Agriculture Reference
In-Depth Information
In some areas corn, cornstalks, sugarbeets, sugar cane, and switchgrasses are
grown specifically to produce ethanol (also known as grain alcohol), a liquid which
can be used in internal combustion engines and fuel cells. Ethanol is being phased
into the current energy infrastructure. E85 is a fuel composed of 85% ethanol
and 15% gasoline that is sold to consumers. Biobutanol is being developed as an
alternative to bioethanol. There is growing international criticism about biofuels
from food crops with respect to issues such as food security, environmental impacts
(deforestation), and energy balance.
According to the International Energy Agency, new biofuels technologies being
developed today, notably cellulosic ethanol, could allow biofuels to play a much big-
ger role in the future than previously thought. Cellulosic ethanol can be made from
plant matter composed primarily of inedible cellulose fibers that form the stems and
branches of most plants. Crop residues (such as corn stalks, wheat straw and rice
straw), wood waste, and municipal solid waste are potential sources of cellulosic
biomass. Dedicated energy crops, such as switchgrass, are also promising cellulose
sources that can be sustainably produced in many regions of the United States.
13.7.2 Biogas
Biogas can easily be produced from current waste streams, such as paper production,
sugar production, sewage, animal waste, and so forth. These various waste streams
have to be slurried together and allowed to naturally ferment, producing methane
gas. This can be done by converting current sewage plants into biogas plants. When
a biogas plant has extracted all the methane it can, the remains are sometimes better
suitable as fertilizer than the original biomass.
13.8 Geothermal Energy
Geothermal energy is an energy obtained by tapping the heat of the earth itself,
usually from kilometers deep into the Earth's crust. Ultimately, this energy derives
from heat in the Earth's core. It is expensive to build a power station to harness this
energy, but operating costs are low resulting in low energy costs for suitable sites.
The International Energy Agency classifies geothermal power as renewable.
Three types of power plants are used to generate power from geothermal energy:
dry steam
flash
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Dry steam plants take steam out of fractures in the ground and use it to directly
drive a turbine that spins a generator. Flash plants take hot water (usually at temper-
atures over 200 C) out of the ground, and allows it to boil as it rises to the surface
then separates the steam phase in steam/water separators and then runs the steam
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