a concise biogas plant construction suitable for ghana and

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A CONCISE BIOGAS PLANT CONSTRUCTION SUITABLE FOR GHANA AND OTHER

TROPICAL COUNTRIES.

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RECEIVEDJAN 1 61998

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A TYPICAL, OPTIMAL SITING APPLICABLE IN THE RURAL AREAS OF GHANA.

DISTBMi OF TH'S,pOCSn^Ut8MtB>

JOSEPH KOFI NANI GBAGBO FOLKECENTER FOR RENEWABLE ENERGY

24-02-1997 to 25-04-1997

PC-Print-ISBN 87-7778-102-3 April 1997

NordvestjyskFolkecenterforVedvarendeEnergiFolkecenter for Renewable Energy

P. O. Box 208 Kammersg&rdsvej 16, Sdr. Ydby, \7760 Hurup, Thy I Denmark jTelefon: 97956600 J Fax: 97956565Int. tel.:+45 97 95 66 00 | Int. fax:+45 97 95 65 65 IPostgiro: 5934133

Biogas plants suitable for Ghana and other tropical countries.

A CONCISE BIOGAS PLANT CONSTRUCTION SUITABLE FOR GHANA AND OTHER

TROPICAL COUNTRIES.

JOSEPH KOFI NANI GBAGBO

FOLKECENTER FOR RENEWABLE ENERGY

24 - 02-1997 to 25-04-1997.

Practical training report, 24-02-1997 to 25-04-1997, By J.K.N. Gbagbo . I

DISCLAIMER

Portions of this document may be illegible electronic image products. Images are produced from the best available original document.

Biotas plants suitable for Ghana and other tropical countries.

Acknowledgement.

I wish to express my sincere thanks to all colleagues at the Folkecenter For Renewable Energy, especially Jane Kruse (Head of training and information) and Mr. Preben Maegard (The Director) for their splendid hospitality coupled with the fantastic co - operation during my entire ,training period.

Again, it is remarkable to congratulate them for the wonderful services they are rendering to the entire world. I refer to the Center as a “Mission House of Renewable Energies” and the Director as the “Great Prophet”, propagating the good news of renewable energies to the world.

Secondly, I wish to thank my supervisor, Engineer Niels Anso, for his incessant support throughout my training period.

Next, I am grateful to Dr. Konrad Blum (The Head of postgraduate programme For Renewable Energies, University Of Oldenburg) for making my training a possibility at the FOLKECENTER.

Finally, I am greatly indebted to Prof. F.O Akuffo, "The head of Mechanical Engineering Department, University of science and technology(UST),Kumasi. Ghana, for his motivation, coupled with advice which obviously helped me to induce my initial interest in the field of renewable energies.

Practical training report, 24-02-1997to 25-04- 1997, By J.K.N. Gbagbo . II


Abstract.

Traditional household fuels play a vital role in developing countries. More than two million people depend on them to meet basic energy needs. Today many of these people are facing a deepening crisis of local wood resources are depleted and more distant forests are cut down. The implications of this crisis extend beyond the supply of energy itself. As the trees are lost, the land which provides the livelihood and feeds the nation have become more vulnerable to erosion and soil degradation. The story in Ghana is not different, where one of the priorities of the Government is to extend the national grid to all parts of the country by the year 2020.

It has however been realised that several rural communities who produced most of Ghana's agriculture products, will still not enjoy electricity from the grid due to the constraint of being too remote from the grid.

In most of these cases biogas as an alternative energy technology is the possible solution. Although there has been a few activities in this direction in the country, there is still the need to educate and carry out more simple, affordable and acceptable biogas plants in these remote areas.

/

This report is intended to be used by people in the field of biogas for workshops, technicians, teachers to educate as well as to carry out hands on constructions in Ghana and other tropical countries.

Chapter 1, discusses the biogas technology, what a biogas plant is, and how it functions. Chapter 2, describes the entire process. Chapter 3, discusses the necessary conditions for fermentation. Chapter 4, the measuring parameters for monitoring the system. Chapter 5, describes the various types of biogas plants suitable for tropical countries, Chapter 6, describes a planning guide for Ghana and other tropical countries. Chapter 7, discusses digester sizing and finally, Chapter 8, describes a concise biogas plant construction suitable for the rural areas of Ghana and other tropical countries.


1.0

1.11.2

1.3

1.4

1.5

2.0

2.1

2.2

2.2.1

2.2.2

2.2.3

2.2.4

2.3

2.3.1

2.4

2.4.1

2.4.2

2.4.3

2.4.3.1

2.4.3.2

2.4.3.3

2.4.3.4

3.0

3.1.

3.2

3.3

3.4

3.5

3.6

3.7

CONTENTSIntroduction

Biogas technology.

What is a Biogas Plant ?

Composition and properties of biogas

How a Biogas Plant works

Advantages of Biogas Plants ( Utilization )

The Process

Anaerobic digestion

The four process steps of anaerobic digestion

The hydrolytic step

The fermentation step

The acetogenic step

The methanogenic step

What is microbiology ?

Micro - organisms which take part in anaerobic degradation

Conditioning of Biogas

Reduction of the moisture content

Reduction of Carbon dioxide content .

Reduction of Hydrogen sulphide content

Absorption onto Ferric hydrate

Addition of Ferrum chloride

Dilution of Hydrogen sulphide concentration

Biological desulphurization

Necessary conditions for fermentation

Water content

Air tightness

Substrate and material balance of Biogas production

Carbon to Nitrogen Ratio ( C / N) of feedstock

Process temperature

Maintaining a suitable pH - balance

Retention Time

1

1

1

2

22

3

4

4

5

5

5

5

6

6

7

7

7

8

8

8

9

9

10

10

10

10

12

13

14

14


3.8 Absence of toxic materials in the digester 14

4.0 Measuring parameters required for monitoring biogas systems 16

4.1 Volatile fatty acids (VFA) 16

4.2 pH Value > 17

4.3 Total solids (TS) 18

4.4 Volatile solids (VS) 18

4.5 Determination of total solids (TS) and volatile solids (VS) 18

4.6 Chemical Oxygen Demand (COD) and Biochemical Oxygen 20

Demand (BOD)

4.6.1 Chemical Oxygen Demand (COD) 20

4.6.2 Biochemical Oxygen Demand (BOD) 20

4.7 Gas composition 22

4.8 Gas yield 23

4.9 Gas production rate 23

5.0 Biogas - Digester types 24

5.1 Technical description * 24

5.2 Batch fermentation 24

5.3 Continuous fermentation 24

5.4 Important types of Biogas Plants for tropical countries 25

5.5 Fixed - Dome plants 25

5.5.1 History 25

5.5.2 Function 25

5.5.3 Digester 26

5.5.4 Gas tightness 26

5.6 Types of Fixed - Dome plants 26

5.6.1 BORDA model 26

5.6.2 CAMARTEC model 27

5.6.3 DEENBANDHU with a hemisphere digester 28A

5.6.4 JANTA model with a brick reinforced, moulded dome 29

5.7 Climate and size 31

5.7.1 Advantages 31

5.7.2 Disadvatages 31

5.8 Floating - drum plants 31

5.8.1 The drum 31

*7*/ /II 1 4** 7C /) / 1 CICl*7 D.. T V \T Z^Z.


5.8.2 . Size 32

5.8.3 Advantages 32


5.9 Water- jacket floating - drum plants 33

5.9.1 Material of digester and drum Advantages 33

5.9.2 Guide frame 33

5.10 Types of floating - drum plants 34

5,11 Balloon plants 34

5.11.1 Advantages 35


5.12 Horizontal plants 35



5.13 Earth - pit plants 36



5.14 Ferrocement plants 36

• 5.14.1 Advantages 36


6.0 Biogas planning guide for Ghana and other tropical countries 38

6.1 Evaluation criteria 38

6.2 Questionnaire 39

7.0 Digester sizing 47

8.0 A concise biogas plant construction suitable for Ghana and

other tropical countries

50

9.0 Conclusion 96

10.0 Reference 98

11.0 Appendix 99

T^rnntinnl twnintna rennrt Oil _ f)1 _ 10Q7 fti • fiA — 1QQ7 Rv T AT A7 /TXi/»aA/i

' Biogas Plants suitable for Ghana and other tropical countries.

1.0 Introduction

1.1 Biogas Technology.

Biogas technology is a technical innovation in which organic waste such as Human excreta, animal dung,, agricultural residue, municipal sewage, vegetable waste or .kitchen residue is fermented under suitable environmental conditions to produce an inflammable gas methane (CH4 ), carbon dioxide (CO2), and traces of other gases such as hydrogen sulphide (H2S ) and nitrogen (N2).

The gas produced is called Biogas, and contains a large amount of methane gas and used directly as natural gas or LPG fuel for heating, cooking, lighting and running a combustion engine. The digested slurry is used as a high quality fertilizer for plant cultivation and raising fish.

1.2 What is a Biogas plant ?

A biogas plant is a plant which digests a mixture of organic materials and water in a container where air is excluded. Biogas and fertilizer are developed in a complicated fermentation process.

The main parts of a biogas plant are illustrated in figure 1.2 :

Fig. 1.2 : The main parts of a biogas plant

Prnf*tinnt Trninina Ran/it*/ 7d • Z)2 - 7QQ7 //> - Od. 1QQ7. Rv _TIC /V fZhnahn

A : A mixing chamber, where the organic material, often dung from cows or pigs, is mixed with water.

B : A digester, an enclosed container where the fermentation process goes on and biogas and fertilizer are developed.

C: A gas store, which is often part of the digester.D : An outlet chamber, or small container for storage of; the fertilizer.

1.3 Composition and properties of biogas.

Biogas is a mixture of gases that is composed chiefly of :

Biogas Plants suitable for Ghana and other tropical countries.

• methane (CH*) 40 - 70 vol. %• carbon dioxide (C02) : 30 - 60 vol. %• other gases 1 - 5 vol. %,

includingo hydrogen (H2) : 0-1

o hydrogen sulphide (H2 S) : 0 - 3 vol. %,

Like those of any pure gas, the characteristic properties of biogas are pressure and temperature dependent. They are also affected by the moisture content. The factors of main interest are:

• change in volume as a function of temperature and pressure,

• change in calorific value as a function of temperature, pressure and water - vapour content, and

• change in water - vapour content as a function of temperature and pressure.

The calorific value of biogas is about 6 kWh/m3 - this corresponds to about half a litre of diesel oil. The net calorific value depends on the efficiency of the burners or appliances.

1.4 How a Biogas plant works.

Dung and water are.mixed in the mixing chamber and lead into the digester. The mixture is kept in the digester for 40 - 60 days. Every day more material is added. No air is allowed into the digester, therefore the material ferments and develops biogas.

The gas collects in the gas store, which is either a movable steel-drum, a fixed dome or a plastic bag. After about 40 - 60 days no more gas develops and the digested slurry - the fertilizer enters the outlet chamber or small container for later use.


1.5 Advantages of Biogas Plants ( Utilization )./

Biogas is a clean and efficient fuel which bums without smoke or smell. Normally, the biogas produced by a digester can be used as it is, just in the same way as any other combustible gas. However, it is possible that there must follow a further treatment or conditioning, for example to reduce the hydrogen sulphide content in the gas. When, biogas is mixed with air in the proportions of 1: 20, highly explosive detonating gas forms. Leaky gas pipes in enclosed spaces constitute a hazard. However, there have been no reports of dangerous explosions caused by biogas so far.

Using biogas for cooking and heating, saves the consumption of kerosine, charcoal and wood. It avoids the need to collect firewood and twigs and eliminates the practice of indiscriminate felling of trees and consequent soil erosion. In country sides and rural areas, biogas can be used to fuel a combustion engine for electricity generation, water pumping, milling and processing.

The slurry produced as a by-product is a better quality manure compared to the ordinary manure from compost. It contains a higher percentage of nitrogen. The digested slurry could be applied directly in its liquid state or dried and bagged for sale as fertilizer. It could also be used for raising fish. The application of digested slurry to crops serves a dual purpose, since it is both a soil conditioner and a fertilizer. The slurry besides furnishing plant food, is of benefit to the soil as it increases the water holding capacity and improves its structure. They improve the economy by creating jobs and also create self - reliance.

Besides the use of the technology for the production of energy and organic fertilizer, many social and environmental benefits are also derived. The use of waste such as sewage sludge, human excreta, animal manure, kitchen residue and industrial waste for biogas production decreases the pollutant strength of the waste.. In this way, health risks and pollution are decreased.

i .Biogas technology serves as an effective control of parasitic diseases, hookworms, roundworms, etc; as most of the diseases causing organisms and pathogens are destroyed in the-digestion process. The digested slurry remains free from foul smell. Mosquitoes and flies are expelled from the surroundings of a biogas plant and therefore do not breed in the slurry.

