Final biogas report

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A Major Project Report
On
“FABRICATION OF BIOGAS PLANT AND BIOGAS PRODUCTION FROM ANIMAL
WASTE”
Submitted In Partial Fulfillment of the Requirement for the Award of the Degree of
BACHELOR OF TECHNOLOGY
(MECHANICAL ENGINEERING)
Submitted By
1. ABHAY UNIYAL (130970104001)
2. PARAS SAKLANI (130970104038)
3. SHIVAM GOSWAMI (130970104058)
4. ADITI DABRAL (130970104005)
5. PRYANKA JAYARA (130970104041)
6. AISHA RAWAT (130970104006)
Under the Guidance of
Mr. PARVEEN KUMAR (Assistant professor)
Department Of Mechanical Engineering
DEPARTMENT OF MECHANICAL ENGINEERING
THDC INSTITUTE OF HYDROPOWER ENGINEERING AND TECHNOLOGY
TEHRI, UTTRAKHAND, INDIA
(UTTARAKHAND TECHNICAL UNIVERSITY, DEHRADUN)
2013 − 2017

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CERTIFICATE
This is to certify that the work which is being presented in thesis entitled “ FABRICATION OF
BIOGAS PLANT AND BIOGAS PRODUCTION FROM ANIMAL WASTE” in partial fulfillment
of the requirement for the award of the degree of Bachelor of Technology and submitted in the
Department of Mechanical Engineering of THDC Institute of Hydropower Engineering and
Technology, Tehri, is an authentic record of our own work carried out under the supervision of Mr.
Paveen Kumar, COD, Department of Mechanical Engineering, THDC Institute of Hydropower
Engineering and Technology, Tehri under Uttarakhand Technical University, Dehradun.
The matter presented in this report has not been submitted by us anywhere for the award of
any other degree of this or any other institute.
Abhay Uniyal [130970104001]
Aditi Dabral [130970104005]
Aisha Rawat [130970104006]
Paras Saklani [130970104038]
Priyanka Jayara [130970104041]
Shivam Goswami [130970104058]
This is to certify that the above statement made by the candidate is correct to the best of our
knowledge.
Date: (Mr. Parveen Kumar)
Guide

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ACKNOWLEDGEMENT
We take this opportunity to express my gratitude to all those people who have been directly
and indirectly with us during the completion of this report. We pay thanks to our Class In
charge Mr. Kapil Kumar Chauhan, & our mentor Mr. Praveen Kumar who has given
guidance and a light to us during this training. His versatile knowledge about
"FABRICATION OF BIOGAS PLANT AND BIOGAS PRODUCTION FROM ANIMAL
WASTE" has eased us in the critical times during the span of the training. Special thanks to
Mr. Jitendra Uniyal for providing us the workshop and guiding us through the process.

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LIST OF FIGURE
FIG 1. Flow Chart Of Anerobic Digestion....................................................................................... 15
FIG 2. Plant Outlay...................................................................................................................... 17
FIG 3. Fixed Dome...................................................................................................................... 18
FIG4. CAMARTEC model.............................................................................................................. 20
FIG 5. Floating Drum Plant........................................................................................................... 21
FIG 6. Low Cost Polyethylene Tube Digester................................................................................ 24
FIG 7. Baloon Plant..................................................................................................................... 25
FIG 8. Volume Of Drawn Gas ....................................................................................................... 29
Fig.9: Gas productionfromfreshcattle manure dependingonretentiontime anddigester
temperature............................................................................................................................... 30
FIG 12. KVIC Pragati Model.......................................................................................................... 34
FIG 13. Bottom Slab.................................................................................................................... 38
FIG 14. Spherical shell of masonry construction............................................................................ 40
FIG 15. Masonry and mortar........................................................................................................ 42
FIG. 16 stirring facilities............................................................................................................... 43
Fig. 17: Mixing tank..................................................................................................................... 44
Fig. 18: Floating Drum Axis ......................................................................................................... 45
Fig. 19: Hemispherical plant with partition wall............................................................................ 46
Fig. 20: Stirring facilities in the digester The impeller stirrer .......................................................... 47
Fig 28:Outlet (overflow) of a floating-drum plant.......................................................................... 48
Fig. 41:Diagram of a gas burner and a lamp Burner:...................................................................... 50
Fig. 29: The gas drum.................................................................................................................. 52
Fig. 30:Forces on the gas drum.................................................................................................... 53
Fig. 31: Floating drum guide frame.............................................................................................. 54
Fig. 32: Costruction Of Digester................................................................................................... 57
Fig.33: Construction of Dome:..................................................................................................... 58
Fig.34: Guide Frame and Walls .................................................................................................... 58
Fig.35 Guide Frame:.................................................................................................................... 59
Fig.36: Cylinder Frame Ring......................................................................................................... 62
Fig.37: Cylinder Cone.................................................................................................................. 63

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TABLE OF CONTENT
Chapter 1: INTRODUCTION 8
1.1 INTRODUCTION 8
1.2 BIOGAS 9
1.3 CHARACTERTICS OF BIOGAS 10
1.4 PROPERTIES OF BIOGAS 10
1.5 FACTORS AFFECTING YIELD 11
1.6 BENEFITS OF BIOGAS TECHNOLOGY 12
1.7 PRODUCTION PROCESS 13
1.8 PRINCIPLES FOR PRODUCTION 14
1.9 ANAEROBIC DIGESTION 14
1.10 FLOW CHART OF ANAEROBIC DIGESTION 16
Chapter 2 : BIOGAS PLANT 17
2.1:Types of Biogas Plants 17
2.2 Fixed-dome Plants 17
2.3 Floating Drum Plants 21
2.4 Low Cost Polyethylene Tube Digester 24
2.5 Balloon Plants 25
2.6 Horizontal Plants 26
2.7 Earth Pit Plants 27
2.8 Ferro-cement Plants 27
2.9 About KVIC Pragati model 28
Chapter 3: LITERATURE REVIEW 29
3.1 Scaling of Biogas Plant 29
3.2 Design of Biogas Plant 38
3.3 Biogas Appliances 49
3.4 Floating Gas Holder Parameters 50
Chapter 4: Fabrication& Instalment Of Plant 60
4.1 Site Selection Process 60
4.2 Construction Material Required 60
4.3 Construction of Foundation/Digester 61
4.4 Fabrication Of Gas Holder 64
4.5 Making Biogas Plant Functional 72
4.6 Maintenance and Using the Gas 75
CHAPTER 6: CONCLUSION AND FUTURE SCOPE 76
6.1 Economics for State of Uttarakhand 76
6.2 Significant Betterment in policies 77
6.3 Marketing 78
REFERENCES 80

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ABSTRACT
In our town we have several small subsistence and large scale dairies ,where daily a large
amount of cow and buffalo dung is available , which can be utilized for better purposes.
Biogas production requires Anaerobic digestion. Project was to Create an Organic Processing
Facility to create biogas which will be more cost effective, eco-friendly, cut down on landfill
waste, generate a high-quality renewable fuel, and reduce carbon dioxide & methane
emissions. Overall by creating a biogas reactor on site in the backyard of a subsistence dairy
as feedstock for our reactor which works as anaerobic digester system to produce biogas
energy. The anaerobic digestion of cow and buffalo dung produces biogas, a valuable energy
resource Anaerobic digestion is a microbial process for production of biogas, which consist
of Primarily methane (CH4) & carbon dioxide (CO2). Biogas can be used as energy source
and also for numerous purposes. But, any possible applications requires knowledge &
information about the composition and quantity of constituents in the biogas produced. This
report showa the complete process of planning, site selection, fabrication and installment of
biogas plant.The results of this project are determined on a large scale 2m radius KVIC
"Pragati" model floating drum plant.

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Chapter 1:
INTRODUCTION
1.1 INTRODUCTION
Due to scarcity of petroleum and coal it threatens supply of fuel throughout the world also
problem of their combustion leads to research in different corners to get access the new
sources of energy, like renewable energy resources. Solar energy, wind energy, different
thermal and hydro sources of energy, biogas are all renewable energy resources. But, biogas
is distinct from other renewable energies because of its characteristics of using, controlling
and collecting organic wastes and at the same time producing fertilizer and water for use in
agricultural irrigation. Biogas does not have any geographical limitations nor does it requires
advanced technology for producing energy, also it is very simple to use and apply.
Deforestation is a very big problem in developing countries like India, most of the part
depends on charcoal and fuel-wood for fuel supply which requires cutting of forest. Also, due
to deforestation It leads to decrease the fertility of land by soil erosion. Use of dung ,
firewood as energy is also harmful for the health of the masses due to the smoke arising from
them causing air pollution. We need an eco-friendly substitute for energy .
Kitchen waste is organic material having the high calorific value and nutritive value to
microbes, that’s why efficiency of methane production can be increased by several order of
magnitude as said earlier.It means higher efficiency and size of reactor and cost of biogas
production is reduced. Also in most of cities and places, kitchen waste is disposed in landfill
or discarded which causes the public health hazards and diseases like malaria, cholera,
typhoid. Inadequate management of wastes like uncontrolled dumping bears several adverse
consequences: It not only leads to polluting surface and groundwater through leachate and
further promotes the breeding of flies , mosquitoes, rats and other disease bearing vectors.
Also, it emits unpleasant odour & methane which is a major greenhouse gas contributing to
global warming.

