air-in-steam analyzer for steam purging

[NIWEngineer]

Hi all,
Reading about purging vessels with steam in the "Hazards of Steam" booklet by BP. They mention this instrument that apparently at one point was available by MSA and is no longer in production. Using it to measure air in steam at the discharge of the vessel during purging may indicate when no more air remains (outside of no-flow internal "pockets", that is) inside the vessel. Anything like that still available? I know the pharmaceutical industry uses steam quality monitors that measure non-condensables for sterile applications, but they do not seem "rugged" enough for the field.

Thanks!

 

[StoneCold]

NIWEngineer

What they are probably talking about in the book is using a Lower Explosion Limit Meter from MSA. Put steam on the vessel and take a small stream off the vent and cool it. Then run the non condensables into the MSA meter. It will pick up the VOC's and tell you if there is still hydrocarbon in the vapor stream, It will also give you a percent oxygen reading so that you can determine the extent of the steam purge.
It is better for you than smelling the vent to tell how complete the purge was.

Regards
StoneCold

 

[NIWEngineer]

Thanks, StoneCold.

Its actually something a lot simpler - though your suggestion of an LEL seems good as well. The "instrument" they are talking about operates on the principle that the pressure of a steam/non-condensables mixture at a certain temperature indicates the percentage of non-condensables present (i.e, zero non-condensables then P=Psat @ given T). In other words, just checking T and P for the discharge and compare that with the saturation conditions. If P is less than the vapor pressure for steam at the measured temperature, then there are non-condensables in the stream.

 

[StoneCold]

NIWEngineer
That seems easier that what I thought they were doing. Learn something every day. Not that I ever use steam out for a purge. We have nitrogen for that.

Regards
StoneCold