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CLOSE THIS BOOKImproved Biogas Unit for Developing Countries (GTZ, 1991, 98 p.)
VIEW THE DOCUMENT(introduction...)
VIEW THE DOCUMENTAcknowledgments
VIEW THE DOCUMENTForeword
VIEW THE DOCUMENTAcknowledgment
VIEW THE DOCUMENT1. Preface
VIEW THE DOCUMENT2. Why biogas ?
VIEW THE DOCUMENT3. Explanation of terms
VIEW THE DOCUMENT4. Biogas extension work
VIEW THE DOCUMENT5. The agricultural biogas unit
VIEW THE DOCUMENT6. Construction of the biogas plant
VIEW THE DOCUMENT7. Construction of cattle stable
VIEW THE DOCUMENT8. Construction of the pigsty
VIEW THE DOCUMENT9. The sanitary biogas unit
VIEW THE DOCUMENT10. Use of slurry
VIEW THE DOCUMENT11. Use of gas
VIEW THE DOCUMENT12. Operation and maintenance
VIEW THE DOCUMENT13. Pending technical issues
VIEW THE DOCUMENT14. Appendix

14. Appendix

CHARACTERISTICS OF PROJECT AREA WHERE THE BIOGAS EXTENSION SERVICE IS ACTIVE.

Country: Tanzania: Population 25 Mill. inhabitants, area: 1,25 Mill square Km, GNP 235 US$ per capita, deriving from Industries 10%, agriculture 59%, services 31%, inflation rate in 1985-1990 25%, local currency 1000 Tsh = 5,30 US$ (May 1990).

Price relations: 1 adult milking cow 75.000 Ths, 1 Biogas Plant of 16 m³ VD costs 170.000 Tshs, or 2-3 in-calf cows, 1 daily wage of unskilled labourer is 200-300 Tshs, 1 bag of cement costs 1.150 Tshs, 1 kg of maize (producer price) gains 15 Tshs, 1 l of kerosene costs 51 Tshs.

Project area: Coffee-banana-belt around Mt. Meru with Arusha being the commercial and cultural centre. Population density: 195 inhabitants/km², altitude: 1200-1500 m above NN, rainfall: 2500 mm p.a., semi-dry season: three months, min-max temperature: 10-30°C.

Theoretical Biogas Potential: 10% of households = 4 biogas plants/ km².

LIST OF FORMS

The following list of forms is a proposal for any private or public Biogas Extension Service. It has proven useful in practice for:

giving the customer a reliable overview over the costs,
not forgetting any details

coming to clear arrangements with the customer and

having a guideline for quantity and cost calculation.

FORM 1

Letter to potential Customers, asks the customer to send a formal request letter including details about his farm set-up. The data mentioned can be used as a reference for later evaluations, e.g. to compare the number of cows at application and after several years.

The first site-visit and the planning starts only after having received the formal request, in order not to waste any time on unserious applicants.

FORM 2
Calculation Sheet for Unit construction

FORM 3

Quantity survey form are forms to easily calculate the needed building materials for Biogas Plant, cowshed, pigsty, toilet, etc.. They are meant for internal use.

FORM 4

Letter to the customer explains all the details being necessary for a satisfactory functioning BGU on his farm: BGP, stable(s), modifications, gas consumption appliances etc..

It clears communication flow, but is not always necessary, as customer is mainly asking for costs, which can be only discussed after Form 5.

FORM 5

Delivery decision and cost calculation is an agreement between the Biogas Extension Service and the customer on who is delivering what. Often it is cheaper for a farmer to have his own workers digging the pit or he has e.g. a cheaper source of sand or his own is own means of transport. The farmer should have the chance to help make his BGU as cheap as possible, but of course this should be based on a clear arrangement.

The form informs about total value of construction, supervision costs and how much is to be paid to the contractor.

FORM 6

Contract is delivered personally and signed by both customer and constructor, after quantities and costs have been agreed on. While signing the contract, the first installment of 50% of the total costs has to be paid. As soon as the first installment is received, material delivery and construction work can start.

