RU2457010C1 - Method of obtaining gas hydrates - Google Patents

Abstract

FIELD: chemistry.

SUBSTANCE: invention relates to a method of producing gas hydrates, for example, methane, propane and carbon dioxide hydrates, for storage and transportation of gas in gas hydrate state. Synthesis of the hydrate takes place in conditions of a metastable state of the substance with crystallisation of two-component amorphous condensates. The condensates are obtained via vacuum deposition of molecular beams of water and gas on the deposited surface at temperature lower than the glass transition point of the mixture.

EFFECT: possibility of obtaining gas hydrates in thermobaric conditions which enable to do without use of high pressure equipment and compression of the water-gas medium, possibility of controlling gas content in the obtained hydrate and control phase state of the obtained product during synthesis thereof.

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Description

The invention relates to a method for producing methane hydrate or another gas hydrate for the purpose of storing and transporting gas in a gas hydrate state. Storage and transportation of natural gas in the form of hydrates is currently considered as an alternative gasification technology. It is estimated that for the development of small and medium-sized gas fields, hydrated technology for storing and transporting natural gas is economically more profitable and technically safer than liquefied and compressed gas technologies. About 80% of the world's natural gas reserves are located in such fields. In a number of Western countries, pilot plants for the production of natural gas hydrates are being developed and put into operation. Active research is being carried out on the possibility of using gas hydrate technology in connection with the development of hydrogen energy. The proposed method for producing gas hydrates contains a number of obvious technological advantages (primarily in terms of energy costs) over known methods for producing a hydrated state.

FIELD OF TECHNOLOGY

In currently known methods for producing gas hydrates, relatively small deviations from the conditions of equilibrium gas dissolution are realized. They are associated with the use of high pressures in laboratory or process equipment. For example, the pressure corresponding to the conditions for the formation of methane hydrate at temperatures close to 0 ° C is tens of bars. The formation of crystalline hydrate requires dispersion of water, which is achieved by prolonged and intensive mixing of the water-gas mixture. Such conditions are used in most known and patented methods for producing gas hydrates for the purpose of their storage and transportation.

A known method of producing gas hydrates, for example methane hydrate (patent RU No. 2270053 C2, 11.11.2003, IPC B01F 3/04), according to which the formation of hydrate occurs in the reactor under compression and cooling of the gas-liquid mixture below the equilibrium temperature of hydrate formation when acting on the mixture shock waves with increasing pressure and with the occurrence of crushing of the gas phase, which provides an increase in the interfacial surface, an increase in the number of centers of nucleation of gas hydrate and, as a result, leads to the intensification of cession hydrate. However, the practical implementation of the method is associated with high energy costs and structural complexity of the necessary technological equipment.

A known method (patent RU 2293907 C2, 08/24/2004, IPC F17C 11/00) converting natural gas and other hydrate-forming gases into a hydrated state for the purpose of storage. When storing natural gas in containers, an aqueous solution of surfactants is used as an aqueous hydrate-forming medium. The solution is maintained at a pressure of 20-30% above the equilibrium value corresponding to the formation of hydrate at a given temperature. Using the method is expected to increase the mass of stored gas per unit volume of the storage tank and simplify the storage method. However, the low rate of hydrate formation under such conditions does not provide the necessary efficiency of using the method in practice.

As a prototype for the present invention, a method for producing methane gas gas or other gas can be used (patent GB 2347938 A, 09/20/2000, IPC C07C 7/152), in which the gas interacts with water in a reactor under thermobaric conditions corresponding to hydrate formation. The flow of water into the reactor, filled with gas, occurs through the nozzles in atomized form. To intensify hydrate formation, an ultrasonic emitter is used, which should destroy the hydration shells on the surface of large drops of water. However, the impossibility of obtaining sufficiently large pressure amplitudes due to the large compressibility of the gas-liquid medium and strong attenuation of radiation with increasing distance from the emitter does not allow to provide the necessary increase in the interphase surface and the number of centers of gas hydrate nucleation, and, as a consequence, the high efficiency of the process.

