Fluidized bed roasting of lime copper concentrate pellets
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c o n c e n t r a t i o n , the t i m e for c o m p l e t e r e a c t i o n of the p e l l e t s i s 5.4 m i n for the 0.32 cm p e l l e t and 12.1 rain for the 0.47 p e l l e t . However, in a c o n t i n u o u s l y o p e r ated f l u i d i z e d bed the r e s i d e n c e t i m e d i s t r i b u t i o n of the p e l l e t s m u s t be c o n s i d e r e d . It has b e e n shown e x p e r i m e n t a l l y f o r p a r t i c l e s of u n c h a n g i n g s i z e without c a r r y - o v e r i n the gas, which a r e o b t a i n e d in the p r e s ent c a s e , that v i g o r o u s m i x i n g of the s o l i d s i n the bed o c c u r s and the r e s i d e n c e t i m e d i s t r i b u t i o n for b a c k m i x flow holds. 3 In a s i n g l e fluidized bed t h i s is,
[1]
E(t) = (1/?)e -t~ while for e q u a l - s i z e d fluidized b e d s t a k e n i n s e r i e s the r e s i d e n c e t i m e d i s t r i b u t i o n of the p e l l e t s i s ,
E(t) =
JJ( t// t)J - l e[-J't/7) ] ?(j - 1)I
[2]
w h e r e j is the n u m b e r of s t a g e s , E(t)dt i s the f r a c t i o n of p e l l e t s s t a y i n g i n the bed for a t i m e b e t w e e n t and t + dt, and w h e r e t i s the a v e r a g e r e s i d e n c e t i m e for the e n t i r e j s t a g e s y s t e m , 7
J ( n u m b e r of p e l l e t s in each bed) [3] = (pellet feed rate) The f r a c t i o n a l c o n v e r s i o n , F(t, Rp) f o r a s h e l l d i f f u s i o n c o n t r o l l e d p r o c e s s is:
1 - F ( t , Rp) = { ~ + c O S(kO~+/ j4 n ~ l a
{for t
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