Angled Catalytic Device for Urea to Ammonia Conversion
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Solution Overview
Problem
Mobile SCR systems face challenges in efficiently injecting and decomposing urea solutions into exhaust streams due to size constraints and high gas flow velocities, leading to incomplete ammonia generation and fouling issues when ammonia is introduced without pre-heating the SCR catalyst.
Innovation Solution
The upstream face of the catalytic device is positioned at an angle of 20-70 degrees relative to the axial flow path, and the injector is angled at 90 ±15 degrees relative to the catalytic device, optimizing the injection and conversion of urea to ammonia within the SCR system, ensuring effective distribution and pre-heating for efficient NOx reduction.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Volume of moving object
If the SCR system is made compact for mobile applications, then the system size is reduced, but the urea solution cannot be completely decomposed and hydrolyzed to ammonia prior to reaching the SCR catalyst
Solution Approach 1:
The patent combines the pyrolysis catalyst and hydrolysis catalyst into a single integrated catalytic device structure. The pyrolysis catalyst layer and hydrolysis catalyst layer are positioned adjacent to each other within the same device, allowing urea to undergo both decomposition and hydrolysis reactions in one compact unit as exhaust gas passes through, thereby achieving complete ammonia generation without requiring separate devices or extended space.
Solution Approach 2:
The catalytic device is positioned upstream of the SCR catalyst to perform preliminary conversion of urea to ammonia before the exhaust reaches the SCR catalyst. This preliminary action ensures that ammonia is already present and uniformly distributed when it contacts the SCR catalyst, eliminating the need for post-injection ammonia generation and preventing ammonia slip and air fouling issues.
2Ease of operation
If ammonia is introduced directly into the exhaust stream without pre-heating the SCR catalyst, then the system operation is simplified, but the ammonia will pass through the SCR catalyst and foul the air
Solution Approach 1:
The catalytic device performs preliminary conversion of urea to ammonia upstream of the SCR catalyst, ensuring that ammonia is generated and uniformly distributed in the exhaust stream before contacting the SCR catalyst. This preliminary ammonia generation eliminates the need for separate ammonia injection systems and pre-heating requirements, as the in-situ generated ammonia is immediately available for SCR reactions without causing air fouling.
3Productivity
If the injector is positioned to optimize urea injection, then the injection efficiency is improved, but the uniform distribution of ammonia across the flow front is compromised
Solution Approach 1:
The patent integrates both pyrolysis and hydrolysis catalyst layers within a single catalytic device structure positioned downstream of the injector. This merged structure ensures that urea is completely converted to ammonia in one location, and the catalytic device's geometry and positioning promote uniform distribution of the generated ammonia across the exhaust flow front before it reaches the SCR catalyst, simultaneously achieving injection efficiency and distribution uniformity.
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 efficiency of urea injection and conversion to ammonia, improving the uniform distribution and reaction efficiency across the SCR catalyst, even at low diesel engine exhaust temperatures and high gas flow velocities, reducing fouling risks and enhancing overall NOx reduction performance.
Implementation Method 1
The catalytic device has an upstream face that is positioned at an angle of about 20-70 degrees relative to the axial flow path... The catalytic device is configured to receive the urea solution from the injector at the upstream face
Implementation Method 2
an injector configured to inject a urea solution into the exhaust flowing along the axial flow path
Implementation Method 3
Selective catalytic reduction (SCR) of nitrogen oxides (NOx) using a reducing agent... NOx reacts with ammonia and is catalytically reduced by a SCR to nitrogen gas (N2) with water as a by-product
Implementation Method 4
urea, which decomposes in heat (i.e., pyrolyzes) to isocyanic acid and ammonia
Implementation Method 5
In water, isocyanic acid then hydrolyzes to create ammonia and carbon dioxide
Data Source
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AI summary
Disclosed are apparatuses, systems, and methods for treating exhaust. The disclosed apparatus and systems typically include a catalytic device for converting aqueous urea to ammonia. The catalytic device may include a pyrolysis catalyst and a hydrolysis catalyst for converting aqueous urea to ammonia. The catalytic device typically includes an upstream face that is positioned at an angle relative to exhaust flow when the device is positioned in a selective catalytic reduction (SCR) system.