New Calcining Technology of Petroleum Coke - ACS Symposium

13 New Calcining Technology of Petroleum Coke 1

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1

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M. Kakuta , H. Yamasaki , H. Tanaka , J. Sato , and K. Noguchi 1

Osaka Research Laboratory, Koa Oil Company, 2-1, Takasago, Takaishi-shi, Osaka 592, Japan Koa Oil Company, 6-2, Ohte-Machi 2-chome, Chiyoda-ku, Tokyo 100, Japan

Downloaded by CORNELL UNIV on July 27, 2016 | http://pubs.acs.org Publication Date: April 14, 1986 | doi: 10.1021/bk-1986-0303.ch013

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This technology concerns a new calcining method for reducing the thermal expansion coefficient of the coke at the calcining stage. The low thermal expansion coefficient is an important factor in determining the quality of calcined coke for the production of graphite electrodes. Whereas the traditional calcining method adopts a one stage process, the new calcining method adopts a two stage process. The experimental results indicate that the development of unique microcracks appears in the coke after the new calcination, regard less of the coke type, and these microcracks contribute to the effective reduction in the thermal expansion coefficient of the coke and the improvement of the puffing characteristics. The optimum process system of this new calcining technology has been studied by using a model calciner pilot plant.

High grade g r a p h i t e e l e c t r o d e s a r e r e q u i r e d t o accomodate t h e adopt i o n o f high-power (HP) and u l t r a - h i g h power (UHP) o p e r a t i o n s i n t h e e l e c t r o - a r c s t e e l i n d u s t r y . C a l c i n e d coke f o r a r t i f i c i a l g r a p h i t e e l e c t r o d e s r e q u i r e a h i g h q u a l i t y s t a n d a r d i n terms o f t h e v a r i o u s p r o p e r t i e s , e s p e c i a l l y a low t h e r m a l e x p a n s i o n c o e f f i c i e n t . The p r o c e s s o f c a l c i n i n g was n o r m a l l y c o n s i d e r e d as a h e a t t r e a t m e n t s t e p a t a temperature r a n g i n g from 1,300°C t o 1,400°C t o ensure t h a t t h e c a l c i n e d coke h a d t h e p r o p e r t i e s a p p r o p r i a t e f o r p r o d u c t i o n o f graphi t e e l e c t r o d e s . F u r t h e r m o r e , many b e l i e v e (1-5) t h a t t h e p r o p e r t i e s o f c a l c i n e d coke a r e h e a v i l y dependent upon t h e m a n u f a c t u r i n g c o n d i t i o n s o f t h e green coke. C o n s e q u e n t l y , v a r i o u s m a n u f a c t u r i n g methods d e v e l o p e d t o g a i n a low t h e r m a l e x p a n s i o n c o e f f i c i e n t c e n t e r e d on p r o d u c i n g a n e e d l e coke a t t h e c o k e r . Thus, new t e c h n o l o g i e s f o r t h e c a l c i n i n g p r o c e s s were p r i m a r i l y aimed a t i m p r o v i n g t h e e f f i c i e n c y and economy o f t h e o p e r a t i o n . Our a t t e n t i o n was f o c u s e d on t h e c a l c i n i n g p r o c e s s and upon i n v e s t i g a t i n g the s t r u c t u r a l changes o f green coke a s t h e y r e l a t e d t o t h e c a l c i n i n g c o n d i t i o n s and c h a r a c t e r i s t i c s o f c a l c i n e d coke (6,7). Then a new c a l c i n i n g method was developed which reduced t h e t h e r m a l e x p a n s i o n c o e f f i c i e n t o f c a l c i n e d coke, 0097-6156/86/0303-0179$06.00/0 © 1986 American Chemical Society

Bacha et al.; Petroleum-Derived Carbons ACS Symposium Series; American Chemical Society: Washington, DC, 1986.

180

PETROLEUM-DERIVED CARBONS

i r r e s p e c t i v e o f t h e t y p e s o f green coke t o be p r o c e s s e d , by a p p r o p r i a t e l y c o n t r o l l i n g t h e h e a t i n g p a t t e r n d u r i n g c a l c i n a t i o n (1,8). The new c a l c i n i n g p r o c e s s h a s been named t h e two-stage c a l c i n i n g p r o c e s s based on t h e p e c u l i a r method adopted. Experimental r e s u l t s i n d i c a t e t h a t unique m i c r o c r a c k s appear i n t h e coke a f t e r t h e new c a l c i n a t i o n and t h a t t h e s e m i c r o c r a c k s c o n t r i b u t e t o t h e e f f e c t i v e r e d u c t i o n i n t h e t h e r m a l e x p a n s i o n c o e f f i c i e n t o f t h e coke and t o t h e improvement o f t h e p u f f i n g c h a r a c t e r i s t i c s . T h i s paper i n c l u d e s an o u t l i n e o f t h i s new c a l c i n i n g method, r e s u l t s o f o b s e r v a t i o n s r e l a t e d t o t h e major causes o f a r e d u c t i o n o f t h e t h e r m a l e x p a n s i o n c o e f f i c i e n t and t h e s t u d y o f t h e optimum p r o c e s s system o f t h i s new c a l c i n i n g t e c h nology.


