In the biomass pelletizing industry, there is such a standard for determining high-quality biomass particles: the diameter error of biomass particles is less than 1MM, the particle water content is less than 10%, the particle density is more than 600 KG/M3, and the biomass particles maintain the highest mechanical durability of about 96.5%.
Only in the granulation process, sometimes the particles are loose, the particle molding rate is low, the length is different, or the particle is not pressed, and even affects the production efficiency of the pellet machine. What are the reasons that affect the quality and production efficiency of biomass granule? TONY and everyone carefully analyzed the main factors affecting the biomass particle mechanism:
1.Raw materials
Biomass particles are made of eucalyptus, birch, poplar, fruit, bamboo and crop straw, and their main components include cellulose, hemicellulose and lignin. The lignin content of biomass itself is high, and it can bond at a high temperature of 70-110 ° C, so the molding of biomass does not need to add any adhesive. The compression molding characteristics of different kinds of raw materials are very different. The type of raw materials not only affects the quality of molding, such as the density, strength, calorific value of biomass particles, but also affects the output and power consumption of biomass pellet machine. This explains why some are pressed into particles and some are more difficult.
2. Raw material particle size
Biomass pellet compression molding has two stages. In the first stage, at the initial stage of compression, lower pressure is transferred to the wood fiber particles, which changes the arrangement structure of the original loose solid particles, and reduces the porosity inside the biomass. In the second stage, when the pressure gradually increases, the large particles of biomass fiber break under the pressure, become smaller particles, and the formation of plastic flow, the particles begin to fill the void, the particles are more closely contacted and meshed with each other, and a part of the residual stress is stored in the forming block, so that the combination between the particles is more firm.
Under the same pressure, the finer the particle size of the raw material, the greater the deformation under pressure, the closer the bond of the molding, the greater the molding density. However, if it is too small, there will be too much powder, and the molding particles are short, so the particle size of the raw material should be controlled in order to ensure that the strength is small and the particle size is one-fourth of the diameter of the grinding tool, so that the biomass lignin can be fully released, and a large amount of powder can be ensured.
The particle size of the raw material also affects the efficiency of the biomass pellet machine and the quality of the molding material. When the raw material particle size is large, the biomass pellet machine will not be able to work effectively, the energy consumption is large, the output is small, the raw material particle size is not uniform, especially when the shape difference is large, the surface of the biomass particle will have cracks, and its density and strength are reduced. At the same time, it will also cause the wear of the biomass pellet press rod and the die to increase, increasing the loss cost.
3.Raw material moisture content
There is an appropriate amount of bound water and free water in the raw material, which have the effect of lubricant, can make the internal friction between the particles smaller, and increase the fluidity, so as to promote the particles to slide under the pressure and chimosis. However, the moisture content of raw materials is too high or too low can not be well formed.
When the moisture content is too low, such as less than 8%, the particles can not be fully extended, and the surrounding particles are not closely combined, so it is not easy to form; When the water content is too high, such as greater than 17%, although the particles can be fully extended in the direction perpendicular to the maximum principal stress, the particles can mesh, but because more water in the raw material is squeezed out and distributed between the particle layers, the particle layers can not be tightly bonded, and it is not easy to form. For biomass particles, the best moisture content of raw materials is about 15%, and the straw can be formed after natural drying, and the required pressure is also small.
4.Granulation temperature
As the temperature rises, the lignin of the raw material begins to soften and can act as a binder. The lignin softening point temperature under the condition of natural water rate is 80 ~ 130℃, when heated to 70-100℃, the adhesion of lignin begins to increase, and the temperature can be melted when it reaches 200 ~ 300℃.
In the actual particle production proces