Biomass Energy

What is Biomass
• Biomass is a key renewable energy resource
that includes plant and animal material, such as
wood from forests, material left over from
agricultural and forestry processes, and organic
industrial, human and animal wastes.
• The energy contained in biomass originally
came from the sun. Through photosynthesis
carbon dioxide in the air is transformed into
other carbon containing molecules (e.g. sugars,
starches and cellulose) in plants.
• The chemical energy that is stored in plants and
animals (animals eat plants or other animals) or
in their waste is called biomass energy or
bioenergy.
• Biomass is a renewable energy source because
we can always grow more trees and crops, and
waste will always exist.
• Some examples of biomass fuels are
wood,crops, manure, and some garbage. When
burned, the chemical energy in biomass is
released as heat. If you have a fireplace, the
wood you burn in it is a biomass fuel.
• Wood waste or garbage can be burned to
produce steam for making electricity, or to
provide heat to industries and homes.
 Contd….
• In past 10 years or so, considerable practical experience has accumulated in India as well as
in other developing and industrialized countries, on biomass energy production and
conversion.
• The importance of bio-energy as a modern fuel has been recognized. India has about 70,000
villages yet to be connected to the electricity grid.
• The availability of biomass such as wood, cow-dung, leaf litter in rural areas is more. Hence a
choice of biomass energy especially in rural areas is more reasonable but at the same time
the technology is being developed to meet the large-scale requirements using biomass.
• One of the major advantages of biomass energy is that it can be used in different forms.
• For e.g., Gas generated from the biomass can be directly used for cooking or it can be used
for running an internal combustion Engine for developing stationary shaft power or
otherwise coupled to generator for generating electric power.
• Biomass is renewable fuel used in nearly every corner of the developing countries as a
source of heat, particularly in the domestic sector.
• Advantages of biomass gasify energy over other renewable energy options:
a)Suitable in most locations.
b)Varying capacity can be installed; any capacity can be operated, even at lower loads; no
seasonality.
c)Need for storage of energy is not required.
• drawbacks of biogas energy over other renewable energy options:
a)It can’t be used directly for cooking, or heating water from the abundantly available dung and
dried plant leaves in rural areas.
b)Capacity determined by availability of dung. Not suitable for varying loads.
c)Not feasible to locate at all the locations.
Top 10 nations in Biomass Electricity
(GWh)
Contd…..
 Usable Forms of Biomass, their
Composition and Fuel Properties
Burning biomass is not the only way
to release its energy. Biomass can be
converted to other usable forms of
energy like methane gas or
transportation fuels like ethanol and
biodiesel. Methane gas is the main
ingredient of natural gas. Smelly
stuff, like rotting garbage, and
agricultural and human waste,
release methane gas - also called
"landfill gas" or "biogas." Crops like
corn and sugar cane can be
fermented to produce the
transportation fuel, ethanol.
Biodiesel, another transportation
fuel, can be produced from left-over
food products like vegetable oils and
animal fats.
 WOOD AND WOOD WASTE
 The most common form of biomass is wood. Direct combustion is the
simplest way to get heat energy. It’s energy density is 16-20 MJ/kg.
 It can be converted into more usable form like charcoalor producer
gas.Charcoal is a clean, dry, solid fuel, black in colour.It has 75-80% carbon
content and energy density is 30 MJ/kg.
 For thousands of years people have burned wood for heating and
cooking.Wood was the main source of energy in India and the rest of the
world until the mid-1800s. In India wood and waste (bark, sawdust, wood
chips, and wood scrap) provide only about 2 percent of the energy we use
today.
 About 84 percent of the wood and wood waste fuel used is consumed by
the industry, electric power producers, and commercial businesses. The
rest, mainly wood, is used in homes for heating and cooking.
 Many manufacturing plants in the wood and paper products industry use
wood waste to produce their own steam and electricity.
 This saves these companies money because they don't have to dispose of
their waste products and they don't have to buy as much electricity.
