Wood pellets are widely used in the home stoves for biomass fuel and industrial boiler or power stations for commercial use. Wood pellets are made from a variety of raw materials sawdust, wood chips, wood shavings, small logs, even scraps of wood leftover from furniture and other manufacturing. So choose suitable pelletizing machines is very important. Here is the complete process of how are wood pellets made.
Step 1: Raw material collection and classification
To collect the raw materials is the first thing when we make wood pellets. Some of the raw material may be wood sawdust, wood chips, wood shavings, lumber mill scrap, and even complete trees. The raw materials may be freshly cut, maybe partially dry or even fully dried. But there is the same standard, The raw materials to produce wood pellet must be under the diameter of 5mm, the moisture content below 8% -12%, Different equipment processes different raw materials. By processing these raw materials in the different machines, the end product has a consistent burn characteristic, moisture content, heat value, and ash content.
Step 2: Remove the bark
The round wood in the factory is fed right into a rotating drum debarker, which rolls the logs against one another to dislodge the bark. and it is an open continuous discharge model. you can select loader or transfer platform side feeder, the logs are readied for chipping. While the bark is used as a fuel for dryer.
Step 3: Chip the wood
Choose disc chipper or drum chipper, Both can Chip the wood into pieces that are 1.5-2.5 cm or smaller. The chips are then delivered on a conveyor belt to the woodchip pile, where they await the next step in the manufacturing process.
Step 4: Crush into smaller size
Choose a hammer mill at the beginning of their milling process. These machines take wood chips and break them down into a consistent smaller size for 5mm, making drying and pressing through the pellet die quick and consistent.
Step 5: Drying the wood fiber
Choose the dryer. the raw materials must be dried. In order to produce high-quality wood pellets, the raw material must maintain the moisture content of 8% – 12%, so the raw material must be put into a dryer to reduce its moisture content. The most common dryer for large pellet plant is the rotary drum dryer, which is the most cost effective choice for large pellet plant. While the most common dryer for small pellet plant is the air flash dryer.
Step 6: Pelletlizer wood
Choose the ring die pellet mill or flat die pellet mill. The flat die pellet mill adopts vertical principle, the raw materials drop down by its own weight into the pelletizing chamber where they are compressed between the rollers and die to form pellets by going through the die holes. The basic pelleting principle of the ring die pellet mill is a simple operation where feed mass is distributed over the inner surface of a rotating, perforated die ahead of each roll, which compresses the feed mass and compresses it into the die holes to form pellets. The most common pellet machine for large wood pellet plant is the ring die pellet mill. While the most common dryer for small and home pellet plant is the flat die pellet mill, which is the most cost effective choice.
Step 7: Cooling the pellets
When the pellets come out of the pellet machine, they will be hot and moist. The temperature is 70°-80°，the moisture content is about 15%，then the pellets go into the Cooling machine, the pellets will be dried into under 10% and cooled into normal temperature. If you are making a small batch, spread them out on a flat area and allow them to cool and dry naturally for 12- 24 hours.
Step 8: The pellets are screened for quality
The pellets go into the screener machine, which is one equipment that using vibrating sifter surface to grade different sizes particles based on the particle size. After that the clean pellets are ready for package， at the same time, the powder will pass through the screener, you can take this part back to the Elevator for re-pelleting.
Step 9: Package the pellets
Choose the Package machine. The Packing Scale is for 10-25kg bags or ton bags. They are all automatic control of fast and slow intake, weighing and letting down of the bag.
Step 10: Storage
The newly formed pellets are then transported to large storage silos, and the packaged pellet bags are transported to a large warehouse. They are all waiting for a new journey.