Making wood pellet is easy or hard? Many people buy wood pellet mill in china or use their own pellet mill to make the pellets, but the quality of many wood pellet mills is not very good in most cases. And the quality of wood pellets is not good, such as can not form, too robust and loose cracking, more powder, low output, etc.
So what is the key？How to make wood pellets? There are several factors that you need to know when you are making wood pellets.
1. The primary thing is the type and quantity of the material.
- If the material size is under 5 mm and the moisture is about 16%, it can be used for making pellets. The material is sawdust and wood powder, etc.
- If the material size is larger than 5mm, it needs to be crushed. The material is Logs, branches, woodblocks, etc.
- If the moisture is higher than 16%, it needs to be dried.
- If the material is crop straw, alfalfa, rice husk, peanut shell, grass, these materials can be used for making pellets, but it is called straw pellets, not wood pellets.
- If the raw material is mildewed and the colour turns black, the cellulose in the sawdust is decomposed by microorganisms，and the material can not be pressed into qualified wood pellets. If you want to use it, it is recommended to add more than 50% fresh wood chips to mix, otherwise it can not be pressed into qualified pellets.
2. Choosing the wood pellet mill
According to the type and quantity of raw materials, you can decide which types of pellet mill be used.
The flat die pellet mill is used at home, and wood pellets can be used as a home heating fuel. There are two types of flat die pellet mill, electric motor flat die pellet mill and diesel engine flat die pellet mill.
The ring die pellet mill is used in the factory. There are two types of ring die pellet mill, gearbox transmission pellet mill and belt transmission pellet mill. The output capability of the flat die pellet mill ranges from around 100 to 700 kg/h at most. While the ring die pellet mill can produce around 600-2000kg/h.
3. The pellet mill die material
The most important thing is choosing and maintenance of pellet mill die. The die is the most important part when we make the wood pellet, and it decides if we could make good quality wood pellets.
The material of pellet mill die should be made of the alloy structure steel or stainless steel ring mold. The user can choose the die according to the corrosion of the raw particle material.
After carburizing and quenching treatment, the hardness is 55-60HRC, The working life of a flat die is 300-500 hours. When one side has worn out, the die can be used with the other side. The output of the ring die is 5000-8000 ton，it should be repaired with the die repair machine in the factory.
4. The compression ratio of pellet mill die
i=d/L
T=L+M
M is the depth of the reduced hole
The Compression ratio (i) is the ratio of die hole diameter (d) and effective length (L) of the die.
According to the different raw materials, The user can choose the compression ratio of the die and adjusts the specific compression ratio, and the ratio is 8-15.
5. The shape of die hole
There are six Shapes of die hole，you need to choose the right and high-efficiency shape according to the nature of the material.
6. The opening rate of die
The opening rate of the pellet mill die is the ratio of the total area of the die hole to the effective total area of the die. In general, the higher the opening rate of the die, the higher the particle yield. If the die has enough strength, the opening rate of the ring die can be improved as far as possible.
7. Matching between pellet mill die and roller
It is the most important technology to improve the efficiency of granulation and prolong the life of the die. New ring die should be with new pressure roller, avoid excessive use of pressure roller.
According to the characteristics of materials and pellet mill, we choose different forms of the pressure roller, in order to achieve the best extrusion efficiency between the die and roller.
8. Gap adjustment between pellet mill die and roller
The key of gap fit is stability. Whether the working gap between die and roller is reasonable or not, it has an important influence on the correct use of die. Generally speaking, the gap between the die and the pressure roller is 0.1-0.3 mm.
From the practical experience, it is better to press the roller to reach the state of “like turning non-rotating” while rotating the ring die by hand. If the gap is not stable, you must adjust it.
If the gap between the ring die and the roller is too large, the material will slip between the roller and the die. If the gap between the die and the roller is too small, the roller is too small, and it will lead to increased wear of the ring die and roller.
In the beginning, the gap between the die and the roller is adjusted s mall .when the granulation is just finished, the gap is adjusted as much as possible during standard granulation, which is beneficial to improve the wood pellets quality.
Besides, when adjusting the gap between die and roller, we should pay attention to the direction of the roller, the adjustment direction of the pressure roll should be opposite to the steering of the die.
9. Control feeding speed, control feeding position, control material layer distribution.
10. Prevent metal or hetero-hard material from entering between wood pellet mill dies and rollers
When a metal or other hard object enters between a die and a pressing roller, the ring die and the pressing roller is easily damaged, so the material should be cleaned up before making wood pellets.
It is necessary to clean up to avoid the material mixed with large pieces of sand, sand, iron, bolts and iron chips and other hard particles. If not cleaned, the inclusion of different hard material accelerated the wear of the die, resulting in the die multiple forces. When the force exceeds the strength limit of the die, the die will appear blind hole too much, rupture phenomenon.