 MUNICIPAL SOLID WASTE, LANDFILL
GAS, AND BIOGAS
 Urban Waste is of two types municipal solid waste (MSW) or garbage and sewage
or liquid waste Trash that comes from plant or animal products is biomass.
 MSW can be a source of energy by either burning MSW in waste-to-energy plants,
or by capturing biogas. In waste-to-energy plants, trash is burned to produce
steam that can be used either to heat buildings or to generate electricity. Sewage
can be used to produce bio gas after some processing.
 In landfills, biomass rots and releases methane gas, also called biogas or landfill
gas. Some landfills have a system that collects the methane gas so that it can be
used as a fuel source.
 Some dairy farmers collect biogas from tanks called "digesters" where they put all
of the muck and manure from their barns.
 Biogas, naturally occurring gas that is generated by the breakdown of organic
matter by anaerobic bacteria and is used in energy production. Biogas differs
from natural gas in that it is a renewable energy source produced biologically
through anaerobic digestion rather than a fossil fuel produced by geological
processes. Biogas is primarily composed of methane gas, carbon dioxide and trace
amounts of nitrogen, hydrogen, and carbon monoxide.
 Nitrogen rich sludge(fertilizer) is also produced as a by product with improved
sanitation as an added bonus.The output of biogas contain about 50-60% CH4,30-
40% CO2,5-10% H2,N2 .5-.7% with trace amount of O2 and H2S.Its density is about
23 MJ/m3.It is used for cooking,lighting,heating and opearting small IC engines.
 BIOFUELS -- ETHANOL AND BIODIESEL
 "Biofuels" are transportation fuels like ethanol and biodiesel that are made from
biomass materials. These fuels are usually blended with the petroleum fuels -
gasoline and diesel fuel, but they can also be used on their own.
 Raw vegetable oil upgraded as biodisel through a chemical process called trans-
esterification where by the glycerine is separated from animal fat or vegetable
oil.The process leaves behind two products-Biodisel and glycerine.
 Using ethanol or biodiesel (C2H5OH) is a colourless liquid biofuel.Its boiling point
is 78°C and energy density 26.9 MJ/kg. Ethanol and biodiesel are usually more
expensive than the fossil fuels that they replace but they are also cleaner burning
fuels, producing fewer air pollutants.
 Ethanol is an alcohol fuel made from the sugars found in grains, such as corn,
sorghum, and wheat, as well as potato skins, rice, sugar cane, sugar beets, and
yard clippings.It can be derived from set biomass containing sugars,starches or
cellulose.the main constituents are legnin and cellulose.
 Biodiesel is a fuel made with vegetable oils, fats, or greases - such as recycled
restaurant grease. Biodiesel fuels can be used in diesel engines without changing
them. It is the fastest growing alternative fuel in the India. Biodiesel, a renewable
fuel, is safe, biodegradable, and reduces the emissions of most air pollutants.
Biomass Resources
• Biomass Resources sometimes
referred to as biorenewable
resources, are all forms of
organic materials including
plant matter both living and in
waste form, as well as animal
matter and their waste
products.
• As such biomass resources are
generally classified as being
either waste materials or
dedicated energy crops. When
plants are cultivated,specially
for the purpose of energy, it is
known as energy Farming.
Forestry Residues
Forestry residues are generated by operations such as thinning of plantations, clearing for
logging roads, extracting stem-wood for pulp and timber, and natural attrition.
Some fast growing energy intensive trees such as eucalyptus, pine, poplar are cultivated for
the purpose of energy.
Harvesting may occur as thinning in young stands, or cutting in older stands for timber or
pulp that also yields tops and branches usable for biomass energy.
Harvesting operations usually remove only 25 to 50 percent of the volume, leaving the
residues available as biomass for energy. Stands damaged by insects, disease or fire are
additional sources of biomass.
