There are a number of reasons why compressed biomass pellets made by pellet mills turn black. These reasons are outlined below:
The following is one of our biomass pellet plant located in Chile. The capacity of this pellet fuel production is 4.5~6 tones per hour. The main raw material of this plant is pine wood and eucalyptus wood. Feel free to contact us for more details of our successful large scale pelletizing projects.
Prior to feeding the raw biomass materials into the pellet mill, they ought to be crushed using a straw crushing machine. The resultant crushed material has to adhere to the size of the die holes through which they will be passed in the pellet mill. This means that they should be smaller than the hole, though not too small. If the crushed material is not just the right size, it will show in the quality of the oil produced (it will be poor quality). Of course, the size of this feedstock will depend on the factory that is making the oil.
The biomass feedstock, once crushed, should have some adhesive force about it. The adhesive ability is mainly based on the lignin content of biomass feedstock.
There are certain standards that the crushed biomass materials must adhere to in relation to their moisture content. Basically, just as with the size of the crushed material, it should be just right. Too wet or too dry will have a negative effect on the final output. Again, as with the previous point, the standards of moisture content for these crushed pellets depends on the factory to which they are taken for processing. Generally, the finished products should have a moisture content of less than 13 percent after drying. This is the standard for most biomass pellet mills.