1) Biomass can be converted into energy through direct combustion, thermo-chemical processes like gasification and pyrolysis, or biochemical processes like anaerobic digestion. 2) There are two main types of biogas plants - fixed dome plants with the digester and gas holder combined, and floating drum plants with a separate gas holder that floats. 3) In anaerobic digestion, bacteria break down biomass in the absence of oxygen to produce a gas called biogas that is 55-65% methane. Several factors affect biogas production rates.

2. CONTENT
Introduction………………………………………………………….......
Photosynthesis process……………………………………………..........
Biomass energy conversion………………………………......................
Direct Combustion……………………………………………...........
Thermo Chemical Conversion............................................................
Biochemical Conversion…………………………………………......
Biogas Generation………………………………………………………
Classification of Biogas plants………………………………………....
Site selection…………………………………………………………….
Prospects of Biomass in India………………………………………....
Advantages & Disadvantages………………………………………....
Application……………………………………………………………....

3. Introduction to Biomass
Pakistan is a land of village
where the energy required for
domestic purpose such as
cooking is met from dried
woods, twigs and leaves of
plants and other dried organic
matter such as cow dung.
This organic matter called as
biomass is available freely as
waste.
It contains stored energy from
the sun.

4. Introduction to Biomass
It is a renewable energy
source because we can
always grow more trees
and crops, and waste
will always exist.
The biomass is fast
renewable forms of
available
energy and
freely as waste and
discarded matters.

6. Photosynthesis Process
Photosynthesis is a
process
converts
chemical
that
carbon
dioxide into organi-
c compounds,
especially
using the
sugars,
energy
from sunlight.

7. Photosynthesis Process

8. Photosynthesis Process
Biomass is produced in the photosynthesis process
which converts the solar energy into biomass energy.
Photosynthesis process only occurs in green plants. It
is the process of combining the carbon dioxide from
the atmosphere with water plus light energy to
carbohydrates (sugars, starches, celluloses, etc.) and
oxygen.
Photosynthesis
6CO2 + 6H2O + light energy C6H12O6 + 6O2

9. Splitting of water molecule into H2 & O2 under influence of chlorophyll.
“Light Reaction”
Hydrogen is transferred to CO2 to form Starch or Sugar.
Light
CO2 Concentration
Temperature

10. Biomass energy
conversion
The various process used
for coversion of biomass
into energy or bio-fuels
can be classified as
follows:
1) Direct combustion
2) Thermo chemical
conversion
3) Biochemical
conversion

11. Direct Combustion
The direct combustion of biomass in presence of oxygen/air to
produce heat and by products is called direct combustion.
The complete combustion of biomass into ash is called
incineration.
This heat energy in the product gases or in the form of steam
can be used for various applications like space heating or
cooling, power generation, process heating in industries or any
other application.
However, if biomass energy by combustion is used as co
generation with conventional fuels, the utilization of biomass
energy makes it an attractive proposition.

12. Direct Combustion

13. THERMO CHEMICAL
CONVERSION
The thermo chemical reaction can convert the
organic biomass into more valuable and
convenient form of products as gaseous and
liquid fuels, residue and by-products etc.
These processes can be carried out in the
following ways:
1) Gasification
2) Pyrolysis

14. Gasification
Heating of biomass
in presence of limited
oxygen
(deficient
and air
O2/air) is
called gasification. It
produces
fuels
gaseous
like
H2, CO, CH4, N2 of
low calorific value.

15. Pyrolysis
It is the heating of biomass in a closed
vessel at tempratures in the range 500oC-900oC
in absence of O2/air. It produces solid, liquid and
gases.
The pyrolysis process can use all type of organic
materials including plastic and rubeers.

16. Biochemical Conversion
In biochemical processes the bacteria and micro
organisms are used to transform the raw biomass
into useful energy like methane and ethane gas.
Following organic treatments are given to the
biomass:
1) Fermentation of biomass (Aerobic digestion)
2) Anaerobic digestion of biomass

17. Fermentation
Fermentation is a process of decomposition of
complex molecules of organic compound under
the influence of micro-organism (ferment) such
as yeast, bacteria, enzymes etc.
The example of fermentation process is the
conversion of grains and sugar crops into ethanol
and CO2 in presence of yeast.

18. Anaerobic digestion
The anaerobic digestion or
anaerobic fermentation
process involves the
conversion of decaying wet
biomass and animal waste into
biogas through decomposition
process by the action of
anaerobic bacteria.
The most useful biomass for
production of biogas are
animal and human waste,
plant residue and other
organic waste material with
high moisture content.

19. Biogas Generation
Biogas contains 55-65% methane, 30-40% CO2, and
the remainders are impurities like H2S, H2, N2 gases.
Cattle dung can produce 0.037 m3 of biogas per kg
of cow dung. The calorific value of gas is 21000 to
23000 kJ/kg or about 38000 kJ/m3 of gas. The
material from which biogas is produced retains its
value as fertilizer or as animal feed which can be
used after certain processing.

20. Biogas Generation
Biogas can be produced by digestion pyrolysis or
hydrogasification. Digestion is a biological process that
occurs in absence of O2 and in presence of anaerobic
organisms at atmospheric pressure and temperatures of
35oC-70oC. The container in which the digestion takes place
is called digester.
When organic matter undergoes fermentation, the
anaerobic bacteria extracts oxygen by decomposing the
biomass at low temperatures up to 65oC in the presence of
moisture. (80-95%), the gas so produced is called biogas.

