Delayed-Coking Process Update - ACS Publications - American

11

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Delayed-Coking Process Update Robert DeBiase, John D. Elliott, and ThomasE.Hartnett Foster Wheeler Energy Corporation, 110 South Orange Avenue, Livingston, NJ 07039

Important recent trends and new developments have contributed to profitable, reliable, and safe operation of delayed cokers. A typical delayed coker consists of four sections: coking, fractionation, coker blowdown, and coke dewatering and handling. The main types of coke dewatering and handling systems are described as pit, pad, railcar, and dewatering bin. General coke types, feedstock considerations, pretreatment and process variables are reviewed with emphasis on recent trends towards minimizing production of fuel grade coke from heavy feedstocks. Typical uses of petroleum coke are discussed, including those for fuel grade coke. Trends and developments on the design of modern delayed cokers include improved heater design, larger coke drums designed for longer life at short operating cycles, extended range hydraulic decoking systems, enclosed blowdown systems and improved energy efficiency. Older delayed cokers can be revamped in a number of ways to increase capacity and improve the yield of desirable products. Delayed c o k i n g i s a p r o c e s s i n g t e c h n o l o g y t h a t has been i n use f o r o v e r f i v e decades. D u r i n g t h i s time, i t has come i n t o widespread use as an economic means f o r u p g r a d i n g heavy c r u d e s , r e s i d u e s , t a r s and decant o i l s t o produce gas, g a s o l i n e , gas o i l and coke. It is seen as an a t t r a c t i v e r e s i d u e u p g r a d i n g p r o c e s s because o f i t s moderate c a p i t a l investment and i t s a b i l i t y as a s i n g l e u n i t , t o p r o c e s s a wide v a r i e t y o f f e e d s t o c k s . As more and more d e l a y e d c o k e r s are b u i l t , new t e c h n o l o g y i s b e i n g developed t o c r e a t e a more p r o f i t a b l e , r e l i a b l e and s a f e o p e r a t i o n . T h i s paper w i l l b r i e f l y r e v i e w the b a s i c a s p e c t s o f d e l a y e d c o k i n g and d i s c u s s r e c e n t t r e n d s and new developments. In d e l a y e d c o k i n g , a r e s i d u a l f e e d s t o c k i s charged t o a f u r n a c e where i t i s r a p i d l y heated and t h e r m a l l y decomposed. The h e a t e r e f f l u e n t then e n t e r s a coke drum where the r e a c t i o n i s 0097-6156/86/0303-0155$06.00/0 © 1986 American Chemical Society

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

156

PETROLEUM-DERIVED CARBONS

completed process

and p e t r o l e u m

mechanism Partial

(1)

it

through

(2)

Cracking of

(3)

Successive liquid

The

coke

applications valuable

coke

and overhead

delayed

coking

vaporization

passes

vapor


for

the

and m i l d

the

vapors

as

are

follows

vapor in

formed.

The

(1_) :

cracking of

the

feed

as

furnace. as

it

passes

through

c r a c k i n g and p o l y m e r i z a t i o n

trapped and

is

the

drum u n t i l

it

of

is

the the

drum. heavy

converted

to

coke.

produced

is

described

feedstocks

mostly

below.

for

elemental

The

carbon

gaseous

downstream

and

processing

and

is

liquid or

used

in

products

sometimes

are

used

as

products. Unit

Description

A typical blowdown is

either

sent

for

vapor

in

and

either is

in

hot

together

to

the

surge.

In

the

the

condensed

the

coker

coking

two

of

the

removed.

to

the

are

the

coker

or

may

gas be

centralized

processing

the

The

unit

the The

where

it

or

are

being and

a pilot

one

cutting

for

in

of

The

with

coke

is

pumped

desired the

coke

the

of

and

drum

coke

the

the

over-

A minimum service

coke

falls

to

coking

coking

coking

The

separation

combines

steaming

through tool.

is

feed

drum and

the

feed

for

section.

After

flanges

tool.

facilities

the

drum i s

bored

the

enters storage.

The

used

feed

drum where

decoked. is

is

of

coke

from

unit.

to

in

the

charge

fractionation

lower

hole

coke

remains

a hydraulic boring

hydraulic

dewatering

the

required, is

upper

and

the

coke

to

heater

diagram equipment

feedstock

cold

coker

r a p i d l y heated

to

The

directed drum

resulting

is

flowing

delayed

flow

heater,

equipment.

the

Next, a

a

The major

fractionator

the

out

to

and

Coker

unit

process

sections.

of

drums

water

with

simplified

bottom recycle.

pressure

gases,

which

other

coke,

other

the

are

coke the

recovery

fractionator

completed.

of

vapor

of

before

while

fractionation

facilities.

within

reaction

vapors

coking,

bottom

temperature head

a

section

an upstream

heater is

1 is

fractionation

preheated

charged

of

handling

with

hydraulic decoking

from

often

coke

a dedicated

Figure and

the

the

consists

with

unit.

coking

included drums

unit

along

processing,

Section.

typical

coker

processed

recovery

Coking

It

delayed sections,

cooling are

using is

high

then

from

the

coke

from

cut

drum the

water. Fractionation the

coker

light coke

gas

wash

are

side

located

reflux the

vapors

is

A typical

as

from

vapors

enter

below

the

vapors.

and

the

wash

The

light

a

are

wash to

The

light

to

gas gas

stripper.

partially

directed

the

Hot

condense

o i l oil The

The

shed

trays

induced

recycle

condensed vapor

the

system.

under

trays.

includes

equipment,

overhead

and heavy

sidestream are

the

section

exchange

fractionator

trays

products. in

fractionator

products

heat

conventional

to

stripped

the

fractionation

attendant stripper

sidestream

steam

gasoline

and

stream

pumped

product

condensed usually and

oil

drum o v e r h e a d

which oil

Section.

fractionator

gas

and

products product

to are

is

overhead and

recovery

the

gas

unit.


