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Question
Explain the principle and working of a biogas plant using a labeled diagram.
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Solution
The arrangement of producing biogas from animals dung, human excreta, industrial and domestic wastes is known as a biogas plant.
Fixed-dome type biogas plant:
Construction: Fixeddome type biogas plant
It consists of a well-like underground tank made of bricks and cement. This tank is called a digester and has inlet and outlet valves. The roof of the tank is dome-shaped. A gas outlet pipe at the top of the dome is fitted. The dome of the digester acts as a storage tank of biogas. There is a mixing tank made above the ground level which is connected to the inlet valve of the digester through a slopping inlet chamber below the ground level. On the other side of the digester, a rectangular tank called an outlet chamber is constructed with bricks and cement. This outlet chamber is connected to the overflow tank which collects the used slurry.
Working: Animals-dung is mixed with water to make a slurry in the mixing tank. This slurry enters the digester through the inlet chamber. The digester is filled partially with slurry so that enough space is left above it in the dome for the collection of biogas. The slurry in the digester is left for about two months for fermentation. Anaerobic microorganisms are responsible for this action. As a result of fermentation, biogas is formed which is collected in the dome. When a sufficient amount of biogas is collected in the dome, it exerts a large pressure on the slurry and forced it to go into the overflow tank through the outlet chamber. The biogas is taken out from the dome through a pipe and used for cooking food or heating water whenever required. Once the biogas plant starts functioning, more and more slurry may be fed into the digester to get the continuous supply of biogas. The used slurry collected in the overflow tank is rich in nitrogen and phosphorus which are essential for the growth of crops and plants. Hence this used slurry can be used as manure.
Fixed-dome type biogas plant:
Construction: Fixeddome type biogas plant
It consists of a well-like underground tank made of bricks and cement. This tank is called a digester and has inlet and outlet valves. The roof of the tank is dome-shaped. A gas outlet pipe at the top of the dome is fitted. The dome of the digester acts as a storage tank of biogas. There is a mixing tank made above the ground level which is connected to the inlet valve of the digester through a slopping inlet chamber below the ground level. On the other side of the digester, a rectangular tank called an outlet chamber is constructed with bricks and cement. This outlet chamber is connected to the overflow tank which collects the used slurry.
Working: Animals-dung is mixed with water to make a slurry in the mixing tank. This slurry enters the digester through the inlet chamber. The digester is filled partially with slurry so that enough space is left above it in the dome for the collection of biogas. The slurry in the digester is left for about two months for fermentation. Anaerobic microorganisms are responsible for this action. As a result of fermentation, biogas is formed which is collected in the dome. When a sufficient amount of biogas is collected in the dome, it exerts a large pressure on the slurry and forced it to go into the overflow tank through the outlet chamber. The biogas is taken out from the dome through a pipe and used for cooking food or heating water whenever required. Once the biogas plant starts functioning, more and more slurry may be fed into the digester to get the continuous supply of biogas. The used slurry collected in the overflow tank is rich in nitrogen and phosphorus which are essential for the growth of crops and plants. Hence this used slurry can be used as manure.
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