Industrial and Laboratory Pyrolyses

21 Pyrolysis of Naphtha and of Kerosene in the Kellogg Millisecond Furnace HARRY P. LEFTIN, DAVID S. NEWSOME, and THOMAS J. W O L F F

Downloaded by UNIV OF MICHIGAN ANN ARBOR on February 18, 2015 | http://pubs.acs.org Publication Date: June 1, 1976 | doi: 10.1021/bk-1976-0032.ch021

Pullman Kellogg, Research & Engineering Development Laboratory, Houston, Tex. JOSEPH C. YARZE Pullman Kellogg, Northeast Operations Center, Hackensack, N.J.

Since net feedstock cost is the most s i g n i f i cant item of o l e f i n s production cost, s e l e c t i o n of cracking conditions conducive to high y i e l d s of the desired products is a very important feature of an economically successful o l e f i n s manufacturing venture. For any s p e c i f i c feedstock, residence time, temperature, degree of conversion and hydrocarbon p a r t i a l pressure are the variables that influence the product d i s t r i b u t i o n achieved i n a steam-pyrolysis process. Of these, residence time and temperature are the most s i g n i f i c a n t variables and the mechanism and k i n e t i c s of the thermal cracking of hydrocarbons indicate that optimum s e l e c t i v i t y to o l e f i n s and maximum feedstock utilization should r e s u l t from operations c a r r i e d out at high temperatures and short contact times. Advances in tube metallurgy have made i t possible for furnace designers to reduce contact times for commercial p y r o l y s i s p l a n t s . Thus over the past decade, design contact times have been reduced in several stages from over 2 seconds to 0.25 seconds, with each step providing an increase in ethylene y i e l d and a decrease in r e l a t i v e tail gas production. In the early stages of p y r o l y s i s development, Kellogg designed a conventional p i l o t plant reactor (1) (0.25 to 1.5 seconds) in order to study the effect of temperature and contact time on product y i e l d s from the p y r o l y s i s of pure hydrocarbons and complex mixtures, ranging from l i g h t naphthas to heavy vacuum gas oils. Yields and operating conditions obtained from this p i l o t plant have been used successfully to design many commercial olefins plants. The accuracy of the operating cond i t i o n s and y i e l d s measured and predicted from this 373

In Industrial and Laboratory Pyrolyses; Albright, L., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1976.


374

INDUSTRIAL

AND LABORATORY

PYROLYSES

p i l o t p l a n t h a v e b e e n c o n f i r m e d by commercial experience. K e l l o g g ' s e v a l u a t i o n of the e f f e c t s of c o n t a c t t i m e o n p y r o l y s i s y i e l d s was f u r t h e r s t i m u l a t e d by i n n o v a t i o n s i n m e t a l l u r g y , w h i c h w o u l d e n a b l e commercial furnace designs at h i g h e r temperatures and s h o r t e r c o n t a c t t i m e s t h a n t h o s e t h a t c o u l d be examined i n the e x i s t i n g p i l o t p l a n t . In o r d e r t o a s c e r t a i n whether p y r o l y s i s i n the low f r a c t i o n a l s e c o n d c o n t a c t t i m e r a n g e would a f f o r d e t h y l e n e and c o - p r o d u c t y i e l d a d v a n t a g e s sufficient to j u s t i f y s t i l l f u r t h e r development of a p r o c e s s , b e n c h s c a l e work was i n i t i a t e d i n t h e K e l l o g g l a b o r a t o r y i n 1965. These bench s c a l e s t u d i e s p r o v i d e d e x p e r i m e n t a l e v i d e n c e on t h e t r e n d s o f p r o d u c t y i e l d s o v e r a c o n t a c t t i m e r a n g e f r o m 0.01 t o 0.10 seconds a t r e a c t i o n t e m p e r a t u r e s from 1400°F (760°C) t o o v e r 2000°F (1093°C). I n v e s t i g a t i o n s w e r e p e r f o r m e d on a w i d e v a r i e t y o f g a s e o u s (2_) a n d l i q u i d p u r e h y d r o c a r b o n s , s i m p l e m i x t u r e s o f p u r e h y d r o c a r b o n s and on a v a r i e t y of l i q u i d f e e d s t o c k s , i n c l u d i n g raffinâtes, n a p h t h a s and g a s o i l s . I t was c l e a r l y e v i d e n t f r o m t h e s e b e n c h s c a l e s t u d i e s t h a t e t h y l e n e a n d b u t a d i e n e y i e l d s c o u l d be i n c r e a s e d s u b s t a n t i a l l y and g a s e o u s and l i q u i d fuel p r o d u c t s d e c r e a s e d p r o p o r t i o n a t e l y by o p e r a t i o n s a t e l e v a t e d temperatures i n t h i s s h o r t c o n t a c t time range. I t was a l s o f o u n d t h a t maximum o l e f i n s y i e l d c a n be o b t a i n e d w i t h i n a n a r r o w r a n g e o f c o n t a c t t i m e s w e l l a b o v e 0.01 s e c o n d s , b u t b e l o w 0.10 seconds. W i t h v e r y h i g h t e m p e r a t u r e s and c o n t a c t t i m e s b e l o w a b o u t 0.01 second, g r e a t l y i n c r e a s e d y i e l d s of a c e t y l e n e , m e t h y l a c e t y l e n e and a l i è n e were o b t a i n e d . Data from the bench s c a l e s t u d i e s c l e a r l y i n d i c a ted s u f f i c i e n t incentive f o r further study. Conseq u e n t l y i n 1968, K e l l o g g d e s i g n e d and c o n s t r u c t e d a p i l o t p l a n t r e a c t o r s y s t e m w h i c h c o u l d be u s e d f o r c r a c k i n g a v a r i e t y o f f e e d s t o c k t y p e s i n t h e optimum c o n t a c t t i m e r a n g e e s t a b l i s h e d by t h e b e n c h s c a l e work. In t h i s d e s i g n , t h e p r o c e s s v a r i a b l e s were i n c o r p o r a t e d i n a manner t h a t a s s u r e d t h a t t h e d a t a obt a i n e d w o u l d be c o m p a r a b l e w i t h e v e n t u a l f u l l s c a l e y i e l d s and p r o c e s s c o n d i t i o n s . The p i l o t p l a n t w i l l be d e s c r i b e d i n d e t a i l i n t h e p r e s e n t p a p e r . D a t a f r o m an e x t e n s i v e s e r i e s o f t e s t s c a r r i e d out i n t h i s M i l l i s e c o n d P i l o t P l a n t Reactor very c l o s e l y c o n f i r m e d a l l of* the t r e n d s p r e v i o u s l y est a b l i s h e d by t h e b e n c h s c a l e s t u d i e s . In a d d i t i o n , p i l o t p l a n t and b e n c h s c a l e e x p e r i m e n t s w i t h t h e same feedstock served to demonstrate the e x c e l l e n t c o r r e s p o n d e n c e b e t w e e n t h e s e two u n i t s a s r e g a r d s p r o d u c t y i e l d s and s e l e c t i v i t y . Reasonably c l o s e c o r r e s p o n -



