burn plastic in rmh?

Plastic bags are pure polyethlyne, I think. Could they be burned in an efficient rmh as cleanly as wood?

I've been burning lots of trash all winter. Plastic bags, plastic spoons, water bottles, paper plates, packaging including plastic wrap.

I always wait until it is really hot and has a good draft before putting any plastic in. I also always have a fan ready to help with the draft to make sure there's no blowback.

I don't think it has significantly extended my firewood but it certainly has helped lower the amount of trash going to the dump. And because the RMH burns so hot it is likely turning all the bad stuff into CO2 instead of putting it into the air.

I'm also not using the ashes in areas where I'm wanting to grow food, just to err on the side of caution.

I hate to be a nay-sayer, but burning plastics releases horrible toxins into the atmosphere. These toxins which include nasties like dioxins come down with the rain, polluting the soil, lakes, streams and oceans. The fact that people manufacture plastics is bad enough for the environment, but burning them too just pollutes even further. Please don't burn plastics.

That's why doing it in an RMH is good. It burns it hot enough that you don't get that stuff.

It's also why I'm pissed that the town I'm in shut down their incinerator. So now instead of completely burning that stuff and getting rid of the bad stuff they're now putting it in the ground.

Here's a handy article:
Burning Garbage to Generate Electricity
and some guidelines:
Canada Guidelines for Burning Solid Waste

It appears that a rocket mass heater at full operating temperature should produce the right environment for proper waste combustion.

Since you're more selective with regards to what goes in, I doubt heavy metal emissions like Mercury or Cadmium is an issue.

That leaves acidic gasses like Sulphur Dioxide. The normal method of dealing with that is by using a lime scrubber through which the exhaust gasses pass.  I would be inclined to run a experiment first to see if that's necessary by making an "acid rain box" on the exhaust outlet to see if you can produce acidified water.

Finally, I didn't realize that marine driftwood was such a significant producer of chlorine compounds, as bad as plastic. That beach bonfire is probably not such a great idea...

I agree in principle with James, but the devil, as they say, is in the details.

I don't think I would use an RMH as an incinerator unless I knew what the highest temperature necessary to completely break down the plastics to water and CO2 was for the specific materials being incinerated, and unless the RMH in question was equipped with thermocouples throughout the burn tunnel and riser capable of showing me real-time temperature readings.

I would also want to be able to test the exhaust stream. I haven't come up with a good way to do this, but I figure bubbling a measured amount of exhaust in a test through a specific amount of water would probably indicate if there were residues left in the exhaust stream that we don't want there, and lab testing would probably even give us parts per million.

Having said that, from all I've read, it is possible to cleanly incinerate plastic, but the burn conditions need to be hot enough, and be consistent.

I don't think it's necessary to incinerate plastic. As Ron mentioned, the impact was mostly felt in the decrease of the amount of trash going to the dump, but in an uncertain burn environment, that's just putting into the air what you would have otherwise sent to the dump.

My favourite relatively new approach to literally decomposing plastics actually involves a honey bee pest that eats beeswax. I don't remember the name, but I read an article that I will try to find that related a story of hand-picking these wax-eating beetle grubs out of a hive and disposing of them in a doubled-up plastic bag. It was discovered that these larvae were actually eating the plastics.

I would want to have tests done on the larval feces, and the larvae themselves, to see what of the plastic was persistent, but my recollection of the article suggested that the breakdown was complete, with all the plastics converted to base components.

As long as nothing nasty is going into the air, I would gather whatever solids remain (ashes or larval), and should they still contain plastics, I would spread them over ground for non-edibles, probably a managed woodlot or shelter belt space, living, vital soil with a fungal-dominant ratio. The plastics would be eaten by the soil and broken down to their molecular components, and just for safety's sake, they would be taken up by trees to be coppiced or pollarded and burnt in an RMH again.

To stress James' point again, low-temperature combustion of plastics is pretty dreadful. Any RMH combustion that can't hold to the extreme temperatures required will produce the dioxins and other stuff that we would all rather not poison ourselves with. That means that probably pretty much any RMH anywhere, unless built for the purpose of incineration, which would probably make it ridiculously overbuilt for even a large household, wouldn't do the trick.

If the exhaust in your RMH isn't clean enough to vent into a greenhouse that you would be happy working in and eating food from, why would it be okay to vent it into the atmosphere? Just to decrease the amount you have to take to the dump?

I think it's theoretically possible to build an RMH incinerator designed to do the job, but that would require some use for the heat generated. I don't think it's worth the risk to the environment, just to save some space at the dump. It's just like the used tire argument. If there is no healthy and safe way to use them, they shouldn't be used and would better be buried somewhere the elements and living organisms won't get them, or they should be processed into a form that can be cleanly combusted as fuel, as can be done with processed used rubber.

