Download The Investigation of the Methods of Preventing the Formation of Gas

The Investigation of the Methods of Preventing the Formation of Gas Hydrate
Seyed Ali Khoddami1, Ali Esfandiari2, Seyed Mohammad Mehdi Parnian3,4
1Department
of Chemical Engineering, Isfahan Branch, Payame Noor University, Isfahan, Iran
Email: [email protected]
2
Department of Chemical Engineering, Isfahan Branch, Payame Noor University, Isfahan, Iran
Email: [email protected]
3Department of Chemical Engineering, Zarghan Branch, Islamic Azad University, Zarghan, Iran
Email: [email protected]
4The Engineer of Natural Gas Measuring and Calculations, National Iranian Gas Company
ABSTRACT
Iran as a country with rich sources of natural gas has to deal with the problem of the formation of gas hydrate
which can be problematic in petroleum and gas industries. The formation of gas hydrate can cause flow
reduction, block the pipeline and sometimes lead to an explosion of pipelines. In terms of the structure, hydrate is
a solid, physically resembling ice and is obtained by physically mixing water with some carbohydrates existing
in natural gas. Almost all the works done recently on predicting the conditions of the formation of hydrate
crystals have been based on the science of thermodynamic. These models all have similar hypotheses. Unlike
experimental models, thermodynamic models benefit from stronger theoretical bases and can consider
intermolecular effects in a better way. All the available models for predicting the characteristics of hydrate phase
use the well-known model of “van der Waals –Platteeuw” which has been reformed.
Keywords: Gas, Hydrate Crystal, Van der Waals, Platteeuw Model, Pipeline, Thermodynamic
INTRODUCTION
Natural gas and crude oil are naturally in contact
with water in underground sources. Water
molecules have strong hydrogen bonds and
therefore hollow spaces (cavities) are formed in
them, shaping a structure similar to a network. Gas
molecules (the guest) are trapped inside “cages” of
hydrogen-bonded water molecules (the host),
interact with them and form a crystalline structure
resembling ice, which is known as gas hydrate.
Gas hydrates or hydrate crystals are frost-like and
can be mistaken with ice or frost. Their general
formula is M.nH2O, with M being the molecule
forming hydrate. These compounds which are
formed in low temperatures and relatively high
pressures are from the family of Klatryts. Klatryts
are formed by a combination of some host
molecules and one or some guest molecules. The
stability of these compounds depends on both
components. Host molecules trap guest molecules
in their hollow spaces. In gas hydrates water is the
host molecules. At suitable pressure and
temperature guest molecules whose size is
appropriate for the hollow spaces are trapped and as
a result hydrate crystal is formed. There are many
gases which can be a host including methane,
ethane, propane, carbon dioxide, hydrogen sulfide,
and so on. The results of the research studies
conducted until 1950 show that there are three
conditions necessary for the formation of hydrate:
-Water in liquid phase or ice
-The existence of small gas molecules such as
methane, ethane, propane and argon
-Low temperatures and high pressures
Problems caused by the formation of hydrate in
pipelines
In 1934, when petroleum and gas industry of the
U.S.A. boosted, this fact was revealed that
obstruction in pipelines in low temperatures is not
because of frozen water, as it was thought for long;
instead, it is because of the formation of hydrate
crystals. Structurally, hydrate is a solid physically
resembling ice, although different in characteristics,
and is obtained by physically mixing water with
some carbohydrates existing in natural gas.by
studying liquid structure of water, researchers have
found out that the hydrogen-bonded cycles in water
molecules are much more stable than open chains
of the same number of molecules. Considering the
ability of water molecules to form hollow, instable
hydrate network, there are four different structures
for hydrates:
*Structure type I
*Structure type II
*Structure type III
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Seyed Ali Khoddami et al
*and a new structure which is still nameless
the adherence of the hydrates to each other and the
formation of block. Therefore, enough space is
created for the absorption of gasses. Without SDS,
hydrate is like a big block with tiny holes. Since
ethylene molecules solve in SDS micelles better
than methane, they are more trapped in hydrate
structure and when in gas mixture, they work as a
filter and absorb more ethylene (1).
