Process and apparatus for separating NO<sub>2 </sub>from a CO<sub>2 </sub>and NO<sub>2</sub>-containing fluid
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Solution Overview
Problem
Current CO2 purification methods from flue gas face challenges in removing NOx, particularly due to the recycling of NO2-enriched fluids, which increases compression energy and equipment size, and the use of wash columns results in CO2 losses or inefficient distillation.
Innovation Solution
A process involving a rectifying distillation column and a fluid separation membrane to separate NO2 from CO2, where the NO2-enriched liquid stream is fed to the membrane, producing a permeate gas enriched in NO2 and a non-permeate liquid stream enriched in CO2, which is then recycled back to the rectifying column, avoiding the need for recycling NO2-enriched fluids or using wash columns.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-affected harmful factors
If NO2-enriched liquid is recycled to the compressor inlet, then NOx removal is improved, but compression energy consumption increases by 5-10% and equipment size increases
Solution Approach 1:
The harmful NO2-enriched liquid stream is extracted and removed from the recycle loop. Instead of recycling it to the compressor inlet, the patent sends it to a wash column where NO2 is washed out with water, and the cleaned stream is then recycled. This extraction breaks the harmful recycle loop while maintaining necessary fluid circulation.
Solution Approach 2:
A wash column is introduced as an intermediary unit between the De-NOx column and the compressor. The wash column uses water as a mediator to remove NO2 from the liquid stream before recycling, preventing the harmful components from entering the compressor while allowing the bulk fluid to be reused.
2Use of energy by moving object
If reflux liquid flow rate to De-NOx column is decreased to reduce NO2 recycle, then compression energy is reduced, but distillation efficiency decreases due to exceeding wettability limit
Solution Approach 1:
The harmful NO2-enriched liquid is extracted and diverted to a separate wash column for treatment. This allows the reflux liquid flow rate in the De-NOx column to be maintained at optimal levels for distillation efficiency, while the extracted NO2-rich stream is handled separately to minimize compression energy requirements.
Solution Approach 2:
The single De-NOx column function is segmented into two separate units: the De-NOx column for distillation and the wash column for NO2 removal. This segmentation allows each unit to operate independently at optimal conditions - the De-NOx column maintains sufficient reflux for efficient distillation while the wash column handles the NO2-rich stream separately.
3Object-affected harmful factors
If wash column is used to treat NO2-enriched liquid, then NOx removal is improved, but CO2 losses occur
Solution Approach 1:
The wash column serves as an intermediary treatment unit that selectively removes NO2 from the liquid stream using water washing. The process is designed to wash out NO2 while minimizing CO2 dissolution and loss. The washed stream is then recycled back to the De-NOx column or compressor, maintaining mass balance and reducing overall CO2 losses compared to alternative approaches.
Solution Approach 2:
The wash column discards NO2 from the liquid stream through water washing, concentrating it in the wash water for separate handling. The cleaned liquid stream is recovered and recycled back into the process, maintaining CO2 in the system while removing harmful NOx components.
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 method effectively reduces NOx content in the CO2 product, minimizing equipment size and energy consumption while avoiding CO2 losses, providing a more reliable and efficient CO2 purification process.
Implementation Method 1
The fluid is fed to a rectifying distillation column. A first gaseous stream is withdrawn from the rectifying column that is enriched in CO2 and deficient in NO2 relative to the fluid comprising CO2, NO2
Implementation Method 2
The NO2-enriched liquid stream is fed to a fluid separation membrane. A second gaseous stream comprising a permeate gas is withdrawn from the membrane that is enriched in NO2 and deficient in CO2 relative to the liquid stream fed to the membrane
Data Source
AI summary
A process for separating carbon dioxide from a fluid containing carbon dioxide, NO2, and at least one of oxygen, argon, and nitrogen comprises the steps of separating at least part of the fluid into a carbon dioxide enriched stream, a carbon dioxide depleted stream comprising CO2 and at least one of oxygen, argon, and nitrogen and a NO2 enriched stream and recycling said NO2 enriched stream upstream of the separation step.