O u t l i n e o f New C a l c i n i n g

Technology

To e v a l u a t e t h e e f f e c t s o f t h e new c a l c i n i n g method, c a l c i n i n g t e s t s were conducted i n two d i f f e r e n t ways, namely, t h e new and t r a d i t i o n a l methods, by u t i l i z i n g t h e r o t a r y k i l n - t y p e e l e c t r i c f u r n a c e . As shown i n F i g u r e 1, t h e t r a d i t i o n a l c a l c i n i n g p r o c e s s i n v o l v e d a one s t a g e p r o c e s s i n t h e c a l c i n e r w i t h a peak temperature o f 1,300°C t o 1,400°C and, a f t e r m a i n t a i n i n g t h i s temperature f o r a w h i l e , c o o l i n g t o t h e room t e m p e r a t u r e . The new c a l c i n i n g p r o c e s s i s a two-stage p r o c e s s i n g i n which green coke i s c a l c i n e d i n i t i a l l y a t a temperature from 600°C t o 900°C, c o o l e d , and r e - c a l c i n e d a t a temperature o f about 1,300°C t o 1,400°C - t h e same l e v e l as t h e t r a d i t i o n a l method. Comparison o f C a l c i n i n g P r o c e s s :

New v s . T r a d i t i o n a l Methods

Materials To i d e n t i f y t h e d i f f e r e n c e s a r i s i n g from t h e new method, s i x d i f f e r e n t t y p e s o f green coke (samples A, B, C, D, Ε and F) were t e s t e d . P r o p e r t i e s o f t h e s e green cokes a r e g i v e n i n T a b l e I . From t h e s e p r o p e r t i e s and a l s o by m i c r o s c o p i c o b s e r v a t i o n r e s u l t s , Coke A was d e f i n e d a s low s u l f u r s t a n d a r d n e e d l e p e t r o l e u m c o k e , and Coke Β as p e t r o l e u m premium n e e d l e coke m a i n l y o f f i b r o u s t e x t u r e , Coke C o f h i g h s u l f u r c o n t e n t , Coke D o f h i g h a s h c o n t e n t , and coke Ε a s coke d e r i v e d from c o a l . Cokes C, D and Ε h a d mixed f i b r o u s and mosaic t e x t u r e s . Coke F h a d h i g h e r d e n s i t y , an e x t r e m e l y low r a t i o o f i m p u r i t i e s , and a good o r i e n t a t i o n o f t h e c r y s t a l l i t e . Coke F i s now produced by t h e l a b o r a t o r y c o k i n g a p p a r a t u s and has been g i v e n t h e name o f "Supreme Coke" (9-11).

T a b l e I . P r o p e r t i e s o f Green Cokes Sample Name V o l a t i l e Matter(wt%) Elemental A n a l y s i s C (wt%) H (wt%) Ν (wt%) S (wt%) Real Density(g/cm ) Ash (wt%) 3

Coke A

Coke C

Coke D

Coke Ε

8.2

Coke Β 7.6

10.6

16.1

7.8

4.0

93.5 3.4 1.6 0.48 1.39 0.08

93.8 3.3 1.1 0.73 1.39 0.05

89.0 3.2 1.1 5.7 1.38 0.08

92.0 4.2 1.3 0.36 1.35 1.22

94.6 2.8 0.8 0.29 1.41 0.11

95.2 3.3 0.2 0.14 1.42 0.00


Coke F


KAKUTA ET AL.

New Calcining Technology of Petroleum Coke

Time (Hr )

Traditional

Method

Time

New

(Hr)

Method

F i g u r e 1. S i m p l i f i e d c a l c i n a t i o n p r o f i l e . Reproduced w i t h p e r m i s s i o n from r e f e r e n c e 8b. C o p y r i g h t 1981 Pergamon P r e s s , I n c .


