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Most of us have come across the gobar gas – literally meaning gas from the cow. It is the same as what is called biogas. This is the gas that is released when bacteria feast on organic matter – typically human and animal feces – and release a gas that is about 50% methane.
While biogas had predominantly been used earlier for heating purposes, its use for power production is also beginning to show a marked rise across the world, and in India too.
How is power produced from biogas? The process is actually quite simple.
Step 1 is generation of biogas. This is done typically using what are anaerobic called digesters. Animal (or human) waste is fed into the digester, where the microorganisms (called methanogenic bacteria) act upon it. Depending on the type of digester, it could take anywhere between 10 days to 15 days for the waste to have been “digested” by the bacteria and the release of biogas.
The biogas thus produced can be used in IC engines specially devised for the use of biogas. These engines are similar in working principles to diesel engines and natural gas engines. These engines produce electricity from biogas.
A bit of observation will lead us to easily understand why this concept will be of enormous interest to specific industry segments. Two segments stand out – industries that employ large numbers of animals and sewage treatment plants that treat human waste. Both these segments have started benefitting from this concept; as a result, we have a few STPs (sewage treatment plants) already generating power from the sludge generated (one of the STPs at Chennai, at a town called Nesapakkam, generates about 500 kW of power from the waste, and uses the power generated for all its electricity purposes).
Some numbers will help understand the potential available for power generation from biogas. The cow population of India (about 225 million) alone generates about 800 million tons of wet dung which translates to about 150 million T of dry weight. 1 Kg of dry cow dung can generate about 1.2 kWh of electricity (it can generate the equivalent of about 4 kWh thermal). Thus, if all cow dung were converted to electricity, that would be 1.2*150*1000 million kWh = 180 TWh. India generated a total of 855 TWh in 2011-12. This implies that cow dung, if entirely converted to power, would have produced about 20% of total India’s power! If the waste of other cattle and human waste were also taken into account, this could be about 30%. That is an awesome number.
Of course, these data hide the actual difficulty in converting even a small portion of animal or human waste into electricity, owing to the infrastructural and social problems associated with these. All the same, waste -> biogas -> power is quite practical to a whole host of industries for whom such waste is available on premises.
More information about waste to energy in general in the Indian context, is available from EAI’s waste to energy resource section. Some of the following YouTube videos provide a more visual account of how to generate biogas from organic waste:
Biogas from food waste – ARTI – http://www.youtube.com/watch?v=BGSl72xZHNk&feature=related
Bio-gas from kitchen waste and bio mass – http://www.youtube.com/watch?v=uppVZGS7bYI&feature=related
Biogas from Vegetarian Food Waste – http://www.youtube.com/watch?v=NZFrPZZIFTs&feature=related
Biogas from Human Waste – http://www.youtube.com/watch?v=_m1nr2v5S8o
And while on sewage, human waste and toilets, etc, a couple of interesting articles on things are emerging
The seat of power – Better sewage treatment is the latest thing in clean energy