|
|
|
|
|
|
| |
|
|
|
|
|
| |
Biomass Facts |
|
|
|
|
|
|
|
|
|
|
|
|
|
|
| |
Biomass is a renewable
energy source because
the energy it contains
comes from the sun.
Through the process of
photosynthesis,
chlorophyll in plants
captures the sun's
energy by converting
carbon dioxide from the
air and water from the
ground into
carbohydrates, complex
compounds composed of
carbon, hydrogen, and
oxygen. When these
carbohydrates are
burned, they turn back
into carbon dioxide and
water and release the
sun's energy they
contain. In this way,
biomass functions as a
sort of natural battery
for storing solar
energy. As long as
biomass is produced
sustain ably - with only
as much used as is
grown - the battery will
last indefinitely.
The most common way to
capture the energy from
biomass was to burn it,
to make heat, steam, and
electricity. But
advances in recent years
have shown that there
are more efficient and
cleaner ways to use
biomass. It can be
converted into liquid
fuels, for example, or
cooked in a process
called "gasification" to
produce combustible
gases. And certain crops
such as switch grass and
willow trees are
especially suited as
"energy crops," plants
grown specifically for
energy generation
|
|
Types of Biomass |
There are many
types of plants
in the world,
and many ways
they can be used
for energy
production. In
general there
are two
approaches:
growing plants
specifically for
energy use, and
using the
residues from
plants that are
used for other
things. The best
approaches vary
from region to
region according
to climate,
soils,
geography,
population, and
so on.
|
|
Energy Crops |
Energy crops,
also called
"power crops,"
could be grown
on farms in
potentially very
large
quantities, just
like food crops.
Trees and
grasses,
particularly
those that are
native to a
region, are the
best crops for
energy, but
other, less
agriculturally
sustainable
crops such as
corn tend to be
used for energy
purposes at
present.
|
Trees.
In addition to
growing very
fast, some trees
will grow back
after being cut
off close to the
ground, a
feature called
"coppicing."
Coppicing allows
trees to be
harvested every
three to eight
years for 20 or
30 years before
replanting.
These trees,
also called
"short
- rotation
woody crops,"
grow as much as
40 feet high in
the years
between
harvests.
|
Grasses.
Thin - stemmed
perennial
grasses used to
blanket the
prairies of the
United States
before the
settlers
replaced them
with corn and
beans. Switchgrass, big
bluestem, and
other native
varieties grow
quickly in many
parts of the
country, and can
be harvested for
up to 10 years
before
replanting.
Thick - stemmed
perennials like
sugar cane and
elephant grass
can be grown in
hot and wet
climates like
those of Florida
and Hawaii.
|
Other
crops. A
third type of
grass includes
annuals commonly
grown for food,
such as corn and
sorghum. Since
these must be
replanted every
year, they
require much
closer
management and
greater use of
fertilizers,
pesticides, and
energy. While
corn currently
provides most of
the liquid fuel
from biomass in
the United
States, there
are more
sustainable ways
to produce
energy from
plants.
|
Oil plants.
Plants such as
soybeans and
sunflowers
produce oil,
which can be
used to make
fuels. Like
corn, though,
these crops
require
intensive
management and
may not be
sustainable in
the longer term.
A rather
different type
of oil crop with
great promise
for the future
is microalgae.
These tiny
aquatic plants
have the
potential to
grow extremely
fast in the hot,
shallow, saline
water found in
some lakes in
the desert
Southwest. In
2004, Green Fuel
Technologies, a
Massachusetts - based
company,
harnessed the
ability to
capture and use
carbon dioxide
emissions from
power plants as
a means to
stimulate algae
growth.[2] The
algae is then
converted into a
various range of
fuels. This
technology,
known as
Emissions - to - Biofuels,
is demonstrating
great promise
and has the
potential to
transform the
way utilities
produce energy.
|
|
Biomass Residues |
|
After plants have been
used for other purposes,
the leftover wastes can
be used for energy. The
forestry, agricultural,
and manufacturing
industries generate
plant and animal wastes
in large quantities.
City waste, in the form
of garbage and sewage,
is also a source for
biomass energy.
|
Forestry.
Forestry wastes are the
largest source of heat
and electricity now,
since lumber, pulp, and
paper mills use them to
power their factories.
One large source of wood
waste is tree tops and
branches normally left
behind in the forest
after timber - harvesting
operations. Some of
these must be left
behind to recycle
necessary nutrients to
the forest and to
provide habitat for
birds and mammals, but
some could be collected
for energy production.
Other sources of wood
waste are sawdust and
bark from sawmills,
shavings produced during
the manufacture of
furniture, and organic
sludge (or "liquor")
from pulp and paper
mills.
|
Agriculture.
