SCR crystallisation is a common problem in Selective Catalytic Reduction systems. It occurs when AdBlue, urea or ammonia deposits form inside lines, injectors or on the catalyst.
This can lead to blockages, reduced performance and high maintenance costs. Fortunately, there are several ways to solve crystallisation, such as cleaning or using dedicated AdBlue additives. It can also be prevented through correct maintenance and high-quality AdBlue.
In this article, you will learn what SCR crystallisation is, how it develops and how to avoid problems.
What exactly is SCR?
Before discussing SCR crystallisation in more detail, it is useful to know what SCR stands for. SCR, or Selective Catalytic Reduction, is a technology used to reduce nitrogen oxides, also known as NOx, in exhaust gases.
It is widely used in diesel engines in vehicles and in industrial processes such as power plants and factories where combustion gases are produced.
The system uses a chemical reaction in which a reducing agent, such as urea or ammonia, is added to the exhaust gases. This technology is effective and helps meet strict environmental standards, such as Euro 6 for vehicles and emission guidelines for industrial installations.
SCR crystallisation
SCR crystallisation refers to a process in which a solid substance forms from an oversaturated solution inside a system that uses SCR technology.
Although crystallisation is a general concept used in many chemical and industrial contexts, in relation to SCR it usually refers specifically to the crystallisation of components such as urea, ammonia or ammonium salts involved in an SCR system.
SCR is often used to reduce NOx emissions in exhaust gases from vehicles and industrial processes. The system works by injecting a reducing agent, usually a urea solution known as AdBlue or DEF, into the exhaust system.
Although Selective Catalytic Reduction is an effective technology, several challenges and problems can occur. The most important issues are listed below.
1. Crystallisation and deposits
Problem: At low temperatures or with incorrect dosing of the reducing agent, such as AdBlue, crystallisation can occur. Urea or ammonia-based compounds may build up in lines, injectors or the catalyst.
Consequences:
- Blocked lines and injectors
- Reduced system efficiency
- Higher maintenance costs
Solution: Maintain correct dosing and optimal operating temperatures, combined with regular maintenance.
2. Temperature dependency
Problem: SCR only works effectively at high temperatures, usually between 250°C and 400°C. With low engine load or short journeys, the temperature may remain too low, causing insufficient NOx reduction.
Consequences:
- Higher NOx emissions during city driving or cold starts
- Potential failure to meet emission standards
Solution: Modern systems combine SCR with a diesel oxidation catalyst and diesel particulate filter to compensate for temperature-related issues.
3. Additional maintenance and costs
Problem: The SCR system requires regular refilling of the reducing agent, such as AdBlue, and periodic maintenance of injectors, lines and the catalyst.
Consequences:
- Higher operating costs
- Vehicle or machine downtime for maintenance
Solution: Using high-quality reducing agents and carrying out preventive maintenance can limit these problems.
4. AdBlue
Problem: AdBlue can freeze at temperatures below -11°C. Impurities in AdBlue can damage injectors and the catalyst.
Consequences:
- Unreliable system operation in cold conditions
- Expensive repairs to damaged components
Solution: Use a heated AdBlue system in cold climates. Make sure you use pure AdBlue from a reliable supplier. Preferably use Lindemann AdBlue.
5. Sensitivity to faults
Problem: SCR systems are complex technologies that rely on several sensors, pumps and electronic components. A defect in one part can disrupt the entire system.
Consequences:
- Reduced efficiency or SCR system failure
- Repairs can be costly and time-consuming
Solution: Test and maintain the system regularly to detect faults early.
Conclusion: SCR crystallisation can cause serious problems
SCR crystallisation can lead to blockages in injectors and lines. It can also reduce catalyst performance by covering active surfaces.
In extreme cases, the system can become damaged and maintenance costs may increase significantly.
How can crystallisation be prevented in SCR systems?
Prevention is better than cure. There are several ways to prevent crystallisation in the SCR system:
- Maintain optimal temperatures: Make sure exhaust gas and SCR temperatures remain high enough to promote evaporation and chemical reactions.
- Correct reducing agent dosing: Overdosing can result in excess urea, which can lead to crystal formation.
- Regular maintenance: Check injectors, lines and catalyst surfaces for deposits and clean them if necessary with an injector cleaner or catalyst cleaner.
- Add an AdBlue additive: AdBlue additives can help prevent SCR crystallisation.
How does an AdBlue additive work?
Regular use of an AdBlue additive can help prevent crystallisation and deposits. It is important to add the additive according to the manufacturer’s specifications.
Excessive use can actually cause problems, so do not simply pour an AdBlue additive directly into the AdBlue tank without following the correct instructions.
Lindemann AdBlue Additive works best when it is mixed with a 10-litre jerrycan of AdBlue before being added to the AdBlue tank. After mixing, you can add the combined product to the AdBlue tank.
An AdBlue additive can be used for the following purposes:
- Preventing crystallisation: It can lower the freezing point of AdBlue and help prevent urea or salt deposits in lines or injectors.
- Dissolving deposits: Additives can break down or dissolve existing crystalline deposits in the SCR system.
- Improving stability: Additives help keep AdBlue stable for longer, especially under changing temperatures.
An AdBlue additive also has many benefits when used preventively:
- Prevents AdBlue crystallisation in the SCR system
- Increases the effectiveness of AdBlue
- Protects AdBlue at temperatures below -10°C
- Prevents contamination of AdBlue injectors
- Protects AdBlue during long-term storage
- Accelerates the conversion of urea into ammonia
- Helps reduce NOx values
- Protects the SCR system
- Prevents blockages in the SCR catalyst
These are all good reasons to add Lindemann AdBlue Additive preventively when filling AdBlue.
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Repair costs for SCR crystallisation
The repair costs for SCR crystallisation can vary greatly depending on the severity of the problem and which parts of the SCR system are affected.
Professional cleaning or replacement of injectors
- Injector replacement: €300 to €800 per injector, depending on the vehicle
- Professional cleaning: €100 to €400
- Self-cleaning with an injector cleaner
Professional cleaning or replacement of the SCR catalyst
- Catalyst replacement: €1,000 to €4,000, depending on the type of vehicle or installation
- Professional cleaning: €300 to €700
- Self-cleaning with a catalyst cleaner
Replacement of the AdBlue pump
- Repair: €200 to €500
- Pump replacement: €800 to €2,000
Sensor problems
- Sensor repair or replacement: €200 to €600 per sensor
Complete SCR system overhaul
- Full overhaul: €3,000 to €8,000, depending on the extent of the damage
Conclusion and summary
The repair costs for SCR crystallisation can range from a few hundred euros for simple cleaning to several thousand euros for replacing major components such as the catalyst or pump.
Regular maintenance and the correct use of AdBlue together with an additive can prevent many problems and significantly reduce costs.
Preventive measures, such as using high-quality AdBlue and regularly cleaning injectors and lines, also help avoid expensive repairs.
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