This document compares three main types of biogas plants: floating gas holder type, fixed dome type, and fixed dome with expansion chamber type. It provides figures and descriptions of each plant type. A comparison table outlines key differences between the plants, such as construction materials, gas pressure, maintenance costs, lifespan, and installation costs. The fixed dome with expansion chamber type is concluded to be the most feasible and cost-effective option for generating renewable energy from biogas at the campus.

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Biomass Conversion Research Centre [Comparison of the biogas Plants]
Comparison among Different Models of
BIOGAS Plants
Absar Saleh
SP09-BEC-001
Department Of Chemical Engineering,
COMSATS Institute of Information Technology, LAHORE

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Biomass Conversion Research Centre [Comparison of the biogas Plants]
CONTENTS
• Types of Biogas Plants.
• Figures of Biogas Plants.
• Comparison Table of the Biogas Plants.
• Summary of the entire comparison.
• Conclusion.
• References.

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Biomass Conversion Research Centre [Comparison of the biogas Plants]
• TYPES OF BIOGAS PLANTS
Generally three tyes of basic biogas plants are existing all over the world. The most abundant countries in producing
biogas are United states of America, United Kingdom, Germany, Indian Subcontinent and China.
The Currently working biogas plants are;
Floating Gas Holder Type Biogas Plant.
Fixed Dome Thpe Biogas Plant.
Fixed Dome type With Expansion Chamber Biogas Plant.
Basic Experimental Setup of all three biogas plants is briefly described below:
I. Floating Gas Holder type Plants:
This type of plant basically comprises of an under ground brick masonry digester connected with an inlet and outlet
covered by a floating steel gas holder for gas collection. Gasholder moves up and down guided by a central guide pipe
depending upon accumulation and discharge of gas. Floating gas holder made of mild steel alone accounts for some 40
percent of the total plant cost and accordingly these plants are much more expansive than fixed dome type. The gas holder
is separated from the digester. A partition is provided in digester to encourage circulation. The floating gas holder
provided at the top of the digester helps to keep the pressure constant. The gas holder rises when the pressure is increased
due to production of gas and allows the generated gas to let out through the gas supply pipe. It lowers when pressure is
decreased to stop the supply of the biogas.

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Biomass Conversion Research Centre [Comparison of the biogas Plants]
II. Fixed Dome Type Biogas Plant:
In fixed dome digester , the gas holder and the digester are combined. Gas is stored in the upper part of the digester. Upper
portion of digester pit itself acts as a gas holder. Displaced level of slurry provides requisite pressure for release of gas for
its subsequent use. The pressure inside the digester varies as the gas is collected. Fixed dome digester is usually built
below the ground level and is suitable for cold regions. AAs the plant does not involves any steel parts, it can be built with
local materials and hence its construction costs are low.
III. Fixed Dome With Expansion Chamber type Biogas Plant:
It has a curved bottom and hemispherical top which are joined at their bases with no cylindrical portion in between.
Displaced slurry following digestion moves to the outlet displacement chamber as there is no displacement space on the
inlet side. An inlet pipe connects mixing tank with the digester. This type of biogas palnt is very cheaper as compared
with the other two types of Biogas plants.

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Biomass Conversion Research Centre [Comparison of the biogas Plants]
• FIGURES OF THE BIOGAS PLANTS
1. Floating Gas Holder Type Biogas Plant.

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Biomass Conversion Research Centre [Comparison of the biogas Plants]
2. Fixed Dome Type Biogas Plant.

