SCR Catalysed Filter for Simultaneous NOx Reduction and Particle Oxidation
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Solution Overview
Problem
Current exhaust gas depollution systems for internal-combustion engines, particularly Diesel engines, face limitations in NOx reduction efficiency due to oxygen-rich conditions, separate functionality of particle filtration and NOx catalytic reduction, and temperature-related catalytic phase deterioration, especially when the exhaust gas temperature is not consistently high.
Innovation Solution
A product and method combining a reductant containing ammonia or ammonia-generating compounds with a catalytic additive for particle oxidation, which includes metallic compounds like ferrocene, injected into the exhaust line based on temperature thresholds and NOx levels, allowing simultaneous NOx reduction and particle filtration in a single element, such as an SCR catalysed filter, to optimize treatment efficiency.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If separate particle filter and SCR catalyst systems are used, then particle filtration and NOx reduction can be performed with dedicated components, but device complexity increases and treatment efficiency decreases in oxygen-rich conditions
Solution Approach 1:
The patent combines the particle filter and SCR catalyst into a single integrated component called an SCR catalysed filter. This merging allows both particle filtration and NOx reduction functions to be performed simultaneously in one element, reducing system complexity while maintaining treatment efficiency through synergistic catalytic actions.
Solution Approach 2:
The integrated SCR catalysed filter performs multiple functions: filtering particles, reducing NOx, and catalyzing regeneration. The catalytic phase within the filter structure provides universal activity for both oxidation reactions (particle combustion and CO oxidation) and SCR reactions (NOx reduction), enabling one component to handle multiple depollution tasks.
2Productivity
If high exhaust gas temperature is maintained for particle filter regeneration, then particle combustion efficiency improves, but catalytic phase deterioration accelerates
Solution Approach 1:
The patent introduces a temperature threshold parameter (e.g., 200°C) that controls when regeneration injection occurs. By monitoring exhaust gas temperature and only initiating regeneration when the threshold is reached, the system ensures sufficient heat for particle combustion while avoiding excessive temperature exposure that would damage the catalytic phase, thus balancing regeneration efficiency with catalyst durability.
Solution Approach 2:
The system continuously monitors exhaust gas temperature and uses this feedback to control the timing of regeneration additive injection. This closed-loop control ensures regeneration only occurs under appropriate thermal conditions, preventing catalytic deterioration from premature or excessive temperature exposure while maintaining effective particle removal when conditions are favorable.
3Reliability
If regeneration additive is injected continuously, then particle filter regeneration is maintained, but loss of substance increases due to waste during non-regeneration periods
Solution Approach 1:
The system performs regeneration injection periodically rather than continuously, activating it only when particle loading reaches levels requiring regeneration (indicated by temperature threshold and pressure differential sensors). This periodic operation maintains filtration capacity when needed while avoiding unnecessary additive consumption during periods when the filter does not require regeneration.
Solution Approach 2:
The system uses the engine's own exhaust heat and flow characteristics to determine when regeneration is needed, rather than relying on external timing signals. By monitoring its own operational state (temperature, pressure differential), the system self-regulates regeneration timing, ensuring additive is consumed only when the filter genuinely needs regeneration, thus minimizing waste.
4Reliability
If SCR catalyst is placed upstream of particle filter, then NOx reduction occurs before particle combustion, but ammonia slip increases and treatment efficiency decreases in oxygen-rich conditions
Solution Approach 1:
The patent merges the SCR catalyst with the particle filter into an integrated SCR catalysed filter where both functions occur in close proximity. This spatial merging allows the catalytic phase to facilitate both SCR reactions and oxidation reactions simultaneously, enabling NOx reduction while the oxygen-rich environment and hot gases promote complete oxidation of any ammonia formed, thereby minimizing ammonia slip.
Solution Approach 2:
The system utilizes the oxygen-rich exhaust environment and elevated temperatures within the integrated filter to promote strong oxidation conditions. These conditions accelerate the oxidation of ammonia (if formed during SCR) to nitrogen and water, effectively converting potential ammonia slip into harmless products and improving overall NOx removal efficiency in lean burn conditions.
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 effective and efficient NOx reduction and particle filtration across varying engine conditions, reducing the risk of catalytic phase deterioration and improving system performance in oxygen-rich environments by controlling the injection timing and flow rate of the additive-reductant mixture.
Implementation Method 1
catalysts of SCR (Selective Catalytic Reduction) type. This SCR catalyst allows to selectively reduce the NOx to nitrogen through the action of a reductant.
Implementation Method 2
additive for catalysing particle oxidation
Implementation Method 3
each urea molecule decomposes in two stages into two ammonia molecules: (NH2)2CO (urea)→NH3 (ammonia)+HNCO (isocyanic acid)
Implementation Method 4
The water contained in this solution is rapidly vaporized under the effect of the exhaust gas temperature
Data Source
AI summary
A product for depollution of exhaust gas includes a mixture of an additive for treating particles and a reductant for eliminating nitrogen oxides (NOx). The reductant can contain ammonia or a compound generating ammonia by decomposition, or a hydrocarbon from a hydrocarbon-containing substance, oxygenated or not. The addictive for treating particles can be an additive for catalyzing particle oxidation.