In this paper, a study of the calcination of lime stone, dolomite and byproduct-gypsum in the new type furnace, especially designed for this purpose, is described.
The natural calcite with over the 99 % purity was used as the raw material and was ground previously to about 50 μ particle size.
When this new type furnace was operated under the pneumatic conveying condition in the range of temperature from 900° to 1300°C, natural calcite is calcined to 80 % CaO by passing through the furnace for about a quarter sec.
On the calcination of calcium carbonate, it particle surface is covered with the resulting porous calcium oxide layer reduce the rate of thermal diffusion in the particle. It was shown that the thermal diffusion in the calcium oxide shell is a rate determining step.
These particles is seemed to be conveying in a flock. and the flock size was suggested to about 100 to 150 μ.
While plaster of Paris was obtained by conveying the byproduct-gypsum through the furnace in the range of temperature from 180° to 250°C.
Various experiment data in calcination of byproduct-gypsum follows.
The rate of the excess air 5. 8, the working capacity 1500 kg/hr. 1 m3 at the furnace, and the heat efficiency was 44%.
From above results it was suggested that this pneumatic conveying calcination process is more available for calcination of powdered material than fluidized bad process or others. (Authors abstrakt)
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