DEBIASE ET AL.

Delayed-Coking Process update


11.

157

u & -H

Q :? ο

.H (A

ω ω υ ο u β* u ω

8

M

Ό" ω fd •Η

ω Ω ι—I

(ϋ υ

-Η

ω CP •Η



158 A portion reflux. battery Coker

This

coking by

stripped


steam,

drum where coker drum

and

settling to

settling

Coke

the

gas

be

coke

accomplish loading.

and

pit

through

a

storage. remaining coke

the

pit

drums.

coke

the

The

with

makes

it

must

into

the

a

large through

settle

to

an o v e r h e a d especially

in

Wheeler coke

is

coke

that

which

filled

loader.

dewatering

Direct in

coke the

with

the to

from to

the

a

small

blowdown facilities

slop the

the

to

to

blowdown

for

blowdown

coker

the

fuel

or

gas

recovered

by

a

coke

and

drum i s

separated.

used

today

being To

include

and d i r e c t

pit

railcar

follows.

the

coke

the

bottom.

into

The

for

drop

from

provides Coke

units this

coke

drum,

days

of

a maze where

large

A typical

the

several is

removed

storage

with

four

approach

pit

any from

capacity or

more

i n many

dewatering

of

coke

of

system

the is

through

fines

Coke

is

that

the

coke

has from

a

coke

storage

pad d e w a t e r i n g

level

a

grade

in

a

by

the

pad w i t h

capacity is

is

pad. pad

maze.

Foster by a

investment

The drawbacks

major

the

decoking water

capital

operation

in

settling

developed

from

lower

The

fines

the

dewatering.

dewatering. onto

packed ports

been

removed

offers pit

pit drop

remaining

system

coke

than

to

of

use

of

front-end and pad

limited

by

illustrated

in

plot

4.

Figure the

circulating

coker

flared

bin,

which

similar

c l a r i f i e d of

removes

are

When

and water

drains

baskets.

A typical

is

filtering

operation

c a n be

implemented

coke

Pad d e w a t e r i n g

simpler area.

the

water

then

a

the

3.

dewatering

fines

by

from

blowdown

treating

sent

then

resultant

coker

goes

back

and

each

suited

depicted

and

and

pumped b a c k the

oil

sent

crane.

cokers.

A new

the

offsite

and water

pit

has

wall

the

in

commonly

of

Wheeler

Traditionally,

of

collected

coke

delayed

is

out

along

dewatering

built type

and

be

Foster

Pad

with

to

and

switched

hydrocarbons

separated the

vapors

description

Figure

the

remaining vapors

recently

difference

as to

blowdown

control

condenser

to

treated

coker

steamed

are

top

are

while

facilities

fines

pit

sent

a drum i s

condensed

Handling System.

Water d r a i n s

the

tower

compressor.

dewatering,

chute,

the

and h y d r o c a r b o n

flow

the

going

tank,

pad dewatering,

A short

In

is

time,

together

blowdown

these

and water

this,

dewatering,

the

drum o r

recovery

After

steam

are

leaves

compressed

overhead

Dewatering

emptied,

to

drum i s

pollution

hydrocarbons

water

Alternatively,

flare

The

and water

recovery.

d r u m may

system.

Steam

with

typical

coke

operations

heavy in

a

this

directed,

hydrocarbons

These

decoking water

fractionator

overhead

both

the

During

system.

The o i l

and

for

service, are

condensed

drum,

the

pumped b a c k

the

hydrocarbons.

cycle

heavy

o i l .

dewatering

a

coke

cooling

the

is

of

of

blowdown

stream.

is

in

2 shows

utilized

injection.

fractionator.

amount

Figure

is

decoking the

the and

oil

System.

to

gasoline

collected

treating.

recovery

from

steamout gas

for

water

to

water

system

increased

from

condensed

sour

Blowdown

cooled

or

the

limits

system. for

of The

railcar

drum i n t o

railcar.

loading a

allows

railcar.

Water d r a i n s

Coke from

the

coke

to

drop d i r e c t l y

and m a j o r i t y the

railcar

to

of a

fines sump

from

remain and


is

DEBIASE ET AL.

Delayed-Coking Process Update


11.


159

160


then

pumped

to

investment, allow

for

small

coke

Figure

a

but

clarifier. requires

r a i l c a r movement. drums.

or

from

by

flow

system,

and c r u s h e r

an

system

directly are

separated is

the

drained

is

capital

drum

to

units

with

system

is

shown

in

bin

is

bin.

slurry, system

gravity requires

transport

the

a

Types

Petroleum

Figures

The

three

are

typically

Needle

main

coke

specialty

Needle

graphite Sponge

is

contains

in

totally with

of

the

capital

investment

gravity

However,

the

and slurry

circulated flow

for

discharged

areas

systems,

coke,

each

type

Usually

are

of

produced

or

decanted

by

a

oil

fibrous

coke.

