3 replies to this topic

[wfwman]

We have a set of air compressors with air dryers running 24/7 at 134 cfm each. Dew points usually run around -50F. After the dryer we have a secondary pot that contains a 4A moleculecular seive bed. This is installed to further dry the air to about -70F and to act as a fail safe when problems arise with the upstream dryers. Recently we had dryer problems and the molecular seive bed became saturated. There is no installed regeneration equipment so when this happens, we simply replace the bed. My questions are:

Will the molecular seive give up moisture to incoming dryer air?

Is it possible to completely dry out the bed with ambient dry incoming air over a very long period of time say a year or does it absolutely require high heat before the molecular seive will give up the moisture?

Thank you for your time.

Edited by wfwman, 08 May 2014 - 10:53 PM.

[Supriyo Mukherjee]

wfwman,

 

As your question here is which I assume: whether we can dry the molecular sieve bed by just blowing it with air(dry). 

 

It will be a very difficult task to achieve this. If you have a problem with increasing temperature of the dry air that you want to blow over what I suggest is to go for PSA system in which you reduce the pressure of the bed and blow air. The molecular sieve vendor will give you details on this.

 

Also would like to know what is the ambient dry air you are talking about. Could I know its dew point.

 

Thanks,

 

Regards

[wfwman]

Thanks for the response. Incoming dry air would be a dewpoint of about -50F. There is no way to lower pressure. I'm not looking necessarily to regenerate. I don't mind replacing the media. I'm just wondering if it is possible to dry the molecular seive out with just this dry air only. Pressure would remain the same at 150-180 psig and temperature would remain ambient. If it is possible, how long would it take for the saturated bed to reach equilibrum with the incoming dry air? A week, a year, 10 years, never?

The reason for the question is that prior to the recent problems, we hadnt had to replace the molecular seive for many years and know there had been times when high dewpoint air was run through the system;yet, the bed was still dry. Hence we wondered if the molecular seive was adsorbing the moisture and then, over a long period of time self regenerating back to a dry bed.

I hope this question is not too confusing.

[Supriyo Mukherjee]

Wfwman,

 

As the incoming air has passed on to the molecular sieve bed and leaves with a dew point of -70deg F.

While the air passed over the last layer/top layer of molecular sieve bed the bed is in equilibrium with -70 deg F. The air with -50 deg dewpoint without reducing pressure or increasing temperature will not be able to regenerate the bed.

 

All I can say a air with -50 deg F dew point cannot regenerate a bed which is in equilibrium with -70 degree Farenheit.  

 

But if you blow the air with reduced pressure which I think you can do as by reducing the pressure by using a PRV(pressure reducing valve). Then the air with lesser pressure can desorb moisture from the bed. If I am not clear what I meant to say please let me know.

 

Regards,

 

 

As you had raised doubts on molecular sieve not adsorbing moisture anymore kindly check its color whether it has turned brownish.

 

The regeneration of the molecular sieve would be possible with increase in temperature surely. Please check if you can install a heater. I could calculate and check what time would be required to desorb it. All I would require then would be adsorbent amount Air inlet temperature.

Edited by Supriyo Mukherjee, 13 May 2014 - 04:00 AM.