The wood pellet machine produces a large amount of granular powder, which adheres to the particles, affecting their appearance and also wasting the production efficiency of the equipment. To solve this problem, it is necessary to start by understanding the forming principle of the wood pellet machine.

The forming principle of the wood pellet machine is to prevent the material from rebounding to its original shape, maintaining a certain shape and strength. The compression process does not require the addition of any adhesives and belongs to the physical forming of fiber materials. From the composition of biomass such as straw and wood chips, it is mainly composed of cellulose, hemicellulose, lignin, resin, wax and other components. Among the various components that make up biomass, lignin is generally regarded as the inherent and best intrinsic adhesive in living organisms. At room temperature, the main part of the original lignin is insoluble in any organic solvent, but lignin is an amorphous substance with no melting point but a softening point. When the temperature reaches around 70℃ to 110℃, it softens and the adhesive force begins to increase. At this point, applying a certain pressure externally can make it closely bond with cellulose, hemicellulose, etc., and at the same time glue together with adjacent biomass pellets.

I. Raw Materials

From the perspective of the pelletizing principle, you should have understood that the first reason to be considered for the excessive amount of powder in the wood pellet machine is the raw material. After cooling and temperature reduction, the strength of the formed fuel increases, and thus biomass solid formed fuel in the form of rods, blocks or pellets with combustion performance similar to that of wood can be obtained. The particle size of the crushed raw materials determines the surface area of the material composition. The finer the particle size, the larger the surface area, and the faster the material absorbs moisture from the steam, which is conducive to the conditioning of the material and also makes granulation and shaping easier. From the perspective of granulation, fine crushing leads to high granulation strength, but it requires a lot of steam. If not handled carefully, it is easy to clog the machine. Moreover, if the raw materials are crushed too finely, it will result in excessive power consumption for crushing. If the particle size is too coarse, it will increase the wear of the ring die and the press roller, making granulation and forming difficult, especially for small-pore ring die forming, which is even more challenging. It will also lead to poor gelatinization effect of the material, resulting in high material consumption, low output and high powder content of the particles. Therefore, it is advisable to use a 0.6-0.8 sieve plate for crushing. This not only avoids the drawback of overly fine particle size but also ensures the particle size of the material, which is conducive to reducing the powder content of the particles. In addition, attention should be paid to the uniformity of the mixture before granulation to lay a good foundation for the subsequent granulation process.

The above has solved the problem of raw material particle size. Another important issue is the moisture content of the raw material. The moisture content for granulation must be between 13% and 20%, which is the most ideal moisture content for granulation. When the moisture content exceeds 20%, the material is prone to slipping between the inner wall of the ring die and the press roller, and even the granulated material cannot be pressed out, reducing the granulation output. When the moisture content is lower than 12%, the material will rub against the machine intensely, reducing the granulation output, and a large amount of unformed powder will be mixed in the granules.

2.if the issue of raw material particle size has been resolved but there is still an excessive amount of powder, then the compression ratio of the mold needs to be taken into consideration.

The compression ratio of the grinding tools in a wood pellet machine is determined based on the raw materials. Let's take a few simple examples of wood. The compression ratio of poplar wood is 1:6, that of pine wood is 1:7, that of hard miscellaneous wood is 1:5, and that of wood shavings is 1. 5.5. The compression ratio of corn stalks is 1:8. Judging from these simple figures, the compression ratios of different raw materials vary. The harder the raw material, the smaller the compression ratio; the fluffier the raw material, the larger the compression ratio. That is to say, the fluffier the raw material, the easier it is to be pressed into shape. The fluffier the raw material, the more fibers it contains, and materials with more fibers are easier to shape. So let's talk about the compression ratio of poplar wood, which is 1:6. What do the 1 and 6 in the number represent respectively? Each small hole of the ring die granulator has diameters of 6mm, 8mm, and 10mm. Here, the 1 represents the diameter of each small hole. If the diameter of the ring die hole is 8mm, then this 1 represents 8, and 6 represents the effective hole diameter. The effective hole diameter is equal to the diameter of the hole multiplied by the effective hole diameter length, that is, 6*8=48. That is 8:48.8:48 is simplified to 1:6, and 1:6 is the compression ratio of poplar wood. This is how it is converted. The quality of the output of the wood pellet machine depends on the compression ratio of the ring die. However, if the customer does not have a high requirement for the forming rate of the wood pellets you produce, you can appropriately reduce the compression ratio. This way, you can increase the output. It can also reduce the service life of the mold and the pressure wheel. If the compression ratio is too small, it is also a factor causing excessive powder content in wood chips.