[Gasification] [Stoves] Grass Fireballs burn cleaner than wood

Thu Dec 28 12:43:22 CST 2006

Paul

You could grind the wood or pellet it to prevent the deep fracturing. I
agree the problem is probably the worst with large fuelwood pieces. The
problem is that in developing countries people don't like to downsize wood
fuel as its labour or equipment/energy intensive.

I reread the listserve archives on grass fireballs. They do seem a bit low
energy and high ash and definitely need another fuel source to help start
the fire. They are smokey to start but not smokey if put into a hot fire. If
you add wood to a hot fire you get smoke, if you add fireballs you get a
much quicker return to a cleaner burn. 

If we could minimize the retting period of grasses or avoid it altogether we
would improve fuel quality. Grass is generally within 7-10% of wood for
energy on a dry matter basis. Through retting we are losing some of the
cellulose and hemicellulose fractions and will increase the ash content and
decrease energy content.  

It would be interesting if we could find a simple way to break the grass up
into shorter sections(3-5cm) and then use a cheap starch source such as
cassava for example as a binder. I wonder if we developed a solar oven to
really dry the grass out if it wouldn't become brittle enough to break up
with little effort. Here in Montreal switchgrass in the spring is 12%
moisture and becomes quite brittle. 

I would think that sugar cane leaves might be readily balled up as they lack
the stem fraction and would be worth trying as a mildly retted field
residue.      

Roger 

-----Original Message-----
From: stoves-bounces at listserv.repp.org
[mailto:stoves-bounces at listserv.repp.org] On Behalf Of Paul S. Anderson
Sent: Wednesday, December 27, 2006 7:10 PM
To: Roger Samson
Cc: 'Steve Redmond'; 'A WoodGas'; 'Greg Manning'; 'A Gasification';
'Discussion of biomass cooking stoves'
Subject: Re: [Stoves] [Gasification] Grass Fireballs burn cleaner than wood

Roger, Jeff, and all,

Wonderful observations and comments!!!!  Seems to make sense.

Now, try this:  The described problem with the wood is NOT the case when the
wood is in small pieces (such as chunks and chips for gasifiers of various
sizes) AND the access of oxygen to the fuel is controlled (as in the various
gasifiers).

Therefore, (hypothesis), the good future of combusting wood resides it the
making of "small wood" (chips and chunks and coppicing and pollarding).
This
can also discourage the cutting of the large wood (big branches and tree
trunks), thereby helping to protect the forests and thereby protect the
fauna
and soil and all that good environmental stuff.

But will anyone listen to such talk?  I agree with Roger that some serious
attention needs to be given to the "bad" of big-wood and to the "good" of
small-wood and fireballs and other alternative fuels.

Paul
-- 
Paul S. Anderson, Ph.D., Geography professor - Emeritus
Telephone:  USA-309-452-7072 (residence and office)
Internet site:  www.ilstu.edu/~psanders
For my gasifier stoves info, go to:
http://bioenergylists.org/contributors#Paul_Anderson

Quoting Roger Samson <rsamson at reap-canada.com>:

