energy from biomass

1. ENERGY TECHNOLOGY (2170505)
B.E. 7TH SEMESTER
CHEMICAL ENGINEERING
G.H. PATEL COLLEGE OF ENGINEERING &
TECHNOLOGY, VALLABH VIDYANAGAR
PREPARED BY: BANSI V KANSAGRA
AD-HOC LECTURER IN CHEMICAL ENGINEERING DEPARTMENT
GCET, V.V.NAGAR

2. GTU QUESTIONS
1 Construction and working of KVIC digester. 4 times
2 Classification of biogas plant. Explain any one.
Or
Fixed dome types of biogas plant.
3 times
3 Discuss different biomass conversion technology. 2 times
4 List 6 site selection criteria explain it. 2 times
5 Discuss factors affecting bio digestion. 2 times
6 Basic steps involved in biogas generation. 2 times
7 What is biomass? List biomass energy resources. 2 times

3. GTU QUESTIONS
8 List Indian types of biogas plant. Explain any one. 1 times
9 What is meant by energy plantation? Its advantage and
disadvantage.
1 times
10 Wet and dry fermentation. 1 times
11 Discuss material used for biogas generation. 1 times
12 What is meant by anaerobic digestion? 1 times
13 Phases involved in generation of biogas from biomass and
factors affecting the same.
1 times

4. INTRODUCTION
• Biomass is organic matter produced by plants, both terrestrial and aquatic
and their derivatives.
• Biomass can be considered a renewable energy source because plant life
renews and adds to itself every year.
• Hence, solar energy →photosynthesis → biomass → energy generation

5. ENERGY PLANTATION
• It is method of tapping maximum solar energy by growing plants.
• Energy farms are ideal solar collectors requiring virtually no maintenance
• Energy plantation means growing select species of trees and shrubs
which are harvestable in a comparably shorter time and are specifically
meant for fuel.

6. BIOMASS CONVERSION TECHNOLOGIES
• A wide variety of conversion technologies is available for manufacturing
premium fuels from biomass
• Some are simple and well understood like digestion and fermentation;
others like gasification.

7. PHOTOSYNTHESIS
• Most important chemical reaction on the earth is the reaction of sunlight
and green plants.
• Photosynthesis, the process by which green plants and certain other
organisms transform light energy into chemical energy.
• During photosynthesis in green plants, light energy is captured and used to
convert water, carbon dioxide, and minerals into oxygen and energy-rich
organic compounds (sugars and starches).
•

8. PHOTOSYNTHESIS

9. BIOGAS GENERATION
• Biogas a mixture containing 55-65 percent methane, 30-40 percent carbon
dioxide and the rest being the impurities can be produced from the
decomposition of animal, plant and human waste.
• It can be used directly in cooking, reducing the demand for firewood.
• Material from which biogas is produced retains its value as a fertilizer.
• Biogas is produced by digestion and pyrolysis.

10. BIOGAS GENERATION
• Digestion is a biological process that occurs in the presence of anaerobic
organisms at ambient P and T of 35-70 ◦C.
• Those which grow in presence of oxygen are called aerobic.
• Those which grow in absence of oxygen are called anaerobic.
• Aerobic fermentation – produces CO2, NH3 and other gases
• Anaerobic fermentation – produces CO2, CH4, H2 and traces of other gases
• Pyrolysis – fats, starches and proteins contained in cellulosic biomass are
broken down into simple compounds

11. FACTORS AFFECTING BIOGAS GENERATION
1) pH
2) Temperature
3) Total solid content of the feed
material
4) Loading rate
5) Seeding
6) Uniform feeding
7) Diameter to depth ratio
8) Carbon to nitrogen ratio
9) Nutrients
10) Mixing or stirring of the content
11) Retentation time or rate of
feeding
12) Type of feed stocks
13) Toxicity due end product
14) Pressure
15) Acid accumulation inside the
digester

