Here's an interesting concept that didn't appear to pan out. Jeremy had done some research on this a while back and the topic was broached by Scott
Date: Sat, 12 Jul 1997 23:43:11 +1000
From: Scott Leimroth < anscott@hinet.net.au
>
Subject: Liquid Scrubber
On submarines, CO2 is removed with a chemical scrubber, called monoethanolamine. MEA is
supplied in liquid form, although it may be a solid dissolved in water. When cold, MEA
takes in CO2, when heated, MEA gives up the CO2. On submarines, the CO2 is pumped
overboard.
Anyone know anything else about this stuff??
Could it have application in a rebreather???
Scott
Date: Sat, 12 Jul 1997 11:19:45 -0400
From: Paul Elliott <
>
Subject: Re: Liquid Scrubber
Scott,
I've wondered about stuff like this. I had no idea what was being used on subs. It seems
to me, though, that you would run into a problem with orientation when trying to apply
this to a rebreather.
[slack jawed, armchair science mode on]
In a sub, there's an excellent chance that the thing is upright, and you could feed gas in
through the bottom of the scrubber container and let it go to the top where it is gathered
and sent on its way sans CO2. In a breather, you don't have that guarantee, and I don't
see how you could feed gas in at one point and expect to get scrubbed gas out somewhere
else for all orientations.
[slack jawed, armchair science mode off. . . well maybe. . .]
That being said, is there anything like this process (gather/scatter CO2) for a dry
scrubber? Looking at the reaction for soda lime, it looks like you can take CO2 saturated
soda lime (aka chalk), and take it back to regular soda lime with the right reaction/kiln.
I don't know if it would be worth screwing with, but has anybody heard of anything similar
being researched?
------------------------------------------------------------------------
Paul Elliott | Software Eng. Northwood Designs, Inc.
class Flames {public: Flames() {delete this ;} ; } ;
Date: Sat, 12 Jul 1997 13:37:33 -0400
From: "Jeremy E. Downs" < JeremyDowns@compuserve.com
>
Subject: Re: Liquid Scrubber
Guys,
This is similar to what really got me going last year in my research. I only have a couple
of minutes here so I'll be quick. Think about this, Use a liquid sorbant material like
that encase it in dual ended hydrophobic membrane scrubber then plumb it into a
rebreather. There is a substantial amount more to this in what you do with the sorbant
next, but that is the basic idea here in a back mounted system. By the way this theory has
already been tested and proven that it can work.
I'll tell more later.
Still tinkerin'
Jeremy
Date: Sat, 12 Jul 1997 16:58:30 -0400
From: Paul Elliott <
>
Subject: Re: Liquid Scrubber
Jeremy,
On human lungs? Breathing through liquid can't be easy, even if you have a huge surface
area. I'm interested in the details, but I still don't see a fail-safe way to do this.
Looking forward to your tinkerin' details,
------------------------------------------------------------------------
Paul Elliott | Software Eng. Northwood Designs, Inc.
class Flames {public: Flames() {delete this ;} ; } ;
Date: Sun, 13 Jul 1997 09:45:51 +1000
From: Scott Leimroth < anscott@hinet.net.au
>
Subject: Re: Liquid Scrubber
Couldn't the gass just percolate through it ?? ;)
How efficient is this stuff, maybe as long as there was a puddle of it somewhere in the
loop(not you lungs) it might be enough?
Still wondering,
Scott
Date: Sat, 12 Jul 1997 20:59:09 -0400
From: Bill Elliott < bill@nwdesigns.com >
Subject: Re: Liquid Scrubber
Jeremy,
I can believe there are other ways to scrub CO2, I find it near
impossible to imagine any way to put liquid in a breathing loop (hydroponic membrane notwithstanding ) and
keep the breathing resistance within acceptable limits. Please elucidate.
Regards,
Bill
Date: Sat, 12 Jul 1997 23:53:57 -0400
From: "Jeremy E. Downs" < JeremyDowns@compuserve.com
>
Subject: Re: Liquid Scrubber
Bill & Paul,
It's simpler to just fax you a sketch, give me your number & I'll show you its really
a trip.
Anybody else out there played with this? I would like to know.
Jeremy
Does anybody have this fax? I lost my copy, and I'll post it here when I get it.
Date: Sun, 13 Jul 1997 00:02:30 -0700
From: Peter Heseltine < heseltin@hsc.usc.edu
>
Subject: Re: Liquid Scrubber
Uh, I just hate to bring this up, but why do you think you can't breathe water, even if it
does have a pO2 of 1.0? Could it be something to do with the effort required, among other
things? Like what do you suppose the WOB would be of pushing your expired air through a
"a liquid sorbant material like that encase it in dual ended hydrophobic membrane
scrubber" at the surface, let alone at depth? Unless of course you plan to have that
nuclear sub on your back to ventilate the loop.
Also my recollection from organic chem 101 is that MEA is even less the kind of stuff you
want in your mouth than LiOH. Still, freeze it to your scrubber membrane by diving cold in
caves and spitting freon through a tiny hole in your front teeth and hey...this is now the
breathing (fruit) loop of the month award. It will go packed in tissue paper into my
bottom drawer along with fisting aligators and phreezing phlegm.
pHreaked
Date: Sun, 13 Jul 1997 12:31:13 -0400
From: "Jeremy E. Downs" < JeremyDowns@compuserve.com
>
Subject: Re: Liquid Scrubber
Peter,
Give me your fax number & I'll show you too. First, breathing gas does not actually go
through the liquid (this is much simpler to just show you a quick sketch). Second MEA is
not what is used, its more of a blend of liquid amines. The idea behind the submarine's
system is similar, not the exact same system.
