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<DIV><FONT face=Arial size=2><STRONG>Hi Peter and
Colleagues,</STRONG></FONT></DIV>
<DIV><STRONG><FONT face=Arial size=2></FONT></STRONG> </DIV>
<DIV><STRONG><FONT face=Arial size=2>I think we should chang the Subject line
for any further discussion.</FONT></STRONG></DIV>
<DIV><FONT face=Arial><FONT size=2></FONT><FONT size=2></FONT><BR><FONT
size=2><STRONG>I'm pleased you were able to qualify some of the details relating
to the pH questions, but more importantly the circumstances in which you
experienced the ash formations.</STRONG></FONT></DIV><FONT size=2></FONT></FONT>
<DIV><FONT face=Arial size=2></FONT> </DIV>
<DIV><FONT face=Arial size=2> > I don't claim to understand the
chemistry, only that observations don't <BR>> always match expectations. This
is why I would like to see others more <BR>> qualified than myself do the
char analysis and research.</FONT></DIV>
<DIV><FONT face=Arial size=2></FONT> </DIV>
<DIV><STRONG><FONT face=Arial size=2>A chemist will always argue that their
explanations are correct, because chemistry is just a bunch of equations I
guess(:-) As you say though, we are surrounded by people more qualified
than ourselves who understand more about what "we" choose to do to make it, one
would hope!</FONT></STRONG></DIV>
<DIV><FONT face=Arial size=2></FONT> </DIV>
<DIV><FONT face=Arial size=2>> In some cases however with a little more
information and the benefit of <BR>> hindsight this can be partly explained.
In regard assumptions, firstly <BR>> you need to be careful that all the fine
ash is in fact being caught <BR>> with and included in the main char and not
elsewhere in the system such <BR>> as the cyclones.</FONT></DIV>
<DIV><FONT face=Arial size=2></FONT> </DIV>
<DIV><FONT face=Arial size=2><STRONG>This would be virtually impossible, as ash
is not going to drop out of a turbulent moving gas flow. When present, only the
larger or heavier ash will stay in the char, but depends a lot, on how you
separate the char in the bottom end from the gas flow. At a guess, anything
under about 15-20 micron will entrain in the gas, if the gas exits with the
char, rather than it be mechanically dropped through the grate into a dead
space. </STRONG></FONT></DIV>
<DIV><FONT face=Arial size=2></FONT> </DIV>
<DIV><FONT face=Arial size=2> >During our recent pilot trial we were
presented with <BR>> firstly fresh eucalyptus wood chips (35-40% mc) then a
load of fine <BR>> planer shavings from a nearby dry mill (8%mc). Using a
initial mix of <BR>> (by volume) of 1:1 of this fine material with the wood
chips we <BR>> collected 12 litres of carbon/mineral dust in <4 hours,
noticing this <BR>> only when the fan started to growl and surge because the
cyclones were <BR>> allowing this material to bypass as their collectors were
full, and it <BR>> began to build up in other parts of the system before
letting go in <BR>> lumps, giving the fan indigestion.</FONT></DIV>
<DIV><FONT face=Arial size=2></FONT> </DIV>
<DIV><FONT face=Arial size=2><STRONG>When you explain it like this, it does
change the issue of ash formation and pH, because blended fuels will
cause a change in the way the packed beds behave, and the way the ash content
can increase.</STRONG> <STRONG>Cyclones at best,
work proportionally down to 5 micron, becoming more efficient as
their size is reduced, hence single cyclones cannot remove fines as well as
multi-cyclone systems. The fan is well proven to create the right phenomena,
where the turbulence and changing pressures agglomerate these fines.
</STRONG></FONT></DIV>
<DIV><STRONG><FONT face=Arial size=2></FONT></STRONG> </DIV>
<DIV><FONT face=Arial size=2>> Something worth looking at when we start up
again in the new year is to <BR>> see if the PH of the cyclone dust is
similar to the char bin.</FONT></DIV>
<DIV><FONT face=Arial size=2></FONT> </DIV>
<DIV><FONT face=Arial size=2><STRONG>One might assume that as the cyclone
collects a visibly greater amount of ash, it's pH may be high. I haven't seen
any pH readings higher than 8.6, but that figure relates to ash removed in a
condensing/cooling phase.</STRONG></DIV>
<DIV> <BR>> The main problem though with the original assumption is that
the ash <BR>> does not concentrate inside the remaining charcoal fraction
beyond the <BR>> effective % change from mass reduction through initial loss
of moisture <BR>> and lighter volatiles. The woody particles first lose their
volatile <BR>> fraction and then ablate as the outer carbon surface is
oxidised, <BR>> becoming smaller to the point of passing through the grate,
the <BR>> inorganic ash freed as the outer layers of the particle oxidise
forms a <BR>> separate very fine particulate with different characteristics
and <BR>> mineral concentration to adjoining char particles and is easily
sieved <BR>> out of the charcoal fraction.</DIV>
<DIV> </DIV>
<DIV><STRONG>While this description fits most bed activity, the mixed fuel
changes the game and the amount of ash formed by combustion. The shavings being
the finer char, it's large surface area reacts faster than the larger chip. It's
rapid consumption opens up the interstitial space between the larger chip, and
this allows more free oxygen to become available for combustion. The swept
surface of the larger chip changes and you can watch the ash form on it's
surface as the interstitial space increases in size. This can affect the gas
analysis, pressure drops across the beds, and temperatures of the exiting gas.
