Introduction to biogas
What is biogas?
• Biogas consists of about 2/3 methane
(CH4), 1/3 carbon dioxide (CO2) a little
hydrogen sulphide (H2S) and a little
hydrogen (H2).
• It is created by the decomposition of
manure and other forms of organic waste
from industry or house holds in anaerobic
(that is oxygen free) tanks.
• Advantages of biogas?
– Biogas is a renewable energy form.
– Biogas is CO2 equivalent reducing.
– Biomass naturally decomposes releasing methane and other
gasses into the atmosphere, by gathering this material,
extracting and burning the gas, the green house gas emission
are significantly reduced.
– By utilizing biogas as an energy source we can reduce our
dependency on fossil based carbon such as coal, oil and natural
gas.
• Disadvantages of biogas
– Biogas can cause obnoxious smells
– Degasification increases the risk of evaporation of ammonia
There are two types of biogas plants in usage
for the production of biogas.
• The fixed- dome type of biogas plant
• The floating gas holder type of biogas plant
Raw materials required
• Forms of biomass listed below may be used
along with water.
• Animal dung
• Poultry wastes
• Plant wastes ( Husk, grass, weeds etc.)
• Human excreta
• Industrial wastes(Saw dust, wastes from food
processing industries)
• Domestic wastes (Vegetable peels, waste food
materials)
Construction of The fixed- dome
type of biogas plant
• The biogas plant is a brick and cement structure having
the following five sections:
• Mixing tank present above the ground level.
• Inlet chamber: The mixing tank opens underground into
a sloping inlet chamber.
• Digester: The inlet chamber opens from below into the
digester which is a huge tank with a dome like ceiling.
The ceiling of the digester has an outlet with a valve for
the supply of biogas.
• Outlet chamber: The digester opens from below into an
outlet chamber.
• Overflow tank: The outlet chamber opens from the top
into a small over flow tank.
Working of biogas plant
• The various forms of biomass are mixed with an
equal quantity of water in the mixing tank. This
forms the slurry.
• The slurry is fed into the digester through the
inlet chamber.
• When the digester is partially filled with the
slurry, the introduction of slurry is stopped and
the plant is left unused for about two months.
• During these two months, anaerobic bacteria
present in the slurry decomposes or ferments
the biomass in the presence of water.
• As a result of anaerobic fermentation, biogas is
formed, which starts collecting in the dome of
the digester.
Working of biogas plant
• As more and more biogas starts collecting, the
pressure exerted by the biogas forces the spent
slurry into the outlet chamber.
• From the outlet chamber, the spent slurry
overflows into the overflow tank.
• The spent slurry is manually removed from the
overflow tank and used as manure for plants.
• The gas valve connected to a system of
pipelines is opened when a supply of biogas is
required.
• To obtain a continuous supply of biogas, a
functioning plant can be fed continuously with
the prepared slurry.
Advantages of fixed dome type of
biogas plant
• Requires only locally and easily available
materials for construction.
• Inexpensive.
• Easy to construct.
Construction of the floating gas
holder type plant
• The floating gas holder type of biogas plant has the following
chambers/ sections:
• Mixing Tank - present above the ground level.
• Digester tank - Deep underground well-like structure. It is divided
into two chambers by a partition wall in between.
• It has two long cement pipes: i) Inlet pipe opening into the inlet
chamber for introduction of slurry.
• ii) Outlet pipe opening into the overflow tank for removal of spent
slurry.
• Gas holder - an inverted steel drum resting above the digester. The
drum can move up and down i.e., float over the digester. The gas
holder has an outlet at the top which could be connected to gas
stoves.
• Over flow tank - Present above the ground level.
Thank you…………….
