the delayed coking process - · pdf filewhile coke drum d-1 is coking, ... in the previous...

37
Page 1 of 37 THE DELAYED COKING PROCESS - Thomas E. Wolf © 2013 by Thomas E. Wolf. All rights reserved. No part of this document may be reproduced or transmitted in any form or by any means, electronic or mechanical, including photocopying, recording, or by any information storage or retrieval system without written permission of the copyright holder, except for the inclusion of brief quotations in a review. Products – o Gasoline (Naphtha) o Diesel (Light and Heavy Coker Gas Oil) o LPG (Propane and Butane) o Fuel gas o Petroleum Coke (predominantly carbon) Heavier, less expensive crude oil produces more residue to process (thus more coke) compared with lighter, more expensive crude oil. Process Description – Basic Process Flow Diagram In this section the delayed coking process will be described by walking through the individual pieces of equipment with a brief description of the various process steps within the equipment. Two diagrams are essential in this effort, Figure 1, the process flow diagram (PFD), and Figure 2, coke drum schematic. The PFD depicts a very simplified two drum delayed coker, showing the major equipment, flow lines, and valves and the coke drum schematic illustrates a few vital parts of the coke drums/table top/drill derrick. In the next section Figure 3 and Figure 4, the temperature-pressure profile, will then be utilized to describe the basic process in an alternate manner. Each of these basic description methods provide the same information but in a slightly different format. Then in a later section, both of these methods will be combined to describe the process in the context of a two drum concurrent, integrated operation with the aid of Figures 5 through 16.

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Page 1: THE DELAYED COKING PROCESS - · PDF fileWhile coke drum D-1 is coking, ... In the previous section, the delayed coking process was described by using the process flow diagram (PFD)

Page 1 of 37

THE DELAYED COKING PROCESS - Thomas E. Wolf

© 2013 by Thomas E. Wolf. All rights reserved. No part of this document may be

reproduced or transmitted in any form or by any means, electronic or mechanical, including photocopying, recording, or by any information storage or retrieval system without written permission of the copyright holder, except for the inclusion of brief quotations in a review.

Products –

o Gasoline (Naphtha)

o Diesel (Light and Heavy Coker Gas Oil)

o LPG (Propane and Butane)

o Fuel gas

o Petroleum Coke (predominantly carbon)

Heavier, less expensive crude oil produces more residue to process (thus more

coke) compared with lighter, more expensive crude oil.

Process Description – Basic Process Flow Diagram

In this section the delayed coking process will be described by walking

through the individual pieces of equipment with a brief description of the various

process steps within the equipment. Two diagrams are essential in this effort, Figure

1, the process flow diagram (PFD), and Figure 2, coke drum schematic. The PFD

depicts a very simplified two drum delayed coker, showing the major equipment, flow

lines, and valves and the coke drum schematic illustrates a few vital parts of the coke

drums/table top/drill derrick. In the next section Figure 3 and Figure 4, the

temperature-pressure profile, will then be utilized to describe the basic process in an

alternate manner. Each of these basic description methods provide the same

information but in a slightly different format. Then in a later section, both of these

methods will be combined to describe the process in the context of a two drum

concurrent, integrated operation with the aid of Figures 5 through 16.

Page 2: THE DELAYED COKING PROCESS - · PDF fileWhile coke drum D-1 is coking, ... In the previous section, the delayed coking process was described by using the process flow diagram (PFD)

Page 2 of 37

The heavy feed, typically from the refinery’s atmospheric and/or vacuum unit,

is introduced into the bottom of the fractionator vessel, T-1. The fractionator tower

(also known as the main fractionator or combination tower) receives the unit feed and

the overhead hot vapors from the coking drum in the bottom tower section. In this

bottom tower section the unit feed is both preheated by hot coke drum overhead

vapors and provided necessary recycle. As the hot vapors travel vertically through

the fractionator, the vapors cool at different rates and the various products are taken

as side cuts from the fractionator. These products can be, from tower bottom to top,

heavy coker gas oil, diesel, kerosene, and naphtha. Note the side cuts are not shown

in the simplified PFD, but only shown as products going overhead from the

fractionator. The preheated heavy feed is then pumped to the coker furnace.

Page 3: THE DELAYED COKING PROCESS - · PDF fileWhile coke drum D-1 is coking, ... In the previous section, the delayed coking process was described by using the process flow diagram (PFD)

Page 3 of 37

stm

stm

D-2

prod

ucts

was

te

prod

ucts

wa

ter

T-2

Cut

ting

Wat

er

Fee

d

Cok

e +

W

ater

wat

er

switc

hin

g va

lve

D-1

H-1

T-1

Figure 1 – Process Flow Diagram

Page 4: THE DELAYED COKING PROCESS - · PDF fileWhile coke drum D-1 is coking, ... In the previous section, the delayed coking process was described by using the process flow diagram (PFD)

Page 4 of 37

The coker furnace or heater, H-1, heats the feed to the temperature at which

thermal cracking occurs, typically between 900 OF and 950 OF. To delay the coking

process and subsequent fouling of the furnace tubes with solid coke, the hot feed

velocity through the tubes is controlled, typically between six to ten feet per second.

