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 under high pressure face challenges such as high energy consumption and the need for additional compression stages, which increase costs and safety concerns due to oxygen compressors.
Innovation Solution
A method involving a booster air compressor to recycle air after it has been used to recover heat from vaporization in the main heat exchanger, allowing all supply air flow rates to be introduced at a temperature close to the column temperature, reducing thermodynamic irreversibility without adding additional compression stages.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If oxygen compressor is used to produce oxygen under high pressure, then oxygen production efficiency is improved, but safety problems occur due to oxygen compressor operation
Solution Approach 1:
The patent replaces the mechanical oxygen compressor with a liquid pumping system that uses liquid oxygen as the working fluid. The pump transfers liquid oxygen from the lower pressure column to the higher pressure column, eliminating the need for direct compression of gaseous oxygen and thereby resolving the safety issues associated with oxygen compressors while maintaining high pressure oxygen production capability
2Stress or pressure
If additional compression stages are added to achieve high pressure oxygen, then oxygen production pressure is improved, but energy consumption increases
Solution Approach 1:
The patent changes the physical state parameter of oxygen from gas to liquid phase during compression. By pumping liquid oxygen instead of compressing gaseous oxygen through multiple stages, the system achieves high pressure oxygen production with significantly reduced energy consumption, as liquid pumping requires much less energy than gas compression
Solution Approach 2:
The patent substitutes the multi-stage gas compression system with a single-stage liquid pumping system. This replacement eliminates the need for additional compression stages while achieving the same high pressure output, thereby reducing overall energy consumption of the oxygen production process
3Device complexity
If feed air is introduced at temperature different from column temperature, then air separation process is simplified, but thermodynamic irreversibility increases
Solution Approach 1:
The patent applies preliminary cooling to the feed air before it enters the distillation column, pre-cooling it to a temperature close to the column operating temperature. This preliminary action reduces the thermal shock and thermodynamic irreversibility that would occur with hot feed air introduction, improving the overall efficiency of the air separation process without significantly increasing system 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 energy consumption and overall costs by optimizing the air separation process, achieving a specific energy gain of 7.1% for oxygen production under 40 bar, while maintaining efficient operation and safety.
Implementation Method 1
cooling and condensation of at least a portion of the air under the second outlet pressure in a heat exchanger
Implementation Method 2
cooling and condensation of at least a portion of the air under the second outlet pressure in a heat exchanger
Implementation Method 3
vaporization of the liquid by heat exchange in the heat exchanger
Implementation Method 4
vaporization of the liquid by heat exchange in the heat exchanger
Implementation Method 5
separating air by cryogenic distillation into a column system comprising a first column and a second column
Data Source
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AI summary
A method for separating air by cryogenic distillation in a system of columns comprising a first column (8) and a second column (9) operating at a lower pressure than the first column, comprising the steps of compressing all of the feed air in a first compressor (6) 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 (230), 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 (5), withdrawal of a liquid (OL) from a column of the system of columns, pressurising the liquid (37) and evaporating the liquid by heat exchange in the heat exchanger (5), and pressure reduction of a portion of the compressed air to a second output pressure, at least partially evaporating said air (107) 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 (108).