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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 |
m³ |
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 Ø 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 Ø 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 Ø 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 |
n² |
n³ |
n |
n² |
n³ |
n |
n² |
n³ |
|
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 |
m³ |
6.0 |
cooking |
55 |
1 |
1 |
|
Biogas |
m³ |
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
 |
