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Biogas

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Biogas• Biogas is a mixture of methane and

carbon dioxide produced by the bacterial decomposition of organic wastes and where methane is used a cooking fuel.

• The organic wastes that can be included in biogas plants are:

Cow dung waste

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Types of biogas plants

Biogas plants

Conventional

Domed shape

Floating type

Modern

Nisargruna biogas

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• In conventional biogas plant, biogas is produced by anaerobic digestion with anaerobic bacteria or fermentation of biodegradable materials such as manure, sewage, municipal waste, green waste, plant material, and crops.• Gas produced is primarily methane (CH4) and carbon dioxide (CO2) and may have small amounts of hydrogen sulphide (H2S), moisture and siloxanes.

Conventional biogas plant

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There are two types of conventional biogas plant :

• Fixed dome biogas plant• Floating drum biogas plant

Conventional biogas plant

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• A fixed-dome plant comprises of a closed, dome-shaped digester with an immovable, rigid gas-holder and a displacement pit, also named 'compensation tank'.

• When gas production starts, the slurry is displaced into the compensation tank.

• Gas pressure increases with the volume of gas stored.

• If there is little gas in the gas-holder, the gas pressure is low.

Fixed dome biogas plant

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Fixed dome biogas plant

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• Relatively low construction costs.• The absence of moving parts and rusting steel parts. • If well constructed, fixed dome plants have a long life span.• The underground construction saves space and protects the digester from temperature changes.• The construction provides opportunities for skilled local employment.

Advantages

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• Fluctuating gas pressure complicates gas utilization.

• Amount of gas produced is not immediately visible.

• Fixed dome plants need exact planning of levels.

• Excavation can be difficult and expensive in bedrock.

Disadvantages

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• A floating-drum plant consists of a cylindrical or dome-shaped digester and a moving, floating gas-holder, or drum.

• The gas-holder floats either directly in the fermenting slurry or in a separate water jacket.

• The drum in which the biogas collects has an internal and/or external guide frame that provides stability and keeps the drum upright.

• If biogas is produced, the drum moves up, if gas is consumed, the gas-holder sinks back.

Floating drum biogas plant

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• Floating-drum plants are easy to understand and operate.• They provide gas at a constant pressure.• The stored gas-volume is immediately recognizable by the position of the drum.• Gas-tightness is no problem, provided the gasholder is de-rusted and painted regularly.

Advantages

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• The steel drum is relatively expensive and maintenance-intensive.

• Removing rust and painting has to be carried out regularly.

• The life-time of the drum is short (up to 15 years; in tropical coastal regions about five years).

• If fibrous substrates are used, the gas-holder shows a tendency to get "stuck" in the resultant floating scum.

Disadvantages

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Industries having biogas plant Nestle:• At around 28 plants of nestle there

exist biogas units.  They use cow manure to generate biogas and bio-fertilizers in order to reduce the environmental impact. environment

Biogas plant installed in nestle, Mexico

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• KhanKhel Dairy Farm:• Biogas-generated electricity from a

dairy manure digester in Punjab (Pakistan) is being used for water pumping at a dairy farm.

Industries having biogas plant

Biogas generated is being used to generate electricity

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• Biogas plant at Pepsico Pune:• 18MT of waste per day • 2500 M3 of biogas per day• Saving 140MT of LPG and

approximately cost of $140 million per annum.

Industries having biogas plant

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Developed by Senior Scientist Dr. Sharad Kale at BARC in Mumbai.

Nisargruna technology has been developed for processing of biodegradable solid waste materials based on aerobic-anaerobic sequential processes.

Nisargruna biogas plant

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Nisargruna technology honoured with Padma Shri Award 2013

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How the Plant Operates ?

A combination of Aerobic + Anerobic Digestion

The main steps of Nisargruna (biogas) production :

1. Hydrolysis2. Acidification3. Methane formation

Plant setup comprises :

• Receiving Platform • Segregating Platform• Mixer• Pre-digester tank• Main Tank (Secondary Digester)• Manure

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Nisargruna Biogas Plant Conventional Biogas Plant

Higher costing Lower costing

Broader scope of raw materials Mainly based on cow dung

Mixers are used for better homogenization

No homogenization

High rate of bio-methanation process Low rate of bio-methanation process

Pre-digestion in aerobic chamber No set-up for pre-digestion

Removal of scum forming protein materials

No set-up to remove scum forming material

Improved structure for better flow, entrapment and enrichment of biogas

Conventional dome structure

Nisargruna Biogas Plant Conventional Biogas Plant

Settling tank for water recycling No water recycling

Biogas has a better fuel value Biogas has low fuel value

Lower CO2 and higher methane levels in biogas

Higher CO2 levels in biogas

More hygienic and less smell Less hygienic and more smell

Higher plant life (40 years) Normal plant life

Manure has high organic content and is weed free

Manure is generally of not very high quality

Comparison with Conventional Plant

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Advantage of biogas plant

• Renewable source of energy• Non polluting.• Reduces landfills• Cheaper in cost• No problem to warm the water in Nisargruna technology as in includes Solar panel.

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Limitation of biogas plant

• Need for regular and optimum feeding in the digester.

• Egg shell, bones cannot be included as the reduces the efficiency of the plant.

• Regular addition of warm water in winters to maintain the optimum temperature for bacteria.

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Economical viability of biogas unit

Cost of LPG (Commercial 19 KG cylinder)= ₹ 88.52/kg

Nisargruna biogas plant of 0.5 MT

Plant construction cost: ₹ 15Lakhs (without subsidy) Plant construction cost : ₹ 9 Lakhs (with subsidy)

Total gas production =25 Kg/day (equivalent to LPG)

Total cost of biogas = 25X88.52X365(days)= ₹ 8.07 Lakhs

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Continued……..Profit from sale of manure =50(kg) X 5 X 365= ₹ 0.91 lakhs/- Total profit generated = ₹ 8.98/-

Payback period = 15/8.98 =1.67 years (without subsidy) Payback period = 9/8.98 = 1.002 years (with subsidy)

Later the gas generated will be free

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