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Essay On Biogas And Gobar Gas

Home Based Mini Portable Bio-Gas Plant

In this project, we try to make smaller size of portable biogas plant for the use
of energy generated by plant at anywhere. This plant would have very high
portability to the scale of a human being able to move the whole plant by
himself at anywhere. In this project, the design would be made keeping in
mind the plastic material of digester which reduce the weight. This project
stands for increase the scope of using the biogas technology and there by
design plant that will suit the customer focusing on portability, functionality
and usability. This project would also help protect the earth's global warming
which has risen to an alarming rate by creation of a non-conventional energy
source.

Chapter 1
Introduction
1.1Introduction
' Bio-gas plants are generally made from stain less steel, zinc, best quality rubber,
mild steel, aluminium etc. The use of construction material to construct the wall of
the digester of bio-gas plant was limited to a specific period of time. Nowadays, the
body of biogas plant is commonly manufactured through casting process.
' Many improvements have been made in manufacture the body structure of biogas
digester such as change of materials to build the structure of the digester and make
innovations in some or the other ways to make the digester be more efficient to
produce methane gas.

' Biogas plants are widely used in various countries of the world after humans knew
the application of methane gas.
' Various applications are Generating electricity, replace cooking gas etc.
' For example in India, the biogas plants are widely used to generate electricity and
use as a substitute for cooking gas. Methane gas can be produced throughout the
fermentation process. Usually, the waste product such as cow dung shall be
fermented to produce methane gas. From the digester, the methane gas will
voluntarily flow out through the gas outlet straight to outlet container. The used cow
dung, after fermentation can be used as manure for crop cultivation. The biogas
digester must be built to be long lasting, which has a characteristic of corrosive
resistance, high tensile strength, and technical stability.
1.2What is Biogas?
' Biogas is the gas produced by anaerobic digestion of waste materials of plant and
animal origin. Biogas is a mixture of methane (60-70%), carbon dioxide (30.40%)
and traces of other gases like hydrogen sulphide and hydrogen. Methane in biogas
provides a source of fuel without smoke.
' Anaerobic digestion (AD) is the process by which plant and animal material is
converted into useful product by micro-organisms in the absence of air. Biomass is
put inside a sealed tank and naturally occurring micro-organisms digest it, releasing
methane that can be used to provide heat and power. The material left over at the
end of the process, known as bio-slurry, is very rich in nutrients so it can be used as
fertilizer. This means that generation of biogas is carried out by using waste
materials of plant or animal origin which can be capacity source of environmental
pollution if disposed of without conversion. Most importantly it provides an
Portable biogas plant 2
alternate source of renewable energy and thus reduces the burden on use of fossil
fuel as a source of energy. The bio-slurry provides organic fertilizer which, unlike
synthetic fertilizers imparts no catastrophic effect on soil as well as environment.
' Bio-gas technology introduce another alternative source of energy and is fall as an
archetypal appropriate technology that we meets the primary need for cooking gas
in village areas. Using local resources, viz. organic wastes, energy and manure are
derived. Realization of this capacity and the fact that India supports the largest cattle
wealth led to the promotion of National Bio-gas Programmed in a major way in the
late 1970s as an answer to the growing fuel crisis.
' Bio-gas is produced by organic wastes by concerted process of different groups of
anaerobic bacteria. An attempt has been made in this feedback on the work done by
our scientists in understanding the microbiel diversity in bio-gas digesters, their
inter actions and factors affecting bio-gas production, some alternate feedstock, and
uses of spent wastes.
' Various different factors such as bio-gas capacity of feedstock, design of digester,
nature of substrate, pH, tempe. , load rating, hydraulic retention time for bio-gas
plant (HRT), C: N ratio, volatile fatty acids for ph (VFA), etc. influence the biogas
production.

