Metabolizer - A recycling center powered by trash!

A mobile power plant that eats trash and turns it into energy, electricity, fuel, and very nearly anything else.

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The Metabolizer is a proof-of-concept waste-to-energy power plant and recycling center that is powered entirely by trash. It is intended to have the same basic metabolism as a living organism, capable of breaking down wastes, including plastics, and turning them into useful things like heat, electricity, fuel, building materials, and 3D printed objects.

This project combines many existing components into a whole system that is more useful than the sum of it's parts. I call it the Metabolizer, because ultimately what we are doing is developing a closed-loop machine metabolism that breaks down complex molecules into simpler ones, inhales oxygen, and exhales CO2- like cyborg mushroom!

This project isn't ready for step-by-step instructions, so instead I layout each component of the system in detail, discuss what it is, what it does, and what it could ideally do, and what design challenges remain to be solved, so that we can all work on solving them together!

Problem Statement:

Unlike all healthy living ecosystems, which regenerate wastes back into living things in an infinite loop powered by sunshine (with fascinating but negligible exceptions), human tend to just make stuff out of stuff that we've either dug up or cut down, and then just throw that stuff away when were done with it. The problem is that we're rapidly running out of "away", and all that stuff we're making is piling up faster than natural systems can break it down again. Waste plastics are a particularly problematic example of this paradigm of consumption, because very few living organisms exist that can break plastics down, and none exist that can do it as fast as we're currently producing them. 

However dire our current situation may be, it is not unprecedented in Earth's history. 360 million years ago, plants suddenly evolved the ability to synthesize Lignin- which was up until that point the most complex organic compound that had ever been synthesized on Earth. For 60 million years (!!!) trees grew, died, fell over, and we're buried, but the solar energy trapped in their chemical bonds was never broken down and released- because no fungi or bacteria existed at that time that could break down woody biomass. That's where most of the worlds coal came from. It wasn't until white-rot fungi evolved specialized enzymes that wood became the 100% compostable component of living systems that we know it as today.

Plastics are mostly made of the same stuff that wood is, and they are extraordinarily energy-dense. A gallon of plastic has roughly the same energy content as a gallon of diesel fuel. So whether or not humans survive the Anthropocene, we'd be flattering ourselves to believe that we could end ALL life on Earth, and that means that eventually SOME living organism will almost certainly evolve a metabolic pathway that can convert the nutrients and solar energy locked up in the plastics in our oceans and landfills, and use those resources and energy to synthesize the physical structures that allow them to continue to live, grow, and self-replicate. It's only natural! It's what life does. 

But why should we wait for humans to go extinct? We built the systems that made the plastic, we can build systems that break them down. We can designs systems that can break down our wastes and use the energy and material in them to meet human needs, for things like food, water, shelter, energy, and information.  We can create human-made systems that integrate with the local ecology, that behave as living organisms do, that resolve the conflict between modern human society and the rest of the biosphere. Don't believe me? Great! That's what makes this project interesting! 

Check it out:

It's possible to use plastic and biomass to make a flammable gas that can power internal combustion engines.

It's possible to use internal combustion engines to do things like shred waste and make electricity. 

It's possible to thermally decompose many common plastics into liquid fuels that can run unmodified gas and diesel engines.

It's possible to use electricity and and shredded plastics to 3D print or mill plastic objects in very nearly any shape (that's why it's called plastic)


The Design Challenge:

This project is my best attempt to design a machine that mimics the metabolism of a living organism, that meets or strives to meet the following criteria:

1) Is capable of metabolizing as many common household waste materials (cardboard, paper, plastic, glass, aluminum, etc, etc, etc) as possible into the resources and energy required to power itself as long as there is trash or biomass available to eat.

2) That is capable of synthesizing and replicating ALL of it's own parts, enabling it to grow, adapt, evolve, and self-replicate. Similar to the Rep-Rap project, the goal would be to...

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  • 1 × "Precious Plastic" shredder box Full plans available at
  • 1 × 5HP Briggs and Stratton engine Easy to come by on craigslist for free- $50 - search for used for lawnmowers, edgers, chippers, and rototillers, or search "Briggs and Stratton"
  • 2 × Band Heater Elements
  • 1 × 3" ABS Y-fitting
  • 1 × Black Steel Pipe Flange

View all 15 components

  • MPCNC what you did there.

