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Biogas Plant Science Fair Project

There are plenty of options for anaerobic digesters as all you need is a gas tight container and some organic waste. I think the simplest method is if you can find two buckets/containers such that one will fit upside down inside the other with some clearance (not that easy to do in spite of the proliferation of plastic containers). The bottom container holds the digesting liquid and the inverted one becomes the gas holder - it may need some guides so it does not topple over as it rises with gas. To avoid the possibility of a gas leak I would use waterproof tape/glue/silicon sealant to hold a plastic tube from the top of the gas space running out through the side of the digester bucket (you will notice a liquid leak!) with enough slack to allow the gas holder to rise (See sketch below, 2004 version, guides not shown - a challenge for you!).

PHOTOGRAPHS OF MOVEABLE GASHOLDER 5M3 BIOGAS PLANT INSTALLED BY PCRET AT JHANG BAHATAR, RAWALPINDI – USING BIO-FERTILIZER 

Source:http://www.pcret.gov.pk

Moveable Gasholder 5 Meter Cube Biogas Plant

Moveable Gasholder 5 Meter Cube Biogas Plant testing

Moveable Gasholder 5 Meter Cube Biogas Plant

Moveable Gasholder 5 Meter Cube Biogas Plant

Moveable Gasholder 5 Meter Cube Biogas Plant Photos USING BIO-FERTILIZER

Moveable Gasholder 5 Meter Cube Biogas Plant Photos, USING BIO-FERTILIZER Results

Moveable Gasholder 5 Meter Cube Biogas Plant Photos, USING BIO-FERTILIZER Results

Moveable Gasholder 5 Meter Cube Biogas Plant Photos, USING BIO-FERTILIZER Results


A Small-Scale Biodigester Designed and Built in the Philippines by Gerry Baron

(Quoted with his kind permission)

Introduction:

(Click the pictures for a high resolution version)
I am a semi-retired engineer in the poultry and piggery business. It's been many years since university chemistry and biology classes.
Basic construction of the biodigester in the Philippines using easily obtained local materials.The Philippines is a tropical country with just a dry and a rainy season. Ambient temperature is in the 30°C to 40°C range year-round -- ideal for biogas. The temperature under direct sun can be much higher. (I have to put shades on some of my digesters!)
For waste management and pollution control, the Department of the Environment and Natural Resources (DENR) has been promoting biogas production in large pig farms specially those already equipped with waste lagoons. Unlike India and their huge Gobar supply, cattle farms are few in the Philippines. We have many pig and poultry farms.
We don't have a "Gobar Gas Research Station". We have very little information, promotion and programs for biogas specially for small-scale systems. Compared to India's 2.9 million family-type biogas digesters in 2000, there are probably less than 100 such units in the Philippines. (www.undp.org/seed/energy/policy/ch_8.htm)
My interest in biogas is motivated primarily by its ability to replace LPG as a cooking gas for most rural households. Its ecological benefit is an added bonus.
biodigester in the garden
With 4-200 liter test digesters working since June and a 2 cubic meter (m3) demo digester working for more than a month, I continue to be very interested with my experiments - "a very useful hobby".
My most efficient digesters use 5 % poultry-manure by volume charged once every 2 weeks. (My 2 m3 digester is fed 100 liters of pre-soaked and well-stirred manure every 2 weeks.) Biogas yield starts at 60 % and drops to 40 % before the next feeding.
The biogas output of my old poultry-manure test digester has dropped sharply at the end of the 5th month. Could it be because of Nitrogen overdose? Except for a small amount of effluent displaced during charging (usually 50 % of charge volume), there appears to be no sediments in the digester. All manure seems to liquefy.  I understand excess nitrogen goes out with sludge and turns into a nitrogen-rich fertilizer.
Storage bladder for the biogas produced by the methane digester I am also concerned about anaerobic bacteria over-population and in-sufficient charging. Grass or biomass is a good alternative but because it floats it will be difficult to load in my digesters. Besides it requires additional work.
I chose to work with poultry-manure after getting lesser biogas yield from pig-manure. My 2 m3 digester produces 1 m3 of biogas daily for cooking. It uses 100 liters of poultry-manure once every 2 weeks. It is a very inexpensive and practical system.
It's something that will appeal to many rural folk. Everyone is welcome to see my demo unit and copy it. I may even provide drawings for FREE. This is my primary objective.
 The biodigester in action - The hard work pays off and produces a clean-burning flame from biogas. Without the piece of wood on top of the burner it would be completely invisible, except perhaps for a heat haze!
It can work, and the construction is not complicated. Fuel produced from manure is clean and cheap. It can be produced where it is needed from simple raw materials.
It really works! Methane from biogas burns with a clean flame.
From a business viewpoint, I plan to sell ready-to-install kits when my design has become problem-free. I also hope to provide design consultancy and building capability for larger applications.
The general design can be found here:
Biodigester design
(My aplogies to all who tried to follow the broken link before)

