Author Topic: Making a Desiccant Air Dryer with Silica Gel  (Read 3139 times)

Offline awemawson

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Making a Desiccant Air Dryer with Silica Gel
« on: February 09, 2017, 09:55:09 AM »
Having got my CNC Plasma Table up and running I've been giving a lot of consideration to the humidity of the air that I supply to it. Moisture in the air badly affects cut quality and the life of the consumables. I do have a refrigeration style air dryer, and I did resurrect it for the Plasma Table. but to be any use it needs to be switched on for long periods of time, and it draws quite a bit of electricity

(Thread here for the rebuild http://madmodder.net/index.php/topic,11815.0.html )

Now there are all sorts of ways of drying air mainly concerning condensing the moisture and draining it away, but there is another method using Silica Gel that has the useful quality that it will absorb large quantities of moisture, and better still it is re-recyclable by the simple expedient of roasting it in the domestic oven  :ddb:

So my plan was to remove as much moisture as possible with a conventional air / water separator then pass the pre-dried air though a column of Silica Gel.

Ideally the column containing the Silica Gel should be transparent, as it is available in a 'self indicating' state whereby it changes colour as water is absorbed - very handy  :thumbup:

I hit on the idea of using a standard 10" water filter container and modifying it for use as a desiccator. These thing are modestly priced, are transparent (or at least mine is), and are designed to take mains water pressure safely.
Andrew Mawson
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Offline awemawson

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Re: Making a Desiccant Air Dryer with Silica Gel
« Reply #1 on: February 09, 2017, 10:08:08 AM »
Now the input and output of this housing are 3/4" BSP female brass inserts, so connections there are no problem at all. The air needs to pass through the bulk of the Silica Gel, then up a tube leading to the output port. The tube somehow needs to have a filter or gauze on it to stop the desiccant blowing straight through to the output. I hit on the idea of using a sintered plastic compressed air exhaust silencer. They are available in all sorts of sizes, and I chose one with a 1/2" BSP male thread.

Then it was a case of making up an adaptor for the filter lid to take the 15mm copper pipe, and joining on the silencer using a standard compression 'tap connector' - it all went rather well and turned out fine.

Initially I was stumped for a bit of brass stock to make the adaptor from, as I didn't want to turn down the only rather large brass bar that I had in stock - then my eyes fell on a 1" BSP to hose barb fitting, just crying out to be modified  :clap:

I designed the adaptor as a push fit into the bore in the lid of the filter, with an 'O' ring as a retainer / air seal. In the event it turned out that the hole in the plastic lid had just the right taper for it to lock solidly - in fact so solidly I had a bit of a struggle to get it out again  :bang:

The adaptor is soldered onto the 15mm copper pipe.
« Last Edit: February 09, 2017, 11:15:42 AM by awemawson »
Andrew Mawson
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Offline awemawson

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Re: Making a Desiccant Air Dryer with Silica Gel
« Reply #2 on: February 09, 2017, 10:13:13 AM »
Now the inlet port is just a vaguely rectangular opening at the top of the filter. To prevent Silica Gel leaking back into the inlet under negative pressure situations (when turning off) I incorporated a fine brass gauze in the opening, bonding it in with high viscosity super glue
« Last Edit: February 09, 2017, 11:17:42 AM by awemawson »
Andrew Mawson
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Offline awemawson

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Re: Making a Desiccant Air Dryer with Silica Gel
« Reply #3 on: February 09, 2017, 10:19:32 AM »
Next to add the pre and post filters. The pre filter is a conventional water separator used for it's intended purpose, whereas the post filter, although again a conventional water separator, I'm using it as it has a 5 micron sieve to sweep up any fine Silica Gel dust that might 'get away'
Andrew Mawson
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Offline awemawson

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Re: Making a Desiccant Air Dryer with Silica Gel
« Reply #4 on: February 09, 2017, 10:24:24 AM »
So no more ado - do a leak test. Well first a safety pressure test with it covered in a towel - shame if the poly carbonate filter housing were to explode. :bugeye:

