THIAGARAJAR COLLEGE (AUTONOMOUS), MADURAI – 625 009.

DEPARTMENT OF PHYSICS - Non Major Elective (NME)

NON-CONVENTIONAL ENERGY - SEMESTER :V CODE: UPH19NE51

UNIT I - BIO-MASS ENERGY

Biomass conversion Technologies – Biogas generation – Classification of bio-gas
plant- Types- KVIC, Janta and Deena bandhu model biogas plant- Gasification of Biomass –
Gasifier – Construction and operation of down draught and up draught gasifier – Application
of Gasifiers
1. Biomass conversion Technologies: Biogas generation

Biomass is converted to biogas by the process of digestion or fermentation in the presence of

micro-organisms. This biogas mainly contains methane which is a good combustible gas. Biogas
consists of 50-55% of methane, 30-35% of CO2 and remaining waste gases like H2, N2, H2S etc.
since it contains a hydrocarbon gas it is a very good fuel and hence can be used in internal
combustion (IC) engines. It is a slow burning gas with calorific value of 5000-5500 Kcal/kg. the raw
material used to generate this are algae, crop residue, garbage, kitchen waste, paper waste, waste
from sugar cane refinery, water hyacinth etc. apart from the above mentioned raw materials excreta
of cattle, piggery waste and poultry droppings are also used as raw materials.
Biogas is generated by fermentation or digestion of organic matter in the presence of aerobic and
anaerobic micro-organisms. Fermentation is the process of breaking down the complex organic
structure of the biomass to simple structures by the action of micro-organisms either in the presence
of O2 or in the absence of O2. The container in which the digestion takes place is known as the
digester.

The digestion takes place in the following steps

i) Enzymatic hydrolysis ii) Acid formation iii) Methane formation.

i) Enzymatic hydrolysis: In this step the complex organic matter like starch, protein, fat,
carbohydrates etc are broken down to simple structures using anaerobic micro-organisms.

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ii) Acid formation: In this step the simple structures formed in the enzymatic hydrolysis step are
further reacted by anaerobic and facultative microorganisms (which thrive in both the presence and
absence of oxygen) to generate acids.

iii) Methane formation: In this step the organic acids formed are further converted to methane and
CO2 by anaerobic micro-organisms (anaerobes).

Biochemical reactions in anaerobic digestion:

There are four key biological and chemical stages of anaerobic digestion:
Hydrolysis
Acido genesis
Aceto genesis
Methano genesis.

Fig.1. Anaerobic pathway of complex organic matter degradation

In most cases biomass is made up of large organic compounds. In order for the microorganisms in
anaerobic digesters to access the chemical energy potential of the organic material, the organic
matter macromolecular chains must first be broken down in to their smaller constituent parts. These
constituent parts or monomers such as sugars are readily available to microorganisms for further

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processing. The process of breaking these chains and dissolving the smaller molecules in to solution
is called hydrolysis. Therefore hydrolysis of high molecular weight molecules is the necessary first
step in an aerobic digestion. Acetates and hydrogen produced in the first stages can be used directly
by methanogens. Other molecules such as volatile fatty acids (VFA‘s) with a chain length that is
greater than acetate must first be catabolised into compounds that can be directly utilized by
methanogens.

The biological process of acidogenesis is where there is further break down of the remaining
components by acidogenic (fermentative) bacteria. Here VFA‘s are generated along with ammonia,
carbondioxide and hydrogensulphide as well as other by-products.

The third stage anaerobic digestion is acetogenesis. Here simple molecules created through
the acidogenesis phase are further digested by acetogens to produce largely aceticacid (oritssalts) as
well as carbondioxide and hydrogen.

The final stage of anaerobic digestion is the biological process of methanogenesis. Here
methanogenic archaea utilize the intermediate products of the preceding stages and convert the min
to methane, carbondioxide and water.

2. Classification of the biogas plants:

Continuous and batch type :

(i) Single stage process

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 Fig. 2: Schematic of single process conventional digester.

