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Re: scrubbers
Once in a blue moon, I actually get to put on my chemist hat around
here. With regard to chemical scrubbers and molecular seives, you have to
be -very- careful to see how your absorbant of choice is affected by
humidity. Some zeolitic seives (which are re-usable after being flushed and
baked with a nitrogen purge) have a higher afinity for water than CO2, so
if the air isn't realy dry beforehand you get little scrubbing action. My
prototype scrubber box will actually put out virtually 0% humidity air, as
I must dry the air before passing it through the zeolite stack to absorb
the CO2. Also, heating before/after passing through the absorbant is an
essential question; many chemical absorbants are inefficient below room
temperature, and subs get colder than that at depth some times. Your
lithium hydroxide is not going to absorb the same amount of CO2 at 45
degrees as it will at 70. This is part of why it is so essential to
overside the absorbant bed.
Gas sensors are inexpensive life insurance. Figure out the points
that measurements are essential (in my scrubber, humidity before the
absorbant and after the dryer, temperature of the absorbant and CO2 before
and after scrubbing are the metrics of scrubber health). I wanted to put in
%O2 sensors too, just never got around to implimenting them in the
prototype before a change in jobs shelved it for a while.
I originally came across this regenerable absorbant during an
engineering course, we were using it to compress Martian atmosphere to
usable pressures using only the diurnal heat cycle and ambient CO2 in the
atmosphere! When the zeolite is cold and dry it absorbs CO2, then you heat
it up and it releases the absorbed gas during the day. Same principle makes
a scrubber that can be regenerated and produces no caustic or irritating
dustm as might occur in hydroxide-based chemical absorbants.
John
John Brownlee
Lunar and Planetary Lab
University of Arizona
jonnie @ lpl . arizona . edu