All's well - no violent explosions so then the leak test. I keep a horticultural hand spray on the shelf full of soapy water, and it's amazingly good at finding even the smallest escape of compressed air - but this was sound (I use Loctite 542 thread sealant on this size plumbing and swear by it)

« Last Edit: February 09, 2017, 05:40:21 PM by awemawson »
Andrew Mawson
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Offline awemawson

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Re: Making a Desiccant Air Dryer with Silica Gel
« Reply #5 on: February 09, 2017, 10:28:15 AM »
Now as the three air assemblies of this set up are all from different manufacturers, mounting it on a wall wouldn't be easy - unless I made up some customised brackets to accommodate their differing mounting styles.

A splash of lay out fluid, a bit of die grinding, drilling, taping, bending, zinc primering and black top coating later and we have an integrated assembly ready to fix on the wall.
Andrew Mawson
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Offline awemawson

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Re: Making a Desiccant Air Dryer with Silica Gel
« Reply #6 on: February 09, 2017, 10:32:30 AM »
Then, like some 'just in time' manufacturing conglomerate, the girl from My Hermes arrived carrying a 3 kg tub of self indicating Silica Gel - I reckon she'd been spying on me and was waiting until just the right time to deliver  :ddb:

So - shove the crystals in - wack it on the wall and try it out  :clap:
Andrew Mawson
East Sussex

Offline awemawson

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Re: Making a Desiccant Air Dryer with Silica Gel
« Reply #7 on: February 09, 2017, 10:36:01 AM »
Does it work?

Well time only will tell. I did do a test cut on the Plasma Table but considerable time hopefully will have to elapse to see if the stuff changes colour ......... unless we do another test :lol:

So - shove a bit of the Silica Gel in a 1 litre pyrex beaker, drip some tap water on it and watch the results.

... well it certainly changes colour so that's a good sign  :clap:
Andrew Mawson
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Offline Spurry

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Re: Making a Desiccant Air Dryer with Silica Gel
« Reply #8 on: February 09, 2017, 10:44:37 AM »
Andrew, I think you would have made a good assistant to Black Adder. "Sire, I have a cunning plan..."
Neat job, it will be interesting to see how long it takes for the crystals to change colour in your filter.
Pete

Offline awemawson

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Re: Making a Desiccant Air Dryer with Silica Gel
« Reply #9 on: February 09, 2017, 10:46:43 AM »
Thanks for the kind words (I think !!) Pete - I've been musing over a desiccant drier for quite some time, but finding a suitable container is what stumped me.
Andrew Mawson
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Offline Brass_Machine

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Re: Making a Desiccant Air Dryer with Silica Gel
« Reply #10 on: February 09, 2017, 11:04:10 AM »
I love seeing stuff like this... even if I am not sure how it is used. This would be in-line from a compressor to the plasma cutter?

Eric
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Offline awemawson

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Re: Making a Desiccant Air Dryer with Silica Gel
« Reply #11 on: February 09, 2017, 11:12:12 AM »
Yes Eric that's right. Any moisture in the air should be scooped up by the Silica Gel
Andrew Mawson
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Offline hermetic

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Re: Making a Desiccant Air Dryer with Silica Gel
« Reply #12 on: February 09, 2017, 11:34:27 AM »
 Hi Andrew, the amount of satisfaction you get from a finished job like that is priceless isn't it. I am at home at the moment, having been crocked with some horrible lurgi the kids brought home from school, and can't wait to get back to my workshop, .................and now as they say in Hull, Err nerr, SNERR!
Keep up the good work!
Phil

Offline awemawson

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Re: Making a Desiccant Air Dryer with Silica Gel
« Reply #13 on: February 09, 2017, 11:40:00 AM »
So Phil is my 'Cheshire Cat' grin getting as far as Hull then  :lol:
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Offline hermetic

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Re: Making a Desiccant Air Dryer with Silica Gel
« Reply #14 on: February 09, 2017, 11:56:23 AM »
 I can tell yer grinning, because I am too! I have one of those filter housings on my workshop rainwater system!
Phil

Offline awemawson

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Re: Making a Desiccant Air Dryer with Silica Gel
« Reply #15 on: February 09, 2017, 12:13:40 PM »
Perhaps we should run a challenge to find other uses for them  :scratch:
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Offline krv3000

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Re: Making a Desiccant Air Dryer with Silica Gel
« Reply #16 on: February 09, 2017, 02:00:19 PM »
that's a proper job :clap:

Offline Pete W.

