ME458
Advanced Energy Engineering
Module - III
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Biomass
Biomass is plant matter such as trees, grasses, agricultural
crops or other biological material.
It can be used as a solid fuel, or converted into liquid or
gaseous forms for the production of electric power, heat,
chemicals, or fuels.
Biomass is considered as a renewable energy source because
the growth of new plants and trees replenishes the supply.
Bio-energy is energy obtained through the conversion of
organic matter, either directly through combustion to generate
heat or converted into a more manageable energy carrier such
as liquid or gas.
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Biomass to Energy
The Sun is the direct or indirect source of nearly all our
energy on earth.
G
Energy can change from one form to another.
Plants capture solar energy through photosynthesis
to make food, a type of chemical energy.
Biomass is a name for plant and animal waste used
as an energy source or fuel.
Biofuels are liquid and gas fuels used for
transportation, heat and electricity.
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Biomass Energy
• Energy obtained from organic matter derived from
biological organisms (plants and animals).
• Classified in to 2 categories
Biomass from cultivated fields, crops and forests.
Biomass from municipal waste, animal dung, agricultural
waste and fisheries waste.
• Biomass energy may be transformed by chemical or
biological processes to produce biofuels like methane,
producer gas, ethanol and charcoal etc.
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Useful forms of biomass
1. Wood – The most common form of biomass is wood. Direct combustion
is the simplest way to obtain heat energy. Its energy density is 16-20
MJ/kg. It can also be converted to more useful forms
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such as charcoal or producer gas. The remainder is lost due to wind,
incomplete combustion, radiation losses and other losses. Smoke,
which is in fact un-burnt tar and carbon, is a health hazard.
2. Charcoal – Charcoal is a clean (smokeless), dry, solid fuel, black in
colour. It has 75-80% carbon content and has energy density of about
30 MJ/kg. It is obtained by the carbonisation process of woody
biomass (heating in the absence of air) to achieve higher energy density
per unit mass. It can be used as fuel in domestic purposes as it burns
without smoke.
3. Biogas – Biogas or landfill gas refers to the gas obtained by the
anaerobic digestion of biomass resources. Biogas contains 55 to 70
% methane and the remaining part is CO2 with small amounts of other
gases such as hydrogen and hydrogen sulfide. The main difference
between natural gas and biogas is related to the carbon dioxide
content. Biogas contains 25–45% of CO2 of the total composition of
biogas, while natural gas contains less than 1%. Moreover, natural gas
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contains other hydrocarbons.
Useful forms of biomass
4. Bio-fuel – The two most common types of bio-fuels are ethanol and
biodiesel. These fuels are usually blended with the petroleum fuels such as
petrol and diesel fuel, but they can also be used on their own. Ethanol and
biodiesel are usually more expensive than the fossil fuels but they are cleaner
fuels with less pollution.
a. Ethanol (ethyl alcohol) – Methanol, ethanol, propanol and butanol
can be used as an alternative fuel. Ethanol is the most widely used
alcohol, primarily as a fuel for transportation or as a fuel additive because
it can be produced in large quantities from fermenting plant-based
material. Ethanol can be combined with petrol in any concentration up to
pure ethanol. Bio-ethanol can be produced from a variety of feedstocks,
including sugarcane, corn, sugar beet, cassava, sweet sorghum,
sunflower, potatoes, hemp, or cotton seeds, or derived from cellulose
waste. The starches and the sugars in these plants are fermented, and the
ethanol is then obtained by distillation. Ethanol is a clean-burning,
particulate-free fuel source. When burnt with oxygen, the end product is
carbon dioxide and water. But, ethanol has a lower heat of combustion.
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Useful forms of biomass
b. Biodiesel –Biodiesel can be produced from different feedstocks,
such as oil feedstock (eg. rapeseed, soybean oils, jatropha,
palm oil, hemp, algae, canola, flax, and mustard), animal
fats, and/or waste vegetable oil. Recycled restaurant oil is
also one of the most important sources of biodiesel. The most
common production method for converting vegetable oil and
animal fats into bio-diesel is transesterification. The purpose
of the transesterification process is to lower the viscosity of the
raw oil to allow proper atomization of the fuel. Biodiesel can be
used to power engines (diesel engines), either alone, as pure
biodiesel or mixed with petroleum diesel in various ratios.
Compared to petroleum diesel, biodiesel is biodegradable and
non-toxic.
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Solar Energy to Biomass
Green plants act like small,
natural chemical factories.
Plants use water and
carbon dioxide as raw
materials for making food.
A green plant uses the
Sun’s energy to make food
and release oxygen.
