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MEE230 RENEWABLE ENERGY SOURCES L T P C3 0 0 3
Objectives1. To provide students an overview of global energy resources.
2. To introduce students to bio-fuels, hydrogen energy and solar energy.3. To enable the students understand the importance of energy efficiencyand conservation in the context of future energy supply.4. To expose students to future energy systems and energy use scenarioswith a focus on promoting the use of renewable energy resources andtechnologies.
Outcome Student will be able to1. Possess the knowledge of global energy resources2. Use the renewable technologies like solar, biomass, wind, hydrogen etc. to
produce energy.
3. Involve in optimizing and selecting an alternate source of energy.UNIT I BiofuelsBiofuels classification Biomass production for energy forming Energythrough fermentation Pyrolysis Gasification and combustion - Biogas -Aerobic and Anaerobic bio conversion process - Feed stock - Properties ofbio-gas composition - Biogas plant design and operation - Alcoholicfermentation.UNIT II Hydrogen EnergyElectrolytic and thermo chemical hydrogen production Metal hydrides and
storage of hydrogen Hydrogen energy conversion systems hybrid systems Economics and technical feasibility.UNIT III Solar EnergySolar radiation - availability- Measurement and estimation- Isotropic and anisotropic models- Introduction to solar collectors (liquid flat- Plate collector - Airheater and concentrating collector) and thermal storage- Steady state transientanalysis- Photovoltaic solar cell - Hybrid systems - thermal storage- Solar arrayand their characteristics evaluation Solar distillation Solar drying.UNIT IV Ocean Thermal Energy ConversionGeothermal - Wave and Tidal energy - Availability - Geographical distribution
- Power generation using OTEC - Wave and Tidal energy - Scope andeconomics - Geothermal energy - Availability - Limitations.
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UNIT V Wind EnergyWind energy - General considerations - Wind Power plant design Horizontalaxis wind turbine - Vertical axis wind turbine - Rotor selection - Designconsiderations - Number of blades - Blade profile - Power regulation - Yawsystem - Choice of power plant - Wind mapping and selection of location-Cost
analysis and economics of systems utilizing renewable sources of energy.Text book1. David Merick, Richard Marshall, (2001), Energy, Present and Future
Options, Vol. I and II, John Wiley and sons.Reference Books1. Gerald W. Koeppl, (2002), Patnams power from wind, Van Nostrand
Reinhold Co.2. Ritchie J.D., (1999), Source Book for Farm Energy Alternative, McGraw Hill.3. Twidell, J.W. and Weir, A.D., (1999), Renewable Energy Resources, ELBS.4. Koteswara Rao, M. V. R., (2006), Energy Resources-Conventional and Non
Conventional, Second Edition, BS Publications.5. Khan, B. H., (2009), Non-Conventional Energy Resources, Second Edition,
Tata McGraw Hill.6. Chetan Singh Solanki, (2009), Renewable Energy Technologies: A Practical
Guide for Beginners, Second Printing, PHI Learning Private Limited.7. Mukherjee, D. and Chakrabarti, S., (2005), Fundamentals of Renewable
Energy Systems, New Age International (P) Limited8. Chauhan, D.S. and Srivastava, S.K. (2006), Non-Conventional Energy
Resources, New Age International (P) Limited
Mode of Evaluation: Assignment / Quiz / Written Examination.
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UNIT-I
1.0 BIOFUELS Biofuel is defined as solid, liquid or gas fuel derived from relatively
recently dead biological material and is distinguished from fossil
fuels, which are derived from long dead biological material.
Theoretically, biofuels can be produced from any (biological) carbon
source; although, the most common sources are photosynthetic
plants.
Various plants and plant-derived materials are used for biofuel
manufacturing. Globally, biofuels are most commonly used to power
vehicles, heating homes cornstoves and cooking stoves.
Photosynthesis
Photosynthesis uses light energy and carbon dioxide to make
triose phosphates (G3P)
G3P is generally considered the first end-product of
photosynthesis
It can be used as a source of metabolic energy, or combined
and rearranged to form monosaccharide or disaccharide sugars,
such as glucose orsucrose, respectively, which can be transported
to other cells, stored as insoluble polysaccharides such as starch,
http://en.wikipedia.org/wiki/Biologyhttp://en.wikipedia.org/wiki/Photosynthesishttp://en.wikipedia.org/wiki/Planthttp://en.wikipedia.org/wiki/Biofuel#Liquid_fuels_for_transportation%23Liquid_fuels_for_transportationhttp://en.wikipedia.org/wiki/Kitchen_stovehttp://en.wikipedia.org/wiki/Glyceraldehyde_3-phosphatehttp://en.wikipedia.org/wiki/Monosaccharidehttp://en.wikipedia.org/wiki/Disaccharidehttp://en.wikipedia.org/wiki/Glucosehttp://en.wikipedia.org/wiki/Sucrosehttp://en.wikipedia.org/wiki/Polysaccharidehttp://en.wikipedia.org/wiki/Starchhttp://en.wikipedia.org/wiki/Biologyhttp://en.wikipedia.org/wiki/Photosynthesishttp://en.wikipedia.org/wiki/Planthttp://en.wikipedia.org/wiki/Biofuel#Liquid_fuels_for_transportation%23Liquid_fuels_for_transportationhttp://en.wikipedia.org/wiki/Kitchen_stovehttp://en.wikipedia.org/wiki/Glyceraldehyde_3-phosphatehttp://en.wikipedia.org/wiki/Monosaccharidehttp://en.wikipedia.org/wiki/Disaccharidehttp://en.wikipedia.org/wiki/Glucosehttp://en.wikipedia.org/wiki/Sucrosehttp://en.wikipedia.org/wiki/Polysaccharidehttp://en.wikipedia.org/wiki/Starch -
