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.

[broncodriver99]

Calrod heater would work as well. Very similar material to what you posted but can be shaped. Sand has some insulative properties so multiple heating elements would likeky be necessary.

[dieselspanner]

Hi Veggie

Cheap and easy - along with 'low tech' a pair of my favourite words! - would be to run the exhaust through the sand.

I realise that it won't provide all the heat you need if your sand box was say a meter square a 75mm pipe in a 'square spiral' 600mm on a side with three turns or so would probably help.

If you cut the pipe wirh a chop saw into 600mm lengths with a 30 degree angle a hexagonal 'spiral' wouldn't be too hard to fab up....

Perhaps run top to bottom with a water drain for condensate, or just vent it at low level out the back of the shed, as a bonus, it shouldn't be too loud either!

A little scrounging at a recycling plant could well provide the raw materials and a little over basic welding skills would do it. It won't have to be pretty, just gas tight, and if it was a dead end the pipe can go back on the scrap heap and the cost would be some electrodes and time.

Just thinkin'

Cheers

Stef

[veggie]

Calrod heater would work as well. Very similar material to what you posted but can be shaped. Sand has some insulative properties so multiple heating elements would likeky be necessary.

Bronco,
I looked up Calrod Heaters. Yes, that would probably work well.
That looks like a good solution. Thanks 

[veggie]

Spanner,
Good idea. In addition to the sand thermal heat store, I can also use the exhaust to additionally heat the same sand, or build a sand heat exchanger by running the exhaust pipe with multiple passes through another sand chamber.
If electrical AND exhaust heat can be captured, then the system efficiency will be exceptional, since I am already capturing the coolant heat and using it to heat the area via radiator/fan.

[mikenash]

Substances such as compacted sand, stone etc will have known properties - the rate at which they will take up heat; and the rate at which that heat will bleed out into cold air - dependant on temperature, ratio of exposed surface area to bulk - and so on . . .

I mention this because a technique widely used here is stone/concrete walls which are exposed to/heated by sunlight during the day - and which slowly release that stored heat at night.  Near me there's a community centre which has massive concrete heat sinks at the back of north-facing (southern hemisphere) rooms which do just that.  They're warm to the touch during the day - and still warm to the touch in the middle of the night.

Obviously it's a new build with good insulation and triple-glazing etc etc - but the point I make is that this is a case of a BIG mass being raised just a few degrees above ambient, then slowly yielding its stored energy back into the room.  SIZE/MASS is the key here.  because it's big - the temperature differential can be small but still work well

Maybe a LOT of sand . . .

[ajaffa1]

Hi Guys, I hate to be a naysayer but what is the point? You are going to have to go through all the effort of filtering, de-watering and centrifuging your waste oil. You are then going to burn it in your Lister to produce electricity, which you are then going to use to heat sand or something similar.
Why not cut out all the effort and inefficiency not to mention wear on your Lister and generator head by building a smudge pot oil burner? They are easy to build, they will burn untreated oil and produce enormous amounts of heat. You could always encase the flue in some sort of thermal mass if you want.

Bob

[dieselspanner]

Hi Veggie

Interesting point Bob makes. I'd not considered it, but when you add that to Mikes comments and have more mass at a lower temperature you get to to about where I am in my barn.

It's a single open plan room, two floors high, 9m long x 5 m wide with a poured steel reinforced concrete floor that rests on 60mm of polystyrene insulation, the depth varies but it must be about 200mm on the average. On top of that is a screed with around 130m of 16mm bore plastic pipe (PEX) in 4 different runs, around the room, none of which is in the areas under the cabinets ect. on that is the flooring, 15mm of good quality concrete tiles (with a very realistic concrete floor

So, probably an eight cubic meters mass.

I ran it in the winter, of a wood burning Rayburn cooker, which was also supplying two large cast iron radiators, two bathroom type heated towel rails  and, with first call on the hot water, a 110 litre tank,

I ordered lots of aquarium type thermometers, with a 1m tail on the sensor (3/4 Euros each) and put them everywhere on the circuits so I could tell where the heat was going, not exactly, as I have no flow meters but enough to give me a good stating point for balancing the system. I also made great use of an infra red thermometer.

To cut a long story short I started with the building stone cold (February, - 10 degrees c outside, +2 inside - I was putting water under the at  +30 degrees c and at the return to the boiler it was coming out at 8 / 10 degrees c. after 3 days of day time running it was coming out at around 20 c

I moved in (a domestic rebellion by me.....) and after a week I was going to bed with the downstairs at 18 degrees ans upstairs in the bedroom part at 21.

By morning downstairs was around 12 / 14 degrees, still - 10 outside. Obviously the larger part of the rise in temperature was caused by the rest of the system.

A far smaller cube of sand at 400f - around 200c, and 10 times hotter than my floor slab would do it do it but you'd have something like a large piece of furniture in the room and have to have system for recovering and distributing the heat later.

I installed the underfloor heating to 'dump' remaining heat from the water rather than as a primary heat source and it's set up in such a way that should I get around to building a small hydro generator I have a dump for the power in the early morning hours when the batteries are topped up.

In conclusion, I'd say that if you wish to use electric to build up a store of heat then I'd look at an under system for the mass and lower temperatures. Not an easy thing to retro fit I know!

