Ammonia Oxidation Catalyst for SCR Ammonia Slip Reduction
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Solution Overview
Problem
Current SCR technologies face challenges with ammonia slip, leading to excess ammonia in flue gases, which contaminates fly ash and contributes to air pollution, equipment corrosion, and health hazards, while also being inefficient in NOx decomposition due to incomplete reactions and high ammonia consumption.
Innovation Solution
A method involving an ammonia oxidation catalyst comprising a zeolite, precious metals, and a base metal, treated with rare earth metals, is used downstream of the primary SCR catalyst to oxidize unreacted ammonia to nitrogen, reducing ammonia slip and maintaining low NOx emissions.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If ammonia injection is increased to improve NOx decomposition efficiency, then NOx removal efficiency is improved, but ammonia slip increases contaminating fly ash and causing air pollution
Solution Approach 1:
The system is divided into two distinct treatment stages: a primary SCR stage for NOx reduction and a secondary oxidation stage for ammonia slip removal. This segmentation allows each stage to be optimized independently, achieving both high NOx decomposition efficiency and low ammonia slip without compromising either function.
Solution Approach 2:
A secondary catalyst system comprising oxidation catalysts (such as platinum, palladium, or rhodium on alumina or silica) is introduced as an intermediary component downstream of the primary SCR catalyst. This intermediary specifically targets and oxidizes unreacted ammonia to nitrogen and water, preventing ammonia slip while maintaining the primary SCR function.
2Productivity
If ammonia injection is increased to improve NOx decomposition rate, then NOx removal is improved, but residual ammonia reacts with sulfuric acid to form ammonium sulfate causing equipment corrosion
Solution Approach 1:
The secondary oxidation catalyst system acts as a mediator that intercepts residual ammonia before it can react with sulfuric acid in the flue gas. By converting ammonia to nitrogen and water in a controlled catalytic process, the system prevents the formation of corrosive ammonium sulfate deposits on equipment surfaces.
Solution Approach 2:
The system converts the harmful residual ammonia, which would otherwise cause corrosion through ammonium sulfate formation, into beneficial nitrogen gas and water through catalytic oxidation. This transforms a harmful substance into harmless or beneficial products, eliminating the corrosion problem.
3Productivity
If ammonia injection is increased to improve NOx decomposition, then NOx removal is improved, but ammonia consumption increases leading to waste
Solution Approach 1:
The secondary oxidation stage provides a feedback mechanism that captures and processes unreacted ammonia from the primary SCR stage. This feedback loop ensures that ammonia is not wasted but rather fully utilized - first for NOx reduction, then for oxidation to nitrogen, maximizing ammonia utilization efficiency.
Solution Approach 2:
The system performs preliminary action by using a controlled amount of ammonia in the primary SCR stage to reduce NOx, then immediately follows up with secondary oxidation to process any unreacted ammonia. This preliminary and follow-up action sequence ensures complete ammonia utilization and prevents waste.
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 minimizes ammonia slip to safe levels, reduces CO concentrations, and maintains low NOx emissions, enhancing the operational stability and safety of combustion equipment while adhering to environmental regulations.
Implementation Method 1
contacting said flue gas stream containing said unreacted ammonia with an ammonia oxidation catalyst in the presence of an oxidant
Implementation Method 2
oxidizing said unreacted ammonia to nitrogen
Data Source
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AI summary
The present invention is directed to a method for removal by oxidation of the excess ammonia (NH3) gas ("ammonia slip") resulting from flue gases that have been subjected to selective catalytic reduction (SCR) for reduction of nitrogen oxides (NOx) with ammonia. More specifically, the inventive method uses an ammonia oxidation catalyst consisting of a zeolite, one or more precious metals, and a base metal compound, to catalyze the oxidation of both ammonia and carbon monoxide (CO), while minimizing the formation of nitrogen oxides (NOx). The present invention is useful in treating flue and exhaust gases.