Wood Fired Destructive Distillation

Hey Woodgassers,

It’s been a long time since my last post. I hope everybody is doing well. I am fixing to start welding up my latest creation. I have most of the parts to build a wood fired destructive distillation unit. Im looking for some feedback on this design. It starts with a tent stove with a 3.5 " flue diameter. This exhaust pipe would run through a 100lb propane tank that has kaowool on the inside and outside. I plan on welding a 4" exhaust pipe all the way through the tank and then running the stove pipe through this for safety. The tank will have a loading port on the top and bottom for the fuel. I have not decided whether the fuel gas outlet will be on top of the tank or bottom. From there, i plan on routing the gas through a couple of small 30lb tanks with valves for collecting liquid fuel, then a gas storage bag, then a water bubbler, and finally back into the stove. What do you guys think? Thanks everybody.

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Why are you doing this ?

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I’m want to build this unit to break down my household trash. Plastic bags, grease, paper napkins and some food garbage would be the feedstocks.

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Can you detail your goals a little more in depth? Example: Are you capturing the off-gas from the retort? Or are you concerned more with producing carbon? Or is the goal to break down garbage? A good old compost bin and chickens is probably a better way to break down garbage. UV will destroy plastic passively.

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The goal is to produce a liquid diesel type fuel and possibly a vaporous fuel as well. It would be easier to burn the retort gas in the stove. Im going for something similar to the Wastebot, but wood/gas fired.

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Ok, I am following you now. For research, check out how crude oil used to be cracked by coal fired benches…a particularly interesting part of this process was super heating the off gas and sending it over incandescent beds of terracotta.
Modern cracking plants still use terracotta.
Old flower pots!
My beef with this is the scale. It’s like melting aluminum one pound at a time. Takes forever to fill the crucible with lil snippets of AL. Same with loading a retort or a bench with clean dry plastic…takes a huge amount of time for something you can get for a $1.50 per gallon down at the Res.
That said, if you are in a Syria type situation…better weld everything using the same thickness mild steel. No leaks, none! Next you will need a really tall flue, to pull hard on your fire box. You can sustain 700f for several minutes at a time if you use bone dry maple split fine. You will need that heat from the moment all the water goes over, til you have broken up the really long chain stuff at the end.
You will need a distillation column. If you pick a temp to pull off at, you can use reflux to narrow down your target chains. For fuel, any mild steel will do. Column packing can be any kind of rings or even round stones. The key will be the temp control at the reflux heat exchanger. Now, thanks to AliExpress you can get a temperature controlled relay for about $6, which can be used to mix the reflux heat exchanger coolant to an exact point. This would dial in your fuel’s cetane rating.
This is a fun project. It would a blast to combine the old cracking tech with modern microcontrollers to ladder up wood and plastic into road motor fuel.
Have you ever thought about microwaving plastic at a frequency that breaks it into 8 to 20 carbo chains?


I have played with this some, but my system was very inefficient I am looking forward to seeing your progress. Remember we like pictures and videos on here.

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I was hoping for Trees have made an enormous phytochemical contribution in anticancer drugs’ development more than any other life form. The contributions include alkaloids that are biosynthesized in various ways and yield. Lead alkaloids isolated from the trees are taxol and camptothecins that currently have annual sales in billion dollars.

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Thanks for the detailed reply. I just want to find a way to turn garbage into a fuel. It will probably boil down to whether I want to separate the plastics out of the equation. I doubt mixed garbage would do good for liquid fuel, would probably do better for a vapourous fuel.

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In my experiances this was inefficient. Allso only a handfull of plastics make good fuel. I boiled down PP, PE and PS for hours and only collected a sample of oil. But to my surprice the small 2stroke started right up on it and run super well!
Hope you figure it out. Plese share. I think the secret might be higher temps and maybee a catalyst?

Pitty you cant use PET since its most abundand…

Other way around it is feed it in a gasifier together with wood or charcoal. I am planing to work on that when l get back to woodgas…



Kristijan, been following your homesteading progress, you’re doing some good work. It would be easier to use heat to distill the garbage and feed this vapour into a charcoal gasifier. I think Koen Von Charcoal ( nickname of respect!) has built a system like this.


Two things puzzle me on this topic if I may ask.
I put up a video show the thermal scan at 3:00 of a small air cooled generator type engine with a close coupled exhaust temp of 440-463F (~220C).
Why not use the wood fuel first gasified to fuel an IC piston generator engine and then use the resultant exhaust temperature/heat energy for the destructive distillation?

Not hot enough?