FORM 7

Material to be delivered by the customer is a form to agree on a certain time, when the building materials supplied by the farmer have to be at the site. If the farmer delays his delivery, B.E.S. or the contractor has the right to supply missing materials in order to avoid delay of construction work.

FORM 8

Slurry Utilisation Agreement is a form with which B.E.S. tries to explain to farmers their duties and B.E.S. inputs in order to establish a sustainable slurry distribution system.

FORM 9


xxxxxxxx

After Sales Service is a contract in which the customer and B.E.S. come to an agreement about sharing the costs for the check-up and necessary modifications of the plant after an operational period of several years.

The above given list of forms should be taken as an example. It depends very much on regional conditions, on the number of BGU's built annually and on the diversity of regularly occuring problems, to which extent a "Form-System" is established.

Forms are created mainly to make a job easier. Things are made clear by writing them down.

EXAMPLE: FORM 2 CALCULATION SWEET FOR UNIT CONSTRUCTION


(for internal use)



Name of Customer

:



Village

:



Date

: ..



It is-required for

phase 1

phase 2

phase 3

Size of plant

:m³

additional inlet

:



toilet complete

:

toilet connection

:

stable Z

:

pigsty R

:

stable modification:




Item

unit

amount


cement

bag

..


sand

ton

..


murrum

ton

..


stones

ton

..


bricks

piece

..


pillars 15 cm

piece

..


purlins 2" x 2"

piece

..


boards 2" x 4"

piece

..


nails 4"

kg

..


roofing nails

kg

..


roof gutter

m

..


gutter holder

piece

..


iron sheets

piece

..


slabs 15 x 15 cm

piece

..


slabs 15 x 30 cm

piece

..


slabs 30 x 30 cm

piece

..


small items


..


Iabour


..


..


..


piping 3/4"

m

..




gas consumption

household stoves

piece

..

canteen stoves, type ..

..

.


canteen stoves ins.pot

.

.


lamps piece

..

.


signature of planner


signature of site engineer

EXAMPLE: FORM 5 COST CALCULATION
Copy to customer)
Name of customer.............................Village...................Date.....
Phase.......................

Item

amount

will be provided by

additional items provided by BES for the price



customer

BES


bricks

........

........

........

........

cement

........

........

........

........

Iime

........

........

........

........

sand

........

........

........

........

murrum

........

........

........

........

stones

........

........

........

........

chippings

........

........

........

........

PVC pipe 4"

........

........

........

........

PVC pipe 6"

........

........

........

........

plain wire

........

........

........

........

chick wire

........

........

........

........

small items

........

........

........

........

galv.pipe 3/4"

........

........

........

........

h. h.stove

........

........

........

........

cant.stove

........

........

........

........

stove modif.

........

........

........

........

Iamp

........

........

........

........

pillars

........

........

........

........

boards

........

........

........

........

gutter

........

........

........

........

metal piec.

........

........

........

........

nails

........

........

........

........

iron sheets

........

........

........

........

small Items

........

........

........

........

Iabour

........

........

........

........

digging

........

........

........

........

.........

........

........

........

........

.........

........

........

........

.........

Total Tshs

........

........

.....

Total value of construction




supervision.........%

..........



Grand Total

...................



Value of customers contribution

.....................



Payment to BES




date:.......

signature customer.......................


signature BES.............................


