Sciencemadness Discussion Board

Drying anad cleaaning air from an air compressor - good methods

RogueRose - 10-5-2017 at 20:41

For a project a few people and I are working on requires a lot of air flow of at least 40 CFM but up to 80-120 possibly. We looked into diaphragm compressors like the ones that are used in air brush guns and other similar applications but the price is outrageous and the CFM at mod pressures drops off a lot, so we are looking at standard cylinder compressors, rotary compressors (like in an AC system) and other similar setups. Oil-less compressor are usually used in O2 concentrators (which this is similar but is for O2, N2 and Ar separation in a glass shop for up to 12 people at once). The oil is an issue if used for medical applications and with the high O2 (88-96%) concentration as I guess it could cause ignition or something.

We already have a lot of standard air compressors as well as lots of AC/regrigerator compressors to generate much more than the needed air flow, probably close to 150-170 CFM & 1 bar so we would like to use these if possible.

There are a number of 250gal, 100gal and a 500g propane tanks which can be used to store compressed air, if needed - so a smaller compressor could be used to fill these slowly and then have capacity when high flow is needed.

I was thinking of using large activated carbon filters which could be converted 30 gal or 100 gal propane tanks, or 20 gal HDPE drums or lots of 3", 4" or 6" PVC pipe. I was planning on using this to filter any oil/hydrocarbons from the air. IDK if this should be placed after the storage tanks or before, or a mix/both.

for removing moisture I was thinking of silicone gel in propane tanks and then place a heater inside or under the tank so the gel can be heated to recharge the silicone gel. This method is used in industry where it is used to dry air and is recharged in metal vessels just like this - so I don't see why this wouldn't work. I'm just not sure if there is a better method. I think putting this before the storage tank may be a good idea to reduce in any possible rust in the tank. Maybe add one on exit as well.

A number of HEPA filters will be added after the carbon and silicon gel. We were thinking of using a truck's 9big engine like V10 -V12 air intake box with something like a K&N air fillter. This should be adequate for pre-filtering the air and is more than large enough for the needed airflow. We also thought of using vacuum cleaner bags as filter medium over 18ft^2 surface (3' x 3' box with the filter fabric over each side)

If we can find a useable 1 micron (or .2 - .45um) filter material that will allow the air flow and not be too restrictive, it will be added at the very end of the filtration process as well as after the seive material so remove any dust that may travel with the gas.

Does anyone see why this wouldn't be enough filtering and be adequate to remove any oils and moisture in the air?

Melgar - 11-5-2017 at 03:45

Can you store your gases in cylinders after they're separated? That way you can have whatever flow rate you need out of the tanks, on demand. It seems like you're planning to run it 24/7 or something, but the stuff you're planning to build it out of doesn't seem anywhere near reliable enough for continuous production.

An ordinary air filter similar to a car's, combined with an inline desiccator should work fine. Perhaps a carbon filter as a final stage. Incidentally, silica gel is the desiccator you want. Silicone gel is just a soft, rubbery polymer.

Sulaiman - 11-5-2017 at 04:06

Maybe a chiller unit after the compressor would be useful ?
it would remove water vapour and/or make the filling of containers easier. (P.V=R.T)

The significant missing parameter in your description is duration or total volume.

RogueRose - 11-5-2017 at 07:01

Quote: Originally posted by Melgar  
Can you store your gases in cylinders after they're separated? That way you can have whatever flow rate you need out of the tanks, on demand. It seems like you're planning to run it 24/7 or something, but the stuff you're planning to build it out of doesn't seem anywhere near reliable enough for continuous production.

An ordinary air filter similar to a car's, combined with an inline desiccator should work fine. Perhaps a carbon filter as a final stage. Incidentally, silica gel is the desiccator you want. Silicone gel is just a soft, rubbery polymer.


I have a new keyboard that is still learning these things and got confused as to what I meant - I obviously know it's silica gel ;) - no really I do, though I often misconfuse them and say the wrong thing. Thanks for pointing that out! :D

As for storage, that is an option, there are proper O2, N2 and Ar tanks available for high pressure but that brings in the need for additional compressors which might be done in a latter stage. The main need is for O2 for some big production projects and class work with lots of people working at once.

The propane tanks could be used as a temp storage and then compress to the high pressure tanks later - that is a definite possibility - but they can also be used to store compressed air for when higher flow is needed at peak demand times (in combination with the high pressure tanks - with the final product).

I forgot to mention that I was planning on including an AC radiator in the line after the compressor and before the filters. This should cool the air (reduce volume) and allow for more water to be extracted. Whether the radiator need be cooled may depend on a number of factors but it will be in a basement like area where it is usually 60F so that may be cool enough. IDK how it could be make cooler very easily without using active cooling like a dehumidifier coil (which could be placed in front of the air intake) and then somehow cool the AC coil with it. Maybe use an empty tube/slot in the AC radiator and if there is one on the dehumidifier as well, run fluid between the two, so liquid cools on the dehumidifier chilling radiator then flows to the AC radiator where it can cool one rung/pass/length of the radiator - then return to the dehumidifier.

IDK if people know, but radiators (in AC's, heat pumps, de-humidifiers, car radiators, etc) often have open holes running through the Al fins that aren't used - some even have tubing through that is crimped but not connected to anything so that it can be used later for something. If an open hole, tubing can be put into it to tap into the unit for whatever reason. People use this on vehicles for doing things like heating water or fuel. I never knew this or why there were empty holes in radiators where I thought tubing should be running. Maybe it isn't necessarily planned for this, but I have seen plenty of people use it for these types of things.

XeonTheMGPony - 14-5-2017 at 15:08

Compressor Coalescing filter > Tank > Coalescing filter > Desiccant > Mechanical particle filter.

Usual what we used for high purity, the desiccant stacks can include other types of scrubbers.

Carbon stack followed by your desiccant and iron powder or what have you if you want to scrub out O2 and so on.