STEAM CRACKING - wrtraining.org

STEAM CRACKING

PETROCHEMICAL TRAINING (1/3)

PETROCHEMICAL ACTIVITIES OVERVIEW

STEAM CRACKERS :LOCATION, FEEDSTOCKS AND PRODUCTS

ETHYLENE

PROPYLENE

BUTADIENE ISO-BUTANE

AUTOMOTIVE GASOLINE

BENZENE XYLENE TOLUENE

REFINERY

TRANSPORTATION

AND

DISTRIBUTION

PETROLEUM

MARKET

DOWNSTREAM PETROLEUM ACTIVITIES PETROCHEMICALS

STEAM CRACKER

• ETHANE

• LPG

• NAPHTHA

• GASOIL

• DISTILLATES

PONAPARAFFINS, OLEFINS, NAPHTHENES & AROMATICS

WHAT YOU NEED TO KNOW ABOUT ORGANIC CHEMISTRY

SATURATED HYDROCARBONS UNSATURATED HYDROCARBONS

SINGLE “C-C” BOND DOUBLE “C-C” BONDS TRIPLE “C-C” BONDS

CHAINS CYCLES

PARAFFINS NAPHTHENES

N-PARAFFINS ISO-PARAFFINS CYCLO-PARAFFINS

Examples

n-Butane

H

H

H

C

H H

H

H

CC

H

H

HC

iso-Butane

C C

CC

C C

HH

HH

H H

H H

H H

H H

Cyclohexane

CHAINS

ACETYLENICS

H

H

H

C HC C

Propyne

C C

CC

C C

HH

HH

H H

BENZENIC CYCLES

AROMATICS

Benzene

CHAINS

OLEFINS (1 x C=C)

DIOLEFINS (2 x C=C)

H

HC

H

HC

Ethylene

H

HC

H

C

HC

H

HC

1,3-Butadiene

H

H

H

C

H

H

C

H

H

C

H

H

H

C

STABLE HC VERY REACTIVE HC

WHAT YOU NEED TO KNOW ABOUT ORGANIC CHEMISTRY

A LITTLE HISTORY

ABOUT STEAM CRACKING

Ethylene from cracking ethane

Diesel fuel steam cracking : 6kT/year of ethylene

1920 1942 1950

Construction of units with a capacity up to 50kT/year of ethylene

1960

Naphtha steam crackers : 300kT/year of ethylene

TODAY

Naphtha steam crackers : 1MT/year of ethylene


CRACKING CONDITIONS


CRACKING CONDITIONS


H

CH

H

PENTANE

H

C

H H

C

H H

C

H

H

C H

H

C5H12

CRACKING C–C BONDS

H

CH

H

ETHANE

H

C H

H H

CH

H

PROPANE

H

C

H

H

C H

H

C2H6 C3H8

CRACKING CONDITIONS


H

CH

H

PENTANE

H

C

H H

C

H H

C

H

H

C H

H

C5H12

CRACKING C–H BONDS

H

CH

H

PENTENE

H

C

H H

C

H H

C

H

C HC5H10 H H HYDROGEN H2


CRACKING CONDITIONS

Steam cracking requires extreme process conditions :

Cracking temperature : 800 – 850°C

Residence time : 0.1 – 0.5 sec

Cracking pressure : slightly higher than atmospheric pressure

Dilution of the feed with large quantities of steam : ~0.6 T of steam per 1 T of naphtha feed

200 300 400 500 600 700 800 900

INCREASING

HC STABILITY

T (°C)

