What are Wood Pellets?

Pellet fuels, also known as pellets, are bio-fuels made from a compressed organic matter. Pellets are made from any of five general categories of biomass: industrial waste and co-products, food waste, agricultural residues, energy crops, and virgin lumber. Wood pellets are by far the most common type of pellet and are made from compacted sawdust along with related industrial byproducts from the milling of lumber, manufacture of wooden products and furniture, and construction.

Wood pellets are made by compressing wood material which is first passed through a hammer mill to create a uniform dough-like mass. This mass is then fed into a press, where it’s squeezed through a die with holes of the size required (generally 6 mm diameter, but sometimes 8 mm or larger). The high pressure of the press causes a substantial increase in temperature, causing the lignin to plasticize slightly, which forms a natural "glue" which holds a pellet together while it cools.

There are four main classifications of wood pellets: “Super Premium” pellets, “Premium” pellets, “Standard” pellets, and “Utility” pellets. The properties which set a Super Premium pellet apart from a Utility pellet are a greater bulk density, higher durability of pellets, reduced inorganic ash from the combustion of wood pellets, and a reduced moisture content which allows the pellets to burn hotter and more thoroughly. Generally, “premium” grade pellets are required for residential stoves, while power plants can tolerate lower grades of pellets.

How efficient are Wood Pellets?

High-efficiency wood pellet stoves and wood pellet boilers have seen innovations in recent years, generally offering combustion efficiencies over 85%. The most recent generation of wood pellet boilers work in a condensing mode and can, therefore, achieve 12% greater efficiency.