compressed air adsorption dryers 2

[1BT]

Can anyone give me a Basic explanation of the difference between a heatless adsorption dryer and a heat generated dryer. I do stress basic!!

Many thanks

Bill

 

[Montemayor]

1BT:

Basically, heatless adsorption dryers use a portion of the product, dried air to recycle back to the spent bed for regeneration (& vents it to atmosphere) using the vapor pressure difference between the water in the spent adsorbent and the dried air. This means that you are going to have relatively inefficient regeneration of the bed as compared to a heat regenerated dryer. The adsorption beds have to be bigger and the net dry product air is less.

A heat regenerated dryer uses heat energy to drive off the captured water on the spent adsorbent and can use either saturated feed air (recycled) or atmospheric air as the medium to regenerate the spent bed, giving a 100% net dry air available from the quantity fed to the unit.

A heatless dryer is a response to simplistic or non-process, low quality air consumers who don't want to meddle or get involved with heating or such items that they consider as complications or maintenance items. The price (or tradeoff) is the inefficiency and the horsepower cost of the net dry air produced. If you are seeking efficiency, low dew point, and low net dry air cost, use the heat regenerated type.

Art Montemayor
Spring, TX

 

[1BT]

Many thanks Art

we are considering replacing a unit that uses steam as the heat source. does this make sense?

Bill

 

[Montemayor]

1BT:

It makes a lot of sense, especially if it's waste steam and can heat the regen stream up to 350-400 oF -- or higher, if possible.

I would assume you're drying air destined for pneumatic instrument use in critical service and, as such should have as low a dew point as possible (you can easily get down to -75 oF regenerating with 400 oF as the final regenerated bed temperature). Adsorption end dew points are very low when the beds are throroughly and efficiently regenerated - and the difference between a -25 oF Dew Point and a -90 oF Dew Point is very slight in energy consumption, but high in product results. Commercially available adsorbents like Activated Alumina can easily dry air down to -100 oF (approx. 1 ppmv) with properly designed and operated regeneration.

I hope this information helps you out.

Art Montemayor
Spring, TX

 

[1BT]

Your assumptions are correct the air is used for critical service. the dew point is minus 40 C @ 4.4 bar.The dessicant is Mobil Sorbead.

Once again many thanks for your reply which has been very helpful.

Regards

Bill

 

[pmureiko]

I recommend paying a little more for a heated air dryer to get much higher process reliablity versus the heatless air dryer. The dryer regeneration process is direct since water desorption is forced due to the heat input. Because of this, proper regeneration is easily checked and restored since you can see whether hot air is coming out of the heater or not.

The heatless dryer is an elegant concept, but weak in practice. You are relying on dry air to be produced by the online bed in order to regenerate the used bed. If for any reason there is regeneration problem, you'll have wet air from the problem bed trying to regenerate the used bed. At this point you are in deep trouble with 2 saturated beds and no way to recover.

And yes, I have actually seen this happen with heatless dryers. We replaced half a dozen dryers in a different plant with heated dryers to fix the wet instrument air problems and fix instrument reliablity problems.