Method and apparatus for air separation by cryogenic distillation
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Solution Overview
Problem
Current air separation processes for producing oxygen and nitrogen at elevated pressures require additional compression stages, leading to high energy consumption and increased costs, while also posing safety risks due to the use of oxygen compressors.
Innovation Solution
A process and apparatus that compress all feed air to a pressure close to the first column, then recycle it through a booster air compressor to recover heat in the main heat exchanger, reducing the need for additional compression stages and enhancing energy efficiency.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Stress or pressure
If additional compression stages are used to produce oxygen at elevated pressures, then the oxygen production pressure is improved, but the energy consumption increases
Solution Approach 1:
The patent combines the compression and heat exchange functions into a single integrated system. The compressed air is cooled in a heat exchanger using the cold from evaporating liquid oxygen, and this pre-cooled air is then directly introduced into the distillation column. This merging eliminates the need for separate cooling stages and reduces overall energy consumption while maintaining high oxygen production pressure.
Solution Approach 2:
The patent applies preliminary cooling to the compressed air before it enters the distillation column. By cooling the compressed air in advance using the cold from evaporating liquid oxygen in the heat exchanger, the system reduces the thermodynamic irreversibility and prepares the air for more efficient distillation, thereby reducing the energy required for the separation process.
2Loss of energy
If feed air is introduced at a temperature close to the column temperature, then the thermodynamic irreversibility is reduced, but the device complexity increases
Solution Approach 1:
The heat exchanger serves multiple functions simultaneously: it cools the compressed air, provides the necessary temperature approach to reduce thermodynamic irreversibility, and uses the cold from evaporating liquid oxygen. This multi-functionality achieves the thermal optimization goal without adding separate dedicated cooling devices, thereby limiting the increase in device complexity.
3Stress or pressure
If oxygen compressors are used to compress oxygen to higher pressures, then the oxygen production pressure is improved, but the safety risks increase
Solution Approach 1:
The patent replaces the mechanical oxygen compression system with a liquid pumping system. Liquid oxygen is pumped to the desired pressure and then vaporized in the heat exchanger. This substitution eliminates the safety risks associated with compressing gaseous oxygen, as liquid pumping is inherently safer and more reliable, while still achieving the required high oxygen production pressure.
4Stress or pressure
If a booster is added to vaporize liquid oxygen under elevated pressure, then the oxygen production pressure is improved, but the device complexity increases
Solution Approach 1:
The patent merges the vaporization function with the heat exchanger that cools the compressed air. The liquid oxygen is vaporized by exchanging heat with the compressed air in the same heat exchanger unit. This combining of vaporization and cooling functions into a single device achieves the required oxygen production pressure without adding a separate booster device, thereby limiting the increase in device complexity.
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 thermodynamic irreversibility and overall costs by efficiently recycling air, achieving a specific energy savings of 7.1% in oxygen production under 40 bar pressure without adding extra compression stages.
Implementation Method 1
cooling and condensation of at least a part of the air under the second outlet pressure in a heat exchanger
Implementation Method 2
vaporization of the liquid by heat exchange in the heat exchanger
Implementation Method 3
reduction in pressure of at least a fraction of the air cooled and condensed under the second outlet pressure down to an intermediate pressure
Implementation Method 4
separation of air by cryogenic distillation
Implementation Method 5
vaporization of the liquid
Data Source
AI summary
A method for separating air by cryogenic distillation in a system of columns comprising a first column and a second column operating at a lower pressure than the first column, comprising the steps of compressing all of the feed air in a first compressor to a first output pressure of at least 1 bar greater than the pressure of the first column, sending a first portion of the air under the first output pressure to the second compressor, and compressing the air to a second output pressure, cooling and condensing at least a portion of the air under the second output pressure in a heat exchanger, withdrawal of a liquid from a column of the system of columns, pressurising the liquid and evaporating the liquid by heat exchange in the heat exchanger, and pressure reduction of a portion of the compressed air to a second output pressure, at least partially evaporating said air in the heat exchanger, optionally additional heating of said air in the heat exchanger, and sending at least a portion of this air to the second compressor.