2nd puzzlement. Ben Peterson distinctly sourced from me bags and bags of PETE clear drinking water bottles for his WasteBot trialing. Shows using these in his demo video.
He DID not want PP or PS plastics. The chlorines. He did not want the colored dyed PETE either. The unknows in those colorants.

Why Kristijan you say can’t use PET/PETE?

Steve Unruh
Oh. The really neat in engine combustion segments are at 9:49-10:07 in that video.

Hi Steve The easiest of all plastics in everyday use are Polyproplene ( the best ) then polyethylene’s low ,medium high density , all of those i have turned to liquid fuel .
All the videos i watched before i started having a play with it all said to not use Pet sue to reasons i forget , but i think it was something to do with oxygen molecule’s or along those lines , there are lots of video’s on line but few have really good end results .
Have you seen the Waste Bot make fuel from 100% PET ? i tried looking for a video of Bens machines running but couldn’t find any and would love to see it in action ? its all good selling a book saying it can be done ,but i would like to see things running with out it being too scripted , i’m not a smart man , but i know my plastics having been in the recycling industry for 30 years .

Steve, l tryed PET and it distiled over in a stinky sticky poridge like mess instead as clear liquid.

What I have wondered about is ROI. How many btu’s does it take to convert plastic to fuel compared to how many btu’s are available from the end product and then factor in plastic supply source, labor and maintenance. I have the same questions about alcohol fuels.

Actually Dave I think you are one of the smartest men on the DOW.
Because you DO. Then Show what you’ve done that can be DIY achievable.

I am not promoting Ben Peterson.
I am not promoting his WasteBot system. I only referenced this because JonathanLT referenced this early on. BenP’s book has nothing to do about his WasteBot system.
I do not know the results. I do not care about the results.
I know exactly what you all can see in his youtube presentations.
He is using real pre-made wood charcoal. For heat. For carbons adding. He is using bought out catalysts. His fabricated apparatus says he is using relatively low pressures and probably low levels of vacuum. Certainly not F-T levels of T&P’s.

I actual home practice recycles separation and directed best-use individual streams solutions. Coffee grounds&spent teas and ALL kitchen vegetable wet wastes to our chickens guts re-processors first. Motor oils once were all saved back for space heating waste oil burners. All non-coated papers and carboards into the bulk woodstove for space heating. Consumer batteries now converted to NiMh rechargeable. (tired of the 1% alkaline leaking destroying my devices!).
Yep. Plastics are a buggabo hole in my system.
We have road-side recycling pick up. Plastics (they do not allow film, or foamed, my engine oil containers). Coated papers. And metal cans are all go into that system. Glass containers into a separate bin. Sigh. Motor oils/trans fluids into one gallon HDPE #2 milk jugs.
I have reconciled the the plastics and such I am forced to direct to landfills were originally derived from coal and oils-gas carbons from below the ground and so back into fixed earth lock-in. Sequestered.

Ha! As a modern auto tech most shops now internally rprocess used antifreeze-coolant in patent systems forced chelating, filtering, additives re-charging buffered for re-use now. And what happens to the remaining toxic sludge stew? Super expensive haz-mat tracked directed (to be landfilled)? Or cheap into the shops dumpster landfilled?

So back to my original question.
Why not use the wasted thrown away IC engine exhaust energy/heat as part of your plastics-to-Fuels systems?
You will need power to make your pressures positive and negative. Whether direct shaft or electric driven. Maybe even be enhanced with forced controllable cooling /refrigeration. More shaft power needed.
Ha! Same question I asked of BenP.

To develop myopic focused in isolation of all other possibilities-turned-to-befits is caviar/bacon fixating. You got yours. Screw the consequences. Leave the left over problems to the left over people.

Steve unruh


There is no free energy. Everything has it’s cost. Proponents of wind power may not be aware that those are mechanical systems and have a life span. At the end of that life span you have a huge machine that is only partially recyclable. There are wind plant graveyards all over the world with piled up carbon fiber rotor blades that no one has figured out how to repurpose economically. as far as recycleability goes, the lead acid battery may top the list. In Michigan there are quite a few bio-mass power plants. Some of these use shredded tires for fuel. Apparently if you burn almost anything hot enough it will break down into it’s basic components. I have melted down milk jugs just to see what would happen. They become very small. Probably end up as a few drops of oil or whatever they started life as. Seems like ideally they would just be burned like other bio-mass and converted to fuel without first liquefying them. Also I figure I’ve earned some carbon credits since I drive anywhere on an average less than twenty five miles a week.

