To establish a small production of pellets at home for the purpose of economical heating of your own home is not an easy task, but to solve it is quite realistic. This is especially interesting for those owners of country houses who have the opportunity to receive raw materials for such production at a low price or even free of charge. Hence the purpose of this article is to tell you how pellets are made according to technology and what equipment you need to make fuel pellets with your own hands.
What and how pellets are made of
The attractiveness of fuel pellets as fuel for domestic boilers is primarily due to ease of use. Pellet boilers are highly automated and require much less attention than conventional solid fuel boilers. As for the calorific value, for dry firewood (15% moisture) and pellets (8%) it differs by 20–25%, although the latter occupy a much smaller volume.
For reference. To achieve a moisture content of 15%, wood must dry under normal conditions for at least 2 years. Then its calorific value will reach 4–4.5 kW / kg, while 1 kg of granules (wood) during combustion emits from 4.5 to 5 kW of heat.
In industrial production, pellets are usually made from these types of raw materials:
- any waste wood, including sawdust and wood chips;
- cereal straw;
- waste processing of sunflower seeds and buckwheat (husk).
The most common fuel pellets made from sawdust and other woodworking waste. Agropellets made from husks and straw are cheaper than wood, but their quality is worse due to the increased ash content. So for home craftsmen the most interesting is the manufacture of pellets from sawdust.
The technology for the industrial production of wood pellets consists of 5 main operations:
- Crushing and grinding. Waste is reduced to particles of the same size using industrial crushers.
- Drying to a moisture content of not higher than 10%. There are several types of dryers, but they are united by one circumstance: to evaporate moisture from a tree, it is necessary to expend thermal energy.
- Steam processing for better granule formation. Humidity increases slightly.
- Pressing sawdust into pellets on a special press - granulator under a pressure of about 300 Bar.
- Cooling and packaging of finished products.
In factory conditions, where high-performance equipment is needed, the most commonly used pellet press is a cylindrical matrix. It is a perforated ring made of thick sheet metal, on the inner surface of which several rollers walk. The raw materials are fed to them with the help of a screw, after which the sawdust is pressed by rollers into the holes of the matrix. The “sausages” coming out from the outside are cut to size with a special knife.
There is also a flat type of matrix used in pellet granulators for lower productivity. This is a sheet of metal with a thickness of at least 20 mm round in shape with many holes. In such a sawdust press, the rollers are on top and press through the holes of the matrix the raw materials coming from the hopper. Such machines can have small dimensions, and therefore are well suited for the manufacture of pellets at home with their own hands.
For reference. The adhesive that binds the sawdust together in the press is lignin. It is released from small particles of wood when exposed to high pressure.
Equipment for the production of pellets
The main role in the technological process is played by the machine for the production of pellets, which is also the most difficult to manufacture.Completely making a granulator with your own hands will not work, because for the manufacture of the matrix and rollers you need metalworking machines - turning, milling, drilling and grinding. So there are 2 options: buy a ready-made matrix pair - rollers or order it from the masters.
Tip. To make a machine for home-made pellets based on purchased parts is a risky decision. You cannot check the quality of the material and the accuracy of processing, and the matrix can quickly fail. It is better to find the necessary material and give an order to specialists - machine tools.
Matrix pair on a pellet press should be made of high-carbon steel St45 or St50, and even better manganese alloyed HVG or 65G. Moreover, after processing the parts must necessarily go through the hardening process in order to achieve a hardness of 58-60 units. To make a matrix on a granulator, it is necessary to withstand all the sizes indicated on the diagram:
On the shaft for rollers, you can use simpler steel - St3, 10 or 20, and it does not need to be hardened. But the working parts of the rolls must be made from the above grades with subsequent hardening, and then put them on the shaft through the bearings, as shown below in the photo.
Important. Hardened parts for the pellet press must go through the grinding process of all work surfaces.
Note. In this design, a do-it-yourself pellet press, the shaft rotates the matrix, and the rollers remain stationary. Pulleys must be selected so that its rotation speed is not more than 250 rpm.
Homemade crusher
It is good when it is possible to get good small wood waste from some production for pellet pressing. If in these wastes there are small branches or slabs, then for their grinding additional equipment will be needed - a crusher. There are many home-made designs, but most of them cut wood into too large chips, from which it is impossible to produce pellets at home.
Your attention is invited to a simple wood waste crusher made of 3 dozen circular saws for a circular saw with carbide brazing. All saws are mounted on one shaft so that between the teeth of each subsequent one they are slightly offset relative to the previous one. A pulley and 2 bearings are placed on the same shaft along the edges, after which the whole structure is fixed to the frame from corners or pipes.
Note. A powerful engine is also needed here, so that the saws can gnaw branches and other small pieces of wood well.
As you know, the unit’s productivity is low, but such a wood waste crusher will make it possible to obtain sawdust suitable for pellet production. If you have a circular saw on the farm, then the chopper can be adapted to its bed, as is done in the photo:
Sawdust dryer
So that wood pellets made by yourself do not crumble at the exit from the granulator matrix, it is necessary to ensure the minimum moisture content of the raw materials. In industry, this occurs in various drying chambers. At home, the master craftsmen adapted to assemble dryers for drum-type sawdust, since their design is the simplest, as shown in the diagram:
Several iron barrels, welded one on the other, are mounted on the frame with a slight tilt to one side. From the inside, blades are welded to the walls of the barrels to mix the raw materials. On the one hand, hot air is supplied inside such an impromptu drum by a gas or electric heat gun. The rotation of the drum is made by an electric motor through a gearbox or a lower belt drive.
For reference. When pellets are made from fresh woodworking waste, the largest energy consumption is accounted for by the drying process. For home production, they can be too large, negating all the benefits of this venture.
What else can be done from sawdust
When wet woodworking wastes cannot be dried for various reasons, then pellets cannot be compressed from them. But it’s quite possible to establish handicraft production of briquettes, although you should not rely on great productivity. Raw sawdust is mixed with water and some kind of astringent (for example, clay or wallpaper glue) and then they form briquettes from them.
True, here, too, you need at least a manual press, and preferably a hydraulic press. Examples of designs of such machines are presented in the photo:
Real factory briquettes, like pellets, are firmly glued together by lignin under high pressure, but this is impossible to achieve at home. That's why the adhesive is added to the mixture, and the density of the products is low, as is the specific heat of combustion. After pressing and drying on the street, light “bricks” are obtained, which burn out in the furnace quite quickly.
Findings
To organize the production of pellets from sawdust at home makes sense in two cases:
- When all equipment is manufactured independently with minimal costs for parts and accessories.
- If you bought a small granulator, whose capacity is enough to produce pellets for your own needs and no less - for sale, in order to recoup the purchased equipment.