Great achievements have been made in the comprehensive utilization of biogas and its by-product manure. In Africa, biogas digesters have yet to be used in any quantity. Kenya is reported to have around 250 floating - drum plants ( 1988). In Tanzania, about 120 biogas plants were built (1984), and Ethiopia is said to have about 100 plants. Egypt has 20, and Ivory Coast a total of 80 family biogas plants (1991). Sudan and Upper Volta also have a few plants.

In Chinese rural areas, more than 20 million biogas plants have been constructed and over 20 million people use biogas as fuel. India has over 630,000 biogas plants and in Denmark, about 13 million KWh electricity is produced annually from biogas. Many developed and developing countries are also investigating into biogas technology as an alternative source of energy as well as for the treatment of organic waste.

Practical Training Report, 24 - 02 -1997 to 25 - 04 -1997, By J.K.N. Gbagbo 3


2.0 The process.

2.1 Anaerobic digestion :

Any kind of organic material (carbohydrate, fat and protein) may be broken down by bacteria decomposition to release gas. However, the type of gas produced depends on whether oxygen is present or not. Decomposition in the presence of oxygen (aerobic digestion) produces carbon dioxide (C02), Hydrogen (H2), ammonia gas (NH4 ), Hydrogen sulphide (H2S), and a residue which can be used as fertilizer. This is the kind of decomposition that happens in the compost heap and on forest floor.

Anaerobic digestion is the decomposition of organic material in absence of oxygen to produce Biogas which consists mainly of methane gas (CH4 ) and carbon dioxide (C02). Small traces of water (H20 ), Hydrogen sulphide (H2S) and Nitrogen (N2) are also produced. The by-product in a form of slurry is superior in Nitrogen compared to that obtained under aerobic decomposition.

2.2 The four process steps of anaerobic digestion.

The process of biogas production is divided into four succession running steps, as shown in Fig. 2.2 .

methanecarbohydratesproteinsfat

glucose amino acids glycerin fattv acids propionic acid

butyric acid alcoholsother compounds

hydrolytic step

fermentative bacteria

fermentative

acetogenic bacteria

acid synthesize

acetogenic

methanoqenic step

methanogenic bacteria

Fig 2.2 : The four - step - model of anaerobic digestion.

___r>______ . u n't tno-r i- n , tnn-r !>.. T rr .r


2.2.X The hydrolytic step :

The organic matter is enzymolyzed externally by extracellular enzyme (cellulase, amylase, protease and lipase) of micro - organisms. Bacteria decompose the long chains of the complex carbohydrates, proteins and lipids into shorter parts. For example, polysaccharides are converted into monosaccharides. Proteins are splitted into peptides and amino acids.

Products of step 1 : amino acids, glycerine, monosaccharides.

2.2.2 The fermentation step :

In this step, facultative and obligate anaerobic degrade the monomers to short chained . fatty acids, alcohol, hydrogen and carbon dioxide. At the same time,, the redox potential for the strict anaerobic bacteria will be decreased by using the rest of oxygen by facultative anaerobic bacteria.

Products of step 2.2.2 : alcohol’s and fatty acids.

2.2.3. The acetogenic step :

The methane bacteria are only able to use acetate, hydrogen and carbon dioxide to build methane. In this step homoacetogenic bacteria synthesize these compounds from the products of the fermentation step.

Products of step 2.2.3 : acetate, carbon dioxide and hydrogen.

2.2.4. The methanogenic step :

Methanogenic bacteria utilize acetate, hydrogen and carbon dioxide to produce methane.

Products of step 2.2.4 : methane, carbon dioxide, hydrogen..

All the steps are in an unstable flowstability to each other. In case of any disturbances like over supply of degradable substances or feeding of toxic substances, the concentration of the fatty acids will increase, the pH -value will decrease and the process can collapse. With any disturbances in the methanogenic step, the fermentation


step will further produce more fatty acids, so the process speed determining step is the utilization of acetate.

Therefore, it is important to control the concentration of volatile fatty acids and the pH - value. However, manure has a very high buffer capacity, this means that the pH - value is a bad indicator for process quality.


2.3 What is Microbiology ?

The word micro biology is a broad term. It is the study of living organisms that are too small to be seen with the naked eyes. So a microscope is use to see an individual cell.The word microbiology includes the study of the following: -(a) Bacteria (bacteriology)(b) Viruses (virology)(c) Yeast and moulds (mycology)(d) Protozoa (protozoology) and some special forms of life.

2.3.1 Micro - organisms which take part in anaerobic degradation.

(a) C6H1206 ——> CH3CH2COOH + CH3COOH + C02 + H2

Propionic acid acetate

(i) Clostridium; Bacillus; Pseudomonas; Microcuccus (Cellulose and other carbohydrates).

(ii) Bacteriodes ruminocola (Proteins).(iii) Bacillus; Atcaligenes; Pseudomonas (Fats).

(b) CH3CH2COOH--------> CH3COOH + COz + 3H2

Propionic acid--------------------- By Synthrophobacter wolinii.

(c) CH3CH2CH2COOH+ 2H20------> 2CH3COOH + 2H2

butyric acid acetate_____________ By Desulphovibrio.

(d) CH3CH2OH-------- > CH3COOH + 2H2ethanol • acetate___________ By Desulphovibrio.

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Chemical reactions by the methanogenic bacteria.

(i) 3H2 + CO > CH4 + h2o

(ii) 4CH3OH > 3CH4 + COz + H20

(iii) 4H2 + COz > CEL + 2H20

(iv) 4HCOOH —> CH4 + 3C02 + 2H20

(v) CH3COOH —> CEL, + C02

(vi) 2HzO+ 4CO > CEL, + 3C02

(vii) 4CH3NH3CI + 2H20 —-—> 3CH4 + C02 + 4NH4C1.

2.4 Conditioning of biogas.

Sometimes the biogas must be treated or-conditioned before utilization. The predominant forms of treatment aim at removing either water, hydrogen sulphide or carbon dioxide from the raw gas.

2.4.1 Reduction of the moisture content.

The biogas is usually fully saturated with water vapour. This involves cooling the gas, e.g. by routing it through an underground pipe, so that the excess water vapour condenses out at the lower temperature. When the gas warms up again, its relative vapour content decreases. The" drying" of biogas is especially useful in connection with the use of dry gas meters, which otherwise would eventually fill up with condensed water:

2.4.2 Reduction of carbon dioxide content.

The reduction of the carbon dioxide content is very complicated and expensive. In principle, carbon dioxide can be removed by absorption onto lime milk, but that produces" seas " of lime paste and must therefore be ruled out, particularly in connection with large scale plants, for which only high - tech processes like micro -

, screening are worthy of consideration. C02 " scrubbing" is rarely advisable, except in order to increase the individual bottling capacity for high - pressure storage.

Practical Training Report, 24 - 02-1997 to 25-04- 1997, By J.K.N. Gbagbo 7

2.4.3 Reduction of hydrogen sulphide content.

The hydrogen sulphide in the biogas combines with condensate to form corrosive acids. Water - heating appliances and utensils and refrigerators are particularly at risk. The reduction of the hydrogen sulphide content may be necessary if the biogas is found to contain an excessive amount, i.e. more than 2% H2S, and is to be used for furling an engine. Since, however, mostbiogas contains less than 1% H2S, desulphurization is normally not necessary, especially if it is to be used for operating a stationary engine.

i


2.4.3.1 Absorption onto ferric hydrate, (Fe(OH)3).

For small - to - medium size systems, desulphurization can be effected by absorption onto ferric hydrate, (Fe(OH)3), also referred to as bog iron, a porous form of limonite. the porous, granular purifying mass can be regenerated by exposure to air. the absorptive capacity of the purifying mass depends on its iron - hydrate content: bog iron containing 5 -10 % ,Fe(OH)3 can absorb about 15 g per kg without being regenerated and approximately 150 g/kg through repetitive regeneration. It is very noteworthy fact that many types of tropical soils (laterites) are naturally ferriferous and, hence, suitable for use as purifying mass.

2.4.3.2 Adding ferrum chloride.

This chemical reaction occurs in two steps. Until a pH - value of 6.92 H2S, dissociates into HS' and H + and over a pH- value of 6.92 H2S is soluble. Adding Fecl2 to the slurry converts it into ions of Fe2+ and Cl", which is the first step.

H2S <—> HS + H —--------------———- (1)

dissociation of ferrum chloride :

Fecl2 <=> Fe2+ + 2CI"--------------------------- (2)

During the second step, the hydrogen sulphide ion dissociates into S 2" and H+ and is followed by a conversion compound of Fe2+ and S 2" to FeS which is insoluble andprecipitates.

HS" <=> S2" + H+ ------------------- :------- ' (3)

this reaction occurs normally at higher pH - values but also at lower values if there is an electron partner for S2" like Fe2+.

S2 + Fe2 <=> FeS !! —------------------------- (4)

Practical Training Report, 24 - 02-1997 to 25 - 04-1997, By J.K.N. Gbagbo 8


Nevertheless there are some problems with this salt because it is usually added in the pre- tank and has to be removed, as well iron has to be present in sufficient amounts and even more as the stoichiometric numbers might indicate.

2.4.3.3 Dilution of H2S concentration.

The concentration of H2S is easily decreased by adding concentrated organic waste which does not contain any sulphur but increases the amount of produced biogas considerably. Substrate with a high energy value and good biodegradability, such as fish oil, fatty sludges, oil mill residues etc.

For example:

12 m3 manure = 300 m3 biogas with 0.2 % H2S / m3 biogas = 0.6 m3 H2S / d

12 m3 manure + 500 litres Of fishwaste (~ 4 %) = 700 m3 biogas = 0.009% H2S

= 900 PPM

Limit for the engine = 1200 PPM

But it is worth to mention that this amount of manure, with increasing biogas production of (about 230 %) by adding concentrated waste the limit for H2S concentration (1200 PPM) is 0.28 % H2S / m3 biogas. The concentration depends also on process operating and it is possible that the limit will be overstepped. Nevertheless, if compared with the costs for other kinds of desulphurization, this method proves advantageous, hence very popular with small biogas plants.

2.4.3.4 Biological desulphurization.

Nowadays the most common method is just to pump a certain amount of air (~ 5 %) into the digester or better in a special desulphurization reactor. In this reactor special ' aerobic sulphuric bacteria’s, which are in the manure, are mobilised on hollow plastic balls, the reactor is filled with degassed manure and from the bottom are let the air and biogas.

The H2S is converted to elementary sulphur and water, the sulphur is brought with the manure to the field where it is utilized by the plants to build up proteins. Former methods of burning the biogas without desulphurization caused heavy emissions of sulphur dioxide.

Practical Training Report, 24-02-1997 to 25 - 04-1997, By J.K.N. Gbagbo 9


3.0 Necessary conditions for fermentation.

Since fermentation is the result of the action of many sorts of anaerobic micro - organisms, the better the living environment for these micro - organisms, the faster the production of biogas. If proper conditions cannot be maintained, production will slow or cease altogether. The optimal living conditions for these micro - organisms are as follows

3.1 Water content.

There must be suitable water content as the micro - organism's excretive and other metabolic processes require water. The water content should normally be around 90 % of the weight of the total contents. Both too much and too little water are harmful. ■ With too much water, the rate of production per unit volume in the digester will fall, preventing optimum use of the digester. If the water content is too low, acetic acidswill accumulate, inhibiting the fermentation process and hence production.

The water content should differ according to the difference in raw materials for the fermentation.

3.2 Air tightness.

The primary requirement for the production of biogas is the absence of oxygen (anaerobic). The methane forming bacteria are obligate anaerobes; they can not function if oxygen is present. This means that the digester will have to be well sealed (air - tight) to ensure that there is no leakage of air. If there is leakage of air, the action of the methanogenic bacteria are inhibited and the production of methane stops.

process failure.

3.3 Substrate (Feedstock) and material balance of biogas production.

In principle, all organic materials can ferment or be digested, hence can be used for the production of biogas. However, only homogenous and liquid substrates can be considered for simple biogas plants: -

faeces and urine from cattle, pigs and possibly from poultry and the wastewater from toilets. When the plant is filled, the excrement has to be diluted with about the same quantity of water, if possible the urine occuring should be used. Waste and wastewater from food - processing industries are only suitable for simple plants if they are homogenous and in liquid form.

, Biogas Plants suitable for Ghana and other tropical countries.

However, the rate of production of production of biogas depends on the nutrient composition of the organic compound and how easily it can be degraded by the bacteria.

Plant material for instance is bounded up in cells strengthened with cellulose and lignin, and are difficult to digest unless they are broken down physically or treated chemically.

Animal wastes have been found the most suitable feedstock for biogas production.This waste has been ground up by the animals teeth and broken down chemically byacids and enzymes in the animal’s gut.

Animal Dung/day(Kg)

Moisture content (%)

C/NRatio

Gas yield per Kg (lit.)

Gasyield/animal/day(lit.)