The functions of gas hydrates
Hydrates were first known as obstructers of gas
pipelines but today their other functions have been
found, through numerous research studies:
 Absorbing carbon dioxide existing in air
 Gas separation process
 Saving and transferring natural gas
 Chilling tank
Storing and transferring natural gas
Since gas hydrate has high gas-storage capacity, it
has been studied as a process to store and transfer
gas. By adding surfactants, the speed of hydrate
formation goes up. In gas holders in 1 atmosphere
pressure, the temperature is reduced to 258k to
make sure of hydrate stability.
Also, using
structure H hydrates for increasing storage capacity
is under investigation. In a research study, the final
costs of gas transfer through hydrate method from
Asalooye in Iran to commercial areas of the world
has been estimated, taking different factors such as
sea water temperature as the cooling source, the
temperature of hydrate holder, cost of transfer and
cost of ship into account. In that study, the methods
of gas transfer are summarized as follows:
-pipeline natural gas
-lliquefied natural gas (LNG)
-Compressed natural gas (CNG)
-Natural gas hydrate (NGH)
-Gas to liquid (GT L)
-Gas to commodity (GTC)
-Gas to wire (GTW)
In this process, natural gas first passes the drier and
loses some water. Then, it enters the reactor, where
pure water and natural gas flow react. To this end,
the temperature in the reactor is reduced to the
desired level by an external cooling cycle. Through
the existing models, equilibrium conditions of
hydrate in proximity of pure water can be predicted.
The temperature of reactor is reduced to 2 Celsius
degrees below equilibrium temperature to maximize
hydrogen production. Then, the mixture of gas
hydrate and released water go to the separator.
Pure water returns to reactor, then. To be stable, gas
hydrate should be 49 c in 1 atmosphere conditions.
To cool hydrate in reactor, propane chilling cycle is
used. Isentropic condenser outcome is 0.8. The
calculations concerning mass- energy equilibrium
are all presented in Mr. Javanmardi’s article in full
details (1). According to the calculations, the final
cost of gas transfer for NGH method is less than
that of LNG. Based on the calculations, the final
cost for LNG is reported to be $1489 m, which is
approximately 48% more expensive than the cost
for NGH. Considering these all, it is of vital
importance to conduct more research on this
method, changing it to a practical method of
transferring gas from the existing gas fields to the
worlds’ commercial markets (1).
Absorbing carbon dioxide existing in air
64% of the rise in the phenomenon of greenhouse
gases is related to the spread of CO2. Deep sea
deposition of carbon dioxide has been proposed as a
method to remove this greenhouse gas from the
atmosphere.in depth of 400 meter or lower, CO2 is
injected and trapped by being solved in water.
Within 100-2000meter distance, CO2 is liquid and
penetrates into the waters of seas and oceans. CO2
hydrate is formed in 500-900 meter depths. The
studies are still investigating CO2 solubility,
kinetics of CO2 hydrate formation and stability of
CO2 hydrate (1).
Gas separation process
Desalination or gas- liquid separation is another
benefit of hydrate. For instance, the formation of
hydrate is a way of obtaining sweet water out of
salty water. By injecting coolness into sea water,
hydrate crystals are formed. After separating them
and heating, sweet water is gained. This method has
not found industrial application yet, as it is costly.
The other benefit of that is separation of CO2 from
the mixture of gasses produced by combustion.
Another process which is called hydrate-based gas
separation is related to THF which is used as
hydrate formation propellant. THF reduces
equilibrium pressure of hydrate formation and
expands hydrate’s stable zone (1).
Separating ethylene from the mixture of
ethylene and methane
Another example of separation is the separation of
ethylene from mixture and ethylene in the presence
of sodium dodecyl sulfate (SDS) as well as in the
absence of it. Separation through hydrate formation
is a hot topic nowadays. Its application is in
systems that because of low boiling point,
separation of the components is difficult. Since the
rate of the formation and destruction of hydrate is
much slower than the rate of condensation and
evaporation in distillation, special attention should
be paid to its kinetic. It has been proven that using
some material like SDS increases the speed and
storing capacity of hydrate. Adding SDS to water
solution caused the formation of micells from SDS
and gas molecules solved in water. When hydrate is
formed, the micell is adsorbed to hydrate while
their tail is molecules in gas phase. The absorption
of this micell reduces surface energy and prevents
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propane induction time is reported to be less than
that of methane-ethane.
It is observed that in first stage, hydrate crystal is
diffused towards gas but it gradually changes to a
flat surface. In the third stage of hydrate formation
in the mixture of methane-propane it is observed
that extra hydrate is formed on the surface of
particles which forms frost. This phenomenon
depends on saturation degree of guest molecules in
water.
