[labnetwork] Steam Humidifier system question

[John Shott]

Rick and the labnetwork community:

Our facility (Stanford Nanofabrication Facility) uses DI water off our 
main DI system for humidity injection/control in the lithography portion 
of our cleanroom.  While I'm not an authority on that sub-system, I'll 
share with you what I know, what I like, and what I don't like about 
that system.

I believe that we have a total of 3 humidifier units that are model STS 
Humidifier made by the Dri Steem Company.   They use campus-wide steam 
to provide the heat source and DI from our lab to be the source of 
moisture.  We have run two DI supply/return loops (one on each side of 
the cleanroom) up into the interstitial space above the clean room to 
provide a DI source up there.  Those lines are run in welded 1/2" PVDF 
lines and have a small valve and 1/4" teflon line that runs from the 
distribution system to each humidifier.

While I don't know the flow through the 1/2" distribution lines, I 
suspect that it falls below the generally accepted minimum velocity 
specs for high-quality DI distribution.  While that is something of a 
concern, our DI system is old enough that this is not the only place 
where that happens so I don't lose sleep over it.

What is the flow that we use for steam generation ... that is, how much 
is actually extracted from those loops?  I don't know, but it's likely a 
piddly little amount.  Well less than 1/2 GPM, I suspect ...

As far as returning it to the main system, however, I think that DI is 
like chewing gum: it's OK to let someone have some, but you DON'T want 
it back when they are done with it.  Even at 1/2 GPM, I'd likely be 
inclined to dispose of that water rather than try to re-use it.  
Certainly, 1/2 GPM can't be converted into steam to humidify a room, so 
I'd ask if they can use less so that you don't feel bad about dumping 
water down the drain.  If their usage is on the order of 100 sccm per 
minute or less, you probably can live with that.

Whether DI is sufficiently corrosive to cause them problems is likely 
their problem (particularly if you aren't getting the "unused" water 
back) ... but I'll bet that it is.  However, the good thing about DI is 
that you won't have problems with "stinky steam" as long as you avoid 
bacteria growth.  Our system used to use some form of "treated water" 
... and we would periodically be able to smell the steam.  Not a good 
thing in a lab where you try to train people to be on the lookout for 
and sensitive to funny smells.


That's at least my initial reaction and relevant experience.  I'll be 
interested to hear what some of the newer facilities have done in this area.

Have a good weekend,

John



On 9/14/2012 12:19 PM, Morrison, Richard H., Jr. wrote:
>
> Hi All,
>
> Facilities at my labs want to run 18megohm to a boiler for humidity 
> control in another lab. I think it should be RO water as 18Megohm 
> water is very corrosive. Any thoughts on this?
>
> Their suggested design would draw 0.5gmp from my supply loop and 
> return it to the DI tank? My belief is that this return water would be 
> contaminated by the boiler system. What do you guys think?
>
> Rick
>

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