21.

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Naphtha and Kerosene

375

d e n c e was o b t a i n e d f o r t e m p e r a t u r e and c o n t a c t t i m e s and r e l i a b l e c o r r e l a t i o n f a c t o r s w e r e d e v e l o p e d t o r e l a t e t h e s e v a r i a b l e s f o r t h e two units. The h i g h l e v e l o f c o n f i d e n c e on t h e e c o n o m i c a d vantages of p y r o l y s i s i n t h i s c o n t a c t time range r e s u l t i n g from b o t h b e n c h s c a l e and p i l o t p l a n t s t u d i e s led t o i n - h o u s e d e v e l o p m e n t work o n a f u r n a c e d e s i g n w h i c h w o u l d be n e e d e d t o c o m m e r c i a l i z e t h i s p r o c e s s . A b o u t 1970, K e l l o g g and I d e m i t s u P e t r o c h e m i c a l Company (IPC) a g r e e d o n a j o i n t d e v e l o p m e n t e f f o r t t o t e s t t h e s e c o n c e p t s on a f u l l s i z e i n s t a l l a t i o n , w h i c h would a l s o s e r v e t o p r o v i d e the a d d i t i o n a l e t h y l e n e c a p a c i t y t h a t IPC r e q u i r e d a t t h a t t i m e . The furnace was i n s t a l l e d i n t h e IPC No. 2 E t h y l e n e P l a n t a t T o k u y a m a , J a p a n (3_) . Although t h i s M i l l i s e c o n d F u r n a c e was d e s c r i b e d e a r l i e r , {4J some o f t h e d e t a i l s o f i t s c o n s t r u c t i o n and o p e r a t i o n a r e r e c o u n t e d b r i e f l y i n the present paper. T h i s f u r n a c e , h a v i n g an e t h y l e n e d e s i g n c a p a c i t y o f 25,000 M T / y r , was operated w i t h n a p h t h a f e e d s t o c k i n 1972 and 1973. Subsequently, s u c c e s s f u l o p e r a t i o n s w e r e a l s o p e r f o r m e d on kerosene, r a f f i n a t e and gas o i l f e e d s t o c k s . Close correspondence o f p r o d u c t y i e l d s and o p e r a t i n g c o n d i t i o n s w e r e o b t a i n e d b e t w e e n t h e c o m m e r c i a l f u r n a c e and t h e l a b o r a tory reactors. These o b s e r v a t i o n s confirmed the development o f t h e M i l l i s e c o n d F u r n a c e a n d P y r o l y s i s p r o c e s s , which p r o v i d e s s u b s t a n t i a l improvements i n y i e l d s and f e e d s t o c k u t i l i z a t i o n , i n t o a d e s i g n t h a t incorporates r e a c t i o n temperatures of 1650-1700°F ( 8 9 9 - 9 2 7 ° C ) and c o n t a c t t i m e s o f l e s s t h a n 0.10 seconds. T h e M i l l i s e c o n d F u r n a c e and P y r o l y s i s p r o c e s s p r o b a b l y r e p r e s e n t s the l a s t important improvement w h i c h c a n be made w i t h r e s p e c t t o t h e s e critical operating v a r i a b l e s since operations at shorter contact t i m e s and c o n s e q u e n t l y h i g h e r t e m p e r a t u r e s unavoidably lead to the p r o d u c t i o n o f s u b s t a n t i a l q u a n t i t i e s of acetylene. W i t h i n the c o n t a c t time range o f the M i l l i s e c o n d F u r n a c e and P y r o l y s i s p r o c e s s , however, e t h y l e n e y i e l d s i n e x c e s s o f 32 wt % c a n e a s i l y be o b t a i n e d i n the p y r o l y s i s o f a t y p i c a l wide range naphtha along with a concomitant t a i l gas/ethylene of w e l l b e l o w 0.5 weight/weight. R e s u l t s and D i s c u s s i o n T h e e f f e c t s o f d e c r e a s i n g c o n t a c t t i m e and i n c r e a s i n g temperatures on p r o d u c t y i e l d s and feedstock c o n v e r s i o n s i n the steam p y r o l y s i s o f a wide range n a p h t h a and a k e r o s e n e w e r e s t u d i e d i n t h e l a b o r a t o r y b e n c h s c a l e p y r o l y s i s u n i t and i n t h e M i l l i s e c o n d Pyrolysis Pilot Plant. The l a b o r a t o r y s t u d i e s c o v e r e d w i d e r a n g e s o f o p e r a t i n g v a r i a b l e s s u c h as r e a c t o r o u t l e t t e m p e r a t u r e [ 1 4 0 0 - 1 7 5 0 ° F (760 t o 9 5 4 ° C ) ] , c o n t a c t


INDUSTRIAL AND LABORATORY


376


PYROLYSES


21.

