Author Topic: Heat sand to 400F  (Read 510 times)

veggie

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Re: Heat sand to 400F
« Reply #15 on: July 25, 2022, 04:56:19 PM »
*** PROJECT CANCELLED ***

After modeling the idea, the numbers do not make sense for a micro system.

Summary....
==========

Specific Heat:
Water = 4182
Sand = 830
Sand holds only 20% of the BTU content capability of water for a given volume.

Raising a 50 gallon tank of water from 68f --> 180f requires ~46,725 BTU's
To store the same amount of heat in 50 gal of sand would require a temperature rise of approx. 900f

Heat transfer factor
Water = 13
Sand = 0.06
Roughly 200 times slower transfer rate in sand. (It holds heat very well ! )
But heating the sand bed would take a considerable amount of time.

So how do the new commercial sand heat storage systems get around these obstacles.
1] They heat the sand to 1800f or more by circulating molted nickel or molten salt through exchanger tubes in the sand bed.
2] With super high differential temperatures, they can rob heat from the bed at greater rates than my proposed 400f project.

For smaller heat reservoir systems water in king. It has the highest specific heat value and storage properties of any readily available media.

« Last Edit: July 25, 2022, 06:50:00 PM by veggie »
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veggie

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Re: Heat sand to 400F
« Reply #16 on: July 25, 2022, 06:57:34 PM »
"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"

Hi Bob,
The biggest issue I have with used oil heaters is that everything I have seen on youtube has been cobbled together with metal scraps. The units glow cherry red when running, and don't have any form of safety shutdown incorporated. They look fine as experiments, but running one in a garage every day (winters) in a residential area looks risky.
I would love to build a small (20K BTU) oil burner system if I could find a reliable and safe design to follow.
If anyone knows a good forum on this subject, or a good design example, please post it.
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dax021

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Re: Heat sand to 400F
« Reply #17 on: July 26, 2022, 04:31:33 PM »
Contact He Who May Not Be Named    (Rhonda & David Smith [glort@hotmail.com])  He had some awesome burners going

mikenash

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Re: Heat sand to 400F
« Reply #18 on: July 26, 2022, 07:38:55 PM »
"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"

Hi Bob,
The biggest issue I have with used oil heaters is that everything I have seen on youtube has been cobbled together with metal scraps. The units glow cherry red when running, and don't have any form of safety shutdown incorporated. They look fine as experiments, but running one in a garage every day (winters) in a residential area looks risky.
I would love to build a small (20K BTU) oil burner system if I could find a reliable and safe design to follow.
If anyone knows a good forum on this subject, or a good design example, please post it.

I know a little bit about drip-feed and other low-tech oil-burners.  I have made six or eight prototypes and currently have one running.  My short conclusion is that they aren't safe for unattended running and that the only reason I'm happy to have one running in my shed is that it has a small oil reservoir and sort of a "bund" (four or five times the capacity of the reservoir) on top of a concrete hearth just in case it has a brain fart & drops a half-litre of hot oil out the bottom

If you search online - there are good ones using dosing pumps metered by things like little arduinos, with thermostats, oil shut-off solenoids and the like.  BUT, I haven't seen one like this that runs reliably that doesn't use an electric fan . . .

In short I haven't seen one that is good and safe that doesn't have several moving parts

Good luck

dieselspanner

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Re: Heat sand to 400F
« Reply #19 on: July 29, 2022, 07:17:37 AM »
Hi all

There might still be a little bit left in the project.......

If you built a 'reservoir' of concrete blocks, laid dry, along on wall, say 6' long x 4' high x 2'thick, run the exhaust through it 2 / 3 times, fill the blocks with sand and insulate the back, ends, top and bottom with a few slabs of polystyrene, you'd have something very similar to the old 1970's storage heaters.

Relativity cheap to build, free to heat, and run. If it didn't work out you could take it apart, buy a bag of cement and make a coal bunker!

It would depend on the layout of your workshop / garage and how many hours a day you ran the genny but there might be something in it.

Cheers
Stef

Tighten 'til it strips, weld nut to chassis, peen stud, adjust with angle grinder.

ajaffa1

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Re: Heat sand to 400F
« Reply #20 on: July 29, 2022, 08:40:24 AM »
I still believe it is possible to build a safe waste oil burner. Many years ago I installed and commissioned a series of steam boilers that ran on diesel or kerosene. They were used to heat huge vats of pig swill that was then pumped to 5000 hungry pigs. These boilers had a fuel tank with a spring loaded shut off valve outside of the building. The valve was opened by a stainless steel wire with a very low melting point metal coupling in it. In the event of excessive heat/fire the coupling would melt and the valve would automatically close.

A second option would be to try and find a vaporizing oil burner out of an oil fired Aga, these are tricky to set up but once adjusted are pretty bomb proof, I ran one for years on all sorts of oils.