When studying methods for producing gas hydrates, no hydrate synthesis options were found from the amorphous solid (glassy) phase of the water-gas mixture without using high pressures. Methods for producing amorphous and crystalline thin films by condensation of molecular beams in vacuum are known and are used in industrial and research practice. (See. Technology of thin films. Handbook. Edited by L. Meissel, R. Glanga. Part 1. - M .: Soviet radio, 1977, 664 p.).

SUMMARY OF THE INVENTION

The objective of the present invention is to develop a method for producing gas hydrates without the use of high pressure (hydrostatic or in shock wave compression), requiring complex technical solutions in the development and manufacture of technological equipment.

The problem is solved in that in the proposed method, gas hydrate is synthesized according to the invention under conditions far from thermodynamic equilibrium, i.e. under conditions corresponding to the metastable state of a two-component water-gas mixture. The low-temperature condensation of rarefied molecular beams in vacuum is used on a surface cooled by liquid nitrogen. In this case, amorphous (glassy) layers of the water-gas mixture are initially formed, which are stabilized by high viscosity. They are characterized by the absence of the structural order inherent in crystals. When amorphous layers are heated, a transition occurs from a glassy to a viscous fluid liquid state and subsequent avalanche-like nucleation and growth of crystallization centers of gas hydrates. The avalanche-like nature of crystallization is due to the state of deep metastability of the condensate — the distant deviation of the two-component liquid mixture from the state of thermodynamic equilibrium. This method requires neither high pressure nor mixing of the mixture. Its advantage is also the versatility for producing hydrates of various gases.

Distinctive features of the claimed invention allow:

- to obtain gas hydrates in thermobaric conditions, allowing dispensing with the use of high pressure techniques and compressing the water-gas medium;

- control the gas content in the resulting hydrate;

- control the phase state of the obtained product during its synthesis.

Analysis of the known technical solutions allows us to conclude that the claimed invention is not known from the level of the investigated technology, which indicates its compliance with the patentability criterion of "novelty." The analysis of patent and scientific and technical information did not reveal the use of a combination of essential features characterizing the claimed solution in known objects according to their functional purpose for solving the task. Therefore, the present invention meets the patentability criterion of "inventive step". The possibility of implementing the claimed invention in the laboratory and industrial conditions of domestic enterprises for the production of gas hydrates, indicates its compliance with the patentability criterion of "industrial applicability".

EXAMPLES OF SPECIFIC IMPLEMENTATION

The inventive method for producing gas hydrates by the example of methane, propane and carbon dioxide hydrates was implemented in laboratory conditions of the Institution of the Russian Academy of Sciences of the Institute of Thermophysics, Ural Branch of the Russian Academy of Sciences (Yekaterinburg) using equipment and devices manufactured by domestic enterprises or purchased from foreign manufacturers.

BRIEF DESCRIPTION OF THE DRAWINGS

Figure 1. Diagram of a method for producing gas hydrate in a vacuum cryostat. 1 - a vacuum chamber, 2 - a copper substrate, 3 - a window, 4 - a mask, 5 - a screen, 6 - liquid nitrogen, 7 - a capacitive sensor, 8 - water-gas condensate, 9 - steam line.

Figure 2. Temperature dependence of the dielectric loss tangent of an amorphous condensate of a water-methane mixture (curve l). The dashed section (l ') of the temperature dependence (l) corresponds to repeated cooling and subsequent heating of the sample after crystallization. Curve 2 is the temperature dependence of tanδ for pure water.

A description of the method for producing gas hydrate is as follows. An amorphous condensate of the water-gas mixture is formed in the vacuum chamber (1) of the cryostat (Figure 1) by the deposition of molecular beams on the surface of a copper substrate cooled by liquid nitrogen (2). Obtaining an amorphous state is ensured by a high cooling rate, which reaches 10 ² -10 ⁷ K / s under such conditions. A vacuum of no worse than 10 ^-4 -10 ^-5 mm Hg is maintained in the cryostat chamber. To precipitate condensates of water-methane and water-propane mixtures, it is necessary to lower the temperature to ~ 65 K. This is achieved by pumping nitrogen vapor from the cryostat. During the deposition of amorphous condensates of the water-carbon dioxide mixture on the substrate, a temperature of 70 K. was maintained. Molecular component beams enter the spray zone via separate steam pipelines (9). The mask (4) allows you to precipitate condensate, a given area. Precipitation at fixed flow rates of water and gas allows to obtain condensates of constant composition. The temperature on the surface of the substrate is controlled by a copper-constantan thermocouple with an accuracy of no worse than 0.5 K. To monitor the condensate, a capacitive sensor (7) is used, which is placed on the substrate and is a film capacitor made by photolithography. The capacitor plates are thin copper strips (0.1 mm wide, 1-3 microns high) deposited on a dielectric plate with a surface of 20 × 20 mm and a thickness of 0.5 mm. By changing the dielectric properties with a change in temperature, one can follow the transformations in the condensate.