Design considerations

I admit my design is very basic and simple. Valves 1 & 2 were not even in my test digesters and in the 2.0 m3 tarpaulin digester shown in the pictures. To remove effluent and sediments, I had to siphon or pump.
biogas from the biodigester burning
I added these valves in the two 10.0 m3 HDPE digesters we built and started up a few days before Christmas. The digesters are partially below ground so removing sediments will not be as simple as opening valve 2. But, the sediments should flow out with increasing pressure in the digester and opening valve 2.
My previous digesters have not produced appreciable quantities of sediments so my experience in this area is limited. With the 10 m3 HDPE digesters, I plan to install another digester or small ponds downstream to collect the sludge (fertilizer) and use the effluent for watering plants.

Codigestion experiments:

I expect the HDPE digesters to begin producing gas last week of January. I will also begin using fruit and vegetable wastes (biomass) in one of my 200 liter test digesters. I might also use said wastes in my 2nd 10.0 m3 HDPE digester.
I have managed to test a few carbon based feedstocks as we last discussed.
They are:
  1. lawn-mower grass cuttings from the greens of a nearby golf course
  2. shredded sweet potatoes (yams) - from waste bin in vegetable market
  3. shredded potatoes - from waste bin in vegetable market
  4. sliced tomatoes - from waste bin in vegetable market
  5. pressed coconut meat - from a native cake bakeshop
The sliced tomatoes and pressed coconut meat did not appear to produce biogas.
(When fed to a working digester, biogas output continued to decline as if no feedstock was added.)
Worse, the pressed coconut meat floats and may be floating inside the digester impeding digestion.
With the grass cuttings, gas production did not drop. In fact, there was a small noticeable increase for a few days.
The yams and potatoes, however, gave a surge in biogas production for a few days. Yams and potatoes (apparently, vegetables that cause flatulence) are good for biogas production.
In all instances, approximately 5 % feedstock by volume was added once and production was observed for two weeks.
I plan to repeat the tests and validate the results.10 m3 biodigesters in operation in the Philippines
Returning from a vacation, we passed a little, remote community that had signs saying they were using biogas. We stopped, interviewed two users and examined their set-ups. Though they invested heavily when their digesters were built in 2001, they are very happy to have them now that LPG prices have almost tripled.
I was able to track down one of the technicians who happily reported that he has built 41 digesters ranging from 5 to 10 m3 since 2000 -- with funding assistance from UNDP.
It was great to find that community with home-type or family-type biodigesters. The find affirms that biogas WORKS!
My biodigester which only costs about 80 % today for what they paid for in 2001 continues to appear to be a great idea for the Philippines. The DOST tech I mentioned above agrees and plans to try my units in his next projects.
The 10 m3 HDPE units installed in our farm are now full of biogas. We are going to test burn the biogas when I go there tomorrow.
I also have a couple of relatives interested in 10 m3 units for their farms. This is getting interesting.