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Photosynthesis Process
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Photosynthesis Process
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Biomass Resources
Forest
Agricultural residues
Energy crops
Sugarcane
Oil producing plants
Aquatic plants
Urban waste
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Composition of urban garbage
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Useful forms of biomass
The energy available from various biomass resources are listed in the
table below.
Available
Sl. Bio-fuel Conversion
Biomass source energy
No. produced technology
(MJ/kg)
Wood chips, saw mill
1. Direct heat Incineration 16 – 20
dust, forest residues.
Gas, 40
Wood chips, saw mill
2. Oil, Pyrolysis 40
dust, forest residues
Char 20
3. Sugarcane crops Ethanol Fermentation 26
4. Animal waste Biogas Anaerobic digestion 4–8
5. Municipal sewage Biogas Anaerobic digestion 2–4
6. Vegetable oil sewage Biodiesel Transesterification 38
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Applications
Water pumping and electricity generation
Heat generation
Cooking stoves
Bio fuels
• Fuel wood
• Charcoal
• Fuel pellets
• Bio ethanol
• Bio gas
• Producer gas
• Bio diesel
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Biomass – Merits and demerits
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Advantages of biomass energy
1. Plants ensure a continuous supply of energy due to their continuous growth and
hence it is a renewable source of energy.
2. The cost of obtaining bio-energy through energy-plantations is less than the cost of
obtaining energy from fossil fuels.
3. The production of biogas (particularly from animal wastes) has additional value in
intensive agricultural systems as a method of avoiding pollution.
4. The forestry and agricultural industries that supply feed stocks also provide
substantial economic development opportunities in rural areas.
5. The pollutant emissions from combustion of biomass are usually lower than those
from fossil fuels.
6. Commercial use of biomass may avoid or reduce the problems of waste disposal in
other industries, particularly municipal solid waste in urban centers.
7. Varying capacity can be installed; any capacity can be operated, even at lower loads,
with no seasonality involved.
Disadvantages of biomass energy
1. Biomass source is often of low energy density.
2. Methane gases produced using biomass is harmful to the Earth’s ozone layer.
3. Capacity is determined by availability of biomass and not suitable for varying loads.
4. It is not feasible to set up at all locations.
5. Transportation of biogas through pipe over long distances is difficult.
6. Crops which are used to produce biomass energy are seasonal.
7. A large number of trees are being cut down in order to produce power. Continuing to
operate on such a large scale will eventually result in the deforestation. 19
Bio Fuel Production Process
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Biomass conversion technologies
Combus t i on El e ct r i c p o w e r
P yr ol ys i s C h a r , oil, b i o g a s
Ther mo-chemi cal conver s i on
Ga s i fi ca t i on Pr oducer gas
Li q u e f a c t i o n Li q u i d fu e l
An a e r o b i c d i ge s t i on Methane
Bi omas s Bi o-chemi cal conver s i on Ae r o b i c d i ge s t i on Compost
Fer mentation Et hanol
Ag r o - c h e m i c a l c o n v e r s i o n Tr a n s e s t e r i fi ca t i on Bi o-d i e s e l
Biom ass conversion
Biomass can be converted into different forms of energy by using various
processes.
For the production of energy from biomass, the term feedstock is used to
refer to whatever type of organic material (wood, plants, animal residues, etc.)
which can be used to produce a form of energy.
Biomass can be converted into three main products, viz., power or heat
generation, transportation fuels (such as ethanol) and chemical
feedstock (such as methane). 21
nd
Biomass Conversion
of
in
Processes
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in
ds,
to
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Physical Conversion of Biomass
2 23
Agrochemical Conversion of
Biomass
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Agro-chemical conversion of
biomass
Agro-chemical conversion can take two pathways.
1. Straight Vegetable Oil (SVO)/Pure Plant Oil (PPO)
2. Transesterification
Straight Vegetable Oil (SVO)/Pure Plant
Oil (PPO)
Vegetable oils are esters of glycerin, commonly called triglycerides.
Vegetable oil can be used as diesel fuel just as it is, without being
converted to biodiesel.
However, it is thicker than diesel fuel. This prevents incomplete
combustion, which would damage the engine by causing a build-up
of carbon. Straight vegetable oil can also be blended with
conventional diesel or processed into biodiesel.
PPO is obtained from edible oil-producing plants such as the African
palm, groundnuts, cotton seeds, sunflower, canola, or non-edible
oils such as jatropha, neem, or even balanites.
These raw oils, unused or used, can be employed in certain diesel
engines, for cooking, or in diesel generators for the production of
electricity.
Transesterification
Biodiesel (fatty acid methyl esters) can be produced from vegetable
oil, animal oil/fats, and waste cooking oil.
Biodiesel has substantially different properties than SVO and results in
better engine performance. In particular, biodiesel has a lower boiling
point and viscosity than SVO.
