steam cracking - wrtraining.org
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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
ABOUT STEAM CRACKING
CRACKING CONDITIONS
ABOUT STEAM CRACKING
CRACKING CONDITIONS
ABOUT STEAM CRACKING
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
ABOUT STEAM CRACKING
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
ABOUT STEAM CRACKING
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
ABOUT STEAM CRACKING
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
ABOUT STEAM CRACKING
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
ABOUT STEAM CRACKING
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
ABOUT STEAM CRACKING
YIELDS FOR VARIOUS FEEDSTOCKS
ABOUT STEAM CRACKING
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
ABOUT STEAM CRACKING
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
ABOUT STEAM CRACKING
ABOUT STEAM CRACKING
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
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
THE STEAM CRACKING PROCESS
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
THE STEAM CRACKING PROCESS
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
THE STEAM CRACKING PROCESS
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
THE STEAM CRACKING PROCESS
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
THE STEAM CRACKING PROCESS
THE STEAM CRACKING PROCESS
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%
THE STEAM CRACKING PROCESS
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
THE STEAM CRACKING PROCESS
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
THE STEAM CRACKING PROCESS
PYROLYSIS FURNACE ADJUSTMENT PARAMETERS
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
THE STEAM CRACKING PROCESS
PYROLYSIS FURNACE ADJUSTMENT PARAMETERS
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
THE STEAM CRACKING PROCESS
THE STEAM CRACKING PROCESS
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
THE STEAM CRACKING PROCESS
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
THE STEAM CRACKING PROCESS
- Eliminate H2S
- Absorb CO2
0.05% water content3 x
THE COLD ZONE
THE STEAM CRACKING PROCESS
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
THE STEAM CRACKING PROCESS
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
THE STEAM CRACKING PROCESS
PYROLYSIS
GASOLINE
C2 CUT : SELECTIVE HYDROGENATION
SELECTIVE HYDROGENATIONS
SELECTIVE HYDROGENATIONS
C2 CUT : SELECTIVE HYDROGENATION
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
SELECTIVE HYDROGENATIONS
C2 CUT : SELECTIVE HYDROGENATION
< 5ppm ACETYLENE
C3 CUT : SELECTIVE HYDROGENATION
SELECTIVE HYDROGENATIONS
SELECTIVE HYDROGENATIONS
C3 CUT : SELECTIVE HYDROGENATION
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
SELECTIVE HYDROGENATIONS
C3 CUT : SELECTIVE HYDROGENATION
> 99.5 ppm Polymer grade
> 94% Chemical grade
HYDROSTABILIZATION
OF STEAM CRACKED GASOLINE
SELECTIVE HYDROGENATIONS
PYROLISIS GASOLINE
MAV [1] 80 - 100
IBr [2] ~60
REACTOR
PYROLYSIS
GASOLINE
HYDROGEN
HYDROSTABILIZED
GASOLINE
RECYCLED
HYDROGENQUENCH
DILUTION
LOOP
HYDROSTABILIZED
MAV < 1
IBr ~40
SELECTIVE HYDROGENATIONS
[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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