Upon exiting the furnace, the hot feed is piped to the switching valve which routes the

feed one of the drums to initiate the coking process.

The PFD shows coke drum D-1 as the coking drum. As the hot feed enters the

empty drum, the coking process begins, with the large drum providing the necessary

residence time to complete the cracking process. Within the drum, the hot liquid feed

is first thermally cracked to coke and vapor, and then the vapor is thermally cracked

as it passes upward through the drum. The solid coke collects in the bottom, the hot

feed passed through the collected solid coke in random channels, the hot cracked

vapor exits the top of the drum and routed to the fractionator bottom. Over time the

drum is filled to a predetermined level at which time that drum is considered filled

and ready to be emptied. This predetermined level is generally called outage and is

measured as the distance from the top nozzle and when this level is reached, time to

switch drums.

As can well be imagined with the quantity of solid coke being produced and

with hot feed channeling upward through the solid coke, tremendous turbulence and

internally applied forces are transmitted to the drum and supporting structures. Also

as the coking process continues a froth or foam forms which can be a problem if

allowed to exit the drum. To counter this, antifoam chemical is injected reduce

carryover of tars and fines from the coke drums to the fractionator.

While coke drum D-1 is coking, drum D-2 is decoking, that is, the solid coke is

first prepared for removal then emptied from the drum bottom. At the beginning of

the decoking sequence drum D-2 contains both hot solid coke and residual hot vapor,

and the vessel shell is also at its maximum temperature. Steam is introduced to

initiate the cooling process. As the drum cooling process progresses the mixture of

residual hot vapor and steam are routed to the quench tower, T-2 (sometimes called

the blowdown tower). The quench tower separates the various products from the

Page 5: THE DELAYED COKING PROCESS - · PDF fileWhile coke drum D-1 is coking, ... In the previous section, the delayed coking process was described by using the process flow diagram (PFD)

Page 5 of 37

contaminated steam (waste) which then is further treated.

Then water is added to complete the cooling sequence. Upon completing the

cooling phase, the drum is deheaded (sometimes described as unheaded), that is, first

the top is removed, then the bottom head; the top head being removed first prevents

the drum shell from collapsing due the vacuum caused by the water exiting the

bottom head. The water is dumped to the coke pad, collected, and processed for

reuse. The solid coke remains in the vessel and must be cut into smaller pieces to

allow it to empty onto the coke pad. To cut the solid coke, high-pressure water is

used.

Figure 2 is a simplified two drum arrangement consisting of two coke drums, a

concrete supporting table top with unloading chutes to direct the dumped water and

the cut solid coke to the concrete temporary storage pad. The water is gravity drained

to a collection point to remove coke fines and process the water for subsequent coke

cutting. The solid coke is removed from the pad by mechanical means such as

overhead cranes or dozers. A steel structure is also supported by the concrete table

top which in turn supports the drill derrick structure. The derrick is utilized to insert

and withdraw the drill stem, a steel pipe rated for the high water pressure, with a

cutting tool on the bottom and connected at the top to the high-pressure water source

via a flexible high-pressure hose. The drill stem is raised and lowered by a motor

driven hoist and the stem is rotated by another motor.

The top of the stem is connected to the crosshead, which facilitates the stem

hoisting and rotating, and a free fall arrestor is installed to protect the installation from

a hoist failure. The cutting tool is designed to direct the high-pressure water both

vertically down and horizontally as the stem is raised and lowered. The cutting tool is

also designed to automatically switch between vertical and horizontal cutting while

the tool remains inside the drum.

Page 6: THE DELAYED COKING PROCESS - · PDF fileWhile coke drum D-1 is coking, ... In the previous section, the delayed coking process was described by using the process flow diagram (PFD)

Page 6 of 37

When the drum is ready for decoking and the top and bottom nozzles opened,

the cutting process begins. The drill stem is lowered into the coke drum with the

cutting tool directing the high pressure water vertically down to cut a pilot hole in the

solid coke the full length of the stem. Once pilot hole is cut the stem is raised, the tool

reoriented to cut horizontally, and the stem both lowered and rotated to cut the coke,

which falls out the drum bottom nozzle to the chute and onto the pad.

RULES OF THUMB

Coking Temperature and Pressure

Typical thermal cracking temperature at coke furnace is in the range of 900 to

950 F.

Typical coking pressures in coke drums are about 15 psig to 20 psig.

