[Stoves] Damp fuel in TLUDs

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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