Homemade Pellets Using a Mill
There are certain specifications recommended by EEC and US Government/State Departments for the production of wood pellets, the main ones are as follows:
- Size: 4mm x 20mm.
- Ash content: between 1% and 6%.
- Density: >600kg/m.
- Calorific Value: >4.7kWh/kg.
- Moisture Content: <10%.
- Chlorine Content :< 800ppm.
- Sulfur Content: <300ppm.
There are several makes of machines available in Europe and the US powered by electricity, that can produce the pellets to the recommended specifications. These mills are designed to fit into most garages or basements, where the wood pellet stove is normally located. The optimum material to use in these machines is ordinary sawdust.
The sawdust can usually be obtained free from most sawmills, wood-working factories or tree-felling projects. These industries will be glad to get rid of it, as long as you load it into bags or a trailer and remove it yourself. There is a listing of sawdust suppliers in the US included in the reference section.
Some people also saw up logs and old pieces of wood to make their own sawdust for the pellet mills as well.
Provided it has not been subjected to wet weather, the sawdust requires no further treatment; except for the addition of a little vegetable oil during processing to bind and moisten if it is too dry.
There are two types of pellet mills suitable for producing homemade pellets. These include the flat die and the ring die mills.
Flat Die Pellet Mill
This was developed in the early1900’s to produce pelletized animal feed, with many farmers still using them for this purpose. A lot of these mills are mass produced in China being cheap and simple to manufacture. However, some makes allegedly lack pellet quality and control of the finished sizes, along with a tendency to wear between the rollers and die plate. Nonetheless, they are still the most popular type of mill used to produce homemade wood pellets, and are also manufactured by numerous European and American companies..
The sawdust is loaded into a hopper located on the top of the mill. From here it is gravity-fed into the mill, falling down to lie on top of the die plate.
The plate is a flat, circular shape about ½" thick incorporating the pellet dies in a circular pattern.
Two rollers (shaped like a dumbbell) revolve around and on top of the die plate. The clearance between the rollers and die plate is small; and being critical, is set at the makers before dispatch. (A sketch is shown below of the flat plate and roller components.)
The rotating rollers compress the sawdust, ramming it into the dies that extrude the produced pellets. These fall through a discharge chute into a container placed underneath. The pellets are quite hot due to the compressing process, so must be handled carefully and allowed to cool before handling.
A sketch of the operating mechanism of typical flat die pellet mill is shown below along with an image of a Pelheat Pellet Mill. (Please click on images to enlarge.)
Flat Die Pellet Mill Image courtesy of www.pelheat.com
Ring Die Pellet Mill
The ring die pellet mill is a modified design of the flat die mill being produced since the early1950’s. Although more expensive to buy, it can produce a more uniform and finished quality product than the flat die model.
In the ring die pellet mill, the sawdust is fed from the integrated supply hopper into an internal rotating drum that has numerous pellet dies incorporated in its surface. A distributer arm guides the sawdust to the circumference of the drum where rollers compress and squeeze the sawdust into the dies. Several paring knives cut the pellets to size as they are extruded from the drum; after which they fall through the bottom discharge chute into a container ready for use.
A sketch of a typical ring die pellet mill's operation along with an image of a Pelheat Ring Die Pellet Mill (cost is $7,995) are shown below. (Please click on image to enlarge.)
Image courtesy of www.PelHeat.com