' A technology is suitable if it gets acceptance. Bio-gas plants have steel gained little
acceptance. Generally bio-gas plants have up to now presumably been
inappropriate. Bicycles are appropriate: if a man buys a bicycle, he is proud. It is a
symbol of his advance, his personal achievements. The bicycle is the need for social
recognition. If the person sit on the bicycle and get down because he doesn't know
how to ride bicycle, it is not the abilities of bicycle's owner. The men learns how to
ride and this adapts himself to his bicycle. The people goes to work on it. It is need
for convenience and lowest-cost transport vehicle. The bicycle breaks down. The
person has no money to repair to have it mender. He saves on other expenditure,
because the bicycle is important for his proud. He walks very long distances to the
mender. He adapts to the needs of the bicycle.
' The person can afford this expenditure without getting into economic difficulties.
The bicycle is appropriate to his economic capacity.
' A biogas plant is correctly operated and maintained if it satisfies the user's need for
recognition and convenience. He for his part is then prepared to adapt to the needs
of the biogas plant.
' Biogas plants are appropriate to the technical abilities and economic capacity of
Third World farmers. Biogas technology is extremely appropriate to the ecological
and economic demands of the future. Biogas technology is progressive.
Portable biogas plant 3
' However, a biogas plant seldom meets the owner's need for status and recognition.
Biogas technology has a poor image ("Biogas plants are built by dreamers for poor
people". If you do not want to seem one of the poor, you do not buy a biogas plant.
The image of the biogas plant must be improved.
' The designer makes his contribution by supplying a good design. A "professional
design" that works. One that is built in conformity with contemporary requirements
and models. The biogas plant must be a symbol of social advancement. The biogas
plant must be technically progressive.
' A biogas plant as an investment is in competition with a bicycle or moped, a radio
set or diesel pump, a buffalo or an extension to the farmhouse. The economic benefit
of a biogas plant is greater than that of most competing investments. However, the
plant must also be worthwhile as a topic for the "chat in the market place". So the
design must not be primitive. So the gas bell must be attractively painted. So the
gas pipe must be laid tidily.
' So the fermentation slurry tank must be decently designed and constructed. So giant
pumpkins and flowers must grow around the plant. A good biogas plant is
appropriate. Appropriate to the needs of its owner and his abilities and capacity. It
is appropriate to the necessities of the future.
1.3 Biogas as alternative source of energy
' Unless an appropriate intervention geared towards the development of alternative
renewable energy source is instituted in the near future, India will find itself in a
dangerous situation in terms of sustaining the availability of fuel wood or its
derivative. Thus deforestation and health hazards cannot be reduced without
providing alternatives to the current way of cooking. In the absence of alternate
renewable source of energy, people will continue relentless deforestation that will
endanger the eco-system and their lives beyond repair. Generation of biogas from
cow manure, human excreta and kitchen waste is considered to be one such
alternative. The present project will focus on exploring the feasibility of the use of
kitchen waste as an alternative source of biogas in a portable way.
Portable biogas plant 4
1.4 Biogas Potential
1.4.1 composition of Biogas
SUBSTANCES SYMBOLS PERCENTAGE
Methane CH4 50-70%
Carbon Dioxide CO2 30-40%
Hydrogen H2 5-10%
Nitrogen N2 1-2%
Water Vapour H2O 0.3%
Hydrogen Sulphide H2S Traces
Table no-1
1.4.2 Methane Consumption
' Cooking: 0.45 cubic meters (8cu. ft.) per person per day
' Lighting: 0.12-0.15 cubic meters (4.5cu. ft.) per hour per lamp
' Driving Engines: 0.45 cubic meters (15cu. ft.) per HP per hour
1.4.3 Non-renewable Value equivalent of Biogas
' 1 kilogram LPG = 0.45 cubic meter biogas
' 1 litre gasoline = 0.54 cubic meter biogas
' 1 litre diesel fuel = 0.52 cubic meter biogas
' 1 kilowatt hr. electricity = 1.0 cubic meter biogas
1.4.4 Uses of Biogas
This can be used for-
1. Cooking (like natural gas).
2. Burning in a mantel to get luminous light (0.75 M3 of biogas can light 7 biogas
lamps for an hour).
3. Running a generator to produce electricity and use fan, radio, television, VCP,
electric bulb etc.(The production of 0.75m3 biogas can generate 1 kw-hr, which
can light 25 electric lamps, each rated of 40w for an hour).
4. Running a pump for irrigation.
5. Running a motor vehicle.
6. Running a refrigeration unit to store fruits and crops.
7. Running an incubator etc.
Biogas can be used for providing heat for raising rice seeding silkworms, killing
injurious insects in grain store and even welding and cutting steel. It can be used as
a fuel for internal combustion engine to power fodder grinders, rice mills, and flour
milling machine, generator, automobiles etc. where there is a shortage of oil. Some
of them are still in process trial and need further development.
Portable biogas plant 5
1.5 Benefits of Biogas
Developing country context including India, the benefits of biogas are now
well recognized. It has resulted in a smoke free kitchen, so women and children are
no longer prone to respiratory infections and can look forward to live longer,
healthier lives. Women are spared from the burden of gathering firewood. Both
these factors will contribute to protecting the forests and allowing the forests to
regenerate. The sludge remaining after digestion is rich in valuable nutrients and
can be used as top quality fertilizer that guarantees better crops. In mind areas when
there is no electricity supply, the use biogas, a source of light has enabled women
to engage in evening study have increased literacy and other home and community
activities. Cattle dung is no longer stored in the home, but is fed directly to the
biogas digester along with toilet waste. The anaerobic digestion process also
destroys pathogens. As a result, sanitation has greatly improved.
The common uses of biogas are for cooking, lighting, running an internal
combustion engine, and the effluent can be used as fertilizer in vegetable
propagation.
Biogas is,
' Renewable
' High nutrient fertilizer produced in excess.
' Environment friendly.
' Reduces methane and carbon dioxide release into the air.
' Cheap to produce.
' Many different uses.
' Reduces landfill sites, sewage drainage, and farm manure.
' Clean/ quiet fuel for cars and trucks.
' A biogas plant supplies energy and fertilizer. It improves hygiene and
protects the environment. Abiogas plant lightens the burden on the State
budget and improves working conditions for the housewife. A biogas plant
is a modern energy source. A biogas plant improves life in the country. A
biogas plant can satisfy these high expectations only if it is well designed.
' A biogas plant supplies energy. However, a biogas plant also consumes
energy. Energy is already consumed in the production of the construction
material:
' for 1 m?? of masonry, about 1000 kWh or 180 m?? of biogas,
' for 100 kg of steel, about 800 kWh or 150 m?? of biogas,
' For 1 kg of oil paint, about 170 kWh or 28 m?? of biogas. Energy is
consumed in transporting the materials of a biogas plant. Construction
and maintenance also consume energy.
' for 1 km of transport by lorry, about 1.5 kWh or 1.05 m?? of biogas
Portable biogas plant 6
' For 1 km of transport by car, about 0.5 kWh or 0.35 m?? of biogas.
A biogas plant must operate for one or two years before the energy put into
it is recovered.
1.5.1 Environmental aspects
The main component of urban solid waste in India is organic food wastes.
Most of the solid wastes are generated in rural and are used as fuel. The combustion
of these organic wastes, such as dung and agriculture residue, in the rural and slum
areas of developing countries cause severe ecological imbalance due to loss of
nutrients and serious indoor air pollution. The most important effects of air pollution
are eye infection and respiratory diseases, ranging from predisposition to acute
infection children o chronic obstructive pulmonary diseases in adults. About 700
million women in developing country may be risk of developing such serious
diseases. The traditional use of these organic wastes as fuel is not only harmful to
health but also a most inefficient way of using the energy. The use of biogas
technology will mitigate the adverse effect on health and ecological imbalance and
unimproved fuel efficiency
1.6 Substrates Used
Substrates are biodegradable materials, which can be used for biogas
production. The substrates, which can be loaded to the biogas digester, are the
following:
' Animal Wastes: Chicken Dung, Hog, Cattle, Goat.
' Household Wastes: night soil and kitchen wastes.
' Crop Residues: Corn Stalks, Rice Straws, Banana Leaves, Corncobs, Peanut
Hulls, Cogon and Bagasse, Water Lily and Grass Cuttings.
' Industrial Wastes: Coconut Water, Filter Pressed Cake, Banana And
Pineapple Peelings, Bottling Wastes, Fish Wastes And Meat Processing
Wastes.
' Sewage sludge
' Residues from agriculture
Portable biogas plant 7
Sr.
no.
SUBSTRATE
Biogas Yield
M3 kg-1
1 Pig Manure 0.25-0.50
2 Cow Manure 0.2-0.3
3 Chicken food Waste 0.35-0.60
4 Human Excreta 0.03[m3/person]
5 Fruit And Vegetable Waste 0.25-0.50
6 Food Waste 0.5-0.6
7 Garden waste 0.2-0.5
8 Leaves 0.1-0.3
Table no-2
1.7 Roots of Biogas (History)
' It is believed that a form of this gas was used to heat water from the 10th to 16th
century. By 1850 the concept of biogas was starting to become better understood
and in sewage processing plant was built to create biogas, and this energy was used
to illuminate streetlights.
' The formation of biogas is a natural phenomenon that naturally occurs in wetland,
manure stack, human and animal intestines. For centuries, humans have harvested
the power of bacteriological digestion, by recovering naturally formed biogases to
use them as cooking gas, heating gas or engine fuel.
' In India hundreds of thousands of family digesters were built to provide cooking
fuel and lighting in rural areas. During the Second World War, German army trucks
were fueled with biogas collected from farmers manure (gas engine).
' Over the last 50 years remarkable progress has been made in the development of
anaerobic digesters (bioreactors) to increase methane (CH4) yield and improve its
process flow technologies. The fuel research and development institute of
Bangladesh science laboratory started trying to produce biogas from cow dung and
other organic substances from immediate after independence with a view to settling
the fuel crisis. In 1976 that institute constructed a 3 m3 floating dome type biogas
plant, for the first time. In 1991 fixed Dome type plant has been constructed.
' Nowadays, hundreds of projects around the world, from small dairy farms to large
municipal waste water treatment plants, are demonstrating that biogas recovery
systems are environmentally and economically sound.
Portable biogas plant 8
1.8 Biogas Digester Technologies
Biogas digester can be divided into two categories:
Fig. 1 types of biogas plant
1.9 FLOATING GAS DRUM
' The gas drum normally consists of 2.5 mm steel sheet for the sides and 2 mm sheet
for the cover. It has welded-in braces. These break up surface scum when the drum
rotates.
' The drum must be protected against corrosion. Suitable coating products are oil
paints, synthetic paints and bitumen paints. Correct priming is important.
' One coat is as good as no coat. Two coats are not enough. There must be at least
two preliminary coats and one topcoat.
' Coatings of used oil are cheap. They must be renewed monthly. Plastic sheeting
stuck to bitumen sealant has not given good results. In coastal regions, repainting is
necessary at least once a year, and in dry uplands at least every other year. Gas
production will be higher if the drum is painted black or red than with blue or white,
because the digester temperature is increased by solar radiation. Gas drums made
of 2 cm wire-mesh-reinforced concrete or fibrocement must receive a gaslight
internal coating.
' The gas drum should have a slightly sloping roof (Figure 29), otherwise rainwater
will be trapped on it, leading to rust damage. An excessively steep-pitched roof is
unnecessarily expensive. The gas in the tip cannot be used because the drum is
already resting on the bottom and the gas is no longer under pressure.
Portable biogas plant 9
1.10 FIXED GAS DRUM
' The top part of a fixed-dome plant (the gas space) must be gaslight. Concrete,
masonry and cement rendering are not gaslight. The gas space must therefore be
painted with a gaslight product. Gastight paints must be elastic, this is the only way
to bridge cracks in the structure.
' Latex or synthetic paints (PVC or polyester) are suitable. Epoxy resin paints are
particularly good. Polyethylene is not very gaslight. Hot paraffin coatings also serve
well. The walls are first heated with a torch. Then hot paraffin (as hot as possible)
is applied. Since the paraffin will only adhere to thoroughly dry masonry, it may
have to be dried out first with the aid of a charcoal fire. Fixed-dome plants produce
just as much gas as floating-drum plants - but only if they are gaslight. However,
utilization of the gas is less effective as the gas pressure fluctuates substantially.
Burners cannot be set optimally.
1.11 Reason for selection of Floating Type
' The other digesters are expensive for rural economy in the absence of subsidy and
loan facility, the provision of which has been made in the national biogas program.
' The dome of other types is fixed. Therefore the temperature is lower compared to
floating type temperature due to the fact that direct sunlight comes in the contact of
the slurry. This in turn affects the performance of anaerobic digestion. Floating type
has better digestion at higher temperature.
' For the construction of other digesters, the area required is more compared to the
other types.
1.12 Alternative wastes
' It was reported the feasibility of using industrial canteen waste as a feedstock in
biogas digesters and suggested a reduction in particle size of the waste below 2 cm,
and feeding at the rate of 8'10 TS, for successful operation. Biomethanation
capacity of market waste was studied and reported that the digestion process was
stable at 20 days HRT with 48% reduction in VS and with biogas production of 35
liter kg' 1 d' 1. Also the biogas production from solid waste is originated from
biscuit and chocolate industry
' Although biogas production technology has established itself as a technology with
great capacity which could exercise major influence in the energy scene in rural
areas, it has not made any real impact on the total energy scenario despite the
presence of about 1.8 million biogas digesters. One of its serious limitations is the
availability of feedstock followed by defects in construction, and microbiological
failure. But on reviewing the literature, one finds a long list of alternate feedstock
and their capacity for biogas production.
Portable biogas plant 10
1.13 Biogas designs
Fig. 2 biogas design (1).
Fig. 3 biogas design (2).
Portable biogas plant 11
Fig. 4 biogas design (3).
Fig. 5 biogas design (4).
Portable biogas plant 12
Fig. 6 biogas design (5).
Portable biogas plant 13
Chapter 2
Objective and Problem statement
2.1 Project Synopsis
' The concept of this biogas plant is different from the conventional biogas plant
which is of the scale of a huge sized dome and is fixed at a place. The energy of the
plant cannot be utilized remotely. In creation of the new design of a portable biogas
digester, the various stages included are Concept generation, Design of the concept
and fabrication. The working model may be presented in the days to come
depending upon the retention time needed for the biogas generation.
' The body of this biogas plant is designed to decrease its weight by using plastic and
PVC material to make it as light as possible thereby increase its portability
characteristic. The portability is magnified by providing this portable biogas plant
with a U shaped handle on the digester to give it the best possible portability onthe-
go and make it user friendly.
' The volume of the body also designed to get the bigger size as possible but still suit
the portability characteristic with it.
' The project involves the developing and analysis of the body shape of the digester
to make it more efficient to produce methane gas and also will concern about the
structure strength, durability, ergonomic factor and convenience. The new concept
of this digester is primarily being focused on the portability factor. All the
specifications will be verified to avoid materials and fund wasting. For the safety
feature, stoppers are provided in order to save the dome from flying away due to
the pressure of the biogas.
' In the overall process of designing, developing and fabricating this plant would
enable the application of the skills learned and would also be the use of all the basic
knowledge of Manufacturing Process I and II, Alternate Energy Sources etc.
2.2 Problem Statement
' Usually all the biogas plants are used to produce methane gas and the size of the
digesters are commonly bigger in size. The conventional biogas plants are the ones
which cannot be mobilized. The rural areas of India highlight the people who are
underprivileged and despite having a conventional sized biogas plant, they are
unable to use it due to absence of portability.
' This portable biogas plant would enable a human being to have the power in hands
using several applications which will be applied to this portable system and carry it
Portable biogas plant 14
to a particular remote area and can utilize the energy and power generated by the
plant remotely.