The entire process of conversion of complex organic compounds into biogas in completed in a single
chamber. This chamber is regularly fed with the raw materials while the spent residue keeps moving
out. Serious problems are encountered with agricultural residues when fermented in a single stage
continuous process
(ii) Double stage process

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 Fig.3. Schematic of two-stage digestion process

The acidogenic stage and methanogenic stage are physically separated into two chambers.
Thus the first stage of acid production is carried out in a separate chamber and only the diluted acids
are fed into the second chamber where bio-methanation takes place and the biogas can be collected
from the second chamber. Considering the problems encountered in fermenting fibrous plant waste
materials the two stage process may offer higher potential of success. However, appropriate
technology suiting to rural India is needed to be developed based on the double stage process
The main features of continuous plant are that:
1) It will produce gas continuously;
2) It requires small digestion chambers;
3) It needs lesser period for digestion;
4) It has fewer problems compared to batch type and it is easier in operation.

(b) Batch plant

The feeding is between intervals, the plat is emptied once the process of digestion is complete. In
this type, a battery of digesters are charged along with lime, urea etc, and allowed to produce gas for
40-50 days. These are charged and emptied one by one in synchronous manner which maintains a
regular supply of gas through a common gas holder. Sometimes the freshly charged digester is
aerated for a few days after which it is closed to atmosphere. The biogas supply may be utilised after
8-10 days.
The main features of batch plant are
1. The gas production in intermittent
2. It needs several digesters for continuous gas production\
3. Batch plants are good for long fibrous materials.
4. The plant is expensive but have less problems and easy for operation.

Dome and Drum Type :

Conventional models of daily fed biogas plants
There are two basic models of biogas plants popular in India:
a. Floating-drum type model biogas plants
b. Fixed-dome type model biogas plants

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a. Floating drum type model biogas plants

These plants are commonly known as KVIC (Khadi Village and Industrial Commission)
plants and were standardized in 1962 and are used widely even now. These plants have an
underground well-shaped digester having inlet and outlet connections through pipes located at its
bottom on either side of a partition wall. An inverted drum (gas holder) made of mild steel is placed
in the digester which rests on the wedge shaped support and the guide frame at the level of the
partition wall and moves up and down along a guide pipe with the accumulation and use of gas. The
weight of the drum applies pressure on the gas to make it flow through the pipelines to the points of
use. The different components of KVIC biogas plants are shown in Fig. a.

The gasholder alone is the costliest component which accounts for about 40% of the total
installation cost of biogas plant. It also needs to be painted regularly for protecting it against
corrosion. These plants can be of any size to cater the needs of the users.

Fig.a. Floating drum type/Khadi Villege Industries Commission Plant (KVIC)

Gas holder:
The gas holder is a drum constructed of mild steel sheets. This is cylindrical in shape with concave
top. The top is supported radially with angular iron stripes. The holder fits into the digester like a

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stopper. It sinks into the slurry due to its own weight and rests upon the ring constructed for this
purpose. When gas is generated the holder rises and floats freely on the surface of slurry. A central
guide pipe is provided to prevent the holder from tilting. The holder also acts as a seal for the gas.
The gas pressure varies between 7 and 9 cm of water column. Under shallow water table conditions,
the adopted diameter of digester is more and depth is reduced. The cost of drum is about 40% of
total cost of plant. It requires periodical maintenance. The unit cost of KVIC model with a capacity
of 2 m3/day costs approximately Rs.14, 000/.
Advantages:

· Easy in construction and operation.

· Provide gas at a constant pressure.

· Gas-volume can be estimated easily with drum height with respect to

its rest position.

· Less chances of leakage of gas.

Disadvantage:

· Transportation to remote villages is difficult and expensive.

· Cost of steel drum is high.

· Corrosion problem occurs after some time, so maintenance is high.

· Life of drum is short in comparison to masonry digester.

b. Fixed dome type model biogas plant

In spite of increasing popularity and acceptance of the KVIC biogas plants by the public,
these biogas plants by and large beyond the reach of most rural people because of high increasing
cost, short life of steel drum. So, there was an apparent need to have alternative inexpensive design
to bring it within the reach of the rural population. Due to these reasons, the floating drum type
biogas plants have been replaced with fixed dome biogas plants. These are :

i. Janta Model Biogas Plants

ii. Deenbandhu Model Biogas Plants

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(i) Janta model biogas plant:
This is the first fixed-dome biogas plant was introduced in the form of the Janta Model
Biogas Plant by Gobar Gas Research Station, Ajitwal in 1978. The main feature of this model is that
the digester and the gas holder are integrated parts of brick masonry structure. The digester is made
of a shallow well having a dome-shaped roof on it. The inlet and outlet tanks are connected with the
digester through large chutes which are called displacement chambers. The gas pipe is fitted on the
crown of the masonry dome and there is an opening on the outlet wall of the outlet displacement
chamber for the discharge of spent digested slurry. The size of these plants is limited to 15 m3 par
day. The different components of Janta Model Biogas Plant are shown in Fig. b.

