[Stoves] Damp fuel in TLUDs
Paul Anderson
psanders at ilstu.edu
Wed Mar 23 10:22:21 CDT 2016
Dear A.D.,
Your message below refers to the "water-gas reaction." It cannot occur
at the relatively low temperatures of pyrolysis, and certainly not occur
in the zone where the char is not glowing red-hot.
Paul
Doc / Dr TLUD / Prof. Paul S. Anderson, PhD
Email: psanders at ilstu.edu
Skype: paultlud Phone: +1-309-452-7072
Website: www.drtlud.com
On 3/22/2016 10:47 PM, Anand Karve wrote:
>
> Dear Paul,
>
> When the water vapour from the wet biomass passes through the layer of
> charcoal formed on top of the burning biomass, the vapour may react
> with the char to form CO and H2. These gases would burn in the flaming
> zone above the layer of charcoal, but such a reaction would result in
> lowering the char yield.
>
> Yours
>
> A.D.Karve
>
> ***
> Dr. A.D. Karve
>
> Chairman, Samuchit Enviro Tech Pvt Ltd (www.samuchit.com
> <http://www.samuchit.com>)
>
> Trustee & Founder President, Appropriate Rural Technology Institute (ARTI)
>
> On Wed, Mar 23, 2016 at 8:46 AM, Paul Anderson <psanders at ilstu.edu
> <mailto:psanders at ilstu.edu>> wrote:
>
> To those interested in TLUDs and char-making,
>
> Yesterday I was with Dave Ely who operated a large double-walled
> TLUD for char making (30 gal barrel inside a 55 gal barrel, as
> TLUD, not as a retort). We did not have much fuel-wood that was
> nicely dry. Dave wrote (after I left before the end of the
> operations):
>
> after breaking down the 55 gal tlud ..., I observed a lot of
> wet tree sap/oily residue. This liquid had to contribute
> greatly in issues of keeping the systems effeciently working.
> When mulberry brush limbs are vertical in the column, and
> heated, the sap oozes out branch points and bottom getting all
> surrounding wood wet, which does not allow efficient heat
> transfer down the column.
>
> Commentary: TLUDs operate with "glowing or flaming" pyrolysis at
> relatively low temperaturs of 550 to 650 deg C. [The high and
> main heat is where the gases are being combusted]. As the MPF
> (migratory pyrolytic front) moves downward, some of the heat
> radiates downward, warming and drying the adjoining pieces of
> fuel. In cases with fuel at 20% Moisture Content (MC) or less,
> the moisture is vaporized and it moves upward. I (and probably
> some others) commented about the "loss" of useful energy that was
> needed to vaporize the moisture. I never thought much about other
> possible outcomes of the excessive moisture in damp fuel. [Maybe
> others have already noted and reported on this issue, but it is
> new to me.]
>
> If the fuel is sufficiently damp (but at what % MC is not known),
> the heat can do at least two things:
>
> 1. Vaporize the water, but that water can condense back into
> liquid on cool fuel, making adjoining fuel increasingly more damp.
>
> 2. Force sap (mainly water) out of the fuel in liquid form,
> making adjoining fuel increasely more damp, or drippings in the
> bottom of the fuel column.
>
> In both cases, there is an increase in the amount of water in the
> next lower area that needs to be heated to pyrolysis temperatures.
> When the amount of water is too much to overcome (that is, to
> evaporate away from the zone of pyrolysis), the MPF is gradually
> weakened and eventually extinquished. And ALSO the amount of
> water vapor in the rising hot gases could be too much to sustain
> the secondary combustion.
>
> So, as Dave observed, as the TLUD proceeds to operate with damp
> fuel, it eventually "floods itself" with watery sap, etc.
>
> Note: In a "typical fire", damp wood does not burn well, but it
> does not have the physical vertical structure that results in the
> acccumulation of excessive moisture in the remaining fuel in lower
> levels.
>
> Also, for char making with "damp-ish" fuel (perhaps above 25%
> MC?), the "flame cap" technology is better suited than is the TLUD
> technology (unless the TLUD heat of one batch is used to pre-dry
> the fuel for later batches).
>
> Paul
>
> --
> Doc / Dr TLUD / Prof. Paul S. Anderson, PhD
> Email: psanders at ilstu.edu <mailto:psanders at ilstu.edu>
> Skype: paultlud Phone: +1-309-452-7072
> Website: www.drtlud.com <http://www.drtlud.com>
>
>
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