DEF Fluid: Understanding Its Composition and Critical Role in SCR Systems

2025-17-09

Introduction

Tall, modern industrial chimney stack emitting clean white vapor against a clear blue sky, symbolizing effective emission control.

In the high-stakes world of industrial emissions control, what is DEF fluid? Diesel exhaust fluid (DEF) constitutes a straightforward blend of urea and deionized water. It energizes selective catalytic reduction (SCR) systems. This permits up to 90% NOx reduction. Its Significance: This article probes the vitality of these two components. Namely, it examines why 32.5% high-purity urea solution and 67.5% deionized water prove crucial to costly SCR systems. Also, discover how Guantong’s SCR technology ensures efficiency and compliance.

Component 1: High-Purity Urea (32.5%)

A gallon container of "UREA DEF Diesel Exhaust Fluid" with clear labeling, highlighting DEF's purity and packaging for diesel systems.

Role: Ammonia’s Safe Carrier

What is urea in DEF? Urea serves as a safe, non-toxic carrier for ammonia in DEF fluid for diesel systems. Urea in DEF decomposes into ammonia (NH₃) within SCR systems, reacting with NOx to form harmless nitrogen and water. Anhydrous ammonia presents hazards: it is flammable and heavily regulated. Conversely, urea solution proves safe. OSHA standards classify it as non-hazardous. Hence, it emerges as ideal for industrial applications.

  • Safety Advantage: DEF fluid obviates risks pertaining to ammonia storage. It curtails safety incidents by up to 50%.
  • Applications: From DEF diesel trucks to power plants, urea ensures reliable NOx emission control.

Purity Requirements

What is DEF made of? High-purity urea, compliant with ISO 22241, is critical to prevent catalyst poisoning. Impurities like biuret (>0.3%) or metals (calcium, magnesium) can damage SCR system catalysts, costing thousands in repairs. Are all DEF fluids the same? No—only ISO-certified DEF fluid ensures performance.

  • ISO 22241 Standards: Limits biuret to <0.3%, ensuring DEF quality.
  • Risk: Agricultural-grade urea can reduce catalyst efficiency by 20%.

Learn more about Guantong’s DEF solutions for ISO-compliant DEF fluid.

Component 2: Deionised Water (67.5%)

Role: High-Purity Solvent

What is DEF fluid made of? Consider this fact: Deionized water constitutes 67.5% of DEF composition. It serves as a solvent to attenuate urea. This guarantees stable injection and forestalls urea crystallization. That is why its purity is critical to avoid scaling in SCR systems.

  • Function: Maintains DEF fluid stability for uniform spray in DEF tanks.
  • Importance: Ensures consistent ammonia production for NOx reduction.

Purity Requirements

Employing tap or regular purified water entails introducing minerals. These (calcium, magnesium) accrete on catalysts, engendering scale. Ultimately, this precipitates permanent failure. What is diesel exhaust fluid made of? Only deionised water meets ISO 22241 standards, ensuring DEF quality.

  • Risk: Mineral deposits can reduce catalyst efficiency by 15–20%.
  • Solution: Guantong’s DEF fluid uses deionised water to protect SCR systems.

Critical Role: DEF’s Chemical Journey in SCR Systems

DEF fluid traverses a precise chemical journey within SCR systems. This culminates in NOx reduction. Moreover, this method furnishes clean air steadily.

  • Injection: DEF fluid for diesel is injected via metering systems into hot exhaust (190–600°C).
  • Atomization: Droplets break into a fine mist for uniform distribution, aided by Coriolis flow meters with ±0.1% accuracy.
  • Evaporation: Urea in DEF vaporises, decomposing into ammonia (NH₃).
  • Reaction: Ammonia engages with NOx upon the catalyst surface. This yields nitrogen and water. These constitute key nitrogen applications in emissions control.
  • Each step warrants optimization. This prevents ammonia slip—excess ammonia inducing corrosion. It also precludes urea crystallization—solid deposits impeding injectors. What is a SCR system? It’s a sophisticated setup where DEF diesel fluid ensures up to 90% NOx conversion.
  • Challenges: Low temperatures (<190°C) cause crystallisation; over-injection leads to ammonia slip.
  • Case Study: A power plant using Guantong’s metering system reduced ammonia slip to <2 ppm, boosting efficiency.

How Guantong Ensures DEF’s Critical Role

This remains evident: Guantong’s advanced technologies optimize DEF fluid performance within SCR systems. They tackle prevalent challenges:

CFD-Optimized Injection

Computational fluid dynamics (CFD) guarantees flawless atomization and mixing of DEF fluid with exhaust gases. This fosters ideal conditions for NOx reduction.

  • Process: CFD simulates spray patterns, optimising injector placement.
  • Benefit: Improves reaction efficiency by 10–15%, reducing DEF fluid consumption.
  • Example: A cement plant using Guantong’s CFD reduced NOx emissions to 50mg/Nm³.

Urea Pyrolysis Furnace

Large industrial urea pyrolysis furnace with extensive piping and structures under a partly cloudy sky, indicating a complex chemical processing facility.

Guantong’s urea pyrolysis furnace operates at 350–600°C. It converts urea solution into ammonia completely. This obviates urea crystallization risks.

  • Advantage: Ensures 100% ammonia production, unlike direct injection’s variable conditions.
  • Support: Process control instruments monitor ammonia output for stability.
  • Case Study: A petrochemical plant adopted Guantong’s urea pyrolysis, cutting maintenance costs by 20%.

Explore Guantong’s urea pyrolysis technology for superior NOx reduction.

Conclusion

Diesel exhaust fluid (DEF) constitutes a simple blend of urea and deionised water. It energizes selective catalytic reduction (SCR) systems. This permits up to 90% NOx reduction. Here’s its significance: This article probes why these two components—32.5% high-purity urea solution and 67.5% deionised water—prove vital to costly SCR systems. Contact us.

Talk To Our Expert