Compressed air 2

[npomies]

Hi,

I'm working on the qualification of a Compressed Air system.
I'm trying to identify acceptance criteria from a air "purity" point of view.
I'm struggling with the water content: Pharmacopieae refers to water vapor (e.g. <67ppm) and ISO refers to dew point... could someone tell me what is the correspondance between these so that I can check which is the most stringent?

Thanks in advance,
NP

 

[quark]

http://www.airproducts.com/Products/fastfacts/charts_n_tables/dewpoint.asp

You have to follow Pharmacopieae. With refrigerated dryers and 0.01mic. filter, you can be able to acheive this or better is to go with zeolite molecular sieves. Take care of oil too(I mean your qualification should include this aspect also).

 

[25362]

Quark has given you a useful link for the tabulated correspondence of dew points at atmospheric pressure to ppm water content as requested by pharmacop[&oelig;]ia.

I think some clarifications are in order. Moisture concentrations in ppm are given on a volume basis (not mass basis, which would be about 62% of the tabulated values).

When moist air is gradually cooled at a given pressure, say a barometric pressure of 29.92 in Hg, or 101,325 Pa, the temperature at which condensation begins is called the dew point. Namely, it is the saturation (vapor pressure) temperature corresponding to the humidity ratio of the moist air mixture.

Thus, if the dew point temperature is, say, -45^oC, the tabulated vapor pressure (of ice) would be 7.202 Pa. The ppm v/v, at a barometric pressure of 101,325 Pa, would be obtained from:

7.202[&times;]1,000,000[&divide;]101,325 ~ 71 ppm​

At -70^oC, with a vp = 0.261 Pa, the corresponding concentration would be:

0.261[&times;]1,000,000[&divide;]101,325 ~ 2.6 ppm​

NB: vapor pressures were taken from the CRC handbook.

 

[npomies]

THanks guys

NP