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Liquid Level Determination In L/ V Separator


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#1 deltaChe

deltaChe

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Posted 17 September 2011 - 09:58 PM

Dear Sir/Madam

I always trouble with design the high liquid level/low liquid level for the liquid/vapor of vertical/horizontal drum and I know this kind problem is trivial and be asked many time in different manner.
Also, I couldn’t find any easy-to-use spreadsheet for this drum sizing probelm.
I read a paper which wrote the formula confused me.

The minimum permissible distance between LLL and bottom of drum- HLL
HLL =56 * Q^0.4 /(1 – gas density / liquid density)^0.2 ( for metric unit)


Is any pro can help me out how this formula come from? Thank you so much.


Note.1 The drum usually is the following:
  • Liquid surge and distillated drum
  • Lube oil separators for compressor discharge
  • Steam drums in boiler service
  • High pressure separators.
I make some summary for the drum sizing procedure as following:
Step 1- choose which type drum fit in your design criteria.
(The vertical drum may have longer holding time compared to the horizontal drum)
Step 2- Base on the drum configuration you selected in step 1, and decide the
Drum with mesh screen or not.( cause the critical velocity may higher in drum with mesh than that with no mesh)
Step 3-Select the type of inlet nozzle for specific types of separator drums.

Note.2 Wire mesh screen (WMS):

WMS are porous blankets of wire or plastic knitted mesh,
Which are used for removing entrained liquid drops from a vapor stream? WMS installed internal for tower, drum, and fixed bed reactor. As vapor and entrained liquid drop pass WMS, the vapor moves freely through the mesh pad, but the drop cause of
Their greater inertia can’t follow the gas stream and collected on the mesh wire.

#2 breizh

breizh

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Posted 18 September 2011 - 08:20 AM

Steven

-Consider this resource for vertical separators , in fact a lot are already available on this forum (search button)
http://www.chemsof.com/spreadsheet.htm


-An other one is an engineering standard .

note : let you try to get a copy of "Coulson & Richarson's "Vol 6


Hope this helps

Breizh

#3 Virginia

Virginia

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Posted 18 September 2011 - 09:58 AM

Steven,
The type of separators to be selected depends on several factors like
1) Gas to liquid ratio in the feed
2) Total feed volume
3) Available plot space
4) Available head room

Setting of high liquid level and low liquid level is a function of residence time. Residence times depends on type of liquid (if 3 phase separators ) is to be designed. E.g. Glycol mixtures have high residence time between 20-60 mins. Residence time is a function of API gravity and also of temperature.

Wire mesh are two types
1) Demister pad - Works on coalescing principle
2) Vane pack - Work on inertial forces as well as coalescing

Separator is sized for
1 ) Vapor -liquid separator - Either gravity settling or using K value for terminal settling velocity
2) Liquid - liquid separator ( for 3 phase separators) - Based on terminal settling velocity

I would recommend you reading API 12 J and GPSA to clarify your doubts further.

Regards

#4 roni rizki

roni rizki

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Posted 25 January 2013 - 02:17 AM

Dear Steven,
My name is Roni, presently working as a Mechanical Engineer in Oil & Gas Company.
We have a new project of 2 phase HP Separator Horizontal and Vertical position and definitely i'am not familiar with this.

Could you help me how to calculate the dynamic capacity? if possible could you give me the calculation in excel if any.
here are the data:

HP Separator,
Operating Pressure : 1000 Psi
Operating Pressure : 150 deg F
Gas Flowrate : 5 mmscfd
Liquid Flowrate : 3000 BPD
Gas Density : 16.88 Kg/m3
Liquid Density : 870 Kg/m3
Vessel Diameter : 36 in
Cylinder Length : 10 ft

Thanks & Regards
Roni.




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