Cattle 10 78-84 25-30 36 . 360

Pig (50 Kg) 2,25 72-77 14-18 • 78 175,5

Chicken (2 Kg)

.0,18 52-55 8-10 62 11,16

Human(Adult)

0,4 80-85 8-10 70 • 28

Straw 20-60 81 -140 5-20

Table 3.3 Properties of most commonly used feedstock.

f These values depend very much on the size of the animal, what it eats, the environmental conditions, etc.

Human, pig-and chicken manure are rich in nutrients and have a higher gas yield per kilogram of manure. However, they need a “starter” or a seeding material such as slurry obtained from a working biogas plant because they do not have enough methanogenic bacteria to start with. Some animals such as goat and sheep manure are good but are in a form of pellets that must be broken down mechanically. Besides, this pellets are difficult to collect.

Cattle and pig dung are the easiest to use. They can be easily handled and collected in large quantities with very little labour.

11Practical Training Report, 24 - 02 -1997 to 25 - 04 -1997, By J.K.N. Ghagbo


3.4 Carbon to Nitrogen ratio (C / N) of feedstock.

One commonly used parameter is the C/N (carbon / nitrogen ) ratio in thefuel stock materials. It has been found that the optimum ratio is between20 and 30 :1 and that too high a ratio restricts the microbial process due to a lack ofnitrogen for cell formation while too low a ratio increases the shift towards ammoniatoxicity.

But there seems to be a wide range of suitable C/N ratios depending on the materials digested..

Raw materials Carbon content in % of raw material

Nitrogen content in % of rawmaterial

C/NRatio

Wheat straw 46 0,53 87:1rice straw 42 0,63 67:1Com straw 40 0,75 53:1Leaves 41 ►

i-* o o 41:1Bean - straw 41 1,30 32:1Weeds / grass 14 0,54 27:1Peanut straw 11 0,59 19:1Fresh sheep dung 16 0,55 29:1Fresh cattle dung 7,3 0,29 25:1Fresh horse dung 10 0,42 24:1Fresh pig dung 7,8 0,60 13:1Fresh human faeces 2,5 0,85 3:1(These are values of the non- decomposed state of the materials.)

In practice, a mixture of 10 - 12% of dung, 30 - 40% of weeds or straw and50% of water has proved ideal.

Table 3.4 : Carbon / Nitrogen contents of different feed materials.

Practical 'Trninino Rcnnrt. _ 1QQ7 ts* _ fiJ _ 7007 Ru T \T CZUnnh.


3.5 Process Temperature.

Under suitable temperature conditions, the micro-organisms become more active and gas production is high. Methanogenic bacteria work better within the temperature range of 30 40 C (mesophilic) and best within the range of 50-60 C(thermophilic). •

However, the energy needed for heating up the slurry to the thermophilic range is a major drawback and renders it inefficient.

It is important that the temperature of the slurry remains constant. Sudden temperature change of more than 5°C a day can cause the methanogenic bacteria to stop working, and this will result in the build up of acids and process failure.

biogas yield

thermophilic

mesophilic

psychrophilic

temperature10°C 20°C '

temperature optima

psychrophilic until 20°C mesophilic 35 - 42°C thermophilic 50 - 60°C

Fig. 3.5 . Three temperature fields, with each another bacteria set.

According to Hashimoto et al. (1980) the specific bacteria growth rate is given by pm = 0.013 (T) - 0.129, and is limited by a temperature of 10 °C.

Practical Training Renort. 24- 02 -1997 to 25 - 04 - 1997. Bv J.K.N. Ghanho 11


In all biological processes, the biochemical reaction speed increases with rising temperature. A common rule says that per each 10 °C, the production of biogas doubles. In practice, temperature is of decisive significance for gas production. Therefore, for instance, the plant should be fed during afternoon hours, i.e., when outside temperature is highest. Otherwise preheated water has to be used. So that the higher the temperature, the higher the gas yield.

In countries with tropically hot climate, good gas yield can be achieved even without heating or insulation. With simple biogas plants only the mesophilic range is of interest.

3.6. Maintaining a suitable pH - balance.

The micro - organisms require a neutral or mild alkaline environment. A too acidic or alkaline environment will be detrimental. A pH between 7 and 8.5 is best for fermentation and normal gas production.

The pH - value for a fermentation depends on the ratio of acidity and alkalinity and the carbon dioxide content, for normal process of fermentation, the concentration of volatile acid measured by acetic acid should be below 2000 PPM; too high a concentration will greatly inhibit the action of the methanogenic micro - organisms.

3.7. Retention Time.

The retention time can only be accurately defined in batch - type facilities. For continuous system, the calculations are based on a mean retention time arrived at by dividing the digester volume by the daily influent rate. Depending on the vessel geometry, the means of mixing, etc., the effective retention time may vary widely for the individual substrate constituents, selection of a suitable retention time thus depends not only on the process temperature, but also on the type of substrate used.

3.8. Absence of toxic materials in the digester.

The micro - organisms that produce the biogas are easily affected by many harmful materials which interfere with their livelihood. The maximum allowable concentrations of such harmful materials are as follows


Substance Symbol Concentration Units

Sulphate so4 5,000 parts per million (PPM)

Sodium chloride Nad 40,00.0 parts per million (PPM)

Copper Cu 100 milligrams per litre

Chromium Cr 200 milligrams per litre

Nickel Ni 200 - 500 milligrams per litre

Cyanide CN . below 25 milligrams per litre

ABS (detergent compound)

20-40 parts per million (PPM)

Ammonia nh3 1,500 - 3,000 ' milligrams per litre

Sodium Na 3,500 - 5,500 milligrams per litre

Potassium K 2,500 - 4,500. milligrams per litre

Calcium Ca 2,500 - 4,500 milligrams per litre

Magnesium Mg 1,000 - 1,500 milligrams per litre

Fig. 3.8Maximum allowable concentrations of harmful substances.

polluting substances such as these can only be accommodated if under these conditions, they must either not be present or their concentrations must be diluted, for example by the addition of water.

Practical Training Report, 24 - 02-1997 to 25-04-1997, By JKN. Gbagbo 15


4.0 Measuring parameters required for monitoring biogas system.

The parameters that are used to monitor and control anaerobic digestion process can be divided into three categories:

(i) Volatile fatty acids and pH.

(ii) Total solids (TS), Volatile solids (VS), Chemical oxygen demand and Biochemical oxygen demand.

(iii) Gas yield, production and composition.

4.1 Volatile fatty acids (VFA).

The VFA are the intermediate products of the digestion process. The consists of acetate, propionate, butyrate, valerate, lactate, and isovalerate. The VFA are the substrate for methanogenic bacteria. However, when in large concentration, they inhibit the growth of methanogenic bacteria and this leads to a decrease in the consumption rate of VFA, C02, and H 2 . Gas production rate is thus'decreased with low CH4 content but high C02 level.

Maximum production of biogas therefore requires successful control of the accumulation of VFA which in turn affects the methanogenic stage and hence the gas production and composition. A continuous monitoring of the VFA, CH4 , and C02 can be used to control the organic matter feeding rate of the digester and hence the anaerobic process. '

The method for the determination of VFA in a digester sludge is based on esterification of the carboxylic acids present, and determination of the esters by the ferric hydroxymate reaction.

A spectrophotometer (Fig. 3.1 ) is used to measure the absorbance which is then computed automatically and records all volatile organic acids present as their equivalent mg/1 acetic acid.

Practical Training Report, 24 - 02- 1997 to 25-04-1997, By J.K.N. Gbagbo 16

Biogds Plants suitable for Ghana and other tropical countries.

Fig. 4.1 Spectrophotometer.

4.2 pH Value.

The pH value for a digester depends on the acidity and alkalinity of the slurry in the digester. The pH value is not a very sensitive indicator of a digester behaviour because significant environmental changes would have already occurred before the pH drops. However, monitoring pH can be very useful because the methanogenic bacteria will only grow with a narrow pH range of between 7 and 8. For a pH value less than 7, the methanogenic bacteria are inhibited and this retards the digestion process.

Practical Training Report, 24 - 02- 1997 to 25-04- 1997, By J.K.N, Gbagbo 17


Furthermore, if the process is to be recovered, maintenance of proper pH is absolutely necessary

pH is determined using a pH meter or a universal litmus paper. The determination of pH with a litmus paper is very simple and fast. It does not require any equipment, however, the results obtained are inaccurate.

4.3 Total solids (TS).

TS is a measure of the dry solid matter left after moisture has been removed from the feedstock. TS contained in a certain amount of material is usually used as the material unit to indicate the biogas production rate of the material. The TS of a feedstock material is also a necessary requirement for computing the quantity of water needed to mix the material to the required moisture content of 88 - 95 %.

TS is determined by drying a sample of the feedstock in an oven at 105°C until its weight remains constant ( when all the water in the feedstock evaporates). The percentage of the dry solid matter remaining, represents the total solids (TS) of the material.

4.4 Volatile Solids (VS).

VS is the measure of the organic matter that can be degraded. It is the part of the total solid that is lost (volatilized) when it is burnt to ash at a temperature of 550°C. The VS of an organic material before and after fermentation provides a good estimate of the percentage of the organic matter that has been degraded to produce biogas.

The reduction in VS is also a means of monitoring the efficiency of the digestion process. VS is expressed as percentage of TS contained in the fermentation material or as percentage of the fermentation material.

4.5 DETERMINATION OF TOTAL SOLIDS (TS) AND VOLATILE SOLIDS (VS).

DATA RECORD AND CALCULATION FORM.

PLANT NAME:TYPE OF MANURE:............OTHER ORGANIC WASTE:

DAILY QUANTITY FED:.. DAILY QUANTITY FED:


SAMPLE SOURCE OF SAMPLE

COLLECTIO N DATE

TESTING

DATE TIME(1)

(2)

SAMPLE (1) (2)

Weight of empty dish (g) .A

Weight of empty dish + sample (g)B

■

Weight of empty dish 4- dry sample after, 15 Hrs (g) C,

Weight of empty dish + dry sample after ............ .......Hrs (g) C?

Weight of empty dish +. dry sample after .................... Hrs (g) C3 . ■

Total duration of heating at 1030 C (Hrs) t,Constant weight of dish + dry sample CDuration of heating at 550 "C (Hrs.) t2Weight of dish + ash (g)

D

CALCULATIONS

Total Solids (TS) %(C-A)/(B-A)x 100

Volatile Solids (VS) %(C-D)/(B-A)x 100

Moisture Content100 - (TS %)

VS as a % of TS(C-D)/(C-A)x 100

Practical Training Report, 24 - 02- 1997 to 25-04- 1997, By J.K.N. Gbagbo .19


4.6 CHEMICAL OXYGEN DEMAND (COD) AND BIOCHEMICAL OXYGEN DEMAND (BOD).

4.6.1 CHEMICAL OXYGEN DEMAND (COD)

In a situation where biogas technology is used in the treatment of sewage or liquid waste, it will be quite inaccurate to determine the organic matter content by using TS and VS. This is because of the very low quantity of solid matter content in the liquid waste. The organic matter content of such liquid waste is often indicated by Chemical Oxygen Demand (COD) and the Biochemical Oxygen Demand (BOD).

The COD is a measure of the oxygen equivalent of the of the materials present in the slurry that are subject to oxidation by a strong chemical oxidant. COD is used to show the degree to which water is polluted.

To a certain extent, it indicates the quantity of oxidizable substances contained in the liquid. Moreover, from the change in COD before and after fermentation, the Yield of Biogas can be estimated.

COD is defined as the mg of Oxygen (02) consumed per litre of sample and it is determined by heating the sample for two hours with a strong oxidizing agent (Potassium dichromate).

The reagents also contain silver and mercury ions. Silver is a catalyst and mercury is used for complex chloride interference’s. Oxidizable organic compounds react, reducing the dichromate ion (Cr 20 7 2" ) to green chromic ion (Cr 3+ ). The amount of Cr ^ produced is determined using calorimetric or titrimetric method, and from this amount, the quantity of oxygen consumed per liter of sample can be determined.

4.6.2 BIOCHEMICAL OXYGEN DEMAND (BOD).

The BOD is a measure of the amount of oxygen consumed by bacteria as they oxidize organic matter in a slurry. It reveals whether the liquid waste can be treated with a biological method (Biogas technology). The higher the BOD is, the more the liquid waste contains organic matter which can be degraded by microbes.

BOD is usually determined after the sample has been cultivated for five in the dark at 20 C . The sample is placed in amber bottles by their caps and vinyl tubing to the closed-end manometer. Inside the bottles above the slurry is air which contains 21 % oxygen.


tBiogas Plants suitable for Ghana and other tropical countries.

Bacteria in the sample make use of oxygen continuously to oxidize organic matter . present in the slurry sample. The air above replenishes the used oxygen and a drop in pressure occurs within the sample bottle.

The drop in pressure causes the mercury in the manometer to rise and indicates a.reading on the mg/1 BOD scale and from this, the BOD is computed.

Fig. 4.6.2 MODEL 2.173B BOD APPARATUS.

The ratio of BOD to COD provides enough information on the extent to which liquid waste can be degraded to produce biogas.

