Cryogenic Nitrogen Separation Using Ejector-Reflux Condensation
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Solution Overview
Problem
Existing cryogenic rectification plants face inefficiencies in nitrogen separation due to high compression requirements and mixing losses in thermosiphon heat exchangers, and prior methods for down-flow heat exchangers are costly and complex, especially for single-column nitrogen generators.
Innovation Solution
A cryogenic rectification plant using a down-flow heat exchanger with an ejector to recirculate oxygen-rich liquid as the motive fluid, eliminating the need for a separate pump and reducing complexity, while the ejector's venturi effect lowers pressure to condense nitrogen-rich vapor efficiently.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of energy
If a thermosiphon heat exchanger is used to condense nitrogen-rich vapor, then the heat exchange process can be sustained, but substantial mixing losses occur and higher compression requirements are needed
Solution Approach 1:
The invention extracts the oxygen-rich liquid stream from the thermosiphon circulation loop and routes it through a separate down-flow heat exchanger. This separation eliminates the mixing losses inherent in thermosiphon operation while maintaining the necessary heat exchange function. The oxygen-rich liquid is taken out, depressurized through an expansion valve, and used to condense nitrogen-rich vapor in a dedicated down-flow configuration.
Solution Approach 2:
The heat exchange process is segmented into distinct functional sections: the thermosiphon provides overall circulation, while a separate down-flow heat exchanger handles the specific task of condensing nitrogen-rich vapor using depressurized oxygen-rich liquid. This segmentation allows each component to operate optimally without the compromises required in a unified thermosiphon design.
2Use of energy by moving object
If a down-flow heat exchanger is used to condense nitrogen-rich vapor, then closer temperature approaches and reduced recirculation are achieved, but the system complexity increases
Solution Approach 1:
The down-flow heat exchanger is designed to serve multiple functions simultaneously: it condenses nitrogen-rich vapor to provide reflux for the distillation column, and it utilizes the depressurized oxygen-rich liquid stream that would otherwise require separate handling. This multi-functionality reduces overall system complexity despite the advanced heat exchanger configuration.
Solution Approach 2:
The system uses its own oxygen-rich liquid stream, after depressurization through the expansion valve, to provide the cooling duty for condensing nitrogen-rich vapor. This self-service approach eliminates the need for external cooling systems and reduces overall compression requirements by utilizing internal process streams efficiently.
3Reliability
If oxygen-rich liquid is recirculated through an ejector, then dry-out in the heat exchanger is prevented, but additional equipment is required
Solution Approach 1:
The ejector serves as an intermediary device that utilizes the pressure differential between high-pressure oxygen-rich liquid from the distillation column and the lower-pressure requirement of the down-flow heat exchanger. This intermediary mechanism enables recirculation without requiring additional pumps or complex control systems, preventing dry-out while adding minimal complexity.
Solution Approach 2:
The recirculation system employs pneumatic-hydraulic principles through the ejector, which uses the kinetic energy of the high-pressure oxygen-rich liquid stream to entrain and recirculate liquid through the down-flow heat exchanger. This approach prevents dry-out conditions while avoiding the need for mechanical pumping equipment.
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 configuration reduces compression requirements, minimizes mixing losses, and lowers fabrication costs by using the oxygen-rich liquid column bottoms as the motive fluid, enhancing the efficiency and simplicity of nitrogen separation in a single-column nitrogen generator.
Implementation Method 1
the ejector's venturi effect lowers pressure to condense nitrogen-rich vapor efficiently
Implementation Method 2
condensing a portion of the nitrogen-rich vapor within a down-flow heat exchanger associated with the distillation column through indirect heat exchange with a combined oxygen-rich liquid stream
Implementation Method 3
thereby partially vaporizing the combined oxygen-rich liquid into an oxygen-rich liquid phase and an oxygen-rich vapor phase
Implementation Method 4
The compressed and purified feed is cooled to a temperature suitable for rectification within the distillation column by way of a main heat exchanger
Implementation Method 5
the expansion of part of the incoming feed or product nitrogen streams can be used for such purposes of refrigeration
Data Source
AI summary
Method and apparatus of separating a nitrogen from a compressed and purified feed stream in a cryogenic rectification plant that employs a distillation column to produce a nitrogen-rich vapor as a column overhead and an oxygen-rich liquid column bottoms. Reflux is generated for the column by condensing part of the nitrogen-rich vapor within a down-flow heat exchanger. A stream of the oxygen-rich liquid column bottoms is introduced into an ejector which draws a stream of an oxygen-rich liquid phase produced from the outlet of a down-flow heat exchanger. The combined oxygen-rich liquid exiting the ejector is fed to the down-flow heat exchanger to condense the nitrogen-rich vapor. In such manner, part of the oxygen-rich liquid phase is recirculated to prevent dry-out of the down-flow heat exchanger outlet and to maintain effective condensation of the nitrogen-rich vapor.