METHANEETHANE

HEXANE

C16ACETYLENICS

NAPHTHALENE

BENZENEPROPYLENE

ETHYLENE

PARAFFINS

AROMATICS

ACETYLENICS

OLEFINS


COKE AND HYDROGEN

HEPTANE

C7H16

PROPANE

C3H8

1-BUTENE

C4H8

BUTADIENE

C4H6

PROPYLENE

C3H6

ETHYLENE

C2H4

BENZENE

C6H6

COKE

ETHYLENE

C2H4

METHANE

CH4

PROPYNE

C3H4

ACETYLENE

C2H2

2-HEPTENE

C7H14

H H

H H H H

H H

H H

H H

CRACKING C-C BONDS

CRACKING C-H BONDS

ADDITION REACTIONS

FEEDSTOCKS AND YIELDS


0 %

METHANE

PROPYLENE

ETHANE

1,3-BUTADIENEOTHER C4

PYROLYSIS GASOLINE

FUEL

10 %

20 %

30 %

40 %

50 %

60 %

70 %

80 %

90 %

100 %

ETHYLENE

HYDROGEN

ACETYLENE

PROPANE + PROPYNE + PROPADIENE

C2 CUT

C3 CUT

C4 CUT

STANDARD YIELDS FOR NAPHTHA

NAPHTHA

C5 – C6 – C7

Paraffins

Naphthenes

Aromatics


YIELDS FOR NAPHTHA

0%

20%

40%

60%

80%

100%

Hydrogen Methane Ethylene Propylene Butadiene Other C4 Gasoline Fuel oil

YIELDS BY FEEDSTOCK

ETHANE PROPANE BUTANE NAPHTHA DIESEL FUEL VACUUM DISTILLATE


YIELDS FOR VARIOUS FEEDSTOCKS


WORLD BREAKDOWN OF FEEDSTOCKS

NATURE OF

FEEDSTOCKS

ETHANE

LPGNAPHTHA

DIESEL FUEL

DISTILLATES

WESTERN EUROPE 16 74 10

NORTH AMERICA 75 18 7

JAPAN 3 97 -

WORLD 42 52 6

0%

20%

40%

60%

80%

100%

WESTERNEUROPE

NORTHAMERICA

JAPAN WORLD

NATURE OF FEEDSTOCK

Ethane / LPG Naphtha Diesel fuel / distillates


WORLD BREAKDOWN OF FEEDSTOCKS FOR ETHYLENE PRODUCTION

Naphtha52%

Butane15.8%

Ethane10.1%

Propane11.5%

Gas oil10.5%

Others0.1%

Naphtha Butane Ethana Propane Gas oil Others

INVESTMENT AND ECONOMICS



FEEDSTOCK ETHANE NAPHTHA DIESEL FUEL

Minimum investment (M$) 350 - 400 450 - 550 550 - 650

INVESTMENT AND ECONOMICS

Steam crackers are complex facilities that require important investments

Key figures for various feedstocks for a 500 kT/year ethylene production, based in Europe :

Pyrolysis furnaces account for ~40% of investments (~200M$)

The remaining ~60% for separation and purification facilities (~300M$)

INTRODUCTION

THE STEAM CRACKING PROCESS


INTRODUCTION

A typical steam cracker plant is made of 3 parts :