Fig b. Janta Model Biogas Plant are shown

The design of this plant is of Chinese origin but it has been introduced under the name
―Janata biogas plant by Gobar Gas Research Station, in view of its reduced cost. This is a plant
where no steel is used, there is no moving part in it and maintenance cost is low. The plant can be
constructed by village mason taking some pre-explained precautions and using all the indigenously
available building materials. Good quality of bricks and cement should be used to avoid the
afterward structural problems like cracking of the dome and leakage of gas. This model have a
higher capacity when compared with KVIC model, hence it can be used as a community biogas
plant. This design has longer life than KVIC models. Substrates other than cattle dung such as
municipal waste and plant residues can also be used in janata type plants. The plant consists of an
underground well sort of digester made of bricks and cement having a dome shaped roof which
remains below the ground level is shown in figure.2. below. At almost middle of the digester, there
are two rectangular openings facing each other and coming up to a little above the ground level, act

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as an inlet and outlet of the plant. Dome shaped roof is fitted with a pipe at its top which is the gas
outlet of the plant. The principle of gas production is same as that of KVIC model. The biogas is
collected in the restricted space of the fixed dome; hence the
pressure of gas is much higher, which is around 90 cm of water column.
Advantages:

Cost is low.

Life span is long.

The design is compact and saves space and well insulates due to earth cover.

Disadvantages:

Highly Skilled Mason is required.

Excavation can be difficult and expensive in bedrock.

Fluctuating gas pressure decrease utilization efficiency.

(ii) Deenbandhu biogas plant:

Fig.c. Deenbandhu biogas plant

Deenbandhu model was developed in 1984, by Action for Food Production (AFPRO), a
voluntary organization based in New Delhi. Schematic diagram of a Deenabandhu biogas plant
entire biogas programme of India as it reduced the cost of the plant half of that of KVIC model and
brought biogas technology within the reach of even the poorer sections of the population. The cost
reduction has been achieved by minimizing the surface area hrough joining the segments of two
spheres of different diameters at their bases. The cost of a Deenbandhu plant having a capacity of 2
m3/day is about Rs.8000/. The Deenbandhu biogas plant has a hemispherical fixed dome type of gas

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holder, unlike the floating dome of the KVIC-design is shown. The dome is made from pre-
fabricated Ferro cement or reinforced concrete and attached to the digester, which has a curved
bottom. The slurry is fed from a mixing tank through an inlet pipe connected to the digester. After
fermentation, the biogas collects in the space under the dome. It is taken out for use through a pipe
connected to the top of the dome, while the sludge, which is a by-product, comes out through an
opening in the side of the digester. About 90% of the biogas plants in India are of the Deenbandhu
type.

Working of biogas plant

Initially the digester is filled with a uniformly premixed mixture of dung and water (1:1 ratio)
and the digester may be filled in three or four days or more time depending upon the availability of
the dung. In order to facilitate gas production, addition of 5 to 10% inoculums, taken from a running
biogas plant, will hasten the process by three to four days. In case no inoculums are available,
sewage sludge can also be added. The first two or three installments of gas will not burn because of
excessive CO2.

When the cattle dung is used as feed stock, the biogas plant is to be filled with homogenous
slurry made from a fresh dung and water in a ratio of 1:1 up to the level of the second step in the
outlet chamber (Fig c).

As the gas generates and accumulates in the empty portion of dome of the biogas plant, it
presses down the slurry of the digester and displaces it into the outlet chamber. The slurry level in
the digester falls, whereas in the outlet chamber, it starts rising with the formation of gas. This fall
and rise continues till the level in the digester reaches the upper end of the outlet opening, and at this
stage, the slurry level in the outlet chamber will be at the slurry outlet. Any gas produced after this
stage will escape through the outlet chamber till the gas is not used.

When the gas is used, the slurry which was earlier displaced out of digester and stored in the
outlet chamber begins to return into the digester. The difference in levels of slurry in digester and
the outlet chamber exerts pressure on the gas which makes it flow through the gas outlet pipe to the
points of utilization of biogas.

