Garbage incinerator

A couple of years ago we built a cleaner garbage incinerator.  I saw a video on YouTube about a commerical system that burned garbage by gasifying the waste, and then burning the smokey gas with injected fresh air.  The system burned hot and cleanly, and they claimed it met EPA regulations.  I've always hated burning barrel smoke, so I wondered if something similar could be built.  Looking more into this I found that several people have made their own cyclonic garbage incinerators and that they work rather well.  Even better, no modifications to the barrel need to be made.  All you need is the lid part with the combustion chamber, air intake and exhaust.

How it works is that the heat causes the garbage to begin to burn, but it only burns partially since the oxygen down in the barrel is limited.  As this hot smoke rises, it is mixed with fresh air being blown into the combustion chamber  in a swirling fashion, where it ignites.  The swirling fire creates a vacuum that pulls up more smoke from the barrel, sustaining the reaction.  As long as the barrel stays hot the burn remains clean.  If there are a lot of plastics or rubbers in the barrel, I've seen the entire barrel glow red hot from bottom to top of the exhaust at night.

The current problem is that by the time the fire burns down into the bottom of the barrel, things are so cold that the smoke doesn't ignite up in the combustion chamber anymore and just exits.  So if you load the barrel right full (but do leave some space for air in between the combustibles), it burns very well for the first 2/3, but the bottom third burns about as clean as a normal open burning barrel.

Construction

We took a normal barrel lid and cut a hole in it, the same diameter as a scrap piece of pipe we had.  The pipe is about 10" in diameter (it was actually an old female ringlock end that was kind of bell-shaped, but that's not required) and about 10" tall.  The actual diameter of this piece of pipe isn't that important, as long as it forms a circular combustion chamber.  We welded that to the lid, covering the whole in the lid we had cut out previously, and then put a cap on the 10" pipe section with a chimney pipe sticking up from that.  This forms the combustion chamber.  Be sure to weld up all the seems so that no smoke, flames, or sparks will escape.  On the side of the combustion chamber we welded a 2" piece of pipe sticking out at a tangent angle. This brings the air into the chamber against the side of the 10" pipe, causing it to swirl.  The pipe needs to be long enough that the plastic hose that attaches it to the air source is far enough away from the barrel that it won't melt.  Also the air pipe can be straight in; it doesn't have to be angled down as ours is shown.  Also it doesn't matter if you put it intersecting the middle of the combustion chamber or near the top.  Probably it should not be near the bottom, though.

Air source

For air we used the exhaust outlet from a normal shop vac.  That seems to be an idea air volume for the 55 gallon barrel.  After wearing out a shopvac doing this, we are now trying to use a variable-speed leaf blower.  The leaf blower can put out about 2-3 times more air volume than we need, so dialing it back is important.  A normal life blower on a light dimmer seems to work also.

Start rubbish burning, then put on the lid and turn the air on.

Smoke hasn't ignited yet.

Smoke has ignited, but smoke is leaking out.

Good and hot now, no smoke.

Barrel is getting very hot, nearly 500oF and reversing the rust, turning it black again.

Improvements

A number of improvements can be made.  One is to insulate the barrel and lid with fiberglass insulation.  This will keep the heat inside, which will ensure that combustibles that gassify down near the bottom of the barrel will still ignite up at the top and burn.

Another improvement might be some way to stir the materials as they burn down so that the ashes have a chance to burn.  In theory, almost all combustibles should be able to burn without leaving hardly any ash behind. 

We have also tried putting little fins in the combustion chamber to direct some of the swirling airflow down towards the bottom of the barrel.  If the barrel was insulated, perhaps these fins would not be needed since we don't really want the fresh air going down into the barrel anyway. We'd rather have things gassify and then burn up top.