Kuwait University
COLLEGE OF ENGINEERING AND PETROLEUM
Chemical Engineering Department
CHE 497: Plant Design
Literature Survey
Production of Natural Gas Liquids
(NGL)
Group # 3
Naser torKi Al-Enazi 206216902
Abdulrahman Sami Alqattan 208111813
Mohammed Mahdi Bouftain 206112461
Abdullah Abdulaziz Alfahad 207115276
Ahmed Haji Al-Mutairi 205114166
Supervised By:
Prof. Mohamed A. Fahim
Eng.Yusuf Ismail
Abstract:
Natural Gas liquids refer to a mixture of light hydrocarbons. These light
components can be extracted using many processes of compression, cooling and
fractionation. The NGL is produced via the previously mentioned units. Reactors,
such as Fischer-Tropsh reactors, are used to increase the production of natural gas
liquids.
The refinery gases will be taken from the refinery units and mostly the gases
are rich with liquids (NGL) so it is preferred to recover these liquids for commercial
benefits. The ethane, propane and butane are types of the (NGL) ,and the component
that this project is concerned in is the butane so the propane and ethane –even the gas
methane- will be converted to butane . After increasing the production of butane, it is
used to produce gasoline with high octane number by alkylation with olefins through
this project. Refinery gas will pass through several treatment process while it goes
through the main process so we can get better conversion. While the treatment process
it should get of (H2s and H2O) to keep the used equipment safety.
The waste CO2 stream can be converted – instead of ejecting it to the
environment - through Satabier reaction to methane, which will further processed by
various types of reactors to increase the production of natural gas liquids (the
butanes).
1
Table of contents:
Abstract
1
introduction
3
History
4
World Production and Consumption
5
Uses
7
Feed stock and product description and their physical and chemical
properties
8
Process Flow Sheets
20
Major equipments in flow sheets
23
Economical analysis
27
Comparison between the process flow sheets
29
Conclusion
30
References
31
2
Introduction:
refinery gas (or process gas) is a general term often used to include all of the
hydrocarbon gaseous products and by-products that emitted from a variety of refinery
processes which this gas generally contains components below cyclohexane. This gas
is usually rich with heavy hydrocarbons called natural gas liquids which include
ethane, propane and butane.
Natural gas liquids recovery is the process used to remove heavier
hydrocarbons liquids from the gas streams. The recovery of natural gas liquids may
yields –especially if the gas is very rich- a source of revenue. The liquids are; ethane,
propane and butanes. Also the recovery is used to avoid the unsafe formation of a
liquid phase reaction during the transport process.
In every case, the specific processing needed is determined by the flow rate,
composition, temperature, and pressure of the produced gas and by the components or
impurities that must be removed to meet delivery specifications, the percentage of the
heavier hydrocarbons present in the gas and on the efficiency of the process used to
recover them.
These liquids can be sold separately as a clean fuels but also can used as a
feedstock petrochemical plants to produce olefins and petrochemicals .Also can be
as feedstock to refineries like butanes, one of the natural gas liquids, can be further
processed by alkylation to produce alkylates which are added to the gasoline pool to
raise the high octane ratings of it.
3
History:
The origin of natural gas liquids can be related with the ancient time related to
the discovery of the natural gas. Natural gas can be dated back to the ancient times in
the Middle East. This discovery has been noticed around Persia, Greece and India.
The Chinese were the first people to discover the value of this valuable natural
resource. At first, natural gas was regarded as unwanted product during drilling
processes but then people started to realize its value. But the recovery of its liquids
especially when it is rich was not recognized. The natural gas was first
commercialized in 1790, until 1900s. In 1910, Dr.Walter Snelling, the U.S. Bureau of
Mines, who investigated gasoline to see why it evaporated so fast and discovered that
the evaporating gases were propane, butane, and other light hydrocarbons. Dr.Snelling
prepared a still that could separate the gasoline into its liquid and gaseous
components. Clearly these gaseous components can be liquefied and then can be
called natural gas liquids but since they are in vapor phase at the ambient temperature
and pressure, they appeared to Dr.Snelling as gases.
