Explain construction and working of a biogas plant with labeled diagram.

CONSTRUCTION

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

• 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.

• 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.