This document discusses various aspects of bioenergy. It begins by defining biogas as a mixture of gases produced from organic waste through anaerobic digestion by bacteria. There are two main types of biogas plants - fixed dome and floating gas holder. The document then discusses the processes of anaerobic digestion, gasification, and liquefaction as three main methods to extract energy from biomass. It provides details on biodiesel production from sources like algae, carbohydrates, oils, and agricultural wastes. The advantages and disadvantages of different bioenergy methods like biogas, gasification, and biodiesel are also summarized.

1. Bioenergy
Arpan Deyasi
Dept of ECE, RCCIIT, Kolkata, India
Course: EI605D
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2. BioenergyCycle
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3. Biogas
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Gas obtained from organic sources
Biogas Energy
Produced through breakdown of organic waste by
bacteria in absence of oxygen
It is a mixture of methane (65%), CO2, H2, H2S

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Biogas Plant
1. Fixed dome type
2. Floating gas holder type

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Fixed dome type

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Fixed dome type
Various forms of biomass are mixed with proportionate quantities of
water in mixing tank, called slurry
Slurry is fed into digester through inlet chamber
After partial filling of digester, plant is kept for a certain time period
In this time-period, anaerobic bacteria present in the biomass
ferments the slurry in presence of water
Biogas is formed, which starts collecting in the dome of digester

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Fixed dome type
Pressure exerted by generated biogas forces the slurry to exit
through outlet chamber
Spent slurry overflows into overflow tank
It is manually removed
Biogas is removed through gas valve when required,
and supplied through pipeline

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Fixed dome type: Features
•Requires locally and easily available materials for slurry
•Inexpensive
•Production cost is very low

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Floating gas holder type

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Various forms of biomass are mixed with proportionate quantities of
water in mixing tank, called slurry
Slurry is fed into digester through inlet chamber
After partial filling of digester, plant is kept for a certain time period
In this time-period, anaerobic bacteria present in the biomass
ferments the slurry in presence of water
Biogas is formed, which starts collecting pressing the gas holder
Floating gas holder type

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Floating gas holder type
Produced biogas, being lighter, rises up and is started collecting
inside gas holder
Gas holder starts moving up, but can’t rise above a certain level
Pressure is exerted on slurry, which goes outside through outlet
chamber and moves to the overflow tank
Gas valve is open to supply the biogas

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Floating gas holder type: Features
•Expensive
•Requires periodic maintenance
•Steel drum may damaged

14. 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
If a power outage occurs generator will cease to operate.
Synchronous generator can also be used to connect to the grid
Biogas can also be used as fuel in a hot water heater if hydrogen
sulphide is removed from the gas supply
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Uses of Biogas

15. It can be used directly for cooking, or heating water from
the abundantly available dung and dried plant leaves in
rural areas
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Advantages of Biogas
Reduces air and water pollution, less greenhouse gas emission
Partially solve waste management problems in agriculture
and food industry

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Capacity determined by availability of dung,
not suitable for varying loads
Not feasible to locate at all the locations
Not attractive in large scale
Disadvantages of Biogas

17. Biomass
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18. Biomass Energy
Source: micro-organism growing on water and land,
and their derivatives
Biomass can be converted into modern energy forms such
as liquid and gaseous fuels, electricity, and process heat to
provide energy services needed by rural and urban
populations and also by industry
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BiomassSources

20. Classification of Biomass Energy
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Biomass from cultivation (field, crop, forest,…)
Biomass derived from organic waste

21. Different ways of extracting energy from biomass
The different methods of biomass extraction can be
broadly be classified as:
a) Anaerobic Digestion
b) Gasification
c) Liquefaction
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22. It is a biochemical degradation process that converts complex
organic material, such as animal manure, into methane and other
by-products
It is a natural process of decomposition
Chemical reactions take place through biological oxidation
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Anaerobic Digestion

