System and method for recovery of nitrogen, argon, and oxygen in moderate pressure cryogenic air separation unit
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Solution Overview
Problem
Moderate pressure cryogenic air separation units face challenges in maintaining high nitrogen and argon recoveries during off-design operating modes without significantly reducing recovery rates compared to normal operating modes, and existing solutions require costly oxygen compressors for oxygen product delivery.
Innovation Solution
A nitrogen and argon producing cryogenic air separation unit with a main air compression system, adsorption-based pre-purifier, heat exchange system, turboexpander, and a turbine air stream column bypass circuit that directs a portion of the exhaust stream to bypass the distillation column, allowing for efficient separation and recovery of oxygen, nitrogen, and argon without the need for oxygen compressors.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of operation
If oxygen compressors are used to deliver oxygen product to customers at sufficient pressure, then oxygen delivery capability is improved, but capital cost and operating cost increase significantly
Solution Approach 1:
The patent makes the oxygen product delivery system self-service by using the liquid oxygen pump (already required for delivering liquid oxygen product) to also provide the necessary pressure for oxygen gas delivery. The system uses its own internal resources - the high pressure liquid oxygen stream and the liquid oxygen pump - to achieve oxygen delivery without requiring separate oxygen compressors, thus eliminating the associated capital and operating costs
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
The solution enables high recovery of nitrogen and argon while maintaining operational efficiency in off-design modes and eliminates the need for oxygen compressors, reducing capital and operating costs by optimizing the location of nitrogen waste draw and using a turbine air bypass arrangement.
Implementation Method 1
an adsorption based pre-purifier unit configured for removing water vapor, carbon dioxide, nitrous oxide, and hydrocarbons from the compressed air stream
Implementation Method 2
a main heat exchange system configured to cool the first part of the compressed and purified air stream and to partially cool the second part of the compressed and purified air stream
Implementation Method 3
a turboexpander arrangement configured to expand the partially cooled second part of the compressed and purified air stream to form an exhaust stream
Implementation Method 4
a distillation column system having a higher pressure column and a lower pressure column linked in a heat transfer relationship via a condenser-reboiler and configured to separate the cooled first part of the compressed and purified air stream and a first portion of the exhaust stream
Implementation Method 5
The argon condenser is configured to condense the argon-enriched overhead against all or a portion of the oxygen enriched stream from the lower pressure column to produce a crude argon stream
Data Source
AI summary
A moderate pressure nitrogen and argon producing cryogenic air separation unit is provided that includes a three distillation column system and turbine air stream bypass arrangement or circuit. The turbine air stream bypass arrangement or circuit is configured to improve argon and nitrogen recoveries in select operating modes by optionally diverting a portion of the turbine air stream to a nitrogen waste stream circuit drawn from the lower pressure column of the cryogenic air separation unit such that the diverted portion of the turbine air stream bypasses the distillation column system.