This

carbon

coke

produced

coke,

to

systems

are

coke

a delayed coke

and

considered aromatic

and

shot

coker

shot

coke.

a

feedstocks.

coke.

A

short

follows.

from

texture of

industry

is

specific

highly

stocks.

form

in

sponge

which

from

This

coke

Coke. as in

pores

be

is

of

aromatic

This

with

coke

for

coke

from

high

with

no

"honeycomb"

with to

coke

type

produced

light

coke

or

are

needle

sponge

small

from

formed

that

as

coke

Coke.

metals

coke

produced

the

is

and

tank

long,

is

use

coke

in

is

thermal

tar,

typically

unidirectional

a premium p r o d u c t , the

manufacture

which

of

large

electrodes.

and

Sponge

of

is

of

a water

drawback

water

and

settle

respectively.

7,

a premium grade

of

to

coke

and g r a v i t y

of

tar

to

and

of

flow

and

characterized sold

amount

to

a

bin.

coke

developed

largest two

the

the

expensive.

grades

Coke.

"needles"

more

the

coke In

dewatering

desirable

the

the

located

allowed

has

gravity

Coke

types

coke

description

6

is

gravity

a

bin.

sump

the

The main

Of

slurry

categorized

is

regular

pyrolysis

The

to

a

water

by

In

Wheeler,

drum where

complete,

requires

the

from

Wheeler

and

dewatering

coke

especially

substantial

in

of

is

coke.

depicted

is

coke

either bin.

drum and d i r e c t e d

facilities.

flow

Foster the

pumped

regulations. it

by of

The

Foster

are

that

dewatering

the

the

then,

a dewatering

crusher

gravity.

which

and

vertical

dewatering

environmental

all

highly

lowest

coke to

i n which

top

coke

from

When

systems

a

by

dewatering

dewatering

coke

on

large

anode

the

the

limited

loading

developed

mounted

crushed

to

drum and

strict

Shot

directed

is

vary

usually

one

coke

coke

offers

decoke

crusher

the

enclosed

is

are

are

the

is a

bin

water

The

system

below

from

to

railcar

drum i n t o

innovation

clarification.

of

is

dewatering

water the

bin

coke

s l u r r y pump,

slurry


the

drum

The

It

A direct

system

time

5.

A dewatering fall

This

extra

low

sulfur

used

in

Another small large

dependent

form,

spheres spheres upon

considered

varieties and

ash

a

form

asphaltene

as

low

generally

often

held

to

of

regular

feeds.

Sponge

heavy

contents

aluminum

sold

of

-

interconnections.

the

frequently

is

resin

It

coke

isotropic

is

can

types.

generally

sold

industry.

High s u l f u r ,

value

grade

fuel

undesirable, together

shot

coke

alone.

feedstocks

such

as

in

Maya,

of

The

coke.

regular

a matrix

as high

of

formation

West T e x a s

coke

is

sponge is

Sour


and


11.

DEBIASE ET AL.


161

RAILROAD HOPPER CAR

Figure

P i t Type

3.

Coke

Figure

4.

Pad Type

Figure

5.

Direct

Handling

Dewatering

Rail

System.

System.

Car Loading.



I COKE DRUM

DEWATERING BIN


WATER TANK

-VA

\

CRUSHER

I

1

γ

/

L

~ë

SLURRY PUMP

Figure

6.

Slurry

SUMP PUMP

Dewatering B i n System.

1

—-a SUMP PUMP

Figure

7.

G r a v i t y Flow Dewatering B i n System


11.

DEBIASE ET AL.


163

some C a l i f o r n i a r e s i d u e s , s h a l e o i l and g i l s o n i t e . Operating c o n d i t i o n s such as temperature, p r e s s u r e and r e c y c l e a l s o a f f e c t s h o t coke f o r m a t i o n .


