Segmented Exhaust SCR System for Low-Temperature NOx Reduction
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Solution Overview
Problem
Internal combustion engines, particularly those in large ships, face challenges in reducing nitrogen oxide emissions at low loads and require flexible and efficient NOx reduction across varying engine loads, as existing SCR reactors are inflexible and ineffective at low temperatures, leading to issues like ABS deposition and reduced power output.
Innovation Solution
A separation device that divides exhaust gas into two streams, directing the hotter combustion gas-rich stream through a smaller first SCR reactor and the cooler scavenging air-rich stream through a second SCR reactor, with controllable valves and a control unit to adjust based on temperature and load conditions, allowing for efficient NOx reduction and preventing ABS formation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a single SCR reactor is used for high nitrogen reduction at high loads, then NOx reduction efficiency is improved, but the reactor becomes ineffective and causes ABS deposition at low loads due to low temperatures
Solution Approach 1:
The exhaust gas flow is divided into two separate streams that can be independently directed to different SCR reactors based on engine load conditions. The first stream goes to a first SCR reactor optimized for high load operation, while the second stream goes to a second SCR reactor optimized for low load operation, allowing each reactor to operate in its optimal temperature range
Solution Approach 2:
The system dynamically adjusts the distribution of exhaust gas between the two SCR reactors based on real-time engine load conditions. At high loads, the majority of exhaust gas is directed to the first SCR reactor, while at low loads, the exhaust gas is redirected to the second SCR reactor, providing adaptive response to changing operating conditions
2Reliability
If a large SCR reactor is used to handle full exhaust gas flow, then NOx reduction capacity is improved, but device complexity and cost increase
Solution Approach 1:
Instead of using one large SCR reactor to handle the entire exhaust gas flow, the system segments the exhaust gas flow and uses two smaller SCR reactors that can be independently controlled. This reduces the size and complexity of each individual reactor while maintaining or improving overall NOx reduction capacity through optimized operation at different load conditions
Solution Approach 2:
Each SCR reactor handles only a portion of the total exhaust gas flow at any given time, rather than requiring one reactor to process the full flow continuously. This partial action approach allows for smaller, less complex reactor designs that are easier to integrate and maintain
3Object-generated harmful factors
If exhaust gas is recirculated to reduce nitrogen oxides, then NOx emissions are reduced, but engine power output decreases due to lower power from one cylinder
Solution Approach 1:
The exhaust gas recirculation is segmented by cylinder, with only specific cylinders directing their exhaust gas through the SCR reactor while other cylinders maintain normal operation. This allows NOx reduction in the recirculated stream without significantly impacting overall engine power output, as the non-recirculating cylinders continue to operate at full capacity
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 NOx reduction at both low and high engine loads, reduces the size and cost of SCR reactors, and prevents ABS deposition, achieving flexible and efficient nitrogen oxide reduction while maintaining engine performance.
Implementation Method 1
a first part of the exhaust gas is directed to a first selective catalytic reduction (SCR) reactor (10)
Implementation Method 2
a second part of the exhaust gas is directed to a second selective catalytic reduction (SCR) reactor (12)
Data Source
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AI summary
The invention relates to an internal combustion engine (1). The internal combustion engine comprises at least two cylinders (2). Each of the two cylinders comprises a combustion chamber (3) and has an inlet for a fuel and an outlet (5) for an exhaust gas with an outlet valve (6). The engine comprises at least one separation device (7) downstream of the combustion chambers (3) for separating the exhaust gas of all combustion chambers (3) into a first and a second exhaust gas stream. A first (8) and a second exhaust line (9) are connected to the at least one separation device (7). The at least one separation device (7) is configured to separate the exhaust gas from the combustion chambers (3) into a first gas stream for the first component exhaust line (8) and a second gas stream for the second component exhaust line (9). A first selective catalytic reduction (SCR) reactor (10) is arranged in the first component exhaust line (8) downstream of the separation device (7). The second component exhaust line (9) and the first component exhaust line (9) are separate from each other at least until the first SCR reactor (10). The first SCR reactor (10) has a maximum capacity of 80% or less of a full load outflow rate of the at least two cylinders (2).