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

Wed Dec 27 10:52:40 CST 2006

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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