Gas hydrate suspensions formation and transportation research

An experimental unit for studying the formation of gas hydrate suspensions and their transport properties is considered. The scheme of installation and the basic processes, which can be studied, are described. The results of studies of gas hydrates and a gas hydrate suspension’ formation in an adiabatic process in a stream of seawater are given. The adiabatic method of obtaining gas hydrates and forming gas hydrate suspensions is offered to use. Directions for further research are outlined.


Materials and methods
In the Laboratory of Gas Hydrates, the experimental unit UOTG 1416.05 operation (Figure 1). The unit allows studying the processes of gas hydrate suspension and changes in the rheological characteristics of the fluids The unit consists of a refrigerating machine, a reactor type, a circulating hydraulic circuit, a system for measuring and feeding the gas of the hydrating agent, an automation system supporting the set parameters, and a system for recording the measured parameters A schematic diagram of the hydraulic circulation circuit of the unit used is shown in Fig   Figure 2. A schematic diagram of the laboratory scientific research unit UOTG 1416.05 1 Homogenizer, 2 Reactor-generator (evaporator of the refrigerating machine of the flooded type), 3 Circulation pump, 4 Cylinder with hydrate Inspection column, 7 Coil, 8 Pressure gauges, 9 Thermo valve, 12 Safety valve, 13 Watt meter, 14 Thermometer, 15 Feeding tank with saltwater.
In the Laboratory of Gas Hydrates, the experimental unit UOTG 1416.05-01 was created 1). The unit allows studying the processes of formation, dissociation and transportation of gas hydrate suspension and changes in the rheological characteristics of the fluids refrigerating machine, a reactor-generator of a refrigerated machine of a flooded ng hydraulic circuit, a system for measuring and feeding the gas of the hydrating agent, an automation system supporting the set parameters, and a system for recording the measured parameters 01 was created and put into of formation, dissociation and transportation of gas hydrate suspension and changes in the rheological characteristics of the fluids.
generator of a refrigerated machine of a flooded ng hydraulic circuit, a system for measuring and feeding the gas of the hydrating agent, an automation system supporting the set parameters, and a system for recording the measured parameters.
formation and transportation of gas A schematic diagram of the hydraulic circulation circuit of the unit used is shown in Fig. 2 The hydraulic circuit is equipped with circulation pump 3, which allows moving both gas-saturated solutions and gas hydrate suspensions. In reactor-evaporator 2, the gas hydrate phase is formed due to the removal of the heat of hydrate formation by the refrigerating machine. Then the gas hydrate suspension is finally formed in the vessel of homogenizer 1. After that, isolation valve 10 is switched to the pumping mode through coil 7 simulating the field pipeline to investigate the transport properties of the resulting suspensions.
When setting up the installation systems, cyclic tests of the hydraulic circuit and the chiller were carried out. According to the test results, dependencies of the system chilling time on the flow rate in the hydraulic circuit were obtained (Fig. 3). The unit under consideration makes it possible to carry out investigations in the pressure range from 0.1 to 5.0 MPa and temperatures from -10 to 25 °C. The initial plan provides the implementation of two fundamentally different methods for obtaining a gas hydrate suspension.
The first method: obtaining a suspension at the apparent interface between the liquid and gas phases, by gradually chilling the pumped medium and sharply raising the pressure in the pipeline to transfer the entire system to the coordinates of the imaging point of system condition Н О − СО .
The second method: obtaining a suspension from the saturated solution of the hydrating agent by cooling it at a pressure sufficient to transfer the whole system to the coordinates of the imaging point of system condition Н О − СО .
When obtaining a gas hydrate suspension, it is necessary to take into account the possibility of forming large aggregates of crystalline structures on the heat exchange surfaces and bends of pipelines. To prevent the hydrate crystals from adhesion, a homogenizer is provided in the preparation of the suspension by the first method, mechanically destroying the hydrate aggregates. In the second method, adhesion of hydrate crystals is prevented by grinding them in a reactor having a flat scraper that removes growing crystals from a cylindrical heat exchange surface. The experiments carried out showed the possibility of obtaining gas hydrate suspensions under certain system parameters [9,10,11].

