Liquid phase Fischer-Tropsch (II) demonstration in the Laporte Alternative Fuels Development Unit. Final topical report. Volume 7, Appendix. Task 1, Engineering modifications (Fischer-Tropsch II demonstration) and Task 2, AFDU shakedown, operations, deactivation and disposal (Fischer-Tropsch II demonstration) [report]

B.L. Bhatt
1995 unpublished
1 Paae 2 9 21 58 72 84 APPENDIX A Reactor Temperature Stability 2 To: B h a r a t B h a t t The Laporte AFDU u t i l i t y o i l loop and r e a c t o r w e r e simulated t o determine how t h e r e a c t o r temperature w i l l respond t o e x t e r n a l d i s t u r b a n c e s and changes i n c o n t r o l a c t i o n . The h e a t exchangers were modeled as lumped systems w i t h t h e c a p a c i t a n c e being t h e sum of t h e capacitance of t h e o i l holdup and t h e m e t a l m a s
more » ... e m e t a l m a s s a s s o c i a t e d w i t h each exchanger. The Fischer-Tropsch r e a c t i o n w a s s i m p l i f i e d t o f i r s t o r d e r and heat g e n e r a t i o n w a s modeled as t h e product of t h e e x t e n t of r e a c t i o n and t h e heat t h a t would be released a t 1 0 0 % conversion of t h e feed. T r a n s p o r t a t i o n l a g between u n i t s determined f r o m volumetric flow and p i p i n g volumes w a s a l s o i n c l u d e d i n t h e model. I. The system i s open l o o p u n s t a b l e . The combination of o i l flow and t h e UA of t h e heat exchanger i n s i d e t h e r e a c t o r is i n s u f f i c i e n t t o c o n t r o l r e a c t o r temperature. .The c o n t r o l a c t i o n of t h e e l e c t r i c h e a t e r i s d e f i n i t e l y needed t o achieve s t a b i l i t y . 11. P r o c e s s p i p i n g should be altered and t h e electric h e a t e r s h o u l d be p l a c e d between t h e w a t e r cooled exchanger and . t h e r e a c t o r i n t h e AFDU. T h i s placement accomplishes two t h i n g s . F i r s t , s t a b i l i t y i s improved by e l i m i n a t i n g t h e p r o c e s s l a g s a s s o c i a t e d w i t h t h e exchangers and p i p i n g which. are p r e s e n t l y between t h e heater and t h e r e a c t o r . Secondly, t h e c o n t r o l a c t i o n w i l l no l o n g e r be a t t e n u a t e d by t h e heat exchangers. Simulation shows t h a t t h e p r o c e s s g a i n through t h e heat exchangers i s about 0 . 5 ( i . e . i n c r e a s i n g the. t e m p e r a t u r e of t h e o i l e n t e r i n g t h e f i n / f a n exchanger by one degree r e s u l t s i n a 0.5 degree temperature r i s e i n t h e o i l e x i t i n g t h e w a t e r c o o l e r ) . Thus i n t h e p r e s e n t c o n f i g u r a t i o n about half of t h e c o n t r o l a c t i o n o f t h e heater i s l o s t b e f o r e it can be applied t o t h e p r o c e s s . MODELS 1. All m o d e l s u s e s t e a d y s t a t e mass b a l a n c e s . 2 . Dynamic energy b a l a n c e s describe t h e response o f t h e 3 . The dynamics of t h e p r o c e s s side o f t h e r e a c t o r and 4 . Steady s t a t e balances describe t h e response o f t h e o i l i n each p r o c e s s u n i t . t h e electric heater are modeled. a i r and w a t e r temperatures i n t h e f i n / f a n a n d w a t e r cooled exchangers r e s p e c t i v e l y . 3 The e x p r e s s i o n s used t o describe t h e p r o c e s s side of t h e r e a c t o r are shown below. As can be s e e n , t h e ' r e a c t i o n w a s s i m p l i f i e d t o f i r s to r d e r . F ( X i -Xo) -R = 0. R = K * Xo * EXP HEAT GENERATION.