Dual SCR Catalyst Exhaust System with Interstage Cooling
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Solution Overview
Problem
Current exhaust gas aftertreatment systems face challenges in minimizing nitrogen oxide emissions due to temperature-dependent ammonia storage and conversion efficiency in SCR catalytic converters, leading to increased nitrogen oxide and nitrous oxide emissions, especially under high engine performance conditions.
Innovation Solution
An exhaust gas aftertreatment system with two SCR catalytic converters in series, where a heat exchanger is used to lower the exhaust gas temperature before the second SCR catalytic converter, allowing for increased ammonia storage and conversion performance without thermal desorption, and an ammonia blocking catalytic converter is added to prevent ammonia emissions.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If the exhaust gas temperature is increased to improve conversion efficiency, then the nitrogen oxide conversion performance improves, but the ammonia storage capacity decreases and thermal desorption occurs
Solution Approach 1:
The exhaust aftertreatment system is divided into two separate SCR catalysts arranged in series, with the first SCR catalyst optimized for high-temperature operation and the second SCR catalyst optimized for low-temperature operation. This segmentation allows each catalyst to operate in its optimal temperature range, resolving the contradiction between high conversion efficiency and ammonia storage capacity.
2Productivity
If the ammonia level in the SCR catalyst is increased to improve conversion efficiency, then the nitrogen oxide conversion improves, but the risk of thermal desorption increases at high temperatures
Solution Approach 1:
The system segments the ammonia storage function across two catalysts: the first SCR catalyst handles high-temperature conversion with lower ammonia storage, while the second SCR catalyst maintains high ammonia storage for low-temperature operation. This segmentation resolves the contradiction by distributing the functional requirements across separate components.
Solution Approach 2:
The first SCR catalyst acts as an intermediary that pre-processes the exhaust gas and protects the second SCR catalyst from high-temperature thermal desorption. By placing the first catalyst upstream, it serves as a buffer that maintains stable ammonia levels in the second catalyst, resolving the reliability issue.
3Device complexity
If a single SCR catalyst is used, then the system complexity is reduced, but the operating range for efficient nitrogen oxide conversion is limited
Solution Approach 1:
The system uses two SCR catalysts with different operational characteristics arranged in series, allowing the system to adapt to a wider range of exhaust gas temperatures and engine operating conditions. This segmentation increases versatility while maintaining manageable complexity through modular design.
Solution Approach 2:
The dual-SCR catalyst system provides multi-functionality by handling both high-temperature and low-temperature nitrogen oxide conversion within a single integrated system. The first catalyst handles high-temperature conditions while the second handles low-temperature conditions, creating a universal solution for various operating scenarios.
4Quantity of substance
If the exhaust gas flow is cooled before the second SCR catalyst, then the ammonia storage capacity increases, but additional cooling components are required
Solution Approach 1:
The first SCR catalyst itself serves as the cooling mechanism for the second SCR catalyst through the exothermic ammonia oxidation reactions it performs. This self-service approach cools the exhaust gas flow naturally without requiring external cooling components, resolving the contradiction between increased ammonia storage and reduced system complexity.
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 configuration enhances the operating range for efficient nitrogen oxide conversion, minimizing emissions by maintaining a high ammonia loading on the SCR catalytic converters and preventing thermal desorption, thereby improving conversion performance and reducing nitrogen oxide emissions.
Implementation Method 1
a heat exchanger is used to lower the exhaust gas temperature before the second SCR catalytic converter
Implementation Method 2
a catalyst for the selective catalytic reduction of nitrogen oxides (SCR catalyst)
Implementation Method 3
the conversion of nitrogen oxides via selective catalytic reduction
Implementation Method 4
an ammonia blocking catalyst is added to prevent ammonia emissions
Data Source
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AI summary
The invention relates to an exhaust aftertreatment system (20) for an internal combustion engine (10), comprising an exhaust system (22) with an exhaust channel (24) in which, in the direction of flow of exhaust gas from the internal combustion engine (10), a first SCR catalyst (34, 36) located close to the engine and a second SCR catalyst (38) located downstream of the first SCR catalyst (34, 36) are arranged. A first metering element (64) for metering a reducing agent into the exhaust channel (24) is provided upstream of the first SCR catalyst (34, 36). A second metering element (66) for metering a reducing agent is arranged downstream of the first SCR catalyst (34, 36) and upstream of the second SCR catalyst (38).It is provided that means for reducing the exhaust gas temperature (50, 52, 80, 82) are provided downstream of the first SCR catalyst (34, 36) and upstream of the second SCR catalyst (38), with which the exhaust gas temperature of the internal combustion engine (10) can be reduced before entering the second SCR catalyst (38). The invention further relates to a method for exhaust gas aftertreatment of an internal combustion engine (10) with such an exhaust gas aftertreatment system (20).