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Biogas plants for individual farms and slaughterhouses. Introduction 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 engine. CDM: 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. RE: PRICE LIST FOR STANDARD BIOGAS PLANTS (FIXED DOME) 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 Contribution The clients 67,450. (51%) 103,120 (54%) 146,740 (56%) contribution CDM contribution 66,000 (49%) 89,500 (46%) 116,130 (44%) FIXED DOME BIOGAS PLANT. 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. Feeding 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. Precautions (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 them. Maintenance and General Care. Daily (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. Monthly Check gas pipeline for leaks with a soup solution. Annually (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 OPERATIONAL PROBLEMS 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 slurry. 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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