1. The hot zone :

Pyrolysis or cracking furnaces

Quench exchangers and quench ring

Separation columns and splitters of the hot separation train

2. The compression zone

A cracked gas compressor

Purification and separation columns

Dryers

3. The cold zone

The cold box

A methanation reactor

Separation columns and splitters of the cold separation train

C2 and C3 converters

A gasoline hydrostabilization reactor

THE HOT ZONE


WATER

QUENCH

COLUMN

NAPHTHA

FEED

TLX

DILUTION

STEAM

0.6 t / t feed

PR

IMA

RY

FR

AC

TIO

NA

TO

R

FO

ST

RIP

PE

R

QUENCH OIL

GA

SO

LIN

E

ST

RIP

PE

RFrom other

furnaces

To other

furnaces

To other

passes

QUENCH RING

CRACKED GAS

TO COMPRESSOR

WA

TE

R Q

UE

NC

H

GASOLINE

C4 AND LIGHTER

FUEL OIL

PYROLYSIS AND PRIMARY FRACTIONATIONHEAT EXCHANGER

PUMP


NAPHTHA FEED

DILUTION STEAMTLX

QUENCH RING

TO PRIMARY

FRACTIONATION

STACK

2.6 m

8.5 m

9.5 m

7.5 m

450°C

200°C

CONVECTION

ZONE

RADIATION

ZONE


PYROLYSIS FURNACESINGLE RADIANT BOX

150°C

850°C

600°C

NAPHTHA FEED

DILUTION STEAM

STEAM + HYDROCARBONS

TO RADIATION ZONE

CONVECTION

ZONE

RADIATION

ZONE

NAPHTHA FEED

NAPHTHA + STEAM

Burners

Refractory

Refractory

TLX


PYROLYSIS FURNACESINGLE RADIANT BOX

CO

NV

EC

TIO

N Z

ON

E

3-pin coil tubes of same Φ

Coil with tubes of increasing Φ

CONVENTIONAL FURNACES

Single vertical tube

m-SEC FURNACES



PROBLEMS ASSOCIATED WITH STEAM CRACKER FURNACES

CREEP :

Slow elongation due to temperature

CARBURIZATION OF THE TUBES :

Enrichment in carbon of the tubes from its inside surface

EROSION :

Due to high speed of gases inside the tubes

FATIGUE :

Due to repeated thermal cycles

24

CrCHROMIUM

51.9961

28

NiNICKEL

58.6934

6

CCARBON

12.0107

30% 35% 0.5%


MECHANISM OF COKE FORMATION

1050 °C

1045 °C

950 °C

820 °C

METAL

COKE

FLUID FILM OF

HEAVY HC

Di = 145 mm

T ~ 820°C

e = 9 mm

HC speed :

200 – 300 m/s

e = 9 mm


PYROLYSIS FURNACE ADJUSTMENT PARAMETERS

1. Influence of cracking temperature :

NAPHTHA COMPOSITION % Vol

PARAFFINS 80

NAPHTHENES 15

AROMATICS 5

Dilution steam t/t of feed 0.6

0 5 10 15 20 25 30 35

Gasoline

Benzene

Butadiene

Propylene

Ethylene

Methane

Hydrogen

EFFECT OF TEMPERATURE ON YIELDS

815°C 835°C 855°C



2. Influence of residence time :

In the 1950’s :

Residence time ~ 0.7 to 1 sec

Ethylene yields ~ 22%

In the 1960’s :

Residence time ~ 0.2 to 0.4 sec

Ethylene yields ~ 28%

In the past few years :

Residence time ~ 0.05 to 0.1 sec

Cracking temperature ~ 900°C

0.9

15.8

28.6

15

4.4

21.7

1.1

14.9

32.2

14.3

3.6

18.9

0 10 20 30 40

Hydrogen

Methane

Ethylene

Propylene

Butadiene

Gasoline

COMPARING FURNACES

m-Sec furnace Conventional furnace

% WEIGHTCRACKING NAPHTHA

Hydrogen H2 0.9 1.1

Methane CH4 15.8 14.9

Ethylene C2H4 28.6 32.2

Propylene C3H6 15.0 14.3

Butadiene C4H6 4.4 3.6

Gasoline C5-200 21.7 18.9

Conventional furnace m-Sec furnace



3. Influence of pressure :

A lower operating pressure :

promotes light olefins formation

reduces coke

Steam cracker furnaces are operated at the lowest pressure possible by :

maintaining the output pressure of the furnaces at a value as close as possible to atmospheric pressure

reducing the pressure of hydrocarbons by injection of steam

STEAM CRACKER FEED STEAM (t) / HC (t)

ETHANE – PROPANE – BUTANE 0.3 – 0.4

NAPHTHA 0.5 – 0.6

DIESEL FUEL 0.6 – 0.8

THE COMPRESSION ZONE



PRODUCT FORMULA % Weight

Hydrogen H2 1.1

Methane CH4 16.2

Ethylene C2H4 29.2

Acetylene C2H2 0.3

Ethane C2H6 7.2

Carbon monoxide

Carbon dioxide

Hydrogen sulfide

CO

CO2

H2S

0.15

Propylene C3H6 14.3

Propane C3H8 0.5

Propyne

Propadiene

C3H4

C3H4

0.5

C4 cut - 8.45

Gasoline C5-200 19.8

Water H2O 2.3

Separation of hydrogen with 95% purity for downstream hydrogenation units

Recovery of methane for use as internal fuel

Required purity : 99.95 % weight

Separated and eliminated

Recycled back to ethane cracking furnaces

Impurities and catalyst poisons to be removed and eliminated

Required purity : 99.5 % weight

Separated and eliminated

Recovery of butadiene and removal of acetylenics

Elimination of unstable diolefins and recovery of benzene

Removal of water to avoid clogging at low temperatures by formation of hydrate crystals


