AVAILABILITY OF BIOMASS
A large, reliable, economic and sustainable feedstock
supply is required for a biorefinery. Current yields for
ethanol from agricultural residues (corn stover, straw
from wheat, rice and other cereals, and sugarcane
bagasse) are about 65 gallons per dry ton.10 Thus, a
moderately sized 65 million-gallon-per-year cellulosic
biorefinery would need 1 million dry tons per year of
feedstock. This could require 500,000 acres or more of
cropland—a supply radius of at least 15 miles. The actual
supply radius could vary from 15 to 30 or more miles,
depending on crop rotation, tillage practices, soil characteristics,
topography, weather and farmer participation.
Research at a variety of sites indicates that economic
delivery of crop residues is achievable at this radius
and beyond—up to 50 miles from the biorefinery site
when short line rail transport is available.11 So, cellulosic
biorefineries of well over 100 million gallon
capacity are possible.
To sustain a commercial-scale biorefinery, cropland
surrounding the site should meet the following criteria:
n Large Area: Minimum of 500,000 acres of available
cropland;
n Sustainable: Cropping practice maintains or
enhances long-term health of the soil;
n Reliable: Consistent crop supply history with dry
harvest weather;
n Economic: High-yielding cropland; and
n Favorable Transport: Easy access from field to
storage and processing facilities.
BIOMASS TO ETHANOL
BIOMASS TO ETHANOL: HYDROLYSIS AND
FERMENTATION
Sugars are the essential raw material for a range of
biobased products from ethanol to bioplastics. In the
case of ethanol, sugar is converted into alcohol through
fermentation. Both corn grain and cellulosic feedstocks,
such as corn stover, straw and wood, are composed of
about 70 percent sugars, making them good candidates
for ethanol production. The challenge lies in extracting
the sugars from these agricultural feedstocks.
In corn grain, the sugars are all of the same variety (6-
carbon molecules of glucose), joined together with
relatively simple bonds to form starch. These simple
bonds can easily be broken using commonly available
amylase enzymes and water in a process called hydrolysis.
Isolating the sugars in cellulosic biomass is a
considerably more complicated task. Cellulosic biomass is
composed of a mixture of 6-carbon glucose sugars in the
form of cellulose and 5-carbon pentose sugars linked to
other 6-carbon sugars in the form of hemicellulose, all
held together by complex chemical bonds bound with a
stiff, fibrous substance called lignin. The biomass must
first be pre-treated to separate the lignin and loosen the
chemical bonds. Cellulase enzymes can then be used to
break the sugar-to-sugar bonds via hydrolysis.
Recent biotech advances have made significant
improvements in cellulase enzymes and pentoseprocessing
microbes, closing the gap on making cellulosic
biomass conversion to ethanol economical. As
commercialization proceeds, further gains will help ensure
sustainable feedstock platforms for fuels and chemicals.
Sugar
content
70% as starch. 30-50% as cellulose.
25-32% as hemicellulose.
Conversion
to individual
sugars
Straightforward conversion
to sugars via amylase
enzymes.
Current starch to sugar
conversion cost 3¢ to
5¢ per gallon ethanol.
Challenge to convert to sugars.
Cellulose to glucose with muchimproved
enzymes approaching
10¢ per gallon.
Current
ethanol
yield
105 to 120 gallons
per dry ton (2.5 to 2.8
gallons ethanol per
bushel).
80 to 90 gallons per dry ton feedstock.
Pentose fermentation to alcohol
still an evolving technology.
Coal must be part of green energy debate
WASHINGTON — Governors pushing alternative energy development are not shying from coal, a major culprit in global warming but also a homegrown energy source and an economic lifeline for many states.
Leaders of coal-rich states say clean-coal technology is a must. Governors from states without coal want more evidence the technology works.
“There’s no doubt there’s a tension and there’s no doubt there is very rapidly growing public opposition to coal,” said Gov. Jim Doyle, D-Wis. His state relies heavily on coal for power although Wisconsin is not a coal producer.
Energy tops the agenda at the governors’ annual winter meeting. The group’s new clean energy initiative seeks to promote renewable fuels such as ethanol and biodiesel and reducing greenhouse gas emissions.
“Next-generation coal is going to need to continue to be part of our energy future for this country,” said GOP Gov. Tim Pawlenty of Minnesota, chairman of the National Governors Association.
“It is abundant, it is available, it is Americanized in the sense that we control the supply,” he said Saturday. “We would be incomplete and doing a disservice to the debate and the ultimate policy direction that we’re going to take if we don’t envision coal being part of that.”
Next-generation coal typically refers to capturing and somehow sequestering or storing the carbon that coal produces. It also envisions reducing or eliminating emissions as coal is burned.
Pawlenty has embraced renewable fuels such as corn-based ethanol and conservation, but he also promotes clean-coal technology.
Such technology is a rallying cry for many coal-producing states. They say it is possible to continue relying on the fossil fuel while minimizing its impact on the environment.
Gov. Ed Rendell, D-Pa., envisions an economic turnaround if clean-coal technology takes off.
“Coal states would be back in business big time and the economies would flourish,” said Rendell, the association’s vice chairman.
Presidents of two of the country’s biggest power companies urged governors not to dismiss coal, calling it the country’s most abundant energy resource.
“We cannot ignore coal, we cannot demonize coal,” said Thomas Farrell, chairman of Richmond, Va.-based Dominion Resources Inc.
Michael Morris, chairman of Columbus, Ohio-based American Electric Power Co., said “the whole notion of delegitimizing coal is something we should all be frightened of.”
Gov. John Baldacci, D-Maine, needs to hear more before he would include clean-coal technology among the promising energy ideas for the country. His state promotes renewable energy produced through wind, solar and even tides.
“You have to deal with the coal states, but I don’t think you want them doing more of what they’re doing until they change what they’re doing and make it truly the next generation,” he said in an interview.
“Not just say clean-coal technology, but really do clean-coal technology.”
Proponents say all energy sources have their problems. The key, says Gov. Brian Schweitzer, D-Mont., is a national energy policy with many options and sources.
That is important because electricity demand will increase in the future. For instance, Schweitzer predicted that 10 years from now a significant number of cars will be plug-in hybrid vehicles, which will require more power plants, not fewer.
Coal “has a CO2 problem, wind has a reliability problem, solar has a price problem, nukes have a price and radiation problem,” Schweitzer said. “So all of those technologies have opportunities. but they all have problems — coal’s no different.”
He added, “What I can say about coal, is we have it. We have it in a greater supply than anyplace else on the planet.”
Doyle, the Wisconsin governor, said the emerging consensus is a mix of approaches. He said the state’s reliance on coal for electricity will decline but definitely not disappear.