Building a methane digester:

To produce 1 m3 of BIOGAS, to cook 3 meals daily for a small family of 4 to 6, you need at least 5 litres of pig manure/day. 8 sows will produce 5+ litres/day easily and your 36 heads total will probably give you at least 15 litres
A 2 m3 digester wil produce 1 m3 of BIOGAS/day -- good for experimental purposes. I suggest your first digester be at least 5 m3. This will produce more BIOGAS when needed and accommodate your farm's growth.
The China Fixed Dome, India Floating Cover and DOST-PSTC designs are the most popular here in the Philippines . Download drawings from the internet but I suggest you get professional help as the building process is not easy. Here are people who can help:
Roberto Bajenting
Trained at Asia-Pacific Biogas Research and Training Center , Chengdu City , Sichuan , China .
Provincial Agrarian Reform Officer, Cebu City
Cell No: +63920-923-6930
Engr Orlando Anselmo
Has installed 35+ DOST-PSTC digesters in Aurora Province
DOST Officer, Baler, Aurora Province
Cell No: +63915-569-9631

Source :http://www.habmigern2003.info/biogas/Baron-digester/Baron-digester.htm

Home made biogas ( Methane ) Gobar gas Generator

You can make biogas energy with a DIY methane generator.

Producing methane from manure using your own small scale waste to energy biogas digester is feasible for many small farms.
Small scale methane from manure setup What is Biogas Energy?Biogas energy is fueled by burning methane produced by the decomposition of organic wastes.


Small scale biogas generator
Methane is a gas – chemically CH4. It is colourless, odourless and, of course, flammable. Methane is widely used as the main constituent of mains natural gas.
Whenever organic materials are decomposed by bacteria anaerobically (i.e. in the absence of oxygen) methane and carbon dioxide are produced.
Small scale manure-to-energy methane generator plans are available here.
Sources of Biogas Energy
Just about any organic waste can be decomposed as a methane generator - plant (soft material is better than woody material) and animal wastes, and even human waste.
On a municipal level, rubbish tips act as biogas digesters and are prodigious methane generators. Even in Perth, Australia, companies are actively harvesting this methane to produce climate friendly biogas electricity.
In fact, because un-burnt methane released into the atmosphere is a powerful greenhouse gas, 10% of our personal impact on the climate comes from the food refuse we put in our garbage bins that ends up decomposing under landfill.
In a small scale waste to energy situation it is possible to generate methane from manure or even sewerage. And biogas energy is constantly being manufactured in digestive systems like yours and your cow’s… yes, farts are methane too!
Check out this video to see how to make a simple home digester:






Pros and Cons of Methane Generator Systems
Advantages
• Makes good use of organic wastes. You can obtain fuel from sewage sludge and animal slurries first, and prevent runoff and methane emissions at the same time – and you still get fertiliser at the end of the process.
• Is a clean, easily controlled source of renewable energy.
• Uses up methane, a powerful greenhouse gas.
• Reduces pathogen (disease agent) levels in the waste.
• Residue provides valuable organic fertilizer.
• Simple to build and operate.
• Low maintenance requirements.
• Can be efficiently used to run cooking, heating, gas lighting, absorption refrigerators and gas powered engines.
• No smell (unless there’s a leak, which you’d want to know about and fix immediately anyway!).
Disadvantages
• Most practical to be generated and used at the source of the waste. This is because the energy needed to compress the gas for transport, or convert it into electricity is excessive, reducing the efficiency of biogas energy production.
• For safety, basic precautions (see below) must be adhered to.
Small Scale Waste to Energy Methane Generator Systems
Biogas Energy
Each kilogram of biodegradable material yields around 0.4 m³ (400l) of gas.
So in practice, in small scale waste to energy systems, if you have some livestock, plus kitchen and human waste you can meet your cooking and lighting needs easily:
• 2 gas rings for a couple of hours a day will use between 1-2 m³
• Gas lights need around 0.1 m3 (100l) per hour.
Driving any kind of engine (eg a generator or a pump) is, however, way beyond the domestic-scale. (Better to go for algal biodiesel!)

