JP2005082686A - Method for producing gas hydrate - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To form a gas hydrate at a lower cost compared to the conventional one in high efficiency by using a high-pressure natural gas extracted from an existing high-pressure transmission pipeline as a feedstock gas, and effectively utilizing the cold possessed by natural ice and snow. <P>SOLUTION: The method for producing the gas hydrate which is a hydrate of a natural gas involves reacting the natural gas and the formed water introduced to a pressure-resistant vessel under a prescribed pressure at a prescribed temperature. Concretely, the method for producing the gas hydrate comprises introducing the high-pressure natural gas (a) extracted from the existing high-pressure transmission pipeline 1, and the formed water (b) extracted from a formed water-feeding line 6 into the interior of the pressure-resistant vessel 8 to form the gas hydrate (c) which is the hydrate of both, on the other hand, storing the natural ice and snow (f), stream of a mountain stream and a flume, spring water (g) of a mountain tunnel, or the like in a reservoir 12 built in the mountain, and removing the heat of formation caused at the formation of the gas hydrate (c) by utilizing the cold possessed by the natural cold water (d) stored in the reservoir 12. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to a method for producing a gas hydrate that produces a gas hydrate that is a hydrate of natural gas and water mainly composed of methane, and more specifically, high-pressure natural gas extracted from an existing high-pressure transport gas pipeline. The present invention relates to a method for producing gas hydrate that can produce gas hydrate as a raw material with high efficiency and at low cost.

  Gas hydrate, which is a hydrate of natural gas and water mainly composed of methane, is a hydrate containing 170 times the gas (in the case of methane) per unit volume, and minus 20 ° C under atmospheric pressure. It is known that the decomposition is suppressed by the self-preserving effect to some extent, and its use as a gas transport means is being studied using this characteristic.

That is, the theoretical composition of methane hydrate having the I-type structure is CH ₄ · 5.75H ₂ O from the number of water molecules (46) and methane molecules (8) contained in the unit cell. . The number ratio of methane molecule to water molecule of 5.75 is called hydration number, and about 220 milliliters of methane (standard state conversion) is included in 1 gram of water for calculation. Further, since the specific gravity of methane hydrate is 0.92, about 170 times as much methane is confined per unit volume of hydrate.

  As a method for producing methane hydrate, a method in which natural gas having a pressure equal to or higher than the phase equilibrium is brought into contact with water or ice is generally used. For example, in a laboratory, 70 ml of deionized water is put into a pressure vessel with an electromagnetic stirrer having an internal volume of about 200 ml, and left to stand at a high-purity methane initial pressure of 50 atm and a starting temperature of 0.2 degrees. Stirring was performed at 500 rpm. Although no change is observed in the reaction system for a while after the start of stirring, the pressure starts to drop suddenly at a certain point. This indicates that methane and water have become gas hydrates. At the same time, an increase in the temperature of the system is observed. This can be interpreted as a latent heat of solidification similar to that seen during ice formation because water molecules crystallize.

  In addition, the apparent period from the start of stirring to the start of the reaction is called the induction time (Induction Time), which is the nucleus that continues to hydrate crystallization through physical absorption of methane gas into water. It seems to have created the local supersaturation necessary for the formation of. In general, the induction time is longer as the temperature is higher or the pressure is lower. For example, when the pressure is 50 atm, the induction time is within one minute at 0 degrees Celsius, whereas at 6 degrees Celsius, Requires more than 5 hours.

  On the other hand, if the generated gas hydrate is once decomposed and then gas hydrate is generated again, the induction time is shortened. This is called the memory effect and is thought to be due to the remaining water molecule clusters with a structure suitable for nucleus formation. As described above, the gas hydrate formation reaction is a phase transition that occurs in response to the incorporation of gas molecules into water molecules and the subsequent supersaturated environment, which is a crystallization process. These induction times, nucleation, crystallographic and other hydrate reaction mechanisms, and kinetic analysis have no established theory, and are hot research topics that are currently being adopted by researchers around the world.

  By the way, from the previous research on the basic physical properties of gas hydrate including methane hydrate, gas hydrate has the following interesting properties that can be applied to industrial technology. Has become clear.

That is,
(A) High gas occlusion (b) Large heat of formation / dissociation (c) High pressure responsiveness to temperature change (d) High reaction selectivity.

