Abstract
This paper is aimed at determining the Wobbe Index (W I) of cattle dung biogas which is the amount of energy delivered to a burner through an injector or orifice especially during combustion. The biogas was produced by anaerobic digestion of cattle dung in a batch digester within two weeks. Pressure and temperature of the digester were monitored at 12 noon daily. The analysis of the combustible biogas using thermal conductivity detector (TCD) revealed CH4 at 0.562, CO2 0.395, H2S 0.018, CO 0.019 and 0.005 moles for NH3 by volume. Its calorific value (C V) using gas calorimeter Junkers was 19.5 MJ/m. The cumulative specific volume of the biogas rose from zero through day 1 to 0.622732 m/kg on the sixth day before recording daily marginal increments with the rest of the days of incubation. The relative density of the biogas also had a sharp rise on the second day at 5.039208 before dropping to 2.51126 and then gradually decreased daily to the end of digestion. The Wobbe Index equally rose from zero on the first day through to 12.08434 MJ/m, 14.07783 MJ/m and 15.87665 MJ/m on days 2, 3, 4 and 5 respectively after which it had logarithmic increments. The volatile solids destroyed also recorded logarithmic rise while the bacterial growth rate followed the zigzag pattern as those of internal energy and enthalpy. It is therefore concluded that parameters like the cumulative specific volume and Wobbe Index increased throughout the incubation period while those that are directly temperature dependent varied with the temperature of the digester.
Highlights
The energy crises as a result of unacceptable upsurge in the prices of the fossil fuels in the 1970s compelled the developed nations to intensify the research in to alternative energy drives
7.0 Results and Discussions The results obtained by using equations (1) to (9) are as shown in Table 1 Table 1: Constituents of the cattle dung biogas and their thermo-physical properties
The biogas constituents are in column 1, the moles of the constituents in 2nd column and their respective molar masses are in column 3
Summary
The energy crises as a result of unacceptable upsurge in the prices of the fossil fuels in the 1970s compelled the developed nations to intensify the research in to alternative energy drives. The observation that the fossil fuels sources are being depleted without corresponding refurnishing made it absolutely necessary, this time around for both the developed and the developing nations to radially launch researches in to alternative and renewable energy sources. Renewable energy sources are many and include: Hydropower, solar, wind, ocean, geothermal and wastes among others. These renewable energy resources except for the wastes do not degrade in the process of usage but are capital intensive and some like hydropower are affected by seasonal changes and are location specific. They can be either synthetic or biological in nature
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