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Paul,<br>
<br>
<div class="moz-cite-prefix">On 11/15/2012 12:03 AM, Paul Muthui
wrote:<br>
</div>
<blockquote
cite="mid:CAJAkcuTQdaQgmAvVaC_Qwqdm702atW4SKKZUzvQVX-nhM4kTjw@mail.gmail.com"
type="cite">Good Day All,<br>
<br>
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.<br>
<br>
Has anyone done this before and what would be the expected
efficiency of such? Is it an idea worth pursuing? <br>
</blockquote>
<br>
There have been a number of efforts at solar heating digesters, such
as the BARC (Bhabha Atomic Research Centre) digester (picture <a
href="http://www.dae.gov.in/ni/ninov02/biogas.htm">here</a>), as
mentioned on Dr. Fulford's site (<a
href="http://www.kingdombio.com/preprocess.html">here</a>). 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. <br>
<br>
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 <a href="http://www.cimne.com/cdl1/spacehome/64">here</a>.
(Information about his efforts and designs is available in a very
good publication-- in Spanish-- found <a
href="http://grecdh.upc.edu/publicacions/llibres/documents/2008_jmh_guia_biodigestores.pdf">here</a>.)
There is a good deal of excellent information about low-cost, found
materials solar greenhouses <br>
<br>
There are some ideas mentioned in the article "Biogas production in
climates with long cold winters" (<a
href="http://www.susana.org/docs_ccbk/susana_download/2-1502-biogascoldclimatesweb-wecf0608.pdf">here</a>)
for using solar heating, and a small but growing number of other
articles.<br>
<br>
<br>
As Paul indicated, the implication of having a completely passive <b>thermosiphon</b>
system is that whatever you want to heat-- in this case, ultimately,
the contents of the digester-- will need to be <i>above</i> 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. <br>
<br>
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.<br>
<br>
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.<br>
<br>
But ultimately yes, solar heating for increased biogas is worth
pursuing.<br>
<br>
<br>
<br>
d.<br>
<div class="moz-signature">-- <br>
<div style="font:Georgia" ;=""><span style="font-size:110%;">David
William House<br>
</span>
<div style="padding-left:3em;font-size:80%;">"The Complete
Biogas Handbook" <code><a href="www.completebiogas.com">www.completebiogas.com</a></code><br>
<em>Vahid Biogas</em>, an alternative energy consultancy <code><a
href="www.vahidbiogas.com">www.vahidbiogas.com</a><br>
<br>
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<code>
<div style="padding-left:2em;">"Make no search for water.
But find thirst,<br>
And water from the very ground will burst."
<div style="padding-left:2em;font-size:80%;">(Rumi, a
Persian mystic poet, quoted in <em>Delight of Hearts</em>,
p. 77) <br>
<br>
<a class="moz-txt-link-freetext" href="http://bahai.us/">http://bahai.us/</a></div>
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