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Superficial Gas Velocity For High Pressure Adsorption


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#1 Miguel

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Posted 28 October 2008 - 01:26 PM

Hello ,

I'm working on a preliminary design for a high pressure (2,500 psig , 150 F ) dehydration adsortion tower, and I'm wondering if there is anyway I could calculate the superficial gas velocity. It's recomended to use 30 ft/min but thats recomended according to J.M Campbell book to 1,200 psig and GPSA tables to calculate gas velocity all work to a max of 1,200 psig.

I would like to know if there's a way to calculate it at 2,500 psig or if vendors are the only ones that could give me that info ?

Regards, and apreciate the feedback

#2 Art Montemayor

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Posted 29 October 2008 - 07:49 AM

Miguel:

Depending on the application, the adsorbent and the gases involved, I usually use a lower superficial gas velocity in my adsorber vessel designs than the Campbell figure you quote.

You ask "if there is anyway I could calculate the superficial gas velocity" and the answer is YES. You take the ACTUAL GAS VOLUMETRIC FLOWRATE and divide it by the adsorber tower's cross-sectional area (under the assumption that the tower is empty). The term "superficial velocity" is a pseudo term. It isn't real. It is only used for comparative purposes. Because the tower is actually filled with adsorbent material, the real gas velocity through the tower is much higher than the superficial velocity.

The manufacturer of the adsorbent material is certainly one of the experts who can establish what the recommended superficial velocity for their specific adsorbent is and they should always be consulted and used in the early design stages of the adsorber vessels. Another critical item that they should be consulted on is the pressure drop exhibited by the adsorber beds and the maximum value tolerated.

If you are worried about using a recommended superficial velocity value at a pressure HIGHER than the one that you intend to adsorb under, bear in mind that the superficial velocity in the high-pressure case will be LOWER than that in the former. This is so because the specific volume of the gas stream is less when subjected to higher pressure – thus, giving you a lower (and more conservative) superficial velocity when using a higher pressure in the same adsorption vertical vessel.

I hope this addresses your "inquietudes".

#3 Miguel

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Posted 29 October 2008 - 08:48 AM

yes, thank you very much for the explanation

ive already contacted some vendors and im currently waiting for some responses

regards

#4 Miguel

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Posted 29 October 2008 - 02:34 PM

hello Mr.Montemayor

i would like to know what L/D ratio is recomended for the tower design


thank you

#5 Art Montemayor

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Posted 29 October 2008 - 07:59 PM


Miguel:

The correct L/D ratio (cylindrical length/O.D.) to use on an adsorber vessel is the one that most fits the needs and goals of the design:

  1. Yields the desired superficial velocity;
  2. Yields an acceptable pressure drop through the bed;
  3. Conforms to any local size and physical constraints;
  4. Complies with an economic fabrication cost while meeting all pressure and temperature requirements.

Besides the above, one usually tries to obtain a height that allows for maintenance without requiring platforms or ladders - if possible. An L/D of approximately 3 to 4.5 is usually what I have applied in the past. As your process pressure increases, the tendency to apply a larger L/D exists because of the obvious effect of cylindrical "hoop stress". The smaller diameters can withstand more pressure with the same wall thickness.


#6 fallah

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Posted 30 October 2008 - 02:29 AM

QUOTE (Art Montemayor @ Oct 29 2008, 08:49 AM) <{POST_SNAPBACK}>
bear in mind that the superficial velocity in the latter case will be LOWER than that in the former.

Dear Art,
I think you mean HIGHER.Please correct me if i am wrong.
Thanks

#7 Art Montemayor

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Posted 30 October 2008 - 06:08 AM

Thank you Fallah. The paragraph was written so bad I had to re-compose it to make it understandable. I have edited the text and it should read better now.

#8 chemical82

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Posted 03 November 2008 - 03:01 AM

Hi everyone
How can I calculate superficial gas velocity in secondary reformer (packed bed reactor in fertilizer plant)
I need it to calculate particle Reyonld No. to find Nusselt No. then to calculate heat transfer coefficient
Re p = Ds * density of gas * superficial gas velocity / viscosity of gas

Re p = Particle Reynolds No.
Ds = Equivalent diameter of catalyst (m)
Thank for everyone

#9 Qalander (Chem)

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Posted 03 November 2008 - 04:16 AM

QUOTE (chemical82 @ Nov 3 2008, 01:01 PM) <{POST_SNAPBACK}>
Hi everyone
How can I calculate superficial gas velocity in secondary reformer (packed bed reactor in fertilizer plant)
I need it to calculate particle Reyonld No. to find Nusselt No. then to calculate heat transfer coefficient
Re p = Ds * density of gas * superficial gas velocity / viscosity of gas

Re p = Particle Reynolds No.
Ds = Equivalent diameter of catalyst (m)
Thank for everyone


Dear chemical82 Hello/Good Afternoon;Wouldn’t it be more appropriate to start a new post afresh!
Regards
Qalander




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