[Stoves] Is there a role for combining torrefaction and char-making stoves? HM

[ajheggie at gmail.com]

On Sat, 25 Feb 2012 09:19:55 -0800, Tom Miles wrote:

>
>about 285 C which is supposed to be the magic temperature for torrefaction.
>When you modify the cellulose and hemicellulose the plastic flow of the
>lignin is not as complete so you do not get thorough bonding. I suspect that
>producers will find a slightly lower temperature that will provide the
>pellet quality but still be more than over-dried wood. 

Tom do you know if lignin is thermoplastic or sort of thermosetting? I
ask because we were told that when steaming wood to bend it and keep
the set bend would only work once.

Also lignin is a large polymerised macro molecule, could the higher
temperature rupture some bonds.

It certainly makes sense to bring all the sawdust up to a plastic
state before the die to save mechanical energy in crushing the cells.
Pellets leaving the die with cold sawdust often are charred on the
outside so with a higher temperature as a starting point how black do
they emerge? Is the die taper different to allow for the less effort
needed? Presumably the compression the wood particles undergo remain
the same. With work being force times distance and the distance
remaining the same  the lower force needed for pre plasticised wood
would be evident in lower power requirement.

Has any work been done on the temperature distribution across the
cross section of a pellet as it is extruded? Difficult to see how but
it would be interesting to know how much heat was either generated in
the middle by the crushing or conducted in from the friction of the
die surface.

Not really relevant for cook stoves because of the high price demanded
for pellets, in UK they are about 4 times the cost of cordwood on a
dry weight comparison.

AJH