Nitrogen Blanketing versus Floating Roof 2

[jmk0407]

From a product contamination standpoint, is nitrogen blanketing a fixed roof tank preferable to using a floating roof tank? I am working on a jet fuel tank farm and am looking into any cost savings that would be associated with decreasing the load on the nitrogen generator at the expense of the increased first cost of a floating roof tank. I'm aware that floating roof tanks are typically used for flammable substances but is there a significant increased possibility of product contamination due to contact with the atmosphere at the seals?


Thanks!

 

[fegenbush]

Are you speaking about an internal floating roof or an external floating roof?

 

[LittleInch]

I used to work extensively with Jet fuels and can't recall any issue with "contamination" from contact with air. The tanks were mainly fixed roof with open vents, but we were in relatively low temperature locations where vapour was not a significnat problem either from hazardous area or emmissions.

Floating roof tanks are predominantly used where vapour emmissions become excessive, but below bubble point. The usual issue with Floating roofs externally is that the seals and rofes can leak rain water into the product, which is a particualr issue with jet fuels, which is maybe what you are thinking of.

Not sure if an internal FR will reduce your Nitrogen load as I guess most of it is simply the result of discharing vapour during filling whilst having to fill the tank during discharge??

My motto: Learn something new every day

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

 

[IFRs]

Must be internal with a N2 blanket. Tons of jet fuel tanks have internal floating roofs in them just for contamination issues - dust, scale, water, air, bird poop, etc. UPS, airports and the defense department in particular. Both full-contact and non-contact. Mostly aluminum. Many have floating suctions to withdraw from the upper layer of product. None of the ones I worked on had N2 and floating roofs. If you use a closed system and N2 blanketing the floating roof will not change your N2 load or expense - that's all from filling and emptying.

 

[jmk0407]

Thanks for the info. To clarify, I meant using an unblanketed internal floating roof tank in lieu of nitrogen blanketing a fixed roof tank.

 

[IFRs]

If you inert the tank you will have no emissions and a good size ongoing cost. If you put a floating roof in, you will have a one time cost and ongoing emissions. What you do depends on your business model and the regulatory environment you are in.

The evaporation rate from the liquid surface won't be slowed down by the N2 blanket but you will have inerted the vapor space and you will have no emissions from tank because you are sending the vapor stream from breathing and filling to a balance tank, flare or reclamation device. With a floating roof you can have varying amounts of emissions depending on the type of floating cover ( non-contact, full-contact, cheap, expensive, etc ) and the options chosen. Some are very, very good and your potential to emit can be surprisingly low.

Probably just what you were finding anyway...