Biogas
Biogas represents an alternative source of energy, derived mainly from organic wastes. In India, the use of biogas derived from animal waste, primarily cow dung has been promoted for over three decades now.
Biogas is a clean fuel produced through anaerobic digestion of a variety of organic wastes: animal, agricultural, domestic, and industrial.
Anaerobic digestion comprises three steps.
- Decomposition (hydrolysis) of plant or animal matter to break down complex organic materials into simple organic substances
- Conversion of decomposed matter into organic acids
- Conversion of acids into methane gas
As the process temperature affects the rate of digestion, it should be maintained in the mesophilic range (30 °C–40 °C) with an optimum of 35 °C. It is also possible to operate plants in the thermophilic range (55 °C–65 °C) under controlled conditions. Apart from temperature, the rate of biogas production also depends on factors such as the carbon: nitrogen ratio, hydraulic retention time, solid concentration, and types of feedstock.
Biogas consists of methane, carbon dioxide, and traces of other gases such as hydrogen, carbon monoxide, nitrogen, oxygen, and hydrogen sulphide. The gas mixture is saturated with water vapour and may contain dust particles. The relative percentages of these gases depend on the quality of feed material and the process conditions. The percentage of methane in the gas determines its calorific value as the other constituents do not contribute to the energy content. The methane content of biogas is appreciably high, at 60%. This provides a calorific value high enough to find use in many energy applications, including power generation.
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Applications
- Cooking Biogas can be used for cooking in a specially designed burner. A biogas plant of 2 m3 capacity is sufficient for providing cooking fuel to a family of four to five.
- Lighting Gas lamps can be fuelled by biogas. To power a 100 candle lamp (60 W), the biogas required is 0.13 m3 per hour.
- Power generation Biogas can be used to operate a dual-fuel engine and can replace up to 75% of the diesel.
Benefits
- Provides a non-polluting and renewable source of energy
- Efficient way of energy conversion (saves fuelwood)
- Saves women and children from drudgery of collection and carrying of firewood, exposure to smoke in the kitchen, and time consumed for cooking and cleaning of utensils
- Produces enriched organic manure, which can supplement chemical fertilizers
- Leads to improvement in the environment, and sanitation and hygiene
- Provides a source for decentralized power generation
- Leads to employment generation in the rural areas
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