Incompatible crudes due to asphaltene precipitation

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Asphaltene precipitation can be disruptive to preheat exchangers and the desalting process. If not managed, refi ners will have fouling and corrosion challenges with their process equipment.

Within a desalter, where it is critical to separate salt, solids and water from oil, asphaltenes can work against the desalting process by strengthening the emulsion stability.

How does it happen?

Asphaltenes precipitate when incompatible crudes are blended in wrong proportions or order. Many crude oils can be blended, but there are a high number of oils that cannot. Some crudes are even self-incompatible and will precipitate asphaltenes by themselves.

To illustrate the challenge of refining hydrocarbons, it is important to note that crude oil is a combination of hydrocarbon molecules, which can aggravate the challenge with the blending of crudes and/or even slop oil into fresh crudes. The blend becomes a mix of several simple and complex molecules and even non-natural contaminants from upstream and midstream processes such as production fluids and metals.

The molecules can be open or straight-chained, single-bonded, saturated molecules (paraffins) or cyclic saturated molecules (naphthenes). Resins and asphaltenes are among the most complex. They both have a high molecular weight, are polar, and are polynuclear aromatic ring molecules.

Unlike resins, though, asphaltenes are not soluble in aromatic-free, low boiling point solvents such as hexane and heptane, keeping the emulsion stability strong. They can also act as surfactants, encapsulating water and salts, which strengthen the emulsion and can be problematic when transferred to the crude unit.

Asphaltenes, however, may precipitate out if the concentration of the paraffi ns in the crude oil or crude oil mixture is right.

How to manage it

To manage asphaltene precipitation from incompatible crudes, Athlon’s experience has been to use (or modify) a crude compatibility model, to predict which single crude, crude blends, and ratio of crude blends will be most likely to precipitate asphaltenes.

The method has provided the company with an extensive crude database, which coupled with onsite compatibility testing makes it possible to predict which crude preheat antifoulant and desalter emulsion breaker technologies and
applications to use to prevent upsets.

HYDROCARBON ENGINEERING 01 2019

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