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Waste andBiomass
Anaerobic
Digestion
Gasification
CombustionCo-firing
Biogas
Gas
Char
PyrolysisBio-Oil
Steam
Gas
Turbine
GasEngine
SteamTurbine
Fuel Conversion Intermediate Generation Product
Ele
ctric
power
Third generation biofuels
Algae fuel
Fourth generation biofuels
Conversion ofvegoil and biodiesel into gasoline
Liquid Biofuels Bioethanol
Biodiesel Biobutanol
Pure Plant Oil (PPO)
Biokerosene
Pyrolysis oil
Gas Biofuels
Biogas Biopropane
Synthetic natural gas (SNG)
Solid Biofuels
Wood
Manure
Charcoal
Figure 1.1 Overview of waste and biomass conversion
routes for power generation
http://en.wikipedia.org/wiki/Vegoilhttp://en.wikipedia.org/wiki/Biodieselhttp://www.bioenergywiki.net/index.php/Bioethanolhttp://www.bioenergywiki.net/index.php/Biodieselhttp://www.bioenergywiki.net/index.php/Biobutanolhttp://www.bioenergywiki.net/index.php/Pure_Plant_Oilhttp://www.bioenergywiki.net/index.php/PPOhttp://www.bioenergywiki.net/index.php/Biokerosenehttp://www.bioenergywiki.net/index.php/Pyrolysis_oilhttp://www.bioenergywiki.net/index.php/Gas_biofuelshttp://www.bioenergywiki.net/index.php/Biogashttp://www.bioenergywiki.net/index.php/Biopropanehttp://www.bioenergywiki.net/index.php/Synthetic_natural_gashttp://www.bioenergywiki.net/index.php/SNGhttp://www.bioenergywiki.net/index.php/Solid_biofuelshttp://en.wikipedia.org/wiki/Vegoilhttp://en.wikipedia.org/wiki/Biodieselhttp://www.bioenergywiki.net/index.php/Bioethanolhttp://www.bioenergywiki.net/index.php/Biodieselhttp://www.bioenergywiki.net/index.php/Biobutanolhttp://www.bioenergywiki.net/index.php/Pure_Plant_Oilhttp://www.bioenergywiki.net/index.php/PPOhttp://www.bioenergywiki.net/index.php/Biokerosenehttp://www.bioenergywiki.net/index.php/Pyrolysis_oilhttp://www.bioenergywiki.net/index.php/Gas_biofuelshttp://www.bioenergywiki.net/index.php/Biogashttp://www.bioenergywiki.net/index.php/Biopropanehttp://www.bioenergywiki.net/index.php/Synthetic_natural_gashttp://www.bioenergywiki.net/index.php/SNGhttp://www.bioenergywiki.net/index.php/Solid_biofuels -
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1.2 BIOGAS
Biogas is produced by the decomposition ofanimal wastes, plant
wastesandhuman wastes
It is produced by digestion, pyrolysis and hydro-gasification
Digestion is a biological process that takes place in the absence
of oxygen and in the presence of an aerobic organisms at ambient
pressures and temperature of35 to 70C The container in which this digestion takes place is called digester
Animal wastes
Cattle dung, urine, goat and poultry droppings, slaughter housewastes, fish wastes, leather and wood wastes, sericulture wastes,
elephant dung, piggery wastes etc.
Agricultural wastes
Aquatic and terrestrial weeds crop residue, stubbles of crops, sugar
can trash, spoiled fodder, bagasse, tobacco wastes, oilcakes fruit
and vegetable processing wastes, press mud, cotton and textile
wastes, spent coffee and tea wastes
Human wastes
Faeces, urine and other wastes emanating from human occupations
Waste of aquatic origin
Marine plants, twigs, algae, water hyacinth and water weeds
Industrial wastes
Sugar factory, tannery, paper etc.
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Table 1.1 Typical Composition of Bio gas
Sl. No. Matter %
1 Methane, CH4 50 75
2 Carbon dioxide, CO2 25 50
3 Nitrogen, N2 0 10
4 Hydrogen, H2 0 15 Hydrogen Sulfide, H2S 0 3
6 Oxygen, O2 0 2
1.2.1 Micro-organisms
Living creatures which are in microscopic in size and are invisible to
unaided eyes
They are called bacteria, fungi, virus etc.
Beneficial bacteria and harmful bacteria
Compost making production ofbiogas, vinegar, etc., are beneficial
Bacteria causing cholera, typhoid, diphtheriaare harmful bacteria
Bacteria can be divided into two groups based on their oxygen
requirement
Bacteria grow in the presence of oxygen is Aerobic
Bacteria grow in the absence of gaseous oxygen is Anaerobic
When organic matter undergoes fermentation through anaerobic
digestion, the gas produced is Biogas
Fermentation:Fermentation is the conversion of a carbohydrate such as
sugarinto an acid or an alcohol. More specifically, fermentation can refer
to the use of yeast to change sugar into alcohol or the use of bacteria to
create lactic acid in certain foods.
1.2.2 Anaerobic Digestion
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Anaerobic digestion is a series of processes in which
microorganisms break down biodegradable material in the absence
ofoxygen
It is widely used to treat wastewater sludges and organic wastes
because it provides volume and mass reduction of the input material
As part of an integrated waste management system, anaerobic
digestion reduces the emission of landfill gas into the atmosphere
Anaerobic digestion is a renewable energy source because the
process produces a methane and carbon dioxide rich biogas suitable
for energy production helping replace fossil fuels
Anaerobic digestion is particularly suited to wet organic material and
is commonly used for effluent and sewage treatment
Anaerobic digestion is a simple process that can greatly reduce the
amount of organic matter which might otherwise be destined to be
landfilled or burnt in an incinerator.
