How much moisture can be controlled in a pellet mill
As we all know, the pellet machine requires the moisture content of the raw material to be between 13-20, but why do we need this range of moisture content? I'm afraid you don't understand, right? You may only know that high moisture content of sawdust tends to clog the abrasive to produce pellets or the press stick to slip. You may know that low moisture content leads to more wood pellets, which leads to poor molding.
Pellet mills are physical compression devices where the moisture content of the wood chips is too low. At the fiber saturation point, only the water in the sawdust binds to the sawdust, and the bound water binds to the amorphous zones of the cell wall consisting of the fiber amorphous zones, hemicellulose, and lignin in the meristem. Although the particles in the perpendicular to the direction of the main stress, in the pressure, under the occurrence of arrangement, combination and deformation, but due to the friction sharply, the mobility of the particles is poor, the particles can not stretch well, resulting in particles can not be formed.
When the moisture content of wood chips is lower than 13 and higher than the fiber saturation point, the moisture in the wood chips is mainly free water and bound water. Under low free water conditions, the compressed sawdust cells are squeezed and deformed, and the intracellular conduits are easily compressed and thinned, increasing the resistance to transporting water. In addition, when the water content is too low, the diffusion ability is weakened, resulting in poor water flow, poor particle fluidity and poor molding effect. When the free water content is higher than 20, although the diffusion ability based on the concentration difference is enhanced and the particle fluidity is good, too much water is extruded between the particle layers in the direction parallel to the main stress, which makes the particle layers combine poorly and the molding is poor. Therefore, controlling the moisture content of wood chips within the right range is an important aspect of wood chip press molding. After talking about the moisture requirement of sawdust pellet mill, it is necessary to mention the influence of sawdust particle size on sawdust pellet molding.
The particle size of sawdust directly affects the quality of molded pellets, as well as production efficiency and power consumption. Generally speaking, raw materials with small particle size are easy to compress, and raw materials with large particle size are not easy to compress. The water resistance, moisture absorption and molding density of raw materials are closely related to the particle size of raw materials. In the same material of different particle size under low pressure, the larger the particle size, the slower the change in molding density, but when the pressure rises to a certain value, the difference is not obvious. The specific surface area of small particles is large, and the wood chips particles are easy to absorb moisture back; but on the contrary, due to the small particle size, the particles are easy to fill between the particles, the compressibility increases, the residual internal stress in the wood chips particles becomes smaller, the hydrophilicity of the molding block decreases, and the water resistance increases. Of course, there should be a small limit. If the particle size of sawdust is too small, it will reduce the ability to match the encapsulation between the sawdust, resulting in poor molding or reduced shatter resistance.
So the pellet machine generally requires the raw material particle size in the range of 1-5mm, when the sawdust particle size is larger than 5MM, it is necessary to increase the friction between the sawdust and the abrasive tool, increase the extrusion friction of the pellet machine, and waste the energy.