  These characteristics can be applied as a high-density gas storage medium, a latent heat storage medium that functions below freezing point, a high-sensitivity power operating medium, a separation medium, etc., and methane hydrate was used from a viewpoint different from resources. Expected to be used for industrial technology.

  As an example of applying the high gas storability of methane hydrate, a natural gas transport and storage system is considered to replace conventional liquefied natural gas. The density of methane gas in methane hydrate is about one-third that of liquefied natural gas, but it is not necessary to cool to the liquefaction temperature (below minus 160 degrees) where the refrigeration effect is low in production, improving energy efficiency. Is done.

Although pressure is required to stabilize methane hydrate, a convenient phenomenon called a self-preserving effect has been observed for transportation and storage. When dispersed in ice, the ice acts as a pressure vessel, and decomposition of methane hydrate is suppressed even at atmospheric pressure (see, for example, Non-Patent Document 1).
“Energy Review”, ERC Publishing Co., Ltd., 1999-11, p. 14-17

  As described above, as a method for producing methane hydrate, a method in which natural gas having a pressure equal to or higher than the phase equilibrium is brought into contact with water or ice is generally used.

  However, in order to increase the pressure of natural gas mainly composed of methane to a pressure higher than the phase equilibrium, for example, not only a gas compressor such as a motor-driven compression turbine is required, but also contact with natural gas and water or ice. Thus, since a refrigerator that removes the heat generated when gas hydrate is generated is necessary, the power consumption for operating these becomes enormous.

For example, when producing a gas hydrate of 70 t / h, a feed gas (natural gas) with a supply amount of 10,000 Nm ³ / h is increased from 0.1 MPa to 5 MPa using a 2.5 MW turbine-type gas compressor. On the other hand, assuming that 0 ° C. cold water is produced by a 3 MW refrigerator (2500 USRT, COP = 3), when the gas compressor and the refrigerator are operated almost continuously yearly, the annual power consumption is 44,000 MWh. The electricity bill will be 500-600 million yen per year. Further, when the amount of CO ₂ produced oil-fired thermal power plant and 0.7kgCO ₂ / kW, in this case, the amount of CO ₂ produced per year is approximately 30,000 tons.

When producing a gas hydrate of 70 t / h, a 5 MW raw material gas (natural gas) is introduced from an existing high-pressure gas line at a supply rate of 10,000 Nm ³ / h, while a 3 MW refrigerator (2500 USRT, COP = 3) Assuming that 0 ° C. cold water is produced when operating gas compressors and refrigerators almost continuously in a year, the annual power consumption is 24,000 MWh, and the electricity bill is 300 to 400 million yen per year. It becomes. Further, when the amount of CO ₂ produced oil-fired thermal power plant and 0.7kgCO ₂ / kW, in the conventional example 1, the amount of CO ₂ produced per year is 20,000 tons.

  However, the existing high-pressure pipeline for gas transportation is constantly pressurized to about 7 MPa, and by using this high-pressure gas pressure to produce gas hydrate, the energy required for gas pressure can be greatly limited. It becomes. As a result, it can be expected to contribute to the prevention of global warming.

  In addition, medium- and high-pressure gas pipelines that supply high-pressure natural gas to medium- and small-scale gas customers around the high-pressure pipeline, that is, small-scale city gas operators and distributed power supply customers, are newly introduced from the existing high-pressure gas line. When laying a gas pipeline, there are many geographical and economic obstacles, and the spread is generally delayed.

  Therefore, if gas hydrate can be manufactured around the existing high-pressure pipeline for gas transportation, small gas transportation to small city gas utilities and distributed power supply customers using the gas storability of gas hydrate is possible. be able to.

  Further, when the periphery of the long-distance high-pressure pipeline for gas transportation is a highland or a cold region, it is extremely convenient to remove the generated heat while maintaining the reaction temperature of the gas hydrate. In other words, in highlands and cold regions, cold water of about 0 ° C. can be obtained relatively easily from natural ice and snow.

  Therefore, natural cold water can be used as it is as the energy for removing the heat generated by the gas hydrate, so that further energy saving can be achieved.

  The present invention has been invented based on such knowledge, and its object is to use high-pressure natural gas extracted from an existing high-pressure transportation pipeline as a raw material gas, while natural ice and snow are possessed. An object of the present invention is to provide a method for producing a gas hydrate capable of producing a gas hydrate at a lower cost and with a higher efficiency by effectively utilizing the cold heat.

