MIDGE biomass stoves are usually made from discarded tin cans. These stoves will burn a variety of small biomass pieces. Tin cans are readily available and are easy to work with. They are also mostly pre-shaped for the units. But the stoves can be readily constructed from a variety of materials. Tins cans are called tincaniun in the world of scavengers. The two burners I currently use have been in service for somewhere around two years now. They are still in good shape. Here is a picture of one of them. The rust is due to the fact that I had to set the stove with the burners out in the rain for a period of time while I did some kitchen work.
Notice that the outside of the unit shows no heat damage. Even the paper residue from the label is still intact. The glue does not even melt! So the outside of these stoves are relatively cool, although I wouldn't want to move one with my bare hands during a full burn.
Here are instructions to make your own MIDGE stove as I currently make them.
Tools :
Side cutting can opener, the type that cuts the outside rim. This leaves the top intact to use as a lid.
Top cutting can opener, the usual kind.
Tin snips.
Can punch, the type that makes triangular holes in cans, like for condensed milk.
Square nose pliers.
Old leather punch, set to 1/4" hole. This may mess up the punch, so don't use a brand new one unless you don't care. Or a 1/4 inch drill.
Eight penny nail.
Hammer.
Small nailset, for enlarging holes.
Tape measure.
Small wood chisel.
Piece of 2X4 lumber, 10 in to 2 feet long.
Medium point magic marker or other marking device.
Pop rivet set. (optional)
Here is a picture of the tools, except for the leather punch. It seems to have evaporated.
Materials:
Two no. 10 tin cans (the big coffee cans, the same style on both).
High heat JB Weld. (optional)
One fruit juice can, the family size one.
One one pound food can, any standard shape will work.
Either asbestos free vermiculite or garden pumice.
A wire coat hanger
A six inch square of 1/4 inch hardware mesh.
Two inch wide aluminum tape.
Step One:
Cut the top off one no. 10 can using the SIDE cutter can opener. Cut the top out of the SECOND can using the TOP cutter can opener. Cut the top out of the fruit juice can using the SIDE cutter. Cut the top out of the one pound can using the SIDE cutter. The results should look like this. Do something else with the body of the second can and the one pound can lid, but save the lid you cut out with the TOP cutter.
Step Two:
Place the fruit juice can on top of the no. 10 lid that was side cut, in the exact middle, like this. Use the uncut end of the can to get better accuracy. Mark around the can on the lid to get a cut line. Do the same thing with the lid that was top cut. Do the same thing with the fruit juice lid and the one pound can, like this. Then mark a line 3/8 in from the mark on the fruit juice can lid. Place the no. 10 lids on the side of the 2X4, like this, and cut closely with the chisel to the line on both lids. This picture shows the lids cut , with the SIDE cut lid taped on the juice can. The lids should be able to slip over the ends of the juice can but be a fairly tight fit. With the chisel, cut to the inner line on the fruit juice lid. This lid needs to fit INSIDE the one pound can. Next, cut a series of radial lines going outward from the hole in the juice lid. Bend the metal tabs just created down, so they fit snugly into the top of the one pound can, like this .
Step three:
Using the eight penny nail and the hammer, punch a series of concentric holes in the bottom of the one pound can. There should be a lot of them, as this supplies the primary combustion air. The can should look like this . Next, using the leather punch or set to 1/4 inch or a 1/4 inch drill bit, drill holes around the top of the one pound can. It should look like this. Make sure the holes are just below the lip of the lid, as air has to enter these holes.
Step four:
Using the can punch, punch ten evenly spaced holes in the side of the first no. 10 can, at the very bottom. This is the can you opened with the SIDE cutter. Using the can punch, punch six evenly spaced holes around the side of the fruit juice can at the bottom. They should look like this.
Step 5:
Tape the SIDE cut lid to the juice can with aluminum tape, just above the triangular punch holes. The punch holes will allow combustion air to flow through the unit. The juice can with the SIDE cut lid is shown here. It is upside down to show the punch holes better. Next, set the juice can inside the no. 10 can, like this. It should center itself and be fairly tight if all was done correctly. To get a much stronger unit, you can pop rivet the two cans together on the bottom.
Step 6:
Using the vermiculite, fill the space between the no. 10 can and the fruit juice can, like this. Make sure that the space is filled completely. This is the insulation for the unit. Clean the rim of the no. 10 can and the no. 10 lid. Place the no. 10 lid over the juice can and onto the top of the no. 10 can, like this. Either tape the lid on with the aluminum tape or glue it on with the JB Weld. In this picture, the lid is glued on with JB Weld and temporarily taped together until the glue cures. The body of the stove is now finished.
Step 7:
Using some 1/4 inch hardware cloth and a coat hanger, make a stand like this. The stand must fit snugly inside the juice can, like this. Make the legs of the stand just long enough that the one pound can will be barely touching the lid of the juice can when the lid is on, like this. Put the one pound can in and set the lid on, like this. You are finished making the stove now.
Operating the stove
To operate the stove, fill the inside can, called the burner, with twigs, wood pellets, wood chips, dried rabbit poo or dried lama poo or any other of a number of dry, small biomass pieces. Many things will burn in these units. Wood pellets burn the best because they have been compacted and are uniform and dense. Put a little, maybe a tablespoon, of kerosene or lamp oil on top of the fuel. DO NOT USE GASOLINE OR CIGARETTE LIGHTER FLUID! OR CHARCOAL LIGHTER FLUID! They are too volatile. Charcoal lighter fluid burns too fast and will not light the fuel. Cigarette lighter fluid or any type of gasoline will cause an explosion! Use only lamp oil or kerosene. You only need a little bit. Do not put so much in that it pools in the bottom. Drop in a very small piece of paper towel and set fire to the paper towel. Move the burning paper around until the whole top is lit. The stove will begin to burn and the flame will grow steady. Soon, you will see fire coming out of the little holes at the top of the burner. The stove is now in full burn. If the flame just flickers and does not grow and if it seems stunted or there is smoke, dump the fuel into a metal container, OUTDOORS, as there is likely to be smoke. Use the nailset to enlarge the holes in the bottom of the burner. It should look like a screen. Then start over with fresh fuel.
Here is a short video of the stove operating. Notice there is no smoke. The stove burns the smoke as fuel. This video shows the stove just under full burn. You can hear a frying noise on the video. That is not the stove. The stove is essentially silent in operation. The flames are about twenty percent larger at full burn. I just fried an egg on this brand new stove and it worked as well as an electric or gas stove. I filled the burner with wood pellets to just below the secondary air holes. The stove burned at full burn from 7:35 a.m. to 8:45 a.m. for a continious burn of one hour and ten minutes. I then snuffed the charcoal by pulling the burner out with pliers and setting it in a metal can with a lid. This saved the charcoal, which can be used in the hibachi outside for grilling.
There are a few drawbacks to these stoves. They are much the same as a campfire. There is some sooting on pans, especially when heating cold water. This is a batch process. When the fuel is gone, you have to reload and start over. They only burn on high, one setting. You need flame spreaders and distance to regulate cooking heat, just like any wood fire. They do not do well in high winds. The wind blows out the flame. They are easy to relight, but in the meantime there is plenty of smoke. But they do burn free fuel!
There are many alterations you can do to the burners to get different effects. The three parameters are: 1. Width of the burner controls the size of the fire. 2. Height of the burner controls the length of the burn. 3. Amount of air supply controls the height of the flame and how vigorously it burns. Don't expect instant gratification with these units. They do have a learning curve, but they are very effective and they run on a wide variety of wood fuels. The fuels for these stoves can be gathered by hand wherever there is brush or trees.
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