Gas engineering

PETROLEUM GAS PROCESSING
(CHEM 433)
ZIN EDDINE DADACH
1

COURSE INTRODUCTION
 This course is designed to cover the
fundamentals of the gas process
operations in the petroleum industry
 An overview of gas processing from
exploration to final production and
transportation as well as gas properties
calculations are included.
2

COURSE FOCUS
 The course focuses on the principles of
 Natural Gas Liquids (NGL)* extraction
 Liquid Petroleum Gas (LPG)**
fractioning
 Liquid Natural Gas production (LNG)
 Some design aspects of major unit
process operation.
3

FUNDAMENTALS
 To understand this course, knowledge of
the basic fundamentals principals and
terminology a plus.
 Review of basic terminologies follows:
4

BASIC TERMINOLOGY (QUICK
REVIEW)
 Matter is the physical material that
makes up the universe; anything
that has mass and occupies space.
 Elements, Atoms, Molecules,
Chemical compounds, and
Mixtures.
5

ELEMENT
 A chemical element, or an element, is a material
which cannot be broken down or changed into
another substance using chemical means.
 Elements may be thought of as the basic
chemical building blocks of matter.
 Depending on how much evidence you require to
prove a new element has been created, there are
117 or 118 known elements.
6

ATOM
 All substances are made up of matter and the
fundamental unit of matter is the atom. The atom
constitutes the smallest particle of an element which
can take part in chemical reactions and may or may
not exist independently.
 N. Bohr (1940) provided the modern concept of the
atomic model. According to Bohr, the atom is made of
a central nucleus containing protons (positively-
charged) and neutrons (with no charge). The electrons
(negatively-charged) revolve around the nucleus in
different imaginary paths called orbits or shells.
7

 Valence shell: the outer most electron
shell of an atom
 Valence electron: an electron in the
outermost shell (very important because
these are the electrons that causes
chemical reactions to occur.
 They are represented by the group
number in the periodic table.
8

REVIEW)
 Periodic table.
9

REVIEW)
 Atomic Mass (weight): mass of 1 mole of an
atom (listed in the periodic table)
e.g. the atomic mass of Al = 27g/mole (or
27g/gmole)
 1 mole contains 6.0022 x 10 23 atoms
 For Aluminum (Al) this means 27 g of
aluminum contains 6.0022 x 10 23 atoms of
aluminum *
 In other words 6.0022 x 10 23 atoms of Al weighs
27g (**question, why not use the weight of 1
atom of aluminum in the periodic table?)
10

MOLECULE
 Two or more atoms chemically combined.
 Diatomic molecule: is a molecule that is formed
by a combination of 2 atoms of the same
element, e.g. N2, O2, H2.
11
H-H
H-H
H-H
H-H
H-H
H-H
H-H
Compound
Diatomic molecule

REVIEW)
 Going back:
 Atomic Mass (weight) is the mass of 1 mole of an
atom
 E.g. The atomic weight of Al is 27 g/g-mole (this is from
the periodic table)
 Molecular Mass (weight) is the mass of 1
mole of ? *
 E.g. The molecular weight of H2O is? **
12

PHYSICAL COMPOUNDS
 Clathrate, is a chemical substance consisting
of a lattice of one type of molecule trapping
and containing a second type of molecule
 A type of physical compound, called a
clathrate, may be formed. A gas hydrate is
one example of a clathrate. These
compounds are relatively unstable
 An example of a clathrate is clathrate
hydrate, a special type of gas hydrate* in
which a lattice of water molecule encloses
molecules of trapped gas.
13

CHEMICAL COMPOUND
 Hydro carbon: Any compound made of carbon and hydrogen
atoms.
 These atoms can combine in a number of ways to satisfy
valence requirements.
 For convenience, these are separated into families (or
homologous) series, each of which is given a name.
 Carbon atoms can link together to form “chains” or “rings”
 Crude oil and natural gas mixtures consist primarily of
“straight chain” hydrocarbon molecules, the bulk of which
are PARAFFINS*.
15

1) PARAFFIN SERIES FORMULA: CNH2N+2
 Hydrocarbons in this series are saturated compounds
because all four bonds are connected either to
another carbon atom or a hydrogen atom, with one
such atom for each bond.
 In Paraffin (CnH2n+2 ) the # of hydrogen atoms is 2
times the # of carbon atoms plus 2 more for the end
of the chain.
 Name of paraffin compounds end with an “ane”
16
CH4 C2H6 C3H8

PARAFFIN SERIES FORMULA:
CNH2N+2 (CONTINUED)
 * Just note and recall that Paraffin hydrocarbons are the most
stable because all valence bonds are fully satisfied as indicated
by the single line linkage.
 Most reactions involve the replacement of hydrogen atoms
with other atoms; the carbon linkage remains stable.
 Longer chain may be formed, however, the only ones normally
identified by name contain ten or less carbons.
 Just note that in referring to a given paraffin hydrocarbon, the
abbreviation C3 for propane, C4 for butane, etc may be used
but,
 Statements like “propane plus fraction ( C3
+) refer to a mixture
composed of propane and larger molecules.
17

PARAFFIN ISOMERS
 When paraffin series molecule contains four or
more carbon atoms there are different ways
these ca be connected without affecting the
formula
 Compounds which have the same chemical
formula but a different molecular structure are
called isomers
 They posses different physical and chemical
properties.
18

2) OLEFIN OR ETHYLENE SERIES
(ALKENES) FORMULA: CNH2N
 The olefin group of compounds is a simple straight
chain series in which all the names end in –ene.
 Ethylene (ethene) C2H4 is the simplest molecule in the
series.
 Hydrocarbon in this series combine easily with other
atoms like chlorine and bromine, without the
replacement of hydrogen atoms.
 Since they are so reactive, they are called unsaturated
hydrocarbons.
19

2) OLEFIN OR ETHYLENE SERIES
(ALKENES) FORMULA: CNH2N
(CONTINUED)
 Unlike the paraffins, the maximum bonding capacity
of the carbon atom is not fully satisfied by hydrogen
or carbon atoms.
 Two adjacent carbon atoms form a “temporary” bond
(in the absence of other available atoms) to meet
bonding requirements fixed by valence.
 The structural formula for the olefins uses a double
line to indicate the double carbon-carbon linkage, the
most reactive point in the molecule.
 With four or more carbons, isomers also may result
from the position of the double bond.
20

3) ACETYLENIC OR ALKYNE
SERIES FORMULA CNH2N - 2
 Acetylene (systematic name: ethyne) is the chemical
compound with the formula C2H2. It is a hydrocarbon and
the simplest alkyne. This colorless gas is widely used as a
fuel and a chemical building block. It is unstable in pure
form and thus is usually handled as a solution.

 It has the formula C2H2.
21

3) ACETYLENIC OR ALKYNE
SERIES FORMULA CNH2N – 2
(CONTINUED)
 There is a triple bond between the carbon
atoms.
 This satisfies the valence requirements but
the carbon linkage is very weak.
 Therefore Acetylene is even more reactive
than olefins.
 Acetylene not only is unsaturated, it is also
unstable chemically.
 In the liquid state is explosive if subjected to a
sudden shock
22

4) DIOLEFINS FORMULA CNH2N - 2
 Same formula as acetylene but contain two
double linkages.
 Di-ethene or di-butene
23

THE ORIGIN OF PETROLEUM GAS
The organic theory:
 According to the original theory, oil originates
from animals and plants.
 Beds of silt (containing tiny organisms), mud,
and sand were buried deep beneath the earth.
 The deepest layers were turned into rock by
the weight of the deposited earth layers.
 Geologists believe that high heat and pressure,
bacteria, chemical reactions, and other forces
transformed the organic remains into oil and
gas.
25

The Inorganic Theory:
 Hydrocarbons are formed by
combination of carbon and
hydrogen in the earth rocks due
to the influence of high
temperature and pressure
26

GEOLOGICAL CONDITIONS FOR OIL
AND GAS FORMATION
 Most oil and gas accumulates in
sedimentary rocks.
 *Sedimentary rocks are one of three
main rock groups (the others are igneous
and metamorphic)
 Sedimentary rocks include common types
such as chalk, limestone, dolomite,
sandstone, conglomerate and shale.
27

SEDIMENTARY ROCK IMAGES
(CHALK)28

(LIMESTONE)
29

(DOLOMITE)
30

(SANDSTONE)
31

(CONGLOMERATE )
32

(SHALE )
33

GEOLOGICAL CONDITIONS FOR OIL
AND GAS FORMATION (CONTINUED)
 Many people think that an oil or gas reservoir is a
large underground container filled with oil or gas
 Some people think its like an underground river.
 In reality a petroleum or gas reservoirs is a rock
formation that holds oil and gas, somehow like a
sponge holding water.
 Physically a large reservoir can be wide and shallow,
narrow and deep or somewhere in between.
34

RESERVOIR ROCKS
 A petroleum reservoir, or oil and gas reservoir, is a
subsurface pool of hydrocarbons contained in porous or
fractured rock formations. The naturally occurring
hydrocarbons, such as crude oil or natural gas, are trapped
by overlying rock formations with lower permeability.
Reservoirs are found using hydrocarbon exploration
methods.
 Porosity and permeability are important factors in
reservoir formation. (QESTION) what's the difference
between porosity and permeability? (next slide)
35

STRUCTURAL TRAPS
 Structural traps are formed by a deformation in
the rock layer that contains the hydrocarbons.
Domes, anticlines, and folds are common
structures. Fault-related features also may be
classified as structural traps if closure is present.
 Structural traps are the easiest to locate by
surface and subsurface geological and
geophysical studies.
 They are the most numerous among trapsand
have received a greater amount of attention in
the search for oil than all other types of traps.
36

STRATIGRAPHIC TRAPS
 Stratigraphic traps are formed
when other beds seal a reservoir
bed or when the permeability
changes (facies change) within the
reservoir bed itself. Stratigraphic
traps can form against either
younger or older time surfaces.
39

POROSITY AND PERMEABILITY
 Porosity is the ratio of the volume of opening (voids)
to the total volume of material. (e.g. Shale is less
porous and carbonate is more porous)
 Permeability is a measure of the ease with fluids will
flow through rock, sediment or soil ( a rock is
permeable when the pores are connected)
 Just as with porosity, the packing, shape, and sorting
of granular materials control their permeability.
Although a rock may be highly porous, if the voids are
not interconnected, then fluids within the closed,
isolated pores cannot move.
40

POROSITY AND PERMEABILITY
(CONTINUED)
REAL ROCK IMAGE
42

ROCK TYPE DISTRIBUTION IN THE EARTH CRUST AND OIL AND GAS
PRODUCTION BY ROCK TYPE*.
43
Carbonates
Sandstone
Shale
Distribution of rock types
42%
37%
21%
Sandstone
Carbonates (more
pores) *
Miscellaneous
Production by rock types
61.5%
36%
2.5%
Class of sedimentary rocks
composed primarily of
carbonate minerals.
Two major types are:
1) Limestone (CaCO3)
2) Dolomite [CaMg(CO3)2]

