A Home-Built Biomass Gasifier for Producing Wood Gas

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I've built a lot of alternative energy projects over the years. See my web site at and my other instructables to see my home-built solar panels, wind turbine, improvised generator, and other projects. I've always wanted to build a wood or biomass gasifier too. Why? Well, the internal combustion engine is really an important part of our society and the basis of a lot of our transportation and portable power technology. It isn't going to be going away any time soon. I've mastered making my own electricity from the sun and wind, but that doesn't help my truck go down the road, power the lawn mower, or run my generator on cloudy, windless days. Those all have internal combustion engines, and they all need fuel to run. I finally decided it was time to master making my own fuel. Why pay the Arabs for it if I can make a working substitute myself?

So what is a biomass gasifier? Basically is a chemical reactor that converts wood, or other biomass substances, into a combustible gas that can be burned for heating, cooking, or for running an internal combustion engine. Gasifiers are an old, but generally overlooked alternative energy technology. Few people these days realize that gasifiers were used extensively by both sides during WWll to power cars, trucks and buses during fuel shortages. Gasifier technology rapidly evolved and matured during the war.

Gasification is achieved by partially combusting the biomass in the reactor, and using the heat generated to pyrolyse or thermally break down the rest of the material into volatile gasses. A well built gasifier will convert wood or other cellulosic biomass into the flammable gases Carbon Monoxide and Hydrogen.

My goals here were to build a gasifier using easy to obtain materials, that would run on readily available fuels, and would produce enough gas to at least run a small generator or other machine powered by an internal combustion engine. In this instructable I am presenting the finished product (so far) that has resulted from many months of experimentation and modification. To see the entire long and winding road I went down to get here, please visit the gasifier section of my web site at
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I saw an article in Mother Earth News about running the "Producer gas" through a barrel of loose hay to catch the tar b4 feeding it to a pickup truck engine.

I love your design and am at awe in how painstaking you've been documenting your discoveries. You inspired me to attempt my own, working from your successes. You will need to remove sulfur compounds if you wish to run an engine. I've been reading up on early sulfur-removal techniques for gas streams....might consider iron oxide impregnated wood chips ie. iron sponge...many mulch companies use iron oxide as an 'all natural' dye in their red curious to know if it would work to convert hydrogen sulfide into iron sulfide....anyway great work!

tpoulton8 months ago

awesome setup. Let me know when I can come visit and have a larger model installed by you on my Jeep Wrangler (I'm willing to pay for parts and booze). Seriously, nice build, I'm jealous of your skills.

The old FEMA article about gassifiers from the 1980's lacks the J-tubes, making it easier to build. But it never states where in the fuel column the flame is. I'd think you'd want the flame at the top, so that the heated air would do pyrolysis on the wood below as the sucking air pulls the flames down. Does anybody know if this is actually how a simple biomass gassifier works?

If I remember correctly, the FEMA version lets the air flow directly down through the biomass that's to be burned? That does work, but by modifying the design to use air inlet tubes, you can have a better burn.

The burn point in the FEMA version, as well, is at the bottom of the tube, rather than the top. What you want is for the biomass to self-feed into the fire, rather than for the fire to simply burn randomly. Having the fire right about at the constrictor plate makes for the hottest burn, letting the ash fall through the grate, while gravity feeds the biomass down to continue the burn at it's most efficient point. The J-tubes used in this particular instructable also help to keep the burn at (or near) it's most efficient location. If you were to use this model to provide fuel for an engine, you would have the option of stopping the engine after awhile to add more fuel, without significantly damaging the burn - you could simply close it back up, and start the engine again. The suction from the carburetor would keep fresh air flowing into the gasifier.

There are also a lot of really neat gasifier projects that people have put up on YouTube. Some run lawnmowers, some run pickup trucks. I've even seen a small one that runs a motorcycle.

rjbatc2 years ago
Wouldn´t a simple water and maybe charcoal filtering system help clean your gas? I think a simple water bubbler takes out a lot of tars. The question is, what to do with the stinky, dirty water then.

