4 replies to this topic

[A mukherjee]

Hi everyone,
I have to get a dew point of (-)40degc at instrument air dryer outlet.For the regeneration of Adsorber bed vendor has specified a temperature of 170 degc.Now due to some power problem we are planning to regenerate the bed at 120 degc.Now vendor is telling us that there will be no problem in getting the dew point at this regeneration temperature(120 degc).Vendor is only increasing the regeneration flow,by around 100Nm3/hr.(Initially it was 1800 Nm3/hr,now 2800 Nm3/hr).
I am only interested in knowing how can we verify that despite the regeneration being carried out at 120 degc,the adsorbent will be able to give (-)40degc dew point?
The type of adsorbent is Activated alumina(AD101).Dynamic adsorption capacity is 7.5%.
Can anyone provide any source of literature regarding this?

[breizh]

This calculator may help you to validate the performance of your air dryer.

http://www.airpower....omerTools.aspx#

Breizh

[Zauberberg]

If you want the correct literature for calculating adsorption/desorption equilibrium, you need to get the adsorption isotherm (at the new temperature) for activated alumina from the vendor. The curve shows relative humidity vs. concentration in solid phase, usually as wt%.

Basically what happens is that, when regenerating at lower temperatures, relative humidity of regeneration stream increases thus reducing the driving force for mass transfer of water from saturated adsorbent to the regeneration gas. Depending on the magnitude of temperature decrease, this can be compensated by increased flow of regeneration gas (or air, whatever is used), or decreased regeneration pressure. If the vendor claims that there will be no problems with lower temperature regeneration, you will always have someone to pull his nose if it doesn't work well.

I remember operating PSA alumina dryers (no heat applied to the regeneration air) and achieving -40 degC dew point temperature (re-calculated at 1 atm) without any problems.

[A mukherjee]

My boss is telling me to consult isostere curves.Can anyone explain me what are those curves ?

[Zauberberg]

Read page 12 of the referenced document and follow the graph on page 25: http://www.adsorptio...dsorberDes2.pdf