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How wood pellets are made

Posted by David Fields on 2 December 2011 at 9:40 am

Wood pellets are essentially biomass materials that have been shredded into sawdust and then compressed through a die cast to create the pellet shape. The materials are then held in place by a binding agent, such as naturally forming lignin, and produced into their 6mm size.

To go into more detail, the production of biomass wood pellets comes from virgin trees or waste materials used in industry (for example, sawdust or waste off cuts from furniture factories). The first step is to break down the wood into fine particles. The finer the particle the stronger the pellet becomes, which reduces the risk of the pellet breaking apart.

These fine particles are then pressed into piece of cast metal that has pre-drilled pellet sized holes, known as a wood pellet die. As the material is pressed into the dies the shape of the hole becomes smaller and compresses into the pellet shape. The force of this compression creates friction, which then heats the pellet and melts any natural or artificial binding agent –holding the wood pellet together as it cools and hardens. If the materials used don’t have sufficient natural binding agents in, such as lignin, then organic materials such as flour and corn starch are used.

It is vital that the wood pellet retains the right combination of dryness and moisture, so that it keeps its shape without breaking but still creates a high enough heat output. The ideal moisture content for high quality wood pellets is 10% or less, and all reputable suppliers adhere to these standards.

Once each of these steps has been taken, you are left with high quality wood pellets ready for use either in small domestic biomass boilers or larger industrial units. 

Photo by Alternative Heat

About the author: David Fields is wood pellet manager at Woodpellets2u.

If you have a question about anything in the above blog, please ask it in the comments section below.

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Rafal

RafalComment left on: 6 December 2011 at 8:28 pm

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