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Rocket stoves for trash incineration?  RSS feed

 
Noah Elhardt
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Location: Senegal, ~600mm rain, 9 mo. dry season
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Has anyone here played around with RS designs for trash incineration? Are there any special considerations that I should keep in mind before starting my first test build?

I hate burning plastic, but before you flog me, hear me out. I live in a country without a functioning trash disposal system. Most trash is mixed with vegetable wastes and dumped outside cities and towns, where it blows all over the countryside or gets lit on fire and smolders for days or weeks. Our farm recycles everything possible, and does its best to minimize plastic waste completely. We do, however, burn what remains, as it beats any reasonable alternative we can think of.

Currently, we burn our trash in barrels. You can imagine the amount of disgusting smoke that ensues.

From everything I've read about rocket stoves, using them to incinerate our trash should result in a hotter, cleaner burn with vastly decreased pollution. Should this be possible by burning plastic and paper trash alone, or will I have to add wood?
 
John Master
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pyrolysis is a process where heat is applied to for instance rubber, or plastic to convert it back into its more basic substances. Look into it (youtube even has a ton of great videos explaining the process). Not sure what kind of trash you have left over as to whether this would apply but maybe you will find a use for it.
 
Glenn Herbert
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From what little I know of pyrolysis (for tires), it needs a sealed pressure vessel, so would be impractical for a single farm. There is a possibility that it might be reasonable to pool an area's resources and trash and make a small-scale pyrolysis unit, producing a bit of diesel fuel. This would be more along the lines of an independent small business or cooperative than a farm activity.
 
Steve Smyth
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Good thought.

I lived for a time where we had no garbage pickup, recycling or landfill for over 100 miles. We composted what we could. Crushed aluminum cans for recycling as the compact small enough that storage was practical.

Everything else went into a 6' diameter 20' deep pit and we periodically threw a load of diesel soaked cardboard & scrap wood. After lighting it would burn for a couple of days.

When the pit began to fill up they would come out and cover the pit using dirt from when it was dug. Then using a huge auger mounted on the back of a truck to dig a now one.

It was functional as far as removing garbage but was environmentally awful. I wonder how RMH design could be tweaked to allow us to cleanly burn certain trash, along with wood, to provide heat and reduce the number of trips that I now take to the landfill.
 
Satamax Antone
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Noah, i think a batch box, super insulated, with a real long heat riser. And a way to recover the heat for some purposes would be intresting.


Dioxins seem to get all burned above 900C°. You would have to start the fire with wood, and maintain it with wood and plastic.


But there's the chlorine of the PVC which is harmfull to the atmosphere. I think a condensate tower after the stove could be interesting, as a chimney. But what do you do with the chemicals extracted?


Another idea, to process plastic, which just popped into my head. Plastic would be easier to feed at a given rate if turned into a liquid or gas. Otherwise the batch box overloard and makes incomplete combustion and black smoke.


So, making the barrel a bit like a water jacket, but wide, and which would accomodate lots of plastic to be melted before burning. Insulated on the outside. So the pyrolysis is done correctly. A metal tube on top, to gather the gases, and send these to the firebox. I think i would insulate that tube, so it doesn't cake with whatever is in the gas. And have another tube at the bottom, which would feed the liquid part of the plastic to the firebox. This tube would absolutely need to be insulated, or even heated. In order for the plastic components not to gel or solidify. The "plastic jacket" would need to be a realy tough container. Supporting high presures. Closing the gas tube at the top, would make the presure increase in the vessel, pushing the liquid plastic at the bottom through the other tube.


May be, even, the gases could be gathered to run an engine or cook with.



But remember, this is only theoretical, and i do not know the environemental problems this could cause, beside dioxin and chlorine being released into the air, and gathering in the surounding soils.

This would be a complicated project. But i think it's worth it. There is several plastic pyrolysis plants on youtube. Turning plastic back into oil. But i'm far away from understanding everything about this all. May be asking the guys who know about woodgas could be interesting too.

Tho, i think someone needs to tackle this isue, or efficient recycling of plastics, besides the old big scale waste incineration. Small scale units, in the vein of the one described above are not impossible. And would be realy good for recycling, and may be, if well thought, could be a step towards self suficiency. I mean, plastic are fed uppon us. And are a anoying, if not toxic waste. The oil has already been extracted. Why not using it. And the "retort" if well thought, could be used to produce wood gas, in a plastic free world.

Making it with a condenser afterwards, which would extract the last components which are prone to condensate, like a cracking tower. Would be clever too. And using it's outside skin to heat water, for example. All of this in a fashion of cogen plant. But it is going to be costly at start.
 
Satamax Antone
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F Styles
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Ive tossed in pieces and went outside and could not smell any plastic.
 
Noah Elhardt
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Location: Senegal, ~600mm rain, 9 mo. dry season
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Very interesting, thanks guys! I see two options:

Use a conventional batch RMH or similar to at least reduce the amount of smoke, dioxins, and air pollution (?)

