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Marcus,<br>
</font><br>
On 10/28/2010 3:03 PM, Markus Schlattmann wrote:
<blockquote cite="mid:4CC9F342.4010906@schlattmann.de" type="cite">I
don't know if I have understood this 100% correctly, but if you
have inlet air you will get a potentially explosive atmosphere
inside the digester. </blockquote>
<br>
If the digester needs to be refilled then it must be opened. And if
it has methane in it, there is no question that at some point, when
air is introduced, there will be a potentially explosive mix. That
will be the case whether one opens the door on the digester without
previous evacuation, whether one introduces air rapidly or slowly,
whether the digester is flexible and allows [only most] of the
biogas to be "squeezed out" before opening, etc. Whatever process is
used, at some point between operating the digester and opening it,
air will have to mix with biogas and a potentially explosive mix
will result.<br>
<br>
But an actual explosion will require not merely an explosive mix,
but as well a spark of some sort. Methane is not self-igniting. As
such, if air can be introduced into the digester in a way that
insures that no spark or flame is introduced, and as well that if
any of the biogas/air mix that is being evacuated does ignite, it
cannot in turn ignite the biogas/air mix in the digester, then there
will not nor cannot be an explosion in the digester. A water trap is
one of the simplest ways of accomplishing the task, since flames
cannot travel down a column of bubbles.<br>
<br>
That was the principle to which I was referring in suggesting to
Yvonne that two flame traps be used, one to force air in, and one to
allow the biogas/air mix out. As long as the mix being forced out is
evacuated into moving air, outside, then in the presence of a spark
it may ignite, but it will not explode because it is not contained.
Likewise, if it ignites, the flame front will not be able to travel
down the column of bubbles into the digester. Sparks and flames
would likewise be excluded from the incoming air by the same means,
since incoming air would likewise be introduced to the digester via
a column of bubbles.<br>
<br>
This is a very simple, and if well designed, very reliable means of
insuring that enough methane can be flushed out of the digester so
that any traces which remain cannot ignite or explode, and at that
point the digester can be safely opened. Using simple measurements--
properly made, i.e. at the pressures experienced when using both
flame traps-- one can find out how much air is forced into the
digester during a given period, and one can then choose a duration
for the evacuation process which will insure a non-flammable mix in
the digester. <br>
<br>
My apologies if this was not clear from my short explanation.<br>
<br>
<br>
<br>
d.<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>
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