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Does injecting wash water ahead of preheat exchangers improve desalter efficiency?
 
Answers
18/05/2010 A: Eric Vetters, ProCorr Consulting Services, ewvetters@yahoo.com
The increased mixing time created by putting wash water into the preheat train can improve desalting efficiency. There is some thinking it is especially effective if you have significant amounts of crystalline salts present in the crude. The increased mixing gives them more time to become water wetted and to dissolve than when the water goes in right at the mix valve. Depending on how your preheat train operates and how robust your desalter is, it can also sometimes cause over mixing, resulting in a larger rag layer and poorer efficiency. It also usually adds DP to the preheat train due to the extra flow. If you are hydraulically limited on your unit, it could also back out crude charge so you need to think about that before you try this option.
18/05/2010 A: Alan Goelzer, Jacobs Consultancy, alan.goelzer@jacobs.com
Simple Answer = YES !
One-third to one-quarter of wash water should be low inorganic TDS / organics-free water injected where the crude oil temperature is 40C to 50C, i.e. after steam preheaters. Balance of wash water injected into the desalter can be stripped sour water with some residual organics and significant inorganic TDS.
Initial wash water will help to break down emulsions between 'water as received' and crude oil, and will tend to block deposition of salt residues on exchanger tubes en route to desalter inlet temperature [150C?].
18/05/2010 A: Sam Lordo, Nalco Company, salordo@comcast.net
Besides being used to keep the cold preheat clean of slit and deposits it can improve desalter efficiency by providing water contact and multiple mixing steps with some of the water-soluble and water-wettable materials, to the degree that it improves efficiency is determined by field testing.