Fuels - Part II
Bio gas :
Bio gas is made from organic waste matter after it is decomposed. The decomposition breaks
down the organic matter, releasing various gases. The main gases released
are methane, carbon dioxide, hydrogen and hydrogen sulphide. Bacteria carry out the decomposition or fermentation. The conditions
for creating bio gas has to be anaerobic that is without any air and in the
presence of water. The organic waste matter is generally animal or cattle
dung, plant wastes, etc. These waste products contain carbohydrates,
proteins and fat material that are broken down by bacteria.
The waste matter is soaked in water to give the bacteria a proper
medium to grow. Absence of air or oxygen is important for decomposition
because bacteria then take oxygen from the waste material itself and in the
process break them down.
are two types of bio gas plants that are used in India. These plants mainly
use cattle dung called “gobar” and are hence called gobar gas plant.
Generally a slurry is made from cattle dung and water, which forms the
starting material for these plants. The two types of bio gas plants are :
gas holder type of plant : The
diagram below shows the details of a floating gas holder type of bio gas
well is made out of concrete. This is called the digester tank T. It is
divided into two parts. One side has the inlet, from where slurry is fed to
the tank. The tank has a cylindrical dome H made of stainless steel that
floats on the slurry and collects the gas generated. Hence the name given to
this type of plant is floating gas holder type of bio gas plant. The slurry
is made to ferment for about 50 days. As more gas is made by the bacterial
fermentation, the pressure inside H increases. The gas can be taken out
through outlet pipe V. The
decomposed matter expands and overflows into the next chamber in tank T.
This is then removed by the outlet pipe to the overflow tank and is
used as manure for cultivation purposes.
dome type of plant : The
diagram below shows the details of a fixed dome type of bio gas plant.
well and a dome are made out of concrete. This is called the digester tank
T. The dome is fixed and hence the name given to this type of plant is fixed
dome type of bio gas plant. The function of the plant is similar to the
floating holder type bio gas plant. The used slurry expands and overflows
into the overflow tank F.