According to executive order 18-01 signed by the Washington State Governor, all newly constructed public buildings and facilities shall be designed to be net-zero energy capable. To respond to the governor’s order, the Washington State Department of Transportation has asked for the design of a system that can use biowaste that accumulated at their safety rest stop areas to generate electricity to power the facilities. The goal of this project seeks to assist WSDOT by designing, building and testing the capability of a small-scale methane energy generator that can be scaled to fit the needs of any rest area.

There are a few methane generators available on the market. However, they are not designed to satisfy needs of net-zero energy and rest areas. In this work, a new net-zero methane generation system is presented to show how it can convert biowaste into methane for electricity at rest areas. The model is composed of two tanks to store the biomaterial, a filtration system to remove undesirable gasses (H~2~S and CO~2~), a generator that runs on methane gas, and a solar array that powers temperature sensing devices.

The biowaste is contained in an area where bacteria can anaerobically digest it. The two 100-gallon tanks are pressure vessels that can build pressure up to 25 psi before four safety release valves vent excess pressure. Methane, Hydrogen Sulfide (H~2~S), and Carbon Dioxide (CO~2~) are produced from the anaerobic digestion of the sludge. To give the bacteria the optimal environment to thrive and produce methane, an exhaust heat exchangertransverses both tanks and heats the sludge to approximately 96 Fahrenheit. A stirrer was installed oneach tank to mix sludge and promote further methane generation.

         The gasses that are produced in the tanks are then passed through a filtration system that removes H~2~S and CO~2~. Red iron oxide, which is present within an ABS pipe, reacts with H~2~S to remove sulfur and produces H~2~O as a byproduct. The remaining gasses convey through a container filled partially with water. The water absorbs theCO~2~ leaving only methane, which can then be combusted in the generator. Both the water and iron oxide can be regenerated by exposing them to air, allowing the contents to be used multiple times before needing to be replaced altogether.

           The generator used in this system is a 1400-watt gas and propane dual fuel generator. The air-fuel ratio of methane is slightly different as compared to propane. A valve was used to adjust the air-fuel ratio for optimal performance. The exhaust from the generator transverses through the heat exchanger, and the heat from the exhaust transfers to the sludge to increase methane production.

            A photovoltaic system was added to the design to power temperature data acquisition equipment.  The energy collected by three 175-watt solar panels was used to charge a laptop that recorded the data from several thermocouples, which were attached to the heat exchanger before and after passing through the tanks. This data was used to track the heat that was transferred to the sludge.

            The methane energy generator is an anaerobic digester that produces green energy from the degradation of human biomatter. The goals of this project include the reuse of waste at public facilities and reducing carbon emissions for net-zero energy. The incentive for such a system is not only environmental but also financial as it generates its own energy and any unused energy generated by the system can be put into the electrical grid. The methane energy generation system can be scaled up, depending on the waste stream. This design is new and flexible, and uses sources of energy otherwise thought to be nuisances to the public that are nuisance items to most.  

 

 

 

            

 

 

 

 

 

 

 

  
 


Design and Assembly of a New Methane Generation System for Energy Conversion From Biowaste

Division / Sponsors: 
Aerospace, Bioengineering, Applied Mechanics, Design Engineering Division, Advanced Energy Systems, Manufacturing Engineering Division, Noise Control and Acoustics, Nondestructive Evaluation, Diagnosis, and Prognosis (NDPD), Nuclear Engineering Division, Process Industries Division, Fluids Engineering, Heat Transfer, Materials, Microelectromechanical Systems, Safety Engineering and Risk Analysis, Computers & Information in Engineering


Paper Proceedings: https://asmedigitalcollection.asme.org/IMECE/IMECE2020/volume/84478

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