182


E x p e r i m e n t a l Techniques. The v o l a t i l e m a t t e r and ash o f t h e green cokes were measured by J I S (Japanese I n d u s t r i a l Standard) M 8812, and t h e s u l f u r was o b t a i n e d by J I S M 8813. The p r o p e r t i e s o f t h e c a l c i n e d coke samples were determined by measuring t h e t h e r m a l expan s i o n c o e f f i c i e n t , apparent d e n s i t y ( t e s t sample o f about 30 grams '3.5-4 T y l e r mesh' was measured by pycnometer method by d i s p l a c i n g w a t e r ) , and r e a l d e n s i t y (about 10 grams '200 T y l e r mesh under' o f t e s t sample was measured by pycnometer method by d i s p l a c i n g n - b u t y l a l c o h o l ) . P o r o s i t y was c a l c u l a t e d from v a l u e s o f t h e apparent and r e a l d e n s i t i e s . T e x t u r e and s t r u c t u r e o f coke samples were o b s e r v e d by p o l a r i z e d l i g h t m i c r o s c o p y and by s c a n n i n g e l e c t r o n m i c r o s c o p y . Green carbon b o d i e s were p r e p a r e d by m o l d i n g ( r o d ; 2x2x8 cm ) and by e x t r u s i o n ( r o d ; 2 cm d i a . and 11 cm l e n g t h ) from a m i x t u r e o f a p p r o p r i a t e l y s i z e d c a l c i n e d coke and c o a l t a r b i n d e r p i t c h . The rods were then baked a t a s l o w r a t e t o 1,000°C i n an e l e c t r i c f u r nace and k e p t a t t h i s temperature f o r an hour. The e x t r u d e d r o d s were f u r t h e r g r a p h i t i z e d a t 2,800°C f o r 0.5 h r . under an argon f l o w . The t h e r m a l e x p a n s i o n c o e f f i c i e n t was measured i n two d i r e c t i o n s - p e r p e n d i c u l a r t o t h e m o l d i n g d i r e c t i o n and p a r a l l e l t o t h e e x t r u d i n g d i r e c t i o n , and t h u s p a r a l l e l t o t h e coke p a r t i c l e a l i g n ment. T e s t p i e c e s were o b t a i n e d on c y l i n d e r s o f 5 mm d i a . and 50 mm l e n g t h c u t from r o d a f t e r h e a t i n g . Bending s t r e n g t h and Young's modulus o f the g r a p h i t i z e d r o d s were determined by J I S R 7202. The p u f f i n g c h a r a c t e r i s t i c was measured i n t h e d i r e c t i o n p a r a l l e l t o t h e m o l d i n g d i r e c t i o n , and t h u s p e r p e n d i c u l a r t o the coke p a r t i c l e a l i g n m e n t . Baked t e s t p i e c e s (1 i n c h d i a . and 1 i n c h l e n g t h ) were used f o r t h e p u f f i n g t e s t i n t h e h e a t t r e a t m e n t r a n g i n g from 100°C t o 2,800°C.


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P r o p e r t i e s o f C a l c i n e d Coke. T a b l e I I shows the p r o p e r t i e s o f c a l c i n e d cokes A, B, C, D and F by the new and t r a d i t i o n a l methods. R e g a r d l e s s o f t h e green coke t y p e , t h e t h e r m a l e x p a n s i o n c o e f f i c i e n t o f c a l c i n e d coke b y t h e new method was l o w e r than t h a t o f t r a d i t i o n a l c a l c i n a t i o n method. P o r o s i t y v a l u e s f o r c a l c i n e d cokes by t h e new method have a h i g h e r v a l u e , r e g a r d l e s s o f t h e coke t y p e , t h a n T a b l e I I . P r o p e r t i e s o f C a l c i n e d Cokes Sample Name Calcining Method CTE (xlO /°C) Real Density(g/cm ) Porosity (%)

Coke C Coke Β Coke A New Τ New τ New Τ 2.1 2.5 1.5 1.9 1.2 1.6 2.040 2.094 2.088 2.095 2.092 2.051 39.1 36.3 37.0 33.1 40.3 35.8

_6

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Coke Ε Sample Name Coke D C a l c i n i n g Method New τ New Τ 2~jT 274 CTE (xl0" /°C) ο7δ~ ΤΤϋ 2.142 Real Density(g/cm ) 2.092 2.082 2.146 33.8 31.8 Porosity (%) 43.6 41.4 Τ: Traditional CTE: Thermal e x p a n s i o n c o e f f i c i e n t (30°C-100°C). T e s t p i e c e s : Molded pieces(1,000°CHT, 5 mm d i a . χ 50 mm l e n g t h ) . 6

3


13.