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Mankind can tackle this problem(threat) successfully with the help of methane , however till
now we have not been benifited, because of ignorance of basic sciences – like output of work
is dependent on energy available for doing that work. This fact can be seen in current
practices of using low calorific inputs like cattle dung, distillery effluent, municipal solid
waste (MSW) or sewage, in biogas plants, making methane generation highly inefficient. We
can make this system extremely efficient by using kitchen waste/food wastes.
1.2 BIOGAS
BIOGAS is produced by bacteria through the bio-degradation of organic material under
anaerobic conditions. Natural generation of biogas is an important part of bio-geochemical
carbon cycle. It can be used both in rural and urban areas.
Table-1.
Composition of biogas. Component Concentration (by volume)
Methane (CH4) 55-60%
Carbon dioxide (CO2) 35-40%
Water (H2O) 2-7%
Hydrogen Sulphide (H2S) 20-20,000 ppm (20%)
Ammonia (NH3) 0-0.05%
Nitrogen (N) 0-2%
Oxygen (O2) 0-2%
Hydrogen (H2) 0-1%
Biogas is somewhat lighter than air and has an ignition temperature of approximately 700 °C
(diesel oil 350 °C; petrol and propane about 500 °C). The temperature of the flame is 870 °C.
Biogas consists of about 60 % methane (CH4) and 40 % carbon dioxide (CO2). It also
contains small proportions of other substances, including up to 1% hydrogen sulphide (H2S).
See also the table in Fig. 38 on page 44.
The methane content and hence the calorific value is higher the longer the digestion process.
The methane content falls to as little as 50% if retention time is short. If the methane content
is considerably below 50 %, biogas is no longer combustile. The first gas from a newly filled
biogas plant contains too little methane. The gas formed in the first three to five days must
therefore be discharged unused. The methane content depends on the digestion temperature.

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Low digestion temperatures give high methane content, but less gas is then produced. The
methane content depends on the feed material. Some typical values are as follows:
Cattle manure 65%
Poultry manure 60%
Pig manure 67%
Farmyard manure 55%
Straw 59%
Grass 70%
Leaves 58%
Kitchen waste 50%
Algae 63%
Water hyacinths 52%
1.3 CHARACTERSTICS OF BIOGAS
Composition of biogas depends upon feed material also. Biogas is about 20% lighter than air
has an ignition temperature in range of 650 to 750 0C.An odourless & colourless gas that
burns with blue flame similar to LPG gas. Its caloric value is 20 Mega Joules (MJ) /m3 and it
usually burns with 60 % efficiency in a conventional biogas stove.
This gas is useful as fuel to substitute firewood, cow-dung, petrol, LPG, diesel, & electricity,
depending on the nature of the task, and local supply conditions and constraints.
Biogas digestor systems provides a residue organic waste, after its anaerobic digestion(AD)
that has superior nutrient qualities over normal organic fertilizer, as it is in the form of
ammonia and can be used as manure. Anaerobic biogas digesters also function as waste
disposal systems, particularly for human wastes, and can, therefore, prevent potential sources
of environmental contamination and the spread of pathogens and disease causing bacteria.
Biogas technology is particularly valuable in agricultural residual treatment of animal excreta
and kitchen refuse (residuals).
1.4 PROPERTIES OF BIOGAS
1. Change in volume as a function of temperature and pressure.
2. Change in calorific value as function of temperature, pressure and water vapour content.

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3. Change in water vapour as a function of temperature and pressure.
1.5 FACTORS AFFECTING YIELD AND PRODUCTION OF BIOGAS
Many factors affecting the fermentation process of organic substances under anaerobic
condition are,
 The quantity and nature of organic matter
 The temperature
 Acidity and alkanity (PH value) of substrate
 The flow and dilution of material
FEED:
Slurry with a solids content of 5-10% is particularly well suited to the operation of
continuous biogas
plants.
1: All feed materials consist to a great extent of carbon (C) and also contain nitrogen (N). The
C/N ratio affects gas production. C/N ratios of 20:1 to 30:1 are particularly favourable.
Mixtures of nitrogen-rich feed material (e.g., poultry manure) and carbon-rich feed material
(e.g., rice husks) give high gas production
2: Feed material tables Straw, leaves and, in particular, water hyacinths can be digested only
in certain types of plants or using special conditioning techniques. For this reason, reliable
information of general validity concerning gas production cannot be given.
Fermentation slurry as fertilizer
During the digestion process, gaseous nitrogen (N) is converted to ammonia (NH3). In this
water-soluble form the nitrogen is available to the plants as a nutrient. A particularly nutrient-
rich fertilizer is obtained if not only dung but also urine is digested. Compared with solid
sludge from fermented straw and grass, the liquid slurry is rich in nitrogen and potassium.
The solid fermentation sludge, on the other hand, is relatively richer in phosphorus. A
mixture of solid and liquid fermented material gives the best yields. The nutrient ratio is then
approximately N:P2O5:K2O= 1:0.5:1. A fermented slurry with a lower C/N ratio has better
fertilizing characteristics. Compared with fresh manure, increases in yield of 5 - 15 % are

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possible. Particularly good harvests are obtained from the combined use of compost and
fermentation slurry.
TABLE 2:- GENERAL FEATURES OF BIOGAS
Energy Content 6-6.5 kWh/m3
Fuel Equivalent 0.6-0.65 l oil/m3
Biogas Explosion Limits 6-12 %
biogas in air Ignition Temperature 650-750 *C
Critical Pressure 75-89 bar
Critical temperature -82.5 *C
Normal Density 1.2 kg/m3
Smell Bad eggs
1.6 BENEFITS OF BIOGAS TECHNOLOGY :
 Production of energy.
 Transformation of organic wastes to very high quality fertilizer.
 Improvement of hygienic conditions through reduction of pathogens.
 Environmental advantages through protection of soil, water, air etc.
 Micro-economical benefits by energy and fertilizer substitutes.
 Macro-economical benefits through decentralizes energy generation and
environmental protection.
A biogas plant supplies energy and fertilizer. It improves hygiene and protects the
environment. A biogas plant lightens the burden on the State budget and improves
working conditions for the housewife. A biogas plant is a modern energy source. A
biogas plant improves life in the country. A biogas plant can satisfy these high
expectations only if it is well designed.
A biogas plant supplies energy. However, a biogas plant also consumes energy. Energy is
already Consumed in the production of the construction material:
- for 1 m³ of masonry, about 1000 kWh or 180 m³ of biogas,
- for 100 kg of steel, about 800 kWh or 150 m³ of biogas,

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- for 1 kg of oil paint, about 170 kWh or 28 m³ of biogas.
Energy is consumed in transporting the materials of a biogas plant. Construction and
maintenance also consume energy:
- for 1 km of transport by lorry, about 1.5 kWh or 1.05 m³ of biogas
- for 1 km of transport by car, about 0.5 kWh or 0.35 m³ of biogas.
A biogas plant must operate for one or two years before the energy put into it is recovered.
The degree of digestion increases with the retention time. Long retention times save energy.
The net energy gain is smaller with short retention times: if the retention time for 50 kg of
cattle dung is reduced from 90 to 45 days, some 790 kWh or 240 m³ of biogas per year is lost.
A biogas plant eases the work of the housewife. However, a biogas plant also creates
additional work for the housewife: dung and mixing water have to be supplied to it. The
fermentation slurry has to be mixed. Long retention times help the housewife. Biogas plants
with short retention times need more labour: To replace 20 kg of firewood by biogas, a
housewife must supply 121 kg of dung and 121 litres of water if the retention period is 45
days. For a 90-day retention period, only 84 litres of dung and of water are required. This
represents a difference of nearly 9 kg of dung and nearly 9 litres of water per m³ of gas per
day. If the plant is filled only every other day, working time is saved - because of the saving
of preparation time. If the biogas plant is too far from the source of water or from the animal
housing, the housewife must perform additional work: the housewife's workload is lightened
by a biogas plant only if the distance to the water source and that to the byre together are less
than a quarter of the distance to the wood collection point. The least amount of work results
from locating the biogas plant directly beside the animal shelter (byre), which should have a
paved floor. This makes it easy to sweep urine and dung into the plant's inlet pipe. Often
enough, no extra mixing water is needed' and the gas yield is considerably higher. The
designer decides in whose interests the biogas plant is economic: a biogas plant for short
retention times is economic for a farmer with many animals and cheap labour. The benefit of
the fertilizer depends primarily on how well the farmer knows how to use it. Assuming that
the digested slurry is immediately utilized - and properly applied - as fertilizer, each daily kg
can be expected to yield roughly 0.5 kg extra nitrogen, as compared with fresh manure. If the
slurry is first left to dry and/or improperly applied, the nitrogen yield will be considerably
lower. The following are the principal organisms killed in biogas plants: Typhoid,
paratyphoid, cholera and dysentery bacteria (in one or two weeks), hookworm and bilharzia
(in three weeks). Tapeworm and roundworm die completely only when the fermented slurry
is dried in the sun.