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The higher the ratio of BOD to COD of any kind of liquid waste , the greater the possibility of treating it with biological method (Biogas technology). For instance, a BOD to COD ratio of 0.2 or less for a liquid waste will be improper to treat it with a biological method.

4.7 Gas Composition.

Biogas is known to consists of methane (CH4 ); carbon dioxide (C02),and small traces of water (H20 ), hydrogen sulphide (H2S) and nitrogen (N2) as shown in Fig. 2.2. The most valuable of these in terms of energy value is methane (CH 4).

The composition of CH4 and C02 is a measure of the microbiological activity in theanaerobic digestion process and therefore can be used as an indicator of digesterimbalance.

A sudden increase in C02 level and decrease in CH4 content is an indication that the methanogenic bacteria activity has been decreased and / or the hydrolytic and acetogenic bacteria has been stimulated. H2S on the other hand has a high corrosive effect and is dangerous to every metal that comes into contact with it.

It is therefore important to monitor the level of H2S. especially when the biogas is to be used in gas motors and generators.

High levels of H2S is dangerous since it reduces the life span of the pipe distribution system and end use device. H2S is reduced by passing the gas through a tube consisting of ferric oxide particles or by adding FeCl 3 solution into the digester. The reaction is as shown below:

Fe2+ + H 2 S------^ FeS

Gas chromatography can be used to automatically measure directly the content of CH4 , C02 ,N2 , and H 2 S and other gases to a very" high degree of accuracy and can generate information of microbiological and digestion performance.

The gases are separated on the basis of molecular sieving as they pass through the detector. The TCD detects the concentration of CH 4, C02 and N2, while the PID detects the concentration of H 2 S.

These results are then integrated automatically to give the percentage composition of each gas.

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4.8 Gas Yield.

Gas yield represents the quantity of gas obtained from unit organic matter. It is expressed as m3 (biogas )/ kg (TS) or m3 (methane) / kg).

The yield of methane is an important parameter in methane fermentation as the resultscan be used to compare the efficiency of different fermentation materials.

The yield of biogas from organic material fed into a digester could be determined using a small laboratory digester and the gas produced measured and analyzed.

Environmental and operational factors that affect the gas yield could be varied and controlled to establish the optimum condition for maximum gas yield.

4.9 Gas Production Rate.

The overall efficiency and economics of a biogas plant is determined by the quantity of biogas it produces. The volume of biogas produced per unit volume of digester per day assists in assessing the efficiency of the biogas plant, the digesttion process and the organic matter used as feedstock, and gas production is high. Methanogenic bacteria work-better within the temperature range of 30 - 40. C (mesophilic) and best within the range of 5Q - 60 C (thermophilic).

However, the energy needed for heating up the slurry to the thermophilic range is a major drawback and renders it inefficient. ' -

It is important that the temperature of the slurry remains constant. Sudden temperature change of more than 5°C a day can cause the methanogenic bacteria to stop working, and this will result in the build up of acids and process failure.



5.0 Biogas - Digester types.

5.1 Technical Description.

In general, biogas digesters can be divided into two main types : - continuous process type digesters in which material is added continuously and biogas production is uninterrupted, and batch type digesters in which material is loaded in one single operation and left to ferment until biogas production ceases. Continuous biogas supply is possible also with batch digesters if a gas storage tank is built into the system.

5.2 . Batch fermentation.

Batch fermentation of material to biogas is usually regarded as the simplest ( and therefore usually the cheapest) biogas production system available. It involves charging an air - tight digester with a substrate, a seed inoculum ( a small amount of substrate containing bacteria from an earlier digesting process used to start a new digesting process) and, in some cases, a chemical catalyst to maintain a satisfactory pH - value. Once loaded, the digester is sealed and allowed to ferment for 30- 180 days depending on the local heating conditions. Gas production builds up to a maximum during this period and then begins to decline as the material loses its ability to produce.

Material in the digester can have a" normal" solids content of 6 -10 % or can beincreased to 20 % for " dry " fermentation. Although batch fermentation is simplerthan fermentation with the continuous, process type digesters, the process takes twiceas long and is therefore better suited to fermentation of more fibrous materials.

1 ;

RC.t-xOVACSL£ Cover .

Q.4ACTOR

-p'GAS OUTLET

CO'VE.R. Ton. SOLIDS ESX7VAL-

-e, MQUip outvct

Principle of batch digester.

5.3 Continuous fermentation.

There are three main types of continuous process biogas digesters : -The fixed - dome ( Chinese type), the floating cover (Indian type) and the plug flow orbag type.

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5.4 Important types of biogas plants for tropical countries.1

The following, most important types of biogas plants are described here:

(i) Fixed-dome plants

(ii) Floating-drum plants

(iii) Balloon plants

(iv) Horizontal plants

(v) Earth-pit plants

(vi) Ferrocemeht plants

Of these, the two most familiar types are the fixed-dome plants and the floating-drum plants.

5.5 Fixed-dome plants

5.5.1 History

Fixed-dome plants are an appropriate technology for developing countries, specially for rural areas. They can, nevertheless, in certain dimensions also be used for agroindustrial and communal wastewater treatment.

In the beginning, fixed-dome plants were mainly built In the People's Republic of China, but are now spread in several countries.

5.5.2 Function

A fixed-dome plant comprises a closed, dome-shaped digester with an immovable, ■ rigid gasholder and a displacement pit. 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. If there is little gas in the holder, the gas pressure is low.

Practical Training Report, 24 - 02 -1997 to 25 - 04 -1997, By J.KN. Gbagbo 25


5.5.3 Digester

The digesters of fixed-dome plants are usually made of masonry. They produce just as much gas as floating-drum plants, but only if they are gastight. However, utilization of the gas is less effective as the gas pressure fluctuates substantially.

Burners cannot be set optimally. If the gas is required at constant pressure (e.g., for engines), a gas pressure regulator or a floating gasholder is necessary. Engines require a great deal of gas, and hence large gasholders. The gas pressure then becomes too high if there is no floating gasholder.

5.5.4 Gas tightness

The top part of a fixed-dome plant (the gas space) must be gas tight. Concrete, masonry and cement rendering are not gas tight. The gas space must therefore b,e painted with a gas tight product (for example Latex or synthetic paints).

Another possibility to reduce the risk of cracking consists in the construction of a weak-ring in the masonry of the digester. This "ring" is a flexible joint between one lower and one upper part of the hemispherical wall.

5.5.5 Substrate

Fixed-dome plants can handle fibrous substances in combination with animal excrement’s, since the motion of the substrate breaks up the scum each day.

5.6 Types of fixed-dome plants

There are different models of fixed-dome plants:

5.6.1 BORDA model :

9APractical Training Report, 24 - 02 - 1997 to 25 - 04 - 1997, By J.K.N. Ghasbo

Biogas _ Plants suitable for Ghana and other tropica! countries.

The BORJDA-plant is a combination of the floating-drum and the fixed-dome plant. It combines the advantages of the fixed - dome plant with the process-stability of the floating-drum plant which garantees a constant gas pressure.

Gas

BORDA - a family-size digester

Fig.5.6.1 : BORDA model

5.6.2 CAMARTEC model:

The CAMARTEC has a simplified structure of a hemispherical dome shell based on a rigid foundation ring only and a calculated joint of fraction, the so called weak / strong ring, which separates the gas storage area from the lower bottom part and prevents the upper dome from propagating cracks. These can occur at the footing of the dome because of high tensile stresses that masonry cannot bear.

Practical Training Report, 24 - 02-1997 to 25-04-1997, By J.K.N. Gbagbo 27

upper dome from propagating cracks. These can occur at the footing of the dome because of high tensile stresses that masorny cannot bear.


Fig. 5.6.2 CAMARTEC model.

Practical Training Report, 24-02- 1997 to 25-04- 1997, By J.K.N. Gbagbo 28


5.6.3 DEENBANDHU MODEL( meaning ” friend of the poor M)with a hemisphere digester

This model is a low - cost rural household popular biogas plant that has been used in the India since 1986.Biogas digesters by and large remains beyond the reach of most rural households. There has been an apparent need to reduce the cost of biogas units and bring them within the reach of a larger segment of the population. Plants of both KVIC and JANATA design involve considerable investment. A possible remedy was introduction of the " Deenbadhu" biogas plant meaning" friend of the poor".They'are built of brick and cement. They are plastered inside to make them tight.

0EEN8ANDHU MODEL

CUTLET

Fig.5.6.3 DEENBANDHU with a hemisphere digester.

29


5.6.4 JANATA model ( meaning " people ") with a brick reinforced, moulded dome

The JANATA model is a fixed - dome model built from bricks replacing the steel model used before. The feature of this model is that the digester and the gas holder are parts of an integrated brick masonry structure. The digester is made of a shallow well having a dome - shaped roof.

IIXJNC TANK

FIXED DOME TYPE 31 OCAS PLANTS

The inlet and outlet tanks are connected with the digester through large chutes and these tanks above the level of the junction of the dome and the cylindrical portion are known as inlet and outlet displacement chambers, the gas pipe is fitted on the crown of the dome and there is an opening on the outer wall of the outlet displacement chamber for the discharge of digested slurry.

Fig. 5.6.4 JANATA model with a brick reinforced, moulded dome.

Practical Training Report, 24 - 02 - 1997 to 25 - 04 -1997, By J.K.N. Gbagbo 30


5.7 Climate and size

Fixed-dome plants must be covered with earth up to the top of the gas-filled space as aprecautionary measure (internal pressure up to 0,1-0,15 bar). The earth cover makes them suitable for colder climates, and they can be heated as necessary. Due to economic parameters, the recommended minimum size of a fixed-dome plant is 5 m3. Digester volumes up to 200 m3 are known and possible.

5.7.1 Advantages :

Fixed-dome plants are characterized by low initial cost and a long useful life (20 years), since no moving or rusting parts are involved. The basic design is compact and well-insulated. Fixed-dome plants creates employment locally.

5.7.2 Disadvantages :

Masonry is not normally gastight (porosity and cracks) and therefore requires the use of special sealant or the construction of a weak-ring. Cracking often causes irreparable leaks.

Fluctuating gas pressure complicates gas utilization, and plant operation is not readily understandable. Fixed-dome plants can be recommended only where construction can be supervised by experienced biogas technicians.

5.8" Floating-drum plants.

5.8.1 The drum

In the past, floating-drum plants were mainly built in India. A floating-drum plant consists of a cylindrical or dome-shaped digester and a moving, floating gasholder, or drum. The gasholder floats either direct on the fermentation slurry or in a water jacket of its own.The drum in which the biogas collects has an internal and external guide frame that provides stability and keeps the drum upright. The gas drum is prevented from tilting. If gas is drawn off, the gasholder falls again.

Practical Training Report, 24 - 02 -1997 to 25 - 04-1997, By J.K.N. Gbagbo 31


5.8.2 Size

Floating-drum plants are used chiefly for digesting animal and human excrement’s on a continudus-feed mode of operation, i.e. with daily input. They are used most frequently by small-to-midsize family farms (digester size: 5-l5m3) or institutions and large agroindustrial estates (digester size: 20- I00m3).

5.8.3 Advantages:

Floating-drum plants are easy to understand and operate. They provide gas at a constant pressure, and the stored volume is immediately recognizable.

5.8.4 Disadvantages:

The steel drum is relatively expensive and maintenance-intensive due to the necessity of periodic painting and rust removal. Therefore the life-time of the drum is short (up to 15 years; in tropical coastal regions about five years). If fibrous substrates are used, the gasholder shows a tendency to get "stuck" in the resultant floating scum.

fl MIXING

OICESTZR

Floating Gas Holder Type Biogas Plant (KVIC Model)Fig. 5.8.4 : Floating-drum plants

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5.9 Water-jacket floating-drum plants.

In spite of these disadvantages, floating-drum plants are always to be recommended in cases of doubt. Water-jacket plants are universally applicable and especially easy to maintain. The drum won't stick, even if the substrate has a high solids content.

Water-jacket plants are characterized by a long useful life and a more aesthetic appearance (no dirty gasholder). Due to their superior hygiene, they are recommended for use in the fermentation of night soil and for cases involving pronounced scumming,e.g. due to rapid evaporation, since the gasholder cannot get stuck in the scum. The extra cost of the masonry water jacket is relatively modest.

5.9.1 Material of digester and drum

The digester is usually made of brick, concrete or quarrystone masonry with rendering. 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. 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 fibro - cement must receive a gaslight internal coating.

The gas drum should have a slightly sloping roof, 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.

i - .

Floating-drums made of glass-fibre reinforced plastic and high density polyethylene have been used successfully, but the construction cost is higher then with steel.

Floating-drums made of wire-mesh-reinforced concrete are liable to hairline cracking and are intrinsically porous. They require a gaslight, elastic internal coating. PVC drums are unsuitable because not resistant to UV.

