[Stoves] Pellet stoves - risks

[Andrew Heggie]

On 6 September 2015 at 05:45, Frank Shields <franke at cruzio.com> wrote:
> Dear Dean, Stovers,

> I think you may be on to something in regards to torrifying to some extent
> before using to get a cleaner combustion. I see the real challenge is
> quality control because torrification takes place in a very narrow range and
> it is so easy to have a ‘run-a-way’ combustion that heats higher than the
> setting you want. I was able to achieve that in my pipes but only after much
> practice and   s l o w l y    raising the temperature to desired amount. Not
> sure how this would be done commercially.  It would be a very interesting
> project.

Frank on the large scale I doubt it is a problem because as you heat
wood up through 100C and drying and then on to the evolution of some
VOCs to this 280 C torrefaction range you are always in an endothermic
reaction, let it slide above 330C and it becomes mildly exothermic, so
with a bit of feed back it should be possible to stay around280C with
no thermal runaway. By thistemperature presumably lignin is quite
plastic so pelleting power should be lower.I'm not sure what chemical
changes are taking place but I'm assuming some hydroxyl groups  are
being lost, making the material less able to attract water i.e
changing from hydrophilic to hydrophobic, so unlike sawdust pellets
torrefied pellets should store better without attracting moisture and
disintegrating. What are they like when dropped in a glass of water
for an hour or two?

With large scale it will also be easy to incinerate the low cv offgas
given off bythe process.

AJH