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Anonymous Poster

Water Draw-Off in Storage Tank

02/24/2010 7:10 AM

I am seeking for an advice for applicable and advanced method to draw-off water out of refined products storage tanks (Diesel, Gasoline and Kerosene). The practice we do to draw-off water is to gauge the tank to determine the level of water presence, then open the drain line manually to draw-off almost 80% of measured quantify. This practice is not accurate and subjected to human error in detraining cut-off point between oily water and pure product.

I appreciate if anyone can present more advanced method better than what we are using, thanks.

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#1

Re: Water draw-off in Products storage tanks

02/24/2010 9:54 AM

You could install an automatic sump system. It would be easiest if you set it up outside your main tank.

To get 100% of the water you will have to put the outlet pipe from your main tank directly in the bottom of the lowest point of your tank. Depending on the size of your tank this could be tough because it may mean cutting into the tank pad to lay your pipe. An alternative method is to have the outlet for your main tank (say a 2 inch line) bend down directly over the lowest point, with a sloped bottom this is the most common method I have seen. You will have some water present in your tank bottom (up to the opening of your pipe) but as long as it is lower than you main tank outlet no water should leave with the fuel.

Once the drain line is set up, send it to a small water draw tank beside your main tank (100 to 200 gallons is sufficient for a large storage tank 25 to 50 for small tanks). Set up a float controlled valve with a float that will only float on water to open a valve when water is present in your water draw tank.

Even if you have more water in your main tank than the water draw tank can hold, it will continue to drain until the water draw tank is full of fuel down to the level where the float shuts the valve.

This system works for good clean fuel very well. It is less effective on long distance pipeline systems because of the volumes of water involved. The water on long distance pipelines is usually dirtier than in a airport or terminal and tends to gunk up the float control.

In most fuel systems even if you have an automatic water draw system, it needs to be manually monitored because if it fails you could overload your water treatment system with fuel.

My suggestion even if you install an automatic system is to train your operations personnel how to tell when water transitions into fuel. It can be tough with clean water and clean fuel, especially gasoline. Usually the best indicator if I cannot see the interface is to listen, water is much heavier and sounds different when it drains into a bucket or drainage system. Most of the water draw methods I have used incorporated an open drain to the product recovery system so we could see, feel and hear the transition.

I have seen some really good product recovery systems designed to recover almost all of the fuel from your drained water, let me know if you need to know about that too.

The third paragraph in this link describes the float I am referring to. This is in a water coalescer designed to remove water and some contaminates from fuel as it is pumped through.

Drew

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#2

Re: Water draw-off in Products storage tanks

02/24/2010 12:54 PM

you can go for measurement of water by water probe based on capacitance principle in which probe forms capacitance with water and not with oil. probe can be inserted in a still well from top or can be installed in level switch type assembly at bottom of tank. Use a shut down valve(ball valve for no leakage) at a bottom most nozzle to make the water draining system automatic.

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#3
In reply to #2

Re: Water draw-off in Products storage tanks

02/25/2010 6:18 AM

Er, why not go for a conductivity-based instrument?

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#4
In reply to #3

Re: Water draw-off in Products storage tanks

02/25/2010 9:14 AM

Reliability. In my experience the contaminates water separated from fuel tends to cause electronic sensors to fail. With a water draw system you do not want to risk it opening a valve because it "thinks" there is water when there isnt. This is costly in several ways; manhours to recover the fuel (especially if it overfills your recovery system) repair/replacement of electronics and temporary or permanent loss of product.

The float valve system has been used for a very long time and does occasionally fail due to gunk or float failure but it is quite reliable.

As I said, the most reliable method is trained operators, but automatics can work too as long as you consider the risks.

Drew

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#5
In reply to #4

Re: Water draw-off in Products storage tanks

02/25/2010 9:27 AM

Good solution Drew

the smaller tank being very similar to having a sight tube

much easier to poke around in a 100 gallon tank then a 5000

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#6
In reply to #5

Re: Water draw-off in Products storage tanks

02/25/2010 11:55 AM

Garth,

You are thinking too small...I was picturing a (small) 500'000 gallon floating pan tank I used to drain water off of at Barksdale AFB. We had a small open container (picture a 80 gallon drum) on the side of the tank with a sloped bottom. We would drain fuel from the sump into there while looking down the open top. Drain till we got clean dry fuel or it got full of water; drain barrel and repeat as necessary.

On the Tank farm in Georgia (state), we had a small pipe stuck out of the bottom of the tank coming from the sump. It opened over a 5 to 10 gallon bucket / funnel that had a drain flowing to the product recovery system. We would open the valve as much as we could without overflowing the drain untill clean dry fuel was observed. On a bad day it would take over an hour, but usually only a few minutes.

You want a tougher one? How about a 2.5 million gallon underground tank. That one, we had to gauge the sump with a tape and bob using water finding paste then pump any water out. We did have an automatic tank gauging system that alerted us to the presence of water, but it worked off of a float attached to a calibrated gauging wire reel.

Drew

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Re: Water draw-off in Products storage tanks

05/15/2010 8:02 PM

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#8

Re: Water Draw-Off in Storage Tank

03/24/2023 8:42 AM

Add a small quantity of methanol, and the problem will go away.

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