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1.7 PRODUCTION PROCESS
A typical biogas system consists of the following components:
(1) Manure collection
(2) Anaerobic digester
(3) Effluent storage
(4) Gas handling
(5) Gas use.
Biogas is a renewable form of energy. Methanogens (methane producing bacteria) are last
link in a chain of microorganisms which degrade organic material and returns product of
decomposition to the environment.
The pH of the fermentation slurry indicates whether the digestion process is proceeding
without disturbance. The pH should be about 7. This means that the slurry should be neither
alkaline nor acid.
1.8 PRINCIPLES FOR PRODUCTION OF BIOGAS
Organic substances exist in wide variety from living beings to dead organisms . Organic
matters are composed of Carbon (C), combined with elements such as Hydrogen (H), Oxygen
(O), Nitrogen (N), Sulphur (S) to form variety of organic compounds such as carbohydrates,
proteins & lipids. In nature MOs (microorganisms), through digestion process breaks the
complex carbon into smaller substances.
There are 2 types of digestion process :
 Aerobic digestion.
 Anaerobic digestion.
The digestion process occurring in presence of Oxygen is called Aerobic digestion and
produces mixtures of gases having carbon dioxide (CO2), one of the main “green houses”
responsible for global warming. The digestion process occurring without (absence) oxygen is
called Anaerobic digestion which generates mixtures of gases. The gas produced which is
mainly methane produces 5200-5800 KJ/m3 which when burned at normal room temperature
and presents a viable environmentally friendly energy source to replace fossil fuels (non-
renewable).

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1.9 ANAEROBIC DIGESTION
It is also referred to as bio-methanization, is a natural process that takes place in absence of
air (oxygen). It involves biochemical decomposition of complex organic material by various
biochemical processes with release of energy rich biogas and production of nutritious
effluents.
BIOLOGICAL PROCESS (MICROBIOLOGY)
1. HYDROLYSIS
2. ACIDIFICATION
3. METHANOGENESIS
HYDROLYSIS: In the first step the organic matter is enzymolysed externally by
extracellular enzymes, cellulose, amylase, protease & lipase ,of microorganisms. Bacteria
decompose long chains of complex carbohydrates, proteins, & lipids into small chains. For
example, Polysaccharides are converted into monosaccharide. Proteins are split into peptides
and amino acids.
ACIDIFICATION: Acid-producing bacteria, involved this step, convert the intermediates
of fermenting bacteria into acetic acid, hydrogen and carbon dioxide. These bacteria are
anaerobic and can grow under acidic conditions. To produce acetic acid, they need oxygen
and carbon. For this, they use dissolved O2 or bounded-oxygen. Hereby, the acid-producing
bacteria creates anaerobic condition which is essential for the methane producing
microorganisms. Also , they reduce the compounds with low molecular weights into alcohols,
organic acids, amino acids, carbon dioxide, hydrogen sulphide and traces of methane. From a
chemical point, this process is partially endergonic (i.e. only possible with energy input),
since bacteria alone are not capable of sustaining that type of reaction.
METHANOGENESIS: (Methane formation) Methane-producing bacteria, which were
involved in the third step, decompose compounds having low molecular weight. They utilize
hydrogen, carbon dioxide and acetic acid to form methane and carbon dioxide. Under natural
conditions, CH4 producing microorganisms occur to the extent that anaerobic conditions are
provided, e.g. under water (for example in marine sediments),and in marshes. They are
basically anaerobic and very sensitive to environmental changes, if any occurs. The
methanogenic bacteria belongs to the archaebacter genus, i.e. to a group of bacteria with

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heterogeneous morphology and lot of common biochemical and molecular-biological
properties that distinguishes them from other bacterias. The main difference lies in the
makeup of the bacteria’s cell walls.
Symbiosis of bacteria:
Methane and acid-producing bacteria act in a symbiotical way. Acid producing bacteria
create an atmosphere with ideal parameters for methane producing bacteria (anaerobic
conditions, compounds with a low molecular weight). On the other hand, methane-producing
microorganisms use the intermediates of the acid producing bacteria. Without consuming
them, toxic conditions for the acid-producing microorganisms would develop. In real time
fermentation processes the metabolic actions of various bacteria acts in a design. No single
bacteria is able to produce fermentation products alone as it requires others too.
FIG 1. Flow Chart Of Anerobic Digestion

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Chapter 2:
BIOGAS PLANT
2.1 Types of Biogas Plants
A total of seven different types of biogas plant have been officially recognised by the MNES.
1. the floating-drum plant with a cylindrical digester (KVIC model),
2. the fixed-dome plant with a brick reinforced, moulded dome (Janata model)
3. the floating-drum plant with a hemisphere digester (Pragati model)
4. the fixed-dome plant with a hemisphere digester (Deenbandhu model)
5. the floating-drum plant made of angular steel and plastic foil (Ganesh model)
6. the floating-drum plant made of pre-fabricated reinforced concrete compound units
7. the floating-drum plant made of fibre-glass reinforced polyester.
2.2 Fixed-dome Plants
A fixed-dome plant consists of a digester with a fixed, non-movable gas holder, which sits on
top of the digester. When gas production starts, the slurry is displaced into the compensation
tank. Gas pressure increases with the volume of gas stored and the height difference between
the slurry level in the digester and the slurry level in the compensation tank. The costs of a
fixed-dome biogas plant are relatively low. It is simple as no moving parts exist. There are
also no rusting steel parts and hence a long life of the plant (20 years or more) can be
expected. The plant is constructed underground, protecting it from physical damage and
saving space. While the underground digester is protected from low temperatures at night and
during cold seasons, sunshine and warm seasons take longer to heat up the digester. No
day/night fluctuations of temperature in the digester positively influence the bacteriological
processes. The construction of fixed dome plants is labor-intensive, thus creating local

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employment. Fixed-dome plants are not easy to build. They should only be built where
construction can be supervised by experienced biogas technicians. Otherwise plants may not
be gas-tight (porosity and cracks).
The basic elements of a fixed dome plant (here the Nicarao Design) are shown in the figure
below.
FIG 2. Plant Outlay
Fixed dome plant Nicarao design:
1. Mixing tank with inlet pipe and sand trap.
2. Digester.
3. Compensation and removal tank.
4. Gasholder.
5. Gas pipe.
6. Entry hatch, with gastight seal.

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7. Accumulation of thick sludge.
8. Outlet pipe.
9. Reference level.
10. Supernatant scum, broken up by varying level.
Basic function of a fixed-dome biogas plant,
1 Mixing pit,
2 Digester,
3 Gasholder,
4 Displacement pit,
5 Gas pipe
FIG 3. Fixed Dome
Function - 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'. The gas
is stored in the upper part of the digester. When gas production commences, the slurry is
displaced into the compensating tank. Gas pressure increases with the volume of gas stored,

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i.e. with the height difference between the two slurry levels. If there is little gas in the gas-
holder, the gas pressure is low.
Digester - The digesters of fixed-dome plants are usually masonry structures, structures of
cement and ferro-cementexist. Main parameters for the choice of material are:
 Technical suitability (stability, gas- and liquid tightness);
 cost-effectiveness;
 availability in the region and transport costs;
 availability of local skills for working with the particular building material.
Fixed dome plants produce just as much gas as floating-drum plants, if they are gas-tight.
However, utilization of the gas is less effective as the gas pressure fluctuates substantially.
Burners and other simple appliances cannot be set in an optimal way. If the gas is required at
constant pressure (e.g., for engines), a gas pressure regulator or a floating gas-holder is
necessary.
Gas Holder - The top part of a fixed-dome plant (the gas space) must be gas-tight. Concrete,
masonry and cement rendering are not gas-tight. The gas space must therefore be painted
with a gas-tight layer (e.g. 'Water-proofer', Latex or synthetic paints). A possibility to reduce
the risk of cracking of the gas-holder consists in the construction of a weak-ring in the
masonry of the digester. This "ring" is a flexible joint between the lower (water-proof) and
the upper (gas-proof) part of the hemispherical structure. It prevents cracks that develop due
to the hydrostatic pressure in the lower parts to move into the upper parts of the gas-holder.
Types of Fixed Dome Plants
 Chinese fixed-dome plant is the archetype of all fixed dome plants. Several million
have been constructed in China. The digester consists of a cylinder with round bottom
and top.
 Janata model was the first fixed-dome design in India, as a response to the Chinese
fixed dome plant. It is not constructed anymore. The mode of construction lead to
cracks in the gasholder - very few of these plant had been gas-tight.
 Deenbandhu, the successor of the Janata plant in India, with improved design, was
more crackproof and consumed less building material than the Janata plant. with a
hemisphere digester