Results and Discussion
Using the unit, studies of the gas-hydrate phase СО adiabatic formation' processes in high-mineralized water and in normally mineralized water (tap water) due to changes in pressure and temperature in the
In the first experiment, the mineralized water circulating in the circuit was saturated with carbon dioxide and cooled by a refrigeration machine in a reactor system increased due to the supply of carbon dioxide, resulting in the formation of a gas hydrate in the form of a finely dispersed suspension that could be observed in the inspection windows ( Fig   Figure 4. A suspension based on carbon dioxide gas hydrate obtained in a reactor of a laboratory unit Let us consider the processes occurring on the P P-T diagram, Figure 5), the water was saturated with carbo g СО / 100 g г Н О) (E. Perkins, 2003) and then cooled to a temperature of + 4 temperature reduction ceased despite the fact that the refrigeration unit contin mode with hydrate particles appearing in the sight glass installed in the plant's high It should be noted that the termination of the decrease in the temperature of the the hydration line (Point 2 ') under the operating refrigeration system is explained by the fact that the formation of all gas hydrates, and The formation of hydrate СО at a thermal energy (E.D. Sloan, C. Koh, 2008). Of special note is the fact that hydrate formation ' (Fig. 5) occurs inside the heat exchanger, from which the heat of hydration was refrigeration machine due to the boiling of coolant R22 As a result of gas hydrate phase formation, hydraulic resistance of circulation loop system СО in the annular gap of the reactor dramatically increased. It led to an increase in the electric power consumption on the circulation pump drive and the rotor of the reactor, which was recorded by means of wattmeter having a channel for outputting informat rheological characteristics of a saturated hydrating solution converted to a gas hydrate suspension is expected and described in previous studies (V.D. Lapshin, A.N. Gulkov The second experiment, conducted as part of the adiabatic formation of the gas hydrate phase, was carried out at a pressure of 1 MPa (Process 1 pumped by the circulation pump through the reactor pressure of 1 MPa. system were held. As water of high mineralization, the seawater of the Peter the Great Bay In the first experiment, the mineralized water circulating in the circuit was saturated with carbon dioxide and cooled by a refrigeration machine in a reactor-generator. Then, the pressure in the circulation e supply of carbon dioxide, resulting in the formation of a gas hydrate in the form of a finely dispersed suspension that could be observed in the inspection windows ( Fig   A suspension based on carbon dioxide gas hydrate obtained in a reactor of a laboratory unit Let us consider the processes occurring on the P-T diagrams. At initial Point 2 (P = 2 MPa, t = + 12 T diagram, Figure 5), the water was saturated with carbon dioxide to a state of complete saturation (3.3 ) (E. Perkins, 2003) and then cooled to a temperature of + 4 °C despite the fact that the refrigeration unit continued to operate in th with hydrate particles appearing in the sight glass installed in the plant's high It should be noted that the termination of the decrease in the temperature of the the hydration line (Point 2 ') under the operating refrigeration system is explained by the fact that the formation of all gas hydrates, and СО hydrate in particular, is accompanied by a powerful thermal effect.
at a pressure of 1 MPa is accompanied by the release of 430 thermal energy (E.D. Sloan, C. Koh, 2008). Of special note is the fact that hydrate formation 5) occurs inside the heat exchanger, from which the heat of hydration was refrigeration machine due to the boiling of coolant R22 [8].
As a result of gas hydrate phase formation, hydraulic resistance of circulation loop system in the annular gap of the reactor dramatically increased. It led to an increase in the electric power consumption on the circulation pump drive and the rotor of the reactor, which was recorded by means of wattmeter having a channel for outputting information to the computer. In general, such change in the rheological characteristics of a saturated hydrating solution converted to a gas hydrate suspension is expected and described in previous studies (V.D. Lapshin, A.N. Gulkov et al, 2015) ment, conducted as part of the adiabatic formation of the gas hydrate phase, was carried out at a pressure of 1 MPa (Process 1-6, Fig. 5). The water saturated with carbon dioxide was pumped by the circulation pump through the reactor-evaporator, as was men ater of the Peter the Great Bay and the Sea of In the first experiment, the mineralized water circulating in the circuit was saturated with carbon generator. Then, the pressure in the circulation e supply of carbon dioxide, resulting in the formation of a gas hydrate in the form of a finely dispersed suspension that could be observed in the inspection windows (Fig. 4).
A suspension based on carbon dioxide gas hydrate obtained in a reactor of a laboratory unit initial Point 2 (P = 2 MPa, t = + 12 , n dioxide to a state of complete saturation (3.3 °C (Point 2 '). At Point 2, ued to operate in the same with hydrate particles appearing in the sight glass installed in the plant's high-pressure circuit. It should be noted that the termination of the decrease in the temperature of the Н О − СО system on the hydration line (Point 2 ') under the operating refrigeration system is explained by the fact that the hydrate in particular, is accompanied by a powerful thermal effect. pressure of 1 MPa is accompanied by the release of 430-450 kJ / kg of thermal energy (E.D. Sloan, C. Koh, 2008). Of special note is the fact that hydrate formation at Point 2 5) occurs inside the heat exchanger, from which the heat of hydration was removed by the As a result of gas hydrate phase formation, hydraulic resistance of circulation loop system Н О − in the annular gap of the reactor dramatically increased. It led to an increase in the electric power consumption on the circulation pump drive and the rotor of the reactor, which was recorded by means of ion to the computer. In general, such change in the rheological characteristics of a saturated hydrating solution converted to a gas hydrate suspension is t al, 2015). ment, conducted as part of the adiabatic formation of the gas hydrate phase, was 5). The water saturated with carbon dioxide was evaporator, as was mentioned above, under a 5

