Oil skimmer

[DaniMP]

Hello !

I have a question for you :

We are adding an oily water storage tank in our facilities, and I want to implement a skimming way of removing the oil phase that will form at the surface of my tank.
Do you have any recommandation ? A floating skimmer inside the tank with an interface detection / a system of valves at different levels to check the phases and manually purge, etc...???

Thank you !
Daniel

 

[LittleInch]

Search "API oil water separator" and there is tons of stuff, but I don't understand why you're doing this yourself. There are many suppliers who offer ready built tanks to do this.

The easiest skimmer is a pipe which rotates and has a slot cut in it. As the oil floats higher than the water it can be easily controlled on a level surface and only the oil flows in. The weir level on the far side of the baffle will allow water to flow over it, but as the oil thickness increases, the oil flows into the slot due to the different density of the oil and water. - look at a few diagrams and you'll figure it out...

My motto: Learn something new every day

Also: There's usually a good reason why everyone does it that way

 

[DaniMP]

Hello LittleInch,

thank you for your answer but I think I didn't make myself understood : the storage tank where I want to have this oil purge would be located upstream my API oil water separator.
As I can not control very well the quality of my water, sometimes there will be a lot of oil coming along, way above what my API separator can accept. That is why I want to remove the layer of oil that will form at the surface of my storage tank beforehand, with a device like this one for example :

http://www.mesarubber.com/oil-skimmer-pontoon.htm

But Iis this method reliable ? Are there other ways more often used in the industry...??

Thank you !
Daniel

 

[IFRs]

It sounds like you need a floating suction. Basically a pipe hinged at the shell nozzle with floats attached to the free end. Or can be done with a coiled hose. Try Google "floating suction".

 

[DaniMP]

Thank you IFRs for your answer !

Yes that would be one solution. But are there any alternative ? What are the best pratices of the industry for skimming an oil phase at the surface of an oily water tank ?

Thank you !!

 

[fegenbush]

If the tank will be filled to the same level continuously, it is possible to use a weir to skim the oil.

 

[DaniMP]

The tank won't be at a same level continuously (thanks fegenbush).

 

[LittleInch]

DaniMP,

what you would normally do in this case is use a three phase or in this case probably two phase separator where you control the level of total liquid and also control the level of the oil water interface level. What you do is create a baffle in your horizontal vessel with the initial section as long as you can make it which then has a nozzle in the base - which is your water outflow to your oily water separator. you control this outflow based on the height of the oil / water interface. This height needs to be lower than the height of your baffle plate.

The nozzle on the floor behind the baffle, the height of which is up to you, depending on the relative flow of water and oil, is your oil outlet and is controlled on overall liquid level.

The trick is to size your outflow nozzles and control valves such that they can handle the max flow of either water or oil without affecting the level too much. similarly the size of your separator is important to provide enough residence time to allow sufficient separation (2-3 mins min) and also to allow variances in flow to not affect the level too much.

My motto: Learn something new every day

Also: There's usually a good reason why everyone does it that way

 

[DaniMP]

Thank you LittleInch. Actually that is what we have in our process. But we have some operating problems and that is why we want to have this skimming option in the storage tank.

regards,
Daniel

 

[IFRs]

You need a skimmer that stays with the liquid level and whose buoyancy changes such that it won't skim when there is no oil present. We have done this often enough with aluminum internal floating roofs that have skimmers suspended underneath them. The general idea is not new, nor is it rocket science. The floating suction is a very common solution for a similar problem - wanting to withdraw the upper liquid preferentially. I know of no others that meet your needs.

 

[LittleInch]

So if you're adding a tank for this, why don't you control the levels such that you maintain a significant oil level and just have a nozzle part way up the tank in the top section of the oil level and control this on interface level and control the overall level on water outflow? Say have a 1m thick oil level and 2m water level in a 5m high tank with your oil nozzle at 2.6m this gives you a lot of room to manoeuvre - basically a vertical separator.

If you are concerned about overwhelming your normal API separator this would simplify things rather than skimmers etc. It is a little odd, but if it does the job then design it right and it should do your job.

My motto: Learn something new every day

Also: There's usually a good reason why everyone does it that way