I am working for Fluor and looking for a party who can make simulations of rollover in an atmospheric butane storage tank for one of our clients. It is stated in numerous articles that models for this phenomenon are readily available for LNG for even these models I can not find. For the ones unfamiliar with this: it concerns the rapid mixing of two layers of liquefied butane inside an atmospheric storage tank resulting in a large amount of vapor boil-off. Thanks.

Dear Sir:

I think I need your clarification on the boil-off gas(BOG) simulation in LNG tank.

1. Just to verify that simulation you mean that 3D model(say: by Fluent) that could show BOG vaporizes, flows and moves

out of tank from BOG pipe, NOT just calculation.

2. Is any heat transfer needed to be modelled? Say duo to the change of ambient temperature or sun radiation.

I worked as a daily Fluent user simulating engine flow and heat transfer and I am now working on LNG tank design calculation.

If you think I can do it , please give me the time frame and cost you are planning so that I will see if myslef or someone I know could fit in it. We will find a contract company per your request.

Thanks

This is easy to do, you must have the density varying according to composition and the density varying according to temperature. If there is no mixed species, there is no roll-over.

You also must have different heat of vaporizations for each gases in the tank and the saturation pressure for the mixture calculated from an appropriate equation of state and the polynomial specifc heats for each gas in the tank.

It works this way:

- The light gases evaporates because of a temperature elevation (so you must have heat transfer) - The top layer keeps the heavy gases, so its density increases - the top layer sink by gravity (buoyancy) - the bottom layer goes up and takes place of the top on and it starts again.

In summary you need to ask for a software that is able to do:

VOF + differenciated evaporation per species(Hv and Psat) + buoyancy + heat transfer.

The density of the liquid varies with concentration AND temperature (boussinesq) The density of the gas could be ideal gas (Viriel if the gas close to Tc,Pc)

There is a roll over in the gas as well but it might be less of interest.

Good luck

Consultant

Dear madam, sir, If I understand it correctly you are referring to normal free convective circulation. However it appears that stratification may take place in the liquid phase while the top density is still lower than the bottom density. Due to the mechanism you describe the 2 densities approach each other and when they are near equal, rapid mixing takes place resulting in immediate boil-off of a large amount of liquid. Please refer to AIChE journal vol. 29 no.2 March 1983 page 199 which describes a LNG model for this. Now I am looking for a validated model that decribes this for butane.

Dear Mr. Rong, I am mainly interested in a model predicting the amount of vapor created by the boil-off when the stratified liquid layers mix. Preferrably together with a calculation of the max. delta T allowable between liquid top and bottom in order to stay away from boil-off. Heat transfer indeed is involved; I think I can't post pdf's here but if you give me an e-mail adress i will forweard some extra info. A dispersion calculation of the BOG coming out of the tank is not necessary. Kind regards, Cees van der Ben

Hello,

This is interesting.

Hopefully stratification SHOULD take place if the top density is still lower than the bottom density.

How rapid is this mixing?

I guess the lighter dissolved gas at the bottom get "liberated" from the mixing.

How could there be this rollover if there is only butane in the mixture? is it possible?

John

[preakzz]

Hi everyone..

I'm a student and currently doing my final year project on this.. I'm really hoping that anyone can assists me on this. But the simulation I'll be doing will not just on the density difference but also with different issuing angles of the bottom filling nozzle. If anyone can help me with this, please do email me at preakzz@gmail.com


Thank you!