Once-Through Main Condenser for Pump-Free Cryogenic Air Separation
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Solution Overview
Problem
Cryogenic air separation systems with downflow main condensers require recirculation pumps to ensure adequate wettability, which increase costs, reduce reliability, and incur efficiency penalties due to power consumption.
Innovation Solution
A cryogenic air separation method using a double column system with a once-through main condenser, where nitrogen vapor from the higher pressure column and oxygen liquid from the lower pressure column are passed in a heat exchange relation, achieving a liquid to vapor mass flowrate ratio of 0.05 to 0.5, eliminating the need for recirculation pumps by utilizing enhanced boiling surfaces.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Temperature
If recirculation pumps are used to ensure adequate wettability of boiling passages, then heat transfer performance is improved, but system cost increases, reliability decreases, and efficiency is reduced due to power consumption
Solution Approach 1:
The system uses the nitrogen vapor flow itself to provide the wetting function that previously required external recirculation pumps. The nitrogen vapor condenses on the boiling passages, providing continuous liquid coverage without requiring separate pumping systems, thereby eliminating the reliability issues and power consumption associated with recirculation pumps while maintaining adequate heat transfer performance
Solution Approach 2:
Nitrogen vapor acts as an intermediary substance that transfers the wetting function from the oxygen liquid recirculation system to the boiling passages. Instead of directly recirculating oxygen liquid through pumps, the nitrogen vapor serves as a mediator that condenses and provides the necessary liquid coverage, eliminating the need for mechanical pumping while maintaining heat transfer effectiveness
2Reliability
If recirculation pumps are used to prevent oxygen boiling to dryness, then safety criteria are satisfied, but device complexity and cost increase
Solution Approach 1:
The nitrogen vapor condensation process self-regulates to prevent oxygen boiling to dryness. As nitrogen vapor condenses on the boiling passages, it automatically maintains liquid coverage without requiring external control systems or recirculation pumps, thereby satisfying safety criteria while reducing device complexity
Solution Approach 2:
The mechanical recirculation pump system is replaced with a thermal process where nitrogen vapor condensation provides the necessary liquid coverage. This substitution eliminates mechanical moving parts and complex control systems while maintaining the safety function of preventing oxygen boiling to dryness
3Temperature
If recirculation pumps are used to ensure adequate wettability during part-load operation, then heat transfer performance is maintained, but power consumption increases
Solution Approach 1:
The system uses the inherent thermal energy of the nitrogen vapor to provide wetting during part-load operation without requiring external power input. The condensation of nitrogen vapor naturally occurs based on the temperature differential, providing continuous heat transfer performance improvement without the power consumption penalty of recirculation pumps
Solution Approach 2:
The system changes the operational parameters by using nitrogen vapor temperature and condensation rate as the controlling mechanism for wetting, replacing the constant power input required by recirculation pumps. This allows the heat transfer performance to adapt to part-load conditions without incurring proportional power consumption increases
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 reduces the need for recirculation pumps, enhancing heat transfer performance, minimizing surface area, and improving wettability characteristics, while maintaining safety and efficiency by ensuring adequate wetting of boiling surfaces.
Implementation Method 1
passing the nitrogen vapor and the oxygen liquid down the once-through main condenser in heat exchange relation wherein at least some but not all of the downflowing oxygen liquid is vaporized
Implementation Method 2
at least some but not all of the downflowing oxygen liquid is vaporized
Data Source
AI summary
A cryogenic air separation system wherein nitrogen vapor from a higher pressure column and oxygen liquid from a lower pressure column each pass down through a once-through main condenser in heat exchange relation and some but not all of the oxygen liquid is vaporized such that the oxygen liquid and vapor exit the condenser in a liquid to vapor mass flowrate ratio within the range of from 0.05 to 0.5 whereby the need for a recirculation pump to ensure avoidance of oxygen boiling to dryness is eliminated.