What Size Methane Generator is Needed?
If generating methane from manure, collect dung for several days to determine average daily dung production. On this basis, the appropriate size biogas digester plant can be calculated.
For example, where 55 kg of dung a day is available a 8 m3 plant is warranted; where it’s only 6 kg of dung a day, a 1 m3 plant will suffice.
For a family of 8 with a few animals (say 8-10 cows), a 10m³ digester is a commonly used size in India, with 2 m³ gas storage.
Ideal Temperatures for Producing Methane from Manure
How long you leave the material in a batch digester depends on temperature (2 weeks at 50°C up to 2 months at 15°C). The average is around 1 month – so gauge how much material you will add each day, and multiply it by 30 to calculate the size of the digester.
While anaerobic digestion occurs between 32° F (0°C) and 150° F (65°C), the optimum temperature range for methane generating microbial activity is 85°F (29°C) to 95° F (35°C).
Little gas production occurs below 60°F (16°C). In colder climates placing the digester in a greenhouse, and perhaps using some of the methane to warm the system, are possible strategies.
Methane Generator Systems
• The biogas digester is the system component where the animal, human and other organic wastes are introduced, usually as a slurry with water, to break down anaerobically.
• A storage container is used to hold the gas produced, from which it is piped for burning as a fuel. Variable volume storage (i.e. flexible bag or floating drum) is easier, cheaper and more energy efficient than high pressure cylinders, regulators or compressors.
• When the digester is emptied, the spent effluent is dried for later reuse as a fertilizer.
Types of Biogas Digesters
The two main digester types of digesters are the continuous and the batch. Continuous digesters have a constant throughput of material, and batch digesters extract the gas from a contained batch of material, which is then emptied and a new batch added.
As firewood for cooking has become scarce, millions of small scale continuous digesters are in use in developing countries, especially India and China. Digesters tend to be larger-scale in developed countries, taking animal slurries and human sewage.
Methane Generator Design
The Indian cylindrical pit design has become a popular choice around the world due to its reliability and simplicity. It comprises two basic parts: a slurry tank and a covered by a gas cap or drum to capture the gas released from the slurry.
Domestic Scale Batch Biogas Digestor
Experimental methane generator project

Small experimental biogas digester at Redfield. Waste material is put into the oil drum, neoprene cover rises when full of gas, gas is tapped into container (upside-down plastic drum with water seal) which rises as more gas enters. When full, gas can be tapped off and used with the little gas ring.
Batch digesters based on a container (see photo, above) are feasible on the domestic scale.
Mini Methane Generator Project
Instructions to make a mini methane generator (suit education project) are in the "Methane-Biogas Production Guide" which, along with heaps of other free eBooks on sustainable living, can be accessed free here.

Methane Safety
Like electricity and other energy systems, safety is usually assured so long as the risks are understood and sensible precautions are followed.
Fire or Explosion Risk
Methane is obviously flammable, and can even be explosive. With this in mind...
• The methane generator digester area must be well ventilated to prevent the accumulation of trapped gases.
• In the vicinity of a digester no naked flames are permitted, electrical equipment must be of suitable quality, normally "explosion proof", and other sources of sparks are any iron or steel tools or other items, power tools, normal electrical switches, mobile phones and static electricity kept a safe distance away.
A flame trap should be incorporated in the supply line, which must be of a minimum of 20 m long. Instructions on building a flame trap can be found here.

Asphyxiation Risk
Biogas displaces air, reducing the oxygen level so any digester area needs to be well ventilated.
Disease
While the spent slurry has lost a lot of its pathogens, there’s a lot of microbial activity at work in producing biogas energy!
So avoid contact with the digester contents and wash up thoroughly after working around the methane generator (especially before eating or drinking).
  Biogas Plant  What is Biogas? How Biogas plant made?  How to Use biogas plant? Part 3 of 3

Time
84. It may take up to three weeks or even a month for the waste in your biogas unit to start making gas. After that, gas will be made for about eight weeks.
85. During these eight weeks, half of the gas will be made in the first two or three weeks and the rest in the last five or six weeks.
86. If you find that not much gas is being made in the last weeks, empty the unit and start again.
Cold weather protection
87. If the temperature where you are often falls below 15°C, you will have to keep the waste mixture in your biogas unit warm.
88. If you put your biogas unit under the ground or partly under the ground, this will help to keep the waste warm.
bi-f31p21a.GIF
Keep the waste warm
89. You can keep the waste mixture in your biogas unit warm by putting leaves, grass, straw or maize stalks around the large drum.
In this chapter, the most important types of biogas plants are described:



Of these, the two most familiar types in developing countries are the fixed-dome plants and the floating-drum plants. Typical designs in industrialized countries and appropriate design selection criteria have also been considered.

