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?
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)
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.
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.
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)