[Stoves] Damp fuel in TLUDs

[Crispin Pemberton-Pigott]

Dear Neil

What a great set of reports. Keep trying!

I agree regarding the moist fuel v.s. super dry. The issue may be that the
stove handles one better than the other. If I were making one to use dry
wood (like a Sahelian stove) it will avoid all pre-heating of the primary
air. 

The dampness definitely helps moderate the burn. If it is wet, you must run
some pre-heating. That the dry-to-wet transition didn't work is a proof of
the concept. If it is wet you have to add energy to overcome the demand for
additional heat. That is best by recycling some of the body heat into the
primary air. If it is really dry it should bypass that function. In short
you can do both, just keep in mind what is needed. 

I have suggested previously that lighting anthracite in a TLUD coal stove is
best done with lignite, not wood. In the same manner wood is best lit with
something like paper, not wood. 

Something I would like to see TLUD'd is goat dung. Air dried. There are a
lot of those little pellets lying around this planet. In Mongolia, because
animals are often penned at night, the goat dung is a metre deep because it
is not used for fuel.

I hope you followed the Muminabad dung burning story. It was quite
successful, though technically it is a processed fuel because it is made
into platters about 45mm thick in the centre with tapered edges.  Co-fired
with wood (cotton stalks etc) it doesn't smoke. 

Regards
Crispin listening for the popular story.

+++++++++

Not sure if this might be relevant, so my apologies if not, but I recall
threads on a wood gas list mostly devoted to running internal combustion
engines from wood gas, a consensus based on experience that the vehicles ran
noticeably better with some moisture content to the wood as opposed to
little or none.  I can't recall any figures if there were any I'm afraid,
and this was mostly empirical observation.  I don't think it could have been
down to an increase in tar as this was fastidiously filtered out to avoid
valves sticking and wrecking engines on cold restart, and the opinion was
that it was down to 'cracking' the water to produce hydrogen and oxygen.
Not sure if the temperatures involved in these 'reactors' might be
significantly higher than in stoves for this not to be relevant.

Incidentally, with the Chinese ND 'ebay' camping stoves that can be run in
TLUD mode I have observed that the behaviour of the stove both in terms of a
steady, more cooking friendly heat output and noticeably less smoke is
reliably obtained by using air dried found wood, even in the winter months
in England!  Whereas my top of boiler dried woodchip which seemed necessary
for a reliable burn in the Reed fan stoves, especially at half power, is
simply too volatile for these stoves and results in a towering inferno and a
lot more smoke than with the damper found wood.  
It is as if these particular stoves were designed for burning found wood in
a northern damp climate, and as such reminded me of what Paal Wendelbo was
always saying about designing the stove to match the fuel.  Even wood that
feels damp after being rained on a day or two previously and that I would
never have considered for the fan stoves, I have cooked on successfully, and
it just needed a little extra of the candle wax gratings sprinkled over the
top to start, but once going the stove would increase its heat output
throughout the burn, being most vigorous as pyrolysis reached the bottom.
Perhaps the small scale and depth (micro
gasification) mitigates against the effect of increasing dampness below the
pyrolysis front Paul mentions?  The only time I have ever had a stove
extinguish itself after a good start was at a transition in the fuel bed I
laid, between damper wood underneath a top layer of dryer.

I have been experimenting with 'poor' fuels.  I even cooked successfully on
elder which is a terrible insubstantial flaky pithy wood, although it
wouldn't be a fuel of choice.  I am also having great success with air dried
rotten pine - it still counts as biomass!  Old wine corks, lollipop sticks,
broken clothes pegs, sawdust, all jumbled up, it burns anything!  
Going to try some poplar next as that has a reputation for being smokey.  
Might be ideal for a TLUD!

Neil Taylor

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