Big Mamma and Little Honey, thats what we called the two giant trash piles left behind by a seventy person party in the desert. This is an annual trip and leaving trash behind is not an option. In 2006 I took a swing at building an incinerator deal with the trash. It wasn't till two years later I had a working model. Not only did it work, it decimated the trash. If for some reason you have a trash problem a barrel incinerator might be for you.
Step 1: How does it work?
Incinerators are basically supercharged camp fires. By introducing a lot of extra air in a specific manner, it increases temperature and accelerates combustion. Air swirls around in the lid until it is forced down into the barrel along the edges. Air is introduced at the edge of the lid which gets it spinning. This rotation continues as the air is channeled into the combustion chamber. The rotation and input location are the key to efficient combustion and keeping the metal parts cool.
This design burns in cycles, the barrel is loaded up and burnt to completion. During a burn cycle, flames shoot several feet out the top and the barrel glows. What surprises people is that there is no extra fuel; no gasoline, kerosine or propane. All it needs is garbage and air.
The large volume of air makes it possible to burn garbage at considerably higher temperatures than those found in a burn pile or a traditional burn barrel. The down side of these high temperatures is that they accelerate the oxidation of the steel. My first successful incinerator got so hot, the barrel was paper thin after several uses.
Icons from the Noun Project: Fan by Murali Krishna, Spring by Adomas Tautkus and Fire by SuperAtic LABS
Step 2: Don't wonder
If you are ever wondering what size that was, what direction that was facing or where something is, don't wonder. It's okay to double check and measure again.
Step 3: Materials
You are making a custom lid that should fit almost any 55 gallon drum. All the flat stock metal in this project is 1/8" thick mild steel. When finished, it's pretty heavy, but the weight is advantageous as it holds the lid down during the most aggressive burns. You will need an entry level metal shop (or a friend who has one) to pull off this build. All told this will cost less than $500.
Two donuts 23.6" OD and 8.75" hole (see below)
8"-12" length of 8" schedule forty pipe
6" flat stock 80" long (padded)
3" flat stock 80" long (padded)
3" diameter Walker Flex Hose (from the auto parts store)
2' of 2.5" OD straight pipe like this (from the auto parts store)
Enough grating to cover the 8" pipe (spark arrestor)
Some metal for handles, I used 1/2" tube stock
1' spare 2"x4" wood
One 55 gallon drum as thick as you can find
One leaf blower gas or electric with high CFM and variable speed
One length of 3" diameter dryer hookup tubing similar to this.
One 6' length of conduit or thick dowel for stirring ashes.
I sourced my steel from Bayshore Metals in San Fransisco. They offer plasma cutting for about $80. If your shop isn't set up to cut the two donuts, I highly suggest saving the time and calling it in. Its perfectly fine to cut your own donuts as well.
Lets do this!
Step 4: Handles
The incinerator is heavy, its nice to have handles. You can use anything you like for handles. The only thing to remember here is to make them deep enough so that if it's hot, you don't burn your knuckles on the lid.
My handles were made from 1/2" tube stock and were bent on the pipe bender.
Step 5: Spark Arrester
It's best not to light the neighborhood on fire so please install a spark arrester. Choose a heavy grade mesh/screen, the high temperatures of the exhaust will melt thinner materials. You should cut about 1/2" larger than you need to cover the schedule forty pipe.
Step 6: Down tubes
These are the secret ingredient. The air spins around inside the lid until these guys channel the air down to the combustion chamber. Using a metal chop saw or an angle grinder with a cutting wheel. Cut two down tubes from your 2.5" OD pipe. Make two 45 degree cuts in each piece so they look like above.
You should try to make these as short as possible. I was trying to make them short and wound up cutting the forward edge. Cutting the forward edge isn't an problem nor is it necessary. Height is an issue so try to keep them short. They should not be more than 3.5" tall.
Once you have cut your two down tubes, clean them up on the grinding wheel and wire brush.
Step 7: Position the down tubes
This is when we decide which disk is the top and the bottom. On the disk that you deem bottom worthy, place your two down tubes. They need to be opposite each other, facing in opposite directions and far enough in so that all the air goes into barrel. An inch and a half is usually far enough from the edge, but please double check your measurements. Make sure the inlets wind up channeling air into the barrel. Once in position, trace your down tubes onto your bottom disk.
Put some tools away.
Step 8: Cut the air inlets
Using a torch, cut out the markings you make for your down tubes.
Step 9: Bottom up
The bottom disk is the one with the inlet holes. Start by welding your exhaust pipe (the schedule forty), to the center of the bottom disk. Similar to the pattern with lug nuts, work your way around the pipe in a star fashion with tack welds. This will prevent welds from pulling your pipe out of alignment. Once the exhaust is welded in place its time to add the down tubes. Make sure the tubes are facing in opposite directions.