Practical Training Report, 24-02-1997 to 25 - 04-1997, By J.K.N. Gbagbo 33


5.9.2 Guide frame

The side wall of the gas drum should be just as high as the wall above the support ledge. The floating-drum must not scrape on the outer walls. It must not tilt, otherwise the paint work will be damaged or it will jam.

For this reason a floating-drum always requires a guide: This guide frame must be designed so that the gas drum can be removed for repair. The drum can only be

■ removed if air can flow into it, either the gas pipe should be uncoupled and the valve opened, or the water jacket emptied.

The floating gas drum can be replaced by a balloon above the digester. This reduces construction costs (channel type digester with folia), but in practice problems always arise with the attachment of the balloon at the edge. Such plants are still being tested under practical conditions.

5.10 Types of floating-drum plants.

There are different types of floating-drum plants:

• KVIC model with a cylindrical digester

• PRAGATI model with a hemisphere digester

• GANESH model made of angular steel and plastic foil

• floating-drum plant made of pre-fabricated reinforced concrete compound units

• floating-drum plant made of fibre-glass reinforced polyester.

5.11 Balloon plants

A balloon plant consists of a heat sealed plastic or rubber digester bag (balloon), in the upper part of which the gas is stored. The inlet and outlet are attached direct to the skin of the balloon. The requisite gas pressure is achieved by weighting down the bag.When the gas space is full, the plant works like a fixed-dome plant- i.e., the balloon is not inflated; it is not very elastic. Since the material has to be weather-resistant, specially stabilized, reinforced plastic or synthetic caoutchouc is given preference. The useful life amounts to 2-5 years.

Practical Training Report, 24-02-1997 to 25 - 04- 1997, By J.K.N. Gbagbo 34

Biogas Plants suitable for Ghana and other tropical countries. ,

The fermentation slurry is agitated slightly by the movement of the balloon skin. This is favourable to the digestion process. Even difficult feed materials, such as water hyacinths, can be used in balloon plant. The balloon material must be UV-resistant. Materials which have been used successfully include RMP (red mud plastic), Trevira and butyl.

5.11.1 Advantages:

Standardized prefabrication at low cost; shallow installation suitable for use in areas with a high groundwater table; high digester temperatures; uncomplicated cleaning, emptying and maintenance. .


Low gas pressure requires extra weight burden; scum cannot be removed. The plastic balloon has a relatively short useful life, is susceptible to damage by mechanical means, and usually not available locally. In addition, local craftsmen are rarely in a position to repair a damaged balloon..

Inflatable biogas plants are recommended, if local repair is or can be made possible and the cost advantage is substantial.

5.12 Horizontal plants

Horizontal biogas plants are usually chosen when shallow installation is called for (groundwater, rock). They are made of masonry or concrete.

5.12.1 Advantages:

Shallow construction despite large slurry space.


Problems with gas-space leakage, difficult elimination of scum.

Practical Training Report, 24-02-1997 to 25 - 04- 1997, By J.K.N. Gbagbo 35


5.13 Earth-pit plants

Masonry digesters are not necessary in stable soil (e.g. laterite). It is sufficient to line the pit with a thin layer of cement (netting wire fixed to the pit wall and rendered) in order to prevent seepage. The edge of the pit is reinforced with a ring of masonry that also serves as anchorage for the gasholder. The gasholder can be made of metal or plastic sheeting.

If plastic sheeting is used, it must be attached to a quadratic wooden frame that extends down into the slurry and is anchored in place to counter its buoyancy. The requisite gas pressure is achieved by placing weights on the gasholder. An overflow point in the peripheral wall serves as the slurry outlet.

5.13.1 Advantages:

Low cost of installation (as little as 1/5 Th. as much as a floating-drum plant), including high potential for self help.


Short useful life, serviceable only in suitable, impermeable types of soil. Earth-pit plants can only be recommended for installation in impermeable soil located above the groundwater table. Their construction is particularly inexpensive in connection with plastic sheet gasholders.

5.14 Ferrocement plants

The ferrocement type of construction can be executed as either a self-supporting shell or an earth-pit lining. The vessel is usually cylindrical. Very small plants (Volume under 6 m3) can be prefabricated. As in the case of a fixed-dome plant, the ferrocement gasholder requires special sealing measures (provenly reliable: cemented- on aluminium foil).

5.14.1 Advantages:

Low cost of construction, especially in comparison with potentially high cost of masonry for alternative plants.




Substantial consumption of necessarily good-quality cement; participating good- quality cement; participating craftsmen must meet high standards; uses substantial amounts of steel; construction technique not yet adequately time tested; special sealing measures for the gasholder.

Ferrocement biogas plants are only recommended in cases where special ferrocementknow-how is available.

Practical Training Report, 24-02-1997 to 25-04-1997, By J.K.N. Gbagbo 17

6.0 Biogas Planning Guide for Ghana and other tropicalcountries.


This guide to planning is intended to serve agricultural extension officers, designers

and workers in the biogas field as a comprehensive tool for arriving at decisions

concerning the suitability of locations for family-sized biogas plants. The detailed

planning outline has a data column for entering the pertinent information and a rating

column for noting the results of evaluation.

6.1 Evaluation criteria.

The evaluation criteria are:

+ Siting condition are favorableo Siting condition are unfavorable, but

a) compensable by project activities

b) not serious enough to cause ultimate failure

Siting condition are not satisfied / not satisfiable

Despite its detailed nature, this planning guide is, as intended, nothing more than a

framework within which the extension officer should proceed to conduct a careful

investigation and give due consideration, however subjectively, to the individual

conditions in order to arrive at a locally practical solution.

By no means is this planning guide intended to relieve the agricultural extension

officer of his responsibility to thoroughly familiarize himself with the on-the-spot

situation and to judge the overall value of a given location on the basis of the

knowledge thus gained.

T T. D — 1,/ />") /flOT 1C n / 1007 Dt. T V AT o


6.2 Questionnaire.

Detailed pbanning guide for bicigas plants0. Initial situation Data RatingAddresses/p roj ect characterizationPlant acronym:Address of operator/customer: Place/region/country: Indigenous proj. org./ex;ecuting org.: Extension officer/advisor:

•

•

General user data Household structure and 'number of persons;User's economic situation: Animals: kind, quantity, housing:Crops: types, areas, manner of cultivation: Non-agricultural activity: Household/farm income: Cultural and social characteristics of user:Problems leading to the "biogas" approach

Energy-supplybottlenecks:Workload for prior source of energy:Poor soil structure/yields: Erosion/deforestation:Poor hygiene and other factors:

Objectives of the measure "biogas plant" User interests:Project interests:Other interests:

Practical Training Report, 24 - 02 -1997 to 25 - 04 -1997, By J.KN. Gbagbo 39


1. Natural /Agriculturalconditions

Data Rating

Natural conditionsMean annual temperature: Seasonal fluctuations: Diurnal variation:

Rating: o +SubsoilType of soil:Groundwater table, potable water catchment area:

Rating: o +Water conditionsClimate zone:Annual precipitation:Dry season (months): Distance to source of. water:Rating: 0 + •Livestock inventory (useful for biogas production)Animals: kind and quantity: 'Type and purpose of housing:Use of dung:Persons responsible for animals:Rating:

o . +

0 +Vegetable waste (useful for biogas production)Types and quantities:Prior use:

Rating: 0 +FertilizationCustomary types and quantities of fertilizer/areas fertilized: Organic fertilizer familiar/in use:Rating:

■

0 +

Practical Training Report, 24 - 02-1997 to 25 - 04-1997, Bv J.K.N. Gbagbo 40


Potential sites for biogas plantCombined stabling/biogas plant possible:Distance between biogas plant and livestock housing:Distance between biogas plant and place of gas consumption:

Rating:

1

- o +

- 0 +Overall rating 1 0 +2. Balancing the energy demand with the biogas production

Data Rating

Prior energy supplyUses, source of energy, consumption:

•

Anticipated biogas demand (kwh/day or 1/d)

for cooking:

for lighting:

for cooling:

for engines:

Total gas demand

a) percentage that must be provided by the biogas plant:b) desired demand coverage:Available biomass (kg/d) and potential gas production (1/d) from animal husbandry pigs: poultry:cattle:Night soil

Vegetable waste

•

A1Practical Training Report, 24 - 02-1997 to 25-04-1997, By J.K.N. Gbagbo


(quantities and potential gas yield)

1.2.

Totals: biomass and potential gas production

a) easy to procure:b) less easy to procure:

Balancing

Gas production clearly greater than gas demand -> positive rating (+)

Gas demand larger than gas production -> negative rating (-); but review of results in order regarding:

a) possible reduction of gas demand by the following measures->b) possible increase in biogas production by the following measures->If the measures take hold:-> qualified positive rating for the plant location (o)

If the measures do not take hold:-> site rating remains negative (-)

Overall rating 2 o +

AOTf/yinirttr Rannrt OA - O'? - 7097 tn ?- Oil - 7007. 7?U .flfT.N. Crhdpbo


3. Plant Design and Construction

Data Rating

Selection of plant design Locally customary type of plant:Arguments in favor of. floating-drum plant: Arguments in favor of fixed-dome plant: Arguments in favor of other plant(s):

Type of plant chosen:

•

Selection of site

Availability of building materials

. Bricks/blocks/stone: Cement:Metal:Sand:Pipi'ng/fittings:Miscellaneous:

•

-

Availability of gas appliances

Cookers:Lamps:

Overall rating 3 0 +4. Plant operation / maintenance / repair

Data Rating

Assessment of plant operationIncidental work:Work expenditure in h: Persons responsible:Rating with regard toanticipatedimplementation: „ ' +

Plant maintenance Maintenance-intensive

Practical Training Report, 24-02-1997 to 25-04-19,97, By J.K.N. Gbagbo


components:Maintenance work by user:Maintenance work by external assistance:Rating with regard tooanticipatedimplementation:

o +

Plant repair

Components liable to need repair:Repairs that can be made by the user:Repairs requiring external assistance:Requisite materials and spare parts:

Rating with regard to expected repair services: - 0 +

Overall rating 4 0 +5. Economic analysis Data RatingTime-expenditureaccountingTime saved with biogas plantTime lost due to biogas plantRating:

o +

- 0 +Microeconomic analysis Initial investment:Cost ofoperation/maintenance/repair:Return on investment: energy, fertilizer, otherwise:Payback time (static): Productiveness (static): Rating:

- 0 +

0 +Quality factors, useful socioeconomic effects and costsUseful effects: hygiene, autonomous energy, better lighting, better working conditions, prestige: Drawbacks: need to .

•

-------------- 01 1007 7007 Rv .TK.N. Gbaebo 44


handle night soil, negative social impact:Rating:

- 0 +0 +

Overall rating 5 - 0 +

6. Social acceptance and potential for dissemination

Data Rating

Anticipated acceptance Participation in planning and constructionIntegration into agricultural setting: Integration into household:Sociocultural acceptance: Rating:

'

0 +

- 0 +Establishing a dissemination strategy Conditions for and chances of the professional-craftsman approach:Conditions for and chances of the self-help oriented approach:

0 +

- 0 +■

General conditions for dissemination Project-executing organization and its staffing:organizational structure: interest and prior experience in biogas technology:Regional infrastructure for transportation: communication: material procurement: Craftsman involvement, i.e.which activities: minimum qualifications: tools and machines: Training for engineers, craftsman and users: Proprietary capital, subsidy/credit requirement on the part of user:

0 +.

Practical Training Report, 24-02-1997 to 25-04-1997, By J.K.N. Gbagbo 45


craftsmen:

Rating: 0 +

Overall rating 6 0 +

7. Summarization

Siting conditions No. Rating

Natural/agriculturalconditions

1. 0 +

Balancing the energy demand and the biogas production

2. - 0

Plant design and construction

3. 0 +

Plantoperation/maintenance/repair

4. 0

Economic analysis5. 0 '+

Social acceptance and potential for dissemination

6. 0 +

Overall rating of siting conditions 0 +


7.0 Digester Sizing.

The energy available from a biogas digester is given by;

E = 'n.Hb.Vb 1

where i\ is the combustion efficiency of burners, boilers, etc. and is approximately ( ~ 60%). In this case, some of the heat of combustion of the methane goes to heating

the Carbon dioxide (C02) of the biogas, and is therefore unavailable for other purposes. The net effect is to decrease the efficiency.

Hb is the heat of combustion per unit volume biogas (20 MJm"1. at 10 cm water gauge pressure; 0,01 atmosphere).And Vb is the volume of biogas.Alternatively,

E = rj. Hm. Fm.Vb 2

this implies that,

, Hb — Hm. Fm 3

Hm is the heat of combustion of methane (56 MJkg"1, 28MJm"1 at STP) and Fm is the fraction of methane in the biogas (~ 0,7 or 70% ).The volume of biogas is given by

Vb = C. m0 4

C is the biogas yield per unit dry mass of whole input (0,2 to 0,4 m3kg'1) and m0 is the mass of the digester input ( Eg. 2kg d"1 per cow).

The volume of fluid in the digester is given by :

Vt = m0 / pm 5)

where pm is the density of dry matter in the fluid (~ 50 kg m"1).

