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I whish you a very long lifetime, Doug,<br>
<br>
but next a "beautiful" 2013<br>
<br>
biomass, energy and char to us all<br>
<br>
Rolf<br>
<br>
<br>
Am 29.12.2012 20:06, schrieb doug.williams:
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<div><font face="Arial" size="2"><strong>Hi Peter and Colleagues,</strong></font></div>
<div><strong></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"><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></font></div>
<div> </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> </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> </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> </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> </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> </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></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> </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></font></div>
<font face="Arial" size="2">
<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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