[Stoves] Heat to sustain TLUD process

[AJH]

On Thu, 31 May 2007 14:34:55 -0600, Thomas Reed wrote:

>We have been measuring the temperature of the reaction zone in a 3"ID 
>TLUD gasifier made from a riser sleeve, so VERY well insulated, at 
>varying air rates of
>4,8,12 liters/min.  We measure peak reaction temperatures of 400-600C.  
>Charcoal does not gasify much below 700 C,

Good this is much as I see.


> since the Boudouard reaction
>
>C + CO2 <==> 2 CO
>
>reverses below about 700 C. 

Agreed, so there is little likelihood of gasification of char being
involved.
>
>At higher superficial velocities in a downdraft gasifier, the peak 
>temperatures can climb to 1000 C and eventually reach a point where  air 
>passes through pyrolysis zone into the char zone.  At even higher 
>velocities you burn up the charcoal and go into combustion mode. 

Yes and basically these velocities cannot be attained in a small stove
without a substantial chimney.
>
>So, I believe we are burning a small amount of the volatile tars at low 
>SV to make "pyrolysis gas" which contains a lot of "prompt" CO, H2, CH4, 
>H2O and CO2. 

The thing is I think this gas also contains highly oxygenated
compounds, like acetic acid and acetone which with the H2O and CO2
make it unlikely you can sustain a flame in the absence of significant
oxygen. No flame then no means to ignite these gases even with good
stoichiometry.


> I wish I had a good gas analyser. 

And me! but in fact we could test this with simpler equipment by
heating an identical amount of the fuel in a sealed container with a
one way vent, to the same temperature and comparing the offgas and
char. I have an electric muffle furnace but no accurate means of
measuring its temperature and I'm not allowed to use it in the house.

Can we control the quoting please for those with lesser internet
connections?

AJH