Cleaning a chemical tank

[rocketscientist]

I have a tough cleaning job. The storage tank is filthy with food grade oil; the flash point is extremely high. The new product must contain no more than 40 ppm water. The storage tanks are thin-walled tanks originally used in a dairy. Steam cleaning is out because of the water and also because oils with a FP of 46 C won't be very impressed by steam. Then again, I heard of our tanks described as pop cans so vacuum failure is a major concern.

Originally, I suggested using the product and pumping it through the tanks after reaction to form product and filtration but this was rejected.

Now, an engineer is suggesting having a guy climb in the tank with soap and water to mechanically clean the tank.

Any ideas?

 

[EricWales]

How big is the tank?

What about a caustic/detergent wash/soak to degrease, then drain the tank and water flush (use a pressure washer) to remove the caustic.

To dry, put someone inside the tank to rag it out to remove the bulk of the water and then use nitrogen/dry air purging to remove the moisture content. Pressure cycles would be good, but it sounds like your tanks aren't up to much.

You can get a dew point meter to test the vented gas for moisture content and therefore determine when the tank is sufficiently dried

To speed up the drying, you could have the tank wrapped in heat blankets (the type used for weld stress relief) in conjunction with the purging, or you could hire a heater for the nitrogen/air depending on how much you are prepared to spend.

 

[rocketscientist]

We're looking at 50,000 gallons. I proposed using bentonite to clean up the stray oil and water after cleaning with hot water and steam. Purging with all can be a problem with an oil tank. Many of these complex oils burst into flames when contacted by air. I hesitate to think what would happen if the oil were contacted with hot air at even modest velocity. Hot N2 is possible but very expensive and big tanks tend to leak.

 

[unclesyd]

There are many ways to attack your problem from many angles,

Contact some people like AIMM who have the equipment to tackle the job from several angles.

You can rent the tank cleaning nozzles.

You can use a foaming system instead of pure liquid.

If the flash point of the oil is 46°C it is going to be had to get the cleared for vessel entry without a lot of work and special gear.

If draining is problem add 5" of water and make 3" hot tap for a draw off nozzle.

http://aimmtechnologies.com/services.html

 

[rocketscientist]

No, I meant "freezing point," not flash point. Obviously, the flash point is extremely high if the freezing point is 46 C. The main issues with the final product are water contamination and odd contaminants like toluene and unreacted polymerization feedstock.

 

[sshep]

In light of the new data about flash/freeze point, your engineers idea to enter and mechanically clean is a sure method. I have worked a few jobs where polymerized and gummy material was cleaned out by simply cutting a large door in the tank side then hydroblasting then squeegy the floor clean straight out the "door".

So long as there is no safety concern with entering, this method is 100% certain to get it as clean as you desire.

best wishes,
Sean

 

[rocketscientist]

We cleaned the first 20,000 gallon tank. A operator got into the tank and shoveled the goop up into a 5 gallon bucket. It took about 6 hours to remove a layer about 4-8 inches deep. Mixing water with a shovel-full of the material produced a lumpy emulsion. After shoveling, the tank was filled with water and a steam coil inside was started. We considered using a steam sparger to improve mixing at the bottom of the tank, the pump circulation was poor despite the discharge line being tangential. We decided not to remove the 1-inch TE nozzle. This is where I would have installed the 3/8-inch tubing with Swagelok tees for sparger nozzles.

The next tank may be more challenging since the oil is pyrophoric and may burn when exposed to air.

 

[vaniska]

Ya this is is a very tough job i think cleaning Cleaning a chemical tank is very tough job........

<a href="

http://www.cpel.com"

]FRP Large Tanks</a>

 

[ash9144]

A couple other ideas...
1. Try a solvent with a high vapor pressure like EtOH that you could circulate through the tank through a cleaning nozzle. When the thick oil is removed you can then steam out the solvent. Of course this option presents you some new challenges to deal with such as handling the solvent and disposal/recovery.
2. Flush tank with new oil until it meets specs. Then you just have to find outlet for the contaminated oil.