[Gasification] [biochar] ICM gasifier project comes to a close

Sat Dec 29 16:03:05 CST 2012

I whish you a very long lifetime, Doug,

but next a "beautiful" 2013

biomass, energy and char to us all

Rolf

Am 29.12.2012 20:06, schrieb doug.williams:
> *Hi Peter and Colleagues,*
> **
> *I think we should chang the Subject line for any further discussion.*
>
> *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.*
> > I don't claim to understand the chemistry, only that observations don't
> > always match expectations. This is why I would like to see others more
> > qualified than myself do the char analysis and research.
> *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!*
> > In some cases however with a little more information and the benefit of
> > hindsight this can be partly explained. In regard assumptions, firstly
> > you need to be careful that all the fine ash is in fact being caught
> > with and included in the main char and not elsewhere in the system such
> > as the cyclones.
> *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. *
> >During our recent pilot trial we were presented with
> > firstly fresh eucalyptus wood chips (35-40% mc) then a load of fine
> > planer shavings from a nearby dry mill (8%mc). Using a initial mix of
> > (by volume) of 1:1 of this fine material with the wood chips we
> > collected 12 litres of carbon/mineral dust in <4 hours, noticing this
> > only when the fan started to growl and surge because the cyclones were
> > allowing this material to bypass as their collectors were full, and it
> > began to build up in other parts of the system before letting go in
> > lumps, giving the fan indigestion.
> *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.* 
> *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. *
> **
> > Something worth looking at when we start up again in the new year is to
> > see if the PH of the cyclone dust is similar to the char bin.
> *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.*
>
> > The main problem though with the original assumption is that the ash
> > does not concentrate inside the remaining charcoal fraction beyond the
> > effective % change from mass reduction through initial loss of moisture
> > and lighter volatiles. The woody particles first lose their volatile
> > fraction and then ablate as the outer carbon surface is oxidised,
> > becoming smaller to the point of passing through the grate, the
> > inorganic ash freed as the outer layers of the particle oxidise forms a
> > separate very fine particulate with different characteristics and
> > mineral concentration to adjoining char particles and is easily sieved
> > out of the charcoal fraction.
> *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.*
>
> > It is the larger (>3mm) screened material we mainly use as biochar, so
> > not all the inorganic ash is contained or therefore being measured as
> > part of this material. So from feed stocks with the same original ash
> > content char with seemingly different characteristics can be collected,
> > quite independent of process yield.
> *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. *
>
> > In contrast as Doug rightly pointed out Pyrolysis chars tend to retain
> > all the original ash content, however as not all of inorganic ash is
> > kept within the gasifier char the result as you can see from above is
> > counter intuitive to the original assumption (as we are not looking 
> at a
> > closed system as the assumption requires)...and certainly offsets the
> > yield difference.
> *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.*
>
> > Doug has relayed as reported to him by others the suggestion that some
> > of this fine mineral ash generated embeds within the pores of the
> > charcoal. I have not seen this with our system, even looking at the
> > chars under a powerful lab microscope.
> *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. *
> >Though when operating in fixed
> > bed mode they can get a light external coating. This does not
> > necessarily mean this is always the case but I can't readily imagine a
> > mechanism for this to occur to any great degree as the char within the
> > pyrolysis/gasification/reduction zones would be experiencing varying
> > degrees of outgassing, so these pores as they occur would be under
> > positive internal pressure resisting plugging for most of their
> > gasification experience.
> *As you describe it here, it can be understood why the ash doesn't 
> enter the porosity of the char.*
> **
> *<Snip>*
>
> > Perhaps even as our steel research experience
> > indicated, that blended chars may give optimum results.
> *Not sure why your steel research crosses over to soil applications, 
> but interested to hear more if you have the time.*
> >Which brings me
> > back to my original concern with the research bias against gasifier
> > chars we have experienced.
> *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.*
> *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(:-)*
>
> > When this is fully overcome, then we might all move another step 
> forward.
> *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. *
> **
> *Happy New Year folks.*
> **
> *Doug Williams*
> *Fluidyne----*
>
>
>
> _______________________________________________
> Gasification mailing list
>
> to Send a Message to the list, use the email address
> Gasification at bioenergylists.org
>
> to UNSUBSCRIBE or Change your List Settings use the web page
> http://lists.bioenergylists.org/mailman/listinfo/gasification_lists.bioenergylists.org
>
> for more Gasifiers,  News and Information see our web site:
> http://gasifiers.bioenergylists.org/

-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://lists.bioenergylists.org/pipermail/gasification_lists.bioenergylists.org/attachments/20121229/267bd17e/attachment.html>