Almost any organic material can be processed with anaerobic
digestion
This includes biodegradable waste materials such as waste paper,
grass clippings, leftover food, sewage and animal waste
Utilizing anaerobic digestion technologies can help to reduce theemission of greenhouse gasses in a number of key ways:
Replacement of fossil fuels
Reducing methane emission from landfills
Displacing industrially-produced chemical fertilizers
Reducing vehicle movements
Reducing electrical grid transportation losses
1.2.3 Types of Anaerobic Digesters
http://en.wikipedia.org/wiki/Oxygenhttp://en.wikipedia.org/wiki/Waste_managementhttp://en.wikipedia.org/wiki/Methanehttp://en.wikipedia.org/wiki/Carbon_dioxidehttp://en.wikipedia.org/wiki/Biogashttp://en.wikipedia.org/wiki/Sewagehttp://en.wikipedia.org/wiki/Landfillhttp://en.wikipedia.org/wiki/Incineratorhttp://en.wikipedia.org/wiki/Automobilehttp://en.wikipedia.org/wiki/Electricity_gridhttp://en.wikipedia.org/wiki/Oxygenhttp://en.wikipedia.org/wiki/Waste_managementhttp://en.wikipedia.org/wiki/Methanehttp://en.wikipedia.org/wiki/Carbon_dioxidehttp://en.wikipedia.org/wiki/Biogashttp://en.wikipedia.org/wiki/Sewagehttp://en.wikipedia.org/wiki/Landfillhttp://en.wikipedia.org/wiki/Incineratorhttp://en.wikipedia.org/wiki/Automobilehttp://en.wikipedia.org/wiki/Electricity_grid -
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Anaerobic activated sludge process
Anaerobic clarigester
Anaerobic contact process
Anaerobic expanded-bed reactor
Anaerobic filter
Anaerobic fluidized bed
Anaerobic lagoon
Anaerobic migrating blanket reactor
Batch system anaerobic digester
Continuous stirred tank reactor (CSTR)
Expanded granular sludge bed digestion (EGSB)
Hybrid reactor
Imhoff tank
Internal circulation reactor (IC)
One-stage anaerobic digester
Submerged media anaerobic reactor
Two-stage anaerobic digester
Upflow anaerobic sludge blanket digestion (UASB)
Upflow and down-flow anaerobic attached growth
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1.2.4 Site selection for Biogas Plant
Distance: The distance between the plant and the site of gas
consumption should be less in order to achieve economy in
pumping of gas and minimizing gas leakage. For a plant capacity of
2 m3
, the optimum distance is 10 m Minimum gradient: For conveying the gas a minimum gradient
of1% must be made available for the line
Open space: The sun light should fall on the plant as
temperature between 15Cto30C is essential for gas generation atgood rate
Water table: The plant is normally constructed underground for
ease of charging the feed and unloading slurry requires less
labour. In such cases care should be taken to prevent the seepage
of water and plant should not be constructed if the water table is
more than 10 feet.
Seasonal run off: Proper care has to be taken to prevent the
interference of run off water during the monsoon. Intercepting
ditches or bunds may be constructed
Distance from wells: The seepage of fermented slurry may
pollute the well water. Hence a minimum of 15 m should be
maintained from the wells
Space requirements: Sufficient space must be available for day
to day operation and maintenance. As a guideline 10 to 12 m2 area
is needed perm3of the gas.
Availability of water: Plenty of water must be available as the
cow dung slurry with a solid concentration of7% to 9% is used
Source of cow dung / materials for biogas generation: The
distance between the material for biogas generation and the gas
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plant site should be minimum to economize the transportation
cost.
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1.3 DIGESTER DESIGNThe design of a digester is based on two factors:
Based on the amount of waste available and the gas produced
based on the wastes
Based on the needs
Most of the digesters are based on the second objective since it is easy to
adjust the feed available than to have insufficient
1.3.1 Design characteristics based on the size
Raw material availability: The gas production is proportional to the
amount of raw material digested.Type of material: C/N ratio of the raw material should be in the optimum
range for better digestion. If the raw material is an easily digestible one,
the size of the digester can be reduced proportionally.
Size of raw materials: The feed material should be cut into pieces so that
the surface area for the reaction is the maximum. Also, the slurry
produced should flow smoothly. The scum produced should be
minimized.
Heating requirements: If the digester is situated in cold areas, sufficient
heating arrangements should be provided to keep the digestion
temperature within the optimum range. Burying the digester under the
ground helps to minimize the temperature fluctuations of the ambient
around the digester
Mixing requirements: Providing a mechanism of mixing the feed inside
the digester helps to ensure the easy availability of feed to the bacteria for
the reactions. Also it provides proper slurry flow inside the digester and
avoids the formation of scum
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Construction materials available: Use of locally available expertise and
materials close to the site for the construction of a digester reduces the
cost. Fabrication from corrosion resistant materials such as wood,
ferrocement, concrete, brick or stone rather than metal may also reduce
costs by extending equipment life. Larger digesters require propermaintenance also. Removal of inert wastes such as sand and rocks
prevents wear on mechanical parts and extends equipmentlife
1.4 Biogas Technology
Biogas is produced from wet biomass through a biological conversion
process that involves bacterial breakdown of organic matter by micro-
organisms to produce CH4, CO2and H2O.The process is known as anaerobic digestion which proceeds in three
steps.
1. Hydrolysis
2. Acid formation
3. Methane formation
Hydrolysis
Organic waste of animal and plants contains
carbohydrates in the form of cellulose, hemi cellulose and lignin
A group of anaerobic micro-organisms breakdowns
complex organic material into simple and soluble organic
components, primarily acetates
The hydrolysis depends on bacterial concentration,
quality of substrate, pH (between 6 and 7) and temperature (30C to40C) of digester contents
Acid Formation
Decomposed simple organic material is acted upon by acetogenic
bacteria and converted into simple acetic acid
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Methane Formation
Acetic acid so formed becomes the substrate strictly foranaerobic methanogeric bacteria, which ferment acetic acid to CH4
and CO2
Biogas consists ofCH4andCO2traces of other gases asH2, CO,N2, O2and H2S
Gas mixture is saturated with water vapourThe methane content of biogas is about 60% which provides
a high calorific value to find use in cooking, lighting and
power generation
Hydrolysis Phase: (C5H10O5) n + H2O n (C5H12O6) (Glucose)Acid Phase: n (C5H12O6) CH3CH (OH) COOH (Lactic acid)Methane Phase: 4H2 + CO2 2H2O + CH4
CH3CH (OH) COOH +H2O +CO2CH3COOH + CH4(Acetic acid)
Table 1.2 Energy Density (Heating values) of various fuels
Sl. No. Primary Resources Energy Density
1 Coal: Anthracite
Bituminous
Coke
32-34 MJ/kg
26-30 MJ/kg
29 MJ/kg
