Environmental Engineering Reference
In-Depth Information
Forestry Thinnings
Forestry materials represent another potential
source of cellulosic feedstock in Oregon. The state
of Oregon is made up of approximately 46 percent
forest land. Much of this land requires thinning,
because of fire suppression practices that prevent
the natural cycle of forest fires. A directed effort
to thin these forestry lands would create healthier
forests and provide valuable cellulosic feedstock
for a local cellulosic ethanol industry. Forestry
thinnings have a conversion ratio of 66 gallons
of ethanol per dry ton. Thinning forestry lands “at
a rate of just 2 percent per year
…
could produce
nearly 200 million gallons of ethanol.” (Graf and
Koehler, 2000).
A potential advantage of using materials from
forestry thinning is the possibility that this can
be a government subsidized activity. Govern-
ment subsidies or grants might make sense since
carefully managed thinning is an activity that is
beneficial to the health of Oregon's forests. This
would create a price advantage in the cost of these
materials for use as cellulosic feedstock.
A potential disadvantage of using materials
from forestry thinning is the pulpwood market.
Since materials from forestry thinning may have
a higher value if they are sold as pulpwood,
sometimes as high as $125 per ton, this would
be a competing economic use for this feedstock.
Fortunately, the pulpwood market has strict
requirements for the quality and conformity of
materials they can use. More than likely the cel-
lulosic ethanol industry would have access to
significant amounts of material that remain after
demands from the paper industry are satisfied
(Graf and Koehler, 2000).
greenwaste is around $15 per ton, making it a very
affordable source of cellulosic feedstock (Graf
and Koehler, 2000).
Urban greenwaste is inexpensive and easy
to collect, however, the total available supply of
cellulosic feedstock from this source is relatively
limited. The Oregon Cellulose-Ethanol Study puts
the available feedstock from urban greenwaste at
somewhere around “270,000 bdt [bone dry tons] of
urban greenwaste generated per year in Oregon.”
(Graf and Koehler, 2000). Compounding this is
the fact that urban greenewaste has a low poten-
tial ethanol conversion at only 46 gallons per dry
ton. The projected yield is far from sufficient to
support a cellulosic ethanol industry based solely
on urban greenwaste.
Hybrid Poplar
Hybrid poplar is a perennial tree that is grown
as a cellulosic energy crop for several reasons.
Hybrid poplars grow in a broad range of climates
and geographic regions. They continue to grow
throughout the entire year, unlike many energy
crops that have short growing season. Hybrid
poplars can also be harvested every 5 to 10 years
and regrown from the remaining roots. All of these
characteristics make hybrid poplar an excellent
source of cellulosic feedstock (Texas State Energy
Conservation Office, n.d.).
A major concern with growing energy crops is
the use of farmland to produce fuels rather than
food. This has been a major criticism against the
corn-based ethanol industry in the mid-western
United States. Hybrid poplar is an attractive
energy crop, because it grows on marginal land.
This means that hybrid poplar can be grown on
farmland that is currently left unused or fallow,
and therefore does not have an impact on normal
food crop production capacity. According to the
DOE and USDA there are tens of millions of acres
of unused farmland available for growing hybrid
poplar (Steeves, 2006).
Poplar farms can yield 10 tons of cellulosic
Urban Greenwaste
Urban greenwaste, comprised mostly of yard
debris, is another potential source of feedstock
for use in an Oregon cellulosic ethanol indus-
try. Currently the majority of this greenwaste is
converted into compost, while a small amount is