' It would also promote the use of renewable source of energy and thereby protecting
the earth and also encourage the sustainable development of the earth.
' For the solution, a portable biogas with such extent of portability that you can carry
it with your own hands can stand as a substitute.
' This problem has now a solution. 'The Portable Biogas Plant' which provides the
portability in the best possible way.
2.3 Objective of this thesis project
' The objectives are given below:
' To design a portable biogas plant for domestic uses.
' To lower the construction cost of portable biogas plant.
' To make the better performance of plant
' Construction of portable model biogas plant.
' To produce organic fertilizer.
2.4 Difference with previous work
' The difference between previous thesis and our thesis;
' We made this plant with better performance which is more efficient than the first
plant.
' The taper section of the digester is eliminated in the new plant which increases the
effective volume of the digester, hence increasing the efficiency.
' The ergonomic factor is improved by providing wheels at the bottom of the digester
and a curved handle which is easy to hold for the movement of the new plant.
Portable biogas plant 15
Chapter 3
Literature review
' Ravi P. Agrahar, G. N. Tiwar (2011), 'Parametric study of portable floating
type biogas plant'
In this paper, an attempt has been made to design and test the performance
of a portable floating type biogas plant of volume capacity 0.018 m3 for outdoor
climatic condition of New Delhi, India. The field study has been carried under the
monsoonal season of New Delhi, India. In this experiment, we have taken an
aluminium made digester of 30 Kg slurry capacity for batch system. In the batch
system, the slurry has been added once to the digester for whole duration of the
process. The rate of biogas production with slurry temperature has been observed.
It has been observed that (i) the biogas production depends strongly on slurry
temperature and (ii) the retention period is nearly 85 days. The range of slurry and
ambient temperature of atmosphere recorded during the observed period have been
found as 26 to 42 ??C and 30 to 40 ??C respectively. Physical and chemical analysis
of biogas and slurry have also been carried out. Further, the CO2 mitigation and
carbon credit has also been evaluated for the present system.
' Anu Andrews Oommen ,(2007), ' Design of Portable Biogas plant'
The initial study for obtaining the data was done with the product context
study, Gemba study, market survey and understanding the technology through
present dealers and other sources. 16 plants were visited as a part of user and gemba
study with questionnaires, which helped in understanding the existing product and
user needs. The method of quality functional deployment (QFD) was adopted to
derive the technical features of the product from the customer needs. Product design
specifications were finalized with the help of QFD. The concept were generated and
finalized to solve the basic needs. From the generated concept, one concept was
finalized after consulting with experts. The final concept was materialized to quasiprototype
in order to validate the concept. The validation pertaining to functionality
and usability factors were recorded. This study shows the need and scope of such
kind of biogas plant in the current scenario to create alternate fuel for cooking.
Portable biogas plant 16
' Sunil MP, Ashik Narayan, Vidyasagar Bhat, Vinay S (2013), 'Smart Biogas
Plant'
The project investigates the development of a low cost, efficient, portable
biogas plant for the generation of energy from discarded kitchen wastes and food
waste. The main purpose of the project is to cut down on the landfill wastes and
generate a reliable source of renewable, decentralized source of energy for the
future. Biogas generation does not require a complex technology and can be applied
globally. Kitchen waste discarded causes public health hazards, the project also
looks into prevention of various diseases including malaria, typhoid and also meets
the social concerns in the society. Household digesters represent a boon for urban
and rural people to meet their energy needs. These digesters help in two ways: one
is to reduce waste and the other is to provide valuable energy.
' Van Helmont recorded that decaying organic material produced FL ammable
gases. In 1776, Volta resolved that there was a direct connection between how much
organic material was used and how much gas the material produced.
' That this combustible gas is methane was established by the work conducted
independently by John Dalton and Humphrey Davy during 1804'1808 (Tietjen
1975).
' A Frenchman, Mouras, applied anaerobic digestion for the first time to treat
wastewater, in his invention of a crude version of a septic tank in 1881, named by
him 'automatic scavenger' (McCarty et al. 1982 ) .
' India is credited for having built the first-ever anaerobic digester, in 1897, when
the Matunga Leper Asylum in Bombay (Mumbai) utilized human waste to generate
gas to meet its lighting needs
' Agapitidis I. and Zafiris C. (2006).
'Energy Exploitation of Biogas: European and National perspectives'. 2nd
International Conference of the Hellenic Solid Waste Management Association.
' Al Seadi, T. (2001).
Good practice in quality management of AD residues from biogas
production. Report made for the International Energy Agency, Task 24- Energy
from Biological Conversion of Organic Waste. Published by IEA Bioenergy and
AEA Technology Environment, Oxfordshire, United Kingdom.
' Al Seadi, T.; Holm Nielsen J. (2004). Utilization of waste from food and
agriculture:
Solid waste: Assessment, Monitoring and Remediation; Waste management
series 4; ELSEVIER; ISBN 0080443214, 735-754.
Portable biogas plant 17
' Amon, T. et al. (2006).
Optimization of methane production from energy crops with the Methane
Energy Value Published by the Federal Ministry for Transport, Innovation and
Technology, Vienna, Austria.
' Angelidaki, I. et al. (2004).
Environmental Biotechnology. AD ' Biogas Production. Environment &
Resources DTU, Technical University of Denmark.
' Ivan Simeonov, Dencho Denchev and Bayko Baykov (2006).
'Development of new technologies for production of heat and electric power
from organic wastes for increasing the economic efficiency of the final products',
Advances in Bulgarian Science, no 1, 15-24,
' Karthik Rajendran, Solmaz Aslanzadeh and Mohammad J. Taherzadeh,
(2012), 'Household Biogas Digesters'
This review is a summary of different aspects of the design and operation of
small-scale, household, biogas digesters. It covers different digester designs and
materials used for construction, important operating parameters such as pH,
temperature, substrate, and loading rate, applications of the biogas, the government
policies concerning the use of household digesters, and the social and environmental
effects of the digesters. Biogas is a value-added product of anaerobic digestion of
organic compounds. Biogas production depends on different factors including: pH,
temperature, substrate, loading rate, hydraulic retention time (HRT), C/N ratio, and
mixing. Household digesters are cheap, easy to handle, and reduce the amount of
organic household waste. The size of these digesters varies between 1 and 150 m3.
The common designs include fixed dome, floating drum, and plug flow type. Biogas
and fertilizer obtained at the end of anaerobic digestion could be used for cooking,
lighting, and electricity
.
' Avinash Kumar Agarwal and Mritunjaya Kumar Shukla, (2009), 'Portable
biogas bottling plant'
Biogas contains about 65% methane, 30'35% carbon dioxide, traces of
hydrogen sulphide and moisture. It has been observed that diesel engines get
severely damaged, when operated on biogas for long duration. Presence of these
corrosive gases make biogas unsuitable for transportation application. By removing
CO2 and trace acidic gases like H2S and moisture, biogas can be converted into
natural gas (which is mainly methane). Natural gas is a more environment friendly
and its usage leads to lower engine wear. CO2 and H2S can be removed successfully
from biogas using suitable scrubber techniques. Remaining methane gas (natural
gas) can be compressed to high pressures of the order of 240 bar using multistage
compression and CNG cylinders can be filled. This bottled gas can be used to
operate automobiles by suitable modifications in the induction system of the
engines. This fuel gas derived from biogas is a good engine fuel. [Received:
February 21, 2009; Accepted: June 11, 2009]
Portable biogas plant 18
Chapter 4
Fermentation theory
4.1 principle of fermentation
BIOGAS production is a microbial process. A microbes involved in
BIOGAS production grow in the absence of air (Oxygen). The most important
organisms are tiny bacteria. Different groups of bacteria act upon complex organic
materials in the absence of air to produce biogas rise in the methane. The process
involved combined action of four groups of bacteria, in four stages in the BIOGAS
plant. The first stage is the degradation of high molecular weight substances like
cellulose, starch, protein, fats, etc. present in organic materials into small molecular
weight compounds like fatty acids amino acid, carbon dioxide and hydrogen, this is
brought about by a hydrolytic group of bacteria, in the second stage the end products
of the first stage are converted into acetate and hydrogen by acetogens, in order to
produce more acetate a third stage is involved in which organism s known as
homoacetogens convert hydrogen and simple compounds produce in the first stage
and second stages into acetate. The fourth stage is the conversion of acetate and
some other simple compounds like format, carbon dioxide and hydrogen into
methane. This is brought about by a unique group of organisms known as
methanogens; methane being lighter than air raises out of the system and can be
collected and used for various purposes.
4.2 Mechanism of biogas fermentation
Biogas fermentation is an anaerobic process by which organic materials are
degraded to produce methane as in end product in the absence of molecular oxygen
.the microbes involved in biogas fermentation are called microbes include nonmethane
producing bacterial and methane producing bacteria .The non-methane
producing bacteria can be divided into two groups
a) Fermentative bacteria
b) Hydrogen producing bacteria.
People knew very few little about the intrinsic law of biogas fermentation until
Hungate carried out an extensive study on the anaerobic cultivating technique of
methane producing bacteria and methane producing bacteria in 1950. He also
worked on the variety of biogas microbes the stability of fermentation process and
Portable biogas plant 19
mutual relationship between the different stages in the whole process of biogas
fermentation in 1979. Brayant divided the process into three phases. They are 1:
Hydrolysis and Fermentation 2: Production of Hydrogen & Acetic Acid 3:
Methangoenesis these phases are describing below with chemical reaction and
schematically illustrated.
4.2.1 STAGE 1: Hydrolysis and fermentation:
Fermentative bacteria, a very complicated and mixed group of are involved
in the first stage of biogas fermentation .They hydrolyse various complex organic
substances .They use the oxygen in air trapped inside the digester and oxygen from
water for breaking down foodstuffs the hydrolyse carbohydrates simple sugars and
alcohol proteins into amino acids and fats into soluble organic mater and long chain
fatty acid s(fulford-1988).
C6H12O6 + H2O C6H12O6 + H2O 2CH3COOH + 2CO2 + 4H2
C6H12O6 C3H7COOH + 2CO2 + 2H2
C6H12O6 + 2H2 2C3H7COOH + H2O
4.2.2 STAGE2: Production of Hydrogen & Acetic Acid
Hydrogen producing acetogenic bacteria take part in the second stage of
Biogas fermentation. The substances produced in the first stage are further
decomposed into volatile fatty acids carbon dioxides and hydrogen, acetic acid is
a major constituent at this stage.
C2H5COOH + 2H2 O CH3COOH + CO2+ 3H2
C3H7COOH + 2H2 O CH3COOH + 3H2
The variety and quantity of fermentative and hydrogen producing acetogenic
bacteria vary with fermentation material .Judging from their reaction to oxygen
they are mostly anaerobic and facultative anaerobic bacteria. If some of air
present at this stages the digestion process stops.
Portable biogas plant 20
4.2.3 STAGE 3: Methaogeneis:
Methane producing bacteria takes part in this stage to convert the acetic
acid, hydrogen carbon dioxide and formic acid produced in the previous stages to
produce methane through metabolism by acetoclastic methane bacteria and
hydrogen utilizing methane bacteria according to reactions-
ACETOCLASTIC
CH3COOH CH4 + CO2
Methane bacteria
Hydrogen Utilizing
CO2 + 4H2 CH4 + 2H2O
Methane bacteria
Fig. 7 the Anaerobic Process
Source: Intermediate Tech. publications,
U.K.1988
Portable biogas plant 21
In fact these stages are not separate from one another each stage provides
substrates, energy and suitable media for succeeding stage. The last stage regulates
and stimulates biogas fermentation and enables the whole system dynamic
equilibrium (yongfy, 1989)
4.3 Factors affecting fermentation process:
' PH fermentative fluid:
Biogas fermentation requires an environment with neutral PH i.e. usually
7.0 to 8.0.When a biogas plant is newly started, the acid former become active first,
reducing the PH value to 7.0 by increasing acid content. The mthanogens then start
using this acid increasing the PH back to neutral. A working plant is therefore
buffered that are the acid level is controlled by the process itself.
' Fermentative temperature:
The gas production efficiency increases with temp. The length of retention
time of material is also determined by the fermentative temperature. The higher the
temperature the faster the slurry is needed. If the fermenting temperature is between
32.20 and 370 the retention time for the fermentation of the cattle dung or plant
waste matter will be between 28and 30 days. Where AS 23.90 it takes between 50
to 70 days to digest the material completely. The Chenghu Research Institute also
ascertained that a higher temperature between 45 to 6000c the retention time then
even reduces to 10 says.
However a stable of fermenting temperature is required to maintain the normal state
of biogas fermentation. Biogas microbes especially method producing bacteria are
sensitive to sudden change of temp. The ideal temp. Is about 3500 C. if the slurry
temp. Is lower than optimum, gas production will be stopped. The generation of
biogas will be slowed down noticeably if there is an abrupt change of temp. Of 1000
C or more.
' Anaerobic Environment:
The main anaerobes among the biogas microbes i.e. the methane producing
bacteria are very sensitive to oxygen. They die if they are exposed to air. So it is
an obvious criterion to create an anaerobic condition for the mehanogenic bacteria.
At the beginning of fermentation, a small amount of oxygen and aerobes get into
the digester along with the feed stuck. These aerobes consume the oxygen and
create suitable anaerobic condition for struck anaerobes. To ensure an anaerobic
environment the digester must be fully seal so that there is no leakage of gas or
water.