2 Brown coal: Lignite (old)
Lignite (new)
Peat
16-24 MJ/kg
10-14 MJ/kg
8-9 MJ/kg
3 Crude petroleum
Petrol
Diesel
45 MJ/kg
51-52 MJ/kg
45-46 MJ/kg
4 Natural gas
Methane (85% CH4)
Propane
Hydrogen
50 MJ/kg,(42 MJ/m3)
45 MJ/kg,(38 MJ/m3 )
50 MJ/kg,(45 MJ/m3)
142 MJ/kg, (12 MJ/m3)
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Mixing Pit
Masonarywork
PartitionWall
Slurry
Outlet pipeInlet pipe
SupportPipe
Gas pipeFloatingGas Holder
Outlet tank
Spent slurry
Figure 1.1 Floating Drum Biogas Plant(KVIC Model)
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Slurry
Gas
Digester
GasValve
GasPipe
Loose Cover
Displacementtank
Foundation
100mm
Removableman hole
cover
Spent
Slurry
Inlet
Figure 1.2 Fixed dome biogas plant (Janta model)
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Table 1.3Comparison between fixed and floating dome digesters
Sl. No. Floating Drum Fixed Dome
1 High capital investmentHigh maintenance cost
LowLow (no moving part)
2 Steel gas holder needsreplacement due tocorrosion
No steel gas holder
3 Life span Digester : 30yearsGas holder : 5 to 8 years
Longer life span
4 Drum space cannot be usedfor other purposes
Space can be used for otherpurposes
5 Effect of low temperatureduring winter is more
Less
6 Suitable for dung. Other
organic materials will cloginlet pipe
Can be adapted / modified for
other materials along withdung slurry
7 Gas released at constantpressure
Variable gas pressure maycause slight reduction inappliance efficiency. Gaspressure regulator is a mustfor engine applications
8 Construction is known tomasons but drum fabrication
requires workshop facility
Dome construction is a skilled job & requires thorough
training of masons9 Locating & rectification ofdefects in drum are easy
Difficult
10 Requires less evacuationwork
More
11 In areas of higher watertable, horizontal plants couldbe installed
Construction of plant isdifficult in high water tableareas
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1.5 Factors affecting Anaerobic Digestion
TemperaturepHAvailability of feed materialCarbon-to-nitrogen (C/N) ratioConcentration of feedMixing and Feeding rateToxic materialsAnaerobic conditionRetention time1.5.1 Temperature
Temperature has a significant effect on anaerobic digestion of
organic material
The optimum temperature for Mesophilic flora is 30 - 40 C and
Thermophilic flora is 50 - 60 C
As the temperature increases, the total retention period
decreases and vice-versa
1.5.2 pH
Measure of pH value indicates the concentration of hydrogen ions and
micro organisms are sensitive to pH of the digested slurry
For optimum biogas production, pH can be varied between 6.8 and 7.2
Control on pH should be exercised by adding alkali when it drops below
6.6
1.5.3 Availability of feed material
Steady supply of substrate and continuous operation of the digester
ensures a higher output than intermittent use
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1.5.4 Carbon-to-nitrogen (C/N) ratio
Methanogenic bacteria need carbon and nitrogen for its survival
Carbon is required for energy while nitrogen for building cell
protein
The consumption of carbon is 30 to 35 times faster than that of
nitrogen
A favourable ratio ofC : N can be taken as 30 : 1
1.5.5 Concentration of feed
The anaerobic fermentation of organic matter proceeds best if the
feeding material contains 7-13 % of solid matter
The usual materials fermented in a biogas plant normally contain
higher percentage of solids and they are therefore usually diluted with
water
From experiments, it is found that a 1:1 (by volume) slurry of cow
dung and water, corresponding to a 10-12% of total solids, is effective
for optimum gas production
1.5.6 Mixing
Stirring of slurry inside the digester is desirable to simulate bacterial
action resulting in higher gas production, though it is not always
essential
Continuous feeding of fresh waste into the digester always induces
some movement in the mass of material in the digester, helping to
expose fresh undigested material to the bacteria
Normally, for small size plants, stirring is not provided
1.5.7 Toxic materials
The main toxic elements are : higher concentrations of ammonia,
soluble sulfides, metallic salts of Cu, Zn, Ni, Na, K, Ca, Mg, etc
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The materials in solution can only be toxic to digestion
1.5.8 Anaerobic Conditions
Inside the digester, strict anaerobic condition has to be maintained since
the methane producing bacteria is sensitive to the presence ofO2
1.5.9 Retention Time
It is the average length of time a sample of waste remaining in the
digester
For batch digestion, it is simply the time from the start-up to the
completion of the cycle
For continuous digestion, the HRT (Hydraulic Retention Time) is the
ratio between the volume of the digester contents to the volume of feed(m3 / (m3/day)). The optimum retention time is found to vary between
14 to 60 days
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1.6 BIOMASS
Biomass refers to the mass of biological material produced from
living processes which includes the materials derived from plants as
well as animals
Chemically biomass refers to hydrocarbons containing hydrogen,
carbon and oxygen which can be represented by C6n(H2O)5n
Biomass is a scientific term for living mater, more specifically any
organic matter that has been derived from plants as a result of
phosynthetic conversion process
Biomass is a sustainable resource that it is constantly being formed
by the interaction of air, water, soil and sunlight
Biomass is a renewable energy resource derived from the
carbonaceous waste of various human and natural activities.
The organic materials produced by plants, such as leaves, roots,
seeds, andstalks (stem)
The term biomass is intended to refer to materials that do not
directly go into foods or consumer products but may have alternative
industrial uses.
The total mass of living matter within a given unit of environmental
area. Plant material, vegetation, or agricultural waste used as a fuel
or energy source
Biomass is a complex mixture of organic materials, such as
carbohydrates, fats, and proteins, along with small amounts of
minerals, such as sodium, phosphorus, calcium, and iron. The main
components of plant biomass are carbohydrates (approximately
75%, dry weight) and lignin (approximately 25%), which can vary with
plant type
Common sources of biomass
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Woody biomass, Crop residues, Animal waste
agricultural wastes, such as corn stalks, straw, seed hulls,
sugarcane leavings, bagasse, nutshells, and manure from cattle,
poultry, and hogs
wood materials, such as wood or bark, sawdust, timber slash,and mill scrap
municipal waste, such as waste paper and yard clippings
Woody Biomass
This includes biomass in the form of trees; trees from forest, from farms,
commercial plantations etc. The use of woody biomass is mainly for
household and industrial application for making furniture, shelter,agricultural tools etc. Woody biomass also has applications supplying our
energy needs. In rural areas, woody biomass is used as fuel wood for
cooking purposes while in urban areas, characoal-an upgraded form
woody biomass is used for cooking.