Practical Training Report, 24 - 02-1997 to 25 -04-1997, By J.K.N. Gbagbo 47


The volume of the digester is given by :

Vd= Vft,. 6

where Vt is the flow rate of the digester fluid, and tr is the Retention Time in the digester ( ~ 8 to 20 days).

An example :

Calculate the following

a) The volume of a biogas digester suitable for the output of four cows.

b) The power available from the digester,

given that the retention time is 20 days, temperature 30 °C, dry matter consumed 2 kgd"1, biogas yield 0,24 m3 kg' \The burner efficiency 0,6 and methane proportion is 0,8.Let the density of the dry matter in the fluid (pm) = 50 kg m "3The heat of combustion of methane (Hm) = L56 MJkg"1, 28MJm"' at STP)

SOLUTION:

Information given :

Retention time (t r ) ”20 days,Temperature ( T) = 30 0 C.

Mass of dry matter consumed per cow = 2 kg d'l,Biogas yield per unit dry mass of whole input (c ) = 0,24 m3 kg"x, Burner efficiency (t]) = 0,6,Methane proportion (f m) = 0,8 .The density of the dry matter in the fluid (pm ) = 50 kg m "3 The heat of-combustion of methane (Hm) = 28MJm"1 at STP .

Required to find:

a) The volume of a biogas digester suitable for the output of four cows.

b) The power available from the digester.



Calculationns:

(a)

Mass of dry master input by the four cows (m 0) =(Mass of dry matter consumed per cow) x ( number of cows)

= 2 kgd'1 x 4 = 8 kgd'1

Fluid volume in the digester is given by,

Vt = m0/pm

= 8kgd'1 /50kgm "3 = 0,16 m3 d 'l

The Digester Volume(Vd) :

= Vd x tr= 0,16 m3d x 20 d

= 3,2 m 3.

(b) The volume of biogas (V b):. = c x mD

= 0,24m3kg'1 x 8kgd"1 = 1,92 m3d'1

Hence the Energy available from the digester (E)/

"H* Hm. Fm. Vb

= 0,6 x 28 MJm'1 X 0,8 X 1,92 m3 d-1

= 26MJd'1 = 7,1 kWh d'1

= 300 W ( continuous, thermal).



8.0 A CONCISE REVISED BIOGAS CONSTRUCTION. SUITABLE FOR GHANA AND OTHER TROPICAL COUNTRIES.

8.1 PERFOMANCE INFORMATION.

GAS OUTPUT:

Theoretically, with a temperature of 35 0 C and an average cycle of 20 days you will obtain approximately "TOO %" gas ; in other words a 15 m3 E.B.3 plant will deliver 15 m3 biogas per 24 hour period. The above performance will in reality seldom be the actual result.

Constant temperature is unfeasible, as warming the digester would be necessary and this is neither easily accomplished nor cost effective. Real temperature will depend on the regional conditions. As a rule of thumb, the temperature of the system will be around 2° C under the air ( ambient) temperature.

Experience has shown that in the lowlands (from the coast to near Nairobi, Kenya one can expect 30 to 50 % biogas per mJ at 25 0 C to 300 C. In other words an E.B.3 system of 15 m3 will give 4.5 to 7-5 m3 per 24 hours.

In the highlands one can expect 15 to 25 % per m3 with a temperature of 18 to 22 0 C, that is to say an E.B.3 15 m" system will give 2.25 to 3.75 m3 biogas.

The gas production can be increased by as much as 20 % by erecting an insulating canopy above the plant.

SITING:

This biogas plant is stationary once it is constructed, it is therefore, critically important that the site be chosen very carefully. The following are some of the very important considerations required for proper siting:

- Performance is dependent upon heat.Choose an open sunny location.

- To reduce the risk of the gas leaks and or blocking of the pipe (gas feed) as well as economic reasons, the plant should be placed as close to the kitchen or point of use as possible and not over 120 metres away from the point of gas use.

Practical Training Report, 24 - 02- 1997 to 25 - 04-1997, By J.K.N. Gbagbo 50

- In order to facilitate the daily operation of the plant it should be placed near the kraal and water supply. If a grazing unit is in existence or planned, the plant should be placed in such a way that the manure can float into the plant.

- While the smell from the biogas plant is almost negligible, it is recommended that the plant be sited up wide away from the house.

- If the slurry from the plant is to be used directly in the fields, the outlet from the plant should be made in such a way that the slurry can be led through a run off system to the vegetables, maize, etc.- The optimal site cannot be found as each siting will have special conditions . requiring individual considerations in each case. A study of " permaculture" design principals may prove of value to siting evaluations.


s

Fig. 0. An example of optimal siting in Ghana.

Practical Training Report, 24 - 02-1997 to 25-04- 1997, By J.K.N. Gbagbo' 51

The biogas plant is near to the stable and water - tank as well as an all - year vegetable garden where the biogas slurry from the outlet chamber can be applied as ah excellent fertilizer, saving money for chemical fertilizers.

Biot’as Plants suitable for Ghana and other tropical countries.

STEP 1.

Upon finding a suitable site for the plant, excavation can begin.- First clear an area 3 metres in diameter for all brush.- Next, drive a stake into the ground at the centre of the site.

Tie a strong string to the stake with a loop, so that the string can revolve freely around the stake, then tie a pointed stick or peg at the other end of the string at a distance of 1 metre from the stake at the centre. Using the pointed stick as a marking tool, draw a circle on the ground and begin excavating as shown in Fig. 1.

Fig. 1.


STEP 2.

The hole is dug roughly cylindrical to a depth of 3 metres and a diameter of 2 metres. As the hole will be cramped in the beginning, 2 or 3 men will be enough to carry out the work. As the digging progresses and the bottom chamber is dug, up to 5 men may be used. About 3 to 10 days may be required depending on soil structure and other conditions.

Fig. 2.Practical Training Report, 24 - 02 - 1997 to 25 - 04 -1997, By J.K.N. Gbagbo 53


STEP 3.

When the cylindrical start hole has reached the desired size and depth, the hollowing out of the digestion chamber can begin.

First, measure 1.3 metres down into the hole from the surface of the ground.

Then, hollow out the lower portion of the cylinder to a diameter of 2.5 metres (again a stick and string can be used to measure the diameter) after removing all the loose earth from the bottom of the hole to a depth of 3 metres, dig a small hole in the centre of the bottom; with dimensions of 40 cm deep and a diameter of 30 cm.

To find the centre of the bottom of the hole place a stick across the top of the hole with a mark at the centre. Divide the hole into two nearly equal halves, then drop a stone from the centre of the stick.

Fig. 3.

Prnr'tiS'nl TV/rrnDrtn/tW W- /)2 — 1QQ7 t/i fi 1 1 fiQ7 T IT \1


STEP 4.

Placing the central guide pipe:

First, place a layer of small stones in the bottom of the small hole in the centre (10 cm deep). Next, place the central guide pipe into the centre of the small hole and fill the hole with concrete ( using a 1:3:5 mixture). Make sure that the central guide pipe stands vertical, use a level, place it alternately at two points 90 0 from each other to insure that the pipe is completely vertical.

Fig. 4.



Finally, secure the pipe at the surface of the ground ( as shown, using boards, rope or wire, or any other similar means.This operation is best performed at the end of the workday, as the concrete must remain undisturbed until it has cured ( hardened completely ) work can continue the following day.

STEP 5.

t

Fig. 5.

Practical Trainina Rcnort. 24-02- 1997 to 25 - 04- 1997, Bv J.K.N. Gbaebo


The following day, build a small wall, around the perimeter of the holes surface, using blocks or natural stones. The dimensions should be, height 30 cm and width 20 cm approximately.

Start the wall by surface soil from the area upon which the wall is to stand. Next pour a 1" thick foundation layer of concrete (1:3:5 ). Use a thick mixture that does not run loosely.

The inner diameter of the wall should be 2.10 metres. This can be accomplished by using the string method used earlier. Using the central guide pipe as the centre point of the string (length of string is approximately 105 cm). The top of the wall must be level.

STEP 6.

When the wall has dried up, it can be shaped to its final size. Use the string method again to maintain a proper diameter.Finish digging the walls as smooth as possible, since this will save cement, in the final stages of the construction.

Dimensions for the upper circle :

From the surface of the ground to the bottom of the upper cylinder is 1 metre, and diameter of 210 cm.

Dimensions for the lower chamber :

Total depth from surface of the ground to bottom of chamber is 3 metres.Next, measure down from the surface of the ground to the neck of the chamber a depth of 1.5 metres.

This is the upper limit of the bottom chamber.

The sloping portion of the lower chamber will start at this level and run upwards at an angle of 45 0 to the lower limit of the top cylinder, as shown in Fig. 6, below.

Practical Training Report, 24 - 02-1997 to 25-04-1997, By J.K.N. Gbagbo 57

Biogas Plants suitable for Ghana and other tropical countries. ■

upper

105cm

lower

150cm

Fig 6.

The diameter of the bottom chamber is 310 cm.Finally, smoothen the bottom of the lower chamber, also the bottom should slope gently towards the centre meeting the top surface of the foundation for the central guide pipe. All edges can be left rounded as this will strengthen the structure and save cement.

STEP 7.

Ferro - cement casting of digester or fermentation tank.Two reasonably skilled Masons and to workers will be needed.Using a mixture of 1 : 3 cement, coat the whole interior surface to a depth, of 1"

Practical Training Rpnnrt. 2d - 07 - 1QQ7 in 9 ■> - OJ - 7007 7?» T V \J fZUnnh**


( 2.5 cm ). This operation must be completed within 6-8 hours to insure correct hardening thus avoiding weak spots.

Fig. 7.0.

Proceed as follows:The cement mixture should be " cast" or thrown onto the earth surface directly from the trowel, instead of being spread on as with an ordinary plaster.If you have difficulty making the 1:3 mixture sticking to the walls try a first undercoat, with 1 :1 mixture. Always wet the surface to be covered before proceeding.



Checking the thickness of the walls will be facilitated by using a depth guage. This can be made using a 4" nail bent as shown in Fig. 7.1.

Fig 7.1.

STEP 8.

PLACING THE REINFORCEMENT WIRE.

Material: (. 3/4 " chicken wire x 90 cm width rolls).This operation is started the day after the first coat of " plaster" has been applied. The entire surface of the interior of the digester will be covered with chicken wire.This operation is the most important in ferro - cement production. Therefore close attention to details is required.

Start by nailing the first round of wire at the top of the digester, and then work down into the chamber.The bottom of the chamber is covered and nailed down wall to wall.All joints are overlapped 15 cm (including the bottom, and the joint between bottom and sides).This job will take 2 men approximately 1 1/2 days to complete. All work must be done correctly and thoroughly to prevent the structure from cracks to shun difficult repairs.

Practical Training Report, 24-02- 1997 to 25 - 04- 1997, By J.K.N. Gbagbo 60


IMPORTANT CONSTRUCTION NOTES:

a. The chicken wire must sit tight to the surface of the structure at all times.

b. Use 4" nails to fasten the wire in place ( or 2 1/2 " or U - nails if available).

c. Nail the wire down as it is worked up in a circle around the tank, nailing as the wireis rolled out will prevent bulges and wrinkles.

d. All overlaps should be 15 cm.

Practical Training Report, 24-02- 1997 to 25 - 04- 1997, By J.K.N. Gbagbo 61


. DETAIL NO.

Fig. 8.1.

STEP 9.

THE SHELF:

When all the chicken wire is nailed in place, the building of the shelf can be started. The pre - cut reinforcing steel bars, ( 25 pieces, 3/8 " x 14 " equals to 12 mm x 50 cm), and the cross bar support for the central guide pipe will be installed now.

AOPractical Training Report, 24-02-1997 to 25 - 04 -1997. Bv J.K.N. Ghaebo


Fig. 9.0.

Proceed by measuring down 90 cm from the ground level land. Hammer the first of the 25 steel rods into the side of the cylinder, leaving 20 cm exposed, sticking level circle using a spirit level placed across the protruding rods.

Practical Training Report, 24 - 02- 1997 to 25-04- 1997, By J.K.N. Gbagbo 63


t • •

•* V.

Fig. 9.1. Leveling the 25 shelf support rods.

The cross bar, central guide support can now be wired into place. Place this cross bar so that you can bind each of the four ends to four of the short rods sticking out of the walls of the cylinder.

Fig. 9.2 Cross bar support.

Detail : Cut 4 pieces of 3/8" x 95 cm. Cut one piece of 2"x5 cm iron pipe. Weld the pipes on the piece of pipe, so that it makes a cross.

The shelf can now be ringed 4 times with steel wire.Accomplish this as follows :Start the first circle of wire close in next to the wall of the cylinder, make one complete wrap at each of the 25 rods (including the 4 rods which are now wired to the guide pipe cross support).Make 4 circles, moving approximately 5 cm in towards the centre of the cylinder with each circle. Make sure that the last round is at the end of the steel rods.


