Cryogenic Air Separation With Three-Column Pressure Cascading
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Solution Overview
Problem
Current air separation systems for gasification processes using cryogenic distillation are inefficient due to suboptimal thermal integration between columns, particularly when there is limited cooling power or a hot end deviation, leading to energy losses and reduced oxygen separation efficiency.
Innovation Solution
The proposed method involves a three-column system where compressed air is processed through a first column, with nitrogen-enriched gas condensed in an intermediate condenser, and oxygen-enriched liquid is further processed in lower-pressure columns, utilizing a cold compressor to reduce pressure and enhance energy efficiency by cascading effects, and incorporating specific vaporizer-condensers and heat exchangers to manage temperature differences effectively.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of energy
If a three-column cryogenic distillation system is used with standard thermal integration, then oxygen separation is achieved, but energy consumption is high due to suboptimal thermal integration between columns
Solution Approach 1:
The patent merges the thermal functions of multiple columns by integrating heat exchangers that allow heat transfer between different pressure columns. The first column (high pressure) transfers thermal energy to the second column (intermediate pressure), which in turn transfers to the third column (low pressure), creating a unified thermal system that recovers energy across the entire distillation train rather than treating each column independently.
Solution Approach 2:
The system utilizes parameter changes by operating three distillation columns at different pressure levels (first column at high pressure, second at intermediate pressure, third at low pressure). This pressure gradient enables efficient thermal integration where condensation in higher-pressure columns provides heat for evaporation in lower-pressure columns, optimizing energy utilization across the system.
2Use of energy by moving object
If thermal integration between columns is enhanced, then energy efficiency improves, but the system complexity increases
Solution Approach 1:
The patent introduces intermediate heat exchangers as mediators between the distillation columns operating at different pressures. These heat exchangers facilitate controlled thermal energy transfer while allowing the columns to operate independently at their optimized pressure levels, thus enhancing energy efficiency without requiring complete system integration that would increase complexity.
Solution Approach 2:
The thermal integration is segmented into discrete heat exchange stages between columns rather than requiring a fully integrated system. Each column maintains its independent pressure operation while exchanging thermal energy through dedicated heat exchangers, allowing progressive energy recovery without creating a monolithic complex system.
3Manufacturing precision
If the hot end deviation is reduced to improve oxygen separation efficiency, then oxygen purity increases, but the system requires more precise temperature control
Solution Approach 1:
The system employs feedback control through temperature sensors and control valves that monitor and adjust the thermal integration between columns. By continuously measuring temperature differences at the hot ends of columns and adjusting heat exchanger operations, the system maintains precise temperature control to minimize hot end deviation and maximize oxygen separation efficiency.
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 significantly reduces energy consumption by cascading pressure in the first column, achieving an appreciable gain in energy efficiency and improving oxygen separation efficiency, especially when the hot end deviation is between 6 and 10°C, allowing for higher oxygen purity and reduced nitrogen consumption.
Implementation Method 1
part of the nitrogen-enriched gas from the first column condenses in a bottom vaporizer-condenser of the second column
Implementation Method 2
a liquid containing at least 85% oxygen is withdrawn from the bottom of the third column, pressurized and vaporized to form a gaseous product containing at least 85% oxygen
Implementation Method 3
a gas enriched in nitrogen from the second column is compressed in a compressor having a temperature lower than ambient temperature
Implementation Method 4
compressed, purified and cooled air is sent to the first column where it separates to form an oxygen-enriched liquid and a nitrogen-enriched gas
Data Source
Figure 1
AI summary
The invention relates to a method for separating air by cryogenic distillation in a set of columns including a first column operating at a first pressure (21), a second column (23) operating at a second pressure which is lower than the first pressure and a third column (25) operating at a third pressure which is lower than the second pressure, wherein the third column includes first and second evaporator-condensers (29, 31) and nitrogen from a cold compressor (47) is sent to one of the evaporator-condensers.