[Stoves] Chinese stove photo sequence

[Todd Albi]

Neil is using an in-insulated TLUD, it appears he places fuel in horizontal
layers, rather than inserting it vertically as design intention.  Vertical
insertion should not require reloading fuel bed for the minimalist cooking
that stove was designed for (trekking stove).  We find stove operates more
efficiently when loaded vertically.  Obviously the higher the moisture
content of fuel, or humidity levels are going to impact combustion
outcomes.

Generally speaking, an insulated natural draft TLUD will handle damper fuel
more efficiently than an uninsulated TLUD.  As well as an insulated fan
TLUD is going to produce less char than a natural draft TLUD, due to
greater secondary mixing.  Our stoves with identical sized combustion
chambers that produce more char are less efficient transferring heat to pot.

All of our low mass insulated gasifier models can be used with damper fuel,
however the higher the moisture content, impurities in fuel, or humidity
are going to all impact emissions escaping from stack or combustion
chamber.  We can cook with green fuel, however now we have smoke.  That is
unpreventable when using high moisture content fuel in a simple cook stove
design.

Regards,

Todd Albi, SilverFire

On Sat, Jan 28, 2017 at 2:14 AM, Andrew Heggie <aj.heggie at gmail.com> wrote:

> On 27 January 2017 at 18:57,  <neiltm at uwclub.net> wrote:
>
> > I would be interested to hear if anyone
> > has successfully burned wood with such
> > a high moisture content in a TLUD, or
> > what anyone has designed a TLUD to
> > tolerate?
>
> Neil with all the strategic and political posts on [stoves] at the
> moment your experiments, which the stoves list was  in the past good
> at, may get swamped.
>
> IIRC Ronal and Tom originally said that with "Denver dry" ( probably
> 10% moisture content on a wet basis) the burn was clean and
> sustainable and left a char residue of 25% of the initial dry mass of
> wood. As moisture content increased the initial change was that the
> yield of residual char decreased. At the time it was suggested that
> the downward pyrolysis front  would not establish with wood above
> about 25% mc wwb.
>
> I surmise the reason this might be is that the energy required for
> pyrolysing a chunk of wood is considerably less than that needed to
> evapourate it's water content. Because much of the energy from the
> pyrolysis front is carried away upward by the convection of offgas
> only the weaker radiative and conduction effects are available to
> start pyrolysing the layer below.
>
> If the wood has higher than ideal moisture content then the available
> heat must evapourate moisture at 100C and then raise the part of the
> wood to ~270C before  the nascent char can itself be formed. The first
> thing the primary air then encounters is this fresh char which then
> provides heat for the ongoing downward migration of the front but the
> front has slowed down because of the time taken to evapourate water so
> more char is consumed before it can be shielded  by the new offgas .
>
> In your case  the 33% mc wwb, part seasoned or re wetted,hazel
> modifies the front because the fuel no longer has a homogeneous
> moisture content. Not having seen other than your photos I suggest on
> encountering the wetter piece of wood the downward migration  at the
> lump of wood ceases and this piece of wood may be burning in updraught
> mode whilst the pyrolysis front continues down around it in the dryer
> wood.
>
> We know if left to its own devices as the pyrolysis front reaches the
> bottom all the air available starts burning the char at a much higher
> temperature than was present during the pyrolysis.
>
> Andrew
>
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