K A K U T A ET AL.

those

processed

under

t r a d i t i o n a l method.

of

unique m i c r o c r a c k s w i t h i n coke

new m e t h o d ,

as

following

(This

of

cokes

A,

Β and F by

two

different

c a l c i n i n g methods

Table

III.

The t h e r m a l

expansion

coefficient

the

new m e t h o d

are

factured

the

i l l

by

effects

two on

characteristics cining

method

diameter two

(20

III)

.

actual

Table

after

IV

III.

This

manufacture

Properties

Name

of

Coke

Calcining

Method

New

of

Bulk

Density

Bending

(g/cm ) 3

Strength(kg/cm ) 2

Young's

Modulus

Dynamic

,

Puffing

(kg/mm ) 2

Fe 0

(%AL) α

Λ

τ

λ

2

0%

3

2

Table

IV.

Properties Sample

of

Calcining

graphite

actual

Coke

Bulk

CTE:

2

on the

2

pieces;

0.6 0.7 1.54 1.56 90 90 740 710 —

χ

50

—

—

Test

—

pieces;

length).

inches

dia.)

Β

0.4 1.65 145 1020 (30°C-100°C).

coefficient

5 mm d i a .

tional

New

mm

length.

New C a l c i n i n g T e c h n o l o g y

mechanisms clearly

(kg/mm )

Thermal expansion Test

Theory

3

F

Traditional

0.2 1.64 140 1120

(g/cm )

the

Tradi

Electrode(20

New

Method

Modulus

mm

Coke

Strength(kg/cm )

Young's

The

Coke

tional

50

by

electrodes.

Β

Shrink

Actual Graphite

Density

Bending

of

Tradi New

cal

large

Rods

ÔT8

6

new of

effect

Extruded Graphite

(xlO~ /°C)

showed

cokes

of

Name

CTE

been

from the the

mm d i a .χ

Extruded pieces

the

indicates

tional

no manu

Puffing

properties

F ae n0s3i o n 1% c o e f f i c i e n t Thermal exp

CTE:

in pieces

showed

new m e t h o d

improved by the

A

calcined

experimentally

1.2 1.0 1.53 1.52 1.52 110 115 105 740 810 740 0.81 0.49 1.13 0.50(30°C - 300°C). 0.16 (2,800°CHT 5

6

the the

shown

electrodes.

obtained

1.0 1.52 115 790 0.45 0.22

(xlO" /°C)

from

are

strengths,

Tradi CTE

to

graphitized

Thus the

shows

electrodes

the

of

on

strengths

Table

obtained

c a l c i n e d coke

methods.

c a l c i n i n g methods.

even

Sample

results

the

mechanical

rods

d u r i n g g r a p h i t i z a t i o n were

inches)

new m e t h o d ,

graphite

Test

between

different

the

(Table

different

extruded

lower.

difference

due

under

mention.)

properties

significant

is

processed

The

no


the

development

by

183


of

the

new c a l c i n i n g t e c h n o l o g y

elucidated through

of

the

effect

the

following

experimental

have

study.

Materials As

starting materials,

and

D)

were

are

shown

used

for

i n Table

Experimental

four

the

different

testing.

types

of

Properties

green of

coke

these

(A,

test

I.

Techniques.

Distribution of .

