How Wood Pellets are Made

How Wood Pellets are Made

How Wood Pellets are Made

Wood pellets became a popular source of home heating back in the 1980's and have had mixed reviews over the years since then. Recently pellets have started making a comeback as an alternative to fossil fuels. Pellets are not only being used for home heating, they area also being used as a form of energy for commercial boilers and power plants. Here is how wood pellets are made.

The pellet making process involves compressing small pieces of wood into a dense cylindrical pellet. This is done by using a roller to shove the wood into a die full of pellet sized holes. The tops of the holes are tapered so the wood must get smaller the deeper into the die it goes.

This compressed the wood into a dense pellet and also heats the pellet by friction and compression. The heat causes binders that are in the wood naturally or added to the mix. After the pellet is extracted, they cool and the binders turn solid again and glue the pellet together. This creates a very dense and hard pellet that will hold together until it is burned.

For some types of wood, pellet manufacturers must add vegetable oil or other binding agents to the wood before it is made into a pellet. But for many types of wood, especially resinous softwood, they naturally contain enough lignins and other binding material so none needs to be added.

Depending on how the raw wood arrives at the pellet mill, there are other steps involved in making pellets. Wood must be in pieces small enough to fit into the dies. With mill wastes like sawdust sometimes it is already small enough. But for solid chunks of wood they will need to be reduced in size. A chipper will grind the larger pieces and then a hammer mill can be used to break the wood into even smaller pieces.

A pellet can be made easily with a pellet mill but in order for the pellet to be of quality, conditions must be ideal. Otherwise the pellet may fall apart before it ever reaches its destination to be burned. The wood must have the proper moisture content of around 15-20%. For most wood this means it will need to be dried. Most pellet mills have driers to reduce the moisture content. These are usually the most energy intensive part of the whole mill and are often pellet fired.

If the wood is already too dry, moisture will have to be added to the mix to get it to the right level. Depending on the wood, a binding agent may have to be added. Corn starch, vegetable oil and other organic material are often used.

Once the pellet is finished and cooled it is bagged or put in other air tight containers to seal out moisture. Dry pellets burn very efficiently and clean in both home heating units and commercial boilers. Since pellets come from trees, they are renewable and are considered to be carbon neutral. As the world searches for clean alternatives to fossil fuels, like coal and petroleum, wood pellets are quickly increasing in demand and will likely continue to do so.

You can learn how to make wood pellets yourself with a small scale pellet mill.

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