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 CAMARTEC model has a simplified structure of a hemispherical dome shell based
on a rigid foundation ring only and a calculated joint of fraction, the so-called weak /
strong ring. It was developed in the late 80s in Tanzania.
FIG4. CAMARTEC model
Climate and Size - Fixed-dome plants must be covered with earth up to the top of the gas-
filled space to counteract the internal pressure (up to 0,15 bar). The earth cover insulation and
the option for internal heating makes them suitable for colder climates. Due to economic
parameters, the recommended minimum size of a fixed-dome plant is 5 m3. Digester volumes
up to 200 m3 are known and possible.
Variations: Some companies are now looking into small pre-fab fixed dome plants made of
fibreglass which appears to be a low cost alternative to construction intensive masoned
plants. A custom made plant can be produced in 2 days and -after transport- installed in less
than 1 day!
2.3 Floating Drum Plants
Floating-drum plants consist of an underground digester and a moving gas-holder. The gas-
holder floats either directly on the fermentation slurry or in a water jacket of its own. The gas
is collected in the gas drum, which rises or moves down, according to the amount of gas
stored. The gas drum is prevented from tilting by a guiding frame. If the drum floats in a
water jacket, it cannot get stuck, even in substrate with high solid content.

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FIG 5. Floating Drum Plant
Drum - In the past, floating-drum plants were mainly built in India. 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.
Size - Floating-drum plants are used chiefly for digesting animal and human faeces on a
continuous feed mode of operation, i.e. with daily input. They are used most frequently by
small- to middle-sized farms (digester size: 5-15m3) or in institutions and larger agro-
industrial estates (digester size: 20100m3).
Disadvantages: 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.

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Water Jacket Floating Drum Plant Water-
jacket plants are universally applicable and easy to maintain. The drum cannot get stuck in a
scum layer, even if the substrate has a high solids content. Water-jacket plants are
characterized by a long useful life and a more aesthetic appearance (no dirty gas-holder). Due
to their superior sealing of the substrate (hygiene!), they are recommended for use in the
fermentation of night soil. The extra cost of the masonry water jacket is relatively modest.
Material of Digester and Drum-
The digester is usually made of brick, concrete or quarry-stone masonry with plaster. The gas
drum normally consists of 2.5 mm steel sheets for the sides and 2 mm sheets for the top. It
has welded-in
braces which break up surface scum when the drum rotates. The drum must be protected
against corrosion. Suitable coating products are oil paints, synthetic paints and bitumen
paints. Correct priming is important. There must be at least two preliminary coats and one
topcoat. Coatings of used oil are cheap. They must be renewed monthly. Plastic sheeting
stuck to bitumen sealant has not given good results. In coastal regions, repainting is necessary
at least once a year, and in dry uplands at least every other year. Gas production will be
higher if the drum is painted black or red rather than blue or white, because the digester
temperature is increased by solar radiation. Gas drums made of 2 cm wiremesh-reinforced
concrete or fiber-cement must receive a gas-tight internal coating. The gas drum should have
a slightly sloping roof, otherwise rainwater will be trapped on it, leading to rust damage. An
excessively steep-pitched roof is unnecessarily expensive and the gas in the tip cannot be
used because when the drum is resting on the bottom, the gas is no longer under pressure.
Floating-drums made of glass-fiber reinforced plastic and high-density polyethylene have
been used successfully, but the construction costs are higher compared to using steel.
Floating-drums made of wire-mesh-reinforced concrete are liable to hairline cracking and are
intrinsically porous. They require a gas-tight, elastic internal coating. PVC drums are
unsuitable because they are not resistant to UV.
Guide Frame
The side wall of the gas drum should be just as high as the wall above the support ledge. The
floating drum must not touch the outer walls. It must not tilt, otherwise the coating will be
damaged or it will get stuck. For this reason, a floating-drum always requires a guide. This

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guide frame must be designed in a way that allows the gas drum to be removed for repair.
The drum can only be removed if air can flow into it, either by opening the gas outlet or by
emptying the water jacket. The floating gas drum can be replaced by a balloon above the
digester. This reduces construction costs but in practice problems always arise with the
attachment of the balloon to the digester and with the high susceptibility to physical damage.
Types of Floating Drum Plants
 KVIC model with a cylindrical digester, the oldest and most widespread floating
drum biogas plant from India.
 Pragati model with a hemisphere digester
 Ganesh model made of angular steel and plastic foil
 floating-drum plant made of pre-fabricated reinforced concrete compound units
 floating-drum plant made of fibre-glass reinforced polyester
 low cost floating-drum plants made of plastic water containers or fibre glass drums:
ARTI Biogas plants
 BORDA model: The BORDA-plant combines the static advantages of hemispherical
digester with the process-stability of the floating-drum and the longer life span of a
water jacket plant.
Advantages: Advantages are the simple, easily understood operation - the volume of stored
gas is directly visible. The gas pressure is constant, determined by the weight of the gas
holder. The construction is relatively easy, construction mistakes do not lead to major
problems in operation and gas yield.
Disadvantages: Disadvantages are high material costs of the steel drum, the susceptibility of
steel parts to corrosion. Because of this, floating drum plants have a shorter life span than
fixed-dome plants and regular maintenance costs for the painting of the drum.
2.4 Low Cost Polyethylene Tube Digester
Digester -In the case of the Low-Cost Polyethylene Tube Digester model which is applied in
Bolivia (Peru, Ecuador, Colombia, Centro America and Mexico), the tubular polyethylene
film (two coats of 300 microns) is bended at each end around a 6 inch PVC drainpipe and is

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wound with rubber strap of recycled tire-tubes. With this system a hermetic isolated tank is
obtained.
FIG 6. Low Cost Polyethylene Tube Digester
One of the 6" PVC drainpipes serves as inlet and the other one as the outlet of the slurry. In
the tube digester finally, a hydraulic level is set up by itself, so that as much quantity of added
prime matter (the mix of dung and water) as quantity of fertilizer leave by the outlet. Because
the tubular polyethylene is flexible, it is necessary to construct a "cradle" which will
accommodate the reaction tank, so that a trench is excavated.
Gas Holder and Gas Storage Reservoir - The capacity of the gasholder corresponds to 1/4 of
the total capacity of the reaction tube. To overcome the problem of low gas flow rates, two
200 microns tubular polyethylene reservoirs are installed close to the kitchen, which gives a
1,3 m³ additional gas storage.
2.5 Baloon Plants - A balloon plant consists of a heat-sealed plastic or rubber bag (balloon),
combining digester and gas-holder. The gas is stored in the upper part of the balloon. The
inlet and outlet are attached directly to the skin of the balloon. Gas pressure can be increased
by placing weights on the balloon. If the gas pressure exceeds a limit that the balloon can
withstand, it may damage the skin. Therefore, safety valves are required. If higher gas
pressures are needed, a gas pump is required. Since the material has to be weather- and UV
resistant, specially stabilized, reinforced plastic or synthetic caoutchouc is given preference.
Other materials which have been used successfully include RMP (red mud plastic), Trevira
and butyl. The useful life-span does usually not exceed 2-5 years.

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Variations: A variation of the balloon plant is the channel-type digester, which is usually
covered with plastic sheeting and a sunshade. Balloon plants can be recommended wherever
the balloon skin is not likely to be damaged and where the temperature is even and high.
FIG 7. Baloon Plant
Simple biogas plants. Floating-drum plant (A), fixed-dome plant (B), fixed-dome plant with
separate gas holder (C), balloon plant (D), channel-type digester with plastic sheeting and
sunshade (E).
2.6 Horizontal Plants - Horizontal biogas plants are usually chosen when shallow
installation is called for (groundwater, rock). They are made of masonry or concrete.
Advantages: Shallow construction despite large slurry space.
Disadvantages: Problems with gas-space leakage, difficult elimination of scum.