Biodiesel is biodegradable, non-toxic and essentially free from sulphur.
Biodiesel can be used in pure form or may be blended with petroleum
diesel at any concentration for use in most modern diesel engines.
Biodiesel can be produced from a variety of feedstock, such as oil
feedstock (rapeseed, soybean oils, jatropha, palm oil, hemp,
algae, canola, flax and mustard), animal fats, and/or waste
vegetable oil.
Biodiesel produces no net output of carbon in the form of carbon
dioxide (CO2).
Two methods that are commonly applied for biodiesel synthesis are
transesterification and esterification processes.
Transesterification
Transesterification is the reaction of
triglycerides (fat/oil) in the presence of Biomass feedstock
catalyst (sodium hydroxide or sodium
methoxide) and alcohol producing biodiesel
and glycerin.
Oil extraction
NaOH
Triglyceride+Methanol Fattyacidmethylester+Glycerin
(Catalyst)
Transesterification Transesterification
The heavier, co-product, glycerol settles out
and may be used as it is or it may be
purified for use in other industries, eg. the Separation of biodiesel
pharmaceutical, cosmetics, etc. from glycerin
The key factors regulating transesterification
are temperature (>240 °C), pressure (>5 Biodiesel
bars), reaction time and mixing. Transesterification process
Transesterification
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Thermo-chemical conversion
of biomass
Thermo-chemical conversion of biomass uses heat and
catalysts in order to convert biomass into thermal energy,
gas or liquid which can be used either directly for the
generation of electric power and heat, or it can be further
processed into fuel and chemicals.
Thermo-chemical conversion of biomass can take place by
the pathways categorized as direct combustion,
pyrolysis, gasification, and liquefaction.
By using these processes, the biomass can be converted
into either a solid fuel, liquid fuel or gaseous fuel which
can be further used for the generation of electricity, heat,
chemicals and fuels.
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Direct combustion of biomass
Exhaust
Steam
Furnace/Boiler Turbine
Electricity
Biomass Storage Pretreatment
Generator
Ash
Condenser
Co ndensate
Direct combustion/Steam turbine system
In direct combustion, biomass is burned in presence of excess oxygen.
The products from the combustion of biomass are heat, light, and
byproducts at temperatures around 800°C–1000°C. This is a result of the
exothermic reaction between the carbon and oxygen in the fuel that
releases a significant amount of heat, while forming water and CO2.
Energy produced by combustion of biomass can be utilized in the
generation of electricity, or used directly for stoves, boilers, district heating
(heat and/or cooling to multiple buildings from a central source), etc.
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Thermo chemical Process
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Direct combustion of biomass
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Direct combustion of biomass
In fluidised bed combustion of biomass, the Flue gas
biomass is fed into a bed of hot inert
particles, such as sand.
The biomass-particle mix is suspended by
an upward flow of combustion air within the
bed.
Fluidized bed
At sufficient flow rates, the bed acts as a
fluid resulting in rapid mixing of particles. Biomass
The operating temperature is normally
controlled within the range 750°C – 950°C.
The rapid mixing and turbulence within the Bottom bed
fluidized bed enables efficient combustion to Ash
be achieved with high heat releases.
As a result of better heat transfer in FBC,
the unit size and hence the capital costs are Combustion air
reduced. Fluidised bed combustion
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Carbonisation
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Carbonisation
3
3 36
Pyrolysis
Charcoal
Biomass Bio-oil
Pyrolysis
(Heating in inert atmosphere)
Biogas
Pyrolysis
The basic thermo-chemical process to convert biomass into a more
valuable and/or convenient product is known as pyrolysis.
The products of pyrolysis are three types of fuels, usually, a gas mixture
(H2, CO, CO2, CH4 and N2, an oil-like liquid (bio-oil- a water-soluble
phase including acetic acid, acetone, methanol and a non-aqueous
phase including oil and tar) and a nearly pure carbon char.
The distribution of these products depends upon the type of feedstock,
the temperature and pressure during the process and its duration and
the heating rate.
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Pyrolysis
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Pyrolysis
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Gasification
e
e
s
,
d
37 40
Gasification
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Gasification
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Biomass gasification-classification
Gasifiers are broadly classified as : -
1. Fixed-bed gasifier – The fixed-bed gasifiers are further classified
as, depending upon the depending on the relative directions of the
solid flow and the gas.
(a) Downdraft
(b) Updraft, and
(c) Cross-draft
The fixed bed gasifiers are suitable for small-scale applications (< 10
MW).
2. Fluidized-bed gasifier – The fluidized bed configurations are cost
effective in large-scale applications that generate over 15 MW.
