Effect of methane on sulfur dioxide and sodium sulfate-lnduced corrosion of nickel-base alloys
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12301. Manuscript submitted October 15, 1973. METALLURGICAL TRANSACTIONS
t u r e , the s a l t l a y e r was found to c o n t a i n i n c l u s i o n s of Sodium s u l f i d e , f o r m e d p r o b a b l y b y the a c t i o n of a r e ducing agent, such a s s o l i d c a r b o n , CO o r unburnt h y d r o c a r b o n . T h i s c o n c l u s i o n is s u b s t a n t i a t e d b y r e c e n t m e a s u r e m e n t s of g a s c o m p o s i t i o n at v a r i o u s p o s i t i o n s a l o n g the c o m b u s t o r of a l a b o r a t o r y b u r n e r r i g . 9'1~ With a p u r e n - h e p t a n e liquid fuel and a wide r a n g e of a i r / f u e l r a t i o s to s i m u l a t e t u r b i n e p r a c t i c e , r e s i d u a l unburnt h y d r o c a r b o n c o n c e n t r a t i o n s a s high a s 100 p p m and CO a s high a s 5000 p p m w e r e r e c o r d e d at c o n s i d e r a b l e d i s t a n c e s f r o m the fuel n o z z l e a l o n g the a x i s of the c o m b u s t o r . In the c a s e of CO the m e a s u r e d l o c a l c o n c e n t r a t i o n s e x c e e d e d the c a l c u l a t e d e q u i l i b r i u m v a l u e s b y 1 to 4 o r d e r s of m a g n i t u d e and it i s e v i d e n t that a p p r e c i a b l e s t a t i o n a r y h y d r o c a r b o n c o n c e n t r a t i o n s m a y e x i s t in the c o m b u s t o r even when e x h a u s t e m i s s i o n s a r e a t an u n d e t e c t a b l e l e v e l . Many m e t a l s , e s p e c i a l l y n i c k e l , c o b a l t and iron, p r o m o t e the d e c o m p o s i t i o n o r c r a c k i n g of g a s e o u s h y d r o c a r b o n s to y i e l d s o l i d c a r b o n d e p o s i t s . l l M e a s u r e m e n t s of c a r b o n d e p o s i t i o n r a t e s in b u r n e r r i g s ~ have shown that a r o m a t i c and naphthenic f u e l s d e p o s i t c a r bon on Monel s u r f a c e s much m o r e r a p i d l y than do p a r affinic f u e l s . With k e r o s e n e , the r a t e of c a r b o n f o r m a tion was o b s e r v e d to be v e r y r a p i d with an a i r - f u e l r a t i o of 60:1 and b e c a m e m o r e m a r k e d with i n c r e a s i n g g a s p r e s s u r e . Although the b e h a v i o r of l a b o r a t o r y b u r n e r r i g s m a y have l i t t l e r e l e v a n c e to a c t u a l t u r b i n e p r a c t i c e , t h e r e is e v i d e n c e that under s o m e c o n d i t i o n s s o l i d c a r b o n d e p o s i t s can f o r m on the f i r s t s t a g e b u c k e t s and n o z z l e s of g a s t u r b i n e s d u r i n g o p e r a t i o n . Such d e p o s i t s a r e often a s s o c i a t e d with i n c o m p l e t e m i x i n g of a i r and fuel in the c o m b u s t o r o r o t h e r malfunction, iS' 14 although s o o t y d e p o s i t s have o c c a s i o n a l l y b e e n r e p o r t e d on t u r b i n e c o m p o n e n t s u n d e r a p p a r e n t l y n o r m a l o p e r a t i n g c o n d i t i o n s when a l a r g e e x c e s s of a i r was p r e s ent. Is E n h a n c e d hot c o r r o s i o n in the r e g i o n s of c a r b o
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