The smaller the drop, the sooner the extra hydrate
forms on it. Based on the experiments conducted,
the size of water drops has no effect on induction
time. So, special equipment should exist for
providing memory water in which hydrate is
formed and then destructed. The findings show if
only a percent of the water is with memory, it is
enough to reduce induction time of all water drops
(1).
Chilling Tanks
One application of the mixture of hydrate and water
is generating coolness in chilling circles. By getting
energy from the environment to melt, it cools the
environment. The important point is that this
material is environment- friendly. Nowadays, CO2
and TBAB hydrates are being studied. Studies have
shown caged molecule in hydrate structure does not
have a considerable effect on its decomposition
heat. Rather, it is the structure of water molecules
which is important. For instance, the structure type
I has less energy than structure type II. Therefore, it
has been attempted to add THF to N2+CO2 hydrate
to change the structure from type I to type II in
order to save more energy.
The process of hydrate formation and the
contributing factors
Many macroscopic studies have been done on
hydrate formation but there are still many
unanswered questions about microscopic structure
of it. Hydrates grow in supersaturated solution of
water and guest molecules ( or in the intersection of
water- guest molecules) in gas or liquid phase (or in
the intersection of ice-hydrate). Therefore, the
features of intersection play important roles in the
mechanism of growth. The penetration of water or
guest molecules in hydrate surface is very important
in the growth of hydrates.
This penetration depends on thermodynamic
conditions (TP) and hydrate- liquid intersection. So,
the position or the way of movement of molecules
on hydrate surface is very important. Experimental
techniques of surface investigation is done in
vacuum. Other techniques of surface investigation
like infrared, Ramon spectroscope, ellipsometry or
surface diffraction are not used due to their lack of
required sensitivity for the surface or the difficulty
of adjustment in high gas pressure. However, quasi
– elastic neutron scattering is a good technique for
achieving the dynamics of water molecules which
has holes between 20 to 500 nm big and creates a
surface about tens m2/g.
Since the interaction between water molecules and
guest molecules is weak and is based on structural
similarity between ice and hydrate, it can be
expected that surface phenomenon in both ice and
hydrate
systems
is
similar.
Therefore,
understanding this phenomenon in ice can help a
great deal to understand it in hydrate.
Self-preservation in hydrates
In a research the separation of gas hydrate to
octagonal structure of ice and methane gas has been
investigated for different sizes. Hydrate samples
from 135 to 263 k heat in one atmosphere pressure.
As for example, particles with sizes between 1000
to 1400 μm remained as hydrate in 263k
temperature. This ability is known as self –
Preservation. The reason behind such a
phenomenon is that a layer of ice which is formed
by hydrate separation works as insulator and
prevents further separation of hydrate and the scape
of methane from hydrate. This effect was first
observed for Xe and Kr hydrates. Ice and methane
hydrate are stored for 2 years at 256k temperature
and one atmosphere pressure. This phenomenon is
called self – Preservation.
Reducing the pressure of hydrate formation
Using additives such as DMCH, neo-hexane,
methyl cyclohexane and 2-2-3 trimethyl butane
reduce the pressure of hydrate formation. On the
other hand, since these molecules are big, they form
structure type H which has better storage ability and
higher energy level than structure type I. In a study,
the addition of DMCH to methane gas at 28903270K temperature and pressure up to 6.7MPA was
investigated. By adding small doses of DMCH,
equilibrium pressure reduced from 3MPA (methane
hydrate type I) to 1MPA (methane hydrate type H)
at 275k temperature.
Surface of hydrate formation and contact angle
In experiments done it has been observed that the
kind of surface water drop is on has an important
effect on contact angle of hydrate formation. The
experiments have been conducted using non-stick
surface and cellophane surface. The shape of water
drop is different on these two surfaces but it has
been found out through experiments that it has no
considerable effect on crystal structure and
induction time. In the research conducted methane-
Hydrate inhibitors
Although hydrates are formed in low temperatures
and high pressures, these conditions can be
provided in any gas or oil pipeline. Therefore,
hydrate formation should be inhibited in order to
prevent obstruction of pipelines.
