What is “Dummy Pump” in an LNG Tank used for?

[bizkitgto]

I’m working on a project where we have a large LNG Storage Tank at an LNG Facility. There are several submerged pumps, and each pump can be pulled out and replaced with a dummy. It also calls for a “dummy pump” to be installed for the LNG Cooldown/first-fill. The dummy pump
appears to be a cylinder that just weighs down the foot valve to allow liquid to flow up the pump column. I don’t understand why this is part of the startup.

Can someone explain why we need a dummy pump and what it is supposed to do? Thai appears to be only needed during the tank cooldown and facility startup.

Thanks!

 

[LittleInch]

I think what it is used for is to flow cold gas vapour into the base of the tank to then purge the nitrogen out the top as most LBG tanks nowadays only have top entry for LNG.

You don't want to spin the pumps backwards with gas flow so they take out a pump and insert a dummy pump to weigh down the foot valve and allow gas flow into the base of the tank.

Best to check out the purging and first fill procedure.

 

[HTURKAK]

Dummy pump has the same dimensions as the real pump. As far as i remember , the pump supplier ( as well as the supplier and designer of the column ) provide a dummy pump to show that the column will allow the pump to pass without obstruction.

 

[shvet]

Guess this device is for the loading on a pump nozzle during the pressure test of the vessel. Check if this vessel is designed to be tested with a blind flange or not.

 

[LittleInch]

Its an atmospheric storage tank, not a PV.

I'm doing work on cryo LPG tanks using old LNG tanks and that's what they use the dummy pumps for - to flow cold gas or perhaps liquid into the bottom of the tank to sweep out the inert gas through the roof vent lines to flare because the normal fill lines are in from the top and you would have a lot of methane and nitrogen mixed up which would be difficult to get to 100% methane gas which you need for the regassification procedure or burning of the Boil Off Gas.

 

[bizkitgto]

Its an atmospheric storage tank, not a PV.

I'm doing work on cryo LPG tanks using old LNG tanks and that's what they use the dummy pumps for - to flow cold gas or perhaps liquid into the bottom of the tank to sweep out the inert gas through the roof vent lines to flare because the normal fill lines are in from the top and you would have a lot of methane and nitrogen mixed up which would be difficult to get to 100% methane gas which you need for the regassification procedure or burning of the Boil Off Gas.

N2 is heavier than natural gas right, wouldn't you be better off purging the nat gas from the top of the tank, and force the N2 out the bottom of the tank through the pump column via the dummy pump?

I don't think you can flow natural gas into the bottom of the tank and force the N2 out the top, you would just mix the two, right?

 

[LittleInch]

Not when it's really cold methane. Then it sits as a layer and goes up forcing the N2 into the top vents.

But you could do it in reverse. That's why you put the dummy pump in- to give you access into the bottom of the tank without breaking the normal pumps.

If you put enough in at a different temperature,no, you have only a small interface zone.

As I said, you need to read the procedure and listen to those who have doe it many times before.

 

[pierreick]

Hi,
You may want to read this paper:

Preventing LNG Stratification and Roll-Over Events

Vicky Athanasiou presents Prevent LNG Tank Stratification and Rollover Events through Operator Training at AspenTech Optimize 24.

www.emersonautomationexperts.com

Pierre