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Re: Making a Desiccant Air Dryer with Silica Gel
« Reply #17 on: February 09, 2017, 03:33:48 PM »
Hi there, Andrew,

Another interesting project up and running, I hope you're not neglecting the livestock!

Somewhere in my filing ('piling' ? ) system, I have a copy of the military specification for the handling and re-activation for silica gel (hasten to add - it's not classified!).

I was always happy with the process when the domestic oven was electric but, nowadays, we cook with gas.

Does anyone know if that's as effective as the electric oven?  (I'm assuming that burning domestic gas produces water vapour.)
Best regards,

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Offline John Rudd

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Re: Making a Desiccant Air Dryer with Silica Gel
« Reply #18 on: February 09, 2017, 03:49:58 PM »
I've worked with silica driers, regenerated with electric heater elements in pressurised vessels...works well...
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Offline PekkaNF

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Re: Making a Desiccant Air Dryer with Silica Gel
« Reply #19 on: February 09, 2017, 04:47:46 PM »
That is very inspiratonal project!

I have a small amount of Silica Gel (probably cheapest and corse, because it is ised to keep boat interior dry during winter) and I have been thinking something similar last two years. Small pack of it is on my work bench as a reminder....but you have solved the pressure vessel nicely. I have been looking for big/least partly transparent normal water separator for modification and I even had a sintered silencer for filter....but you actually made it.

Very good idea and execution.

What is the next step? Coalescing filter to produce air bearing quality air?
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Offline appletree

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Re: Making a Desiccant Air Dryer with Silica Gel
« Reply #20 on: February 09, 2017, 05:02:55 PM »
At the power station where I worked for 40 years in the instrumentation dept, the electrical dept used an industrial martindale hot air blower (hair drier) to blast air through desiccant tubes used as moisture absorbers in very big motors (huge). This was in the times of demarcation believe it or not, if a SWA gland (steel wire armoured) required fitting to an instrument cable, an electrical fitter was called in, (its a wonder the country did not go bankrupt) oh it did?
I do not know if it was efficient or not i.e. slow cook versus forced draft either way thats what they did.

In my workshop i would use my refrigerant compressed air drier normally used for paint spraying. But yes a container containing desiccant that can be regenerated is good however i wonder about flow rates (distance velocity). There is more than one way to skin a cat, why you wold want to is a different question.

 

Offline awemawson

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Re: Making a Desiccant Air Dryer with Silica Gel
« Reply #21 on: February 09, 2017, 05:36:56 PM »
Thanks for the various comments chaps  :thumbup:

Appletree - my motivation making the desiccator was not to have to run the refrigerant drier for long periods. It needs to run for at least an hour before the copper coil of tubing is cold enough, by which time I would have cut whatever I'm cutting on the plasma table, and gone in for a cup of tea  :lol:
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Offline awemawson

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Re: Making a Desiccant Air Dryer with Silica Gel
« Reply #22 on: March 04, 2017, 06:38:13 AM »
I was so pleased with the way this drier works I made a second one  :lol:

This second one takes air directly from the compressor and dries it, hence my whole air distribution system will now have properly dried air. I'm sure that there will be existing moisture in the pipework, but after a bit the newly dried air should absorb and flush it out.

Looking at the picture starting on the left is the Regulator / Water Separator taking 150 psi from the compressor and reducing it to 100 psi - the water separator is the float type that blows water down the small pipe to the outside.