Page 7: THE DELAYED COKING PROCESS - · PDF fileWhile coke drum D-1 is coking, ... In the previous section, the delayed coking process was described by using the process flow diagram (PFD)

Page 7 of 37

Pad

Chute

Table Top

CokingDrum

Structure

Cutting Deck

Cutting Tool

Drill Stem DriveDrill Stem Withdrawn

DerrickCrosshead and Free Fall Arrestor

High Pressure Water Hose

Decoking Drum

Drill Stem Inserted

Figure 2 – Coke Drum Schematic

Page 8: THE DELAYED COKING PROCESS - · PDF fileWhile coke drum D-1 is coking, ... In the previous section, the delayed coking process was described by using the process flow diagram (PFD)

Page 8 of 37

Process Description – Basic Pressure Temperature Profile

In the previous section, the delayed coking process was described by using the

process flow diagram (PFD) and coke drum schematic. Another way to illustrate the

basic coke drum operation will be employed in this section, the pressure-temperature

profile for one complete cycle. In the next section, both of these methods will be

combined to describe the process in the context of a two drum concurrent, integrated

operation with the aid of Figures 3 through 16.

Below are two simplified pressure-temperature profiles for one complete coke

drum cycle, the first depicts the temperature and pressure over time as an individual

drum progresses through an entire coking cycle. The second profile overlays a

description of what is causing the pressure and temperature to change. A brief

explanation of each sequence segment is also provided.

Page 9: THE DELAYED COKING PROCESS - · PDF fileWhile coke drum D-1 is coking, ... In the previous section, the delayed coking process was described by using the process flow diagram (PFD)

Page 9 of 37

Simplified Pressure - Temperature Profile

(Single Drum, One Complete Cycle)

Not To Scale

Cycle Duration (hours)

Tem

per

atu

re (

deg

F)

Pre

ssu

re (

psi

g)

Temperature Profile

Pressure Profile

Figure 3 – Simplified Pressure-Temperature Profile

Cycle Duration (hours)Not To Scale

Simplified Pressure - Temperature Profile

Tem

per

atu

re (

deg

F)

Pre

ssu

re (

psi

g)

Temperature Profile

Pressure Profile

Steam Preheat, then

Hot Vapor Preheat

Steam Strip

Water Quench

Coking

Drill and Decoke

Rehead, Purge, Test

Unhead, Drain

Figure 4 - Simplified Pressure-Temperature Profile

Page 10: THE DELAYED COKING PROCESS - · PDF fileWhile coke drum D-1 is coking, ... In the previous section, the delayed coking process was described by using the process flow diagram (PFD)

Page 10 of 37

Preheat (or warm up) period – Preheat is the coke drum warm-up period prior

to introducing hot feed from the furnace. With the drum having been previously

emptied of coke, re-headed, purged of oxygen with steam, and tested for gasket leaks,

the vessel temperature is relatively cold, but not ambient. The preheat period is a

controlled temperature and pressure increase to bring the vessel closer to the hot feed

temperature; first with steam preheat, then hot vapor preheat from the coking drum.

This controlled temperature increase is necessary to minimize adverse thermal stress

and strain on the drum, primarily the skirt/cone/shell junction.

Coking segment (feed fill portion of cycle) – After the drum has been

preheated, feed is introduced into the drum from the furnace and the thermal cracking

process begins. Hot feed entering the bottom of the drum forms coke and releases

light ends (hydrocarbon vapors) overhead to the fractionator tower. This is the

longest segment in the sequence and is half (50%) of the total cycle duration.

Steam stripping (also referred to as steam out and steam to blowdown) – High

pressure steam is introduced initially to the overhead vapors en route to the

fractionator tower to remove additional light ends remaining on coke. Then the

balance of steam and hydrocarbon vapors are sent to the quench tower for separation

of sour water (waste) and additional light ends recovery. Steam stripping also acts as

the first stage in the cooling down process prior to decoking the drum.

Quench water segment – Water is introduced into drum to cool or quench the

coke, at first at a slow rate, until the water has cooled the drum level at least above the

skirt/cone/shell junction. Then after this level is achieved, the quench water rate can

be accelerated to speed this portion of the cycle. The initial slower rate is necessary to

reduce the thermal shock of cooling on the crack susceptible skirt/cone/shell junction

and bulge creation in the lower portion of the cylindrical portion of the shell.

Unhead, Drain segment – the top and bottom heads are removed, and the

quench water is drained from drum to pad.

Page 11: THE DELAYED COKING PROCESS - · PDF fileWhile coke drum D-1 is coking, ... In the previous section, the delayed coking process was described by using the process flow diagram (PFD)

Page 11 of 37

Drill portion – The drill stem is first lowered from the derrick and inserted

through the top manway nozzle with the cutting tool set to blast high-pressure water

vertically down to drill a pilot hole the full length of the coke.

