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> cooled to liquid temperatures via refrigeration Do you actually need to refrigerate it to keep it liquid? My SodaStream machine works with room temperature.

by jannes 5y ago

lbotos 5y ago
"It can only exist at a pressure above 5.1 atm (5.2 bar; 75 psi), under 31.1 °C (88.0 °F)" - https://en.wikipedia.org/wiki/Liquid_carbon_dioxide https://en.wikipedia.org/wiki/Liquid_carbon_dioxide So depending where you are you'd need refrigeration
- ClumsyPilot 5y ago
  It doesnt need refrigeration for storage, CO2 is stored at higher pressure The refrigeration is needed because the process of compression produced huge amount of heat. And because of that, this method of storing energy is twice less efficient than batteries are
  - magicalhippo 5y ago
    Though they could store some of this heat for later when they want to extract the CO2 gas again, I suppose.
    - surbas 5y ago
      Which according to the article is what’s happening. They store heat in steal piles, and release it back on expansion.
  - cedilla 5y ago
    Charging batteries also produces a huge amount of heat. In general, storing energy is never free. It's the tyranny of the second law of thermodynamics.
  - ErikVandeWater 5y ago
    Yes, the critical point for condensation of CO2 is 31 C: https://courses.lumenlearning.com/physics/chapter/13-5-phase-changes/ https://courses.lumenlearning.com/physics/chapter/13-5-phase... However, I imagine you could wait for your too-hot-to-condense gas to cool and condense. That would probably be vastly more efficient than adding refrigeration. It would depend on the materials used for the pressure tank, whether you can add more surface area and the external temperature. You could even put the CO2 Tank under water in a deep lake/ocean. Then you don't have to have such thick materials to contain the pressure. The CO2 could be dissipating its heat and pressurizing as you pump it down (use a flexible tube so the water is compressing the CO2). For the return journey, use a rigid pipe so it doesn't lose energy pushing outward on a flexible pipe.
- deleted 5y ago
  [deleted]
mabbo 5y ago
My understanding is that the energy released comes from the CO2 being heated back up and turning into a gas, causing it to expand. This spins turbines.
beervirus 5y ago
Sodastream doesn’t use liquid CO2, just compressed gas.
- xaduha 5y ago
  Demonstrably not true. In fact you can refill your Sodastream canister with dry ice, google it. 400 grams of it sure as heck doesn't stay solid and I'm pretty sure it can't be gas at that pressure in that amount of space. EDIT: https://en.wikipedia.org/wiki/Supercritical_carbon_dioxide https://en.wikipedia.org/wiki/Supercritical_carbon_dioxide, you can't slosh it. https://www.youtube.com/watch?v=GEr3NxsPTOA https://www.youtube.com/watch?v=GEr3NxsPTOA
  - beervirus 5y ago
    It looks like you’re right. Whoops.

> cooled to liquid temperatures via refrigeration Do you actually need to refrigerate it to keep it liquid? My SodaStream machine works with room temperature.

by jannes 5y ago

> cooled to liquid temperatures via refrigeration Do you actually need to refrigerate it to keep it liquid? My SodaStream machine works with room temperature.

lbotos 5y ago

"It can only exist at a pressure above 5.1 atm (5.2 bar; 75 psi), under 31.1 °C (88.0 °F)" - https://en.wikipedia.org/wiki/Liquid_carbon_dioxide https://en.wikipedia.org/wiki/Liquid_carbon_dioxide So depending where you are you'd need refrigeration

ClumsyPilot 5y ago
It doesnt need refrigeration for storage, CO2 is stored at higher pressure The refrigeration is needed because the process of compression produced huge amount of heat. And because of that, this method of storing energy is twice less efficient than batteries are
- magicalhippo 5y ago
  Though they could store some of this heat for later when they want to extract the CO2 gas again, I suppose.
  - surbas 5y ago
    Which according to the article is what’s happening. They store heat in steal piles, and release it back on expansion.
- cedilla 5y ago
  Charging batteries also produces a huge amount of heat. In general, storing energy is never free. It's the tyranny of the second law of thermodynamics.
- ErikVandeWater 5y ago
  Yes, the critical point for condensation of CO2 is 31 C: https://courses.lumenlearning.com/physics/chapter/13-5-phase-changes/ https://courses.lumenlearning.com/physics/chapter/13-5-phase... However, I imagine you could wait for your too-hot-to-condense gas to cool and condense. That would probably be vastly more efficient than adding refrigeration. It would depend on the materials used for the pressure tank, whether you can add more surface area and the external temperature. You could even put the CO2 Tank under water in a deep lake/ocean. Then you don't have to have such thick materials to contain the pressure. The CO2 could be dissipating its heat and pressurizing as you pump it down (use a flexible tube so the water is compressing the CO2). For the return journey, use a rigid pipe so it doesn't lose energy pushing outward on a flexible pipe.
deleted 5y ago
[deleted]

mabbo 5y ago

My understanding is that the energy released comes from the CO2 being heated back up and turning into a gas, causing it to expand. This spins turbines.

beervirus 5y ago

Sodastream doesn’t use liquid CO2, just compressed gas.

xaduha 5y ago
Demonstrably not true. In fact you can refill your Sodastream canister with dry ice, google it. 400 grams of it sure as heck doesn't stay solid and I'm pretty sure it can't be gas at that pressure in that amount of space. EDIT: https://en.wikipedia.org/wiki/Supercritical_carbon_dioxide https://en.wikipedia.org/wiki/Supercritical_carbon_dioxide, you can't slosh it. https://www.youtube.com/watch?v=GEr3NxsPTOA https://www.youtube.com/watch?v=GEr3NxsPTOA
- beervirus 5y ago
  It looks like you’re right. Whoops.