This is followed by an 'oiler' that although in circuit is NOT used or filled - it happened to be integral with the regulator so stayed there.

Then comes the new desiccant filter made exactly like the previous one.

This is followed by a large volume filter / water separator, just being used as a filter, as by this stage there should be no water to separate  :ddb:

Not pressured up yet as you can see from the gauges as the Loctite 542 needs another hour to go off.

« Last Edit: March 04, 2017, 07:10:51 AM by awemawson »
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Offline awemawson

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Re: Making a Desiccant Air Dryer with Silica Gel
« Reply #23 on: April 22, 2017, 06:14:56 AM »
So the time has come for the first regeneration cycle of the self indicating silica gel crystals of my main air dryer. (This is the one that all the air from the compressor flows through)

Unscrewing the housing showed that the outer layers must be most exposed to the moist air, as tipping them into a baking tray there seemed to be far less turned blue than you'd think from looking at them in situ.

They are now in the oven at 140 deg C for a couple of hours. Meanwhile the dryer is back in service, as the 3 Kgs of silica gel that I originally bought not only filled this dryer and the one I fitted to my CNC Plasma Table, but was enough to re-fill this one while the fan oven does it's stuff driving off the water.

I'm really pleased with the performance of this dryer - it's so simple and yet seems very effective.

Andrew Mawson
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Offline DICKEYBIRD

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Re: Making a Desiccant Air Dryer with Silica Gel
« Reply #24 on: April 22, 2017, 06:46:07 AM »
Very nice Andrew!  I'm always learning new things from your threads; thanks.

I'm curious what kind of pressure drop you're getting across it.  Does it get cooler as well?

If I ever do any more spray painting, I'll need to make one of those!
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Offline awemawson

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Re: Making a Desiccant Air Dryer with Silica Gel
« Reply #25 on: April 22, 2017, 06:52:40 AM »
Thanks Dickeybird

I've not measured the pressure drop but it will be minimal. The sintered silencer I'm using seems to present very little resistance blowing through it, and the silica gel crystals are large enough to have big gaps for air flow.

The air is not really expanding within the dryer so I'd not expect much cooling effect, though again I've not measured it - if air is flowing then I'm using the tool that's using the air, not feeling the dryer  :ddb:
« Last Edit: July 23, 2017, 06:53:44 AM by awemawson »
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Offline shipto

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Re: Making a Desiccant Air Dryer with Silica Gel
« Reply #26 on: April 22, 2017, 06:56:42 AM »
Well theres no doubt it works to some extent at least. good job :thumbup:
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Offline awemawson

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Re: Making a Desiccant Air Dryer with Silica Gel
« Reply #27 on: April 22, 2017, 07:07:34 AM »
So I thought I'd take a peek at at after it had been cooking for one hour. Superficially it all looked to have turned back to the original orange, but when I raked the surface there were still a few blue crystals, So I gave it a goodly stir up and have left it for it's second hour.

Certainly when I opened oven door, masses of steam came out to the extent that my glasses fogged up  :clap:

I seem to remember that silica gel can absorb it's own weight in water - now there's roughly 1kg cooking, so up to a litre of water if it was all used up.

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Offline awemawson

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Re: Making a Desiccant Air Dryer with Silica Gel
« Reply #28 on: April 22, 2017, 07:09:32 AM »
Well theres no doubt it works to some extent at least. good job :thumbup:

Oh it's most certainly working, there is a noticeable difference in my shop air.
Andrew Mawson
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Offline shipto

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Re: Making a Desiccant Air Dryer with Silica Gel
« Reply #29 on: April 22, 2017, 10:05:23 AM »
It's a good solution to remember, I may have mentioned we used to have a dragun brand plasma at work with built in air that had no drying and ate consumables at a extraordinary rate

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Offline awemawson

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Re: Making a Desiccant Air Dryer with Silica Gel
« Reply #30 on: April 22, 2017, 10:37:55 AM »
The recycled silica gel is noticeably darker than the original - I suspect that I may have over cooked it - I'm sure that the water has been driven off, but perhaps I've affected whatever chemical is being used as a moisture indicator  :scratch:

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Offline mattinker

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Re: Making a Desiccant Air Dryer with Silica Gel
« Reply #31 on: April 22, 2017, 11:26:23 AM »
Try a few grains "test" to see whether the colour changes!

