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FIXED - DOME PLANT by fjwuxn


									Biogas plants for individual farms and slaughterhouses.

Biogas technology is an old and well- tested technology that has been in Kenya for more than 20 years. A
number of farmers and institutions already used biogas an alternative fuel for cooking and lighting.

From a number of studies made on behalf of the climate change convention, one of the main sources of
Methane (a major GHG) has been identified as animal dung. The methane so produced contributes to the
global warming through the reduction of OH and the formation of water vapor in the atmosphere. The
animals and slaughterhouses in Kenya are among the main producers of Methane.

The use of methane will not only ensure that no methane is emitted into the air but also help in the
reduction of using other energy sources, firewood for cooking and kerosene for lighting.

As a local and small contribution to climate change mitigation through the reduction of methane (a GHG)
emissions, farmers and slaughterhouses are ready to install biogas plants to harness captive methane in
the form of biogas with the express intention of reducing their energy bill.

The approach is for the farmer or slaughterhouse to purchase all necessary biogas construction materials
and then when ready we undertake the construction of the biogas plants including all the piping to the
point of use. Where the amount of biogas is large enough, we shall help in the conversion and connection
to diesel engines that will then use the biogas as a substitution for 60% of the diesel used to run the diesel

Since the use of biogas ensures that the other alternative energy sources are not used and remembering
that not using the biogas still leads to the methane gas being released into the atmosphere anyway, under
the CDM programme, it will be possible for us to quantify exactly how much carbon dioxide that will not
be emitted.

Project constrains:
The construction of a biogas plant is very site specific, the recipient has to have:
     1. A constant and easy supply of the feed material, (animal dung.).
     2. A constant and reliable water supply.
     3. Able to purchase the construction materials.
It is also important that a proper and qualified constructer is used for the construction of the biogas plant.
Due to the time it takes to construct a biogas plant ( 4 weeks on average), the construction costs are rather
high for the clients [ranging from Ksh. 60,000.00 (US$ 790.00) to Ksh 150,000.00 (US$1974.00)].

The project approach:
The approach is to deal with each project as an individual project whereby the biogas client will be
considered on an individual basis. The client shall purchase the required construction materials and the
project will then help pay for the technical component for construction. After completion of the
construction and commissioning, the next construction can then be undertaken. It is suggested that the
payment for the technical component is held in trust by the Canadian embassy that can also be the project
collaborating agency in Kenya.

Materials list and labour for standard biogas plants to be constructed.
Item                       16m3                       30m3                      50m3
                           Amount       Price (Ksh)   Amount       Price        Amount      Price
                                                                   (Ksh.)                   (Ksh.)
Water Proofing additive        7kg      1050             12kg      1800          18kg       2700
Bricks                     1700pcs      25500         2300pcs      34500        3400pcs     51000
Cement                       25bgs        18000           36bgs         25920         52bgs         37440
Lime                         7bgs         2100            14bgs         4200          20bgs         6000
Sand (tons)                  4            3000            8             6000                   12   9000
Aggregates (tons)            4            4000            8             8000                   12   12000
PVC pipe 4”                      3m       700                 3m        700           3             700
PVC pipe 6”                      3m       1500                3m        1500              6m        3000
Chicken wire                 20           4500             40m          9000               40m      9000
Plain wire                   80           1600                100m      2000              120m      2400
Neck set                     Item         1500                          1500                        1500

Digging work                              4000                          8000                        12000
Total                                     67,450                        103,120                     146,740

Technical component.
Labour charge                             18000                         29000                       43500
Transport – supervision                   15200                         19000                       22800
Supervision charges                       27000                         32500                       37500
Overhead costs                            5800                          9000                        12330

TOTAL = KSHS.                             66,000                        89,500                      116,130

The          clients 67,450. (51%)
                                                   103,120 (54%)               146,740 (56%)
CDM contribution     66,000 (49%)                  89,500 (46%)                116,130 (44%)

 A biogas unit is an asset a farming family it produces good manure and clean fuel and improve sanitation.

Manure for agriculture and aquaculture.
Farmers conceive the importance of biogas units as a supplier of quality cook ing and lighting gas, but it also
supplies larger quantities of good quality manure. Generally speaking, one third to half of all cattle dung is lost. A
biogas plant increases the availability of organic manure.

 The manure produced through biogas has a comparative advantage over ordinary manure in terms of both quality
and quantity. About 70 - 75% of the original weight of cattle dung is conserved in a biogas unit while in open
compost pits 50% or more is lost. Similarly, almost all the nitrogen content in cattle dung is conserved in a biogas
unit while a substantial part of this is lost during composting. Biogas manure, known as „ digested slurry “
contains a higher percentage of other plant nutrients.

Comparison of plant nutrient content in digested slurry (DS) and farmyard manure (FYM).
Plant nutrients                  Digester Slurry (%)               Farmyard manure (%)
Nitrogen (N)                     1.5 –2.0                          0.5 – 1.0
Phosphorus (P 2O5 )              1.0                               0.5 – 0.8
Potash (K2 O)                    1.0                               0.5 -0.8
 It is a good source of micronutrients like zinc, iron, manganese and copper, which have become a limited factor in
a lot of soils. Also, the complete digestion of cattle dung in biogas units kills seeds of weeds. Organisms causing
plant disease are also killed. The use of digested slurry as manure improves soil fertility and increases crop yield by
10 -20%. It is recommended that the manure should be applied at the rate of 10 tones per hectare in irrigated areas
and 5 tones per hectare in dry land hectares. The manure can be used in conjunction with normal dosages of
chemical fertilizers. Such a practice will help get better returns from fertilizers, minimize the loss of fertilizers
from the soil and provide balance nutrition to crops. Digested slurry has been found useful for raising fish.