Feedstocks As crudes become h e a v i e r w i t h h i g h e r l e v e l s o f s u l f u r and m e t a l s , i t becomes more d i f f i c u l t t o produce a c c e p t a b l e m a r k e t a b l e coke q u a l i t y w h i l e maximizing d e s i r a b l e l i q u i d product y i e l d . This mandates t h a t r e f i n e r s and d e s i g n e r s s c r u t i n i z e p h y s i c a l p r o p e r t i e s , upstream p r o c e s s i n g and downstream requirements when s e l e c t i n g a feedstock. The p h y s i c a l p r o p e r t i e s o f a c e r t a i n f e e d s t o c k t h a t determine the y i e l d s and p r o d u c t q u a l i t i e s i n c l u d e g r a v i t y , c h a r a c t e r i z a t i o n f a c t o r , carbon r e s i d u e , s u l f u r c o n t e n t and m e t a l s c o n t e n t . The l a s t t h r e e p r o p e r t i e s a r e o f s p e c i f i c importance. Carbon Residue. The carbon r e s i d u e i s one f a c t o r used t o determine coke y i e l d as a percentage o f f r e s h f e e d , and i s d e f i n e d as t h e carbon r e s i d u e r e m a i n i n g a f t e r e v a p o r a t i o n and p y r o l y s i s o f t h e f e e d s t o c k i n a s p e c i f i e d procedure. A l l other operating conditions b e i n g t h e same, as t h e carbon r e s i d u e i s i n c r e a s e d , more coke w i l l be produced. I n r e c e n t y e a r s , as t h e q u a l i t y o f crudes has d i m i n i s h e d , t h e carbon r e s i d u e o f vacuum r e s i d u e f e e d s t o c k s has i n c r e a s e d from t y p i c a l v a l u e s o f 10 t o 20 weight % t o 20 t o 30 w e i g h t % and more. S u l f u r Content. Another i m p o r t a n t f e e d s t o c k p h y s i c a l p r o p e r t y r e l a t e d t o d e l a y e d c o k i n g i s t h e s u l f u r c o n t e n t . The s u l f u r p r e s e n t i n t h e f e e d s t o c k tends t o c o n c e n t r a t e i n t h e coke, where the s u l f u r l e v e l i s u s u a l l y e q u a l t o o r h i g h e r than t h a t o f t h e f e e d s t o c k . S u l f u r l e v e l s as h i g h as 4 weight % i n today's f e e d s t o c k s can cause u n a c c e p t a b l y h i g h l e v e l s o f s u l f u r i n t h e coke p r o d u c t . The r e s u l t i n g coke may n o t be a c c e p t a b l e f o r m e t a l l u r g i c a l use and may be a problem when burned as f u e l . M e t a l s Content. When p r o d u c i n g coke f o r e l e c t r o d e o r anode u s e , f e e d s t o c k m e t a l s c o n t e n t must be reviewed r e l a t i v e t o coke p r o d u c t s p e c i f i c a t i o n s . As i n t h e case o f s u l f u r , m e t a l s tend t o c o n c e n t r a t e i n t h e coke. The most common upstream p r o c e s s i n g methods f o r p r o d u c i n g r e g u l a r coke f e e d s t o c k s a r e atmospheric and vacuum d i s t i l l a t i o n . Another upstream f e e d s t o c k p r e p a r a t i o n p r o c e s s i s v i s b r e a k i n g . Other a l t e r n a t i v e s i n c l u d e c h a r g i n g heavy crude o i l o r a s p h a l t from a s o l v e n t d e a s p h a l t e r . Charging whole crude w i l l a l l o w t h e c o k e r f r a c t i o n a t o r t o o p e r a t e as both a crude u n i t , by d i s t i l l i n g o f f t h e l i g h t e r p o r t i o n o f t h e crude, and a d e l a y e d c o k e r by c o k i n g and c r a c k i n g t h e h e a v i e r r e s i d u a l f r a c t i o n . However, c h a r g i n g whole crude i s g e n e r a l l y l i m i t e d t o heavy crudes w i t h m i n i m a l d i s t i l l a t e . Examples o f r e g u l a r grade coke f e e d s t o c k and p r o d u c t y i e l d s a r e given l a t e r . When p r o d u c i n g needle coke, t h e r e f i n e r must be more s e l e c t i v e i n d e t e r m i n i n g i f a f e e d s t o c k i s s u i t a b l e . Needle coke has a h i g h l y c r y s t a l l i n e s t r u c t u r e which must be produced from an



164 aromatic that

feedstock

meets

use

are

a pilot

to

be

plant

Because currently

of

considering coker.

the

coke

use

as

to is

properties

after

upstream

Process

Variables

operating

product

quality

are

heater

of

the

recycle At

yield

fresh

constant

increases

desired

but

can be

tendency

the

shorter can

be

of

low

an o u t l e t

temperature (VCM) or 8

of

pitch to

12

could

increased

operate

at

The the

at

a

low,

low

low

effect

coke

liquid

Regular

Grade

Illustrated qualities yields

of

were

operating

fuel

Recycle

produces

In

the

may b e

yields

liquid addition,

suitable

and

for

product

residue,

coker

feedstock.

with

and

dictate

These

drum p r e s s u r e

Table

the

the

variables

and

the

ratio

remove

or, are

often

which

the

from the as

the

causing

coke

the

a

the

increased,

formed

drum

heater

with

at

well.

combustible

high

is

increases,

Operating

effect

of

desirable

the

coke

delayed

If

too the

material

possibly designed

a

soft

tar

so

that

an

yield

cokers

v a p o r i z i n g more liquid is

heavy

hydrocarbons

correspondingly

have

been

designed

to

pressure. ratio the in

often

on

-

the

the

production ratio

increased. furnace

reduced

product

from

coke

recycle

to

is

is

analogous

decreased,

Reduction of

because the

of

to

the recycle

lowered

minimum

rate

which

qualities.

Typical

Yields

estimated

representative for

is

coke

difficulties

the

is

are

over

temperature, to

product

This

produced.

the

I

liquid

range

to

volatile

usage is

the

temperature line

cause

products

established

conditions

narrow

certain

has

Operation

several

ratio,

Modern u n i t s

As

acceptable Coke

in

the

is

recycle

of

s t i l l

residue

reduced.

temperature.

excessively

drum

production throughput.

