Pressure Built Up Unit (PBU) Adding Pressure to LNG ISO Tank

[ReynoldKenko]

HI,

We want to raise the pressure of Liquefied Natural Gas (LNG) ISO tank from 1.5 barg to 7 barg, Does it possible to use Pressure Built Up Unit (PBU) which installed in closed circuit (ISO tank > PBU >ISO tank) to reach the target pressure of LNG inside the ISO Tank?

The Capacity of ISO tank is 40ft and PBU is 300Nm3/h.

Thank you

 

[LittleInch]

Can't you just let it warm up a bit?

7 bar looks to be about -130C.

But if you want to keep it at -168 then yes, that's one way to do it, but you will need either a compressor, a pump or do it in one batch.

I asusme you mean 40ft^3? How much is liquid and how much as?

 

[ReynoldKenko]

Yes we want to warm it up a bit by using the PBU and let it back to ISO tank, and let the circulation of LNG running until the pressure reach 7 barg.

So, do you think it would achieve the target pressure?

 

[LittleInch]

Yes, once the temperature gets to about -130C.

Your diagram is very simplistic ans shows no pump, no pressures or temperatures.

You don't want to have so little flow that you create loads of vapourised gas

 

[Compositepro]

The pressure build unit is a vaporizer. Liquid gravity-flows to the vaporizer and warm vapor flows back to the vapor space. When the vapor valve to the tank closes the vapor will push liquid out of the vaporizer, back to the tank, and pressure stops increasing. It can reach any pressure up to the vapor pressure of LNG at ambient temperature (much higher than 7 bar).

 

[LittleInch]

I started to think it was going to work that way. The only issue then is whether the warmer vapour in the gas phase starts to condense and reduce pressure when it is in contact with the colder liquid, but I guess you just repeat the exercise if it does.

 

[georgeverghese]

You are planning to run this PBU in thermosyphon mode, so the PBU should be at some elevation below the min low level in the tank. To know what this delta in elevation should be, you need info on pressure drop through the PBU, dp through single phase liquid feed line, dp through 2phase exit line from PBU back to tank. The 2phase return line should be free draining, no pockets permitted.
The drawing shows an ambient heated high fin vaporiser for this PBU; are you happy with the thermal design of this unit? Does the vapor generation match what you require?

You say this is an ISO tank - design pressure should be at least 9-10barg if you want to operate at 7barg. Pressure control valve should be on liquid feed line to PBU.