Decoking period (or coke cutting) – After the pilot hole is completed, the drill

stem is raised and the cutting tool hydroblasting nozzle is reoriented to blast

horizontally. The drill stem is then both rotated and reinserted, cutting the coke, and

allowing coke and cutting water to exit bottom nozzle.

Re-heading, Purge, Test – The top and bottom heads are then reinstalled (re-

headed), the drum purged with steam to remove air, and the drum steam tested to

ensure top and bottom gaskets are sealed. The cycle is then repeated.

RULES OF THUMB

Coking cycle time

Typical cycle range 30 to 40 hours TOTAL, but could be lower or higher, and

the cycle segments are approximately:

o Preheat 10% to 12%

o Coking 50%

o Steam Stripping 4% to 5%

o Quench 14% to 15%

o Drain 5% to 6%

o Drill and Decoking 10%

o Rehead, Purge, Test 4% to 5%

o TOTAL CYCLE 100%

Caution – sometimes in the literature ‘coking cycle’ is described as being in the

15 to 20 hour range, when described this way, only the Coking portion (50%) of

the Total Cycle is being expressed. This can be misleading at times, and in this

document, ‘coking cycle’ is defined to mean the Total Cycle.

Page 12: THE DELAYED COKING PROCESS - · PDF fileWhile coke drum D-1 is coking, ... In the previous section, the delayed coking process was described by using the process flow diagram (PFD)

Page 12 of 37

Process Description – Two Drum Operation

In the previous two sections, the delayed coking process was described by

using two different methods to explain the steps in the process. The first utilized the

process flow diagram (PFD), and coke drum schematic. The next section used the

pressure-temperature profile. The following pages combine the process flow diagram

and the pressure temperature profile to follow the many steps of a complete two drum

operation.

Page 13: THE DELAYED COKING PROCESS - · PDF fileWhile coke drum D-1 is coking, ... In the previous section, the delayed coking process was described by using the process flow diagram (PFD)

Page 13 of 37

Cyc

le S

tep

On

e

Dru

m D

-1 h

as p

revi

ousl

y be

en p

ress

ure

test

ed w

ith

stea

m to

ens

ure

ther

e ar

e no

leak

s pr

ior

to c

onti

nuin

g th

e cy

cle.

Ste

am is

app

lied

to d

rum

D-1

as

the

firs

t ste

p (s

team

pre-

heat

) in

the

war

m-u

p pr

oces

s an

d th

e te

mpe

ratu

re b

egin

s to

incr

ease

. T

he v

apor

s

are

rout

ed to

the

quen

ch to

wer

T-2

.

At t

his

poin

t, d

rum

D-2

is e

ndin

g th

e co

king

por

tion

of t

he c

ycle

and

the

drum

tem

pera

ture

is r

elat

ivel

y co

nsta

nt a

t the

cok

ing

tem

pera

ture

. O

verh

ead

gas

from

D-2

cont

inue

s to

be

sent

to th

e fr

acti

onat

or T

-1 fo

r th

e fe

ed p

rehe

at a

nd s

ubse

quen

t pro

duc

t

sepa

rati

on.

Feed

ent

ers

the

low

er s

ecti

on o

f the

frac

tion

ator

T-1

to b

e pr

ehea

ted

by

the

hot o

verh

ead

vap

ors

from

the

on-l

ine

dru

m’s

(D-2

) cok

ing

cycl

e. T

he p

rehe

ated

feed

is

pum

ped

to th

e fu

rnac

e H

-1 w

here

the

feed

is h

eate

d to

cok

ing

tem

pera

ture

and

rou

ted

via

the

swit

chin

g va

lve

(sho

wn

as th

e th

ree

way

val

ve) t

o th

e co

king

dru

m D

-2.

Whe

n

dru

m D

-2 is

full,

it is

sw

itch

ed o

ff li

ne to

beg

in th

e d

ecok

ing

sequ

ence

s.

Page 14: THE DELAYED COKING PROCESS - · PDF fileWhile coke drum D-1 is coking, ... In the previous section, the delayed coking process was described by using the process flow diagram (PFD)

Page 14 of 37

prod

ucts

was

te

T-2

T-1

stm

D-2

tem

p

Fee

dw

ater

D-1

H-1

thre

e w

ay v

alve

time

D-2

D-1O

pen

Clo

sed

LE

GE

ND

stm

wat

er

prod

uct

Figure 5 – Cycle Step 1

Page 15: THE DELAYED COKING PROCESS - · PDF fileWhile coke drum D-1 is coking, ... In the previous section, the delayed coking process was described by using the process flow diagram (PFD)

Page 15 of 37

Cyc

le S

tep

Tw

o

Dru

m D

-1’s

war

m-u

p (p

re-h

eat)

con

tinue

s w

ith th

e ho

t ove

rhea

d v

apor

rer

oute

d

from

dru

m D

-2.

