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Organic waste or biomass offers America a
tremendous opportunity to use domestic and sustainable
resources to provide its fuel, power, and chemical needs
from plants and plant-derived materials.
The Office of Energy Efficiency
and Renewable Energy Biomass Program includes major programs
for developing and improving technology for biomass power;
for making biofuels such as ethanol (from biomass residues
as well as grain) and renewable diesel; and for making
plastics and chemicals from renewable, biobased materials.
Types of Biomass
as Biofuel Source
Types
of biomass normally used for energy:
- forest debris
and thinning
- residues from wood products industry
-
agricultural wastes
- fast-growing trees and crops
-
wood and wood wastes
- animal manures
- non-hazardous,
organic portion of municipal solid waste
Benefits from Biomass
Currently, 80% of the country’s energy is supplied by fossil
fuels, which are finite and nonrenewable. As a renewable
energy source, BioPower offers an alternative to
conventional energy sources in the form of environmental,
rural economic growth, and national energy security
benefits.
The Biomass Program is also the lead agency in the
multi-agency Biomass Research and Development Initiative
working to coordinate and accelerate all federal biobased
products and bioenergy research and development in
accordance with the Biomass Research and Development Act of
2000.
Fossil fuel combustion generates sulfur dioxide, nitrogen
oxide, and other undesirable air emissions. Although
BioPower is also generated through a combustion process, it
produces fewer emissions than conventional sources.
Biomass can actually improve environmental quality by
offsetting fossil fuel use and related emissions and by
using wastes that are creating land use problems.
BioPower growth can also create new markets and employment
for farmers and foresters, many of whom currently face
economic hardship. It can establish new processing,
distribution, and service industries in rural communities.
Today in
parts of the developing world and until several decades ago in the U.S.,
biomass was primarily used to provide heat for cooking and comfort.
Technologies have now been developed which can generate electricity from the
energy in biomass fuels. The scale is small enough to be used on a farm or
in remote villages, or large enough to provide power for a small city.
Biomass Power Overview
Biomass power technologies convert renewable biomass fuels
to heat and electricity using equipment similar to that used
with fossil fuels. Next to hydropower, more electricity is
generated from biomass than any other renewable energy
resource in the United States. A key attribute of biomass is
its availability upon demand – the energy is stored within
the biomass until it is needed. Other forms of renewable
energy are dependent on variable environmental conditions
such as wind speed or sunlight intensity.
What is Biomass?
Wood is
the most commonly used biomass fuel for heat and power. The
most economic sources of wood fuels are usually wood
residues from manufacturers, discarded wood products
diverted from landfills, and non-hazardous wood debris from
construction and demolition activities. Use of these
materials for electricity generation can recoup the energy
value in the material while avoiding landfill disposal.
In the
future, fast-growing energy crops may become the biomass
fuel of choice. These energy crops will be genetically
tailored plants designed to be fast-growing, drought
resistant, and readily harvested, allowing them to become a
competitively-priced fuel. The U.S. Department of Energy is
working with national labs, agricultural and forestry
groups, power companies, and other governmental agencies to
make energy crops a viable fuel source in the near future.
Economics of BioPower
The
cost to generate electricity from biomass varies depending
on the type of technology used, the size of the power plant,
and the cost of the biomass fuel supply. Biomass power
systems range in size from a few kW (enough for an average
U.S. home) for on-site generation units, up to 80 MW for
power plants. Each MW of BioPower capacity generates enough
electricity in a year to power about 525 average U.S. homes.
Limitations on locally available biomass resources generally
make it uneconomical to exceed 100 MW in size. Once advanced
biomass power systems (gasification combined-cycles) become
commercially available, larger generation units will be more
feasible.
Today,
cofiring offers power plant managers a relatively low cost and low risk
route to add biomass capacity. These projects require small capital
investments per unit of power generation capacity. Cofiring systems range in
size from 1 to 30 MW of BioPower capacity. When low cost biomass fuels are
used, cofiring systems can result in payback periods as low as 2 years.
A typical existing coal fueled power plant produces power
for about 2.3 ¢/kWh. Cofiring inexpensive biomass fuels can
reduce this cost to 2.1 ¢/kWh. In today’s direct-fired
biomass power plants, generation costs are about 9 ¢/kWh. In
the future, advanced technologies such as gasification-based
systems could generate power for as little as 5 ¢/kWh. For
comparison, a new combined-cycle power plant using natural
gas can generate electricity for about 4 to 5 ¢/kWh at
today’s gas prices.
For biomass to be economical as a power plant fuel,
transportation distances from the resource supply to the
power generation point must be minimized, with the maximum
economically feasible distance being less than 100 miles.
