Heat sand to 400f

[veggie]

I'm looking for ideas.
I can only heat stored water to 212f, but sand can be heated to to 800 degrees and used as a thermal battery.
I don't want to go as high as 800 yet, but I would like to fill a steel tank (maybe 50 gallon size) an try to heat it to 400f.
Then insulate it just enough to still allow for heat to radiate for X number of hours.

Application: Run the lister for x hours to electrically heat up the sand to 400f.
Observe the system to see how long the system can heat the garage in winter.
Start engine .... heat sand ..... Start engine .... heat sand .....Start engine .... heat sand .....
Automate later.
Power the engine with waste oil.

Problem:
How to electrically heat the sand to 400f ?
Basic water heating elements will probably burn up.
I can provide 2kw to 3kw of electricity at 120 volts or 240 volts.

Any ideas for an electrical device to heat fully heat several hundred pounds of sand ?   

[veggie]

... Was thinking 3 or 4 of these placed at different levels in the media.

[Henry W]

Heating sand, I think it's a great idea.

When I was a kid living in up state New York, I took survival course in Boy Scouts. In the winter we used to heat up rocks in a fire pit. The rocks were rolled in a low lying area and a floor was built over it with branches than covered with pine needles and leaves. A tent would be set up right over it. The tent would stay warm for hours.

We've survived sleeping out doors below -10°F.

In the morning we would boil water in a paper coffee cup by dropping in a super heated stone. Simple and effective. Its amazing how much heat is stored in rocks and stone.

I would think sand would work the same. It might possibly work better than storing hot water since your able to heat sand to extreme high temperatures.

[Henry W]

... Was thinking 3 or 4 of these placed at different levels in the media.

I think stove elements might work. You might be able to use an ST head and run it up till it only makes 180 to 200 volts. I would think there would be no concern of not reaching 60 Hz. This could prolong the life of stove elements.

I wonder if a 400 Hz generator head running at 200 volts or below just for this purpose it might work better?

[Henry W]

Just did a quick search and found these.


https://youtu.be/UvNv_gM_ZUk

https://www.treehugger.com/seasonal-thermal-energy-storage-gets-hot-sand-battery-5525833

[veggie]

Yes, the process is beginning to gain interest in the thermal energy storage world.
In my case, I am interested to build a micro version which can release heat all night in my garage during winter. Thus reducing (or eventually eliminating) my heating bill for that building.

Running the exhaust pipe through a second sand heat exchanger may make the system even more thermally efficient. During the several hours of sand heat saturation, the system is also pushing coolant heat into the building via the fan/radiator.

What interests me is that this energy is electrically transported to the sand bed...
No pumps
No pipes
No valves

Just an AC relay and a few temperature monitoring devices. The controls can be as simple or as fancy as one cares to make them.

[Tom Reed]

If you 240v water heater elements at 120v they should work fine at 25% of rated wattage. They are also easy to mount right up the side of your barrel.

[Henry W]

A system as this would be perfect for cold climates. It would be a simple build once the system is drawn out.

I've been reading more and intrested to learn more.

It seem like it would be a pretty safe system when using it at the temperature your thinking of.

[veggie]

If you 240v water heater elements at 120v they should work fine at 25% of rated wattage. They are also easy to mount right up the side of your barrel.

Good point Tom. They are also inexpensive.

[veggie]

This fellow builds one heated by wood.
Same principle.
https://www.youtube.com/watch?v=kzj1PCA_jxA

[Henry W]

Tom, it is a good point. So simple what was I thinking.

If a short/small used electric water heater can be found and install a 240 volt low wattage element in it, than fill it with sand it would be a good test to see how it works. A 20 amp 120 volt outlet wall outlet can be used as a power source.

https://www.grainger.com/product/GRAINGER-APPROVED-Water-Heater-Element-Low-Watt-2E496

[Tom Reed]

That's only going to be 500 watts, but I guess 4 to 6 of them would be reasonable. It would also make a good load bank. When testing I'd put a couple of thermocouples in the sand and have 1 attached to the element so you know how the heat transfer is progressing through the sand.

[Westcliffe01]

If sand is considered a good form of heat storage, why not use steel ?  It costs about $1/lb, its heavy so you can get lots of it in a confined space. It would have much better conductivity than sand. The problem I would see is that if you are trying to get it to 400F the heat transfer coefficient will be high when the system is cold but then steadily decrease as it goes up in temperature.  The hottest thing you have to work with is the exhaust and that may peak at 800F in a diesel that is running efficiently.  Once again if you make yourself a burner that runs with a combustion blower the system would have a much higher overall efficiency, especially if the gas coming out the outlet of your heat storage device is then used to heat water because at 400F there will be plenty of reserve to heat water that boils at near to 200F.

[mobile_bob]

there used to be an old russian man, he had a full on machine shop out in his stone barn, complete with all the line shaft driven machine tools, powered by a steam engine, and later by a rather old large frame electric motor

out in the middle of the floor was a southbend precision lathe, where he spent hours machining parts. he was a gifted gunsmith, and built many high power rifles in that barn.

one day he passed on to the "big shop" and there was a auction and it was all gone.

the guy that bought the home site, and barn was out one day and happened to notice an electric cord going down into the dirt floor so he decided to pull it up to see where it went.

it went over to a rectangular sand box, that was right in front of where the concrete pad was that the lathe sat on,  he pulled up more wire and got a shovel and started to dig

he dug up 6 old steam irons, all sitting with the hot plate facing up.

that is what kept the old man's feet warm on cold winter days while spending hours at that lathe.

necessity is the mother of invention.

i often wondered the questions he must have got in town, when he asked to buy 6 steam irons.

bob g

[veggie]

I came across these heating strips which look interesting.
They are made by Wattco.

750 watts
Max. Temp of 1000F
Length = 23"

So 3 or 4 of these would use the 2250 to 3000 watts from a listeroid.