Utilization of nitrogen-enriched streams produced in air separation units comprising split-core main heat exchangers
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Solution Overview
Problem
Current cryogenic air separation methods face challenges in energy efficiency and cost associated with raw material and equipment, particularly in the distribution and utilization of nitrogen-rich streams for pre-cooling and regeneration in air purification units, lacking a mechanism to maintain flow consistency and optimize energy use.
Innovation Solution
A process involving sequential compression and cooling of air streams through main and booster compressors, with nitrogen-enriched streams being divided and reused in heat exchangers to achieve indirect heat exchange, allowing for regulated flow and temperature optimization between air pre-cooling and purification units, enhancing energy efficiency and reducing equipment size.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Use of energy by moving object
If nitrogen-enriched streams are divided and fed into both higher pressure and lower pressure heat exchangers, then heat exchange efficiency is improved, but flow distribution control and energy optimization become complex
Solution Approach 1:
The nitrogen-enriched stream is divided into two separate streams, with one fed into the higher pressure heat exchanger and the other into the lower pressure heat exchanger. This segmentation allows independent optimization of heat exchange conditions in each pressure level, improving overall energy efficiency while maintaining manageable control complexity through dedicated flow paths.
Solution Approach 2:
Different pressure levels are applied to different nitrogen-enriched streams based on local heat exchange requirements. The higher pressure stream optimizes heat transfer coefficient, while the lower pressure stream matches the pressure of the air stream being cooled, creating locally optimized heat exchange conditions in each exchanger.
2Use of energy by moving object
If feed air stream temperature is lowered through pre-cooling, then energy efficiency improves, but the temperature control and heat exchange requirements become more stringent
Solution Approach 1:
The feed air stream undergoes pre-cooling before entering the main heat exchanger by exchanging heat with the nitrogen-enriched stream. This preliminary cooling action reduces the temperature difference that must be managed in subsequent heat exchange stages, improving overall energy efficiency while simplifying temperature control in the main rectification process.
3Ease of manufacture
If adsorbent volume is reduced in air purification units, then equipment cost decreases, but the capacity and effectiveness of air purification may be compromised
Solution Approach 1:
The temperature of the feed air stream entering the air purification unit is optimized through the heat exchange process. By controlling the temperature parameter of the pre-cooled air, the purification capacity per unit volume of adsorbent is enhanced, allowing reduced adsorbent volume while maintaining purification effectiveness.
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 improves energy efficiency by lowering the temperature of feed air streams, reducing adsorbent volumes, decreasing equipment costs, and optimizing the power consumption of the booster air compressor, while ensuring adequate flow for air purification, thus enhancing the overall operation of the air separation apparatus.
Implementation Method 1
The resulting compressed and purified air stream can be cooled within a main heat exchanger against return streams to a temperature suitable for its rectification
Implementation Method 2
a first part of the boosted pressure air stream is partially cooled in a high pressure heat exchanger through indirect heat exchange with a pumped oxygen liquid
Data Source
AI summary
An air separation apparatus and process, which produces gaseous oxygen and/or nitrogen products at an elevated pressure through internal compression of respective liquid products, are disclosed. Split-core main heat exchangers are employed to warm up product streams generated in an air rectification unit against 1) a main feed air stream in the low-pressure heat exchanger and 2) at least one boosted pressure air stream in the high-pressure exchanger. Because the boosted pressure air stream is at a higher pressure and temperature than the main feed air stream, after separate heat exchange in the split main heat exchangers, the subsidiary waste nitrogen stream exiting the high-pressure heat exchanger is also warmer than the subsidiary waste nitrogen stream exiting the low-pressure heat exchanger. The warmer waste nitrogen stream is fed into the air purification unit for regeneration purposes and the cooler waste nitrogen stream is introduced into the nitrogen water tower to perform cooling duty. The two subsidiary waste nitrogen streams are also connected on the warm side of the main heat exchangers to allow flexible distribution of the flow.