As I understand it, water is definitely helpful at removing tars from the air via a bubbler system. However, doing so would mean putting a lot of water vapor into the system by way of evaporation. The hottest point in the combustion process in the gasifier should take care of cracking (that's actually the technical term!) the tars, making them into combustible gasses. If it's not hot enough, then perhaps a narrower restriction plate might help. Also, simple air filters (old-fashioned hay or dry pine needles work well) will also absorb a lot of the tars while letting the combustibles flow through.

i like your design a lot but do you think i could run a steam engine off of this

It would be fairly inefficient to use this to run a steam engine on - it's main purpose is to produce flammable gasses that are clean enough to run a vehicle's internal combustion engine with. While you could use the simple burner on the end of the pipe to provide heat for the boiler on a steam engine, you'd also have to provide air flow (via air pressure or an in-line blower motor) to keep the air moving through the system.

It's actually more efficient (for steam engines, at least!) to simply burn your combustibles so they heat the boiler directly.

One offshoot of gasifiers is called a "rocket stove." You could use a rocket stove to more efficiently provide heat for your boiler.

korlich1 year ago
So, dumb question here. What keeps that rubber cap on top of the hopper from bursting into flames? Isn't there a blazing inferno just a couple feet under it? Very intriguing and simple design. First "doable" one I've seen so far. Thanks!
If you welded the pipe fittings and other points than it could get pretty much as hot as you wanted although I see you dont have access to a welder.You can usually find a fabricator shop that will weld it for free or at a low price.
TheWilks11 year ago
Wood gasifiers are confusing to me but I was looking at your design and was wondering if you could put a valve where the rubber piece is to allow easier access? And just to make sure that where you put your fuel right?
AtomRat2 years ago
Hi there! This is by far the best gasifier design I have seen for home use! I too have had a journey creating them, and I love how you have mixed so many designs into yours! It is definitely open for more modification, I would like to suggest some further ideas:

I am now on my way to attempting methanol creation from bio-gas which requires a fluid bed reactor, and from what I know now, these can be made and simplified just as easy as we can do with these wood gas burners.

Once the gas leaves the unit, you can further purify it by using:
- Filters: several can be placed along the gas process. I know of cyclone, water, fluid bed and fiberglass. ( sorry, only just heard that in the vid )

Clean the gas further by condensing it to a liquid, easier to separate by adding a simple condensing unit.

Peltier or Stirling modules for energy production off the burner.

