All About Wood Pellets

Wood pellets are a manufactured biomass fuel.  They are made from wood waste materials and are held together by natural plant ligin and are condensed into pellets under heat and pressure.  Due to the uniform size and shape of pellets (between 1-1½ inches by approximately 1/4-5/16 inches in diameter), it makes them easy to store and use as traditional fossil heating fuels.  Pellets take up less space in storage than other biomass fuels because they have a higher energy content by weight (roughly 7,750 Btu per pound at six percent moisture content) due to their nature and low-moisture content (typically between 4-6 percent moisture by weight).

The Pellet Mill Process

'Raw Material' - The production of wood pellets begins with the generation of the raw material. In most cases, this raw material is a byproduct of some other wood processing operation.  Hardwood flooring mills are one good example: they produce large quantities of clean, dry sawdust and small blocks in their operations.  This makes an ideal raw material for pellet production; however, as the interest in pellet production grows, some mills are generating pellet-making raw materials from “round wood.”

'Drying' - The pellet raw material must be consistently dried to a low content (below 4 percent on a dry-weight basis). Because of the high temperatures and pressures during the manufacturing process, excess moisture can cause problems.   However, this low moisture content is also one of the reasons that wood pellets burn so well.

'Processing Material' - Once the feedstock has been dried, it is fed into a hammer mill that makes the wood particles a consistent size. This helps make the pellets a consistent density so that they provide a consistent heating value.

'Formation of the Pellets' - The pellets are extruded, or formed, using special dies. High pressures and temperatures are generated in this process, which softens components of the wood (the lignin) and binds the material in the pellet together.

'Bagging and Storage' - Once the pellets are formed and cooled, they can be packaged in bags or stored in bulk.  Most people buy pellets by the ton (a pallet of fifty 40-pound bags), and have them delivered to their home.  Pellets can be stored indefinitely, but they must be kept dry to prevent deterioration.

Environmental Benefits of Wood Pellets

Pellet fuel is carbon neutral and prevents the risks of global warming. When you heat with biomass, carbon dioxide is released into the atmosphere. Trees absorb this carbon dioxide in equal amounts as they grow therefore burning pellets does not increase the amount of this greenhouse gas in the atmosphere.  Arsenic, carbon monoxide, and the greenhouse gas carbon dioxide are just a few of the air and water pollutants resulting from the use of all nonrenewable fossil fuels as a heat and an energy source.  Even if the supply of nonrenewable fossil fuel was unlimited, the economic and associated environmental costs of transporting and burning ever-increasing amounts of nonrenewable fossil fuels are simply unsustainable. In fact, pellets burn more efficiently (system efficiency averages at 80 percent!) than other fuels, emissions from pellet burners meet even the most stringent EPA requirements.  Any remaining ash in the burn chamber, when removed, is of little consequence.  Once the ash is emptied, it can actually double as a fertilizer. Finally, pellet storage poses no soil or water contamination risks.  A spill can be cleaned with a shovel and not a hazardous waste crew.

Economic Advantages of Wood Pellets

Given that pellets are manufactured regionally they are never a monetary drain on a town, city or county.  Pellets provide jobs, pellet dollars stay in the region, and the entire community relies less on foreign energy. We know that fossil fuels are extremely price volatile.  A crisis or an international event that chokes fossil fuel supplies can cause spikes in costs.  The US’s need to increase our importation of foreign oil will continue unless we act on solutions like pellet fuel.  Pellet fuel costs have been virtually constant when compared to fossil fuels.