RESERVOIR ROCKS (EROSION AND
DEFORMATION)
 For a rock to be an effective reservoir, it must
contain adequate porosity and permeability
that is properly sealed against erosion and
tectonic (movement) destruction.
 Many reservoirs and traps have been
generated and eliminated by erosion and
deformation. They are called dead oil.
44

GENERATION OF CRUDE OIL
 Organic material in shale averages approximately 1% of the shale
rock volume. Clay mineral constituents comprise the remaining
99 percent
(some shale has greater concentrations some lower)
 Kerogen* is an insoluble, high molecular weight, polymeric (i.e.
consisting of a polymer) compound which comprises about 90%
of the organic material in shale/rock.
 The remaining 10% is bitumen** of varying composition, which is
believed to be altered kerogen.
(See diagram next slide)
46

GENERATION OF CRUDE OIL (CONTINUED)
47
Mineral Material 99%
Shale (rock)
Organic Material 1%
Kerogen 90%
Organic Material
Bitumens 10%
Percentage of (mineral and organic material), and (bitumen and
kerogen), and (mineral material) in rock

KEROGEN AND KEROGEN
TYPES
 Labile kerogen breaks down to form heavy
hydrocarbons (i.e. oils), refractory kerogen
breaks down to form light hydrocarbons (i.e.
gases) and inert kerogen forms graphite.
 A Van Krevelen diagram is one example of
classifying kerogens, where they tend to form
groups when the ratios of hydrogen to
carbon and oxygen to carbon are compared.
48

KEROGEN TYPE 1&2
 Type I
 Hydrogen:Carbon ratio > 1.25
 Oxygen:Carbon ratio < 0.15
 Tend to produce oil.
 Type II
 Hydrogen:Carbon ratio < 1.25
 Oxygen:Carbon ratio 0.03 to 0.18
 Tend to produce a mix of gas and oil.
49

KEROGEN TYPE 2 SULFUR
AND TYPE 3
 Type II-Sulfur
 Similar to Type II but high in sulfur.
 Type III
 Hydrogen:Carbon ratio < 1
 Oxygen:Carbon ratio 0.03 to 0.3
 Material is thick, resembling wood or coal.
 Tend to produce gas.
50

 Type IV (residue)
 Hydrogen:Carbon < 0.5
51

MIGRATION OF CRUDE OIL
 Even though shale is relatively impermeable,
oil is created in its pores.
 As tectonic forces moves the petroleum
forming rocks out of there birthplace, great
pressures from overlying formations squeeze
the petroleum out of the relatively
impermeable shale into cracks and into more
permeable formations such as sandstone (i.e.
carbonate rocks)
52

SUMMARY (OIL MIGRATION)
53
Original
Organic
Matter
Graphite
Kerogen
Mature
Kerogen
Crude Oil
Methane
Losing Hydrogen Gaining Hydrogen

OIL AND GAS TRAPS
 If the rock containing the oil is very pores and very
permeable, petroleum will escape.
 Something must stop the oil from escaping and
migrating.
 A trap is any combination of physical factors that
promotes accumulation and retention of the
petroleum in one location (its an arrangement of
rocks that contained hydrocarbons)
*
54

CLASS WORK TO BE SUBMITTED
(USE THE INTERNET)
1. Traps can be grouped into three basic types? Name them.
2. How is an anticline trap formed?
3. What is a seal?
4. Scan or sketch figures showing common structural traps.
5. Sketch a dome trap showing the oil and water layers.
6. What is a plug trap is?
7. What causes a stratigraphic trap to form? Scan or sketch
relevant figures.
56

OIL AND GAS TRAPS (CONTINUED) ANSWERS
57
Structural Trap Stratigraphic Trap
*ANSWERS
1)3 type of traps
• Structural traps: Occurs due to the deformation of a
reservoir (includes: anticline traps , fault traps and dome plug
traps)
• Stratigraphic traps: Occurs when porosity and permeability
changes within a formation
• Combination

2) In an anticline trap the rock layers that were originally laid down
horizontally were folded upward into an arc or dome.
3) Seal is formed when a fault occurs.
58
B

4) Scan or sketch figures showing common structural traps.59

5) A sketch of a dome trap showing the oil and water layers.60

6) Plug trap: Oil and gas are also found associated with
domes. A dome that has a core of rock, called plug,
that has pushed into the other formation may create a
plug trap. Usually a plug is made of nonporous salt
that has pierced, deformed, or lifted the overlaying
strata.
61

7) Stratigraphic trap is caused either by a nonporous formation
sealing off the top edge of a reservoir bed or by a change of
porosity and permeability within the reservoir bed itself.
62

EXPLORATION METHODS
 Exploration was ones a matter of good luck and guess work
 Now it uses many techniques and scientific principles
 Most successful method was to drill near and oil seeps* (where
oil is actually present on the surface)
 Today, surface and subsurface, study is the leading technology in
discovering oil and gas.
 Aerial and satellite images and other instrumentation are used
to gather information that helps determine where to drill.
 Then specialist examine the rock fragments and core samples
brought up while drilling the well and running special tools into
the hole to get more information about the formation and
possible oil or gas traps.
64

EXPLORATION METHODS (CONTINUED)
 Finally examining, correlating and
interpreting the information and the
data makes it possible for the oil
companies to accurately locate
structures that may contain
hydrocarbon and if the hydrocarbons
are worth exploiting.
65

EXPLORATION METHODS
SUMMARY
Exploration methods include:
1) Surface geological studies
2) Oil and gas seeps.
3) Geophysical surveys (e.g.
seismic surveys)
4) Reservoir development tools
66

CLASS WORK
Surface geological studies include areal photographs and satellite images. List at
least 2 types of equipment used to take images, and explain briefly what
information each equipment gives.
1) Explain what oil and gas seeps are?
2) Geophysical surveys includes the use several methods listed below, briefly
explain each method and list any sub methods.
 Magnetic and electromagnetic surveys (list each one and explain)
 Gravity surveys
 Seismic surveys (VERY IMPORTANT)
 3D seismic surveys
 Explosive Methods
 Modern land methods
 Marine Seismic Methods.
67

CLASS EXERCISE (ANSWERS, DISCUSSION AND EXPLANATION)
 Answers:
1) 2 types of equipment used to take images:
 LandSat:
 Landsat satellites have mapped all the earth's land masses this is continuously done.
 The purpose is to primarily map vegetation and observe long-term changes to the earths
surface.
 LandSat also carry sensors especially built for geological application
 It provides visible, thermal, and infrared images of all land-masses and coastal areas.
 Landsat data is then interpreted and enhanced
 Explorationists can then buy the data.
 Radar
 Radar devices bounce high frequency radio waves off land features to a satellite or airplane.
 Returned signals form a low-resolution relief map (map of a terrain- topography like)
 It is useful in searching areas for potential oil-trapping structures at a glance (diagram on
next page)
68

EXAMPLE OF A RADAR RELIEF
MAP
69

OIL AND GAS SEEPS
 Seeps are oil and gas that
come to the surface along
porous beds or faults. They
are marked and well-
documented worldwide.
70

CLASS EXERCISE (ANSWERS, DISCUSSION AND EXPLANATION)
[CONTINUED]
2
71
Crude oil seep
Gas seep

CLASS EXERCISE (ANSWERS, DISCUSSION AND EXPLANATION) [CONTINUED]
3) Geophysical surveys include:
 Magnetic and electromagnetic surveys (list each one and
explain):
 Magnetometer surveys: detects slight variation in the
earths magnetic field which results in predicting the
characteristics of overlaying sediments.
 Magnetotellurics: Works on the theory that rocks of
different composition have different electrical
properties. It measures the naturally occurring flow of
electricity between rocks then reveals subsurface
structures based on the electrical data.
72

GRAVITY SURVEYS
 Gravity surveys (e.g. of an equipment used is
gravimeter or gravity meter):
 It works on the theory that some rocks are denser
than others which causes a slight variation in the
earth's gravitational field.
 For example scientists can locate salt domes
based on gravitational methods since salt domes
are usually associated with minimum gravity
compared, for example, with ordinary and
anticline domes. (EXAMPLE ON NEXT SLIDE)
73

74

 Seismic surveys
 Seismic exploration utilizes an acoustic (sound) source such
as an artificial earthquake ( or dynamite explosion).
 Acoustic waves travel through the formation and reflect back
to a detector (called geophones) where travel time is
measures.
 The geophones send the signals to a recorder (called a
seismograph) where the signals are magnified and a
seismogram is produced.
 *
75
Class exercise (Answers, Discussion and explanation) [Continued]

 Correlations of the records produce a two
dimensional cross-section that illustrates the
reflections and demonstrates the subsurface
structures. (See also the diagram on the wall)
- (See Diagram on next slide for set up)
76

Seismic surveys (continued) – Set-Up
 Reflected and refracted seismic
 Seismic exploration
77

Seismic surveys (continued) – Set-Up
 Seismic line showing productive anticline in lower sediments.
78

 Seismic surveys (continued) more photos
79

 3D seismic survey:
 In this method many seismic surveys are ran close to each other to create a series
of seismic sections of an area.
 Computer programs paste the section together to form a cubic image of the area.
 Explosive Methods
 Early seismic method using dynamite to create seismic vibration.
 Modern Land Methods
 In general newer methods have replaced dynamite to create vibration in the earth*.
For example Vibroseis which generates continuous low- frequency sound waves.
80

 Marine Seismic Methods:
 It uses similar equipment as exploration on land but uses it
on a ship.
(End of exercise)
81

RESERVOIR DEVELOPMENT TOOLS
 When a surface and subsurface information of a
formation indicates a strong possibility of
hydrocarbon existence, an oil company may then drill
an exploratory well or wells
 As the drilling progresses, underground rocks are
then tested by means of core sampling and well
logs.
 The gathered data determines whether the reservoir
has enough oil or gas to justify completing the
exploration and then production.
83

RESERVOIR DEVELOPMENT TOOLS (CONTINUED)
 Well logs are records that give information about the
formation through which a well has been drilled.
 The log gives the geophysical and other information of
a well per depth.
84

TYPES OF WELL LOGS
1) Well Logs:
 Driller’s log
 Wireline log
2) Sample logs:
 Core Samples
 Cutting Sample
85

1) WELL LOGS
 Driller log:
 It’s the most common log where the log contains
information about the kind of rocks and fluids
encountered at different depths.
 It gives also gives information when the formation
is altered from soft to hard rock.
 It gives an idea of how long it takes to drill the
well (for future drilling purposes)
 Gives other formation issues encountered during
drilling.
86
JPEG Image

1) WELL LOGS [CONTINUED]
 Wireline logs:
 A wireline is a metal cable (line) that run through the well
hole with several tools attached to it.
 Each tool takes a different measurement.
 Each measurement gives an indirect information about the
formation down the well.
 Wireline logging often involves complex calculations and
interpretations of the data provided from the tool.
 Oil service companies (e.g. Schlumberger, Baker Atlas,
Halliburton) uses the information to decide if the oil or gas in
the well is economically feasible.
87