T (°C)

P (bar)

-200 -150 -100 -50 0 50 100 150 200

0.1

0.5

2

3

5

10

20

30

50 PROPADIENEACETYLENE

30 – 35 bars

COMPRESSION – WASHING – DRYING

CRACKED GAS

HEAT EXCHANGER

1st STAGE 2nd STAGE 3rd STAGE

CAUSTIC

SCRUBBER

4th STAGE

CRACKED GAS

TO DEMETHANIZER

WATER WATER WATER

WATERDE

ET

HA

NIZ

ER

DRYER

MOLECULAR

SIEVES

INTERSTAGE HC CONDENSATES TO GASOLINE STRIPPER

C3 AND HEAVIER

TO DEPROPANIZER

METHANE

ETHANE


- Eliminate H2S

- Absorb CO2

0.05% water content3 x

THE COLD ZONE


CRACKED GAS

FROM DRYER

DEMETHANIZER

PROPYLENE

ETHYLENE

ETHYLENE

METHANE

HYDROGEN

METHANE

HYDROGEN

C2+ TO DEETHANIZER

ETHYLENE

METHANE 98%

METHANATION REACTORCO INTO METHANE

H2 95% - CO ~1500ppm

WATER

DRYER

HYDROGEN 98%

TO DHU

COOLING

H2 AND CH4 SEPARATION

METHANATION

COLD BOX

METHANE

DEETHANIZER

C2 CUT FROM

DEMETHANIZER

ACETYLENE

HYDROGENATION

“C2 HYDRO”

HYDROGEN 95%

ET

HA

NE

/ E

TH

YL

EN

E

SP

LIT

TE

R

DE

PR

OP

AN

IZE

RETHYLENE AND PROPYLENE

• SEPARATION

• PURIFICATION

ETHYLENEPURITY 99.9%

ACETYLENE 5ppm max

METHANE / ETHANE 0.1%

ETHANERECYCLED BACK

TO CRACKING FURNACES

MA AND PD

HYDROGENATION

“C3 HYDRO”

