1、Type of Raw Materials
Different kinds of raw materials, its pelletizing process are quite different, among the large quantity agricultural and forestry waste, some are much easier to shape into pellets after crushing, but some are quite difficult. The type of raw materials will affect the quality of pellets forming, such as the density, strength, calorific value of wood pellets, etc., and also has a certain impact on the output and power consumption of wood pellet machine https://www.zenopelletmachine.com/product/wood-pellet-machine/ .

2、Raw Material Size
The raw material particle size is also an important factor affecting the pellet forming. Generally speaking, the finer the size of raw materials, the higher pellets strength will be, but it is not suitable for adjusting humidity and easy to agglomerate bonding. And also if the crushed raw materials too fine, this will result in high energy consumption of crushing.

If raw material particle size is too coarse, this will increase the wear and tear of the die and pressure roller, pellets forming much more difficult, especially for the small diameter die, this will cause the material softening paste effect poor and result in high material consumption, low yield, the output of final pellets will also contain high powder rate.

The following are the results of the different size materials pellets forming based on our test, we are taking the corn straw as material, with most suitable ring die compression ratio, most suitable moisture content and final pellets diameter 8mm, please check the final result below :

Particle Size Range(mm) Density(ton / m3)
0~1 1.13
1~5 1.25
5~10 1.01
>10 0.79

3、Moisture Content of Raw Materials
When the moisture content of raw materials too low, the friction between raw materials will limit the sliding and extension, so the combination of raw materials is not close enough, pellets forming will not firm or even difficult to shape; when the moisture content of raw materials too high, although the flow of raw material particles is good, can be fully extended, and mutual engagement, but the excess water will be extruded from the raw materials, distributed between the raw materials, raw materials between the particles will difficult to closely fit, will also cause forming is not firm, or even difficult to shape.

The humidity required to produce pellets is different for different raw materials, subject to temperature and other factors, most of the raw material humidity required is 8% to 15%, but there are some special materials need higher humidity, such as teak wood need even up to 50%, etc., It’s better to pre-test them before making pellets because this will affect the final pellets quality. For excessive humidity of the raw materials must be processed to reduce moisture before pelletizing, usually through the drying process.

4. Forming Pressure
Forming pressure is the most basic condition of material pellets forming. Only with sufficient pressure, the raw material can be compressed into pellets. However, the pressing pressure is closely related to the shape and size of the ring die. If ring die compression ratio is too small, the effective length of the die hole is short, the material in the ring die hole pressing pressure is small, they will be easily to squeeze out the ring die, although the yield is high but the final pellets will be loose and the appearance is not smooth;

If ring die compression ratio is too large, the effective length of the die hole is long, the greater the pressure of the material in the die hole, the final pellets density is higher, the pellets is smooth and good quality, however the output of the pellet mill will be reduced and the cost of the pelletizing will be increased accordingly. The following is the corn stalk pelletizing result with different ring die compression ratio for your reference :

Compression Ratio
Density(ton / m3)
Production Capacity(kgs/h)
Power Consumption(kw*h/t)
3.5 0.91 500 64
4 1.05 780 46.21
4.5 1.21 900 46.78
5 1.23 800 54.23
5.5 1.22 650 71.32

Conclusion
In the actual biomass pellets production process, the nature of raw materials, pre-treatment methods, equipment parameters, etc. are interacting with each other, so it is also necessary to consider the unit energy consumption, production rate, maintenance and production cost, etc., Combine them with actual statistics to come up with the most ideal pelletizing procedure in wood pellet production line https://www.zenopelletmachine.com/product/wood-pellet-production-line/, then you can produce the best strength and durability biomass pellet fuel.