Q & A > Question Details
Are there other methods of removing salt from crude oil besides using Desalter?
18/05/2016 A: Eric Vetters, ProCorr Consulting Services, ewvetters@yahoo.com
For light crudes a significant amount water containing the bulk of the salts can be settled in crude tankage as long as there is sufficient residence time. Filtration and coalescence is not generally practical because of the high volume of solids that would be generated from most crudes. Centrifuges are quite expensive relative to desalters so are not commonly used. That leaves desalters as the primary option for the vast majority of refiners.
18/05/2016 A: Morgan Rodwell, Fluor Canada Limited, morgan.rodwell@fluor.com
Salt in crude oil is usually dissolved in connate water that is associated with the oil. Salt is not soluble in oil iteself, although there are examples of crystalline salt being present in some oils.
Desalting oil is really a process of diluting the connate water with clean water, and then removing the water down to a low level. The traditional way of doing this is via gravity separation of oil and water, often assisted by electrostatic fields to assist in water droplet coalescence, and this is still a very effective method.
Because the basic process is separating oil and water, you could use a centrifuge, but at scale this will likely have high CAPEX and OPEX, and if the oil contains some solids (i.e. sand), the centrifuge design may be difficult.
18/05/2016 A: Prabu Natarajan, Natco Uk Ltd, prabunatarajanuk@yahoo.com
Desalters are used normally when less 1% or less water in the crude is required. Desalter does exactly the same job as a dehydrator except that low saline/fresh water is mixed with the high saline produced water to dilute the dissolved salt. Thus, by removing water down to 1% or less, a desalter removes proportionate dissolved salt.
If dehydration is not a mandatory requirement, fresh water can be added even upstream of a gravitational separator which actually does the same job as the Desalter but with high % water in the crude i.e 5 to 10% and it may vary depending upon density, op. temp, residence time etc.
To answer your question, diluting pro water with less saline water and removing the mixed water from crude simply removes the salt. Using a desalter is more advantageous as the water and salt removal efficiency is comparatively high and produces much valuable crude