So his discovery is related to the second important source of the natural gas
liquids, which are the refining gas emitted from different units of refineries plants. In
the beginning of refining processes, Arab countries have been producing large
quantities of refinery separator off-gases to reduce the volatility of petroleum
fractions products so that they are stabilized, which are mostly flared and are not
utilizing the recovery and production the natural gas liquids from it, which this project
is concerned of.
Early efforts in the 20th century for natural gas liquids recovery involved
compression and cooling of the rich gas stream. Also the lean oil absorption process
was developed in the 1920s to increase recovery of the liquids with increased amounts
of butane . In order to further increase production of liquids, refrigerated lean oil
absorption was developed in the 1950s to increase the yield by cooling the lean oil to
increase its absorptive properties. Recently developed techniques and processes were
developed which may increase the recovery to 90% such as cryogenic refrigeration
which is the widely and the common process used for recovering natural gas liquids.
The natural gas liquids such as butanes can be used to increase the octane
number of gasoline by alkylation process. Alkylation is another twentieth century
refinery innovation, and developments in petroleum processing in the late 1930s.
Some of alkylation processes includes sulfuric acid alkylation process which was
introduced in 1938, and hydrogen fluoride alkylation was introduced in 1942. Also
polymerization processes which were came into use at 1930s
4
World production and consumption:
Natural gas liquid production comes from processing the gas that is a set of
production processes is the purification of raw natural gas extracted from wells after
gas and pushed to the surface by oils. After treatment most of the methane content of
natural gas, which then become the characteristics significantly different from the
properties of raw gas, and the NGL, consist of small hydrocarbon like methane,
butane and benzene.
Year
1980
1982
1984
1986
1988
1990
1992
1994
1996
1998
2000
2002
2004
2006
Production (Thousand barrel per Day )
3446.13
3631.79
3878.00
4162.92
4488.69
4640.34
4847.46
5461.89
5773.67
6061.96
6465.75
6876.91
7393.21
7794.61
5
NGL gas liquids production by country:
Rank Country
1
2
3
4
5
6
7
8
9
10
11
12
United States
Saudi Arabia
Canada
Mexico
Russian Federation
Algeria
United Arab
Emirates
Norway
Qatar
Venezuela
United Kingdom
Kuwait
Production (Thousand barrel per
Day )
1738.78
1427.00
685.21
427.41
416.61
309.93
300.00
286.21
280.00
215.00
142.30
130.00
The consumption of NGL in North America and Asia Oceania is the highest
rate because of the economic demand of this reign.
6
Uses:
Uses for the butane:
It is used as lighter fuel, cooking and camping. And the pure butane like
isobutene can be used as refrigerants, and it can be mixed with propane and other
hydrocarbon to make Liquefied petroleum gas as fuel for vehicles.
Uses for the gasoline:
It is used as a solvent, and it is used as fuel for cars and can be used to produce
rubber, dyeand is used in the production of other chemical such as polymers, plastic
and phenol.
Uses for the NGL:
NGL is cleanest burning fossil fuel, it produces less emissions than oil and
because of it used in many things that need energy specially that need burring, it is
used as fuel for cars, cooking, camping and heating.
7
Feed stock and product description and their physical and
chemical properties:
Hydrogen:
Is an element that has symbol (H), and it is the lightest and the most presence
gas in the universe (75%) and it is odorless, nonmetallic, colorless, non toxic gas with
the molecular formula H2.And it is used in industry like Ammonia, methanol,
Hydrochloric acid and welding.
Table-1 Hydrogen Physical and Chemical Properties
Molecular weight
1
Color
Colorless
Phase
Gas
Melting point
14.01 K, -259.14 °C, -434.45 °F
Boiling point
20.28 K, -252.87 °C, -423.17 °F
Density
(0 °C, 101.325 kPa)
0.08988 g/L
Triple point
13.8033 K (-259°C), 7.042 kPa
Liquid density at m.p.
0.07 (0.0763 solid)[2] g·cm−3
Liquid density at b.p.
