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<p><font face="Liberation Sans">Hi James and Bjorn,</font></p>
<p><font face="Liberation Sans">Bjorn's comments to you reminded me
of more issues that we experienced with candles, which in hind
sight looked simple to resolve at the time (just throw in a few
more $$$ at the black hole). Pre-coating involved obtaining
talcum dust, and using that to reduce the pore size of the
ceramic pore structure. We also had a preference for removing
all larger dust particles using cyclones, so only the finest
dust reached the candle surfaces. This in turn created very
rapid pressure drop across the ceramic wall, requiring more
frequent pulsing. In the end, we let all the solids in gas
suspension go to the candles so that a more mixed filter cake
formed on the surface. Yes I said filter cake, because the
candle surface only provides a platform for the impacting mixed
particles to collect, because if they enter the ceramic pores,
then they will block rapidly. From memory, we worked with our
flow rate at 7-9" inches W.G. with the pulse initiating at
around 14" W.G. If you are tempted to work at hight pressure
differentials, the ceramic wall can collapse, because the gas
temperatures through the ceramic pores in localized spots is
squeezed releasing more heat, weakening the ceramic fibres which
collapse.. If you plan to operate at higher temperatures to
start with, then watch the rates of pulsing to keep the pressure
drop low.</font></p>
<p><font face="Liberation Sans">By accident during maintenance,
grinder sparks ignited the soot cake on the candles and residual
dust in the exit soot auger. Rather than try to put it out
because it was a very low level smolder, we closed it up and let
it burn out overnight. It left only white ash, but it turned out
positive as a way to clean the candles after a bad run, but care
must be taken not to allow moving air entry during this
smoldering combustion.</font></p>
<p><font face="Liberation Sans">We tried high temperature filter
bags and quickly found they block in a blink, and are destroyed
if a spark gets in. There is also an issue of the back pulse not
working with the system supplied that worked perfectly for dry
dust. The size of the filter boxes also required them to be
insulated, but condensation issues could not be over come
compounding their operational and maintenance problems.<br>
</font></p>
<p><font face="Liberation Sans">One last comment to remember, is
that carbon dust caking in elevated gasification temperatures,
will bond together, making it very different from those free of
carbon free dust. This of course brings conflicting views from
those presented by the candle manufactures. We found that
suggestions from the manufacturer (a really dedicated team)
related to just the filtration principles on which the
technology was founded, having no personal expertise in the
black arts of gasification. <br>
</font></p>
<p><font face="Liberation Sans">Metal screen bio-oil filtration
works at a cost, but you then have to dispose of the toxic waste
oil. It was promoted as a fuel for combustion in boilers etc,
but this I think was as attempt to clean up the gasification
image to attract funding. I doubt if appropriate studies were
made on the resulting combustion emissions(:-)</font></p>
<p><font face="Liberation Sans">So much enthusiasm and still we
struggle with filtration issues.<br>
</font></p>
<p><font face="Liberation Sans">Must finish to start my day!</font></p>
<p><font face="Liberation Sans">Doug Williams,</font></p>
<p><font face="Liberation Sans">Fluidyne.<br>
</font></p>
<p><br>
</p>
<br>
<div class="moz-cite-prefix">On 01/11/17 00:54, Björn Kuntze wrote:<br>
</div>
<blockquote type="cite"
cite="mid:008d01d3523f$00cd2ce0$026786a0$@mastergas.de">
<pre wrap="">Dear James,
I can´t say anything to the flue gas fitering system, but I may be able to
contribute to the filtering of product gas from gasification processes:
In Germany nowadays most projects use bag filters with working temperatures
of 120 - 160°C. Others use hot gas filtration at around 400°C using
stainless steel mesh filter materials. Wet gas cleaning with oil scrubbers
or electrostatic filters is used in older projects but not common at all for
new projects.
For fifteen years there were (and there still are) people advertising their
high temperature filter systems (candles like Herding, or BWF and metal
mesh). They claim that these filters can handle tar load. But, according to
my experience, with tar in the gas you will never get happy at all. It is
not even an issue of the filter concept. Due to harmful substances in the
tar you cannot even organize maintenance of such system when following
health and safety regulations. So such filter won´t help you either.
Furthermore, as already stated, once condensing conditions appear, the whole
thing is gone.
The candles (no matter who is the manufacturer) typically do have a problem
when the dust in the gas is very fine (soot...). In the past the
"overdesigned" filters typically turned out to be "underdesigned" in the
real project with the filter manufacturer saying: "we did not expect that
there is so much fine dust...". So they start with precoating. At the end
some projects had to order a second filter of same size to run in parallel.
I know a few projects where this was the recommended solution.
So, if you go for that, increase the filter surface right from the beginning
no matter what the manufacturer tells you.
You might also consider the German company Calida Cleantech GmbH
(<a class="moz-txt-link-freetext" href="http://www.calida-cleantech.de/en/">http://www.calida-cleantech.de/en/</a>) (formerly LignoGen GmbH). They also
provide hot gas candle filter systems. I know one of their projects in
Germany where they filter product gas quite well. I know that they are
interested in projects filtering pyrolysis gas. You might contact them.
Mit freundlichen Grüßen / with best regards
Björn Kuntze
MasterGas UG (haftungsbeschränkt)
Bloherfelder Anger 7
26129 Oldenburg
Germany
Geschäftsführer: Björn Kuntze
Mobil: +49 (0) 177 345 1557
Email: <a class="moz-txt-link-abbreviated" href="mailto:kuntze@mastergas.de">kuntze@mastergas.de</a>
Web: <a class="moz-txt-link-abbreviated" href="http://www.mastergas.de">www.mastergas.de</a>
Handelsregister: HRB 211272 – Amtsgericht Oldenburg
USt-ID-Nr: DE307863882
St.-Nr: 64/213/02649
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-----Ursprüngliche Nachricht-----
Von: Gasification [<a class="moz-txt-link-freetext" href="mailto:gasification-bounces@lists.bioenergylists.org">mailto:gasification-bounces@lists.bioenergylists.org</a>] Im
Auftrag von James Joyce
Gesendet: Dienstag, 31. Oktober 2017 00:48
An: <a class="moz-txt-link-abbreviated" href="mailto:gasification@lists.bioenergylists.org">gasification@lists.bioenergylists.org</a>
Betreff: [Gasification] Candle filter experiences
We are just about to order candles for a flue gas filtration application at
350 deg C. We have also been asked to design a 400 deg C candle filter
system for pyrolysis gas, for installation ahead of a condenser.
This is one example (not necessarily the supplier we will use)
<a class="moz-txt-link-freetext" href="http://www.herding.de/files/hGlobal/Downloads/Technical_product_descriptions">http://www.herding.de/files/hGlobal/Downloads/Technical_product_descriptions</a>
/ALPHA/UK/Herding_ALPHA_Biomass_Filterunit_uk.pdf
I have read some of the case studies for larger gasifiers. I am interested
to know what experiences, if any, have been had with candle filters at the
smaller scale (say 2-20 tonnes per day of biomass gasified). Reliability is
my main interest, number of hours between replacement ... and performance as
far as downstream equipment such as condensers and engines are concerned.
Regards,
James
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</pre>
</blockquote>
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