How to Setup Bio Gas Plant

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BIO GAS1. Energy CrisisEnergy is a necessary concomitant of human existence. Although manysources of energy exist in nature, it is coal, electricity and fossil oil which have beencommercially exploited for many useful purposes. This century has witnessed the phenomenalgrowth of various industries based on these energy sources. They have application inagricultural farms and have domestic use in one form or other. Fossil oil, in particular hasplayed the most significant role in the growth of industry and agriculture, which would be

recorded in the history of progress of human race in golden words. Whether it is flying in the airor speeding automobiles on the roads or heating and prime moving in the industry or petro-chemicals and fertilizers for farms or synthetics for daily use or cooking at home, all have beenmade possible by one single source fossil oil. By now, it has penetrated so deep into themechanism of human living that man is not prepared to accept the fact that this useful source ofenergy is not going to last very long. But that is the fact of life. Once fossil oil was availableeasily and at lower prices irrespective of its origin of supply. It has now been scarce and costly.The immediate effect of this is that the world is in a grip of inflation and rising prices. Today,energy crisis has mainly emerged from the fear that the boons of fossil oil may turn into a baneas the disappearance of fossil oil would compel the habits and practices of living of the societyto change. That is the crisis and that is the compulsion for search alternate sources ofenergy.2. Bio-Gas as one of the Alternate Renewable Sources of Energy

It is evident that no single source of energy would be capable of replacing fossil oil completely

which has diverse applications. On the other hand, dependence on fossil oil would have to be

reduced at a faster pace so as to stretch its use for longer period and in critical sectors till some

appropriate alternative energy sources preferably renewable ones are made available.

Presently, the country is spending a fortune in importing fossil oil which can hardly be afforded

for long on the face of developmental needs. Methane gas and more popularly known as bio-

gas is one such alternate sources of energy which has been identified as a useful hydro-carbon

with combustible qualities as that of other hydrocarbons. Though its calorific value is not highas some products of fossil oil and other energy sources, it can meet some needs of household

and farms. Following table would provide an idea of comparative heat values and thermal

efficiency of commonly used fuels in the household and farms.

Table-1

Commonly used fuels Calorif ic values in Kilo calories Thermal efficiency

Bio-gas 4713/M3 60%

Dung cake 2093/Kg 11%

Firewood 4978/Kg 17.3%

Diesel (HSD) 10550/Kg 66%

Kerosene 10850/Kg 50%

Petrol 11100/Kg

These calorific values or heat values indicate that bio-gas can perform works similar to fossil oilin domestic cooking, lighting etc., with better efficiency depending upon the methane content init. The bio-gas has also the potential for use in internal combustion engines used for pumpingwater etc. for which research and development works are in progress. Biogas, therefore, has abright future as an alternate renewable source of energy for domestic and farm use.3. Bio-Gas,its Production Process and CompositionIt would be useful to know what bio-gas is and what itsproperties are-

(i) Bio-gas: Itmainly comprises of hydro-carbon which is combustible like any hydro-carbons

and can produce heat and energy when burnt. The chemical formula of the hydro-carbon is

CH4 where C stands for carbon and H for hydrogen and chemically the gas is termed as

methane gas. The chemical formula of some other commonly used hydrocarbons derived from

fossil oil viz. petrol, kerosene, diesel, etc. are C6H14 , C9H20 and C16H34 respectively. Unlike

these hydro-carbons which are derived from direct chemical processes, bio-gas is produced

through a bio-chemical process in which some bacteria convert the biological wastes into useful

bio-gas comprising methane through chemical interaction. Such methane gas is renewable

through continuous feeding of biological wastes and which are available in plenty in rural areas

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in the country. Since the useful gas originates from biological process, it has been termed as

bio-gas in which methane gas is the main constituent.

(ii) Production Process:The process of bio-gas production is anaerobic in nature and takes

place in two stages. The two stages have been termed as acid formation stage and methane

formation stage. In the acid formation stage, the bio-degradable complex organic compounds of

solids and cellulose presents in the waste materials are acted upon by a group of acid forming

bacteria present in the dung and reduce them into organic acids, CO2, H2, NH4 and H2S.