0.07099 g·cm−3
Thermal conductivity
0.1805 W·m−1·K−1
Critical point
32.97 K, 1.293 MPa
Heat of fusion
(H2) 0.117 kJ·mol−1
Crystal structure
hexagonal
Electronegativity
2.20 (Pauling scale)
Element category
nonmetal
Electron configuration 1s1
Critical point
32.97 K, 1.293 MPa
Heat of vaporization
(H2) 0.904 kJ·mol−1
Molar heat capacity
(H2) 28.836 J·mol−1·K−1
8
Carbon dioxide:
Is a chemical compound with a chemical formula (CO2), and it is composed of
two oxygen atom and one carbon atom, and it is natural state is gas but it is has solid
state (at-78.5) called ice dry. And it is used in industry like food industry, petroleum
industry and chemical industry.
Table-2 CO2 Physical and Chemical Properties
Molecular formula CO2
Color
colorless
Molar mass
44.01 g mol−1
Melting point
-78 °C, 194.7 K, -109 °F
Boiling point
-57 °C, 216.6 K, -70 °F (at 5.185 bar)
Density
1562 kg/m3 (solid at 1 atm and −78.5 °C)
770 kg/m3 (liquid at 56 atm and 20 °C)
1.977 kg/m3 (gas at 1 atm and 0 °C)
Odor
Odorless
Solubility in water 1.45 g/L at 25 °C, 100 kPa
Acidity (pKa)
6.35, 10.33
Viscosity
0.07 cP at −78.5 °C
Std enthalpy of
formation ΔfHo298
−393.5 kJ·mol−1
Standard molar
entropy So298
214 J·mol−1·K−1
Molecular shape
linear
Dipole moment
Zero
Exact mass
43.989829244 g mol−1
MSDS
External MSDS
ATC code
V03AN02
Refractive index
1.1120
9
Hydrogen sulfide:
Is a chemical compound with a chemical formula (H2S), and it is composed of
two hydrogen atom and one sulfur atom, and it is colorless and flammable gas and it
is heavy than air and for that we can find it on deep places . And it is used in medicine
industry.
Table-3 Hydrogen sulfide Physical and Chemical Properties
Molecular weight
34.08 g mol−1
Color
Colorless
Systematic name
Hydrogen sulfide
Melting point
-82 °C, 191 K, -116 °F
Boiling point
-60 °C, 213 K, -76 °F
Density
1.363 g dm-3
Odor
faint rotten egg
threshold
0.0047 ppm
Molecular formula
H2S
Solubility in water
4 g dm-3 (at 20 °C)
Acidity (pKa)
7.0
Basicity (pKb)
6.95
Vapor Pressure
1740 kPa (at 21 °C)
Molecular shape
Bent
Dipole moment
0.97 D
Std enthalpy of
formation ΔfHo298
−21 kJ·mol−1
Standard molar
entropy So298
206 J·mol−1·K−1
Specific heat capacity, C 1.003 J K-1 g-1
Refractive index (nD)
1.000644 (0 °C)
10
Methane:
Is a chemical compound with a chemical formula (CH4), and it is composed of
four Hydrogen atom and one carbon atom, and it is the first in the alkane group and
the most abundant organic compound on earth. And it is used to prepare many organic
compounds like CCL4 and FCL, and it is also used in industry like plastic, nylon and
alcohol.
Table-4 CH4 Physical and Chemical Properties
Molecular weight
16.04 g mol−1
Color
colorless
Molecular formula
CH4
Melting point
-182 °C, 90.7 K, -296 °F
Boiling point
-164--160 °C, 109-113 K, -263--256 °F
Density
655.6 μg mL−1
Odor
Odorless
MSDS
External MSDS
Threshold limit
500ppm
Solubility in water
22.7 mg L−1
Autoignition
temperature
537 °C
log P
1.09
Viscosity
0.07 cP at −78.5 °C
Molecular shape
Tetrahedral
Flash point
−188 °C
Explosive limits
5–15%
Std enthalpy of
formation ΔfHo298
−74.87 kJ mol−1
Std enthalpy of
−1
combustion ΔcHo298 −891.1–−890.3 kJ mol
Related alkanes


Methyl iodide
Diiodomethane
11
Ethane:
Is a chemical compound with a chemical formula (C2H6), and it is composed
of six Hydrogen atom and two carbon atom, and it is the second in the alkane group
that is aliphatic(HC), and it is colorless and odorless gas at standard temperature and
pressure. And it is used in chemical industry like the production of ethylene.