Portable biogas plant 22
' Effective of toxins on biogas fermentation:
Industrial effluent can contain toxic materials which may kill methane
producing bacteria. Antibiotics, pesticides, detergent, chlorinated hydrocarbon such
as chloroform and other organic solvent also kill bacteria and there by stop the
functioning of digester. Therefore, care must be taken so that the fermentation
materials and water used are not polluted by such materials.
' Water content:
Suitable water content is required for the metabolic activities in biogas
fermentation. The water content should be around 90% of the weight of total
content. Too much or too much little water both is harmful.
4.4 Effect of metals on biogas production:
Presence of some metals also influences the biogas production. The addition
of calcium (5mm) cobalt (50 ??g g' 1 TS), iron (50 mm), magnesium (7.5 mm),
molybdenum (10'20 mm), nickel (10 ??g g' 1 TS) individually as well as in
combination enhanced the biogas production and attributed this to the increased
methanogenic population in the digesters. The addition of nickel at 2.5 ppm
increased the biogas production from digesters fed with water hyacinth and cattlewaste
blend and attributed this to higher activity of nickel-dependent metaloenzymes
involved in biogas production. The iron or manganese at 1100 ??g g' 1 of
dry matter did not influence the yield of biogas. However, the addition of iron as
ferrous sulphate at 50 mm level showed faster bioconversion of both the cow dung
and poultry waste. In the case of cobalt, (0.2 mg l' 1) improved the gas yield and
methane content of gram clover silage-fed digester. The addition of cobalt, nickel,
and iron increased the biogas production from mango peel-fed digester which was
several folds higher than the control. The addition of borax and di-borane at 0.2 g/l
increased the gas production from digesters fed with water hyacinth as the substrate.
4.5 Fermentation materials and gas production
Any substance can be digested in the biogas plant, but the rate and
efficiency of digestion of the fermentation depends on the physical and chemical
form. The cattle dung is the easiest feed stock for the digest as it already contains
the right bacteria and is broken down chemically by acids and enzymes in the
animals gut. Raw materials containing cellulose lignin are difficult to digest. Gas
production from different fermentation materials depends on temp. Retention time,
correct operation of the plant etc. bacteria are most active a temp. Of 350c and stops
at 100c.
Portable biogas plant 23
4.6 Analysis of the products of biogas (theoretically):
The products of the biogas are CO2, CH4, H2S etc. and it has unknown the
percent weight of these gasses. First, it is required to find out the present weight
analysis of the products of biogases. In some cases the analysis of the gases may
also be calculated from an analysis of the product. The or sat apparatus, schematic
sketch of which is shown in following figure, is one device that can be used to
make analysis of the products of gases.
Portable biogas plant 24
Chapter 5
Work history
5.1 work history
The step by step work done during this entire term for the conduction of this
dissertation is described below. The various activities are listed below.
' Problem statement
Existing biogas problem of portability.
' Concept generation
Creation of idea of a home base mini portable biogas plant.
' Literature survey
Referred internet and books for theory of biogas plant for statistics and the
current biogas plant scenario. The basic of biogas studied.
' Concept planning
Review the type of biogas plant.
' Select final concept
The fixed dome type biogas plant was selected for the creation of a portable
one
' Design specification and material selection
Calculation based on digester design carried out. Material selection plastic and PVC
done due to ease of portaility.
5.2 Various Parts of our Portable Biogas Plan
TYPE I
' Inlet hose
' Outlet Elbow
' Digester
' Dome
' Outlet gas pipe
' Gas tube
' Handle
Portable biogas plant 25
' Bunsen Burner
Sr.
no.
Part Diameter (m) Height Length (m)
1 Inlet pipe 0.0508 - 0.4
2 Outlet Pipe 0.1016 - 0.25
3 Digester 0.3012 0.6069
4 Air Gap 0.0040 - -
5 Gas Valve 0.02 - -
6 Gas Tube 0.02 - 1.0
Table no-3
5.3 Raw Material Specifications
The basic raw material we will be using in the digester will be cow dung.
Furthermore, after the complete start of yield of the biogas, other raw materials
may be used. The raw material specifications of the cow dung are provided below:
At 15
0
C, 1 Kg of dry dung gives 0.186 m
3
of gas. The ratio of dry dung
to water in dung is 1:4. Normally 1 Kg of wet dung is mixed with to get the slurry.
The duration of each cycle depends upon the ambient temperature. Hence if the
gas requirement and duration of cycle are known, then the amount of the water and
dung required can be estimated.
The volume of the slurry is equivalent to the 50%of the volume of the
digester. Hence the slurry would be kept at the half level of the digester.
Portable biogas plant 26
Chapter 6
Designs
6.1 Shape and static loading
' A biogas plant should be watertight. The gasholder must be gaslight. For this reason
a biogas plant must have no cracks. But structures of masonry or concrete always
crack. One can try to keep the cracks small. And one can determine the position
where the cracks are to arise.
' Cracks always arise where the tensile stresses are highest. Tensile stresses arise
from tensile forces, flexure, displacements, and settling and temperature
fluctuations. When mortar or concrete sets, shrinkage cracks also form. Stresses are
high where the "external" forces are high. "External" forces are earth pressure, dead
weight and applied load. Stresses are highest where the "internal" forces are highest.
"Internal" forces are flexural, normal, gravitational and torsional forces. The
"external" forces can be reduced by favourable shaping of the structure. The liquid
pressure and earth pressure are less in a low biogas plant. This is because both
depend directly on the height.
' The "internal" forces can also be reduced by favourable shaping of the structure. If
the "external" forces can act in one direction only, high "internal" forces arise. If,
however, the "external" forces can be distributed in a number of directions, small
"internal" forces arise. This is the case with all curved surfaces or "shells".
' Slabs will support a heavier load than beams for a given thickness of material. A
curved shell supports more than a flat slab. A shell cuned in more than one
dimension supports more than a shell of simple curvature. Curved structural
components are more rigid; the stresses are smaller in them. Just imagine how thick
the shell of a hen's egg would have to be if it were shaped like a cube! Cracks arise
where stresses are high. Particularly high stresses - "peak stresses" - arise at points
where the stress pattern is disturbed. Such disturbances occur at edges, angles,
corners and under concentrated, applied or other loads. Disturbances arise along the
line of intersection of surfaces. Cracks form at these points due to peak stresses.
Peak stresses always arise at the edges of angular structures. For this reason the gas
space of a fixed-dome plant must never be angular.
' Cracks arise owing to tensile stresses. If a component is under compression, it is
free from cracks. The gas space of a fixed-dome plant should therefore always be
Portable biogas plant 27

