1. BIOMASS ENERGY
COURSE: RENEWABLE AND NONCONVENTIONAL ENERGY (PE EE
501C)
SWETDRI GHOSH
LECT . EE , SIR RAJENDRA NATH MUKHERJEE GOVT.
POLYTECHNIC
2. INTRODUCTION
• Anything produces by biological process is called
biomass.
• It is actually more condensed form of solar energy.
• Some good example of biomasses are Bagasse,
Straw, cow dung, human and animal waste.
• Some good biomass producer are Subabul,
Eucalyptus , Water Cynthia.
• 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 energy and
available freely as waste and discarded matters.
3.
4. 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 produce carbohydrates
(sugars, starches, celluloses etc.)and
oxygen.
• 6CO2 + 6H2O + light energy= C6H12O6
+ 6O2
5. STEPS IN PHOTOSYNTHESIS
• Splitting of water molecule into H2 & O2 under influence of chlorophyll. “Light
Reaction”
• Hydrogen is transferred to CO2 to form Starch or Sugar.
6. 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
7. 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.
8. Biomass gasification
• Biomass gasification means incomplete combustion of biomass resulting in
production of combustible gases consisting of carbon monoxide (CO), hydrogen
(H2) and traces of methane (CH4). This mixture is called producer gas.
• Producer gas can be used to run internal combustion engines (both compression
and spark ignition), can be used as substitute for furnace oil in direct heat
applications and can be used to produce, in an economically viable way,
methanol—an extremely attractive chemical which is useful both as fuel for heat
engines as well as chemical feedstock for industries.
• Since any biomass material can undergo gasification, this process is much more
attractive than ethanol production or biogas where only selected biomass materials
can produce the fuel.
9. Biomass gasification
• The production of generator gas (producer gas) called gasification, is partial
combustion of solid fuel (biomass) and takes place at temperatures of about
1000°C. The reactor is called a gasifier.
• The combustion products from complete combustion of biomass generally
contain nitrogen, water vapour, carbon dioxide and surplus of oxygen.
• However, in gasification where there is a surplus of solid fuel (incomplete
combustion) the products of combustion are combustible gases like carbon
monoxide (CO), hydrogen (H2) and traces of methane and useless products like
tar and dust.
• The production of these gases is by reaction of water vapour and carbon dioxide
through a glowing layer of charcoal.
• Thus the key to gasifier design is to create conditions such that
• (i) biomass is reduced to charcoal, and
• (ii) charcoal is converted at suitable temperature to produce CO
and H2.
10. Types of gasifiers
Since there is an interaction of air or oxygen
and biomass in the gasifier, they are classified
according to the way air or oxygen is introduced
in it. There are three types of gasifiers.
• Updraft: The air passes through the
biomass from bottom and the combustible
gases come out from the top of the gasifier.
• Downdraft: The air is passed from the
tuyers in the downdraft direction. These can
be two types . i) Single throat, mainly used
for stationary applications. ii) Double throat
used for variable load as well as automotive
applications.
• Crossdraft: Air passes across the bio-
mass
11. Advantages and Disadvantages of
various types of gasifiers
• Updraft type:
• Advantages:
a) Small pressure drop.
b) Good thermal efficiency.
c) Little tendency towards slag formation.
• Disadvantages:
a) Great sensitivity to tar and moisture and
moisture content of fuel.
b) Relatively long time required for start up
of IC engine.
c) Poor reaction capability with heavy gas
load.
• Downdraft type:
• Advantages:
a) Flexible adaptation of gas
production to load.
b) Low sensitivity to charcoal
dust and tar content of fuel.
• Disadvantages:
a) Design tends to be tall.
b) Relatively long time required
for start up of IC engine. Not
feasible for very small particle
size of fuel
• Crossdraft type:
• Advantages:
a) Short design height.
b) Very fast response time to
load.
c) Flexible gas production.
• Disadvantages:
a) Very high sensitivity to slag
formation.
b) High pressure drop.
12. Reaction Chemistry
• 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 as
steam. The combustion reaction is
exothermic and yields a theoretical
oxidation temperature of 1450°C.
The main reactions, therefore, are
• C + O2 = CO2 (+393 MJ/kg mole)
• 2H2 + O2 = 2H2O (–242 MJ/kg mole)
• 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)
• C + H2O = CO + H2 (–122.6 MJ/kg mole)
• CO + H2O = CO + H2 (+ 42 MJ/kg mole)
• C + 2H2 = CH4 (+ 75 MJ/kg mole)
• CO2 + H2 = CO + H2O (–42.3 MJ/kg mole)
• Equations in bold are main reduction reactions and being endothermic have
the capability of reducing gas temperature. Consequently, the temperatures
in the reduction zone are normally 800–1000°C. Lower the reduction zone
temperature (~700–800°C), lower is the calorific value of gas.
13. Reaction Chemistry (cont..)
• Pyrolysis zone:
• Wood pyrolysis is an intricate process.
• The products depend upon temperature, pressure,
residence time and heat losses. However, following
general remarks can be made about them.
• Up to the temperature of 200°C only water is driven off.
• Between 200° and 280°C carbon dioxide, acetic acid
and water are given off.
• The real pyrolysis, which takes place between 280° and
500°C, produces large quantities of tar and gases
containing carbon dioxide.
• Besides light tars, some methyl alcohol is also formed.
• Between 500° and 700°C the gas production is small
and contains hydrogen.
• Drying zone:
• Finally, in the drying zone the main
process is of drying of wood.
• Wood entering the gasifier has moisture
content of 10–30 per cent.
• Various experiments on different
gasifiers in different conditions have
shown that on an average the
condensate formed is 6–10 per cent of
the weight of gasified wood.
• Some organic acids also come out
during the drying process. These acids
give rise to corrosion of gasifiers
15. Efficiency of a wood gasifier
• The average energy conversion efficiency of wood gasifiers is
about 60–70 per cent and is defined as
• ηgasifier=
Calorific value of gas/kg of fuel
Average calorific value of 1kg of fuel
• 1 kg of wood produces 1.5 m3 of gas with average calorific value of
5.4 MJ/m3. Average calorific value of wood (dry) is 19.8 MJ/kg.
• Hence: ηgasifier=
1.5 (m3 ) ×5.4(MJ/m3)
19.80 (MJ/kg) ×1(kg)
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 hydro gasification.
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.
• 3) Methane Gas Formation: In this stage, acetates and simple CO2
are converted into CH4. This is carried out by methanogenes.
