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The Investigation of the Methods of Preventing the Formation of Gas Hydrate Seyed Ali Khoddami1, 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 GMP Review, 2015; V17(1) 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 87 GMP Review, 2015; V17(1) Seyed Ali Khoddami et al 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 88 GMP Review, 2015; V17(1) Seyed Ali Khoddami et al 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. 89 GMP Review, 2015; V17(1) Seyed Ali Khoddami et al 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 90 GMP Review, 2015; V17(1) Seyed Ali Khoddami et al 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 91 GMP Review, 2015; V17(1) Seyed Ali Khoddami et al 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 92 GMP Review, 2015; V17(1) Seyed Ali Khoddami et al 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 93 GMP Review, 2015; V17(1) Seyed Ali Khoddami et al 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] References [1] Zarinabadi, Soroush, Samimi, Amir, "Scrutiny Water Penetration in Three-layer Polyethylene Coverage," Journal of American science, U.S.A., 2011 [2] Hedayati, Abbas., Almasinia, Babak., Samimi, Amir, "Optimize pictures of industrial radiography in corrosion and sediment recognizing in oil or gas transmit pipe lines" , International Journal of Chemistry; (IJC), pp.20-29, Issue: 05, 2014 [3] Samimi, Amir, Zarinabadi, Soroush. 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