12. BIOGAS FROM PLANT WASTES
• Subject of biogas production from fresh plant wastes is not at all new.
• Biogas production was a common feature even 40 years ago on many
European farms.
• The process of biodigestion as already described is carried out generally in
following two recognized systems:
1. Batch fermentation
2. Continuous fermentation

13. BIOGAS FROM PLANT WASTES
• In batch fermentation, the feeding is between intervals. The plant is
emptied once the process of digestion is complete.
• In continuous fermentation, the feeding is done every day and digested
slurry equivalent to the amount of feed overflows from the plant.
• Continuous process may be completed in a single stage or separated into
two stages.

14. BIOGAS FROM PLANT WASTES
• Single stage process: it is completed in a single chamber. This
chamber is regularly fed with the raw materials while the spent residue
keeps moving out.
• Double stage process: the acidogenic stage and methanogenic stage are
physically separated into two chambers.
• In the first stage acid production is carried out in a separate chamber and
only the diluted acids are fed into the second chamber and bio gas can be
collected from the second chamber.

15. SELECTION OF 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) Source of cowdung / material
for biogas generation

16. FUEL PROPERTIES OF BIOGAS
• Biogas generated by anaerobic
fermentation of organic wastes, essentially
contains methane and carbon dioxide in
large production.

17. UTILIZATION OF BIOGAS
• Biogas can be directly used for cooking by supplying the gas though pipes
to households from the plant.
• Biogas has been effectively used as a fuel in industrial high compression
spark ignition engines.
• To generate electricity an induction generator can be used and is the
simplest to interface to the electrical grid.
• Induction generators derive their voltage, phase, and frequency from the
utility and cannot be used for stand-by power.

18. UTILIZATION OF BIOGAS
• If a power outage occurs generator will cease to operate.
• Synchronous generator can also be used to connect to the grid. However,
they require expensive and sophisticated equipment to match the phase,
frequency and voltage of the utility grid.
• Biogas can also be used as fuel in a hot water heater if hydrogen sulfide is
removed from the gas supply.

19. CLASSIFICATION OF BIOGAS PLANTS
• Biogas plants are mainly classified as:
1. Continuous and batch types
2. The dome and the drum types
3. Different variations in the drum type

20. 1. Continuous and batch types:
a) Continuous plant:
• There is a single digester in which raw material are charged regularly and
the process goes on without interruption.
• In this case the raw material is self buffered or thoroughly mixed with the
digesting mass where dilution prevent souring and the biogas production is
maintained.
• Continuous process may be completed in a single stage or separated into
two stages

21. a) Continuous plant:
i. Single stage process:
• The entire process of conversion of complex organic compounds into
biogas in a single chamber.
• This chamber is regularly fed with the raw materials while the spent
residue keeps moving out.
• Serious problem encountered with agricultural residues when fermented in
a single stage continuous process.

23. a) Continuous plant:
ii. Double stage process:
The acidogenic stage and methanogenic stage are physically separated
into two chambers. Thus the first stage of acid production is carried out
in a separate chamber where bio-methanation takes place and the biogas
can be collected from the second chamber.
• Main feature of continuous plant are:
1. It will produce continuously
2. It requires small digestion chambers.

25. b) Batch plant:
• The feeding is between intervals. In this type a battery of digesters are
charged along with lime, urea etc. and allowed to produce gas for 40-50
days.
• There are charged and emptied one by one in synchronous manner which
maintain a regular supply of the gas through a common gas holder.
Main feature of the batch plant are:
i. The production in it is intermittent, depending upon the clearing of the
digester.

26. b) Batch plant:
ii. It needs several digesters for continuous gas production
iii. Batch plant are good for long fibrous material

27. 2. The dome and the drum types
There are numerous models of a biogas plant mainly two main types are
usually used:
1. The floating gas holder plant
2. Fixed dome digester

28. a) The floating gas holder plant :
• It is used in India is known as KVIC plant. The fixed dome digester is
called the Chinese plant. There are different shapes in both the designs,
cylindrical rectangular, spherical etc.
• Again the digester may be vertical or horizontal.
• Rusting of the gas holder as well as the cost of the gas holder are the main
drawbacks of this system.