Cheers, Matthew.

Offline awemawson

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Re: Making a Desiccant Air Dryer with Silica Gel
« Reply #32 on: April 22, 2017, 01:08:16 PM »
Yes I have Matthew and it does  :thumbup:

It turns out the the orange indicator in the silica gel is Methyl violet, but I've not been able to find anything about it's temperature stability. However I have found that the gel will recycle at a lower temperature - 120 deg C rather than the 140 I aimed for and possibly overshot  :scratch:

I think the gel will work still very effectively, but the indicator colour change, although it happens, isn't quite as definitive.
« Last Edit: April 23, 2017, 06:00:38 AM by awemawson »
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Offline mattinker

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Re: Making a Desiccant Air Dryer with Silica Gel
« Reply #33 on: April 22, 2017, 01:46:32 PM »
That makes me think of other comparative tests, new and old! I think you've probably started thinking about that having begun tests! i would have though that it was the indicator capacity that would change, not the water absorption. It'll be interesting to see what you come up with!

cheers Matthew.


Offline Will_D

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Re: Making a Desiccant Air Dryer with Silica Gel
« Reply #34 on: April 23, 2017, 05:06:37 AM »
Suggest you weigh out say 50 grams, leave in damp place for some time, weigh it again.

During drying weigh it say every 30 mins and watch what happens to the weights.
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Offline russ57

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Re: Making a Desiccant Air Dryer with Silica Gel
« Reply #35 on: April 25, 2017, 12:18:31 AM »
Just a minor warning... I had a similar water filter split. I have no idea why, and I had bought it second hand so it may well have been damaged a earlier. Fortunately, it split a day after we returned from holidays and wife heard the bang and the water running.
 If yours was to fail, the result might be more spectacular.  It might be worth considering a protective shield of some sort?

-russ


Offline SwarfnStuff

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Re: Making a Desiccant Air Dryer with Silica Gel
« Reply #36 on: April 25, 2017, 01:11:28 AM »
Oh dear! Russ, you just reminded me of the time when our filter popped an 'O' ring. Unfortunately we were actually on holidays not just arrived home like you. Couldn't get the back door open so went to the front. Stepped inside and found myself in 1/2" of water.
   Thankfully the insurance covered new floor coverings. I then moved the filter outside. Ain't hind sight a wonderful thing.
       Still, here we are discussing compressed air so no risk of flooding, just a (shielded) bang? I cannot recall whether the specs for the water filter were discussed.
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Offline awemawson

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Re: Making a Desiccant Air Dryer with Silica Gel
« Reply #37 on: April 25, 2017, 02:23:20 AM »
Mine's rated at 160 psi but only supplied with air regulated to 100 psi so should have a bit of safety margin. However it is a sensible warning, having had a 25 mm 'stop end' blow off I'm aware of the power stored in compressed air.

In the case of my main desiccant drier, it is housed in an unmanned Portakabin, so there should be no risk to life and limb.

In the case of the one on my CNC Plasma Table, it is more exposed, but the input air is regulated down to 70 psi, so a higher safety margin.
Andrew Mawson
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Offline russ57

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Re: Making a Desiccant Air Dryer with Silica Gel
« Reply #38 on: April 25, 2017, 06:24:13 AM »
That's good. Still, a vessel giving way at 70 psi would possibly not go unnoticed 😨


-russ


Offline Ed ke6bnl

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Re: Making a Desiccant Air Dryer with Silica Gel
« Reply #39 on: April 25, 2017, 10:13:45 AM »
I made one years ago from a receiver for a large air cond. system. had screens in there and probably safe for excess of 300 psi. has a top that is removable with several screws. NOT CLEAR and it is out side on my car lift. I have never changed or reheated the silcone bead. sits for long period in the hot sun and seem to be ready all the time.
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Offline Ed ke6bnl