As

pressures,

pressure.

the

carbon

yield

a delayed

in

production of

of

lowers

then be

effect

also

delayed

residue the

coke

a

most modern

of

in

given

equipment.

pressure the

Thus,

a

only

a

produced.

As

and

residue

recycle

can

% VCM c o k e

hydrocarbons.

the

residue,

shows

and d i f f i c u l t

cutting

in

of

content,

crudes

been

carbon

coke

transfer

Above

will

be

weight

decreased.

is

and

hard

too

coke

A decrease is

there

temperature

is

the

I

increase

adjusted.

hydraulic

the

for

and

an

run-lengths.

existing

the

sulfur

in

have

upstream

metals

the in

temperature,

heater

excessively

units

lower

variables

pressure

temperature

in

feed.

with

effect,

tested

desulfurization.

yields

outlet

to

be

levels

years

Medium A r a b i a n vacuum

control

coke for

feedstocks

should

impurity

in

and

general,

recent

reduction

Table

residue

and

and in

a desulfurized

coke.

coking

without

Three

from

grade

sulfur

reduction

increased

produced

anode

also

the

In

production

refiners

the

units

Due

yield

to

Needle

a premium p r i c e

quality.

desulfurization

addition

contents. product

increased

content.

commands

coke

product

processed,

desulfurization

and m e t a l s

electrodes.

needle

assure

residue

In

for

the

being

sulfur

graphite

used

to

low

specifications

in manufacturing

which


with

stringent

yields

delayed

generalized operation

and

Product

and

coker

Qualities

product

feedstocks.

correlations

using

noted.


The typical


Sulfur,

Wt%

Sulfur,

Gravity,

Coke,

Wt%

Wt%

Wt%

°API

Wt%

Wt%

°API

380°F+, Wt%

Sulfur,

Gravity,

Gas O i l ,

4

C -,

Wt%

°F

Estimated

C -380°F, Wt%

Gas,

Naphtha,

Dry

Products

Operation

Sulfur,

Carbon,

°API

Con.

Point,

Cut

I.

Gravity,

TBP

Feed

TABLE

and

32.5 5.7

44.7 23.9 2.7

14.0 55.0 1.1

8.8

950+ 2.6 23.3 4.4

Venezuelan

Yields

37.1 5.2

40.2 23.6 2.0

13.6 55.5 0.9

9.1

-Maximum

1.5 28.5 4.0

Tar

Visbreaker

for

Medium

Regular

31.0 6.5

46.5 25.7 2.9

14.0 58.9 0.6

8.5

Yield-

1,000+ 7.0 21.0 4.8

Arabian

Liquid

Properties

Venezuelan

Product

Production

12.6 1.2

67.5 28.9 0.3

13.1 58.6 0.1

6.8

1,000+ 17.0 6.5 0.5

Arabian

Desulfurized

Coke

Medium

Grade


North

7.7

Coke

26.4 1.2

46.0 34.9 0.5

19.9 62.1 0.1

Anode

1,000+ 15.2 16.7 0.7

African

I'

I

> m m H

166


Needle Coke O p e r a t i o n - T y p i c a l Y i e l d s and P r o d u c t

Qualities

Table I I shows e s t i m a t e d y i e l d s and p r o d u c t q u a l i t i e s f o r t h r e e t y p i c a l needle coker f e e d s t o c k s . The f e e d s t o c k s a r e c o n s i d e r e d d e s i r a b l e needle c o k e r f e e d s t o c k s because o f t h e i r h i g h d e n s i t y , low s u l f u r c o n t e n t and h i g h l y a r o m a t i c n a t u r e . Note t h e h i g h p r o d u c t i o n o f coke, t h e r e s u l t o f h i g h p r e s s u r e and h i g h r e c y c l e r a t i s , w h i c h i s t y p i c a l i n needle coke p r o d u c t i o n .


Table I I .

E s t i m a t e d Y i e l d s and P r o d u c t P r o p e r t i e s For Needle Coke P r o d u c t i o n

