NOx Removal via NO to NO2 Oxidation and Water Scrubbing
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Solution Overview
Problem
Existing SCR technologies for NOx removal from flue gas at elevated pressures suffer from reagent slip, leading to increased costs and risks of salt precipitation and corrosion, particularly when ammonia is used, due to incomplete conversion and residual reagent precipitation as carbonate/bicarbonate.
Innovation Solution
The method involves using a less than stoichiometric amount of reagent for SCR, followed by compression and/or oxidizer injection to enhance NO conversion to NO2, which is then removed with water, minimizing reagent slip and optimizing catalyst operation at high pressures.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If a stoichiometric amount of reagent is supplied for complete NOx conversion, then NOx removal efficiency is improved, but reagent slip occurs causing salt precipitation and corrosion
Solution Approach 1:
The patent applies preliminary action by converting NO to NO2 before the SCR reaction occurs. This is achieved through oxidation in a first reactor using oxygen or oxidizing catalysts, preparing the nitrogen oxides in a form that will react more completely with the reagent in the subsequent SCR stage, thereby reducing reagent slip while maintaining high removal efficiency
Solution Approach 2:
The patent changes the oxidation state parameter of nitrogen oxides from +2 (NO) to +4 (NO2) before the SCR reaction. This parameter change enables more complete conversion with stoichiometric reagent amounts, preventing the harmful effects of reagent slip while achieving high NOx removal efficiency
2Object-affected harmful factors
If a less than stoichiometric amount of reagent is supplied, then reagent slip is reduced, but NOx conversion is incomplete
Solution Approach 1:
The patent performs preliminary oxidation of NO to NO2 before the SCR reaction. This preliminary action increases the reactivity of nitrogen oxides toward the reagent, allowing complete conversion with less than stoichiometric reagent amounts, thus reducing reagent slip while maintaining high removal efficiency
Solution Approach 2:
The patent changes the chemical composition parameter of the flue gas by converting NO to NO2 beforehand. This parameter change enables the SCR reaction to proceed more efficiently, achieving complete NOx conversion with reduced reagent dosage and preventing reagent slip
3Productivity
If oxidizer injection is used to enhance NO conversion to NO2, then NOx removal efficiency is improved, but device complexity increases
Solution Approach 1:
The patent applies self-service by utilizing oxygen already present in the flue gas or on the catalyst surface to oxidize NO to NO2. This eliminates the need for separate oxidizer injection systems, reducing device complexity while maintaining high NOx removal efficiency through the enhanced SCR reaction
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 at least 80-95% NOx removal efficiency while preventing reagent slip, reducing operational costs and minimizing corrosion risks by ensuring complete conversion of NOx to NO2, which can be easily removed with water.
Implementation Method 1
contacting the flue gas with a catalyst at a temperature between 250-400° C. The consequent reaction causes conversion of NOx into N2 and water
Implementation Method 2
supplying an oxidizer into the flue gas after contacting the flue gas with the catalyst for conversion of NO into NO2
Implementation Method 3
compressing the flue gas in at least one compression stage
Data Source
AI summary
A method for removing NOx from flue gas by SCR includes supplying a reagent for the SCR reaction of NOx into the flue gas, then contacting the flue gas with a catalyst. Supplying the reagent includes supplying a less than stoichiometric amount of reagent, and after contacting the flue gas with a catalyst a final NOx removal step is provided.