RU2718795C2 - Method of producing gas hydrates by condensation of nanoclusters - Google Patents

Abstract

FIELD: oil and gas industry.

SUBSTANCE: invention relates to production of gas hydrates for storage and transportation of gas in power engineering and gas industry. Hydrate formation is carried out in oncoming molecular beams of rarefied steam and gas, which enter the vacuum chamber through de Laval nozzles with reduction of temperature at nozzle outlet below 100 K and condensation to form crystalline ice nanoclusters of cubic diamond-like structure. Formation of clusters is accompanied by capture of gas molecules and formation of crystal hydrate phase. Content of gas in the crystallized condensate obtained at maximum achieved efficiency of the capture of gas molecules exceeds 50 wt %. Such content is achieved due to additional gas sorption during formation of crystalline condensate, which is a gas-saturated nanoporous medium containing a crystalline hydrate phase and crystalline ice.

EFFECT: method increases rate of formation of gas hydrate, reduces consumption of coolant required for cooling of substrate, increases productivity of producing gas hydrates.

1 cl, 1 dwg

Description

The invention relates to the production of gas hydrates with the aim of applying hydrated technologies for storing and transporting gas in the energy and gas industries. Storage and transportation of natural gas in the form of hydrates is currently being considered as an alternative to storage and transport technologies for liquefied and compressed gas. According to available estimates, for the development of small and medium-sized gas fields, hydrated technology for storing and transporting natural gas is economically more profitable and safe. About 70% of the world's natural gas reserves are located in such fields. In this regard, the development of cost-effective methods for producing gas hydrates and the intensification of the hydration process are relevant.

FIELD OF TECHNOLOGY

Currently known methods for producing gas hydrates are associated with the use of high pressures in the range from 30 to 250 bar in laboratory and technological equipment at temperatures below the equilibrium temperature of hydrate formation. 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 hydrates in this case requires a long and intensive mixing of the water-gas mixture. Such conditions are used in most known and patented methods for producing gas hydrates. To intensify the hydrate formation process, various methods are proposed, among which are finely dispersed spraying of a water-gas mixture in a gas atmosphere, impact by shock waves on an aqueous medium saturated with gas, vibration and ultrasound exposure. 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 projects of converting greenhouse gases (mainly carbon dioxide) to a gas hydrate state and their disposal on the bottom of the oceans are discussed.

The proposed method of producing gas hydrates ensures the continuity of the process and contains a number of obvious technological advantages (primarily in terms of productivity and energy costs) over known methods.

Currently, a number of methods for producing gas hydrates are known.

A known method of producing gas hydrates in gas hydrate desalination and purification of sea and mineralized water (patent RU 2405740 C2, 02.24.2009, IPC C02F 1/00, B01F 3/04), according to which hydrate formation occurs in the reactor under gas-liquid compression and cooling the mixture is below the equilibrium temperature of hydrate formation when shock waves act on the mixture with increasing pressure and with the occurrence of crushing of drops of liquefied gas and gas hydrate shells on the surface of liquid drops. However, the practical implementation of the method is associated with high energy costs and structural complexity of the technological equipment.

A known method of producing methane hydrate or other gas (patent GB 2347938 A, 09/20/2000, IPC C07C 7/152), in which the interaction of gas with water occurs in a reactor under thermobaric conditions corresponding to the formation of a hydrate. 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.

The 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 lead to an increase in the mass of stored gas per unit volume of the storage tank and simplification of 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.

A known method of producing gas hydrates, for example, methane hydrate (Pat. RU No. 2270053 C2, 2006), according to which the formation of the hydrate occurs in the reactor under compression and cooling of the gas-liquid mixture below the equilibrium temperature of hydrate formation when the mixture is subjected to shock waves with increasing pressure and 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 an intensification of the hydrate process azovaniya. However, the practical implementation of the method is associated with high energy costs and structural complexity of the technological equipment.

A known method of producing gas hydrates, for example, Freon-134-a in a cyclic process of boiling-condensation in a closed volume of water (International Journal of Heat and Mass Transfer. 2017. V. 108. P. 1320-1323.). The essence of the method is as follows. The volume of the high-pressure chamber is half filled with water. Water is cooled to a temperature of 2-5 ° C. Then, gaseous Freon-134-a is fed into the chamber, which condenses at a given temperature and forms a liquid layer at the bottom of the chamber. When heating the lower part of the chamber, freon boils. Rising up a column of liquid water, freon bubbles fall into the region of lower temperature, where a hydration film grows on their surface. On the surface of the water, the bubbles are destroyed, leaving flakes of gas hydrate. Gaseous freon, which has not been converted to gas hydrate, condenses on the walls of the chamber and flows to the bottom, mixing with a fluidized bed of liquid freon. The process is cyclic and continues until all the gas passes into the hydrated phase. However, the application of this method is limited to gases having a density in the condensed state higher than the density of water.

The closest technical solution to the claimed invention should be considered a method of producing gas hydrates (RF Patent 2568731, 2014, C1), in which hydrate formation occurs in gas-saturated layers of amorphous ice obtained by low-temperature vacuum condensation of supersonic molecular beams of rarefied steam and gas onto a cooled substrate . Crystallization of amorphous condensates under conditions of strong metastability 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. However, the low productivity of the method limits its use on an industrial scale.

SUMMARY OF THE INVENTION

The present invention is devoid of the above drawback associated with the need to remove the heat of condensation, and allows us to solve the problem of not only significantly increasing the rate of formation of gas hydrate, but also significantly lowering the flow rate of the refrigerant needed to cool the substrate.

