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Sludge generation tends to be solids-limited --
electrostatic forces between the oil, water, and solids keep the oil and water
from separating. Big solid particles make sludge and small ones make
emulsions. Something like ten pounds of sludge and float is generated for
every pound of solids that enters the separator. It's hard to do anything
about the solids that come in with the crude, but anything the refinery can do
to keep solids out of the drain (catalyst and coke fines, dirt getting into
drains) will cut back on sludge generation. Chemical surfactants used to
clean equipment need to be carefully kept from going to primary separation as
well. Sometimes refineries send all wastewater (like boiler and cooling
tower blowdown, which contain high solids) to primary separation and if it's
possible to pipe them into wastewater treatment after the
oil separation step and limit the feed to the separator to oily
wastewaters, sludge generation can be dramatically reduced. Limiting
turbulence can reduce sludge and float generation as well. Some oil
recycle loops (like float) might contain a lot of solids.
Once the sludge is generated, there are several dewatering
options that allow for more oil recovery from the sludge. But the best
thing to do is to prevent it from being generated in the first
place.
Hope this helps.
-Kirsten
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Kirsten Sinclair Rosselot, P.E. Process Profiles P.O. Box 8264 Calabasas, CA 91372-8264 (818) 878-0454
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