[Digestion] Digester Heating by a thermosiphon system

David david at h4c.org
Fri Nov 16 21:01:13 CST 2012


Paul,

On 11/15/2012 12:03 AM, Paul Muthui wrote:
> Good Day All,
>
> I am looking into ways if heating my biogas digester to increase 
> specific gas yield. I have thought of using a thermosiphon, whereby 
> I heat my primary liquid and then pass it through coils inside the 
> digester.
>
> Has anyone done this before and what would be the expected 
> efficiency of such? Is it an idea worth pursuing?

There have been a number of efforts at solar heating digesters, such 
as the BARC (Bhabha Atomic Research Centre) digester (picture here 
<http://www.dae.gov.in/ni/ninov02/biogas.htm>), as mentioned on Dr. 
Fulford's site (here <http://www.kingdombio.com/preprocess.html>). 
That digester appears to couple passive solar hot water with an active 
system for circulating the water in the digesters. BARC has a design 
which it licenses to other many companies, but it appears to be a 
design that emphasizes effluent safety rather than biogas production.

Jaime Martí Herrero in Bolivia has built a lot of passively solar 
heated digesters in the high cold altiplano, information about which 
can be found here <http://www.cimne.com/cdl1/spacehome/64>. 
(Information about his efforts and designs is available in a very good 
publication-- in Spanish-- found here 
<http://grecdh.upc.edu/publicacions/llibres/documents/2008_jmh_guia_biodigestores.pdf>.) 
There is a good deal of excellent information about low-cost, found 
materials solar greenhouses

There are some ideas mentioned in the article "Biogas production in 
climates with long cold winters" (here 
<http://www.susana.org/docs_ccbk/susana_download/2-1502-biogascoldclimatesweb-wecf0608.pdf>) 
for using solar heating, and a small but growing number of other articles.


As Paul indicated, the implication of having a completely passive 
*thermosiphon* system is that whatever you want to heat-- in this 
case, ultimately, the contents of the digester-- will need to be 
/above/ the collector. Thus to have a truly passive heating system, 
either you would put the digester at the top of a south-facing slope, 
or raise it relative to the collector in some other way. It should be 
possible in the right circumstances to produce a concentrating 
collector that injects steam into the digester, but it would require a 
clever design to make such a heater largely or completely passive, if 
indeed such a thing is possible.

Finally, you may wish to find out more about the Larkin thermosiphon 
(or thermosyphon) design, intended to avoid reverse thermosiphon 
(night sky cooling) without the use of valves, i.e. in a completely 
passive manner.

As far as the efficiency of any of these approaches, that is a very 
complex question, and in any case cannot be answered without 
specifying some further parameters. Are Jaime's passive and very 
low-tech designs "efficient"? Surely it depends on what is of greatest 
value (which we then efficiently conserve), which in turn is a matter 
of culture, situation, and similar circumstances and idiosyncratic 
choices.

But ultimately yes, solar heating for increased biogas is worth pursuing.



d.
-- 
David William House
"The Complete Biogas Handbook" |www.completebiogas.com|
/Vahid Biogas/, an alternative energy consultancy |www.vahidbiogas.com

|
|
"Make no search for water.   But find thirst,
And water from the very ground will burst."
(Rumi, a Persian mystic poet, quoted in /Delight of Hearts/, p. 77)

http://bahai.us/
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