Materials engineering and development for coal fired MHD power generators
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(EPRI) is s u p p o r t i n g c o m p l e m e n t a r y d e v e l o p m e n t work.3 In c o n s i d e r i n g m a t e r i a l s for MHD power, two r e lated o b s e r v a t i o n s a r e noteworthy: a) m a t e r i a l s a r e c r u c i a l to c o m m e r c i a l s u c c e s s ; and b) m a t e r i a l s t r e s s e s , p a r t i c u l a r l y in the g e n e r a t o r , a r e unique. MHD power c o n v e r s i o n has no d i r e c t p r e c u r s o r in e s t a b l i s h e d power c o n v e r s i o n technology. No r o t a t i n g p a r t s a r e i m p o s e d b e t w e e n the fuel c o m b u s t o r and the power take-off. MHD g e n e r a t o r s place g r e a t e s t p r e m i u m on m a x i m u m r e s i s t a n c e to elevated t e m p e r a t u r e e l e c t r o c h e m i c a l s t r e s s e s r a t h e r than m e c h a n i c a l s t r e s s e s . The t r a n s f e r e n c e of elevated t e m p e r a t u r e m a t e r i a l s p r o b l e m s f r o m the m e c h a n i c a l to the e l e c t r o c h e m i c a l r e g i m e is m o r e u n d e r s t a n d a b l e when one r e c o g n i z e s MHD as an e l e c t r o m a g n e t i c t u r b i n e . Heat fluxes a r e also c o n s i d e r a b l y higher than in c o n v e n t i o n a l power c o n v e r s i o n c y c l e s . After a b r i e f d e s c r i p t i o n of MHD d e s i g n p r i n c i p l e s , the p a p e r will a t t e m p t to d e s c r i b e the g e n e r a t o r e l e c t r o c h e m i c a l and t h e r m a l s t r e s s e n v i r o n m e n t . A s u m m a r y of the p e r f o r m a n c e of s o m e of the m o r e p r o m i nently t e s t e d g e n e r a t o r m a t e r i a l s will then be p r e s e n t e d . M a t e r i a l r e q u i r e m e n t s for the c o m b u s t o r , a i r h e a t e r , b o i l e r , and other plant components, while f o r midable, do not p r e s e n t uniquely new c h a l l e n g e s as does the g e n e r a t o r and will not be d i s c u s s e d in this p a p e r . The p a p e r will conclude with a b r i e f s u m m a r y of t e s t r e s u l t s in r e l a t i o n to d e s i g n c r i t e r i a . B. DESIGN PRINCIPLES MHD power g e n e r a t i o n is b a s e d on the d i r e c t conv e r s i o n of heat to e l e c t r i c a l e n e r g y by expanding a heated, e l e c t r i c a l l y conducting fluid through a m a g netic field. Thus, the e s s e n t i a l difference b e t w e e n a n MHD g e n e r a t o r and a c o n v e n t i o n a l t u r b i n e - d r i v e n g e n e r a t o r is that in the MHD g e n e r a t o r the r o t o r is r e placed by a high velocity, ionized working fluid. The i n t e r a c t i o n of this high t e m p e r a t u r e conducting fluid with a s t r o n g , t r a n s v e r s e magnetic field induces an e l e c t r o m a g n e t i c field a p p r o x i m a t e l y p r o p o r t i o n a l to the p r o d u c t of the m a g n e t i c field and the velocity. Spatial r e l a t i o n s h i p is analogous to c o n v e n t i o n a l gen-
ISSN0360-2133/78/0210-0161$00.75/0 9 1978AMERICANSOCIETYFOR METALSAND THE
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