Since the organic acids are the main products in this stage, it is known as acid forming stage

and this serves as the substrates for the production of methane by methanogenic bacteria.

In the second stage, groups of methanogenic bacteria act upon the organic acids to produce

methane gas and also reduce CO2 in the presence of H2 to form methane (CH4). At the end ofthe process the amount of oxygen demanding materials in the waste product is reduced to

within the safe level for handling by human beings. There are four types of methano-genic

bacteria; Methano-bacterium, Methano-spirillium, Methano-coccus and Methano-circina. These

bacteria are oxygen sensitive and photo-sensitive and do not perform effectively in the

presence of oxygen and light.

ConstituentsThe gas thus produced by the above process in a bio-gas plant does not contain

pure methane and has several impurities. A typical composition of such gas obtained from the

process is as follows:

Table-2

Methane 60.0%

Carbondioxide 38.0%

Nitrogen 0.8%

Hydrogen 0.7%

Carbon-monoxide 0.2%

Oxygen 0.1%

Hydrogen Sulphide 0.2%

The calorific value of methane is 8400 kcal/ m3 and that of the above mixture is about 4713Kcal/ m3. However, the bio-gas gives a useful heat of 3000 kcal/m3. If similar heat values areto be obtained from other sources of fuel, the equivalent quantities of those fuel have to besubstantial as may be seen from Annexure-III. It is not the quantity which is so important butwhile bio-gas is renewable, others are not.4. Scope of Bio-Gas PlantsThe basic feed materialfor, bio-gas plants in India has been considered to be cattle dung which is available in plenty.The estimated cattle population of 238 million in the country has the potential to produce about1000 million tonnes of dung every year. According to an estimate (1977) of Khadi and VillageIndustries Commission (KVlC), bio-gas plants of average family size may provide energyequivalent to 5432 million liters of kerosene which in terms of current prices may cost well overRs. 1000 crore per annum. Although, cattle dung has been recognized as the chief raw materialfor bio-gas plants, other materials like night-soil, poultry litter and agricultural wastes are alsoused where they are socially acceptable. In addition to combustible gas, the bio-gas plantswould also be a source for conserving organic manure, rich in NPK. It is estimated thatrecoverable dung from 236 million cattle can add about 3.5 million tonnes of Nitrogen to the soilevery year and for ensuring its conservation bio-gas plants can be very useful. The scope for

bio-gas plants in India, therefore, is substantial if the benefits accruable from such plants areexploited by people living in rural areas.

5. Major Benefits of Installing Bio-Gas Plants

It is estimated by the Govt. of India, Ministry of Energy, that alternative sources of energy like

bio-gas plants, wind mills etc. may reduce the dependence on conventional sources of energy

by about 20% by the turn of the century, provided promotional efforts are continued. Presently,

the cooking media in rural areas consist of burning dung cake, fire-wood and to some extent

kerosene where it is available easily. The installation of bio-gas plants would directly replace

the use of above three and in saving them, following gains would be made:

(i) Nearly 30% of available dung which is burnt and wasted would be recovered as bio-gas

plants conserve the dung while producing bio-gas. Again, the dung after digestion in gas plant

preserves more of NPK in the dung solids and cellulose which otherwise gets lost if heaped in

the open.