Forest residues normally have low density and fuel values that keep transport costs high, and
so it is economical to reduce the biomass density in the forest itself.
Some plants produce seeds to yield vegetable oil on pressing. This serves as a liquid bio
fuel(biodisel).There are two categories of oil producing plants(a)Wild plants jojoba and karanja
(b) agricultural crops.
Oil Producing plants
The majority of plant-based oils come from the oil-rich seeds and fruits of a limited
number of specialised oil crops, such as canola, soybean, sunflower, olive, coconut and oil
palm.
The benefits to be derived from plant oil fuel industry are
Most of these plants are adaptable and hardy.
Simple technology involve in oil extraction and filtering .
The leftover biomass known as cake can be used in biogas plant.
Most of the plants are of low cost ,require low input.

Aquatic Plants:
Some water plants grow faster than land based plant and provide raw material for
producing biogas or ethanol. Example:Kelp,seaweed,algae

Urban Waste:
 Urban Waste is of two types municipal solid waste (MSW) or garbage and sewage or
liquid waste. Energy from MSW can be obtained from direct combustion or as a landfill
gas. Sewage can be used to produce biogas after some processing.
Biomass Conversion Technologies
 Biomass Conversion Technologies
The different methods of biomass extraction can be broadly be classified as:
i)Physical method
ii)Incineration(Direct Combustion)
iii)Thermochemical method
iv)Biochemical method
 Physical method:The simplest form of physical conversion of biomass is through
compression of combustible material.Its density is increased by reducing the
volume by compression through the processes called briquetting and pelletization.
 Pelletization:It is a process where wet wood is pulverized,dried and forced under
pressure through an extrusion device.The extracted mass is in the form of pellets
5-10 mm dia and12 mm long,facilitating its use in steam power plants and
gasification system.It reduces the moisture to about 7-10% and increases the heat
value of boimass.
 Briquetting: is the process to improve the characteristics of biomass as a
renewable energy resource by densification. Densification means less volume
needed for the same amount of energy output. The energy content of briquettes
ranged from 4.48 to 5.95 kilojoule per gram (kJ/g) depending on composition,
whereas the energy content of sawdust, charcoal and wood pellets ranged from
7.24 to 8.25 kJ/g. Biobriquettes molded into a hollow-core cylindrical form
exhibited energy output comparable to that of traditional fuels.
Expelling Agro products:

Concentrated vegetable oils may be obtained from certain agro products and may be
used as fuel in disel engines.
However difficulties arise with direct use of plant oil due to high viscosity and
combustion deposits.
Therefore these oils are upgraded by a chemical method known as transesterification to
overcome these difficulties.

Examples are seeds (sunflower,soya beans) Nut(oil palm),Fruits (olive),Leaves

Fuel Extraction:
Occasionally, liquid or solid fuels may be obtained directly from living or freshly cut
plants.
The materials are called exudates and are obtained by cutting into (tapping) the stems
or trunks of the living plants or by crushing freshly harvested material.
 Incineration
 The burning of organic residue from plants, agricultural, forestry and
municipal waste to produce energy.
 To convert biomass into energy, organic matter is burned in a boiler to
make steam. The steam then turns a turbine, which is connected to a
generator that produces electricity or provide the heat for the industrial
process, space heating, cooking.
 This is just one of the more simple methods of converting biomass from
waste into energy.
 The major advantage of incineration is that makes
waste management easier and more efficient, because incineration can
burn up to 90% of the total waste generated and sometimes even more.As
a comparison, landfills only allow organic decomposition, so nonorganic
waste keeps accumulating.
 Incinerators produce smoke during the burning process. The smoke
produced includes acid gases, carcinogen dioxin, particulates, heavy
metals, and nitrogen oxide. These gases are poisonous to the
environment. Research has shown that dioxin produced in the plant is a
cancer forming chemical.
 Thermo-chemical processes
 Thermo-chemical processes do not produce useful energy directly
but under controlled temperature and oxygen conditions.