    Sam Smith4 days ago 0 comments

    So far I've been able to turn trash into energy, and I've been able use that energy to shred trash- including plastics. Most plastics in the waste stream are recycleable, and although you could burn them for energy, it's a waste of a precious and useful meta-material, and since plastics are made from fossil fuels, it still adds net carbon to the air, unlike burning cardboard or woodchips, which there is no shortage of. So it makes sense to build the plastics that are clean and recyclable into new stuff. My ultimate goal would be a machine that can fabricate as many of it's own parts as possible, using trash as the raw material, which would then make it capable of not only metabolism, but also adaptation, growth, and self-replication... further blurring the lines between technology and ecology.

    I'm looking into a few ways of doing that, and one of these is attempting to a create large format, low-resolution 3D printer head that skips the filament-making step. People always ask me if you can make 3D printer filament out of recycled plastic, and intuitively that makes sense, and the answer is yes, you CAN... But since recycled plastic almost always has various impurities in it, and you would be using a DIY machine that you have to build yourself, and because filament needs be the exact same diameter, +/- a few microns, over a span of hundreds of feet, it's actually a really difficult to turn waste plastics into a high-quality enough filament to print with in a typical desktop 3D printer without a lot of headaches, and it's often just not worth the trouble given the cost and availability of commercial filament spools (you can buy recycled PET filament from various vendors, but that's not the same as being able to make your own). In addition to that, the common recyclable plastics you could use for printing- primarily Polyethylene, Polypropylene, and PET (Polyethylene Terephthalate), while all technically 3D printable, all have properties that make them less-than-ideal when compared to PLA or ABS for desktop printing. PP and PE have relatively high warping/cooling issues which can lead to bad prints, and while PET prints well, it absorbs water from the air, so all recycled PET has to be dried and stored properly before it can be printed, adding an extra step and complication. So while all of the materials are printable, there is a very real reason 3D printing of recycled plastics is not more common.

    So I've been trying to design an extruder, based on the precious plastic extruder, which uses a wood auger to move recycled plastic flakes into a heated barrel and out a small nozzle, but placed on a vertical axis and designed so it can be easily mounted on a CNC gantry, so it can for large-format, low resolution printing directly from recycled plastic flakes. Above is my current version, which is my 4th iteration. My original design used a NEMA34 stepper motor, which worked but was crazy overkill. This one uses a 4:1 planetary geared NEMA23 stepper for extrusion, and 2x 300W heater bands. Thats way more power than you need, but the heaters were cheap on Amazon, and where the right diameter. 

    Original design!
    Works, but suuuuuper heavy!

    So I started looking for a cheap, open source, easy-to-modify CNC gantry, and I found the MPCNC, which stands for Mostly Printed CNC. The MPCNC is open-source, fairly well documented, cheap to build, and uses standard hardware, readily available tubing or conduit as rails, and 3D printable parts, all of which fit well into my design criteria of being "disruptively replicable". So for several months I've been working on building the gantry, and yesterday I got it moving for the first time! Now I'm in the troubleshooting phase. Currently the motors are wired wrong (parallel rather than series) and they sometimes don't have enough current to move the gantry. I'm hoping to re-do the wiring soon and see if that helps. It's always something!

    But I'm excited about the MPCNC as part of the metabolizer, because...

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  • Because I was...Inverted

    Sam Smith6 days ago 0 comments

    So it's been a little while since my last log, and here's why: As of my last log, I have successfully used kegs and home brewing fittings to produce a clean flammable gas from locally harvested woodchips and I take as a reasonable indication that I can also produce flammable gas with any locally-available dry biomass, including shredded burnable trash, such wood waste, yard waste, and cardboard. So now the question has become, how do I actually get useable power out of this gas that I can now make? 

    Part of the reason that wood gas/syn gas is not more widely used is that it has a considerably lower energy content than gasoline or natural gas. It's still quite potent as a fuel, but depending on how you make it, it can be 10-50% less calorific than gas. The way I'm doing it doesn't introduce any air into the gas, which keeps it from being diluted with atmospheric Nitrogen, and keeps it on the high side of that range. Still, when you run this kind of gas in an engine designed for gasoline, it produces slightly less power per stroke, and so then engine runs at slightly lower RPM.

    This isn't really a problem for the engine, as long as the fuel is clean an the air:fuel ratio is right, but it IS a problem for most cheap portable generators (see above), because until quite recently, most generators were designed to produced electricity using a type of generator that produces 60 hertz pure sinewave AC power ONLY WHEN IT IS SPINNING AT EXACTLY 3600RPM, which is the speed that most gas engines are designed to spin at. If you feed them syngas instead of gasoline, which is quite easy to do otherwise, they'll still run but they'll spin slightly-or significantly- slower, and produce AC power that is not quite 60hz, and not quite 120V, which can cause appliances designed to run at 120V to either not work or not work well. 