LEFTiN E T A L .


377

t i m e (0.01 t o 0.40 s e c o n d s ) , o u t l e t p r e s s u r e and s t e a m to o i l r a t i o s . S i m u l t a n e o u s l y , r u n s u s i n g t h e same f e e d s t o c k s were b e i n g p e r f o r m e d a t Tokuyama, J a p a n i n t h e I d e m i t s u 25,000 m e t r i c t o n p e r y e a r M i l l i s e c o n d Furnace. T h e l a t e r m e a s u r e m e n t s w e r e o v e r a more r e s t r i c t e d range of v a r i a b l e s , s p e c i f i c a l l y , those c o n d i t i o n s s p e c i f i e d i n the K e l l o g g M i l l i s e c o n d Furnace and Pyrolysis process. T a b l e I summarizes the i n s p e c t i o n s and p r o p e r t i e s o f t h e f e e d s t o c k s e m p l o y e d i n t h e s e studies. The n a p h t h a i s a wide r a n g e K u w a i t n a p h t h a and i s f a i r l y t y p i c a l o f t h e n a p h t h a f e e d s encountered i n many o l e f i n u n i t s . TABLE I P Y R O L Y S I S FEEDSTOCK INSPECTIONS NAPHTHA

KEROSENE 46.0

71 .0

API° D i s t i l l a t i o n , °F Vol% IBP 10 20 40 60 80 90 95 E.P. Type A n a l y s i s , V o l % Paraffins Cyclic Paraffin Aromatics M o l e c u l a r Weight H/C A t o m i c R a t i o

99 131 143 1 66 195 234 281 331 385

31 5 345 355 372 392 417 437 453 476

73.5 21 .2 5.3 93 2.16

49.1 28.2 18.2 157 1 .93

F i g u r e 1 shows t h e y i e l d s o f p r i n c i p a l p r o d u c t s o b t a i n e d from the steam p y r o l y s i s o f the naphtha f e e d s t o c k as s e v e r i t y i s v a r i e d , w h i l e c o n t a c t t i m e s a r e m a i n t a i n e d w i t h i n 0.01 t o 0.1 s e c o n d . The o p e n c i r c u l a r p o i n t s are data o b t a i n e d i n the K e l l o g g M i l l i s e c o n d P i l o t P l a n t , while the c l o s e d p o i n t s are data obtained i n t h e M i l l i s e c o n d Bench S c a l e U n i t , and t h e square p o i n t s are the d a t a observed with the commercial M i l l i s e c o n d F u r n a c e a t T o k u y a m a (3^) . These data c l e a r l y e s t a b l i s h that e x c e l l e n t correspondence exists between the e x p e r i m e n t a l r e s u l t s from these u n i t s . The o b s e r v e d a g r e e m e n t i s e v e n more r e m a r k a b l e when one c o n s i d e r s t h a t the s c a l e - u p f a c t o r s between the bench s c a l e - p i l o t p l a n t and t h e p i l o t p l a n t - c o m m e r c i a l furnace are o f the o r d e r of 10 and 1 0 , respectively, f o r an o v e r a l l s c a l e - u p f a c t o r o f 10 . 2

3

5


INDUSTRIAL

A N D

LABORATORY


378


PYROLYSES

21.

LEFTiN

ET

AL.


