Thermal decomposition of limestone in a fluidized bed
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T H E R M A L
d e c o m p o s i t i o n of l i m e s t o n e is e x p r e s s e d b y the equation of CaCOs = CaO +
C02
This r e a c t i o n is of g e n e r a l i m p o r t a n c e in v a r i o u s fields of e x t r a c t i v e m e t a l l u r g y and c h e m i c a l i n d u s t r i e s , and m a n y works have b e e n c a r r i e d out in o r d e r to c l a r i f y the m e c h a n i s m of this r e a c t i o n . It was shown by the e a r l i e r w o r k e r s that the t h e r m a l d e c o m p o s i t i o n of l i m e s t o n e o c c u r s at the i n t e r f a c e b e t w e e n c a l c i u m c a r b o n a t e and the d e c o m p o s e d o u t e r s h e l l of c a l c i u m oxide 1'2 and that the r a t e of this r e a c t i o n is p r o p o r t i o n a l to the a r e a of i n t e r f a c e and to the d i f f e r e n c e in C02 p r e s s u r e between its . e q u i l i b r i u m value and the b a c k p r e s s u r e applied to the s p e c i m e n , z'4's Most of t h e s e works w e r e c a r r i e d out at t e m p e r a t u r e s below 900~ On the other hand, Satterfield anf Feakes6 decomposed an agglomerate of precipitated calcium carbonate at the temperature above 1200~ and found that the temperature at the center of the agglomerate remains unchanged during the course of thermal decomposition. Narsimhan 7also derived a rate equation of thermal decomposition of a single limestone particle in which he assumed that the rate of heat transfer across the outer decomposed shell of CaO to the decomposing interface determines the overall rate. He emphasized that the calculated reaction time coincides with the experimental results obtained by Satterfield and Feakes. Philbrook and Natesans developed a mathematical expression of the overall rate of thermal decomposition of a single limestone particle in which the rates of interfacial reaction and of heat and mass transfer steps were involved. They also mentioned that this model s u c c e s s f u l l y i n t e r p r e t e d the e x p e r i m e n t a l r e s u l t s obt a i n e d by F u r n a s ~ and Joseph, Beatty and B i t s i a n e s . 9 Hills l~ also i n v e s t i g a t e d the d e c o m p o s i t i o n of a single s i n t e r e d s p h e r e of CaCO~ and p r o p o s e d that the r a t e of the r e a c t i o n is c o n t r o l l e d by the t r a n s f e r of heat t o w a r d s the r e a c t i o n i n t e r f a c e and by the t r a n s f e r of CO2 gas away f r o m the i n t e r f a c e .
It is intended in this work to d e r i v e a m a t h e m a t i c a l e x p r e s s i o n of t h e r m a l d e c o m p o s i t i o n of l i m e s t o n e p a r t i c l e s in a batch type fluidized bed. It is also p u r s u e d h e r e to c l a r i f y the c o n t r i b u t i o n s of r a t e s of heat and m a s s t r a n s f e r and of the i n t e r r a c i a l r e a c t i o n to the o v e r a l l r a t e of t h e r m a l d e c o m p o s i t i o n . In the p r e v i ous p a p e r , 11 two of the p r e s e n t a u t h o r s d e r i v e d a r a t e equation of t h e r m a l d e c o m p o
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