[Gasification] Candle filter experiences

Tue Oct 31 14:06:25 CDT 2017

Hi Doug and James,

yeah, I missed to report at least one thing that always happens when it comes to hot gas candles: the increase of pressure drop over the time of operation. 

Doug mentioned this point. 

As far as I know, the pressure drop increases always over the time. So the jet-pulse cleaning (or reverse flow cleaning) will have to be done more often at much shorter intervals, Since you will have to use inert gas for this procedure, this will really become an issue after a short time. So very quickly somebody will come up with the idea of burning the dust away in an atmosphere with oxygen. This procedure will work may be two or three times. It will not be a lasting solution. It will not remove the mineral dust and it might even result in melting of the ceramic structure or slagging of the ash…

So, frequent replacements of the quite expensive filter elements should be considered right from the start anyway.

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:   kuntze at mastergas.de

Web:    www.mastergas.de

Handelsregister:  HRB 211272 – Amtsgericht Oldenburg

USt-ID-Nr:  DE307863882

St.-Nr:         64/213/02649

--------------------------------------------------------------------------------

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Von: Gasification [mailto:gasification-bounces at lists.bioenergylists.org] Im Auftrag von Doug
Gesendet: Dienstag, 31. Oktober 2017 19:23
An: gasification at lists.bioenergylists.org
Betreff: Re: [Gasification] Candle filter experiences

Hi James and Bjorn,

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.

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.

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.

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. 

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(:-)

So much enthusiasm and still we struggle with filtration issues.

Must finish to start my day!

Doug Williams,

Fluidyne.

On 01/11/17 00:54, Björn Kuntze wrote:

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
(http://www.calida-cleantech.de/en/) (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:   kuntze at mastergas.de <mailto:kuntze at mastergas.de> 
Web:    www.mastergas.de <http://www.mastergas.de> 

Handelsregister:  HRB 211272 – Amtsgericht Oldenburg
USt-ID-Nr:  DE307863882
St.-Nr:         64/213/02649

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nicht der bestimmungsgemäße Adressat sind, unterrichten Sie bitte den
Absender und vernichten Sie diese Mail. Anderen als dem bestimmungsgemäßen
Adressaten ist es untersagt, diese E-Mail zu lesen, zu speichern,
weiterzuleiten oder ihren Inhalt auf welche Weise auch immer zu verwenden.
Wir verwenden aktuelle Virenschutzprogramme. Für Schäden, die dem Empfänger
gleichwohl durch von uns zugesandte mit Viren befallene E-Mails entstehen,
schließen wir jede Haftung aus.

The information contained in this email is intended only for its addressee
and may contain confidential and/or privileged information. If the reader of
this email is not the intended recipient, you are hereby notified that
reading, saving, distribution or use of the content of this email in any way
is prohibited. If you have received this email in error, please notify the
sender and delete the email. We use updated antivirus protection software.
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transmitted via email.
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-----Ursprüngliche Nachricht-----
Von: Gasification [mailto:gasification-bounces at lists.bioenergylists.org] Im
Auftrag von James Joyce
Gesendet: Dienstag, 31. Oktober 2017 00:48
An: gasification at lists.bioenergylists.org <mailto:gasification at lists.bioenergylists.org> 
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)
http://www.herding.de/files/hGlobal/Downloads/Technical_product_descriptions
/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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