Anaerobic Digester

Anaerobic Digester
(http://www.adelaide.edu.au/biogas/fair/)

Thursday, November 13, 2008

Project Update

My project has advanced in numerous ways since my first inception of the project. My original plan was to build a very small digester (Gatorade bottle size) in order to experiment with materials that I could use for digestion. The next order of business on my plan of attack was to build a “medium-scale” digester that would be able to produce a small flame. I built both of these digesters and researched the use of anaerobic digestion – which would have completed my original project – in about half of the time I allotted for myself. Since then, I have expanded my project in three ways that are all very closely linked.

1. I have been in contact with Paul Harris of the University of Adelaide in South Australia and Brad Frazee of Intrepid Technology & Resources, Inc. I have tried to get a hold of the Idaho National Laboratory but I have had no success yet. Paul Harris has helped me a ton with ratios of organic matter introduced into digester systems and gas produced. Every kilogram of volatile solids consumed in the digester produces about 0.5 cubic meters of methane. (17.6 cubic feet.) And about 70% of the volatile solids in the system will be destroyed. Brad Frazee gave me a lot of information on the Whitesides Dairy in Rupert, Idaho. The digester system at the Whitesides Dairy produces about 30 million cubic feet of methane per year. This information has helped me a lot in determining whether or not a digester large enough could be built for our school. Brad told me that in order to produce about 160,000 cubic meters of methane that we need for the school we would need 800 cows. These cows would produce 13,000 gallons of manure per day.
2. With the above information I have decided to go forward with my designs for an industrial-sized digester for The Community School. I have acquired the information about the annual natural gas usage at The Community School, which has helped out a lot with my project in determining how much methane needs to be produced.
3. Once I talk to Brad Frazee again I will have the information that I need for designing and building a digestion system at The Community School. I will know if digester systems are scalable and how big the housing building will have to be. The only problem with the digester system at school would be the number of cows that we need. I plan on contacting the architect that built the two new buildings at school in order to design another building at school.

I am very excited about the progress that I have made on my project, because when I think back on it, my original ideas would have left me well short of what I wanted to accomplish. The development of the design for a digester at The Community School is a great way to exercise my interest in mechanical and architectural engineering. Although the available land at school may pose a problem to ever designing a system that significantly decreases the annual natural gas cost at the school, this project is very possible. I know this because the Whitesides Dairy plant produces more than five times the amount of methane that the school uses annually.

Friday, November 7, 2008

School Digester

I have been in contact with Brad Frazee of Intrepid Technology & Resources, Inc. about the Whitesides Dairy biogas facility in Rupert, Idaho. The Whitesides plant produces about 30 million cubic feet of methane per year (~850,000 cubic meters.) In order to produce the 160,000 cubic meters of methane per year for the school Brad said that we would need approximately 800 cows, which would produce a total of 13,000 gallons of manure per day.

A facility this size would be very possible to build but the capital cost per cubic foot of methane would be high. The cost of the equipment does not scale down to our required size very well.

I have found that natural gas produces 1,000 Btus per cubic foot of natural gas. The methane produced from biogas produces about 600 Btus per cubic foot of biogas. This may sound like the biogas does not help much at all, but this methane would otherwise be released into the atmosphere. The school requires approximately 3.3489 billion Btus per year. The gym/theater building is the most inneficient building at school; using approximately 40% (1,376,500,000 Btus per year) of the natural gas that is routed to the school uses.

Anaerobic Digester Design

Anaerobic Digester Design
This picture was taken from Paul Harris of The University of Adelaide in Roseworthy, South Australia, Australia. (http://www.adelaide.edu.au/biogas/fair/.)