Thermal storage with water vapour?

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FALCON_12
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Thermal storage with water vapour?




by FALCON_12 » 03/11/22, 20:26

Hello,


Like some of us I looked for heat storage solutions. While studying PCMs (Phase Change Materials) I noticed that the latent heat of passage to the vapor state of water was high:

To change 1000 g of water from the state of ice to that of water it takes 335 kJ
To heat 1000 g of liquid water at 0°C to 100°C requires 419 kJ
To convert 1000 g of liquid water at 100°C to vapor it takes 2257 kJ

It therefore takes 5.4 times more energy to turn water into vapor.
enough to raise its temperature by 100°C.

Image

Would it then be possible to use this fact to store thermal energy by evolving
a volume V of water around its vaporization temperature?

I also saw that the boiling temperature of water decreases with the pressure while its latent heat increases with this decrease, this could make it possible to work at a lower temperature (for example, at 0.2 bar the water boils at 60°C and at the same temperature its latent heat of vaporization became 2360 kJ/kg).

http://pravarini.free.fr/Images/Teb.jpg

http://pravarini.free.fr/Images/ChaleurLatente.jpg

One could then think of storing heat in an instrumented (pressure, temperature) and thermally insulated tank containing water whose temperature would oscillate around the boiling point. I know that on an industrial scale there are vapor accumulators. Are there equivalent systems for individuals? couldn't we build such a system ourselves? (pressure cooker...)
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Re: Thermal storage




by Christophe » 03/11/22, 20:34

New York, and probably other American agglomerations (to be checked), uses steam networks for district heating...so yes, water vapor is a good way to store (and transport) heat...

The downside: from memory, 1 gram of water vapor (at 100.1°C) takes up 400 times more volume than the same gram at 99.9°C...

So you have to increase the pressure to have interesting quantities of heat...in small volumes...
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Re: Thermal storage




by sicetaitsimple » 03/11/22, 21:46

Christophe wrote:The downside: from memory, 1 gram of water vapor (at 100.1°C) takes up 400 times more volume than the same gram at 99.9°C...

Well yes, there is no miracle.
I haven't checked the numbers, but if indeed 1kg of steam contains much more kJ than 1kg of water at the same temperature, it also takes up much more volume...
Regarding New York, no need to go that far. From memory, the CPCU (Parisian Urban Heating Company) sends out steam from its production units at around 25bar and 240°C. /- 2°C).
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Re: Thermal storage




by FALCON_12 » 13/11/22, 11:35

sicetaitsimple wrote:
Christophe wrote:The downside: from memory, 1 gram of water vapor (at 100.1°C) takes up 400 times more volume than the same gram at 99.9°C...

Well yes, there is no miracle.
I haven't checked the numbers, but if indeed 1kg of steam contains much more kJ than 1kg of water at the same temperature, it also takes up much more volume...
Regarding New York, no need to go that far. From memory, the CPCU (Parisian Urban Heating Company) sends out steam from its production units at around 25bar and 240°C. /- 2°C).



Thanks for the information. I found a table on the net that talks about these questions.

https://www.thermexcel.com/french/tables/vap_eau.htm

I dreamed of imagining a tank with a volume V=67 m3 (4.05³) capable of withstanding a pressure P of 30 bars. In such a tank, if I understood correctly, 100 liters of water vaporized at Tv=234°C would fit exactly. The stored energy would then be worth 280200 kJ or 78 kWh.

I have no concept of mechanical and thermal resistance of the tanks, is it possible to use a pressure of 100, 200 or 300 bars? The table stops at 30 bar but I would have liked to rate V and Tv at such pressures. I don't have the mathematical laws that govern these quantities, do they exist anyway?

I would try to extrapolate the curves later to answer this question. Maybe the tank size would become reasonable. As for the temperature, it might not exceed that of melting steel.
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Re: Thermal storage with water vapour?




by Remundo » 13/11/22, 12:20

water vapor is not a good way to store heat because of the volume and the pressures it generates.

when for example you speak of 300 bar, you need a submarine hull at 3000 m depth to withstand the pressure. But in addition to keep the heat, this shell should be fully insulated. Nothing impossible, but really heavy and expensive.

Preferably, the latent heat of salts passing from the solid state to the liquid state will be used.

It is moreover a choice that has been tested in some concentrated solar power plants.

The nature of the salt to be melted is chosen according to several criteria: temperature of change of state, chemical properties, cost...

If the heat comes from a fuel, the best way to "store" it is to keep the chemical energy in the fuel and burn it on demand.

The heat has the rascality to escape irretrievably, even taking precautions, it's a matter of time.

Another approach to heat storage (but this time low temperature) is to use the ground directly in inter-seasonal use: see DLSC
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Re: Thermal storage




by sicetaitsimple » 13/11/22, 12:53

FALCON_12 wrote:I dreamed of imagining a tank with a volume V=67 m3 (4.05³) capable of withstanding a pressure P of 30 bars. In such a tank, if I understood correctly, 100 liters of water vaporized at Tv=234°C would fit exactly. The stored energy would then be worth 280200 kJ or 78 kWh.

Basically agree with what Remundo said, we do not generally store in the form of steam, except in some processes where there are significant needs for steam but of short duration. In this case, the storage makes it possible not to oversize the steam production unit.

That said, if you want to continue "having fun" with some calculations:
- I think there is an error of a factor of 10 in your calculation, it is 1000kg of steam that you could store in your tank.
- the values ​​from 30bar to 100bar are available on the site you indicated, on another page.

Good luck!
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Re: Thermal storage with water vapour?




by Macro » 14/11/22, 14:00

FALCON_12 wrote:I also saw that the boiling temperature of water decreases with the pressure while its latent heat increases with this decrease, this could make it possible to work at a lower temperature (for example, at 0.2 bar the water boils at 60°C


The boiling temperature of the water decreases when the pressure decreases... 0.2 bars to have them on earth... Not too possible, even on Everest you must still be at 0.35... To be at 0.2 bar de Pa must be around 12000m....
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