21. Principle of biogas production
Biogas production takes place in three stages:
1)Hydrolysis: In this stage, matters with heavy
molecular weight are disintegrated into lower
molecular weight. This process takes place by
hydrolytic bacteria.
2)Acid Formation: In this stage, organic matters
are converted into acetates and H2. This
conversion takes place by acetogenes. Then H2
and C are converted into acetate by acetogenes.

22. Principle of biogas production
3) Methane Gas Formation: In this stage,
acetates and simple CO2 are converted into
CH4. This is carried out by methanogenes.

23. Factors affecting biogas
production
The rate of production of biogas depends on the
following factors:
1) Temperature & Pressure
2) Solid concentration & Loading rate
3) Retention period
4) pH value
5) Nutrients composition
6) Toxic substances
7) Digester size & shape
8) Stirring agitation of the content of digestion

24. The Dome and the Drum Type
 Mainly two types of biogas plants are normally used:
 The floating gas holder plant
 Fixed dome digester
 In a floating gas holder, gas holder is separated from the
digester. While in fixed dome digester, the gas holder and the
digester are combined.
 The fixed dome is best suited for batch process especially
when daily feeding is adopted in small quantities.
 The fixed dome type plant is generally built below the ground
level and is suitable for cooler regions.

25. Fixed Dome type Biogas Plant
 Invented in china in 1930s.
 Underground brick masonry compartment (fermentation chamber) with a dome
on the top for gas at the storage.
 Fermentation chamber and gas holder are combined as one unit.
 A fixed-dome plant consists of an enclosed digester with a fixed, non-movable
gas space. The gas is stored in the upper part of the digester.

26. Fixed Dome type Biogas Plant
The biogas plant is a brick and cement structure having the following
five sections:
Mixing tank present above the ground level.
Inlet tank: The mixing tank opens underground into a sloping inlet
chamber.
Digester: The inlet chamber opens from below into the digester
which is a huge tank with a dome like ceiling. The ceiling of the
digester has an outlet with a valve for the supply of biogas.
Outlet tank: The digester opens from below into an outlet chamber.
Overflow tank: The outlet chamber opens from the top into a small
over flow tank.

27. Fixed-Dom Type

28. Working of Fixed Dome type Biogas Plant (1/2)
 The various forms of biomass are mixed with an equal quantity
of water in the mixing tank. This forms the slurry.
 The slurry is fed into the digester through the inlet chamber.
 When the digester is partially filled with the slurry, the
introduction of slurry is stopped and the plant is left unused for
about two months.
 During these two months, anaerobic bacteria present in the slurry
decomposes or ferments the biomass in the presence of water.
 As a result of anaerobic fermentation, biogas is formed, which
starts collecting in the dome of the digester.

29.  As more and more biogas starts collecting, the pressure
exerted by the biogas forces the spent slurry into the outlet
chamber.
 From the outlet chamber, the spent slurry overflows into the
overflow tank.
 The spent slurry is manually removed from the overflow tank
and used as manure for plants.
 The gas valve connected to a system of pipelines is opened
when a supply of biogas is required.
 To obtain a continuous supply of biogas, a functioning plant
can be fed continuously with the prepared slurry.
Working of Fixed Dome type Biogas Plant (2/2)

30. Floating gas holder type of biogas plant
The floating gas holder type of biogas plant has the following
chambers/ sections:
 Mixing Tank - present above the ground level.
 Digester tank – inside the digester, the slurry is fermented.
Biogas is produced through bacterial action.
 It has two long cement pipes
 Inlet pipe opening into the inlet chamber for introduction of slurry.
 Outlet pipe opening into the overflow tank for removal of spent slurry.
 Gas holder - an inverted steel drum resting above the
digester. The drum can move up and down i.e., float over the
digester. The gas holder has an outlet at the top which could
be connected to gas stoves.
 Over flow tank - Present above the ground level.

32. Floating Drum plants

33. Working (1/2)
 Slurry (mixture of equal quantities of biomass and water) is
prepared in the mixing tank.
 The prepared slurry is fed into the inlet chamber of the digester
through the inlet pipe.
 The plant is left unused for about two months and inserting of
more slurry is stopped.
 During this period, anaerobic fermentation of biomass takes
place in the presence of water and produces biogas in the
digester.
 Biogas being lighter rises up and starts collecting in the gas
holder. The gas holder now starts moving up.

34.  The gas holder cannot rise up beyond a certain level. As more and
more gas starts collecting, more pressure begins to be exerted on the
slurry.
 The spent slurry is now forced into the outlet chamber from the top
of the inlet chamber.
 When the outlet chamber gets filled with the spent slurry, the excess
is forced out through the outlet pipe into the overflow tank. This is
later used as manure for plants.
 The gas valve of the gas outlet is opened to get a supply of biogas.
 Once the production of biogas begins, a continuous supply of gas
can be ensured by regular removal of spent slurry and inserting of
fresh slurry.
Working (2/2)

35. Different variations in the drum type
 There are mainly two variation in floating type plant. One
with water seal and other without water seal.
 Water sealing makes the plant completely anaerobic.
 Cylindrical shape of the digester is preferred because
cylinder has no corners and so that there will be no chances of
cracks due to faulty construction. This shape also needs
smaller surface area per unit volume, which reduces heat
losses also.
 Moreover the scum formation may be reduced by rotating gas
holder in the cylindrical digester.

36. Site selection
Following factors must be considered while selecting the site for
a biogas plant:
1. Distance
2.Minimum gradient
3.Open space
4.Water table
5.Seasonal run off
6.Distance from wells
7.Space requirements
8.Availability of water
9.Sources of cow dung/materials for biogas generation