Figure


Figure


Figure


Figure


Figure


Figure


Figure


Figure


Figure


Figure


Figure


Figure


Figure


Figure

SQUARE AND CUBIC NUMBERS, GEOMETRICAL FORMULAE

n

n

n

1,00

1,00

1,00

2,00

4,00

8,00

3,00

9,00

27,00

1,05

1,10

1,18

2,05

4,20

8,62

3.05

9,30

28,37

1,10

1,21

1,33

2,10

4,41

9,26

3,10

9,61

29,79

1,15

1.32

1,52

2,15

4,62

9,94

3,15

9,92

31,28

1,20

1,44

1,73

2,20

4,84

10,85

3,20

10,24

32,77

1,25

1,56

1,95

2,25

5,06

11,39

3,25

10,56

34,33

1,30

1,69

2,20

2,30

5,29

12,17

3,30

10,89

35,94

1,35

1,82

2,48

2,35

5,52

12,98

3,35

11,22

37,60

1,40

1,96

2,74

2,40

5,76

13,92

3,40

11,56

39,30

1,45

2,10

3,05

2,45

6,00

14,71

3,45

11,90

41,06

1,50

2,25

3,38

2,50

6,25

15,63

3,50

12,25

42,88

1,55

2,40

3,72

2,55

6,50

16,58

3,55

12,60

44,74

1,60

2,56

4,10

2,80

6,76

17,58

3,60

12,98

46,66

1,85

2,72

4,49

2,65

7,02

18,81

3,65

13,32

48,63

1,70

2,89

4,91

2,70

7,29

19,68

3,70

13,89

50,85

1,75

3,06

5,38

2,75

7,56

20,80

3,75

14,06

52,73

1,80

3,24

5,83

2,80

7,84

21,95

3,80

14,44

54,87

1,85

3,42

6,33

2,85

8,12

23,15

3,85

14,82

57,07

1,90

3,51

6,86

2,90

8,41

24,39

3,90

15,21

59,32

1,95

3,80

7,41

2,95

8,70

25,67

3,95

15,60

61,63


Figure


INFLUENCE OF ALTITUDE AND TEMPERATURE ON BIOGAS


Figure


Examples:

The calorific value of biogas at sea level and 20°C is about 6 kwh/m³

Calorific value of biogas at sea level and 40°C:

= (6 kwh/m³ · 273°C) / (273°C + (40°C - 20°C)) = 5.59 kwh/m³

where: 273°C = absolute zero point of temperature

Calorific value of biogas 1,000 m above sea level and 20°C:

= (6 kwh/m³ 10,000 kp/m²) / (10,000 kp/m² + (1,000 m · 1,2 kp/m³)) = 5.36 kwh/m³

where: 10,000 kp/m² = atmospheric pressure at sea level,
1,2 kp/m³ = density of air

Calorific value of biogas at 1,000 m above sea level and 40°C:

= (6 kwh/m³ · 10,000 kp/m² · 273°C) / [(273°C + (40°C - 20°C)) · 10,000 kp/m² + (1,000 m 1,2 kp/m³)] = 4.99 kwh/m³


GAS PROPERTIES, CALORIFIC VALUES AND GAS CONSUMPTION

Properties of combustible gases

Gas

Constituent value

Composition to air kwh/m³

Calorific speed= 1

Density requirement cm/sec.

Combustion m³/m³

Air

Methane

CH4

100

9.94

0.554

43

9.5

Propane

C3H8

100

25.96

1.560

57

23.8

Butane

C4H10

100

34.02

2.077

45

30.9

Natural Gas

CH4; H2

65;35

7.52

0.384

60

7.0

City Gas

H2; CH4; N2

50;26;24

4.07

0.411

82

3.7

Biogas

CH4; CO2

80 40

5.98

0.940

40

5.7

Biogas compared with other fuels

Fuel

Unit u

Calorific value kwh/u

Application

Efficiency%

Biogas equivalent m³/u

u/m³ biogae

Cow dung

kg

2.5

cooking

12

0.09

11.11

Wood

kg

5.0

cooking

12

0.18

5.56

Charcoal

kg

8.0

cooking

25

0.81

1.64

Hard coal

kg

9.0

cooking

25

0.59

1.45

Butane

kg

13.6

cooking

60

2.49

0.40

Propane

kg

13.9

cooking

60

2.54

0.39

Diesel

kg

12.0

cooking

50

1.83

0.55

Diesel

kg

12.0

engine

30

2.80

0.36

Electricity

kwh

1.0

motor

80

0.56

1.79

Biogas

6.0

cooking

55

1

1

Biogas

8.0

engine

24

1

1

Examples of Biogas consumption

Household burner: 200 - 500 l/h
Some figures of gas consumption from India: Boiling 1 l of water: 40 l; boiling 5 l of water 165 l; cooking 500 grice: 140 l; cooking 1000 g rice: 175 l; cooking 350 9 pulses: 270 I; cooking 700 g pulses: 315 l