Table-3Percent NPK

N P2O5 K2O

Bio-gas slurry 1.4 1.0 0.8

Farm Yard Manure (FYM) 0.5 0.2 0.5

Town Compost 1.5 1.0 1.5

The benefits derived from bio-gas plants in terms of manure and useful energy are illustratedat Annexure 1& II. The average NPK content of Farm Yard Manure (FYM) is about 0.5, 0.2 and0.5 percent respectively and it may be observed that biogas slurry is rich in NPK by more thanfour times than ordinary dung when converted into FYM. When the country is faced withshortage of fertilizers and has to spend enormous amounts for its import, the application of bio-gas slurry can replace the chemical fertilizers to a large extent. Bio-gas slurry or FYM not onlyadds NPK but it proves the soil porosity and texture. These are established benefits. (ii)Second major benefit is that rural people would gradually stop felling trees. Tree felling basbeen identified as one of the major causes of soil erosion and worsening flood situation.Government has started massive afforestation programme to tackle the erosion and flood




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situation. Continued deforestation has been causing ecological imbalances in the environmentin which we live. Bio-gas plants would be helpful in correcting this situation.(iii) In rural areaskerosene is used for lighting lantern and cooking in a limited way wherever kerosene supplyhas been made possible. Whatever quantity is used can be replaced by bio-gas as it can beused for lighting and cooking. This would reduce the dependence on fossil oil directly and insaving foreign exchange.

(iv) Lastly, the most important social benefit would be that the dung being digested in the

digester, there would be no open heap of dung to attract flies, insects and infections. The slurry

from digesters can be transported to the farm forapplication in the soil, thus keeping the

environment clean forinhabitation. Also, gas cooking would remove all the health hazards

ofdung cake orfire wood cooking and would keep the woman folk free fromrespiratory and eye

diseases which are prevalent in the villages.

6. History of Technological Development, Past Achievements, Future Programme and Role of

Institutional Finance History of Technological DevelopmentThe bio-gas technology is not new

to India. Its experimentation started in 1940 when Dr. S.V. Desai after visiting Dadar sewage

purification station at Bombay took up an experimental gas plant at Indian Agricultural

Research Institute (IARI). The cattle dung fermentation followed next which was patented by

Shri Jasbhai J Patel in 1951. However, the model had undergone several modifications and in

1954 the plant was named Gramlaxmi III. The same model has been propagated by KVIC in a

nation wide programme since 1962. This KVIC model has stood the test of time although many

institutions and individuals kept experimenting for better models and introduced several models

but not good enough to completely replace the KVIC model. However, the late seventies saw

the new Janata model where the difference in cost was about 20%. Even this model has not

affected the popularity of KVIC model. Its designs etc. has been discussed later in this paper.

Past Achievements and Future Programmes

All along since 1962, KVIC was the sole agency forpromotion of bio-gas plants independent of

government programme. The threat of oil embargo during the last Arab-Israel war in 1973

made the Government to include Bio-gas plants as alternative sources of energy to reduce the.

dependence on fossil oil on its Vth Five Year Plan. The target set was one lakh gas plants forthe plan period. However only 80,000 gas plants were reported to have been installed inspite

ofthe fact that government provided 25-50% subsidy to the users. It was more vigorously

pursued in the VI Five Year Plan with a target of 4 lakh gas plants. It is estimated that at the

end ofVIPlan the achievement is no more than 45% of its target. The programme ofbio-gas

plants are now covered under the National Biogas and Manure Management Programme

(NBMMP) of Govt. of India, Ministry of Non Conventional Energy Sources. The NBMMP will be

implemented with a physical target of 1.60 lakh biogas plants during FY 2003-2004.

It can be noted from the above discussion that during last 21 years, the achievement has not,

been appreciable. The government is now convinced that bio-gas plant technology is not a

failure. However, social environment has to be more favorable for the speedier progress. For

example, China has taken a rapid stride in the same field where the social environment is

favorable to bio-gas technology.

The Relevance of Chinese ExperienceA comparative study of India and China carried out by

Centre for Application of Science & Technology to Rural Areas (ASTRA), Indian Institute of

Science, Bangalore gives a striking revelation of the achievement of China in the field of bio-

gas. India started the experimentation much earlier and actual programme started in 1967

where as China took to this technology only in 1970. Even after a late start, China over took

India to reach anunbelievable target within a short span of 7 years. However, with persistent

efforts thereafter, the Indian programme got some fillip but there is still a long way to go to tap

the potential. This can be observed from the following:

Table-4Year Population of Bio-Gas Plants India

India China

1973 8,000 5,000

1980 80,000 72,00,000

1998 27,50,000 69,00,000

The achievement of China deserves all appreciation as they have managed to install so manynumbers without much of cattle dung but with sources which are within easy reach. The dailyfeed in Chinese gas plants consists of 20 kgs. waste from four pigs, 4 kgs. waste from 5 hu-mans, 6 kgs. of straw and poultry litters. All these are available with majority of Chinese familiesand so they have been successful in popularizing the gas plant, as feed was not a constraint. InIndia, rural population would perhaps not adopt such raw materials as their Chinesecounterparts do. In our country. rural people are ready to handle cattle dung but not other rawmaterials and number of such families owning 4-5 cattle are not many. Only 20% of thehousehold own 4-5 cattle. Unless the remaining rural families adopt raw materials like Chinesehave done, very limited success can be hoped. Chinese have followed the programme with allseriousness inspite of the fact that they are self-sufficient and exporter of fossil oil. WhenChinese could take advance measures to counter the future energy crisis, we should be morevigilant in taking this programme seriously.However, a word of caution is added here that sincelarge number of plants are failing in the field, sufficient care should be taken to select the typeof plant and for sound construction.Role of Institutional FinanceThe responsibility for providingtechnical guidance, installation, supervision and also subsidy has been entrusted to KVIC andthe states by the Government who have acquired sufficient experience due to their longassociation with the bio-gas programme. However, it has been observed that most of the plantusers fail to raise their own contribution due to lack of resources. This made the financialinstitutions difficult to play its role in meeting the credit requirement. During the year 1974-75the commercial banks entered the fray. The Government has now attached top priority to thebio-gas programme in which banks have a special role to play in making the programmesuccessful. It is in this context that bank officials would have to acquaint themselves with thetechnology, operations, field problems, post installation maintenance and economical and




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social aspects of bio-gas plants and its programme so that formulation, appraising andprocessing of schemes become easier.

7. Main Features of the Bio-Gas Plant

On the basis of the gas holder the present bio-gas plants are classified mainly into two groups -

fixed dome type or floating drum type. Both the type of plants have the following functional

components:

(i) Digester : This is the fermentation tank and is built partially or fully underground. It is

generally cylindrical in shape and made up of bricks and cement mortars. It holds the slurry

within it for the period of digestion for which it is designed.

(ii) Gas holder: This component is meant for holding the gas after it leaves the digester. It maybe a floating drum or a fixed dome on the basis of which the plants are broadly classified. The

gas connection is taken from the top of this holder to the gas burners or for any other purposes

by suitable pipelines. The floating gas holder is made up of mild steel sheets and angle iron

and is required to exert pressure of 10 cms of water in the gas dome masonry and exert a

pressure upto 1m of water column on the gas.

(iii) Slurry mixing tank: This is a tank in which the dung is mixed with water and fed to the

digester through an inlet pipe.

(iv) Outlet tank and slurry pit: An outlet tank is usually provided in a fixed dome type of plant

from where slurry in directly taken to the field or to a slurry pit. In case of a floating drum plant,

the slurry is taken to a pit where it can be dried or taken to the field for direct applications.

8. Broad Basis of Plant Design

For designing a bio-gas plant, there is a need to match the gas requirement to the feed material

available so that there is a continuity of gas production and supply without interruption. For this;

it is useful to know the average requirement of gas for different uses, dung produced per day

and average gas production per units of different feed materials. Some basic information on

these aspects are furnished in annexure I to VI.

The design of a plant may be determined in the following manner:

(a) Bio-Gas requirement: Make use of Annexure IV to decide the total requirement of gas per

day. If we take a case where gas requirement is 3 cum, further consideration of the design may

be followed as observed in the following paragraphs:

(b)Raw Material Requirement : To find out the quantity of equivalent dung for production of 3

cum gas refer Annexure V. By dividing 3 cum by 0.04 cum. which is equivalent to 1 kg of

dung it would reveal the total quantity of dung required for the purpose. In this case it is

3/0.04= 75 kgs. Thereafter, refer Annexure VI to know the number at animals necessary to

produce 75 kgs. of dung.