    BUT! In the past 10-20 years, a new style of generator has come on the market, called "inverter generators", which produce 120VAC power from fuel in a different way. Inverter generators use a permanent magnet DC generator to produce DC electricity, and feeding that variable-voltage DC power into an inverter that can accept a wide range of DC voltages, and convert it efficiently into pure sinewave, voltage controlled, 120VAC. If you're familiar with solar power setups, it's basically an MPPT charge controller and pure sinewave inverter, combined into one unit. The advantage of this design is that it is not only more efficient at producing electricity, but allows the engine to spin at different speeds without affecting the output power. 

    This is what the "ECO-throttle" feature does on some generators- it lets the system speed up and slow down the engine (thus consuming less fuel) in response to the load demand on the generator. You can't do that on a non inverter generator. This design is also what makes it possible to build "dual fuel" generators, which have become more common in recent years. Propane and Gas also have different energy contents (Gas produces more power than Propane, which produces more power than wood-gas) and so until recently it was fairly difficult to switch a generator between gas and propane. But since inverter generators convert whatever DC voltage is being produced, they don't care if it runs faster or slower. 

    All this is to say, it is way more feasible now than it ever has been before to make clean, efficient, and modular (these units are parallel capable, and can act as one generator when you need more power) electricity, using any dry biomass as the fuel. I'm also really excited to see that generators like this one are available on Amazon Prime for less than $1000! My original plan was to use a DC motor to produce power that I would feed into a charge controller, battery bank, and then a sinewave inverter, and I may still do that. But since I want this project to be as easily replicable as possible, it's exciting that a product exists that (may) lower that barrier to...

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  • Warmer...

    Sam Smith07/02/2018 at 18:59 0 comments

    I scored this patio heater at the Portland Goodwill Bins for $15! It's missing the glass tube that keeps the gas contained, but you can order replacements on Amazon for $60, and what it does have is a really nice ceramic catalyst and pilot light/starter mechanism, which is worth the $15 by itself. The catalyst will ensure that all the hydrocarbons passing through it are completely broken down, ensuring complete combustion. And adding in the glass tube will be a neat safety feature. 

    When woodgas is properly condensed, only two gases that should remain after the cooling process- CO and H2. All the other gases- water vapor and longer chain hydrocarbons, should be condensed into liquids and captured by the condenser. What that means is that if you are doing it right, your fuel should produce ZERO soot. Soot is carbon-based particulate that comes from incomplete or unbalanced combustion of hydrocarbons. 

    If your gas is just CO and H2, it will burn to CO2 and H2O- no soot to speak of. So by burning the gas inside a clear glass tube, I can both check and demonstrate to others that the gas I'm producing is clean, and that I'm not adding any soot or particulate to the atmosphere.

    I also ordered this valve and servo motor, following this project from Thingiverse, and was able to successfully actuate the valve, with a high degree of precision, using a rheostat knob attached to an Arduino. This is going to be really important for the project, because the air-fuel ratio is critical for any kind of combustion, but particularly for internal combustion engine. Every modern car engine has an ECU that is able to read all sorts of data points and adjust it's air/fuel ratio accordingly. I want to do the same for the Metabolizer, and I want to create a platform that can create replicable results.

    So I'm making every valve, switch, and actuator I use controllable by servos, steppers, or relays, so that they can eventually be computer controlled. This way, even if I'm controlling them manually at first, I can "Record" the states of every switch, valve, and actuator, as the machine runs, so once I get a set of parameters that work well, I can play them back again and again, and in this way systematically improve my results.

    Luckily, a ton of Open Source code and hardware already exists for this stuff, so I'm able to grab most of what I need from Thingiverse. However, I am working on designing my own laser cuttable Airflow gate, for controlling the air flow into the engine. This essentially bypasses the on-board throttle, and gives me full control over the air-fuel ratio.

    I'm trying to do this using a servo motor and Coroplast/corrugated Polypropylene- the stuff they make political lawn signs out of. This material is strong, light, fairly chemical and heat resistant, and common in the waste stream. By cutting it up into rectangles, and then cutting holes out of the rectangles, and stacking them all together, I can create a simple high-flow adjustable air-gate. When the circle is rotated by the servo, the flutes in the material become more and more mis-aligned with the flutes in the fixed rectangle, restricting air-flow. 