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 Comparison among KVIC, Janta and Deenbandhu biogas plants

Sr. No. KVIC Janata Deenbandhu

1 The digester of this plant is a deep well shaped Digester of this plant is a shallow well shaped Digester is made of segments of two spheres: one for
masonry structure. In plants of above masonry structure, No partition wall is the bottom and other for the top.
3m3 capacity a partition wall is provided in provided.
middle of the digester.
2 Gas holder is generally made of mild steel. It is Gas holder is an integral part of the masonry The structure described above includes digester and the
inverted into the digester and goes up and down structure of the plant. Slurry from the gas gas storage chamber. Gas is stored in the same way as
with formation and utilization of gas. storage portion is displaced out with the in the case of Janata plants.
formation of gas and comes back when it is
used.
3 The gas is available at a constant pressure of Gas pressure varies from 0 to 90 cm of water Gas pressure varies from 0 to 75 cm of water column.
about 10 cm of water column. column.
4 Inlet and outlet connections are provided Inlet and outlet tanks are large masonry Inlet connection is through A.C pipe. Outlet tank is a
through A.C pipes structures designed to store the slurry large masonry tank designed to store slurry displaced
displaced out of the digester with the out of the digester with the formation of gas.
formation of gas.
5 Gas storage capacity of the plant is governed by It is the combined volume of inlet and outlet It is the volume of outlet displacement chamber and is
the volume of gas holder and is 50% of gas displacement chambers and is 50% of gas 33% of gas produced per day.
produced per day. produced per day.
6 The floating mild steel gas holder needs regular There is no moving part and hence no There is no moving part and hence no recurring
care and maintenance to prevent the gas holder recurring expenditure. It also has long expenditure. It also has a long working life.
from getting worn out because of corrosion. It working life.
also has short life span.

7 Installation cost is very high. It is cheaper than the KVIC type plants. It is much cheaper than KVIC and Janata type plants.
8 Digester can be constructed locally but the Entire plant can be built by a trained mason Entire plant can be built by a trained mason using
gasholder needs sophisticated workshop using locally available materials. locally available materials.
facilities.

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3. Gasification of Bio-mass:

Biomass Gasification Plant works on the principle of heating the organic feed material at
higher temperatures (>700 °C) in controlled atmosphere (oxygen) to produce a combustible gas
called Synthetic Gas/Producer gas which is used as fuel to run a generator for energy generation,
whereas, Biogas Generation Plant is simple in operation. It works on the principle of anaerobic
digestion of the organic feed material to produce biogas which is a mixture of Methane, Carbon
Dioxide, Hydrogen Sulphide etc. This plant is a complex structure and follows relatively
sophisticated operation procedure. The advantage associated with Biomass Gasification is that the
Synthetic Gas/Producer gas produced as the fuel burns more efficiently than the direct burning of
feed stock i.e. Wood etc.

Gasification of biomass involves thermal decomposition in the presence of controlled air. It

is the conversion of solid carbonaceous fuel in to combustible gas mixtures normally known as
producer gas.

Biomass gasification is the thermo chemical conversion of solid biomass into combustible
gas mixtures. Gasification is carried out in a reactor known as a gasifier which converts biomass into
combustible gases by controlled-temperature oxidation with ambient air and subsequent reduction of
the products of combustion with the char. The typical composition of the producer-gas generated
inside the gasifier is given below

COMPOSITION PERCENTAGE ( %)

CO 25

H2 16-20

CO2 10-12

CH4 1-2

N2 Rest

These gases can be cooled, piped and used in furnaces or in internal combustion engines to generate
power.

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Gasifier
Gasifier is an equipment which can gasify a variety of biomass such as wood waste,
agricultural waste like stalks and roots of various crops, maize cobs, etc. The gasifier is
essentially a chemical reactor where various complex physical and chemical processes take place.
Biomass gets dried, heated, pyrolysed, partially oxidised and reduced, as it flows through it.