Jeremy
Date: Wed, 30 Jul 1997 16:46:31 -0400
From: "Jeremy E. Downs" < JeremyDowns@compuserve.com
>
Subject: Liquid sorbant
Does anyone out there have any experience with or knowledge of a liquid compound known as
hydroxyethyl piperazine (HEP) in the use as a renewable CO2 sorbant, or what it's
characteristics may be in our interests.
thanks,
Jeremy
Date: Sat, 19 Jul 1997 16:16:52 -0700
From: Peter Heseltine < heseltin@hsc.usc.edu
>
Subject: Re: Membrane scrubber
Jeremy - thanks for the fax. I have not had time to sit and absorb the details yet and I
would like to check some of the references quoted. So, sorry that I have not gotten back
to you sooner and that the following is only after a first reading.
Microtubular gas exchange systems are now widely used in Europe and some in the US as a
way to filter air/gas and also to exchange properties. e.g. heat and certain more
diffusible chemicals. I think that the system works because it is designed to be used in
the comparatively large space of a submarine or an EVA suit. Using a liquid which will
absorb CO2 and then give it up (recharge) has obvious theoretic advantages, but also a
number of disadvantages come to mind.
Expense, size issues and increase in the work of breathing: The flow-rate has to be high
because my guess is that 10 liter loop volume is pretty close to the maximum ambient
pressure gas you can swim with without needing a lead anchor to keep you down. With that
volume the flow rate has to be high enough to allow you to take a 2L breath and yet
achieve a gas dwell-time sufficient to remove CO2 down to about FCO2 of 0.3% average. (As
an aside for semi-closed fan(atic)s, I think that venting 10% of your gas on each breath
increase your effective loop volume by 10%, maybe more). On a closed system, pushing that
volume of air through a microtubular system would probably require a large effective
absorbant surface area. Microtubules do that. But in that volume, including displacement?
Also, I know that gas to membrane to CO2 absorbant contact is less efficient (more dwell
time) than gas to CO2 absorbant. Between the microchannels and the added displacement you
would have to have something a lot more efficient than sofnolime on a weight/volume basis.
You could bond the CO2 absorbant to the inside wall of the microtubule, but now this
sounds like a microtubular version of sofnolime. You also now have potential contact and
aspiration into your lungs of whatever this compound is, as tiny bits break off. Expense?
For what actual benefit? I guess that's not a huge problem if you are recharging the CO2
absorbant and not throwing it away. I would think that a CO2 meter would be essential here
to assure that your absorbant has recharged and is functioning correctly.
I suppose if your CO2 absorbent "recharges" by off gassing CO2 say overnight,
that's pretty cool. Hey, if you could also have an endothermic reaction take place, while
recharging you could use it as an air conditioner in your tropical hotel room while you
sleep! Perpetual motion! Dive, sleep, dive, sleep, chill.
I'm interested to hear more.
pH
Date: Sun, 20 Jul 1997 23:32:25 -0400
From: Bill Elliott < bill@nwdesigns.com >
Subject: Re: Membrane scrubber
The liquid scrubber thing was very interesting. I only had a chance to
speed read it and have probably missed something, but my biggest concern is that it would
seem that to reactivate the liquid you need to heat it up. This means power, batteries
etc. This is a real problem to me. I want something that is passive and doesn't require
external energy to suck my CO2! If you have a heater failer who wants to stop breathing to
avoid the CO2 buildup? ;)
An interesting question would be, given an equal volume relative to a
typical cannister, would the liquid last as long without recharging as a cannister full of
Sofnolime? If so, then you could make a case for the liquid scrubber, because you could
reuse it by recharging it after the dive. Obviously I have to read the article in more
depth, perhaps some of these answers are spelled out.
Regardless, thanks for the food for thought Jeremy. Whether the liquid
scrubber is remotely viable or not, we never get ahead in anything, unless we stick our
neck out and ask some questions.
Regards,
Bill
Date: Tue, 22 Jul 1997 15:44:26 -0400
From: "Jeremy E. Downs" < JeremyDowns@compuserve.com
>
Subject: Re: Membrane scrubber
Bill Elliott wrote:
>my biggest concern is that it would seem that to reactivate the liquid you need to
heat it up.
Yes this issue concerns me too, we need to look into various options in the design. There
are aparently quite a few substances that can be used as liquid sorbants, hopefully one of
them will be right for our application. I'll ask the researchers about this.
> An interesting question would be, given an equal volume relative to a typical
cannister, would the liquid last as long without recharging as a cannister full of
Sofnolime?
Heseltine brought up the same idea I'll look into it. Im sure it would take a considerably
larger sorbant volume to handle such a configuration since it would not be actively
recharging itself. It might be possible that you could find a happy medium with a slightly
larger sorbant volume and some form of early detection (temp. guage?), this should give an
acceptable bailout where the sorbant would give you time to take care of deco and get home
safely. You could possibly even adjust the volume according to the dive plan.
> Regardless, thanks for the food for thought Jeremy. Whether the liquid
scrubber is remotely viable or not, we never get ahead in anything, unless we stick our
neck out and ask some questions.
Exactly I'm just a dive geek who found a cool idea out there. I do not have the expertise
to do this on my own, however this list has many talented people on it with different
backgrounds and knowledge, if we all tried to work together on this system we just might
be able to make it fly.
Anybody want in? (this is not a business offer, I'm not in it to become another
manufacturer, just a chance for everybody to work together for our common good)
And that is pretty much it. It's an interesting idea, but has some implementation details that are a bit scary on the relibility and predictability scales. Should it be thrown out? Probably, but I don't think that the topic has been exhaustivly covered.
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