1) WELL LOGS [CONTINUED]
 There are different types of wireline logs:
a) Electrical Logs
b) Nuclear Logs
c) Acoustic Logs
88

A) ELECTRICAL LOGS
 *Induction Log: records conductivity (weak
current) that flows naturally in the rocks. It
gives an idea about the thickness and
boundary of each layer in the borehole.
(called spontaneous potential log i.e. SP log)
 Resistivity Log: records resistance in the
borehole (hydrocarbons do not conduct
electricity while all waters do)
89
1) Well Logs [continued]

B) NUCLEAR LOGS
 Gamma ray log:
 measures radioactivity to determine what type of
rocks are present in the well.
 For example shale emits more radioactive elements
than sandstone.
 Neutron log:
 The tool sends atomic particles (neutrons) through
the formation.
 When the neutrons collide with hydrogen, the
hydrogen slows them down.
 When the detector records slow neutrons, it means
that there more hydrogen is present (i.e. maybe more
hydrocarbons than water)
90

C) ACOUSTIC LOGS
 It gives information about the density of the rocks
(how dense the rock is)*
 The acoustic or sonic log records how fast sound
travels through a rock.*
 The speed of sound traveled depends on how dense
a formation is, and how much fluid it contains.
Example: shale is less porous therefore the sound will
travel faster and you will get a high acoustic signal
back. (E.g. of signal on the board)
91

C) ACOUSTIC LOGS (CONTINUED)
 The probe contains a single transmitter at the base of
the probe and two receivers located above the
transmitter.
92

SAMPLE LOGS
Sample logs:
 Core Samples
 Cutting Sample
93

CORE SAMPLES
1) A core is a cylindrical column of rock that shows the
sequence of rocks as they appear within the earth.
2) It provides the most accurate information about the
underground formation about Porosity, permeability,
composition, fluid content, and geological age.
94

CUTTING SAMPLES
 As a regular bit drills a hole, it breaks up the rock into
pieces called cuttings. The cuttings flow out of the hole
where geologists can use them to analyze the rock being
drilled.
 Since cuttings are fragments of rocks and do not form a
continuous sample like a core, they are not as useful cores
are to the geologists.
 Cuttings may not all come from the bottom of the hole but
may include pieces of formations that have sloughed off
closer to the surface.
 Even with these limitations, however, cuttings can provide
useful data and are regularly examined during drilling.
95

Homework by internet (10%) to be
submitted February 27th
Based on the information of the handouts and using the
internet, write a report about the oil and gas
reservoirs:
a) How they are formed?
b) How they can be trapped?
c) The exploration techniques ( surface and sub-surface
analysis)
d) The logs used to analyze them (drilling techniques)
e) Attach all the documents used.
96

THE DIFFERENT TYPES OF GASES
97

ASSOCIATED GAS
A mixture of petroleum gases that range
from methane to butane and traces of
liquid condensate (pentane to heptane)
It is produced from an oil well dissolved
in the oil.
It is separated from the oil by liquid-gas
separator in the degassing station.
The gas contains non-hydrocarbon gases
such as CO2 and H2S as well as some
98

TYPICAL PROCESS OF AN
ASSOCIATED GAS
99

NON-ASSOCIATED GAS
 Gas occurring alone as natural
gas, not in solution or as free gas
with oil or condensate.
 It contains mainly methane and
ethane. It may also contains
impurities such as CO2 , H2S and
water
100

WET AND DRY GAS
 Natural gas is often found dissolved in oil at the high
pressures existing in a reservoir.
 It can be present as a gas cap above the oil. Such natural
gas is known as associated gas. There are also reservoirs
that contain gas and no oil. This gas is termed non-
associated gas.
 Associated gas usually contains some light liquids and
hence is sometimes called “wet gas.”
 Non-associated gas, coming from reservoirs that are not
connected with any known source of liquid petroleum, is
“dry gas.”
101

SOUR AND ACID GAS
 Sour gas is natural gas or any other gas containing
significant amounts of hydrogen sulfide (H2S).
 Natural gas is usually considered sour if there are more
than 5.7 milligrams of H2S per cubic meter of natural gas,
which is equivalent to approximately 4 ppm by volume[1].
 On the other hand, natural gas that does not contain
significant amounts of hydrogen sulfide is called "sweet
gas.")
 any gas that contains significant amounts of acidic gases
such as carbon dioxide (CO2) or hydrogen sulfide.
 Thus, carbon dioxide by itself is an acid gas but it is not a
sour gas.
102

GAS SWEETENING
 Before a raw natural gas containing hydrogen
sulfide and/or carbon dioxide can be used, the
raw gas must be treated to remove those
impurities to acceptable levels, commonly by an
amine gas treating process.[1][2]
 The removed H2S is most often subsequently
converted to by-product elemental sulfur in a
Claus process or it can be treated in a WSA
Process unit where the by-product is sulfuric
acid.
103

ACID REMOVAL BY
ABSORPTION
104

WHAT IS LNG?
 Liquefied natural gas, or LNG, is natural gas that has been
supercooled to minus 260 degrees Fahrenheit (minus 162
degrees Celsius).
 At that temperature, natural gas condenses into a liquid.
When in liquid form, natural gas takes up to 600 times less
space than in its gaseous state, which makes it feasible to
transport over long distances.
 In the form of LNG, natural gas can be shipped from the
parts of the world where it is abundant to where it is in
demand.
106

 LNG is an energy source that has much lower air emissions
than other fossil fuels, such as oil or coal.
 LNG is odorless, colorless, non-corrosive and non-toxic. Its
weight is less than one-half that of water.
 Natural gas is the world’s cleanest burning fossil fuel and it
has emerged as the environmentally preferred fuel of
choice.
107

NATURAL GAS COMPOSITION
 The primary component of natural gas is methane (CH4),
the shortest and lightest hydrocarbon molecule.
 Natural gas as a fossil fuel also contains heavier gaseous
hydrocarbons such as ethane (C2H6), propane (C3H8) and
butane (C4H10), as well as carbon dioxide and sulfur-
containing gases in varying amounts.
 Fossil natural gas also contains in varying amounts and is
the primary market source of helium, a non-renewable
and valuable resource.
108

NATURAL GAS COMPOSITION
 Methane (CH4) 80-95 %
 Ethane (C2H6) 5-15 %
 Propane (C3H8) and Butane (C4H10) < 5 %
109

HEATING VALUE
 Natural gas is mainly used as a combustible
 Quantities of natural gas are measured in normal cubic
meters (corresponding to 0 °C at 1 atm) or in standard
cubic feet (corresponding to 60 °F and 30 inches
mercury).
 The gross heat of combustion of one normal cubic meter
of commercial quality natural gas is around
39 megajoules (≈10.8 kilowatt-hours), but this can vary
by several percent.
 In U.S. units, one standard cubic foot of natural gas
produces around 1,000 British Thermal Units (BTUs).
110

HEATING VALUE OF NATURAL GAS
 The actual heating value when the water formed does not
condense is the net heat of combustion and can be as
much as 10 percent less.
 In the United States, natural gas is often sold at retail in
units of therms (th), where 1 therm = 100,000 BTU.
 Wholesale transactions are generally done in decatherms
(Dth), or thousand decatherms (MDth), or million
decatherms (MMDth).
 A million decatherms is roughly a billion cubic feet of
natural gas.
111

WHAT IS LPG ?
 Liquefied petroleum gas (also called LPG, GPL, LP Gas, or
autogas) is a flammable mixture of hydrocarbon gases
used as a fuel in heating appliances and vehicles.
 It is increasingly used as an aerosol propellant and a
refrigerant, replacing chlorofluorocarbons in an effort to
reduce damage to the ozone layer.
 Varieties of LPG bought and sold include mixes that are
primarily propane, mixes that are primarily butane, and -
most common - mixes including both propane C3H8 and
butane C4H10, depending on the season — in winter more
propane, in summer more butane
112

 Propylene and butylenes are usually also present in small
concentration.
 A powerful odorant, ethanethiol, is added so that leaks
can be detected easily.
 The international standard is EN 589. In the United States,
thiophene or amyl mercaptan are also approved odorants.
 Blended of pure, dry "isopropane" (refrigerant designator
R-290a ) and isobutane (R-600a) have negligible ozone
depletion potential and very low global warming potential
and can serve as a functional replacement for R-12, R-22,
R-134a,and other chlorofluorocarbon or
hydrofluorocarbon refrigerants in conventional stationary
refrigeration and air conditioning systems.[4]
113

ENVIRONMENT
 As a low-carbon, low-polluting fossil fuel, LPG is
recognized by governments around the world for
the contribution it can make towards improved
indoor and outdoor air quality and reduced
greenhouse gas emissions
114

WHAT IS NGL?
 Natural Gas, the source of Natural Gas Liquids is a
natural mixture of gaseous hydrocarbons found in the
ground or obtained from specially driven wells.
 The composition of natural gas varies in different parts of
the world. Its chief component, methane, usually makes
up from 80% to 95% its composition.
 The balance is composed of varying amounts of ethane,
propane, butane, and other liquid hydrocarbon
compounds.
 They include Ethane, Propane, Butanes (Iso and Normal),
and condensate, all of which can be extracted from gas
plants. Propane and Butanes can also be extracted during
Crude Oil refining.
116

 Normal Butane is a refining blend stock for gasoline and is
also used as a Petrochemical feedstock,
 Iso-Butane is a refining feedstock for alkylation, MTBE &
TAME manufacturing and a component of gasoline octane
blends.
117

NATURAL GAS TYPICAL PROCESS118

CALCULATING THE DIFFERENT
PROPERTIES OF GASES.
119

GAS COMPOSITION BY
CHROMATOGRAPHY
 Chromatography involves a sample being dissolved in a
mobile phase (which may be a gas, a liquid or a
supercritical fluid).
 The mobile phase is then forced through an immobile,
immiscible stationary phase.
 The phases are chosen such that components of the
sample have differing solubilities in each phase.
 A component which is quite soluble in the stationary phase
will take longer to travel through it than a component
which is not very soluble in the stationary phase but very
soluble in the mobile phase.
120

PHYSICAL PROPERTIES OF
NATURAL GAS.
 I) COMPOSITION BY GAS CHROMATOGRAPHY:
 As a result of these differences in mobilities, sample
components will become separated from each other as they
travel through the stationary phase.
 Typical composition of natural gas:
a) Methane (CH4) 70-90% WT
b) Ethane (C2H6) 5-15
c) Propane (C3H8) and Butane (C4H10) < 5
d) Nitrogen, helium, carbon dioxide and trace amounts of
hydrogen sulfide, water and odorants can also be present.
121

OTHER COMPONENT
e) Natural gas also contains and is the primary
market source of Mercury is also present in small
amounts in natural gas extracted from some
fields[3].
The exact composition of natural gas varies
between gas fields.
122

