Fouling and coking are persistent challenges in HFO visbreaking units, leading to reduced heat transfer efficiency, increased energy consumption, and frequent shutdowns. This blog examines the root causes of fouling and explores practical solutions to minimize its impact on operations.

Understanding Fouling Mechanisms

Fouling in visbreaking units occurs due to:

Thermal Cracking Byproducts – Asphaltenes and heavy polyaromatics polymerize, forming coke deposits.

Inorganic Contaminants – Metals (Ni, V, Fe) and salts in the feed catalyze coke formation.

Poor Mixing & Hot Spots – Uneven heating in furnace tubes accelerates localized coking.

Key Strategies to Reduce Fouling

1. Feed Pretreatment

Desalting – Removing chlorides and metals reduces catalytic coke formation.

Filtration & Deasphalting – Pre-processing heavy feeds to remove asphaltenes can significantly reduce fouling.

2. Optimal Operating Conditions

Temperature Moderation – Running at the lower end of the cracking temperature range (450–470°C) minimizes excessive thermal degradation.

Residence Time Adjustment – Shorter residence times in coil visbreaking reduce coke formation.

3. Advanced Furnace Design

High-Velocity Burners – Improve heat distribution and reduce hot spots.

Online Spalling Systems – Some units use steam-air decoking to remove deposits without shutdowns.

4. Antifoulant Additives

Dispersants – Keep asphaltenes suspended, preventing agglomeration.

Metal Passivators – Reduce the catalytic effect of Ni and V on coking.

5. Predictive Maintenance & Monitoring

Fouling Rate Tracking – Using infrared thermography and pressure drop monitoring to predict fouling buildup.

Machine Learning Models – Analyzing historical data to optimize cleaning cycles.

Conclusion

Fouling and coking in HFO visbreaking units can significantly impact operational efficiency and maintenance costs. By implementing feed pretreatment, optimizing operating conditions, using antifoulant additives, and adopting predictive maintenance strategies, refiners can extend run lengths and improve profitability.