As with the forestry
industry, most crop
residues are left in the
field. Some should be
left there to maintain
cover against erosion
and to recycle
nutrients, but some
could be collected for
fuel. Animal farms
produce many "wet
wastes" in the form of
manure. These wastes are
commonly spread on
fields, not just for
their nutrient value,
but for disposal. Runoff
from overfertilization
threatens rural lakes
and streams and can
contaminate drinking
water. Processing crops
into food also produces
many usable wastes.
|
Cities.
People generate biomass
wastes in many forms,
including "urban wood
waste" (such as shipping
pallets and leftover
construction wood), the
biodegradable portion of
garbage (paper, food,
leather, yard waste,
etc.) and the gas given
off by landfills when
waste decomposes. Even
our sewage can be used
as energy; some sewage
treatment plants capture
the methane given off by
sewage and burn it for
heat and power, reducing
air pollution and
emissions of global
warming gases.
|
|
Converting Biomass to
Energy
|
The
old way of converting
biomass to energy,
practiced for thousands
of years, is simply to
burn it to produce heat.
The heat can be used
directly, for heating,
cooking, and industrial
processes, or
indirectly, to produce
electricity. The
problems with burning
biomass are that much of
the energy is wasted and
that it can cause some
pollution if it is not
carefully controlled.
An approach that may
increase the use of
biomass energy in the
short term is to burn it
mixed with coal in power
plants - a process known
as “co - firing.” Biomass
feedstock can substitute
up to 20 percent of the
coal used in a
boiler. The benefits
associated with biomass
co - firing include lower
operating costs,
reductions of harmful
emissions, and greater
energy security.
Co - firing is also one of
the more economically
viable ways to increase
biomass power generation
today.
A number of
noncombustion methods
are available for
converting biomass to
energy. These processes
convert raw biomass into
a variety of gaseous,
liquid, or solid fuels
that can then be used
directly in a power
plant for energy
generation. The
carbohydrates in
biomass, which are
comprised of oxygen,
carbon, and hydrogen,
can be broken down into
a variety of chemicals,
some of which are useful
fuels. |
|
|
Corn
is one of the most
energy - intensive crops,
and current corn - based
ethanol production uses
just the kernels from
the corn plant, and not
even the entire kernel.
By making ethanol from
energy crops, we could
obtain between four and
five times the energy
that we put in, and by
making electricity we
could get perhaps 10
times or more. In the
future, to make a truly
sustainable biomass
energy system, we would
have to replace fossil
fuels with biomass or
other renewable fuels to
plant and harvest the
crops.
Another important
consideration with
biomass energy systems
is that biomass contains
less energy per pound
than fossil fuels. This
means that raw biomass
typically can't be
cost - effectively shipped
more than about 50 miles
before it is converted
into fuel or energy. It
also means that biomass
energy systems are
likely to be smaller
than their fossil fuel
counterparts, because it
is hard to gather and
process more than this
quantity of fuel in one
place. This has the
advantage that local,
rural communities
- and
perhaps even individual
farms - will be able to
design energy systems
that are
self - sufficient,
sustainable, and
perfectly adapted to
their own needs.
|
|
Environmental Benefits |
Biomass energy brings
numerous environmental
benefits - reducing air
and water pollution,
increasing soil quality
and reducing erosion,
and improving wildlife
habitat.
Biomass reduces air
pollution by being a
part of the carbon cycle
(see the box below),
reducing carbon dioxide
emissions by 90 percent
compared with fossil
fuels. Sulfur dioxide
and other pollutants are
also reduced
substantially.
Water pollution is
reduced because fewer
fertilizers and
pesticides are used to
grow energy crops, and
erosion is reduced.
Moreover, agricultural
researchers in Iowa have
discovered that by
planting grasses or
poplar trees in buffers
along waterways, runoff
from corn fields is
captured, making streams
cleaner.
In contrast to
high - yield food crops
that pull nutrients from
the soil, energy crops
actually improve soil
quality. Prairie
grasses, with their deep
roots, build up topsoil,
putting nitrogen and
other nutrients into the
ground. Since they are
replanted only every 10
years, there is minimal
plowing that causes soil
to erode.
Finally, biomass crops
can create better
wildlife habitat than
food crops. Since they
are native plants, they
attract a greater
variety of birds and
small mammals. They
improve the habitat for
fish by increasing water
quality in nearby
streams and ponds. And
since they have a wider
window of time to be
harvested, energy crop
harvests can be timed to
avoid critical nesting
or breeding seasons |
|
 |
| |
|
|
|
|
|
|
|
|
|
