Selective Catalytic Reduction System with Hydrolysis Reactor
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Solution Overview
Problem
Current selective catalytic reduction (SCR) systems are limited by DEF deposits forming on surfaces, reducing efficiency, and require lower DEF dosage rates due to transient ammonia production, which does not proportionally increase with dosage, limiting NOx conversion.
Innovation Solution
A numerical model is used to predict ammonia concentration on a hydrolysis catalyst, allowing for optimized DEF dosage control through a controller integrated with sensors, enabling more accurate modeling of chemical reactions and state transitions to enhance NOx conversion.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If DEF dosage rate is increased to improve NOx conversion, then NOx conversion efficiency is improved, but DEF deposits form on surfaces reducing system efficiency
Solution Approach 1:
The system performs preliminary hydrolysis of DEF to ammonia in a separate hydrolysis reactor before the SCR catalyst, allowing the main SCR system to operate at optimal dosage rates without excessive DEF injection that would cause deposits. The hydrolysis step pre-processes the DEF, converting it to ammonia that can be more efficiently utilized.
Solution Approach 2:
Ammonia acts as an intermediary substance between DEF and the SCR catalyst. Instead of dosing DEF directly onto the SCR catalyst where it would form deposits, the system converts DEF to ammonia in a hydrolysis reactor first, then introduces the ammonia to the SCR catalyst for NOx reduction, eliminating the deposit formation issue.
2Reliability
If DEF dosage rate is kept low to prevent deposit formation, then deposit formation is reduced, but NOx conversion efficiency decreases
Solution Approach 1:
The hydrolysis reactor performs preliminary conversion of DEF to ammonia, allowing the SCR system to achieve high NOx conversion without requiring high DEF dosage rates. This pre-processing step enables efficient ammonia utilization at lower overall DEF dosing levels.
Solution Approach 2:
The hydrolysis reactor serves as an intermediary processing stage that converts DEF to a more readily usable form (ammonia), allowing the SCR catalyst to operate at optimal efficiency with reduced DEF dosage requirements, thereby preventing deposits while maintaining high NOx conversion.
3Productivity
If ammonia production is increased proportionally with DEF dosage, then NOx conversion is improved, but transient ammonia production on hydrolysis catalyst limits the proportional increase
Solution Approach 1:
The hydrolysis reactor provides continuous ammonia production from DEF, ensuring a stable and sustained supply of ammonia to the SCR catalyst. This continuous action eliminates the transient fluctuations in ammonia production, allowing for steady-state operation at optimized dosage rates.
Solution Approach 2:
The hydrolysis reactor performs preliminary and continuous conversion of DEF to ammonia, creating a stable ammonia supply that can be proportionally increased with DEF dosage without transient effects. This pre-processing ensures that ammonia production keeps pace with DEF dosing requirements.
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 optimizes NOx conversion by allowing higher DEF dosage rates without deposit formation, improving the efficiency of SCR systems in treating exhaust gases.
Implementation Method 1
The DEF contains urea which undergoes a thermolysis and hydrolysis within the exhaust passage whereby ammonia is produced
Implementation Method 2
The ammonia passes into a SCR catalyst where it reacts with the exhaust gas, wherein nitrogen oxides (NOx) present in the exhaust gas are converted to nitrogen and water
Implementation Method 3
evaluating the numerical model to derive a predicted concentration of ammonia generated by the hydrolysis catalyst
Data Source
AI summary
Selective catalytic reduction (SCR) systems are known and are generally included in the exhaust systems of diesel engines in order to treat the exhaust gases of such engines. Such systems typically involve the introduction of a diesel exhaust fluid (DEF) into exhaust gas flowing in an exhaust passage of an engine. DEF dosing systems are limited by the amounts of DEF that can be delivered without deposits forming on surfaces of the aftertreatment system. A numerical model of a hydrolysis catalyst is provided. The model comprises a spatial model of a hydrolysis catalyst to be modelled, where the hydrolysis catalyst is divided into a plurality of discrete spatial units. For each of the discrete spatial units, values for a plurality of matter state parameters are determined.