System and method for high recovery of nitrogen and argon from a moderate pressure cryogenic air separation unit
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Solution Overview
Problem
Moderate pressure cryogenic air separation units face challenges in achieving high recovery of argon and nitrogen, with existing methods limiting argon recovery and increasing energy consumption due to elevated pressures.
Innovation Solution
The system employs a multi-bed temperature swing adsorption unit for air purification, a turboexpander for refrigeration, and a distillation column system with specific pressure ranges to enhance argon and nitrogen recovery, utilizing high purity oxygen for condensation and regeneration, and an argon superstaged column for efficient separation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Quantity of substance
If high purity liquid oxygen is used as refrigerant in the argon condenser, then argon recovery is improved, but the argon column and other columns must operate at higher pressures
Solution Approach 1:
The system changes the temperature parameter of the liquid oxygen stream by subcooling it from its normal boiling point to a lower temperature (below -183°C) before using it as refrigerant in the argon condenser. This parameter change increases the temperature difference available for heat exchange, enabling effective argon condensation at lower column pressures (1.5-2.8 bar) rather than requiring higher pressures.
2Use of energy by moving object
If a turboexpander is used to provide refrigeration, then energy consumption is reduced, but the system complexity increases
Solution Approach 1:
The turboexpander is integrated into the process flow to produce refrigeration from the expansion of process gases themselves. The expansion of nitrogen-rich or air streams through the turboexpander generates the cold energy needed for the system, making the refrigeration self-sufficient and reducing external energy consumption without requiring separate refrigeration systems.
3Quantity of substance
If the argon column operates at conventional low pressure, then argon recovery is limited, but operating at elevated pressure increases energy consumption
Solution Approach 1:
The low pressure column acts as an intermediary between the high pressure nitrogen column and the argon column. It receives nitrogen-rich stream from the high pressure column, separates additional nitrogen, and provides an oxygen-enriched bottoms stream to the argon column. This intermediary function enables the argon column to operate at low pressure (1.5-2.8 bar) while still achieving high argon recovery through proper feed composition control.
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 achieves nitrogen recovery of 98% or greater and improves argon recovery, reducing energy costs and operational complexity while maintaining high product purity.
Implementation Method 1
an adsorption based pre-purifier unit configured for removing water vapor, carbon dioxide, nitrous oxide, and hydrocarbons from the compressed air stream
Implementation Method 2
a main heat exchange system configured to cool the first part of the compressed and purified air stream to produce a vapor air stream and to partially cool the second part of the compressed and purified air stream
Implementation Method 3
a turboexpander arrangement configured to expand the partially cooled second part of the compressed and purified air stream to form an exhaust stream that imparts refrigeration to the air separation unit
Implementation Method 4
a lower pressure column having an operating pressure between 1.5 bar and 2.8 bar linked in a heat transfer relationship via a condenser reboiler
Implementation Method 5
an argon-enriched overhead that is directed to the argon condenser, which is configured to condense the argon-enriched overhead against the subcooled oxygen enriched stream from the lower pressure column
Implementation Method 6
a subcooler arrangement operatively coupled with the distillation column system and configured to subcool a kettle oxygen stream from the higher pressure column and a nitrogen stream from the condenser-reboiler via indirect heat exchange with the nitrogen overhead stream from the lower pressure column
Data Source
AI summary
A moderate pressure air separation unit and air separation cycle is disclosed that provides for up to about 96% recovery of argon and an overall nitrogen recovery of 98% or greater. The air separation is configured to produce a high purity oxygen enriched stream which is used as the refrigerant to condense the argon in the argon condenser, with the resulting vaporized oxygen stream used to regenerate the temperature swing adsorption prepurifier unit. Argon recovery is facilitated with the use of an argon superstaged column.