line to be pre-cooled to a temperature close to the final operating temperature, so that when normal operation starts, the cooling demand is already satisfied and the system can reach operational temperature much faster.
Solution Approach 2:
The cooling function is segmented into two distinct phases: a start-up cooling phase using a dedicated cooling expansion valve, and a normal operation phase using the standard expansion valve. This segmentation allows each valve to be optimized for its specific function, with the cooling expansion valve having a larger capacity specifically for the high cooling demand during start-up.
2Reliability
If standard expansion valves are used during start-up, then the system operates normally, but thermal shocks occur due to insufficient cooling capacity
Solution Approach 1:
The cooling expansion valve acts as an intermediary component specifically for the start-up phase. It mediates the high cooling demand during start-up by providing a dedicated high-capacity cooling path, preventing thermal shocks to the exchange line and separation equipment before they are fully cooled and ready for normal operation.
Solution Approach 2:
The system dynamically switches between two expansion valve configurations: during start-up, the cooling expansion valve is opened to provide high cooling capacity; during normal operation, the standard expansion valve is used with the cooling valve closed. This dynamic adaptation allows the system to optimize cooling capacity according to operational phase without permanently increasing complexity.
3Productivity
If cooling time is reduced by increasing cooling power, then operational efficiency improves, but thermal stresses may damage the exchange line
Solution Approach 1:
The preliminary cooling phase using the cooling expansion valve gradually reduces the temperature of the exchange line and separation equipment before normal operation begins. This gradual pre-cooling prevents sudden thermal shocks by allowing the equipment to adapt to lower temperatures progressively, thereby reducing thermal stresses while still achieving fast overall cooling.
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 significantly reduces cooling time, allows for faster temperature attainment, and mitigates thermal shocks by rebalancing the exchange line with high flows, enhancing the operational efficiency and reliability of cryogenic separation units.
Implementation Method 1
The liquid fraction 3 is expanded via the expansion valve 50 to low pressure and revaporized in the exchange line via the exchange passages 13
Implementation Method 2
The mixture 1 to be separated is introduced at room temperature and under a pressure of 40 bar absolute into the plate heat exchanger 10 to be cooled there via the exchange passages 11
Implementation Method 3
the fluid 1, then two-phase, is extracted from the exchanger and separated into its vapor fraction 2 and its liquid fraction 3 in the liquid-gas separator 30
Data Source
Figure 1
Figure 2
AI summary
The invention relates to a method for the cryogenic separation, the cooling or the liquefaction of a fluid using an exchange line, that comprises extracting from said exchange line at least one dual phase fluid (11), separating said dual phase fluid into at least one vapour fraction (4) and one liquid fraction (5) in a phase separator (40), expanding at least one portion of the liquid fraction (5) using a first expansion means (60, 90), reinjecting, reheating and at least partially vaporising said expanded liquid fraction in the exchange line, the first expansion means being a valve, wherein during the cooling of said exchange line, at least a fraction of the fluid extracted from the exchange line (2, 4 or 5) and/or from the phase separator (40) is expanded in second expansion means (61, 71, 81, 91) parallel to the first expansion means (6), while during a normal operation, the second expansion means is essentially closed.