Figure 5. Processes in the laboratory unit shown in the Stackelberg
Thus, through the operation of the refrigeration machine, the temperature of the homogeneous system Н О − СО was reduced from 12 previously described case, when a suspension with a continuously increasing fraction of the dispersed phase was formed in the circulation loop After reaching a temperature of 2 in the hydraulic circuit increased sharply to 2 MPa (Point 2 the gas hydrate phase in the entire circuit simultaneously (Fig   Figure 6. Formation of the gas hydrate phase simultaneously in the entire hydraulic circuit Further, the experiments were carried out on isobars 3, content of the gas hydrate phase in the circulating hydraulic circuit with the increase this case, each time the imaging point of system state Points 3 ', 4', 5 '). It is characteristic that an increase in the content of the gas hydrate phase was observed with increasing pressure only up to a value corresponding to the coordinates of quadrupole point should be noted that above quadrupole point Q_2, carbon dioxide passes from the vapor state to the liquid Processes in the laboratory unit shown in the Stackelberg-Rosenbom diagram Thus, through the operation of the refrigeration machine, the temperature of the homogeneous system was reduced from 12 °C to 2 °C, with significantly less energy consumption than in the previously described case, when a suspension with a continuously increasing fraction of the dispersed phase was formed in the circulation loop. rature of 2 °C, the pressure of circulating water, saturated with carbon dioxide, eased sharply to 2 MPa (Point 2'', Fig. 5), which led to the instant formation of the gas hydrate phase in the entire circuit simultaneously (Fig. 6).
Formation of the gas hydrate phase simultaneously in the entire hydraulic circuit Further, the experiments were carried out on isobars 3, 4 and 5 MPa, which led to an increase in the content of the gas hydrate phase in the circulating hydraulic circuit with the increase this case, each time the imaging point of system state Н О − СО returned to the equilibrium line (at oints 3 ', 4', 5 '). It is characteristic that an increase in the content of the gas hydrate phase was observed with increasing pressure only up to a value corresponding to the coordinates of quadrupole point should be noted that above quadrupole point Q_2, carbon dioxide passes from the vapor state to the liquid

Rosenbom diagram
Thus, through the operation of the refrigeration machine, the temperature of the homogeneous system , with significantly less energy consumption than in the previously described case, when a suspension with a continuously increasing fraction of the dispersed , the pressure of circulating water, saturated with carbon dioxide, 5), which led to the instant formation of Formation of the gas hydrate phase simultaneously in the entire hydraulic circuit 4 and 5 MPa, which led to an increase in the content of the gas hydrate phase in the circulating hydraulic circuit with the increase of pressure in it. In returned to the equilibrium line (at oints 3 ', 4', 5 '). It is characteristic that an increase in the content of the gas hydrate phase was observed with increasing pressure only up to a value corresponding to the coordinates of quadrupole point . It should be noted that above quadrupole point Q_2, carbon dioxide passes from the vapor state to the liquid

4.Conclusions
The conducted experiments testify to the operability of the unit offered.
The possibility of realizing two fundamentally different methods of gas hydrate suspensions' formation has been confirmed.
Studies confirm the validity of the assumption that there is no need for mechanical destruction of large hydrate crystals to prevent the formation of hydrate plugs in pipelines at certain phase and environment ratios in the dispersed system.
The validity of the assumptions about the transport properties of gas hydrate suspensions has been experimentally demonstrated.
Further studies will be focused on studying the influence of various factors on the stable gas hydrate suspensions' formation and their transport properties.