Anyone use a membrane air dryer?

[knighty]

I have 3 acrew compressors with refrigeration air dryers, both feed into a 2000litre air receiver and we take air off from there. Both run at 10bar.

Don't really need 2 compressors, u der normal use only 1 ever runs, 2nd us more if a backup than anything else.

Both compressors have their own air tanks, every tank has an automatic drain valve.

Unplugged a pipe for a machine in the factory last week and there was quite a bit of water vapor in it, cant feel any moisture if i plug an blow gun in etc

Sp I'm thinking I should add extra air drying after main receiver take off... maybe that moisture was a fluke or months of build up but either way there's sone expensive kit I want to protect.


Does anyone have experience with membrane air dryers? They look like the best thing since sliced bread but I've no experience and the Internet is a bit lax on real world reviews :-(

 

[brightspark]

ad a decent size water seperator on the outlet of the tank or fit one next to the expensive machine if its a fair run from the tank

 

[winchman]

Only had dealings with Desiccant dryers (-50+), work very well but I doubt they are cheap to either buy or run, horses for courses I suppose?

 

[knighty]

Are separators that good? Always assumed they'd only pull out water droplets not humidity etc. ?

Not thst I realky know anything about them....

 

[knighty]

Only had dealings with Desiccant dryers (-50+), work very well but I doubt they are cheap to either buy or run, horses for courses I suppose?

I've got one... bought it used ago... trued it but didn't like that it used a trickle of air 24/7

 

[Brad93]

What's a membrane drier?

 

[knighty]

looks like a really long normal filter

air goes through the membrane but water/moisture is too big so get filtered out... or something like that :-o

 

[timgunn1962]

We use them on small control air systems at work.

We only have low flow: typically only about 1 CFM of continuous air usage to an electropneumatic valve positioner, plus a bunch of pneumatically actuated butterfly valves that move very seldom.

We went for the membrane dryers because the plant is out of the way, exposed to all weathers, gets visited by someone fairly non-technical maybe 2 or 3 times a week and by a service engineer every 3 months (unless it breaks). We needed something as close to foolproof as possible.

The plant feeds landfill gas to generators, which generate power to the grid. Because of the way we got paid for the power, the potential cost of an unplanned plant shutdown during extreme cold weather was truly eye-watering and we decided we needed protection to -25 degC.

The membrane dryer purge air consumption in our case is pretty close to the 1 CFM continuous air flow bled off at the electropneumatc positioner, doubling the air consumption. It is relatively wasteful of air, but acceptable for our process.

We run a 3 HP, 150 litre reciprocating compressor to provide the air and we aim to keep the duty cycle under 20%.

They work well for us, but they aren't necessarily suitable for other applications.

What does the air do in your machines? What pressure does it need to be to do it? What temperature range does the air see between the refrigerant dryer and the machine?

The lowest temperature a refrigerant dryer will get the compressed air down to is usually about 5 degC (much lower and the condensate will freeze). If you run it through a coalescing filter at that temperature to remove any mist, you'll have compressed air with a pressure dew point of 5 degC. The "pressure" part matters (a bit). If you dry to 5 degC at 10 barg (11 bara) and reduce the pressure to 6 barg (7 bara), I "think" the dewpoint will come down to just under zero degC. CAVEAT: It's 30 years since I did the calculations and I'm no expert.

Without knowing your process, I'd guess a decent autodrain coalescing filter immediately before each machine would get the job done. If you can, distribute the air at higher pressure than the machine needs and run through the coalescing filter, then the regulator, at the machine inlet.

It's worth mentioning that we use quite a few Dropouts at work. Bu**ered if I know how/why they work, but they certainly seem to. We do use coalescing filters downstream because I can't bring myself to place absolute trust in anything I don't understand. When I get to visit the plants, the Dropout is always taking out the water and the coalescer is almost always completely dry. We use the 1/2" DO300.

 

[knighty]

It's all most all for a thermoformer, it's patfood, but bacon packets are the same design... machine takes in a roll of film, heats it, vacuum it into a mould to make the tray shape, then it moves along, meat drops in, goes a long a bit further, they're vacuum packed and a film lid is heat sealed on, bit further along some knives come up and cut between the packets

there's a lot of moving parts to it, nothing especially delicate or precise... but the machines cost a bloody fortune, quite a few pistons going up and down etc.

there's a conveyor right after it which takes 2 lines of packets and sorts them into a single line... it's a terrible design, few pistons in that too

I'm waiting on the installers to come back and sort our a few problems but there's a label applicator after that, doesn't use any air but has a £10k printer sitting ontop of it... I fancy a decent cover for it with an airline blowing a trickle of dry air into to keep it all nice and dry (very humid environment, steam clean down multiple times a day, drums of 80'C water tipped over the floor etc. etc.)

compressors run at 10bar, it's 10bar right up to the machines, they have their own regulators, running at 9bar.... they're advertised as running at 8bar but they need 9 to run properly, there's no drop out fitted to it as standerd

not sure on cfm used... advertised at 30cfm but a 30cfm screw compressor easily keeps up with it... one of the compressors is inverter driven and it'll run the air supply for everything with about 50% load on the compressor (no idea if 50% inverter load on a 30cfm compressor is 15cfm... probably not but I have no idea)

refrigerant dryers... the one with a display runs about 1 to 2'C in use, other doesn't have a display, think it's about the same - both compressors have air coolers before the refrigerant dryers, they dump a lot of heat, air out of the dryers feels cool/cold