Upon further consideration, I think it would be a great thing if nobody tried to dispose of plastics in their RMH. The risks far outweigh the rewards, and those rewards are at the expense of our collective health.

I think the most permacultural solution to plastics is to stop buying them. Vote with your dollar. If you want to burn packaging, buy stuff that is packaged in cardboard and paper. Demand that plastic packaging, plasticised coatings on paper and cardboard, and bags be abandoned by society. Put out of business those that make disposable plastics. If you happen to be in one of those businesses, change your model and benefit from the PR that restructuring and rebranding to environmentally friendliness will yield, rather than fighting the undertow of social consciousness that will eventually pull you under.

As to the future of synthetics, I think that the most useful thing we could do is leave petroleum in the ground for now. We will probably need raw materials for new, long-life synthetic materials later, and if we've burnt them all, we'll be shit outta luck. When we can more cleanly extract petroleum from the ground, and when we can make it into highly-durable, highly advanced synthetic materials that can be completely, effectively, and cleanly recycled ad infinitum, it might be worth looking at again.

-CK

I don't have a science background; i'm a retired guidance counselor but have read a bit about the molecular components of materials mostly over the past 10 years of experimenting with and building mass heaters. My understanding is that plastic material is, at its core, petroleum, which is compressed fossils, hence the name, along with being called "hydrocarbons", molecules composed of hydrogen and carbon. What I don't understand is the difference in the length of the various molecules and how/if that affects burning/pollution: long chain hydrocarbons such as petroleum, for example, I think burn differently than short chain molecules.
PVC and many petroleum based combinations are probably really really bad. I would welcome more comments like the above to help us get informed. I have a huge  ("sad") sack of poly bags that I want to get rid of in the least bad way possible.

March is grass burning time in central Illinois and our rural neighborhood is often covered with a smoky haze. I wonder if burning certain waste plastics in my rmh is adding--- a lot, a little, or just CO2--- to our air.

ps. I haven't burned many bags--- yet. but the few I put in melted, then, when liquid, appeared to burn as clean as the wood with zero smoke. But I don't have testing instruments beyond my eyes and nose.

Smell can be a good indicator, but dangerous in some cases. That's why going by temperature is probably the best idea, and the best way to do that is with a thermocouple.

As to the best, safest way to dispose of your poly bags, if they can't be recycled, and probably even if they can, in most cases, I think the safest way to dispose of the plastic is to find a place like a hole in a mountain desert plateau deep enough that surface water never reaches it and high enough that the water table never hits it, and bury it there.

No sun, no wind, no moisture, no freeze/thaw cycles, nothing that will break it down and cause it to go places we don't want it, and it will remain intact practically forever.

When Paul Stamets finally breeds or finds a variety of mushroom that breaks down plastics into soil food, then we could dig it all back up again, inoculate that shit, and feed it back to the woodlot or shelter belts.

-CK

I agree with James and would not burn anything made of petroleum or its byproducts.   To say that "it's likely" an RMH is hot enough to burn away the bad stuff is not sufficient for me - I only trust laboratory testing and even then, with great skepticism.   If you haven't done the testing to ensure the minimum temperature your RMH can consistently burn, and test the exhaust for pollutants, then I wouldn't do it.   The best way to deal with toxic stuff is to just not bring it into the house.  How many plastic bags do you have?    Reduce consumption of plastic packaged goods and then dig a hole on your own property to enclose the "junk trash".      I'm lucky to live in a city that provides recycling and trash pickup (albeit with high taxes).   But my philosophy is that if each individual had to be responsible for their own trash, they'd be a lot more conscious about their purchasing habits.     Is there a thread on this topic?   I'll take my rant over there..... :)

James Freyr wrote:I hate to be a nay-sayer, but burning plastics releases horrible toxins into the atmosphere. These toxins which include nasties like dioxins come down with the rain, polluting the soil, lakes, streams and oceans. The fact that people manufacture plastics is bad enough for the environment, but burning them too just pollutes even further. Please don't burn plastics.

https://en.wikipedia.org/wiki/Dioxins_and_dioxin-like_compounds#Environmental_sources

If your burning wood in your RMH then your already, in a way, burning plastics like lignin and hydrocarbons like acetic acid. With that said, some plastics could burn clean(maybe) if its hot/long enough to crack the hydrocarbon chains to their small pieces it should burn or escape unburned(not oxidized) without leaving deposits. Watch out for plastics with chlorine in them like PVC unless you want hydrogen chloride (among other things) going through your system. In theory If it isn't cracked all the way down then there is risk of black flammable goop collecting in the cooler parts of your heater. I would personally avoid it unless absolutely necessary like in an emergency.

Please don't burn plastics. Not on this planet anyway. Plastic is evil.