SCR Mixing Device with Radial Elevations for Cold Start Evaporation
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Solution Overview
Problem
Existing mixing devices for introducing liquid additives into gas streams, such as in SCR processes, face challenges with incomplete evaporation and uneven distribution due to thermodynamic conflicts between heat input and deposit formation, leading to reduced efficiency and increased counterpressure, especially during cold starts.
Innovation Solution
A mixing device with a gas guide section featuring radially projecting elevations in the heating section to enhance evaporation and mixing, combined with active heating and a metering system, which influences the gas flow to prevent deposit formation and ensure efficient additive distribution.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If high heat input is provided to rapidly evaporate the reducing agent and mix it with exhaust gas, then evaporation efficiency is improved, but local deposit formation increases due to excessive water evaporation and vaporization
Solution Approach 1:
The mixing device is divided into distinct functional sections: a first mixing section for initial additive injection and a second mixing section for final mixing. This segmentation allows controlled heat input in the first section to promote evaporation without excessive local heating, while the second section completes mixing with more moderate thermal conditions, preventing deposit formation.
Solution Approach 2:
Different thermal conditions are applied to different spatial zones within the mixing device. The first mixing section receives higher heat input to ensure rapid evaporation of the reducing agent, while the second mixing section operates at lower temperatures to complete mixing without causing local overheating and deposit formation. This local differentiation of thermal quality resolves the contradiction between evaporation efficiency and deposit prevention.
2Quantity of substance
If the mass of sprayed additive is increased to improve conversion, then more ammonia is available for NOx conversion, but the number of edges increases leading to increased deposits and backpressure
Solution Approach 1:
The additive injection process is segmented into two stages: initial injection into the first mixing section followed by secondary mixing in the second section. This segmentation allows the additive mass to be distributed more uniformly throughout the exhaust stream, preventing local concentration peaks that would otherwise lead to excessive edge formation and deposits.
Solution Approach 2:
The first mixing section acts as an intermediary zone where the reducing agent is partially evaporated and pre-mixed with exhaust gas before entering the second mixing section. This intermediate processing step ensures that when the full additive mass is introduced, it is distributed more evenly, reducing local edge formation and subsequent deposit accumulation.
3Use of energy by stationary object
If passive heating by hot exhaust gas is used to heat the mixing device, then no additional energy input is required, but during cold starts the surface temperatures are too low to achieve satisfactory additive conversion
Solution Approach 1:
Heating elements are installed in the mixing device to provide preliminary active heating, especially during cold start conditions. This preliminary action raises the surface temperatures of the mixing sections to levels sufficient for effective additive evaporation and conversion, overcoming the limitation of passive exhaust gas heating during transient cold conditions.
Solution Approach 2:
The heating elements are controlled to operate based on the thermal state of the exhaust gas and mixing device surfaces. During normal operation when exhaust gas temperature is sufficient, the heating elements remain inactive and the system relies on passive heating. During cold starts or transient conditions, the heating elements activate to supplement thermal input, allowing the system to serve itself across the full range of operating 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 configuration significantly improves the evaporation and mixing of additives, adheres to deposit limit dosage rates, and reduces counterpressure, enhancing the overall efficiency of the SCR process while preventing component damage from corrosion.
Implementation Method 1
a heating device for actively heating at least one heating section of the gas guide section
Implementation Method 2
the gas guide section has at least one elevation in the heating section that projects radially into the gas flow to influence the flow of the gas flow
Implementation Method 3
a metering device for introducing the additive into a metering area of the gas guide section
Implementation Method 4
Through thermolysis and hydrolysis, ammonia and CO2 are formed from the urea solution
Implementation Method 5
Through thermolysis and hydrolysis, ammonia and CO2 are formed from the urea solution
Implementation Method 6
The ammonia thus produced can react in a suitable catalyst with the nitrogen oxides contained in the exhaust gas, thus efficiently removing them from the exhaust gas
Data Source
Figure 1~2
Figure 3~5
Figure 6
AI summary
The present invention relates to a mixing device for introducing and distributing a liquid additive into a gas stream (G), particularly for an exhaust system of an internal combustion engine. The mixing device comprises a gas guide section (12) for guiding the gas stream (G) and a metering device (14) for introducing the additive into a metering area of the gas guide section (12). Furthermore, a heating device (18) is provided for actively heating at least one heating section (16) of the gas guide section (12). The heating section (16) is arranged in the metering area and/or downstream of the metering area. The gas guide section (1) has at least one radially projecting elevation (24) in the heating section (16) to influence the flow of the gas stream (G) and thus to condition the additive.