■

Fig. 9.3. Wiring the shelf.

When the wire rings have been completed the chicken wire can be fastened over the shelf as with the rest of the inside surface of the digester. Fasten the chicken wire firmly to the steel and maintain the 30 cm overlaps.

Practical Training Report, 24 - 02 -1997 to 25 - 04 - 1997, By J.K.N. Gbagbo 65

Biogas Plants suitable for Ghana and other tropical countries

Fig. 9.4. Chicken wire overlap of 15 cm.

STEP 10.

SECOND COAT AND NIL.

Proceed with the second coat just as with the first. The chicken wire will be covered with 1" of 1:3 cement, plaster. This second coat will be trowelled to a smooth finish, using a wooden float.

When this coat has dried to a point where it is possible to run your finger over the surface without scratching it, or leaving a mark, this gives an indication that it is time for the final finish coat, a thin mixture of cement and water called nil.To apply this nil mixture, splash it on the wall using a can or small bucket. Then draw it out to a thin even covering with a steel trowel. This procedure will insure watertight surface.

Proceed by plastering and finishing (nil - coating) the upper cylinder. Thereafter the upper shelf, followed by the sloping sides, the sides of the bottom chamber, and finally the floor.

The underside of the shelf will be the most difficult. However, once the upper layer of the shelf has been set, but is still wet, apply an extra wet layer of plaster, with extra cement in it, to the underside of the shelf.

Biogas • Plants suitable for Ghana and other tropical countries.

Fig. 10.1

Note that the nil coat will be next, but impossible to apply to the underside of the shelf and the sloping wall while they are still wet. Here it is easiest to wait until they are dry and apply the nil coat with a wash brush.

Rounding the comers can be accomplished with the side of a bottle.

Practical Training Report, 24 - 02-1997 67


Fig. 10.2.

STEP 11.

INSTALLATION OF INLET AND OUTLET PIPES.(

The procedure is the same whether you use PVC pipe, pre-fabricated cement pipe or ferrocement pipe ( site - formed, Fig. 11.0, shows a special section of inlet and outlet pipes ).

First dig two holes, one on each side of the digester opening as shown in Fig. 11.0.

C.0Practical Training Report, 24-02- 1997 to 25 - 04 -1997, Bv J.K.N. Gbaebo

The holes are dug deep enough to gain access to the outside surface of the tank at the middle of the sloping portion. Once this area is exposed you are ready to make holes in the tank which will accept the inlet and outlet pipes. Before punching these holes ( using hammer and cement chisel) you must ascertain their correct size and locations. Two very important factors affecting the success of the digester must be dealt with here : -

1. The liquid level in the tank must be 85 cm from the upper surface of the shelf.2. The inlet pipe's entry point must be at a higher level than that of the outlet pipe's.


Fig. 11.0.

How to find the centre of the holes

Recommended procedure :

Establish a level reference line by running a leveled string across the top of the system as in Fig.l 1.1. This gives you a common reference for all measurements.

Practical Training Report, 24 - 02 -1997 to 25 - 04-1997,ByJ.K.N. Gbagbo 69


Next establish the maximum liquid level line by measuring up from the top of the shelf, 85 cm, and place a mark.

Now measure from the 85 cm mark up to the level string. Let us say for example that this distance is 30 cm. We now measure down from the string this 30 cm at.the upper end of the outlet pipe.

Now measure down, again from the string, 25 cm at the upper end of the inlet pipe. Now you have the heights of the upper ends of the outlet and

Fig. 11.1

Practical Training Report. 24 - 02 - 1997 to IS-fiJ- 7007 t it \r nu..„u„


f

Fig. 11.2

Fig. 11.3

Practical Training Report, 24-02 -1997 to 25-04-1997, By J.K.N. Gbagbo 71


Figs. 11.4.

inlet pipes relative to one another and to the ground level. Both pipes should have a slope of 45 0 ( 1:1 ).

This can be roughly determined simply by digging the holes as wide as they are deep. (this angle can be checked by a protractor, by a level with a 45 0 window or by

measuring run an rise ascertaining that they are the same 1:1).

The lower end of both pipes are now cemented in place : use a 1:3:5 mixture and cover the area where the pipes enter the sloping wall of the digester with this mixture. The flanges on the pipe will facilitate this operation, as the pipes will then remain in the desired position with less effort, and no one is needed to hold the pipe in place from below.

When the lower ends of the pipe has been thoroughly covered at their point of entry into the digester, begin filling the holes, tramping at regular intervals to insure a well compacted closure of earth around the two pipes all the way up to the surface.Next coat the joints at their points of entry on the inside of the digester. Finally after these inside joints have dried completely, cover them well with bitumen.

Practical Training Report, 24 - 02- 1997 to 25 - 04- 1997, By J.K.N. Gbagbo 79


LEVEL REFERENCE LINE-

Fig. 11.6.

Practical Training Report, 24 - 02- 1997 to 25 - 04- 1997, By J.K.N. Gbagbo 73

Biogas Plants suitable, for Ghana and other tropical countries.

STEP 12.

INLET AND OUTLET CHAMBERS, AND THE STIRRING DEVICE :

Outlet chamber :

Cut an oildrum into two equal halves, bury the one half under the outlet pipe so that the discharged slurry can run directly down into the half barrel.

This can also be done by constructing the chambers in block work on site.

Inlet and mixing chamber :

Next take the other half of the oil drum and make a hole in the bottom that just fits over the inlet pipe. Then pour a concrete bottom in the oil drum which covers all but the opening of the inlet pipe.

This creates a feeding chamber to the system, by making a plug or cover for the inlet opening, you will be able to use the chamber as a mixing chamber as well. The stirring device is made very simple by a straight piece of 2" x 2" wood and 3 metres long.

In one end a round piece of rubber from an old tyre 4" in diameter is nailed or screwed on. On the opposite end a handle 6" long is nailed or screwed on, as shown in Fig. 12.1.

/

6" lone 2"x 2" wood'.

3 meter-long 2"x 2” wood.

Round rubber from- old tver 4" in diameter.

Fig. 12.1.Practical Training Report, 24 - 02 - 1997 to 25 - 04 - 1997, Bv J.K.N. Ghaebo n a

Biogas ■ Plants suitable for Ghana and other tropical countries.

By pushing the wood with the rubber up and down in both the inlet and outlet pipes, the pipes get cleaned from dry manure and the manure is stirred up into the fermentation tank.

It is important to push the wood through both the inlet and outlet pipes once in order toclean them before daily filling it.After the daily filling push the wood 10 times up and down in both the inlet and outlet pipes in order to get the fresh manure mixed well inside the fermentation tank.

THE FABRICATION OF FERRO-CEMENT PIPES.

Place a 4 metre P. V/C. pipe (4 " ) on two supports, ( as shown in Fig. 12.2 ).Paint the section of pipe between the two supports with used oil. Next wrap with newspaper (one page at a time ) with a few centimetres overlap. Then wrap chicken wire one time around securing it to itself.The excess wire can be hung down below the pipe out of the way.Coat this layer of wire with ferro-cement, when the first coat has dried, wrap the wire once again around the pipe securing the final wrap to itself again.Then apply the last coat of ferro - cement.

FABRICATION .f FERRO CEMENT PIPE / INPUT- OUTPUT

NOTE-'FLANGE

Fig. 12.2.Practical Training Report, 24 - 02 - 1997 to 25 - 04 - 1997, By J.K.N. Gbagbo 75


THE FLANGE :

A flange may be cast at the end of the pipes, which will be in the tank! This will facilitate placing the pipe and will also insure a good seal, as shown in Fig. 12.3 ,

THE GAS TANK

There are generally two basic systems for storing gas. The first, called the Fixed - Dome system, derived from the Chinese Biogas plants and is built up in blocks and cement.

The second is called the Moving or Floating - Drum type invented in India, it consists of a metal drum or tank which moves up or down with varying gas pressure, its open end being placed over the digester chamber. It is this second type of system we will use in the E. B. 3 plant. Fig. 12.4. shows such an example.

Fig. 12.4.

Practical Training Report, 24-02-1997 to 25 - 04- 1997,By J.K.K Gbagbo 76


CONSTRUCTION OF THE E. B. 3 - GAS TANK.

Materials:

1. Three (3) used, 210 litre oil drums in very good condition.2. One (1)4 .ft x 8 ft iron sheet of l mm thickness.3. One (1) metre of 2" pipe.4. Sixteen (16) metres of 3/4" ( or 10mm ) reinforcing rod.

Building Instructions:

Pre-cut the 10 mm Reinforced rods into the following pieces of bars(a) 3 pcs. of 90 cm long(b) 6 pcs. of 85 cm long, and(c) 6 pcs. of 125 cm long.

Next, weld two of the 85 cm pieces at right angles to one 90 cm .pipe, as in Fig. 12.4.1. The weld two pieces of 125 cm" long, running as diagonals from the 4

comers of the above construction, as in Fig. 12.4.2. Repeat this procedure for a total of 3 such units. Now weld these 3 units to the 1 metre long 2" steel pipe. Attach them 5 cm from the ends of the pipe, at 1200, between the points of attachment, as in Fig.12.4.3,

Furthermore, remove the tops and bottoms of three (3) oil drums. This can be done with a cold steel chisel and a hammer, or if available a pneumatic chisel. A cutting torch can also be used, but this method requires foregoing safety precautions and 'should not be attempted by inexperienced workers, as there is danger of a serious explosion. The drums are now cut up in the side and opened out forming a curvedsheet of steel, as in Fig. 12.4.4. These sheets will form the sides of the tank.

W TL -

VELD175 CM LONG

WELD

Fig. 12.4.1. , Fig. 12.4.2.

, Practical Training Report, 24 - 02 -1997 to 25 - 04 -1997, By J.KN. Gbagbo 77


Fig. 12.4.3. Fig. 12.4.4.

THE TOP OF THE TANK.

The top of the tank is cut from the 4'[ x 8" sheet of 1 mm iron sheet. Then proceed as follows: -Measure 90 cm from both the long side and the short side at 90° , to the edge of thesheet. Where these two lines meet, make a dent in the steel plate.

This will be the centre point for the circle defining the top of the tank, as in Fig. 12.5.0.

Practical Training Report, 24 - 02 - 1997 to 25-04- Z997 fiv TV m


‘The top of the tank;

' 240 or 8

180cm60cm

55cm

cut of:EXTRAPIECE

CUT OF

90cm

E£6tra PiecePipe of top— from oil'drum With 3/4" tred*4> welded on

+rrw-)- .'Pipe of top from oil drum With 2 tredgfl we.ld on

(Welding -sign

Fig. 12.5.0.

Next make a " compass" for making the circle on the steel by putting two nails at opposite ends of a board, 85 cm apart, as shown in Fig. 12.5.1.

Practical Training Report, 24 - 02 -1997 to 25 - 04-1997, By J.K.N. Gbagbo 79

60cm

I 12

0cm


3*

Fig 12.5.1.

Now using this compass, score a clearly visible mark of the steel plate using the dent made earlier as your centre point, as in Fig 12.5.2.

Fig 12.5.2.

This method can also be used for scoring the actual cutting line. Place the nails 90 cm apart for this operation.

Next, cut the end of the sheet off before cutting the circle. Measure 60 cm in from the long end, and cut across the sheet, making sure, however, that there is at least 5 cm between this cut and the cut line of the circle where the two meet at the middle of the sheet.Now, take this piece and weld it to the large piece as shown in detail, Fig 12.5.3. Remember, there must be 5 cm material outside the inner circle drawn on the larger sheet to maintain the 5 cm overrun all the way around the top.

Practical Training Report, 24 - 02 -1997 to 25-04- 1997, By J.K.N. Gha'ebo 80


k180

Fig. 12.5.3.

There will now be a small segment remaining to be filled out to complete the top piece. This is completed with two final pieces. The smallest and the next to the consists of a 15 cm wide piece cut from the top of the drum, which is in the best condition. Cut this piece in such a way as to include to the two openings in the lid. Reed the two openings well centered in this piece, as in Fig 12.5.4.

Fig 12.5.4.

Practical Training Report, 24 - 02 - 1997 to 25 - 04 -1997, By J.K.N. Gbagbo


Now turn the 2" opening around so that it sits toward the centre of the piece when this is welded into place. Weld the entire piece, holes toward the centre of the lid, into place, Fig 12.5.5.

Fig 12.5.5.

Finish the top by filling the last remaining segment with the triangle which you now cut from the opposite side of the top, as in Fig 12.5.6.

Fig 12.5.6.

Practical Training Report, 24-02- 1997 to 25 - 04 -1997. Bv J.K.N. Ghavho on


Cut this comer off by measuring 55 cm out from the comer along both sides and cut across the diagonal connecting these two points.When all the welding in this stage is complete find the dent marking the centre of the circle defining the top. Retrace the circle using the special compass built earlier, on this time score the entire circle.

