Dr TLUD recently shared some new TLUD Stove operation tips which should be helpful to TLUD stove users.
- 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.
- “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.