Comment by to11mtm
3 days ago
I don't know numbers but I at least remember my paintball physics;
As far as the storage vessel, CO2 has much lower pressure demands than something like, say, hydrogen. On something like a paintball marker the burst disc (i.e. emergency blow off valve) for a CO2 tank is in the range of of 1500-1800PSI [0].
A compressed air tank that has a 62cubic inch, 3000PSI capacity, will have a circumference of 29cm and a length close to 32.7cm, compared to a 20oz CO2 tank that has a circumfrence of 25.5cm and a length of around 26.5cm [1]. The 20oz tank also weighs about as much 'filled' as the Compressed air tank does empty (although compressed air doesn't weigh much, just being through here).
And FWIW, that 62/3000 compressed air vs 20oz CO2 comparison... the 20oz of CO2 will almost certainly give you more 'work' for a full tank. When I was in the sport you needed more like a 68/4500 tank to get the same amount of use between fills.
Due to CO2's lower pressures and overall behavior, it's way cheaper and easier to handle parts of this; I'm willing to bet the blowoff valve setup could in fact even direct back to the 'bag' in this case, since the bag can be designed pessimistically for the pressure of CO2 under the thermal conditions. [2]
I think the biggest 'losses' will be in the energy around re-liquifying the CO2, but if the system is closed loop that's not gonna be that bad IMO. CO2's honestly a relatively easy and as long as working in open area or with a fume hood relatively safe gas to work with, so long as you understand thermal rules around liquid state [also 2] and use proper safety equipment (i.e. BOVs/burst discs/etc.)
[0] - I know there are 3k PSI burst discs out there but I've never seen one that high on a paintball CO2 tank...
[1] - I used the chart on this page as a reference: https://www.hkarmy.com/products/20oz-aluminum-co2-paintball-...
[2] - Liquid CO2 does not like rapid thermal changes or sustained extreme heat; This is when burst discs tend to go off. But it also does not work nearly as well in cold weather, especially below freezing. Where this becomes an issue is when for one reason or another liquid CO2 gets into the system. This can be handled in an industrial scenario with proper design I think tho.
So… it’s a compressed air battery but with a better working fluid than air.
I remember wondering about using natural gas or propane for this a long time ago. Not burning the gas but using it as a compressed gas battery. It liquifies easier than air, etc., but would be a big fire risk if there were leaks while this is not.
Seems neat.
> Not burning the gas but using it as a compressed gas battery. It liquifies easier than air, etc., but would be a big fire risk if there were leaks while this is not.
FWIW Back in the day, Ammonia was used for refrigeration because it had the right properties for that process; I mention that one because while it's not a fire risk it's definitely a health risk, also it's a bit more reactive (i.e. leaks are more likely to happen)
> Seems neat.
Agreed!
Maybe use excess power to produce methane via the sabatier reaction, store that, and then burn it in turbines or use it in fuel cells when needed.
It’ll be interesting to see how the economics of these various solutions play out.
The problem with that is usually efficiency. Electrochemical or thermal production of methane from CO2 and H2O is not very efficient, and then you're burning it, which is only heat engine efficiency.
Batteries or direct mechanical storage (compressed gas, pumped hydro, etc.) are both a lot more efficient.
This would make sense if solar gets so cheap that it's something to do with the surplus, and it would be a way to electrify things like long haul aviation where batteries are too heavy. We are flying LNG rockets, so LNG planes are totally possible, or you could upgrade methane to butane or propane which are quite easy to compress to liquid form. Jet engines run great on light weight fuels like that.
Except you have to trap and recycle the uncompressed CO2, hence that enormous bag to hold all that gas. Color me skeptical.
With compressed air, you just release the air back to the atmosphere.
> With compressed air, you just release the air back to the atmosphere.
The issue with compressed air is that you have to build more of the system to handle higher pressures and/or have a more robust regulator design, plus the pressures required to compress CO2 back to liquid are typically lower than what you'd need to store a useful final volume compressed air...
Also, As far as having an 'open loop' (i.e. venting to atmosphere), that's typically got it's own problems, mostly that when you need new air you have to make sure it's 'pure', not just things like dust but even whether there's water vapor.
They mention that and say it fits in a huge inflatable tent, which rings true. CO2 is more dense than nitrogen and oxygen which are most of air, and if you're storing it at ambient pressure you don't need a super strong vessel.
Fantastic detail, thank you.
>cubic inch
>cm
>oz