[Stoves] TLUD advances -- Two more uses of char

[Paul Anderson]

Dear all,

These two and many other "tips" need to be collected and told to TLUD 
stove users.   One avenue is in Christa's Manual,   Another is in stove 
manuals and at training sessions.   And at websites, etc.

1.  Charcoal to extinguish hot charcoal:   When dealing with small 
amounts of hot charcoal as in the residential TLUD stoves, one easy way 
to extinguish hot charcoal is to dump it into a somewhat larger amount 
of already extinguished (cold) char.   The cold char takes up much of 
the heat, extinguishing the hot char.   Be sure that it is well mixed 
and sufficiently cooled to avoid re-ignition.  This is best done in 
containers that can be sealed.   Containers of metal or ceramic are 
best, but even wood could be used if the quantity of cold char is 
sufficient to prevent the hot char from reaching the sides.   As always, 
be careful because oxygen to a small hot ember can lead to much greater 
combustion.

2.  "Space fillers" in loose fuels in TLUD devices:

General note about fuel in TLUDs:
In general, dry biomass fuels in TLUDs need to appropriately fill most 
of the air-space in the fuel chamber.   This is accomplished with 
smallish pieces such as wood chips, pellets, short-cut twigs, and shells 
of seeds.   Also, careful packing with vertical wood-segments or 
straight-ish reeds can occupy the space.   But twisted sticks and 
long-ish pieces that bridge inside the fuel chamber leave too much space 
unoccupied.   In those cases, the space can be appropriately occupied by 
adding small pieces, as named above.   Shake the TLUD to assure that the 
pieces have settled in well, and add more as needed.   These fillers 
will also pyrolyze and become charcoal.

Inert materials as "space fillers":   Technically, the space fillers 
could be inert materials such as ball bearings or pebbles (of rock that 
will not shatter with this heat) or fired clay balls.  Although they 
could function effectively, they would require separation after the 
batch is unloaded and cooled.   But there is one material that solves 
these inconveniences and costs.  It is charcoal.

Charcoal as a space filler:   TLUD stoves make charcoal. Therefore, 
charcoal is not a fuel for TLUD stoves.   However, small pieces of 
charcoal (but not charcoal fines) can also be used as "space fillers" to 
solve the need to restrict air flow in the fuel chamber.   The char will 
not pyrolyze and will not burn (char-gasify or oxidize) as the pyrolysis 
front moves downward through that biomass fuel.

a.  Char is abundant for TLUD users, and at no additional cost, and is 
not consumed.

b.  Unlike small pieces of biomass as fillers, char pieces cannot catch 
on fire and then fall down to the lower areas of the fuel chamber and 
igniting fire there.

Charcoal as a reducer of thermal output:   Clearly in the above 
statements when charcoal is used as a space filler, the fuel chamber 
contains less biomass and therefore less heat will  be generated (which 
is desirable for simmering and some other cooking needs).

Another variation is to have well packed (mainly straight) wood or reeds 
or stems as a vertical bundle in the middle of a TLUD fuel chamber.  
Then load in small charcoal all around the bundle to fill in the 
remaining space.   When used (pyrolyzed), the fuel will yield heat in 
proportion to its cross-sectional area of the fuel bundle, not of the 
entire cross-sectional area of the fuel cylinder.  This is because the 
annulus of char is essentially non-combustible at the pyrolytic 
temperatures in the TLUD reactor.

Variations of all of the above need to be tested and even measured.   
(This will be utilized at the Stove Camp at Aprovecho 22 - 26 July 2013).

Note:  Credit for much of the above goes to Dr. Jack Bacon, a senior 
scientist at the NASA Johnson Space Center in Houston, TX.   Jack, a 
leader in the local chapter of Engineers Without Borders (EWB-JSC), 
suggested charcoal as fillers during discussions in April 2013 with Paul 
Anderson about an EWB project to use TLUDs for heat in a fruit dryer in 
Rwanda.

Dr TLUD

-- 
Paul S. Anderson, PhD  aka "Dr TLUD"
Email:  psanders at ilstu.edu   Skype: paultlud  Phone: +1-309-452-7072
Website:  www.drtlud.com