Table-5 Ethane Physical and Chemical Properties
Molecular weight
30.07 g mol−1
Color
colorless
Molecular formula
C2H6
Melting point
-183 °C, 90.4 K, -297 °F
Boiling point
-89 °C, 184.6 K, -127 °F
Density
1.3562 mg cm−3 (at 0 °C)
0.5446 g cm−3 (at 184 K)
Odor
odorless
Solubility in water
0.0568 g L
Vapor pressure
~4.2 MPa
Acidity (pKa)
50
Basicity (pKb)
-36
MSDS
External MSDS
Autoignition
temperature
472 °C
Explosive limits
3.0–12.5%
Related alkanes


Flash point
Methane
Propane
−135 °C
Std enthalpy of
formation ΔfHo298
−84 kJ mol−1
Std enthalpy of
combustion ΔcHo298
−1561.0–−1560.4 kJ mol−1
Specific heat capacity, C 52.49 J K−1 mol−1
12
Propane:
Is a chemical compound with a chemical formula (C3H8), and it is composed
of eight Hydrogen atom and three carbon atom, and it is the third in the alkane group
that is aliphatic (HC). And it is used as vehicle fuel (LPG).
Table-6 Ethane Physical and Chemical Properties
Molecular weight
44.1 g mol−1
Color
colorless
Molecular formula
C3H8
Melting point
-188 °C, 85.5 K, -306 °F
Boiling point
-42--42 °C, 230.9-231.3 K, -44--43 °F
Density
2.0098 mg mL−1 (at 0 °C, 101.3 kPa)
Odor
odorless
Solubility in water
40 mg L−1 (at 0 °C)
Vapor pressure
853 kPa (at 21.1 °C)
log P
2.236
MSDS
External MSDS
Autoignition
temperature
540 °C
Explosive limits
2.37–9.5%
Related alkanes


Flash point
Ethane
Butane
−104 °C
Std enthalpy of
formation ΔfHo298
−105.2–−104.2 kJ mol−1
Std enthalpy of
combustion ΔcHo298
−2.2197–−2.2187 MJ mol−1
Specific heat capacity, C 73.60 J K−1 mol−1
13
I-Butane:
Is a chemical compound with a chemical formula (C4H10), and it is composed
of ten Hydrogen atom and four carbon atom and it represent the R group of the amino
acid leucine, ant it is the isomer of the butane and also called methylpropane. And it
used in refrigerators.
Table-7 I-Butane Physical and Chemical Properties
Molecular weight
58.12 g mol−1
IUPAC name
isobutane
Molecular formula C4H10
Melting point
-159.6 °C, 114 K, -255 °F
Boiling point
-11.7 °C, 261 K, 11 °F
Density
2.51 kg/m3, gas (15 °C, 1 atm)
593.4 kg/m3, liquid
Color
colorless
Solubility in water Insoluble
Vapor pressure
853 kPa (at 21.1 °C)
MSDS
External MSDS
Autoignition
temperature
460 °C
Explosive limits
1.8–8.4%
EU classification
Highly flammable (F+)
flammable gas
Flash point
14
Butane:
Is a chemical compound with a chemical formula (C4H10), and it is composed
of ten Hydrogen atom and four carbon atom, and it is the fourth in the alkane group
that is aliphatic (HC), and it is liquefied, flammable and colorless gases. And it used
as a source of fuel for cooking, camping, and in this case the trade name of it is
liquefied petroleum gas.
