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[Matteo Giorgio Marrano]

Goodmorning guys,
i'm trying to define the dimensions of a desalter, given a specific flowrate.
In details, i have two desalter in series (1st and 2nd stage desalters)

I would like to define the overall dimensions of the vessel, not the exact ones, before asking the desalter supplier. I also know that the dimensions will depend on other characteristic like desalting efficiency, quantity of salt in the crude oil etc....Here i would like to understand only what is a typical value for the residence time in a desalter vessel.

These are my data:

FLowrate:
45000 BPD
V=312 m^3 (volume flowrate)
G=250000 kg/h (mass flowrate)
density=800 kg/m3

design pressure=10.2barg
design temperature=93°C

operating pressure=8.5/7 barg (1st stage-2nd stage)
operating temperature=65°C

salinity in water formation=200000 mg/l
outlet allowable salt content in oil=81 PTB

In order to define the overall dimensions of the vessel i have to know the residence time.
Referring to a horizontal separator a typical residence time could be from 5 to 15 min, is this valid also for the desalter or i have to choose something else?

In the datasheet there is in my hand (not calculated by me), the given dimensions are 3600mm*12300mm.

The formula used to define the vessel diameter and lenght is the following (given from horizontal separators design).

t=residence time
holdup volume=V.hold=t*V

R=L/D=2.5

Diameter=D=cubic root [(V.hold*4)/(3.14*R)]

Lenght=L=2.5*D

Whit this formula and a residence time of 15 min, it gives me 3400mmx8500mm, quite distant from 3600mmx12300 given in the datasheet.

Should i have to change the residence time or the L/D ratio in order to obtain the dimensions given in the datasheet?Is there any other thing to be considered?
In example, if i put R=3 and t=25 min, the dimensions are 11500mmx3800mm, similar to the datasheet.

Is it correct to use that kind of formula to obtain the dimension of the vessel or should i use the settling velocity of the dispersed phase in the continuous one?

I would like to point out that this is only a preliminary design of the vessel, the final one will be done by the supplier of the desalter.

thanks
Matteo