|
Bioenergy
|
Forward
The purpose of
this paper is to
provide the reader
with comprehensive
knowledge of the
biomass energy
sector. Biomass is
plant matter
and animal waste
that
can be harvested to
create bioenergy in
the form of electricity,
heat, steam and fuels.
Biomass has great
potential to contribute
considerably more
to the renewable
energy
sector.
Already, in the
U.S., residues from
mill
operations
are the largest
source of biomass
for power plants
and combined-heat-and-power
projects. Photo
Credit: NREL
biomass research website
Agricultural
residues such
as orchard prunings
and nut hulls
as
well as forest
residues are
also important contributors
to power plants
in combined heat
and power (CHP) operations, particularly
in
California. Landfill
gas projects
are growing steadily,
while animal
waste
digestion projects
and energy crop
plantations are
still at an early
stage of commercialization. [1]
In
Europe, urban wood waste is an
important source
of bioenergy. In
developing nations,
a major source
of biomass is
timber cut by the
rural
poor specifically
for heating and
cooking. [1]
|
Biomass
Basics and Environmental
Impact |
Introduction
Biomass is any organic
matter, particularly cellulosic or lingo-cellulosic matter,
which is available on a renewable or recurring basis, including
trees, plants and associated residues; plant fiber;
animal wastes; industrial waste; and the paper component
of municipal solid waste [2].
Plants store
solar energy through photosythesis in cellulose and
lignin cells. Cellulose is defined as a polymer, or
chain, of 6-carbon
sugars; lignin
is the
substance, or “glue,” that holds the cellulose chain together [2].
When burned, these sugars break down and release energy exothermically, giving
off CO2, heat
and
steam. The byproducts of this reaction can be captured and manipulated
to create electricity, commonly called biopower,
or
fuel known as biofuel. (Both short for "biomass power" and "biomass
fuel" respectively)
[3].
Biomass
is considered to be a replenishable resource—it
can be replaced fairly quickly without permanently depleting
the Earth’s
natural resources. By comparison, fossil fuels such as
natural gas
and coal require millions of years of natural processes
to be produced. Therefore, mining coal and natural gas
depletes
the Earth’s resources for thousands of generations.
Alternatively, biomass can easily be grown or collected,
utilized and replaced.
Moreover, using
biomass to create energy has positive environmental implications.
Carbon dioxide is a naturally occuring gas. Plants collect
and store carbon dioxide to aid in the photosynthesis process.
As plants or other matter decompose, or natural fires occur,
CO2 is released. Before the anthropomorphic discovery of
fossil fuels, the carbon dioxide cycle was stable; the same
amount that was released was sequestered, but it has since
been distrupted. In the past 150 years, the period since
the Industrial Revolution,
carbon
dioxide levels in the atmosphere have
risen
from around
150
ppm to 330 ppm, and are expected to double before 2050!
(please see diagram below)
Courtesy of
NASA at http://rst.gsfc.nasa.gov/Sect16/carbon_cycle_diagram.jpg
Back
to Top
An overwhelming
majority of scientists now link carbon dioxide with rising
temperatures
in the
atmosphere and other issues associated with climate change.
Scientists
are predicting a rise in average temperature 2-10 degrees
Celsius.
This change may
seem
insignificant, but note that the former ice age
resulted from an average of 5 degrees Celsius drop in temperature
[4]. This
small
shift in average temperature has huge implications
for melting
ice sheets, which would raise global water levels up
to 30 feet, flooding the coastal cities in which most of
the
world
currently resides. Additionally, more extreme weather
patterns are predicted
to occur, as well as habitat loss, spread of disease
and a whole host of other problems. The amount of CO2 pumped
into the atmosphere today will remain for at least
a hundred
years, since the half life will outlive all of us.
In order
to curb CO2 emissions, we must take active strides to reduce
our emissions. At present, the United States is responsible
for 25% of the world's emissions, and is currently
dedicated to a policy which actually encourages the release
of more carbon dioxide into the atmosphere, claiming it
to be an indication of economic growth. Burning biomass will
not solve the currently unbalanced carbon dioxide problem.
However, the contribution that biomass could make to the
energy sector is still considerable, since it creates less
carbon dioxide than its fossil-fuel counterpart.
Conceptually, the carbon dioxide
produced by biomass when it is burned will be sequestered
evenly by
plants growing to replace the fuel. In other words, it
is a closed cycle which results in net zero impact (see
diagram below). Thus, energy derived from biomass does not
have the negative environmental
impact
associated
with
non-renewable
energy sources. [5]
Courtesy of
ORNL at http://bioenergy.ornl.gov/papers/misc/bioenergy_cycle.html
Biomass is an attractive
energy source for a number of reasons. First, it is a renewable
energy source as long as we manage vegetation appropriately.
Biomass is also more evenly distributed over the earth's
surface than finite energy sources, and may be exploited
using less capital-intensive technologies. It provides
the opportunity for local, regional, and national energy
self-sufficiency
across the globe. It provides an alternative to fossil
fuels, and helps to reduce climate change. It helps local
farmers
who may be struggling and provides rural job opportunites.
[6]
Back
to Top
Bioenergy
ranks second (to hydropower) in renewable U.S. primary energy production
and accounts for three percent of the primary energy production
in the United States [7]. For a brief biomass history,
please click here.
Biomass Energy Conversion
Bioenergy conversion requires a comparison with other energy
sources that are displaced by the bioenergy. Thus,
biomass for power must be compared to coal,
natural gas, nuclear, and other power sources including other renewables.
While comprehensive data is not available, one study by REPP shows that
emissions from biomass plants burning waste wood would
release far less sulfur dioxide
(SO2), nitrogen oxide (NOx) and carbon dioxide (CO2) than coal plants built
after 1975. The comparison with combined cycle natural gas power plants
is more ambiguous, since biomass releases far more
sulfur dioxide, similar levels
or greater levels of nitrogen oxide, but far less carbon dioxide than combined
cycle natural gas plants.
Back
to Top
Life-cycle impacts
Several studies by the National Renewable Energy Laboratory
examined the “life-cycle” impact
of bioenergy for power. That is, the studies examined the air, land and water
impacts of every step of the bioenergy process, from cultivating, collecting,
and transporting biomass to converting it to energy. One study found that
a bioenergy operation featuring biomass gasification
with combined-cycle power
plant technology would release far less SO2, NOx, CO2, particulate matter,
methane and carbon monoxide than coal power plants meeting new federal air
pollution standards.
Back
to Top
Sources Cited:
[1]
Center For Renewable Energy and Sustainable Technology
(CREST).
Biomass FAQs. Discussion Section. www.repp.org.
[2] "What is Biomass?"
American
Bioenergy Association. http://www.biomass.org/index_files/page0001.htm
May 12,
2005
[3] "Biomass
FAQs." Office of Energy Efficiency and Renewable
Energy. Department of Energy. http://www.eere.energy.gov/biomass/biomass_basics_faqs.html#biomass.
July 2005.
[4] "History of Climate Change." Athena
Curriculum Earth, an affiliate of NASA. Available Online
at http://vathena.arc.nasa.gov/curric/land/global/climchng.html,
as of June 24, 2005.
[5] "Bioenergy."
http://www.montanagreenpower.com/renewables/bioenergy/ May12,
2005.
[6]
Kirby, Alex."UK Boost for Biomass Crops." BBC News Science
and Nature. http://news.bbc.co.uk/1/hi/sci/tech/3746554.stm.
Oct 19, 2004.
[7] See
Footnote 3
|
| |