MOLECULAR WEIGHT
Average MW: 19.5
Average MW= Σ ( yi.MWi)
123

DENSITY OF NATURAL GAS
Average density (kg/m3): 0.7 - 0.9
Average density ( lb/ft3): 0.044 - 0.056
The density of gases depends on the compressibility factor
ρ= P.MW/z.R.T
For ideal gases ( low pressures below 10
atm and high temperatures)
ρ= P.MW/R.T
124

LISTEN...LEARN....THINK...ENJOY YOURSELF
EQUATIONS OF STATE FOR
REAL GASES
 The ideal-gas equation is very simple, but its
range and applicability are limited.
 Several equations of state have been proposed in
the literature to describe the behavior of real
gases
 We will discuss :
Van der Waals equation
 Beattie- Bridgeman equation

VAN DER WAALS EQUATION OF STATE
 Proposed in 1873
 It has two constants
 a/v2 is a correction of the ideal gas equation related
to the intermolecular forces
 b is a correction of the ideal gas equation related to
the volume occupied by the gas molecules
RTbv
v
a
P  ))(( 2

DETERMINATION OF A AND B
cr
cr
P
TR
a
64
27 22

cr
cr
P
RT
b
8


BEATTIE- BRIDGEMAN EQUATION
OF STATE
 Proposed in 1928
 It has five experimental constants
232
u
v
A
)Bv)(
vT
c
1(
v
TR
P 
)1(....).......1( 00
v
b
BBand
v
a
AA 

WHAT CAUSES DEVIATION FROM
IDEAL GAS BEHAVIOR?
 Intermolecular forces called Van Der Waals forces . There
are three such types of Van Der Waals forces:
 London Dispersion Forces which are forces that exist
between molecules as a result of positive nuclei of one
molecule attracting the electrons of another molecule..
 Dipole-Dipole interactions which are forces that exist
between polar molecules where the positive end of one
molecule attracts the negative end of another molecule.
 Hydrogen bonding interactions are forces that exist
between molecules that have a hydrogen atom bonded to
a highly electronegative atom such as Oxygen, Nitrogen, or
Flourine.

WHAT IS THE COMPRESSIBILITY
FACTOR?
 The term "compressibility" is used in thermodynamics to
describe the deviance in the thermodynamic properties of a real
gas from those expected from an ideal gas.
 The compressibility factor is defined as
 In the case of an ideal gas, the compressibility factor Z is equal
to unity, and the familiar ideal gas law is recovered:
 Z can, in general, be either greater or less than unity for a real
gas.

REAL PHASE REGION
 The deviation from ideal gas behavior tends
to become particularly significant (or,
equivalently, the compressibility factor stays
far from unity) :
near the critical point,
 in the case of high pressures
 low temperatures.
In these cases, an alternative equation of state
better suited to the problem.

COMPRESSIBILITY
FACTOR
 The compressibility factor can be estimated
from figure 3-2 page 56 if we know the
reduced temperature and the reduced
pressure of the gas:
 PR= P/PC and TR= T/TC
The compressibility factor Z is almost the same
for all the gases at the same reduced pressure
and reduced temperature . This is called the
principle of corresponding states

PC AND TC : KAY’S RULE
 Kay’s rule (Page 56):
 Pc= Σ yi.Pci
 Tc= Σyi.Tci
 Tci and Pci from tables 3.1 and 3.2
 Do example 3.1 page 57
133

NATURAL GAS CONTAINING
CO2 AND H2S
 Two methods available:
 1) Approach proposed by Robinson et al:
 2) Approah proposed by Wichert and Aziz:
The second method uses adjustments of the Pc’ and Tc’ which
is found from Kay’s combination rule. It has a correction
factor ε, found from figure 3.3 page 58
134

CORRECTION FOR TC’
Tc”= Tc’-0.556 ε ( SI)
Tc”= Tc’- ε ( FPS)
135

CORRECTION IN PC’
 Pc”= Pc’.Tc” / {(Tc’+0.556.B.ε.(1-B))} (SI)
 Pc”= Pc’.Tc” / {(Tc’+B.ε.(1-B))} (FPS)
 Pc’ and Tc’ from Kay’s rule
 ε from figure 3.3
 B mole fraction of H2S in gas
136

FIGURE 3.3 PAGE 58
 Figure 3.3 can be estimated by the equation:
 ε= 120 ( A0.9- A1.6) +15 (B0.5-B4)
 ε= correction factor
 A total mole fraction ( H2S +CO2) in the gas
 B mole fraction CO2 in the gas.
137

FIGURE 3.3 PAGE 58
 Figure 3.3 can be estimated by the equation:
 ε= 120 ( A0.9- A1.6) +15 (B0.5-B4)
 ε= correction factor
 A total mole fraction ( H2S +CO2) in the gas
 B mole fraction H2S in the gas.
 Do example 3.2 page 59.
138

HEATING CONTENT OF LIGHT
HYDROCARBONS
139

HEAT OF COMBUSTION
 A large part of crude oil will be used as fuel:
 1) Fuel gas
 2) Gasoline for engine
 3) fuel oil
The heat of combustion (ΔHc
0) is the energy released as heat
when a compound undergoes complete combustion with
oxygen under standard conditions.
The chemical reaction is typically a hydrocarbon reacting with
oxygen to form carbon dioxide, water and heat:
C2H6 + 3.5 O2  2CO2 +3H2O + Heat
140

HEAT OF COMBUSTION
 By measurement:
The heat of combustion is traditionally measured with a
bomb calorimeter.
 By calculation:
It may also be calculated as the difference between the
heat of formation (ΔfH0) of the products and
reactants.
141

CALORIMETRY TO MEASURE HEAT
OF COMBUSTION OF METHANE
CH4 (g) + 2 O2 (g) → CO2 (g) + 2 H2O (l)
 The enthalpy change for this reaction is measured by
pressurizing a strong metal reaction vessel (called a bomb)
with a mixture of methane and oxygen gas.
 The bomb is immersed in a calorimeter filled with water.
An electrical current is passed through ignition wire (a fine
iron wire), which ignites the wire and the gas mixture.
 The heat balance for this calorimetry experiment is:
 0 = qcal + qwire + qcomb
142

 The heat for the calorimeter, qcal, is determined from the
heat capacity of the calorimeter and the temperature
change for the calorimetry experiment.
 Typically the amount of water in the calorimeter is always
the same; therefore Ccal includes the heat capacities of the
calorimeter, the water, and the bomb itself.
 The burning of the ignition wire releases heat, qwire, and
this heat must be included in the calculations. (This heat is
treated separately, because the amount of ignition wire
used varies from one measurement to the next.)
143

COMBUSTION EXPERIMENT
 The heat released by the combustion
reaction is qcomb, which is related to the
molar enthalpy of combustion by
 ΔHcomb = qcomb /nmethane Combustion
experiments are general conducted
with a large excess of oxygen, so that
the fuel (methane in this case) is the
limiting reactant.
144

MOLAR ENTHALPIES OF
FORMATION
 Combustion reactions are often used to calculate the
molar enthalpies of formation.
 For example, the standard molar enthalpy of combustion
for methane can be expressed in terms of the standard
molar enthalpies of formation of the reactants and
products:
 ΔHo
comb = 2 ΔHo
f,water + ΔHo
f,carbon dioxide - ΔHo
f,methane - 2 ΔHo
f,oxygen
 ΔHo
comb is measured experimentally.
 ΔHo
f,oxygen = 0, because oxygen is a pure element.
 The other molar enthalpies of formation are known from
independent measurements.
145

 For example, one could determine the heat of
combustion of hydrogen to obtain the molar enthalpy of
formation for water.
 For liquid water, ΔHo
f = -285.8 kJ mole-1
 For gaseous carbon dioxide, ΔHo
f = -393.5 kJ mole-1
146

HEATING VALUE=
HEAT OF COMBUSTION
 The heating value or energy value of a substance, usually
a fuel or food (see food energy), is the amount of heat
released during the combustion of a specified amount of
it.
 The energy value is a characteristic for each substance. It is
measured in units of energy per unit of the substance,
usually mass, such as: kJ/kg, J/mol, kcal/kg, Btu/m³.
 Heating value is commonly determined by use of a bomb
calorimeter.
147

HIGHER HEATING VALUE
 The quantity known as higher heating value (HHV) (or
gross energy or upper heating value or gross calorific value
or higher calorific value HCV) is determined by bringing all
the products of combustion back to the original pre-
combustion temperature, and in particular condensing any
vapor produced.
 Such measurements often use a temperature of 25 °C. This
is the same as the thermodynamic heat of combustion
since the enthalpy change for the reaction assumes a
common temperature of the compounds before and after
combustion, in which case the water produced by
combustion is liquid.
148

LOWER HEATING VALUE
 The quantity known as lower heating value (LHV) (or net
calorific value or lower calorific value LCV)) is determined
by subtracting the heat of vaporization of the water vapor
from the higher heating value.
 This treats any H2O formed as a vapor. The energy required
to vaporize the water therefore is not realized as heat.
 LHV calculations assume that the water component of a
combustion process is in vapor state at the end of
combustion, as opposed to the higher heating value (HHV)
(a.k.a. gross calorific value or gross CV) which that
assumes all of the water in a combustion process is in a
liquid state after a combustion process.
149

 For hydrocarbons the difference between HHV and
LHV depends on the hydrogen content of the fuel. For
gasoline and diesel the higher heating value exceeds
the lower heating value by about 10% and 7%,
respectively, for natural gas about 11%.
 A common method of relating HHV to LHV is:
 HHV = LHV + hv x (nH2O,out/nfuel,in)
 where hv is the heat of vaporization of water, nH2O,out is
the moles of water vaporized and nfuel,in is the number
of moles of fuel combusted.[1]
150

 Most applications which burn fuel produce water vapor
which is not used and thus wasting its heat content.
 In such applications, the lower heating value is the
applicable measure. This is particularly relevant for
natural gas, whose high hydrogen content produces much
water.
 The gross energy value is relevant for gas burnt in
condensing boilers and power plants with flue gas
condensation which condense the water vapor produced
by combustion, recovering heat which would otherwise be
wasted.
151

SOME VALUES FOR LIGHT
HYDROCARBONS
Component HHV ( MJ/kg) LHV (MJ/kg)
hydrogen 141.8 121
Methane 55.50 50
Ethane 51.9 47.8
Propane 50.35 46.35
Butane 49.50 45.75
Pentane 45.35
gasoline 47.30 44.40
152

HEATING VALUE OF A
MIXTURE
 GHV (HHV)= Σ( GHV)i.yi
 Net heating value or LHV = Σ (LHV)i.yi
153

WOBBLE NUMBER W0
 The Wooble number is related to the behavior of a fuel in
a burner.
 Two gases with the same Wooble number give the same
heat release at the burner tip for the same pressure drop
across the burner orifice ( Assuming T and P constants).
 The Wooble number is a burner compatibility to a given
fuel and is defined as ( page 36):
 W0= GHV/ √ρ
( gross heating value or HHV divided by the square root of the
relative density of the gas).
 Wo has a unit of MJ/m3 ( SI).
154

