SCR Catalyst NH3 Fill Control During Temperature Changes
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Solution Overview
Problem
Existing SCR catalyst systems face challenges in maintaining high nitrogen oxide conversion efficiency during dynamic temperature changes, leading to ammonia slip and inefficiencies due to the decrease in ammonia storage capacity with increasing temperature, particularly in systems with multiple catalysts.
Innovation Solution
A method involving an inverse SCR model that virtually divides the catalyst into bricks, determining desired ammonia target fill levels based on efficiency, temperature, and other physical variables, ensuring steady state conditions to maintain high NOx conversion by adjusting ammonia dosing accordingly.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Speed
If the SCR catalyst operates at high temperature to improve reaction rate, then the nitrogen oxide conversion speed increases, but the ammonia storage capacity decreases leading to ammonia slip
Solution Approach 1:
The control system calculates the required ammonia dosing in advance based on predicted temperature changes and catalyst state. By pre-dosing ammonia before temperature-induced capacity loss occurs, the system maintains adequate NH3 storage capacity while operating at high temperatures for fast NOx conversion.
Solution Approach 2:
The system continuously monitors catalyst temperature, ammonia fill level, and NOx conversion efficiency, using this feedback to dynamically adjust the ammonia dosing rate. This closed-loop control ensures the catalyst operates at optimal fill level despite temperature variations that would otherwise reduce ammonia storage capacity.
2Reliability
If the ammonia dosing rate is increased to maintain high fill level during temperature increase, then the NOx conversion efficiency is maintained, but the system complexity increases
Solution Approach 1:
The control algorithm pre-calculates the required ammonia dosing based on temperature predictions and catalyst state models, avoiding the need for complex real-time adjustments. This preliminary calculation approach maintains reliable NOx conversion while simplifying the control system architecture.
Solution Approach 2:
The system uses its own operational parameters (temperature, fill level, conversion efficiency) as input to its control algorithm, allowing the SCR system to self-regulate without external intervention. This self-service capability maintains conversion efficiency while keeping the control logic relatively simple and self-contained.
3Reliability
If a second SCR catalyst is added downstream to handle ammonia slip, then the ammonia conversion completeness improves, but the device complexity increases
Solution Approach 1:
Instead of adding a second catalyst to handle ammonia slip, the system pre-doses ammonia based on temperature predictions to prevent slip from occurring in the first place. This preliminary action approach maintains complete ammonia conversion with a single catalyst, avoiding the complexity of multi-catalyst systems.
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
Ensures high NOx conversion efficiency and reduces ammonia slip by dynamically adjusting ammonia dosing based on real-time operating conditions, preventing interruptions in the SCR system's performance.
Implementation Method 1
The degree of coverage of the catalyst with adsorbed NH3 determines its efficiency
Implementation Method 2
Selective catalytic reduction (SCR) using ammonia (NH3) or ammonia-releasing reagents is a promising method for mitigating nitrogen oxides
Implementation Method 3
As the temperature increases, the ability of SCR catalyst 22 to store ammonia decreases
Data Source
AI summary
A method is for exhaust aftertreatment of an internal combustion engine having at least one selective catalytic reduction (“SCR”) catalyst supplied with exhaust gas of the engine. The method includes virtually dividing the SCR catalyst into n-bricks in a direction of flow of the exhaust gas, and determining desired NH3 target fill levels for the SCR catalyst as a function of a desired target NOx conversion efficiency. The method further including assuming a steady state condition for the determination of the desired NH3 target fill levels, and determining the desired NH3 target fill levels for the at least one SCR catalyst by an inverse SCR model of a current NOx concentration upstream of the SCR catalyst, an SCR catalyst temperatures of the bricks, an exhaust mass flow, an oxygen concentration, an exhaust pressure upstream of the SCR catalyst and a desired target NOx conversion efficiency.