biogas producer

[Guy Sellers]

My goal is to produce biogas with as lowtech, low maintenance, cheap materials as possible. I want the ability to produce around 1-3 cubic metres a day of buranble biogas for simple uses such as cooking and heating so I can skip the cost of cleaning the gas. I was given the brilliant idea (by Paul Harris - Adelaide University) of using a tractor tyre for gas collection. Now my major problem seems to be the actual plug flow digester.I have a whole heap of questions that need answering, I hope you don't mind. What size digester do I need? What is the best material to use? How do you stir the slurry but also keep it airtight? How do you get the gas from the digester up the specific tube with enough pressure to fill a tractor tyre? How do you measure the C:N ratio? What is the lowest maintenance way of removing floating scum? (does it need to be removed?) And finally what is the most concentrated form of VS? i.e what material can I use that would have the biggest ratio of minimum solids input to maximum gas production output? (has this been researched?) My initial idea was to simply use the human wastes from an individual Household, but this wouldn't be enough to produce 1-3 cubic meters a day so I was wondering what would be best to use to top it up. Otherwise what else can I do to make biogas more attractive as a cleaner/cost effective alternative for mainstream household users?
Would appreciate any advice, Cheers.

[This message has been edited by Guy Sellers (edited 12-17-2000).]

[Bob]

Whew! Many questions.

For starters, have you checked out some of the resources available on this site?

Here is a page discussing the basic theory and ideas behind our digester design.

From there you can browse to other pages, including a design tool that you can use to play "what if" games -- and answer a lot of your questions yourself. (Note: this requires a free plug-in that only runs under Netscape. You can get it here. We're working on an IE solution as well, but unfortunately not available yet.)

And here is a drawing showing construction details of a unit you can build from a plastic tank.

Here is a link to a drawing showing the same tank, but with description of the operation of each part instead of construction.

For basic sizing purposes, figure that you can get about 2 - 2.5 times the volume of your digester per day, of biogas. And about 0.4 m3 of biogas/kg of volatile solid per day. Of course this will vary, depending on a whole lot of things, like what you feed it, and the temperature.

[Guy Sellers]

I know, there certainly are a lot of questions. Thankyou so much for the effort you have obviously gone to . I want to make sure that I experience as few problems as possible by forecasting them befre they happen. You have been a great help. Cheers!!