The Quadrafier Gasifier:
A learning gasifier rig of updraft, downdraft, crossdraft, and fluidized bed on a single frame.
Jim Mason. Jan/Feb 2007

Recetly I tired of my ever growing notebook of complex gasifier designs, all unbuilt, and decided to just get started building some simple and quick ones. It seemed far more would be learned by building multiple ones in quick iteration, using readiliy obtainable obtainium, than trying to straight out build the imagined "perfect" one. The process turned out to be vastly more educational than I ever imagined.

I decided to build one of each of the 4 main types of gaifiers (updraft, downdraft, cross-draft and fluidized bed) on the same frame and at the same size, allowing for easy comparisons between types. (ok, maybe I will eventually need a TLUD and a cyclonic one too, but for now, a 4 in 1 covers my main interests.)

To make it interesting (and fast and cheap), I decided that I could only build with junk i had lying around the shop, and a few home depot parts. Purposely quick and crude and without any specialized parts. While learning, I was also curious to see how absolutely simple and hammer and wrench fab tech these can be made with. Expensive McMasterCarr orders and complicated heat recycling and embedded processor temp and mixture sensing/control will come later.

The result is the "Quadrafier Gasifier "

V1.0: Updraft

On New Year's Eve 06/07, several friends and I built our first gasifier using an old 2x tank air compressor set. I was a bit stunned how easy it is to build and get basic gas, as well as how flexible it was on fuels (which I later learned was only the case with updraft designs). Of course this was tarry and wet gas, but it burned clean as nat gas on your stove. even running coal. clean coal is not a myth . . . ;-)

The pictures at the link above show a short chemistry lesson on what is happening to educate the locals. welding and plumbing. then coffee drying on the wood stove, then filing the coffee grounds into the unit. set up of unit in yard. various lighting attempts, with success after awhile. then some poofs on a combined fuel of coffee and wood. then the hot tub and champagne reward afterwards. (we were trying for midnight new years eve, but didn't actually get it fired until 1am.)

We ran it on sawdust, cubed wood, coffee grounds and coal dust. all worked fine, but the coffee grounds were very difficult to get to light. though once lit, they burned fine. it should really run on any biomass that is reasonably dry and dense.

The tank we used is 6" in diameter and about two feet long. I put an angle fill pipe about 2/3 of the way up. the gas outlet is an existing 1/2" pipe fitting in the tank. The distance difference between fill point and gas outlet was to encourage dust settling, and used a gravity loop for the air in at the bottom.

As i have been long confused about the grates, and didn't have anything to use that was fine enough or heat resistant enough, i decided that a pipe protruding to the center of the tank in the base, and then curved upward outside the tank, would allow air in and not allow fuel out. my other main reason for this was that i wanted to be able to run dusts, like coal dust and coffee grounds, which seemed like a difficult proposition for grates. so gravity was engaged, and gravity proved to work rather well.

V2.0: Open Hopper Stratified Downdraft

all stratified downdraft pictures are temporarily here

The stratified downdraft was built from the same 2x air compressor tank as used for the first updraft. as for fuel, we ran: pellet wood, sawdust, coffee grounds, coal dust, coal chunks, pizza crusts, pistachio nut shells and cardboard. the pellets ran well, as did chunk coal, but the granular and loose paper fuels packed up more than in the updraft. makes sense, as in an updraft, the draft is working against gravity. but not yet a fluidized bed.

tar seemed modest, but it was difficult to really tell, as much time was spent starting and stopping and getting fuels packed in it, during which the cool running would produce tar. but once hot, things seemed ok, though i don't have have a tar testing rig set up.

we piped the gas into a 5kw genset, a typical 10hp briggs and stratten generac type. using a ball valve and some pipes, we made a wood gas "carburetor", retaining the original carburetor butterfly as the throttle. then we started the engine on gasoline. turned the gasoline off, fiddled with the air/woodgas mixture, and it continued to run just fine. we were all a bit stunned. soon we were making sparks with the power out of the generator.

V3.0: Crossdraft Gas-Can-i-Fier

The crossdraft unit was built from a 5 gal jerry type metal gas can. the existing fuel bung was piped with 2" black pipe for the gas exit, using some stainless steel mesh for the grate. The air inlet is movable so the distance between air inlet and grate can be varied for different load conditions. plumbing reducer couplings on the end of the air inlet allow for easy changing of air inlet volumes.

I did not allow myself to use the welder for this version. The only power tool used in the making was a drill and an angle grinder with a cut off wheel to make the fuel loading hopper. The fuel hopper doesn't even have a hinge other than bending the metal back to fill it. It doesn't get much easier that this. Build time: 4 hours.

We are running wood pellets in the pictures below. The first run melted the sealtite electrical flex conduit i was testing, so i went back to the flexible exhaust pipe and aluminum tape.

The sealed hopper proved to be much more sensitive to fuel moisture than either the open hopper stratified downdraft, or the updraft. On the first real run, it started strong, but was quickly overwhelmed by steam from the drying fuel inside the gasifier. Seeing the increased sensitivity to fuel moisture with the sealed hopper design was rather interesting. The argument for an open hopper or monorator type design clear.