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use Rocket Mass Heater to _Make_ firebrick?  RSS feed

 
pollinator
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I did a search and didn't find if anyone has looked into this.

From wikipedia, there's a discussion of an article using a vertical kiln (1000C) to make firebrick, and according to Erica Wisner on permies the RMH will often burn up to 2600 F (1400 C).  SO--why not cut out the middle-man? can you line your rocket mass heater with fragments of ceramic/aluminum/silica combination in something sticky that will hold it together while it burns and sets? 

The purpose: appropriate technology for people with only local materials.  It appears you can extract aluminum from soil (opensourceecology.org), you can get silica from sand, and that's the basic content of firebrick/refractory brick. 

Otherwise, it seems you have to have a source of firebrick you can salvage from or make a less safe, replace-componenets-every-five-years-or-else version of the rocket mass heater.  Still not bad, but if you could make your own fire brick in the system safely that would be great.

Thoughts?
 
Joshua Myrvaagnes
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OR--is there a more "tensegritive" way of handling the problem of insulating the burn chamber? what if we rethought the whole thing and made it much simpler--instead of a wall, a stomach-lining-type thing?  in other words, make a layering of various materials that gradually attenuate the heat, instead of attempting to make a wall (a more human concept).

Where does nature handle extremely high temperatures? in a volcano, what keeps most of the heat contained? there are no firebricks, there is no safety-rated lab-tested burn chamber.  And of course, the output is not safe, volcanoes kill animal, plant, human life and spew lots of emissions into the atmosphere, I'm not saying just think like a volcano, but the vast majority of the volcano is being stored safely underground most of the time.  Where else does this occur in nature? you have underwater volcanoes, you have meteors attenuating a lot of heat in the atmosphere before hitting the ground (mostly)...

 
gardener
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Without actually having studied the processes, I am skeptical of it being practical for an individual to isolate and recombine the materials for decent-quality firebrick. Firing to set the liner materials would not be so much of a problem.

A large part of the issue would be the character of local clays. Some natural clays are kaolin-rich, and can be fired to high stoneware temperatures like 2300F (while shrinking considerably); This material when crushed into "grog" and incorporated into a clay binder might make a decent firebrick-like material. Other natural clays (probably a majority), especially iron-rich ones, can only be fired to 1800 to 2000F before softening or even melting.

I agree that a layered approach would be ideal, with a thin liner of strong material backed by increasingly lightweight insulating materials.
 
Joshua Myrvaagnes
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Thanks Glenn.

Here's another thought: what if you had a portable, reusable element that you could use to make a new rocket mass heater complete with firebrick lining, then remove and use it for the next one, and pass it around the village?

Here's what I mean: it would be shaped like this: ^ and insulate the top two sides of the part your baking into a wall, so only the bottom part would get fired (baked).  Then, you rotate your chamber, now that the bottom has baked and is hard, and you do the second wall, again on the bottom, with the triangle on the top and one baked side like this /V; then you do the final side with the two baked sides as your walls: ^

Or, if it is supposed to be round, you could do instead of a ^ shaped tool, something more like this shape: Ω and then rotate it around and re-bake the missing part.  Another advantage of this is you only need two bakings this way, instead of three, but the original instrument is a little harder to make.

It would have to be made out of aluminum I guess, instead of iron, so as not to melt, but once that hurdle is crossed once the tool is reusable.

As for clay contents, what about adding sand to it? or rice stalks/grain stalks/anything that's high in silica? or the fairly omnimpresent aluminum soda cans? 
 
Glenn Herbert
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Perhaps you meant a baking tool would have to be made of iron instead of aluminum so as not to melt?

I think it would be difficult to fire the parts of a combustion core this way. In any case, simply having a hot fire in the combustion chamber would fire all but the feed adequately. You might be able to add a temporary extension to the feed to move the fire up to the permanent feed mouth and fire that part. Alternatively, you could make the feed in several sections like bricks (only interlocking to some degree for stability after assembly), and fire those individually in the far end of the burn tunnel of a functioning system before assembling them into their final system.

I have built kilns from native clay, and fired them while the clay is still damp. (There is no way around this with a kiln built into the ground in a humid climate.) The inner surface shrinks and cracks, especially in the hottest parts, but becomes very hard and durable. If you filled the cracks with new clay after the first firing, you could get a fairly seamless interior. The clays I had available were not high-firing and did not have any grog incorporated, which would have improved their stability.
 
Joshua Myrvaagnes
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Cool, this gives me a sense of what it is, that it's already standard.  Hadn't seen that in the discussion of rocket mass heaters as appropriate technology, so now that's clear.

I guess I'd misunderstood that you _couldn't_ use iron at this high a temperature, but sure, if you can then sure, iron. 

I had in mind West Africa, in terms of available parts, and there the soil is not moist during the dry season.  But the fires there are usually more for cooking than for heat, so a simple rocket stove would probably suffice. 

it sounds like the iron cover is unnecessary, though, and that the tunnel will maintain enough structure even with cracking.

Thanks!

 
Glenn Herbert
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For the highest efficiency, extreme materials which require some specialized technology may be needed. But for good efficiency in a low-tech, low-income environment, you can easily achieve consistent results with simple techniques and local materials. At the most basic, firing some clay and crushing it into grog (sand/gravel sized particles), and using that in the inner liner as a large part of the clay/cob mix, can give good stable and durable results. Mixing outer layers of cob with increasingly high concentrations of straw or other fine organic material will result in lots of tiny insulating airspaces. So with this basic knowledge, a good RMH can be built entirely from material on hand and (nearly) free.
 
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