pore

size

was


B,

C

samples

184



d e t e r m i n e d by t h e mercury p o r o s i m e t e r . I n t e r l a y e r s p a c i n g s and ap p a r e n t c r y s t a l l i n e s i z e s were o b t a i n e d by X-ray d i f f r a c t i o n method ( 6 ) . T e s t p i e c e s were p r e p a r e d from green cokes A and Β by c u t t i n g them i n t o specimens o f 5 mm χ 5 mm χ 50 mm. D i m e n s i o n a l changes d u r i n g c a l c i n a t i o n were o b t a i n e d by a d i f f e r e n t i a l d i l a t o m e t e r u s i n g q u a r t z as t h e s t a n d a r d m a t e r i a l . The h e a t i n g r a t e s were lO°C/min up t o d e s i g n a t e d temperature under an argon gas atmosphere. T h e o r e t i c a l E x p l a n a t i o n . The major f a c t o r s o f t h e t h e r m a l e x p a n s i o n c o e f f i c i e n t o f c a l c i n e d coke a r e t h e degree o f p r e f e r r e d o r i e n t a t i o n o f t h e c r y s t a l l i t e s and v o i d s t r u c t u r e (12-14). F o r example, t h e t h e r m a l e x p a n s i o n c o e f f i c i e n t i s l o w f o r n e e d l e coke because i t i s s t r o n g l y a f f e c t e d by t h e p r e f e r r e d o r i e n t a t i o n o f i t s c r y s t a l l i t e s . We found t h e l a t t e r f a c t o r - v o i d s t o be i m p o r t a n t . E x p e r i m e n t a l r e s u l t s showed t h a t when green coke was c a l c i n e d under t h e new methods, and t h e d e r i v e d c a l c i n e d coke was o b s e r v e d by s c a n n i n g e l e c t r o n m i c r o s c o p y ( F i g u r e 2) and i t s pore s i z e d i s t r i b u t i o n was measured by mercury p o r o s i m e t r y ( F i g u r e 3 ) , m i c r o c r a c k s o f s i g n i f i c a n t s i z e s (1 t o 60 microns) were d e v e l o p e d . T h i s was an i m p o r t a n t c o n t r i b u t i o n t o the r e d u c t i o n o f t h e t h e r m a l e x p a n s i o n c o e f f i c i e n t s o f t h e c a l c i n e d coke p r o c e s s e d under t h e new method. D i m e n s i o n a l changes o f green coke d u r i n g c a l c i n a t i o n were meas u r e d between each h e a t t r e a t m e n t , u t i l i z i n g h e a t i n g p a t t e r n s o f t h e new and t r a d i t i o n a l c a l c i n i n g p r o c e s s e s . An example o f such measure ments on Coke A and Β i s g i v e n i n F i g u r e s 4 and 5. W h i l e coke mate r i a l c o n t i n u e d t o expand u n t i l i t reached about 600°C, q u i c k c o n t r a c t i o n s s t a r t e d a t t e m p e r a t u r e s above 600°C ( 1 5 ) . S p e c i f i c a l l y , under t h e new c a l c i n i n g method a c o n s i d e r a b l e c o n t r a c t i o n was observed d u r i n g t h e peak temperature p e r i o d o f t h e p r i m a r y p r o c e s s i n g , f o l lowed by some c o n t r a c t i o n d u r i n g t h e c o o l i n g stage o f t h e p r i m a r y p r o c e s s i n g . D u r i n g t h e secondary p r o c e s s i n g , a s l i g h t e x p a n s i o n was o b s e r v e d d u r i n g h e a t i n g , f o l l o w e d by a c o n t r a c t i o n up t o t h e f i n a l c a l c i n i n g t e m p e r a t u r e . On t h e o t h e r hand, d i m e n s i o n a l changes ob s e r v e d on coke p r o c e s s e d under t h e t r a d i t i o n a l c a l c i n i n g method i n d i c a t e d c o n t r a c t i o n from 600°C t o t h e f i n a l c a l c i n i n g t e m p e r a t u r e , showing t h a t t h e p r o c e s s o f d i m e n s i o n a l changes d i f f e r s between t h e new and t r a d i t i o n a l c a l c i n i n g p r o c e s s e s . These f a c t s i n d i c a t e t h a t development and i n c r e a s e o f m i c r o c r a c k s under t h e new c a l c i n i n g method was d e r i v e d from s p e c i a l d i s t r i b u t i o n o f s t r e s s w i t h i n t h e coke caused by t h e e x p a n s i o n and c o n t r a c t i o n d u r i n g t h i s h e a t t r e a t ment p a t t e r n . T a b l e V shows t h e X-ray parameters o b t a i n e d from t h e cokes b y two d i f f e r e n t c a l c i n i n g methods. X-ray d i f f r a c t o m e t r y o f i n t e r l a y e r s p a c i n g ( d o o 2 ) and apparent c r y s t a l l i n e s i z e (Lc) i n d i c a t e d no p a r t i c u l a r d i f f e r e n c e between cokes p r o c e s s e d under t h e two methods. F u r t h e r m o r e , no s p e c i f i c d i f f e r e n c e s were found on t h e s e samples a f t e r g r a p h i t i z a t i o n . These f a c t s show t h a t t h e new c a l c i n i n g method would n o t l e a d t o adverse e f f e c t s on t h e development and r e a r r a n g e ment o f coke c r y s t a l l i n e s . From t h e s t u d y o f t h e new c a l c i n i n g method, t h e f o l l o w i n g f a c t s were r e v e a l e d ( 1 6 ) : 1. D u r i n g t h e p r i m a r y p r o c e s s i n g , t h e t h e r m a l e x p a n s i o n c o e f f i c i e n t o f c a l c i n e d coke changes, and t h a t t r e a t m e n t a t t h e range o f 700°C t o 900°C i s e f f e c t i v e .