SENSIBLE HEAT AND
ENTHALPY OF GASES
155

SENSIBLE HEAT
 Sensible heat is calculated when there is temperature
change with no change in phase.
 We need the heat capacities Cp and Cv to estimate the
enthalpy needed or released due to a change of
temperature ∆T.
 For an ideal gas, constant pressure process or a liquid:
∆h= ∫cp.dT
 Cp= A+BT+CT2
156

SENSIBLE HEAT FOR GASES
 In general Cp is a function of temperature but
the calculation of Cp at the average
temperature is often used, therefore
 Tav= (T1+T2)/2
 ∆h=∫Cp(T).dT= Cp.av ( T2-T1)
157

FIG 8.3 FOR ESTIMATION OF
SPECIFIC HEAT FOR NATURAL GAS
 For real gas:
∆h= ∫cp.dT+ ∫{V-T(δV/δT)p }dP
From fig 8.3 page 222.
Do example 8.2 page 222.
158

ENTHALPY OF GASES
 Figures 8A.2 to 8.A14 pages 234-247.
 For Gases MW=16-30
159

IMPORTANCE OF VISCOSITY
 Viscosity is another important property of a gas used
primarily in flow calculations.
 Viscosity describes a fluid's internal resistance to flow and
may be thought of as a measure of fluid friction.
 Viscosity is a measure of the resistance of a fluid which is
being deformed by either shear stress or tensile stress.
 In everyday terms (and for fluids only), viscosity is
"thickness" or "internal friction". Thus, water is "thin",
having a lower viscosity, while honey is "thick", having a
higher viscosity.
 Put simply, the less viscous the fluid is, the greater its
ease of movement (fluidity).
161

COUETTE FLOW162
Laminar shear of fluid between two plates. Friction between the fluid
and the moving boundaries causes the fluid to shear. The force
required for this action is a measure of the fluid's viscosity. This type of
flow is known as a Couette flow.

APPLIED FORCE –VISCOSITY
 The applied force is proportional to the area and velocity
gradient in the fluid and inversely proportional to the
distance between the plates. Combining these three
relations results in the equation:
F= μ.A.(u/y)
 where μ is the proportionality factor called viscosity.
163

SHEAR STRESS
 This equation can be expressed in terms of shear stress (
ζ=F/A). Thus as expressed in differential form by Isaac
Newton for straight, parallel and uniform flow, the shear
stress between layers is proportional to the velocity
gradient in the direction perpendicular to the layers:
ζ=μ.(δu/δy)
164

DYNAMIC VISCOSITY
 Dynamic viscosityThe usual symbol for dynamic viscosity
used by mechanical and chemical engineers — as well as
fluid dynamicists — is the Greek letter mu (μ).[4][5][6] The
symbol η is also used by chemists, physicists, and the
IUPAC.[7]
 The SI physical unit of dynamic viscosity is the pascal-
second (Pa·s), (equivalent to N·s/m2, or kg/(m·s)). If a fluid
with a viscosity of one Pa·s is placed between two plates,
and one plate is pushed sideways with a shear stress of one
pascal, it moves a distance equal to the thickness of the
layer between the plates in one second.
165

 The cgs physical unit for dynamic viscosity is the poise[8]
(P), named after Jean Louis Marie Poiseuille.
 It is more commonly expressed, particularly in ASTM
standards, as centipoise (cP). Water at 20 °C has a
viscosity of 1.0020 cP or 0.001002 kg/(m·s).
 1 P = 1 g·cm−1·s−1.
 1 Pa·s = 1 kg·m−1·s−1 = 10 P.
 The relation to the SI unit is
 1 P = 0.1 Pa·s,
 1 cP = 1 mPa·s = 0.001 Pa·s.
166

KINEMATIC VISCOSITY
 In many situations, we are concerned with the ratio of the
inertial force to the viscous force (i.e. the Reynolds
number, Re = VD / ν) , the former characterized by the
fluid density ρ. This ratio is characterized by the kinematic
viscosity (Greek letter nu, ν), defined as follows:
ν=μ/ρ
 The SI unit of ν is m2/s. The SI unit of ρ is kg/m3.
167

 The cgs physical unit for kinematic viscosity is the stokes
(St), named after George Gabriel Stokes. It is sometimes
expressed in terms of centiStokes (cSt). In U.S. usage,
stoke is sometimes used as the singular form.
 1 St = 1 cm2·s−1 = 10−4 m2·s−1.
 1 cSt = 1 mm2·s−1 = 10−6m2·s−1.
 Water at 20 °C has a kinematic viscosity of about 1 cSt.
 The kinematic viscosity is sometimes referred to as
diffusivity of momentum, because it has the same unit as
and is comparable to diffusivity of heat and diffusivity of
mass. It is therefore used in dimensionless numbers which
compare the ratio of the diffusivities.
168

VISCOSITY OF GASES
 Viscosity in gases arises principally from the molecular
diffusion that transports momentum between layers of
flow. The kinetic theory of gases allows accurate prediction
of the behavior of gaseous viscosity. Within the regime
where the theory is applicable:
1) Viscosity is independent of pressure and
2) 2) Viscosity increases as temperature increases.
169

JAMES CLERK MAXWELL
 To understand why the viscosity is independent of
pressure consider two adjacent boundary layers (A and B)
moving with respect to each other. The internal friction
(the viscosity) of the gas is determined by the probability a
particle of layer A enters layer B with a corresponding
transfer of momentum.
 Maxwell's calculations showed him that the viscosity
coefficient is proportional to both the density, the mean
free path and the mean velocity of the atoms. On the
other hand, the mean free path is inversely proportional to
the density. So an increase of pressure doesn't result in
any change of the viscosity.
170

EFFECTS OF TEMPERATURE
ON GAS VISCOSITY

171

VISCOSITY FROM CORRELATIONS

172

GRAPHICAL APPROXIMATION
Fig 3.18 page 79 gives the viscosity of gases at atmospheric
pressure and a different temperatures as a function of their
density and molecular weight.
Fig 3.19 gives the effects of pressure and temperature on the
viscosity calculated in fig 3.18.
173

CLASS WORK
 Study of the paper “ Comparison of
correlations for viscosity of sour natural
gas “ by O. Jeje and L. Mattar in
“Canadian International Petroleum
Conference”.
174

INTRODUCTION
 Natural gas condensate is a low-density mixture of
hydrocarbon liquids that are present as gaseous
components in the raw natural gas produced from many
natural gas fields.
 It condenses out of the raw gas if the temperature is
reduced to below the hydrocarbon dew point
temperature of the raw gas.
 The natural gas condensate is also referred to as simply
condensate, or gas condensate, or sometimes natural
gasoline because it contains hydrocarbons within the
gasoline boiling range.
177

Raw natural gas may come from any one of three types of gas
wells.
 Crude oil wells – Raw natural gas that comes from crude
oil wells is called associated gas. This gas can exist separate
from the crude oil in the underground formation, or
dissolved in the crude oil.
 Dry gas wells – These wells typically produce only raw
natural gas that does not contain any hydrocarbon liquids.
Such gas is called non-associated gas.
 Condensate wells – These wells produce raw natural gas
along with natural gas liquid. Such gas is also non-
associated gas and often referred to as wet gas
178

PROCESS DESCRIPTION
 The raw natural gas feedstock from a gas well or a group of
wells is cooled to lower the gas temperature to below its
hydrocarbon dew point at the feedstock pressure and that
condenses a good part of the gas condensate
hydrocarbons.
 The feedstock mixture of gas, liquid condensate and water
is then routed to a high pressure separator vessel where
the water and the raw natural gas are separated and
removed.
 The raw natural gas from the high pressure separator is
sent to the main gas compressor.
180

 The gas condensate from the high pressure separator
flows through a throttling control valve to a low pressure
separator.
 The reduction in pressure across the control valve causes
the condensate to undergo a partial vaporization referred
to as a flash vaporization.
 The raw natural gas from the low pressure separator is
sent to a "booster" compressor which raises the gas
pressure and sends it through a cooler and on to the main
gas compressor.
181

 At the raw natural gas processing plant, the gas will be
dehydrated and acid gases and other impurities will be
removed from the gas.
 Then the ethane (C2), propane (C3), butanes (C4) and C5
plus higher molecular weight hydrocarbons (referred to as
C5+) will also be removed and recovered as byproducts.
 The water removed from both the high and low pressure
separators will probably need to be processed to remove
hydrogen sulfide before the water can be disposed of or
reused in some fashion.
 Some of the raw natural gas may be re-injected into the
gas wells to help maintain the gas reservoir pressures.
182

LIQUID-VAPOR EQUILIBRIUM
 It is convenient to represent a liquid-vapor equilibrium
with the equilibrium constant K.
 By definition: K= yi/xi
183

FUGACITY OF GAS
 In chemical thermodynamics, the fugacity (f) of a real gas
is an effective pressure which replaces the true mechanical
pressure in accurate chemical equilibrium calculations.
 It is equal to the pressure of an ideal gas which has the
same chemical potential as the real gas.
 For example, nitrogen gas (N2) at 0°C and a pressure of
100 atm has a fugacity of 97.03 atm. This means that the
chemical potential of real nitrogen at a pressure of 100
atm has the value which ideal nitrogen would have at a
pressure of 97.03 atm.
186

 Fugacities are determined experimentally or estimated for
various models such as a Van der Waals gas that are closer
to reality than an ideal gas.
 The ideal gas pressure and fugacity are related through the
dimensionless fugacity coefficient φ:
Φ = f/P
 For nitrogen at 100 atm, the fugacity coefficient is 97.03
atm / 100 atm = 0.9703. For an ideal gas, fugacity and
pressure are equal so is 1.
187

K VALUES FROM FUGACITIES
 Fugacities are used to correct the non-ideal behavior of
gases at high pressures ( above 3.5 MPa) or close to the
critical point.
Ki= yi/xi = f0
i,l / f0
I,v
 f0
i,l= fugacity of component i in the pure liquid state
 f0
I,v= fugacity of component I in the pure vapor state
 Applying the law of ideal solutions ( Not ideal gas law)
fi,l= f0
I,l. xi and fi,v= f0
I,v.yi
 At equilibrium , we have fi,l= fi,v
188

Fugacity coefficient for gas φi = fi/ P.yi
 For liquids : φi,l = fi/ P.xi ?
 At equilibrium : Ki= φi,l / φi,v
K values pages 140-154
189

RELATIVE VOLATILITY
 The relative volatility αi for component (i) is the ratio of its
distribution coefficient and the distribution coefficient of a
reference component (r):
αi = ( Ki/Kr)
190

BOILING (BUBBLE) POINT
OF A MIXTURE
 At a given pressure, the boiling point or bubble point of a
multi-component mixture must satisfy the relationship:
Σ (yi)= 1= Σ (Ki.xi)= Kr. Σ (αi.xi)
where Kr= ( 1/ Σ (αi.xi)
The test is to compare the value of Kr calculated with the
value of Kr given in the chart for the assumed temperature.
 K values found in tables for a given pressure and
temperature.
191

