[Digestion] Small Scale Digester Heating

[Paul Harris]

G'day Kyle,

Yes, we had birds and mice pull out rockwool insulation and when we 
tried styrene balls they leaked out any holes. If you are underground 
you need to keep water away, so closed cell foam would be good (but 
possibly expensive) - as others have said you have to look at what is 
available locally (and relative costs may change considerably, so what 
is cheap here may be very expensive where you are).

Happy dgesting,
HOOROO

Mr Paul Harris BEng (Ag) (Melbourne)
Visitor at The University of Adelaide

On 4/10/2012 11:55 PM, Takamoto wrote:
> Dear Biogas List,
>
> Thank you all for the advice and encouragement. It can be done which 
> is good news.
>
> Mr. Karve, could you explain your concept a little bit more? Is it 
> passive or active (requires a pump)? and what is the name of the 
> sponge rubber insulation material?
>
> Manuel, you mention that electricity is required for control. It seems 
> that a battery could be used for control and last for several years. 
> Is this true? At most you could use a tiny solar panel to charge a 
> battery for all of the control power you need. How much stirring is 
> actually required? If you are heating the bottom of the digester then 
> there should be some convection in the tank just from thermal 
> differences. Even so, I think I have seen that stirring only increases 
> gas production by around 20%.
>
> Peter, how much power did your system require for pumping? Is there a 
> way to do away with the pump? How much did a cloudy day affect the 
> heating system? How much power was required to run your control system 
> (if any)? It is good to hear that your mesophilic digester was able to 
> produce better fertilizer than the ambient temperature digester. I 
> have seen a website for a company in Australia called biobowser. Is 
> that the same company? It looks like a beautiful technology all 
> packaged into one easy (?) to install modular unit. Is there a reason 
> why their smallest unit is for 100kg per day? Could their system be 
> scaled down?
>
> Paul, to better understand the rough spreadsheet you made, you found 
> that one twelfth of the additional biogas was used for heating so the 
> net effect was a significant increase in biogas to the user. Have you 
> had bad experience with animals in your insulation? Would you 
> recommend avoiding some kinds of insulation? Are there some 
> insulations that a good for underground installations?
>
> One of the ideas I proposed was to bubble a small amount of air 
> through the digester so that there was a slight aerobic reaction that 
> generates heat and keeps the digester warm. Is there any validity to 
> this idea? Has it ever been done? Or would the amount of oxygen 
> required to raise the temperature of a digester by 17C degrees kill 
> the methanogenic bacteria?
>
> All the best wishes,
>
> Kyle

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