    I'm not sure if this will work, but I think it will, and if it does it will be a cheap, easy to build, easy to compute-control air-flow actuator! Stay tuned!

  • Super-calorific gaseous mixture combusts producing motion!

    Sam Smith06/25/2018 at 16:00 0 comments

    Got the engine running on woodchips last night! I've been studying and researching this stuff for years, and I've seen other people do it, but still, getting an engine running on woodgas in my own backyard is incredibly satisfying. 

    I tightened up all my connections, and they all seemed to hold up much better this time. I also ended up with considerably more liquid than I expected in the tar trap- about 1/4 of a liter just from maybe a gallon or so of woodchips.

    When I cleared out the keg to put the new woodchips in, I found that the old batch had become a very nice, very completely-pyrolyized biochar!

    Success! Next steps are to get my 8HP propane engine running on woodgas, and figure out some sort of low-pressure gas storage system to even out differences between gas output from the reactor, and gas consumption from the engine.

  • Fire in the hole!

    Sam Smith06/24/2018 at 17:40 0 comments

    Last night I fired up my test setup for the first time, and on my first try I successfully created a reasonably clean, flammable syngas! There's still a long way to go, but it's always satisfying when a test actually works the way you had hypothesized it would.

    Experiment Setup:

    I used a 5 gallon steel keg, inside an old turkey fryer, on top of a high-BTU propane burner. The turkey fryer part is mostly just for insulation and stability. I cranked up the propane burner to full blast, and waited about 15-20 minutes before I started getting gas. The condenser coil was connected with CSST gas fittings and 2" tri-clamp brewing fittings. At the bottom of the condenser was a liquid trap for catching the tars, followed by and addition water bath cooling coil, but I bypassed that part for the purposes of this experiment.

    For feedstock, I just used woodchips I got from a tree that had be recently chipped on my street. The material was mostly dry, but probably still had around 10-15% moisture content.


    What learned from this test:

    -I can indeed produce a clean, flammable gas using the basic approach I thought I could. This process is well-known and well-documented, so I was pretty sure I could, but its still satisfying to get it working my own backyard.

    -I will need to pre-dry my material, but I already knew that. It took a bit of time to transition from steam to gas. 

    -There was gas leaking from some of my seals, particularly the top fitting and the T fitting above the liquid trap. The other one was solid tho, which suggests its possible to make them gas tight (I mean, that's what they're designed for) but I need to tighten them up, and some high temp furnace sealant around the ring couldn't hurt.

    -I need to get a carbon monoxide detector. CO isn't that dangerous in an open environment, and when completed, this machine won't produce any in a way that could be inhaled. While experimenting tho, I should invest in some safety equipment. Safety third and all that.

  • Well, that escalated quickly.

    Sam Smith06/17/2018 at 18:46 0 comments

    I spent some time diving into the detail work on my model (which is now available on the SketchUp 3D warehouse), and I really like what I've ended up with. It's admittedly more ambitious, but I always wanted to make this project a work of art, not just engineering.

    I want to build something that embodies the energy flux of solar energy through living systems- a shrine to the chemical process of metabolism that makes all life possible. What better shape for that than a torus? 

    It also doesn't hurt that I built a 30' toroidal steel pavilion for a Burning Man art project in 2016, which has been pickling in playa dust under my porch for the past two winters, and has developed a very nice rusted patina.

    "Entrainment" installed at Shift Festival, 2016

    In fact, most of the components of this new system are cobbled together from bits and part I already have from older projects (seems appropriate). I've already got a Harbor Freight trailer, a 30' toroidal structure made up of twelve 1" steel 6' radius rings that break down into 10' sections, a 4500W propane powered generator I scored on Craigslist for $40, and about 100' of 1" stainless steel gas tubing I got at the Rebuilding Center for $6. 

    So I think I can put together an impressive installation for not that much money.

    The basic idea is that the machine will use computer-controlled heating coils (Ni-Chrome or Induction) to heat up 5.5 gallon kegs that are filled with compressed, shredded, and dried biomass, such as woodchips, yard waste, food scraps, and eventually even sorted non-recycleable or degraded plastics (HDPE, LDPE, and PP). 