Comparable data f o r the p y r o l y s i s of kerosene f e e d s t o c k s a r e shown i n F i g u r e 2. Again the y i e l d s and s e l e c t i v i t i e s o f t h e p r o d u c t s a r e i n e x c e l l e n t agreement. These o b s e r v a t i o n s p r o v i d e s t r o n g e v i d e n c e of the r e l i a b i l i t y of K e l l o g g s p y r o l y s i s t e s t f a c i l i t i e s to p r o v i d e d a t a t h a t c a n be u s e d d i r e c t l y f o r p l a n t d e sign. As a r e s u l t , i t i s now p o s s i b l e t o d e t e r m i n e r a p i d l y , and i n a d v a n c e , t h e e c o n o m i c d i f f e r e n c e s b e tween c a n d i d a t e f e e d s t o c k s u s i n g the bench s c a l e u n i t ; and t o s e t t h e b a s i s f o r t h e c o m m e r c i a l p l a n t d e s i g n w i t h i n the framework o f the d e s i r e d p r o d u c t slate f l e x i b i l i t y u t i l i z i n g the p i l o t p l a n t u n i t . A complete d i s c u s s i o n o f the economic advantages o f the M i l l i s e c o n d F u r n a c e and P y r o l y s i s p r o c e s s i s b e y o n d t h e s c o p e o f t h e p r e s e n t p a p e r as t h i s w o u l d i n v o l v e c o n s i d e r a t i o n s o f u t i l i t i e s e f f i c i e n c i e s as w e l l as c a p i t a l i n v e s t m e n t , i n a d d i t i o n to y i e l d and product slate values. I t i s , however, d e s i r a b l e to i l l u s t r a t e the order o f magnitude of the y i e l d and f e e d s t o c k u t i l i z a t i o n advantages t h a t acrue to M i l l i s e c o n d Furnace o p e r a t i o n s . T a b l e I I shows t h e y i e l d s and c o n v e r s i o n s o b t a i n e d i n p i l o t p l a n t s t u d i e s o f a wide range naphtha c a r r i e d out under c o n d i t i o n s of c o n v e n t i o n a l s h o r t r e s i d e n c e time p y r o l y s i s (0.35 s e c o n d s ) and a l s o u n d e r M i l l i s e c o n d F u r n a c e contact time. I t w i l l be n o t e d t h a t a t t h e s h o r t e r c o n t a c t time of the M i l l i s e c o n d Furnace, substantial g a i n i n s i n g l e p a s s e t h y l e n e and b u t a d i e n e y i e l d s a r e obtained. S i m i l a r y i e l d advantages are observed over the e n t i r e range of o p e r a t i n g s e v e r i t i e s . Propylene y i e l d , on t h e o t h e r h a n d , a p p e a r s t o be b u t little e f f e c t e d by t h i s c h a n g e i n c o n t a c t t i m e . Consequently, i t c a n be c o n c l u d e d t h a t t h e M i l l i s e c o n d F u r n a c e p r o v i d e s h i g h e r e t h y l e n e and b u t a d i e n e y i e l d s and r e d u c e d methane p r o d u c t i o n a t any s e v e r i t y l e v e l . M o r e o v e r , a t any f i x e d e t h y l e n e c a p a c i t y s i g n i f i c a n t l y less feedstock i s required. Experimental A. Bench S c a l e . The e x p e r i m e n t a l a r r a n g e m e n t i s shown i n F i g u r e 3. L i q u i d f e e d s t o c k and w a t e r were s e p a r a t e l y metered from p r e s s u r i z e d feedtanks i n t o a p r e h e a t e r - v a p o r i z e r and f i n a l l y i n t o t h e p y r o l y s i s r e a c t o r c o n t a i n e d i n an e l e c t r i c a l l y h e a t e d furnace. Power i n p u t t o t h e f u r n a c e t r a n s f o r m e r was controlled manually. T e m p e r a t u r e p r o f i l e s were measured w i t h a c a l i b r a t e d Chromel-Alumel thermocouple manually d r i v e n along the e n t i r e l e n g t h o f the r e a c t o r . P r e s s u r e s were m e a s u r e d w i t h c a l i b r a t e d B o u r d o n g a g e s s e n s i t i v e t o ±3 torr. On l e a v i n g t h e r e a c t i o n z o n e , t h e g a s e s w e r e 1


379




5

ce

8

w ο

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•Η

S

oo ο

03


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LEFTiN E T A L .


381

Table I I P y r o l y s i s o f a Wide Range N a p h t h a ( P i l o t P l a n t Data)

Furnace Contact

Type Time, s e c .

Conventional 0.3

Millisecond Less

than

Severity

High

High

Tail

17.6

16.7

0 .6

1.0

28.2

31.0

6

3.9

3.3

C3IU

0.6

1.3

C H 2

Gas

2

C Hi* 2

C H 2

C H 3

6

12.5

12.7

C H 3

8

0.5

0.2

CifH

6

3.6

4.9

CifHe

2.7

2.8

Ci»Hio

0 .2

0.5

29.6

25.6

c + 5


0.10


382

INDUSTRIAL AND LABORATORY

PYROLYSES

r a p i d l y c o o l e d by a d m i x t u r e w i t h a r e c y c l e d s t r e a m o f c o o l e d p r o d u c t g a s u s i n g t h e m e t h o d d e s c r i b e d by H a p p e l and K r a m e r ( 5_) . I n t h i s way, a r a p i d d i r e c t quench was achieved without the u s u a l c o m p l i c a t i o n s t h a t r e s u l t from i n t r o d u c i n g l a r g e volumes o f i n e r t quench d i l u e n t . P r i o r t o e n t e r i n g t h e r e c y c l e g a s pump, t h e q u e n c h e d p r o d u c t s w e r e f u r t h e r c o o l e d a g a i n s t t a p w a t e r i n an i n d i r e c t h e a t e x c h a n g e r a n d t h e c o n d e n s e d w a t e r and l i q u i d p r o d u c t s w e r e s e p a r a t e d by means o f a s m a l l cyclone separator. B o t h t h e h e a t e x c h a n g e r and c y c l o n e were i n t e g r a l p a r t s o f t h e quench gas r e c y c l e s y s t e m . Net p r o d u c t gas p a s s e d t h r o u g h a s a m p l i n g v a l v e and a wet t e s t m e t e r and was t h e n vented. T h e r e a c t i o n z o n e was an a n n u l u s b e t w e e n an o u t e r t u b e o f 1/8" NPS S c h 40 p i p e a n d an i n n e r t u b e o f 3/16" OD w h i c h s e r v e d a s t h e t h e r m o c o u p l e w e l l . Both tubes w e r e 347 s t a i n l e s s s t e e l . The f u r n a c e c o m p r i s e d a water-cooled c y l i n d r i c a l s h e l l equipped with F i b e r F r a x ( U n i o n C a r b i d e Corp.) i n s u l a t i o n , a c e r a m i c b a f f l e and a s p l i t c y l i n d r i c a l g r a p h i t e h e a t i n g e l e m e n t t h a t was c o n c e n t r i c w i t h the r e a c t o r . Stainless steel fittings were used t o f i x t h e r e a c t o r t o t h e t o p o f t h e f u r n a c e , w h i l e a t t h e b o t t o m i t was f r e e t o move w i t h i n a p a c k i n g g l a n d a t the p o i n t where the r e a c t o r o u t l e t e n t e r e d t h e quench gas m i x i n g chamber. The packing g l a n d a l s o s e r v e d t o e f f e c t a gas s e a l between t h e n i t r o g e n - f i l l e d f u r n a c e s h e l l and the r e a c t o r o u t l e t . N i t r o g e n p r e s s u r e i n t h e f u r n a c e s h e l l was maintained s l i g h t l y a b o v e t h a t o f t h e r e a c t o r o u t l e t so t h a t a s m a l l amount o f n i t r o g e n l e a k e d c o n t i n u o u s l y i n t o t h e p r o d u c t stream a t t h e r e a c t o r o u t l e t . Nitrogen content o f t h e t o t a l g a s s a m p l e was d e t e r m i n e d along with the p r o d u c t a n a l y s i s by mass s p e c t r o m e t r y and was subt r a c t e d from t h e gas y i e l d i n c a l c u l a t i n g t h e o v e r a l l m a t e r i a l balance f o r the runs. The r e a c t o r w a l l s were p r e t r e a t e d w i t h a m i x t u r e o f steam, h y d r o c a r b o n , and e t h y l m e r c a p t a n p r i o r t o each s e r i e s of runs. W a l l p o i s o n i n g was maintained by c o n t i n u o u s a d d i t i o n o f m e r c a p t a n t h r o u g h o u t the course of each run. The o b s e r v a t i o n t h a t t h e maximum l e v e l o f c a r b o n o x i d e s p r o d u c e d i n any o f t h e r u n s n e v e r e x c e e d e d 0.1 mol % o f t h e t o t a l p r o d u c t gas i n d i c a t e d t h a t t h e s u l f i d i n g p r o c e d u r e was effective i n r e d u c i n g c o m p l i c a t i o n s due t o c a t a l y t i c r e a c t i o n a t the tube w a l l . D i s t i l l e d water, used f o r the generat i o n o f r e a c t i o n s t e a m , was d e g a s s e d a n d f r e e d o f c a r bon d i o x i d e p r i o r t o b e i n g c h a r g e d t o t h e r e s e r v o i r . R o t a m e t e r s w e r e u s e d o n l y t o e s t a b l i s h and m a i n t a i n t h e instantaneous flow r a t e s . I n t e g r a l f e e d r a t e s were determined p e r i o d i c a l l y from r e a d i n g s o f the c a l i b r a t e d s i g h t g l a s s e s on t h e f e e d r e s e r v o i r s .



