Splitting Wall for Axial SCR Dosing Module Evaporation
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Solution Overview
Problem
The evaporation of liquid UREA in axially symmetric dosing modules for SCR systems is inefficient at low exhaust gas temperatures and velocities, leading to reduced evaporation and increased risk of solid deposits and incorrect NH3 dosing due to inadequate heat transfer and energy exchange.
Innovation Solution
The exhaust gas stream is split into two streams, with the inner stream being accelerated and axial, and the outer stream swirled around the development axis, enhancing mixing and evaporation by creating a radial distribution of the spray and increasing gas velocity for improved heat transfer.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Temperature
If the exhaust gas temperature is low, then the available energy for evaporation is reduced, but the evaporation process becomes even less efficient due to reduced temperature difference
Solution Approach 1:
The exhaust gas flow is divided into two separate flows: an inner flow that is accelerated axially and an outer flow that is swirled. This segmentation allows the inner flow to provide high-velocity axial movement for efficient evaporation while the outer flow creates radial distribution through centrifugal force, resolving the contradiction between low temperature and evaporation efficiency
Solution Approach 2:
The patent changes the velocity parameters of the exhaust gas by accelerating the inner flow and creating swirl in the outer flow. This parameter change increases the kinetic energy available for evaporation and heat transfer, compensating for the low thermal energy available at low exhaust gas temperatures
2Speed
If the mean gas velocity is low, then the available energy for evaporation is reduced, but the heat transfer efficiency is further reduced
Solution Approach 1:
The gas flow is segmented into inner and outer streams with different velocity characteristics. The inner stream is accelerated to high velocity to improve heat transfer efficiency, while the outer stream provides radial distribution. This resolves the contradiction between low gas velocity and heat transfer efficiency
Solution Approach 2:
The patent introduces dynamic elements by creating a swirled outer flow that rotates around the central axis. This dynamic motion enhances mixing and heat transfer through centrifugal effects, compensating for the low mean gas velocity
3Quantity of substance
If the spray mass flux is high, then the cooling effect on wall surfaces is increased, but the risk of solid deposits increases
Solution Approach 1:
The spray is subjected to radial distribution through the swirled outer gas flow, which spreads the liquid droplets over a larger area. This reduces the local spray mass flux and cooling effect on wall surfaces while maintaining overall evaporation efficiency, preventing solid deposit formation
Solution Approach 2:
The patent introduces radial motion through swirl, adding a rotational dimension to the primarily axial spray flow. This radial outwards deflection distributes the spray over a larger circumferential area, reducing the concentration of liquid on any single wall surface and minimizing deposit risk
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 solution improves UREA evaporation at low gas velocities while minimizing backpressure at high velocities, reducing the risk of deposits and ensuring accurate NH3 dosing by optimizing the gas flow and spray distribution within the dosing module.
Implementation Method 1
the inner predominantly axial gas stream avoids deposits near the point of injection of the urea based solution spray
Implementation Method 2
enhanced evaporation of the liquid droplets passing through the shear region at the interface between the axial and swirled gas streams
Implementation Method 3
the outer annular swirl is providing a radial outwards deflection of the spray by centrifugal force resulting in an increased area of distribution of the spray
Implementation Method 4
the cooling effect of the spray to the pipe walls is also reduced because of the increased gas velocity and convection heat transfer created by the outer annular swirl on the outer wall of the pipe
Implementation Method 5
The evaporation of the liquid (water) and the decomposition (thermolysis and hydrolysis) of the UREA requires some energy
Implementation Method 6
The splitting wall comprises winding walls, for inducing a swirl on the outer gas stream
Data Source
Figure 1~2
Figure 3
Figure 4
AI summary
Device for improving the purifying liquid evaporation in an axially symmetric dosing module for an SCR device, the dosing module (DM) being able to dose a urea-based reducing agent into a gas exhaust stream generated by a combustion engine, the dosing module (DM) comprising an housing (20) developing symmetrically along a development axis (X); dosage means (55) for dosing the urea-based reducing agent, arranged along said development axis (X); an inlet opening (9) for conveying the gas exhaust stream into the dosing housing (20), arranged annularly with respect to the dosage means (55); wherein the device comprises a splitting wall (1), arranged within the inlet opening (9) for defining at least two separate annular gas stream paths (F1, F2), one (F1) annular and coaxial with respect to another (F2), one (F2) of them shaped for inducing a different axial speed into a respective gas stream with respect to another.