Production of pellets
Pellets or fuel pellets, are renewable, environmentally friendly bio-fuel whose energy is converted into heat energy by burning. Raw materials for pellets are mainly wood-processing and agricultural waste, which previously fell into a garbage dump: sawdust and cod, straw, husk and stems of sunflower, corn, etc.
Stages of wood pellet production
The production of fuel pellets (pellets) is carried out in several stages, and the process is called pressing. Let's consider more each of the processes.
- Wood crushing.
In order to begin the production of pellets it is necessary to grind the prepared raw material by means of a crusher for further drying. At the first stage the wood is crushed to medium size which can be called large crushing.
- Drying of pellet semi-finished product.
Material drying is of particular importance. According to the technical regulations raw materials should not contain more than 12% moisture. The minimum moisture content is at least 8%.
- Repetitive grinding of wood for fuel pellets.
After drying it is necessary to crush the raw material again. This happens with the help of a hammer mill. At the outlet the wood particles should not exceed 4 mm in the case of industrial pellets and no more than 1.5 mm for first grade pellets.
- Water preparing.
Before this process the production of fuel pellets should be taken very seriously. This procedure serves to ensure that the particles are best compressed in the next step. Therefore, it is necessary that the humidity is 8-12%. After all, wood with a moisture content of less than 8% is poorly glued during pressing. To achieve the required raw material humidity there is used a dosing unit for water in a mixing vessel, usually screw mixers, which have built-in water inlets (for soft sorts of coniferous wood) or steam (in the case of pressed solid varieties of wood such as oak or beech, as well as low-quality or stale raw materials).
- Pressing the pellets.
When the mass is sufficiently moistened, the pressing process starts, which is the main stage in the production of fuel pellets. The presses can be of different design: a plane or a cylindrical matrix, an empty matrix or a matrix of a continuous type. Biomass under high pressure is extruded through the round holes of the matrix, particles of this biomass, due to the content of residues of lignin in the wood , are combined, forming a dense mass and turning into granules.
Wood pellets leaving the press are quite hot (70 ° -90 ° C) and soft. Therefore, they need to be cooled down - it helps the superfluous moisture to get out of the finished product and the granules then solidify and become ready for shipment.
- Sifting and packaging.
At the last stage, the production of wood fuel pellets is sifting and packaging. Sifting is necessary for the separation of unpressed, or scattered on sawdust, granules.
Production of heating pellets is non-waste. Therefore, the products left after sifting are recycled. Finished and packed wood pellets can be stored indefinitely for a long time, it is only necessary not to expose them to reallocation.