26 | P a g e
2.7 Earth Pit Plants - Masonry digesters are not necessary in stable soil (e.g. laterite). It is
sufficient to line the pit with a thin layer of cement (wire-mesh fixed to the pit wall and
plastered) in order to prevent seepage. The edge of the pit is reinforced with a ring of
masonry that also serves as anchorage for the gas-holder. The gas-holder can be made of
metal or plastic sheeting. If plastic sheeting is used, it must be attached to a quadratic wooden
frame that extends down into the slurry and is anchored in place to counter its buoyancy. The
requisite gas pressure is achieved by placing weights on the gasholder. An overflow point in
the peripheral wall serves as the slurry outlet. Advantages: Low cost of installation (as little
as 20% of a floating-drum plant); high potential for self help approaches. Disadvantages:
Short useful life; serviceable only in suitable, impermeable types of soil. Earth-pit plants can
only be recommended for installation in impermeable soil located above the groundwater
table. Their construction is particularly inexpensive in connection with plastic sheet
gasholders.
2.8 Ferrocement Plants - The ferro-cement type of construction can be applied either as a
selfsupporting shell or an earth-pit lining. The vessel is usually cylindrical. Very small plants
(Volume under 6 m3) can be prefabricated. As in the case of a fixed-dome plant, the
ferrocement gasholder requires special sealing measures (proven reliability with cemented-on
aluminium foil).
WHY FLOATING DRUM?
Advantages:
Simple, easily understood operation, constant gas pressure, volume of stored gas visible
directly,
few mistakes in construction.
Disadvantages:
High construction cost of floating-drum, many steel parts liable to corrosion, resulting in
short life (up to 15 years; in tropical coastal regions about five years for the drum), regular
maintenance costs 15 due to painting.
In spite of these disadvantages, floating-drum plants are always to be recommended in cases
of doubt. Water-jacket plants are universally applicable and especially easy to maintain. The
drum won't stick, even if the substrate has a high solids content.

27 | P a g e
Floating-drums made of glass-fibre reinforced plastic and highdensity polyethylene have
been used successfully, but the construction cost is higher than with steel. Floating-drums
made of wire-mesh-reinforced concrete are liable to hairline cracking and are intrinsically
porous. They require a gaslight, elastic internal coating. PVC drums are unsuitable because
not resistant to UV. The floating gas drum can be replaced by a balloon above the digester.
This reduces construction costs (channel type digester with folia), but in practice problems
always arise with the attachment of the balloon at the edge. Such plants are still being tested
under practical conditions.
2.9 About KVIC Pragati Model
 Model name - KVIC Pragati Model Biogas Plant
 Model Type - Floating Drum
 Biogas Production / 24hrs - 6 cubic m
 Major Parts - Gas Holder - 3.086 cubic
 Digester - 5.36 cubic m
 RT (Retention Time) – 16
 Cost Of Plant – Rs. 55,150
 Subsidy – Rs.11,000
 ROI – 2.24 yrs
 Annual Profit – Rs.19,657

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Chapter 3:
LiteratureReview
3.1 Scaling of Biogas Plant
To calculate the scale of a biogas plant, certain characteristic parameters are used. These are
as follows for simple biogas plants:
- Daily fermentation slurry arisings (Sd),
- Retention time (RT)
- Specific gas production per day (Gd), which depends on the retention time and the feed
material.
The following additional concepts and parameters are also used in the theoretical literature:
- Dry matter (DM). The water content of natural feed materials varies. For this reason the
solids or dry matter content of the feed material is used for exact scientific work (see
table in Fig. 2).
- Organic dry matter (ODM or VS). Only the organic or volatile constituents of the feed
material are important for the digestion process. For this reason, only the organic part
of the dry matter content is considered.
- Digester loading (R). The digester loading indicates how much organic material per day
has to be supplied to the digester or has to be digested. The digester loading is calculated in
kilograms of organic dry matter per cubic metre of digester volume per day (kg
ODM/m³/day). Long retention times result in low digester loadings. In a simple biogas plant,
1.5 kg/m3/day is already quite a high loading. Temperature-controlled and mechanically
stirred large-scale plants can be loaded at about 5 kg/m3/day. If the digester loading is too
high, the pH falls. The plant then remains in the acid phase because there is more feed
material than methane bacteria. The size of the gasholder - the gasholder volume (VG, see Figure 6)—
depends on gas production and the volume of gas drawn off .

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FIG 8. Volume Of Drawn Gas
.
Fig. 6:
Digester and gasholder Each biogas plant consists of a digester (VD) and a gasholder (VG). For calculation
purposes, only the net digester volume or gas space is relevant. In the fixed-dome plant (C), the net gas space
corresponds to the size of the compensating tank (Vo) above the zero line.
The zero line is the filling limit. Gas production depends on the amount and nature of the fermentation slurry,
digester, temperature and retention time (Figures 7,8).

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Fig. 9: Gas production from fresh cattle manure depending on retention time and
digester temperature
The curves represent averages of laboratory and empirical values. The values vary a wide range
owing to differences in the solids content of the dung, animal feeds and types of biogas plant.
Regular stirring increases gas production. The 26-28 °C line is a secure basis for scaling in the
majority of cases.
For a specific digester volume and a known amount of fermentation slurry, the actual retention time is
given by the formula
RT(days) = VD (l) -:-Sd (l/day)

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Example:
Digester volume (VD): 5360 l
Cow dung: 150 kg
Water: 1.25 *cow Dung: 187.7kg
Daily supply (Sd): 337.5 l/day
Retention time (RT):
5360 l -:- 337.5 l/day = 15.88 days ~ 16 days
If the digester size is given and a specific retention time is required, the daily amount of feed is
calculated by the formula
Sd (l/day) = VD (l) . RT(days)
The ratio of gasholder volume (VG) to daily gas production (G) is called the gasholder
capacity (C).
Example:
Gasholder volume (VG): 3m³ (1500l)
Daily gas production (G): 6 m³
Gasholder capacity (C):
3 m³/6 m³ = 0.625 = 50%.
The required gasholder capacity and hence the required gasholder size is an important
planning
parameter. If the gasholder capacity is insufficient' part of the gas produced will be lost. The
remaining volume of gas will not be enough. If the gasholder is made too large, construction
costs
will be unnecessarily high, but plant operation will be more convenient. The gasholder must
therefore be made large enough to be able to accept the entire volume of gas consumed at a
time.
It must also be able to accept all the gas produced between consumption times. Furthermore,
the
gasholder must be able to compensate for daily fluctuations in gas production. These
fluctuations
range from 75 % to 125 % of calculated gas production.

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GAS HOLDER CAPACITY:
Daily gas production: 6000 l
Hourly gas production: 6000 -:- 24 = 250 l/h
Assumption
Gas consumption
from 0600 to 0800 hrs =2h
Duration of gas consumption: 6 h
To simplify the calculation, uniform gas consumption is assumed. Hourly gas consumption:
3000 l -:- 6 h = 500 l/h
21
Gas is also produced during consumption. For this reason, only the difference between
consumption and production is relevant to the calculation.
DG = 500 l/h - 250 l/h = 250 l/h
The longest interval between periods of consumption is from 2100 to 0600 hrs (9 hours). The
necessary gasholder size is therefore:
VG(2) = 250 l/h x 9 h = 2250 l
VG(2) is the maximum relevant gasholder size. With the safety margin of 25%, this gives a
gasholder size of
VG = 2250 l x 1.25 = 2812 l
The required gasholder capacity is thus:
C = 2812 l -:- 6000 l= 0.468 ~ 47 %
Digester/gasholder ratio
The form of a biogas plant is determined by the size ratio between the digester and the
gasholder.