Pyrolysis Tar

Decanted Oil

-3.9 0.5

-0.7 0.5

14.4

10.3

9.8

C -380°F, Wt% G r a v i t y , °API S u l f u r , Wt%

16.7 54.9 0.04

3.5 41.7 0.09

8.4 59.8 0.01

Gas O i l , 380°F+, Wt% G r a v i t y , °API S u l f u r , Wt%

15.7 23.3 0.7

31.2 11.5 0.2

41.6 16.9 0.3

Coke, Wt% S u l f u r , Wt%

53.2 1.0

55.0 0.6

40.2 0.6

Feed

Thermal T a r

G r a v i t y , °API S u l f u r , Wt%

2.4 1.0

Products Dry Gas,

C -, Wt%

Uses o f Petroleum

Coke

Petroleum coke i s e s s e n t i a l l y pure carbon and can be u t i l i z e d wherever one would use a s i m i l a r carbon p r o d u c t . I t may be used as a f u e l s u b s t i t u t e f o r c o a l and can sometimes be used as a f e e d s t o c k f o r a p p l i c a t i o n s such as p a r t i a l o x i d a t i o n . Depending on i t s p r o p e r t i e s , p e t r o l e u m coke has f o u r b a s i c u s e s : f u e l , f e e d s t o c k f o r downstream p r o c e s s i n g , m e t a l l u r g i c a l a p p l i c a t i o n s , and f o r s p e c i a l t y g r a p h i t e and carbon p r o d u c t s . As a f u e l , t h e most common uses o f petroleum coke a r e i n f i r i n g cement k i l n s and steam g e n e r a t o r s . I n t h e cement i n d u s t r y , p e t r o leum coke i s s u i t a b l e as f u e l i n k i l n s because o f i t s low a s h c o n t e n t , h i g h h e a t i n g v a l u e and t h e p r o c e s s ' s h i g h s u l f u r a l l o w a n c e s . As much as 50% coke can be burned i n c o m b i n a t i o n w i t h b i t u m i n o u s c o a l o r 75% coke when burned i n c o m b i n a t i o n w i t h o i l and/or g a s . The o n l y l i m i t a t i o n on coke f o r cement k i l n f i r i n g may be i t s m e t a l s c o n t e n t . F o r steam g e n e r a t i o n , two o p t i o n s a r e a v a i l a b l e . The most common i s t h e b u r n i n g o f p e t r o l e u m coke i n p u l v e r i z e d f u e l b o i l e r s . T h i s u t i l i z a t i o n o f t e n r e q u i r e s t h a t downstream e n v i r o n m e n t a l p r o c e s s i n g o f t h e f l u e gas be employed. Another method r e c e n t l y developed by F o s t e r Wheeler f o r u s i n g h i g h s u l f u r petroleum coke as f u e l f o r steam g e n e r a t i o n i s b u r n i n g low q u a l i t y coke i n a s u l f u r c a p t u r e f l u i d i z e d bed b o i l e r . The f l u e gas meets e n v i r o n m e n t a l



11.

DEBIASE ET AL.


167

s t a n d a r d s f o r NOx and SOx. The o n l y e n v i r o n m e n t a l c o n s i d e r a t i o n i s the removal o f a s h from t h e f l u e gas i n a baghouse and removal o f the spent l i m e s t o n e . F l u i d i z e d bed b o i l e r s can be d e s i g n e d t o burn petroleum coke a l o n g w i t h t h e o p t i o n o f b u r n i n g h i g h s u l f u r c o a l o r heavy f u e l o i l . (2_) A p o t e n t i a l l y a t t r a c t i v e use f o r low q u a l i t y , r e g u l a r grade coke i s t o g a s i f y i t t o produce ammonia s y n t h e s i s gas, f u e l gas, o r hydrogen. F o s t e r Wheeler has i n v e s t i g a t e d p r o m i s i n g schemes f o r a i r p a r t i a l o x i d a t i o n (APO), where t h e coke i s p a r t i a l l y combusted w i t h a i r a t e l e v a t e d p r e s s u r e t o generate a gas c o n s i s t i n g e s s e n t i a l l y o f hydrogen, carbon o x i d e s , hydrogen s u l f i d e and n i t r o g e n . A f t e r s h i f t c o n v e r s i o n , hydrogen s u l f i d e and carbon d i o x i d e a r e removed by s c r u b b i n g . S u l f u r may be r e c o v e r e d e i t h e r as s u l f u r i c a c i d o r e l e m e n t a l s u l f u r . Depending on the d e s i r e d end p r o d u c t , n i t r o g e n may be p a r t i a l l y removed by c r y o g e n i c s e p a r a t i o n and f u r t h e r removed by p r e s s u r e swing a d s o r p t i o n (PSA). R e s i d u a l carbon monoxide i s removed by methanation o r by PSA. One o f t h e l a r g e s t uses o f petroleum coke i s f o r anodes employed i n t h e p r o d u c t i o n o f aluminum. T h i s usage demands a somewhat premium f e e d s t o c k t o produce sponge coke t h a t i s low i n m e t a l and s u l f u r c o n t e n t i n o r d e r t o meet p r o d u c t q u a l i t y s p e c i f i c a t i o n s . A f t e r p r o d u c t i o n i n a d e l a y e d coker, anode q u a l i t y coke must be c a l c i n e d t o remove VCM and m o i s t u r e . A s p e c i a l i z e d a p p l i c a t i o n o f p e t r o l e u m coke i s the p r o d u c t i o n o f e l e c t r o d e s f o r the s t e e l i n d u s t r y . F o r t h i s a p p l i c a t i o n , i t i s n e c e s s a r y t o use needle coke because i t s low c o e f f i c i e n t o f t h e r m a l expansion and low r e s i s t i v i t y . The needle coke must have low s u l f u r and low metals c o n t e n t . A f t e r p r o d u c t i o n i n a d e l a y e d c o k e r , needle coke i s crushed and c a l c i n e d i n p r e p a r a t i o n f o r e l e c t r o d e production. By 1980, s p e c i a l a p p l i c a t i o n s accounted f o r a p p r o x i m a t e l y 11% o f t h e t o t a l coke p r o d u c t i o n i n t h e U n i t e d S t a t e s . These uses i n c l u d e t i t a n i u m pigments, carbon r a i s e r s and s y n t h e t i c g r a p h i t e (3_). A s p e c i a l t y use o f green coke i s as a h i g h p u r i t y r e a c t a n t i n the p r o d u c t i o n o f c a l c i u m and s i l i c o n c a r b i d e . (4_) Coke C a l c i n i n g When petroleum coke i s u t i l i z e d f o r anode and e l e c t r o d e p r o d u c t i o n and some s p e c i a l t y a p p l i c a t i o n s , i t i s n e c e s s a r y t o c a l c i n e i t t o remove m o i s t u r e and hydrocarbon VCM. P r o d u c t q u a l i t i e s , a l o n g w i t h p r o d u c t i o n r a t e , a r e based on f e e d s t o c k c o m p o s i t i o n , k i l n temperat u r e p r o f i l e , k i l n r e s i d e n c e time and c o o l i n g p r o c e d u r e s . The two methods a v a i l a b l e f o r c a l c i n i n g coke c o m m e r c i a l l y a r e t h e r o t a r y k i l n (5^) shown i n F i g u r e 8 and the r o t a r y h e a r t h (€0 shown i n F i g u r e 9. In t h e r o t a r y k i l n p r o c e s s , coke i s f e d t o a r o t a t i n g c y l i n d r i c a l f u r n a c e s l o p e d s l i g h t l y toward t h e d i s c h a r g e end. Coke f l o w s down t h e k i l n c o u n t e r c u r r e n t t o t h e h o t gas f l o w . M o i s t u r e i s l i b e r a t e d from t h e coke i n the f e e d zone, then t h e coke passes through t h e combustion zone where VCM i s l i b e r a t e d . As coke l e a v e s the k i l n , i t i s d i s c h a r g e d t o a c o o l e r where i t i s quenched w i t h water and then c o o l e d w i t h ambient a i r . Recent d e s i g n s have i n c o r p o r a t e d energy e f f i c i e n t f e a t u r e s such as a i r p r e h e a t and steam