Fixed-dome plants

The costs of a fixed-dome biogas plant are relatively low. It is simple as no moving parts exist. There are also no rusting steel parts and hence a long life of the plant (20 years or more) can be expected. The plant is constructed underground, protecting it from physical damage and saving space. While the underground digester is protected from low temperatures at night and during cold seasons, sunshine and warm seasons take longer to heat up the digester. No day/night fluctuations of temperature in the digester positively influence the bacteriological processes.
The construction of fixed dome plants is labor-intensive, thus creating local employment. Fixed-dome plants are not easy to build. They should only be built where construction can be supervised by experienced biogas technicians. Otherwise plants may not be gas-tight (porosity and cracks).
The basic elements of a fixed dome plant (here the Nicarao Design) are shown in the figure below.

[IMAGE] Fixed dome plant Nicarao design: 1. Mixing tank with inlet pipe and sand trap. 2. Digester. 3. Compensation and removal tank. 4. Gasholder. 5. Gaspipe. 6. Entry hatch, with gastight seal. 7. Accumulation of thick sludge. 8. Outlet pipe. 9. Reference level. 10. Supernatant scum, broken up by varying level.
Source: TBW

[IMAGE] Basic function of a fixed-dome biogas plant, 1 Mixing pit, 2 Digester, 3 Gasholder, 4 Displacement pit, 5 Gas pipe
Source: OEKOTOP

Function

A fixed-dome plant comprises of a closed, dome-shaped digester with an immovable, rigid gas-holder and a displacement pit, also named 'compensation tank'. The gas is stored in the upper part of the digester. When gas production commences, the slurry is displaced into the compensating tank. Gas pressure increases with the volume of gas stored, i.e. with the height difference between the two slurry levels. If there is little gas in the gas-holder, the gas pressure is low.

Digester

Bio Gas Plant Photo Gallery
Bio Gas Plant construction in Pakistan
bio gas plant installation
 biogas system

Implementation Of Biogas Technology At NUST H-12 Campus Pakistan

bio gas plant construction in India

Construction of a Biogas plant in Mirpurkhas Sindh Pakistan

Construction of a Biogas plant in Mirpurkhas Sindh Pakistan

Construction of a Biogas plant in Mirpurkhas Sindh Pakistan

Construction of a Biogas plant in Mirpurkhas Sindh Pakistan


Introduction to the Commercialized Household Fiberglass Reinforced Plastic Digester






 


Domestic Biogas Plant
Bio-gas plant diagram

Domestic Biogas Plants produce renewable fuel from organic biomass and are primarily used in developing countries and rural areas as an alternative to using fossil fuels, whose combustion contributes to global warming. Biogas is a carbon neutral fuel that is produced when bacteria degrade biological material in the absence of oxygen, a process known as anaerobic digestion, or fermentation of biodegradable materials such as biomass, manure, sewage, or municipal waste1 . The fuel consists primarily of methane (CH4 or natural gas) and carbon dioxide (CH4) mixed with trace gases and can be used to generate electricity for cooking and heating when it is burned.

BIOGAS TECHNOLOGY: A TRAINING MANUAL FOR EXTENSION

source: http://www.fao.org/docrep/008/ae897e/ae897e00.htm


TABLE OF CONTENTS
PREFACE
TABLE OF TABLES
TABLE OF FIGURES
TABLE OF CHARTS
TABLE OF ANNEXES
ACRONYMS AND ABBREVIATIONS
RELEVANT UNITS AND CONVERSION FACTORS
INTRODUCTION TO MANUAL
SESSION ONE : SYSTEM APPROACH TO BIOGAS TECHNOLOGY
1.1 Introduction
1.2 Components of a Biogas System
1.2.1 Biogas
1 2.2 Methanogenic Bacteria or methanogens
1.2.3 Biodigester
1.2.4. Inputs and their Characteristics
1.2.5 Digestion
1.2.6 Slurry
1.2.7 Use of Biogas
1.3 Implications of Biogas System
1.4 Session Plan
1.5 Review Questions
1.6 References
1.7 Further Reading Materials
SESSION TWO : RELEVANCE OF BIOGAS TECHNOLOGY TO NEPAL
2.1 Introduction
2.2 Energy Situation in Nepal
2.2.1 Tradition Sources of Energy
2.2.2 Commercial Sources of Energy
2.2.3 Sources of Alternative Energy
2.3 Biogas in Other Countries
2.4 Biogas Potential in Nepal
2.5 Uses of Biogas
2.5.1 Cooking
2.5.2 Lighting
2.5.3 Refrigeration
2.5.4 Biogas-fueled Engines
2.5.5 Electricity Generation
2.6 Biogas and Agriculture
2.7 Biogas and Forests
2.8 Biogas and Women
2.9 Health and Sanitation
2.10 Municipal Waste
2.11 Economy and the Employment
2.12 Session Plan
2.13 Review Questions
2.14 References
2.15 Further Reading Materials
Production of Biogas - Fixed Dome Type Biogas Plant

