Oily Water Skimmer Separator has problem of Oil Accumulation

[memo94]

Hi,

I am working in an offshore oilfield as a Process Engineer and I am new employee here.
The company has asked me to make an study and do some recommendation to solve a problem that is very old it is as old as the platform itself!!

Separated water from 2nd and 3rd stage oil/water/gas separators, and also water outlet from desalter are being treated in the Oily Water Skimmer Separator to decrease oil content to the lowest possible level befor disposing the water to the sea.
The Skimmer consists of some inclined plates that oily water will be distributed on the topside of them and the oily water will flow through these plates in a Laminar flow and oil dropletes will be released and collected on top and through an over flow will be collected in a compartment that will be recycled back to the system, and from bottom the water with low HC content will be sent to caisson and then disposed to the sea

and Now the Problem:

The Crude oil dropletes are sticking to the surface of these plates and after 1 week the performance of the Skimmer will decrease, and some times the oil content of the outlet is higher than the inlet!!!!!!!!!

Please, anyone before hase faced with such a problem?!
Why these oil droplets are sticking to the plates surface?

And most important question:

How can I solve this problem?

Many thanks for your replys.


Mehran

 

[MikeHalloran]

A "study" means you measure what it's doing, or not doing, so as to size its replacement or help you understand how to improve it. So, do that.

If I knew how to solve your problem >just like that<, my salesperson would be climbing onto your rig, and I would be watching satellite TV on a really big yacht. I'm not.

The oil is sticking to the plates because they are oleophilic. Perhaps the skimmer once had a wiper made of oleophobic material. Perhaps the plates were intended to be discarded or recycled and replaced.

The good news is, it never really worked, so any improvement you can make is a good thing.

The other good news is, lots of people make skimmers commercially. They advertise in metalworking rags, and I assume in oil industry rags also.

The bad news is, none of them work well forever, many don't work well at all, and you can't tell the difference from advertising.

The good news is, you have a test mule there, on which you can personally evaluate the effectiveness of different skimmer principles on an actual working oil/water stream.

Maybe you can arrange some small scale onsite demos.

Maybe you'll learn enough to make a better skimmer, so you can watch satellite TV, etc. Good luck.








Mike Halloran
Pembroke Pines, FL, USA

 

[ck1999]

The are also membrane systems that are suppose to work to separate out oil from water. Especially at neutral pH or in plain water. I believe there is a company in SC called separation dynamics that sell such a unit. I am vaguely familiar with the way they work, but you may want to contact them. But, as Mike mentioned there is upkeep needed to be performed to alloy this equipment or any equipment to work properly.

ck1999

 

[IFRs]

An air-sparged hydrocyclone can remove pretty much anything from the water. Try a google search...

 

[shoffman83]

Did I here desalter? Have the lamella plates ever been changed? Are they so pitted from years of operations that the oil has soemthing to grab onto? And if the salt build up is bad, you could be generating an emmulsion rather than breaking it. (thus the higher oil content in discharge versus overflow).

Most lammella separators do not feed ontop of plates, but pass the water through the plates. If you feed ontop of plates, you are generating a downward velocity which is fighting your upward "floation forces". If the downward velocity gets too high, there is no way oil can rise against it to the top, and your separator will plum not work.

LOts of stuff on how to study this (theoretical and other). And tons of vendors.....

 

[memo94]

Thank you very Much for all of your replies!

I did some test and finally found there is a communication between oil and water compartment (in addition to the overflow!!!)
I convinced the managment through my tests and finally the skimmer separator was opened for internal inspection, and guess what?!!!
Yea I was right, there is a window on the weir for inspection of oil compartment through water compartment. the gasket of these window was damaged and all of these problem was initiated by this gasket!!!!
Now the gasket is repalced and all of the problems are solved.
Oil content of the outlet water is 10 ppm!


Anyway thanks for all of the replies.

Regards,
Memo