[Stoves] T-LUD heat feedback. Was: Particles and particle types

[AJH]

On Thu, 02 Nov 2006 09:23:34 -0600, Paul S. Anderson wrote:

>1.  Heat feedback in the T-LUDs:  can you please restate/describe that and say
>what is strong heat feedback or the overall objective.  I assume it is more
>than just pre-drying the fuel by using the flue gases.

To keep a fire running any new fuel has to be heated up to the point
it either generates some offgas by pyrolysis or the char ignites.
Otherwise the fire simply goes out. So in order to get the next bit of
fuel contributing to the fire it has to be heated up to around 300C.
If the fire is incapable of supplying the heat to do that it goes out.

Take a lit match and hold it with the head up vertically, what
happens? Do the same thing with the match head vertically down, what
happens apart from burning your finger?
>
>2.  Tom Reed has reported T-LUD operation with 30% moisture content.

He also reported that to do this all the char was consumed! The heat
to volatise and dump the moisture has to come from somewhere.
  
>Do you or
>others have experience with higher MC, such as 50% or 60%? 

Well yes but it's not straightforward. Given the idea that oven dry
wood has a lower heating value of about 18'6MJ/kg and that water in
the wood "costs" 2.7MJ/kg to vent to flue then theoretically there is
enough heat in a sample of wood at 87%mc wwb to sustain combustion. Of
course losses are such that you cannot succeed in doing this.

>  70% is so
>fantastically high that success in your work would revolutionize our views of
>fuels and stoves/furnaces.

Well it shouldn't because it's really not worthwhile and the
complications make it all costly. The simple fact is that air drying
of wood to season it is still the most cost effective means of
"refining" the raw product into something that is both usable and
relatively easy to burn to an acceptable level of pollutants in the
effluent.
>
>3.  Please send a description and results of your high speed wood 
>dryer. Specifically, is it applicable for chips, chunks, and/or cord 
>wood?

We've ceased trading so we don't have a web presence anymore but our
biggest commercial offering is still in operation drying poplar wood
for a commercial kindling packaging operation. In essence it was a
very large fan oven built into an insulated shipping container. It
dried boards, chunks, and logs from 60% to 30% average mc in 16 hours
operation, removing 7 tonnes of water in the process. Unfortunately
the customer did not want the full kit which would have doubled
efficiency and run on waste. This is not a topic for stoves so we'll
take it offlist if you want any more detail.

Drying wood is expensive and not particularly efficient, which is why
I have been experimenting with alternatives.


>
>4.  If the T-LUD pyrolysis gases are in with such vast amounts of water vapor,
>what are the prospects or requirements for successful combustion of the gases?

As you can imagine they're not good. Tami posted she considered
temperatures of 1200C were necessary for good combustion, now factor
in the amount of water vapour you have needed to produce and you can
see the massflow dilutes temperatures well below this level, though I
see no visible smoke at lower temperatures, subject to caveats about
measurement accuracy.

AJH