LNG-Refrigerated Air Separation With Indirect Nitrogen Cooling

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Solution Overview

Problem

Existing cryogenic air separation processes using LNG-based nitrogen liquefiers face safety hazards and increased capital costs due to direct injection of potentially hydrocarbon-laden liquid nitrogen into distillation columns, and require larger high-pressure columns as all incoming air is introduced as vapor.

Innovation Solution

LNG-derived refrigeration is used to liquefy a nitrogen stream, which is then heat exchanged against the air feed to the distillation column system, reducing vapor feed to the high-pressure column and avoiding direct introduction of liquefied nitrogen into the distillation columns, thereby minimizing hydrocarbon leakage and reducing column diameter.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Loss of energy

If liquefied nitrogen is directly introduced into the distillation column system, then refrigeration is provided efficiently, but safety hazards increase due to potential hydrocarbon leakage from LNG heat exchangers

Engineering Contradiction:

Improverefrigeration efficiencyVSAvoidsafety hazard from hydrocarbon contamination

Core Design Contradiction:

Loss of energyVSObject-affected harmful factors

Solution Approach 1:

The patent introduces a second heat exchanger as an intermediary device between the LNG heat exchanger and the distillation column system. This intermediate heat exchanger receives liquefied nitrogen from the first heat exchanger and transfers the refrigeration to the air feed, preventing direct contact between potentially hydrocarbon-contaminated nitrogen and the distillation column system while maintaining efficient heat transfer

Inventive Principle:

Principle #24Intermediary (Mediator)

2Device complexity

If all incoming air is introduced as vapor to the high-pressure column, then the process is simple, but capital costs increase due to larger column diameter requirements

Engineering Contradiction:

Improveprocess simplicityVSAvoidcapital cost

Core Design Contradiction:

Device complexityVSEase of manufacture

Solution Approach 1:

The patent changes the physical state parameter of the air feed by liquefying a portion of it in the second heat exchanger using refrigeration from liquefied nitrogen. This parameter change from vapor to liquid phase allows for reduced high-pressure column diameter while maintaining process effectiveness, thereby reducing capital costs

Inventive Principle:

Principle #35Parameter changes

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 reduces the capital costs associated with larger high-pressure columns and mitigates safety hazards by preventing hydrocarbon contamination in the oxygen product, while maintaining efficient refrigeration and oxygen recovery.

Implementation Method 1

LNG-derived refrigeration is used to liquefy a nitrogen stream in the process

Methodology Applied

Scientific EffectHeat exchange: Heat Exchanger

Implementation Method 2

liquefy a nitrogen stream

Methodology Applied

Scientific EffectLiquefaction: Condensation

Implementation Method 3

the liquefied nitrogen is heat exchanged against the air feed to the distillation column system

Methodology Applied

Scientific EffectHeat exchange: Heat Exchanger

Data Source

PatentUS7552599B2Air separation process utilizing refrigeration extracted from LNG for production of liquid oxygen

Publication Date: 2009.06.30 AIR PROD & CHEM INC

AI summary

A cryogenic air separation process is set forth wherein, in order to provide the refrigeration necessary when at least a portion of the oxygen product is desired as liquid oxygen, LNG-derived refrigeration is used to liquefy a nitrogen stream in the process. A key to the present invention is that, instead of feeding the liquefied nitrogen to the distillation column, the liquefied nitrogen is heat exchanged against the air feed to the distillation column system.