Exhaust Gas Purifier Backflow Prevention
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Solution Overview
Problem
Existing exhaust gas purifiers with a casing configuration that forms both catalyst and bypass passages are prone to backflow, which can degrade the SCR catalyst due to the recirculation of exhaust gases, particularly in configurations where the main and bypass passages are joined at an exhaust downstream side.
Innovation Solution
Incorporating a dual backflow prevention system within the casing, including a first and second backflow prevention section, along with a reducing agent injector that uses compressed air to prevent or reduce backflow by generating a flow that counters exhaust gas recirculation, and optimizing the opening ratios in the casing walls to minimize backflow along the catalyst outer wall portion.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If a casing is used to form both catalyst passage and bypass passage, then device integration is improved, but backflow of exhaust gas occurs causing catalyst degradation
Solution Approach 1:
The internal space of the casing is segmented into distinct catalyst passage and bypass passage regions using partition walls and backflow prevention sections. This segmentation prevents exhaust gas from the bypass passage from flowing back into the catalyst passage, thereby protecting the SCR catalyst while maintaining the integrated casing structure.
Solution Approach 2:
Backflow prevention sections act as intermediary elements positioned at the junction between the catalyst passage and bypass passage. These sections selectively allow forward flow of exhaust gas while blocking backward flow, serving as a mediator that prevents harmful backflow into the catalyst passage without compromising the integrated design.
2Adaptability or versatility
If bypass passage is added to switch flow between catalyst and bypass, then operational flexibility is improved, but backflow risk increases
Solution Approach 1:
The backflow prevention sections are strategically positioned at specific locations where backflow is most likely to occur, such as at the junction between catalyst passage and bypass passage. This localized approach provides targeted backflow prevention exactly where needed, maintaining reliability without compromising the operational flexibility provided by the bypass passage.
3Reliability
If opening ratio in catalyst outer wall portion is reduced, then backflow prevention is improved, but exhaust gas flow resistance increases
Solution Approach 1:
The opening ratio of the catalyst outer wall portion is optimized to a specific parameter range that balances backflow prevention with exhaust gas flow resistance. By carefully controlling this geometric parameter, the design achieves effective backflow prevention while minimizing energy loss from increased flow resistance.
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
Effectively prevents or reduces backflow into the catalyst passage, thereby protecting the SCR catalyst from degradation and maintaining its effectiveness in reducing NOx emissions.
Implementation Method 1
NOx included in an exhaust gas is reduced by contact with the SCR catalyst to be changed into nitrogen and water
Implementation Method 2
a backflow prevention section that prevents or reduces a backflow of an exhaust gas from the second exhaust passage to the catalyst passage
Implementation Method 3
a reducing agent injector that uses compressed air to prevent or reduce backflow by generating a flow that counters exhaust gas recirculation
Data Source
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AI summary
An exhaust gas purifier (100) includes a casing (10), SCR catalysts (first SCR catalyst (25) and second SCR catalyst (26)), a first backflow prevention plate (31), and a second backflow prevention plate (32). In the casing (10), at least a part of the catalyst passage (52) and at least a part of the bypass passage (53) are formed. The SCR catalysts are disposed in the catalyst passage (52) and selectively reduce NOx included in an exhaust gas flowing in the catalyst passage (52). The first backflow prevention plate (31) prevents or reduces a backflow of an exhaust gas from a second exhaust passage (54) to the catalyst passage (52).