Richard J Kinch wrote:
Paul writes:


Well, actually that's a common method for really large volumes in
industrial settings.


After a refrigerated dryer, right?

No refrigeration at all. This method employes dryer beds in parrallel,
one in service and one regenerating, connected via three way valves.
After some time interval, less than the time of moisture breakthrough
for the bed, the three way valves switch, lining up the in service bed
to regen and the newly regened bed to in service. The regening bed is
then vented to atmosphere and a relatively smaller flow of dried air is
purged through the bed. The reduced pressure releases the trapped
moisture in the dessicant and to vent (PSA or pressure swing
absorption). This is all done with timers or PLC's, with moisture
measurement instruments to monitor the air dew points.

The primary driers (one on each compressor) give plant air with -40 to
-60 degree F or better dew points. For instrument air some of the dried
air goes to another set of drier beds giving dew points of -150 deg F or
lower. If I remember correctly -164 deg F is no moisture and its not
uncommon to see dew points just about that low. I've got a table at
work relating ppm H2O to dew points that would be more precise.

Now these are pretty big compressors, 1000 to 1500 HP, and corresponding
large volumes of air, but I'll bet that this process would scale down
with no problems.

Just where the economics curves for refrigeration vs desiccant dryers
cross is unknown to me.

Regards
Paul


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