Why the colors of pellet compressed by the wood pellet mill become black?

What’s the reason that the color of the pellet becomes black after compression? According to many years experience, we sum up the reasons below: 

 

1.Blacking by the carbonization 

The raw material like sawdust saw powder has risen to 190-200 degree when go through the ring die of wood pellet mill. So they become black when pass by the die holes due to the carbonization. In this case, the blacking of pellet not only affects the quality of pellet fuel, but also increases the thermal value of pellet fuel. The horizontal type ring die pellet mill usually generates the above situation. 

 

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2.The feedstock is too dry 

The same kind of feedstock has different result of pellet fuel after compression due to the different moisture content. For example, the moister content which is higher than 25% can not form; when the moisture content is between 20-25%, it may produce a large amount of vapor during the compression of pellet fuel. The pellet fuel surface has many fractures with low density, which belongs to low quality product; when the moister is between 15-20%, the pellet fuel surface has elegant luster with length longer than 5cm, high hardness and high thermal value, which belongs to high quality pellet fuel. It is very popular among the clients; when the moisture content is 10-15, the pellet fuel is short with low density, which is easy to become black sometimes. At this time, the pellet fuel has bad outlook and low quality.

3.Enzyme change of the raw material 

The feedstock has went through the enzyme change after many year’s wind and rain, so the compressed pellet become black certainly. Under this condition, the pellet has good luster with less fractures at the surface, but the thermal value become low due to the enzyme change. This kind of pellet is not approved by the clients.  

 

How to make the good quality pellet fuel by the pellet mill? we have summed up several conditions required by the pelletizing process.

a.the requirement of feedstock size after crushing

Before entering into the pellet mill, the raw material must be crushed by the straw crushing machine. The size of the crushed material based on the diameter of pellet and size of die holes of pellet mill. Too big or too small can greatly affect the production, or even the material are not discharged. Each factory has different requirement to the size of the crushed material. It is necessary to consult the question before purchasing. 

b. the feedstock must have the stickiness ability.
If it has no stickiness, the product compressed by the pellet mill are deformed or are very loose, which are easy to crush during transportation. 
 

c. Strict standard of moisture content of feedstock

When entering into the pellet mill, the moisture content of crushed material should keep in a certain scope. If it is too dry, it can not form. If it is too wet, it is easy to loose, which can both affect the output of pellet. For each factory, it has its own adaptability of moisture content, but the moisture content of finished products should be kept below 13%. For pellet mill, The standard that the pellet has no enzyme change after compressing is 13%.

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