clean air 4

[pelts]

Our lab has an inductive couple plasma [IPC] Optical Emission System anaylizer. This is new to our lab. It needs an air supply of 28litres/min. @ 100psi.
Our plant has 75 hp screw compressor, lots of air. Can we source our air from the plant source and clean it? Or should be install a seperate oiless compressor for the IPC?
Air needs to be very dry and free of hydocarbons.
Has anyone out there had experience in this?
Thanks

 

[PSE]

You can likely source you air from the current compressor and heavily filter and dry it. There are several companies that offer this type of equipment.

http://www.parker.com/ead/cm1.asp?cmid=362

You may need to work through and consider the pressure drops for the various filters based on your need to determine if sufficient capacity remains. You could then compare potential cost of operation/maintenance of the filter system to a dry pump (which will still likely need some downline filtering anyway and separate air lines installed).

Regards,

 

[Ashereng]

Just a thought.

If it is lab equipment, and clean air will affect the reading, wouldn't it be better to use bottled air rather than trying to clean the dirty plant air (yes, I realise that plant air systems have filters, dryers, etc, but we are not talking lab grade here).

If a lab result goes wonky, would anyone "analyze" the air source? Or, would they assume that the lab result is good, and go off referencing a faulty lab result?

In my line of work, we take the lab result as gospel - no one has thought that the lab result due to the lab is a problem. Oh, we test because the sample is contaminated, took the wrong sample, the equipment isn't performing ... Never heard of anyone questioning the lab equipment itself. Probably, it's because we don't know enough about the lab to question it intelligently.

My suggestion would be to ensure if a lab equipment needs air (and only air), that is what you go and buy.

 

[griffengm]

Pelts,
Ashereng has a good idea but you should take a look at expected use before committing to any system. In other words, how many hours/minutes per day do you expect to use this instrument? How much time can you tolerate for cleaning filters and how much mess? Who gets the job of checking filters/air supply?
20% of the process may end up maqking 80% of the work!

Griffy

 

[kenvlach]

I've used lots of bottled gases. My advice: forget the bottled air -- you will rapidly grow tired of changing out cylinders every 30 minutes (28litres/min. = 1 CFM, but if measured at 100 psi this may be 7 SCF/min. Most cylinders are ~235 SCF). Your Fire Dept. will also want good securing to a fireproof wall.

I suggest a Balston® Model 76-02 Compressed Air Dryer (coalescing filter + membrane dryer). See the Parker link above. Practically automatic; change the coalescing filter once a year.

About the only plant air suitable for analytical instruments is in shops that do aerospace spray painting.

 

[Ashereng]

pelts,

I guess it comes down to how much air, and how clean the air is. And, also, what happens to a contaminated result, what the consequences are.

I suggest you to to a lab with similar equipment as yours, and doing roughly what you will be doingm, and ask the lab manager what he is using, and what he wished he would have done had he known better.

A lab that is not reliable will VERY QUICKLY lose jobs. If I suspect my lab because of systemic problems (not just a bad test or an inexperienced tech), I'd take ALL of my business elsewhere now.

 

[pelts]

Thanks to everyone. Our lab is essentially for our own testing. Accuracy is foremost.
I brought in an air expert from one of the filter companies.
Confirmed your concensus, and we will work with the shop air and with very good filters and dryer in series with the lab equipment. Thanks again. Pelts

 

[PSE]

One further recommendation. Run new lines from the dryer/filter system and still use "point of use" filters. Running CDA through the existing lines can cause the scale to flake off the inner walls as it dries out and could wreak havoc on any instrumentation downstream.

Regards.

 

[pelts]

Our plan is to "tee" into the air system on a main line near the compressor. We will run a "down drop" at that point down to a mechanical water trap. The new [nylon] air line will run verticle from the drop, and on to a set of coalescing and moisture/oil filters. The clean air then enters a refrigerated dryer and proceeds to a final bank of coalescing filter and moisture/oil filter. This air then continues into the IPC Anaylizer.
The filters in series will have electric sensors that will shut off the air supply as the filters may become full. The IPC will shut down sensing no air.
Hopefully this system will work for us.
We welcome any further input in this matter.
Thanks, Pelts

 

[Ashereng]

pelts,

I for one would like to know how the air system works out for you. Keep us posted.

 

[kenvlach]

pelts,
The old, tried-and-true design will work, but IMHO refrigeration drying takes up more space, uses much more energy and requires more maintenance than the membrane type.

One concern is the "nylon line." Is this reinforced hose? Plant air is normally > 100 psig, so a compressed air-approved grade of ABS is the only allowable plastic piping (unless some recent change in the law, which your building inspector may not be aware of, anyway). A 1988 OSHA letter reads in part:
"Furthermore, sections 842.32, 842.43 and 849.52(b) of the American National Standards Institute/American Society of Mechanical Engineers (ANSI/ASME) B31.8-1986, Gas Transmission and Distribution Piping Systems Standard, limit the operating pressure of plastic piping distribution systems to 100 pounds per inch (psi) and prohibit the installation of such systems above ground except where ". . . the above ground portion of the plastic service line is completely enclosed in a conduit or casing of sufficient strength to provide protection from external damage and deterioration."

"The filters in series will have electric sensors that will shut off the air supply as the filters may become full."
-- what about self-draining filters (for the liquids)?

 

[pelts]

Kenvlach:
The "Nylon line" is the same line/hosing we use on our machinery to supply air cylinders and air valving. This is not a main supply line, but a small 3/8" line, tee'd from a 2" black iron pipe main line.
I would be suprised if anybody found this configuration not acceptable.
Our filters are self draining. We have three in series , two before the refrig. air dryer. One at the "Tee" and another just before the air dryer. Final filtering just in front of the IPC anaylizer
We have the system up and running today. I am purging air through the system for 24 hrs. and will test it for moisture content tomorrow.
I think we are good to go.
The burning question is how often we might have to replace the coalescing filters. Thanks for your input, Pelts