Oil & Water Separation

[robjul]

Hello,

I am designing a system where Processed Used Oil will be shipped via a Lorry and will then be pump to an atmospheric storage tank. From the tank, it will finally be delivered to the end-user for use as Fuel Oil.

I am not sure whether to provide an oil & water separator upstream of the pump as I am worried that the Processed Used Oil might have been contaminated with water?

Also, which is correct to use to separate the oil from water, a 2-phase Separator, coalescer, K.O. Drum, or Scrubber?

My utmost thanks!

 

[zdas04]

None of those. Use a gun barrel (atmospheric tank with either a weir gate or weir nipple and an oil skim line).

David

 

[robjul]

Hi David,

It was great relief knowing none of those I thought of in separating oil & water is recommendable. I'll appreciate it much if can go further in providing some more details on how to instal a weir gate or weir nipple and an oil skim line. Sorry for the inconvenience but honestly, I've never these kind of installations inside a tank.

Many thanks, indeed.

 

[shahyar]

How much water you can "guess" in your oil? its concentration in water (ppm), dictate the best mechanism.What is the flowrate?

 

[robjul]

Hi Shahyar,
As of this date,I am still waiting some feedback from the client regarding the required parameters (capacity, temp., pressure, viscosity, density, etc.)for the design of the Processed Used Oil System.

As I initially understand, the term "Processed Used Oil" means that the oil (used oil coming from Petrol Stations)had already been processed (meaning some impurities like debris, metal and water contents, etc, had already been removed/filtered/treated beforehand). However, although we could presume that the oil is relatively clean for use as Fuel oil, I am having some doubts that the oil could still have the chance of having some minute amount of adsorbed water in it considering the adversed effect of water when heated?

Looks like a two phase separator for the Processed Used Oil with minute amount of adsorbed water is not a proper engineering approach for the system? I am thinking of using a "gun barrel" as suggested by David above but I have not received any response yet on how a gunbarrel tank looks like? Any idea on what is a gunbarrel tank is, and how does it work?

Or any other suggestions to ensure the "cleanliness" of the Processed Used Oil is most welcomed. Many thanks!

 

[zdas04]

This site has been having problems with flagging new posts and I missed your question in the noise.

I've attached some pages from my Facilities Engineering course. These systems are easy to make with the external wier (the internal wier version is more expensive, but less prone for the wier piping to freeze). They are used in Oil & Gas all over the world. The trick to success with a gun barrel is that it has to be a continuous process, slugs overwhelm them. Adding a heated pre-treat tank is an innovation I've used in several sites that has worked well.

The concept is very scaleable. Capacity is really based on your heating capacity more than anything else. I generally run both the the pre-treat tank and the gun barrel at 150F - 160F. If you are looking at ppm level water content I'd probably run it 170F-180F, but getting that number right is more trial-and-error than any science.

David

 

[robjul]

Thanks much indeed David, for the gun barrel pics. So, both gun barrel tank & 2 phase separator work on the same liq/liq separation principle? Am I right? Appreciate your comments on what basis and justification do I have to choose one from the other?

Though not important, am also thinking why it was called a gun barrel 'coz I might be asked the same question and I don't know the answer.

 

[zdas04]

I have no idea why it is called a gun barrel.

A 2 phase separator is a pressure vessel. A gun barrel is an atmospheric tank. Consequently, the retention time can be much longer in a gun barrel (a 400 bbl 2-phase ANSI 300 separator would cost about a million dollars, a 400 bbl gun barrel is a few tens of thousands).

David

 

[robjul]

It was indeed quite a substantial saving opting for the atm tank! Does this cost include a Pre-treat tank? I'll get back to you when I had received the data that I had requested from my client.

Many thanks again, David!

 

[robjul]

Hello to my colleagues,
Whilst waiting for some data from my client, I had a chance to talked to an Operator of an Oil Depot which consist of several storage tanks for different petroleum products. I was told that during product offloading from the tankers at the pier, some water is picked-up and settled at the bottom of the tanks for 24 hours afterwhich, the oily water is finally discharged into the OWS. During rainy season, oil (from leaks, overflow, gantry, etc.) is also washed out and also goes into the OWS.

The OWS is a rectangular concrete compartment which looks like a Septic Tank. The only difference is that the OWS have 3 equal compartments inside separated by concrete walls. The concrete walls have holes (somewhere slightly above middle) that holds the 90 degree C.I. soil pipes where the oily water flows from one compartment to the other. Once in a while, the three 3 compartments are inspected and if there is substantial oil above the water, the oil is being manually skimmed off and placed in drums.

1. What is the relevant API standard for this design? I had seen API 421 but the design is different from above.
2. Do we have any reference somewhere in this forum that can give me some guidelines on the design of this particular OWS Separator? I had already conducted some researches (including books) and it looks like as long as OWS Separator design is concerned, the discussions always end up using either a pressure vessel or tank, unlike the one above which is just a concrete rectangular compartment.
3. Somebody told me that this design belongs to the Civil professionals? If so, please advise any reference material.

Many thanks!