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FIG 11. Ratio of Digester / Gas Holder
Calculating volume of digester:

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FIG 12. KVIC Pragati Model.
Volume of Digester (VD) : Radius of Hemisphere - Radius of Spherical Cap
r = 180cm
h = 150cm
Volume of Hemisphere(VH) = 2/3 πr3
= 6.78 m3
Volume of Spherical Cap(VC) = πh(3a2+h2)/6
a = Radius of Sphrical Cap
h = Height of Spherical Cap
VC = 1.427m
3
VD = VH - VC

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VD = 5.36m
3
Volume of Gas Holder
10 INCHES

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Volume of Gas Holder (VH): Vol. of Cylinder(Vcyl) + Vol. of Cone(Vcone)
VH = Vcyl + Vcone
Cylinder:
r= 1m
h = .9m
Vcyl = 2.82m
3
Cone:
r=1m
h=0.254m
Vcone = 0.266m
3
VH = 3.086 m
3
65 mm

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Volume of Digester/gasholder ratio
R = VD /VH
VD = 5.36m
3
VH = 3.086 m
3
R = 1.78/1
R = 1.8/1
For floating-drum plants with a low digester/ gasholder ratio (1:1 to 3:1), the best shape for
the digester is a cylinder. If the ratio is larger, shell and vault structures are worthwhile
3.2 Design Of Biogas Plant
Bottom slab
The bottom slab is loaded at its edge by the weight of the digester wall. In the case of a
spherical shell, the weight of the earth load also acts on it. The bottom slab distributes the
weight over the ground of the site. The larger the foundation area, the less settlement will be
experienced. The more even the loads, the more even the settlement. The more even the
settlement, the less the risk of cracking. A "rigid" shell distributes the weight better than a
"soft" slab. The weight of the fermentation slurry presses uniformly on the ground. Where the
ground is of unequal consistency (e.g., boulders in loamy soil), loads must be distributed
within the bottom slab. If the slab is too weak, it will break and cease to be watertight.
A "rigid" shell distributes the loads better than a "soft slab". A vaulted shell is the best
foundation shape. But a concial shell is easier to excavate. The only implement required is a
straight piece of wood. Building material available locally is used for the bottom slab. One of
the following will be chosen on grounds of economy:
- quarry stone with a cement mortar filling and a cement floor,
- brick masonry with a cement floor,
- concrete.
Steel ring reinforcement at the outer edge increases the load bearing capacity of the bottom.

38 | P a g e
However, such reinforcement is not usually necessary. It is more important for the ground to
be firm and clean. If the soil consists of muddy loam, it must first be covered with a thin layer
of sand.
FIG 13. Bottom Slab
The bottom slab A flat slab must be flexurally rigid if it is to distribute the edge loads over
the entire surface
(a). Shells ate flexurally rigid
(b). Proceeding from a conical shell to a spherical shell
(c). Possible forms of construction: Quarrystone with cement mortar
(d). Masonry with cement floor
(e) and concrete

39 | P a g e
(f). Underneath the wall the bottom slab should be made out of massive concrete.
Spherical shell of masonry construction
The construction of a spherical shell from masonry (Figure 21) is completely problem-free.
Every bricklayer can master this technique after once being shown how to do it. Concreting a
vault, on the other hand, calls for much more skill and craftsmanship owing to the
complicated formwork
- the one exception being when the masoned shell is intended to serve as permanent
formwork. A spherical shell of masonry is simple to construct because the radius always
extends from the same centre. A trammel (A) is the only aid required. Bricks are stacked to
get the right height for the centre. Lean mortar is used for the stack, which is subsequently
demolished (M). No centring is necessary for laying the bricks.

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FIG 14. Spherical shell of masonry construction
Construction of a spherical shell from masonry When the bricks are laid, it is important for
their tops to be parallel with the bottom edge of the trammel (B), from the very first course.
The bricks are laid perpendicularly and centrally to the trammel (C). In the upper part
- when the trammel is standing at a steeper angle than 45°

41 | P a g e
- the first brick in each course must be held until the circle is complete. Each brick in between
must be held only until the next brick is set. For this purpose, clamps (D) or counterweights
of stones tied together (E) are used. The bricks can also be supported with sticks. The mortar
must be mixed from finely sieved sand (maximum particle size 3 mm). If the sand is too
coarse, the mortar will be difficult to work. It has to "stick" to the sloping, narrow surface of
the brick. Compo (cement/ lime) mortar is "stickier" than pure cement mortar. "Squeezed
joints" (Q) should be used. The trowel should have straight sides, so that the squeezed-out
mortar can be scraped off and reused (F). As in any masonry construction, the joints must be
offset (G). The terminal ring is rendered. The last but one course of bricks is laid on end (J).
When backfilling, the footing point must be tamped particularly well: one man filling and
two men tamping (H).
Masonry and mortar
The mortar and bricks should have about the same strenght. If the bricks are soft, the mortar
must also not be too hard. If a good brick is thrown on to the ground three metres away, it
must not break. If the bricks are of poor quality, the walls must be thicker. Mortar consists of
sand, water and the binders. Cement gives a solid, watertight mortar. Cement mortar is brittle
in masonry construction. Lime gives a soft, sticky mortar. For masonry construction, cement
mortar should always include a certain amount of lime. This makes it more workable, and the
masonry becomes more watertight.
Mixing ratio:
Masonry mortar 2 (cement) : 1 (lime): 10(sand) or 1 (cement) : 6 (sand)
Rendering mortar 1 (cement) : 4 (sand)
better 1 (cement) : 3 (sand)
The most important part of the mortar is the sand. It must be clean. It should not contain any
loam, dust or organic matter. Mortar sand with a high proportion of dust or loam "eats up"
much more cement than clean sand.

42 | P a g e
FIG 15. Masonry and mortar
Fig. 22: T
testing of mortar sand 1. Fines (loam, dust): Water glass 1/3 sand, 2/3 water. stir vigorously.
Leave to stand for one hour. Measure fines. A maximum of 10 % of the amount of sand is
permissible. 2. Organic matter: Bottle with stopper (not cork) to be filled with 1/3 sand and
2/3 soda lye (3 %). Shake repeatedly within an hour. Leave to stand for 24 hours. Water
colour clear or light yellow: good; red or brown: bad. The bricklayer or works foreman must
check the sand before use (Figure 22). Sand may contain not more than 10% dust or loam,
otherwise it must be washed. Soda Iye can be used to test whether the sand contains
excessive organic matter. The following points are important when rendering:
- The rendering mortar must be compressed by vigorous, circular rubbing.

43 | P a g e
- All edges must be rounded.
- All internal angles must be rounded with a glass bottle.
The parts of a biogas plant and their functions
The feed material is mixed with water in the mixing tank (Figure 23). Impurities liable to
clog the plant are removed here. The fermentation slurry flows through the inlet (Figure 24)
into the digester. A stick is inserted through the inlet pipe' to poke and agitate the slurry. The
bacteria from the fermentation slurry are intended to produce biogas in the digester (Figure
25). For this purpose they need time. Time to multiply and to spread through- ' out the slurry.
The digester must be designed so that only fully digested slurry can leave it. Partitions
(Figure 26) ensure that the slurry in the digester has long flow paths. The bacteria are
distributed in the slurry by stirring (with a stick or stirring facilities, see Figure 16). If stirring
is excessive, the bacteria have no time "to eat". The ideal is gentle but intensive stirring about
every four hours. Optimum stirring substantially reduces the retention time.
FIG. 16 stirring facilities

44 | P a g e
Fig. 17: Mixing tank
Mixing tank at inlet Grit and stones settle at the bottom of the mixing tank. For this reason
the inlet pipe (p) should be 3-5 cm higher than the tank bottom. A round, cylindrical shape is
cheapest and best for the mixing tank. If the tank is filled in the morning and then covered,
the slurry heats up in the sun until the evening (c). Only then is the plug removed (s).

45 | P a g e
Fig. 18: Floating Drum Axis
The inlet The inlet must be straight. The axis of the inlet pipe should, as far as possible, be
directed into the centre of the digester. This facilitates stirring and poking. The inlet should
be as high as possible, so that gritty deposits do not block the inlet pipe. In fixed-dome
plants, the inlet pipe must not pass through the gas space(a). For fibrous feed material,
the diameter should be 200-400 mm.

46 | P a g e
Path of the fermentation slurry in the digester Fresh fermentation material is lighter than fully
digested sludge. For this reason the former quickly rises to the surface and then sinks
only gradually. The digestion process has two phases. The better these phases are separated,
the more intensive he gas production. The fermentation channel (A) satisfies these conditions
best. Tandem plants are expensive and complicated (D). The deeper the digester, the lower
and less uniform its temperature.
Fig. 19: Hemispherical plant with partition wall
The principle of the fermentation channel isobtained by the fact that the inlet and outlet pipes
are close together. The partition wall extends up above the surface level of the fermentation
slurry. The gasholder must therefore float in a water jacket. The "horizontal KVIC gobar gas
plant", which is similar in design, works perfectly with high gas production.

47 | P a g e
Fig. 20: Stirring facilities in the digester The impeller stirrer
(a) has given good results especially in sewage treatment plants. The horizontal shaft
(b) stirs the fermentation channel without mixing up the phases. Both schemes originate
from large-scale plant practice. For simple household plants, poking with a stick is the
simplest and safest stirring method
(c). What matters is not how good the stirring arrangements are but how well the stirring is
performed.
The fully digested slurry leaves the digester through the outlet (Figure 28).