under pressure at every point. The liquid pressure of the fermentation slurry is
directed outwards. The earth pressure is directed inwards. If the two forces balance
reliably, the load on the structure is relieved. In a vaulted shape' the external loading
is obtained even if the earth is stiff and cracked owing to drought. A round shape is
always a good shape,
' Because a round shape has no corners. Because its load pattern is more favourable.
And because it uses less material. A round shape is often easier to build than an
angular one. The rounder the better!
6.2 design specification
' The volume of the digester Vd in m3 is given by:
Vd = Vf XTr
Where Vf = volume of the Slurry Fluid in m
3
Tr = Retention Time in days
' The volume of the Slurry Fluid Vf in 'm
3
' added per day is given by:
Vf = mo / rm
Where mo = Dry Mass of Slurry in kg
rm = Density of dry mass (~50kg/m
3
)
' The Dry mass weight mo' of biomass added per day in 'kg is given by:
mo =Vf X rm
' The volume of biogas generated in m3 is given by:
Vb = C X mo
Where C = Biogas/Dry mass
Portable biogas plant 28
6.3 Calculation
TYPE: 1
TO find the volume of the digester Vd in 'm'
Average Diameter D in m = = (0.1524+0.45)/2
= 0.3012 m
Therefore,
Volume of Tank Vd = Pi/4 D
2
H; Where H=Height of Digester Tank
=0.785 ?? (0.3012)2 ?? 0.48
=0.0348 m2
The Retention Time Tris estimated using the ambient temperature of the process of
fermentation which is 14-15 Days at 30-35
0
C.
To find the volume of the Slurry Fluid Vf (m3
)
Volume of Fluid Vf =Vd / Tr; Where Tr= Retention Time
=0.0348 / 14
=0.00248 m
3
To find the dry mass weight of biomass = mo'(kg)
Dry mass Weight mo (kg) = Vf X rhom; Where rhom= Density of dry mass
~ 50 kg/ m
3
= 0.00248 X 50
= 0.124 kg/day
Portable biogas plant 29
To find the Volume of Biogas generated
Volume of biogas Vb in m3 =C Xmo; Where C= Biogas/Dry mass ~ 0.2-0.4 m3/kg
=0.4 X 0.124
=0.049~1.0 m3
=0.05 m3
Hence it is estimated that the biogas generated per day will be 0.5 m3
Portable biogas plant 30
Chapter 7
Advantages of our portable biogas plant
over other plants
7.1 comparison.
Sr
no.
Parameter Our
portable
biogas plant
Sintax
type
biogas
plant
Traditional
type biogas
plant
1 Portability Easily
moveable
Carry in
truck
Stationary
2 Material of
Construction
Plastic,
PVC
Polyethylene Bricks and
Concrete
3 Space required 1 m2 /- 6.25 m2 10 to 100 m2
4 Effect of
Temperature
Very less Moderate Large
5 Gas pressure Constant Constant Vary
6 Maintenance None None High
7 Amount of
Feed
Very less Less Large
8 Investment Negligible Less High
9 Payback period 1 month 2 years 3-4 years
10 Installation Easiest Moderate Cumbersome
Table no-4
Portable biogas plant 31
7.2 Required Area Comparison
The area occupied by our portable biogas plant compared with conventional biogas plant
as well as other portable ones is shown below,
OUR
PORTABLE
BIOGAS
PLANT
CONVENTIONAL
BIOGAS PLANT
OTHER PORTABLE
BIOGAS PLANT
AREA
(m2)
1-2 m2 ~10 to 100 m2 ~6.25 m2
Table no-5
Portable biogas plant 32
Chapter 8
Result Analysis

