When oil leaves the unit

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There are several factors that cause emulsion stability (or hinder demulsification) and contribute to increased possibility of oil leaving the desalter with the brine.

Upstream chemicals are important to the drilling, production and transportation of hydrocarbons. They protect assets, provide fl ow assurance and ensure phase separation so that produced hydrocarbons meet pipeline specifications. However, they can also create issues and challenges that have to be met once crude enters a refinery.

Hydrate inhibitors, biocides, amine-based hydrogen sulfi de (H2S) scavengers, flocking polymers and paraffin inhibitors are the most common upstream chemistries that create emulsion stability challenges for refiners.

Hydrate inhibitors (e.g. methanol) are a major cause of emulsion stability. They are often used to keep wells workable when temporarily shutting down for events such as hurricanes. Note that emulsion stability is not the worst part of methanol in crude. Methanol is a co-solvent, which allows for an increase in oil-in-water dispersion and also increases total organic carbon (TOC) and chemical oxygen demand (COD) in the water moving to the wastewater treatment plant.

Flocking polymers are also used to compress rags in order to meet the <1% basic sediment and water (BS&W) specifi cations. Flocking, which is the process of depositing many small particles onto a surface, does not resolve the rag/emulsion layer. The issue is intensifi ed when the emulsion is mixed with water in the desalter, as the emulsion rehydrates and can cause signifi cant issues. Paraffin inhibitors will generally convert compounds into a sulfonate, which act as surface active agents, and stabilise emulsions by concentrating at the oil/water interface. Table 1 presents the functional chemistries that impact desalter emulsion stability and phase separation issues. Identifying these chemistries in the incoming hydrocarbon will allow refi ners to put in preventative treatment programmes. fig 1 2 When oil leaves the unit

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