Biomass
Processing Residues. All
processing of biomass yields byproducts
and waste streams collectively
called residues, which have significant
energy potential. Not all residues can
be used for electricity generation, some
must be used to replenish the source
with nutrients or elements. Still, residues
are simple to use because they have already
been
collected.
• Pulp
and paper operation residues. Plants
are made up of lignin, hemicellulose and
cellulose fiber [2]. Because of
its chemical and physical properties, lignin
breaks down much easier than cellulose. Pulping
is the separation and breaking
down of
the lignin fibers of a plant in order to
"suspen[d] the cellulose fibers" to
create paper. [2] Leftover pulp creates a
residue.
These residues are the
byproducts
of logging and
processing
operations. Processing of wood for products
produces sawdust and a collection
of bark, branches and
leaves/needles chipped or pulped. In general,
paper mills utlize their pulp residue to
create energy for the paper mill, which consumes
a vast amount of electricity in order to
run. For more on paper pulp creation please
visit Paper
On The Web
• Forest
residues,
which includes wood from forest thinning operations
that reduce forest fire risk, biomass not harvested or removed from logging
sites in commercial hardwood and softwood stands as well as material resulting
from forest management operations such as pre-commercial thinnings and
removal of
dead and dying trees.
• Agricultural
or Crop Residues are the leftovers of harvesting. They
can be collected with conventional harvesting equipment while harvesting
the primary crop
or afterwards into pellets, chips, stacks or bales [3]. Agriculture crop
residues include corn stover (stalks and leaves), wheat straw, rice straw
and processing
residues
such as nut hulls.
With approximately
80 million acres of corn planted annually, corn stover is expected to
become a major biomass
resource for bioenergy applications [6].
In some areas, especially dry climates, the residues must be
left to replenish the soil with nutrients
for the next
season and
can
not
be completely utilized [3]. The soil can not take out all the nutrients
from the residues, which translates to rotting and wasted energy sitting
on top of the fields.
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Animal
waste, such
as cattle, chicken and
pig manure, can be
converted to gas or burned directly for heat and power generation.
In the developing world, dung cakes are used as a fuel
for cooking [3]. Furthermore, most animal wastes contain high levels
of methane. Thus, this method is very unsafe, as the levels
of harmful chemicals
given
off by the biomass is hazardous to the health
of users, causing 1.6 million deaths annually in the developing nations
[3]. Since, animal
wastes farms
and
animal
processing
operations
create large
amounts of animal wastes that constitute
a complex source of organic materials with environmental consequences,
utilizing the manure to produce energy properly lowers the environmental
and health impacts. These wastes can be used to make many products and
generate
electricity through methane recovery methods and anaerobic
digestion [4].
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Urban
wood waste. According
to a fact sheet supplied by the California Integrated Waste Management
Board, wood waste is the largest source of waste from construction
products [5], generating close to 4 million tons of waste in California
alone. Urban wood waste generally
consists of lawn and tree trimmings, whole tree trunks,
wood pallets and any other construction and demolition wastes made
from lumber. This rejected material can easily be collected after
a construction or demolition project and turned into mulch, compost
or used to fuel bioenergy plants [5].
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Municipal
Solid Waste.
Residential, commercial,
and institutional
post-consumer
wastes contain a significant
proportion of plant derived
organic material that constitute
a renewable
energy
resource. Waste paper, cardboard, wood waste and yard wastes
are examples of biomass
resources
in municipal
wastes. The International Energy Agency
(IEA) is conducting research
on municipal wastes and
their use in creating bioenergy.
The study will be conducted
through the end of 2006.
For more information, please
see IEA
Website.
Landfill
gas. The
natural byproduct of bacterial digestion
of organic garbage contains vast amounts
of methane which can be captured,
converted and used to create energy most
often through anaerobic
digestion (AD). These
wastes are collected and recycled through
a process called anaerobic
digestion and composting. Collection
of landfill waste as an organic renewable
resource for bioenergy is beneficial
for a number of reasons, including protection
of public health through treatment of
waste,
decreasing landfill space and
inevitably decreasing odors associated
with a landfill, aiding
in waste management practices. Samir
Khanal at Iowa State
University
has written a paper detailing sulfide
odor control. For
the text of this short write up
please click here.
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Energy
crops are bioengineered
to be fast-growing plants, trees or
other herbaceous biomass which are harvested
specifically
for
energy production use. These
crops can be grown, cut and replaced
quickly. For
a complete list of potential plants which
may be used as energy crops, please see
the Handbook
of Energy Crops.
Herbaceous
Energy Crops
Herbaceous energy crops are perennials that
are harvested annually after taking two to
three years to reach full productivity. These
include grasses such as switchgrass,
miscanthus (Elephant grass),
bamboo, sweet sorghum, tall fescue, kochia,
wheatgrass, and others. These crops are generally
grown for fuel production.
Woody Energy Crops
Short-rotation woody crops are fast growing
hardwood trees harvested within five
to eight years after planting. These
include hybrid
poplar (seen below), hybrid willow, silver
maple, eastern cottonwood, green ash,
black
walnut, sweetgum,
and sycamore.
Industrial Crops
Industrial crops are being developed and
grown to produce specific industrial chemicals
or
materials. Examples include kenaf and straws
for fiber, and castor for ricinoleic acid.
New transgenic crops are being developed
that produce the desired chemicals as part
of the
plant composition, requiring only extraction
and purification of the product.
Agricultural Crops
These feedstocks include the currently
available commodity products such as
cornstarch and
corn oil; soybean oil and meal; wheat
starch, other
vegetable oils, and any newly developed
component of future commodity crops.
They generally
yield sugars, oils, and extractives,
although they
can also be used to produce plastics
and other chemicals and products.
Aquatic Crops
A wide variety of aquatic biomass resources
exist such as algae, giant kelp,
other seaweed, and marine microflora. Commercial
examples
include giant kelp extracts for thickeners
and food additives, algal dyes, and
novel biocatalysts for use in bioprocessing
under extreme environments [7]
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Sources
Cited:
[1]
Montana
Greenpower (May
12, 2005).
[2]
Paper
On The Web (May 16,
2005).
[3]
Thomas B. Johansson, ed et al. "Biomass
for Energy: Supply Prospects." Renewable
Energy: Sources for Fuels and Electricity.
Island Press: Washingtong, D.C. 1992.
p. 609.
[4]
Animal Waste Management. The University of
Arizona. http://ag.arizona.edu/animalwaste/awenergy.html.
July 5, 2005.
[5]
Quality Management Pamphlet provided by
the IEA Bioenergy Sector at http://www.novaenergie.ch/iea-bioenergy-task37/Dokumente/managementpaw3.PDF
or http://www.novaenergie.ch/iea-bioenergy-task37/publicationspublic.htm
[6] "Ag
economist: U.S. soybean acreage down, but
not out." Purdue University. http://news.uns.purdue.edu/html4ever/2005/050331.Hurt.planting.html
[7] National
Renewable Energy Laboratory. www.nrel.gov.
