[Stoves] Broken Brick Mixed with Charcoal

[andrew]

On Wednesday 26 December 2007 12:21, Paul S. Anderson wrote:
> John, the comments about making CO from CO2 plus hot C are
> correct, but is the benefit of the brick pieces based on allowing
> air to flow through the char, or is it because the brick pieces
> help give the needed height (thickness of layer)
> of the hot char with which the CO2 can react?  Your taught me
> years ago that we
> need about 15 layers of the fuel-partical size above the hot coals
> for the CO creation to best take place.  Perhaps the brick is
> simply helping to have that height.

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. 
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.


AJH