design of biogas digesters

7/28/2019 Design of Biogas Digesters

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DESIGN OF BIOGAS

DIGESTERSBy

SHARATH CHANDRA. J (2012H148035H)

K. VENKATESH (2012H148038H)


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Energy FormsPrimary energy sources

(A) Fossil energy sources (B) Renewable energy sources (C) Nuclear fuel

Hard coal Water Uran

Brown coal Sun Pluto

Petroleum Wind Thor

Natural gas Geothermal heat

Oil shale Tides Tar sand

Gas hydrateBiomass

Secondary

Energy

Sources

Biogas

Landfillgas


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Biogas generally comprise of 55-65 % methane, 35-4carbon dioxide, 0.5-1.0 % hydrogen sulfide and traceswater vapor.

Average calorific value of biogas is 20 MJ/m3 (4kcal/m3).

Critical temperature required for liquefaction of methis -82.1oC at 4.71MPa pressure, therefore use of biogalimited nearby the biogas plant.

An estimate indicates that India has a potential generating 6.38 X 1010 m3 of biogas from 980 million toof cattle dung produced annually.

The heat value of this gas amounts to 1.3 X 1012 MJaddition, 350 million tones of manure would also prodalong with biogas.


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POTENTIAL OF BIOGAS IN INDIA

* Cattle population : 300 million

* Farm families : 75 million

* Own 4 or more cattle : 43 million* Potential of setting up

family size BGP : 12 million

* Established till Dec 2009 : 4.1 million

* Dung collection (55% efficiency) : 1575 million kg/day

*Gas production : 39.85million cu-m of gas/day*Assuming 60% eff. equivalent to = 112695 million K. Cal/day

= 12.37 million L of kerosene= 14.54 million L of crude oil= 16.26 million Kg of coal= 23.94 million lit. of fire wood

= 131.04 million kWh. of electricity


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ORGANIC WASTES & THEIR ESTIMATEDAVAILABILITY IN INDIA

Sr.

No.

Organic Wastes Estimated Quantity

1. Municipal Solid waste 30 million tons/year

2. Municipal liquid waste 12000 million litres/day

3. Distillery (243 units) 8057 kilolitres/day

4. Press mud 9 million tons/year

5. Food & fruit processing wastes 4.5 million tons/year

6. Willow dust 30000 tons/year

7. Dairy industry waste 50-60 million litres/day

8. Paper & pulp industry waste (300 mills) 1600 m3/day

9. Tannery (2000 units) 52500 m3 waste water/day

Source: MNES Report, Renewable Energy in India and business opportunities, MNES. Govt. of India, New D


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BIOGASPRODUCTION PROCESS

Biogas production process (Anaerobic digestion) is a multiple-stage process i

which some main stages are:

Chemical reactions involved in biogas production:C6H12O6 3CO2 + 3CH4

CO2 + 4H2 > CH4 + 2H2O

CH3COOH > CH4 + CO2


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Overview of commercially viabletechnologies

Family size biogas plants (1 to 10 m3

)

Large scale biogas plants (10 to 140 m3

Large scale plants above 1000 m3


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Out

In letGas Out let Dome

Digester

FIXED DOME TYPE

BIOGAS PLANT


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An outline of fixed dome biogas plant

Detailed structural design of fixed dome biogas plant


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Out let

Pipe

In let

Pipe

Digester

Drum

FLOATING DRUM TYPE

BIOGAS PLANT

Gas

outletInlet

Outlet

Benefits:

Capacity to maintain ste

pressure of biogas by the

movement of gas holder

Inbuilt provision for scum

breaking

Volume of gas is known

observing the position of th


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Fixed Dome type family siBiogas plant

[1] Deenbandhu

[2] Modified for solid state* Water : (-) 3/4th* Space : (-) 3/4th* Gas : (+) 30%* Operation easier

* Cost almost same

1

2


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Then if we need 28 kg of bio gas to be equivalent to one bottle of Butane (14 kg)based on calorific value of butane is double of calorific Value of bio gas, which canbe enough for one home during one month.

Amount of dry waste needed per month= 28 kg biogas / 0.15 kg biogas/ 1 kg drywater = 186.67kg waste / month

If we used the ratio 1: 1 water to be added then we need 186. 67 litre of water tobe added to our 186. 67kg of organic waste then the total volume we Need 373.33litres (~375L).

Tank Volume = Volume of mixture + 20% of mixture volume for gas space

= volume of mixture (1+0.2)

= 375 Litter (1.2) = 450 Litre, (SAY 500 Litter) tank volume we need

= 1/2 m^3 tank volume will be good choice

DESIGN CALCULATIONS FOR A SMALL

FAMILY DIGESTER

Sketch of a family digester (0 5 m^3)


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Sketch of a family digester (0.5 m^3).


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Running cost

The annual running costs are:

1. Annual running cost to operate the digester =10% of digester cost [37] + water cost =

2500+5000= 7500/Year

2. (5000) water cost/year =200Liter/40day * 365 day/year=1825 Litre/Y

Biogas profit

Profit of produced biogas = (700 / one butane bottle /month) * 12 month/Year = 8400/Year.

Fertilizer Profit.

Price of 1 ton fertilizer 5000/Ton

Yearly fertilizer produced = 200kg /40 day x 365 day /year = 1825 kg/year

= 1.825 ton/year =>Yearly fertilizer profit = 1.825ton x 5000 = 9000/year

ECONOMIC EVALUATION OF A FAMILY

TYPE BIOGAS PLANT


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Total income/Year = biogas profit+ Fertilizer profit [37]

Total income/Year = 17400

The profit /year = income profit - running cost [37]

The profit /year = 17400 7500 = 10000/-

The Simple Bay Back Period

= capital cost /annual profit [37] = 25000 / 10000= 2.5 years

This means, the rural family will get back the capital cost within a time period

less than three years which is a reasonable period.

ECONOMIC EVALUATION OF A FAMILY

TYPE BIOGAS PLANT


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Conclusions

The suitable family digester type is the single stag patch digester WithV=0.5m. This will make a benefit of10000/year and the Simple payback

period of it is less than three years.

Under ideal conditions temperature 35 C, pH value 6-7, and retention time 40

days in rural India, it is possible to produce about 0.15 kg of gas per kg drywaste at atmospheric pressure.

Biogas is a source of renewable energy usually contains about 50 - 70 % CH 4,

30 - 40 CO 2, and other gases , it has a heat value of 34200kJ/kg(9.5 kWh / kg) which equals 1/2 heat value of C4H10.


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Recommendations

More researches and practical studies have to be done to improve biogasplants in our country.

The Indian government has to fund most of digesters which can be built inrural areas with good cooperation between farmers and related sectors as

energy, environment and agricultural sectors to improve and apply digestersin India.

Strong backing in the new waste strategy should mean that we start to fulfil

this potential, with the widespread introduction of food waste collectionmanagement and the construction of more AD plants across the nation.


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Like biofuel. biogas is used as a substitute to mainstream fossil fuels. Itcan either be fed through the grid and used for heating purposes, or burnt

in large power stations and converted to electricity."

Thank You

design of biogas digesters

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