The methods of hydrate inhibition:
a) Keeping gas flow pressure lower than the
required pressure for hydrate formation at
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a temperature and combining specific
percentage of vapor phase
b) Keeping the temperature of gas flow
higher than the required temperature for
hydrate formation at a pressure and
combining specific percentage of vapor
phase
c) Preventing the formation of water liquid
phase by reducing the amount of water in
the system through dehumidification of the
gas entering pipeline
d) Injecting inhibitors
Inhibitors are divided into two groups:
thermodynamic inhibitors and special inhibitors.
Thermodynamic inhibitors
 Thermodynamic inhibitors are normally
alcohols, glycols and electrolytes. They
make P-T thermodynamic equilibrium
curve be skewed to left, which cause
hydrate to be formed at lower temperatures
at the same pressure.
Figure 1-2 is a
schematic diagram of the functionality of
these inhibitors. Similar to deicers, these
materials reduce water’s freezing point.
The most common thermodynamic
inhibitors
are
methanol,
ethanol,
monoethylene glycol (MEG), diethylene
glycol (DEG), triethelene glycol (TEG)
and chloride of the elements of the first
and second group of the periodic table.
However, in recent years, new inhibitors
have been utilized. Unlike thermodynamic
inhibitors, these inhibitors do not change
the phase equilibrium. They retard
nucleation
of
hydrate
formation,
preventing the growth of hydrate crystals
(6).
Figure1: The function of thermodynamic inhibitors in altering the diagram of thermodynamic equilibrium
molecular weight than alcohols and are easier to be
recycled and used again. Generally, methanol has
two main advantages over ethylenglycol (and other
glycols):
-they have more inhibitive abilities
-they are more cost-effective
Preventing hydrate formation by alcohols and
glycols
In 1998, Svartas (6) proved low doses of methanol
do not increase thermodynamic stability of hydrate.
SKatz et.al (6) showed by reducing the volatility of
alcohols, their ability in preventing hydrate
formation decreases. In other words:
methanol<ethanol<isopropanol
The advantage of volatility is that volatile alcohols
such as methanol go to gas phase after evaporation
and if hitting water while moving through gas
pipelines solve and inhibit hydrate formation,
according to Makagon (6). The required methanol
dose in gas industry is 0.3 kg for every 1000cubic
meters of gas. Stange et.al (6) showed the required
dose in cold areas might be more than what was
mentioned by Makagon. Compared to alcohols,
glycols( ethylenglycol, diethylenglycol, and
triethylenglycol) have one more hydroxyl factor,
making them able to make more hydrogen bonds
with water molecules. Glycols normally have more
Inhibiting hydrate formation through using salts
Salts are ionized in solution and the forces between
water bipolar (0—H+) and the produced ions are
much bigger than van der waalse forces between
water molecules and guest molecules. The
agglomeration of water molecules around the ions
produced by salt, decreases the solubility of guest
molecules in water. These two effects together (the
existence of water molecules around salt ions and
solubility decrease of gas guest molecules) increase
the pressure and decrease the temperature of the
point where hydrate is expected to form. Makagon
(6) showed inhibitive ability of salts has a direct
relationship with the number of released irons and
inverse relationship with ion radius. Therefore, the
best inhibitors are those that release maximum
number of cations with minimum ion radius.
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However, using salts has some disadvantages too
including corrosion and sedimentation in cold areas.
Unlike anti-agglomeration method, this method
does not require liquid hydrocarbon phase. It
retards nucleation of hydrate formation, preventing
the growth of hydrate crystals. Kinetic inhibitors
have two advantages: low doses are required and
they are highly efficient. Kinetic inhibitors are
divided into 3 groups: inhibitors which retard the
growth of hydrate crystals, inhibitors which prevent
accumulation of hydrates, and binary or twopurpose inhibitors. Retarding inhibitors retard
nucleation of hydrate formation, preventing the
growth of them. Cumulative inhibitors decrease the
tendency of hydrated to agglomerate and
accumulate, as a result, hydrate suspends in liquid.
Special inhibitors
These inhibitors which have been widely developed
in recent years, can solve the problem of hydrate
formation in low dosage ( under 2% of the weight
of water phase). Unlike thermodynamic inhibitors,
these inhibitors do not change the phase
equilibrium. They retard nucleation of hydrate
formation, preventing the growth of hydrate crystals
(6). They are divided into 2 categories: antiagglomerants and kinetic inhibitors
Anti-agglomeration method
In this method, surfactants are used, which cause
water to be suspending in the solution and hydrate
to be formed in small particles in water. A lot of gas
is consumed for hydrate formation but surfactant
prevents the agglomeration of hydrate particles and
obstruction of pipelines. For the efficiency of this
method, hydrocarbon liquid phase is required (6).