HYDROGEN 95%

C4+

C3 CUT

C2 CUT

C3+

PR

OP

AN

E /

PR

OY

LE

NE

SP

LIT

TE

R

PROPYLENEPURITY 99.5%

MA + PD 15ppm max

ETHANE / PROPANE 0.5%

PROPANE


C3 AND HEAVIER

FROM DEETHANIZERCOMPRESSION ZONE

C4+ FROM

DEPROPANIZER DE

BU

TAN

IZE

R

GASOLINE

HYDROSTABLIZATIONUNSTABLE DIOLEFINS

HYDROGENATION

HYDROSTABILIZED

GASOLINE• MOTOR GASOLINE

• BENZENE RECOVERY

C4 CUT

GASOLINE FROM

GASOLINE SPLITTERHOT ZONE


PYROLYSIS

GASOLINE

C2 CUT : SELECTIVE HYDROGENATION

SELECTIVE HYDROGENATIONS



C2 CUT % Weight

ETHANE 19

ETHYLENE 80

ACETYLENE 1

ACETYLENE SPECIFICATION

< 5ppm

< 0.0005%

REACTOR 1 REACTOR 2

DE

ET

HA

NIZ

ER

REACTOR 3

C2 CUT % VOL

ETHANE 19

ETHYLENE 80

ACETYLENE 1

HYDROGEN HYDROGEN

C2 CUTTO ETHANE / ETHYLENE SPLITTER

C2 CUT HYDRO

HYDROGEN

METHANE

ETHANE

ETHYLENE

REGENERATION

IN PROGRESS



< 5ppm ACETYLENE





C3 CUT % Weight

PROPANE 3 – 5

PROPYLENE 85 – 92

PROPYNE 3 – 6

PROPADIENE 2 – 4

PROPYNE / PROPADIENE

SPECIFICATION

< 3-4 %

DE

PR

OP

AN

IZE

R

C3+ CUT

C3 CUT % VOL

PROPANE 5

PROPYLENE 90

METHYLACETYLENE 3

PROPADIENE 2

REACTOR 1 REACTOR 2

HYDROGEN HYDROGEN

C3 CUTTO PROPANE / PROPYLENE SPLITTER

C3 CUT HYDRO

HYDROGEN

PROPANE

PROPYLENE

C4+ CUTTO DEBUTANIZER



> 99.5 ppm Polymer grade

> 94% Chemical grade

HYDROSTABILIZATION

OF STEAM CRACKED GASOLINE


PYROLISIS GASOLINE

MAV [1] 80 - 100

IBr [2] ~60

REACTOR

PYROLYSIS

GASOLINE

HYDROGEN

HYDROSTABILIZED

GASOLINE

RECYCLED

HYDROGENQUENCH

DILUTION

LOOP

HYDROSTABILIZED

MAV < 1

IBr ~40


[1] Maleic Anhydride Value

[2] Bromine index

A TYPICAL STEAM CRACKER PLANT

OTHER FEEDS :

• ETHANE (C2)

• LPG (C3-C4)

• GASOIL (C10-C20)

• DISTILLATES (C20-C40)

ETHYLENE

PROPYLENE

BUTADIENE

AUTOMOTIVE GASOLINE

BENZENE

C2 CUT

C3 CUT

C4 CUT

GASOLINE

STEAM CRACKINGNAPHTHA

Thermal cracking of hydrocarbons :

at high temperature :

800°C

during a very short time :

0.2 sec

in presence of steam :

0.6 t / t feed

under low pressure :

2-3 bars

C5 – C6 – C7

Paraffins

Naphthenes

Aromatics

A TYPICAL STEAM CRACKER PLANT

1,3 – BUTADIENE

EXTRACTION

FUEL

NAPHTHA

FEED 1. CRACKING

2. PRIMARY FRACTIONATION

3. WATER SCRUBBING

1. COMPRESSION

2. WASHING

3. DEETHANIZATION

4. DRYING

1. COOLING

2. SEPARATION OF H2 / CH4

3. DEMETHANIZATION

CRACKED

GAS

METHANATIONCO CH4

H2

HYDROGEN

FUEL GASMETHANE

C2+ CUT

DE

ET

HA

NIZ

ER

C2 CUT

C2

HYDROC2= / C2 SPLITTER

ETHYLENE

ETHANERECYCLED BACK

TO CRACKING FURNACES

C3+ CUT

C3 CUT

C3

HYDRO

DE

PR

OP

AN

IZE

R

C3= / C3 SPLITTER

PROPYLENE

PROPANE

DE

BU

TA

NIZ

ER

INT

ER

ST

AG

E H

C

CO

ND

EN

SA

TE

S

GASOLINE

C4 CUT

C4

HYDRO

BUTADIENE

OTHER C4

GASOLINE

HYDRO

STABILIZATION

GASOLINE POOL

BENZENE RECOVERY

H2

H2

H2

BENZENE

NAPHTHA

ETHYLENE

PROPYLENE

PYROLYSIS GASOLINE

H2 + FG

Pyrolysis fuel

POLYETHYLENE

VINYL CHLORIDE

ETHYLBENZENE

ETHYL OXIDE

PVC

STYRENE POLYSTYRENE

STYRENE-BUTADIENE RUBBER

POLYPROPYLENE

ACRYLONITRILE

OXO ALCOHOL

PROPYLENE OXIDE

CUMENE

PLASTICS

FIBERS

PHENOL

ACETONE

BUTADIENE

EXTRACTIONC4 CUT

BUTADIENE BUTADIENE RUBBER

STYRENE-BUTADIENE RUBBER

ISOBUTENE

RECOVERY

ISOBUTENE

OTHER C4

BEZENE

EXTRACTION

CYCLOHEXANE

BENZENE FREE GASOLINE

STEAM

CRACKING1460

245

150

115

105

55

305 85

33

125

220

450

Stream in 1000 T/year

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