The one thing I have realised from this thread is that if I do another barn conversion involving a diesel generator the exhaust will be in a trench filled with concrete under the ground floor!

I hope this gives you some real world information to work with

Cheers
Stef

[veggie]

Hi Guys, I hate to be a naysayer but what is the point? You are going to have to go through all the effort of filtering, de-watering and centrifuging your waste oil. You are then going to burn it in your Lister to produce electricity, which you are then going to use to heat sand or something similar.
Why not cut out all the effort and inefficiency not to mention wear on your Lister and generator head by building a smudge pot oil burner? They are easy to build, they will burn untreated oil and produce enormous amounts of heat. You could always encase the flue in some sort of thermal mass if you want.

Bob

Hi Bob,

The Lister is already there. It sits idle waiting for a power outage, I don't see using it for garage heating and greenhouse lighting as a bad thing.
There is NO WAY I'm going to build an oil burner to leave in my garage unattended. I don't trust my Oil Burner building skills enough to go down that road which would also require chimney holes and stove pipes cut through the roof.   99% of the DIY oil burners I have seen on YouTube would never pass any kind of safety regulations.

Also, my wiring and cooling system is already in place. All that's needed is a sand reservoir and some electric elements.
The system I am pondering uses my operational machine that all is ready to go.
If I wait for power outages to use my system, it may still be like new 20 years from now     so it could now earn it's keep by offsetting the current heating costs.
And when winter temps here in Canada dip to -25C, it could make a substantial difference according to my calculations.
Using the cooling system, generator (sand heat) and possibly capturing some exhaust heat in a heat exchanger, the system may approach 70% in thermal efficiency.
This project does require further research and it would not be difficult to program a model where different amounts of sand and different bed temperatures can be tried in order to get the optimal reservoir size.
If the res is too big, the Lister has to run too long to get it up to temperature.
If it's too small, the res looses most of it's heat too soon causing excess engine run cycles.
So the goal here is to have the Lister run 4 hrs in the AM and 4 hrs in the late PM.
Who knows, maybe the model will show that the number don't work. But if they do work, I am interested to build it.

[ajaffa1]

Hi Veggie, I wasn`t aware where you live. Minus 25 in winter is seriously cold, where I now live, we hardly ever get a frost. I used to be an extreme skier and have experienced temperatures below minus 40 centigrade. The water on your eyeballs start to freeze over at between minus 25 and minus 30, makes for serious visibility issues, the faster you are going the worse it gets!
My initial thoughts were that you should fit a reverse cycle heat pump but that is never going to work with outside temperatures that low.
Another option would be a ground source heat pump but these are very expensive and cost a lot to install.
Going back to my skiing days, I spent a lot of time in Austria where a lot of bars and restaurants are heated by a thermal mass heater. These look like and are the same size as a wood fired brick pizza oven without any openings. I have no idea as to how they are heated but I would guess they are connected to a boiler of some sort. They have an surface temperature of around 30 centigrade and usually have a round seat built around them so tired skiers can warm themselves.
So going back to your idea, I think it could work but I am worried about how many electric heating elements you are going to burn out trying to get this to work. Back in the 1970`s electric night storage heaters were all the go. These had electric elements cast into concrete, with a fan blower to distribute the heat when you needed it. They were very heavy and not very efficient. If you could find a whole lot of them in a junk yard you could probably stack them, wire them and bury them in sand or gravel.
Looking forward to what you come up with.
Bob

[veggie]

Bob,
Yes, your comment about elements burning out is well noted.
I was thinking it may be necessary to control the ramp-up of the heating time so that the sand has a chance to absorb the heat from the elements.
Something like low frequency Pulse Width Modulation using a relay. (On..off..on..off..on..off).
If the elements cannot shed their heat fast enough (as they would in water) then they may fail.
So I have to do more research on what methods are available to heat sand with electricity.

cheers

[veggie]

I came across these heating strips which look interesting.
They are made by Wattco.
240 VAC
750 watts
Max. Temp of 1000F
Length = 23"

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

[ajaffa1]

Hi Veggie, been thinking about your project today, rain stopped me doing what I had planned. I quite like the look of those heating elements but I have grave doubts about how you are going to safely connect this to the electric supply. At the temperatures you are seeking to achieve the insulation on the feed wires will melt with catastrophic results. To make this work you are going to need custom made ceramic insulators which could be expensive.
I did come up with a simple way to make a test rig, if you go to your local scrap metal merchant or council tip, you should be able to find and old air compressor cylinder. These come in many different sizes, you should be able to find one that will easily contain one or more heating elements. Find a safe way to fit the elements then cut a hole in the top and fill it with sand, cover the hole with a piece of steel and weld/screw it in place. Do not try to achieve a perfect seal, we do not want to build a pipe bomb! It is vital that steam from wet sand and the any rise in internal air pressure can escape.
If the experiments work out you could probably build bigger units using steel hot water cylinders.
I still think you are out of your mind, I`d be going for a thermal mass chimney system and smudge pot oil burner, but what do I know? Good luck and keep us informed.
Bob

[veggie]

ajaffa1,
Hi Bob, thanks for the suggestions.
I have 20 gal and a 60 gal compressor air tanks.
They both have threaded connections added for heating elements.
Was planning to use the smaller one first.