The

war

min

g ga

s is

firs

t rou

ted

to th

e qu

ench

tow

er T

-2, b

ut d

urin

g St

ep

Two

the

vapo

r is

div

erte

d to

the

frac

tiona

tor

T-1.

The

war

m-u

p st

eps,

bot

h st

eam

pre

-hea

t and

hot

ove

rhea

d va

por,

are

mea

sure

s

take

n to

red

uce

the

ther

mal

sho

ck o

f int

rodu

cing

hot

feed

from

the

furn

ace

H-1

to th

e

rela

tivel

y co

ld d

rum

D-1

.

With

the

feed

no

long

er b

eing

sen

t to

drum

D-2

and

the

over

head

vap

ors

bein

g ro

uted

to

D-1

, D-2

tem

pera

ture

beg

ins

to d

ecre

ase.

Page 16: THE DELAYED COKING PROCESS - · PDF fileWhile coke drum D-1 is coking, ... In the previous section, the delayed coking process was described by using the process flow diagram (PFD)

Page 16 of 37

prod

ucts

was

te

T-2

T-1

stm

D-2

tem

p

Fee

dw

ater

D-1

H-1

thre

e w

ay v

alve

time

D-2

D-1O

pen

Clo

sed

LE

GE

ND

stm

wat

er

prod

uct

Figure 6 - Cycle Step 2

Page 17: THE DELAYED COKING PROCESS - · PDF fileWhile coke drum D-1 is coking, ... In the previous section, the delayed coking process was described by using the process flow diagram (PFD)

Page 17 of 37

Cyc

le S

tep

Th

ree

D

-2 is

then

ste

amed

out

(pur

ged

with

ste

am) t

o re

cove

r th

e ba

lanc

e of

the

prod

uct

oils

rem

aini

ng o

n th

e co

ke, t

he te

mpe

ratu

re o

f D-2

con

tinue

s to

dec

reas

e. T

he s

team

and

oil v

apor

are

rou

ted

initi

ally

to th

e fr

actio

nato

r T-

1 be

fore

sw

itchi

ng to

the

quen

ch to

wer

T-

2 w

hen

mos

t of t

he r

ecov

erab

le h

ydro

carb

ons

have

bee

n st

ripp

ed fr

om th

e co

ke.

As

the

vapo

r ri

ses

thro

ugh

T-2,

res

idua

l pro

duct

s ar

e se

para

ted

and

the

sour

wat

er v

apor

is

reco

vere

d fo

r fu

rthe

r pr

oces

sing

.

D

-1 h

as b

een

preh

eate

d an

d th

e ho

t fee

d a

t cok

ing

tem

pera

ture

from

the

furn

ace

H-1

is s

wit

ched

into

dru

m D

-1 to

sta

rt th

e co

king

por

tion

of i

t’s

cycl

e.

Page 18: THE DELAYED COKING PROCESS - · PDF fileWhile coke drum D-1 is coking, ... In the previous section, the delayed coking process was described by using the process flow diagram (PFD)

Page 18 of 37

pr

oduc

ts

was

te

T-2

T-1

stm

D-2

tem

p

Fee

dw

ater

D-1

H-1

thre

e w

ay v

alve

time

D-2

D-1O

pen

Clo

sed

LE

GE

ND

stm

wat

er

prod

uct

Figure 7 - Cycle Step 3

Page 19: THE DELAYED COKING PROCESS - · PDF fileWhile coke drum D-1 is coking, ... In the previous section, the delayed coking process was described by using the process flow diagram (PFD)

Page 19 of 37

Cyc

le S

tep

Fou

r

Dru

m D

-1 c

onti

nues

the

coki

ng p

orti

on o

f the

cyc

le a

nd r

emai

ns a

t cok

ing

tem

per

atu

re.

Qu

ench

wat

er is

then

add

ed to

dru

m D

-2 to

coo

l the

cok

e in

pre

para

tion

of

cutt

ing

and

du

mpi

ng fr

om th

e d

rum

. T

he q

uenc

h w

ater

is a

dded

slo

wly

unt

il th

e dr

um

is c

oole

d ab

ove

the

skir

t/co

ne/s

hell

junc

tion

area

. A

fter

this

poi

nt is

rea

ched

, the

que

nch

wat

er r

ate

is in

crea

sed

to s

peed

the

coke

coo

l dow

n tim

e w

ith th

e w

ater

flow

con

trol

led

to

ensu

re th

e pr

essu

re g

ener

ated

by

the

vapo

riza

tion

of w

ater

doe

s no

t exc

eed

the

relie

f val

ve

set p

ress

ure.

Th

e st

eam

and

oil

vapo

rs fo

rmed

dur

ing

the

wat

er q

uenc

h ar

e ro

ute

d to

the

quen

ch to

wer

T-2

.