Table-8 butane Physical and Chemical Properties
Molecular weight
58.12 g mol−1
IUPAC name
Butane
Molecular formula
C3H8
Melting point
-140--134 °C, 133-139 K, -220--209 °F
Boiling point
-1-1 °C, 272-274 K, 30-34 °F
Density
2.48 mg mL−1 (at 15 °C)
Odor
Odorless
Solubility in water
61 mg L−1 (at 20 °C)
Color
Colorless
log P
2.745
MSDS
External MSDS
Autoignition
temperature
288°C
Explosive limits
1.8–8.4%
Related alkanes


Flash point
Propane
Pentane
−60 °C
Std enthalpy of
formation ΔfHo298
−126.3–−124.9 kJ mol−1
Std enthalpy of
combustion ΔcHo298
−2.8781–−2.8769 MJ mol−
Specific heat capacity, C 98.49 J K−1 mol−1
15
I-Pentane:
Is a chemical compound with a chemical formula (C5H12), and it is composed
of twelve Hydrogen atom and five carbon atom, and it is also called methylbutane,
and it is highly flammable liquid at room temperature. And it used in the industry of
toothpaste.
Table-9 I-pentane Physical and Chemical Properties
Molecular weight
72.15 g/mol
IUPAC name
2-Methylbutane
Molecular formula
C5H12
Melting point
−159.9 °C (113.3 K)
Boiling point
27.7 °C (300.9 K)
Density
0.616 g/ml, liquid
Color
colorless
Solubility in water
Immiscible
Autoignition
temperature
420 °C
Explosive limits
1.4–7.6%
EU classification
Highly flammable (F+)
Harmful (Xn)
Dangerous for
the environment (N)
<−51 °C
Flash point
Std enthalpy of
formation ΔfHo298
−179 kJ/mol
Std enthalpy of
combustion ΔcHo298
−3504 kJ/mol
Standard molar
entropy So298
260.7 J·K−1·mol−1
16
Pentane:
Is a chemical compound with a chemical formula (C4H10), and it is composed
of ten Hydrogen atom and four carbon atom, and it is the fifth in the alkane group
that is aliphatic (HC), and it is colorless, transparent and odorless liquid. And it is
used to produce the polystyrene foam and in labs as solvents.
Table-10 Pentane Physical and Chemical Properties
Molecular weight
72.15 g mol−1
IUPAC name
Pentane
Molecular formula
C5H12
Melting point
-130--129 °C, 142.7-144.1 K, -203--200 °F
Boiling point
36-36 °C, 309.0-309.4 K, 97-97 °F
Density
626 mg mL−1
Odor
Odorless
Solubility in water
40 mg L−1 (at 20 °C)
Color
Colorless
log P
3.255
MSDS
External MSDS
Autoignition
temperature
260°C
Explosive limits
0–~8.3%
Standard molar
entropy So298
263.47 J K−1 mol−1
Flash point
−49.0 °C
Std enthalpy of
formation ΔfHo298
−174.1–−172.9 kJ mol−1
Std enthalpy of
combustion ΔcHo298
−3.5095–−3.5085 MJ mol−1
Specific heat capacity, C 167.19 J K−1 mol−1
17
Hexane:
Is a chemical compound with a chemical formula (C6H14), and it is composed
of fourteen Hydrogen atom and six carbon atom, and it is the sixth in the alkane
group that is aliphatic (HC), and it is colorless, transparent and petrolic liquid. And it
is used as solvent, cleaning agent and thermometer liquid.
Table-11 hexane Physical and Chemical Properties
Molecular weight
86.18 g mol−1
IUPAC name
Hexane
Molecular formula
C6H14
Melting point
-96--94 °C, 177-179 K, -141--137 °F
Boiling point
68-69 °C, 341.6-342.2 K, 155-156 °F
Density
654.8 mg mL−1
Odor
Petrolic
Solubility in water
9.5 mg L−1
Color
Colorless
log P
3.764
MSDS
External MSDS
Autoignition
temperature
234 °C
Explosive limits
7.7%
Standard molar
entropy So298
296.06 J K−1 mol−1
Flash point
−23.3 °C
Std enthalpy of
formation ΔfHo298
−199.4–−198.0 kJ mol−
Std enthalpy of
combustion ΔcHo298
−4180–−4140 kJ mol−1
Specific heat capacity, C 265.2 J K−1 mol−1
18
Octane:
Is a chemical compound with a chemical formula (C8H16), and it is composed
of sixteen Hydrogen atom and eight carbon atom, and it is the sixth in the alkane
group, and it is colorless, transparent and petrolic liquid. And the most important use
for the octane when it used as gasoline for cars and heating.
