# Store energy in lime CaO?

1. Dec 21, 2005

### magi

Hello.

I am working on an idea if it would be possible to store heat energy in quicklime CaO.
We are to use a solar parabolic trough to concentrate the sunlight and get a temperature in focus around 1000 C degres.

In that temperature it is possible to burn limestone to quicklime and then save it in a airtight storage.
1000 kg have about 320 kWh and can be bought in my country for around 45 \$/1000 kg.

Does anyone know if I am wrong about this becouse it seems to ok to save energy this way.
The parabolic trough need to be around 25 m2 to be able to burn enough CaO in one summer.
To save energy to heat a house I need to burn around 15000-25000 kg to be able to heat a house over the winter.
1000 kg CaO takes around 1-1.5 m3 so big storage is needed.

First time you need to reach 900 C but if you store the unloaded lime in a air tight storage you then only need to burn, load lime at 550 C.

After the winter the reaction with water have turned CaO to Ca(OH)2 and it can be burned again (only this time at 550 degrees) to store energy for the next winter.

Does anybody here know if it is possible to reach 1000 C in a parabolic trough with a vacuum tube in focus?
The vacuum tube will be about 2-3 m long and to be able to burn
maybe 15 000 kg lime Ca(OH)2 in a summer I need around 25 m2 area parabolic trough so it will be maybe 10 m high and 2 m wide.

If its no problem can I use two vacuum tubes on 2 m length and then use two parabolic trough about 5 m high and two m wide and still be able to reach 1000 C in the tube?

Or maybe it is a matter of how fast I can transport Ca(OH)2 through the tube to get it burned in any of the two cases?

If it works you dont ever need to buy heat to your house again.
It will also be able to run a steam engin with generator becouse you get 400 C when you poor water on CaO and turn it to Ca(OH)2.
CaO and Ca(OH)2 is managed as powder and can be transported in small pipes with transport screw.
Transport of powder in tubes with screws works just as well on earth as on the moon.
Molten salts store about 1/4 of energy/ton.

Do you think it is possible?
Have anyone heard if someone does something like this?

I found a PDF-document that NASA did about it, so it seem possible.

http://purl.access.gpo.gov/GPO/LPS58424

Regards Magi

Last edited: Dec 22, 2005
2. Dec 22, 2005

### Astronuc

Staff Emeritus
I have heard of thermal storage in molten salts, which is used in some solar power systems in order to provide thermal energy during periods of reduced or no sunlight (i.e. night).

A specific volume of 1-1.5 m3/Mg seems reasonable based on a density of CaO as 3.3-3.4 ×103 kg/m3(http://en.wikipedia.org/wiki/Calcium_oxide) [Broken]. One presumably needs a dehydrator or calciner.

Solar power systems work well with liquids/slurries, but a main technical matter will be separating the water from the CaO. One will have to look at the energy required to transport the mass. Ideally, in a thermal storage system, one minimizes mass transfer. Realize that the moon's gravity is about 1/6 of earth's - and that will have an effect on energy required for mass transfer.

As for temperature at the focal point of the collector, that will be determined by the energy flux and absorption by the medium. It might be worthwhile making a simple parabolic mirror (or magnifying glass) and focusing it on a piece of hydrate lime and measure the temperature - doing this for several different masses and mirror sizes. Also pay attention to how the efficiency and max temperature change with respect to mass of the hydrated lime, i.e. as water evaporates.

I'll read the NASA paper before I offer further comments. Nevertheless, it is an idea worthy of investigation.

Last edited by a moderator: May 2, 2017
3. Dec 27, 2005

### magi

I have been talking to a some people at companies that burn lime for use in cement and concreate.

They think the idea is very good and somebody should really try it out, they say.

The first time you need to burn limestone you dont get back as much enery as you load it with but when you recycle the Ca(OH)2 it only need to be burned at 550 C degrees and you then get back a lot of the energy you use to load it.

Please try to discuss this with energy people and lime companies and make some real tests becouse the people ive been talking to think it should work.

Regards Magi