Desalter emulsion separation by emulsion recycle

Abstract

A petroleum desalting process in which fluid from interfacial boundary layer between the settled water layer and the settled oil layer or emulsion-water layer in the vessel is withdrawn from the desalter and recycled to the crude oil inlet of the desalter to improve separation of the oil and water phases.

Description

CROSS-REFERENCE TO RELATED APPLICATIONS[0001]This application claims priority to U.S. Provisional Application Ser. No. 61 / 911,153 filed Dec. 3, 2013, herein incorporated by reference in its entirety.FIELD OF THE INVENTION[0002]This invention relates to petroleum desalters and their operation.BACKGROUND OF THE INVENTION[0003]Crude petroleum normally contains salts that may corrode refinery units; salt is removed from the crude oil by a process known as “desalting”, in which hot crude oil is mixed with water and a suitable demulsifying agent to form a water-in-oil emulsion which provides intimate contact between the oil and water, transferring salt into the water. The salty emulsion is then passed into a high voltage electric field inside a closed separator vessel. The electric field forces water droplets to coalesce, forming larger water droplets. As the water droplet volumes increase, they settle to the bottom of the tank under gravitation. The desalted oil forms at the upper layer ...

AI Technical Summary

Benefits of technology

The present invention describes a method for desalting crude oil by removing a fluid interface between water and oil, which can be recycled back to the crude oil for better water resolution. The method includes mixing the crude oil with water and using a hydrocarbon diluent to aid in separating oil from solids. The emulsified oil and water enter a desalter vessel where water droplets coalesce and settle at the bottom, and the oil and emulsifying solids form an emulsion layer between them. The water is then removed from the bottom of the vessel while the oil is removed from the top. A settling drum can be used to further reduce the amount of non-emulsified water returning to the process. The technical effects of this method include improved water separation and reduced non-emulsified water returning to the process.

Problems solved by technology

Finely-divided solid particles in the crude may also act to stabilize the emulsion, and it has been found that solids-stabilized emulsions present particular difficulties.

The growth of stable emulsion layer reduces workable volume and may short the electric circuit and force unplanned and costly desalter shut down.

To mitigate the rag layer buildup in some cases, emulsion is withdrawn from the unit; alternatively or in addition, costly demulsifiers may be added to the oil phase upstream of the desalter although with limited success.

Additionally, processing crudes with high rag layer formation tendencies in current desalter configurations may cause poor desalting (salt removal) efficiency due to solids build up at the bottom of the vessel, and / or a solids-stabilized rag layer leading to erratic level control and insufficient residence time for proper water / oil separation.

Solids-stabilized emulsion layers have become a major desalter operating concern, generating desalter upsets, increased preheat train fouling, and deteriorating quality of the brine effluent and disruption of the operation of the downstream wastewater treatment facilities.

These feeds are, however, being introduced to refineries in greater quantities despite two main disadvantages related to the efficacy of desalting.

First, the viscosity of these crudes can be quite high, so transport of water through the feed is slower than in high API gravity crude.

Intractable emulsions of this kind comprising oil, water and solids make adequate separation and oil recovery difficult.

This results in expensive treating or handling procedures or pollution problems as well as the fact that crude oil is also lost with these emulsions and slop streams.

These stable emulsions may not be completely separated by heating and conventional gravity settling and require specialized separation equipment.

Currently practiced centrifuge separation approach has, however, numerous reliability and cost drawbacks centering on the separation of the oil and water phases before they can be reintroduced to refinery process units (e.g. crude distillation, coker, etc.) or the waste water treatment plant.

As one problem area arises from the relatively high viscosity of the emulsions formed from heavy oil feeds, various proposals for dilution of the emulsions to reduce their viscosity have been made.

These processes, however, are energy-intensive requiring significant amounts of heat in the flash vaporization.

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