168


STACK


AIR

IN

BURNER

C A L C I N E D COKE TO Q U E N C H I N G AND C O O L I N G

F i g u r e 8.

T y p i c a l Rotary K i l n C a l c i n e r .

STACK GREEN COKE FEED IN

STATIONARY RABBLES

r— R O O F / B U R N E R S "7 MR

'

AIR

/

ni.

AIR

ϋ ϋ ϋ ϋ ΰ ΰ

ROTATING CIRCULAR TABLE

C A L C I N E D COKE TO Q U E N C H I N G AND C O O L I N G

F i g u r e 9.

T y p i c a l R o t a r y Hearth

Furnace.


IN

11.

DEBIASE ET AL.

generation

facilities

hydrocarbons In green and

is

gently

path

moved


toward

energy

efficient

Design

Features

Through

a high

of

equipment

becomes

have

Today's

To while

been thus

with

heater

instituted heater

ratio

increase

heater

Of

These

through

Heaters

features

With

hydraulic cutting coke

computer

controlling life

analysis. stress

c a n be

Decoking significant equipment early

delivered 27

foot

coke

through

flow

preventing

parallel

coil

and temperature

range

between

9

{1) coke

Wheeler

in

coke

drums

used

cycles

that

rapid

has been

a n d 110 f e e t

Wheeler

decoking

has been on coke

able

in to

drum

life

by m o n i t o r i n g and

heating

and c o o l i n g ,

handling f a c i l i t i e s of delayed

from m e c h a n i c a l d e v i c e s drums

drums.

to the use of hoses

Coke Steam,

but are sent

w i t h most

be as energy

thereby

the

to

improved m e t a l l u r g y and

by F o s t e r

the advent

flexible

previously. pool,

i s used

each

that

Foster

indicate

and coke

since

diameter

gas and water As

to

equipment

i n t h e drum a r e no l o n g e r

settling oil,

coil

with

i n diameter

on a drum d u r i n g

changes

diameter

described

Results

steam

more

reduces

coke

extended.

has evolved

small

feet

more

refiner

with

which

The f i r s t

today's

shortened

in a

to the

have been i n c o r p o r a t e d size.

Another development of

Injection

capacity,

u p t o 27

the effect

tubes,

run lengths

to

recent

c o n d i t i o n s and

and independent

is

the

designed

the heater

that

notable

increased

(1_)

resulted

are designed

permit

to

drums

have

been

costs. crudes

necessary

of

i n normal o p e r a t i o n .

i n diameter.

drum

flux.

state-of-the

Most

operating

between

heat

and r e l i a b l e

and

flexibility

space

were

length.

Wheeler

pieces

technology

heavier

i t h a s become

design.

optimize

a "black a r t "

investment

today's

a n d more

t h e most

determine

with

g i v i n g more

t h e new d e v e l o p m e n t s

employ

with

and a i r preheat.

economical

have

and longer

10 f e e t

for

and minor

a s new

versatility

boxes

to average

from

Both major

and c a p i t a l

by Foster

drum d e s i g n ,

by

combine

i t s own s e t o f b u r n e r s

12 m o n t h s

generation

and updated

run lengths

the o i l v e l o c i t y

control.

as steam

Fire

i n the tubes.

havings to

must

capacity,

dimensions

regulate coking

t h e coke b e d ,

be e q u i p p e d

coking has evolved

design,

run lengths.

o f peak

above

can also

efficiency,

improvements

liberal

table

circular

furnace

assuring a safe,

t r a d i t i o n a l coker

later

zone

in a

necessary

low o p e r a t i n g

improving heater

increase

the hearth

coke,

circular

the heat

examined

conservative to

of

refining process.

