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<DIV><FONT face=Arial size=2><STRONG>Hi Pete,</STRONG></FONT></DIV>
<DIV><FONT face=Arial size=2><STRONG></STRONG></FONT> </DIV>
<DIV><FONT face=Arial size=2><STRONG>You need a reply to this, and your post
about cheap gas analyzers.</DIV>
<DIV><BR></STRONG>I probably have no business asking entering into this
discussion since I am neither a chemist nor a physicist, but---</DIV>
<DIV> </DIV>
<DIV><STRONG>This is an open forum, not an exclusive "club" for only academics,
who need us as much as we need them (:-)</STRONG></DIV><STRONG></STRONG>
<DIV><BR>Over the last several months I have been trying to learn the “truth”
about the dissociation of the water in my wood chips into Hydrogen and
oxygen. I had previously read someplace that it was a pretty simple
process. You just heat water to somewhere above 350 degrees C and there
you go.</DIV>
<DIV> </DIV>
<DIV><STRONG>Gasification does hide a complex set of temperature related
phenomena, but because we have to have packed incandescing carbon beds to
make it all work, </STRONG><STRONG>a minimum temperature to create the
exothermic heat requirement to create permanent gases begins at "about" 850C.
Water literally gulps up this heat, so if you don't have plenty of
high temperature heat generation in the oxidation zone, a proportion of
the tar and water laden pyrolysis gases pass through
uncracked.</STRONG></DIV><STRONG></STRONG>
<DIV><BR> Well, lately I have become quite disconcerted as I have read
that there are so many other factors that can be involved, that it’s anybody’s
guess as to whether it will happen at all.</DIV>
<DIV> </DIV>
<DIV><STRONG>When you understand the order of created thermal phenomena within
packed carbon beds, you begin to identify if any system you build or buy,
will be best suited to your end need.</STRONG> </DIV>
<DIV> <BR>Some of the variables:</DIV>
<DIV><BR>Pressure</DIV>
<DIV> </DIV>
<DIV><STRONG>Only if you are talking about Syngas, not producer gas made with
air.</STRONG></DIV><STRONG>
<DIV><BR></STRONG>Temperature (obviously)</DIV>
<DIV> </DIV>
<DIV><STRONG>Yes.</STRONG></DIV>
<DIV><STRONG><BR></STRONG>Residence time</DIV>
<DIV> </DIV>
<DIV><STRONG>Only means deeper beds after the very hot oxidation zone, which can
be mechanically dropped to shed char, but, possibly at cost to the CO
%.</STRONG></DIV>
<DIV> </DIV>
<DIV>Presence or absence of carbon and form of that carbon. And,
apparently, the availability of carbon from other molecules.</DIV>
<DIV> </DIV>
<DIV><STRONG>All carbon like coal, coke, or charcoal from any biomass will
become incandescent if you pass air through it, but you get mainly CO as the
combustible gas, and it also brings in the nitrogen dilution factor. Early
updraft gasifiers had a boiling water bath under the grate, so wet steam both
cooled the grate bars, and turned to H2 as it passed through the incandescent
oxidation zone, then had a long contact/dwell time passing through the upper
bed.</STRONG></DIV>
<DIV><BR>And apparently, the list goes on and on.<BR> <BR>So what is an
ordinary human with a stratified downdraft gasifier to do to reliably pry
enough hydrogen out of the process to make it worth doing?</DIV>
<DIV> </DIV>
<DIV><STRONG>DIY gasification is never less than a steep learning
curve, which unfortunately can leave you disappointed with the results.
That you target or identify H2 as your desired gas, should have in the first
instance, told you that your gasifier isn't made to maximize this specific
gas. You will get some, but probably, <12% </STRONG><STRONG>at a
guess.</STRONG></DIV>
<DIV><STRONG></STRONG> </DIV>
<DIV><STRONG>Your second posting regarding low cost gas sensors is likely to
also create some grief if all you do is hook them up and expect them to work as
specified.</STRONG></DIV>
<DIV><STRONG>You may or not know that gas analyzers need to be calibrated
against a cylinder of prepared gases, and this is very expensive. Add to this
the special regulator for the cylinder, and you can start thinking a small truck
would be of better value(:-)</STRONG></DIV>
<DIV><STRONG></STRONG> </DIV>
<DIV><STRONG>Playing with dirty gases can also throw out calibrations, so be
really careful if you go down that track.</STRONG></DIV>
<DIV><STRONG></STRONG> </DIV>
<DIV><STRONG>Hope this may be of some assistance.</STRONG></DIV>
<DIV><STRONG>Doug Williams.</STRONG></DIV>
<DIV><STRONG></STRONG> </DIV>
<DIV><STRONG></STRONG> </DIV>
<DIV><STRONG></STRONG> </DIV>
<DIV><STRONG></STRONG> </DIV>
<DIV><BR> <BR></DIV></FONT></BODY></HTML>