Ok, so we did it again today and made significant progress and learned a lot. Keep in mind the we are working under the premise (yet to be verified by us under controlled conditions) that in order to have a successful burn of oyster shell it is best to maintain 1000C for 10-12 hours.

 

We used a very accurate high temp. thermometer in our effort today. We quickly realized that we could not get the kiln to go over 800C. The reason is that our kiln walls were not thick enough and we were losing too much heat through the walls of the kiln. We dry stacked additional brick against the sides of the kiln and piled dirt on and around the kiln in an effort to insulate. We were able to get the temp up to 950C but we were only able to consistently sustain a temp around 850C. We also made the hole at the rear of the kiln way too big and were also losing heat there. We were able to keep at between 800c and 900c for about 8 hours. I am going to the site tomorrow to pick up the shells and will take them to our lab on Tuesday to crush and sieve them and then test their reactivity.       

 

Various improvements we are considering.

 

The first is using fire brick on the interior walls of the kiln. Traditionally I suppose that they could have used klinkers but I don't know where to get enough of those for our process. Fire brick is the only substitute I can think of. Any better suggestions?  

 

The second is building the kiln in essentially three layers. One wythe of fire brick, one 3" layer of dirt, and then an additional wythe of regular brick. 
Hopefully, this will help eliminate the problem of heat loss.

 

We will also reduce the size of the hole at the rear of the kiln to no larger than one brick in dimension.

 

We will also move the fire closer to the oyster shells. Currently we have an 18"+/- gap between the fire box and the oyster shell level above. We will raise the fire at least 3" closer. This should give us additional heat closer to the shells.

 

As far as verifying the conditions we are trying to attain, our plan is to put oyster shells in a pottery kiln set at 1000C for 10 hours and see what type of product is produced. If we produce a highly reactive quicklime using these parameters we will then proceed to reduce the time frame at 1000C until the quality of the material produced drops markedly.          

 

Things are progressing well and we are encouraged. Any suggestions at this point would be appreciated. Building a freestanding kiln is an interesting challenge. I am coming to appreciate the wisdom of building a kiln in a hillside or a hole in the ground for the insulating capabilities of both these types of situations.     

 

Brian