Dead stock removal from tanks.

[mrtangent]

Dear all,

We have a large storage tank 4000 te. Which we used to store a relative non-toxic "safe fluid". Due to the location of the nozzle on the tank we have a significant dead stock (100 + tonnes ) this is a significanty working capital costs.

We have as yet failed to get a method to reduce this volume. We dont want to put anthing in the tank which would make the product toxic ete and were limited on modifying the tank.

So any one else considered / solved the problem ?

We have considered putting things in the base of the tank but again we face contaimination / risk.

 

[unclesyd]

Depending on your location there are people that specialize in emptying tanks. They use a truck mounted vacuum system or skid mounted pumps to move the fluid. Your best bet would be to get in touch with one of these companies.

If you have specific problems let everyone know.

 

[mrtangent]

Thanks for the reply. I was'nt perhaps as detailed as I could have been.

Our specific problem is we dont want the dead stock in the tanks. Ie
for example at 2000 tes, only 1900 is usable. but we are charged for 2000 in working capital. Which is a sigificant cost factored over several years.

We want to improve our working volume. Ie, by filling the sump of the tank in with some cheap material, ie inert solid of some kind or pump mods. But would appreciate some advice.

 

[phcontrol]

1. Assuming that the fluid is lighter than water and that the tank bottom is clean enough to avoid piercing a hole in it, consider buying a large bladder made of non-contaminating plastic or rubber. Ensure it has a long fill-up connection of the same material so it can be tied at the entry manhole or roof. Drop it in while filling it with water. It will end on the tank bottom filling it according to the shape-volume you selected.

2. If the nozzle is large enough to accomodate a protruding pipe of smaller diameter and if your company can afford to empty the tank once, an internal L shaped extension of the nozzle could be welded to a new flange outside of the tank (no weld to the vessel).This flange would be sandwhiched between the existing vessel flange and that of the outside connecting pipe. Internally, the long end of the L can go as close to the bottom as deemed safe to avoid sucking in the mudd from the bottom.

 

[mrtangent]

Thanks Ph control,

Can you recommend a company or web site to find out more about these bladders ?

 

[dhamo]

If the tank has a drain line in the tank at a lower elevation than the pump suction line, then connect the drain line to the pump suction line. Line size and pump NPSH need to be checked for implementing this.

 

[jay165]

How 'bout a hot tap? Fill the tank with enough water to cover 3' over the top of the new nozzle. API 650 has (I think, it's been a while) rules on sizes, etc.

 

[mrtangent]

Thanks Jay/Dhamo

Unfortunatly we have an NPSH issue with the pump and locations which probit lower takeoff from the tank :-(

 

[phcontrol]

An internet search on Google for "tank bladder" would give you about 50 supply sources. You can select the one that best suits your application and location. Here is just one of them:

http://www.perma-type.com.

I hope this helps.

 

[mariodupuis]

Did you thinck about using a second pump with lower capacity but more NPSH to suck the product out of your tank when your at low level?

 

[atfab]

I have put a bladder into a storage tank for this exact scenario. There are several things to consider which include but are not limited to:
What to fill the bladder with? This depends upon the product in the tank and what could be compatible with the liquid in the tank if it leaks.
Is there turbulance in the tank?
Is there a floating roof with legs that need to sit on the bottom of the tank?
What elastomer material is compatible with the liquid in the tank?
Each application can take on different limitations that need to be considered. Let me know how I can help further.

 

[mrtangent]

Thanks atfab,

Can you advise where you purchased the bladder ?

How did you verify that the bladder would be leak tight ?,
pressures testing. ?

What about bladder decay over say 20 years ? how would you inspect the bladder / remove filler on leak ?

 

[jmw]

You don't say what the fluid is in your tank.
The big question is, why was the tank designed this way in the first place? One reason why the tank outlet is above the bottom of the tank is that some fluids have contaminants that settle out during storage. For example, heavy fuel oils have sediments and asphaltenes that setle out and collect in the bottom of the tank. Over time you will find you don't actually have product in the bottom of the tank but sludge. Every so often you will need to run the tank down and clear out the sludge. So is it a fair assumption that you have dead stock? maybe not. Before attempting any of the solutions abovem be wary that introducing anything into the tank to dsiplacce the dead fluid that you don't suddenly find yourself with a whole set of new problems such as poisening the downstream process with concentrated sludges. Alternatively, you may find that what you add sits on top of what has collected and you are no better off but the accountants are happy.

 

[mrtangent]

Thanks Jmw,

Very good points. Some things to consider. I think the tank design was just a copy of typical tank designs. The fluid is a clean fluid and not flammable only combustable. Mostly water free into 0's ppms. The design I am guessing is a copy of a tank design.

I take on board your commend regarding the accountants and usable material. To me its just the same as the end of year targets (get inventory down and then we run flat out in Janurary !).