Nitrogen Oxide Scrubbing via Segmented Low-Pressure Absorption
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Solution Overview
Problem
Current methods for removing nitrogen oxides from gas streams in nitric acid production, especially in low-pressure plants, are inefficient and costly due to high residual nitrogen oxide content in exhaust gases, leading to increased compression and system design complexities.
Innovation Solution
A method involving a two-reactor system where a NOx-containing gas stream is scrubbed with an aqueous liquid in a countercurrent flow, followed by contact with an oxygen-rich gas to form nitric acid, with the enriched liquid being recycled and used to enhance absorption tower efficiency, reducing nitrogen oxide content significantly.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If higher pressures are applied in absorption towers to reduce residual nitrogen oxide content, then nitrogen oxide removal efficiency is improved, but compression costs and system design complexity increase significantly
Solution Approach 1:
The absorption process is divided into multiple absorption towers operating in series at low pressure (1-5 bar), with each tower removing a portion of the nitrogen oxides. The gas stream passes through multiple stages, progressively reducing NOx content without requiring high pressure compression throughout the entire process.
Solution Approach 2:
The gas stream is pre-treated by cooling and condensing water vapor before entering the absorption towers. This preliminary action prepares the gas for more efficient absorption in subsequent stages, improving overall removal efficiency without requiring high pressure.
2Reliability
If multiple absorption towers operating in series are used to increase absorption capacity, then nitrogen oxide removal efficiency is improved, but process engineering costs and system complexity increase
Solution Approach 1:
The system uses multiple absorption towers (typically 2-4 towers) connected in series, with each tower performing a segment of the overall absorption task. The gas stream flows through each tower sequentially, with nitrogen oxides being progressively removed at each stage, achieving high overall removal efficiency through distributed processing.
Solution Approach 2:
The absorption towers operate continuously in series, with the gas stream flowing uninterrupted through each tower. The liquid absorbent is recirculated through each tower, maintaining continuous absorption action throughout the system, maximizing the utilization of each tower's capacity.
3Ease of manufacture
If low-pressure absorption towers are used to reduce compression costs, then equipment costs are reduced, but residual nitrogen oxide content in exhaust gas increases
Solution Approach 1:
The low-pressure absorption process is segmented into multiple towers operating in series. Each tower operates at low pressure (1-5 bar), keeping equipment costs low, but the cumulative effect of multiple stages achieves high nitrogen oxide removal efficiency, reducing residual content to acceptable levels without requiring high pressure compression.
Solution Approach 2:
Each absorption tower performs a partial absorption function, removing a portion of the nitrogen oxides. By using multiple towers in series, the system achieves excessive removal capacity beyond what a single tower could provide, ensuring residual nitrogen oxide content is reduced to very low levels while maintaining low operating pressure.
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 effectively reduces nitrogen oxide content by 50% or more in exhaust gases, supporting conventional denitrification methods and reducing the need for expensive cleaning chemicals, while generating nitric acid that can be reused in nitric acid production processes.
Implementation Method 1
nitrogen oxides from the gas stream dissolve into the scrubbing liquid, enriching it with nitrogen oxides
Implementation Method 2
The scrubbing liquid enriched with nitrogen oxides is then introduced into the headspace of a second reactor and brought into contact with an oxygen-rich gas. This gas is introduced into the second reactor at an arbitrary point, for example, but not necessarily, into its lower region, and then passes through the second reactor in countercurrent flow to the scrubbing liquid. An aqueous liquid containing nitric acid collects in the sump of the second reactor.
Data Source
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AI summary
According to the inventive method for cleaning nitrogen oxide-containing gas streams, a NOx-containing gas stream is first fed into the bottom region of a first reactor (scrubber) and passed countercurrently to a scrubbing liquid. The NOx-enriched scrubbing liquid is then brought into contact with an oxygen-rich gas in a second reactor, forming an aqueous liquid containing nitric acid. This aqueous liquid containing nitric acid is subsequently separated into two partial streams, one of which is discharged, while the second partial stream is returned to the first reactor and used to scrub the gas stream. The method leads to a significant reduction in the nitrogen oxide concentration in the remaining exhaust gas.