 These processes are more convenient and cost effective than the
thermal processes. They convert biomass feedstock into energy
carriers , such as producer gas, oils or methanol.
 Energy carriers are more energy dense and therefore give better
fuel efficiency and reduce transport costs. They are used in internal
combustion engines and gas turbines.
 Thermo-chemical conversion is the controlled heating and/or
oxidation of biomass as part of several pathways to produce
intermediate energy carriers or heat.
 Thermo-chemical conversion processes include three
subcategories: pyrolysis, gasification, and liquefaction.
 Contd….
 Pyrolysis • Thermal conversion (destruction) of organics in
the absence of oxygen
• In the biomass community, this commonly refers to lower
temperature thermal processes producing liquids as the
primary product
• Possibility of chemical and food byproducts
 Gasification • Thermal conversion of organic materials at
elevated temperature and reducing conditions to produce
primarily permanent gases, with char, water, and
condensibles as minor products
• Primary categories are partial oxidation and indirect heating
 Carbonization: Process used for the production of charcoal
 Liquification: A liquid product is obtained through catalytic
liquification process.
 Biochemical conversion
 Biochemical conversion of biomass involves use of bacteria, microorganisms and
enzymes to breakdown biomass into gaseous or liquid fuels, such as biogas or bio-
ethanol.
 Biomass wastes can also yield liquid fuels, such as cellulosic ethanol, which can be
used to replace petroleum-based fuels.
 Alcoholic fermentation. Ethanol is a volatile liquid fuel that may be used in place of
refined petroleum. It is manufactured by the action of micro-organisms and is
therefore a fermentation process. Conventional fermentation has sugars as feedstock.
 C12H22O11+H2O yeast −→4C2H5OH+4CO2
 Anaerobic digestion. In the absence of free oxygen, certain microorganisms can
obtain their own energy supply by reacting with carbon compounds of medium
reduction level to produce both CO2 and fully reduced carbon as CH4.
 The process (the oldest biological ‘decay’ mechanism) may also be called
‘fermentation’, but is usually called ‘digestion’ because of the similar process that
occurs in the digestive tracts of ruminant animals.
 The evolved mix of CO2CH4 and trace gases is called biogas as a general term, but
may be named sewage gas or landfill-gas as appropriate.
Urban Waste to Energy Conversion
 Energy recovery from
waste is the conversion of
non-recyclable waste
materials into usable
heat, electricity, or fuel
through a variety of
processes, including
combustion, gasification,
pyrolization, anaerobic
digestion and landfill gas
recovery.
 This process is often
called waste to energy.
MSW to energy incineration plant
 Contd…
 Municipal solid waste incineration (MSWI) is the burning of waste in a controlled process within a
specific facility that has been built for this purpose. The primary goal of MSWI is to reduce MSW volume
and mass and also make it chemically inert in a combustion process without the need of additional fuel
(autothermic combustion).
 As a side effect it also enables recovery of energy, minerals and metals from the waste stream . There
are always about 25% residues from incineration in the form of slag (bottom ash) and fly ash. Bottom
ash is made up of fine particulates that fall to the bottom of the incinerator during combustion, whilst fly
ash refers to fine particulates in exhaust gases which must be removed in flue gas treatment.
 These residues need further attention and, in the case of the hazardous fly ash, a secure place for final
disposal.
 The combustible materials in waste burn when they reach the necessary ignition temperature and come
into contact with oxygen, undergoing an oxidation reaction.
 The reaction temperature is between 850 and 1450ºC, and the combustion process takes place in the
gas and solid phase, simultaneously releasing heat energy. A minimum calorific value of the waste is
required to enable a thermal chain reaction and self-supporting combustion (so-called autothermic
combustion), i.e. there is no need for addition of other fuels.
