[Stoves] What about carbonization? Re: Composting at 70 deg C ?

[Crispin Pemberton-Pigott]

Dear Kevin

>We have the "High Temperature Carbonization" (HTC) process, where biomass
is reacted with water and temperature, to "fix" the carbon. At lower
temperatures and pressures, the process would proceed, but at a somewhat
slower rate.

The term is related to the carbon that does not come out of coal. It was
transferred to other fuels. Come out of coal when heated to about 420, that
is. It was termed fixed because it remained when all the H2 had been burned
out, and the O2, taking C with it. The fixed carbon was always in there. It
is not 'converted' in any sense of the word. The fuel goes from having a
volatile fraction (which includes some of the carbon) and what will
ultimately be labelled a non-volatile fraction, i.e. what is left. Thus the
term fixed is a misnomer. It is merely what 'would be left over' if treated
in a certain manner. You can't point to any particular Carbon atom and say,
'This one is fixed and that one is not' when in the native state.

It has been very frustrating for me looking at coal and trying to get people
to admit what the actual carbon content is. They will happily tell you what
is left after heating, but lots of hydrocarbons leave during that process.

>I did a quick Google on "Temperature of Formation of Coal", and other than
frequent repetition of "Coal is formed when biomass is subjected to
temperature and pressure for a considerable period of time", there is
nothing specific about the minimum temperature, pressure and time required
to form coal. Coal formation seems to be a loosey goosey collection of
intuitives.

Exactly. Who says it has to be hot? Everyone does, apparently, who learned
it from someone else who said the same thing. German pile drivers pounding
long wooden poles into the ground for foundations discovered that the bottom
charcoaled/'coaled' during installation. Whole, standing trees are found in
coal seams. It is not clear what all the possible routes are to a pile of
'fixed carbon'.

It seems to me that it is quite possible to heat biomass to 70 C and have it
decompose, and there will be a higher fraction of C in the output than in
the beginning. The term 'fixed carbon' is simply being misunderstood to be
something that is the result of 'converting' something. 70 deg C biomass
will be a high volatiles, carbon enhanced, lower mass fuel. No big deal.

Charcoal is normally made with the idea of lowering the volatiles to about
15% of the total mass. That burns visibly cleanly in a shallow open fire
suited to roasting meat. Great!  Note that the blackening of pots does not
happen with high carbon fuels, but does with low carbon, high volatiles
fuels.  Interesting. Very interesting.

It is apparently easier to burn high carbon fuels cleanly in simple devices.
Also interesting, and instructive.

Regards
Crispin in central Canuk-land (or is it Obama-land North?)