[Stoves] Short Documentary on TLUD and Biochar in Bangladesh (in Bangla)

[Andrew Heggie]

On Mon, 29 Oct 2018 at 12:55, Julien Winter <winter.julien at gmail.com> wrote:
  >Having heard some anecdotal tales of 'spontaneous combustion' (that
may have actually been caused by incomplete quenching) of bags of
biochar in USA, I suggested that making sure that the char was
hydrated before storage was safest.

When char is freshly made it is dry but slightly hygroscopic, so it
will absorb water from the atmosphere as air diffuses into the bulk.
On turning from vapour to a molecule weakly attached to a solid the
water gives up it's latent heat of vaporisation, as char is also a
good insulator  this means that the middle of the bulk gets hot enough
to be above the auto ignition temperature of the char which is around
200C.

Spread in a thin layer it is unlikely to get hot enough.

Crispin used the term "quenching" pot  and to my mind quenching means
to rapidly cool something, like putting it in contact with a cold
surface or dousing it with water (or dipping a red  hot piece of high
carbon steel in oil to harden it).

When one just puts the char in a pot and covers it to exclude oxygen
and then allows it to cool down and extinguish any combustion I would
call that snuffing.

Andrew