Wood Pellet Mill

A wood pellet mill, sometimes referred to as a pellet press, is a type of mill that turns wood chips, sawdust, and other powdered raw materials (biomass) into pellets.

The way pellet mills work is the complete opposite of how grinding mills do. Wood pellet machines work by fusing smaller materials to form a single large mass, which is then cut into pellets. However, grinding mills take larger masses and break them down into smaller bits.

While convenient and effective, a wood pellet mill does not run automatically. Therefore, it requires a pellet mill operator, whose job is to make sure that the machine makes the right pellet size and that the pellet is of the highest quality.

Wood Pellet Millcan help farmers to ease the financial burden and increase their income. It can reduce the purchase of commercial coal and reduce cash expenditure by increasing the consumption of biomass energy of farmers. The collection and supply of biomass materials can create a large number of new jobs and bring direct benefits to farmers.

It improves the living quality of farmers and improves rural environmental conditions. The sulfur and ash content of biomass fuels are far lower than coal. The combustion temperature is also lower that it can be used to replace coal to reduce emissions of sulfur dioxide, nitrogen oxides and ash. The application of pellet mill can not only improve indoor hygiene of farmers, but also reduce ash storage and freight volume of the village.

Wood Pellet Millis conducive to ensuring the energy supply and improving the energy efficiency. The coal saved can be used in large capacity generating units or other purposes, which can ease the tight supply of coal, also avoid the waste caused by low using efficiency of coal in the countryside.

Wood Pellet Millcan reduce the emission of carbon dioxide and clean the atmosphere. During the biomass growth - combustion cycle, the net increase of carbon dioxide in atmospheric is zero.

Wood Pellet Millis conducive to sustainable development. Biomass energy is a renewable energy, and its sustainability is better than non-renewable energy sources such as oil, natural gas and coal.

Wood Pellets Production in Wood Pellet Plant
Because woody material’s density is higher than that of other common biomasses, wood pellet mill usually can make pellets from a wide range of biomass raw materials like agricultural residues. The pellets manufacturing process is determined by the raw material but usually includes the following steps: treatment of raw material, screening, grinding, drying, pelletizing, cooling, sifting, and packaging. How to make wood pellets? Below are the detailed steps of manufacturing wood pellets for large scale production.

Grinding Woody Raw Material
Before pelletizing, it is important to make sure that the woody material is dry and homogeneous. This process is also known as milling, crushing, pulverizing or comminution. In this grinding process, first of all, raw material should be filtered before grinding to remove materials like stone or metal. If the particle of raw material is too big, wood pellet’s quality decreases or even worse you cannot get wood pellets, as the particle’s size is too big to be pressed into the holes in the die. However, it should also be noticed that raw material can be ground too fine, causing the material to lose its ‘fibre’ nature and thus not bind in the pelleting stage. Therefore, a large wood hammer mill is necessary in the grinding process for pulverizing.

Drying Woody Raw Material
Rotary dryerRotary dryer is used to dry woody particles to guarantee that the moisture content is 8-10%. Drum driers are the most common type of equipment used in North America. In the past, natural gas was the most common fuel source. However, with a rise in fossil fuel costs, many producers have been switching to waste wood. In contrast to using natural gas, waste wood is cheaper and provides the opportunity to market environmental benefits associated with green house gas (GHG) emissions. These environmental benefits can be important when selling to markets with significant environmental regulations like the European market. Generally, wood fibre can be pelletized at moisture as high as 17%. However, the optimal level is 12% or less. Raw woody materials can also be too dry to pelletize, so you need to find the right balance between high and low moisture content.

Pelletizing to Make Wood Pellets
Commercial wood pellet millWood pelletizing machine, also known as wood pelletizer and wood pellet extruder. In wood pellet plant, ring die wood pellet maker is used to make wood pellets. The name ring die (also called rotary die) comes from the fact that the two (or more sometimes) rotary rollers push raw woody material from inside a ring die to the outside where it can be cut into the desired same length. Depending on the material being palletized, a delicate refining and balancing of settings is necessary. The most important adjustments are made by changing the die. A die is essentially a metal plate with holes in it. A die works by providing the appropriate amount of resistance as the press wheel attempts to push the raw material through the holes in the plate. The appropriate amount of resistance allows the raw material to heat up and soften so that it can be reshaped and compacted into the desired shape. (Notice: If a die provides too much resistance the material being palletized can become scorched. If too little resistance is provided, the raw material will not be compressed and simply pass through the holes.)

