Exhaust Bypass Mechanism for SCR Crystallization Prevention
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Solution Overview
Problem
The existing UREA-SCR system faces challenges in achieving a high NOx reduction rate, particularly at engine startup, due to temperature delays and crystallization phenomena in the SCR system, leading to reduced NOx conversion efficiency.
Innovation Solution
A post-processing system with a bypass mechanism that controls the flow of exhaust gas by using multiple switches and bypass pipes to direct high-temperature exhaust gas directly to the SCR, bypassing the DOC and DPF, and includes an ammonia oxidation catalyst to optimize NOx reduction, preventing crystallization by adjusting urea injection based on engine and temperature conditions.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-affected harmful factors
If exhaust gas flows through DOC and DPF before SCR, then soot and smoke are reduced, but temperature delay occurs and crystallization phenomenon happens at engine startup
Solution Approach 1:
The exhaust gas flow path is segmented into multiple routes: a main path through DOC-DPF-SCR for normal operation, and a bypass path through the first bypass pipe for engine startup. The first switch controls the selection between these paths, allowing the system to segment the flow based on operational conditions to prevent crystallization while maintaining soot reduction.
Solution Approach 2:
The system dynamically adjusts the exhaust gas flow path based on engine operating conditions. The first switch opens or closes to direct exhaust gas either through the bypass pipe to the SCR front end or through the conventional DOC-DPF path. This dynamic control prevents crystallization at startup while maintaining effective soot and smoke reduction during normal operation.
2Object-affected harmful factors
If exhaust gas is cooled while moving through DOC and DPF, then harmful materials are reduced, but time delay occurs when reaching SCR operating temperature
Solution Approach 1:
At engine startup, the system takes preliminary action by directing exhaust gas through the first bypass pipe directly to the SCR front end, bypassing the DOC and DPF. This preliminary routing ensures that the SCR receives hot exhaust gas immediately, preventing time delay in reaching operating temperature while still allowing soot and smoke reduction through the DOC and DPF during normal operation.
Solution Approach 2:
The system dynamically switches the exhaust gas flow path based on temperature requirements. The first switch controls the routing to either the bypass pipe for rapid heating or the conventional path for comprehensive filtration. This dynamic adjustment eliminates time delay when the SCR needs to reach operating temperature quickly.
3Productivity
If urea is injected at low temperature, then NOx reduction can occur, but crystallization phenomenon occurs in the pipe
Solution Approach 1:
Before urea injection at low temperature, the system takes preliminary action by directing exhaust gas through the first bypass pipe to the SCR front end, ensuring the exhaust gas temperature is sufficiently high to prevent crystallization. This preliminary routing action protects the system from crystallization while enabling NOx reduction.
Solution Approach 2:
The first bypass pipe acts as an intermediary pathway that mediates between the cold exhaust gas source and the SCR component. By routing exhaust gas through this intermediary bypass, the system prevents direct contact between cold exhaust gas and the SCR, thereby preventing crystallization while still enabling effective NOx reduction.
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 enhances NOx reduction rates and prevents crystallization in the piping system, ensuring effective NOx conversion even at engine startup, thereby improving the overall efficiency of the UREA-SCR system.
Implementation Method 1
bypassing high-temperature exhaust gas to a front end of an SCR
Implementation Method 2
converting NOx into N2 (nitrogen) and O2 (oxygen)
Implementation Method 3
UREA-SCR (selective catalytic reduction) system
Implementation Method 4
DOC (diesel oxidation catalyst)
Implementation Method 5
DPF (diesel particulate filter)
Implementation Method 6
NH2-CO-NH2, which is obtained by thermally decomposing urea using high-temperature exhaust gas
Implementation Method 7
AOC which oxidizes ammonia in the exhaust gas passing through the SCR
Data Source
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AI summary
A post-processing system apparatus and a control method according to the present disclosure include: an exhaust pipe which has one end that is connected with an engine so as to allow exhaust gas to flow thereinto, and the other end that is opened to discharge the exhaust gas; a DOC which primarily reduces soot and smoke in the exhaust gas flowing into the exhaust pipe; a DPF which secondarily reduces soot and smoke in the exhaust gas passing through the DOC; an SCR which reduces NOx (nitrogen oxide) in the exhaust gas passing through the DPF; an AOC which oxidizes ammonia in the exhaust gas passing through the SCR and reduces NOx (nitrogen oxide); a first bypass pipe which branches off from the exhaust pipe between the engine and the DOC and bypasses the entirety or a part of the exhaust gas to a front end of the SCR; and a first switch which is provide at a point where the first bypass pipe branches off from the exhaust pipe in order to control an amount of exhaust gas that is bypassed to the first bypass pipe.