The problem is solved in that the opposing molecular beams of rarefied steam and a hydrate forming gas, for example, methane, enter the vacuum chamber through Laval nozzles, which allow them to be accelerated to supersonic speeds. The adiabatic expansion of supersonic molecular flows leads to a drop in temperature at the nozzle exit below 100 K and the formation of crystalline ice nanoclusters of a cubic diamond-like structure. The formation of ice clusters is accompanied by the capture of gas molecules and the formation of a crystalline hydrate phase.

When studying the methods for producing gas hydrates, no hydrate synthesis options were found in the interaction of counter supersonic steam and gas flows with the condensation of nanoclusters of the crystalline hydrate phase.

The invention solves the problem of increasing the speed and cost-effectiveness of producing gas hydrates without the use of high-pressure technology, requiring significant energy costs for its generation and complex technical solutions in the development and manufacture of technological equipment.

EXAMPLES OF SPECIFIC IMPLEMENTATION

The inventive method for producing gas hydrates is implemented for methane, ethane, propane and carbon dioxide in the laboratory conditions of the Federal State Budgetary Institution of Science, 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 FIGURE

Fig. 1. Scheme of a method for producing gas hydrate in a vacuum cryostat. Installation for producing gas hydrates during condensation from supersonic molecular steam and gas flows. 1 - vacuum chamber, 2 - Dewar vessel, 3 - liquid nitrogen, 4 - Laval nozzles, 5 - steam pipe, 6 - gas inlet.

The description of the method for producing gas hydrate using methane hydrate as an example is as follows. The formation of gas hydrate occurred in a chamber with a capacity of 300 cm ³ with preliminary pumping of air to a pressure of no worse than 10 ^-3 mm RT. The walls of the chamber are cooled with liquid nitrogen. The experimental setup is shown in Fig. 1. Molecular beams of rarefied steam and methane simultaneously enter the chamber through Laval nozzles, which accelerate them to supersonic speeds. The opposite direction of the vapor and gas beams ensures their overlap at the exit of the nozzles. It is known that the adiabatic expansion of the molecular flow of rarefied steam at the exit of a supersonic nozzle leads to a decrease in temperature and the formation of crystalline nanoclusters of a cubic diamond-like structure. The cluster size depends on the pressure at the inlet to the nozzle. The higher the pressure, the larger the cluster size and, consequently, the fraction of the crystalline phase in the flow. The formation of ice clusters is accompanied by the capture of gas molecules and the formation of a crystalline hydrate phase. The water tank and gas bottle are placed outside the chamber at room temperature. By changing the flow of steam and gas through the nozzles, the rate of the condensation process and the productivity of the hydrate production process are regulated. Cooling the walls of the chamber with liquid nitrogen allows you to save crystalline condensate for an unlimited time. When heated, its conservation was observed up to the melting temperature of the sample. Self-preservation ensured the stability of methane hydrate in a metastable state at temperatures above its equilibrium dissociation temperature of ~ 192 K. About 273 K, melting and decomposition were observed, which was accompanied by intense gas evolution.

The methane content in the crystallized water-gas product obtained at the maximum achieved performance of the condensation process exceeded 50 mass. % This means that the volume of gaseous methane released during melting was 1000 times the volume of water. This content was achieved due to additional gas sorption during the formation of crystalline condensate, which was a gas-saturated nanoporous medium containing a crystalline hydrate phase and crystalline ice. The gas content in the obtained samples significantly exceeded the theoretical value corresponding to the maximum filling of the cavities of the formed clathrate framework with methane molecules, at which its concentration does not exceed 15 weight percent.

For research purposes, the advantage of the proposed method lies in the possibility of changing the concentration of components in the range from 0 to 100 mass. % to study the structure and properties of water-gas condensates.

The proposed method is suitable for producing a hydrate of any gas. An industrial version of the installation for the production of gas hydrates can be implemented with an increase in the volume of the chamber and the consumption of steam and gas due to the cassette organization of steam pipelines. The results of the experiments are of interest in connection with the development of economical and safe technologies for the storage and transport of gases. In the future, the method can be used to obtain hydrogen hydrate to solve the problem of its storage and transport in connection with the development of hydrogen energy.

INFORMATION SOURCES

1. Pat.RU 2405740 C2, 02.24.2009, IPC C02F 1/00, B01F 3/04.

2. Pat. GB 2347938 A, 09/20/2000, IPC C07C 7/152.

3. Pat.RU 2293907 C2, 08.24.2004, IPC F17C 11/00.

4. Pat.RU No. 2270053 C2, 2006.

5. RF patent 2568731, 2014, C1.

Int. J. Heat Mass Transfer. 2017. V. 108. P. 1320-1323.6. AA Chernov, DS Elistratov, IV Mezentsev, AV Meleshkin, AA

Int. J. Heat Mass Transfer. 2017. V. 108. P. 1320-1323.

Claims (1)

A method of producing gas hydrates, for example methane hydrate, for their storage and transportation, during the condensation of nanoclusters in supersonic molecular beams of rarefied steam and gas, characterized in that the molecular beams enter the vacuum chamber into the spray zone through Laval nozzles towards each other and have an output temperature from the nozzles is below 100 K, which ensures the formation of a cubic diamond-like structure in the expanding vapor stream of ice nanoclusters with the capture of gas molecules and the formation of crystalline hydrate th phase.

Images