Floating Dome Type Biogas Plant – Working with Neat Sketch

A floating dome type biogas plant is a widely used design in India for small to medium-scale biogas production. It is particularly popular in rural and agricultural areas due to its simplicity, ease of operation, and efficient handling of animal and organic waste. The most well-known model of this type is the KVIC (Khadi and Village Industries Commission) model.

Construction and Components

The floating drum biogas plant consists of the following main components:

1. Digester Tank:
   • A cylindrical underground tank usually made of brick, concrete, or RCC.
   • This is where anaerobic digestion takes place.
   • Organic matter (cow dung mixed with water in 1:1 ratio) is fed here.
2. Floating Gas Holder (Drum):
   • A metallic or plastic drum that floats over the slurry in the digester.
   • It rises and falls based on the gas produced.
   • Collects and stores the biogas generated by digestion.
3. Inlet Pipe and Inlet Chamber:
   • Allows feeding of slurry into the digester.
   • Typically connected to a mixing tank.
4. Outlet Pipe and Outlet Chamber (Displacement Tank):
   • Excess digested slurry overflows here.
   • This slurry is nutrient-rich and used as organic fertilizer.
5. Gas Outlet Pipe:
   • Draws gas from the gas holder to the appliances like stove or lamp.

Neat Sketch

Working Principle

1. Feeding the Slurry:
   Cow dung or other organic waste is mixed with water in equal proportion and poured into the digester through the inlet pipe.
2. Anaerobic Digestion:
   Inside the digester, in the absence of oxygen, anaerobic bacteria break down the organic matter. This process typically takes 30-40 days depending on the temperature.
3. Gas Generation:
   The digestion process releases biogas (mostly methane and carbon dioxide), which starts to accumulate in the floating drum placed above the slurry.
4. Gas Collection:
   As gas pressure builds up, the drum rises. The gas can be drawn through a pipe connected to the drum and used for cooking, lighting, etc.
5. Slurry Displacement:
   As gas builds up and the drum rises, the digested slurry is displaced into the outlet tank. This effluent is rich in nutrients and used as organic fertilizer.

Advantages of Floating Dome Biogas Plant

1. Simple Operation:
   Easy to construct, use, and maintain. Suitable for rural areas with limited technical support.
2. Visual Indication of Gas Production:
   The drum’s height acts as an indicator of gas level, making monitoring simple.
3. Durability:
   If built with quality materials, the plant can last for 15-20 years with periodic maintenance.
4. Dual Benefits:
   Provides both clean cooking fuel and organic manure.

Disadvantages

1. Steel Drum Corrosion:
   The metal drum can corrode due to contact with slurry and moisture, requiring regular painting or galvanization.
2. High Initial Cost:
   Slightly more expensive compared to fixed dome models due to the steel drum.
3. Regular Maintenance:
   Needs periodic checks for leaks or wear and tear in the drum.

Applications in India

• Domestic use: Cooking, lighting.
• Rural electrification: Small biogas generators.
• Waste management: Efficient way to manage animal waste.

The floating dome biogas plant is a practical and proven model widely adopted in India for household and small farm-scale energy production. Its straightforward design, efficient gas collection system, and multipurpose utility make it an ideal choice for rural communities. Despite some maintenance needs, its advantages far outweigh the disadvantages, especially in supporting sustainable energy and agriculture.