The gas produced in the gasifier is a clean burning fuel having heating value of about 950-
1200 kcal/m3. Hydrogen (18% - 20%) and carbon monoxide (18% - 24%) are the main constituents
of the gas.
A gasifier is a cylindrical vessel. From top of the gasifier, the necessary quantities of wood
chips are loaded. The bottom of the gasifier is sealed by a gap. The gas generator has a single air
nozzle fixed at an angle to the cylindrical vessel. It is also used for ignition and to monitor the
combustion zone. The gas take off point is located at the bottom. During operation it must be
ensured that the bottom gap is in place and no air would leak through it into the system which is very
important for good performance of the generator.
Construction and Operation of downdraft gasifier

Fig. 1. Schematic view of a Down draft Gasifier

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The bed in a gasifier may be divided into four zones for convenience to understand the chemical
reactions. The four zones are:
a. Dry zone
b. Pyrolysis zone
c. Combustion zone and
d. Reduction zone.
The fuel must pass through all these zones to be completely gasified.
a. Drying Zone:
The drying zone is generally at the top of the gasifier, above the pyrolysis zone. Here the
temperature is not high enough to cause chemical breakdown of the fuel. But any moisture in the
fuel is driven off in the form of water vapour.
b Pyrolysis Zone:
The pyrolysis zone is generally above the combustion and reduction zones. No air is admitted
into this zone and it draws heat from the hotter regions. Once the temperature reaches about 400C.,
a self-sustaining exothermic reaction takes place in which the natural structure of the wood or
other organic material being used as fuel breaks down and water vapour, methanol, acetic acid and
a considerable quantity of heavy hydrocarbons are evolved. The solid material remaining after
pyrolysis is carbon in the form of charcoal.
c. Combustion Zone
The basic chemical reaction that takes place in the combustion zone is the combination of
oxygen in the air with carbon from the fuel to produce carbon dioxide. This is an exothermic
reaction, the temperature ranges between 900C - 1300C in this zone.

C + O2  CO2 (+3938000 kJ/kmol)

If hydrogen is present in the combustion zone then it also reacts with oxygen and produces
water vapour. This is also an exothermic reaction.
2H2 +O2  2H2O
d. Reduction Zone:
From the combustion zone, the hot gases are drawn into the reduction zone. The principle in
the reduction zone is that of carbon dioxide with hot carbon to produce carbon monoxide. This is an
endothermic process. It is referred to as the “Bourdouard” reaction. It is the major combustible
component in the producer gas.
C + CO2  2CO (-172600 kJ/kmol)

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Another important reduction reaction occurs between water vapour and carbon resulting in the
formation of carbon monoxide and hydrogen.
C+H2O  CO + H2
This is called as “water gas” reaction. This is also (in endothermic reaction and takes place at about
900C.
Construction and Operation of Updraft gasifier:

In updraught gasifier air enters below the combustion zone and producer gas leaves near the
top of the gasifier as shown if figure above.. This type of gasifier is easy to build and operate. The
gas produced has practically no ash but contains tar and water vapour because of the passing of gas
through the unburned fuel. Hence, up draught gasifiers are suitable for tar free fuels like charcoal,
especially in stationary engines

Fig.2. Schematic view of a updraft Gasifier

The bed in a gasifier may be divided into four zones for convenience to understand the
chemical reactions. The four zones are:
1. Dry zone
2. Pyrolysis zone
3. Reduction zone and
4. Oxidation zone.
The fuel must pass through all these zones to be completely gasified.
The drying zone is generally at the top of the gasifier, above the pyrolysis zone. Here the
temperature is not high enough to cause chemical breakdown of the fuel. But any moisture in the
fuel is driven off in the form of water vapour. The pyrolysis zone is generally above the combustion

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and reduction zones. No air is admitted into this zone and it draws heat from the hotter regions. Once
the temperature reaches about 400C., a self-sustaining exothermic reaction takes place in which
the natural structure of the wood or other organic material being used as fuel breaks down and water
vapour, methanol, acetic acid and a considerable quantity of heavy hydrocarbons are evolved.
The solid material remaining after pyrolysis is carbon in the form of charcoal.
From top to bottom the processes are:
1. The down flowing fuel is dried by up flowing hot gases with good heat recovery.
2. Down flowing dry fuel is then pyrolysed by the up flowing gasification gases, producing prompt
gas/vapor and charcoal and recovering their heat.
3. Down flowing charcoal at 800-1200°C reacts with up flowing CO2 and H2O resulting from
charcoal combustion to produce CO and H2
4. Down flowing charcoal burns with entering air at the grate at very high temperatures
5. Down flowing ash falls to ash disposal The updraft counter flow gasifier is occasionally used for
biomass in situations involving high ash or where the tars don’t need to be removed for subsequent
combustion.