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C a r b o n d e p o s i t s f r o m p r e v i o u s runs were b u r n e d out and t h e r e a c t o r was s u l f i d e d f o r two h o u r s a t 6 0 0 ° C and one h o u r a t 7 5 0 ° C p r i o r t o e a c h s e r i e s o f runs. F u r n a c e t e m p e r a t u r e was s l o w l y r a i s e d t o r u n c o n d i t i o n s w i t h s t e a m and n i t r o g e n f l o w i n g t h r o u g h t h e reactor. F i n a l adjustment to the d e s i r e d temperature was made w i t h f e e d and w a t e r a t t h e r e q u i r e d f l o w rates. F u r n a c e p o w e r was c o n t r o l l e d t o m a i n t a i n a c o n s t a n t r e a c t o r t e m p e r a t u r e a n d t h e r u n was started o n l y a f t e r t h i s had r e m a i n e d c o n s t a n t f o r a t l e a s t 45 m i n u t e s . A f t e r a l l i n i t i a l r e a d i n g s h a d b e e n made, the c o m p l e t e t e m p e r a t u r e p r o f i l e was r e c o r d e d ( t h i s r e q u i r e d a p p r o x i m a t e l y 25 m i n u t e s ) . At the completion o f t h e p r o f i l e , t h e t h e r m o c o u p l e was r e t u r n e d t o t h e p o s i t i o n o f maximum t e m p e r a t u r e and a g a s s a m p l e was removed f o r a n a l y s i s . Complete temperature p r o f i l e s were r e c o r d e d c o n t i n u o u s l y d u r i n g t h e e n t i r e r u n p e r i o d w h i c h n o r m a l l y r a n g e d b e t w e e n one and t h r e e hours. Two g a s s a m p l e s w e r e t a k e n f o r d u p l i c a t e a n a l y s e s by mass s p e c t r o m e t r y and o n e f o r g a s c h r o m a tography. These were s p a c e d between t h e f i r s t third and t h e f i n a l t h i r d o f t h e r u n p e r i o d . U s u a l l y the r e s u l t s o f t h e d u p l i c a t e mass s p e c t r o m e t r i c d e t e r m i n a t i o n s f e l l w i t h i n the e s t a b l i s h e d l i m i t s o f t h i s a n a l y t i c a l m e t h o d , and t h e a v e r a g e d v a l u e s w e r e t h e n used. However, o c c a s i o n a l l y t h e d e v i a t i o n s were l a r g e r and i n t h o s e c a s e s t h e r u n s w e r e r e p e a t e d u n t i l g o o d a g r e e m e n t was o b t a i n e d . A l l c a l c u l a t i o n s of y i e l d s and c o n v e r s i o n s a r e b a s e d on m a s s s p e c t r o s c o p i c d a t a and g a s c h r o m a t o g r a p h y was u s e d o n l y f o r i d e n t i f i c a t i o n o f t h e i s o m e r s w i t h a p a r t i c u l a r mass number and t o estimate the isomer d i s t r i b u t i o n s . Runs w e r e c a r r i e d out on b o t h f e e d s t o c k s a t t e m p e r a t u r e s b e t w e e n 1 4 0 0 ° and 1750°F ( 7 6 0 ° and 9 5 4 ° C ) w i t h d i l u t i o n s j e a m c o r r e s p o n d i n g t o 0.5 and 0.75 w e i g h t r a t i o on t h e n a p h t h a and k e r o s e n e , r e s p e c t i v e l y . A l l r u n s were i s o b a r i c a t a t o t a l p r e s s u r e o f 22 p s i g . Material b a l a n c e s g e n e r a l l y f e l l w i t h i n 100±3% f o r a l l e x p e r i ments . B. P i l o t Plant Reactor. B a s i c a l l y the p i l o t p l a n t i s c a p a b l e o f p r o v i d i n g d a t a t h a t c a n be u s e d with c o n f i d e n c e i n the d e s i g n of f u l l s c a l e commercial units. To a c h i e v e t h e s e g o a l s , a p i l o t r e a c t o r was developed, which i n c l u d e d i n i t s d e s i g n such commercial f u r n a c e r e l a t i o n s h i p s as c o n t a c t t i m e , t e m p e r a t u r e p r o f i l e , p r e s s u r e d r o p and p r e s s u r e p r o f i l e , b u l k - t u b e s k i n temperature r e l a t i o n s h i p , t u r b u l e n t flow regime, time t o quench, e t c . T h i s was d o n e so t h a t i t t r u l y r e p r e s e n t e d i t s c o m m e r c i a l c o u n t e r p a r t . In a d d i t i o n , a s t r i n g e n t s e t o f o p e r a t i n g g r o u n d r u l e s were e s t a b l i s h e d upon which a l l p i l o t o p e r a t i o n s would



