For ages, cow’s excreta traditionally has been used as manure in the fields, but they are also a source of viable energy biogas, which is capable of providing electricity for domestic purposes. One cow can produce over 30 gallons of manure a day. 100 cows can produce about 30,000 gallons of manure. All that manure can be turned into serious energy generation process for powering electrical equipments for various domestic purposes.
Cow dung is used in many developing countries for generating energy. It has a lot of potential to reduce carbon footprint. By capturing and storing CO2 from biogas into the ground, the biogas becomes carbon negative and scrubs our past CO2 emissions out of the atmosphere.
All the collected cow dung is fed into an anaerobic digester. Anaerobic Digester:
The digester is built to hold 21 days of farm waste at roughly 100o. Bacteria convert the waste into various products, one of which is methane gas. Gas produced by the bacteria builds up the pressure in the concrete vessel, and a pipe delivers the biogas to a modified natural gas engine.
The biogas fuels the engine, which in turn spins an electric generator to create electricity. Waste heat from the engine is used to keep the digester warm and offsets fuel purchase on the farm.
One cow’s waste can produce enough electricity to light two 100-watt light bulbs for 24 hours a day. The energy is fed onto the electrical system for distribution to customers.
Dry Solid Waste:
Digested Manure is processed through a mechanical seperator. The odourless solids can be used to replace sawdust or sand as bedding for the animals. Solids not used for bedding may be further processed and sold to public.
Cow dung gas is 55-65% methane, 30-35% carbon dioxide, with some hydrogen, nitrogen and other traces. Its heating value is around 600 B.T.U. per cubic foot.
Cow dung slurry is composed of 1.8-2.4% nitrogen (N2), 1.0-1.2% phosphorus (P2O5), 0.6-0.8% potassium (K2O) and 50-75% organic humus.
About one cubic foot of gas may be generated from one pound of cow manure at around 28°C. This is enough gas to cook a day’s meals for 4-6 people in India.
About 1.7 cubic metres of biogas equals one litre of gasoline. The manure produced by one cow in one year can be converted to methane, which is the equivalent of over 200 litres of gasoline.
Gas engines require about 0.5 m3 of methane per horsepower per hour. Some care must be taken with the lubrication of engines using solely biogas due to the “dry” nature of the fuel and some residual hydrogen sulphide, otherwise these are a simple conversion of a gasoline engine.