How to build a gasifier by Sabbadess (Stephen)

Legal Disclaimer: This document is for educational purposes only. Gasifiers make explosive, poisonous, cancer causinggas. Do not use them indoors. Do no inhale the gasses. Don’t be stupid. Gasifiers run VERY hot. Do not touch anysurface with bare skin while in operation or for four days afterward. Do not operate on a combustible surface. Do notdispose of ashes in combustible grass. Don’t be stupid. Do not pipe the gasses indoors. It can kill you and your entirefamily. Don’t be stupid!

Caveats about this document:

1.) I don’t believe in tar cracking. I feel that the onlyway to get rid of it is by incineration.

Let’s start with a hopper full of fuel.

Air Flow

Raw Wood

Pyrolysis zone - woodthermally breakingdown into tar gas andcharcoal

Combustion Zone - Tars andchar burning

Reduction Zone - CO2 andchar react to form carbonmonoxide

Ash and char

Gas out

The problem here isthat if there is too muchtar gas for the oxygenpresent, the tar doesn’tget burned and it goesout in the gas. This isbad. This why theFEMA design hasissues.

OK. So the FEMA can release tar. Let’s fix it. Add an air tight lid and some nozzles toreduce the volume of the pyrolysis zone and tar gas generation. I am also going towiden the system just for illustration clarity.

Gas out

Air in Air in

Uh! Oh! We just ran into the next problem. The nozzle flows are splatting into eachother like fire hoses pointing at each other! This drives the hot air up creating an archedpyrolysis zone. If that sticky tar glues the fuel together and connects with the sidewallwe will have a bridging condition, the fuel will hang up, and stop flowing.

Gas out

Air in Air in

Tar arch

Let’s fix that problem… By angling the nozzles down, the pyrolysis zone is invertedand in tension. The nozzles are constantly burning out space and the fuel is tearing thearch away from the sidewall.

Gas out

Air in Air in

Uh! Oh! There is still another problem! The tar has an oxygen free path to therestriction and out of the machine! I hate when that happens!

Gas out

Air in Air in

Let’s fix that problem! Add oxygen just above the restriction to torch the tar that mightbe escaping.

Gas out

Air in Air in

Air in

Still not quite perfect…I want to be sure the tar gas is burned not just a lot of neighboringchar so let’s add a “hot well” to limit the oxygen’s dispersion, a reduction tube, and a grateplate.

Gas out

Air in Air in

Air in

Wow! That looks like Victoria!

Gas out

Air in Air in

Air in

Now we have to take care of some char flow issues. Char flows through a gasifier at a 60degree angle. So put the upper most nozzles where a 60 degree cone intersects the wall.

Gas out

Air in Air in

Air in

60 deg

Restriction

Don’t put any stuff in the flowing fuel or it will cause feed jams.

Gas out

Air in Air in

Air in

60 deg

Restriction

If you have a large hopper like a propane tank, you may need a third row of nozzles tocontrol the pressure drop. The top nozzles act as “chippers” to reduce the size of twigs.

Gas out

Air in Air in

Air in

60 deg

Restriction

Air in

Air in

Alternatively you can make a 2.5 stage unit. This one I have actually tested. I found that my unsorted chips didn’t flow wellenough with just three nozzles close to the hot well and one secondary. I suspect that the “columns” of non burning fuel created toomuch drag on the fuel that was flowing. I added three more nozzles at the wall and everything worked much better.

Gas out

Air in(3X)Air in(3X)

60 deg

Restriction

Airin(1X)

14.25 in.(propane tank)

10 in. 10 in.

Then I tried it with preheat.. The outlet heat exchanger proved to be very effective for the cost.

45 degnozzles

Gas out

3/4 in.secondary airinlet pipe

Stainless gas flexline

2in pipe X12in long

2in teewithweldedbushing

Notice that there aren’t any cones or hourglasses in thismachine. They aren’t necessary in fact they are detrimental.Steel should only be run at a MAXIMUM of 500F. Putting1800F radiating combustion on a metal surface is a recipe forheat loss that is needed for reduction. It will also oxidize awaythe metal quickly.

The classic reduction bell is also a bad idea because it slowsthe gas flow and lets ash build up leading to plugging.