Biomass in this context is solid fuel from wood. There are three main forms biomass fuel – cordwood, wood chips, and pellets.
Most often used in home fireplaces or wood stoves, cordwood can also be used in schools and commercial buildings where 8-inch diameter or greater trees are readily available. It is important to cut the cordwood into pieces short enough to fit into the boiler, split them to dry to at or lower than 20% moisture content, and stack the wood out the weather with airflow.
A cord of wood is based on the dimensions 4′ x 4′ x 8′ which adds up to 128 cubic feet. Many other dimensions can be used as long as they add up to 128 cubic feet. A full size 8′ pickup bed stacked to the top of the bed is about 1/2 cord.
The most common tree species used in Alaska are: birch, spruce, hemlock, cedar, aspen, and cottonwood (poplar). The BTU values differ with species. View a sample here: http://firewoodresource.com/firewood-btu-ratings/
Burning cordwood in an EPA certified, high-efficiency, low-emission boiler or wood stove is important in maximizing the BTU content of the wood and minimizing emissions. Cordwood (birch) at $330 per cord is equivalent to $18.75/MMBTU.
Cordwood requires manual labor for harvesting, processing, and loading the stove or boiler. This can provide jobs for community members.
In buildings where automation of fuel delivery is important, wood chips can deliver.
Wood chips are a lightly processed wood where tree limbs and trunks are chipped into smaller pieces. This means the flexibility of using a smaller (or larger) diameter tree. There is currently no wood chip size standard sized. However, a chip of around 2” is recommended with a moisture content of less than 25% is suitable for most chip boilers.
Wood chips often use an auger or conveyer belt to feed a boiler, and the boilers often heat small community buildings up to large commercial or community buildings. Storage sheds with day bins are required for storing and using wood chips.
Wood chips require manual labor for harvesting and processing the wood, and feeding the wood into a boiler is automated.
Wood pellets are a densified wood product with a moisture content of between 10-20%. Pellets are used in small home pellet stoves up to large commercial and community installations, and can be purchased in 40 lb bags, large 1-ton super sacks, or delivered in bulk and put into silos. At $295/ton, pellets are equivalent to a cost of $31.73 MMBTU.
Pellets are stored in an inside day bin or outside silo and are automatically fed into a pellet stove or boiler. In Alaska, pellets are available for bulk or 40lb bag purchase from Superior Pellet Fuels in North Pole.