Mr. Norman Lieberman – I have an old seminar manual from 1996. You have explained optimizing crude desalter operation – but do not explain optimizing the desalter temperature. Is there a single value? I’m trying to train a young process engineer assigned to our crude pipe still.
--Bob , Louisiana
Bob – Anything I wrote in 1996 is outdated. I’m much smarter now. There is no single optimum desalter temperature. A desalter outlet temperature of 300°F may damage the desalter electrical components. I’m sure anything below 220°F is too cold.
Raising the desalter temperature will cut viscosity and s.g., which will reduce height of emulsion and brine (BS & W) carry-over into deslated crude. However, the increased solubility of water in hotter crude will increase desalter amps and water content of desalted crude. The extra water in fractionator feed will promote corrosion in top few trays of the tower due to H2O condensation.
Another big problem is vaporization in the desalter. I have one client in Indiana who runs their desalter at 45 psig and thus cannot increase desalter temperature much over 220°F without stirring up the contents with vaporization of steam and light hydrocarbons. Keep the desalter inlet at least 10°F below the calculated bubble point of the crude taking into account that it is saturated with water.
A typical desalter outlet temperature for heavy (18°API) Venezuelan crude is 285°F. A typical desalter temperature for a light, sweet crude (35°API) is 245°F. If you have excessive growth in the emulsion layer, a warmer desalter will be optimum. If BS & W is less than 0.1 wt%, a lower desalter temperature may be optimum. Hope this longish answer helps.
--Regards, Norm
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