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4. Applications of gasifier:
(i) Microscale applications
Generally, these gasifier applications get classified for lower power ranges between 1 – 7
kW. This is the range used by most of the farmers for irrigation purpose in the developing countries.
The equipment must be simple, cheap, light in weight and easily transportable. Ideally, the charcoal
gasifiers which are manufactured locally can meet such specific requirements.
(ii). Small-scale applications
Generally, these gasifier applications get classified for power ranges between 7 – 30 kW. The
size of such applications is appropriate for the villages in some developing countries. The cost
should be minimal and it should need less maintenance and operations. Also, it should be reliable
and economically sustainable. The designs should be simple. Moreover, the gasifiers serving such
applications need proper testing.
(iii) Medium scale applications
Generally, these gasifier applications get classified for power ranges between 30 - 500 kW.
These applications are widely used in the small to medium agricultural industries and forestry
industries. Generally, they are used in sawmills, wood cutting industries, and in generating power.
They can be used for supplying power to the remote areas.
The manufacturing, installations can be a bit costly as it requires high equipment and supply
of fuels and such matter to the gasifier. Increase in demand for such type of equipment can result in
lower productions costs. Also, it can impact the standardization of the parts.
(iv). Large-scale applications
Generally, this gasifier application gets classified for higher power ranges between 500 kW
and above. Thus, they are costly and need the utmost care while construction and delivery.
Gasifiers that are costly and highly equipped such as the fixed bed installations serve these
applications. The design is complex and thus needs to be developed by specialized construction
firms and high engineering. The equipment is fully automated and has high customizations.
(v) Other Gasifier Applications
Most of the gasifiers serve many other purposes such as generation of heat. This high
demand and usage are because of the minimal requirements for the tar and moisture content.
As per the high demand of gasifiers and their applications, in future, it can spread across various
industries like
 Pulp industries , Cement industries
 Metallurgy
 Lime industries

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(vi). Direct Thermal Applications.
The primary application for direct heat gasifiers is in industries where fuel oil or coal is being
used to generate process heat or run furnaces and kilns. Industries commonly used for this purpose
are:
1. Cement manufacture, 2. Glass making, 3.Brick making, 4. Ceramics and Pottery.
5. Rubber manufacture, 6.Food processing, 7.Crop drying, 8. Fertilizer production and 9.Chemical
Gasification In Power Generation
Biomass gasification is a process that converts agricultural and industry solid waste
into a clean source of electricity by unlocking the energy in these materials. Using
advanced thermal conversion technology that involves heat, and finely controlled oxygen
supply, the biomass waste is transformed into hydrogen, Carbon Monoxide, Methane and
other inert gasses producing electricity.

The most attractive means of utilising a biomass gasifier for power generation is to
integrate the gasification process into a gas turbine combined cycle power plant. This will
normally require a gasifier capable of producing a gas with heat content close to 19
MJ/Nm3. A close integration of the two parts of the plant can lead to significant efficiency
gains.

Working:

Biomass gasification occurs in four stages:

(i) Drying: water vapor is evaporated off the biomass
(ii) Pyrolysis: the intense heat decomposes the dry biomass into organic gasses, vapors,
carbon and tar, in the absence of oxygen.
(iii) Reduction: the water vapor interacts with carbon, creating hydrogen, carbon monoxide
and methane.
(iv) Combustion: some of the carbon and organic chemicals burn with oxygen to produce
heat, enabling the final stages of the gasification to occur
The resulting gaseous mixture called “producer gas,” “wood gas,” or “syngas,”. This
combination of hydrogen, carbon monoxide and methane provides the energy required to
drive the internal combustion generator set.

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 The syngas from the gasifier must first be cleaned to remove impurities such as
alkali metals that might damage the gas turbine. The clean gas is fed into the combustor of
the gas turbine where it is burned, generating a flow of hot gas which drives the turbine,
generating electricity.

Hot exhaust gases from the turbine are then utilised to generate steam in a heat
recovery steam generator. The steam drives a steam turbine, producing more power. Low
grade waste heat from the steam generator exhaust can be used within the plant, to dry the
biomass fuel before it is fed into the gasifier or to preheat the fuel before entry into the
gasifier reactor vessel.

Another potential use for the combustible gas from a biomass gasification plant is as
fuel for a fuel cell power plant. Modern high temperature fuel cells are capable of operating
with hydrogen, methane and carbon monoxide. Thus product gas from a biomass gasifier
could become a suitable fuel. As with the integrated biomass gasification combined cycle

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plant, a fuel cell plant would offer high efficiency. A future high temperature fuel cell
burning biomass might be able to achieve greater than 50% efficiency.

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