Pressure drop through an adsorber 3

[skuntz]

We are designing a very simple process air dryer using a desiccant in a packed column. I need to estimate the pressure drop of the airflow though the column. Can anyone point me to the resources to help?

 

[EmmanuelTop]

Consider these values:

Minimum: DP/L = 0.01 PSI/FT

Delta P
------- = A? V + B? V2
L

Where ? -P/L is pressure drop/bed depth, psi/ft
? is fluid viscosity, centipoise
V is superficial fluid velocity, ft/min
? is fluid density, lbm/ft3
A & B are dimensional constants

A & B constants:
(for several Particle Mesh Ranges)

psi-min/centipoise-ft2 psi-min2/lbm
4 –8 mesh bead 0.0560 0.0000889
1/8” extrudate 0.0722 0.000124
8-12 mesh bead 0.152 0.000136
1/16” extrudate 0.238 0.000210

 

[willem79]

what do V and V2 stand for?

 

[skuntz]

Thank you. Two questions:

1. Does "V2" mean V*V?
2. What is the source of this relation?

Thanks again.

 

[EmmanuelTop]

Should be as: V, and V^2, respectively.
The velocity is a single number for given vessel diameter.

 

[skuntz]

EmmanuelTop:

Thanks again, but could you tell me where you got the equation?

 

[EmmanuelTop]

My adsorption technical service training.
You can believe to these figures, they have been verified in the field, many times.

 

[EmmanuelTop]

Take into account the aging of desiccant. The equations I have given apply for fresh beds. Depending on the regeneration principle (pressure-swing or temperature-swing), you will see different rates of pressure drop increments over time - with those encountered in TSA units being much higher as compared to PSA units (most of air dryers). For thermally regenerated desiccants, it's a common thing to see 2 times higher pressure drop when the adsorbent is close to the end of active life.

Depending on service (dew point requirements) you have to choose between Silica Gel, Activated Alumina, or Mol Sieve. If you are in warmer region, select Alumina charge and you'll get the best results. Mol Sieves have higher regeneration requirements but also have lower dew points - it all depends what you need.

Best regards,

 

[ayoyo]

you can find the equation in Campbell reference book as well.

 

[skuntz]

What is this reference (Campbell)?

 

[TD2K]

Google 'ergun equation'. Your dessicant supplier will be able to give you the pressure drop coefficients for your dessicant.

 

[ayoyo]

Gas Conditioning & Processing - Campbell
or you can refer to GPSA - chapter 20 - dehydration.

If you know the supplier of dessicant that you are going to buy, suggest to get the curve of pressure drop/length vs gas flux across packed bed from them, it will be more accurate.

 

[quark]

Check Unit Operations in Chemical Engineering by McCabe and Smith for packed bed pressure drops. As far as I remember, the Ergun equation is a function of v and v[sup]3[/sup] (v is superficial velocity)

 

[laliyo]

I think attached PP presentation might help you......

 

[laliyo]

Sorry...the link is not working. I will upload it......

 

[ayoyo]

skuntz,
Page 17 in the presentation showed you a curve that i mean to you : pressure drop per lenght of bed vs superficial velocity.

Thanks, Laliyo.