STEPS OF CALCULATION
1) Assume the temperature T
2) Find the corresponding Ki
3) Select a reference component and calculate αi
4) Kr is calculated from: Kr= ( 1/ Σ (αi.xi)
5) The assumed T is compared to the temperature of the
reference (r) for the calculated Kr
6) the composition yi is calculated by:
 yi= ( αi.xi/Σαixi)
192

DEW POINT OF A MIXTURE
Σxi = Σ (yi/Ki)=(1/Kr).Σ (yi/αi)
193

CLASS WORK
 Do example 5.1 page 117 and 5.2 page 118
194

NGL STABILIZATION:
DEW POINT CONTROL
 Once the NGL has been extracted from the gas, it must be
stabilized to meet sales specifications.
 In some cases, the NGL product is a stabilized condensate
consisting only of C5+ having a vapor pressure less than
14.4 psia.
 In other cases , the NGL product is a C4+ mixture which can
be added to crude oil stream for sale.
 In NGL recovery, the NGL product is a C2+ or C3+ which can
be fractionated to produce C1, C2, C3, C4 and C5+
196

STABILIZATION BY DISTILLATION
 Stabilization of natural gas liquids (NGLs) or field
condensate is a process utilizing controlled flashing and
in some cases, a distillation of the liquid to allow it to be
stored in atmospheric vessels.
 The distillation of the liquid can also used to remove
objectionable non-hydrocarbon components, most
notably CO2, from the sales liquid.
197

MEMBRANE TECHNOLOGY
 An improved, membrane-based method of treating gas
evolved during natural gas liquids (NGL) stabilization, to
separate the very light hydrocarbon gases, methane in
particular, from the heavier hydrocarbons.
 The membrane acts as a demethanizer and establishes a
vapor/liquid equilibrium during phase separation that is
different than would otherwise obtain.
 This can increase NGL production and reduce the weight
of C3+ hydrocarbons in the off-gas from the stabilizing
phase separators.
198

FLASH CALCULATION
 Flash (or partial) evaporation is the partial vapor that
occurs when a saturated liquid stream undergoes a
reduction in pressure by passing through a throttling valve
or other throttling device.
 This process is one of the simplest unit operations. If the
throttling valve or device is located at the entry into a
pressure vessel so that the flash evaporation occurs
within the vessel, then the vessel is often referred to as a
flash drum.
 If the saturated liquid is a multi-component liquid (for
example, a mixture of propane, isobutane and normal
butane), the flashed vapor is richer in the more volatile
components than is the remaining liquid.
199

MATERIAL BALANCE
 Total and partial:
 A) Total: F= V+L
 B) partial: Fzi= Vyi + Lxi
 For Feed flow-rate F = 1mol, we obtain:
 A) xi = zi/ ( L+VKi)
 B) yi= zi/{ V+(L/Ki)}
201

 Knowing that Σxi= 1 and Σyi=1 , we will obtain:
Σxi = Σ{zi/ ( L+VKi)} =1
Σyi= Σ [zi/{ V+(L/Ki)}] =1
At equilibrium: Σyi – Σxi =0, we obtain the flash
equation:
Σ{zi ( Ki-1)} / {V( Ki-1) +1} =0
202

STEPS FOR SOLVING FLASH
CALCULATION
 1) find K from P and T
 2) assume V and L ( L=F-V)
 3) solve the flash equation
 4) if not equal to zero, assume new V and L
 Solve example 5.3 page 119.
203

NGL FRACTIONATION BY
DISTILLATION
204

SELECTION OF KEY
COMPONENTS
 Selecting Key components: If we have a
mixture ( A,B,C,D), the separation
should be only between two of the
four components:
 Ex:
 A and B are light and heavy keys
 B and C are light and heavy keys
 C and D are light and heavy keys.
205

LIGHT AND HEAVY
COMPONENTS
 If we want to separate B and C
 B is called the Light (L) key
 C is called the Heavy (H) key
 A is called light component
 D is called heavy component
 It is assumed that the light
components are all at the top and the
heavy components all in the bottom.
206

MINIMUM OF STAGES BY FENSKE
EQUATION
 The Fenske equation used for a binary distillation is also
used for multicomponent distillation to estimate the
minimum number of stages at total reflux:
 Nm=(log {xLD. D/xHD. D} .{xHW. W/xLW. W})/ log ( αLAV )
 With αLAV = √ (αLD. αLW )
207

DISTRIBUTION OF THE OTHER
COMPONENTS
 (xi,D. D/xiw. W)= (αi,AV)Nm.(xHD.D/xHW.W)
208

RMINIMUM
 Underwood shortcut method is used for the Minimum
Reflux ratio.
 Solving the two following equations:
 1-q= Σ {αi,av.xiF/(αi,av-θ)}
 Rm+1= Σ {αi,av.xiD/(αi,av-θ)}
 1) As an approximation, the values of xiD in the second
equation can be taken from the Fenske equation.
209

NUMBER OF PLATES
 2) The value of θ of the first equation is found by trial and
error. It is located between the α value of the light and
heavy keys.
 3) Having the value of θ , we find Rm from the second
equation.
 4) R= 1.5 Rm
 4) Using Figure 11.7.3, we can estimate the number of
stages N
210

LOCATION OF THE FEED
 Log ( Ne/Ns)= 0.206. log [(xhf/xlf).(W/D).( xlw/xld)2 ]
 Ne is the number of theoretical stages above the feed
plate.
 Ns is the number of theoretical stages below the feed
plate.
211

EXAMPLE OF NGL FRACTIONATION
UNIT
212

SECTIONS OF THE UNIT
The natural gas liquefaction ( NGL) is
divided into 4 sections:
 The feed preparation Section
 The expansion and separation Section
 The recovery Section
 The propane refrigerant Section
213

FEED PREPARATION
SECTION
The feed preparation section contains:
 Feed Gas Scrubber D-405
 Feed Gas separator D-401
 The feed gas/ gas off exchanger E-401
 The gas and liquid dehydrators
 Purpose of the section: To remove any liquid
from the inlet gas and to prepare the inlet
feed gas for cooling and separation
214

EXPANSION SECTION
The expansion and separation section contains:
 High Level Gas Chiller E-402
 Low Level Gas Chiller E-404
 Chiller Separator D-403
 Expander Feed Separator D-404
 Expander KT-100
 Cold gas/ off gas exchanger E-405
 Intermediate gas/off gas exchanger E-403
215

OBJECTIVE OF
EXPANSION SECTION
 Purpose of the section:
 Cool the inlet feed gas in a series of
heat exchangers and to provide
several feeds at various temperatures
to the demethanizer D-402
216

SEPARATION SECTION
The separation section contains:
 Demethanizer Column D-402
 Demethanizer Reboiler E-406
 Compression Section K-100 and KT-100
 Two product booster pumps P-401A/B
217

REFRIGERATION
SECTION
 Propane refrigerant is used
 Cooling takes place in the high
Level Chiller E-402 and Low Level
Chiller E-404
218

 Pressurized inlet gas enters NGL
recovery Unit
 Entrained liquid is removed by
scrubber
 The liquid from the scrubber is dried
and then feed the demethaniser
 The gas from the scrubber is dried
and then cooled by the overhead gas
from the demethanizer
220

 The gas then enters the feed gas separator D-401
 The liquid from the separator combines with the liquid
from the bottom of the scrubber to go to the
demethanizer
 - The gas leaving the separator is chilled by passing
through three heat exchangers
 - high level gas chiller E-402
 - Intermediate gas-gas heat exchanger E-403
 - Low level Chiller E-404
221

 From the low level chiller, gas enters the
chiller separator D-403 which remove
any additional liquid
 - The remaining gas is cooled in a cold
gas exchanger E-405
 - Then enters the expander feed
separator KT 100
 - The liquid from the expander
separator enters the demethanizer
222

 The gas from the expander separator E-
404 enters the expander
 - The expander reduces the
temperature and pressure of the gas
and condenses as much C2+ as possible
 - The gas stream from the expander D-
404 feeds the demethanizer
 - the expander is also used to provide
power to the residue gas compressor
223

FEED PREPARATION SECTION
 TI-350: indicates inlet feed gas to gas
Scrubber D-405 ( 0-650C)
 HC-350: This is a manual valve to
control the flow of inlet gas to the feed
gas scrubber D-405
 HS-400: This hand switch initiates the
plant emergency shut down by closing
the inlet feed valve HC-350
225

 FI-405: Indicates the inlet feed gas
vapor from the top of the scrubber
D-405 ( 0 -1600 kNm3/d
 FI-406: Indicates the liquid flow from
the bottom of D-405 ( 0-50 m3/h)
 LC-350: this controls the level of
liquid in the scrubber D-405 by
regulating the flow of methane to the
D-402. Flow shown by FI-406
226

FEED GAS SEPARATOR D-401
 LC-411: controls the liquid level
in the feed gas separator D-401
by regulating the flow of liquid
from the bottom of D-401 to tray
20 of D-402
 TI-400: Indicates the vapor
temperature exiting the top of D-
401
227

TYPE OF GASSES.
 Exercise B): Use the internet or any other sources to answer
the following questions:
1. What is an associated gas?
2. Search (internet or any other source) for a typical associated
gas composition of an oil field, preferably in the UAE, and
attached/copy the table.
3. What is a non-associated gas.
4. What is the difference between a wet gas and a dry gas.
(include a table showing an example of a mol% of a dry gas
components compared to a wet gas)
(Will discuss and will review the answers after you are done…
next slide)
228

HIGH LEVEL GAS CHILLER
 LC-401:This controls the propane
refrigerant level in the shell side of
the High level gas chiller E-402
 LAH-401: this alarm will start when
the level of the liquid in the shell side
of E-402 rises above 80% as read in
LC-401
229

 PC-405: from 0 to 7 Barg , this controls
the pressure in E-402 by regulating the
flow of propane vapor from the chiller
to the inlet of second stage of
compressor ( not simulated)
 PAH-405: This alarm when the pressure
in the gas chiller E-402 rises above 2.94
as read in PC-405
230

LOW LEVEL GAS CHILLER
 LC-402:This controls the liquid propane in the
shell side of E-404 by regulating the flow of
propane from the propane tube side of E-409
 LAHL-402: Alarm when the propane
refrigerant level in shell side of E-404 rises
above 80% or falls below 20%
 PC-406 : from 0 to 3.5 barg, this controls the
pressure in E-404 by regulating the flow of
propane vapor from the chiller to first stage of
the compressor ( not simulated)
231

 PAH-406: Alarm when the pressure in E-404
rises above 0.62 Barg as read in PC-406
 Ti-404: indicates the temperature of the
effluent from the tube shell of E-404.
Indicates also the temperature of the feed
entering D-403
 LC -403: Controls the level of D-403 by
regulating the flow from the bottom of the
separator to tray 14 of D-402
232

EXPANSION SECTION
 PC-401:from 0 to 50 Barg, this controls the pressure of
the expander feed separator through a split-range
control. This is also the pressure at the inlet to the
expander section.
 PAHL- 401: alarm when the pressure in D-404 rises
above 48.0 Barg or falls below 44.13 Barg as read at PC-
401
 TI-405: Indicates the temperature of the feed gas as it
enters D-404. this is also the temperature of the feed gas
from the tube side of E-405
233

