Urea Spray Pipe Hydrolysis Catalyst to Prevent Exhaust Clogging
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
The thermal decomposition of urea into high-melting-point substances like cyanuric acid and melamine leads to pipe clogging in exhaust systems, reducing NOx reduction efficiency and causing operational issues in diesel engines.
Innovation Solution
A device with a urea-solution supply pipe, spray nozzle, and a hydrolysis catalyst layer on the inner pipe wall, using TiO2 to promote hydrolysis of isocyanic and cyanic acids, converting them into ammonia and carbon dioxide, thereby reducing cyanuric acid formation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Quantity of substance
If urea is thermally decomposed by exhaust gas heat to produce ammonia, then ammonia supply for NOx reduction is improved, but high-melting-point substances (cyanuric acid, melamine) are formed causing pipe clogging and reduced decomposition efficiency
Solution Approach 1:
The invention changes the chemical reaction pathway by introducing a hydrolysis catalyst that alters the temperature and reaction conditions. Instead of direct thermal decomposition at high temperatures, urea undergoes hydrolysis at lower temperatures (100-200°C) to produce ammonia, avoiding the formation of high-melting-point substances while maintaining efficient ammonia supply
2Quantity of substance
If urea is thermally decomposed by exhaust gas heat, then ammonia is produced for NOx reduction, but pipe clogging occurs due to scale formation from high-melting-point substances
Solution Approach 1:
The invention changes the reaction parameters by using a hydrolysis catalyst to lower the reaction temperature from thermal decomposition temperatures (>200°C) to hydrolysis temperatures (100-200°C). This parameter change prevents the formation of high-melting-point substances like cyanuric acid and melamine that cause pipe clogging, while still producing sufficient ammonia for NOx reduction
Solution Approach 2:
The invention introduces a hydrolysis catalyst as an intermediary substance that facilitates the urea-to-ammonia conversion. The catalyst (containing alkali metal hydroxide, alkaline earth metal hydroxide, or their oxides/hydrogen carbonates) acts as a mediator to enable low-temperature hydrolysis, preventing direct thermal decomposition pathways that lead to clogging substances
3Quantity of substance
If urea undergoes thermal decomposition to form cyanuric acid and melamine, then ammonia is generated, but NOx reduction performance at downstream location decreases
Solution Approach 1:
The invention changes the reaction temperature parameter from high-temperature thermal decomposition to lower-temperature hydrolysis (100-200°C). This parameter change ensures that urea converts to ammonia through hydrolysis rather than decomposition, maintaining high ammonia availability at downstream locations where NOx reduction occurs, thus preserving NOx reduction performance
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
Prevents pipe clogging by decreasing cyanuric acid formation, maintaining NOx reduction efficiency, and preventing engine performance degradation.
Implementation Method 1
a hydrolysis catalyst layer configured to promote hydrolysis of urea is formed
Implementation Method 2
a TiO2 catalyst to promote hydrolysis of isocyanic and cyanic acids
Implementation Method 3
a urea-solution spray nozzle connected near a tip of the urea-solution supply pipe
Implementation Method 4
through thermal decomposition of urea by heat of exhaust gas
Data Source
Figure 1
Figure 2
AI summary
It is an object of the present invention to provide a device and a method for suppressing formation of a high-melting-point pipe-clogging substance by promoting hydrolysis of isocyanic acid and cyanic acid and decreasing the amount of cyanuric acid formed. This object is achieved by: disposing a urea-solution supply pipe (6) configured to supply pressurized air and a urea solution into a pipe through which exhaust gas flows; connecting a urea-solution spray nozzle (7) near a tip of the urea-solution supply pipe (6), providing a mixing section (8) configured to mix the exhaust gas flowing through the pipe and a sprayed urea solution sprayed from the urea-solution spray nozzle (7), circumferentially providing a metal sheet (9) on all or part of an inner wall surface of the pipe in a belt-like manner around the mixing section (8), and forming a hydrolysis catalyst layer (10) configured to promote hydrolysis of urea on an inner surface of the metal sheet (9).