NOx Catalyst Ammonia Distribution Control
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Solution Overview
Problem
Existing exhaust gas control systems face challenges in improving NOx purification rates while minimizing ammonia slip, as the distribution of ammonia adsorption across the NOx reduction catalyst affects both the purification efficiency and the likelihood of ammonia slipping out of the system.
Innovation Solution
A control method and apparatus that monitor and adjust the ammonia adsorption distribution across the NOx reduction catalyst, using a control device to optimize ammonia supply based on real-time adsorption data, ensuring maximum adsorption without excessive slip by targeting specific thresholds and positions within the catalyst.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If the amount of ammonia supplied to the NOx reduction catalyst is increased to improve the NOx purification rate, then the NOx purification rate is improved, but ammonia slip occurs when the ammonia exceeds the upper limit of adsorption capacity
Solution Approach 1:
The NOx reduction catalyst is divided into multiple sections along the exhaust gas flow direction, and the ammonia adsorption amount is calculated separately for each section. This segmentation allows the control device to identify which specific section has insufficient adsorption capacity and target ammonia supply to that section, rather than uniformly increasing supply across the entire catalyst, thus improving purification efficiency while avoiding excessive ammonia slip.
Solution Approach 2:
The control device calculates the ammonia adsorption amount in advance for each catalyst section based on operating conditions and exhaust gas composition, and determines the required ammonia supply amount before actual injection occurs. This preliminary calculation ensures that ammonia is supplied optimally to match the catalyst's actual adsorption capacity, preventing both insufficient purification and excessive slip.
2Stability of the object's composition
If the ammonia adsorption amount is distributed uniformly throughout the NOx reduction catalyst, then the ammonia distribution is even, but the NOx purification rate is lower compared to concentrated upstream distribution
Solution Approach 1:
The invention applies different ammonia adsorption targets to different sections of the catalyst based on local requirements. The control device calculates the ammonia adsorption amount for each section individually and supplies ammonia preferentially to sections with higher purification needs, creating a non-uniform but optimized distribution that maximizes NOx purification rate while maintaining overall system stability.
3Productivity
If the ammonia adsorption amount is concentrated in the upstream side of the NOx reduction catalyst, then the NOx purification rate is improved, but ammonia slip becomes more likely when the catalyst becomes saturated
Solution Approach 1:
By segmenting the catalyst into multiple sections and calculating ammonia adsorption amounts for each section separately, the control device can monitor the saturation status of upstream sections and redirect ammonia supply to downstream sections when upstream capacity is exhausted. This prevents ammonia slip by ensuring ammonia is supplied only to sections that can actually adsorb it.
Solution Approach 2:
The ammonia supply strategy is made dynamic by continuously calculating the adsorption capacity of each catalyst section based on real-time operating conditions. The control device adjusts the ammonia supply distribution among different sections dynamically, shifting supply from saturated upstream sections to unsaturated downstream sections, thereby maintaining high purification efficiency while preventing ammonia slip throughout varying operating conditions.
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 enhances NOx purification rates by maximizing ammonia adsorption while minimizing ammonia slip, allowing for more efficient exhaust gas treatment without unnecessary reductions in ammonia supply.
Implementation Method 1
ammonia is supplied to the NOx reduction catalyst from an upstream side of the NOx reduction catalyst... The ammonia generated from the urea water is adsorbed to the NOx reduction catalyst
Implementation Method 2
The urea water injected into the exhaust gas decomposes in the exhaust gas so as to generate ammonia
Implementation Method 3
A redox reaction is promoted between the ammonia adsorbed to the NOx reduction catalyst and the NOx in the exhaust gas that flows into the NOx reduction catalyst, and as a result, the NOx is removed from the exhaust gas
Data Source
AI summary
An exhaust gas control apparatus includes a control device controlling a urea addition valve for adding urea from an upstream side of a NOx reduction catalyst. The control device obtains an ammonia adsorption amount distribution through the NOx reduction catalyst. When an ammonia adsorption amount in a predetermined part on a downstream side equals or exceeds a predetermined threshold, the control device controls the urea addition valve to stop the urea supply or reduce the amount thereof. The urea addition valve is controlled based on an adsorption amount distribution obtained from a model on which the catalyst is divided into cells such that an ammonia adsorption amount in a first cell positioned furthest upstream equals or exceeds a predetermined threshold close to a saturation adsorption amount and an ammonia adsorption amount in a second cell positioned downstream of the first cell reaches a predetermined target value smaller than the threshold.