Aqueous Urea Solution pH Control for SCR Deposit Reduction
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Solution Overview
Problem
Urea deposits form on the walls of the exhaust system and SCR catalyst in diesel engines, reducing the efficiency of exhaust gas treatment and SCR catalyst performance due to secondary reactions forming high molecular weight compounds, which are difficult to remove at typical thermal decomposition temperatures.
Innovation Solution
Incorporating water-soluble organometallic catalyst precursors like titanium acetate, titanium bis(ammonium lactato)dihydroxide, and zirconium dioxide into the diesel emission fluid (DEF) to decompose isocyanic acid into ammonia and reduce high molecular weight deposits at lower temperatures, and maintaining the pH of the aqueous urea solution at ≤ 10.0 using CO2, air, or NOx introduction.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If high thermal decomposition temperatures are used to remove deposits, then deposit removal efficiency improves, but energy consumption increases and system durability decreases
Solution Approach 1:
The patent changes the chemical parameters of the decomposition environment by introducing catalyst precursors (transition metal compounds) that enable deposit decomposition at lower temperatures. This parameter change allows the same deposit removal function to be achieved with reduced thermal energy input, resolving the contradiction between removal efficiency and energy consumption
2Stability of the object's composition
If higher pH levels are maintained in the urea solution, then catalyst precursor stability improves, but organometallic catalyst precipitation occurs
Solution Approach 1:
The patent applies parameter changes by controlling the pH level within a specific range (7-10) to simultaneously achieve catalyst precursor stability and prevent organometallic catalyst precipitation. This optimized parameter range resolves the contradiction between stability and reliability
3Reliability
If pH control measures are implemented, then catalyst precipitation is prevented, but system complexity increases
Solution Approach 1:
The patent implements self-service by utilizing the exhaust gas stream itself as the pH control agent. The exhaust gas naturally contains CO2 which dissolves in the urea solution to form carbonic acid, automatically controlling the pH without requiring external intervention or complex control systems, thus preventing catalyst precipitation while minimizing system complexity
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
Reduces deposit formation and improves SCR system efficiency, decreases fuel consumption, and extends the lifetime of the exhaust system by converting isocyanic acid to ammonia at lower temperatures, while preventing catalyst precipitation due to pH fluctuations.
Implementation Method 1
introducing exhaust gas comprising CO2 into said reservoir
Implementation Method 2
introducing air into said reservoir
Implementation Method 3
introducing NOx into said reservoir
Implementation Method 4
decompose isocyanic acid into ammonia and reduce high molecular weight deposits at lower temperatures
Data Source
Figure 1
Figure 2
Figure 3A~3C
AI summary
The present invention is directed at stabilization of aqueous urea solutions containing organometallic catalyst precursors. Stabilization can be achieved by monitoring and controlling the solution pH.