Table-12 Octane Physical and Chemical Properties
Molecular weight
114.23 g mol−1
IUPAC name
Octane
Molecular formula
C8H18
Melting point
-57--57 °C, 216.0-216.6 K, -71--70 °F
Boiling point
125-126 °C, 398.2-399.2 K, 257-259 °F
Density
703 mg mL−
Odor
Petrolic
Solubility in water
9.5 mg L−1
Color
Colorless
log P
4.783
GHS signal word
DANGER
Autoignition
temperature
220 °C
Explosive limits
6.5%
Standard molar
entropy So298
361.20 J K−1 mol−1
Flash point
13 °C
Std enthalpy of
formation ΔfHo298
−252.1–−248.5 kJ mol−1
Std enthalpy of
combustion ΔcHo298
−5.53–−5.33 MJ mol−1
Specific heat capacity, C 255.68 J K−1 mol−1
19
Process flow sheets:
Process flow diagram 1:
Feed 1 is fed to a reactor to convert Carbon dioxide to Methane, then it sent
to an absorber to remove the water. The bottom product from absorber are mixed
with feed 2,3 and 4 then send to a second absorber to remove H2S and send to a series
of distillations Demethanizer (T-103), Demethanizer (T-104) and Depropanizer (T105) to separate Methane, ethane and Propane respectively. Methane, Ethane and
propane are fed to a Fischer-Tropsch reactors to produce Butane at stream 25 that
mixed with the top product from debutanizer stream 24. Then the mixed butenes
(stream 26) is fed at an alkylation reactor to produce Gasoline.
20
Process flow diagram 2:
Process description:
Feed 1 and 3 are mixed then send to absorber to remove H2S from feed. Next
feed 4 mixed wit it and send to distillation (depropanaizer) T-102, the over head
product ( line 9 ) contain C1,C2 and C3 are enter a series reactors to produce C4. Feed
2 contain ( CO2 ) reacted with H2 in Reactor R-102 to produce CH4 that mixed with
line 13 . The bottom product from T-102 contain C4+ so it send to distillation to
separate C4 from C5+ , line 10 contain C4 mixed with line 25 to produce gasoline in
alkylation reactor .
21
Process flow diagram 3:
Process description:
Refinery gas feed-1 and refinery liquid feed-3 are mixed together the
superheated to a single gas phase. The stream 6 is fed to amine absorpter to absorb
H2S and reduce it from the gas feed to ppm levels. The treated gas is fed to the
Depropanizer to separate heavier hydrocarbons (C4+) and the overhead gas product
consists of (C1, C2, C3, H2). Then the Depropanizer overhead product is fed to the
Fischer-Tropsch reactor (R-102) , which converts C1 to C4, also another stream is
fed to reactor (R-102) which is:
The dehydrated effluent from the Sabatier reactor, it consists mainly of CH4.
Details are: CO2 feed-2 is fed to the Sabatier reactor with stochiometric amount of
H2, CH4 and H2O are produced, then gas is fed to (R-102)-reactor.
After converting the gas to C4, the produced H2 is recycled back to R-101
(stream 15). Also some of unreacted (C1,C2 and C3) are recycled to (R-102)-reactor.
Then the C4 product fed to an absorber for removing water. The liquefied butanes
(stream 20) are mixed with the overhead product from the depropanizer and fed to an
alkylation reactor R-103 to produce Gasoline.
22
Major equipments in flow sheets:
H2S removal:
To remove H2S from a gas of light hydrocarbons, various methods are used
like chemical adsorption and physical adsorption. Chemical adsorption is chosen
because the gas feed is very rich with heavier hydrocarbons so that they will not be
dissolved.
Also designers avoid to use chemical adsorption because it is inefficient to
separate H2S with the presence of CO2 selectively, but since CO2 is not present in gas
feed-1, chemical adsorption is more favorable. Although the energy required for the
regeneration of the amine (solvent) is high.