Step 10: Spacer blocks
Take a measurement of the highest of your down tubes. Usually they are a little off and that is okay. Add a quarter inch to this measurement and cut three pieces from your 2x4 that length. These will be used to hold the top clear of the down tubes during welding. Mark the top of each block with an X.
Step 11: Add the top
Now things are starting to take shape. Arrange the blocks evenly around the bottom disk and make sure their tops are all facing up. Slide the lid on over the exhaust pipe and rest it on the blocks. There may have been some warping during the inlet cutting so I like to clamp the lid down against the block before I tack it in place. Just as you did with the bottom disk and the exhaust pipe, use the star pattern and work your way around tacking as you go.
Step 12: Sanity Check
We should be looking at the same thing. If you haven't done so already, connect the dots with all your spot welds. These welds will need to be (for the most part) air tight so keep that in mind as you work your way around. Its time to take out those spacer blocks too, make sure you have three blocks sitting aside.
Step 13: Outer wall
The outer wall is made from the 6" flat stock. Start by tacking the leading edge to the top and bottom donuts. The top should be flush and the bottom should have some 2" hanging below. Its important that the outer wall goes on and the top stays flush so be mindful when making those initial tacks.
Step 14: Work your way around
As you make progress around the lid tack it every 2". If there is warping you can use a clamp to get your lid in order. As you finish the outer wall use one or two compression straps to force the ring onto the lid.
Put some tools way.
Step 15: Trim the end
In the materials list it called for an 80" length of steel. That extra bit was nice for bending but now it is in the way. Mark the extra and trim it off using an angle grinder with a cutting wheel.
Step 16: Inner ring
The goal here is to make a groove that the barrel lip will fit in. The inner ring is made from the 3" flat stock. Since the outer wall is already in place you will need to pre-coil your inner ring. Its okay to be sloppy, the only important thing is that it fits inside the outer wall. Once in place, tack the ring just outside an inlet hole. The thickness of the 2x4 is kind of perfect for spacing so clamp the inner ring to your block and tack as you go. As you approach the end, you will have some leftover just as with the outer wall. Mark it and trim that too.
While we are here you can install the spark arrester to the underside of the lid.
Step 17: Inlet
The Walker Flex Hose is where this party starts. Cut one end of the hose to 45 degrees. The actual angle is steeper, but my saw tops out at 45. It's important to position this tube in the correct orientation to the down tubes. The correct position is inline with the down tube openings and just after a down tube. Hold your inlet against the lid and mark it. With a torch carve open the lid to make space for your inlet. The inlet will be stainless or galvanized. The fumes coming off this metal are not good for you and will compromise your weld if you aren't careful.
Call your Mom.
Step 18: Test it
Thats it! Wad up a piece of paper towel and put it in your barrel. Add the lid and put some air in there. You should see the paper towel swirling around. This is a good sign that your incinerator will work. The less turbulence in the barrel the better. If you pass the air test, you can add some fire. I tested mine with a small cardboard box, you can see it HERE.
For testing you can reverse a shop vac.
When you area ready to burn use the 3" dryer duct and attach it to your leaf blower. Start on low, you can turn it up later.
Step 19: Load Instructions
In order for your incinerator to work you need to load it properly. It will burn plastics and wet waste but it needs enough dry material to cut though the rough stuff.
Start slow and get a feel for what she can and can't do (do a few 1/2 burns).
Think of your loads as layers.
The top and bottom layers should always be cardboard or something easy to burn.
The next layer from the bottom can be something harder to burn like plastic or kitchen waste.
Then you need more cardboard.
Then another hard to burn layer.
In addition to this recipe, I like to throw a small piece of wood in with the hard to burn layers. A piece like the blocks you used to hold the lid during welding.
Icon: Pyramid by Benni from The Noun Project
Step 20: Burn Instructions
Before your start make sure you are good to go. Don't wonder, double check the gas tank for your generator or your leaf blower. If the air supply is cut during a burn cycle the barrel turns into a gasifier. This is a bit sketchy because when you start it up again all that available fuel ignites and sometimes lifts the lid off the barrel.
Place a fire extinguisher about 15' from your barrel.
Start the leaf blower and keep it on low.
Light a small fire on the top of the barrel.
Put the lid on and wait till you see the fire is going.
Turn the leaf blower to medium.
Enjoy the show.
When things get boring, about half way through, turn the blower to high.
When the barrel starts to smoke, you are done with this cycle.
Run the blower another 5-10 minutes and turn it off.
When cool, take the lid off and stir the ashes (this is surprisingly important).
Rinse and repeat.