 LC-404:this controls the liquid level in the chiller separator
D-404 by regulating the flow of liquid from the bottom of
separator to tray 8 of D-402
 LAH-404: Alarm when the liquid level in D-404 rises above
80% as read at LC-404
 HC-401: Manual control adjusts the position of the inlet
louver vanes in expander4 section
 HS-401:switch that determines witch controller HC-401 or
PC-401 will regulate the position of the expander inlet
vanes
234

 FC-403: from 0 to 1600 kNm3/d, this
regulates the inlet flow to the compressor
section
 FAL-403: Alarm when compressor recycle (
anti-surge) flow falls below 750.KNm3/d as
read in FC-403
 HS 100: this switch operates the expander
section KT-100. When the switch in ON , the
expander is in operation
235

DE-METHANIZER
 AAH-401 : Alarm when the concentration of
methane in the bottom of the demethanizer
D-402, rises above 2% as read in AC-401
 AC-401: Controls the methane composition
in the bottom of the demethanizer D-402
from 0 to 10% by sending a remote set-point
signal to the demethanizer reboiler effluent
temperature controller TC-403
236

 FI-408: this instrument indicates the flow of
the methane product from the bottom of the
demethanizer D-402 to the product pipeline .
This flow is regulated by the Demethanizer
level controller LC-400.
 HS-401A-B : this are the product booster
pumps. These pumps draw methane product
from the bottom of the demethanizer D-402
and send it to the product line
237

 LAHL-400: This alarm fires when the
level in the bottom of the demethanizer
D-402 rises above 80% or below 20% as
read at LC-400
 LC-400 : this controls the level in the
bottom of the demethanizer by
regulating the flow of methane product
from the bottom of D-402 as read in FI-
408
238

 PAHL-402 : Alarm when the pressure in
the top of D-402 rises above 13.48 Barg
or below 10.69 Barg as read in PC-402
 PC-402: Controls the pressure in the
top of D-402 by regulating the flow of
vapor from the discharge of the
compression section K-100
239

 TAH-401 D-402 TRAY-1 Temperature:
 This alarm is on when the temperature of
TRAY-1 of D-402, rises above -95C as read in
TC-401
 TC-401( -125C to -200C):
 This controls the temperature of the feed of
tray-1 of D-402 by regulating the amount of
gas bypassing KT-100 and flows directly from
the top of D-403
240

 TC-403: ( from -20C to 100C):
 This controls the effluent
temperature from the D-402 re-
boiler E-406 by regulating the flow
of heating medium to the re-boiler.
This controller can receive a signal
control from the D-402 methane
composition controller AC-401
241

 TI-410: Indicator top of D-402
 -1250C to -500C
 TI-411: Indicator tray 24 of D-402
 -1000C to 100C
 TI-412 : Indicator of bottom D-402
 -500C to 100C
242

CLASS WORK
 Work the NGL fractionation
plant using hysys.
243

ACID & SOUR GAS
 Acid gas is natural gas or any other gas mixture which
contains significant amounts of hydrogen sulfide (H2S),
carbon dioxide (CO2), or similar contaminants.
 The terms acid gas and sour gas are often incorrectly
treated as synonyms.
 Strictly speaking, a sour gas is any gas that contains
hydrogen sulfide in significant amounts;
 Hydrogen sulfide is a toxic gas. It also restricts the
materials that can be used for piping and other
equipment for handling sour gas, as many metals are
sensitive to sulfide stress cracking.
245

GLOBAL WARMING
 an acid gas is any gas that contains significant amounts of
acidic gases such as carbon dioxide (CO2) or hydrogen
sulfide.
 Thus, carbon dioxide by itself is an acid gas but not a sour
gas.
 Carbon dioxide is the main gas responsible for global
warming.
246

CONVERTING H2S
 Before a raw natural gas containing hydrogen sulfide
and/or carbon dioxide can be used, the raw gas must be
treated to reduce impurities to acceptable levels and this
is commonly done with an amine gas treating process.
 The removed H2S is most often subsequently converted
to by-product elemental sulfur in a Claus process
 or alternatively converted to valuable sulfuric acid in a
WSA Process unit.
247

REASONS FOR REMOVING
CO2 AND H2S
 Carbon dioxide, hydrogen sulfide, and other contaminants
are often found in natural gas streams.
 CO2 when combined with water creates carbonic acid
which is corrosive. CO2 also reduces the BTU value of gas
and
 in concentrations of more that 2% or 3 % the gas is
unmarketable.
 H2S is an extremely toxic gas that is also tremendously
corrosive to equipment.
 Amine sweetening processes remove these contaminants
so that the gas is marketable and suitable for
transportation.
248

DIFFERENT PROCESSES
 Chemical solvent processes
 Physical solvent processes
 Dry adsorbents processes
249

CHEMICAL SOLVENTS
 Monoethanolamine (MEA)
 * Diethanolamine (DEA)
 * Methyl- Diethanolamine
(MDEA)
 * Diglycolamine (DGA)
 * Hot Potassium Carbonate
250

PHYSICAL SOLVENTS
 Physical solvent processes:
 * Selexol
 * Propylene Carbonate
 * Sulfinol
 * Rectisol
251

DRY ADSORBENTS
* Molecular sieve
 * Activated charcoal
 * Iron sponge
 * Zinc oxide
252

AMINE GAS SWEETENING
SOLUTIONS
 Amine gas sweetening is a proven
technology that removes H2S and CO2
from natural gas and liquid hydrocarbon
streams through absorption and
chemical reaction.
 Each of the amines offers distinct
advantages to specific treating
problems.
253

MEA
 Used in low pressure natural gas
treatment applications requiring
stringent outlet gas specifications
254

MDEA
 MDEA (Methyldiethanolamine)
 Has a higher affinity for H2S
than CO2 which allows some
CO2 "slip" while retaining H2S
removal capabilities.
255

DEA
 DEA (Diethanolamine)
Used in medium to
high pressure treating
256

PIPERAZINE
 Nowadays, Piperazine mixed with
MDEA or the hindered amine AMP are
the most effective amine mixtures
because :
 1) Piperazine has fast kinetics with
CO2 and H2S
 2) MDEA and AMP require less energy
for the regeneration of the amine.
257

IONIC LIQUIDS
 Some Ionic liquids are now under investigation in many
laboratories around the world as the new solvent to be
used for acid gas removal:
 They have the advantage to use less energy than amines
for their regeneration
 BUT they have slow kinetics with the acid gases, they are
very viscous and still expensive in the market.
258

CHEMICAL REACTIONS
 MEA is a suitable compound and, in absence
of other chemicals, suffer no degradation or
decomposition at temperatures up to its
normal boiling point.
 MEA reacts with H2S as follows:
 2(RNH2) +H2S ↔ (RNH)2S
 MEA reacts with CO2 as follows:
 2(RNH2) +CO2 ↔RNHCOONH3R
259

PROCESS FOR ACID REMOVAL
BY AMINE SOLUTIONS
260

ABSORPTION /STRIPPING
UNIT
261

PROCESS DESCRIPTION
 The Amine Treating Unit removes CO2 and H2S from sour
gas and hydrocarbon streams in the Amine Contactor. The
Amine (MDEA) is regenerated in the Amine Regenerator,
and recycled to the Amine Contactor.
 The sour gas streams enter the bottom of the Amine
Contactor. The cooled lean amine is trim cooled and enters
the top of the contactor column.
 The sour gas flows upward counter-current to the lean
amine solution. An acid-gas-rich-amine solution leaves the
bottom of the column at an elevated temperature, due to
the exothermic absorption reaction.
 The sweet gas, after absorption of H2S by the amine
solution, flows overhead from the Amine Contactor.
264

 The Rich Amine Surge Drum allows separation of
hydrocarbon from the amine solution.
 Condensed hydrocarbons flow over a weir and are
pumped to the drain.
 The rich amine from the surge drum is pumped to the
Lean/Rich Amine Exchanger.
 The stripping of H2S and CO2 in the Amine Regenerator
regenerates the rich amine solution.
 The Amine Regenerator Reboiler supplies the necessary
heat to strip H2S and CO2 from the rich amine, using
steam as the heating medium.
265

 Acid gas, primarily H2S and water vapor from the
regenerator is cooled in the Amine Regenerator
Overhead Condenser.
 The mixture of gas and condensed liquid is collected in
the Amine Regenerator Overhead Accumulator. The
uncondensed gas is sent to Sulfur Recovery.
 The Amine Regenerator Reflux Pump, pumps the
condensate in the Regenerator Accumulator, mainly
water, to the top tray of the Amine Regenerator A
portion of the pump discharge is sent to the sour water
tank.
266

 Lean amine solution from the Amine Regenerator is cooled
in the Lean/Rich Exchanger.
 A slipstream of rich amine solution passes through a filter
to remove particulates and hydrocarbons, and is returned
to the suction of the pump.
 The lean amine is further cooled in the Lean Amine Air
Cooler, before entering the Amine Contactor.
267

PRODUCT SPECIFICATIONS
 The Amine Treating Unit removes CO2 and H2S from sour
gas and hydrocarbon streams totaling 14.5 MMSCFD.
 The acid contaminants are absorbed by counter flowing
amine solution (MDEA).
 The stripped gas is removed overhead, and the amine is
sent to the regenerator.
 In the regenerator, the acidic components are stripped by
heat and reboiling action and disposed of, and the amine is
recycled.
268

EQUIPMENT'S SPECIFICATIONS
 The amine contactor is 5 feet in diameter by 65 feet
tangent to tangent with 22 trays.
 The Rich Amine Surge drum, D-101, provides
approximately 30 minutes of residence time which allow
separation of the hydrocarbon from the amine solution.
 The Amine Regenerator is 8 feet in diameter by 70 feet
tangent to tangent with 22 trays.
 The Regenerator Reboiler, E-202, uses 60 psig steam as
heating medium which provides the heat for regeneration
of the amine solution.
269

PROCESS CONTROL OF THE UNIT
270

PROCESS CONTROL OF THE
UNIT
 The sour gas stream, 14.5 MMSCFD, enters the bottom of
the Amine Contactor at 95 0F and 140 psig.
 The cooled lean amine is trim cooled in exchanger E-103
and enters the top of the absorber column at 105 0F.
 The lean amine solution temperature is 100 higher than
the feed gas to prevent any hydrocarbon condensation
and foaming problems.
 This temperature differential is maintained by TDIC-103,
which allows bypassing of lean amine around the Lean
Amine Trim Cooler E-103.
271

 The sour gas flows upward counter-current to the lean
amine solution in T-101.
 An acid-gas-rich-amine solution leaves the bottom of the
column at an elevated temperature, 1350 F, due to the
exothermic absorption reaction.
 The rich MDEA solution temperature is monitored by TI-
105.
 Rich amine leaves the bottom of the column on level
control LIC-101 to the Rich Amine Surge Drum D-101.
272