48 | P a g e
Fig 28:Outlet (overflow) of a floating-drum plant
The outlet should be placed below the middle of the digester, otherwise too much fresh feed
material will flow out of the plant too soon, thus reducing gas production by as much as 35 %
(b). The height of the outlet determines the level of the surface of the fermentation slurry (c-
f). This should be 8cm below the top edge of the wall. If this is not the case, difficulty will be
experienced in painting. If the outlet is too low, digester volume is lost (d). If it is too high,
the slurry will overflow the edge ofthe wall (e). The biogas is collected and stored until the
time of consumption in the gasholder. The prim requirement for the gasholder is that it must
be gaslight. Floating gasholders are held by a guide. In fixed-dome plants, the compensating

49 | P a g e
tank acts as a storage facility for the slurry displaced by the biogas. In this case the gas is
collected and stored in the upper part of the digester. The gas pipe carries the biogas to the
place where it is consumed. Condensation collecting in the gas pipe is removed by a tap or
water trap. Flexible gas pipes laid in the open must be UV-resistant.
3.3 Biogas appliances
Biogas appliances are domestic appliances. They serve a practical purpose. However, they
are also relevant to the self-image of the housewife or master of the house. The biogas plant
will be looked after better the higher the prestige value of the gas appliances. For this reason
even simple, inexpensive gas appliances made in the village should be of appealing design.
They must be not only cheap but also, and in particular, "modern". Most households cook on
two flames. Two-flame burners are preferred. The burners (Figure 41) should be set initially
and then fixed. Efficiency will then remain at a high practical level.

50 | P a g e
Fig. 41:Diagram of a gas burner and a lamp Burner:
The values given are rules of thumb for a gas pressure of 5-10 cm WG. If the pressure is
higher, the mixing chamber (M) must be enlarged so that the gas particles can mix adequately
with oxygen. The gas/air mixture is regulated by means of the adjusting screw (J). A burner is
correctly adjusted if only half of all the flames are burning before the pan is placed in
position. Lamp: Things to watch for include the right
area ratio between the air hole and the gas nozzle (a), adequately sized gas/air mixing
chamber (b) and an air trap (c) that ensures a sufficiently high temperature around the gas
mantle without causing a shortage of oxygen for combustion.

51 | P a g e
In villages without electricity, lighting is a basic peed and a status symbol. However, biogas
lamps have low efficiency. This means that they also get very trot.' If they hang directly
below the roof, there is a fire risk. The mantles do not last long. It is important that the gas
and air in a biogas lamp be thoroughly blended before the mixture reaches the gas mantle,
and that the air space around the mantle be adequately warm. Particular problems also arise
with biogas-operated refrigerators. The composition of biogas varies substantially from day
to day. The gas pressure fluctuates excessively with the amount of gas stored even in a
floating-drum plant. Special' stable-burning jets are therefore needed - especially if the
refrigerator is thermostatically controlled and the flame burns only when required. On every
ignition there is a risk of the flame going out. Gas will then discharge without burning. The
gas supply must therefore automatically be cut off if the flame goes out.
3.4 Floating Gas Holder Parameters
The gas drum normally consists of 2.5 mm steel sheet for the sides and 2 mm sheet for the
cover. It has welded-in braces. These break up surface scum when the drum rotates.
The drum must be protected against corrosion. Suitable coating products are oil paints,
synthetic paints and bitumen paints. Correct priming is important. One coat is as good as no
coat. Two coats are not enough. There must be at least two preliminary coats and one topcoat.
Coatings of used oil are cheap. They must be renewed monthly. Plastic sheeting stuck to
bitumen sealant has not given good results. In coastal regions, repainting is necessary at least
once a year, and in dry uplands at least every other year. Gas production will be higher if the
drum is painted black or red than with blue or white, because the digester temperature is
increased by solar radiation. Gas drums made of 2 cm wire-mesh-reinforced concrete or
fibrocement must receive a gaslight internal coating. The gas drum should have a slightly
sloping roof (Figure 29), otherwise rainwater will be trapped on it, leading to rust damage.
An excessively steep-pitched roof is unnecessarily expensive. The gas in the tip cannot be
used because the drum is already resting on the bottom and the gas is no longer under
pressure.

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Fig. 29: The gas drum
The gas drum should have a slightly sloping roof. When the cover plate is cut, a wedge (k)
should be cut out. The cover plate must be rather larger than the diameter of the drum (see
calculation at bottom left). Inaccuracies can more easily be corrected if a lateral overhang of
2 cm is allowed.

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Fig. 30:Forces on the gas drum
The gas pressure and the weight of the metal itself give rise only to tensile forces in the jacket
sheet. No reinforcements are necessary for these to be withstood (a). The loads from the
guide tube must be reliably transmitted to the cover plate (b). A flange plate (b1 ) or angle
iron (b2) is required for this purpose. The braces are stressed when the drum i,s rotated (c).
They should not simply butt on to the metal but end in a corner (c, ) or at an angle (c2).
The side wall of the gas drum should be just as high as the wall above the support ledge. The
floating-drum must not scrape on the outer walls. It must not tilt, otherwise the paintwork
will be damaged or it will jam. For this reason a floating-drum always requires a guide (see
Figures 31 and 32). The guide frame must be designed so that the gas drum can be removed

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for repair. The drum can only be removed if air can flow into it, either the gas pipe should be
uncoupled and the valve opened, or the water jacket emptied.
Fig. 31: Floating drum guide frame
An external guide frame (A) is cheapest. It is made of tubular steel, sectional steel or wood.
The guide tube also acts as the gas outlet. With scheme (B), the open pipe is problematic. It
cannot be reliably painted. The tidiest, but also the most expensive, solution is a guide with
internal gas outlet (C). For the water trap (D) see also Figure 40. Guide frames for heavy gas
drums must withstand large forces. All joints and anchor points must be just as strong as the
pipes themselves.

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Chapter - 4
FABRICATION & INSTALLMENT OF PLANT
4.1 Selection Of Site
Location: Nehrugram , Dehradun
Number of Cows: 16
Number of Family Members: 8
Cow Manure Availability/Day : 160 - 320 Kg
A small scale dairy was selected as site for the plant. The size of the plant agreeable for 160
kg to 320 kg cow manure available everyday is 6m3 . Certain aspects were taken into
consideration before selecting the site:
1. Manure availability should be relevant to the size of the plant.
2. All of the cows should be tied to facilitate manure availability.
3. Atleast 40 kg of manure is necessary for operation of smallest biogas plant.
4. There should be adequate space for slurry exit.
5. Cattle should be near the biogas plant.
6. Water supply should be adequate, Equal amounts of manure and water are required when
digester is filled with slurry.
If plant owners are considering human faeces as fuel , it is necessary people do not use more
than 1 litre of water every time they use the toilet otherwise the slurry will be very thin.
Though there is no accurate guide to tell the size of biogas plant by the number of animals but
it is generally considered that two cattle are required for a plant of 2m3 or manure from 60 -
70 people is required.
4.2 Construction Material Required:
1. Steel Rods Diameter: 1cm
2. Bending tools
3. Mild Steel Sheets

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Breadth: 92 cm
Thickness: 1mm
Length : As Required
4. Cement
5. Sand
6. Bricks
7. PVC pipe(4 inch)
4.3 Construction Of Foundation /Digester:
The digester is that part of the plant where the manure is stored to go through anaerobic
digestion. The construction of digester takes place according to processes mentioned in
section 3.3 Design of Plant.
Specification of Digester:
Slurry Holding Capacity: 5.36 m3
Shape : Hemispherical or Dome Type
Radius of Hemisphere: 1.80 m
Height : 1.50 m
Construction Material : Bricks, Cement, Concrete
The Digester was constructed using help of Civil workers already efficient in making such
domes. The workers were outsourced by KVIC for the plant.

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Fig. 32: Costruction Of Digester

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Fig.33: Construction of Dome:
Fig.34: Guide Frame and Walls

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Fig.35 Guide Frame:
4.4Construction Of Gas Holder:
The Gas holder is the part of the plant which stores biogas. The gas generated anaerobically
in the digester is stored in the gas holder. The volume of the gas holder depends on the usage
of gas /day. The volume of the gas holder was determined in section 3.3 . The gas holder
volume determined was 3 m3 . The gas holder was fabricated completely by the design team.
Specifications of the gas holder are given below:
Volume of Gas Holder: 3 m3
Material : Iron and Mild Steel
Welding Process : SMAW (Shielded Metal Arc Welding)
Welding Rod: E6013
Bending Machine : Manual
Hammering : Manual
Ambient Temperature: 31 °C

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List Of Equipments :
Manual Bending Machine
Hammers
Anvil
Sheet Cutting Machine
Welding Machine
Inch Tapes
Steel Rules
Large Nails
List Of Material:
Iron Rods : Radius = 1cm
Mild Steel Sheets : Width = 100cm , Thickness =1mm
Hollow Steel Pipe : Outer Diameter = 65mm , Thickness = 2mm
Steel Angles for Support.
Diagram:

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Fabrication:
To fabricate a gas holder , it is necessary to have a basic skeletal system. A frame is
fabricated using iron rings.
Step 1:
Making rings of diameter 198 cm using steel rods and manual bending machine.