  In order to solve the above-mentioned problems, the gas hydrate production method of the present invention comprises reacting natural gas mainly composed of methane introduced into a pressure vessel and generated water at a predetermined pressure and temperature, In the gas hydrate manufacturing method for generating gas hydrate which is a hydrate of the above, high-pressure natural gas extracted from an existing high-pressure transport pipeline and generated water extracted from a generated water supply line are placed in the pressure vessel. Introducing gas hydrate, which is a hydrate of both, natural ice and snow, mountain stream and Tanigawa stream, mountain tunnel spring water, etc. are stored in a reservoir constructed in the mountains and stored in this reservoir The heat generated when the gas hydrate is generated is removed by using the cold heat possessed by natural cold water.

  Here, the gas pressure of the high-pressure natural gas extracted from the existing high-pressure transport pipeline is 5 to 7 MPa. Moreover, the water temperature of the natural cold water stored in the water tank constructed in the mountains is 0 degreeC-5 degreeC.

  As described above, the present invention reacts natural gas mainly composed of methane introduced into a pressure-resistant vessel with produced water at a predetermined pressure and temperature, and gas hydrates thereof are hydrates. In the gas hydrate manufacturing method for generating gas, the high-pressure natural gas extracted from the existing high-pressure transport pipeline and the generated water extracted from the generated water supply line are introduced into the pressure vessel, and both hydrates are introduced. While generating a certain gas hydrate, natural ice and snow, stream water of mountain stream and valley river, spring water of mountain tunnel, etc. are stored in a reservoir constructed in the mountains, and the cold heat stored in the natural cold water stored in this reservoir In order to remove the heat generated during the gas hydrate generation using gas, a gas compressor that boosts natural gas mainly composed of methane to a predetermined pressure is not necessary, and the gas compressor is driven. Power consumption is also unnecessary.

  Further, not only a refrigeration machine that removes generated heat generated when gas hydrate is generated, but also the power consumption for driving the gas compressor is unnecessary. As a result, the gas hydrate can be manufactured inexpensively and efficiently compared to the conventional case.

In addition, as described above, the present invention eliminates the need for power to operate the gas compressor and the refrigerator, and thus can suppress CO ₂ generated during power generation, thereby preventing global warming. Can contribute.

  In addition, since the present invention can manufacture gas hydrate around the existing high-pressure pipeline for gas transportation, the gas hydration property of the gas hydrate can be used to make small city gas operators, distributed power supply customers, etc. Small gas can be transported.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings.

  FIG. 1 is a schematic configuration diagram of a gas hydrate manufacturing apparatus according to the present invention. In FIG. 1, reference numeral 1 denotes an existing high-pressure transportation pipeline that supplies high-pressure (for example, 5 to 7 MPa) natural gas a from a gas field or LNG base 2 to a large city 3.

  Reference numeral 4 denotes a gas hydrate generation plant, which is supplied from a high-pressure natural gas (for example, 5 to 7 MPa) a supplied through a gas conduit 5 branched from an existing high-pressure transport pipeline 1 and a generated water supply line 6. The produced water b is reacted to produce a natural gas hydrate c.

  As shown in FIG. 2, the gas hydrate production plant 4 introduces high-pressure natural gas (for example, 5 to 7 MPa) a extracted from an existing high-pressure transport pipeline 1 into a production tank 8 that is a pressure vessel. The generated water b introduced into the spray nozzle 7 via the generated water supply line 6 is sprayed from the spray nozzle 7, and the natural gas hydrate c is generated by contact response at that time.

  The natural gas hydrate c generated as described above is taken out of the system from the delivery pipe 9. Further, the produced water b in the production tank 8 circulates continuously in the circulation line 10 provided in the production tank 8, and during this time, the heat generated during the gas hydrate production is removed by the heat exchanger 11.

  Returning to FIG. 1, reference numeral 12 denotes a water storage tank, which is installed in a cave (cavity) 19 provided on a slope 18 of a mountain having a relatively high altitude. The water storage tank 12 stores, for example, natural ice and snow f, water from mountain streams and valley rivers, spring water g from mountain tunnels, and the like.