Crop Residues
This includes crops and plant residues produced in the field. These are
the residues that remain after taking out seeds from the crops. For
instance, husk, bagasse, cereal straw, nut shells etc. The crop residues
have several applications. It can be used for livestock feeding, as manure
together with animal dung as source of nutrients for soil.
Animal Waste
The animal dung and poultry manure come in this category. Animal waste
is a good source of nutrients and is used as a fertilizer. Animal dung is
also used for cooking either directly by burning or converting it into
biogas, which is then burned to cook food. Thus animals also fulfill our
needs.
1.6.1. Advantages
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It is renewable source Energy storage is an in-built feature of it It is an indigenous source requiring little or noforeign exchange
The pollutant emissions from combustion ofbiomass are usually lower than those from fossil fuels
Commercial use of biomass may avoid or reduce theproblems of waste disposal in other industries, particularly
municipal solid waste in urban centres
The nitrogen rich bio-digested slurry and sludgefrom a biogas plant serves as a very good soil conditioner and
improves the fertility of the soil
Varying capacity can be installed; any capacity canbe operated, even at lower loads, with no seasonality involved
The forestry and agricultural industries that supplyfeed stocks also provide substantial economic development
opportunities in rural areas.
1.7 BIOMASS CONVERSIONS
Physical Method (Briquetting and Pelletization processes)
Direct combustion, such as wood waste and bagasse
(sugarcane refuge)
Thermochemical conversion(gasification and liquefaction)
Biochemical conversion(anaerobic digestion and fermentation)
1.7.1 Pyrolysis
Pyrolysis is the chemical decomposition of a condensed substance
by heating
Pyrolysis of organic materials produces combustible gases,
including carbon monoxide, hydrogen and methane, and other
hydrocarbons
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1.7.2 Gasification
Gasification is the process of converting solid fuels to gaseous fuel
Gasification is a process that converts carbonaceous materials, such
as coal, petroleum, orbiomass, into carbon monoxide and hydrogen
by reacting the raw material at high temperatures with a controlledamount ofoxygen and/orsteam. The resulting gas mixture is called
synthesis gasorsyngas and is itself a fuel.
1.7.3 Fermentation
In a general sense, fermentation is the conversion of a carbohydrate
such as sugar into an acid or an alcohol
More specifically, fermentation can refer to the use of yeast to
change sugar into alcohol or the use of bacteria to create lactic acid
in certain foods
Fermentation occurs naturally in many different foods given the right
conditions, and humans have intentionally made use of it for many
thousands of years
Sugars are the most common substrate of fermentation, and typical
examples of fermentation products are ethanol, lactic acid, and
hydrogen
Industrial fermentation, the breakdown and re-assembly of
biochemicals for industry, often in aerobic growth conditions
In food science, fermentation may mean:
Fermentation (food), the conversion of carbohydrates into alcohols
or acids under anaerobic conditions used for making certain foods
1.7.4 Alcoholic Fermentation
In brewing, alcoholic fermentation is the conversion of sugar into
carbon dioxide gas (CO2) and ethyl alcohol
This process is carried out by yeast enzymes
http://en.wikipedia.org/wiki/Coalhttp://en.wikipedia.org/wiki/Petroleumhttp://en.wikipedia.org/wiki/Biomasshttp://en.wikipedia.org/wiki/Oxygenhttp://en.wikipedia.org/wiki/Steamhttp://en.wikipedia.org/wiki/Syngashttp://www.wisegeek.com/why-does-yeast-make-bread-rise.htmhttp://en.wikipedia.org/wiki/Industrial_fermentationhttp://en.wikipedia.org/wiki/Food_sciencehttp://en.wikipedia.org/wiki/Fermentation_(food)http://en.wikipedia.org/wiki/Coalhttp://en.wikipedia.org/wiki/Petroleumhttp://en.wikipedia.org/wiki/Biomasshttp://en.wikipedia.org/wiki/Oxygenhttp://en.wikipedia.org/wiki/Steamhttp://en.wikipedia.org/wiki/Syngashttp://www.wisegeek.com/why-does-yeast-make-bread-rise.htmhttp://en.wikipedia.org/wiki/Industrial_fermentationhttp://en.wikipedia.org/wiki/Food_sciencehttp://en.wikipedia.org/wiki/Fermentation_(food) -
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1.8 Types of Gasifiers
Counter-current fixed bed (Up draft gasifier)
Co-current fixed bed (Down draft gasifier)
Cross-flow gasifier
Fluidized bed gasifier and Entrained flow gasifier
Table 1.4 Typical composition of producer gas
Application of Biomass Gasification Processes
Large scale applications (500 kW and above)
Medium scale applications (30-500 kW)
Small scale applications (7-30 kW)
Micro scale applications (1-7 kW)
Sl.No. Gas %
1 Carbon monoxide 18 22%
2 Hydrogen 13 19%
3 Methane 1 5%
4 Heavier hydrocarbons 0.2 0.4 %
5 carbon dioxide 9 12%
6 Nitrogen 45 55%
7 Water vapour 4%
Hearth Zone(Oxidation Zone)
Reduction Zone
Distillation Zone(Pyrolysis zone)
Drying Zone
Gas
Feed
Grate
Ash Zone
Air
Figure 1.3 Updraft gasifier
200C
400C
600C
950C
1300C
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1.8.1 Updraft Gasifier
In the updraft gasifierthe feed is introduced at the top and theair at the bottom of the unit via a grate
Immediately above the grate the solid char (the residual solidremaining after the release of volatiles) formed higher up the gasifier is
combusted and the temperature reaches about 1000C. Ash falls through the grate at the bottom and the hot gases passupwards and are reduced.
