Process and apparatus for separating air using a split heat exchanger
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Solution Overview
Problem
The existing cryogenic air separation processes using a split main heat exchanger system and subcooler configuration face inefficiencies in oxygen production, particularly in managing heat transfer across multiple streams, leading to suboptimal thermal performance and increased capital costs.
Innovation Solution
A process and apparatus that utilize a multi-column distillation system with a split heat exchanger configuration, where a first heat exchanger section handles higher-pressure streams and a second heat exchanger section handles lower-pressure streams, along with an expander to manage nitrogen-enriched fractions, optimizing heat transfer and pressure management to enhance oxygen and nitrogen production efficiency.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of energy
If a single heat exchanger is used to transfer heat between multiple streams, then heat transfer efficiency is improved, but device complexity and capital cost increase
Solution Approach 1:
The main heat exchanger is divided into two separate heat exchangers: a high-pressure heat exchanger handling higher-pressure streams and a low-pressure heat exchanger handling lower-pressure streams. This segmentation allows each heat exchanger to be optimized for its specific pressure range, reducing overall system complexity while maintaining effective heat transfer across all streams through coordinated operation
2Device complexity
If multiple heat exchangers are used in parallel, then device complexity is reduced, but thermal performance deteriorates
Solution Approach 1:
Each heat exchanger is assigned specific streams based on their pressure characteristics - the high-pressure heat exchanger handles higher-pressure streams while the low-pressure heat exchanger handles lower-pressure streams. This local optimization ensures that each heat exchanger operates within its optimal pressure range, maintaining thermal efficiency while simplifying the overall system design
3Productivity
If subcoolers are used to subcool liquid streams, then refrigeration efficiency is improved, but device complexity increases
Solution Approach 1:
The subcooling function is integrated into the existing high-pressure and low-pressure heat exchangers rather than adding separate standalone subcoolers. The high-pressure heat exchanger subcools the liquid oxygen stream while the low-pressure heat exchanger subcools the nitrogen-rich stream, merging the subcooling function with the existing heat exchange infrastructure and avoiding additional 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 configuration improves the thermal efficiency and reduces capital costs by optimizing heat transfer across streams, achieving better refrigeration and product yield in oxygen and nitrogen production compared to traditional methods.
Implementation Method 1
cooling the first portion of the compressed feed air stream in the first heat exchanger section
Implementation Method 2
cooling and condensing pressurized air stream
Implementation Method 3
multi-column distillation system comprising a lower-pressure column and a higher-pressure column
Implementation Method 4
withdrawing an oxygen-enriched fraction from the higher-pressure column and withdrawing a nitrogen-enriched fraction from the higher-pressure column
Implementation Method 5
expanding the nitrogen-enriched fraction withdrawn from the position intermediate the first (warmer) end and the second (colder) end of the first heat exchanger section in an expander to produce work and reduce the pressure
Data Source
AI summary
Process and apparatus for the separation of a compressed feed air stream to produce an oxygen product using a distillation column having a lower-pressure column and a higher-pressure column, a higher-pressure heat exchanger and a lower-pressure heat exchanger where the gaseous nitrogen expander receives a nitrogen-enriched fraction from a position intermediate the warmer end and the colder end of the higher-pressure heat exchanger.