Download a .pdf book you can google called: Wood Gas As Engine Fuel
It provides an extreme amount of info on our beloved burners. Hope any of this helps.
p.s - unfortunately I became a victim of lack of information and ended up in emergency from Carbon Monoxide poisoning. As you can guess, I stay clear of the smoke these days :(
MTtoo2 years ago
You have written a very informative and well written i9nstructable. You have touched every detail and told of the consequences of doing that operation some other way. Excellent reading. Very easy to follow. Like all the rest of of the things you have built over the years (on your website). I have followed your work for a long time. Would like to ask a question. Many years ago (about the gas shortage of 1980) I was readung up on the wood gasifiers. Some knowledgeable person was explaining the different wood types used as fuels. I was thinking that a hardwood that gave off a lot of heat and little smoke would be the best. According to this fellow, the best fuels were the ones that produced a lot of smoke. Smoke = carbon monoxide. I am sure you have studied the wood types. What are your suggestions?
Thanks again for your great work.
hi. i am shabir khan.i am from pakistan.i saw this gas maker today and i am going to make it.because here is gas shortage to spread quicly.i am very than full to you for make best wishes with you make it in a car injine we intence need here for that.i am very thank full to you again.
Has anybody ever tried to build a externally heated Gasifier? Using e.g. some of the produces gas. It would have three benefits: It's easy to "ignite" (just using some leftover gas from last run), you don't get CO² in the produced gas and temperature is easy to control.
What are reasons to not do it like this?
I'm making a ceramic gasifier that will compress the gas instead of using a blower for use and possibly for later ignition of the gasifier, and I'm waiting for it to come out of the kiln, but in the meantime, I was wondering if you think it would be possible to ignite the thing electronically, or would i have to clean it out each time i want to start it? Also, do you think that a ceramic gasifier might work temperature wise (ceramics are fiered at around 2500 degrees the last time).
Uptonb3 years ago
Congrats on being a finalist, and good luck!
Ogg13 years ago
Kudos for a wonderful Instructable! It does however prompt the following question: How does a gasifier compare to a small boiler/steam engine for stationary installations like turning a generator? What I am thinking about here is a comparison of the efficiecy, safety and practicality for those of us with plentiful supplies of wood. Steam power, while not so common today certainly has a long history and is a mature technology.
frankcox Ogg13 years ago
Steam is superior but prohibitively expensive.
A steam engine to drive a generator would run you 30k + . They are wonderfully efficient but not cheap.
A modern, large boiler and turbo-alternator set would definitely have a superior efficiency to a dustbin sized gasifier and converted petrol engine, but we must compare "apples with apples". A small scale boiler and reciprocating steam engine would probably have a poorer overall energy conversion efficiency, as well as being considerably more expensive.
Ogg1 tgothan3 years ago
That is what I was really fishing for. I have all this wood that is currently going to waste and I am searching for a practical approach to using it. Heat is an obvious choice and I have acquired two wood stoves to that end but as electricity is becoming more expensive I would like to address that as well.
mdavis19 (author)  Ogg13 years ago
Well, like you said, steam power is not so common today. Internal combustion engines are everywhere though, and cheap and easy to obtain. A gasifier will power them from wood or other waste biomass. If you don't happen to have a steam engine, your steam efficiency is zero. If you need to turn a generator, which is easier to build, a steam engine, or a gasifier?
The technology to build a steam engine is light years ahead of a wood gasifier.
A small steam engine will cost 30 - 40K , there is a reason for it.
They are incredible machines , the speed of an old steam powered wooden launch would amaze you. Internal combustion replaced steam because it was cheaper and safer , not because it was better.

The licences to run a steam engine cost more than the gasifier.
Ogg1 mdavis193 years ago
You do make some very good points. As to which one is easier to build that is debatable. It kind of depends on your personal talents and inclinations. A small steam engine can be driven from either a boiler or a solar concentrator and that may present certain operational advantages.

I was more hoping to stir up a little input from the engineers out there than you personally. Once again I would like to commend you on an excellent instructable. I can only hope to someday contribute something of such elegance.
tgothan3 years ago
A good instructable. I have built several larger gasifiers, which used waste wood from drymills to generate around 40 kW(E). I have several suggestions, the most useful for quick startups is fitting a 1" tube from outside the gasifier to just above its hot zone. You then simply push a lit, kerosene-soaked wad on the end of a wire into the burn zone. An old hair dryer blowing down this tube would get things going in under 15 minutes (you can see this down the tube). The test was to light the pilot nozzle on the gas outlet. If it burned steadily, you could remove the wire and blower, seal the starter tube with a screw cap seal and start the alternator engine. There was no need to unpack the hopper to add hot coals.
junkhacker3 years ago
Would it remove much tar if you sent the output gas through a tube tightly filled with charcoal? The idea being that the tar would become deposited on the charcoal as it pushed through, and as it cooled. This tar heavy charcoal could be reused as fuel,where the tar would have a second chance to be cracked, and fresh charcoal put in the tube.
tinkerist3 years ago
i just read your website write-up. that's some excellent experimental engineering you got going on there. i would like to drop you a suggestion on creosote and sulfur removal (the excess sulfur in syn-gas can be a problem for engines due to it's corrosive qualities).
for the creosote/tar, i have seen designs where the gas is percolated through a water reservoir. this would be much simpler than your spray design and potentially more manageable than a cyclone separator, as maintenance would largely consist of changing out the water regularly. of course, the more and smaller holes the gas goes through at the bottom of the percolator, and the more time it's in contact with the water the more effective it will be. you might consider a condenser down circuit from this to remove excess water.
as to the sulfur, the most common method i've seen is running the gas through a column full of steel wool. the steel bonds with the sulfur and provide a surface for it to crystallize, making little yellow florettes. there's a way to remove the sulfur from the steel wool and reuse it a few times before it rusts to bits, but i can't remember how to do that right now. i don't think it takes very much steel wool to remove a significant amount of sulfur but a longer column with more steel wool would probably be more effective and require maintenance less often.