Unlike thermodynamic inhibitors which should be
used in high dosage, surfactant is used in low dose,
only between 0.5 to 2 weight percent (6). In
addition, the inhibitive ability of one weight percent
of surface-active substance is reported to be equal
to 25 weight percent methanol (6).
Hydrate formation on the presence of inhibitors
The most common thermodynamic inhibitors are
methanol (monoethylen glycol, MEG). Figure 1-16
shows the effect of methanol on water-methane,
water- ethane and water- propane systems. The data
are measured by Jhaveri et.al in 1965. As it can be
seen, at a given temperature, equilibrium pressure
increases with increasing methanol dose. Or at a
fixed pressure, the temperature of hydrate formation
decreases. Inhibitors such as methanol and sodium
chloride are mainly in liquid phase and their
quantity in vapor phase and hydrate is
inconsiderable (6).
Kinetic inhibitors
Figure 2: the effect of methanol on equilibrium conditions of hydrate formation in water-methane, waterethane and water- propane systems (6)
different pressures. As it can be seen sodium
chloride is a stronger inhibitor. However, since it is
corrosive and has limited solubility, it has no
practical application.
Robinson et. al (6)and Roberts et.al (6) measured
temperature decrease in hydrate formation as a
result of using methanol and sodium chloride in
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Figure 3: the decrease in the temperature of hydrate formation in methane, ethane and propane due to
using methanol and sodium chloride at different pressures (6)
sum of the values of temperature fall due to using
only one of the inhibitors at a time is almost equal
to the time when both inhibitors are used together.
However, Nasirfar et.al (6) showed this is true only
in low concentrations of inhibitors.
Doolabi et. al (6) were the first people who used
two inhibitors together. They used a mixture of
methanol and sodium chloride in water- methanecarbon dioxide system. They concluded that the
Figure 4: the data for hydrate formation of a mixture of methane and carbon dioxide in the presence of
two inhibitors
studied and compared preventive effect of 10
weight percent ethylene glycol and 10 weight
percent sodium chloride on 4-part system of carbon
dioxide, methane, ethane and nitrogen, finding out
sodium chloride is a stronger inhibitor than ethylene
glycol.
Fan et al (6) measured equilibrium pressure of the
formation of carbon dioxide hydrate. In the
presence of inhibitors such as methanol and
ethylene glycol(EG). The findings showed using 10
weight percent methanol is more inhibitive than the
same amount of ethylene glycol. In addition, they
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Figure 5: equilibrium pressure of the formation of carbon dioxide hydrate in the presence of methanol,
and ethylene glycol as inhibitors (6)
\
Figure 6: equilibrium pressure of the formation of carbon dioxide, methane, ethane and nitrogen hydrate
in the presence of sodium chloride and ethylene glycol as inhibitors(6)
\
method of LNG. Therefore, it is not cost-effective
and secure for power points to use these fuels.
Common methods of gas transfer at peak times in
power points are: LNG1،CNG2،GtL3،ANG4 and etc.
All these methods have advantages and
disadvantages, making them more or less useful.
For instance, in CNG method, the costs of gas
compression are really high. Also, because of the
high pressure in this process, pipelines should be
very thick, which is very expensive. The method of
ANG depends on the characteristics of the sorbent.
And finally the method of GTL is not appropriate
for transferring large volumes of gas, as well as
needing modern technology (22). In New England,
central Atlantic and southern Atlantic, LNG is the
Improving the conditions of hydrate formation
In recent years, natural gas has been widely used in
the world’s energy markets. It replaced coal in 1989
and become the second most important energy
source in the U.S.A after oil. Natural gas is a
cleaner fuel than coal, as it releases less carbon
dioxide and sulfur oxide when burning. It is also
cheaper than other fuels. As the consumption of
natural gas increases, it is very important to find
methods to provide this gas (21). Although the
demand for natural gas is increasing in world’s
markets, its application is limited, due to some
problems. For instance, gas transfer at the present
time is only possible through pipelines or expensive
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most common method of gas transfer (23). The
flexibility of this method is much more than other
methods and its storage capacity is approximately
615, the temperature about -260 c and pressure is
about 30 psi (24). With such high storage capacity
and low operational pressure, this method is
considered appropriate for natural gas transfer.