You need all these parameters recorded as it happens to really see what is
actually happening.</STRONG></DIV>
<DIV> <BR>> It is the larger (>3mm) screened material we mainly use
as biochar, so <BR>> not all the inorganic ash is contained or therefore
being measured as <BR>> part of this material. So from feed stocks with the
same original ash <BR>> content char with seemingly different characteristics
can be collected, <BR>> quite independent of process yield.</DIV>
<DIV> </DIV>
<DIV><STRONG>The selective separation from a relatively small char production
doesn't appear to have any economic sense, unless "there is gold in that there
char". What it does show however, is that the remaining larger char is the
slowest to pass through the bed, thanks to the exothermic heat provided from the
shaving char. </STRONG><BR> <BR>> In contrast as Doug rightly pointed
out Pyrolysis chars tend to retain <BR>> all the original ash content,
however as not all of inorganic ash is <BR>> kept within the gasifier char
the result as you can see from above is <BR>> counter intuitive to the
original assumption (as we are not looking at a <BR>> closed system as the
assumption requires)...and certainly offsets the <BR>> yield
difference.</DIV>
<DIV> </DIV>
<DIV><STRONG>As we cannot always see how these differing circumstances within
any process originate, some of these discussions are difficult to articulate. It
always helps to stimulate discussion when you provide more specific detail as in
this reply.</STRONG><BR> <BR>> Doug has relayed as reported to him by
others the suggestion that some <BR>> of this fine mineral ash generated
embeds within the pores of the <BR>> charcoal. I have not seen this with our
system, even looking at the <BR>> chars under a powerful lab microscope.
</DIV>
<DIV> </DIV>
<DIV><STRONG>This was a simplistic description of how ash will entrain and
coat the char porosity, rather than fill it as it transports through the system,
so long as ash is present, the char will have a positive pH factor.
</STRONG></DIV>
<DIV> </DIV>
<DIV> </DIV>
<DIV>>Though when operating in fixed <BR>> bed mode they can get a light
external coating. This does not <BR>> necessarily mean this is always the
case but I can't readily imagine a <BR>> mechanism for this to occur to any
great degree as the char within the <BR>> pyrolysis/gasification/reduction
zones would be experiencing varying <BR>> degrees of outgassing, so these
pores as they occur would be under <BR>> positive internal pressure resisting
plugging for most of their <BR>> gasification experience.</DIV>
<DIV> </DIV>
<DIV><STRONG>As you describe it here, it can be understood why the ash doesn't
enter the porosity of the char.</STRONG></DIV>
<DIV><STRONG></STRONG> </DIV>
<DIV><STRONG><Snip></STRONG></DIV>
<DIV> <BR>> Perhaps even as our steel research experience <BR>>
indicated, that blended chars may give optimum results.</DIV>
<DIV> </DIV>
<DIV><STRONG>Not sure why your steel research crosses over to soil applications,
but interested to hear more if you have the time.</STRONG></DIV>
<DIV> </DIV>
<DIV> >Which brings me <BR>> back to my original concern with the
research bias against gasifier <BR>> chars we have experienced.</DIV>
<DIV> </DIV>
<DIV><STRONG>Simple. You need a lot of gasifiers to create commercially viable
char quantities, and Australian politics isn't interested in gasifiers as a
working technology.</STRONG></DIV>
<DIV><STRONG>At best, you might find a guy looking for a paper to write to get
funds to do more research so that he can have an academic
career(:-)</STRONG></DIV>
<DIV> <BR>> When this is fully overcome, then we might all move another
step forward.</DIV>
<DIV> </DIV>
<DIV><STRONG>Sounds like wishful thinking for the majority of places that should
be actively supporting development programmes, but yes, we plod on
regardless, but I am not sure I will see the day within my lifetime.
</STRONG></DIV>
<DIV><STRONG></STRONG> </DIV>
<DIV><STRONG>Happy New Year folks.</STRONG></DIV>
<DIV><STRONG></STRONG> </DIV>
<DIV><STRONG>Doug Williams</STRONG></DIV>
<DIV><STRONG>Fluidyne----</STRONG></DIV>
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