 During incineration, exhaust gases are created which, after cleaning, exit to the atmosphere via a pipe or
channel called a flue. These flue-gases contain the majority of the available fuel energy as heat, as well
as dust and gaseous air pollutants which must be removed via a flue-gas purification process. Excess
heat from combustion can be used to make steam for electricity generation, district heating/cooling or
steam supply for nearby process industry.
 Plants that utilize cogeneration of thermal power (heating and cooling) together with electricity
generation can reach optimum efficiencies of 80%, whereas electricity generation alone will only reach
maximum efficiencies of about 20%.
 Contd…
 sewage to energy conversion
 Whilst effectively treating the sewage, anaerobic
digestion generates a high grade of gaseous fuel – sewage gas.
 The methane produced can be utilized for generating electricity –
renewable energy – through a biogas engine thereby making
the sewage treatment plant meet its electricity requirements.
 Biomass gasification
• Biomass gasification involves burning of biomass in a limited supply of air to give a
combustible gas consisting of carbon monoxide, carbon dioxide, hydrogen, methane,
water, nitrogen, along with contaminants like small char particles, ash and tars. The gas is
cleaned to make it suitable for use in boilers, engines and turbines to produce heat and
power (CHP).
 Biomass gasification
• During combustion, the volatiles and char are partially burned in air or
oxygen to generate heat and carbon dioxide. In the reduction phase, carbon
dioxide absorbs heat and reacts with the remaining char to produce carbon
monoxide (producer gas). The presence of water vapour in a gasifier results
in the production of hydrogen as a secondary fuel component.
 Biomass gasification
• Biomass gasification provides a means of deriving more diverse forms of energy from the
thermo-chemical conversion of biomass than conventional combustion. The basic
gasification process involves devolatization, combustion and reduction. During
devolatization, methane and other hydrocarbons are produced from the biomass by the
action of heat which leaves a reactive char.
 Contd….
 There are two main types of gasifier that can be used to carry out this conversion, fixed bed
gasifiers and fluidized bed gasifiers.
 The fixed bed gasifiers have been the traditional setup used for gasification, operated at
temperatures around 1000 0C.
 Among the fixed bed gasifiers, there are three major types and these are updraft, downdraft
and cross-draft gasifiers.
 The conversion of biomass into a combustible gas involves a two-stage process. The first, which
is called pyrolysis, takes place below 600°C, when volatile components contained within the
biomass are released. These may include organic compounds, hydrogen, carbon monoxide, tars
and water vapour.
 Pyrolysis leaves a solid residue called char. In the second stage of the gasification process, this
char is reacted with steam or burnt in a restricted quantity of air or oxygen to produce further
combustible gas. Depending on the precise design of gasifier chosen, the product gas may have a
heating value of 6 – 19 MJ/Nm3.
 In the downdraft gasifier, the gasification agent (air or O2) is fed into the middle of the bed
(combustion zone) above the stationary grate and the producer gas flows out of the gasifier
from the bottom of the gasifier beneath the stationary grate. In this type of gasifier, the fed solid
fuel moves downwards together with the gases through a drying zone, a pyrolysis zone,
an oxidization (combustion) zone and a reduction zone. In the drying zone, moisture is
vapourized and the solid fuel is dried. With downwards motion, the dry solid fuel is further
heated and the dried solid fuel is decomposed to char and gases (pyrolysis). With continuous
downwards motion, gasification agent is injected, thus partial combustion of char and some
combustible gases occurs, providing needed heat to maintain the target gasification
temperature. Then the gases and the char move to the reduction zone in which the gasification
reactions occur and the producer gas is formed.
 Downdraft gasifier
 The temperature in each zone is different.
In the drying zone, the temperature is
normally at 200 °C or lower before the
solid fuel is degraded. Temperature in the
pyrolysis zone is up to 500–600 °C
depending on the equivalence ratio (ER)
(the ratio of oxygen provided to the
stoichiometric oxygen demand).
