Feasibility study for commercial packaging of biogas in Uganda
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About 92% of Uganda’s energy demands are satisfied by wood and charcoal which according to NFA biomass study, (2009) has caused loss of 27% of the total forest and tree cover in the last fifteen years. Many nationalities in Uganda and East Africa are cattle keepers therefore the raw material (cow dung) won’t be a challenge. From the researched design, a family with between 5 to 10 cows can produce a minimum of 2.3m3of gas which is adequate for lighting and cooking for an average rural household income of six people. The gas produced from the decomposition of the cow dung is called biogas. In Uganda, most of the biogas generated is used on site by only those who own biogas plants and therefore most of the people in rural and urban areas have no access to biogas. Therefore, this report presents a feasibility study for commercial packaging of biogas in Uganda. The potential of biogas generation was first quantified through different organic wastes. The wastes included livestock wastes from cattle, goats. Sheep, chicken, pigs and other livestock. The biogas from all livestock waste was estimated to be 1,258.37M m3 per year, human wastes generated 106.85m3 for an estimated population of 10,000 people for every person producing 250g per day. Municipal solid waste generated in Kampala was found to be 1,000 tonnes daily and 78% of this was biodegradable and produced 367m3 of biogas. The total potential was found to be 3,450,473.85m3 each day which showed a very large potential of biogas in Uganda and therefore need for packaging of the gas. Due to the very large potential, the technology to produce this gas was then looked at. The different technologies analyzed included; fixed- dome digesters, floating dome, and tubular bio-digester and plug flow reactors which were small scale digesters. The large scale digesters were the batch-type digesters, continuous-type digesters, vertical digesters, horizontal digesters and lagoon over anaerobic digesters. Different methods for cleaning the gas to increase its heating value and density were looked at since it’s a necessity before the gas is packaged. The methods involved water scrubbing, organic physical scrubbing, chemical scrubbing, cryogenic upgrading, desulphurization and in-situ methane enrichment. Comparison of different upgrading techniques was made and water scrubbing gave a methane content of 97%. Compression and storage processes followed where a 3-bar single-stage double acting compressor and 6-bar single-stage double acting compressor were considered for the compression of the gas. The temporal storage tank at a pressure of 5 bar was to be used from which the gas is then compressed to 6kg gas cylinders as the final packaging materials. Lastly the economic evaluation was carried out and this included capital costs mainly for construction of a 50m3 biogas digester, compression and storage container costs, operation and maintenance costs and then annual revenue from the sale of packaged biogas. The net present value (NPV), internal rate of return (IRR), profitability index (PI) and payback period were then calculated.