Make a 6 cm hole in the centre for the 2" pipe, as in Fig 12.5.7.Now place the 2" pipe with the 3 welded frames attached, into the hole.The next steps will be most easily performed by placing the top assemble on two long, 2 metres beams as shown in details in Fig 12.5.7. This will give needed clearance.

Fig 12.5.7

You are now ready to mount the 3 oil drums which were split open and partially pulled out earlier. Begin by tacking the first drum to one of the vertical frames, as in Fig 12.5.8.



Fig 12.5.8.

Thereafter spot- weld the drum to the top piece, following the scored circle around. Until the vertical frame appears, spot -weld to this, and continue until all the three drums are in place. Overlap 5 cm at the seams when the entire assembly is spot - welded in place.Finally, weld all seams together as well as the sides of the drums onto the iron sheets. Remember to weld the 2" pipe hole as well.Gas and Oxygen welding equipment is used for all welding work and must be carried out with great care to insure biogas tight welding. (Also note that biogas is lighter than air). Therefore, before painting the tank, it must be tested for gas tightness.

This can be done by placing the tank into position over the filled fermentation chamber, remember to fasten the 3/4 " and 2" threads. Then spread soap solution over all potential leakage areas. Bubbles will indicate leaks.

Weld to gas tight status on the spot, as in Fig 12.5.9.

The handles can be added now by welding four pieces of reinforced bar bent as shown in Fig 12.5.9, to the top of the tank at regular intervals.

Practical Training Report, 24 - 02-1997 to 25 - 04 - 1997, By J.K.N. Gbagbo 84-

Biogas Plants suitable for Ghana and other tropical'countries.

Finally, remove tank from the fermentation chamber, clean it thoroughly and paint it with bitumen.

Fig 12.5.9 A, and B : TESTING FOR GAS TIGHTNESS.

Practical Training Report, 24 - 02-1997 to 25-04-1997, By J.K.N. Gbagbo


MAINTENANCE :

Experience in Kenya shows that while the steel in oil drums is quite thin, these tanks can hold up to 6 years with proper maintenance. They are very cheap at approximately 1,500 / - DKR.It is therefore imperative that the following maintenance rules must be followed : - Insure that there is always a " skin" of oil, old motor will do, on the surface of the slurry (this also helps to keep mosquitoes away ), so that the tank moves up and down in a thin layer of oil. Spread oil on top of the tank regularly. During the yearly emptying of the fermentation chamber, clean the tank thoroughly and re - paint it with bitumen, Also make sure that the tank is completely dry before painting it.Results in Kenya have demonstrated that failure to follow these simple maintenance procedures results in the tank rusting up completely inside of 2 to 3 years, so it is plain to see, there is money and work to be saved by maintenance.

GUIDELINES FOR DAILY MAINTENANCE.

1. Removal of scum layer: The scum layer is part of the fermentation material which rises to the surface of the fermentation tank where it prevents free movement of the gas tank. Scum is concentrated between the fermentation tank and the gas tank and can therefore easily be noticed, as shown in Fig. 13.1.

from herehereback

Gastank

Fig. 13.1.

Removal of the scum layer is done using a rake or a hoe which can easily be lowered into the tank. When the top layer has been removed the job should be completed, the best way to ensure this is to move the gas tank from one side to another and if the tank

Prartirnl Training Rmnrt 1/ m toot #/. is n.t " TTr‘r ™ • '


moves freely, it implies that the scum layer has been removed. After removal of the scum, the gas tank should be pushed from one side to another at least five times, however, care should be taken not to bend the gas pipe, when moving the gas tank.

, This is illustrated in Fig. 13.2.

Fermentation tank

Fig. 13.2.

2. Cleaning of overflow :

The overflow of the fermentation tank should be cleaned everyday to prevent old slurry forming a thick layer at the top of the overflow since this will prevent new slurry from passing through the overflow. Emptying the overflow is easily done using a bucket.The slurry from the overflow is an excellent fertilizer and can be applied to crops immediately or stored as compost. Because of the high nitrogen content in biogas slurry, it should be applied to young plants or trees.

3. Feeding the plant:

Feeding the plant should be done everyday to ensure a continuous flow of material and slurry through the biogas digester.

a) Using Cow manure : Fill up a drum with dung from approximately ten (10) cows and add 100 litres of water. Mix the cow manure and water till a uniform colour is reached. Move the stirring device at least ten times after feeding the biogasdigester.



b) Using pig manure : Fill up a drum with dung from approximately 20 pigs and add 100 litres of water. Mix the pig manure and water till a uniform colour is reached. Stir at least ten times after feeding the biogas digester.

FAULT FINDING.

a) If little or no gas is produced, it can be because of several reasons. However, gas production failure is usually caused by minor problems which can easily be solved. The best way to find out if the digester is functioning properly is to mark out a line at the water level of the gas tank, as shown in Fig. 14.1.

tank -Fermentatio

Fig. 14.1.

When the marking has been carried out, no gas should be consumed for 24 hours. After 24 hours, the gas tank should have risen considerably above the mark, if not, then there is a leakage of gas.

b) Check if the gas tank can be moved freely, if not see guideline one in the daily maintenance.

c) Add pressure on top of gas tank, not more than 160 kg, as in Fig. 14.2.

Practical Training Report, 24 - 02- 1997 to 25-04 - 7997 /?» I tc m


Fig. 14.2.

d) Condensation water:

. Disconnect the gas pipe at the gas cooker and hold the pipe in an upright position so that if it contains any water it will run out by itself.

Also blow in the pipe to force out any dirt in the pipe. Furthremore, make a water trap when disconnecting pipes from the gas tank and take off pressure from the gas tank.

e) Water trap:

A water trap is a piece of pipe which is formed like a " U" and has water in it to prevent gas from escaping through the pipe.

A water trap is positioned at the lowest point of the pipe where it collects water formed in the pipe. When disconnecting pipes from the gas tank always make a .water trap.'This is shown in Fig. 14.3.



Water leve

Fig. 14.3 : Water trap.

Practical Training Rennet i t n-> 1007 t*. i.-


f) Lamp :

If light fades, becomes weak or produces a " blubbing" sound, the lamp should be cleaned, take out the jet of the lamp and clean it with petrol. After the jet has been cleaned a string should be pulled through the jet, as shown in Fig. 14.4.

Gas

Fig. 14.4.

Practical Training Report, 24 - 02-1997 to 25-04- 1997, By J.K.N. Gbagbo 91


■r

Gastank

Outlet

■X ail dru

15"m3 Fermentation tank of ferro-cement

Fig. 14.5 : The completed digester.

nnPractical Training Report, 24 - 02- 1997 to 25-04- 1997, By J.K.N. Gbaabo


MATERIALS FOR THE EASY BIOGAS PLANT NO. 3 AT 15 m3.

Fermentation tank: Prices.

a: 15 bags of cement.b: 5 tons of river bed sand.c: 1/2 ton small stones (for making concrete)d: 18 blocks 5 " x 9" x 18" or natural stonese: One (1) 1/4 rolls of chicken - wire.f: 5 kg of 4 " nails.g: 12 metres of 3/8 " iron - rod.h: 4 metres of 11/2" iron pipe.i: 4 litres of Bitumen paint:

Inlet and outlet pipes :

a: 4. metres of 4" P: V. C. pipes or

b:: 4metres of4"concrete pipes, c: Site made ferro-cement pipe :

You heed 3 metres 4" P. V. C. pipe used for form - work, cement, sand and chicken - wire are included in materials

for fermentation tank.

Inlet and outlet chambers:

a: One old oil drum cut into two ORb: 45 blocks 5 "x 9" x 18 " or natural stones.

Gas tank :

a: 3 old oil drums.b: One 4 ft x 8 ft x 1 mm thick iron sheet, c: One metre 2 " iron pipe.

Gas piping:

Piping and fittings are individual depending on the distance and type of materials used.

GAS PIPING.

Biogas accumulated in a gas tank is transported to cooker and lamp through piping which connects the gas outlet on the gas tank with the cooker and lamps.

Types of piping :

Biogas piping may consist of three types of pipes , with the following characteristics :Practical Training Report, 24 - 02 -1997 to 25 - 04 -1997, By J.K.N. Gbagbo 93

a) Galvanized iron water pipes are the most durable but also the most expensive and difficult to seal for gas tightness in the joints.

b) Plastic hose pipes for example., watering of gardens, are cheaper than iron and the most gas tight, as it has no joints.

However, this type of piping cannot be placed underground, as it is collapsible.

c) - PVC water pipes are the cheapest and easiest to seal gas tight with PVC glue in the joints, but they are vulnerable to sunshine and rough handling. They must therefore be placed underground. They can be placed both under - or above - ground.

i) Ground piping : Before deciding on the type of piping to be used, considerations have to be given as to whether the piping should be placed under ground or above ground. Underground piping may look convenient, but if gas leak should occur in the piping then it will be a difficult task to locate and repair the underground piping.

ii) Above - ground piping : In this case, it is much easier to check for gas leaks. The plastic hose pipe, tied onto a support of galvanized wire, 3 mm, is ideal for this purpose. However, if a pipeline has to be hung over a long distance, it is a disadvantage because of the many poles to support the piping. Therefore, and for other reasons, it is always important to design the siting of the biogas plant in such a way that the distance of the piping is kept to a minimum.

Diameter of Piping : The internal diameter of the piping depends on the following :

a) The length of the piping.If the length is shorter than 10 metres, then a 1/2 " piping is sufficient.If the distance is. longer, the diameter has to be increased to 3/4" or more.

b) The quantity of gas to be transported.If more than 3 burners or lamps are to be used at the same time, then 1/4 " has to be added to the diameter of the piping recommended.

The weight of the gas tank which presses the biogas through the piping:If a piping has been underdesigned, or more burners have been connected than designed for, then more gas can be transported through the piping by adding weight to the gas tank with for .example stones and bricks. However, by increasing pressure in the piping, there is greater risk of creating gas leaks.Condensation water : Biogas contains water vapour which condenses into water in a gas pipe.This condensation water must be drained out of the piping or the trapped water will block the transport of gas. To shun this blockage of the gas pipe, it is important to let all sections of the gas piping slope from a high point towards a low point from where condesation water can be drained out of the piping.Such a drainage point is called a water trap, because it lets water out of.the piping without letting any gas out. A water trap consists of a simple length of piping bent as a " U Such a" U" is connected to the gas piping with a" T " and filled with water up till the bottom of the " T ", so that the water does not block the pipe. A water trap must be placed at any low point on the gas pipe.


In practice only one water trap is required if the gas pipe is hung above the ground in the following way:The gas pipe slopes upwards from the gas tank towards a high point in e.g. a tree. Condesation water in that length of pipe will run back into the biogas plant by itself. The gas pipe slopes from this point in a tree towards a low point outside the house and a water trap is placed there. From the water trap the piping slopes upwards into the cooker and lamps in the house in such a way that all condesation water will run towards the water trap.



JSuK

'

Biogas Plants suitable for Ghana and other tropica! countries.

9.0 CONCLUSION

Since Ghana is still on the demonstration phase of Biogas plants in only three out of the ten regions, this report is suppose to serve as a flexible tool to enable the users to integrate new simple, affordable and acceptable strategies Using locally available • materials to design plants which the ordinary poor rural dweller of the country could afford.

Ghana being an agricultural country and blessed with a lot of forest, has abundant and naturally growing bamboos which are sometimes not used effectively. It will therefore be a good option to integrate the new version of biogas plant which has recently been developed by Raymond Myles. This is shown below.

Woven reinforcement for biogas installations in India.

The bricks have been replaced with woven bamboo, which constitute the reinforcement in a wood - concrete construction.

Practical Training Report, 24-02-1997 to 25-04 - 1997. Bv .LK./V Ghnvho


This will eliminate the cumbersome task of bricks transport and the use of wood for baking the bricks. The bamboos On the other hand are free to cut in the forest. Ghanaians, are already talented in weaving hence less burden.After substituting the bamboos, the next step will be to find another antidote to the steel gas holder. I hope this information will assist fellow Ghanaians and people in other tropical countries where the biogas technology is not yet matured in implementing it.



10.0 References.

1. Renewable Energy ResourcesBy John W. Twindell and Anthony D. Weir.

2. Manual on DEENBANDHU Biogas Plant By J.B. Singh, Raymond Myles, Anil Dhussa.

3. Report on Biogas Plants By Jom ForwerkFolkecenter for Renewable Energy( February - August, 1994)

4. Biogas PlantsThe danish Missionary Council Development Office, Copenhagen, 1992.By Niels E. Graulund, Christian W. Rasmusse, Hanne B. Graulund.

5. Biogas Manual BORDABy G. Eggeling, H.U.R Guldager, G. Hilliges, L. Sasse, C. Tietjen, U. Werner.

6. India sets the example in the biogas sector By Preben Maegaard.



11.0 APPENDIX

The map of the republic of Ghana.

Practical Training Report, 24-02- 1997 to 25-04- 1997, By J.K.N. Gbagbo 99

a concise biogas plant construction suitable for ghana and

Documents