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Re: Making a Desiccant Air Dryer with Silica Gel
« Reply #40 on: April 25, 2017, 10:16:45 AM »
I made one years ago from a receiver for a large air cond. system. had screens in there and probably safe for excess of 300 psi. has a top that is removable with several screws. NOT CLEAR and it is out side on my car lift. I have never changed or reheated the silica bead. sits for long period in the hot sun and seem to be ready all the time.
   
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Offline awemawson

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Re: Making a Desiccant Air Dryer with Silica Gel
« Reply #41 on: April 25, 2017, 12:30:25 PM »
Ed, if the silica gel is in a sealed container the moisture will be retained however warm the sun is  :scratch:
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Offline PK

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Re: Making a Desiccant Air Dryer with Silica Gel
« Reply #42 on: April 25, 2017, 05:36:07 PM »
Mine's rated at 160 psi but only supplied with air regulated to 100 psi so should have a bit of safety margin. However it is a sensible warning, having had a 25 mm 'stop end' blow off I'm aware of the power stored in compressed air.

In the case of my main desiccant drier, it is housed in an unmanned Portakabin, so there should be no risk to life and limb.

In the case of the one on my CNC Plasma Table, it is more exposed, but the input air is regulated down to 70 psi, so a higher safety margin.
I've used those exact filter cases for desiccant and coolant at 100PSI for years..

Offline awemawson

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Re: Making a Desiccant Air Dryer with Silica Gel
« Reply #43 on: April 25, 2017, 06:05:38 PM »
That's comforting to know PK  :thumbup:
Andrew Mawson
East Sussex

Offline Ed ke6bnl

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Re: Making a Desiccant Air Dryer with Silica Gel
« Reply #44 on: April 25, 2017, 07:11:36 PM »
Ed, if the silica gel is in a sealed container the moisture will be retained however warm the sun is  :scratch:
that make sense my only thought is that it get warm and leaves the silica gel and maybe in the 50 foot air line attached and on the first use it is moved out with the air and the remainder is dry air. Some of the line goes under ground and it use to have water with air and i do not see that since it was installed
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Offline awemawson

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Re: Making a Desiccant Air Dryer with Silica Gel
« Reply #45 on: July 23, 2017, 06:47:35 AM »
Today it was time once more to 'cook' my silica gel to remove the moisture that it had trapped. Last time the crystals, which turn blue/black when damp, lost their nice orange hue on cooking, probably because the indicator had broken down at the 140/150 deg C that I used.

This time I set the electric oven to 120 Deg C, cooked for three hours and they have returned to a nice orange  :thumbup:

(It's now cooling under cling film to keep the moisture out)

Andrew Mawson
East Sussex

Offline SwarfnStuff

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Re: Making a Desiccant Air Dryer with Silica Gel
« Reply #46 on: July 24, 2017, 02:36:01 AM »
Great to read that your regenerative desiccant air dryer is working as designed Andrew.
 :mmr:
Regards,
John B
Converting good metal into swarf sometimes ending up with something useful. ;-)

Offline RodW

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Re: Making a Desiccant Air Dryer with Silica Gel
« Reply #47 on: July 24, 2017, 04:58:44 AM »
A very god project and I'm sure you saved quite a lot for a bigger desiccant drier compared with the commercial one I bought.



THis has a filter/regulator, coalescent filter and finally a dessicant drier which cost me about AUD $220. THe final filter is a motorguard style "toilet roll" filter which seems obligitory on all plasma cutters I've seen in operation.
RodW
Brisbane, Australia

Offline howsitwork?

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Re: Making a Desiccant Air Dryer with Silica Gel
« Reply #48 on: July 25, 2017, 04:18:14 PM »
Andrew

Well impressed, can't think how I missed this project.

Ian