Higher up the gasifier again, the biomass is pyrolysed and in thetop zone, the feed is dried, cooling the gases to around 200300C In the pyrolysis zone, where the volatile compounds arereleased, considerable quantities of tar are formed which condenses
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partly on the biomass higher up and partly leaves the gasifier with the
product gas
The temperature in the gasification zone is controlled by addingsteam to the air used for gasification, or by humidifying the air
Due to the low temperature of the gas leaving the gasifier, theoverall energy efficiency of the process is high but so also is the tar
content of the gas
The filtering effect of the feed helps to produce a gas with a lowparticulate content
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Ash pit
Pyrolysis Zone
Heart Zone(Oxidation Zone)
Air
Biomassfeed
Gas
Grate
Drying Zone
Air
Reduction Zone
Figure 1.4 Downdraft Gasifier
1.8.2 Downdraft Gasifier
In the downdraft gasifier, the feed and the air move in the samedirection. The product gases leave the gasifier after passing through
the hot zone, enabling the partial cracking of the tars formed during
gasification and giving a gas with low tar content
Because the gases leave the gasifier unit at temperatures about9001000C, the overall energy efficiency of a downdraft gasifier is low,due to the high heat content carried over by the hot gas
The tar content of the product gas is lower than for an updraftgasifier but the particulates content of the gas is high
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Drying Zone
Pyrolysis Zone
Reduction Zone
Oxidation Zone
Ash pit
Air Gas
Biomass feed
Grate
Figure 1.5 Cross draft Gasifier
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1.9.3 Cross-flow Gasifier
In a cross-flow gasifier the feed moves downwards while the air isintroduced from the side, the gases being withdrawn from the opposite
side of the unit at the same level
A hot combustion/gasification zone forms around the entrance of theair, with the pyrolysis and drying zones being formed higher up in the
vessel
Ash is removed at the bottom and the temperature of the gas leavingthe unit is about 800900C Gives a low overall energy efficiency for the process and a gas withhigh tar content
1.9 Types of Zone
1.9.1 Pyrolysis zone
Wood pyrolysis is an intricate process that is still not completely understood.
The products depend upon temperature, pressure, residence time and heat
losses. However following general remarks can be made about them. Upto the
temperature of200C only water is driven off. Between 200 and 280C carbondioxide, acetic acid and water are given off. The real pyrolysis, which takes
place between 280 and 500C, produces large quantities of tar and gasescontaining carbon dioxide (Tars can be easily defined as undesirable and
problematic organic products of biomass gasification). Besides light tars, some
methyl alcohol is also formed. Between 500 and 700C the gas production issmall and contains hydrogen. Thus it is easy to see that updraft gasifier will
produce much more tar than downdraft one. In downdraft gasifier the tars have
to go through combustion and reduction zone and are partially broken down.
1.9.2 Combustion zone
The combustible substance of a solid fuel is usually composed of elements
carbon, hydrogen and oxygen. In complete combustion carbon dioxide is
obtained from carbon in fuel and water is obtained from the hydrogen, usually
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as steam. The combustion reaction is exothermic and yields a theoretica
oxidation temperature of1450CThe main reactions, therefore, are:
C + O2 = CO2 (+ 393 MJ/kg mole) (1)
2H2 + O2 = 2H2O (- 242 MJ/kg mole) (2)
1.9.3 Reaction zone
The products of partial combustion (water, carbon dioxide and uncombusted
partially cracked pyrolysis products) now pass through a red-hot charcoal bed
where the following reduction reactions take place.
C + CO2 = 2CO (- 164.9 MJ/kg mole) (3)
C + H2O = CO + H2 (- 122.6 MJ/kg mole) (4)
CO + H2O = CO + H2 (+ 42 MJ/kg mole) (5)
C + 2H2 = CH4 (+ 75 MJ/kg mole) (6)
CO2 + H2 = CO + H2O (- 42.3 MJ/kg mole) (7)
Reactions (3) and (4) are main reduction reactions and being endothermic have
the capability of reducing gas temperature. Consequently the temperatures in
the reduction zone are normally 800-1000C. Lower the reduction zonetemperature (~ 700-800C), lower is the calorific value of gas.
Table 1.5 Biomass gasification chemical reactions
Gasification stage Reaction formula Reaction heat
Stage I:
Oxidation and otherexothermic reactions
C+2
1 O2CO Exothermal
CO+2
1 O2CO2C+O2CO2(C6H10O5)nnCO2+nH2OH2+ 2
1 O2H2OCO+H2OCO2+H2CO+3H2CH4+H2O
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Stage II:
Pyrolysis
(C6H10O5)nCxHz+nCO Endothermic(C6H10O5)nCnHmOy
Stage III:
Gasification(Reduction)
C+H2OCO+H2 EndothermicC+CO22COCO2+H2CO+H2OC+2H2CH4 Exothermic
Table 1.6 Types of Biomass and Properties
Type of Biomass Lower HeatingValue (kJ/kg)
MoistureContent (%)
AshContent(%)
Bagasse 7,700 - 8,000 40 - 60 1.7 - 3.8Coconut shells 18,000 8 4
Coffee husks 16,000 10 0.6
Cotton residues:
stalks
gin trash
16,000
14,000
10 - 20
9
0.1
12
Maize:
cobs
stalks
13,000 - 15,000 10 - 20 2
3 - 7Palm-oil residues:
fruit stems
fibers
shells
debris
5,000
11,000
15,000
15,000
63
40
15
15
5
Rice husk 14,000 9 19
Straw 12,000 10 4.4Wood 8,400 - 17,000 10 - 60 0.25 - 1.7
Peat 9,000 - 15,000 13 - 15 1 20
Charcoal 25,000 - 32,000 1 - 10 0.5 - 6
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1.10 Ethanol Fuel
Ethanol is also known as ethyl alcohol or fermentation alcohol
Ethanol provides a valuable liquid fuel alternative to a transportation
sector
Ethanol is a colorless, clear liquid that looks like water and is
completely miscible with it
It is widely used in medicines, lotions, tonics, colognes, rubbing
compounds, and solvents and also for organic synthesis Ethanol is more volatile than water, flammable, burns with a light blue
flame, and has excellent fuel properties for spark ignition interna
combustion engines
Ethanol has a somewhat sweet flavorwhen diluted with water; a more
pungent, burning taste when concentrated; and an agreeable ether-like
odor
Ethanol is a member of the alcohol family and has the chemica
formula C2H5OH in which C, H, and O refer to carbon, hydrogen, and
oxygen atoms, in that order
1.11 Ethanol production
1. Fermentation ofsugars derived from sugar, starch, or cellulosic materials
2. Reaction ofethylene with water
The formeris favored for production of fuel. The latterhas been used to make
industrial grade ethanol for solvents, cosmetics, medicines, and so on, but
purification of fermentation ethanol is displacing ethylene-derived ethanol for
these applications
1.11.1 Production of ethanol from cellulosic biomass
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Ethanol can be produced from biomass by the hydrolysis and sugar
fermentation processes.
