Axial Flow Reactor for N2O Removal with Monolithic Catalysts
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Solution Overview
Problem
Current methods for removing nitrous oxide (N2O) from nitric acid production processes are inefficient, leading to high greenhouse gas emissions and require large, complex reactors with stringent ammonia slip requirements, which increase costs and pose environmental risks.
Innovation Solution
An axial flow reactor design using monolithic shaped catalysts with axial flow direction, where a reducing agent like ammonia is added and passed through two stages: the first for N2O decomposition and the second for residual ammonia oxidation, reducing catalyst volume and reactor size while maintaining effective N2O removal and low ammonia slip.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Quantity of substance
If conventional radial flow reactors with pellet catalysts are used for N2O removal, then N2O decomposition can be achieved, but the reactor size and catalyst volume become excessively large
Solution Approach 1:
The patent changes the flow direction parameter from radial to axial, and changes the catalyst shape parameter from pellets to monolithic structures. These parameter changes enable much higher space velocities (up to 100,000 h-1 compared to 1,000-5,000 h-1 for radial flow), allowing effective N2O removal with dramatically reduced catalyst volumes while maintaining high conversion efficiency.
Solution Approach 2:
The patent transitions from radial flow (flowing outward from center) to axial flow (flowing linearly through the catalyst bed). This dimensional change in flow pattern, combined with monolithic catalyst structures, creates a more efficient contact between gas and catalyst, enabling high productivity with minimal catalyst volume.
2Quantity of substance
If ammonia is used as reducing agent for N2O removal, then N2O decomposition is effective, but ammonia slip creates environmental risks and requires strict control
Solution Approach 1:
The patent divides the single-reactor system into two separate stages: first reactor for N2O removal and second reactor for ammonia oxidation. This segmentation allows each reactor to be optimized for its specific function, ensuring high N2O conversion while completely eliminating ammonia slip in the final effluent.
Solution Approach 2:
The patent introduces a second reactor as an intermediary treatment stage between the N2O removal reactor and the atmosphere. This intermediary stage oxidizes any residual ammonia before discharge, acting as a safety barrier that eliminates the harmful ammonia slip while preserving the effectiveness of the first stage.
3Reliability
If large catalyst volumes are used to ensure low ammonia slip, then ammonia slip can be controlled, but reactor complexity and capital costs increase
Solution Approach 1:
The patent segments the ammonia slip control function into a dedicated second reactor rather than requiring excessive catalyst volume in the first reactor. This segmentation simplifies the overall design by assigning specific functions to specific units, making the system more manageable and less complex than a single oversized reactor.
Solution Approach 2:
The patent extracts the ammonia oxidation function from the N2O removal process and places it in a separate second reactor. This extraction allows the first reactor to focus solely on N2O removal with optimized catalyst volume, while the second reactor handles ammonia slip control, reducing overall system complexity.
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 results in a more compact, cost-effective reactor with reduced ammonia slip and lower N2O emissions, achieving N2O reduction with a smaller catalyst volume and lower capital expenditures, while ensuring environmental safety by minimizing ammonia slip and greenhouse gas emissions.
Implementation Method 1
a first monolithic shaped catalyst active in decomposing nitrous oxide with the reducing agent
Implementation Method 2
decomposing nitrous oxide with the reducing agent to provide a gas with a reduced amount of nitrous oxide
Implementation Method 3
a second monolithic shaped catalyst active in oxidation of the residual amounts of the reducing agent
Data Source
AI summary
A process for the removal of nitrous oxide (N2O) contained in a process off-gas in an axial flow reactor. The process includes the steps of (a) adding an amount of reducing agent into the process off-gas; (b) in a first stage passing in axial flow direction the process off-gas admixed with the reducing agent through a first monolithic shaped catalyst active in decomposing nitrous oxide by reaction with the reducing agent to provide a gas with a reduced amount of nitrous oxide and residual amounts of reducing agent; and (c) in a second stage passing the gas with a reduced amount of nitrous oxide and residual amounts of the reducing agent in axial flow direction through a second monolithic shaped catalyst active in oxidation of the residual amounts of the reducing agent.