Fixed Bed updraft gasifier
Biomass feed
Producer gas
Drying zone
Pyrolysis zone
Reduction zone
Combustion zone
Air
Ash
Fixed-bed updraft gasifier
4
4
Fixed Bed downdraft gasifier
Biomass feed
Drying zone
Pyrolysis zone
Combustion zone
Air Air
Reduction zone
Producer gas
Ash
Fixed-bed downdraft gasifier
4
5
Fixed Bed cross draft gasifier
Biomassfeed
Dryingzone
Pyrolysis zone
Combustionzone
Air Producergas
Reductionzone
Fixed-bedcross-draft gasifier
4
6
Fluidised Bed Gasifier
Producer gas
Fluidised bed
B iom ass
A ir
Fluidised bed gasifier
4
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Liquefaction
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Liquefaction
Pre-treated H2 + CO
slurry inlet NaCO3
Biomass
Liquefaction reactor
4
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Bio-chemical conversion of
biomass
• The process makes use of metabolic action of
microbial organisms on bio mass to produce
liquid and gaseous fuels.
• Bio-chemical conversion can take two pathways
viz.,
• Anaerobic digestion
• fermentation
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Anaerobic digestion
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Fermentation
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Comparing biochemical and thermo-
chemical conversion process
Aspect Biochemical Thermo-chemical
Sugar- Woody feedstock such as
Raw material wood,agricultural residue,forest
crop,Feedstock,starch,co
Residue and some types of
rn
municipal waste
Reactor mode Batch-process. Continuous-process.
Reaction time 2 days. Less than10 minute.
By-products Organic residue. Producer gas/electricity.
Biogas plant
• Biogas is a flammable fuel gas with 60% CH4 and
rest CO2
• A biogas plant converts wet biomass into biogas by
the process of anaerobic fermentation.
• The anaerobe bacteria carries out digestion of
biomass without oxygen and produces methane and
carbon dioxide.
• There are 2 types of biogas plant designs
Fixed dome type
Floating drum type
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Biogas plant
Biogas is a flammable fuel gas with 60% CH4 and rest CO2.
The gas can be upgraded by removal of CO2 and the gas with high
heating value can be used in I.C. engine.
The main applications of biogas are (i) cooking. (ii) domestic
lighting and heating and (iii) I.C. engines.
Biogas plant (biogas digester) converts wet biomass into biogas
(methane) by the process of anaerobic fermentation.
The bacteria called anaerobe carries out digestion of biomass
without oxygen and produces methane (CH4) and carbondioxide
(CO2).
There are two major types of biogas designs promoted in India,
viz., floating drum and fixed dome type.
Fixed dome type digester
Slurry inlet tank
Outlet tank
Gas
Digester
Fixed dome type digester
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Biogas plant- fixed dome type
The pressure inside the digester increases as the biogas is liberated.
The biogas gets collected in the upper portion of the digester in a
dome shaped cavity.
The outlet pipe is provided at the top of the fixed dome.
The fixed dome type digester can be fed on daily basis with small
quantities of the slurry.
The excess slurry in the digester gets accommodated in the
displacement chamber.
In the fixed dome type digester biogas plant (constant volume), the
digester and gas-collector (gas dome) are enclosed in the same
chamber.
The digester is conveniently built at or below ground level in
comparatively cooler zone.
The slurry (cattle dung and water in the ration 1:1 for gobar gas
plant) is fed from the inlet.
Floating drum type digester
Slurry inlet tank
Gas
Sludge
Gound level
Central guide
Outlet tank
Inlet pipe
Outlet pipe
Digester
Partition wall
Floating dome type digester
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Biogas plant- floating drum type
Slurry inlet tank
Gas
Sludge
Gound level
Central guide
Outlet tank
Inlet pipe
Outlet pipe
Digester
Partition wall
Floating dome type digester
In this design (constant pressure), a dome made floats above the slurry
in the digester.
The floating drum normally has a central guide which facilitates its
vertical up and down movement.
The gas generated in the slurry gets collected in the dome and the dome
arises.
The weight of the floating steel cylinder ensures that the gas produced is
under constant pressure, which gives this type of digester its main
advantage.
Comparing fixed dome and floating
drum biogas plant
Fixed dome Floating drum
Digester and gas holder can be Digester, masonry, gas holder can
masonry or concrete structure. be mild steel or fiberglass.
Requires high masonry skills. Low masonry skill is required.
Low reliability due to high
construction failure. High reliability.
Variable gas pressure. Constant gas pressure.
Digester could be inside the Requires space above ground for
ground. three tanks; inlet, digester, outlet.
Economics of biomass power
generation
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Future prospects of biomass
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THANK YOU
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