Domestic fuel.
Biogas is a clean and efficient fuel for cooking purposes. It saves the consumption of kerosene charcoal and
wood. It avoids the need to collect firewood and twigs and thus saves the labour of women and children normally
spend considerable time and energy to cover long distances daily to collect fuel.
 It eliminates the practice of indiscriminate felling of trees and consequent soil erosion.
 It is an efficient fuel for cooking purposes; it alleviates the drudgery of women‟s lives and provides spare time for
women‟s activities that can make a contribution to the family income. Children can read under biogas illumination,
during erratic supply of electricity or shortage of kerosene.

Sanitation and health.
Biogas units are effective for the sanitary disposal of human excreta. Attaching latrines with a biogas unit can
eliminate this. By putting all human and animal excreta into a biogas unit the problem of waste disposal is solved
at the family level itself. During decomposition of night - soil in a biogas unit, most of the diseases – causing
organisms are killed. This can serve as an effective control of parasitic diseases, hookworm, roundworm, etc.

The digested slurry remains free from foul smell and most of pathogens. Mosquitoes and flies do not breed in
digested slurry. Thus biogas units improve sanitation. The incidence of eye diseases among women and children is
also reduced as burning of biogas does not cause any smoke in the kitchen. Biogas, being a clean fuel, does not
cause air pollution. It is considered a better fuel than natural gas and liquefied petroleum gas because it does not
contain Sulphur. Sulphur, on burning, gets converted into Sulphur dioxide, which is responsible for many lung
diseases. There is no danger of explosion of biogas as it contains carbon dioxide, which acts as a fire extinguisher,
it is also lighter than Air and so it quickly dissipates in the air instead of pilling on the floor like LPG gas.

Operation and maintenance.
Starting the plant.
 Fill the plant with a correct mixture of dung slurry (dung and water in ratio 1:1) through the inlet chamber. The gas
pipe should be disconnected or the safety valve, if any, should be opened during filling so as to avoid build - up of
any pressure in the dome. The digester should not be filled to more than 75 – 80% of its volume, under any
circumstances thus allowing some volume for storage of gas. The quantity of slurry recommended for the particular
size of plant should be added daily.

Gas production and use:
The production of gas and filling of the gas chamber would take about 7 – 20 days. The initial gas stored may not
be combustible and should be allowed to escape. Purge air from all delivery lines by allowing gas to flow out prior
to first use. Ensure that condensed water is able to flow out from the pipeline through the water trap. The slurry
should be added only after the production of inflammable gas has started, i.e. after about 20 days of initial filling of
the plant up to the recommended level. The only stirring which can be done in a fixed dome plant is by moving a
bamboo pole up and down in the inlet and outlet openings. This will help in breaking of scum if done at least once
a day.
     (i)      Always ensure that gas valves are closed to avoid wasting of gas.
     (ii)     Never allow anyone to enter the gas plant when it has slurry inside.
     (iii)    Always keep the openings of the outlet and inlet chambers firmly closed by putting concrete covers on

Maintenance and General Care.
   (i)    Add dung slurry to the plant. Keep ratio of dung and water at 1:1.
   (ii)   Make sure that no stones and sand is getting into the plant during feeding.
   (iii)  Clean the gas burner.
   (iv)   The water traps should always contain water otherwise the Gas will leak out through the gas trap.
Check gas pipeline for leaks with a soup solution.
    (i)     Check for gas and water leaks and repair them.
    (ii)    Check gas pipelines for leakages.
    (iii)   At intervals of some years check for any solid sediment at the bottom of the digester plant by inserting
            a long stick in the plant and determining the change in depth. It should be completely emptied to allow
            for removal of the solids and plastering of the inside portion of the plant. Take the necessary safety
            precautions when performing this task.
Note: The digested (old) slurry should be recycled along with fresh slurry in order to increase the bacterial
population in the digester, for about 100 litres of fresh slurry about 2 litres of old slurry can be added. This will
speed up and increase gas production.

Common problems encountered with biogas units and remedial measures.
Defect                            Cause                               Remedy
No gas after the first filling of Lack of time.                       It may take 3 – 4 weeks
the plant.
Slurry level does not rise in        i.   Gas pipe blocked by water a. Add more slurry.
inlet and outlet chambers even            condensate.                 b. Check and correct
though gas is being produced.       ii.   Insufficient pressure.      c. Rotate the agitated slurry with a wood
                                   iii.   Gas outlet blocked by scum. pole.

No gas at stove but plenty in        i.   Gas pipe blocked by water      a. Remove water condensate from
the plant.                                condensate.                    moisture trap. b. Increase weight on
                                    ii.   Insufficient pressure.         gasholder.                               c.
                                   iii.   Gas outlet blocked by scum.    Disconnect the outlet valve from the
                                                                         hosepipe and clean it by pouring water.
Gas does not burn.               Wrong kind of gas                       Add properly mixed slurry
Flame far from burner.           Pressure too high or deposition of      Adjust gas outlet valve and clean nozzle.
                                 carbon on the nozzle.
Flame dies quickly                Insufficient pressure                Check quantity of gas. Increase pressure
                                                                       by breaking the scum by stirring the
Unsanitary condition around - Improper digestion                       - Add correct quantity of slurry
biogas unit.                                                           - Use slurry for composting of crop
                                 - Improper disposal of slurry         residues
Leakage of gas from the dome and gas storage area of fixed - dome type biogas plant is the most common problem,
which occurs mainly due to faulty construction by untrained masons.

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