KAKUTA ET AL.

F i g u r e 2.

Scanning e l e c t r o n micrographs o f t h e c a l c i n e d c o k e s . A - l ; Coke A ( t r a d i t i o n a l method). A-2; Coke A (new method).

Reproduced w i t h p e r m i s s i o n from r e f e r e n c e 8 b . C o p y r i g h t 1981 Pergamon P r e s s , I n c .




F i g u r e 2.

Scanning e l e c t r o n micrographs of the c a l c i n e d cokes. B - l ; Coke Β ( t r a d i t i o n a l method). B-2; Coke Β (new method). Reproduced w i t h p e r m i s s i o n from r e f e r e n c e 8b. C o p y r i g h t 1981 Pergamon P r e s s , I n c .




KAKUTA ET AL.



188

Temperature (X10°C) 20 40 60 80 100 120 140 2.0 1.0 0

2.0 1.0

π

0

-1.0


1

1 ι *C

[ τ

-1.0

y,

g-2.0

\

Temperature (X10°C) 20 40 60 80 100 120 140

§-2.0

V.

1

\ Wx

\

-4.0

WW

ί

ης

-

Coke A •A—

\

Traditional Method New Method

:

Coke Β --·--

-6.0 -7.0

Traditional Method

-8.0 -9.0

New Method

-10.0

F i g u r e 4. D i m e n s i o n a l changes o f coke d u r i n g c a l c i n a t i o n . Reproduced w i t h p e r m i s s i o n from r e f e r e n c e 8 b . C o p y r i g h t 1981 Pergamon P r e s s , I n c . Temperatature( C )

200

400 600 800

Tempe ratature(°C)

-4.78r

200

400 600 800

Γ

Coke A

F i g u r e 5. D i m e n s i o n a l changes o f coke d u r i n g c o o l i n g p r o c e s s o f p r i m a r y s t e p and h e a t i n g p r o c e s s o f secondary s t e p under new c a l c i n i n g process. Reproduced w i t h p e r m i s s i o n from r e f e r e n c e 8 b . C o p y r i g h t 1981 Pergamon P r e s s , I n c .


13.

KAKUTA ET AL. T a b l e V.


189

Comparison o f X-Ray Parameters O b t a i n e d from t h e Coke M a n u f a c t u r e d by t h e Two D i f f e r e n t Methods

Sample Name Calcining Method C a l c i n e d Coke d o o 2 (A) Le (A)

Coke A Coke Β Coke C Coke D TradiTradiTradiTradiNew t i o n a l New t i o n a l New t i o n a l New t i o n a l 3.444 3.440 3.447 3.446 3.447 3.446 3.442 3.440 38 40 38 40 42 41 38 40

G r a p h i t i z e d Coke d o o (A) 3.366 3.366 3.365 3.364 3.365 3.365 3.366 3.366 Le (Â) 840 880 1000 1000 460 460 810 740 Reproduced with permission from reference 8b. Downloaded by CORNELL UNIV on July 27, 2016 | http://pubs.acs.org Publication Date: April 14, 1986 | doi: 10.1021/bk-1986-0303.ch013

