Electrostatic Heater Treater & Desalter

An electric field promotes coalescence of fine water droplets, supporting water and salt removal from the crude.

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Horizontal electrostatic treater and desalter with transformer housings, firetube heating section and skid-mounted controls

Project reference

Crude Desalting Equipment for TAQA at Atrush Kurdistan Region of Iraq 2019

ScopeTwo electrostatic dehydrators and two crude cross exchangers for a 50,000 BOPD production facility.

Application

Dehydration and Salt Removal

Electrostatic heater treaters are often used in lieu of mechanical treaters. They are selected where the treated oil has to reach a lower BS&W figure or a lower salt content than a mechanical unit can deliver, or where plot space is constrained.

Process

Where It Differs from a Mechanical Treater

Like mechanical heater treaters, electrostatic units generally have a heating section using gas fired firetubes to provide the heat.

In the coalescing section, however, electric transformers generate an electrostatic grid that enhances coalescence. Fine water droplets are drawn together into larger ones that settle out of the oil. Electrostatic treatment can achieve lower BS&W and salt targets, or reduce plot area, where feed properties and design basis support it.

On desalting duty, fresh wash water is injected and mixed into the crude upstream of the vessel. The salt dissolves into that water, and the grid then coalesces and removes the water — taking the dissolved salt out with it.

System configuration

Major Equipment Within the System

System configuration varies with process duty, operating conditions and project requirements.

Electrostatic heater treater and desalter, cutaway illustration

Inlet Heat Exchanger

Preheats the incoming emulsion, reducing the load on the firetube and the fuel gas used.
Inlet Device

Spins the incoming flow so that free gas leaves upwards and the liquid flows down below the firetube.
Free Water Knock-Out Section

Draws free water off below the firetube, so that it is not heated.
Heating Section

Gas-fired firetube, protected by a heat shroud, that brings the emulsion to treating temperature.
Electrostatic Grid and Transformers

The grid polarises the water droplets so that they coalesce and settle out of the crude.
Water Outlet Header

Withdraws water and solids along the full length of the vessel.

Also in the vessel

Gas sections: outlet gas cooling and outlet gas scrubbing
Crude settling: water settling zone ahead of the treated oil outlet

Options

Mud wash header: fluidises solids that settle in the bottom of the vessel, where inlet crude properties call for it
Desalting: fresh wash water injected and mixed into the crude upstream of the vessel

Final equipment arrangement and delivery format depend on process duty, transport constraints and site requirements.

Specifications

Compared with a Mechanical Treater

Aspect	Mechanical	Electrostatic
Heating section	Firetubes	Gas fired firetubes
Coalescing section	Mechanical coalescers	Electrostatic grid generated by electric transformers
Footprint	Larger for equivalent duty	Smaller than a comparable mechanical unit
Treated oil BS&W	Higher	Lower
Salt content	Higher	Lower

Grid voltage, treating temperature, vessel size and the achievable BS&W and salt figures are set by SPEC engineering against your crude properties and target specification.

Advantages

Why Electrostatic Treaters

Lower BS&W

The applied field reaches droplets a mechanical coalescer would leave in the oil.

Lower salt content

Wash water dissolves the salt, and removing that water takes the salt out with it.

Smaller footprint

Can reduce plot area compared with a mechanical treater of equivalent duty, where the design basis supports it.

Evidence

Delivered

For TAQA's 50,000 BOPD Atrush production facility in the Kurdistan Region of Iraq, SPEC designed, fabricated, tested and supplied the desalting equipment: two electrostatic dehydrators and two crude cross exchangers.