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<div class="moz-cite-prefix">G'day Takamoto,<br>
<br>
You have to look at the tradeoff between cost of a larger digester
at ambient temperature (where you get all the biogas to use!) and
the cost (capital, operational and maintenance!) of installing
insulation (loved by birds and mice?) and a heating system on a
smaller digester. Of course you also have to consider the energy
cost of heating the digester - if you want more gas do you get it
by using some of the gas to heat the digester?<br>
<br>
Based on a steady state model (see <a class="moz-txt-link-freetext" href="http://biowattsonline.com/">http://biowattsonline.com/</a> for
a web version) and a 4 cubic metre digester you should be able to
go from 3 beef cattle to 11 beef cattle, so would get about 4
times the gas. My simple Excel model shows the heater about halves
the cost of biogas but nearly doubles the digester capital cost
and uses about 1/12 of the increased gas production (about half of
the ambient gas production - most of the gas is used to heat the
effluent if insulation is 50 mm thick) - I used 20 ambient and 35
digester temperature.<br>
<br>
Happy Digesting,<br>
HOOROO<br>
<pre class="moz-signature" cols="72">Mr Paul Harris BEng (Ag) (Melbourne)
Visitor at The University of Adelaide</pre>
On 3/10/2012 11:05 PM, Takamoto wrote:<br>
</div>
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cite="mid:131B5316-631B-4B86-994C-AE6D3CE6309C@takamotobiogas.com"
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Dear Biogas List,
<div><br>
</div>
<div>I have been thinking about the biggest hurdles to producing
more gas from small scale biogas systems (4 cubic meters to 12
cubic meters) and by far the biggest barrier is heat. From the
literature I have read it seems that if you increase the
temperature of the digester from about 18C (the temperature of
our digesters) to 37C you can nearly double the gas yield per
unit of input and nearly halve the retention time which would
reduce the capital costs.</div>
<div><br>
</div>
<div>Does anyone know of tests that have been done or ideas that
have been put forth to heat small scale digesters in a
controlled manner? (For the moment assume that such a process
could be managed on many disparate, small scale biogas systems.
That is the next challenge.) The processes I was thinking of
were 1.) to heat the biogas system with biogas from the system
itself or 2.) to bubble a very slight amount of air through the
digester so that there was a slight anaerobic reaction that
would produce heat and warm the digester. Or 3.) you could use
sunlight to warm the digester if you can warm the digester and
not the gas holder as warming the gas holder will only cause the
gas to expand and no heat will be transferred to the slurry.</div>
<div><br>
</div>
<div>These methods are probably most applicable to fixed dome and
floating drum.</div>
<div><br>
</div>
<div>Have either of these ideas been tried? Are there other ideas
out there?</div>
<div><br>
</div>
<div>Cheers,<br>
<div apple-content-edited="true">
<span class="Apple-style-span" style="border-collapse:
separate; color: rgb(0, 0, 0); font-family: Helvetica;
font-style: normal; font-variant: normal; font-weight:
normal; letter-spacing: normal; line-height: normal;
orphans: 2; text-align: -webkit-auto; text-indent: 0px;
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-webkit-border-vertical-spacing: 0px;
-webkit-text-decorations-in-effect: none;
-webkit-text-size-adjust: auto; -webkit-text-stroke-width:
0px; font-size: medium; ">Kyle<br>
<br>
<br>
</span>
</div>
<br>
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<br>
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<pre wrap="">_______________________________________________
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for more information about digestion, see
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</pre>
</blockquote>
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