Industrial burner: 1000 - 3000 l/h

Refrigerator (100 l volume): 30 - 80 l/h

Gas lamp: 120 - 180 l/h

Generation of 1 kwh electricity: 700 l

Biogas/Diesel engine per bhp: 420 l/h

FORMULAE FOR THE DIMENSIONS OF FIXED DOME PLANTS

Vs

[I/day]

volume of feed material

RT

[days]

wanted retention time

h

[m]

depth of expansion chamber = 0.45 m the overflow is in level with the peak of the sphere of the digester

VG

[m³]

wanted gas storage space


VG

= r³ · 2.09 - (r - 0.45)² · p(r - 0.15)

VD

[m³]

required digester volume


VD

= (Vs · RT)/1000


VD

= (R3 · 2.09) - (VG/2) - 0.45² · p(R - 0.45)

p

[m]

maximum gas pressure (= lowest slurry level)


p

= a (0.45² · p(R - 0.15) + VG)/(p · (R - 0.30)

The real and active volume of the digester in fixed dome plants depends on the gas storage space actually utilized. This is normally not exactly known. Therefore, an approximate calculation of dimensions is sufficient. In the table below, the average digester volume VD is given which occurs with a chosen radius R. The relation between radius r and the volume of the expansion chamber (which is equal to the volume of the gas storage space) is based on a depth of the expansion chamber of 0.45 m. In order to keep the gas pressure below 1 m of W.C., the gas storage capacity should not exceed max VG.

Dimensions of Fixed Dome Plants


Digester


Expansion

chamber

R m

avg. VD m³

max VG m³

r m

VG m³

1,50

5,10

2,50

0,90

1,05

1,80

5,30

3,00

1,00

1,31

1,70

8,00

3,00

1,10

1,61

1,80

10,00

3,50

1,20

1,93

1,90

12,00

3,50

1,30

2,29

2.00

14.00

4,00

1,40

2.66

2.10

17,00

4,00

1,50

3,07

2,20

19,00

4,50

(1.60)

(3.51)

2.30

22.00

4,50

(1.70)

(3.97)

2,40

25,00

5,00

(1.80)

(4.46)

2.50

29,00

5,00

(1.90)

(4.98)

2,60

32,00

5,50

(2.00)

(5.53)

2,70

37,00

6,00



2.80

41,00

6,00

For VD >3.00 m³ it is advisable to construct several chambers or expansion channels instead of spherical chambors

2,90

46,00

6,00



3,00

51,50

6,50



3,10

57,00

7,00



3,20

63,00

7,00



3,30

69,00

7,50



3,40

76,00

7,50



3,50

83,00

8,00




Figure

FORMULAE FOR THE DESIGN OF BIOGAS BURNERS

Starting Values

QR

[kcal/h]

prescribed heat requirement

VF

[m³/h]

fuel flow rate

h

[m W.C.]

prescribed gas pressure

Geometrical data

do

[mm]

= 2.1 (VF/h)

d

[mm]

= 6 · do

I max

[mm]

= 7 · d

I min

[mm]

= 1.35 · d

Gas pressure 0.60 m W.C. (fixed dome plants)

D

[mm]

= 1.25 · d

L

[mm]

= 1.20 · d

n

[number]

= 50 · do² (dH = 2.5 mm)

Gas pressure 0.10 m W.C. (floating drum plants)

D

[mm]

= 1.30 · d

L

[mm]

= 1.50 · d

n

[number]

= 20 · do² (dH = 2.5 mm)


Figure


Figure

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