The most economical conditions exist when the energy use is
located at the site where the biomass residue is generated
(i.e., at a paper mill, sawmill, or sugar mill). Modular
BioPower generation technologies under development by the
U.S. Department of Energy and industry partners will
minimize fuel transportation distances by locating
small-scale power plants at biomass supply sites.
Biomass
is the second-most utilized renewable energy resource in the
United States in terms of electricity generation.
Approximately 7,000 MW of operating installed capacity
generate around 37 billion kWh per year—the amount of
electricity used by 4 million average U.S. homes combined,
or the entire state of Colorado. Generating this amount of
electricity requires around 60 million tons of biomass per
year.
The
most economic forms of biomass for generating electricity
are residues. These are the organic byproducts of food,
fiber, and forest production. Common examples used for power
are sawdust, rice husks, and bagasse (the residue remaining
after juice has been extracted from sugar cane). Low-cost
biomass sources are also common near population and
manufacturing centers where clean wood waste materials are
available in large quantities. Examples are pallet and crate
discards and woody yard trimmings.
Biomass
is plentiful in various forms across the country. Woody
biomass is concentrated in the Southeast, with high
concentrations also in the Northeast, Pacific Northwest, and
the Upper Great Lakes region. Herbaceous/grassy biomass is
plentiful in the Midwest states, while cropland is
concentrated in the upper Midwest, Lower Great Lakes region,
and in the Mississippi delta. Research is presently underway
to commercialize energy crops that are well-suited to
regional climate conditions. Examples are: switchgrass in
the Midwest and Southeast, willow in the Northeast, and
hybrid poplars in heavily forested regions. Animal manures
have reached excessive quantities in a number of rural areas
throughout the country, especially on the Delmarva peninsula
(an area encompassing Delaware, Maryland, and Virginia) and
in areas of North Carolina, Georgia, Arkansas, Alabama,
Mississippi, Minnesota, California, and Washington.
Electricity from Biomass/Technologies at Work
There are
four primary classes of BioPower systems: direct-fired,
cofired, gasification, and modular systems.
Most of today’s BioPower
plants are direct-fired systems that are similar to most fossil-fuel
fired power plants. The biomass fuel is burned in a boiler to produce
high-pressure steam. This steam is introduced into a steam turbine, where it
flows over a series of aerodynamic turbine blades, causing the turbine to
rotate. The turbine is connected to an electric generator, so as the steam
flow causes the turbine to rotate, the electric generator turns and
electricity is produced.
While steam generation technology is very dependable and proven, its
efficiency is limited. Biomass power boilers are typically in the 20-50 MW
range, compared to coal-fired plants in the 100-1500 MW range. The small
capacity plants tend to be lower in efficiency because of economic
trade-offs; efficiency-enhancing equipment cannot pay for itself in small
plants. Although techniques exist to push biomass steam generation
efficiency over 40%, actual plant efficiencies are in the low 20% range.
Co-firing
involves substituting biomass for a portion of coal in an
existing power plant furnace. It is the most economic
near-term option for introducing new biomass power
generation. Because much of the existing power plant
equipment can be used without major modifications, cofiring
is far less expensive than building a new BioPower plant.
Compared to the coal it replaces, biomass reduces
sulphur dioxide (SO2),
nitrogen oxides (NOx), and other air emissions.
After "tuning" the boiler for peak performance, there is
little or no loss in efficiency from adding biomass. This
allows the energy in biomass to be converted to electricity
with the high efficiency (in the 33-37% range) of a modern
coal-fired power plant.
Biomass
gasifiers operate by heating biomass in an
environment where the solid biomass breaks down to form a
flammable gas. This offers advantages over directly burning
the biomass. The biogas can be cleaned and filtered to
remove problem chemical compounds. The gas can be used in
more efficient power generation systems called
combined-cycles, which combine gas turbines and steam
turbines to produce electricity. The efficiency of these
systems can reach 60%.
Gasification systems will be coupled with fuel cell systems
for future applications. Fuel cells convert hydrogen gas to
electricity (and heat) using an electro-chemical process.
There are very little air emissions and the primary exhaust
is water vapor. As the costs of fuel cells and biomass
gasifiers come down, these systems will proliferate.
Modular systems employ some of the same technologies
mentioned above, but on a smaller scale that is more
applicable to villages, farms, and small industry. These
systems are now under development and could be most useful
in remote areas where biomass is abundant and electricity is
scarce. There are many opportunities for these systems in
developing countries.
Frequently Asked Questions
What are some useful terms?
What is biomass?
Biomass is any sort of vegetation-trees, grasses, plants
parts such as leaves, stems and twigs, and ocean plants.
From it, we can extract a wealth of stored energy. Biomass
is available from various industries—including agriculture,
forest products, transportation, and construction—that
dispose of large quantities of wood and plant products.
Whether cultivated or growing wild, biomass represents a
huge renewable energy source.