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be b a s e d . M o s t i m p o r t a n t o f t h e s e w e r e : (1) m a t e r i a l b a l a n c e s b e t t e r t h a n 1 0 0 ± 1 . 5 % m u s t be o b t a i n e d c o n s i s tently; (2) g o o d r e p r o d u c i b i l i t y m u s t be o b t a i n e d o v e r l o n g o p e r a t i n g t i m e p e r i o d s ; (3) y i e l d s m u s t b e d e t e r m i n e d w i t h h i g h d e g r e e s o f a c c u r a c y ; a n d (4) t h e r e l a t i o n s h i p between c o m m e r c i a l and p i l o t p l a n t r e a c t o r s m u s t be known. A s i m p l i f i e d flowsheet o f the p i l o t p l a n t i s shown i n F i g u r e 4. P r o c e s s steam i s c o n s t a n t l y g e n e r a t e d a t a p r e d e t e r m i n e d r a t e f r o m w e i g h e d and m e t e r e d w a t e r w h i c h i s v a p o r i z e d by s t e a m . T h r e e s y s t e m s f o r m e t e r i n g and m e a s u r i n g h y d r o c a r b o n f e e d s h a v e b e e n i n c o r p o r a t e d : one f o r g a s e o u s f e e d s s u c h a s e t h a n e , one f o r l i q u i d s u n d e r p r e s s u r e s u c h as p r o p a n e o r b u t a n e , and one f o r n o r m a l l y l i q u i d f e e d s t o c k s such as naphthas o r gas o i l s . Each type f e e d c a n be f e d i n d e p e n d e n t l y o r two o r more c a n be f e d s i m u l t a n e o u s l y a s w o u l d be r e q u i r e d i n c o - c r a c k i n g operations. Two f e e d t a n k s h a v e b e e n i n s t a l l e d i n o r d e r t o p e r m i t s i d e - b y - s i d e c o m p a r i s o n s o f two o r more l i q u i d f e e d s t o c k s . I t i s a simple matter, there f o r e , to run each f e e d s t o c k a t i d e n t i f i c a l r e a c t i o n conditions. L i q u i d s t o c k s a r e m e t e r e d by d u a l - h e a d Lapp r e c i p r o c a t i n g pumps, a n d h o u r l y f e e d r a t e s a r e d e t e r m i n e d by w e i g h t . The h y d r o c a r b o n s a r e i n j e c t e d i n t o s u p e r h e a t e d steam a t 400°F ( 2 0 4 ° C ) , f l a s h e d , and mixed w i t h the steam. The m i x t u r e i s t h e n s u p e r h e a t e d t o a b o u t 800-1000°F (427°-538°C) as r e q u i r e d b e f o r e i n j e c t i o n i n t o the r e a c t o r . The r e a c t o r s e c t i o n c o n s i s t s o f a v e r t i c a l e l e c t r i c a l l y - h e a t e d f u r n a c e i n which the r e a c t o r tube is placed. The f u r n a c e h a s s e p a r a t e l y c o n t r o l l e d z o n e s w i t h a p p r o p r i a t e t e m p e r a t u r e and h e a t i n p u t measurement f a c i l i t i e s f o r each zone. Fluid tempera t u r e m e a s u r e m e n t s a r e made a l o n g t h e l e n g t h o f t h e reactor with calibrated couples located i n adiabatic z o n e s and t e m p e r a t u r e p r o f i l e s c a n be v a r i e d . Reactor p r e s s u r e s a r e c o n t i n u o u s l y m o n i t o r e d and p r e s s u r e d r o p (ΔΡ) and p r e s s u r e p r o f i l e a c r o s s t h e r e a c t o r c a n be controlled. S i n c e each r e a c t o r r e p r e s e n t s a s p e c i f i c commercial c o i l , m u l t i p l e r e a c t o r s have been d e s i g n e d to c o v e r the commercial c o n t a c t time range o f i n t e r e s t . In t h e s e s t u d i e s a r e a c t o r d e s i g n e d f o r o p e r a t i o n b e t w e e n 0.01 a n d 0.10 s e c o n d s was employed. R e a c t o r e f f l u e n t i s quenched e i t h e r by d i r e c t i n j e c t i o n o f w a t e r o r s t e a m , o r by i n d i r e c t h e a t e x c h a n g e a g a i n s t w a t e r , d e p e n d i n g on t h e p a r t i c u l a r requirements. These f a c i l i t i e s not o n l y p e r m i t simu l a t i o n o f c o m m e r c i a l t r a n s f e r l i n e and q u e n c h