Biomass wastes contain a complex mixture of carbohydrate polymers
from the plant cell walls known as cellulose, hemi cellulose and lignin.
In order to produce sugars from the biomass, the biomass is pre-
treated with acids or enzymes in order to reduce the size of the feedstock
and to open up the plant structure.
The cellulose and the hemi cellulose portions are broken down
(hydrolyzed) by enzymes or dilute acids into sucrose sugar that is then
fermented into ethanol.
The lignin which is also present in the biomass is normally used as a fuel
for the ethanol production plants boilers
1.11.2 Production of ethanol from sugar crops
The hydrolysis process breaks down the cellulosic part of the
biomass or corn into sugar solutions that can then be fermented into
ethanol
Yeast is added to the solution, which is then heated.
The yeast contains an enzyme called invertase, which acts as acatalyst and helps to convert the sucrose sugars into glucose and fructose
The fermentation process takes around three days to complete and is
carried out at a temperature of between 250C and 300C
1.11.3Production of ethanol from starch crops
Corn grain contains about 70% starch, 10 to 11% crude protein, 4.5 to
6.0% oil, 6% hemicellulose, 2 to 3% cellulose, 1% lignin, and 1% ash and isthe dominant choice for current fuel ethanol production by dry or wet
milling operations
In a typical dry mill, grain is milled to a powder, heated with water
addition to about 851C, mixed with alpha-amylase enzyme, held for up to
an hour, heated further to 110 to 1501C to liquefy the starch and reduce
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bacteria levels, cooled back to about 85C, and held with more alpha
amylase for about 1 hour
the stream is cooled further, and glucoamylase enzyme added to
complete conversion to sugars known as dextrose
This overall saccharification operation occurs by the hydrolysis
reaction:
(C6H10O5) n+nH2OnC6H12O6 C6H12O6 is a glucose sugar molecule formed when the alpha bonds
linking n units ofC6H10O5 in long chains of starch are broken and combined
with n molecules of water, H2O
Yeast then ferment glucose to ethanol and carbon dioxide
C6H12O62C2H5OH+2CO2
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The process flow for ethanol production is explained below
A simplified process flow diagram for production of ethanol from cane
sugar, corn, and cellulosic biomass. All have similar fermentation and
ethanol recovery operations but use different approaches to release sugars
and generate different co-products
Sugar can be directly extracted from sugarcane, and the residua
bagasse is used as a boiler fuel to provide much of the energy for the
extraction and ethanol production and recovery operations
In a corn dry mill, corn is ground, and enzymes and heat are added to
hydrolyze starch to sugars for conversion to ethanol, while the oil, protein,
and fiber in corn are recovered after fermentation as an animal feed known
as DDGS (Distillers Dried Grains)
Wet mills first fractionate corn to separate corn oil, corn gluten mea
(CGM), and corn gluten feed (CGF) to capture value for food and anima
feed, and the starch can then be hydrolyzed to sugars for fermentation to
ethanol For cellulosic biomass, heat and acids or enzymes hydrolyze the
hemicellulose and cellulose portions to release sugars that can be
fermented to ethanol
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1.12 Biodiesel
Biodiesel is a non-toxic, biodegradable diesel fuel made from vegetable oils,
animal fats, and used or recycled oils and fats
Biodiesel is made using the process oftransesterification
Biodiesel is produced by chemically reacting a fat oroil with an alcohol, in
the presence of a catalyst (sodium hydroxide)
The product of the reaction is a mixture ofmethyl esters, which are known
as biodiesel and glycerol, which is a high value co-product
Transesterification is the process of using an alcohol (e.g., methanol or
ethanol) in the presence of a catalyst, such as sodium hydroxide or
potassium hydroxide, to chemically break the molecule of the raw
renewable oil into methyl or ethyl esters of the renewable oil with glycerol
as a by-product
Biodiesel can be made from various components such as; vegetable oil,
animal fats, and waste or recycled oils and fats, such as waste fryer oil
Biodiesel is made by mixing methanol and sodium hydroxide to make
sodium methoxide
The sodium methoxide is then mixed with vegetable oil and allowed tosettle
Glycerin forms on the bottom, while the methyl esters (biodiesel) float to
the top
Biodiesel Production
Three Basic Methods to Making Biodiesel
There are three basic methods of biodiesel (methyl ester) production from oils
and fats.
They are;
Base catalyst transesterification of the oil with methanol.
Directed acid catalyzed esterification of the oil with methanol.
Conversion of the oil to fatty acids, and then to methyl esters with
acid catalysis
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Figure 1.7 Process flow for Biodiesel Production
Oil
WashWater
Reactor Separator
AcidulationandFFA
Separation
MethanolRemoval
Neutralizationand
MethanolRemoval
WaterWashing
Dryer
Methanol /water
rectification
FinishedBiodiesel
Methanol&
Catalyst
Acid
Free FattyAcid
Glycerol
(50%)
Acid
Water
Water
MethanolStorage
CrudeGlycerol
(85%)
MethylEsters
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Figure 1. 7 shows the schematic diagram of the processes involved in
biodiesel production from feedstocks containing low levels of free fatty
acids
This includes soybean oil, canola (rapeseed) oil and higher grades of waste
restaurant oils.
