Method for air separation by cryogenic distillation
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Solution Overview
Problem
Conventional air separation units face inefficiencies in reducing the discharge pressure of the main compressor, particularly when producing high purity oxygen, leading to higher electrical consumption and larger compressor sizes.
Innovation Solution
The process involves cold compressing the nitrogen flow from the medium pressure column and thermally coupling it with the low pressure column, reducing the pressure at the main air compressor discharge, while optimizing heat exchange to maintain low operating pressures.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Use of energy by moving object
If the discharge pressure of the main compressor is reduced to minimize electrical consumption, then energy efficiency improves, but the ability to maintain adequate heat exchange between the medium pressure column and low pressure column deteriorates
Solution Approach 1:
The nitrogen flow from the medium pressure column is divided into two separate flows: one portion is cold compressed to provide refrigeration for the low pressure column, while another portion maintains heat exchange in the main vaporizer-condenser. This segmentation allows independent optimization of each function, enabling reduced compressor discharge pressure while maintaining heat exchange reliability.
Solution Approach 2:
A cold compressor is introduced as an intermediary device between the medium pressure column and low pressure column. This cold compressor takes nitrogen at cold temperatures from the medium pressure column top and compresses it to provide refrigeration for the low pressure column, thereby decoupling the pressure requirements of the two columns and enabling reduced main compressor discharge pressure.
2Device complexity
If a conventional single vaporizer-condenser system is used, then device complexity is minimized, but the ability to decouple medium pressure column pressure from vaporizer-condenser pressure deteriorates
Solution Approach 1:
The nitrogen flow is segmented into multiple streams with different destinations and functions. One stream goes to the cold compressor for refrigeration duty, another stream maintains heat exchange in the main vaporizer-condenser, and potentially a third stream provides refrigeration in an intermediate vaporizer. This segmentation enables pressure decoupling while maintaining manageable system complexity.
Solution Approach 2:
The main vaporizer-condenser is designed to handle multiple nitrogen streams simultaneously - both the cold compressed nitrogen from the cold compressor and the nitrogen from the medium pressure column top. This multi-functionality allows the system to achieve pressure decoupling without requiring separate dedicated heat exchange equipment for each nitrogen stream.
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 significantly reduces electrical consumption and compressor size by effectively lowering the operating pressure, enhancing the efficiency of air separation units producing high purity oxygen.
Implementation Method 1
the cold necessary to keep the device cold is provided by expansion of air or nitrogen in a cryogenic turbine
Implementation Method 2
cold compress (that is to say to compress it in a compressor having an inlet temperature of at most -150 ° C) the nitrogen flow
Implementation Method 3
the heat exchange between the MP column and the low pressure (LP) column is provided by a single vaporizer-condenser, the main vaporizer-condenser of the unit
Implementation Method 4
process for separating air by cryogenic distillation
Data Source
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AI summary
The invention relates to a method for air separation by cryogenic distillation in a column system that includes at least a first column (100) operating at a first pressure, and a second column (102) operating at a second pressure that is lower than the first pressure, the head of the first column being thermally connected to the tank of the second column via a vaporizer-condenser (21), a first portion of a nitrogen-enriched gas (17) is drawn from the head of the first column, compressed in a compressor (19) having an inlet temperature no higher than -150°C and condensed in the vaporizer-condenser, an oxygen-rich fluid (43) is drawn from the lower portion of the second column and heated in the exchange line, a nitrogen-rich gas (41) is drawn from the upper portion of the second column and heated in the exchange line, and a second portion of the nitrogen-enriched gas is expanded in a turbine without having been compressed.