 The sweet gas, after absorption of H2S by the MDEA solution,
flows overhead from T-101 under pressure control PIC-101,
monitored by the H2S and CO2 analyzers, AI-102 and AI-103.
 The temperature and flow rate of the gas are monitored with TI-
104 and FI-101.
 The Rich Amine Surge Drum D-101 allows the amine solution 30
minutes of residence time, which allows separation of
hydrocarbon from the amine solution.
 The drum pressure is maintained by a backpressure controller,
PIC-102, at 5 psig.
 Condensed hydrocarbons flow over a weir and are
pumped to the drain system using P-102.
273

 The rich amine from the surge drum is pumped by P-101
to the Lean/Rich Amine Exchanger E-101.
 The rich amine enters the tube side at 1350 F, where it is
heated to 2260 F by the hot lean amine solution from the
regenerator bottoms.
 The hot lean amine solution enters the Lean/Rich
Exchanger on the shell side at 265 0 F.
 The stripping of H2S and CO2 in the Amine Regenerator, T-
201, regenerates the rich amine solution.
 The Amine Regenerator Reboiler supplies the necessary
heat to strip H2S from the rich amine, using 60-psig steam
as the heating medium.
274

 Acid gas, primarily H2S and water vapor from the
regenerator is cooled to 120 0F in the Amine Regenerator
Overhead Condenser.
 The temperature of the overhead gas is monitored by TI-
202 The mixture of gas and condensed liquid is collected in
the Amine Regenerator Overhead Accumulator.
 The pressure is maintained at 16 psig with PIC-201
controlling the acid gas from the Regenerator
Accumulator, D-20, to Sulfur Recovery.
275

 The condensate in the Regenerator Accumulator D-201, mainly
water, is pumped by the Amine Regenerator Reflux Pump, P-202,
to the top tray of the Amine Regenerator.
 The reflux flow is regulated by level controller LIC-201 and is
monitored by FI-203. A part of the pump discharge is sent to the
sour water tank.
 Lean amine solution from the Amine Regenerator is cooled from
265 degrees F to 189 degrees F in the Lean/Rich Exchanger.
 A slipstream of rich amine solution is controlled by PDIC-202
through a filter F-201 to remove particulates and hydrocarbons,
and returned to the suction of P-201.
 The lean amine is further cooled in the Lean Amine Air Cooler, E-
102, to 130 0 F.
276

ADVANCED CONTROL
 The cooler the lean amine temperature, the better the
H2S absorption. However, lowering the MDEA solution
temperature below the gas inlet temperature can cause
hydrocarbons to condense with resulting foaming.
 The lean amine solution temperature is maintained 100
higher than the feed gas to the Amine Contactor. TDIC-103
allows bypassing of lean amine around the Lean Amine
Trim Cooler, E-103, to maintain this 100 difference.
277

SULFUR RECOVERY UNIT:
CLAUS PROCESS
278

SULFUR RECOVERY PROCESS
 The most practical method for
converting hydrogen sulfide to
elementary sulfur
 Best suited for gases containing more
than 50% hydrogen sulfide is the
 PARTIAL COMBUSTION PROCESS.
279

 Hydrogen sulfide is burned with 1/3 the stoichiometric
quantity of air
 2H2S + 3O2 → 2H2O + 2SO2
 The hot gases are sent to a reactor with alumina as
catalyst to react sulfur dioxide with unburned hydrogen
sulfide to produce free sulfur
 2H2S + SO2 → 2H2O + 3S
280

 Carbon sulfide (COS) and carbon disulfide CS2
have presented problems in many Claus plant
operations.
 These compounds are formed in the combustion
step.
 Unconverted, these compounds represent a loss
of sulfur recovery.
 They are in the tail gas of the Claus process and
sent to the Scot process
281

 Natural Gas usually contains significant quantities of water
vapor.
 Changes in temperature and pressure condense this vapor
altering the physical state from gas to liquid to solid.
 This water must be removed in order to protect the
system from corrosion and hydrate formation.
284

DALTON’S LAW
 In 1810, an English scientist by the name of John Dalton
stated that the total pressure of a gaseous mixture is equal
to the sum of the partial pressures of the components.
 This statement, now known as Dalton's Law of Partial
Pressures, allows us to compute the maximum volume of
water vapor that natural gas can hold for a given
temperature and pressure.
 The wet inlet gas temperature and supply pressures are
the most important factors in the accurate design of a gas
dehydration system.
 Without this basic information the sizing of an adequate
dehydrator is impossible
285

EXAMPLE
 As an example, one MMSCF (million standard cubic feet) of
natural gas saturated @ 80 0F and 600 PSIG (pound per square
inch gauge) will hold 49 pounds of water.
 At the same pressure (600 PSIG) one MMSCF @ 120 0 F will hold
155 pounds of water.
 Common allowable water content of transmission gas ranges
from 4 to 7 pounds per MMSCF.
 Based upon the above examples, we would have two very
different dehydration problems as a result of temperature alone.
 There are many other important pieces of design information
required to accurately size a dehydration system. These include
pressures, flow rates and volumes.
286

HYDRATES IN NATURAL GAS
 All gasses have the capacity to hold water in a vapor state.
This water vapor must be removed from the gas stream in
order to prevent the formation of solid ice-like crystals
called hydrates.
 Hydrates can block pipelines, valves and other process
equipment.
 The dehydration of natural gas must begin at the source
of the gas in order to protect the transmission system.
287

ELIMINATION OF WATER
 The source of the gas moved through the transmission
lines may be producing wells or developed storage pools.
 Pipeline drips installed near well heads and at strategic
locations along gathering and trunk lines will eliminate
most of the free water lifted from the wells in the gas
stream.
 Multi stage separators can also be deployed to insure the
reduction of free water that may be present.
288

PIPELINE DRIPS
 Natural gas transmission pipelines often contain liquids
that can interfere with the proper operation of the
pipeline and related equipment such as compressors,
regulators, filters, meters and valves.
 The liquid contaminants normally include hydrocarbon
condensations, lubrication oils, produced water, and
chemicals used in production, treatment, compression or
dehydration of the gas.
 Gas transmission pipelines have typically used below
grade liquid separators known as “drips” that are
installed in the pipeline at regular intervals to collect the
liquids carried in a gas stream.
289

INDUSTRIAL PROCESSES TO
REMOVE WATER
 Water vapor moved through the system must be reduced
to acceptable industry levels.
 Typically, the allowable water content in gas transmission
lines ranges from 4 lb. to 7 lb. per MMSCF.
 There are basically three methods employed to reduce
this water content. These are:
 1. Joule-Thomson Expansion
 2. Solid Desiccant Dehydration
 3. Liquid Desiccant Dehydration
292

JOULE THOMSON VALVE
 Joule-Thomson Expansion utilizes temperature drop to
remove condensed water to yield dehydrated natural gas.
 The principal is the same as the removal of humidity from
outside air as a result of air conditioning in your house.
 In some cases glycol may be injected into the gas stream
ahead of the heat exchanger to achieve lower
temperatures before expansion into a low temperature
separator.
293

SOLID DESICCANT
DEHYDRATION
 Solid desiccant dehydration, also known as solid bed,
employs the principal of adsorption to remove water
vapor.
 Adsorbents used include:
 silica gel (most commonly used),
 molecular sieve (common in NGV dryers),
 activated alumina and
 activated carbon.
294

ADSORPTION PROCESS
 The wet gas enters into an inlet separator to insure
removal of contaminants and free water.
 The gas stream is then directed into an adsorption tower
where the water is adsorbed by the desiccant.
 When the adsorption tower approaches maximum
loading, the gas stream is automatically switched to
another tower allowing the first tower to be regenerated.
296

REGENERATION
 Heating a portion of the mainstream gas flow and
passing it through the desiccant bed regenerates the
loaded adsorbent bed.
 The regeneration gas is typically heated in an indirect
heater. This unsaturated regeneration gas is passed
through the bed removing water and liquid hydrocarbons.
 The regeneration gas exits the top of the tower and is
cooled most commonly with an air-cooled heat exchanger.
 Condensed water and hydrocarbons are separated and the
gas is recycled back into the wet gas inlet for processing.
297

TEG METHOD
 The third method of dehydration is via liquid desiccant and
is most common in the Northeast United States.
 This method removes water from the gas stream by
counter current contact in a tray type contactor tower with
tri-ethylene glycol (TEG)
 Natural gas enters the unit at the bottom of the adsorber
tower and rises through the tower were it intimately
contacted with the TEG solution flowing downward across
bubble trays.
 Through this contact, the gas gives up its water vapor to
the TEG.
298

TEG METHOD
 The water laden TEG is circulated in a closed
system, where the water is boiled from the TEG.
 The regenerated TEG then is recirculated to the
contacting tower.
299

PRINCIPLE OF THE PROCESS
 Glycol dehydration is a liquid desiccant system for the
removal of water from natural gas and natural gas liquids
(NGL). It is the most common and economic means of
water removal from these streams.
 Glycols typically seen in industry include:
 1) Triethylene glycol (TEG), TEG is the most commonly
used glycol in industry.
 2)Diethylene glycol (DEG),
 3) Ethylene glycol (MEG), and
 4) Tetraethylene glycol (TREG).
301

OBJECTIVE OF THE PROCESS
 The purpose of a glycol dehydration unit is to remove
water from natural gas and natural gas liquids.
 When produced from a reservoir, natural gas usually
contains a large amount of water and is typically
completely saturated or at the water dew point.
 This water can cause several problems for downstream
processes and equipment. At low temperatures the water
can either freeze in piping or, as is more commonly the
case, form hydrates with CO2 and hydrocarbons (mainly
methane hydrates).
302

PLUGGING AND CORROSION
 Depending on composition, these hydrates can form at
relatively high temperatures plugging equipment and
piping. Glycol dehydration units depress the hydrate
formation point of the gas through water removal.
 Without dehydration, a free water phase (liquid water)
could also drop out of the natural gas as it is either cooled
or the pressure is lowered through equipment and piping.
 This free water phase will contain some portions of acid
gas (such as H2S and CO2) and can cause corrosion.
303

PROCESS DESCRIPTION
 Lean, water-free glycol (purity >99%) is fed to the top of an
absorber (also known as a "glycol contactor") where it is
contacted with the wet natural gas stream.
 The glycol removes water from the natural gas by physical
absorption and is carried out the bottom of the column.
 Upon exiting the absorber the glycol stream is often
referred to as "rich glycol". The dry natural gas leaves the
top of the absorption column and is fed either to a
pipeline system or to a gas plant.
 Glycol absorbers can be either tray columns or packed
columns.
304

 After leaving the absorber, the rich glycol is fed to a flash
vessel where hydrocarbon vapors are removed and any
liquid hydrocarbons are skimmed from the glycol.
 This step is necessary as the absorber is typically operated
at high pressure and the pressure must be reduced before
the regeneration step.
 Due to the composition of the rich glycol, a vapor phase
having a high hydrocarbon content will form when the
pressure is lowered.
 After leaving the flash vessel, the rich glycol is heated in a
cross-exchanger and fed to the stripper (also known as a
regenerator
305

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