2

2. A f t e r t h e c o m p l e t i o n o f t h e p r i m a r y p r o c e s s i n g , t h e coke must be c o o l e d t o room t e m p e r a t u r e . No s i g n i f i c a n t e f f e c t s r e s u l t from c o n t i n u e d c a l c i n i n g p r o c e s s from t h e p r i m a r y t o secondary p r o c e s s i n g w i t h o u t t h i s c o o l i n g . Thermal e x p a n s i o n i s n o t a f f e c t e d by a change o f c o o l i n g r a t e i n t h e new c a l c i n i n g p r o c e s s . 3. Thermal e x p a n s i o n c o e f f i c i e n t o f c a l c i n i n g coke w i l l remain a l m o s t unchanged even i f t h e p r i m a r y p r o c e s s i n g i s r e p e a t e d . A l though t h e e f f e c t s o f t h e atmosphere and h e a t i n g r a t e d u r i n g c a l c i n a t i o n on the d e n s i t y o f c a l c i n e d coke can be r e c o g n i z e d , t h e e f f e c t s on t h e t h e r m a l e x p a n s i o n c o e f f i c i e n t were m i n i m a l ( 1 ) . Study on t h e optimum P r o c e s s System A commercial s c a l e two-stage c o n t i n u o u s c a l c i n i n g p r o c e s s h a s been c o n c e p t u a l l y d e s i g n e d and a model c a l c i n e r p i l o t p l a n t has been i n s t a l l e d . T h i s p i l o t p l a n t c o n s i s t s o f f i r s t s t a g e and second s t a g e r o t a r y k i l n s . F i g u r e 6 shows t h e p i l o t p l a n t (300 mm i n s i d e d i a . χ 3500 mm l e n g t h , and coke f e e d r a t e o f 20 kg/H). T h i s model c a l c i n e r i s d e s i g n e d t o e s t a b l i s h t h e optimum c a l c i n i n g c o n d i t i o n s and e q u i p ment c o n f i g u r a t i o n f o r economic c o n t i n u o u s p r o d u c t i o n o f two-stage c a l c i n e d coke and t o o b t a i n b a s i c d e s i g n and e n g i n e e r i n g d a t a f o r a commercial c a l c i n e r (17 ,18). P a r t i c u l a r a t t e n t i o n , i n t h e d e s i g n o f t h i s model c a l c i n e r , was g i v e n t o t h e u t i l i z a t i o n o f combustion h e a t o f v o l a t i l e m a t t e r e m i t ted from t h e coke f e e d and t o o b t a i n i n g an a c c u r a t e h e a t b a l a n c e d a t a f o r t h e two-stage c a l c i n i n g system. T e s t r e s u l t s o b t a i n e d t h r o u g h t h e o p e r a t i o n o f t h i s model c a l c i n e r p i l o t p l a n t a r e summarized as f o l l o w s . The exhaust gas from f i r s t s t a g e k i l n c o n t a i n s c o m b u s t i b l e gases (H , C H i * and C O ) and i t has an approximate c a l o r i f i c v a l u e o f 640 k c a l / m ( 0 ° C , 1 atm). F i g u r e 7 shows a s c h e m a t i c diagram o f the model c a l c i n e r used f o r s t u d y i n g an economic c o n t i n u o u s two-stage c a l c i n i n g system. The exhaust gas from f i r s t s t a g e k i l n i s f e d as f u e l f o r second s t a g e kiln. The o p e r a t i o n o f t h i s two-stage c a l c i n i n g system i n d i c a t e d t h a t the exhaust gas from f i r s t s t a g e k i l n , w i t h a u x i l i a r y f u e l b u r n i n g , c o u l d be u t i l i z e d as f u e l f o r second s t a g e k i l n and t h e combustion of t h e exhaust gas i n second s t a g e k i l n d i d n o t cause any d i f f i c u l t i e s i n m a i n t a i n i n g a s t a b l e o p e r a t i o n o f second s t a g e c a l c i n a t i o n . 2

3



F i g u r e 6.

Photograph o f model c a l c i n e r .


Ο Ζ ™

CO

D m < m D η >

ι

c

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T3

1

13.

KAKUTA ET AL.

191


Raw Coke

Fuel(Auxiliary)

fil

Fuel

to Atmosphere

Exhaust Gas 1st

Stage

2nd

Stage

Calcined Coke


Figure 7.

Schematic diagram o f two-stage c a l c i n i n g system.

T a b l e V I summarizes a t y p i c a l h e a t b a l a n c e i n second s t a g e o f the above c a l c i n i n g system (Case A) i n comparison w i t h t h a t o f an a l t e r n a t i v e system (Case B) i n which t h e exhaust gas from f i r s t s t a g e k i l n i s n o t u t i l i z e d f o r second s t a g e c a l c i n a t i o n . The amount, com p o s i t i o n and temperature o f t h e exhaust gas from f i r s t s t a g e k i l n determine t h e a u x i l i a r y f u e l r e q u i r e m e n t s f o r second s t a g e k i l n . By t h e u t i l i z a t i o n o f combustion h e a t o f v o l a t i l e m a t t e r e m i t t e d from t h e coke f e e d , t h e c a l c i n i n g p r o c e s s c a p a b l e o f economic produc t i o n o f two-stage c a l c i n e d coke can be d e s i g n e d .

