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After-burn plastic smoke from garbage?

Nathanael Szobody

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I've got plastic. In the middle of Africa, plastic is everywhere. Everything in the market comes home in a cheap plastic bag, neighbor kids leave cheap flashlight parts laying around, well-meaning visitors from other countries bring us 'useful' plastic things. Plastic bags literally blow in on the wind into my yard, and broken flip-flops kick around until i pick them up. Polyester clothing wears out and kids drag it into my yard to make forts and flags and stuff.

So I burn it and produce carcinogenic gas. Is there anyway i could build a simple kiln with an after burner to further break down the plastic smoke? How about a pipe full of active compost that 'consumes' the stuff? Any ideas?

-Nathanael

Phil Stevens

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What about burning it in a flame cap kiln, such as a kontiki as used for making biochar? I toss bits of old baling twine in as I'm making char, and a soil scientist I know is one of the authors of a study where all the leftovers from greenhouse tomato production, including the plastic twine, were pyrolysed and used to grow a crop.

https://www.researchgate.net/publication/284738588_Closing_the_Loop_Use_of_Biochar_Produced_from_Tomato_Crop_Green_waste_as_a_Substrate_for_Soilless_Hydroponic_Tomato_Production

As long as there is an active flame cap all the volatile fractions should be consumed and the process will be smokeless. I would keep any chlorinated plastics out until I learn more about their tendency to form dioxins.

Devin Lavign

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I can't advise you on the burning issue, though the info Phil gave sounds like a good step in the right direction.

Something I can offer is possible alternatives. There are many threads here at permies discussing ways to recycle plastics into something else. Finding constructive uses for the stuff. There is also a lot of resources and info on the subject outside permies.

Here are just a few threads here at permies.

Plastic bag baskets https://permies.com/t/31307/Plastic-Bag-Basket

Plastic bags into sleeping mats https://permies.com/t/69851/permaculture-upcycling/ungarbage/Upcycling-plastic-bags-sleeping-mats

More general plastic bags into plastic yarn https://permies.com/t/53592/ungarbage/Precious-Waste-Reusing-Plastic-Bags

This thread is more general and does have limited discussion on burning https://permies.com/t/93124/ungarbage/Repurposing-plastic

Those are just a few, and as I mentioned you can find lots of other info out there around the web.

It is horrible how much plastics have invaded the world and there sadly seem no end to the damage they are doing in nature. Finding creative ways to use the plastic waste could help not only to reduce the waste but serve as possible income and resource from what was a waste product.

"Where will you drive your own picket stake? Where will you choose to make your stand? Give me a threshold, a specific point at which you will finally stop running, at which you will finally fight back." (Derrick Jensen)

Nathanael Szobody

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The plastic I usually deal with is pretty degraded; I don't think it is suitable for most up-cycling projects.

The flame cap on the burner sounds interesting, Phil. Where can I eget plans on how to build one. I read the abstract on the article you linked to, but it seems to be more about the process than the design of the kiln.

Thanks!

-Nathanael

Phil Stevens

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Here's a link to Ithaka Institute's how-to for making and using a pit kiln:

https://www.ithaka-institut.org/en/ct/111-Dig-your-own-soil-Kon-Tiki--

And here is a post about my version in a pile of dirt at my place:

https://permies.com/t/102652/volcano

The main thing to remember is that you want a decent bed of embers before you add anything "questionable" and I would start by introducing a mix of plastic and dry biomass as you go.

Nathanael Szobody

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Thanks Phil,

One problem: I don't have lots of wood to burn. It's actually illegal to cut down trees here. I can get together a bunch of small branches, but not enough to fill a pit with coals. Perhaps a long narrower hole that would take a much smaller amount of wood in the bottom? It's gonna hurt to burn my mulch though...

-Nathanael

Michael Cox

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This is basically a waste disposal problem, right?

You are right to consider burning a viable option, especially if done well - as in suitably hot, so that it burns completely. Those conditions are hard to get if you only have limited fuel available. I would probably consider collecting the material to one spot, then once per year have one larger hot burn. This gets it out of your wider environment immediately, but also ensures that you can do the burn in the cleanest way possible. And you can stockpile fuel for the bigger fire over a longer period of time as well.

The key thing seems to be to get it to stop blowing around your neighbourhood.

Moderator, Treatment Free Beekeepers group on Facebook.
https://www.facebook.com/groups/treatmentfreebeekeepers/

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David Baillie

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Hi,
I don't suggest burning plastic unless you have to BUT when I make charcoal for my gasifiers I sometimes use a top lit updraft gasifier to make the charcoal. The idea is that you fill it with wood or wood chips, light the top and let it burn down to coals. Once the top layer turns to charcoal the red hot coals act as a sort of catalytic converter that breaks down the woods into clean burning gas. I have experimented with small layers of plastic shredded sandwiched between the wood. It works well. I think you have too much to make it work properly but maybe as a partial solution. it uses Sticks, wood chips, shells... easy to make , very efficient. I can't tell you how clean it burns you would have to experiment.
TLUD is the acronym you need to look up
here is a mother earth lecture on it a few years ago:

Michael Cox

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Yes, the TLUD approach would be good in this situation. It gives you control, and also reduces the amount of wood you need to need to get the heat and ensure a clean burn. I'd be concerned about variable size waste. You might need to chop things up a bit to ensure good air flow etc...

