On Tue, 8 Aug 2017 11:44:11 -0700, "Bob La Londe"
wrote:

Well, after doing nothing more really than my regular monthly service a week
or so early I have dry air again. I ran the air dryer for about 8 hrs
yesterday with zero moisture build up in any of the downstream separators.
I used it simultaneously for two mills with air seal high speed spindles and
assorted other air tools while putting the output shaft and wheel spindle
back together on the front axle of my little 3320 tractor.

I guess the system was just really wet, and needed to be dried out slowly
and tediously.

I think I am still going to add desiccant driers after the separators at the
machines as a second line of defense.

Bob,

Let me make a suggestion based on industrial experience.

In places where clean, dry air is imperative, say a nuclear plant for
instance, the air system is divided up into two parts, instrument air
and BOP (balance of plant air).

The BOP air is dried with a freezing type refrigeration system. One
cannot get the dew point below 32 deg with a conventional refrigerated
dryer. The reason is that below 32 deg, the water freezes to the
evaporator.

The freezing type system has two evaporator dryers and hardware to
switch the flow from one dryer to the other and to defrost the frozen
one. The moisture is allowed to freeze in the active dryer.

When it's time to defrost, usually controlled by a timer, the air flow
and refrigerant flow are switched to the other column while the hot
gas from the refrigeration compressor is used to thaw the first one.

Since most of the plant is located in unconditioned spaces, here in
the South, a dewpoint target of 0 deg F is used.

The instrument air is dried with an alternating column desiccant
system. It takes its air feed from the BOP output. This system has
two columns and instrumentation to detect when a column is saturated
(dew point rises). The air flow is switched to the other column while
the wet one is regenerated by a flow of hot air. The dewpoint target
is typically -40 deg F.

To put this in perspective, between 4 and 6 100 hp compressors are
running, depending on demand.

What I suggest you do is separate your air system into two parts. One
part for BOP comes straight out of the refrigeration system. For your
dry air system, feed is taken from refrigerant dryer and fed into a
desiccant dryer. Preferably a two column unit with a hand valve to
switch between columns.

Typically the column will be clear and the silica gel will be of the
indicator type - blue when dry, pink when wet. You'd have to do a
manual regeneration of the wet column. The usual method is to spread
out the beads in a ceramic bowl and put the assembly in a microwave
oven. As the water is driven off, the beads turn blue again. Dry
silica gel just barely absorbs microwaves so the system is
self-limiting.

Or you could spend a bit more on a self-rejuvenating system such as

https://www.mcmaster.com/#compressed...ryers/=18v6phg

The advantage of this architecture is that air for such things as air
tools and blow guns will be adequately dried by the refrigeration
system while the few SCFM of dry air will be really clean and really
dry.

John

John DeArmond
http://www.neon-john.com
http://www.tnduction.com
Tellico Plains, Occupied TN
See website for email address