(c) Digester Design : When dung is mixed with an equal quantity of water, it gives a slurry

which has a specific gravity of 1.089. So the volume of slurry fed per day would be equal to (75

+ 75)/ (1000 x 1.089) = 0.138m3

Therefore, for a 50 days retention plant, the volume of the digester has to be equivalent to

0.138 x 50 or 6.9 m3 say 7 m3.

The recommendation of KVIC is to have a digester volume of 2.75 times the volume of gasproduced per day. The commissions recommendation for the depth of the plant is between 4 to

6 m according to the size but for economical use of building materials, a depth to diameter ratio

between 1.0 to 1.3 are considered ideal for all types of plants. In a floating drum plant, a

continuous ledge is built into the digester at a depth 10 cm. shorter than the height of the gas

drum to prevent the gas holder from going down when no gas is left in it. It helps in preventing

the gas inlet being choked. It also guides the gas bubbles rising from the side of the plants into

the gas bolder. In some plants slurry is fed at the bottom and removed at the top. When the

digester diameter exceeds 1.6 m, a partition wall is provided in the digester to prevent short

circuiting of slurry flow and increasing its retention period. Some standard dimensions of such

floating drum plants are given at Annexure VII. In case of fixed dome plants, the volume of

digester comes to between 1.5 times to 2.75 times the gas produced per day. Here, the higher

the plant capacity, the lesser becomes the ratio of digester volume to gas produced per day.

(d) Gas Holder Design: The design of a gas holder is influenced by the digester diameter and

distribution of gas use during the day. For domestic plants, the gas holder capacity is kept at 60

per cent of a days gas production and in case of laboratories, it is kept at 70 per cent of the

days gas production. In a floating drum plant, the gas holder diameter is 15 cm. less than the

diameter of the digester and accordingly the other dimensions are decided. The gas holder can

be given a rotary movement around its guide to break the scum formation at the top. In a fixeddome plant the dome angle is kept between 17and 21and it gives a pressure upto 100 cm.

of water. Due to higher pressure, the diameter of gas pipelines can be reduced and the gas can

be taken to greater distance. In this plant, care should be taken to provide and an earth

pressure equivalent to 100 cm of water column from the top of the dome. Always use Aclass

bricks in the domes for better stability.

(e) Inlet Tank : Before the dung is fed into the plant, it is mixed with water in a tank to give a

solid content of 7.5 per cent to 10 per cent in the slurry. This tank also helps in removing grass

and other floating materials from the raw materials to prevent excessive scum formation in the

plant. This tank is connected to the digester by an asbestos cement pipe. The floor of the

mixing tank is given a slope opposite to the direction of inlet pipe to help heavy inorganic solid

particles to settle and get separated from the slurry.

9. Base Pre-requisites of Bio-Gas System




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(i) Land and Site: While selecting a site for a bio-gas plant, following aspects should be

considered:

(a) The land should be leveled and at a higher elevation than the surroundings to avoid runoff

water.

(b) Soil should not be too loose and should have a bearing strength of 2 kg/cm2

(c) It should be nearer to the intended place of gas use.

(d) It should also be nearer to the cattle shed/ stable for easy handling of raw materials.

(e) The water table should not be veryhigh.

(f) Adequate supply of water should be there at the plant site.

(g) The plant should get clear sunshine during most part of the day.

(h) The plant site should be well ventilated as methane mixed with oxygen is very explosive.

(i) A minimum distance of 1.5m should be kept between the plant and any wall or foundation.

(j) It should be away from any tree to make it free from failure due to root interference.

(k) It should be at least 15m away from any well used for drinking water purpose.

(l) There should be adequate space for construction of slurry pits.

(ii) Feed for gas plants: The feed for gas plants in India mainly comprises of dung from cattle.

Although, quantity of dung per cattle depends upon health, age, t


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How to Setup Bio Gas Plant

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