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Fig.36: Cylinder Frame Ring
Manual hammering is used to give the rings a perfect circular shape. Radius of ring is
checked after hammering every defected section. During hammering the rings is welded
temporarily to the sheet below it.
Step 2:
After making two rings of diameter 198cm , bracing is given to both rings . First ring is used
to support base of the holder. The second ring forms the frame for the conical section of the
holder. The height of this conical section is 10 inches. At the centre of both rings is a square
plate, to which all the bracings are attached.

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Fig.37: Cylinder Cone

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This concludes the basic skeletal system of the gas holder, this skeleton is now given a height
of 90cm using mild steel sheets. The center to center distance between lower and upper rings
is 90cm.
Step 3:
Rings are now welded to mild steel sheets of width 90cm

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Step 4:
After completing the cylindrical circumference the conical section is covered with sheet
cutouts welded precisely to the frame.
Step 5:

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The construction of gas holder is completed , handles are now attached to the holder to
facilitate rotation. The gas holder is then painted black to facilitated an increased rate of
anaerobic digestion.
4.5 Making biogas plant functional :
To make the biogas plant functional the first and foremost part is the availability of manure.
Before placing the drum, the user has to add 6 tonnes of cow manure and 8 tonnes of water to
the digester pit. After this the gas holder is places above the guide frame. Extreme precaution
must be taken if this process is being done manually.

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After placing the biogas plant , gate valve and PVC pipeline are attached to the kitchen stove.
The plant is left for a period of 40 days to facilitate production of gas. During this period the
gate valve should be closed.
After 40 days the drum will rise to indicate production of gas. The first batch of gas should
not be used since the methane content is low and it is not suitable for combustion . Below is
the picture of a completely functional biogas plant.

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Testing the flame to find the quality of biogas is necessary .
If the biogas is giving blue flame during combustion, it indicates complete combustion of gas.

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Blue flame indicating complete combustion of gas.
4.7 Maintenance and Using the Plant:
It is very easy to operate KVIC pragati model biogas plant, A 6m3 capacity biogas plant
requires 150 kg of cow manure and water equivalent to 1.25 times of the cow manure.
Hence, It is necessary to add 150 kg of cow manure and 187.5 litre of water to the digester
everyday. Equal amount of slurry will come out of the digester every day. Digested slurry
will go into the compost pit, this slurry is high in nitrogen content and can be used as
compost. It is necessary to rotate the holder from time to time to break the dried sludge. Gas
holder should also be painted every year to facilitate maximum production of gas.

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Chapter 5
CONCLUSION & FUTURE SCOPE
5.1 Economics for State of Uttarakhand
• Cost of Installation
For studying the economics of . KVIC model of family size 6 m3 biogas plant, the cost of
construction and installation, annual operational cost and income from biogas thus produced
are calculated by taking into account the current prices of the local market of Dehradun,
Uttarakhand (India). The Government of India, for promoting the use of biogas, irrespective
of the model and the capacity of biogas plant to be installed by any family, is providing a
fixed amount of subsidy of Rs. 11000/- through its nodal agencies for biogas plant of 6m3
volume . Hence, for knowing the actual cost to be incurred for installation of a biogas plant,
an amount of Rs. 11000/- is uniformly subtracted from the calculated cost of 6m3 capacity
• Annual operational cost
Annual operational cost of a biogas plant involves the annual depreciation on civil
construction work and other installations, annual maintenance charges and cost of dung
required to run it per annum. As per established standards, the life of the civil work, gas
holder and gas supply line is considered to be 25, 10 and 20 years, respectively, rendering the
corresponding annual depreciation to be 4%, 10% and 5%.

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5.2 Problem in policies and areas for improvement
• The balance 50% of the CFA will be released as second instalment after the
receipt of Utilization Certificate of the previous releases and receipt of Audited
Statement of Account up to previous to previous year and based on the
satisfactory physical progress (40% of the annual targets) achieved during the
year of programme implementation. - Due to this policy, Agents and people suffer
lack of funds .
• The programme will be implemented by State Nodal Departments / State Nodal
Agencies and Khadi & Village Industries Commission (KVIC), Biogas
Development and Training Centres (BDTC), other State Government Agencies /
Organizations / Departments, etc. However, within the State, the programme
Name of
component
Quantity Rupees/Quant
ity
Bricks 1650 bricks 5
Cement 14 Packet
(50kg eack)
400
Sand 40 cubic feet 2800
Stone blast 20 cubic feet 1500
Brick blast 20 cubic feet 1500
PVC pipe(4
inch)
10 feet 500
Holder +
frame
- 18000
Labour - 11000
Pipeline
- 2000
Stove - 1500
Gate Valve - 500
Transport - 2000
Sum - 55150
Subsidy - 11000
Total(Sum-
Subsidy)
- 44150

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implementing State Nodal Departments / State Nodal Agencies and KVIC,
BDTC, etc. could also take help by identifying other skilled organizations that
would function within their overall control. However, in one State there may not
be more than two agencies excluding KVIC. - This creates lack of competition for
plant setups, and agencies take People for granted and process is unnecessarily
lengthened.
• For Jammu & Kashmir, Himachal Pradesh, Uttrakhand, Niligiri of Tamil Nadu,
Sadar Kurseong & Kalimpong Sub-Divisions of Darjeeling, Sunderbans (W.B.)
and Andaman & Nicobar Islands, Subsidy is Rs.11,000 for 6 Cubic Meter Plant. -
This amount of subsidy is insufficient.
5.3 If Biogas Gives Better Returns , What Happened? Why Isn't it popular?
A technology is appropriate if it gains acceptance. Biogas plants have hitherto gained little
acceptance. Simple biogas plants have up to now presumably been inappropriate.
Bicycles are appropriate: if a person buys a bicycle, he is proud. It is a sign of his advance,
his personal progress. The bicycle is appropriate to the need for social recognition. If the
person mounts the bicycle and falls off because he does not know how to ride it, it is not
appropriate to the abilities of its owner. The person learns to ride and thus adapts himself to
his cherished bicycle. The person goes to work on his bicycle. It is appropriate to his need for
convenience and low-cost transport. The bicycle breaks down. The person has no money to
spare to have it mended. He saves on other expenditure, because the bicycle is important for
his pride and his convenience. He walks long distances to the repairer. He adapts to the needs
of the bicycle.
The person can afford this expenditure without getting into economic difficulties. The bicycle
is appropriate to his economic capacity. A biogas plant is correctly operated and maintained
if it satisfies the user's need for recognition and convenience. He for his part is then prepared
7to adapt to the needs of the biogas plant. Biogas plants are appropriate to the technical
abilities and economic capacity of Third World farmers. Biogas technology is extremely
appropriate to the ecological and economic demands of the future. Biogas technology is
progressive. However, a biogas plant seldom meets the owner's need for status and
recognition. Biogas technology has a poor image ("Biogas plants are built by dreamers for
poor people". If you do not want to seem one of the poor, you do not buy a biogas plant. The
image of the biogas plant must be improved. The designer makes his contribution by
supplying a good design. A "professional design" that works. One that is built in conformity
with contemporary requirements and models. The biogas plant must be a symbol of social
advancement. The biogas plant must be technically progressive. A biogas plant as an
investment is in competition with a bicycle or moped, a radio set or diesel pump, a buffalo or
an extension to the farmhouse. The economic benefit of a biogas plant is greater than that of
most competing investments. However, the plant must also be worthwhile as a topic for the
"chat in the market place".
So the design must not be primitive. So it must be well made. So the gas bell must be
7attractively painted. So the gas pipe must be laid tidily. So the fermentation slurry tank must
be decently designed and constructed. So giant pumpkins and flowers must grow around the
plant. "A good biogas plant is appropriate. Appropriate to the needs of its owner and his
abilities and capacity. It is appropriate to the necessities of the future."

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REFERENCE
 Biogas Plants by Ludwig Sasse
A Publication of the Deutsches Zentrum für
Entwicklungstechnologien - GATE in: Deutsche
Gesellschaft für Technische Zusammenarbeit (GTZ)
GmbH - 1988
 KVIC biogas plant booklet
 Biogas Handbook by Teodorita Al Seadi, Dominik Rutz, Heinz Prassl, Michael
Köttner, Tobias Finsterwalder,Silke Volk, Rainer Janssen
 mnre.gov.in
 Researchgate.com
 google.co.in
 Comparative study of economics of different models of
family size biogas plants for state of Punjab, India
K. Jatinder Singh, Sarbjit Singh Sooch
 Built to sell - John Warrillow

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