7. Biomass Conversion Research Centre [Comparison of the biogas Plants]
3. Fixed Dome type With Expansion Chamber Biogas Plant.
Biomass Conversion Research Centre [Comparison of the biogas Plants]
Fixed Dome type With Expansion Chamber Biogas Plant.
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Biomass Conversion Research Centre [Comparison of the biogas Plants]
• COMPARISON TABLE OF DIFFERENT MODELS
Properties Floating Gas Holder
Type Biogas Plant
Fixed Dome Type Biogas
Plant
Fixed Dome with
Expansion Chamber
Type Biogas Plant
Experimental Setup The digester of this Plant
is a deep well shaped
masonry structure. In
these is a partition in
middle of the digester.
Digester of this plant is a
shallow well shaped
masonry structure. No
partition wall is provided.
Digester id made of two
segments of two spheres
one each for the top and
Bottom.
Biogas Holder Gas Holder is generally
made of the mild steel. It
is inverted into the
digester and goes up and
down with the formation
and utilization of gas.
Gas holders the integral
part of the masonry
structure of the plant.
Slurry from the gas storage
portion is displaced out of
the digester with the
formation of gas and comes
back when it is used.
The structure described
above includes digester
and the gas storage
chamber. Gas is stored in
the same way as in the
F.D type plant.
Gas Pressure Remains Constant about
10 cm of water.
Varies from 0-90 cm of
water.
Varies from 0-75 cm of
water.
Maintenance Cost Of maintenance is
high because gas holder
is to be prevented from
corrosion.
Cost of maintenance is low. Cost of maintenance is
low.

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Biomass Conversion Research Centre [Comparison of the biogas Plants]
Life Span Life span is short. Life span is comparatively
long.
Life span is between the
other two plants.
Extra features Identifying the defects in
gas holder is easy.
Space above the gas holder
can be used.
Ther is no moving part
so no recurring
expenditure.
Required work place Requires relatively less
excavation.
Requires more excavation
work.
Requires high excavation
work.
Construction Digester can be
constructed locally. The
gas holder needs
sophisticated workshop
facilities.
A trained mason using
locally available materials
can build entire plant.
Entire plant can be build
by a trained mason using
locally available
materials.
Installation Cost Installation cost is very
high. Over Rs. 6900.00
(Indian Currency)
It is Cheaper then previous
and the plant costs about
Rs.5400.00 (Indian
Currency)
It is much Cheaper than
both plants and its plant
design costs Rs.4000.00
(Indian Currency).

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Biomass Conversion Research Centre [Comparison of the biogas Plants]
• SUMMARY OF THE ENTIRE COMPARISON.
From the study of entire comparison of the biogas plants we got the basic construction aspects and the experimental setup
of a biogas plant that is generally an underground construction of a biogas digester with local materials such a as bricks,
sand, cement etc. the instrumentation needed for the construction of the biogas plant are;
• An underground digester – may be made of bricks, stones, concrete etc
• An inlet pipe with a substrate receptacle,
• An outlet pipe of exhauster slurry,
• A floating gas dome for gas collection,
• A gas outlet pipe
Raw material supplied to the biogas plant can be cow dung ,human waste, wheat crops, sewage, paper waste, field grass
and other cellulosic materials.
• CONCLUSION
Using the described methods of the biogas plants operation the third type of biogas plant which is fixed dome type with
expansion chamber is more feasible and economically favorable than that of other two types of biogas digester palnts to
get the benefits of renewable energy produced from gas at our campus.

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Biomass Conversion Research Centre [Comparison of the biogas Plants]
• REFERENCES
• Biomass for Renewable energy, Fuels and Chemicals (2006), Donald L Klass
• Bio Renewable Resources (2004), Robert C Brown
• Renewable Energy Resources (2005), G N Tiwari and M K Ghosal
• Stewart, D and McLeod, NewZealand Journal of Agriculture, sept.1980
• Wikipedia: http://www.wikipedia.com/
• Microgy: http://www.microgy.com/technology.htm
• Feasibility of an campus biogas operation at the university of Waterloo (2April 005)
• Research Journal : Landfill Biogas and its use for Energy Generation, University of Sao Paulo
• Ofoefule, Akuzuo U. , Nwankwo, Joseph I , Ibeto, Cynthio N, (Biogas Production from paper easte and its blend
with cow dung), Advances in applied sciences research 2010
• Pelagia research Library: http://www.pelagiaresearchlibrary.com
• Oumer Salim Mohamed Kaba, 2007 , Pilot Project for the installation of domestic biogas
• Academic journals: http://www.academicjournals.com/INGOJ
• Journal of achievements in materials and manufacturing engineering (2009) JAMMEP.Vindis,B.Mursec, M.
Janzekovic, F. Cus
• Uzodinma, E.O. and Ofoefule,A.u. , (Biogas production from blends of field grass with animal waste)
• Technical note series, KARI Techniacal Note.10,january2003 (biogas Production)