= EXTENT * HRXN E = 23652 Deg Rankine (-E/T) EXTENT = ( X i -Xo)/Xi A f i r s t o r d e r expression i s used t o describe t h e dynamics of t h e o i l temperature i n t h e v a r i o u s h e a t exchangers. The t i m e c o n s t a n t f o r t h e o i l i s shown below. RESULTS The dynamics of labeled cl. c2. t h r e e p r o c e s s and c3 i n t h e 1 and 2 t h e electrical heater c o n f i g u r a t i o n s w e r e s t u d i e d and are p l o t s . t h a t follow. I n c o n f i g u r a t i o n s i s placed b e f o r e t h e f i n / f a n c o o l e r i n t h e flow sheet. f i n / f a n and t h e heater i s f i r i n g a t 90% of c a p a c i t y . I n c o n f i g u r a t i o n 2 3 0 % of t h e o i l bypasses t h e f i n / f a n and t h e heatez f i r e s a t 50% of c a p a c i t y . I n c o n f i g u r a t i o n 3 t h e heater i s p l a c e d between t h e water c o o l e r and t h e r e a c t o r . A small amount o f o i l is bypassed around t h e f i n / f a n (3%) and t h e h e a t e r f i r e s a t 50%. I n c o n f i g u r a t i o n -1 there i s no bypass around t h e The first d i s t u r b a n c e t o t h e system w a s a 10000 b t u / h r decrease i n t h e r e a c t o r h e a t l e a k . p r o p o r t i o n a l c o n t r o l l e r which manipulated t h e f i r i n g of t h e heater to maintain t h e r e a c t o r temperature a t a n a r b i t r a r y set p o i n t . Figure 1 shows t h a t a l l t h r e e process c o n f i g u r a t i o n s did a n a c c e p t a b l e job m a i n t a i n i n g r e a c t o r t e n p e r a t u r e b u t t h a t c o n f i g u r a t i o n 3 w a s c l e a r l y s u p e r i o r . F i g u r e 2 show t h a t much less c o n t r o l a c t i o n , 52 o f span vs. 1 0 % of span, i s needed f o r c o n f i g u r a t i o n 3. A c o n t r o l l e r g a i n of twenty w a s used for t h e The second d i s t u r b a n c e s t u d i e d w a s an a b r u p t 0 . 5 Deg F change i n t h e r e a c t o r temperature set p o i n t . Figure 3 shows a n overshoot of 80% of t h e i n t e n d e d change for c o n f i g u r a t i o n 1 and 2 and a 15% overshoot f o r c o n f i g u r a t i o n 3. Figure 4 shows again t h a t much less control a c t i o n a f t e r t h e i n i t i a l jump i s needed t o c o n t r o l t h e r e a c t o r f o r c o n f i g u r a t i o n 3 . It should be k e p t i n mind t h a t t h e d i s t u r b a n c e s i n t r o d u c e d i n t h i s s t u d y are s m a l l . It is h i g h l y l i k e l y t h a t t h e c o n t r o l system i n t h e AFDU w i l l need t o c o n t r o l much larger u p s e t s t h a n t h o s e s t u d i e d here. Since c o n t r o l a c t i o n is roughly p r o p o r t i o n a l t o t h e s i z e of d i s t u r b a n c e , I expect t h a t i n t h e p r e s e n t p r o c e s s c o n f i g u r a t i o n t h e c o n t r o l a c t i o n w i l l s a t u r a t e and c o n t r o l c o u l d be 1ost.The combination o f better c o n t r o l w i t h less c o n t r o l a c t i o n make c o n f i g u r a t i o n 3 ( h e a t e r between water c o o l e r and r e a c t o r ) a much moze r o b u s t p r o c e s s choice t h a n c o n f i g u r a t i o n 1 or 2 (heater b e f o r e b i d f a n c o o l e r ) . 4 51 8.6 I 51 8.5 LL 0 518.4 8 518.2 a 518.1 51 8 DECREASEHEATLEAKBY ' 10000 BTU/HR * m I ! T i t m m m m m m m m m m m m m m m m m m m m m m m m m m m m m m m m 8 m rn t f m 8 8 m m m m m m m m m m 8 m B m =. m m 8 m e a a a a a m m I I I I l a I I 1 0 0, 0 ccl 0 0 0 b CO ua 6 0 * . 0 0 c? 0 Q? 0 k 0 (9 0 u! 0 6 d 7 F E L t 0 (? 0 CY 0 -. 0 0 0 P A P Iu P 0 P P P 4 P (D A Reactor Temperature, Deg F P P P P P P v I v I v I m c n m I u O P c n Q , + 4 --L --L A P (D t c t t t c t t t t t t t t h t t t t t t t t t t t t t t t t . t t t t t t c * m m m e : 0 m 8 m m m e m m m 8 m m 8 8 8 m m m 8 m m m . . m : m m 8 m m . . 8 8 m .. : m 0 0 ' r 0 Q, 8 0 d 0 m c? 0
doi:10.2172/208330 fatcat:upmlrraqozhrjobmti4wwz2vc4