SCR Catalyst Fabric Filter Bags for Low-Temperature NOx Removal
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Solution Overview
Problem
Conventional SCR catalysts exhibit low efficiency in reducing NOx emissions at gas temperatures below 250°C, which limits the effectiveness of nitrogen oxide removal from flue gases in combustion facilities.
Innovation Solution
The method involves forming nitrogen dioxide (NO2) externally and injecting it into the flue gas upstream of fabric filter bags catalyzed with SCR catalysts, promoting the 'fast' SCR reaction by maintaining equimolar amounts of NO and NO2, achieved through ammonia oxidation using a precious metal catalyst and subsequent cooling and oxidation of nitrogen monoxide to NO2.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Temperature
If conventional SCR catalysts are used at low gas temperatures, then the fabric filter bags can operate within their temperature limits, but the NOx removal efficiency is significantly reduced
Solution Approach 1:
The patent changes the chemical composition parameters of the flue gas by injecting NO2 to create equimolar amounts of NO and NO2. This parameter change enables the fast SCR reaction mechanism to occur at low temperatures (below 250°C), thereby improving NOx removal efficiency without increasing gas temperature and protecting the fabric filter bags from thermal damage.
Solution Approach 2:
The patent introduces NO2 as an intermediary substance that facilitates the fast SCR reaction. By injecting NO2 into the flue gas, it acts as a mediator that enables the catalytic conversion of NOx to nitrogen and water at low temperatures, bridging the gap between the temperature constraints of fabric filter bags and the efficiency requirements of SCR catalysts.
2Reliability
If additional units are installed to remove NOx from flue gas, then NOx reduction can be achieved, but the system complexity and operational requirements increase
Solution Approach 1:
The patent merges the NOx removal function with the existing fabric filter bag system by integrating SCR catalysts into the filter bags themselves. This combination eliminates the need for separate SCR reactors and reduces system complexity, while maintaining effective NOx reduction capability through the fast SCR reaction mechanism enabled by NO2 injection.
Solution Approach 2:
The fabric filter bags are given multiple functions: they continue to remove particulate matter as before, and simultaneously serve as the reaction medium for SCR catalysts to remove NOx. This multi-functionality reduces the need for additional dedicated equipment and simplifies the overall system architecture.
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 enhances the low-temperature activity of SCR catalysts, improving NOx reduction efficiency at temperatures below 250°C, thereby meeting regulatory requirements for NOx emission reduction.
Implementation Method 1
Selective Catalytic Reduction (SCR) of NOx, nitrous oxide compounds are selectively reduced to harmless nitrogen and water by reaction with a reduction agent, e.g. ammonia, over a catalyst
Implementation Method 2
catalytically oxidizing ammonia or a precursor thereof with an oxygen containing atmosphere to an effluent gas containing nitrogen monoxide and oxygen in presence of an oxidation catalyst
Implementation Method 3
cooling the effluent gas to ambient temperature and oxidizing the nitrogen monoxide in the cooled effluent gas to the nitrogen dioxide containing effluent gas
Implementation Method 4
oxidizing the nitrogen monoxide in the cooled effluent gas to the nitrogen dioxide containing effluent gas
Data Source
AI summary
Method and system for the removal of nitrogen oxides, from flue gas at low temperatures.