The heating of the obtained condensates is accompanied by their softening, i.e. the transition from a solid amorphous (glassy) state to a liquid viscous fluid, and subsequent spontaneous crystallization. Figure 2 shows the change in the dielectric loss tangent (tanδ) when heating an amorphous condensate of a water-methane mixture at a rate of 0.05 K / s. For comparison, the figure shows the temperature dependence of tanδ of water condensate. At a temperature T _g = 115 K, a noticeable increase in tanδ is observed, which is associated with structural relaxation in the softening (glass transition) region of the two-component condensate. The temperature T _g at which there is a sharp change in the properties of the substance (dielectric constant, dielectric loss tangent, heat capacity, etc.) upon softening is called the glass transition temperature of the substance. A sharp drop in the sensor readings at a temperature T _c = 150 K is due to crystallization of the deposited sample. The increase in tanδ following crystallization is characteristic of the crystalline state. The accuracy of determining the glass transition temperatures T _g and crystallization T _s is ± 1 K. The presence of methane in the sample leads to a decrease in the glass transition temperature by -20 K, crystallization temperature by -10 K compared to their values for pure water. The glass transition temperatures T _g and crystallization of 7 s for condensates of the water-propane mixture slightly differ from their values found for pure water at a heating rate of 0.05 K / s and are 137 K and 167 K, respectively. For condensates of the water-carbon dioxide mixture, the temperatures Glass transition and crystallization are 135 K and 166 K, respectively. Crystallization of amorphous condensates under conditions far from thermodynamic equilibrium leads to the formation of gas hydrate. The avalanche-like nucleation of crystallization centers freezes gas molecules and does not lead to their displacement by the crystallization front. The concentration of methane in the crystallized condensate reaches 15 mass percent. This corresponds to the complete filling of the cavities of the resulting clathrate framework with gas molecules. A single volume of the obtained gas hydrate contains 160-180 volumes of methane gas. The concentration of propane in the crystallized condensates of the water-propane mixture was 10-13 mass percent. This means that a single volume of gas hydrate contains 50-70 volumes of gaseous propane. The concentration of carbon dioxide in the condensates was 20-22 weight percent. This corresponds to a content of 150-170 volumes of gaseous carbon dioxide in a unit volume of gas hydrate.

An industrial version of a plant for the production of gas hydrate can be implemented with an increase in the volume of the vacuum chamber, the amount of incoming water-gas mixture and an increase in the cooled surface on which condensate is deposited and subsequent hydrate synthesis. Further, after removing it from the plant and granulating it is possible to obtain a product suitable for storage and transportation.

INFORMATION SOURCES

1. B.C. Yakushev, V.G. Kwon, S.I. Dolgaev, S.E. Podenok, V.A. Istomin. Hydration technologies for gasification of Russian regions. Gas industry. 2009. Special issue, No. 640, pp. 75-79.

2. Technology of thin films. Directory. Ed. L. Meissel, R. Glanga. Part 1. - M .: Soviet Radio, 1977, 664 p.

3. Patent RU No. 2270053 C2, 11.11.2003.

4. Patent RU 2293907 C2, 08.24.2004.

5. Patent GB 2347938 A, 09/20/2000.

6. Patent RU 2045718 C1, 05.29.1992.

7. Patent RU 2200727 C2, 02.07.1997.

Claims (1)

A method of producing gas hydrates for their storage and transportation, characterized in that the hydrate synthesis occurs under the conditions of a metastable state of the substance during crystallization of two-component amorphous condensates obtained by vacuum deposition of molecular beams of water and gas on a cooled surface at a temperature below the glass transition temperature of the mixture.

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