13 replies to this topic

[DANA-IF]

Dear  all ,

 

I'm using the  online file http://checalc.com/calc/vertsep.html for a two phase vertical separator 

 

 

 

 I'd like to know please  why the vessel diameter  depend from the hold up and surge time ?.

 

A s I know , DVD =( 4* Qv/3,14 *Uv )1/2 where  DVD: vessel internal diameter 

                                                                      Qv :vapor flow rate (ft3/s)

                                                                       Uv : terminal velocity ( ft/s)

 

Thanks a lot !

 

REGARDS !

 

[Chemitofreak]

Hi,

 

In vertical separator, diameter is not dependent on the hold-up and surge time.

 

In your case you have specified L/D ratio, hence the moment the length changes (due to surge volume/ hold-up) the diameter automatically changes.

 

Revert in case of any query.

Edited by Chemitofreak, 12 April 2017 - 05:36 AM.

[Bobby Strain]

You can find some better tools at my website. Just Google my name to find it.

 

Bobby

[sgkim]

Hello DANA,

 

For vertical separators the diameter seems to be √2 times larger than that calculated by the equation you quoted.  

 

U = (4Q/πD^2) ...............(1)

(Uv-U)*θ ≥  H .................(2)    <= settling length of droplets shall be larger than the vertical distance that vapor moved

H = U*θ ........................(3)

 

Where,

      Qv= vapor flow

      D= vertical vessel diameter selected, ft

      H= vertical length that vapor moved or liquid settled, ft 

      U=  vertical (upward) gas phase velocity, ft/s 

      Uv= terminal (downward) velocity of liquid droplets, ft/s  

      θ = residence time of vapor for settling, s

 

From eq(2) & eq(3),   (Uv - U)*θ ≥ U * θ   then   Uv ≥ 2U, or U ≤ Uv/2...............(4)

 

And from eq(1) and eq(4),     (4Q/πD^2  ≤   Uv/2   then

 

D ≥  {8 Q/(π Uv)}^(1/2)  ...................(5)   <=  Diameter with √2 times larger than that calculated by the original equation you quoted.   

 

Please comment, thanx in advance, 

 

~Stefano

[Pilesar]

I have never used Stefano's eq(2) in sizing separators. As long as the terminal velocity is greater than the vertical velocity, then the droplets will theoretically settle. The 'distance the vapor moved' does not seem relevant as long as the force of gravity on the droplets is greater than the force exerted by the upward moving vapor. DANA-IF's equation should determine the vessel diameter large enough for drops to settle.

   As to DANA-IF's original question, the liquid holdup requirements are a criteria for separator sizing used in conjunction with the velocity equation. If there is significant liquid, the volume of the separator which must be reserved for liquid can be quite large. When the vertical vessel diameter is sized only with the terminal velocity equation, this can result in a very tall, skinny vessel. Increasing the diameter above that which is required by the vapor velocity can improve the vessel economics. If the liquid volume reserve requirement is large enough, it becomes cheaper to use a horizontal separator.

[Aries Satriyo]

DANA.,

 

There are many calculation out there at cyberspace. One of them is here., I try to give you some information as follow :

 

https://sites.google...ards/what-s-new

 

This is a calculation in Excel and  you can down load freely. Just try it.

[Bobby Strain]

You best check anything you use online. And if it is for a real project, don't use them without validating the results.

 

Bobby

[Aries Satriyo]

Bobby.,

 

Yes., I used it this Excel Calculation in my Project with Government also Contractor that I was charged as a Process Engineer. Result was Ok.,  They accepted my calculation depend on Excel calculation.......he he...

[Bobby Strain]

Done correctly, one will size the separator to meet the requirements with the lowest cost. Most spreadsheets don't do this. Instead the "poke & hope" method is used. So, I don't place any credibility that any government or contractor accepts a calculation. Mostly they don't have a clue.

 

Bobby

[breizh]

Hi ,

Additional input .

All this helps .

Breizh

[sgkim]

Thanks Breizh,

 

Pretty good and comprehensive design guides are introduced - based on vast and extensive practical experiences.  Lots of internal options should be considered to minimize the separotor cost by applying effective separation mechanisms. 

 

~Stefano   

Edited by sgkim, 21 April 2017 - 04:15 AM.

[Aries Satriyo]

Bobby.,

 

Thank you for your advice...next ...I will check and recalculate for this Excel. Many thanks.

[Bobby Strain]

Aries,

       I looked at the application for vertical two-phase separator sizing. The sheets are password protected as is the VBA code. I never use such, because you can't see what is being done. However, the password protection is no impediment. The password is cracked quickly. So, I looked at the VBA code. My assessment is that this is an academic exercise written by someone who does not know how to program. And has no design experience. And you cannot possibly understand the calculations. So, it fails all my first tests. I wouldn't use such calculations. Sizing vertical separators is quite a simple task. Sizing horizontal separators is not so well understood. The reference for your link I know quite well. The author is an academic, and probably never had to design a separator for real service. The procedure from the article, and hence the Excel calculations, will result in grossly oversized horizontal separators. For real projects, you should look to recognized sources like GPA and API if you don't have experience or access to good guides such as Shell's DEP. Everyone seems to have them. They, too, are conservative. Of course, I have good stuff, too, based on 50 years of design and research.

 

Bobby

[Aries Satriyo]

Booby.,

 

Thanks., you were right depended on your experiences for years. Now., I have been re-calculated again for my note . I also have made calculated depend on API & GPA. Here now., I have been charged as Process Engineer at Review-Design in Gas Processing Plant in my country in indonesia. Sales gas have been produced at 70 MMSCFD but   we have faced more difficult operation at Thermal Oxidizer ( TOX ) since we have made a load with more flowrate from a well gas .Then., a gas plant stop.

Besides., I was calculated with Breizh's references

 

Thanks Bobby

 

Thanks Breizh.

 

Thank you.