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technique, but a l s o permit study of the e f f e c t s of t r a n s f e r l i n e r e s i d e n c e t i m e on p r o d u c t y i e l d s . The q u e n c h e d g a s i s f u r t h e r c o o l e d t o room temperature with cold water. The c o n d e n s e d h e a v y h y d r o c a r b o n s and w a t e r a r e s e p a r a t e d from t h e gas i n t h e p r i m a r y receiver. The r e s u l t i n g g a s i s s u c c e s s i v e l y c o o l e d to 3 2 ° F (0°C) and 2 0 ° F ( - 6 . 7 ° C ) and a d d i t i o n a l l i q u i d hydrocarbons are separated i n these secondary and tertiary receivers. A l l l i q u i d p r o d u c t s are combined and s e n t t o a f l a s h drum f o r d e p r e s s u r i n g w h i c h r e s u l t s i n the s e p a r a t i o n o f a f l a s h gas which i s m e a s u r e d a n d a n a l y z e d by m a s s s p e c t r o m e t r y . Liquid p r o d u c t s a r e w i t h d r a w n f r o m t h i s drum and t h e o i l and w a t e r a r e s e p a r a t e d and w e i g h e d . At t h i s p o i n t the p r o d u c t gas c o n t a i n s e s s e n t i a l l y a l l t h e C 4 · s a n d l i g h t e r and m o s t o f t h e C 5 s . In o r d e r t o o b t a i n a g a s o l i n e p r o d u c t c o n t a i n i n g t h e C 5 s, as i s d o n e c o m m e r c i a l l y , t h e p r o d u c t g a s i s c o m p r e s s e d and t h e n f e d t o a d e b u t a n i z e r , w h e r e 9 5 % o f t h e C 5 s and h e a v i e r a r e f r a c t i o n a t e d o u t o f t h e g a s . In o r d e r t o a v o i d l o s s o f t h e l i g h t ends and C 4 s, t h e l i q u i d p r o d u c t from t h e d e b u t a n i z e r i s c o l l e c t e d i n a bomb a n d a d d e d t o t h e o t h e r l i q u i d p r o d u c t s d u r i n g f i n a l d e b u t a n i z a t i o n i n the l a b o r a t o r y . A p r o d u c t gas sample i s c o l l e c t e d t h r o u g h o u t the d u r a t i o n o f a r u n and t h i s c o m p o s i t e i s a n a l y z e d b y a mass s p e c t r o m e t e r . I n a d d i t i o n , a number o f o n - l i n e a n a l y t i c a l i n s t r u m e n t s have been p r o v i d e d f o r monitoring u n i t performance and p r o d u c t g a s c o m p o s i tion. A Beckman M o d e l A-3 d e n s i t y i n s t r u m e n t c o n t i n u o u s l y r e c o r d s t h e p r o d u c t gas d e n s i t y w h i c h , t o g e t h e r w i t h t h e gas measurement and l i q u i d h y d r o c a r b o n weight, e n a b l e s a m a t e r i a l b a l a n c e t o be d e v e l o p e d w i t h i n minutes a f t e r a run i s terminated. Since density ( c o m p o s i t i o n ) o f t h e p r o d u c t gas i s v e r y s e n s i t i v e t o o p e r a t i n g c o n d i t i o n s , i t i s i n v a l u a b l e i n r e l a t i n g the p e r f o r m a n c e o f t h e r e a c t o r and t h e s t e a d i n e s s o f a run. An o n - l i n e g a s c h r o m a t o g r a p h i s a l s o u s e d t o d e t e r m i n e t h e c o n c e n t r a t i o n s o f t h e more i m p o r t a n t c o m p o n e n t s s u c h a s H 2 , C H 4 , C 2 H 4 , and C 3 H 6 . These a n a l y s e s , i n c o n j u n c t i o n w i t h the p r o d u c t gas volume measurement, p e r m i t y i e l d s o f the major components t o be c a l c u l a t e d w i t h i n 30 m i n u t e s a f t e r c o m p l e t i o n o f a run. More i m p o r t a n t l y , t h e o n - l i n e i n s t r u m e n t p e r m i t s t h e e f f e c t o f r e a c t o r c o n d i t i o n s on p r o d u c t y i e l d s t o be s c r e e n e d r a p i d l y , a n d e n a b l e s t h e s e l e c t i o n o f reactor conditions required to achieve a p a r t i c u l a r product d i s t r i b u t i o n . C a l i b r a t e d s c a l e s and gas m e t e r s were employed 1