Tertiary amine (MDEA) is the used solvent because it is more selective for H2S
adsorption. The process is insensitive to operating pressure, and process temperature
ranges from(100-400oF), loading is 0.4 with
40% conc, The reaction for tertiary amine to form salts is:
R1R2R3N +H2S --> R1R2R3NH+HS−
Demethanizer
Demethanizers used as a stripping columns to remove methane from the NGL
product. Demethanizers also act as the final cold separator, a collector of cold NGL
liquids, and source of recovering some refrigeration by cooling warm inlet streams.
Demethanizer usually operates at a conditions of (-115 to -110 C) and (200 to 400
psig).
Deethanizer:
A distillation process used to separate ethane as overhead vapor product from
the propane and traces of heavier hydrocarbons. Due to purity specifications of
butane, it recommended to recover ethane highly from the feed (may reach >90%),
and this is done through external refrigeration and expansion although it will cost
much.
Gas feed is externally refrigerated through propane refrigeration cycle system, and
then expanded is promote condensation, then fed to the deethanizer distillation
process, at operating pressure ranges from (26-30bars), number of trays is (25-35),
trays efficiency ranges (60-80%) and reflux ratio from (0.6-1)
Depropanizer:
A distillation process used to separate propane as overhead vapor product
from butanes and heavier hydrocarbons. The process is similar from debutanizer in its
mechanism but differs in operating conditions and its diameter is smaller than the
debutanizer, also taller because of larger number of trays required to make a sharp cut
23
between the butane and propane fractions*. The operating pressure is (16-19bars),
reflux ratio is (1.8-3.5), Number of trays is (30-40) and tray efficiency (80-90%).
Debutanizer:
A distillation process used to separate butanes (n & iC4) as overhead vapor
product from heavier hydrocarbons as bottom products. Curtain temperature and
pressure at feed equilibrium conditions are selected to ensure that the product meets
the volatility and products purity specifications.
The operating pressure ranges from (4.8 – 6.3 bars to keep the volatile hydrocarbons
of the mixture in liquid state then supplying sufficient heat to separate usually
between the highest boiling gaseous component (butanes) and the lowest boiling
liquid component (pentanes). The reflux ratio ranges (0.8 – 0.9) and number of trays
ranges between (25 – 35), and tray efficiency ranges from (85-95%).
Fischer-Tropsch Reactor:
C1 –C3 can be converted to Butane by using Fischer-Tropsch reactor. The
hydrocarbons are fed to dehydrogenation process which convert it to carbon
monoxide and hydrogen at a conditions of 300-700 C and 2-4 bar, Then the
rich carbon monoxide is sends to Fischer-Tropsch reactor which preferred
operates at 200-270 C and 500-3000 Kpa using a supported catalyst
comprising a metal oxide or sulfide of Mo, W, Re, Ru, Ni plus an alkali earth
metal.
Reaction operate in two steps
first step is convert hydrocarbons into CO
CnHn+2 + nH2O  nCO + 2n+1H2
Second step Convert CO into C4
2n+1H2
+ nCO  C4H6 + 4H2O
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Ethane to Butane:
Ethane is converted to LPG in a combination process which comprises directly
passing olefin effluent from thermal cracking of Ethane over a special Crystalline
aluminosilicate zeolite of the ZSM-5 type and recovering C3+ Hydrocarbons.
First Ethane with water passes to thermal cracker. Ethene is converted to an
olefin-rich gas at reaction conditions including temperatures of about 1500-1600 F ,
Pressures of 20-50 psig. The olefin-rich gas is cooled and sends to the “M-2 Former”
wherein it is converted to useful C3+ products over a special type of crystalline
aluminosilicate zeolite catalyst. The product from M-2 Former is cooled and sends to
a separator to separate C5+ and C4.
2C2H6  C4H10
Carbon dioxide to Methane:
Carbon dioxide can be converted to Methane by adding Hydrogen in
stoichiometric ratio to the CO2 feed and then fed to the reactor at 400 C and 1 atm
with a catalyst Rhoduim-alumina according to the reaction:
CO2 + 4H  CH4 + 2H2O
process convert methane to ethane:
there are invention to relates methane to producing ethane with
catalyst that selected from metal hydride or metal organic compounds.It is
single step process with non-oxidition catalyst this reaction in tempreture
range preferred at 20 C to 500 C at total absolute pressure 0.1 Mpa to 50
Mpa to product ethane with high selectivity. the catalyst use to avoid energy
and high tempereture range in beyond 800 C without catayst for this process
so the best converter to get 99.9% of ethane from methane at P = 5Mpa and
T = 250 C and 300 mg per 1.33*10^-4 ml per minints.
