Production of Wood Pellets From Soft Wood
Wood pellets made from softwoods are made much like pellets made from hardwood. The price difference between hardwood and softwood pellets reflects the cost of the woods, not the heating performance. Softwood pellets provide more heat energy due to the high amount of wood resins they contain, though the pelleting process minimizes the differences between hardwood and softwood. Does this Spark an idea?
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Grinding the Wood
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The mill prepares the softwood for pelleting by chipping and grinding it until it is as fine as sawdust. If it is already in small pieces, it is ready to use as it is; otherwise a hammer mill can reduce it to whatever fineness it needs to be for pelleting.
Drying the Wood
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An oven or kiln dries the ground softwood to a moisture level between 6 and 20 percent, depending on the consistency of the wood. Some moisture is necessary for pelleting, but too much is detrimental.
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Mixing the Wood
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Consistency is key to quality pelleting, so mixers combine different batches of ground wood to equalize moisture and other factors. The mixers may also incorporate other ingredients to add quality.
Pelleting the Wood
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The pelleting machine heats and presses the prepared ground softwood into molds in the shape of the finished pellets. The lignins in the wood respond to the heat by binding the softwood particles together like glue.
Finishing and Packaging the Pellets
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When the pellets leave the pelleting machine, a sifter screen removes any remaining wood dust or fragments. Air drying removes any residual moisture which could otherwise remain trapped in the packaging and could cause the pellets to swell. Once the pellets are dry, packagers seal the pellets into moisture-proof bags and they are ready for storage or shipping.
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References
- Photo Credit pellets image by Rupert Roth from Fotolia.com
