Two-Stage Catalyst System for NOx and N2O Removal
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Solution Overview
Problem
Current methods for removing NOx and N2O emissions in nitric acid production are inefficient, leading to high greenhouse gas emissions and ammonia slip, requiring complex and costly reactor designs with strict emission regulations.
Innovation Solution
A process involving a two-stage catalyst system where ammonia is added to the process off-gas, with a first stage using a catalyst like titanium dioxide and vanadium oxide for NOx reduction and a second stage employing a cobalt compound catalyst for N2O decomposition, reducing the overall reactor size and complexity while minimizing ammonia slip.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If a single-stage catalyst system is used for NOx and N2O removal, then the reactor design becomes simpler, but the removal efficiency of both pollutants cannot be achieved simultaneously
Solution Approach 1:
The patent divides the pollutant removal process into two sequential stages: first stage using SCR catalyst for NOx removal, second stage using decomposition catalyst for N2O removal. This segmentation allows each catalyst to be optimized for its specific function, achieving high removal efficiency for both pollutants while maintaining manageable system complexity through modular design.
2Reliability
If ammonia is added in excess to ensure complete NOx removal, then NOx conversion increases, but ammonia slip increases causing safety risks
Solution Approach 1:
The patent performs preliminary NOx removal in the first stage using SCR catalyst, converting most NOx before the gas enters the second stage. This preliminary action reduces the ammonia dosage required in subsequent stages, thereby minimizing ammonia slip while ensuring complete NOx removal through the combined two-stage process.
Solution Approach 2:
The first stage SCR catalyst acts as an intermediary that pre-processes the off-gas by removing the majority of NOx. This intermediary step protects the second stage from handling excessive ammonia loads, enabling precise ammonia dosing and reducing harmful ammonia slip in the final effluent.
3Adaptability or versatility
If N2O is removed downstream the absorption tower, then the removal position is optimal for process integration, but the reactor size becomes very large
Solution Approach 1:
The patent employs decomposition catalysts in the second stage that exhibit high activity at the existing off-gas temperature and pressure conditions downstream of the absorption tower. By selecting catalysts with optimized parameters for these conditions, high N2O conversion is achieved in a compact reactor volume, maintaining process integration benefits without requiring oversized equipment.
4Ease of manufacture
If conventional SCR catalysts are used for both NOx and N2O removal, then catalyst selection is simplified, but N2O removal efficiency remains insufficient
Solution Approach 1:
The patent segments the catalyst selection into two specialized functions: conventional SCR catalysts (vanadium-based) for first stage NOx removal, and decomposition catalysts (iron, copper, or cobalt zeolites) for second stage N2O removal. This segmentation ensures each catalyst type is optimized for its specific pollutant, achieving high N2O removal efficiency while maintaining ease of manufacture through selection from well-established catalyst technologies.
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 achieves significant reduction of NOx and N2O emissions with lower ammonia consumption and operational costs, meeting stringent emission standards while simplifying reactor design and reducing greenhouse gas contributions.
Implementation Method 1
NOx is typically removed by the known selective catalytic reduction (SCR) process through reaction with ammonia as reducing agent to nitrogen and water
Implementation Method 2
passing the effluent gas through a catalyst comprising a cobalt compound and being active in decomposition of nitrous oxide
Implementation Method 3
oxidation of the residual amounts of the reducing agent
Data Source
AI summary
Process for the removal of NOx (NO, NO2) and nitrous oxide (N2O) contained in a process off-gas comprising the steps of (a) adding an amount of a NOx reducing agent into the process off-gas;(b) in a first stage passing the process off-gas admixed with the reducing agent through a catalyst active in selective catalytic reduction of NOx with the reducing agent and providing an effluent gas comprising the nitrous oxide and residual amounts of reducing agent; and(c) in a second stage passing the effluent gas through a catalyst comprising a cobalt compound and being active in decomposition of nitrous oxide and oxidation of the residual amounts of the reducing agent.