Just days ago, the Forest Service
announced a proposal to convert woody biomass produced on forested
lands to cellulosic ethanol to offset annual U.S. gasoline consumption
by 15 percent (or by 35 billion gallons).
The Forest Service identified “small trees”
and “unhealthy underbrush” removed from forests during
fuel reduction treatments as the feedstocks for celluosic ethanol.
Although cellulosic ethanol holds an important place in our nation’s
energy future, these claims regarding ethanol production are unrealistic.
A more realistic analysis reveals that this technology is still
not commercially available; forest thinning alone cannot supply
this volume of fuel; forest biomass is difficult to transport; and
environmental impacts need to be more carefully analyzed.
Currently, there are no commercial cellulosic ethanol plants in
operation in North America, only pilot facilities each producing
less than one one-hundredth of one percent of the 35 billion gallons
of ethanol per year described above. A cellulosic ethanol facility
capable of producing 20 million gallons of ethanol is slated to
open in 2008, but time will tell.
If cellulosic ethanol plants eventually become common, the proposed
level of production would place an enormous demand on our forests.
Producing 35 billion gallons of ethanol requires approximately 427
million tons of biomass. Thinning forests for fuel reduction treatments
removes about 10 tons of biomass per acre. Therefore 42.7 million
acres of forest lands would have to be thinned annually to achieve
this target – an area equivalent to 31 percent of all accessible
Forest Service lands.
The Department of Energy recently noted that fuel reduction treatments
on all private and federal forest lands could sustainably supply
only 60 million dry tons of biomass annually with only 20 percent
from federal lands. Clearly the annual sourcing of 427 million tons
of biomass from fuel reduction treatments is unrealistic.
Forest biomass, especially "small trees and underbrush"
represent a bulky, low density feedstock making transportation and
storage a serious logistical problem.
One ton of biomass is equivalent to about four cubic
yards volume, and biomass can be transported only about 50 miles
before the energy consumed in transportation starts to take a major
bite out of the energy embodied in the biomass. This means ethanol
distilleries would have to be built in a tight network across the
country.
What about the realities of scale for an individual cellulosic ethanol
plant? One of midsize ethanol plant producing 20 million gallons
of ethanol per year would require about 670 tons of biomass per
day or about 244,000 tons of biomass each year. Each year, about
1 million cubic yards (one football field piled over a mile high)
would be delivered to this site by over 8,000 individual deliveries.
All 35 billion gallons of ethanol from forest lands would require
147 million trucks loads of biomass delivered to stills nationwide.
Assuming a conservative average haul distance of 25 miles, this
would represent 11.8 billion miles of truck transit or about 15
percent of today’s total US truck transit just for the delivery
of biomass to ethanol stills.
Environmental impacts of cellulosic ethanol facilities must also
be considered. Each gallon of ethanol produced consumes about 4
gallons of water. Thus, a 20-million gallon-per-year ethanol plant
will consume (vaporize) 80 million gallons of water annually.
The production of 35 billion gallons of cellulosic
ethanol would consume some 140 billion gallons of water annually.
In just 35 years a volume equivalent to Great Salt Lake would be
consumed. An additional, larger volume of water is chemically and
thermally altered within ethanol plants and must be treated prior
to return to natural water bodies.
Production of cellulosic ethanol from forest biomass has significant
potential, but our expectations must be realistic.
Fuel reduction treatments will at most supply 60 million
tons of biomass annually for both biofuel and for electricity generation.
Assuming all logistics are overcome and half of the
biomass goes to ethanol production, then we could expect forest
thinning to provide about 2.5 billion gallons of ethanol.
This level of production, combined with improved fuel
economy and increased conservation, has the potential to make a
significant contribution to our nation’s energy independence
without placing an unreasonable strain on our forest resources.
Thomas H. DeLuca, Ph.D. is a senior scientist
with the Wilderness Society in Bozeman, Montana where he specializes
on issues in forest ecology, land resources, and environmental sustainability.
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