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t h r o u g h o u t t h i s work. Gas m o l e c u l a r w e i g h t s w e r e d e t e r m i n e d by d i r e c t m e a s u r e m e n t o n a d e n s i t o m e t e r , and b y c a l c u l a t i o n s b a s e d on m a s s s p e c t r o m e t e r a n a l y s e s . A r e v i e w o f 61 c o n s e c u t i v e r u n s showed an average m a t e r i a l b a l a n c e o f 99.6% w i t h a s t a n d a r d d e v i a t i o n o f ±1.2%. A f u r t h e r c h e c k on t h e r e l i a b i l i t y o f t h e m a t e r i a l b a l a n c e i s o b t a i n e d b y i n d i v i d u a l C and H b a l a n c e s w h i c h a r e b a s e d on a n a l y t i c a l C/H determinations. These comparisons are n o r m a l l y i n good a g r e e ment . A c c u r a c y w i t h w h i c h y i e l d s c a n be d e t e r m i n e d i s l a r g e l y a f u n c t i o n of the a n a l y t i c a l techniques employed. The a n a l y t i c a l s c h e m e i s shown i n F i g u r e 5. F i n a l y i e l d s o f g a s e o u s c o m p o n e n t s a r e b a s e d on m a s s s p e c t r o m e t e r a n a l y s e s w h i c h h a v e an a c c u r a c y o f ± 2 % r e l a t i v e t o t h e amount p r e s e n t f o r t h e m a j o r o l e f i n i c components. A l l l i q u i d p r o d u c t s a r e c o m b i n e d , and a f t e r comp l e t e water s e p a r a t i o n , the h y d r o c a r b o n p o r t i o n i s debutanized. The r e s u l t i n g s t a b i l i z e d l i q u i d i s f r a c t i o n a t e d i n t o two o v e r h e a d c u t s f o r a n a l y t i c a l e x p e diency. Y i e l d s o f i n d i v i d u a l components t h r o u g h the Cg a r o m a t i c s , as w e l l as f u e l o i l y i e l d s , c a n be d e termined quantitatively. In c e r t a i n s i t u a t i o n s , " s c r e e n i n g " o f o p e r a t i n g c o n d i t i o n s may be d e s i r e d b e f o r e " b a l a n c e r u n s " a r e made. T h i s i s a c c o m p l i s h e d by a l t e r i n g t h e p r o c e s s v a r i a b l e s and o b s e r v i n g t h e e f f e c t s o f t h e s e a l t e r a t i o n s on t h e g a s d e n s i t o m e t e r and t h e o n - l i n e p r o d u c t gas c h r o m a t o g r a p h , which c o n t i n u o u s l y m o n i t o r t h e reactor effluent. I t i s s i m p l e , f o r example, t o p r e s c r i b e a r e a s o n a b l e e t h y l e n e y i e l d and t a i l g a s ratio and l o c a t e t h e b e s t s e t o f p r o c e s s v a r i a b l e s t o g i v e these r e s u l t s . Maximizing y i e l d s or optimizing o p e r a t i n g c o n d i t i o n s , t h e r e f o r e , c a n r e a d i l y be a c c o m plished. Hundreds o f " b a l a n c e r u n s " and innumerable s c r e e n i n g r u n s h a v e b e e n made i n t h e p i l o t p l a n t on f e e d s r a n g i n g from ethane t h r o u g h heavy gas o i l . The r e s u l t s o f t h e most r e c e n t t e s t s a t h i g h s e v e r i t y were employed i n t h e d e s i g n o f the commercial Millisecond Furnace. Commercial M i l l i s e c o n d Furnace Working i n c l o s e c o o p e r a t i o n with Idemitsu P e t r o c h e m i c a l Company, K e l l o g g d e s i g n e d a p r o t o t y p e o f the M i l l i s e c o n d Furnace with a nominal ethylene c a p a c i t y 25,000 m e t r i c t o n s a y e a r . This furnace, shown i n F i g u r e 6, a l s o s e r v e d a s an e x p a n s i o n t o I d e m i t s u s No. 2 E t h y l e n e P l a n t a t T o k u y a m a , J a p a n . The v e r y s h o r t c o n t a c t t i m e s r e q u i r e d i n t h e M i l l i s e c o n d Furnace are o b t a i n e d through the use of 1


In Industrial and Laboratory Pyrolyses; Albright, L., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1976. DEBUT GAS

C?

DISTILLATION

Α. S. Τ. Μ.

DEBU TA NI Ζ Α ΤΙ Ο Ν

HYDRO CARBON^

WATER HYDROCARBON SEPARATION

WATER

MASS SPECTROMETRY THRU

£-T3 CHR OMA TO GRA ΡH Y (PROCESS) CH4-C2H4-C3H6

CHROMA TO GRA Ρ H Y c^a C5 SPLITS

Figure 5. Analytical scheme

Β A TCH FRACTIONATION

425 °F

CUTU2

CUT&I I. Β.Ρ ΤΟ 125 °F

PONA

BREAKDOWN

AROMATICS

5

FUEL OIL ASTM DIST\ °API SULFUR C/H HEAT OF\ COM BUSTION

SULFUR

GASOLINE °API ASTM OC TANE BROMINE& I C/H

GAS CHROMA TOGRA P.H Y C BREAKDOWN


ET

AL.



LECTIN

Figure 6. 25,000 MT/yr millisecond furnace



390

INDUSTRIAL AND LABORATORY PYROLYSES

small diameter tubes. These pass s t r a i g h t through t h e r a d i a n t s e c t i o n and a r e f i r e d from b o t h s i d e s by burners located i n the furnace arch. P r e h e a t e d p r o c e s s f e e d p l u s d i l u t i o n steam i s d i s t r i b u t e d u n i f o r m l y to t h e tubes through individual l e a d s and i s r a p i d l y h e a t e d t o r e a c t i o n temperation. The o l e f i n s - r i c h g a s p r o d u c e d t h e n e x i t s t h e r a d i a n t s e c t i o n f l o o r and i s immediately quenched t o h a l t t h e r e a c t i o n and f i x t h e p r o d u c t composition. C o m b u s t i o n f l u e g a s e s t r a v e l downward p a r a l l e l t o the tubes and pass t h r o u g h t u n n e l s a t t h e r a d i a n t s e c t i o n f l o o r i n t o t h e c o n v e c t i o n s e c t i o n where a h i g h l e v e l o f h e a t r e c o v e r y i s o b t a i n e d a s s u r i n g maximum f u e l e f f i c i e n c y and optimum o p e r a t i n g e c o n o m i c s . In t h e c o u r s e o f c o m m e r c i a l o p e r a t i o n s , e x t e n s i v e y i e l d d a t a were c o l l e c t e d on v a r i o u s l i q u i d f e e d s t o c k o p e r a t i o n s over t h e f u l l s h o r t r e s i d e n c e time range and v a r y i n g h y d r o c a r b o n p a r t i a l p r e s s u r e . Y i e l d s were d e t e r m i n e d i n t h e f i e l d by a s p e c i a l sample c o n d i t i o n i n g a n d a n a l y s i s s y s t e m (

Industrial and Laboratory Pyrolyses

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