[Stoves] Thick wood and MC in micro-gasifiers was Re: Smoke-free biomass pellet fueled stove

Josh Kearns yeah.yeah.right.on at gmail.com
Mon Nov 12 13:55:41 CST 2012


Perhaps along similar lines (???), I have observed that water-quenched TLUD
chars exhibit an increase in sorption capacity relative to dry-quenched
chars produced under otherwise similar conditions.

The question came up regarding shutdown procedure for a 55-gal TLUD - some
users may find it more convenient/safer to douse the thing with water to
rapidly cool it rather than reconfiguring the unit (while hot) to seal the
top and bottom.

Steam is sometimes used as an activating agent in AC manufacture, so I
hypothesized that a wet quench could result in a "pseudo-activation" since
water added directly to hot char makes lots of steam (be careful if you try
this!).

I did some preliminary tests with pine pellets in a 1-gal Toucan TLUD (ND)
and quenched with lab water spiked with background NOM to simulate a
situation where non-treated water would be used for this purpose. The
result was about a 50% increase in herbicide uptake (batch mode) using the
wet-quenched char.

Have others witnessed any similar effects? Any theoretical or empirical
support for a "pseudo-steam-activation" hypothesis? Alternative hypotheses
or mechanisms?

Josh



On Mon, Nov 12, 2012 at 9:40 AM, Tom Reed <tombreed2010 at gmail.com> wrote:

> Dear Crispin, Paul and Aul:
>
> The water-gas reaction
>
>             C + H2O ===> CO + H2
> DH.    420.                 280.    280.
> DH (delta H, but my I pad has no delta symbol), the heat produced by the
> reaction  is -(560-420)
> =. -140 kJ/(12 g of C).  In other words you would have to add 140 g of
> heat (plus enough heat to reach reaction temperature) to make the reaction
> go.
>
> <><><>
>
> My memory is that I dried wood chips in a 230 F oven for several hours,
> then prepared 7 bags of equal weight chips (100 g ?) and added enough water
> to each bag to bring total weight to 5,10,15, 20, 25, 30 % moisture, and
> then let the bags sit for a few days to equilibrate the water and chips.  I
> then burned each sample until only charcoal remained (flame color changed
> fro yellow to blue) in our WoodGas battery blown stove.
>
> I was delighted to find 30,25,20,15,10,5 and 1% charcoal remaining.  From
> this it seemed obvious that each lowest layer of charcoal, in order to
> ignite the subsequent layer of chips below it, had to be partially burned
> in order to remove the water from the next layer of wood chips in order to
> ignite it.  Dry wood burns; wet wood won't.
>
> Since that experiment in my Denver lab, I have moved twice and would have
> difficulty finding my original notebook.  But the experiments made so much
> sense, that I am sure the above description is in essence correct.
>
> Onward...
>
> Tom Reed
>
>
> Thomas B Reed
> 280 Hardwick Rd
> Barre, MA 01005
>
> 508 353 7841
>
> On Nov 12, 2012, at 9:10 AM, Paul Anderson <psanders at ilstu.edu> wrote:
>
> > Dear Andrew,        with copies to Tom and Morgan
> >
> > I am sending a copy of this reply to Tom Reed <tombreed2010 at gmail.com>
> .  This is the only email address he now uses, in case anyone else wants to
> note it down.
> >
> > Tom did those experiments with known moisture a few years ago. Perhaps
> he still has the notes.   I think it was not prepared as a formal report.
>  I believe he said it was nearly linear, with about 0% char when MC reached
> 30%.
> >
> > 150mm diameter is beyond anything I have ever tried.   I marvel when the
> 70 mm branches pyrolyzed all the way through in the experiments done by my
> Ugandan associates.   There is a photo of the loaded fuel in the Quad TLUD
> in the report of test results by CREEC on the Quad stove  (see the report
> at    www.drtlud.com  ).   Thickness (diameter) increases the length of
> time of the operation of the stove (quite logically).   Jackson, the CREEC
> technician, did a great job with having 3 different sizes of the same wood
> in the three different runs.     But we do not have funding for running
> repeated tests to get sufficient replications.
> >
> > The issues include being too thick so that the pyrolysis gases are too
> slow / too little to sustain a good flame at the upper combustion part of
> the TLUD.
> >
> > I hope that CSU can put that into their computer model.   And I hope
> that CSU will write something to the Stove Listserv or tell us where they
> are writing something.   So far they hold the biggest pot of funding for
> research about micro-gasifiers, except for the big companies like Philips
> (and what BP did in the past).
> >
> > Paul
> >
> > Paul S. Anderson, PhD  aka "Dr TLUD"
> > Email:  psanders at ilstu.edu   Skype: paultlud  Phone: +1-309-452-7072
> > Website:  www.drtlud.com
> >
> > On 11/12/2012 5:53 AM, ajheggie at gmail.com wrote:
> >> [Default] On Sun, 11 Nov 2012 20:01:02 -0600,Paul Anderson
> >> <psanders at ilstu.edu> wrote:
> >>
> >>> Crispin and all,
> >>>
> >>> I think that the char being created in a TLUD  is not hot enough to
> >>> cause the water gas reaction.
> >> I take this view too, and even if it were hot enough the endothermy of
> >> the reaction would limit it.
> >>
> >> If this phenomena is important to us, e.g we want to maximise char
> >> retention, then it's worth knowing the optimum fuel moisture content.
> >> Also I had found there was a limit to the size of particle that could
> >> be thoroughly charred. I found I could not successfully scale up a
> >> tlud device to chare 150mm cross section longs which I hade carefully
> >> dried. What I never got round to trying, as I lost the farm workshop
> >> due to redevelopment, was seeing if such logs would char if embedded
> >> in smaller material.
> >>
> >> I no longer have a useful tlud device that will consistently produce
> >> measurable results but it may be worth doing some runs with oven dried
> >> wood chips which have been then re wetted with the correct amount of
> >> water to give samples of 0-25%mc wwb and weigh the char produced when
> >> lit with the same amount of liquid fuel. I would especially like to
> >> see the results when fed with primary air maintained at a constant
> >> flow.
> >>
> >> AJH
> >>
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-- 
Josh Kearns
PhD Candidate
Environmental Engineering
Engineering for Developing Communities
University of Colorado-Boulder

Director of Science
Aqueous Solutions
www.aqsolutions.org

Mobile: 720 989 3959
Skype: joshkearns
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