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Paul,<br>
<br>
<div class="moz-cite-prefix">On 11/20/2012 12:43 AM, Paul Muthui
wrote:<br>
</div>
<blockquote
cite="mid:CAJAkcuThQbHDBoibQJ2NMnRJOHQoVpaXbh3RNVHYOH2DFsQt4g@mail.gmail.com"
type="cite"><br clear="all">
<div>G'day All,</div>
<div><br>
</div>
<div>How much energy is given out in the digesters as a result of
anaerobic reaction? I can't seem to get any publication with
enough details on this. I would like to know the temperature
rise that would be caused by the reaction. <br>
</div>
</blockquote>
<br>
Dr. Fulford is correct, in essence, in that according to ordinary
experience, no functional metabolic heat is available from anaerobic
digestion, as contrasted to the very considerable metabolic heat
available from aerobic digestion (at about 40% of the energy
provided as methane in the former case). However:<br>
<br>
<blockquote>
<blockquote>
<h3><a
href="http://ebookbrowse.com/self-heating-of-anaerobic-digesters-using-energy-crops-pdf-d61331597">Self-heating
of anaerobic digesters using energy crops</a></h3>
H. Lindorfer, R. Kirchmayr, R. Braun<br>
Water Sci Technol. 2006;53(8):159-66.
<h4>Abstract</h4>
With the increasing application of energy crops in agricultural
biogas plants and increasing digester volumes, the phenomenon of
self-heating in anaerobic digesters appeared in some cases.
Until now this development was just known from aerobic systems.
To get an idea of the thermodynamics inside an anaerobic
digester, a detailed analysis of all heat fluxes in a full scale
agricultural biogas plant was carried out. Several experiments
were realised to quantify the influences of different internal
and external energy sources. To estimate the impact of
self-heating in anaerobic systems, data of other full scale
agricultural biogas plants in Austria were collected.
Alternatives to the cooling of the digesters are discussed
basing on individual experiences of several plants. A connection
between carbohydrate rich substrates, especially with high
starch contents, and the self-heating could be shown. But from
the results it can be assumed that heat enthalpy due to
anaerobic microbial metabolism plays a key role in self-heating,
which is in contrast to the current thermodynamic knowledge.<br>
</blockquote>
</blockquote>
<br>
And <a
href="http://www.matheon.de/about_us/people/list_members.asp?action=detail&id=812"
class="grextext">Prof. Dr. Christof Schütte</a>-- a mathematician,
to be sure, but as applied to biological systems-- goes so far as to
<a href="http://www.matheon.de/research/show_project.asp?id=134">claim</a>
that<br>
<br>
<blockquote>
<blockquote>"Knowledge of the net energy production of anaerobic
fermenters is important for reliable modelling of the efficiency
of anaerobic digestion processes. Furthermore energy balancing
is crucial, because present biogas plants still suffer from
severe instabilities caused by self-heating and full-scale
plants typically have to be cooled down."<br>
</blockquote>
</blockquote>
<br>
<br>
These studies and statements, however, have a context, which is the
Austrian/German biogas industry, where digestion is a high-tech
(some might say gold-plated) affair in large part because of the
previous regime of above-market price guarantees for electricity
from biogas. That is to say, the digesters being analyzed and
discussed above are very likely extremely well insulated.<br>
<br>
But as far as I know for the kinds of digesters with which you are
working-- underground masonry, if I'm not mistaken-- I believe you
can assume that the contents of the digester will be at ambient
temperature six feet deep.<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>
</code></div>
<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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