29. b) 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 digester is usually built below ground level and is suitable
for cooler regions.
• Local materials can be used in this construction. The pressure inside the
digester varies as the gas is collected.

30. 3. Different variations in the drum types
• There are two main variations in the floating drum design. One with water
seal and the other without water seal.
• Water sealing makes the plant completely anaerobic and corrosion of the
gas holder drum is also reduced.
• The other variations are of materials used in both in construction of the
digester, which are suited for clayey soils and sandy tracks.
• Horizontal plants are suited for high ground water level or rocky areas.
These are not recommended when retention period is 30 days.

31. 3. Different variations in the drum types
• 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.

32. 3. Different variations in the drum types
• 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.

33. TYPES OF BIOGAS PLANTS
• It can be grouped under two broad heads:
1. Floating gas holder
2. Fixed dome digester
• In floating gas holder plant gas holder is separate from the digester. But in
the fixed dome digester, the gas holder and the digester are combined.
• The family size biogas plants available today in India are broadly of two
types.
1. Khadi village industries commission (KVIC) model
2. Janta model

35. 1. Khadi village industries commission (KVIC) model
• The KVIC plant is steel drum type or floating gas holder design in which
the digestion takes place in a masonary well and the drum floats as the gas
collects and is taken out from the top.
• The drum in the KVIC model is the costliest component and its life is
comparatively less.
• The floating gas holder digester developed in India is of masonary
construction with gas holder made of M.S. plates.

36. 2. Janta model
• Janta model or fixed dome digester is a drum less type similar in
construction to the KVIC model except that the steel drum is replaced by a
fixed dome roof of masonary construction.
• Required skilled masons for construction

37. 3. Flexible bag type combined digester
• Digester is made of plastic
material and can be easily
installed.
• The short life of material due to
the effect of ultraviolet rays is a
main drawbacks.

38. 4. Digester with floating gas holder and water seal
• When absolute segregation of the
slurry is required a floating gas
holder with water seal is used.

39. COMMUNITY BIOGAS PLANTS
• Individual / Family type biogas plants cannot be installed by poor farmer
since they cannot beat the high cost through they are highly subsidized
department of non-conventional energy sources.
• The large quantities of cow dung & other organic wastes in rural areas can
be used to produce significant amount of biogas in an organised way. Such
biogas plant in rural areas are called community biogas plants or
sometimes also called as biogas farming.
• The development of these biogas plants is an answer to the rising prices of
crude Oil or in village where there is no availability of electricity..

40. COMMUNITY BIOGAS PLANTS
• Community biogas plants could also emerge as an alternative to fossil fuels
whose availability is depleting as years passby. It will also play an
important role in the rural economy.
• Another major point which favours the installation of community biogas
plants as compared to individual plants is its lower cost/m3 of gas
generation, cost of supervisory staff & other maintenance cost.
• The biogas so generated can be used for heating, generation of lower in an
engine/ generator to right up the village, pumping of waste, running of
mills etc.

41. COMMUNITY BIOGAS PLANTS
• Biogas can produce approximately 1.5kWh/m3 of gas.
• Shortage of gas can be met by alternative routes which may be gasification
using biomass such word, waste of crops, vegetables using biomass etc
which are readily available in village.
• Another advantages of biogas production is to reduce emissions with
reduction in wastes.