There are several results obtained by this dissertation:
' The volume of the biogas that will be generated per day for biogas plant is calculated
and found out to be 0.05 m3/day.
' The volume of the slurry fluid for biogas plant is calculated and found out to be
0.497 m3/day
' The dry mass of the biomass to be added per day for biogas plant is calculated and
is found out to be 0.24 kg/day.
' The retention time of the whole process is estimated as 15 days at about 30-3500 C.
Portable biogas plant 33
Chapter 9
Conclusion
' We conclude from this dissertation that the biogas plant developed is highly
portable in nature and can be remotely taken to any place and the energy
generated from the plant can be utilized portably.
' Several applications of this biogas plant can be made which would further
increase the usability of the plant.
' This portable biogas plant can also be used in the application of PETROMAX
which provides a light and not a flame.
' This application can be useful to the rural Indian people who work at night in the
farms to make their ends meet.
Portable biogas plant 34
Chapter 10
Reference
' http://igadrhep.energyprojects.net/
' http://en.wikipedia.org/wiki/Biogas
' www.biogas-india.com
' www.envitec-biogas.com
' www.biogas-renewable-energy.info/
' www.instructables.com/id/Bio-gas-plant-using-kitchen-waste/
' www.google.com ' for finding some knowledge about it.

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Biogas typically refers to a mixture of different gases produced by the breakdown of organic matter in the absence of oxygen. Biogas can be produced from raw materials such as agricultural waste, manure, municipal waste, plant material, sewage, green waste or food waste. Biogas is a renewable energy source.

Biogas can be produced by anaerobic digestion with methanogen or anaerobic organisms, which digest material inside a closed system, or fermentation of biodegradable materials.[1]

Biogas is primarily methane (CH
4) and carbon dioxide (CO2) and may have small amounts of hydrogen sulfide (H
2S), moisture and siloxanes. The gases methane, hydrogen, and carbon monoxide (CO) can be combusted or oxidized with oxygen. This energy release allows biogas to be used as a fuel; it can be used for any heating purpose, such as cooking. It can also be used in a gas engine to convert the energy in the gas into electricity and heat.[2]

Biogas can be compressed, the same way as natural gas is compressed to CNG, and used to power motor vehicles. In the United Kingdom, for example, biogas is estimated to have the potential to replace around 17% of vehicle fuel.[3] It qualifies for renewable energy subsidies in some parts of the world. Biogas can be cleaned and upgraded to natural gas standards, when it becomes bio-methane. Biogas is considered to be a renewable resource because its production-and-use cycle is continuous, and it generates no net carbon dioxide. Organic material grows, is converted and used and then regrows in a continually repeating cycle. From a carbon perspective, as much carbon dioxide is absorbed from the atmosphere in the growth of the primary bio-resource as is released ,when the material is ultimately converted to energy.

Production[edit]

Main article: Anaerobic digestion

The biogas is a renewable energy that can be used for heating, electricity, and many other operations that use a reciprocating internal combustion engine, such as GE Jenbacher or Caterpillar gas engines.[4] To provide these internal combustion engines with biogas having ample gas pressure to optimize combustion, within the European Union ATEX centrifugal fan units built in accordance with the European directive 2014/34/EU (previously 94/9/EG) are obligatory. These centrifugal fan units, for example Combimac, Meidinger AG or Witt & Sohn AG are suitable for use in Zone 1 and 2 .

Other internal combustion engines such as gas turbines are suitable for the conversion of biogas into both electricity and heat. The digestate is the remaining inorganic matter that was not transformed into biogas. It can be used as an agricultural fertiliser.

Biogas is produced either;

Projects such NANOCLEAN are nowadays developing new ways to produce biogas more efficiently, using iron oxide nanoparticles in the processes of organic waste treatment. This process can triple the production of biogas.[5]

Biogas plants[edit]

A biogas plant is the name often given to an anaerobic digester that treats farm wastes or energy crops. It can be produced using anaerobic digesters (air-tight tanks with different configurations). These plants can be fed with energy crops such as maize silage or biodegradable wastes including sewage sludge and food waste. During the process, the micro-organisms transform biomass waste into biogas (mainly methane and carbon dioxide) and digestate.

Key processes[edit]

There are two key processes: mesophilic and thermophilic digestion which is dependent on temperature. In experimental work at University of Alaska Fairbanks, a 1000-litre digester using psychrophiles harvested from "mud from a frozen lake in Alaska" has produced 200–300 liters of methane per day, about 20%–30% of the output from digesters in warmer climates.[6]

Dangers[edit]

The air pollution produced by biogas is similar to that of natural gas, but with an additional risk from the toxicity of its hydrogen sulfide fraction and any unburned methane that escapes is a potent and long lived greenhouse gas.

Biogas can be explosive when mixed in the ratio of one part biogas to 8-20 parts air. Special safety precautions have to be taken for entering an empty biogas digester for maintenance work. It is important that a biogas system never has negative pressure as this could cause an explosion. Negative gas pressure can occur if too much gas is removed or leaked; Because of this biogas should not be used at pressures below one column inch of water, measured by a pressure gauge.

Frequent smell checks must be performed on a biogas system. If biogas is smelled anywhere windows and doors should be opened immediately. If there is a fire the gas should be shut off at the gate valve of the biogas system.[7]

Landfill gas[edit]

Main article: Landfill gas

Landfill gas is produced by wet organic waste decomposing under anaerobic conditions in a biogas.[8][9]

The waste is covered and mechanically compressed by the weight of the material that is deposited above. This material prevents oxygen exposure thus allowing anaerobic microbes to thrive. Biogas builds up and is slowly released into the atmosphere if the site has not been engineered to capture the gas. Landfill gas released in an uncontrolled way can be hazardous since it can become explosive when it escapes from the landfill and mixes with oxygen. The lower explosive limit is 5% methane and the upper is 15% methane.[10]

The methane in biogas is 20 times more potent a greenhouse gas than carbon dioxide. Therefore, uncontained landfill gas, which escapes into the atmosphere may significantly contribute to the effects of global warming. In addition, volatile organic compounds (VOCs) in landfill gas contribute to the formation of photochemical smog.

Technical[edit]

Biochemical oxygen demand (BOD) is a measure of the amount of oxygen required by aerobic micro-organisms to decompose the organic matter in a sample of material being used in the biodigester as well as the BOD for the liquid discharge allows for the calculation of the daily energy output from a biodigester.

Another term related to biodigesters is effluent dirtiness, which tells how much organic material there is per unit of biogas source. Typical units for this measure are in mg BOD/litre. As an example, effluent dirtiness can range between 800–1200 mg BOD/litre in Panama.[citation needed]

From 1 kg of decommissioned kitchen bio-waste, 0.45 m³ of biogas can be obtained. The price for collecting biological waste from households is approximately €70 per ton.[11]

Composition[edit]

The composition of biogas varies depending upon the substrate composition, as well as the conditions within the anaerobic reactor (temperature, pH, and substrate concentration).[13]Landfill gas typically has methane concentrations around 50%. Advanced waste treatment technologies can produce biogas with 55%–75% methane,[14] which for reactors with free liquids can be increased to 80%-90% methane using in-situ gas purification techniques.[15] As produced, biogas contains water vapor. The fractional volume of water vapor is a function of biogas temperature; correction of measured gas volume for water vapour content and thermal expansion is easily done via simple mathematics[16] which yields the standardized volume of dry biogas.

In some cases, biogas contains siloxanes. They are formed from the anaerobic decomposition of materials commonly found in soaps and detergents. During combustion of biogas containing siloxanes, silicon is released and can combine with free oxygen or other elements in the combustion gas. Deposits are formed containing mostly silica (SiO
2) or silicates (Si
xO
y) and can contain calcium, sulfur, zinc, phosphorus. Such white mineral deposits accumulate to a surface thickness of several millimeters and must be removed by chemical or mechanical means.

Practical and cost-effective technologies to remove siloxanes and other biogas contaminants are available.[17]

For 1000 kg (wet weight) of input to a typical biodigester, total solids may be 30% of the wet weight while volatile suspended solids may be 90% of the total solids. Protein would be 20% of the volatile solids, carbohydrates would be 70% of the volatile solids, and finally fats would be 10% of the volatile solids.

