The main appeal of wood and biomass pellets is its carbon neutrality. Living plants take in carbon dioxide and expel oxygen. After the plant dies, this carbon dioxide is released naturally during decomposition or when the plant is burned as a source of biomass energy. Net gain in atmospheric carbon dioxide: zero. In contrast, burning fossil fuels releases carbon dioxide that would otherwise have remained stored, accelerating global warming. Furthermore, biomass energy utilizes materials that might have otherwise been discarded as waste.
Why not burn logs, woodchips, or other raw forms of biomass? One reason is moisture content. Even in seasoned wood the moisture content tends to be around 30 percent; compare this with less than ten percent for wood pellets. The result: significantly less smoke from burning pellets. Second, pellets produce less ash since contaminants such as soil and bark, found in woodchips, are removed during pelletization. Third and most importantly is energy density, which is more than three times greater in wood pellets than in woodchips. This greatly reduces storage and stove-volume requirements. More fuel can be transported in a given truck space, and more energy can be stored at your site. Lastly, pellets are more easily and predictably handled. Their uniform shape and size allows for a smaller and simpler feed system that reduces costs. This high density and uniform shape can be stored in standard silos, transported in rail cars and delivered in truck containers.
To recap the convenience of pellets:
- Density of around 650 kilograms per cubic meter
- Flows like a liquid; ideal for automatic systems
- Can be used in stoves and boilers
- Can be used in small and large scale applications
- Easy to handle, store and transport
- Improved combustion characteristics over raw material
Wide range of raw materials
Sawdust is the most common raw material used to make pellets, as it requires less pretreatment before entering the mill. Nonetheless, a variety of raw materials have been shown to make viable pellets. Options range from a diverse array of wood waste (residual sawdust, wood shavings and wood peelings, etc.), yard debris (grass, leaves, sticks, forsythia, wisteria and bushes), farm waste (corn cobs, corn stalks, and straw from plants) and other residual biomass waste.