[Stoves] Broken Brick Mixed with Charcoal

[Paul S. Anderson]

Quoting andrew <list at sylva.icuklive.co.uk>:
>
> The concept is that you need a sufficient height of hot char for the
> rising CO2 to have the chance to react with and be reduced back to
> CO. You mention a dimensionless 15 pieces and Tom Reed has
> previously posted a 20 particle diameter figure. You will see from
> this that if the particles are 1mm in diameter the depth would be
> 20mm but if 1cm diameter it rises to 200mm. So intuitively it
> relates to the size:space ratio of the column and is a measure of
> the probability of a molecule of CO encountering a hot carbon atom.

So far so good.

> Adding inert brick to this equation will have exactly the opposite
> effect, it will both decrease the possibility of the  CO meeting a
> carbon atom but also enable the primary airflow to keep the area
> oxygen rich, favouring the production of CO2.

This above second paragraph is based on the assumption that the same 
quantity of
air is passed through A) 100% charcoal and B) charcoal with brick.  Yes, then
there would be proportionately more air per unit of char.

But what if the air supplied is only half (and we assume 50-50 mix char and
brick and same particle sizes).  Then the proportion of air per char 
unit would
be the same as in Case A.  This would be a great way to have a "smaller fire"
(smaller amount of total heat output) while using the same size of 
device.  And
the temperature of the reactions should be the same as in Case A) once the
device has reached the same temperature throughout.

Then the created CO2 (half the quantity) would rise through the same height of
the fuel+brick pile where it would encounter half the amount of char, again
being in the same proportion as in Case A.  Therefore I disagree with the
statements in Andrew's second paragraph above.

Of course, I could be quite incorrect in this matter.  So I await confirmation
or an alternative explanation.

Paul

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