[Stoves] Damp fuel in TLUDs

Wed Mar 23 22:22:53 CDT 2016

Dear Paul,
in the charring kiln that we have developed, the charcoal above the burning
biomass glows red hot. Secondly, if, in a charcoal brazier, you introduced
a small amount of water by means of a metal tube, below the burning
charcoal, you can see a blue flame spurting out of the charcoal. The flame
vanishes as soon as you shut off the water.
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 8:52 PM, Paul Anderson <psanders at ilstu.edu> wrote:

> 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 ( <http://www.samuchit.com>
> 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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