SCR Catalyst Temperature Control for Ammonium Sulphate Prevention
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Solution Overview
Problem
Current methods for reducing nitrogen oxides and sulphur oxides in exhaust gases from internal combustion engines, particularly those fueled with high-sulphur content fuels, face challenges due to the reaction of ammonia with sulphur oxides, leading to catalyst inhibition and acid plume formation, especially in turbocharged engines where sulphur trioxide is formed and not effectively captured.
Innovation Solution
The method involves overdosing ammonia to capture sulphur trioxide as ammonium sulphate or bisulphate downstream of the SCR catalyst system, allowing for its removal in a wet scrubber, with ammonia slip adjusted to maintain minimal fouling in downstream equipment, either by keeping it above 10 ppm for condensation in a waste heat boiler or below 2 ppm for optimized SOx scrubber operation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-generated harmful factors
If ammonia is used as reducing agent in SCR to reduce NOx, then NOx reduction is achieved, but ammonia reacts with sulphur oxide to form ammonium sulphate or ammonium bisulphate which condense on the catalyst and inhibit it
Solution Approach 1:
The exhaust gas is heated to maintain temperature above the condensation temperature of ammonium sulphur compounds before they can condense on the catalyst. This preliminary thermal treatment prevents the harmful condensation reaction that would inhibit catalyst activity, allowing the SCR process to proceed effectively.
Solution Approach 2:
The temperature parameter of the exhaust gas is controlled to be above the condensation temperature of ammonium sulphur compounds. By changing and maintaining this critical temperature parameter, the system prevents the formation of condensing ammonium sulphate or bisulphate on the catalyst surface, thereby preserving catalyst activity while still enabling NOx reduction.
2Use of energy by moving object
If exhaust gas temperature is reduced after turbocharger to improve efficiency, then energy recovery is improved, but temperature drops below condensation temperature causing ammonium sulphate formation and catalyst inhibition
Solution Approach 1:
The system performs preliminary heating of the exhaust gas to maintain it above the condensation temperature of ammonium sulphur compounds. This preliminary action ensures that even as the gas expands and cools through the turbocharger, the temperature remains sufficient to prevent harmful condensation, thus allowing energy recovery without creating the harmful byproduct.
Solution Approach 2:
The exhaust gas is pre-heated beforehand to create a thermal buffer that compensates for the cooling effect during expansion through the turbocharger. This prior cushioning of thermal energy ensures the temperature stays above the critical condensation point, preventing ammonium sulphate formation while still enabling efficient energy recovery.
3Adaptability or versatility
If high sulphur content fuel is used to maintain operational flexibility, then fuel versatility is improved, but sulphur oxide in exhaust reacts with ammonia to form acid plume
Solution Approach 1:
The temperature parameter of the exhaust gas is maintained above the condensation temperature of ammonium sulphur compounds through active heating. This parameter change prevents the chemical reaction between ammonia and sulphur oxide from producing condensing ammonium sulphate or bisulphate, thereby eliminating acid plume formation while allowing the engine to operate on high sulphur content fuels.
4Object-generated harmful factors
If ammonia slip is increased to capture SO3 as ammonium sulphate downstream, then SOx removal is improved, but downstream equipment fouling increases
Solution Approach 1:
The temperature of the exhaust gas is maintained above the condensation temperature of ammonium sulphur compounds throughout the system. This parameter change ensures that even when ammonia slip occurs and reacts with SO3 to form ammonium sulphate or bisulphate, these compounds remain in vapor phase and do not condense on downstream equipment surfaces, thus preventing fouling while still achieving SOx removal.
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 reduces NOx and SOx emissions by converting sulphur trioxide into water-soluble compounds for easy removal, minimizing fouling and ensuring efficient operation of downstream equipment by adjusting ammonia slip levels.
Implementation Method 1
the reduction of NOx to nitrogen (N2) is usually conducted by using ammonia or urea as reducing agents over a suitable catalyst in the so-called selective catalytic reduction (SCR)
Implementation Method 2
The reaction products are ammonium sulphate or ammonium bisulphate, which condense on the SCR catalyst
Implementation Method 3
wherein the exhaust gas is passed through the catalyst system at a temperature above condensation temperature of ammonium sulphur compounds formed by reaction with ammonia in the exhaust gas
Implementation Method 4
The relatively high temperature, however, means that some of the SO2 in the exhaust gas is oxidized to SO3 across the SCR catalyst
Data Source
AI summary
Method for reducing oxides of nitrogen and sulphur in exhaust gas from a lean burn internal combustion engine.