What's the difference between
biomass and
biofuel?
"Biofuel" is short for "biomass fuel." In practice, we tend
to use different terms for different end uses—electric power
or transportation. We tend to use "BioPower" for biomass
power systems that produce electricity and "biofuels" for
liquid fuels for transportation.
What is biomass power?
Biomass power is the use of biomass
feedstocks instead of the usual fossil fuels (natural
gas or coal) to produce electricity.
What type of energy do plants produce?
During photosynthesis, plants combine carbon dioxide from
the air and water from the ground to form carbohydrates,
which form the building blocks of biomass. The solar energy
that drives photosynthesis is stored in the chemical bonds
of the structural components of biomass. If we burn biomass
efficiently (which extracts the energy stored in the
chemical bonds), then oxygen from the atmosphere combines
with the carbon in plants to produce carbon dioxide and
water.
How much biomass exists right now?
If we took all the biomass available today, the energy
content in that fuel would produce an estimated 2,740
Quads, with just 1 Quad equal to 1,000,000,000,000,000
Btus.
How can biomass be used?
It can produce electricity, liquid fuels, gaseous fuels, and
a variety of useful chemicals, including those currently
manufactured from petroleum. Because the energy in biomass
is less concentrated than the energy in fossil fuels, new
technologies are required to make this energy resource
competitive with coal, oil, and natural gas. Industry and
agriculture need superior
energy crops and cost-effective conversion technologies
to expand the use of renewable biomass.
How much biomass is being used as fuel?
At present, the world population uses only about 7% of the
annual production of biomass. There is an abundance of
biomass that we can tap.
What is the make-up of biomass?
While the actual ratio of components varies among species,
biomass averages 75% carbohydrates or sugars and 25% lignin.
How much biomass is used for energy today?
Worldwide, biomass is the fourth largest energy resource
after coal, oil, and natural gas. It is used for heating
(such as wood stoves in homes and for process heat in
bioprocessing industries), cooking (especially in
many parts of the developing world), transportation
(fuels such as ethanol) and, increasingly, for electric
power production. There are estimates of about 35,000
MW of installed capacity using biomass worldwide, with
about 7,000 of that in the United States. Most of this
capacity is in the pulp and paper industry in combined heat
and power systems.
Is municipal solid waste (MSW) considered
biomass?
In its mixed waste form, MSW typically contains materials
not suitable for use at BioPower facilities. Although a
large fraction of the mass of municipal solid waste
originates from plant matter the mixture with other urban
wastes precludes its use in BioPower facilities. Materials
recovery facilities that keep clean biomass materials (e.g.
wood pallets, wood shavings and tree trimmings) segregated
from other wastes are a potential source of biomass fuels.
Biomass, when used in modern power systems, produces fewer
emissions than conventional solid fuels used in power
plants.
How is biomass used to produce power?
Biomass is one of the oldest fuels known to humanity.
Although basic, the primitive campfire illustrates the
nature of using biomass for power. When the biomass is
burned, it produces heat. In a power plant, this heat is
used to turn water into steam. The steam is then used to
turn
turbines, which are connected to electric generators.
Gasifiers heat the biomass to convert it into a gas that
can be used in high efficient power systems, such as
combustion turbines or fuel cells.
What are energy crops?
Energy crops are crops that are grown for the specific
purpose of producing energy (electricity or liquid fuels)
from all or part of the resulting plant. Switchgrass,
alfalfa, willow, poplar and eucalyptus are examples of
plants that can be grown as energy crops.
What are the best biomass fuels for power
systems?
Right now, wood is most widely used because wood-fired power
systems have been in use for a long time and are well
understood. In addition, there is an abundance of wood
residue available for use in power systems from
bioprocessing industries such as the wood products industry.
However, the development of
gasifiers may make many other
biomass fuels usable for producing electricity.
Where are biomass resources located?
Virtually every part of the world has a biomass resource
that can be tapped to create power.
What are biomass gasifiers?
Biomass
gasifiers are reactors that heat biomass in a low-oxygen
environment to produce a fuel gas that contains from one
fifth to one half (depending on the process conditions) the
heat content of natural gas. For biomass, this process takes
place at about 850 degrees C.
What is renewable energy?
Renewable energy is any energy source that can be either
replenished continuously or within a moderate timeframe.
Renewable power sources include solar power, biomass power,
wind power, hydropower, and geothermal power.
Is biomass really a renewable energy?
Yes. If biomass is cultivated and harvested properly, it is
a renewable resource that can be used to generate power on
demand, with no net additional contribution to global
air emissions.
What are examples of modern power systems
that can be fueled by biomass gasifier?
The gas produced from a gasifier can drive highly efficient
devices such as
turbines and
fuel cells to generate electricity.
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