Rate of reduction of pyrrhotite in hydrogen
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IN a study on the d e s u l f u r i z a t i o n of coal char in hydrogen and h y d r o g e n / w a t e r - v a p o r m i x t u r e s , Zielke e t a l . ~ found that d e s u l f u r i z a t i o n is inhibited by the p r e s e n c e of s m a l l amounts of HaS in the gas. This r e t a r d a t i o n in the r a t e of d e s u l f u r i z a t i o n was a t t r i b uted to the p r e s e n c e of p y r r h o t i t e in the char. M o r e over, it was found a also that in the l a t e r stages of the h y d r o - d e s u l f u r i z a t i o n of a high-sulfur coal char, the r a t e of desulphurization was controlled by the r e d u c tion of p y r r h o t i t e embedded in the char. In o r d e r to obtain a b e t t e r understanding of the r a t e of d e s u l f u r i z a t i o n of char in hydrogen, a study of the reduction of p y r r h o t i t e in Ha was undertaken.
fective diffusivity of A r - C O a in porous iron was d e t e r mined at room t e m p e r a t u r e by using the e x p e r i m e n t a l technique employed p r e v i o u s l y , s The b a s i c feature of this technique is that the flux of COa through a porous substance is fixed by the s t o i c h i o m e t r y of a fast c h e m ical r e a c t i o n with a solid phase ( a s c a r i t e ) . The o v e r a l l r a t e of diffusion is then d e t e r m i n e d e x p e r i m e n t a l l y f r o m the weight change due to the r e a c t i o n . F o r these diffusivity m e a s u r e m e n t s c y l i n d r i c a l p e l l e t s , mounted in epoxy cement, were used. The porous iron p e l l e t s w e r e obtained by hydrogen reduction of p y r r h o t i t e at 600, 800, and 900~ RESULTS
EXPERIMENTAL The r a t e m e a s u r e m e n t s were made with t e c h n i c a l grade p y r r h o t i t e , containing about 34 pct sulfur together with the following minor i m p u r i t i e s : 0.32 pct CaO, 0.10 pct SiOa, 0.08 pct MgO, and 0.05 pct AlaOs. The p y r r h o t i t e p a r t i c l e s were s c r e e n e d to v a r i o u s size r a n g e s , while the l a r g e r p a r t i c l e s were handpicked and ground to s p h e r o i d a l shapes. The s a m p l e s were contained in a platinum b a s k e t which was s u s pended in the hot zone of a v e r t i c a l r e s i s t a n c e furnace, with the platinum suspension wire connected to an aut o m a t i c r e c o r d i n g balance. The t e m p e r a t u r e in the hot zone was m e a s u r e d with a c a l i b r a t e d P t / P t - 1 0 pct Rh thermocouple positioned in close p r o x i m i t y to the basket. The furnace t e m p e r a t u r e was controlled to within •176 The s a m p l e s w e r e lowered into the hot zone while a flow of helium was maintained through the r e a c t i o n tube. When the t e m p e r a t u r e of the s a m p l e stabilized, hydrogen was admitted and the weight-change m e a s u r e m e n t s w e r e s t a r t e d . In all e x p e r i m e n t s the hydrogen flow was 21 (STP)/min (diam of r e a c t i o n tube 5.5 cm); s i m i l a r r a t e data were obtained with a h y d r o gen flow of 11/min. F o r the i
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