2CH4  C2H6
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Alkylation:
alylation is the process to produce gasoline range materials such as octane and
iso-octane from reacting isobutane with olifins such as
butene, propelene. using the AlkyClean process which employs a zeolite acid catalyst.
the reaction takes place in two step reactors, first nC4 is converted to butene (olefin).
then preheated and fed to the second reactor (in the presence of iC4) in liquid phase
reaction, the reaction is operated at temperature (122-194C)
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Economic analysis:
The feed gases are taken from the waste of the refineries. So It is almost
comes from free, instead of get rid of these waste, converting it into a value
gasoline. Gasoline price on 17-Feb-2012 was 31.062 $/lb.
Gasoline price is increasing from discovering it until now. At 1990 the value was
9.944 $/lb, at 2000 was 12.633 $/lb and at 2010 the value was 23.914 $/lb. it.
The average increasing per year is 2.5 $/lb, so it is predicting in 2020 the price of
Gasoline will be 47.65 $/lb.
Gasoline Price
Dollar/lb
35
30
25
20
15
10
5
0
27
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Comparison between the process flow sheets:
Process flow diagram 1:
6 distillations are used in Process flow diagram 1 and 5 reactors. Using a lot of
distillations means more cost. To maximize production of butane 3 Fischer-Tropsch
reactor are used. The advantage of this diagram is that it needs a lot of energies to
refrigerate the feed for separate C1 and C2.
Process flow diagram 2:
6 distillations are used in Process flow diagram 2. C1, C2 and C3 are fed to a
series of reactors to maximized Butane production instead of separating them. Many
recycled stream are used in this Flow diagram. Recycled exit Hydrogen and the
unreacted (C1,C2,C3) from the series of reactors. Separating C3+ from C4-C5 from
the first is more preferred because it easier and more economical. The advantages of
this sheet are it is fed into a series of reactors that reduce the conversions of product in
each reactor and has a side product.
Process flow diagram 3:
6 distillations are used in Process flow diagram 3. This flow sheet is preferred
because it is using the famous Fischer-Tropsch reactor that maximized the production
of liquid butane. Also the recycled (C1, C2 , C3) and Hydrogen are increases the
production of liquid Butane (C4). The disadvantages of this sheet is Fischer-Tropsch
reactor does not convert all feed into C4 and it is produce water that cause freezing in
the plant.
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Conclusion:
Process flow diagram 3 is the recommended sheet because it maximize the
production of the Butane, it is more economical by without using refrigerators and it
has many recycle streams. Plant for production of liquid Butane is absolutely
profitable because it comes from the waste of the refinery gases that make pollution
for the environment. Adding a reactor to convert liquid Butanes into Gasoline will
make this plant more profitable that prevent a major source for fusel fuel .
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References:
1. "Engineering Data Book", by the Gas Processors Suppliers Association,
volumes 1&2.
2. "The Chemistry and Technology of Petroleum",H. Heinemann, 4th edition.
3. "Petroleum and Gas Processing" ,H. Al-Abdelal, M. A. Fahim, edited @2003.
4. "Handbook of Petroleum Processing", D. Jones, edited @2006.
5. "Fundamental of Natural Gas Processing", L. Faulkner, edited @2006.
6. "Handbook of Natural Gas Transmisson and Processing", S. Mokhatab,
edited @2006.
7. "Natural Gas Liquids and LNG Production from Crudes and Wet Gases", S.
Desouky, @2002
8. US 6914083 B2: Fisher-Tropsch Process
9. US 4100218: Ethane Conversion Process
10. US 7473814 B2: Process for Converting Methane into Ethane
11. US 4275255: Conversion of Mixed Butanes into Gasoline
12. US 6015931: Process to Convert Propane into Ethylene Propane and C4
olefins
13. http://www.eia.gov/petroleum/gasdiesel/
14. www.wikipedia.com/naturalgasprocessing
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