SCR Reducing Agent Delivery System Emptying Method
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Solution Overview
Problem
Existing methods for emptying the reducing agent delivery system of an SCR catalytic converter face issues with crystallization of the urea-water solution in the metering valve, leading to blockages and preventing pressure equalization during the emptying process, especially at low temperatures.
Innovation Solution
A method utilizing a reversing valve to switch between delivery and return operations, initiating pressure reduction, and operating the pump at varying output levels to create negative pressure, ensuring the urea-water solution is pumped back into the tank without crystallization in the metering valve, allowing for independent emptying of the system lines.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If the delivery module is emptied into the tank via the delivery line with ventilation via the metering module and pressure line, then the system can be emptied, but the water component evaporates in the first seconds leading to urea crystallization and blockage of the metering valve
Solution Approach 1:
The harmful effect of evaporation and crystallization is extracted and isolated by switching off the metering valve during emptying operations, separating the emptying process from the normal delivery path through the metering module
Solution Approach 2:
Before emptying begins, the metering valve is switched off in advance to prevent the harmful evaporation-crystallization sequence from occurring in the first place
2Reliability
If the metering valve is closed during emptying to prevent crystallization, then blockage is avoided, but pressure equalization cannot be completed
Solution Approach 1:
The emptying process is segmented into distinct phases: initial emptying with metering valve closed (preventing crystallization), followed by a separate pressure equalization phase where the valve is opened, allowing both goals to be achieved sequentially
Solution Approach 2:
The emptying process continues uninterrupted through both phases - first the reducing agent is emptied into the tank, then pressure equalization is completed, ensuring continuous productive operation without premature termination
3Productivity
If the pump operates at high output to speed up emptying, then productivity increases, but the risk of crystallization increases due to faster evaporation
Solution Approach 1:
The high pump output that would normally accelerate harmful evaporation is converted into a benefit by simultaneously closing the metering valve, transforming the fast flow into a controlled emptying process that prevents crystallization while maintaining high productivity
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 method effectively prevents crystallization in the metering valve and enables efficient emptying of the reducing agent solution into the tank, ensuring pressure equalization and system integrity, even at low temperatures, without requiring structural changes to the existing controller or equipment.
Implementation Method 1
the delivery module is changed over from the delivery mode to the return operation... As a result of the closure of the metering valve and the operation of the delivery module in return operation, a negative pressure is produced in the pressure line
Implementation Method 2
the metering valve, which controls the flow of reducing agent from the metering module through the pressure line, is closed
Implementation Method 3
the water component of the urea-water solution can evaporate, which leads to the urea crystallizing out... This emptying method is independent of crystallization of the reducing agent solution in the metering valve
Implementation Method 4
the water component of the urea-water solution can evaporate, which leads to the urea crystallizing out
Data Source
AI summary
The invention relates to a method for emptying a reducing agent delivery system belonging to an SCR catalytic converter, which comprises a delivery line and a return line, each line connecting a reducing agent tank to a delivery module, and which comprises a pressure line that connects the delivery module to a metering valve. The method comprises the following steps: closing (50) the metering valve, and switching the delivery module from a delivering function to a returning function, by switching (51) a switching valve from a first position to a second position. This enables a reducing agent solution to be returned (52) from the return line, the delivery line and the delivery module by means of the delivery module and the delivery line into the reducing agent tank. Subsequently, the metering valve is opened (53) and a reducing agent solution is returned (54) from the metering valve and the pressure line, and also from the return line, via the delivery line into the reducing agent tank. Additionally, the metering valve is closed again (55) in order to empty (56) the return line and the delivery module.