as an added bonus, you might be able to find uses for the creosote and sulfur. they're both flammable and, thus, potentially usable as fuel. they have other uses as well.
also, it occurred to me that you might get less tar by making your j-tubes more nearly flush to the inside of the flame zone, or building up the constriction zone to a more conical shape toward the air induction points. my logic on this is that some of the gasses and tar might be bypassing the flame zone through the areas outside of the air induction, where your highest heats would be. does that make sense? i know what i mean but i'm not sure if i'm stating it clearly.
mdavis19 (author)  tinkerist3 years ago
A conical constriction is used in some gasifier designs. I had the idea of building that originally. The problem is, the section below the top of the cone is a dead leg. Material (mostly ash and char) gets trapped there and cannot move down. Once that space fills up with inert material, there is no real difference between a conical constriction and a planar constriction. The only real advantage that I can see to the conical design is that some of the liquids produced that aren't thermally cracked can be trapped in the dead space below the top of the cone. In the end, I decided it wasn't worth the extra effort to make a cone.
what about cutting back the j-tubes a little, increasing the diameter of the flame zone?
one more thing. did you notice any increase in performance when you extended the tube below the flame zone? if so, would it be due to airflow somehow?
mdavis19 (author)  tinkerist3 years ago
No, I did not see any improvement in performance. My idea was to extend the length of time that gas and tar exiting the reaction zone would be in contact with hot charcoal in hopes of cracking more tar and getting better reduction of combustion by-products. It didn't work because (as I realize now) the char exiting the reaction zone cools quickly. Only a short distance below the reaction zone it is already too cold for any further reactions to occur.
bennelson3 years ago
Here's a basic one some friends and I were working on.
he neat thing about gasifiers is that they can almost be as simple or complicated as you want them to be.
Maybe i missed something about it, but is the compressor or any other forced air system only used on startup or for the whole burn? Thanks
mdavis19 (author)  {Havoc}.Goliath3 years ago
If the gasifier is being used to produce gas to power an engine, then the forced air system would only be used for startup. After that, the manifold vacuum of the engine would take over driving the system.
ALogan973 years ago
How much more efficient would this be than using pyrolysis to break down algae to produce gas fuel? I'm doing a project for the Google Science Fair about it, but I want to know if I should switch to gasification instead of pyrolysis.
There are 'pellet' stoves for sale that burn either wood pellets or corn!
Also there are off the shelf usable parts for your gassifier......restricter plate and shaker etc.....
Corn ,in some years, goes currently for 643.00 cents per bushel/50lbs bag or better yet grow your own^_^ Gives you something to do with all that 'franken corn' {genetically modified}nobody wants to eat
metalarts3 years ago
Is it possible that the "tar" that you mentioned is in fact uncrystalized creosote?If so,you might allow it to harden and use it as a heat source in your gas generator.
Nice project! This technology has been used in Brazil and do not know why it was abandoned
In the 301s and 40's years, in Brazil has used a very similar system to feed the engines of transport trucks and tractors. You can see something on the links below
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