Overfill protection to EFR tanks

[satendra14]

Hi,

I am new to storage tanks analysis. Can anybody tell me what are the ways to protect EFR tanks from overfill.
I am asking for mechanical systems.


Regards,
Satendra

 

[Latexman]

EFR?

Good luck,
Latexman

Technically, the glass is always full - 1/2 air and 1/2 water.

 

[satendra14]

EFR- Extrenal floating roof tanks..

 

[Duwe6]

Put an Overflow pipe just below the max roof level -- secondary seal almost touching the rim angle. Size this pipe such that no combination of pumps can put in more liquid than the overflow can drain.

Instrumentation-wise, I would put a high-level switch where the roof will trip it about a foot prior to the overflow starting draining.

 

[don1980]

You'll find good advice in this thread.

http://www.eng-tips.com/viewthread.cfm?qid=205837

 

[satendra14]

I read that thread, it really doesnot confirm the need of overflow slots or overflow protection on EFR tanks..
One of the post from "IFRs" says that he is designing tank from years and have not given overflow protection to tanks..

[highlight #F57900]IFRs (Petroleum) 1 Jan 08 15:02
FYI - the "vents" you see in the tank shell or fixed roof are for ventilation, per API 650 Appendix H. They serve to reduce fixed roof underside corrosion and keep the air/vapor mixture above the IFR below the LEL. The tank will be protected from pressure or vacuum as a by-product of the huge holes required for adequate ventilation (2 square feet per 10 feet of tank diameter). Many of the tanks that I design have no shell vents or overflow ports. You really won't hurt the floating roof that much by forcing it into the fixed roof rafters while a overfill (read "spill") costs so much more that any IFR damage is worth the extra protection of additional shell height. High, high-high and emergency alarms and shutoffs seen to do the trick. I have been designing, manufacturing, installing and repairing aluminum and steel IFRs since 1977 and designing tanks for nearly that long also[/highlight]

Also API 2350 and API 650 does not clearly adress the mechanical arrangement for overfill protection on EFR tanks...

Please guide..

 

[LittleInch]

You say you're new to storage tank analysis. It should be clear now that there is no such thing as a "mechanical" system to protect them from overfill.

This sort of tankage normally relies on instrumented protection systems with level guages (often with pre set alarms)and separate high and high high level switches closing the inlet valve. The only "dumb" system available is an overflow, but that brings with it the key quesstion - where are you taking the overflow? How big is the tank / bund? What happens when that fills up?

A tank overflow, especially open vents with product just pouring down the sides is a recipe for disaster - the Buncefield tank farm explosion in part resulted from uncontrolled gasoline flow pouring out of the roof vents and creating a huge vapour cloud which subsequently exploded....

I think if there was a reliable "mechanical" overfill device it would be in regualar service by now.

Ultimately if an EFR tank overfills, the roof will become unstable and fluid will start to flow over the rim. The roof may sink or break, but the tank should stay in one piece.


My motto: Learn something new every day

Also: There's usually a good reason why everyone does it that way

 

[satendra14]

Thanks "LittleInch",

I am analysing tank its datasheet says tank roof is of strong seam construction and also they have provided Emergency Vent to tank.

If tank roof is as strong as tank wall and seals are of mettalic material. Then do we need to give mechanical system to protect tank from overfilling and externla fire scenario??

Can i provide overflow line after certain height in EFR tanks... If roof reaches the level of Overflow slot/ overflow line then excess liquid will be taken care of oveflow slot.. this will protect roof/tank to get any damage. For fire case i can provide emergnecy vent, coz as i said if roof is of strong contruciton it will not damage due to fire vapors and also metallic seals have design pressure as good as tank design pressure.

In general EFR tanks seals are of rubbery material and roof is of weak construction so in case of fire tank will be protected at expense of tank roof but i have here differnet condition..

Please correct me if i am in wrong direction.



Thanks & Regards,
Satendra Deshmukh