However, there are problems which make it
imperfect; its operational costs are extremely high;
it needs large, complex facilities in the points of
production and consumptions; and it has safety
problems because LNG is quickly evaporated and
releases flammable gasses in the environment. To
fulfill the existing needs, search has continued and
attempts have been made to find cheap, safe
methods with high storage capacities. One of these
methods is NGH8, gas transfer through hydrate. But
hydrate too has its own drawbacks which have
inhibited this method to be used in industry (25).
Angles (1996) showed that in an inactive hydrate
formation system only1/4-14 % of the water in the
system (depending on the conditions of the system
and the existing gasses) is used for the formation of
hydrate network, forming hydrogen bonds. The rest
of it penetrates into the holes, occupying the spaces
between the holes. As a result, the existing space in
the system is mainly used by water. If hydrate is
used for gas transfer, large equipment is required,
while only a small part is efficiently occupied by
gas (26).
Jank and Rogers (2000) showed that a characteristic
of gas hydrate is that it can store as much gas as
180 times more than its volume. Its high storage
capacity as well as the advantages below have
changed it to an important phenomenon in industry:
1- slow separation of gas from hydrate
2- flammable gasses being caged in water
3- low storage pressure
However, there are 3 reasons why it has not been
used in industry yet:
1- hydrate formation is relatively slow for
industrial use
2- separating and packing hydrate particles
for transfer are difficult
3- a large part of the volume of the hydrate
network is occupied by water (27)
Acotani et.al (2007) stated that in spite of vast
studies on the advantages of using hydrate in
industry, a hydrate- based technology which can be
successful used in industry has not been introduced
yet. The biggest challenge in this process is finding
methods to produce hydrate with high speed.
Recently, methods have been proposed to improve
solubility of gas in water and consequently increase
the speed of hydrate formation (28).
industrial importance of hydrate. Since gas hydrate
exists in a temperature higher than freezing point of
water, it can lead to obstruction of pipelines,
nozzles, taps and other equipment. After Homrashit,
1934 showed pipeline obstruction had been caused
by hydrate formations, interests about this
phenomenon increased. Many research studies have
focused on pressure and temperature conditions of
hydrate formation. Hydrate formation preventive
methods are: decreasing the amount of water in
solution; keeping the temperature high; reducing
system pressure; injecting inhibitors. Inhibitors are
materials which make hydrate form at lower
temperatures at a specific pressure. Alcohols,
glycols and salts are examples of inhibitors (29).
According to Makagon(1981) an inhibitor should
have the following conditions (30):
a) An inhibitor should
1- Be able to decrease the temperature of
hydrate formation as much as possible.
2-be completely soluble in water and also
should be easily recycled
4- be available and cheap
And also
1- An inhibitor shouldn’t react with the
components of gas flow and make solid sediment
2- An inhibitor shouldn’t be inflammable or
increase inflammability of gas
3-The viscosity, freezing point and pressure of ice
shouldn’t be lower than it
The
abovementioned
methods
change
thermodynamic equilibrium of hydrate formation
and are called thermodynamic inhibitors, because
by changing combination percentage, temperature
and operational pressure, they make the system
thermodynamically unstable. As far as system ids
unstable, hydrate won’t form. Another method is
using kinetic inhibitors. They let the system remain
in thermodynamically stable conditions, while the
growth of hydrate crystals is prevented.
Leatherhouse et. al (1996), Makagon et.al(1994)
and Kalograkis et.al(1993) studied the effect of
kinetic inhibitors(31-36). As the studies on kinetics
of hydrate formation are not as vast as the studies
on thermodynamic, the application of kinetics in
industry
is
more
limited.
Afchangi
et.al(1997)investigated the existing models of
predicting equilibrium conditions of hydrate
formation. To predict the pressure of hydrate
formation, they used Parrish-Prauznitz model and
the equation SRK (2).Izad Panah et.al (2006)
investigated the kinetics of hydrate formation
through using natural thermodynamic way in
chemical reactions kinetics. They used Mickleson
method to analyze stability. They considered
hydrate phase as a solid solution and using van der
Waals –Platteeuw equation, they found fugacity of
components in hydrate phase. They also suggested
a relationship for super-saturated crystallization of
multiple-component gas hydrate. In addition, they
offered experimental data for kinetic of propane
Conclusion
Hydrate as a problem in gas and petroleum
industry
Fast progress of gas and petroleum industry,
especially in North America, has increased
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hydrate formation in fixed volume and pressure and
investigated hydrate formation (3). Dalvand et. al
(1998) modeled multiple-phased system of hydrate
formation in natural gas pipelines. By making a
change in Parrish-Prauznitz model, they increased
the accuracy and precision of statistic
thermodynamic method for predicting conditions of
hydrate formation and used this model for
predicting the conditions of hydrate formation 3phase and 4-phase equilibriums ( with or without
inhibitors).