 The oxidation zone has the highest
temperature of up to 1500 °C at which
tars and other heavy hydrocarbons are
thermally cracked into lighter
hydrocarbon gas.
 Below the oxidation zone, the remaining
char, ash, the producer gas and water
vapour flow through the reduction zone in
which the vapour can react with char
(steam gasification reaction), CO (water–
gas-shift reaction) and with CH4 (steam–
methane-reforming reaction) to form
hydrogen which is desired.
 Contd…
 Advantage of the downdraft fixed bed gasifiers is that the
tars are cracked down in the oxidation zone, thus the
producer gas has lower tar content compared to other
types of gasifiers.
 However, the producer is easily contaminated by ash and
other fine particles, and a separation device (e.g., two-
stage cyclone and ceramic filter) is needed to clean the
producer gas.
 Another setback with this type of gasifier is relatively high
temperature of the exit producer gas, resulting in lower
gasification efficiency. Due to the large variation of
temperature profile within the gasifier, this type of gasifier
is used at small to medium scale (100 kWth–5 MWth).
 Updraft gasifiers
 Updraft gasifiers are one of the simplest and most common
types of gasifier for biomass.
 In these gasifiers, the feed is introduced from the top, and
air is introduced from the bottom through grate. Feed and
air move counter currently in the gasifier.
 The lowest portion of the gasifier is essentially the
“combustion” zone where the char formed due to drying
and devolatilization of biomass is combusted. This helps in
raising the temperature of the lower portion of the gasifier
to about 727 °C.
 Hot gases passing upward through the bed of downflowing
biomass are reduced in the portion immediately above the
combustion zone. Further up the gasifier, the hot gases
pyrolyze the biomass and dry it. These processes cool the
gases to about 200-300 °C.
 Pyrolysis of biomass results in release of volatiles and the
formation of a sizeable amount of tar. Some of this tar may
leave with the outgoing gases.
 The overall efficiency of the process could be high due to
the low temperature of the gases leaving the gasifier. In
addition, the gas flowing through the packed bed of
biomass undergoes “filtration” as the particulate matter
entrained with it is captured by the bed material.
 This helps in lowering of the particulate content of the
outgoing gas. The humidity of the gasifying air plays a major
role in controlling the temperature of the gasification.
 Cross draft gasifier.
 In this design, the biomass feed is introduced
from the top and the air is from the side of the
gasifier.
 The biomass moves down as it gets dried,
devolatilized, pyrolyzed, and finally, gasified
while the air exits from the opposite side of the
unit.
 The exit for the gas is more-or-less at the same
level as that of entrance. The combustion and
gasification zone is located near the entrance of
the air while the devolatilization and pyrolysis
zones are at a higher level than the entrance and
exit.
 The producer gas leaves the gasifier at almost
the same temperature as gasification (~ 800-
900 °C). Thus, the heat loss from this gasifier is
high, which reduces its thermal efficiency.
 Secondly, the overall residence time of the
producer gas in the high temperature zone is
small (as the gas enters and exits from opposite
ends), and hence, tar cracking is limited. This
leaves a significant amount of tar in the outgoing
gas.
 Fluidized bed gasifier
 In a typical fluidized bed (bubbling or circulating)
air enters from the bottom, but is fuel fed from the
side or top.
 In either case, the fuel is immediately mixed
throughout the bed owing to its exceptionally high
degree of mixing .
 Thus, the fresh oxygen (in air) entering the grid
comes into immediate contact with fresh biomass
particles undergoing pyrolysis as well as with
spent char particles from the biomass, which has
been in the bed for some time.
 Oxygen's contact with the fresh biomass burns the
tar released, while its contact with the spent char
particles causes the char to burn.
 Though the solids are back-mixed, the gases flow
upward in plug-flow mode. This means that further
up in the bed neither older char particles nor fresh
pyrolyzing biomass particles come in contact with
the oxygen.
