Filtering martian atmosphere

[Drosta]

So, utilising a large powered vent I can pretty easily pressurise a pipe network to condense pollutants and then pass them through a condensation valve and out but CO2 is proving to be more difficult. It can certainly be done, but I need to keep the pipe contents below -8C ish to do it and the temperature rises fairly rapidly even when the Martian atmosphere is at its coldest at night. So I've gone ahead and started using an atmospherics filtration unit but that seems a bit impractical as even at a modest 5Mpa of "air" in the tank we're talking about 100K mols of CO2 to 2-3k mols of N and O2. Plus I started doing it this way because I dislike the idea of using the magic filter box that doesn't really exist irl. So I was wondering what some of you might suggest as a solution.
I was thinking of things like maybe capturing the low temp liquid pollutant and running it through a heat exchanger. Or I could use a pipe with an AC unit if I can stabilize the warm pipe. Maybe a loop with the condensation/evaporation chamber. I dunno. I have very little experience with all of these tools so any tips would be great. Thanks

[powerkek]

Once you've separated the liquid pollutant from the other gases you can evaporate it for more cooling, using a purge valve or the phase change device. I do that with Vulcan's 130C night air, should work much better on Mars.

But if you're just trying to get O2 and N, the most effective way is probably with a portable scrubber. For low concentrations it works much better than the filtration unit. Wrench it down onto a portables connector to get a pipe connection, and add a wireless battery charger to keep it going.

[Drosta]

yeah, im actually just starting to monkeybrain my way around it this morning again, and I've attached a few passive liquid drains to the gas pipe. which seems to be working quite well. now i'll just make an IC to turn the vent on when it's very cold outside and the liquid drains should do alot of the work. i mean, eventually i'll want to collect the liquid Pol and CO2 and use it. but for now, i just need the breathable air. :)

[Drosta]

Side note. to prevent CO2 evaporation in my liquid tank and pipes I tried to use a pressurant valve to boost the pressure to 6Mpa but then the tank explodes. Lol

[Alizia Kaline]

If your only problem is to keep CO2 at -8° on Mars, it's not a problem. Collect the air only during the night, store it in a big tank at 40MPa to use it during day.

But to be honest, it's a crazily complex filter for nothing. I use gas filter in series to filter marsian air and it works pretty well. Passive drain to expel the pullutant and only collect air during day to keep it > 15°, ready to be used in my base. I recommend to filter the CO2 at the end to preserve the pressure in all the filters and to use pump to empty their output to have the maximum pressure diff.

If you really want to keep CO2 as liquid, I assume you can use Nitrogen to pressurize it and keep it cold in a big tank (for the mass effect). You can use the night cold temperature to refresh the Nitrogen/CO2 mix.

[Drosta]

Originally posted by Alizia Kaline:

If your only problem is to keep CO2 at -8° on Mars, it's not a problem. Collect the air only during the night, store it in a big tank at 40MPa to use it during day.

But to be honest, it's a crazily complex filter for nothing. I use gas filter in series to filter marsian air and it works pretty well. Passive drain to expel the pullutant and only collect air during day to keep it > 15°, ready to be used in my base. I recommend to filter the CO2 at the end to preserve the pressure in all the filters and to use pump to empty their output to have the maximum pressure diff.

If you really want to keep CO2 as liquid, I assume you can use Nitrogen to pressurize it and keep it cold in a big tank (for the mass effect). You can use the night cold temperature to refresh the Nitrogen/CO2 mix.

I was mostly toying around to see if I could. And I like keeping my base air at lower temperature anyway so I can do a small flush into the base every once in a while to bring the ambient temperature inside down once it starts rising due to machines and whatnot convecting their energy out into the air. But I take your point.

What I'm actually struggling to understand is how to make the liquid usable. I thought maybe attaching an expansion valve would just release cold gas into a pipe but it ends up causing alot of pipe stress immediately. So I'm not sure how to use it now, other than as a liquid in a heat exchanger setup.

[powerkek]

You need to use a liquid pump before the expansion valve to regulate its input, since the valve has almost no flow limit. And you might need some way to release the nitrogen from this section, I'm pretty sure the liquid pump also pumps gas so it will build up.

Or if you keep your liquid pipes single-element and don't needlessly stuff them with nitrogen gas, you can just use a purge valve to safely draw gas out if them. People tend to get scared of evaporation, but it's just the first few liters until the liquid pipe reaches its correct pressure and then it stops. Check the phase change graph.

[Drosta]

Originally posted by powerkek:

You need to use a liquid pump before the expansion valve to regulate its input, since the valve has almost no flow limit. And you might need some way to release the nitrogen from this section, I'm pretty sure the liquid pump also pumps gas so it will build up.

Or if you keep your liquid pipes single-element and don't needlessly stuff them with nitrogen gas, you can just use a purge valve to safely draw gas out if them. People tend to get scared of evaporation, but it's just the first few liters until the liquid pipe reaches its correct pressure and then it stops. Check the phase change graph.

Thanks I'll try that. Didn't consider the pump

[Alizia Kaline]

WIth pure CO2 at -20°, it will auto-pressurize and stay liquid (like water at 0+°). It should never reach -55 or it will freeze and higher than -15 is dangerous (evaporation should reduce temperature).

Lower the temperature is, lower the pressure needed will be high. You can get this gas formed with a purge valve and use it where you want.