Aft

er d

rum

D-2

has

coo

led

, the

wat

er is

dra

ined

to th

e co

ke p

ad, a

nd th

e dr

um

unh

ead

ed, b

oth

top

and

bot

tom

.

Page 20: THE DELAYED COKING PROCESS - · PDF fileWhile coke drum D-1 is coking, ... In the previous section, the delayed coking process was described by using the process flow diagram (PFD)

Page 20 of 37

LE

GE

ND

stm

wat

er

prod

uct

time

D-2

D-1O

pen

Clo

sed

stm

D-2

tem

p

Fee

dw

ater

D-1

H-1

thre

e w

ay v

alve

prod

ucts

was

te

T-2

T-1

Figure 8 - Cycle Step 4

Page 21: THE DELAYED COKING PROCESS - · PDF fileWhile coke drum D-1 is coking, ... In the previous section, the delayed coking process was described by using the process flow diagram (PFD)

Page 21 of 37

Cyc

le S

tep

Five

D

rum

D-1

con

tinu

es th

e co

king

por

tion

of t

he c

ycle

at c

okin

g te

mp

erat

ure

.

Aft

er d

rum

D-2

has

bee

n d

ehea

ded

, the

dri

ll st

em is

low

ered

into

the

top

of th

e dr

um w

ith th

e cu

ttin

g he

ad p

ositi

oned

for

vert

ical

dow

n cu

ttin

g, th

e hi

gh p

ress

ure

wat

er

pum

p st

arte

d, a

nd th

e pi

lot h

ole

is d

rille

d th

roug

h th

e en

tire

leng

th o

f the

cok

e be

d.

Page 22: THE DELAYED COKING PROCESS - · PDF fileWhile coke drum D-1 is coking, ... In the previous section, the delayed coking process was described by using the process flow diagram (PFD)

Page 22 of 37

prod

ucts

was

te

T-2

T-1

Cu

ttin

g W

ate

r

stm

D-2

tem

p

Fee

dw

ater

D-1

H-1

thre

e w

ay v

alve

time

D-2

D-1O

pen

Clo

sed

LE

GE

ND

stm

wat

er

prod

uct

Figure 9 - Cycle Step 5

Page 23: THE DELAYED COKING PROCESS - · PDF fileWhile coke drum D-1 is coking, ... In the previous section, the delayed coking process was described by using the process flow diagram (PFD)

Page 23 of 37

Cyc

le S

tep

Six

D

rum

D-1

con

tinu

es th

e co

king

por

tion

of t

he c

ycle

at c

okin

g te

mpe

ratu

re.

In d

rum

D-2

, the

dri

ll st

em is

rai

sed

, the

cut

ting

head

rep

ositi

oned

for

hori

zont

al

cutt

ing,

and

the

coke

is th

en c

ut fr

om th

e to

p do

wn.

The

cok

e an

d cu

ttin

g w

ater

em

pty

onto

the

coke

pad

via

the

chut

e at

the

bott

om o

f the

cok

e dr

um ta

ble

top.

Dru

m D

-2’s

tem

pera

ture

is s

igni

fican

tly lo

wer

, but

doe

s no

t rea

ch a

mbi

ent t

empe

ratu

re d

urin

g th

is

deco

king

pro

cess

.

A

fter

the

coke

is r

emov

ed fr

om d

rum

D-2

, the

dru

m is

reh

eade

d, p

urge

d of

air

, an

d pr

essu

re te

sted

with

ste

am.

Page 24: THE DELAYED COKING PROCESS - · PDF fileWhile coke drum D-1 is coking, ... In the previous section, the delayed coking process was described by using the process flow diagram (PFD)

Page 24 of 37

prod

ucts

was

te

T-2

T-1

stm

D-2

tem

p

Fee

dw

ater

D-1

H-1

thre

e w

ay v

alve

Co

ke

+ W

ater

time

D-2

D-1O

pen

Clo

sed

LE

GE

ND

stm

wat

er

prod

uct

Figure 10 - Cycle Step 6

Page 25: THE DELAYED COKING PROCESS - · PDF fileWhile coke drum D-1 is coking, ... In the previous section, the delayed coking process was described by using the process flow diagram (PFD)

Page 25 of 37

Cyc

le S

tep

Sev

en

At t

his

poin

t, d

rum

D-1

is e

ndin

g th

e co

king

por

tion

of t

he c

ycle

and

rem

ains

at c

okin

g te

mp

erat

ure.

Whe

n d

rum

D-1

is fu

ll, it

is s

wit

ched

off

line

to b

egin

the

dec

okin

g p

orti

on o

f the

cyc

le.

Dru

m D

-2 h

as b

een

pres

sure

test

ed w

ith

stea

m a

nd s

team

is th

en c

onti

nued

to

be a

pp

lied

to d

rum

D-2

as

the

firs

t ste

p (s

team

pre

-hea

t) in

the

war

m-u

p pr

oces

s w

ith

the

vapo

r ro

ute

d to

the

quen

ch to

wer

T-2

.

