<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN">
<html>
<head>
<meta content="text/html; charset=ISO-8859-1"
http-equiv="Content-Type">
</head>
<body bgcolor="#ffffff" text="#000000">
<font face="Georgia"><br>
Dear Dr. Fulford and others,<br>
</font><br>
On 11/20/2010 9:22 AM, David Fulford wrote:
<blockquote cite="mid:4CE803D7.7000306@kingdombio.com" type="cite">
<meta content="text/html; charset=ISO-8859-1"
http-equiv="Content-Type">
<title></title>
David and listers, Hello,<br>
<br>
The microbes do not seem to be affected significantly by pressure,
at least up to the 1 atmosphere found in small dome plants as used
in India, Nepal and China. In the 1970s there were reports of some
earlier work in India that suggested less gas was generated at
higher pressures; but gas analysis demonstrated that the reduction
in volume at higher pressures was mainly due to carbon dioxide
dissolving in the slurry.... So, [perhaps] the answer is that the
relationship between pressure and biogas production seems rather
complicated.<br>
</blockquote>
<br>
It seems to me, then (all things considered) that pressure in the
great majority of situations is not worth any attention. Three
things lead me to this conclusion. First, most applications and
appliances that use biogas are satisfied with pressures that are
measured in inches of water, not feet, and second very few digesters
are likely to be built that exceed 30 feet in depth, at which point
the pressure is doubled. (The majority of those deep digesters--
which after all would have to be quite large and which would
therefore generally tend to be fairly sophisticated-- would almost
certainly be agitated, not plug-flow.) Finally, since long
experience, even if not multiple studies, confirm that the effect
even of a doubling of standard atmospheric pressure tends to be so
slight as to avoid notice, most of us will never need to consider it
as a factor.<br>
<br>
I would still love to find some studies that discuss the matter, but
for the time being the sole driver is now simple curiosity, and no
longer the potential for practical impact.<br>
<br>
<br>
d.<br>
<br>
<div class="moz-signature">-- <br>
<div style="" ;=""><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>
<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>
</div>
</div>
</div>
</body>
</html>