[Digestion] Starch & Sugar VIDEO

[Steve&Anne]

Hello Marcel

Marcel wrote..........

Am thinking a lot about design for an experimental setup - size is a  
considerable factor, as is cost.

Wondering about floating dome (per ARTI) or polyethylene tube type  
(http://www.ias.unu.edu/proceedings/icibs/ibs/info/ecuador/install- 
polydig.htm)

SR replies.....
Given that your design is to be experimental - my advice is that if you 
have some intended use for the gas - put a good bit of consideration 
into the gas collection / storage area of the design.
I found with my small scale installation is that the amount of storage 
(and collection rate) actually determines the overall design. To explain 
- polyethylene tube or tractor inner tube allows a relatively small 
volume collection and with a little applied weight (which back pressures 
the digester - the feed tube now tends to become an outflow) will burn 
well at a cooker type burner (for a limited time). My experience is that 
I can boil 700 ml of water from say 7 degrees C with less than 20 litres 
of biogas. Sometimes a lot less than 20 lt, seems to depend on the 
content's temperature in the digester. Varies seasonally <15 °C to 
around 22°C (contents).

My suggestion is that if you want more than just a demonstrable flame, 
then the floating dome is a consideration or perhaps fix fast the dome 
and feed into poly tube solely to hold gas (rather than have contents 
and gas all within the some bag).

Another method  would be to have a plastic drum as the digester - a 
plastic film pulled across the top and sealed to the drum with silicone 
RTV - all tubes and gas pipes would be entered through the side or 
bottom of the digester drum (easier to seal) - the gas pipe leads to a 
PE tube bag.

Hope to be helpful
kia ora
Steve Rodda
New Zealand

One comment on the ARTI design -  IMO - I suspect that this digester 
system would be larger, conventionally. It is smaller because the gas 
production rate is higher - review Dr Karve's posts to the stoves group.