SCR System NOx Removal Low-Temperature Efficiency
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Solution Overview
Problem
Current methods for reducing nitrogen oxides (NOx) at low temperatures, such as those found in exhaust gases from boilers and gas turbines, are inefficient and costly, as they require increased catalyst amounts or improved catalyst efficiency, which is difficult to achieve, and result in the production of carcinogenic byproducts like formaldehyde.
Innovation Solution
The composition of exhaust gas is adjusted to a NO2/NOx ratio of approximately 0.5 using a combination of fixed and moveable oxidation catalysts to enhance the efficiency of fast selective catalytic reduction (SCR) reactions, allowing effective NOx removal at temperatures of 300° C. or below without increasing catalyst amounts.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of energy
If the temperature of the exhaust gas is low, then energy recovery is maximized, but the de-NOx efficiency decreases and catalyst amount must be increased
Solution Approach 1:
The patent changes the chemical composition parameter of exhaust gas by controlling the NO/NO2 ratio to approximately 1:1, which enables fast SCR reaction to occur efficiently at low temperatures (200-300°C), thereby maintaining high de-NOx efficiency without increasing catalyst amount while energy recovery is maximized
2Productivity
If the amount of de-NOx catalyst is increased, then de-NOx efficiency is improved, but operation cost increases due to additional blower power
Solution Approach 1:
The patent changes the exhaust gas composition parameter (NO/NO2 ratio ≈ 1:1) to enable fast SCR reaction, which achieves high de-NOx efficiency with a smaller catalyst amount, thereby avoiding increased operation costs associated with larger catalyst volumes and higher blower power requirements
3Object-generated harmful factors
If ethanol is sprayed to remove yellow plume, then NO2 is removed, but carcinogenic formaldehyde is produced and operation cost increases
Solution Approach 1:
The patent converts the harmful NO2 that causes yellow plume into beneficial N2 through fast SCR reaction by controlling exhaust gas composition (NO/NO2 ratio ≈ 1:1) and using ammonia injection, thereby removing yellow plume without producing carcinogenic formaldehyde and reducing operation costs
Solution Approach 2:
The patent introduces ammonia as an intermediary substance that reacts with NO2 in the fast SCR process to convert it into harmless N2 and H2O, providing an environmentally friendly alternative to ethanol injection that does not produce formaldehyde
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 enables effective NOx removal at low temperatures, reduces operational and catalyst-related costs, and minimizes the production of yellow plumes during gas turbine startup, using existing SCR facilities with oxidation catalysts or ozone generators.
Implementation Method 1
a non-thermal plasma or ozone generator may be used to oxidize NO included in the exhaust gas at 150-200° C., as shown in FIG. 1, so as to convert the NO in the exhaust gas to NO2
Implementation Method 2
fast selective catalytic reduction (SCR), The associated reaction is as follows. 2NO+2NO2+4NH3→4N2+6H2O
Data Source
AI summary
The present disclosure relates to a method for removing nitrogen oxides (NOx) more effectively at 300° C. or below in boilers, gas turbines, incinerators, diesel engines, glass melting furnaces, etc. by selective catalytic reduction (SCR). To this end, an oxidation catalyst is mounted in front of a NOx-reducing device based on selective catalytic reduction and the NOx composition, i.e. the ratio of NO:NO2, in the exhaust gas is adjusted to about 1:1, such that de-NOx catalytic reaction is carried out under optimized fast SCR condition and de-NOx efficiency at low temperature can be maximized.