 Any tar released moves up in the bed and leaves
along with the product gas. For this reason, tar
generation in a fluidized-bed gasifier is between
the two extremes represented by updraft and
downdraft gasifiers, averaging about 10 mg/Nm3.
Biomass Liquefaction
 Biomass to Ethanol production
 Ethanol, C2H5OH, is produced naturally by certain micro-organisms from sugars under
acidic conditions, i.e. pH 4 to 5. This alcoholic fermentation process is used worldwide
to produce alcoholic drinks. The most common micro-organism, the yeast
Saccharomyces cerevisiae, is poisoned by C2H5OH concentration greater than 10%,
and so stronger concentrations up to 95% are produced by distilling and fractionating.
 When distilled, the remaining constant boiling point mixture is 95% ethanol and 5%
water. removal of water by co-distillation with solvents such as benzene. Only about
0.5% of the energy potential of the sugars is lost during fermentation, but significant
amounts of process heat are required for the concentration and separation processes.
 This process heat may be provided from the combustion or gasification of otherwise
waste biomass and from waste heat recovery.The sugars may be obtained by the
following routes, listed in order of increasing difficulty.
 Directly from sugarcane : Usually commercial sucrose is removed from the cane
juices, and the remaining molasses used for the alcohol production process .These
molasses themselves have about 55% sugar content. But if the molasses have little
commercial value, then ethanol production from molasses has favourable commercial
possibilities, especially if the cane residue (bagasse) is available to provide process
heat.
In this case the major reaction is the conversion of sucrose to ethanol:
C12H22O11 +H2O yeast −→4C2H5OH+4CO2
In practice the yield is limited by other reactions and the increase in mass of yeast.
The fermentation reactions for other sugars, e.g. glucose, C6H12O6, are very similar.
 Contd….
 From sugar beet: Sugar beet is a mid-latitude root crop for obtaining major supplies of sugar. The
sugar can be fermented, but obtaining process heat from the crop residues is, in practice, not as
straightforward as with cane sugar, so ethanol production is more expensive.
 From starch crops :Starch crops, e.g. grain and cassava, can be hydrolyzed to sugars. Starch is the
main energy storage carbohydrate of plants, and is composed of two large molecular weight
components, amylose and amylopectin. These relatively large molecules are essentially linear, but
have branched chains of glucose molecules linked by distinctive carbon bonds. These links can be
broken by enzymes from malts associated with specific crops, e.g. barley or corn, or by enzymes
from certain moulds (fungi). Such methods are common in whisky distilleries,corn syrup
manufacture and ethanol production from cassava roots. The links can also be broken by acid
treatment at pH 1.5 and at 2 atmospheres pressure, but yields are small and the process more
expensive than enzyme alternatives. An important by-product of the enzyme process is the residue
used for cattle feed or soil conditioning.
 From cellulose: Cellulose comprises about 40% of all biomass dry matter. Apart from its combustion
as part of wood, cellulose is potentially a primary material for ethanol pr a polymer structure of
linked glucose molecules, and forms the main mechanical-structure component of the woody parts
of plants. These links are considerably more resistant to breakdown into sugars under hydrolysis
than the equivalent links in starch. Cellulose is found in close association with lignin in plants, which
discourages hydrolysis to sugars.
 Acid hydrolysis is possible as with starch, but the process is expensive and energy intensive.
Hydrolysis is less expensive, and less energy input is needed if enzymes of natural, wood-rotting
fungi are used, but the process is slow. Prototype commercial processes have used pulped wood or,
more preferably, old newspaper as input. The initial physical breakdown of woody material is a
difficult and expensive stage, usually requiring much electricity for the rolling and hammering
machines.
 Substantial R&D led to processes with improved yields and potentially cheaper production, key
features of which are acid-catalysed hydrolysis of hemicellulose, more effective enzymes to
breakdown cellulose, and genetically engineered bacteria that ferment all biomass sugars (including
5-carbon sugars, which resist standard yeasts) to ethanol with high yields.
Contd....