Source and principle of biogas plant

Biogas plant

Biogas is produced by decomposition of organic waste in the absence of oxygen. The fuel so produced is a clean and efficient fuel. It is a mixture of methane (CH₄), carbon dioxide (CO₂), hydrogen (H₂) and hydrogen sulphide (H₂S).

The main constituent of biogas is methane (upto 75%).

Raw Materials Required

• Cow and buffalo or other animal dung
• Wastes of polutary farm
• Agriculture wastes ( Husk, grass, weeds etc.)
• Human excreta
• Industrial wastes(Saw dust, wastes from food processing industries)
• Domestic wastes (Vegetable peels, waste food materials)

Principle

Biogas is produced as a result of anaerobic fermentation of biomass in the presence of water.

Construction

The biogas plant is a brick and cement structure having the following five sections:

• Mixing tank; for mixing of organic waste and water; present above the ground level
• Inlet chamber, which let the mixture to get into the main body. The mixing tank opens underground into a sloping inlet chamber
• Digester: Digester is a place in biogas plant where mixture is decomposed in the absence of oxygen. 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: Through outlet chamber decomposed organic waste goes out.The digester opens from below into an outlet chamber
• Overflow tank: If something goes overflow then it is used.The outlet chamber opens from the top into a small over flow tank

Working Principle of biogas plant:-

• Available biomass mainly cow dung, agriculture waste and kitchen wastes are mixed with an equal quantity of water in the mixing tank. Slurry so produced is fed in to the chamber.
• The slurry so made by mixing organic waste and water is fed into the digester through the inlet chamber. In order to have a proper digestion of organic waste, the temperature of the slurry must be maintained around 35 ^oC. Drop in temperature will reduce the anaerobic activity which may reduce the production of biogas.
• 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 decompose or ferment 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
• The spent slurry overflows into the overflow tank and is used for manure for plants. Organic manure is excellent as fertilizers.
• 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
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Advantages of Fixed Dome Type of Biogas Plant

• For the construction only local materials can be used.
• It is very less expensive, thus feasible for all people to install it.
• No big high tech is required so easy to construct

Advantages of Biogas as a Fuel

• Can be used as domestic fuel
• It is for street lighting
• For generation of electricity
• High calorific value

• Clean and excellent fuel containing upto 75% methane
• No residue produced
• No smoke produced
• Non - polluting
• The slurry is periodically removed and used as excellent manure which is rich in nitrogen and phosphorous
• Economical
• Can be supplied through pipe lines
• Burns readily - has a convenient ignition temperature
  
  Advantages of Biogas Plants
• Reduces burden on forests and fossil fuels
• Produces a clean fuel - helps in controlling air pollution
• Provides nutrient rich (N & P) manure for plants
• Controls water pollution by decomposing sewage, animal dung and human excreta

Limitations of Biogas Plants

• Initial cost of installation of the plant being high, and is beyond the reach of an average rural Indian
• Number of cattle owned by an average family of farmers is inadequate to feed a biogas plant