Sorry but please explain"gun barrel"

Gun barrel to me is something thar fires artillery shells or is a very thick pipe but clearly to you is something else.

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On the "please explain 'gun barrel'" item, see:
https://www.glossary.oilfield.slb.com/en/Terms/g/g...
https://www.esd-simulation.com/blog/summer-series-...

On the original question- "capacity" as I normally see it is just the tank capacity, unrelated to the maximum flow rates; can't help on the rest.

Well you learn something new every day here on E-T.

It looks to me like the second link better explains the gun barrel thing which is the simple tube on the side of the wash tank.

It looks to me like the size of the wash tank is determined by incoming flow of oil / water. the degree of emulsification, the size of the droplets of oil and how much oil in water you are allowed in the water disposal.

Simple gravity separators need time to separate the two liquids effectively. The smaller the tank the less time it has.

So must the wash tank be higher than the tanks - no but the level in the receiving tank will need to be lower otherwise it will all go wrong.

That second link is a good explanation of how it works.

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There are experts who design these tanks and they are pretty good at it. There is some science and some art / magic. Understanding the liquids and solids involved as well the operating conditions drives the design. I know a guy who does this and have participated in some decent sized ones. Interesting projects for me...

Seems like y'all are up to speed on what a gun barrel is (or gunbarrel, some folks spell it both ways). I think I've heard the term wash tank before, although I feel like that implies something different. It is essentially a large separator, operated at a very low pressure, to remove a little bit of oil and vapor (if present) from a lot of water. Other options for this would be an API separator and/or daf or something.

Reason why I was asking about it was because I wasn't sure if a "1000 bbl gunbarrel" is the description of it's volume capability, or it's throughput. I don't have a lot of MSAs with vendors, just fabricators, so if there was a way for me to determine the throughput capacity of one of 'em that would help a great deal.

Capacity can indeed mean one of two things so I'm sorry for not being more specific. I'm looking for throughput capability, beyond what the external piping would limit of course.

The second link above is a good explanation of a gunbarrel. (I'll stick to the one-word name from here on out. I think I got caught by autocorrect.)

When I have questions about guns I'll definitely head over to the 2nd Amendment forums. :D


Sounds like there's not a really well known set of equations beyond perhaps using something for a simple-weir style 3 phase separator to determine required residence time for separation. I suppose special internals and piping would be "gravy", so to speak.

I would hazard a guess that the 1000 bbl is the physical volume of one of these things and not the throughput.


As said above the throughput will vary hugely depending on the input to the tank ( water cut, droplet size etc,) the required oil in water in oil in the outlet and other physical things like internal baffles, diffusers, location of nozzles on the tank etc.

I've seen similar in terms of large volume oily water systems where all these factors came into play.

There is some good reading in the design of API gravity separators, but these are designed for small amounts of oil in water. I guess you're looking at water cuts of <95%??

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The last ones I did were 27,000 barrel. There were a lot of interesting features, baffles, slots, troughs, etc. Not my design but I worked with the designer. I never expected to see this on a forum!!!

LittleInch - I'm expecting to see > 95% water at max rates, and probably > 99% water at minimum rates.

IFRs, would you care to share the vendor from whom you purchased?

Gunbarrels are atmospheric tanks were originally developed in the oil and gas industry to dehydrate (remove water from) crude oil. With the advent of larger and larger produced water volumes they have also been used, albeit incorrectly, to separate oil from water. A gunbarrel tank has the inlet in a degassing boot, which is a concentric pipe extended up through the top, roof, or deck of the tank several feet. The inlet fluid enters the boot below its midpoint. Liquids fall down, while lighter gases separate. The gas is piped through the roof and into the top portion of the tank (the gas phase). The boot extends down through the roof to within a few feet from the bottom of the tank in what is refered to as the "downcomer" pipe. Oil and water exit the downcomer at the bottom. The downcomer may have a horizontal spreader plate attached at the bottom to aid in distributing the inlet oil, which naturally, rises when separated, from the water. Water exits the gunbarrel tank through a sidewall connection and enters an external riser pipe known as the water leg. The water rises up the water leg to a spillover point, and falls down through the spillover point in a second pipe back to grade, where it turns to enter the next tank. The spillover point establishes the water-oil interface (contact level) inside the gunbarrel tank. This spillover point can be calculated using a simply hydraulics formula:

Spillover Point = desired height of water inside the tank x the specific gravity of the water, times the desired height of the oil times the specific gravity of the oil, all divided by the specirfic gravity of the water.

The capacity of a gunbarrel tank used to dehydrate crude oil is shown in industry accepted nonographs like this one:

https://res.cloudinary.com/engineering-com/image/upload/v1556893502/tips/GUNBARREL_SIZING_NOMOGRAPH_FOR_KBW_HEGB_PAPER_g1uxl2.pdf

Since about 1950 gunbarrel tanks have been misuded as oil-water separators in high water cut applications. Gunbarrels fail to perform in these applications because the dominant phase is water, which flows directly from the bottom of the downcomer out of the tank into the nearby water leg inlet, at too high a velocity for oil-water separation to occur. The lack of adequate retention time to achieve Stokes Law oil-water separation means that the majority of the inlet oil exits to the water leg and is carried in the downstream tanks, defeating the intended purpose of the gunbarrel tank for these applications. It is common for up to 99% of the inlet oil to remain in the effluent water in these applications.

A solution was patented in 1991. It is known as the HWSB Skim Tank. This tank is designed to separate very small quantities of oil from very large quantities of water. Since 1991 many thousands of these HWSB Skim Tanks have successfully replaced gunbarrel tanks, separating and capturing over 99% of all entrained oil in the produced water fed into them. The HWSB Skim Tank resembles the gunbarrel tank from the outside, but the internals are significantly different. The inlet fluid enters the HWSB and rises to near the top of the fluid level where oil separates. Water falls down through the majority of the tank's area. Two downward slanted internal spreader baffles maximize the water retention time so the oil has time to separate. Water exits near the bottom of the HWSB into a water leg much the same as in the gunbarrel. HWSB Skim Tanks routinely separate all oil from water leaving less than 50 parts per million of oil in the effluent water. HWSB is an acronym for "Hydrodynamic Water Separation Breakthrough". The HWSB patents are currently owned by KBK Industries, Rush Center, Kansas.

Also you probably want to look at tilted plate interceptors if you're approaching 99% water cut (basically oily water).

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