Date of Graduation

1979

Document Type

Dissertation/Thesis

Abstract

An i n v e s t i g a t i o n o f t h e b itu m in o u s c o a l d i s s o l u t i o n phenomena has been undertaken in order to develop information which would be useful in the design and scale-up considerations for a commercial liq u e fa c tio n p la n t. The experim ental data o f t h i s study were derived from p i l o t p l a n t s u s i n g v a r i o u s c o a l l i q u e f a c t i o n p r o c e s s e s . The d a t a were analyzed in order to b e tte r understand the phenomena which occurs in the preheater and reacto r sections during the liquefaction of coal. Estimates o f the hydrodynamic c h a r a c te r is tic s o f th e two phase flow in the coal liquefaction re acto r such as the d ifferen t flow p atte rn s, liquid hold-up and axial dispersion e ffe c ts, were performed u tiliz in g various correlations available from the lite ra tu re . Two d i f f e r e n t s t a g e s were found t o e x i s t i n t h e c o a l d i s s o l u t i o n r e a c t i o n s . In t h e i n i t i a l s t a g e o f c o a l d i s s o l u t i o n , a f i r s t - o r d e r re a ctio n scheme is proposed, whereby coal undergoes a fa s t thermal r e a c t i o n p r o d u c i n g p r e a s p h a l t e n e a s t h e p re d o m in a n t p r o d u c t . C o n v e r sio n fo r t h i s re a c tio n is c a lc u la te d based on the amount o f p y rid in e so lu b le s formed. The r a t e c o e f f i c i e n t f o r t h i s stag e i s found to follow an Arrhenius type temperature dependence with an activ atio n energy of 4855 Kcal/g-mole. In the second stage o f coal d isso lu tio n , a slower firs t-o rd e r rate expression is proposed in which the preasphaltene is converted to benzene solubles with subsequent rehydrogenation of the coald e r i v e d s o l v e n t . A s e m i - e m p i r i c a l c o r r e l a t i o n f o r t h e d i s s o l u t i o n rate co efficien t in the second stage reaction is presented, which reasonably accounts for the effects of temperature, hydrogen p a rtia l 198 p r e s s u r e and o f p a r t i c u l a r im p o r ta n c e — r e a c t o r h y d r o d y n a m i c s . However, the r a t e c o e f f i c i e n t was found to be p r a c t i c a l l y independent of coal p a rtic le size. Finally, the ra te of hydrogen absorption during coal dissolution is modeled by assuming th a t the gas and liq u id phases are in e q u ilibrium a t th e i n t e r f a c e . The o v e r a l l gas a b so r p tio n c o e f f i c i e n t (K^a) was found t o be a f u n c t i o n o f s u p e r f i c i a l g as v e l o c i t y .

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