Process and apparatus for the separation of air by cryogenic distillation
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Solution Overview
Problem
Current air separation processes using cryogenic distillation face inefficiencies in regenerating adsorption materials, particularly in warming nitrogen for regeneration, often relying on electrical heaters or compression heat, which can result in pressure drops and inefficient heat utilization.
Innovation Solution
A process and apparatus that utilize dual heat sources for warming nitrogen, including compression heat and electrical heating, with a closed heat exchange circuit to optimize regeneration temperature and reduce pressure drop, allowing for flexible heat distribution during regeneration periods and redirecting excess heat for external heating applications.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Use of energy by moving object
If compression heat from the final stage of the compressor is used to preheat the nitrogen, then energy efficiency is improved, but the nitrogen pressure is reduced due to pressure drop in the heating system
Solution Approach 1:
A water-based heat exchange circuit is introduced as an intermediary medium to transfer heat from compressed air to nitrogen. The compressed air heats the water in a first heat exchanger, and the heated water then heats the nitrogen in a second heat exchanger. This indirect heat transfer pathway avoids direct mixing and allows independent pressure control of the nitrogen stream while efficiently utilizing compression heat.
Solution Approach 2:
The heating process is divided into two separate stages using two distinct heat exchangers. The first heat exchanger handles heat transfer from compressed air to water, and the second heat exchanger handles heat transfer from water to nitrogen. This segmentation allows each stage to be optimized independently and maintains nitrogen pressure by avoiding direct contact with the compressed air system.
2Temperature
If all of the stream heated using compressed air is further heated using an electric heater, then the regeneration temperature is achieved, but the nitrogen pressure is further reduced due to additional pressure drop
Solution Approach 1:
The water-based heat exchange circuit serves as an intermediary that can be integrated with the existing electric heater system. The water absorbs heat from the compressed air and transfers it to the nitrogen stream, reducing the thermal load on the electric heater and minimizing the number of heating components the nitrogen must pass through, thereby reducing overall pressure drop.
3Use of energy by moving object
If a closed heat exchange circuit is used to warm nitrogen, then heat utilization efficiency is improved, but the device complexity increases
Solution Approach 1:
The water-based heat exchange circuit is designed to serve multiple functions: it preheats nitrogen for regeneration, can provide process heating when excess heat is available, and can be integrated with existing compressed air system components. This multi-functionality justifies the added complexity by providing versatile heat management capabilities throughout the air separation process.
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 enhances the efficiency of nitrogen regeneration by minimizing pressure drop and optimizing heat usage, while also enabling the reuse of excess heat for external heating purposes, thus improving the overall air separation process.
Implementation Method 1
cooling the air by indirect heat exchange with water in a first heat exchanger
Implementation Method 2
the water is heated by indirect heat exchange with air by means of a closed circuit
Implementation Method 3
the nitrogen-enriched gas is warmed by indirect heat exchange with the heated water in a second heat exchanger
Implementation Method 4
compressed air is purified to remove water and carbon dioxide by adsorption
Data Source
Figure 1
Figure 2
AI summary
Nitrogen (21) from an air separation unit is warmed using air (3) taken between a first and second stage (C1, C2) of the air compressor, compressing air sent to the air separation unit. The warmed nitrogen (11) is then used as a regeneration stream for the purification unit (E) of the air separation unit.