    The application of heat in the absence of oxygen causes the hydrocarbons in the material to break apart and vaporize into smaller hydrocarbon chains, and escape from the keg in the form of a thick hot smoke. That smoke is directed into a series of stainless steel condensers (the smaller torus in the center of the structure), and as the smoke is pushed through this condenser it cools back down to ambient temperature, causing the hydrocarbons that make up the smoke to condense into liquids as they cool. These liquids drain back via gravity to the bottom of the torus, where they can be tapped off and collected to be refined into biofuels, or simply safely recirculated into the reactor.

    After the gas has been cooled back to room temperature, the only 2 gasses that remain are Hydrogen (H2) and Carbon Monoxide (CO), both of which are invisible, odorless, colorless, and highly flammable. When introduced to oxygen, they readily combust into Carbon Dioxide and Water Vapor, releasing heat in the process. An interesting property of Syngas (which is what the mixture of CO and H2 is sometimes called) is that unlike propane (C3H8) or gasoline (C8H18) or other complex hydrocarbon fuels, Syngas is made up of such simple molecules that when it burns, it should not produce soot of any kind. You know that kind of wavy, perfectly clear, hot exhaust that jet engine makes? It should look like that.

    And that's kind of a neat idea, I think, since people are (rightly) conditioned to not burn plastic or trash, because doing so without proper containment, condensation, and filtration IS very dirty and very toxic, and produces a toxic smoke. So the central hearth of the Metabolizer is designed to be made out of CNC-cut folded sheet metal polygons that glass panels will fit into, making the structure into 360 degree a viewing window that allows people to see the combustion going inside (which will hopefully take the form of a fire tornado). If the machine is built and operated properly, there should be no soot build up of any kind on the glass- which is sort of a showy way to prove to everyone that the machine is not releasing any toxic compounds into the air (Look ma, no VOCs!).

    Speaking of Jet Engines, I am suspicious that the two cones that make up the inside of the torus could be made into a sort of low-pressure jet engine,...

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  • Party Time! Keg-cellent!

    Sam Smith06/05/2018 at 18:12 0 comments

    This project requires reaction vessels that can handle high temperatures, and are corrosion resistant. My original idea was to use 5-gallon stainless steel "Cornelius" style kegs as the reaction vessels to produce syngas, because kegs are readily available, and stainless steel can handle the temps I'll be working with. But I soon found out that the rubberized handles on Corny kegs are very difficult to remove- you basically have to burn them off, which is, uh, kind of the opposite of what I want to do (I would like the toxic smoke to stay INSIDE the machine, thank you very much). So I put out a call to facebook for REAL kegs, and my friends came through! I now have these 3 slimline style Sanke kegs to experiment with!

    When I got home, I started trying to figure out how to make a secure and gastight, but also quickly removable connection to the top of these kegs to collect the gas, and once I realized the taps I thought I could use weren't going to be secure enough, was afraid I would have to custom machine something, which is not only tedious and expensive, but also makes the project that much more difficult for other people to replicate.

    (this screenshot is from

    So I jumped on google, and was very pleased to discover that there is a HUGE range of every possible stainless steel fitting and connector I could possible hope for, readily available for not that much money, because of the home-brew industry. You can get stainless steel fittings in every shape and thread, butterfly valves, sight glasses, check valves, manifolds, and basically any other connection you can imagine, all with inter-compatible 2" tri-clamp connectors. Unnnnnng I'm in maker heaven. It's like a lego set for building complex, modular, high-temperature and corrosion-resistant machinery. 

    I ended up ordering a clamp system and this 1" NPT pipe thread fitting. This should let me securely and quickly attach my Corrugated Stainless Steel condensers to the kegs, without worrying about gas leakage or fabricating my own janky connectors. Once these parts arrive, I can start experimenting with making fuel! I'm going to start with wood pellets, because of their high energy content, flowable shape, and low toxicity. Stay tuned!

  • Oh shit, now I have to actually build this.

    Sam Smith05/30/2018 at 19:21 2 comments

    Welp, I just received my $1000 from Hackaday for being a finalist in the Open Hardware Challenge, and now I have to figure out what I'm going to build with it! I can't help but turn this machine into an art piece, not just a bit of engineering. I want to build something that will get people's attention and demonstrate what this thing is capable of. 

