Ammonia Oxidizer for SCR Flue Gas Ammonia Slip Reduction
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Solution Overview
Problem
The existing SCR and SNCR systems for reducing NOx emissions from power plants result in ammonia slip, leading to downstream equipment fouling, fly ash contamination, and potential health and environmental hazards due to excess ammonia in the flue gas, which is not effectively managed.
Innovation Solution
A chemical oxidation process is introduced using an ammonia oxidizer in the flue gas exhaust duct upstream of the fly ash collecting device to reduce residual ammonia concentrations to less than 20 ppm, allowing higher ammonia injection levels for improved NOx reduction without causing equipment fouling or environmental harm.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If higher ammonia injection levels are used to improve NOx reduction, then NOx removal efficiency is improved, but ammonia slip increases causing downstream equipment fouling and fly ash contamination
Solution Approach 1:
The invention extracts and removes the harmful excess ammonia from the flue gas stream using a secondary oxidation system. This allows the primary SCR/SNCR system to operate with higher ammonia injection levels for improved NOx removal efficiency, while the extracted excess ammonia is then oxidized and removed, preventing downstream equipment fouling and fly ash contamination.
Solution Approach 2:
The invention changes the chemical state of ammonia by introducing a secondary oxidation process that converts excess ammonia into other compounds. This parameter change (from ammonia to oxidized products) allows the system to maintain high ammonia injection levels for NOx reduction while eliminating the harmful effects of ammonia slip through chemical transformation.
2Productivity
If excess ammonia is used to maximize NOx reaction, then NOx reduction is improved, but downstream equipment reliability deteriorates due to ammonium sulfate/bisulfate formation
Solution Approach 1:
The invention applies preliminary action by removing excess ammonia through secondary oxidation before the flue gas reaches downstream equipment. This preventive measure eliminates the root cause of ammonium sulfate/bisulfate formation and equipment fouling, ensuring downstream equipment reliability while allowing aggressive ammonia injection for maximum NOx reduction.
3Object-affected harmful factors
If ammonia injection is increased to achieve maximum NOx removal, then environmental compliance is improved, but fly ash quality deteriorates due to ammonia contamination
Solution Approach 1:
The invention introduces a secondary oxidation system as an intermediary between the ammonia injection/NOx reduction process and the fly ash collection system. This intermediary removes excess ammonia from the flue gas, preventing it from contaminating the fly ash while allowing high ammonia injection levels to achieve environmental compliance for NOx emissions.
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 process effectively reduces ammonia slip, minimizing downstream equipment issues and fly ash contamination, enabling safer and more environmentally friendly disposal of fly ash while maintaining effective NOx reduction capabilities.
Implementation Method 1
adding an oxidizing chemical reagent from the chemical reagent addition system to form an ammonia oxidation zone in the flue gas exhaust duct
Data Source
AI summary
A process is described that removes by chemical oxidation the excess ammonia (NH3) gas from flue gases that have been subjected to selective catalytic reduction (SCR) and selective non-catalytic reduction (SNCR) of oxides of nitrogen (NOx) by ammonia injection. Methods for the removal of residual ammonia from flue gases prior to fouling air pre-heaters or deposition on fly ash are discussed.