Desalter Operations 1

A. Thirumaran:

A crude oil desalter operates by emulsifying a low percentage of fresh water into the crude as a water-in-oil emulsion, which in turn solubilizes inorganic chloride salts and picks up entrained brine. The wash water is subsequently separated from the crude by electrostatic and/or chemical demulsification techniques and discarded. The object of this exercise is to minimize chloride concentrations in the crude oil and, subsequently, to minimize hydrochloric acid formation in atmospheric and vacuum distillation columns and acid corrosion of these unit's overhead receivers.

Orenda

Oil-in-water emulsions are almost always formed in circumstances where the continuous phase is water, which is not the case in crude oil desalters.

May be chillboy is confused by the "reverse" O/W emulsions sometimes appearing in the separated down-going water phase. These are broken by addition of suitable emulsion-breakers.

25362:

Thanks! Good point!

Orenda

To cope with the appearance of oil in a desalter's water effluent HydProc (March 2005) suggests applying one or more of these procedural remedies:

1. Raise the interface level
2. Use demulsifiers
3. Drain -reducing the width of- the interface emulsion band
4. Reduce the mixing valve pressure drop
5. Check for any upset in the wahswater source
6. Raise the crude oil inlet temperature

Chemical and electrostatic treatment is used in the desalters to remove salt and water from the crude. Pressure drop in the mix valve is typically set at 10 psi. However, when the processing of heavy Maya or (14 degree API) naphthenic crudes is attempted, the oil/water mixture forms a stable emulsion in the desalter. This prevents economic processing of this low cost crudes; several problem areas were identified which could contribute to stabilizing emulsions. One was the high shear-rate mixing found in the mix valve. When this occurs one has to increase the chemical desemulsification agent, reduce the wide of the emulsion band,tray to avoid the electric shutdown of desalter electrodes and reduce the mixing valve pressure drop.

Demulsifiers are good for high BS&W crudes. In addition to 0707's advice you may also try:

a. keeping the interface at lower levels
b. reducing the wash water proportioning rate
c. avoiding fluctuations of the interface

good luck