    What better shape than a torus to represent the infinitely reciprocal nature of living systems? The picture below is the concept I'm currently working with- a 4x4 harbor freight trailer carrying an engine, generator, battery bank, charge controller, gear reducer, and shredder, and a biomass reactor that produces the gas that runs the engine. The shredder shreds pre-sorted trash, the trash is fed into the reactor which breaks it down into gaseous fuels, gas is run through the condenser that collects and sorts fuels by their molecular weight, until the gas is clean enough to power and internal combustion engine. The gas powers the engine, then engine turns a common shaft, and off of that shaft rotational power is converted into 12VDC electricity by car alternators, which charge the batteries, which gives the machine the ability to constantly monitor its power output and turn the engine on and off as needed.

    The inner torus is a condenser coil that distills out volatile tars and heavy hydrocarbons, and sorts them by their molecular weight, hopefully this will produce fuels that are useful on their own. I'm planning to do this with a series of mason jars (because they are cheap and can handle relatively high temps). They aren't pictured yet in the sketch above, but it would look something like this:

    The outer torus is mostly just for show and structure (and to keep folks from getting too close to the reactor), but I'm going to put addressable LEDs along the poles so I can get a nice swirling light effect. I already have this structure from an art project I did for Burning Man in 2016, and it's currently just rusting under my porch, so I'm excited to get to use it again.

    The goal is to build a machine that can run all night long on the gas produced from thermally composing shredded burnable trash, including non-PVC plastics, in the absence of oxygen.

    It will start on propane, which will produce hot exhaust and electricity to power water heating elements inside the reaction vessel. Once the reaction vessel is warmed up the system will transition over to syngas fuel. New fuel material will be fed via vacuum lines and a cyclone filter to the top of the reactor, where it will fall down into the reaction chamber and turn into ash and gas, and the ash will be removed from the reactor every morning with a shop vac.

    That's the plan for now! Stay tuned! 

  • You condense if you want to, you can leave those tars behind

    Sam Smith05/01/2018 at 23:57 0 comments

    You condense! You condense! OK that's enough of that. Let's talk about condensers. A big part of this project is the condenser system. When you heat biomass or some plastics (imagine a keg filled with woodchips for now) in a closed vessel without access to oxygen, the molecules that make up the wood will start to decompose into smaller molecules. Here is the chemical structure of Lignin- one of the primary components of wood.

    Notice how this molecule is just a crazy arrangement of Carbon, Oxygen, and Hydrogen? It's made up of the same molecules that oil and gas (and you) are, but it's much larger and heavier. In order to use it as a fuel, we need to break it down into smaller bits. In a perfect reactor, these wood molecules would get so hot so fast that they would all break ALL the way down to their simplest possible components- Hydrogen gas (H2) and Carbon Monoxide (CO), which is what we will use to run our engine.

    In practice, however, there will always be uneven heating, especially when the reactor is just heating up. So complex hydrocarbons will tend to break apart into slightly-less complex hydrocarbons, which looks like a thick, acrid smoke. These complex hydrocarbons are gaseous at high temps, but will condense out of the smoke at lower temperatures. So if you can heat up biomass, and then cool the smoke that comes off ALLLLL the way down to ambient temperatures (around 70F), all of the gummy, nasty, sticky, and sometimes toxic tars and solvents will condense out of the gas, and the only gasses that remain gasses at ambient temps are the CO and H2 that we will use to run the engine.

    So we need a cheap, safe way to condense out these tars. You can create a system that captures these molecules and sorts them by their molecular weight, which allows you to produce analogs for diesel and gasoline, but that's a phase 2 project. For now, we want to build a system that will:

    -Be able to handle high temps without corroding

    -Be readily available so that people can replicate it

    -Be easy to work with and require minimal tools or welding

    -Have a high surface area and/or thin walls for high heat transfer

    The best solution I have come up with to solve this problem is using "CSST" flexible gas tubing. This stuff is so great. It's marketed as a flexible piping system for natural gas, and you can buy it in 75-ft rolls at home depot or lowes. But the great thing about this stuff is that once it is removed from a house, it generally can't be re-installed to code, so if there is a ReStore or other material salvage spot in your city, it's pretty easy to find used. I scored a huge roll of it at the Rebuilding Center in Portland.

    Cut away the plastic sheathing (and keep it, I think it's Polyethylene, and we can shred it later...) and you've got an uncoated, high surface area hand-flexible stainless steel condenser! For simplicity's sake, I'm going to try and build a back-flow design, where the gas is cooled in an upward spiral, and the condensed tars drip back into the reactor. But in the future I'd like to design a multiple condenser system that collects the tars as they cool, to harvest valuable liquid fuels and chemicals. But doing so is complicated and dangerous (some of these compounds are VERY VERY toxic. Please don't f*ck around with them, or, if you do, please at least be professional about it)

  • Scooooore!