Make a more complicated pressurised contraption to achieve pyrolysis and recapture the gasified and/or liquid plastics as oil and/or liquid wastes.

The second sounds like a more complete solution, but both are a huge improvement on what we have going right now. Perhaps I'll start with the former and work on the latter once I've had time to do more research, think more, and have the time.
 
Rebecca Norman
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food preservation greening the desert solar trees
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Noah Elhardt wrote:I hate burning plastic, but before you flog me, hear me out. I live in a country without a functioning trash disposal system. Most trash is mixed with vegetable wastes and dumped outside cities and towns, where it blows all over the countryside or gets lit on fire and smolders for days or weeks. Our farm recycles everything possible, and does its best to minimize plastic waste completely. We do, however, burn what remains, as it beats any reasonable alternative we can think of.


I'm in the exact same situation here, except that we bury our unrecyclable unreusable garbage in a big pit in the desert nearby. The idea being that hopefully the plastics are inert and not very harmful that way. There's almost no risk of leaching because the climate is so dry. But year by year the amount of garbage generated at our school increases, and I've started wondering if a good hot rocket stove might incinerate all those nasty dioxins and other compounds.

Well, I'm not sure if perlite or vermiculite, fireclay, and firebrick are available, so I'm not sure we can make a good hot rocket stove, but I'm thinking about it.

BTW here's a conundrum: Europeans who care about the environment are often convinced that incinerator technology is perfectly safe and clean, whereas Americans who care about the environment are convinced of the opposite.
 
F Styles
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I did a test with plastic in my rocket mag stove after the dragon was good and hot and the plastic incinerated to a point i couldnt tell when walking outside that i was burning plastic, so my analysis is that high temperatures seem to at least lower the plastic burn smell. that is all i can do to test.
 
Satamax Antone
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F Styles wrote:I did a test with plastic in my rocket mag stove after the dragon was good and hot and the plastic incinerated to a point i couldnt tell when walking outside that i was burning plastic, so my analysis is that high temperatures seem to at least lower the plastic burn smell. that is all i can do to test.


Carefull, burning PVC can be realy dangerous.

https://toxtown.nlm.nih.gov/text_version/chemicals.php?id=84

http://www.dailykos.com/story/2012/6/2/1096855/-PSA-Burning-Plastic-Can-Kill-You

http://www.ecmag.com/section/miscellaneous/effects-toxic-gases-emitted-burning-electrical-insulation
 
Noah Elhardt
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Location: Senegal, ~600mm rain, 9 mo. dry season
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Satamax Antone wrote:Carefull, burning PVC can be realy dangerous.


You said previously that dioxins "burn off" at 900 C. Does this mean that the danger of burning PVC is reduced if it is done above that temperature? In our case, these plastics are already being burned, so I only have the potential, I think, of improving the situation by changing burner designs to something hotter and with a chimney.
 
Satamax Antone
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Noah. I'm just scientificaly oriented. Not a scientist.

I read that most of the dioxins disapear above 900C°. And yes, if burned at lower temps, plastic gives off dioxins. Which are realy dangerous. We've had a big problem in the seventies and eighties in France, with incinerators, poluting fields around. Fields which still contain traces 20 or 30 years later.

So yes, switch to an insulated batch rocket, lenghten the heat riser as practical, so it will have less the tendency of overloading. There's something about the chlorine, combining with something else at higher temps. But can't remember from the top of my head.

Rebecca, may be look at the bengali firepit, for a solution. As described into the Evans's book.
 
F Styles
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Satmax thanks for the info. i figured the dragon had to be at full speed and temps to do the test and not to start out with low temps. the idea was to see if the smell of plastic was obvious and at high temps it was not. so with my limited test results it seems as though whatever went into the rocket mag got incinerated pretty well.
 
Glenn Herbert
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Rebecca, I have built pottery kilns entirely from native clay, so it can be done without any commercial materials.

My local clay (glacial deposits) is fully capable of firing to 2000F without issues, and starts to vitrify, shrink and distort above 2200F or so. All clays are different, and yours may be more or less capable. Mixing the clay with fine dried grasses to make a porous honeycomb material gives it some insulating quality, and surrounding it with a good layer of loose dry dirt helps a lot. Perlite would be more efficient, but is not indispensable.
 
F Styles
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Glenn Herbert wrote:Mixing the clay with fine dried grasses to make a porous honeycomb material gives it some insulating quality, and surrounding it with a good layer of loose dry dirt helps a lot. Perlite would be more efficient, but is not indispensable.


Do you prefer grass over sawdust, why?
 
Glenn Herbert
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For a strictly insulating mix, I think either could work. What I build also has to be self-supporting as it dries, and the grass temper helps a lot with that.
 
I agree. Here's the link: http://stoves2.com
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