Calcination of Finely Divided Limestones

The calcination of finely divided limestones (ranging from 5 pm to 5 mm) is of interest in connection with  

The process has been studied by several investigators (e.g. [15.11, 15.12]), but no consensus has emerged regarding the mechanisms that control the calcination rate. The following paragraphs sununarise some of the conclusions drawn by various researchers. 

At temperatures below 900 °C, the dissociation of 5 to 10 pm particles appears to be controlled by chemical kinetics [15.13] and an Arrhenius activation energy of 46 kcal/mole has been determined. However, above 900 °C, the apparent activation energy decreases markedly, indicating that chemical kinetics no longer control the rate of dissociation. The time to achieve 80 % calcination for such a particle size varies from 0.55 sec. at 850 °C to 0.03 sec. at 1250 °C [15.13]. 

Muller and Stark [15.14] reviewed literature relating to particle sizes of 20 to 30 pm and concluded that reactors operating below 900 °C require residence times ranging from 10 sec. to several minutes, whereas reactors with temperatures above 900 °C require residence times ranging from a few tenths of a second to a few seconds for % % calcination. 

Campbell et al. [15.15] studied the calcination of precipitated calcium carbonate, as produced in the re-causticising cycle of a Kraft (sulfate) pulp mill, and concluded that an activation energy of 50 kcal/mole applies to calcination at temperatures of 1165 and 1240 °C. 

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The calcination of finely divided limestone is addressed in section 15.7. 

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