From the armchair…
Yes a small engine can give a high enough exhaust gas temp to do some of the processing. Remember PV=nRT tho. The exhaust has to expand to atmospheric pressure or power robbing back pressure occurs. The expansion takes some of the temperature down.
Doug Williams was using exhaust to dry his fuel chunks and they were getting too hot. So there is enough exhaust gas to do something, but is it enough to validate Tom C’s ROI question?
We operate between the two extremes of simply buying cheap pump fuel and the Syrian Experience. In our cases, there is another metric…Return of Fun. If experimenting with, and designing a plastic cracking plant is Fun then the inefficiencies don’t matter too much. If one is in a situation like those poor devils in Syria, where all one has is time and plastic bags, well…it got done, let’s say that.
Do I need to know how to do this? Yep. Return of Fun on this would be huge, then why haven’t I done this… it’s expensive.
The general principles I know about this…
Inorder to make the ROI positive, the scale has to be large. I looked at this in 2014, and came up with an estimate of 3 yards of concrete to hold the fire box and bench. That equates to a month of site prep, forming up, and pouring. Then there is the fire brick…I am still unsure how to work with that stuff.
I would only use one feed stock. I have been making biodiesel for 18 years, and learned how impossible it is to make fuel with multiple feed stocks. So let’s say I go to the junkyard and have him give me all the plastic gas tanks. The feed stock has to fit through the bench door. So, I have to cut them up somehow. Somehow enough plastic has to be inserted into the bench, to make running the batch worthwhile. The bigger the door the more chances for a fatal leak to occur. Maybe this is where Steve’s exhaust gas comes in…liquify the plastic and inject it into the bench with hydraulics. Anyhow, there is the whole material handling problem.
The next principle, goes back to PV=nRT… plastic cracks into short chain molecules in a range of temperatures and pressures. This range can be shifted by the use of catalysts.
Cracking is endothermic…you have to put energy in to break up the molecules. The variables for a home cracking plant go something like this. What is the lowest pressure that will work? The plant needs to hold pressure. Can I build it to hold pressure? Probably not. Can I do it at atmospheric? Yes but then the temperature has to go way up. Can I use a catalyst? The cheapest one I found was Terracota. Terracotta cracking plants have to constantly regenerate the terracotta as it gets coated with carbon. So there is this time spent processing catalyst. So what temp is needed at atmospheric to crack in a bench with no catalyst? About 700f.
The off gas… It needs to be sent into a distillation column. I have been distilling alcohol for 20 years. It simply is not efficient to reheat the distillate three times. A distillation column with a reflux loop can concentrate the distillate at the target boiling point. So let’s say my target is 50f (that’s some heavy gasoline). The reflux keeps sending everything whose boiling point is hotter the 50f back down the column, or routes it back into the bench. Everything below 50f comes over…gas and liquid. In one sense cracking plastic is easier alcohol distillation because there is less water to deal with.
Eventually I will have to build this plant. Right now the collapse in demand for fossil fuels, has allowed me to achieve the proper Return of Fun from burning diesel in my equipment, and reshaping the face of the earth. In fact, my boys have observed my formula for Fun…I start a large internal combustion engine and move a great amount of weight. I am at a complete loss as to why that is so satisfying…other guys my age want blondes in Corvettes…


As always Bruce Jackson I’ll take input from your much-researched-read, thinking, DOing armchair any day you wish.

Let me introduce you a bit from back-in-the-day . . . you were DOing woodgas and charcoal way before me:


'Course you’ve advanced a heck’a’lot in the last 15 years.
Burning wood grows no moss.

Best Regards
Steve Unruh

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Oh Steve,
I have failed in keeping the faith in sustainable fuel. Thanks for the intro. It is nice to be remembered. We need to turn towards the people who have hours of run time. I think of Mr. Wayne, Matt Ryder, and Greg Manning.
I usually pick low hanging fruit. Lately, down at the Res, fuel was $.98 per gallon for high octane gasoline. Diesel was even cheaper. I took advantage, and bought several hundred gallons of both. But…
The oil industry has been built on a house of cards since the FED dropped interest rates. The WSJ article explained the frackers were 280 billion in debt, before COVid. Now they are on life support…you cannot drill for $27 a barrel. My guys in the Athabasca Tar Sands are turning off the heaters. It takes years to heat that patch up, enough to extract oil. If our guys in the Permian, and Bakken can’t produce, and the Canadians are scaling back, then where do we get the oil? Ahem, the latest dictator in Venezuela? Bin Laden’s buddies? I am worried. I remember '73. I remember '08.
I think it’s coming again. That helpless feeling when you can’t afford the gas to do something as simple as cut the lawn.
So yes, let’s explore all the alternatives. Especially the ones where we don’t depend on somebody else.