Desulfurizing iron-carbon melts with lime under reduced pressures
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attention h a s b e e n given r e c e n t l y to l i m e a s a d e s u l f u r i z i n g agent, e s p e c i a l l y in the c l e a n i n g of s o u r s t a c k g a s e s . The findings r e p o r t e d in t h i s p a p e r m a y have s o m e b e a r i n g upon t h i s p r o b l e m even though the e m p h a s i s is d i r e c t e d e x c l u s i v e l y to the d e s u l f u r i z i n g of i r o n . The d e s i r a b i l i t y of u s i n g s o l i d l i m e d u r i n g o r j u s t a f t e r the b l a s t f u r n a c e o p e r a t i o n , when the c a r b o n c o n tent of the i r o n is s t i l l quite high, and the c o n s e q u e n t a c t i v i t y of oxygen is low, h a s b e e n d e m o n s t r a t e d b y t h e r m o d y n a m i c c a l c u l a t i o n s . The r e a c t i o n which c a n b e u s e d to d e s c r i b e the o v e r a l l p r o c e s s i s C a O ( s ) + C_(gr) + S_(pct) ~ CaS(s) + CO(g).*
[1]
*The nomenclature used in the chemical reactions throughout this paper indicates the standard states or the compounds as follows: CS (g), CO (g): the gases at 1 atmosphere partial pressure, sulfur or oxygen dissolved in liquid iron with respect to a reference state. S_(pet),O (pc0: the (hypothetical) 1 pet solution in pure, liquid iron. _C(gr): carbon dissolved in liquid iron with respect to graphite as the standard state. CaS(s), CaO(s): pure, solid calcium sulfide or calcium oxide.
t r a t e d in F i g s . l ( a ) and l(b). In m e c h a n i s m (a), l i m e a c t s only a s a g e t t e r f o r the s u l f u r and d o e s not e n t e r into the a c t u a l d e s u l f u r i z a t i o n r e a c t i o n . In m e c h a n i s m (b), the r a t e - l i m i t i n g s t e p in the d e s u l f u r i z a t i o n is the s u l f u r - o x y g e n diffusion t h r o u g h the CaS with the s u b s e quent d e o x i d a t i o n of the i r o n b y c a r b o n . E x p e r i m e n t s w e r e d e s i g n e d to m e a s u r e and c o m p a r e the r a t e s of f o r m a t i o n of CaS on CaO c r y s t a l s which w e r e e i t h e r i m m e r s e d in a c a r b o n - s a t u r a t e d i r o n m e l t o r held at t e m p e r a t u r e in the effluent g a s e s a b o v e the m e l t . E X P E R I M E N T A L PROCEDURE T i m e and t e m p e r a t u r e s t u d i e s w e r e m a d e on s i n g l e c r y s t a l s of f u s e d l i m e , which w e r e e x p o s e d to 700 g of s u l f u r i z e d , c a r b o n - s a t u r a t e d , liquid iron. A s c h e LI QUID IRON
SOLID CoS
GAS
SOLID CoO
All of the standard states are at the temperature in question.
E q u i l i b r i u m c a l c u l a t i o n s have shown that with c a r b o n m o n o x i d e p a r t i a l p r e s s u r e s a s high a s 1 a t m o s p h e r e the e q u i l i b r i u m s u l f u r c o n t e n t o r c a r b o n - s a t u r a t e d i r o n can b e r e d u c e d to a s low a s 10 p a r t s p e r m i l l i o n b y t h i s r e a c t i o n . 1'~ Iron, e s p e c i a l l y h i g h - c a r b o n o r h i g h - s i l i c o n i r o n , can be e f f e c t i v e l y
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