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Anaerobic digester is a device that promotes the decomposition
of manure or “digestion” of the organics in manure to simple
organics and gaseous biogas products
Biogas is formed by the activity of anaerobic bacteria. Microbial
growth and biogas production are very slow at ambient
temperatures
Anaerobic Digester

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Anaerobic Digester

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Advantages of Anaerobic Digestion
Produces methane and CO2 which can be used as fuel
Reduces the volatile content of sludge
Reduction in number of pathogens
Liquid is easily devoid of waters as it forms a separate
layer without solid

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Disadvantages of Anaerobic Digestion
Possible formation of explosive gases
Slow process, requires constant monitoring
Difficult for maintenance and cleaning job

27. Gasification is a process that exposes a solid fuel to high
temperatures and limited oxygen, to produce a gaseous
fuel
This is a mix of gases such as carbon monoxide, carbon
dioxide, nitrogen, hydrogen and methane
It is a thermo-chemical conversion process
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Gasification

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Gasification Process

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Gasification Process
1. Drying of Fuel
Fuel wood pellets are heated and dried at the top of
gasifier unit. Moisture content in the wood pellets is
removed
2. Pyrolysis
Gaseous products from de-volatilization are
partially burnt with the existing air

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Gasification Process
3. Combustion
Output obtained from pyrolysis process reacts with
the remaining char in absence of oxygen at very high
temperature (800°C – 1000°C)
4. Reduction
Hot gas formed in the combustion process is
converted into producer gas

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convenience – one of the resultant gases, methane, can
be treated in a similar way as natural gas, and used for
the same purposes
It produces a fuel that has had many impurities removed
and will therefore cause fewer pollution problems when
burnt
Advantages of Gasification
This can be used to make almost any hydrocarbon (e.g.,
methane and methanol), which can then be substituted
for fossil fuels

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Disadvantages of Gasification
Complex equipment required
High maintenance cost

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Liquefaction
Biomass energy is
converted into liquid
phase at low
temperature and high
pressure in presence of
catalysts

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Biodiesel

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Biodiesel
Alternative fuel without major change in existing technologies
Environment friendly, originated from organic source

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Sources of Biodiesel
1. Algae
Algae come from stagnant ponds in the natural world, and more
recently in algae farms, which produce the plant for the specific
purpose of creating biofuel
Advantage of algae are (i) no CO2 back into the air, (ii) self-generating
biomass, (iii) can produce up to 300 times more oil per acre than
conventional crops
2. Carbohydrate (sugars) rich biomaterial
It comes from the fermentation of starches derived from agricultural
products like corn, sugar cane, wheat, beets, and other existing food
crops, or from inedible cellulose from the same

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Sources of Biodiesel
3. Oils rich biomaterial
It comes from existing food crops like rapeseed (aka Canola),
sunflower, corn, and others, after it has been used for other
purposes, i.e food preparation
4. Agriculture wastes (organic and inorganic sources)
It comes from agricultural waste which is concentrated into
charcoal-like biomass by heating it
Very little processing required, low-tech, naturally holds CO2 rather
than releasing it into the air

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Production of Biodiesel

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Usability of Biodiesel
Vehicular use
Railway usage
Aircraft
As a heating oil
Cleaning oil spills
In generators

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Advantages of Biodiesel
It contains less polycyclic aromatic hydrocarbons, which
is the cause of cancer
Fewer emission of greenhouse gases
Free of sulphur and lead, non-toxic
Can be blended with conventional diesel fuel, shorter
ignition delay compared with conventional fuel

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Disadvantages of Biodiesel
Impact on food security
Problem in overall Carbon balance
More expensive
Release NO which creates smog
Causes problem at low temperature

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References
1. Non conventional Energy, A. V. Desai, New Age International
Publishers Ltd.
2. Renewable energy resources and emerging technologies, D.P.
Kothari, Prentice Hall of India Pvt. Ltd.
3. Er. R K Rajput, Non-Conventional Energy Sources and Utilisation
(Energy Engineering), S. Chand Publishing
4. B.H Khan, Non Conventioanl Energy Resources, Tata McGraw-Hill
Education