Flash Column for Removing O2 and NOx from Alkanolamine

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Solution Overview

Problem

Conventional methods for recovering high purity carbon dioxide from gaseous sources, such as flue gas, face challenges due to the absorption of oxygen and nitrogen oxides (NOx) by alkanolamine, leading to unwanted degradation and corrosion, as well as difficulties in achieving low NOx content in the final product due to chemical equilibrium changes during purification.

Innovation Solution

Introducing a flash column between the absorption and stripper columns, where the liquid is unsaturated with respect to O2 and NOx, allowing these gases to be removed before reaching the stripper, thereby shifting the NO+½O2NO2 equilibrium and reducing NOx content in the stripper off-gas, which simplifies further purification.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Productivity

If alkanolamine is used as absorbing agent to recover carbon dioxide from gaseous source containing oxygen and nitrogen oxides, then carbon dioxide recovery is achieved, but oxygen and nitrogen oxides are also absorbed causing degradation and corrosion

Engineering Contradiction:

Improvecarbon dioxide recoveryVSAvoiddegradation and corrosion

Core Design Contradiction:

ProductivityVSObject-affected harmful factors

Solution Approach 1:

The absorption process is divided into two separate columns: a first absorption column for carbon dioxide absorption and a second absorption column for oxygen and nitrogen oxide removal. This segmentation allows each column to be optimized for its specific function, preventing the harmful effects of oxygen and nitrogen oxide absorption while maintaining high carbon dioxide recovery efficiency.

Inventive Principle:

Principle #1Segmentation

Solution Approach 2:

The harmful components (oxygen and nitrogen oxides) are extracted from the gas stream in a separate second absorption column before the carbon dioxide-rich absorbent enters the stripper. This extraction prevents these components from causing degradation and corrosion during the carbon dioxide recovery process.

Inventive Principle:

Principle #2Taking out (Extraction)

2Manufacturing precision

If conventional scrubbing, oxidation, adsorption or distillation is used to remove NOx from stripper off gas, then nitrogen oxide removal is achieved, but chemical equilibrium changes make it difficult to reduce NOx content

Engineering Contradiction:

ImproveNOx content in productVSAvoidpurification process complexity

Core Design Contradiction:

Manufacturing precisionVSDevice complexity

Solution Approach 1:

Oxygen and nitrogen oxides are removed from the absorbent solution in advance during the absorption process in the second absorption column, before the carbon dioxide stripping step. This preliminary removal prevents NOx from being released in the stripper off gas, eliminating the need for complex downstream purification processes and maintaining stable chemical equilibrium.

Inventive Principle:

Principle #10Preliminary action

3Manufacturing precision

If flash column is introduced between absorption and stripper, then O2 and NOx are removed from liquid phase, but additional equipment is required

Engineering Contradiction:

Improvepurity of carbon dioxideVSAvoidnumber of columns

Core Design Contradiction:

Manufacturing precisionVSDevice complexity

Solution Approach 1:

The second absorption column serves multiple functions: it absorbs oxygen, nitrogen oxides, and carbon dioxide from the gas stream. By combining these functions into a single column, the system achieves high carbon dioxide recovery and effective removal of harmful components without requiring separate dedicated columns for each function, thus limiting the increase in device complexity.

Inventive Principle:

Principle #6Universality (Multi-functionality)

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 significantly reduces O2 and NOx in the stripper off-gas, making subsequent purification more efficient and cost-effective, resulting in high purity carbon dioxide production, suitable for food-grade applications.

Implementation Method 1

absorbing the feeding gas in an alkanolamine-containing absorbing agent, by which the feeding gas is separated into a carbon dioxide-depleted gas and a carbon dioxide-rich liquid

Methodology Applied

Scientific EffectAbsorption: Absorption (physical)

Implementation Method 2

separating by means of flashing the liquid obtained in step c into a NOx- and oxygen-rich gas and a NOx- and oxygen-depleted liquid leaving the flash column

Methodology Applied

Scientific EffectFlashing: Phase Change

Implementation Method 3

separating the liquid obtained in step e into a carbon dioxide-rich gas and a carbon dioxide-depleted liquid by means of stripping

Methodology Applied

Scientific EffectStripping: Distillation

Data Source

PatentUS7829049B2Method for recovery of high purity carbon dioxide from a gaseous source comprising nitrogen compounds

Publication Date: 2010.11.09 UNION ENGINERING A/S

AI summary

The present invention describes a method for recovery of high purity carbon dioxide, which is substantially free of nitrogen oxides. The present invention also discloses a plant for recovery of said high purity carbon dioxide comprising an absorption column, a flash column, a stripper column, and a purification unit.