[Stoves] Broken Brick Mixed with Charcoal

[John Davies]

Dear Stoves Friends,

 The account of how pieces of brick between the charcoal allowed the same 
heat output for half the charcoal, or inversely gave twice as much heat for 
the same mass of charcoal, set me thinking. The comments by Ken, Lanny and 
Crispin  ( added below ) allowed the penny to drop.

What we have in a charcoal fuel bed is typically a gasification process.
1. Oxygen combines with carbon at the grate level producing CO2 and giving 
off the heat of combustion, now I forget the units of heat produced, but we 
can call it  X.  the temperature is above 800C

2. This hot  CO2  heats the charcoal above but cannot burn it as there is no 
oxygen. The CO2 now combines with Carbon to produce CO. But this is an 
endothermic reaction and takes up about half the heat that was initially 
produced. If this gas leaves the bed without being burned by oxygen, only 
half the potential heat of the carbon is realised.

3. If the conditions are right to mix oxygen with this gas and burn it the 
lost heat is released again. This is typically what is happening in a close 
coupled gasifer/ burner combination, which is the system my coal stove uses.

It becomes quite clear that the pieces of brick in the fuel bed are acting 
as chimneys to pass oxygen through the bed and mixing it with the CO either 
higher in the bed and/or at the surface where there is an ignition source 
allowing close to 100% of the potential energy to be released. With the high 
temperature of the CO and O2 conditions are very good to have a total 
combustion of the CO with little excess air.

The reactions are as follows:

1  C + O2  > CO2 + X heat

2.  CO2 + C + 1/2 Xheat > CO

3.  2CO + O2  > CO2 + 1/2 Xheat.


Wishing you well over the festive season,

John Davies.

----- Original Message ----- 
From: "ken goyer" <kgoyer at comcast.net>
To: "STOVES (E-mail)" <STOVES at listserv.repp.org>; "AidAfrica" 
<mail at aidafrica.net>
Sent: Sunday, December 23, 2007 12:42 AM
Subject: [Stoves] Broken Brick Mixed with Charcoal


> Dear friends, Somehow this email to me from Dan Wolf escaped being posted,
> so I have resent it.
> The most interesting part is about charcoal conservation by mixing brick
> scraps with the charcoal. I try and avoid charcoal experimentation but
> maybe I should start. Does anyone have any ideas about this?
> Best regards,  Ken

Lanny wrote:

If not broken bricks is there another material and shape that would provide
a hot irradiative surface and aid in maintaining air passages through the
fuel?
Lanny

Crispin wrote:
If anyone is going to the region to test stoves could the please collect
some CO numbers for the stoves with and without the broken brick pieces?

I suspect the additive is helping to reduce the CO level (giving off extra
heat).

Thanks
Crispin