[Stoves] Crispin´s kiln. (was Re: Traditonal Charcola Making Process / retort

[Crispin Pemberton-Pigott]

Dear Andrew

I have not given up on this - just too many things on the go!

You wrote:

Sent: July 5, 2007 11:04 PM
[snip]

[1] Crispin says some combustion air is allowed in to burn char which
leaves pores in the stove body, so there is a massflow and energy
contribution from this.

I had not given this enough thought.  The dry mass of charcoal in the PK11
mix is 10%. At a firing mass of about 4 Kg the stove has 400 gm of charcoal
in it.  This has quite a lot of heat, were it to be burned properly.

So I agree there is heat released by the burning of the charcoal powder, but
it won't by at full heat because it is removed in the form of CO and the
temperature in the kiln is too low to ignite it.  I expect it is all
released as CO from the top of the furnace. If I could measure CO2 I guess I
could prove it.

I was looking for a heat content for a kilo of charcoal burned to CO but I
have not found a consistent figure. Perhaps you can offer something.

Suppose all the carbon burned out and the temperature did not rise at all?
It means there is a balance in heat put in from elements and heat from
burning carbon (to CO) minus loses from air flow and through or into the
walls.

It will be an interesting modelling calculation to see if there is any
meaningful benefit from the burning of the carbon.  All the carbon burns out
of the clay at or before 600 C.  The air hole is open at the time, wasting a
certain amount of the heat and venting the CO. If the charcoal weren’t
there, I wouldn't need to hold it at 600 with air flowing through, so I
expect there is a net loss if you put charcoal into the clay.  It will
probably take more total heat to burn the charcoal out than it will yield,
given all the kiln losses involved.

While the electrical power consumption is known for firing 28 stoves, it in
fact the real heat required includes the heat contribution made by the
charcoal. It means the bottom line - power required - does not change but
there is a change in the equation further up.

One might find that the power requirement would increase if the charcoal
were to be removed and substituted with something like silicon xenospheres.
I have been thinking about various plastic beads or wax that might also
serve as cavity producing ingredients.

Regards
Crispin