Experimental Analysis of Biogas Compression and Purification from Biogas Digester: A Case Study at Sidist Killo Campus
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Date
2019-07
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Addis Ababa University
Abstract
The study encourages a way to recover energy from food wastes with the objective of producing clean
biogas fuel (methane) from a food waste by using anaerobic digestion (biological decomposition).
This waste to fuels technology reduces the amount of waste to be sent to the living areas, recovers
energy from bio waste, helps to generate income from the selling of the produced biogas fuel
(methane) and solves the energy problems. This thesis assesses the compression and purification of
biogas mainly methane through anaerobic digestion, using a 10m
3
digester installed at Sidist killo
campus.
Biogas which is a clean and environmental friendly fuel emerged as one of the potential alternative fuels.
Raw biogas contains about 60-70% methane (CH4), 30-40% carbon dioxide (CO2), traces of hydrogen
sulfide (H2S) and fractions of water vapors. But its wide spread use is disadvantaged by the associated
problems like low energy density due to the presence of impurities, generation at low pressures and the
absence of means for storing and transporting. Biogas is widely used for cooking and lighting, but its
commercial use has not been realized due to difficulties in its storage and transportation.
This work intends to establish a facility at the site of biogas production in the sidist killo campus for
purifying, compressing, bottling and making it transportable. Solution identified to the problem is to
increase the energy density of the gas through removal of incombustible and corrosive gas and
consequent compression which is experimented on this paper. This paper presents all the results of
removal of impurities of biogas which are mainly carbon dioxide gas, hydrogen sulphide and water from
biogas using reasonable chemicals selected. Sodium hydroxide, activated carbon powder and silica gel
are chemicals selected to remove carbon dioxide, hydrogen sulphide and moisture respectively from the
raw biogas.
Experimental results are evaluated by ever-changing the amount of chemical used from 0 up to 10 gm.
As a result, the purity of biogas increases with increasing the amount of chemicals. The gas purified after
the scrubbing unit constitutes 61% of methane which is in the acceptable range of methane content in the
biogas. Further, compression of biogas was carried out by a commercial compressor and stored into a
500lt biogas bag and tire inner tube at a pressure of 2 and 1 bar respectively. And finally the stored
biogas is bottled in to 2lt commercial gas cylinder using modified cycle pump at a pressure of 5 to 8 bar
which a normal person can exert
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Keywords
Biogas Compression, Biogas Digester, Purification