42. DESIGN CONSIDERATION OF DIGESTER
• Digester takes may be of any convenient shape and provided with a cover
to retain to the gas. The cover may be a fixed one or floating. A number of
factors are to be account to arrive an optimum size of a biogas plant.
• These are:
1. The volume of waste to be digested daily
2. The type and amount of waste available for digestion consistently
3. Period of digestion

43. DESIGN CONSIDERATION OF DIGESTER
4. Methods of stirring, the contents if any
5. Method of adding the raw waste and removing digested slurry
6. Efficiency of the collection of the raw waste
7. The climate condition of the region
8. The availability of other cellulosic fermentable waste in that area
9. Information about sub soil condition and water table
10. Type of the cover

44. METHODS FOR MAINTAINING BIOGAS
PRODUCTION
1. Insulating the gas plant:
• For reducing the heat losses from the digester, the external surface of the
digester is adequately insulated.
• For this reason Janta type of plant generally constructed below ground
level.
• In the floating dome design 54% of heat loss occurs.

45. METHODS FOR MAINTAINING BIOGAS
PRODUCTION
2. Composting:
• The heat released in aerobic composting of agriculture residues around the
annular ring in the upper part of the digester could be utilized to raise the
digester operating temperatures.
• T rise of 8-10 ◦C above ambient temp even during the coldest season.
• Under optimum conditions of moisture, composting is complete in 3-4
weeks and the released heat varies with time.
• This is the least expensive method for getting more biogas during winter

47. METHODS FOR MAINTAINING BIOGAS
PRODUCTION
3. Hot water circulation
• This system has been reported to be efficient for maintaining temperatures
of the fermented slurry at the desired level. The cost of the system,
however comes higher.

48. METHODS FOR MAINTAINING BIOGAS
PRODUCTION
4. Use of chemicals:
• Use of chemicals such as area and urine have been suggested by some
workers to increase the digester temperature.
• The actual heat gains and the corresponding economics in raising the
temperature have not been worked out yet.

49. METHODS FOR MAINTAINING BIOGAS
PRODUCTION
5. Solar energy systems:
• The solar heat to the biogas digester could be provided in two distinct
ways:
• The active and the passive means. The active systems involve heating of
the digester feed or direct of the digester contents.
• In the first method the incoming feed is preheated using solar energy
during the day and fed to the digester when it attains desired temperature.

50. METHODS FOR MAINTAINING BIOGAS
PRODUCTION
• The passive method involves the construction of a ‘green house’ around
the digester to capture the radiant heat energy.
• In another method a solar canopy is used to enhance the biogas production
for the low T in winter, polythene or plastic sheet is used for canopy.
• This method is not effective at higher hills, because of snow and low T.

51. STARTING A BIOGAS PLANT
• To decide the type of waste like agricultural waste or human waste.
• If the digester is to be fed with animal/human waste then it is not necessary
to be inoculated because it contains necessary bacteria although not in a
proper number as required.
• These bacteria get activated under favorable environment and start
working.
• If the digester is to be operated on agricultural/forest residues then
inoculation in necessary otherwise there will be no gas formation.

52. ALTERNATIVE LIQUID FUELS (ALCOHOL
FUELS)
• Ethanol: is produced naturally by certain micro-organisms from sugars
under acidic conditions, pH 4 to 5. this alcoholic fermentation process is
used world wide to produce alcoholic drinks.
• The most common micro organism, the yeast Saccharomyces cerevisiae, is
poisoned by ethanol concentrator greater than 10% and so higher
concentrations upto 95% are produced by distilling and fractionating.
• Alcohols can be used for heating and lighting, in simple heaters on wick
lamps or in pressure stoves and lanterns.

53. ALTERNATIVE LIQUID FUELS (ALCOHOL
FUELS)
• Methanol: has been used successfully in gas turbines methanol has also
been used developmentally in fuel cells, device in which the chemical
energy of the fuel is converted directly to electrical power. If fuel cells
prove practicable, this could provide a significant market for methanol.
• Ethanol has greater potential for use as an industrial solvent and chemical
than as liquid fuel. For example, about half the ethanol sold in the U.S.A.
is used as a solvent.

54. REFERENCE
[1] Energy Sources by G D Rai Khanna Publication New Delhi.