 

 Raw Materials Required

Forms of biomass listed below may be used along with water:
  • Animal dung
  • Poultry wastes
  • Plant wastes ( Husk, grass, weeds etc.)
  • Human excreta
  • Industrial wastes(Saw dust, wastes from food processing industries)
  • Domestic wastes (Vegetable peels, waste food materials)

Principle


Biogas is produced as a result of anaerobic fermentation of biomass in the presence of water.

Construction


The biogas plant is a brick and cement structure having the following five sections:
  • Mixing tank present above the ground level
  • Inlet chamber: The mixing tank opens underground into a sloping inlet chamber
  • Digester: The inlet chamber opens from below into the digester which is a huge tank with a dome like ceiling. The ceiling of the digester has an outlet with a valve for the supply of biogas
  • Outlet chamber: The digester opens from below into an outlet chamber
  • Overflow tank: The outlet chamber opens from the top into a small over flow tank
  • Fixed dome type to produce biogas

Working

  • The various forms of biomass are mixed with an equal quantity of water in the mixing tank. This forms the slurry
  • The slurry is fed into the digester through the inlet chamber. The temperature of the slurry must be maintained around 35 oC. Any drop in temperature will reduce the anaerobic activity and hence the yield of biogas
  • When the digester is partially filled with the slurry, the introduction of slurry is stopped and the plant is left unused for about two months
  • During these two months, anaerobic bacteria present in the slurry decompose or ferment the biomass in the presence of water
  • As a result of anaerobic fermentation, biogas is formed, which starts collecting in the dome of the digester
  • As more and more biogas starts collecting, the pressure exerted by the biogas forces the spent slurry into the outlet chamber
  • From the outlet chamber, the spent slurry overflows into the overflow tank
  • The spent slurry is manually removed from the overflow tank and used as manure for plants
  • The gas valve connected to a system of pipelines is opened when a supply of biogas is required
  • To obtain a continuous supply of biogas, a functioning plant can be fed continuously with the prepared slurry

Advantages of Fixed Dome Type of Biogas Plant
  • Requires only locally and easily available materials for construction
  • Inexpensive
  • Easy to construct
  • Due to the above reasons, this plant is also called the Janata Gobar gas plant.

Advantages of Biogas as a Fuel


  • As domestic fuel
  • For street lighting
  • For generation of electricity

  • High calorific value
  • Clean and excellent fuel containing upto 75% methane
  • No residue produced
  • No smoke produced
  • Non - polluting
  • The slurry is periodically removed and used as excellent manure which is rich in nitrogen and phosphorous
  • Economical
  • Can be supplied through pipe lines
  • Burns readily - has a convenient ignition temperature Uses of Biogas
    • Biogas is used

Biogas Plant Design

Introduction:
Biogas is based upon the use of dung to produce gas which is used as domestic fuel especially in rural areas. This technique is based on the decomposition of organic matter in the absence of air to yield gas consisting of methane (55%) and carbon dioxide (45%) which can be used as a source of energy.
Biogas is a gaseous fuel which may be directly burnt in a gas burner for the use as a cooking fuel or source of direct heat for thermal applications. It has a calorific value of 5871 kCal/m3.

Biogas Plant

The plant where biogas is produced is called biogas plant. The design of the plant is tailored to use cattle dung as feed stock. Cattle dung and water is mixed in the ratio of 1:1 and the resultant slurry containing 9% total solids is fed to the biogas plant by gravity. This slurry is retained in the digester for a period of 35-50 days. During this retention period, 35-40 liters of biogas is recovered per kg of dung fed.