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Nathanael Szobody

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Thanks guys. I'll try stockpiling it for a bigger burn then. That sounds more efficient.

I'm wondering if it would be good to design a specifically plastic burner composed of two layers: the bottom layer is hot coals with plastic waste put on top, enclosed, while the top later is a grill with a hot kindling fire on it exposed to the air. Would this accomplish the physics we're looking for?

-Nathanael

Michael Cox

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I understand where your proposal is coming from, but your intuition is wrong. The fire beneath is unnecessary and unhelpful. We think "heat rises" and that is true for convection, but the heat that is "cooking" the plastic is radiation coming from hot coals. Embers above will do an excellent job of heating the plastics beneath, without need for an additional heat source beneath. In fact, the heat source at the bottom is potentially counter productive - you might make lots of plastic fumes before the fire is hot enough above to burn them completely.

I would go for something like an oil drum up on blocks, with the top and bottom open. Pack the bottom with a mix of plastic and flammable scraps of wood, cardboard and the like. Pack the top with a layer of twigs, wood etc... anything that is nice and dry that will burn hot and leave an ember. Light the TOP and ensure that the flames spread over the whole area. The barrel acts like a chimney forcing all the gasses to go through the combustion zone. And in your conditions, burning dry material and plastics, it should go hot and fast. Ensure nothing flammable is within a considerable distance, as the radiative heat alone could potentially ignite stuff.

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Michael Cox

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A few thoughts... you could consider making a small gasifier.

Moderator, Treatment Free Beekeepers group on Facebook.
https://www.facebook.com/groups/treatmentfreebeekeepers/

David Baillie

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An anila design stove might work as well with less need to break down the plastic. In that one a central core has wood in it that burns down to coals with the plastic on the outside layer boiling off gas to holes in the bottom that then flows through 5he char. Ratios will be the hard part to figure out to assume the energy dense plastic does not overwhelm the reactive hot char...

https://www.google.com/search?client=ms-android-samsung-ss&biw=360&bih=321&tbm=vid&ei=ll-IXLSmHcLajwTEuriwBQ&q=anila+stove&oq=anila+stove&gs_l=mobile-gws-serp.3..0.67136.67136.0.67893.1.1.0.0.0.0.209.209.2-1.1.0....0...1c.1.64.mobile-gws-serp..0.1.209....0.EylDJpVtW9Q

Devin Lavign

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While looking around the internet for camping rocket cookstoves I saw this article for a cook stove that burns wood/plastic with no toxic emissions. http://www.takepart.com/article/2014/11/12/low-pollution-stove-can-cook-dinner-generate-electricity-and-charge-phone and thought of this thread. How if these were available in your area there might be a lot less plastic trash floating around.

It can also burn plastic and wood without toxic emissions as long as the material—which emits volatile organic compounds when burned—doesn’t exceed 8 percent of the mass being used as fuel, according to Webb.

Sadly the stove did not get funded on Indiegogo only reaching 29% funding. https://www.indiegogo.com/projects/burn-trash-to-cook-food-and-generate-electricity#/

Maybe it is time for them to try again? There is a lot more news about the plastic crisis these days than back in 2014 when they tried before.

The company http://www.energant.com/ has a clean burning biomass stove, but didn't end up producing the plastic burning one.

Phil Stevens

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If they left off the TEG that would improve the affordability. Sure looks like a viable option for places where there is a fuel shortage combined with plastic surplus.

C. Letellier

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You need to watch the types of plastic burned. Chlorinated plastics can spread PCBs when burnt. That is things like PVC and vinyl. Some plastics are fairly safe to burn but others are not. So learn the difference.

Country oriented nerd with primary interests in alternate energy in particular solar. Dabble in gardening, trees, cob, soil building and a host of others.

Devin Lavign

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Phil Stevens wrote:If they left off the TEG that would improve the affordability. Sure looks like a viable option for places where there is a fuel shortage combined with plastic surplus.

I agree, but understand that most of the places these are designed for also have limited electric. So I imagine they added it to be an alternate source of electricity for people who might not have any in their own home.

Maybe having two different models one with the TEG and one without, giving the option? Or even making the TEG an upgrade to add in later?

But the real critical tech is the clean burning of plastic to help reduce the waste issue.

Nathanael Szobody

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Michael Cox wrote:
I would go for something like an oil drum up on blocks, with the top and bottom open. Pack the bottom with a mix of plastic and flammable scraps of wood, cardboard and the like. Pack the top with a layer of twigs, wood etc... anything that is nice and dry that will burn hot and leave an ember. Light the TOP and ensure that the flames spread over the whole area. The barrel acts like a chimney forcing all the gasses to go through the combustion zone. And in your conditions, burning dry material and plastics, it should go hot and fast. Ensure nothing flammable is within a considerable distance, as the radiative heat alone could potentially ignite stuff.

Sounds like a plan. Only i think I'll make it out of bricks on legs for air intake. I have VERY limited materials.

-Nathanael

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