> Just before Christmas I had the pleasure to visit Jeff Davis 30 miles
south
> of Lake Erie.  Apparently I was his first stoves-list visitor and so now
it
> is no longer a secret lab. As a result of the experience I am becoming
more
> of a fireball fan than wood fan when it comes to clean combustion.
>
> I spent a little bit of my holiday examining chunk wood burning side by
side
> with versus Jeff's switchgrass fireballs in a sealed fireplace. The
problem
> of dry wood combustion as I now see it is that wood really wants to
release
> its energy rapidly, this is especially the case with dry wood. As the fire
> starts, the wood ignites quickly and soon fractures along the fibre lines
in
> the split firewood. A little bit later it splits perpendicular across the
> fibrelines to form burning chunks that are stilled attached to the log. As
> an amateur combustion specialist like me sees it, too much carbon is
> released too quickly without adequate oxygen to enable complete combustion
> when wood is burned. This is especially the case when the "crevices" form
in
> the burning logs (yellow flames are observed in these areas while the
areas
> without crevices appear to have a superior quality of flame). All in all,
> burning wood seems to be conducive to incomplete combustion and a high
> particulate load.
>
> In contrast the switchgrass fireballs did not fracture and have a nice
blue
> flame that is emitted, they also burn more slowly like charcoal and from a
> largely even surface. The fireballs have their fibres cross bonded as the
> balls naturally agglomerate in the cement mixer in about 15 minutes. There
> are no crevices formed. It's even difficult to break the fireballs by
hand.
> The way I see it the carbon in fireballs is released in a more controlled
> manner from the fuel source which enables a better control of the
combustion
> process and the extended burn. With wet wood burning (as you mention
below),
> I would surmise that you have a more gradual release of the carbon than
with
> dry wood fuel. With our Mayon Turbo rice hull stove we had about a 70%
> reduction in particulate load when tested compared to the 3 stone fire
> burning fuelwood. Wood seems to me to be just a very problematic fuel to
> burn cleanly in simple small combustion appliances.
>
> After visiting Jeff Davis I am now convinced more than ever that a big
part
> of the solution to having cleaner combustion is through developing solid
> fuels that release their carbon in a more controlled manner. Of course
there
> are also sustainability issues with wood fuel use and that is another
reason
> to develop alternative fuels. It might be a good compromise to use
fuelwood
> to get the fire started and also to provide a quick heat to get the pot up
> to temperature. The fireballs would then continue to release their heat
and
> act as the primary fuel for finishing the cook as the heat demand
> diminishes.
>
> In 2007 I would like to see more work done on alternative solid fuels as a
> solution to improving indoor air quality. These grass fireballs can be
made
> for a mere pittance almost anywhere and with or without an improved stove
> will likely result in significant improvements in indoor air quality. I
> think Jeff Davis development of grass fireball production using stones to
> help agglomerate fibres in cement mixers is a beautiful example of
> sophistication in simplicity. It could have significant impact on rural
> development especially in areas experiencing wood fuel shortages. It could
> also have commercial fuel applications.
>
> In 2007 we need more work on optimizing grass fireball production and on
> testing emissions of various solid fuels versus wood in unimproved and
> improved stoves. I hope we can get some practical projects started in
> developing countries and see how communities receive the grass fireball
> fuel.
>
> Cheers
> Roger Samson
> www.reap-canada.com
>
>
> -----Original Message-----
> From: stoves-bounces at listserv.repp.org
> [mailto:stoves-bounces at listserv.repp.org] On Behalf Of Thomas Reed
> Sent: Wednesday, December 27, 2006 10:06 AM
> To: Greg Manning
> Cc: Steve Redmond; A WoodGas; A Gasification; STOVES at LISTSERV.REPP.ORG
> Subject: [Stoves] Wet wood better?
>
> Dear All:
>
> I love paradoxes and non-obvious truths.  Since wet firewood is very
> hard to light and burn, you might think that bone dry (or even Denver
> dry) firewood would burn best.
>
> However, the exchange below points to the fact that this may not be so.
> In our WoodGas campstoves we find that wood up to 30% moisture (at
> least) burns with a bluer flame and less left over charcoal, since the
> air passes through the pyrolysing wood to the charcoal to generate
> enough heat for drying AND pyrolysis.
> ------------------------------------------------------------------------
> Tom Miles's nephew, (Shelton?) discovered in the 1970s in well
> controlled stove testing that 15% moisture content gave more heat and
> less emissions than dryer wood.  This is because the pyrolytic flame is
> localized at the air entry point, rather than heating the whole log and
> allowing it to smoulder with insufficient air.
>
> I hope Tom Miles can give us more details.  And what is nephew doing now?
> ------------------------------------------------------------------------
> So, use your intuition, but keep a weather eye out for contrary effects.
>
> YOurs truly,
>
> TOM REED                  BEF STOVEWORKS
>
> Greg Manning wrote:
>>  Writing this on Christmas Day,
>>
>>  Merry Christmas everyone!
>>
>>
>>  B) I have been conversing with Steve Redmond from Vermont, "Off List"
for
>> the last little bit, and was somewhat skeptical of his "Wet Woodchip"
>> burning.....
>>
>>  I will say this.... I am now a convert !
>>
>>  Hold on, he's doing woodchip batch mode, for heat only see
>> (http://www.sredmond.com/vthr_index.htm) Where as, I'm doing downdraft
>> gasification for engine use, BUT, we (I), am currently running a split
>> cordwood fired "wood boiler" for heat only, simply because of automation
>> issues that I am still working on, for the gasifier/engine setup. (I will
>> admit the gasifier has been an on and off, uphill battle, but I am making
>> progress, even though slowly).
>>
>>  In the mean time, I built a batch fired 300 some odd gallon boiler to
>> replace the gasifier's heat output (like an outdoor boiler) but this unit
>> would be considered an "Updraft gasifying boiler" see:
>> http://www.youtube.com/watch?v=UsV-uEwg7_Q#GU5U2spHI_4 for a video clip.
>>
>> Anyhow, On with the findings....
>>
>>  For downdraft gasifier use.... NOPE, wet woodchips do NOT work... BUT...
>> cordwood in the "boiler"....
>>
>> LOL, Split cordwood (1/4 split, 6" and under, 6th's split for larger),
the
>> samples I'm testing measure 18-25%MC, which I would consider "Wet" for
>> cordwood, even though this is not freshly cut (fresh cut would be 30% and
>> above). WITH AN EXISTING BED OF COALS, a good load (20kg) of this "split
> wet
>> cord wood" I toss the entire load into the boiler, and set the forced air
>> for 20 min. or so, and "TA-DA" the stuff burns nicely !!!!
>>
>>  WAIT ! when I say nicely, what I mean is that the entire load does NOT
> try
>> to all go up at once... Rather, the water content "moderates" the burn,
by
>> the time the water content is boiled off, the forced draft has turned
off,
>> and it is now a conventional draft unit. At this point, since the
> volatiles
>> and water are gone, there is simply a nice bed of glowing orange char....
>>
>>  HERE'S the neat thing... we all know blue or brown smoke from a wood
>> appliance means VOC's are being emitted to the air, IN this case... only
>> "white smoke" AKA "water vapor".
>>
>>  I will say.... Steve Redmond is on to something.....
>>
>>  I've proved it to myself..... NOW for some samples to be sent to the
>> lab..... for confirmation.
>>
>>  Greg Manning,
>>  Brandon, Manitoba, Canada
>>
>>  P.S. I realize that with a water content the "fire" is not as hot, BUT,
> in
>> this configuration of heating water, (not room air, like a fireplace)
the
>> process runs slower, BUT I gain more heat transferred to the water, and
> less
>> up the chimney.... what could be better !
>>
>>
>> --
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>>
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>>
>>
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