Hi,

I'm designing/sizing a precalciner, how do I relate the residence time to the degree of calcination? And how different it is in terms of heat transfer if I use a calciner where both solid and gas flows downwards from the conventional upward suspension flow? Thnx

Hallo branco,

the theoretical residence time for meal particles are < 3,0 sec. depending on size and mixing condition with gas.

The residence time for to ensure good combustion depends on

a.mixing intesity of kiln gas with tertiary gas (if available) and combustion gas 

b. the amount of Oxygen available e.g. in-line calciner or seperate line calciner

c. type of fuel used as well as its distribution during combustion.

e.g. recommended min. retention in in-line calciner for oil > 3,0 sec. and for alternative fuel in general > 5,0 sec.

Additionally the design of the calciner should consider later installation of staged combustion for NOx reduction.

If you are interested in optimal design of calciner you can contact via this forum.

Best regards,

WiZi

While the basics of combustion have been discussed already, kindly take the material characteristics also into consideration. If possible a TGA/DTA curves would be of great help. This will provide insight into the reaction characteristics of the material and will give u an idea on the required temperature to be maintained in the calciner to achieve the required degree of calcination. If u do not get the TGA/DTA curves, then try with the basic muffle furnace atleast.

In our plant the calciner temperature varies sometimes by upto 50 Deg C to achieve the same level of calcination due to poor burning characteristics of the material.