[Stoves] 40% yield of charcoal

[adkarve]

Dear Stovers,
For the last couple of years we have been reading in this forum about a
charcoal making process that yielded almost 40% char. This process was
developed in Hawaii. All that was revealed about this process was that it
was conducted under pressure.
A chemical technologist in Pune (India), with whom we are collaborating in
another project, demystified this particular charcoal making process.
According to him, the Hawaiian process mimicked the formation of mineral
coal in nature, where biomass got heated while buried under tons of soil and
rock. One can imitate this process in a laboratory by filling wet biomass in
a pressure vessel and heating it to 200 degrees celsius.  The water in the
biomass gets converted into steam, which exerts pressure on the biomass. The
volatiles that normally escape from the biomass in the process of pyrolysis,
are not allowed to escape because the biomass is under pressure. As a
result, the tar is retained in the charcoal, adding to the weight of the
charcoal. That is the secret of the 40% charcoal yield. This charcoal is
however of a poor quality, because when one ignites it in a stove, the
volatiles escape from it, giving rise to smoke and soot. Autoclaving
distillery effluents with high organic content at 200 degrees C, under
pressure, is already being practised in some distilleries in India, as a
measure of pollution control.
Yours
A.D.Karve