Rolf explains the dividends of the U shaped, plug flow system.
“Ede” Werner Edelmann feels like an Einstein of biogas. He organized the conference to pick all of our brains on a new technology he and his team have developed. There were field visits, presentations and sharing in the field of “Applied Fartology” as Ede often reminded us. (At the border crossing from Tanzania, Ede insisted that his occupation was “Professor of Fartology,” which stumped the border guards.)
The technology Ede and Rolf showed us on a field visit is a U-Shaped, plug-flow digester which is based on a Swiss technology called Kompogas. Ede, Rolf, et al. installed their first iteration at a convent in Tanzania. This iteration was made with cement, but it was easy to see that this could be made with plastic tarps similar to those used for fishponds in Kenya. Such a system would be easy to install, easy to remove and perhaps would be a good technology to combine with Pay-as-you-go biogas technology that we are developing.
There were a bunch of biogas tech nuts in attendance at the conference
- SNV the Dutch development organization that is behind some of the biggest biogas programs in the world and now is looking into how plastic biogas systems could be the future for biogas programs in Africa.
- Afrisol a biogas contractor of 100+ meter cubic systems in Kenya.
- Simgas a mass producer of small scale plastic biogas systems and at the conference presented on how to maximize the effectiveness of biofertilizer (digester effluent). It seems that a significant portion of the Nitrogen is lost during drying of biofertilizer.
- Jua Nguvu a company based at the Coast in Kenya now involved with Ede in the development of the U-shaped, plug-flow.
- Camrtec a development organization based in Tanzania now developing a domestic biogas system that requires no additional water and therefore would be appropriate for areas with little water.
- Katani a sisal processing factory which has the largest biogas system in East Africa as far as I know at 1,700 meters cubed, which we were lucky enough to visit. See below.
This
biogas system running since the mid ’00s takes sisal waste as a
substrate and runs two 150kW generators. The farm is looking to expand
its biogas production.
- Plug Flow Design: meaning the digestate isn’t mixed but is pushed along in an even “plug”.
- Rationale: All digestate is in the digester for the same amount of time (compared to mixed digester with, let’s say, a 40 day retention time where 1/40th of the effluent has been in the digester less than 1 day). Also, better hygenization since all effluent has a longer residence time.
- Low Pressure.
- Rationale: less leaks. Because it is low pressure, they use a gas diffuser as a burner head which works at very low pressures (2cm water column).
- Low Tech.
- Rationale: less fixing.
- U-Shaped: Digester itself is U-shaped from the birds-eye-view.
- Rationale: smaller footprint and easier to use effluent to innoculate fresh material (necessary because there is no mixing).
- High Solids Content in digester
- Rationale: If you can stuff twice as much cow dung into a digester you will double the gas production while your capital costs of installation remain the same. In theory. In theory this digester can handle 25% Total Solids, more than twice that of a typical digester in Africa.
- Low Cost.
- Rationale: kinda obvious.
The small amount of pressure in the system is produced by a hinged
“door” laying on top of a bag. A system I hadn’t seen before, but seems
to work. See picture below.
Pressure applicator system.
