Air separation unit and method for production of nitrogen and argon using a distillation column system with an intermediate pressure kettle column
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Solution Overview
Problem
Conventional three-column air separation units face challenges in producing high purity nitrogen and argon with high power consumption and limited product flexibility, as they struggle with efficient separation due to tight approaches between operating and equilibrium lines, particularly in the lower pressure column, leading to poor oxygen recovery and increased energy use.
Innovation Solution
A four-column arrangement is introduced, comprising a higher pressure column, a lower pressure column, an intermediate pressure kettle column, and an argon column, which includes a once-through kettle column reboiler and condenser, and an integrated argon condenser within the lower pressure column, allowing for additional nitrogen reflux and improved argon recovery by leveraging excess distillation driving forces and optimizing reflux generation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If a conventional three-column arrangement is used for normal purity oxygen and argon production, then oxygen and argon products can be obtained, but the lower pressure column separation is challenged with virtual pinch near the top and tight approach between equilibrium line and operating line, leading to poor oxygen recovery and high power consumption
Solution Approach 1:
The patent divides the distillation system into four separate columns: a high pressure column, a low pressure column, an intermediate pressure kettle column, and an argon column. This segmentation allows each column to operate at optimized pressure levels and perform specific separation functions, eliminating the virtual pinch point problem that occurs in conventional three-column arrangements. The intermediate pressure kettle column specifically addresses the separation challenge in the lower pressure column by providing an additional separation stage at intermediate pressure.
Solution Approach 2:
The patent introduces a new dimension to the distillation system by adding pressure as a variable dimension. Instead of operating all columns at the same pressure, the system uses four different pressure levels (high, intermediate, low, and argon column pressure). This dimensional change allows the system to exploit pressure-dependent volatility differences and create favorable operating conditions that improve separation efficiency while reducing the tight approach between operating and equilibrium lines.
2Manufacturing precision
If a conventional three-column arrangement is used, then oxygen product is produced, but the tight approach between equilibrium line and operating line in the bottom section of the lower pressure column results in poor oxygen recovery
Solution Approach 1:
The patent segments the distillation process into four independent columns, each optimized for specific separation tasks. The low pressure column handles the main oxygen production, while the intermediate pressure kettle column and high pressure column provide additional separation stages that enhance oxygen recovery. This segmentation allows the system to achieve high oxygen recovery without compromising production efficiency, as each column operates independently at its optimal pressure and flow conditions.
Solution Approach 2:
The intermediate pressure kettle column acts as an intermediary between the high pressure and low pressure columns. It receives feed from the high pressure column and provides refined product to the low pressure column, serving as a mediator that enhances the overall separation efficiency. This intermediary column improves oxygen recovery by providing an additional separation stage that operates at intermediate pressure, bridging the gap between high and low pressure operations.
3Quantity of substance
If a conventional three-column arrangement is used with elevated pressure nitrogen product, then nitrogen product is obtained, but the flow rate of elevated pressure nitrogen product being about the same as oxygen product flow rate challenges the lower pressure column separation
Solution Approach 1:
The patent segments the nitrogen production function across multiple columns: the high pressure column produces elevated pressure nitrogen, the intermediate pressure kettle column provides additional nitrogen reflux, and the low pressure column produces low pressure nitrogen. This segmentation allows the system to meet high nitrogen product flow rate requirements without compromising separation quality, as the burden on any single column is reduced.
Solution Approach 2:
The intermediate pressure kettle column serves multiple functions: it produces nitrogen reflux for the low pressure column, generates elevated pressure nitrogen product, and provides thermal coupling between pressure levels. This multi-functionality allows the system to handle high nitrogen product flow rates while maintaining separation quality, as the kettle column's diverse roles distribute the separation workload across different pressure levels.
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 enhances oxygen and argon recovery, reduces power consumption, and provides higher purity nitrogen product streams by generating additional nitrogen reflux and supplemental elevated pressure nitrogen products, addressing the limitations of conventional three-column systems.
Implementation Method 1
a main condenser-reboiler disposed in the lower pressure column and configured for thermally coupling the higher pressure column and the lower pressure column by liquefying at least a portion of the nitrogen-rich overhead from the higher pressure column against oxygen liquid bottoms in the lower pressure column
Implementation Method 2
liquefying at least a portion of the nitrogen-rich overhead from the higher pressure column against oxygen liquid bottoms in the lower pressure column to yield the first reflux stream and the second reflux stream
Implementation Method 3
a once-through kettle column reboiler and a once through kettle column condenser. The kettle column reboiler is configured to boil a portion of the descending liquid in the kettle column against a first part of the argon-oxygen side stream to yield an ascending vapor stream in the kettle column
Implementation Method 4
The once through kettle column condenser configured to condense all or a portion of the nitrogen rich overhead of the kettle column against a portion of the oxygen-rich bottoms of the kettle column
Implementation Method 5
The argon condenser is configured to condense the argon overhead against a portion of the oxygen liquid bottoms from the lower pressure column
Data Source
AI summary
An air separation unit and associated method for separating air by cryogenic distillation using a distillation column system including a higher pressure column, a lower pressure column, an intermediate pressure kettle column, and an argon column arrangement is provided. The disclosed air separation unit and method is particularly suited for production of an argon product as well as several nitrogen products wherein a portion of the nitrogen overhead intermediate pressure kettle column is taken as an intermediate or elevated pressure nitrogen product. The present air separation unit and associated method employs a once-through kettle column reboiler, a once-through kettle column condenser while the argon condenser condenses an argon-rich vapor stream against a pumped oxygen stream from the bottom of the lower pressure column.