[Stoves] Damp fuel in TLUDs

Anand Karve adkarve at gmail.com
Tue Mar 22 22:47:15 CDT 2016


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)

Trustee & Founder President, Appropriate Rural Technology Institute (ARTI)

On Wed, Mar 23, 2016 at 8:46 AM, Paul Anderson <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
> Skype:   paultlud    Phone: +1-309-452-7072
> Website:  www.drtlud.com
>
>
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