Wood Pellet Cooling
Wood pellet coolerCooling is critical to pellet’s strength and durability. As wood pellets leave pellet extruder, they are hot and soft. And these wood pellets are gradually air cooled, which allows the lignin to solidify and strengthen the pellets. In contrast to the drying process, cooling does not involve the addition of energy. Wood pellet cooler supplied by GEMCO is also reliable. This pellet cooling machine is counter flow designed and cools pellets rationally, and it can avoid the cracking or breaking of wood pellets. The wood pellet cooler includes 1200*1400 grid, has a dwell time of approximately 10-15 minutes, and has a rotary airlock installed on the top of the machine. Cool air flows from bottom to top, while the pellets drop from top to bottom, in this way, the pellets are cooled completely.

Sifting Wood Pellets
Wood pellet screenAfter cooling, wood pellets are passed over a wood vibrating screen to remove any fine material. These “fines” are augured back into the palletizing process to ensure that no raw material is wasted. Sifting, also called screening or sieving, ensures that the fuel source is clean and as near to dust free as possible. Once screened, wood pellets are ready to be packaged for the desired end use.

Wood Pellet Packaging
Wood pellet packaging machinePellets can be distributed in bulk form, by track, rail or ship or bagged in smaller quantities. If they are packed in bags, a wood pellet packaging machine is indispensable. Wood pellets do not degrade over time, as long as they are stored in dry conditions. Therefore, it’s better to pack them in bags that isolate moisture and air.

Grinding Before Using
Most roller and flat dies in pellet machine are processed by high-heat treatment. After planing, drilling, milling, and quenching process, there are usually many rags inside the die holes, which may influence the pelletizing effects and production. Therefore, before starting a new pellet machine, or after replacing a new die, you need to grind it thoroughly.

Pretreatment Of Raw Materials
The suitable moisture content of biomass materials should between 14% and 20%. Dry materials are hard to take shape, damp materials will make the pellets loose. The size of the raw materials should be less than the hole size of pellet mill dies. Generally, the hole size of the pellet mill die is 6mm and 8mm, and the size of raw materials should be under 5mm, or they may block the holes and reduce pellet production.
The adhesive force determines the forming rate of the pellets. Most biomass materials contain lignin, which would melt under high temperature and serve as binder. But some materials like rice husk has low adhesive force. It need to be mixed with sawdust or binders to make pellets.

The Thickness And Length Of The Wood Pellets
The thickness of wood pellets is determined by the hole size of the die. The length is determined by the slicer. In flat die pellet machine, the slicer is installed under the flat die, while in ring die pellet machine, the slicer is installed outside the ring die. Both of them can be adjusted to achieve different sizes. For your own use, it is better to be short. For transportation and selling, it recommend to be a little long.

Don’t Shut Down The Machine Right After Making Pellets
When you finished making pellets, don’t shut the pellet machine down at once. Add some mixed oil and biomass materials to the pellet machine and let it run for 1-2 min. In this way, we can fill the die holes with oil mixture, so that we can directly start making pellets the next time. With this process, we can not only maintain the mold, but also save time. When the pellet machine stops, loosen the adjusting screw and clear away the left materials.

The Maintenance Of Roller, Die, Shafts And Gearbox
You should eliminate all hard objects and metal blocks in raw materials before feeding them into the pellet machine, or they would cause damage to the roller, die or main shaft. You can install a tubular magnet on the feed hopper.
The heat inside the pelletizing chamber can reach up to 80℃, and the roller sustains high pressure during operation. As there is no dust protector in the pellet machine, so you need to clean up the bearing every 2-5 hours, and lubricate it with oil. After every 8 working hours, the main shaft need to be oiled. The gearbox need cleaning every half a year.

How To Replace Roller And Die
When the rollers wears out, you can replace the roller shell or the whole set of roller. If the bearing get loose or locked, you need to replace the bearing and even the shaft.
In ring die pellet machine, just loosen the hoop chuck, take the old ring die apart and replace it with a new one. If the ring die is fixed with screws, you need to shake the ring die gently, and remove the screw with even strength.
In flat die pellet machine, the flat die is installed with retaining nuts in the keyway. On the 2 sides of the flat die, there are two symmetrical screw holes. You can use the screw driver to push them out, or use a magnet to pull them out. During your pushing or pulling, keep the flat die vibrating with a hammer, so that the screw won’t stuck in the screw hole.

Protection Of The Drive Engine
Choose the matched power according to the required production. If the power is not enough, the production will be low and the pelletizing effect is poor. If the power is too large, it will consume more power, accelerate the weariness, and shorten the service life of roller and die.