First the methanol and the catalyst (sodium hydroxide) are mixed. After the
methanol and catalyst are mixed, they go into a reactor, where the oil is
added to the mix and agitated for approximately one hourat 60C. Glycerin and methyl esters are the two major products created after the
reaction is complete and the excess methanol has been removed from the
mixture
Gravity is used to separate the two products, since they have different
densities
After separation from the glycerol, the methyl esters enters a neutralization
step and then pass through a methanol stripper, usually a vacuum flash
process before water washing
Acid is added to biodiesel to neutralize any residual catalyst and to splitany soap that have formed during the reaction
Soaps will react with acid to form water soluble salts and free fatty acids
The salts will be removed during the water washing step and the free fatty
acids will stay in the biodiesel
The water washing step is intended to remove any remaining catalyst
soaps, salts methanol, or free glycerol from the biodiesel
The glycerol stream leaving the separator is only about 50% glycerol
It contains some of excess methanol and most of the catalyst and soap
In this form, the glycerol has little value and disposal may be difficult
The methanol contents requires glycerol to be treated as hazardous waste
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The first step in refining the glycerol is usually to add acid to split soaps
into free fatty acids and salts
The free fatty acids are not soluble in the glycerol and will rise to the top
where they can be removed and recycled
After acidulation and separation of the free fatty acids, the methanol in the
glycerol is removed by vacuum flash process, or another type of
evaporator
At this point the glycerol should have a purity of approximately 85% and is
typically sold to a glycerol refiner
The methanol that is removed from the methyl ester and glycerol streams
will tend to collect any water that may have entered the process
This water should be removed in a distillation column before the methano
is returned to the process
1.13 Energy Plantations
Cultivation of any type of plants that store enormous amount of solar
energy within and thereby posses high fuel value is termed as Energy
Plantations
Common species of plantations Eucalyptus
Casuarina
Terminalia
Leucaena Sagassum (seaweed)
Water Hyasynth
Acavia
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Example: Design a biogas plant suitable to fulfil the cooking needs of a family of12
members. Estimate daily requirement of biogas, the number of animals required and
size of the digester. Make necessary assumption. Assume
350 litres of biogas is required per day per person for cooking and average
production of dung per animal per day as 10 kg. Also assume average gas
production from dung is about 40 litres/kg of fresh dung; slurry density as 1090kg/m3
and retention period is 50 days.
Step -1: Amount of gas required per day
Number of family members = 12 (adults)(Two children may considered as equivalent to one adult for cooking energy purpose
only)
Considering 350 litres/day/person for cooking
Total amount of gas required = 12 350 = 4200 litres/day(1000 litres of gas is equivalent to 1 m3 of gas)
Step 2: Number of animals required to fulfil daily gas requirement
Amount of gas produced from a kg of fresh dung = 40litres/kg
Total amount of dung required = Total gas required / gas per kg of dung
= 4200/40 = 105kg
Thus in order to have 105 kg of dung, number of cows required
= 105/10 = 10.5 say 11 cows
Step 3: Design of digester and gas holder
In order to make slurry, water should be added to equal amount of dung
Total mass of slurry = dung + water = 105 + 105 = 210 kg
Density of slurry = 1090 kg/m3
Volume of slurry per day = Total mass of slurry / density
= 210/1090 = 0.192m3
Retention period of slurry = 50 days
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Total volume of the digester = per day volume of slurry retention
period
= 0.192 50 = 9.63 m3
As about 90% volume is occupied by the slurry
Therefore required volume of digester = 9.63 / 0.9 = 10.7m3
Dimension of the digester
Depth to diameter ratio should between 1 and 1.3
7.10D3.14
D2
= m3
Thus diameter of digester D = 2.188 m
Depth of the digester H = 2.844 m
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1. A community biogas plant is used for the following needs of a village having 100 adults and 50
children. Cooking needs of the people of the village and five lamps of 100CP used for one hour in the
evening. Assume 350 litres of biogas is required for cooking per person per day; 125 litres of biogas
required for lighting per lamp per hour and average production of dung per animal per day as 10 kg.
Also assume average gas production from dung is about 40 litres/kg of fresh dung; slurry density as
1090kg/m3 and retention period is 50 days. Calculate the size, depth and dome height of the digester
and the number of cows required to feed the plant. Take dome height as 0.25D. and Depth as 1.3D
where D is the diameter of the digester.
Number of family members = 100+25 = 125 members
(Since two children may considered as equivalent to one adult for cooking purpose only)
Step-1:
Gas required for cooking alone = 350 125 = 43,750 litres/day
Gas required for lighting = 125 5 1 = 625 litres/day
Total amount of biogas required = 43,750 + 625 = 44375litres/day
Step-2:
Total amount of dung required = 44375/40 = 1109.375 kg
Number of cows required = 1109.375/10 = 110.93 = 111 say
Total mass of slurry = 1109.375 + 1109.375 = 2218.75kg
Density of slurry = 1090kg/m3
Therefore volume of slurry = 2218.75/1090 = 2.0355m3
Retention period = 50 days = 2.0355 50 = 101.78 m3
As about 90% volume is occupied by the slurry
Therefore required volume of the digester = 101.78/0.9 = 113.08 m3
Step-3:
Dimension of digester
Assume depth to diameter ratio as 1.3D:1.0D
32
m08.113D3.14
D =
Diameter of the digester D = 4.80m
Depth of the digester H = 1.3 4.80 = 6.24 m
Digester dome height Hdome = 0.25 4.80 = 1.2m.
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Fuel derived from organic matter (obtained directly from plants, or indirectly from
agricultural, commercial,domestic, and/orindustrial wastes) instead of from fossil products
See also fossil fuels.
any fuel derived from renewable biological sources, as plants or animal waste; esp., a liquid
fuel for automotive engines made from corn or soybean oil
Biofuels are fuels derived from living plants, animals or their byproducts which are not more
than 20-30 years old. Biofuels contain stored solar energy and are a renewable source
of energy, since the plants can be grown again. Unlike petroproducts, all biofuels are
biodegradable and do not damage the environment when spilled. As demand and prices of
crude oil increase, more countries are encouraging the use of biofuels by offering tax
incentives.
Wood from trees and manure from cattle (cow dung) are the most widely used biofuels used
for cooking and other household applications in poor countries. Biogas for cooking is
derived from industrial and household waste by the anaerobic digestion. Biogas contains
methane. Chemical processes can also be used to produce biogas from industrial waste
Microalgae may be used as an energy source in future, as their yield per acre is the highest
compared to other sources.
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Gas
Ratio compared toDry Air(%) Molecular
Mass- M -
(kg/kmol)
ChemicalSymbol
Boiling Point
Byvolume
Byweight
(K) ( oC)
Oxygen 20.95 23.20 32.00 O2 90.2 -182.95
Nitrogen 78.09 75.47 28.02 N2 77.4 -195.79
CarbonDioxide
0.03 0.046 44.01 CO2 194.7 -78.5
Hydrogen 0.00005 ~ 0 2.02 H2 20.3 -252.87
Argon 0.933 1.28 39.94 Ar 84.2 -186
Neon 0.0018 0.0012 20.18 Ne 27.2 -246
Helium 0.0005 0.00007 4.00 He 4.2 -269
Krypton 0.0001 0.0003 83.8 Kr 119.8 -153.4
Xenon 9 10-6 0.00004 131.29 Xe 165.1 -108.1
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