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Vacuum Unit Slopwax Entrainment Simulation


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#1 CMEngineer

CMEngineer

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Posted 10 January 2019 - 05:45 PM

Hi all,

 

I am hoping for some advice in regard to modelling a VDU new slopwax draw.

 

Currently I have 2 side draws, LVGO and HVGO. The overflash is 5% on feed or 10 t/h and it also contains entrained residue.

I want to draw a new side stream (slop wax) and need to simulate the entrainment in order to get the physical properties of the slop wax correct, whereby slopwax = overflash + entrainment.

I am going to model the entrainment outside the column and route residue and the overflash draw to a mixer.

I am just wondering what the composition of the overflash directly from the column should be (without the entrainment modelled externally)

Would it be a 50% Vac Residue 50% HVGO  mix? Or some other ratio?

In order to model the overflash I was just going to change the Vac Residue and HVGO cutpoints on feed such that the stream consisted of Vac Residue front end and HVGO back end.

 

Also can anyone advise what a typical overlap between Vac Residue and HVGO should be?

This will give me a good idea of how much HVGO is still left in the Vac Residue (in the original case with no slop wax draw)

 

I hope you can help.

 

Many thanks,

 

CM


Edited by CMEngineer, 10 January 2019 - 05:47 PM.


#2 PingPong

PingPong

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Posted 11 January 2019 - 03:48 AM


I am just wondering what the composition of the overflash directly from the column should be (without the entrainment modelled externally)

Would it be a 50% Vac Residue 50% HVGO  mix? Or some other ratio?

It can be anything.

How much liquid entrainment from the feed there will be in your particular column is anybodies guess.

It depends on the velocity and flow regime of the entering feed.

It depends on how the feed inlet is configured in the column.

Whether there is a vane type inlet device at the feed nozzle, or whether the feed is tangential into the column, or .....

 

All you can do in the simulation is assume a certain percentage of the liquid feed being entrained and send that to the wash section bottom stage together with the vapor part of the feed.

 

If this is an existing column you can determine the entrained liquid content by lab measurement of metals and asphaltenes in the slop wax.

 


Also can anyone advise what a typical overlap between Vac Residue and HVGO should be?

This will give me a good idea of how much HVGO is still left in the Vac Residue (in the original case with no slop wax draw)

The output from the simulation will tell you the composition of the column bottoms so you can easily see how much components lighter than the cutpoint are in the vacuum residue.

In order to model the overflash I was just going to change the Vac Residue and HVGO cutpoints on feed such that the stream consisted of Vac Residue front end and HVGO back end.

That sounds like nonsens so I suggest you don't do it like that.

The simulation output will give you the compositions of all streams.

You can do two simulations: one without entrainment, which gives you the composition of the overflash,

and one with entrainment which gives you the composition of the slop wax.


Edited by PingPong, 11 January 2019 - 03:51 AM.





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