Classification of Biogas Plants

Biogas generates from the disintegration of organic substrate and being lighter than air, rises upwards. This gas is collected in various types of drums. Therefore, according to the method of gas storage, biogas plants are of two types:
  1. Floating dome biogas plants
  2. Fixed dome biogas plants
Floating dome design: This design consists of a tank or a well with a partition wall to prevent shorting of influent fresh dung slurry with the outgoing spent slurry. The gas produced is trapped under a plastic or a metallic drum. With the continuous production more gas is trapped under this bell and the drum rises. This acts as a gas storage unit and when the tap above is released, the gas is discharged at more or less constant pressure.
Fixed dome design: This is designed to reduce the overall cost of the biogas plant. In this, the slurry is fed to a spherical masonry plant. When the gas is produced owing to the rigid nature of the masonry dome, the trapped gas exerts a pressure on the slurry surface and a corresponding amount of slurry is displaced into a wide outlet and inlet. As a result, the pressure of gas stored varies significantly.
 
RESOURCE :http://www.tutorvista.com
Biogas Plant in India


Jo Lawbuary, HES
Contents
Introduction
Why biogas?
Methanogenesis
Evolution of biogas technology
Dissemination of biogas technology
Factors hindering spread of biogas
Conclusion
References

Tables and Figures

Tables:
  1. Estimated potential of renewable technologies in India
  2. Different biogas plants recognised by MNES
  3. Daily dung requirements and dung fed
Figures:
Fig1. Process of methanogenesis
Fig2a. common biogas plants a: KVIC floating-drum model
Fig2b. Camartec fixed-dome model

Frontispiece:
Biogas promotion poster produced by the Khadi and Village Industry Commission
Introduction
Mahatma Gandhi, in his vision for India, envisaged a system of devolved, self-sufficient communities, sustaining their needs from the local environment, and organising income generating ventures around co-operative structures. Fifty years on, and Gandhi's vision of Swadeshi (self-sufficiency) for India, despite interpreted by some as a romantic and bucolic notion, is perhaps more urgent than ever. Diminishing forests, and a burgeoning, mainly rural biomass-dependent population of 984 million, necessitates a co-ordinated effort of rural India to supply itself with a dependable and sustained source of energy.
Biomass alone currently meets 57% of the national energy demand, (Tata, 1998) yet is rarely featured in any 'official' statistics of energy use, given perhaps its scattered nature, and its low status as fuel. Indeed, according to statistics, in 1995, 63.3% of India's energy production was from its reserves of low-grade coal, 18.6% from petroleum, while hydroelectricity, natural gas and nuclear accounted for 8.9%, 8.2%, and 1% respectively (EIA, 1998).
India's overall energy production in 1995 was approximately 8.8 quadrillion Btu (quads), while consumption was 10.5 quads. India's energy demand is increasing, and its inability to step up production to meet demand, has increased India's reliance on costly imports, the gap between consumption and production projected to widen into the next century, as demand for energy is projected to grow at an annual rate of 4.6% - one of the highest in the world (EIA, 1998). Energy for developing industries, transport, and a drive towards the electrification of India over the last three decades of an expanding residential sector, so that currently, a great percentage of villages in the subcontinent have access to the grid- as much as 90%, according to recent figures (EIA, 1998), have contributed to the energy production deficit.
However, as mentioned earlier, the conventional statistics do not take into account the informal and unorganised use of biomass, which is reputed to account for 57% of total energy, therefore, effectively energy from biomass more than equals the marketable energy production of 8.8 quads (However, given the inherent difficulty in estimating such a figure, there must be a wide margin of error, potentially). Fuelwood is the primary source of biomass, derived from natural forests, plantations, woodlots and trees around the homestead (Agarwal, 1998). Alarm regarding the state of India's forests, which were being lost at an estimated rate of 1.5 million hectares (Mha) in the early 1980's has kick started an intense afforestation and forest regeneration scheme that attempts to share management of forest resources between the forest department and local user communities. Afforestation appears to be showing up on satellite images on the subcontinent (Hall and Ravindranath, 1994), but whether ultimately, more fuelwood will be available to rural communities, will be more a political question.

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