They used coefficient ratio for
predicting pressure and temperature (4). Sadeghi
et.al (2009) modeled hydrate formation in systems
containing hydrate structure ameliorator. They
reformed and improved the latest model of
predicting conditions of hydrate formation in the
presence of ameliorators to add to the precision of
predictions. They investigated hydrate formation in
the presence of ameliorators such as Para toluene
sulfonic acid (PTSA), and sodium dodecyl sulfate
(SDS) (5).
[7]
[8]
[9]
Acknowledgment
Special thanks’ to “National Iranian Gas Company”
for supporting this article. Also thanks as Mr. Amir
Samimi (the Head of NHT unit at Isfahan Oil
Refinery Company) who helps us about this article.
[10]
[11]
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effect on environment." Australian journal of
basic and applied science, pp. 752-756, 2011
[4] Samimi, Amir., Zarinabadi, Soroush., Samimi,
Marzieh., "Solar Energy Application on
Environmental
Protection",
International
Journal of science and investigations, France,
2012
[5] Samimi, Marzieh., Samimi, Amir., "NonClimatically Factors
Causing
Weather
Changes", International Journal of science and
investigations, France, pp.35-31, 2012
[6] Samimi, Amir., "Study an Analysis and
Suggest New Mechanism of 3 Layer
Polyethylene Coating Corrosion Cooling Water
Pipeline in Oil Refinery in Iran", International
[12]
[13]
[14]
[15]
[16]
[17]
[18]
94
Journal of Innovation and Applied Studies,
ISSN 2028-9324 Vol. 1 No. 2 Dec. 2012
Samimi, Marzieh., Samimi, Amir., "Explosion
of Resources Management in Iran",
International Journal of Innovation and
Applied Studies, ISSN 2028-9324 Vol. 1 No. 2
Dec. 2012
Samimi, Amir.,
Zarinabadi, Soroush., "
Application Solid Polyurethane as Coating in
Oil and Gas Pipelines," International Congress
of Chemical and Process Engineering , CHISA
2012, and 16 Conference on Process
Integration, Modelling and optimization for
Energy Saving and Pollution,2012
Zarinabadi, Soroush., Samimi, Amir., "
Investigation Results of Properties of Stripe
Coatings in Oil and Gas Pipelines,"
International Congress of Chemical and
Process Engineering , CHISA 2012, and 16
Conference on Process Integration, Modelling
and optimization for Energy Saving and
Pollution, Check, 2012
Rezaei, Rohollah., Samimi, Amir., "Effects of
Phosphorus and Nitrate in Wastewater
Shahinshahr City Use for Oil Refinery",
International Journal of Innovation and
Applied Studies, ISSN 2028-9324, 2012
Samimi, Amir.," Preservation Ways and
Energy Consumption in Oil Refinery",
International Journal of Chemistry; (IJC),
Austria, pp41-47, 2013
Dadashzadeh, Ata, Samimi, Amir, “An
Environmentally Friendly Approach toward the
Treatment of Wastewater", International
Science and Investigation journal ,2014
Samimi, Amir," Micro-Organisms of Cooling
Tower Problems and How to Manage them",
International Journal of Basic and Applied
science, Indonesia, pp.705-715, April 2013
Samimi, Amir,” Evaluation of the Safety
Management System, Environment and Health
in the Oil Industry”, Second National of HSE
Conference in Iran, Mahshahr, Iran, 2012
Metcalf and Eddy, 2008. Wastewater
engineering: treatment, disposal, reuse. Tata
McGraw-Hill, New Delhi
Samimi, Amir, “The Investigation of Factors
Causing Weather Changes," International
Science and Investigation journal ,Malaysia,
Vol.4, 2015,
Anderson J., 2006. The environmental benefits
of water recycling and reuse. Water Science
and Technology.
Metcalf & Eddy, 2007. Water Reuse, Issues,
Technology and Application, McGraw-Hill.