Table V I . (Unit:

Heat B a l a n c e o f Model C a l c i n e r

(Second Stage)

k c a l / h r . - c a l c i n e d coke o f 1 kg) Case A

I n p u t Heat Combustion Heat o f F u e l Combustion Heat o f 1 s t . Stage Exhaust Gas Combustion Heat o f Coke & VM S e n s i b l e Heat o f Coke & A i r ( T o t a l I n p u t Heat) Output Heat S e n s i b l e Heat o f Coke S e n s i b l e Heat o f F l u e Gas D e c o m p o s i t i o n & V a p o r i z a t i o n Heat o f VM Heat Loss ( T o t a l Output Heat) VM: V o l a t i l e M a t t e r

Case Β

512 667 675 18 1,872

1,024

513 786 10 563 1,872

513 658 10 508 1,689

-6 5 5 10 1,689

Conclusion A p p l i c a t i o n o f t h e new c a l c i n i n g t e c h n o l o g y reduces t h e t h e r m a l e x p a n s i o n c o e f f i c i e n t , r e g a r d l e s s o f t h e t y p e s o f green coke. Major cause f o r r e d u c t i o n o f t h e t h e r m a l e x p a n s i o n c o e f f i c i e n t and improve ment o f t h e p u f f i n g c h a r a c t e r i s t i c s i s t h e development o f unique m i c r o c r a c k s (1 t o 6 0 ym) w i t h i n p r o c e s s e d coke. These m i c r o c r a c k s f u n c t i o n as v o i d s t o absorb and r e l a x t h e e x p a n s i o n o f c r y s t a l l i t e s . Development o f m i c r o c r a c k s under t h e new c a l c i n i n g p r o c e s s seems t o have been caused by s p e c i f i c d i s t r i b u t i o n o f s t r e s s w i t h i n t h e coke a r i s i n g from s i g n i f i c a n t e x p a n s i o n and c o n t r a c t i o n f o l l o w i n g t h e h e a t treatment p a t t e r n s .


192



These microcracks may have some e f f e c t i n terms of mechanical strength when these cokes are processed into a r t i f i c i a l graphite electrodes. However, no s i g n i f i c a n t difference i n strength between graphitized t e s t pieces obtained from actual electrodes under the new and t r a d i t i o n a l method w a s found. An optimum commercial new process system has been studied by using a model c a l c i n e r p i l o t plant. By using two commercial plants conventionally, the t r i a l pro duction of two-stage calcined coke has been c a r r i e d out and calcined coke samples have been d i s t r i b u t e d to the graphite electrode manu facturing companies for t h e i r evaluation. Acknowledgments The authors wish to thank people of Koa O i l Company Marifu Refinery and Osaka Research Laboratory for t h e i r assistance.

Literature Cited 1. 2. 3. 4. 5. 6. 7. 8.

9. 10. 11. 12. 13. 14. 15. 16. 17. 18.

Yoshimura, K. U.S. Patent 4 100 265, 1978. Thomas, R. Hydrocarbon Proc. 1975, June, P97. Mantell, C.L. "Carbon and Graphite Handbook" Interscience Publ. Kurami, E. J . Japan Petrol. Inst. 1973, 16, (5), 366. Shea, F.L. U.S. Patent 2 775 549, 1956. and Hackley, R.C. U.S. Patent 2 922 755, 1960. Kakuta, M.; Kohriki, M.; Tano, T.; Sanada, Y. Tanso 1979, No. 95, 135. Kakuta, M.; Tanaka, H. 3rd International Carbon Conf. Baden– Baden, Preprints, 1980, P406. a. Noguchi, Κ.; Kakuta, M.; Tanaka, H.; Sato, J . 3rd Interna tional Carbon Conf. Baden-Baden, Preprints, 1980, P401. b. Kakuta, M.; Tanaka, H.; Sato, J.; Noguchi, K. Carbon 1981, 19, (5), 347-52. Kakuta, M.; Kohriki, M.; Sanada, Y. J . Materials Sci. 1980, 15, 1671. Kakuta, M. International Symp. on Carbon, Toyohashi, Japan, Preprints 1982, P527. Kakuta, M.; Tsuchiya, N.; Tanaka, H.; Noguchi, K. Sixth London International Carbon and Graphite Conf., London, Preprints, 1982, P10. Mrozowski, S. Proc. 1st and 2nd Carbon Conf., Pergamon Press 1956, P31. Collins, F.M. Proc. 1st and 2nd Carbon Conf., Pergamon Press 1956, P177. Okada, J . Proc. 4th Carbon Conf., Pergamon Press 1960, P547 and P553. Wallouch, R.W.; Fair, F.V. Carbon 1980, 18, (2), 147-53. Kakuta, M. 117 Committee of the Japan Sec. for Promotion of Science, 1979, No. 153. Noguchi, K.; Komi, N. U.S. Patent 4 169 767, 1979. Noguchi, K.; Komi, N. U.S. Patent 4 265 710, 1981.

RECEIVED December 18, 1985


New Calcining Technology of Petroleum Coke - ACS Symposium

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