    Sam Smith04/25/2018 at 07:57 0 comments

    I just scored this working propane-powered electric-start 4500W generator unit on craigslist, including a new starter battery and a 1/2-full tank of propane for $60! Apparently there is an issue with the generator unit that makes the breaker trip- seems like an internal short. It might be fixable, but the guy didn't want to have to deal with it, so he sold it to me cheap. This is a huge score for me, because I was going to remove the generator part anyway, at least to extend the driveshaft so I could also connect the gearbox and shredder. 

    So if I can get generator part working, that's a bonus. But the reason I'm interested in this engine specifically is that it's already set up to run on gaseous fuels, which makes it much easier to run it on charcoal, syngas, or biogas without having to modify the carburetor or air intake.  It also has a 1- 1/2" NPT threaded pipe fitting already fitted onto the exhaust, which makes it easy to just screw on my own fittings and capture the waste heat from the exhaust stream. It also gives me the option of recirculating the exhaust gases into the biomass reactor, which allows for precision control of the air -fuel mixture within the reactor. 

    Here's a photo of the engine I've been working with so far- notice the janky pipes I've stuck on there- none of them are very secure. This is a major upgrade for $60! Stay tuned!

View all 13 project logs

  • 1
    The Engine

    What it does: The engine turns chemical energy into rotational shaft power (and heat). 

    What it is: I'm currently using a 5HP Briggs and Stratton go-kart engine. These engines are cheap and they're everywhere- usually attached to go-karts, lawnmowers, chippers, etc. You can find them on craigslist for $0-80, and new from places like Harbor Freight for $100-200 Get one that doesn't require oil mixed in, and if you can find one with easy-to-modify exhaust and air-intake ports, that's a big plus, because we're going to be modifying them so that we can run the engine on a gaseous fuel.

  • 2
    The Gearbox

    What it does: The gear box takes the 2000-3000RPM shaft power from the engine and uses a series of gears to reduce the speed and multiply the torque. A gear ratio in the range of 30:1-50:1 is ideal, with an output RPM in the ballpark of 100RPM. This gets us the torque we need for the shredder to shred right through anything.

    What it is: There are many strategies for gear reduction- car transmissions, gear and pulley systems, hydraulics, worm drives.... It's a whole thing. I'm using a worm-drive style 40:1 industrial gearbox I found at salvage yard for $5. That was a lucky score- finding a good gearbox is one of the more difficult/expensive parts to source. Check craigslist.

  • 3
    The Shredder

    What it does: The shredder shreds up waste into small bits so that it is easier to process, and reduces waste volume significantly. Think of it as the metabolizer's teeth. It mechanically decomposes incoming feedstock to prepare it for further chemical decomposition.

    What it is: The shredder I'm using is a "Precious Plastic" open-source shredder. The shredder box cost me about $400 to get the parts cut, and a few days to assemble. You don't have to use a PP shredder, but they're the best open source option I know of. An industrial shredder might work a bit better if you can find one, but the scale of the PP design is ideal for backyard processing. Wood chippers don't really work well enough for our purposes, as they are designed for wood and tend to try to "whack" things apart, which doesn't work well for plastics. Industrial paper shredders are and option, but their motors are often under powered and must be modified. Don't even try using a cheap paper shredder.

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Tony wrote 06/25/2018 at 16:07 point

I'm afraid Manta103g has a few good points, but I don't think they're show stoppers. For instance, it'd be great to have this machine fuel itself off the plastics, but, if that's gonna spew toxic gasses then maybe we can find a way to just compress waste plastic into bricks. In fact I think they're already starting to make houses that way, so, theoretically we could start pressing plastic into slabs that a table top CNC machine could cut pieces that snap together to make tiny houses, or even little bike trailers people can sleep in and lock their stuff in for security... 

Then we'd have something we could get known for, enabling us to garner the attention and social capital to build something even more sophisticated, such as a robotic decomposer.  What do you think?

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Sam Smith wrote 06/25/2018 at 17:00 point

Manta103g does have a few good points, but they're not show stoppers, and it annoys me when people tell me so authoritatively that something isn't possible. 

To be fair, I'm learning too and by no means and expert, but I disagree with Manta103g's hot take, and with the caveat that I very well could be and am willing to be wrong, here is why: 

It's true that some plastics off-gas toxic vapors even when melted (not even burned). This is NOT true for all plastics, but it is for ABS, and it's true that ABS fumes from 3D printers are dangerous. It turns out that's actually caused by nano-particles or UFPs.