Benefits of manure derived biogas[edit]

High levels of methane are produced when manure is stored under anaerobic conditions. During storage and when manure has been applied to the land, nitrous oxide is also produced as a byproduct of the denitrification process. Nitrous oxide (N2O) is 320 times more aggressive as a greenhouse gas than carbon dioxide[18] and methane 25 times more than carbon dioxide.[19]

By converting cow manure into methane biogas via anaerobic digestion, the millions of cattle in the United States would be able to produce 100 billion kiloWatt hours of electricity, enough to power millions of homes across the United States. In fact, one cow can produce enough manure in one day to generate 3 kiloWatt hours of electricity; only 2.4 kiloWatt hours of electricity are needed to power a single 100-Watt light bulb for one day.[20] Furthermore, by converting cattle manure into methane biogas instead of letting it decompose, global warming gases could be reduced by 99 million metric tons or 4%.[21]

Applications[edit]

Biogas can be used for electricity production on sewage works,[22] in a CHPgas engine, where the waste heat from the engine is conveniently used for heating the digester; cooking; space heating; water heating; and process heating. If compressed, it can replace compressed natural gas for use in vehicles, where it can fuel an internal combustion engine or fuel cells and is a much more effective displacer of carbon dioxide than the normal use in on-site CHP plants.[22]

Biogas upgrading[edit]

Raw biogas produced from digestion is roughly 60% methane and 29% CO
2 with trace elements of H
2S: inadequate for use in machinery. The corrosive nature of H
2S alone is enough to destroy the mechanisms.[23][24]

Methane in biogas can be concentrated via a biogas upgrader to the same standards as fossil natural gas, which itself has to go through a cleaning process, and becomes biomethane. If the local gas network allows, the producer of the biogas may use their distribution networks. Gas must be very clean to reach pipeline quality and must be of the correct composition for the distribution network to accept. Carbon dioxide, water, hydrogen sulfide, and particulates must be removed if present.[23]

There are four main methods of upgrading: water washing, pressure swing absorption, selexol absorption, and amine gas treating.[25] In addition to these, the use of membrane separation technology for biogas upgrading is increasing, and there are already several plants operating in Europe and USA.[23][26]

The most prevalent method is water washing where high pressure gas flows into a column where the carbon dioxide and other trace elements are scrubbed by cascading water running counter-flow to the gas. This arrangement could deliver 98% methane with manufacturers guaranteeing maximum 2% methane loss in the system. It takes roughly between 3% and 6% of the total energy output in gas to run a biogas upgrading system.

Biogas gas-grid injection[edit]

Gas-grid injection is the injection of biogas into the methane grid (natural gas grid). Until the breakthrough of micro combined heat and power two-thirds of all the energy produced by biogas power plants was lost (as heat). Using the grid to transport the gas to customers, the energy can be used for on-site generation,[27] resulting in a reduction of losses in the transportation of energy. Typical energy losses in natural gas transmission systems range from 1% to 2%; in electricity tranmission they range from 5% to 8%.[28]

Before being injected in the gas grid, biogas passes a cleaning process, during which it is upgraded to natural gas quality. During the cleaning process trace components harmful to the gas grid and the final users are removed.[29]

Biogas in transport[edit]

If concentrated and compressed, it can be used in vehicle transportation. Compressed biogas is becoming widely used in Sweden, Switzerland, and Germany. A biogas-powered train, named Biogaståget Amanda (The Biogas Train Amanda), has been in service in Sweden since 2005.[30][31] Biogas powers automobiles. In 1974, a British documentary film titled Sweet as a Nut detailed the biogas production process from pig manure and showed how it fueled a custom-adapted combustion engine.[32][33] In 2007, an estimated 12,000 vehicles were being fueled with upgraded biogas worldwide, mostly in Europe.[34]

Measuring in biogas environments[edit]

Biogas is part of the wet gas and condensing gas (or air) category that includes mist or fog in the gas stream. The mist or fog is predominately water vapor that condenses on the sides of pipes or stacks throughout the gas flow. Biogas environments include wastewater digesters, landfills, and animal feeding operations (covered livestock lagoons).

Ultrasonic flow meters are one of the few devices capable of measuring in a biogas atmosphere. Most of thermal flow meters are unable to provide reliable data because the moisture causes steady high flow readings and continuous flow spiking, although there are single-point insertion thermal mass flow meters capable of accurately monitoring biogas flows with minimal pressure drop. They can handle moisture variations that occur in the flow stream because of daily and seasonal temperature fluctuations, and account for the moisture in the flow stream to produce a dry gas value.

Legislation[edit]

European Union[edit]

The European Union has legislation regarding waste management and landfill sites called the Landfill Directive.

Countries such as the United Kingdom and Germany now have legislation in force that provides farmers with long-term revenue and energy security.[35]

United States[edit]

The United States legislates against landfill gas as it contains VOCs. The United States Clean Air Act and Title 40 of the Code of Federal Regulations (CFR) requires landfill owners to estimate the quantity of non-methane organic compounds (NMOCs) emitted. If the estimated NMOC emissions exceeds 50 tonnes per year, the landfill owner is required to collect the gas and treat it to remove the entrained NMOCs. Treatment of the landfill gas is usually by combustion. Because of the remoteness of landfill sites, it is sometimes not economically feasible to produce electricity from the gas.

Global developments[edit]

United States[edit]

With the many benefits of biogas, it is starting to become a popular source of energy and is starting to be used in the United States more. In 2003, the United States consumed 147 trillion BTU of energy from "landfill gas", about 0.6% of the total U.S. natural gas consumption.[34] Methane biogas derived from cow manure is being tested in the U.S. According to a 2008 study, collected by the Science and Children magazine, methane biogas from cow manure would be sufficient to produce 100 billion kilowatt hours enough to power millions of homes across America. Furthermore, methane biogas has been tested to prove that it can reduce 99 million metric tons of greenhouse gas emissions or about 4% of the greenhouse gases produced by the United States.[36]

In Vermont, for example, biogas generated on dairy farms was included in the CVPS Cow Power program. The program was originally offered by Central Vermont Public Service Corporation as a voluntary tariff and now with a recent merger with Green Mountain Power is now the GMP Cow Power Program. Customers can elect to pay a premium on their electric bill, and that premium is passed directly to the farms in the program. In Sheldon, Vermont, Green Mountain Dairy has provided renewable energy as part of the Cow Power program. It started when the brothers who own the farm, Bill and Brian Rowell, wanted to address some of the manure management challenges faced by dairy farms, including manure odor, and nutrient availability for the crops they need to grow to feed the animals. They installed an anaerobic digester to process the cow and milking center waste from their 950 cows to produce renewable energy, a bedding to replace sawdust, and a plant-friendly fertilizer. The energy and environmental attributes are sold to the GMP Cow Power program. On average, the system run by the Rowells produces enough electricity to power 300 to 350 other homes. The generator capacity is about 300 kilowatts.[37]

In Hereford, Texas, cow manure is being used to power an ethanol power plant. By switching to methane biogas, the ethanol power plant has saved 1000 barrels of oil a day. Over all, the power plant has reduced transportation costs and will be opening many more jobs for future power plants that will rely on biogas.[38]

In Oakley, Kansas, an ethanol plant considered to be one of the largest biogas facilities in North America is using Integrated Manure Utilization System "IMUS" to produce heat for its boilers by utilizing feedlot manure, municipal organics and ethanol plant waste. At full capacity the plant is expected to replace 90% of the fossil fuel used in the manufacturing process of ethanol.[39][40].

Europe[edit]

The level of development varies greatly in Europe. While countries such as Germany, Austria and Sweden are fairly advanced in their use of biogas, there is a vast potential for this renewable energy source in the rest of the continent, especially in Eastern Europe. Different legal frameworks, education schemes and the availability of technology are among the prime reasons behind this untapped potential.[41] Another challenge for the further progression of biogas has been negative public perception. [42]

In February 2009, the European Biogas Association (EBA) was founded in Brussels as a non-profit organisation to promote the deployment of sustainable biogas production and use in Europe. EBA's strategy defines three priorities: establish biogas as an important part of Europe’s energy mix, promote source separation of household waste to increase the gas potential, and support the production of biomethane as vehicle fuel. In July 2013, it had 60 members from 24 countries across Europe.[43]

UK[edit]

As of September 2013[update], there are about 130 non-sewage biogas plants in the UK. Most are on-farm, and some larger facilities exist off-farm, which are taking food and consumer wastes.[44]

On 5 October 2010, biogas was injected into the UK gas grid for the first time. Sewage from over 30,000 Oxfordshire homes is sent to Didcot sewage treatment works, where it is treated in an anaerobic digestor to produce biogas, which is then cleaned to provide gas for approximately 200 homes.[45]

In 2015 the Green-Energy company Ecotricity announced their plans to build three grid-injecting digesters.