Page 26: THE DELAYED COKING PROCESS - · PDF fileWhile coke drum D-1 is coking, ... In the previous section, the delayed coking process was described by using the process flow diagram (PFD)

Page 26 of 37

prod

ucts

was

te

T-2

T-1

stm

D-2

tem

p

Fee

dw

ater

D-1

H-1

thre

e w

ay v

alve

time

D-2

D-1O

pen

Clo

sed

LE

GE

ND

stm

wat

er

prod

uct

Figure 11 - Cycle Step 7

Page 27: THE DELAYED COKING PROCESS - · PDF fileWhile coke drum D-1 is coking, ... In the previous section, the delayed coking process was described by using the process flow diagram (PFD)

Page 27 of 37

Cyc

le S

tep

Eig

ht

Dru

m D

-2’s

war

m-u

p (p

re-h

eat)

con

tinue

s w

ith th

e ho

t ove

rhea

d va

por

rero

uted

from

dru

m D

-1 w

hich

als

o in

itiat

es D

-1 c

oolin

g. T

he w

arm

ing

gas

is fi

rst r

oute

d to

the

quen

ch to

wer

T-2

, but

dur

ing

Step

Eig

ht th

e va

por i

s di

vert

ed to

the

frac

tiona

tor

T-1.

Page 28: THE DELAYED COKING PROCESS - · PDF fileWhile coke drum D-1 is coking, ... In the previous section, the delayed coking process was described by using the process flow diagram (PFD)

Page 28 of 37

LE

GE

ND

stm

wat

er

prod

uct

time

D-2

D-1O

pen

Clo

sed

stm

D-2

tem

p

Fee

dw

ater

D-1

H-1

thre

e w

ay v

alve

prod

ucts

was

te

T-2

T-1

Figure 12 - Cycle Step 8

Page 29: THE DELAYED COKING PROCESS - · PDF fileWhile coke drum D-1 is coking, ... In the previous section, the delayed coking process was described by using the process flow diagram (PFD)

Page 29 of 37

Cyc

le S

tep

Nin

e

D

-1 is

then

ste

amed

out

(pur

ged

with

ste

am) t

o re

cove

r th

e ba

lanc

e of

the

prod

uct

oils

rem

aini

ng o

n th

e co

ke.

The

stea

m a

nd o

il va

por

are

rout

ed in

itial

ly to

the

frac

tiona

tor

T-1

befo

re s

witc

hing

to th

e qu

ench

tow

er T

-2 w

hen

mos

t of t

he r

ecov

erab

le h

ydro

carb

ons

have

bee

n st

ripp

ed fr

om th

e co

ke.

D-1

’s te

mpe

ratu

re c

ontin

ues

to c

ool.

H

ot fe

ed fr

om th

e fu

rnac

e H

-1 is

then

sw

itch

ed in

to d

rum

D-2

to s

tart

the

coki

ng

por

tion

of t

he c

ycle

.

Page 30: THE DELAYED COKING PROCESS - · PDF fileWhile coke drum D-1 is coking, ... In the previous section, the delayed coking process was described by using the process flow diagram (PFD)

Page 30 of 37

LE

GE

ND

stm

wat

er

prod

uct

time

D-2

D-1O

pen

Clo

sed

stm

D-2

tem

p

Fee

dw

ater

D-1

H-1

thre

e w

ay v

alve

prod

ucts

was

te

T-2

T-1

Figure 13 - Cycle Step 9

Page 31: THE DELAYED COKING PROCESS - · PDF fileWhile coke drum D-1 is coking, ... In the previous section, the delayed coking process was described by using the process flow diagram (PFD)

Page 31 of 37

Cyc

le S

tep

Ten

Dru

m D

-2 c

onti

nues

the

coki

ng p

orti

on o

f the

cyc

le a

t cok

ing

tem

pera

ture

.

Que

nch

wat

er is

then

add

ed to

dru

m D

-1 to

coo

l the

cok

e in

pre

para

tion

of

cutt

ing

and

dum

ping

from

the

dru

m.

The

ste

am a

nd o

il va

pors

form

ed d

urin

g th

e

wat

er q

uenc

h ar

e ro

uted

to th

e qu

ench

tow

er T

-2.

The

que

nch

wat

er is

add

ed s

low

ly

until

the

drum

is c

oole

d ab

ove

the

skir

t/co

ne/s

hell

junc

tion

area

. A

fter

this

leve

l is

reac

hed,

the

quen

ch w

ater

rat

e is

incr

ease

d to

spe

ed th

e co

ke c

ool d

own

time

with

the

wat

er fl

ow c

ontr

olle

d to

ens

ure

the

pres

sure

gen

erat

ed b

y th

e va

pori

zatio

n of

wat

er d

oes

not e

xcee

d th

e re

lief v

alve

set

pre

ssur

e.

