Two-Stage Partial Condensation for CO₂ Separation Without Freezing
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Solution Overview
Problem
Existing methods for separating carbon dioxide from gas mixtures at subambient temperatures face challenges, particularly in avoiding the risk of freezing and controlling two-phase flows in expansion valves, which leads to unpredictable fluid properties and potential valve deterioration.
Innovation Solution
A process involving two partial condensation stages with intermediate heat exchange to maintain a stable liquid temperature, using a first and second phase separator, and an indirect heat exchanger to ensure the liquid remains above the triple point temperature of carbon dioxide, preventing freezing and optimizing energy use.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the liquid is heated before the expansion valve to avoid freezing, then the risk of freezing is reduced, but partial vaporization occurs causing two-phase flow that disturbs valve control and accelerates valve deterioration
Solution Approach 1:
The invention changes the temperature parameter of the liquid entering the expansion valve by mixing it with warmer liquid from the first phase separator. This raises the liquid temperature above the triple point of CO2, preventing freezing during expansion while avoiding the need for external heating that would cause vaporization and two-phase flow
Solution Approach 2:
The invention uses an intermediary substance (the warmer liquid from the first phase separator) to transfer thermal energy to the cold liquid from the second phase separator. This indirect heat transfer through liquid mixing achieves temperature adjustment without introducing gas phase, thus maintaining single-phase liquid flow to the valve
2Temperature
If the liquid is heated before the expansion valve, then the temperature is raised to prevent freezing, but the measurement of physical parameters regulating valve opening becomes disturbed
Solution Approach 1:
The invention changes the temperature parameter through internal mixing rather than external heating. The liquid from the first phase separator (at higher temperature) mixes with the liquid from the second phase separator (at lower temperature), achieving the desired temperature elevation while maintaining homogeneous liquid phase that does not interfere with measurement accuracy
3Device complexity
If a single partial condensation stage is used, then the process is simpler, but the liquid temperature may drop below the triple point of CO2 causing freezing
Solution Approach 1:
The invention segments the condensation process into two distinct stages: a first partial condensation stage producing liquid at a higher temperature, and a second partial condensation stage producing liquid closer to the triple point. By separating the condensation into stages and mixing the liquids, the system achieves reliable freezing prevention while maintaining process efficiency
Solution Approach 2:
The invention merges the liquid streams from the two separate condensation stages before sending them to the expansion valve. This combination allows the warmer liquid from the first stage to heat the colder liquid from the second stage, ensuring the mixed liquid temperature remains above the CO2 triple point and preventing freezing during expansion
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 prevents freezing and maintains stable fluid properties at the expansion valve, reducing energy losses and improving control, resulting in a more efficient and reliable separation process.
Implementation Method 1
the gas will partially condense, the liquid being particularly enriched in carbon dioxide
Implementation Method 2
The expansion in a valve of the liquid at equilibrium coming from the pot will generate a partial vaporization which will cause a significant drop in the temperature at the outlet of the valve
Implementation Method 3
The expansion in a valve of the liquid at equilibrium coming from the pot will generate a partial vaporization which will cause a significant drop in the temperature at the outlet of the valve
Implementation Method 4
the carbon dioxide-enriched liquid coming from the column heats up, or even vaporizes at least partially, by heat exchange with the gas of the first phase separator
Data Source
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AI summary
An apparatus for separating a gaseous mixture containing at least 35 mol% carbon dioxyde, and at least one gas lighter than carbon dioxide comprising a first phase separator (15), a pipe for sending the first partially condensed flow from the exchange line to the first phase separator, a cooling means (23), a pipe for sending a gas from the first phase separator, containing less carbon dioxide than the gaseous mixture, to be cooled by the cooling means, so as to form a second partially condensed flow, a second phase separator (27), a pipe for sending the second partially condensed flow to a second phase separator, a first valve (21), a pipe for sending a liquid withdrawn from the first phase separator, containing more carbon dioxide than the gaseous mixture, to expand in the first valve to reduce the pressure by 300mbar at most and to form a first expanded liquid, and mixing means for mixing the first expanded liquid with a second liquid coming from the second phase separator upstream from a third valve.