Wood-Chip Heating Systems - Biomass Energy Resource Center

CHAPTER TWO
Wood Chips and Other
Types of Biomass Fuels
In this book the terms wood chips and biomass
are used interchangeably, because wood
chips are the fuel currently burned by almost
all the facilities that use biomass energy in
the Northeast. Biomass generally means any
biological matter that can be burned for energy,
including cordwood, wood chips, sawdust, bark,
various other forms of chipped sawmill wastes, and
wood shavings or other ground-up wood from wood
manufacturing operations. Other, less usual forms of
burnable biomass include straw, corncobs, nut shells,
seed hulls, pine cones, and some food-processing
wastes.
Wood pellets are another form of biomass fuel
— but for a number of reasons, pellets are not included
in this discussion of wood burning. Unlike most other
biomass fuels, pellets are a manufactured product.
They therefore have a considerably higher price per Btu
than other forms of biomass, and so do not carry the
price advantage that makes biomass attractive. Pellets
are generally better-suited to smaller heating plants
than to the systems considered here. Pellets are easier
to store and handle automatically, compared to wood
chips, and pellet systems are usually simpler and less
expensive to install.
Although wood chips are by far the most prevalent
form of biomass fuel in the Northeast, potential users
should be aware that local markets and changes in
markets over time may present attractive opportunities
for burning other biomass fuels. For example, sawdust
might be available inexpensively from a local source.
While there are practically no sawdust burners outside
the wood products industry in the Northeast, in eastern
Canada it is fairly common to burn sawdust for energy
in agricultural and commercial settings.
Mill Residue Chips
For institutional users in the Northeast, sawmills
are the main source for wood chips. Mills typically chip
their slab wood and other residues that are unsuitable
for lumber. Stationary mill chippers usually include
some sort of screening and rechipping to make the
product more uniform in size and quality. The typical
mill chip is about the size of a matchbook. A goodquality
mill chip is considered a high-grade product,
both for combustion systems and as a feedstock for
paper mills. For this reason, the price is likely to be
higher than for whole-tree chips, which are described
in the next segment.
Most sawmills chip directly into tractor trailer vans
for immediate delivery. Some store the chipped product
in metal silos, which are excellent for keeping the fuel
clean and dry. Other mills may stockpile the fuel in
open piles.
Users should be very cautious about burning fuel
that has been stored outdoors. Surface moisture from
rain and snow may make it harder to burn. Also, gravel
and rocks may be picked up when chips are scraped
off the ground to load into the delivery truck. Both
excess moisture and foreign matter will defi nitely
cause problems with chip handling and combustion
equipment.
Whole-Tree Wood Chips
Whole-tree chips come from harvesting operations
in the woods. (Chips are typically rectangular, about
1/2-1” x 1-3” x 1/4”.) Large portable chippers that can
reduce whole trees to chips blow the chips into tractor
trailer vans (the term van refers to the trailer). The
trucks then go on the road immediately to deliver to
customers.
WOOD CHIP HEATING SYSTEMS
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