|
|
|
|
|
Biogas |
Biogas
typically refers to a gas produced by the
biological breakdown of organic matter in
the absence of oxygen. Organic waste such as
dead plant and animal material, animal dung,
and kitchen waste can be converted into a
gaseous fuel called biogas. Biogas
originates from biogenic material and is a
type of biofuel.
Biogas is produced by the anaerobic
digestion or fermentation of biodegradable
materials such as biomass, manure, sewage,
municipal waste, green waste, plant
material, and crops. Biogas comprises
primarily methane (CH4) and carbon dioxide
(CO2) and may have small amounts of hydrogen
sulphide (H2S), moisture and siloxanes.
The gases methane, hydrogen, and carbon
monoxide (CO) can be combusted or oxidized
with oxygen. This energy release allows
biogas to be used as a fuel. Biogas can be
used as a fuel in any country for any
heating purpose, such as cooking. It can
also be used in anaerobic digesters where it
is typically used in a gas engine to convert
the energy in the gas into electricity and
heat.[2] Biogas can be compressed, much like
natural gas, and used to power motor
vehicles. In the UK, for example, biogas is
estimated to have the potential to replace
around 17% of vehicle fuel.[3] Biogas is a
renewable fuel, so it qualifies for
renewable energy subsidies in some parts of
the world. Biogas can also be cleaned and
upgraded to natural gas standards when it
becomes biomethane.
Biogas is practically produced as landfill
gas (LFG) or digester gas. A biogas plant is
the name often given to an anaerobic
digester that treats farm wastes or energy
crops. Biogas can be produced using
anaerobic digesters. These plants can be fed
with energy crops such as maize silage or
biodegradable wastes including sewage sludge
and food waste. During the process, an
air-tight tank transforms biomass waste into
methane producing renewable energy that can
be used for heating, electricity, and many
other operations that use any variation of
an internal combustion engine, such as GE
Jenbacher gas engines.[4] There are two key
processes: Mesophilic and Thermophilic
digestion.[5] In experimental work at
University of Alaska Fairbanks, a 1000-litre
digester using psychrophiles harvested from
"mud from a frozen lake in Alaska" has
produced 200–300 litres of methane per day,
about 20–30 % of the output from digesters
in warmer climates.
Landfill gas is produced by wet organic
waste decomposing under anaerobic conditions
in a landfill. The waste is covered and
mechanically compressed by the weight of the
material that is deposited from above. This
material prevents oxygen exposure thus
allowing anaerobic microbes to thrive. This
gas builds up and is slowly released into
the atmosphere if the landfill site has not
been engineered to capture the gas. Landfill
gas is hazardous for three key reasons.
Landfill gas becomes explosive when it
escapes from the landfill and mixes with
oxygen. The lower explosive limit is 5%
methane and the upper explosive limit is 15%
methane.[9] The methane contained within
biogas is 20 times more potent as a
greenhouse gas than is carbon dioxide.
Therefore, uncontained landfill gas, which
escapes into the atmosphere may
significantly contribute to the effects of
global warming. In addition, landfill gas
impact in global warming, volatile organic
compounds (VOCs) contained within landfill
gas contribute to the formation of
photochemical smog.
The composition of biogas varies depending
upon the origin of the anaerobic digestion
process. Landfill gas typically has methane
concentrations around 50%. Advanced waste
treatment technologies can produce biogas
with 55–75% methane, which for reactors with
free liquids can be increased to 80-90%
methane using in-situ gas purification
techniques[12] As-produced, biogas also
contains water vapor. The fractional volume
of water vapor is a function of biogas
temperature; correction of measured gas
volume for both water vapor content and
thermal expansion is easily done via a
simple mathematic algorithm which yields the
standardized volume of dry biogas. |
|
|
Enerim.it - Kimera
s.n.c. via M.Mariano 127 - 73043 - Copertino (Lecce) |
|
|
|
 |
|