From wikipedia "ABS is stable to decomposition under normal use and polymer processing conditions with exposure to carcinogens well below workplace exposure limits.[20] However, at higher temperatures (400 °C) ABS can decompose into its constituents: butadiene (carcinogenic to humans), acrylonitrile (possibly carcinogenic to humans), and styrene.[20]

Lower temperatures have also shown that ultrafine particles (UFPs) may be produced at much lower temperatures during the 3D printing process.[21]Concerns have been raised regarding airborne UFP concentrations generated while printing with ABS, as UFPs have been linked with adverse health effects.[22]"

And all plastics, not just ABS, will decompose into a toxic smoke when heated.

But that doesn't mean that ABS cannot be safely decomposed into into a fuel, and in my mind, it actually is a decent argument for why ABS should be decomposed into fuel instead of being recycled, since melting/recycling it releases dangerous compounds whereas when used for fuel those compounds can be more easily contained. 

Check it out- ABS is Acrylonitrile Butadiene Styrene, chemical formula: (C8H8)x·(C4H6)y·(C3H3N)z). It's chemical structure is composed entirely of Carbon, Hydrogen, and Nitrogen. If you throw it onto an open pit fire, it will decompose into short-er but still fairly complex hydrocarbons, which can be all sorts of toxic compounds- styrene, benzen, toulene...

So don't do that! People have this idea that burning plastics is toxic, because it is when you do it in an open fire, at low temperatures.

If instead you shred ABS and heat it inside an air-tight reactor vessel, such that it gets hot and decomposes in the absence of oxygen, it will still break apart into smaller hydrocarbons, and some of them are toxic, but none of them are gaseous at atmospheric temperature and pressure.

If you cool the gas stream boiling out of the reactor in a condenser that cools the gas ALLLL the way back down to around 70F, which is what my condenser coil does, the only 2 compounds that remain gaseous at that temperature are Hydrogen (H2) and Carbon Monoxide (CO). 

H2 and CO are both combustible, and when mixed with O2, they combust into CO2 and H20- both non-toxic and 100% bio-compatible compounds. Now, I'm in favor of burning wood chips until I can guarantee the system is 100% safe and air-tight before working with more dangerous feedstocks, and I'm not there yet.

But ABS can in fact be thermally decomposed ALL the way back down to CO2, H20, and N2, and that makes those elements available to build built back into living things again. It essentially frees those organic elements so they can participate in the cycle of life again. 

And doing so releases heat, and also accumulates liquid hydrocarbons that condense out of the gas. I'm working on a centrifuge design that will sort them by their molecular weights, and then pump them into separate storage containers, so even the potentially dangerous ones can be stored without ever coming into contact with humans. 

The undesirable compounds- the ones that are either too heavy or too light to be useful by themselves, can simply be reflowed back into the reaction vessel, where they will break apart further into even smaller compounds, over and over, until they make it to CO and H2. And the desirable compounds- including analogues for gasoline and diesel fuels- can be filtered, stored, and used later as bio-fuel.

And the process necessarily produces waste heat and energy, which I intend to use to recycle as many of the other common recyclable and non-toxic plastics (HDPE, LDPE, PP, PET) into new objects- using molds, 3D printers, and extruders- which we could turn into building materials, and I think turning them into snap-together tiny homes is an awesome place to start!

Hope all that helps! Again, I'm not saying that doing any of this is trivial or easy, but I am saying that it is definitely possible, and I intend to figure out how to do it as best I can. 

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manta103g wrote 06/18/2018 at 23:35 point

No way to accomplish your target since some plastics, decompose to highly toxic gases, if heated. This is the reason, you should never print anything 3D in closed space to avoid inhaling highly toxic vapour gases. Many ppl are not aware, 3D printer should be operated in large,  ventilated space only.  Interest in ABS is below zero, since you cannot process ABS into fuel and workshops prefer clean ABS granules on input. Seperation of plastics is highly complicated issue, what comes next is cleaning and washing, just another highly expensive process. This is the reason China factories showed interest in PET bottles only, since PET can be processed alike nylon into usable PET yarn. I can tell you more and more and more about why the world doesn't love plastics processing. We have too much raw oil and gas to manufacture clean raw plastics, so interest in used plastics is low. What is hot today are metals and metals processing.

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Michael Barton-Sweeney wrote 05/02/2018 at 16:56 point

Nice project!

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