Visual Clues Give Insight into Ethylene Service Fouling

Fouling is an unfortunate part of ethylene and reactive monomer production. This handy guide will give you some clues as to what’s happening in your process based on the type of fouling you are seeing.

Fouling and unwanted polymer formation are ongoing issues in ethylene, butadiene, and reactive monomer processing plants. A study by Cagnolatti (HSB Soloman Associates) in 2015 (1) found that fouling is one of the top three reasons ethylene plants experience unplanned shutdowns.

During an outage, dirty equipment may be taken out of service for cleaning and inspection as needed (2) and deposit samples may be taken for chemical identification. Often, the chemical identity is already suspected — polybutadiene in the top of the debutanizer or polystyrene in the primary fractionator. Chemical analysis of the deposit is often performed to identify something unusual — for example, excess iron in the deposit.

Many plant operators assume that all foulants are similar and they give little consideration to the color, texture, and location of the foulant. Engineers often forget to ask insightful questions, such as “Why is the foulant found in one location and not another?” or “Why is the deposit sticky or rubbery and not crystalline?”

The temperature, monomer concentration, oxygen concentration, rust, feed rates, feedstocks, feed impurities, and equipment design all impact the location, texture, and appearance of the foulant. These factors provide clues that will help you to better interpret what is happening in the process and how to tackle fouling. This article describes how to combine visual observations with analytical techniques to gain a comprehensive view of system operation and improve production and maintenance of the ethylene plant.

Observing the appearance of foulant is particularly valuable for determining what is occurring in distillation towers, reboilers, and baskets/strainers. This article focuses primarily on these pieces of equipment, but also touches on other areas of the ethylene plant such as compressors and quench and dilution steam systems.