SCR Filter with Downstream Catalyst for NOx Conversion
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Solution Overview
Problem
Current diesel engine exhaust treatment systems face challenges in managing backpressure and maintaining catalytic activity over a wide temperature range, particularly in reducing NOx emissions effectively while avoiding excessive catalyst loading, which can lead to increased fuel inefficiency and reduced catalytic durability.
Innovation Solution
A method involving a particulate filter with a first SCR catalyst and a downstream flow-through substrate with a second SCR catalyst, both with specific zeolite compositions, to achieve targeted NOx conversion and controlled backpressure within an operational window, utilizing a honeycomb wall flow filter with optimized porosity and catalyst loading to balance NOx reduction and particulate removal.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If higher catalyst loadings are used on the wall flow filter to achieve NOx reduction goals, then NOx conversion efficiency is improved, but back pressure increases which adversely impacts fuel efficiency
Solution Approach 1:
The invention divides the NOx reduction function into two separate components: a wall flow filter with a first SCR catalyst for particulate removal and some NOx conversion, and a downstream flow-through substrate with a second SCR catalyst for additional NOx conversion. This segmentation allows each component to have optimized catalyst loading without excessive back pressure, as the flow-through substrate creates minimal flow resistance compared to a heavily loaded wall flow filter.
Solution Approach 2:
The wall flow filter acts as an intermediary component between the engine and the downstream SCR catalyst. It performs dual functions of particulate matter filtration and initial NOx conversion, preparing the exhaust stream for the second SCR catalyst which then completes the NOx reduction process with minimal additional back pressure.
2Reliability
If the exhaust gas stream is cooled to condense volatile organic fraction for removal, then particulate matter removal is improved, but the temperature may drop below the threshold for effective SCR catalyst operation
Solution Approach 1:
The wall flow filter with the first SCR catalyst performs preliminary NOx conversion before the exhaust gas undergoes cooling for particulate matter removal. This ensures that some NOx reduction occurs at higher temperatures where the catalyst is more effective, while the subsequent cooling phase can proceed to condense volatile organics without worrying about dropping below the SCR operating threshold, since the second SCR catalyst on the downstream substrate is positioned to receive the cooled exhaust.
3Volume of moving object
If a single heavily loaded SCR catalyst is used on the wall flow filter, then space utilization is improved, but catalytic durability and resistance to poisoning decrease
Solution Approach 1:
The invention segments the SCR catalyst function across two separate substrates: the wall flow filter and the downstream flow-through substrate. This segmentation allows each catalyst to have moderate, optimized loadings rather than one heavily loaded catalyst, improving resistance to poisoning and thermal degradation while maintaining compact space utilization through the integrated design.
Solution Approach 2:
The invention changes the operational parameters of the SCR system by distributing the catalyst loading across two components with different flow resistance characteristics. The wall flow filter handles higher temperature conditions with its catalyst, while the downstream flow-through substrate handles lower temperature conditions, optimizing catalytic durability across the entire temperature range.
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 enables efficient NOx conversion across a range of temperatures, maintains low backpressure, and ensures high hydrothermal stability, achieving over 50% NOx conversion with minimal backpressure increase, thus optimizing space utilization and meeting regulatory emission targets.
Implementation Method 1
Ammonia selective catalytic reduction (SCR) is a NOx abatement technology... In the ammonia SCR process, NOx (defined as the sum of NO + NO2) is reacted with ammonia (or an ammonia precursor such as urea) to form dinitrogen (N2) over a catalyst typically composed of base metals.
Implementation Method 2
passing the gas stream having the intermediate NOx concentration through a second substrate loaded with a second SCR catalyst disposed downstream of the particulate filter effective for NOx conversion
Implementation Method 3
There are many known filter structures that are effective in removing particulate matter from diesel exhaust, such as honeycomb wall flow filters... The filter is a physical structure for removing particles from exhaust
Data Source
Figure 1A~1B
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AI summary
Emissions treatment systems and methods for treating an engine exhaust gas stream containing NOx and particulate matter are disclosed including a particulate filter comprising a first SCR catalyst for NOx conversion a second SCR catalyst for NOx conversion on a substrate disposed downstream of the particulate filter. The system NOx conversion and the system back pressure increase lie within a targeted operational window.