designs

increase

improve

calcining

the rotating

supplies

such

delayed

technology

technology

of

liberated

zone.

and C o n s i d e r a t i o n s

available,

design.

the

of

A combustion

hearth

features,

the years,

to

h e a r t h method

volatiles,

A rotating

i n which

i n the combustion

the center

rabbles.

by l i b e r a t e d

calcination.

art

as designs

as a f u e l

fed to the perimeter

by s t a t i o n a r y

formed

as w e l l

are used

the p r o p r i e t a r y rotary

coke

169


with

i s dewatered o i l and water

water,

the

removed

while

blowdown

and r e c y c l e d .

refinery units,

the delayed

as p o s s i b l e .

with the

t o c u t coke

t o a blowdown

t o an e n c l o s e d

undergone Decoking

by one o f

are separated

efficient

employed

high pressure

the a b i l i t y

directed

have

coking.

coker

Modern c o k e r

from

systems cooling

pond o r

system

where

has been

updated

h e a t e r s now


the

170


incorporate preheat

to

designed

boiler raise

for

design,

Revamps

expand

with

in

least

expense

the of

to

coke

it

is

to not

capacity in

is

coke

drum c y c l e .

than

16 to

is

to be

hours

more

handle Another

the

the

coking

coker. the

this

as

If

pressure

port

reduce

valves

condenser

helpful.

The

capacity

easiest

way

have

decrease

at

is

to

the

the

drum.

hours

12

methods

when

or

for

refiners

a visbreaker the

area

to

into

to

will

less

and

heavier any

by

s t i l l the

cycles allow

coke

feedstocks section

that

will

modification. an

very

coking

If

the

allow

existing

coking

is

of

is shorten

of

employed

delayed a

able

length

retrofit

visbreaker

permits,

this

investment.

fractionation is

capacity

do

This

production without

section,

to

increasing

processing the

the

the

been

successfully coke

of

load,

minimum c a p i t a l

case,

to

plot

heater

to

These

open

such

to

capacity new

Refiners

another

distillate

option

unit

and

In

full

accomplished

the the

The

with

shortened

coke.

for

alternative add

time.

also

of

operating

and

to new

the

Methods

proved

is

adding

whether

fractionator

that

substantially

another

is

lowering

This

increased.

applicable

added

heat

option

than

capacity.

also

the

have

cost

pumparounds

has

adequate

are

delayed

and

yield.

decoking

a

generation,

as

possible.

concern

pressure.

capacity

than

heater

often

increasing

adequate

Other

little

in

fractionator

determined

may b e

drum t o

o i l

air

longer

as

while

the

drop

for

liquid been

possible

heavy

main

the

cycle,

often

cokers

less

Wheeler

produce

but

or

no

for

incremental

Adding upper

section

coking

each

air

are

improvements steam

sufficient

beds

option

has

Foster for

generation

Heaters

added where

the

has

operating

drums

shorten

cycles

the

preheat,

lower

and p r e s s u r e

lower it

fractionator the

to

delayed a

lines.

duty

Once

feed

revamps

packed

expensive

increase

steam

excess

20%

units

fractionator

vapor

overhead

at

section

using

the

had

existing

F o r most

include

with

addition

other

units

fractionation increasing

preheat,

efficiency.

Retrofits

their

units.

In

have

with

and

Refiners


air.

cokers

integration

heater

operation

excess

5-10%

feedwater

the

service.

similar

section

may

coking

has

to be

modified.

Summary Since

its

remained and

inception, basically

operating

philosophy

coking

has

sulfur

feedstocks,

and to

evolved

qualities.

more

on-stream

come,

important

the

basic

to

have

and

coking

residual

a wide

delayed

process

substantially. range

equipment

has

energy

expected

upgrading

of

feedstocks, of

to

been

continue

heavy,

product

updated

efficient

equipment

Delayed

today's

producing acceptable

a more is

the

changed

s t i l l

Processing

delayed

but

process

while

time

process

unchanged,

to

provide

operation. to

remain

high yields In

an

process.


years

11. DEBIASE ET AL.


Literature Cited 1. 2. 3.


4. 5. 6.

DeBiase, R., and E l l i o t t , J . D., Oil and Gas Journal, 16, 81 (1982). Nagy, R.L., Broeker, R. G., and Gamble, R. L . , "Firing Delayed Coke in a Fluidized Bed Steam Boiler", paper presented at the 1983 NPRA Annual Meeting, San Francisco, CA, March 20-22 (1983). Fasullo, P.Α., Matson, J., and Tarrillion, T., Oil and Gas Journal, 44, 76 (1982). Guthrie, V . B . , Ed., Petroleum Products Handbook, McGraw-Hill Book Company, New York, 1960; Chapter 14. Kennedy Van Saun Corporation's Technical Brochure No. COK 1/82(2). Allred, V.D., "Rotary Hearth Calcining of Petroleum Coke", paper presented at the 100th National Meeting of the American Institute of Metallurgical Engineers, New York, NY, March 1-4 (1971).

RECEIVED February 23, 1985


171

Delayed-Coking Process Update - ACS Publications - American

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