Failing all that you could contact Lord Volderglort and ask him how to make an oil burner that will heat a large mass of concrete or sand very quickly, so you can fire it up for 15 to 30 minutes while you are present and then turn it off. The thermal mass should keep you warm for a few hours and then you can fire it up again.
Bob

mikenash

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Re: Heat sand to 400F
« Reply #21 on: July 30, 2022, 12:01:51 AM »
I still believe it is possible to build a safe waste oil burner. Many years ago I installed and commissioned a series of steam boilers that ran on diesel or kerosene. They were used to heat huge vats of pig swill that was then pumped to 5000 hungry pigs. These boilers had a fuel tank with a spring loaded shut off valve outside of the building. The valve was opened by a stainless steel wire with a very low melting point metal coupling in it. In the event of excessive heat/fire the coupling would melt and the valve would automatically close.

A second option would be to try and find a vaporizing oil burner out of an oil fired Aga, these are tricky to set up but once adjusted are pretty bomb proof, I ran one for years on all sorts of oils.

Failing all that you could contact Lord Volderglort and ask him how to make an oil burner that will heat a large mass of concrete or sand very quickly, so you can fire it up for 15 to 30 minutes while you are present and then turn it off. The thermal mass should keep you warm for a few hours and then you can fire it up again.
Bob

See pic?  Crap image but the salient bit is the pipe that's glowing red hot.  It's either 150mm or 125mm (I forget which) and it's a mild-steel weld-bend with a 5mm or 6mm wall.  The burner heats it from ambient (maybe 6 degrees C in this case) to glowing in about ten mins using oil at the rate of maybe a couple of litres an hour?  It's about as safe as you're gonna get for a drip-feed with no moving parts that can be used domestically

I can send pics/details/plans if needed

Certainly if you extended that pipe by a couple of metres and put fins all over it and ran it through a bathtub full of sand . . .

Cheers

veggie

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Re: Heat sand to 400F
« Reply #22 on: August 02, 2022, 07:04:52 PM »
Thanks mikenash,

"Certainly if you extended that pipe by a couple of metres and put fins all over it and ran it through a bathtub full of sand . . ."

I think if I could build a reliable, small, safe waste oil burner, I would not need the sand at all.
Just run the burner constantly along with some safety shutdowns which cut the fuel supply if needed.
I do agree that  an oil burner/heater is the most efficient way to heat with used oil.
Also needed would be a method of rapid/easy cleaning since waste oil leaves a lot of ash and crap in the burn pot.

Does the burner in that picture have a forced air supply or is it self-drafted?

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mikenash

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Re: Heat sand to 400F
« Reply #23 on: August 02, 2022, 08:02:15 PM »
Thanks mikenash,

"Certainly if you extended that pipe by a couple of metres and put fins all over it and ran it through a bathtub full of sand . . ."

I think if I could build a reliable, small, safe waste oil burner, I would not need the sand at all.
Just run the burner constantly along with some safety shutdowns which cut the fuel supply if needed.
I do agree that  an oil burner/heater is the most efficient way to heat with used oil.
Also needed would be a method of rapid/easy cleaning since waste oil leaves a lot of ash and crap in the burn pot.

Does the burner in that picture have a forced air supply or is it self-drafted?

Hi Veggie

I'm keen on "keep it simple" so the burner has no fan.  Really, of course, the flue - which is about four metres long - is the secret to a good draft as you will understand

It's a lousy pic, sorry

The burn pot is just that, a stainless steel, copper-bottomed pot I bought for $2 at the Salvation Army store.  There is a couple of lugs sticking out above it, and a bit of 50X10 flat underneath it with a couple of 13mm holes that match the holes in the two lugs.  There are two shorth lengths of M12 galv rod & some nuts that run from the lugs down to the flat and hold the pot in place. 

The pot is perfectly-sized to fit into the O-ring groove of a NB200mm profile steel flange - so, as it sits up into the groove, it makes quite a good "seal" and is positively located.

I guess it takes about 2 minutes to take it off to clean (loosen the nuts, drop it down, slide it out).  Beneath the whole thing there's a giant stainless bowl about 500mm in diameter and about 200mm deep that just slides in and out.  It's both a "bund" and an easy way to catch any mess when it gets a scrape-out/clean.  I paid $15 for it on FB marketplace

There's no denying they are dirty, messy things

I have a couple of boxes of throw-away gloves and a few cans of brakleen - and I figure they're just the cost of running the thing.  Maybe $10 a month?

I'm fortunate in that I have a source of a great deal of "used" oil which is effectively "new" oil contaminated with metal particles but no combustion byproducts or random automotive fluids.  It's an industrial gear oil from a specific application.  If I let it stand in 200 litre drums for a year or two - then just the bottom few inches is sludge and the rest is effectively "clean" - so my fuel is 100% consistent, free, readily-available and as "clean" as it can be

FWIW I'm just making some changes to the design to improve the "cook-top" function of the top of the burner and to increase the size of the reservior to maybe two or three litres.  But I'd never leave it burning unattended

Happy to help with details or drawings if needed.  Cheers