Magnetite oxidation in a traveling grate pellet plant: A computer model
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A m a t h e m a t i c a l m o d e l of the p a c k e d b e d of a t r a v e l i n g g r a t e p e l l e t i z i n g m a c h i n e has b e e n w r i t t e n . This m o d e l a l l o w s s i m u l a t i o n of the t e m p e r a t u r e p r o f i l e s in the p a c k e d b e d of the m a c h i n e while m a g n e t i t e o x i d a t i o n o c c u r s . Knowledge of k i n e t i c d a t a for m a g n e t i t e o x i d a t i o n of o r e b a l l s of the c o n c e n t r a t e c o n c e r n e d is r e q u i r e d for s i m u l a t i o n . T e m p e r a t u r e s m e a s u r e d d u r i n g i n d u s t r i a l pot t e s t s c o m p a r e w e l l with t h o s e p r e d i c t e d b y the m o d e l . R e s u l t s f o r o r e b a l l s of two c o n c e n t r a t e s w e r e c o m p a r e d . ~r~
&HE o b j e c t of i r o n o r e p e l l e t i z i n g is to take f i n e l y g r o u n d o r e c o n c e n t r a t e s and p r o d u c e f i r m , h a r d b a l l s about ~ in. in d i a m e t e r . T h e s e p e l l e t s m u s t be s t r o n g enough to w i t h s t a n d the t r i p f r o m the m i n e at which t h e y w e r e p r o d u c e d to a b l a s t f u r n a c e . They m u s t have s u f f i c i e n t s t r e n g t h and s u i t a b l e c h e m i c a l p r o p e r t i e s to serve as blast furnace burden material. I r o n o r e p e l l e t s a r e heat h a r d e n e d a f t e r b a l l i n g . In c o m m e r c i a l p r a c t i c e a shaft f u r n a c e , t r a v e l i n g g r a t e , o r t r a v e l i n g g r a t e and k i l n c o m b i n a t i o n a r e n o r m a l l y u s e d for t h i s h a r d e n i n g p r o c e s s . In o r d e r to p r o d u c e a s u i t a b l e p e l l e t , e a c h o r e c o n c e n t r a t e b a l l m u s t be h e a t e d c o r r e c t l y . Heating m u s t be c o n t r o l l e d so that the r e q u i r e d p h y s i c a l and c h e m i cal properties develop. With m a g n e t i t e o r e s , c o m p l e t e o x i d a t i o n of m a g n e t i t e to h e m a t i t e is i m p o r t a n t . If o x i d a t i o n is i n c o m p l e t e , the r e s u l t i n g p e l l e t c o n s i s t s of a c o r e of m a g n e t i t e s u r r o u n d e d b y a s h e l l of h e m a t i t e . This c a u s e s p o o r c o m p r e s s i o n s t r e n g t h s which m a y l e a d to b r e a k up in shipping and handling. It is a l s o known that r e duction k i n e t i c s f a v o r the use of h e m a t i t e in the b l a s t furnace. Oxidation of m a g n e t i t e s i g n i f i c a n t l y a f f e c t s the d e sign and o p e r a t i o n of t r a v e l i n g g r a t e p l a n t s . In t h e s e , h e a t i n g is done b y p a s s i n g hot a i r t h r o u g h a p a c k e d b e d of g r e e n p e l l e t s . Hot a i r e n t e r s the top of the b e d . Its flow r a t e and t e m p e r a t u r e a r e c o n t r o l l e d so that a s t i m e p r o g r e s s e s e a c h b a l l w i l l be p r o p e r l y h e a t e d . The g r e e n p e l l e t s at the top of the b e d a r e the f i r s t to e x p e r i e n c e o x
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