CO2 Purification Column Pressure Split for Self-Refrigeration
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Solution Overview
Problem
Existing carbon dioxide purification methods are thermally inefficient, leading to increased compression and refrigeration energy consumption, and often result in carbon dioxide products with significant impurities due to high reboiling temperatures and reliance on external refrigeration.
Innovation Solution
A self-refrigerated carbon dioxide purification apparatus that operates at a lower pressure, utilizing a main heat exchanger and reboiler to cool and liquefy the feed stream, and includes a stripping column with contacting elements to separate impurities, achieving efficient heat transfer and high purity carbon dioxide recovery without external refrigeration.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Use of energy by moving object
If the feed stream is introduced into the stripping column at feed stream pressure, then the stripping column operates at high pressure, but insufficient heat transfer occurs from the feed stream to the reboiler
Solution Approach 1:
The system segments the pressure operation into two distinct zones: the stripping column operates at reduced pressure (below feed stream pressure) to enable sufficient heat transfer from the feed stream to the reboiler, while the product carbon dioxide is recovered at super atmospheric pressure through the compression section, resolving the contradiction between heat transfer efficiency and operating pressure
Solution Approach 2:
The patent changes the pressure parameter of the stripping column operation from high pressure (feed stream pressure) to reduced pressure (below feed stream pressure), which fundamentally alters the heat transfer dynamics and enables the feed stream to provide sufficient heat to the reboiler while maintaining efficient stripping operation
2Temperature
If external refrigeration is used to cool the feed stream, then the feed stream can be cooled effectively, but energy consumption increases
Solution Approach 1:
The system employs self-refrigeration where the feed stream itself serves as the refrigerant. The feed stream is cooled in the main heat exchanger by heat exchange with the outgoing product stream and flash vaporization, eliminating the need for external refrigeration systems and significantly reducing energy consumption while achieving effective cooling
Solution Approach 2:
The patent converts the typically harmful effect of flash vaporization (which wastes energy) into a beneficial refrigeration effect. The flash vaporization of a portion of the feed stream provides cooling to the remaining liquid feed stream, transforming an energy loss into a useful refrigeration source that cools the feed stream without external refrigeration
3Productivity
If high reboiling temperatures are used in the stripping column, then stripping efficiency improves, but carbon dioxide product contains significant impurities
Solution Approach 1:
The patent changes the temperature parameter by operating the stripping column at reduced pressure, which lowers the reboiling temperature of carbon dioxide. This temperature reduction prevents thermal degradation and contamination that occur at high temperatures, while the reduced pressure maintains effective stripping efficiency through enhanced volatility differences between carbon dioxide and impurities
Solution Approach 2:
The patent introduces a fractionation section with fractionation trays as an intermediary between the stripping section and the product withdrawal point. This fractionation section acts as a mediator that separates and removes impurities from the carbon dioxide product stream, ensuring high purity product while maintaining effective stripping in the stripping section
4Ease of operation
If compression is applied to carbon dioxide stream with impurities for pipeline introduction, then the carbon dioxide can be transported, but electrical power costs increase due to added impurity volume
Solution Approach 1:
The system performs preliminary purification action by removing impurities from the carbon dioxide stream before compression and pipeline introduction. The stripping column and fractionation section eliminate impurities in advance, so that subsequent compression operates only on pure carbon dioxide, minimizing the volume and energy required for compression and pipeline transport
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 apparatus achieves high purity carbon dioxide recovery at reduced energy costs by lowering reboiling temperatures, minimizing compression energy, and eliminating external refrigeration, while enhancing carbon dioxide liquefaction and recovery efficiency.
Implementation Method 1
a main heat exchanger and reboiler to cool and liquefy the feed stream
Implementation Method 2
cool and liquefy the feed stream
Implementation Method 3
reboiler to initiate the formation of an ascending vapor phase within the stripping column
Implementation Method 4
contacting elements to contact a descending liquid phase with an ascending vapor phase within the stripping column to strip impurities from the descending liquid phase
Implementation Method 5
feed stream is expanded to an operational pressure of the stripping column that is less than that of the feed stream
Data Source
AI summary
An Apparatus for purifying a feed stream containing carbon dioxide in which the feed stream, after having been compressed and dried, is partly cooled and then used to reboil a stripping column. Thereafter, the feed stream is further cooled and expanded to a lower operational temperature of the stripping column. A carbon dioxide product stream composed of the liquid column bottoms of the stripping column is expanded at one or more pressures to generate refrigeration, then fully vaporized within the main heat exchanger and compressed by a compressor to produce a compressed carbon dioxide product. Refrigeration is recovered in the main heat exchanger from a column overhead stream extracted from the stripping column within the main heat exchanger either directly or indirectly by auxiliary processing in which carbon dioxide is further separated and optionally recycled back to the main compressor used in compressing the feed stream.