The search for new and improved energy renewal systems has been widespread for years at a global level. One of the techniques that are increasingly being employed involves the utilization of biowaste, both human and animal, to generate energy through a process called upgrading, which separates specific elements from the biogas produced in the digestion of the organic matter. The methane obtained from this process is used as fuel to a generator. One of the environments where this technology could prove to be advantageous, but where it hasn’t been applied yet, is the transportation field. Under request of the Washington State Department of Transportation (WSDOT), the purpose of this project is to convert biogas from organic waste to usable energy at highway rest areas in Washington State, decreasing raw waste accumulation at sewage lagoons and providing means to electrical-grid independence for these sites. The system obtained from this process will therefore constitute a significant improvement both from an environmental and financial standpoint, eventually producing net zero energy buildings.In this paper, the designed system takes previously unused biowaste and extracts biogas from the waste, which is obtained through anaerobic digestion. This biogas contains principally methane (CH4) and carbon dioxide (CO2), but includes hydrogen sulfide (H2S), potentially harmful substances that would normally escape into the environment. Because of the nature of the processes involved in this project, research was conducted in several fields, including biology, chemistry and engineering. The students also examined the work of the previous teams, and received a prototype produced in one of the past iterations of the project. The preexisting methane generating apparatus was analyzed, in order to identify its principal issues, such as being unable to generate methane continuously, having a poorly-functioning scrubber and a lack of moisture removal, and propose appropriate modifications to solve them. These modifications were focused on increasing both efficiency and functionality of the system. Particular attention was given to insulation and leak prevention, both fundamental aspects for the success in this experiment.&nbsp;Temperature is rather important in the first stage of the methane generating process, as biogas production is generally more efficient between 30℃ and 50℃. A heating mat was selected to provide heat to the sludge, and an agitator was included in the design of the first tank, where the anaerobic digestion happens. The biogas obtained then undergoes scrubbing to remove CO2 and H2S, with the use of a water column and iron sponge respectively. Moisture in the fluid is condensed and removed by a water trap, and the gas, now principally methane, is directed to a generator that employs it to produce electrical energy. The system is intended to be independent from an energy point of view, relying only on a photovoltaic system produced by a team of Saint Martin’s University students.&nbsp;&nbsp;Throughout the project, it was found that a more hospitable environment requires a relatively stable heat source and less disruptive agitation. The team considered the possible advantage given by the application of biofilms, to ‘seed’ the digester tank with methanogens strains known to produce higher levels of methane. Additionally, the team has proposed changes to the digester tank, which will prevent gas leakage. Biogas containment is a necessary factor for both safety and efficiency, and isolation from oxygen is critical to the anaerobic digestion process.

Biogas Upgrading System for the Generation of Electricity From Methane Combustion

Paper Proceedings: https://asmedigitalcollection.asme.org/IMECE/IMECE2021/volume/85543

ASME 2021 International Mechanical Engineering Congress and Exposition (IMECE2021)

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