Germany[edit]

Germany is Europe's biggest biogas producer[46] and the market leader in biogas technology.[47] In 2010 there were 5,905 biogas plants operating throughout the country: Lower Saxony, Bavaria, and the eastern federal states are the main regions.[48] Most of these plants are employed as power plants. Usually the biogas plants are directly connected with a CHP which produces electric power by burning the bio methane. The electrical power is then fed into the public power grid.[49] In 2010, the total installed electrical capacity of these power plants was 2,291 MW.[48] The electricity supply was approximately 12.8 TWh, which is 12.6% of the total generated renewable electricity.[50]

Biogas in Germany is primarily extracted by the co-fermentation of energy crops (called 'NawaRo', an abbreviation of nachwachsende Rohstoffe, German for renewable resources) mixed with manure. The main crop used is corn. Organic waste and industrial and agricultural residues such as waste from the food industry are also used for biogas generation.[51] In this respect, biogas production in Germany differs significantly from the UK, where biogas generated from landfill sites is most common.[46]

Biogas production in Germany has developed rapidly over the last 20 years. The main reason is the legally created frameworks. Government support of renewable energy started in 1991 with the Electricity Feed-in Act (StrEG). This law guaranteed the producers of energy from renewable sources the feed into the public power grid, thus the power companies were forced to take all produced energy from independent private producers of green energy.[52] In 2000 the Electricity Feed-in Act was replaced by the Renewable Energy Sources Act (EEG). This law even guaranteed a fixed compensation for the produced electric power over 20 years. The amount of around 8 ¢/kWh gave farmers the opportunity to become energy suppliers and gain a further source of income.[51]

The German agricultural biogas production was given a further push in 2004 by implementing the so-called NawaRo-Bonus. This is a special payment given for the use of renewable resources, that is, energy crops.[53] In 2007 the German government stressed its intention to invest further effort and support in improving the renewable energy supply to provide an answer on growing climate challenges and increasing oil prices by the ‘Integrated Climate and Energy Programme’.

This continual trend of renewable energy promotion induces a number of challenges facing the management and organisation of renewable energy supply that has also several impacts on the biogas production.[54] The first challenge to be noticed is the high area-consuming of the biogas electric power supply. In 2011 energy crops for biogas production consumed an area of circa 800,000 ha in Germany.[55] This high demand of agricultural areas generates new competitions with the food industries that did not exist hitherto. Moreover, new industries and markets were created in predominately rural regions entailing different new players with an economic, political and civil background. Their influence and acting has to be governed to gain all advantages this new source of energy is offering. Finally biogas will furthermore play an important role in the German renewable energy supply if good governance is focused.[54]

Indian Subcontinent[edit]

Biogas in India[56] has been traditionally based on dairy manure as feed stock and these "gobar" gas plants have been in operation for a long period of time, especially in rural India. In the last 2-3 decades, research organisations with a focus on rural energy security have enhanced the design of the systems resulting in newer efficient low cost designs such as the Deenabandhu model.

The Deenabandhu Model is a new biogas-production model popular in India. (Deenabandhu means "friend of the helpless.") The unit usually has a capacity of 2 to 3 cubic metres. It is constructed using bricks or by a ferrocement mixture. In India, the brick model costs slightly more than the ferrocement model; however, India's Ministry of New and Renewable Energy offers some subsidy per model constructed.

Biogas which is mainly methane/natural gas can also be used for generating protein rich cattle, poultry and fish feed in villages economically by cultivating Methylococcus capsulatus bacteria culture with tiny land and water foot print.[57][58][59] The carbon dioxide gas produced as by product from these plants can be put to use in cheaper production of algae oil or spirulina from algaculture particularly in tropical countries like India which can displace the prime position of crude oil in near future.[60][61] Union government of India is implementing many schemes to utilise productively the agro waste or biomass in rural areas to uplift rural economy and job potential.[62][63] With these plants, the non edible biomass or waste of edible biomass is converted in to high value products with out any water pollution or green house gas (GHG) emissions.[64]

LPG (Liquefied Petroleum Gas) is a key source of cooking fuel in urban India and its prices have been increasing along with the global fuel prices. Also the heavy subsidies provided by the successive governments in promoting LPG as a domestic cooking fuel has become a financial burden renewing the focus on biogas as a cooking fuel alternative in urban establishments. This has led to the development of prefabricated digester for modular deployments as compared to RCC and cement structures which take a longer duration to construct. Renewed focus on process technology like the Biourja process model[65] has enhanced the stature of medium and large scale anaerobic digester in India as a potential alternative to LPG as primary cooking fuel.

In India, Nepal, Pakistan and Bangladesh biogas produced from the anaerobic digestion of manure in small-scale digestion facilities is called gobar gas; it is estimated that such facilities exist in over 2 million households in India, 50,000 in Bangladesh and thousands in Pakistan, particularly North Punjab, due to the thriving population of livestock. The digester is an airtight circular pit made of concrete with a pipe connection. The manure is directed to the pit, usually straight from the cattle shed. The pit is filled with a required quantity of wastewater. The gas pipe is connected to the kitchen fireplace through control valves. The combustion of this biogas has very little odour or smoke. Owing to simplicity in implementation and use of cheap raw materials in villages, it is one of the most environmentally sound energy sources for rural needs. One type of these system is the Sintex Digester. Some designs use vermiculture to further enhance the slurry produced by the biogas plant for use as compost.[66]

In Pakistan, the Rural Support Programmes Network is running the Pakistan Domestic Biogas Programme[67] which has installed 5,360 biogas plants[68] and has trained in excess of 200 masons on the technology and aims to develop the Biogas Sector in Pakistan.

In Nepal, the government provides subsidies to build biogas plant at home.

China[edit]

The Chinese have experimented with the applications of biogas since 1958. Around 1970, China had installed 6,000,000 digesters in an effort to make agriculture more efficient. During the last years the technology has met high growth rates. This seems to be the earliest developments in generating biogas from agricultural waste.[69]

In developing nations[edit]

Domestic biogas plants convert livestock manure and night soil into biogas and slurry, the fermented manure. This technology is feasible for small-holders with livestock producing 50 kg manure per day, an equivalent of about 6 pigs or 3 cows. This manure has to be collectable to mix it with water and feed it into the plant. Toilets can be connected. Another precondition is the temperature that affects the fermentation process. With an optimum at 36 C° the technology especially applies for those living in a (sub) tropical climate. This makes the technology for small holders in developing countries often suitable.[70]

Depending on size and location, a typical brick made fixed dome biogas plant can be installed at the yard of a rural household with the investment between US$300 to $500 in Asian countries and up to $1400 in the African context.[71] A high quality biogas plant needs minimum maintenance costs and can produce gas for at least 15–20 years without major problems and re-investments. For the user, biogas provides clean cooking energy, reduces indoor air pollution, and reduces the time needed for traditional biomass collection, especially for women and children. The slurry is a clean organic fertilizer that potentially increases agricultural productivity.[70]

Domestic biogas technology is a proven and established technology in many parts of the world, especially Asia.[72] Several countries in this region have embarked on large-scale programmes on domestic biogas, such as China[73] and India.

The Netherlands Development Organisation, SNV,[74] supports national programmes on domestic biogas that aim to establish commercial-viable domestic biogas sectors in which local companies market, install and service biogas plants for households. In Asia, SNV is working in Nepal,[75] Vietnam,[76] Bangladesh,[77] Bhutan, Cambodia,[77] Lao PDR,[78] Pakistan[79] and Indonesia,[80] and in Africa; Rwanda,[81] Senegal, Burkina Faso, Ethiopia,[82] Tanzania,[83] Uganda, Kenya,[84] Benin and Cameroon.

In South Africa a prebuilt Biogas system is manufactured and sold. One key feature is that installation requires less skill and is quicker to install as the digester tank is premade plastic.[85]

Associations[edit]

  • American Biogas Council
  • Canadian Biogas Association
  • European Biogas Association[86]
  • German Biogas Association[87]
  • Indian Biogas Association[88]

Society and culture[edit]

In the 1985 Australian film Mad Max Beyond Thunderdome the post-apocalyptic settlement Barter town is powered by a central biogas system based upon a piggery. As well as providing electricity, methane is used to power Barter's vehicles.

"Cow Town", written in the early 1940s, discuss the travails of a city vastly built on cow manure and the hardships brought upon by the resulting methane biogas. Carter McCormick, an engineer from a town outside the city, is sent in to figure out a way to utilize this gas to help power, rather than suffocate, the city.

The Biogas production is providing nowadays new opportunities for skilled employment, drawing on the development of new technologies.[89]

See also[edit]

References[edit]

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Pipes carrying biogas (foreground) and condensate
Biogas production in rural Germany
"Biogaståget Amanda" ("Amanda the Biogas Train") train near Linköping station, Sweden
Simple sketch of household biogas plant

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