Aft

er d

rum

D-1

has

coo

led

, the

wat

er is

dra

ined

to th

e co

ke p

ad, a

nd th

e dr

um

unhe

aded

, bot

h to

p an

d b

otto

m.

Page 32: THE DELAYED COKING PROCESS - · PDF fileWhile coke drum D-1 is coking, ... In the previous section, the delayed coking process was described by using the process flow diagram (PFD)

Page 32 of 37

prod

ucts

was

te

T-2

T-1

stm

D-2

tem

p

Fee

dw

ater

D-1

H-1

thre

e w

ay v

alve

time

D-2

D-1O

pen

Clo

sed

LE

GE

ND

stm

wat

er

prod

uct

Figure 14 - Cycle Step 10

Page 33: THE DELAYED COKING PROCESS - · PDF fileWhile coke drum D-1 is coking, ... In the previous section, the delayed coking process was described by using the process flow diagram (PFD)

Page 33 of 37

Cyc

le S

tep

Ele

ven

D

rum

D-2

con

tinu

es th

e co

king

por

tion

of t

he c

ycle

at c

okin

g te

mpe

ratu

re.

A

fter

dru

m D

-1 h

as b

een

deh

ead

ed, t

he d

rill

stem

is lo

wer

ed in

to th

e to

p of

the

dru

m w

ith th

e cu

ttin

g he

ad p

ositi

oned

for

vert

ical

dow

n cu

ttin

g, th

e hi

gh p

ress

ure

wat

er

pum

p st

arte

d, a

nd th

e pi

lot h

ole

is d

rille

d th

roug

h th

e en

tire

leng

th o

f the

cok

e be

d.

Page 34: THE DELAYED COKING PROCESS - · PDF fileWhile coke drum D-1 is coking, ... In the previous section, the delayed coking process was described by using the process flow diagram (PFD)

Page 34 of 37

prod

ucts

was

te

T-2

T-1

Cu

ttin

g W

ate

r

stm

D-2

tem

p

Fee

dw

ater

D-1

H-1

thre

e w

ay v

alve

time

D-2

D-1O

pen

Clo

sed

LE

GE

ND

stm

wat

er

prod

uct

Figure 15 - Cycle Step 11

Page 35: THE DELAYED COKING PROCESS - · PDF fileWhile coke drum D-1 is coking, ... In the previous section, the delayed coking process was described by using the process flow diagram (PFD)

Page 35 of 37

Cyc

le S

tep

Tw

elve

D

rum

D-2

con

tinu

es th

e co

king

por

tion

of t

he c

ycle

at c

okin

g te

mpe

ratu

re.

In d

rum

D-1

, the

dri

ll st

em is

rai

sed

, the

cut

ting

head

rep

ositi

oned

for

hori

zont

al

cutt

ing,

and

the

coke

is th

en c

ut fr

om th

e to

p do

wn.

The

cok

e an

d cu

ttin

g w

ater

em

pty

onto

the

coke

pad

via

the

chut

e at

the

bott

om o

f the

cok

e d

rum

tabl

e to

p. D

rum

D-1

’s

tem

pera

ture

is s

igni

fican

tly lo

wer

, but

aga

in d

oes

not r

each

am

bien

t tem

pera

ture

dur

ing

this

dec

okin

g pr

oces

s.

A

fter

the

coke

is r

emov

ed fr

om d

rum

D-1

, the

dru

m is

reh

eade

d, p

urge

d of

air

,

and

pres

sure

test

ed w

ith s

team

.

Page 36: THE DELAYED COKING PROCESS - · PDF fileWhile coke drum D-1 is coking, ... In the previous section, the delayed coking process was described by using the process flow diagram (PFD)

Page 36 of 37

pr

oduc

ts

was

te

T-2

T-1

stm

D-2

tem

p

Fee

dw

ater

D-1

H-1

thre

e w

ay v

alve

time

D-2

D-1O

pen

Clo

sed

Co

ke

+ W

ate

r

LE

GE

ND

stm

wat

er

prod

uct

Figure 16 - Cycle Step 12

Page 37: THE DELAYED COKING PROCESS - · PDF fileWhile coke drum D-1 is coking, ... In the previous section, the delayed coking process was described by using the process flow diagram (PFD)

Page 37 of 37

T.E. Wolf has over 40 years petroleum and petrochemical experience, including 25 years in project management. He holds a BS degree in Mechanical Engineering and is a registered Professional Engineer.

© 2013 by Thomas E. Wolf. All rights reserved. No part of this document may be reproduced or transmitted in any form or by any means, electronic or mechanical, including photocopying, recording, or by any information storage or retrieval system without written permission of the copyright holder, except for the inclusion of brief quotations in a review.