Aluminium Floating Roofs - dormant loss 1

[Sundar S]

Hi people, Good day!

We are handling aluminium floating roofs for gasoline storage. For the past 2 months we have kept the floating roof dormant without any receipt or delivery in the tank. We find the vapour losses are more than usual for these two months. The physical stock in start of September was 2060 Metric Tonnes and by end of October the stock was 2045 Metric Tonnes. We lost almost 7 Metric Tonnes of gasoline each month. Could you guys give your feedback on how the losses are happening and please suggest whether this is normal and what can be the solution for this.

Note: The IFR diameter is 73 feet and the seals and IFR was found intact while we inspected last week through the inspection hatches. Also, this is a free vented tank. No N2 blanketing is provided.

Thank you all in advance.

 

[LittleInch]

By "dormant" do you mean that the roof stayed at its fixed position?

How are you measuring mass?

If level has the temperature changed?
Is there a leak in one of the valves?

but this sounds about right to me - Just think what the losses would be WITHOUT and IFR. You might be looking at 4 or 5%, not 0.35%

IFRS are good, but they are not absolute seals. Gasoline has a high vapour pressure. What sort of temperature do you have?

Maybe the tank temperature just heated up and increased the emissions compared to when it gets colder product in from a ship or a pipeline.

How can you compare this to "Usual". Nothing is normally that accurate when the tank is in normal operation.

Remember - More details = better answers
Also: If you get a response it's polite to respond to it.

 

[3DDave]

Theft?

 

[HTURKAK]

Also, this is a free vented tank.????


Mr. SUNDAR,

You should look vapor recovery systems .. Without knowing the design internal pressure, IMO, at least PV should be at roof ..

You may search the forum for VRU ..

Good luck..










Tim was so learned that he could name a
horse in nine languages: so ignorant that he bought a cow to ride on.
(BENJAMIN FRANKLIN )

 

[LittleInch]

Maybe the tank expanded a little bit more in the heat? Who know - you need to look at all possibilities of measurement error or change over time.

But gasoline in an IFR tank with open vents will lose some mass to the vapour phase and drift out of the vents.

Remember - More details = better answers
Also: If you get a response it's polite to respond to it.

 

[Sundar S]

Hi LittleInch,

Thanks for your valuable feedback.

We measure dip of the liquid on a daily basis and converted into mass by calcs
Nope there are no leak on any of the valves which was checked on a regular basis.

Temperature ranges from 25deg C to 36 deg C.

Yes Gasoline in an IFR tank with open vents will loose some mass. You are correct, however free venting to be done in order to meet the safety regulations else we should provide a nitrogen blanketing which is not economical.

Thanks,
Sundar S

 

[Sundar S]

Hi 3DDave,

There is no chance for theft.

 

[Sundar S]

Hi HTURKAK,

Thanks for your feedback.
As this is an Internal Floating Roof with a fixed roof tank there is no need for an additional vapor recovery system. This is how we operate the IFR tanks. Your suggestion of PV is a great idea however safety regulations will not permit those unless the tank is N2 blanketed to avoid any flammable vapor formations.

Anyways Thanks.

 

[3DDave]

Five people stole 3,000 long tons of Canadian Maple Syrup from sealed barrels stacked in a warehouse basically by hand.

You think you lost 15 metric tons over a similar period of time.

---

15/2060=.7%; thermal expansion of gasoline is .07%/degree F and you say you have an 11C (19 degree F) temperature variation which would produce a 1.3% change in volume - volume is the method you are using to measure mass.

What you should measure is the gauge pressure at the bottom of the tank which will remain constant regardless of temperature as long as the mass in the tank stays the same.

 

[Sundar S]

Hi 3DDave,

Thanks for your feedback will look into it

 

[IFRs]

What is the LEL of the atmosphere above the IFR? If it is consistently below 10% your losses may not be from evaporation.

Is there any blending or mixing?

Are you using the API methodology for your calculations? See API MPMS Chapter 11, used by many in the industry to calculate the effect of temperature and pressure on the bulk volumes of petroleum products.

You can use Tanks4 to estimate the evaporation losses from the IFR tank and compare that to the estimated losses from a fixed roof tank. Tanks4 is available at

https://www.epa.gov/air-emissions-f...ks-emissions-estimation-software-version-409d