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

[AJH]

On Sat, 07 Jul 2007 10:23:21 -0300, Kevin Chisholm wrote:

>
>The last impression I had was that the "3.5" was kw-hr of energy per 
>stove fired,

Yes that's the figure Crispin gave.


> not 3.5 kW of average power input. Over an 18 hour cycle, 
>the total energy consumption would be 3.5x28 = 98 kw-hr of electrical 
>energy consumed over a 18 hour period.

Yes, by deduction, and this is the average power of the 5.4kW I gave.

>It might be that the electric kiln can be filled to a higher degree of 
>volume capacity. 

OK but Crispin still appeared to need some convection to transfer heat
evenly.

>There is no need to be concerned about different 
>atmosphere considerations because of gas flow. I understand that wood 
>gas can be used to create different firing conditions... ashing effects, 
>and reducing/oxidizing atmospheric effects. Some desired pottery effects 
>can only be attained in wood fired pottery kiln

Yes this was the experience I had with my expensive plate maker
friend, the ash and the reducing atmosphere gave the "metallic" glaze.

>
>An arc has an intense energy emission characteristic.... say 10,000 
>degrees C, while the resistance heating surface temperature is perhaps 
>down to the 800 to 1200 C range. Thought would probably have to be given 
>to diffusing the intensity so that some stoves near the arc are not 
>melted to a puddle of slag, while others are still raw. t2^4 - t1^4 
>considerations can be of great significance.

Good points but again some shielding and circulation may mitigate
this.
>> 
>> Look at how crude it can be
>
>What I see is resourcefulness!! :-) 

Yes give these people access to information, via the internet??, and
what may they do?

>
>The raw stoves have significant quantities of water content. Excessige 
>heating rate can seal the surface of the stove bodies while there is 
>still free or bound water within the clay. The result can be spalling or 
>cracking of the stove bodies because of localized "steam explosions."

Yes that's why Crispin gave the rate of heating for various stages of
the kiln cycle.

I still think there is scope, in a batch sequential system, for using
the heat from one firing to dry the next firing. One of the points Ken
Goyer makes in his presentation is that at least one kiln was not
insulated because it meant the pottery would not cool quickly enough
to allow another firing. A simple natural circulation by swapping
flues and clearing a sand filled passageway may allow the cooling to
do some work whilst still having an insulated kiln.

AJH