Oily water separation.
Oily water separation.
(OP)
Hi folks,
I'm trying to get information on upgrading our wastewater system. We currently process up to around 5000bbls/day of waste water and are looking to revamp the whole system. One question I have is if height of a tank and volume outweigh surface area when trying to separate oil from water. Our current system uses box style canals that are only 5' deep but probably have a total volume of 1000bbls capacity. I'd like to make our primary separation a cylindrical tank with a height of 25' and a total volume of 2500 bbl cap., though it would probably be operated around the 15' level so 1500 bbls. Heat is another factor that is possible using this tank that we wouldn't have in the canal design. Thanks
I'm trying to get information on upgrading our wastewater system. We currently process up to around 5000bbls/day of waste water and are looking to revamp the whole system. One question I have is if height of a tank and volume outweigh surface area when trying to separate oil from water. Our current system uses box style canals that are only 5' deep but probably have a total volume of 1000bbls capacity. I'd like to make our primary separation a cylindrical tank with a height of 25' and a total volume of 2500 bbl cap., though it would probably be operated around the 15' level so 1500 bbls. Heat is another factor that is possible using this tank that we wouldn't have in the canal design. Thanks





RE: Oily water separation.
Orenda
RE: Oily water separation.
I appreciate you taking the time to reply. We currently do utilize a DAF system. The problem is that when we do have carry under from the Desalting system, due to the minimal capacity of the canals, and the weir that is supposed to keep the oil layer from carrying into the water side,the oil becomes too much for even the DAF tank, and CPI (corrugated plate intercepter)to handle. Any thoughts on using height vs. length. 1500bbl cylindrical tank equipped with heat tracing vs. 1000bbl horizontal canal system 4.5' deep.
RE: Oily water separation.
Though I've been away from crude desalting operations for a number of years, your problem seems to be more related to desalter operational issues, leading to excessive oil carryunder with the desalter wash water discharge. If this is so, then I would be more inclined to search out the desalter issues, maybe with the assistance of such firms as Petreco, Baker-Hughes, etc. and minimize the oil loading from that point, rather than trying to treat the symptoms of the problem by modifying the oily water discharge/separation/treatment system.
Orenda
RE: Oily water separation.
O/W separators work well under steady state conditions. Unfortunately, it is rare to get steady state conditions in industrial wastewater.
I actually had a system like you are describing many years ago. The O/W separator was not working properly because of varying hydraulic conditions. The tank in the system was originally intended to be an equalization tank, but the operators turned off the mixer and allowed the oil to accumulate.
If you have a bottom outlet on the tank, the long retention time in a tank will enable most of the oil to separate.
RE: Oily water separation.
RE: Oily water separation.
RE: Oily water separation.
Anyway you cut it, this approach will most likely be a less expensive direction to proceed in than a revamp of your oily water discharge system, both in terms of Capex and Opex.
Orenda
RE: Oily water separation.
This worked, but was expensive.
I devised a flow sheet for using a classic evaporator to separate water from the oil phase, then blending the oil phase back into the refinery feed and using the water as "plant water."
A test was performed by Swenson Evaporator. The results are available in a California Department of Health Services report.
The work went no further, as Unocal became engrosed in business dealings that eventually led to the sale of their California assets to other firms.
I have further info, if this seems to hold promise for you.
RE: Oily water separation.
I agree with you Orenda that the desalters are the root cause of our carry under, but even beyond that we've outgrown our water treatment system, and are looking to improve our effluent before our those restrictions are imposed on us. I will check out some of those contractors to see what they have to say about helping with our desalters. Does anyone have experience with a heater treater? Maybe preheating and treating the crude oil before with water and chemical before the exchanger train and desalters to get a better mix? Anybody know of a de-emulsifier that works well with various sweet and sour blends of crude oil? Thank you all again.
RE: Oily water separation.
I can't imagine desalting crude of any variety without suitable preheat....this is part of the specific support that the desalter contractors will provide, for the individual or blended crudes being run.
Demulsifier selection is case dependent, and though many of these formulatiuons are wide-ranging in their performance, they still require suitable bottle testing to pick and choose the appropriate product(s) for your system and crude blends. The vendors of these products, e.g. Baker-Hughes, Nalco, GE Betz, et al are expert at this.
Orenda
Orenda
RE: Oily water separation.
RE: Oily water separation.
***** Start Here:
DEWATERING OF REFINERY SLUDGES
USING A FORCED CIRCULATION EVAPORATOR
DRAFT REPORT
DOHS CONTRACT NO. 89-T0120
DECEMBER 1990
California Department of Health Services
Alternative Technologies Division
Toxic Substances Control Section
******* End Here
I note that your phase separations are done at elevated temperatures, so some of the necessary heating capability is already in place. The NaCl portion of the aqueous phase will stay with the heavy bottom product, but that is OK, as, ultimately, it will leave the refinery with the heaviest tar products.
RE: Oily water separation.
RE: Oily water separation.
RE: Oily water separation.
RE: Oily water separation.
RE: Oily water separation.
RE: Oily water separation.
The entering stream consisists of water, salt and crude petroleum. Two streams leave the evaporator. The light (overhead) stream is water with some light organic low molecular weight material (say pentane on up through C18). The heavy (bottoms) stream consists of asphaltic materials plus the salt.
The light end is condensed (at, say 30 degC). And the water is separated from the organic by decanting.
The heavy end can be blended with other heavy material destined for sale as asphalt. The salt leaves your refinery as part of your asphalt product.
Operation of the evaporator requires some design features that are hard to describe without drawings. Get a copy of the report issued by the California DOH (see above).
Buena suerte.
RE: Oily water separation.
RE: Oily water separation.
Are you sure that significant amounts of chlorides will go overhead with the water vapor?
RE: Oily water separation.
RE: Oily water separation.
The source of the feed to the DAF was all the watery sludges, including washdown, spill, desalter, etc.
The overflow from the DAF was stored in a pair of tandem tanks that were used as phase separators. Sometimes the separation was good giving 50/50 organic/aqueous mix. On other occasions the separation was lousy, <5% organic.
RE: Oily water separation.
http://www
RE: Oily water separation.
It looks to me as though the Pall unit will do a good job on "easy" emulsions, but will fail with really stable emulsions. Maybe you can send a sample to Pall and have them run a test. Also ask them for references at petroleum refineries who are presently using the units on streams similar to yours. Then call the references. Find out what the real operating experience has be with a unit in a similar service.
RE: Oily water separation.