[PSUBS-MAILIST] CO2 absorbent duration

Mon Feb 12 13:11:26 EST 2018

Yes, you can re-seal it. If you ensure that there is no moisture gain, or moisture loss to below the factory-supplied moisture content (used will typically be wetter unless it has been allowed to dry out), and no further consumption due to CO2 exposure, you should be good to go. It will still have a shelf-life though, as you aren't halting the evaporation/condensation equilibrium reaction, so employ used media with caution.

Per the rules, CO2 must be maintained below 0.5% by volume (5000 ppm) at all times. Atmospheric air contains 0.041% by volume (410 ppm). Lower is obviously better, and provides a safety margin for scrubber failure / changeover, so I would target the low end by design. It will be more comfortable for the occupants. If your scrubber can't keep up with CO2 production, the level will eventually rise to the limit. Depending on your mission duration, a slow rise may be tolerable, so ultimately this is a tradeoff. If your scrubber can keep up with the CO2 production, there's no reason you shouldn't be able to drive the level down to atmospheric equivalent or better.

Sean

-------- Original Message --------
On Feb 12, 2018, 10:48, Brian Cox via Personal_Submersibles wrote:

> Thanks Sean,
>
>           That's way more efficient than what I figured, I was using the low range of an estimated time length.   Is it possible to re-seal the absorbent after a short dive?  What kind of CO2 level should I realistically hope to maintain or would be acceptable ?   2000 ppm  ?
>
> Brian
>
> --- personal_submersibles at psubs.org wrote:
>
> From: "Sean T. Stevenson via Personal_Submersibles" <personal_submersibles at psubs.org>
> To: personal_submersibles at psubs.org
> Subject: Re: [PSUBS-MAILIST] CO2 absorbent duration
> Date: Mon, 12 Feb 2018 12:19:32 -0500
>
> Per ABS UVSHF (2018):
>
> CO2 production reference:
> 0.0523 kg (0.115 lbm) per hour per person
>
> The moisture is actually necessary for the reaction. This is why Sofnolime is supplied in sealed containers - to retain the factory moisture content, and to isolate the material from the ~400 ppm of CO2 in atmospheric air. The reaction occurs in three steps:
>
> 1) carbon dioxide gas dissolves in the water,
> 2) the aqueous CO2 reacts with aqueous sodium hydroxide to form sodium bicarbonate,
> 3) the sodium bicarbonate reacts with calcium hydroxide to form calcium carbonate, regenerating the sodium hydroxide catalyst in the process, and producing water.
>
> Overall, the calcium hydroxide is consumed, and calcium carbonate and water are created.
>
> As water is necessary for the process, it isn't a problem chemically, but it can become a problem in excess when it begins to dissolve the scrubber particles and allow the channels between granules to clog, or if it appreciably changes the available surface area of the granules that the process gas is exposed to, or of course in intimate breathing loops (i.e. rebreathers) if excess water containing dissolved caustics makes it to the inhalation side.
>
> Scrubber duration will be a function of cumulative particle surface area. Fine grades have more area, but also present more resistance to airflow, and a greater chance of clogging once saturated with water. Larger grades lessen these problems, but are less efficient.
>
> The technical data sheet for the grade of Sofnolime you are using will list a nominal scrubbing capacity in terms of liters CO2 captured per kilogram of media, but this should only be used as a starting point because scrubber efficiency is dependent on surface area of the media, dwell time, temperature, moisture present, etc. Perform some testing to determine the actual time to breakthrough (>500 ppm) of your scrubber design / media combination.
>
> Sean
>
> -------- Original Message --------
> On Feb 12, 2018, 09:17, Brian Cox via Personal_Submersibles < personal_submersibles at psubs.org> wrote:
>
>> Hi All,
>>                Trying to figure out an approximate time that the Sofnolime will last for a "normal" person ( let's me out I guess !)  from my reading it looks like around 1.5 lbs would last about an hour, but there seems to be quite a bit of variability .    Between the efficiency of the air flow and the other factors that number could change.   Also, for those of you experienced with this ,  does the material become all waterlogged from humidity?  and if so is it possible to store half used absorbent?   Wouldn't the moisture be a problem?
>>
>> Thanks
>>
>> Brian
>
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