SCR Urea Injection Control for Crystallization Prevention
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Solution Overview
Problem
The existing SCR systems face challenges in controlling the large amount of aqueous urea solution injection, leading to urea crystallization in the engine exhaust pipeline and SCR reactor, especially within the normal operation exhaust temperature range of 200°C - 300°C, which affects the efficiency and emissions.
Innovation Solution
A method and device that use an ammonia loading amount model and an SCR efficiency model to calculate precise urea injection amounts, combining these with a urea injection amount limit value to prevent crystallization, involving sensors for real-time data and models for optimizing urea injection based on catalyst temperature, exhaust gas flow rate, and nitrogen-oxygen compound concentrations.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If the urea injection amount is increased to treat more NOx, then the NOx reduction efficiency is improved, but the urea crystallization occurs in the exhaust pipeline and SCR reactor
Solution Approach 1:
The patent implements dynamic control of urea injection amount based on real-time exhaust gas temperature, flow rate, and SCR reactor ammonia loading amount. The control system continuously adjusts the injection rate to match actual reduction needs, preventing excessive injection that would cause crystallization while maintaining sufficient injection for effective NOx reduction.
Solution Approach 2:
The system uses feedback from ammonia loading amount calculations and temperature sensors to adjust urea injection in real-time. By monitoring the ammonia loading amount in the SCR reactor and exhaust gas temperature, the control system optimizes injection amount to prevent crystallization while maintaining reduction efficiency.
2Quantity of substance
If the urea injection amount is large, then more ammonia is produced for NOx reduction, but the spray accumulates as liquid film on exhaust pipe wall surface
Solution Approach 1:
The patent changes the injection parameters (amount, timing, distribution) of urea based on real-time measurements of exhaust gas temperature, flow rate, and ammonia loading amount. By optimizing these parameters, the system ensures sufficient ammonia production for NOx reduction while preventing liquid film accumulation on pipe walls.
3Reliability
If the urea injection amount is precisely controlled to prevent crystallization, then the SCR system reliability is improved, but the control system complexity increases
Solution Approach 1:
The system performs preliminary calculations of ammonia loading amount in the SCR reactor before adjusting urea injection. By predicting the ammonia loading state based on current injection rate and reactor conditions, the control system proactively prevents crystallization before it occurs, improving reliability without requiring overly complex real-time control mechanisms.
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 allows for precise control of urea injection, preventing urea crystallization and optimizing SCR system performance, thereby enhancing engine efficiency and reducing emissions.
Implementation Method 1
the urea undergoes hydrolysis and pyrolysis reactions at a high temperature to produce NH3
Implementation Method 2
the urea undergoes hydrolysis and pyrolysis reactions at a high temperature to produce NH3
Implementation Method 3
NH3, which is used to reduce NOx on a surface of the catalyst of the SCR system
Implementation Method 4
injection, atomization and evaporation of the aqueous urea solution, hydrolysis and pyrolysis gas-phase chemical reactions of urea
Data Source
Figure 1~2
Figure 3~4
Figure 5~7
AI summary
The present application provides a method for controlling an injection amount of an SCR urea injection system in an engine, the method comprising: using an ammonia loading amount model to calculate a current ammonia loading amount in an SCR reactor on the basis of an injected aqueous urea solution amount and a consumed ammonia amount; obtaining a first urea injection amount on the basis of a target ammonia loading amount and the current ammonia loading amount; using an SCR efficiency model to calculate a second urea injection amount on the basis of a catalyst temperature, an exhaust gas mass flow rate and an aging coefficient in the SCR reactor, a nitrogen-oxygen compound concentration upstream of the SCR reactor, and the current ammonia loading amount; combining the first and second urea injection amounts to obtain a combined urea injection amount; and obtaining a target urea injection amount injected to the SCR reactor on the basis of the combined urea injection amount and a urea injection amount limit value. Using the method described above, the amount of urea injected into the SCR reactor can be precisely controlled, thereby preventing the occurrence of urea crystallization in an engine exhaust pipeline and the SCR reactor.