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How are wood pellets made?
Wood pellets are made through a manufacturing process that involves compressing dry wood fibers, typically sawdust or wood shavings, into small cylindrical pellets. This process not only utilizes wood waste and byproducts but also creates a highly efficient and compact fuel source for various heating and energy applications. In Canada, most pellet mills use exclusively sawmill residues. Here’s a step-by-step overview of how wood pellets are made:
- Raw Material Selection: The first step in wood pellet production is selecting the raw materials. Sawdust, wood shavings, wood chips, and even logging residues can be used. The quality and type of wood can influence the final pellet’s characteristics.
- Drying: The raw material must be properly dried to reduce its moisture content. Moisture content in the range of 10-20% is ideal for pellet production. Drying can be accomplished using large rotary dryers or similar equipment.
- Size Reduction: Once dried, the wood material is typically passed through a hammer mill or similar equipment to reduce it to a uniform size. This process ensures that the pellets have consistent density and combustion properties.
- Pelletizing: The prepared wood material is then fed into a pellet mill. Inside the pellet mill, the material is compressed by a roller and die. The compression generates heat, which softens the lignin (a natural binding agent in wood) and causes the wood particles to stick together. This results in the formation of small pellets with a diameter typically ranging from 6 to 8 millimeters and a length of about 10 to 30 millimeters.
- Cooling: The newly formed wood pellets are hot and soft. They are passed through a cooling system to reduce their temperature and harden them. This can involve using cool air or a water bath to cool the pellets.
- Screening and Sieving: After cooling, the pellets are screened to remove any fines or oversized pellets, ensuring that the final product meets the desired specifications.
- Packaging: Once screened and inspected, the wood pellets are typically packaged in bags, totes, or bulk containers, ready for distribution and sale.
It’s important to note that the quality of wood pellets can vary based on factors like the type of wood used, the moisture content, and the production process. High-quality wood pellets have consistent size, low moisture content, and minimal ash content, making them ideal for use in residential heating stoves, industrial boilers, and power plants. Wood pellets are a renewable and environmentally friendly fuel source, as they are made from wood waste and byproducts, reducing the need for new timber harvesting.