  Since the cold water d stored in the water tank 12 is 0 ° C. to 5 ° C., the cold water d is supplied to the heat exchanger 11 of the gas hydrate production plant 4 through the pipeline 20.

  The gas hydrate production plant 4 can be constructed anywhere as long as it is in the vicinity of the existing high-pressure transport pipeline 1, but natural cold water d is easily available and the produced natural gas hydrate is produced. For the convenience of transporting c with a vehicle 13 such as a tank lorry, it is desirable that small and medium-sized gas customers, that is, small city gas operators and distributed power supply customers, are in the vicinity of the region.

  The natural gas hydrate c generated in the gas hydrate generation plant 4 is constructed by a vehicle 13 such as a tank lorry in the vicinity of an area where a small-scale city gas company or a distributed power supply customer is located. After being transported to the gasification plant 14, as shown in FIG. 3, it is stored in the storage tank 15 by utilizing the self-preserving effect.

  When the natural gas hydrate c stored in the storage tank 15 using the self-preserving effect is regasified, the storage tank 15 is depressurized or heat exchange provided in the storage tank 15 is performed. Regasification is performed by supplying hot water e to the vessel 16. The natural gas a produced by regasification is supplied through the gas pipe 17 to the above small city gas business operators, distributed power supply consumers, small and medium cities, eco stations, and the like.

  Next, the present invention will be described in more detail with reference to examples.

(Example)
FIG. 4 is a schematic configuration diagram of a gas hydrate production apparatus according to the present invention. When producing a natural gas hydrate c of 70 t / h, a high pressure (5 MPa) is supplied to the generator 8 from an existing high pressure gas line (not shown). ) Is introduced (10,000 Nm ³ / h), while the produced water b is introduced from the produced water supply line 6.

  The heat generated by the reaction between the natural gas a and the produced water b is removed by introducing a part (circulated water) b of the produced water to the heat exchanger 11. At that time, the circulating water b is cooled to 5 ° C. by the heat exchanger 11.

  On the other hand, in a water tank 12 provided in a cave in the mountain, cold spring water from a mountain tunnel is stored, and 0 ° C. cold water d is 100 t / h from the water tank 12 toward the heat exchanger 11. Supply in proportions.

Therefore, according to the present invention, the main power consumption is as follows.
・ Gas compressor: 0MW
・ Cold freezer: 0MW
・ Total: 0MW
That is, according to the present invention, the annual power consumption of the gas compressor and the refrigerator is 0 MWh, and the electricity cost related to the gas compression is 0 yen per year.

Also, if 0.7kgCO ₂ / kW amount of CO ₂ produced oil-fired thermal power plant, in the present invention, the amount of CO ₂ produced per year becomes zero tons will contribute to the prevention of global warming.

(Comparative Example 1)
FIG. 5 is a schematic configuration diagram of a conventional gas hydrate production apparatus. When a natural gas hydrate c is generated under the same conditions as in the present invention, a raw material gas having a supply amount of 10,000 Nm ³ / h by a gas compressor 21 is shown. (Natural gas) a is pressurized from 0.1 MPa to 5 MPa, while cold water d at 0 ° C. is artificially generated by a 3 MW refrigerator (2500 USRT, COP = 3) 22.

Therefore, the main power consumption of Conventional Example 1 is as follows.
・ Gas compressor: 2.5MW
・ Cooling machine: 3MW
・ Total: 5.5MW
That is, in Conventional Example 1, the annual power consumption of the gas compressor and the refrigerator is 44,000 MWh, and the electricity bill is 500 to 600 million yen per year.

Further, when the amount of CO ₂ produced oil-fired thermal power plant and 0.7kgCO ₂ / kW, in the conventional example 1, the amount of CO ₂ produced per year is approximately 30,000 tons.

(Comparative Example 2)
FIG. 6 is a schematic configuration diagram of a conventional gas hydrate production apparatus. When generating natural gas hydrate c under the same conditions as in the present invention, a raw material gas (natural gas) a of 5 MPa is supplied from the high-pressure gas line 1. While introducing at an amount of 10,000 Nm ³ / h, cold water d at 0 ° C. is artificially generated by a 3 MW refrigerator (2500 USRT, COP = 3) 22.

Therefore, the main power consumption of Conventional Example 2 is as follows.
・ Gas compressor: 0MW
・ Cooling machine: 3MW
・ Total: 3MW
That is, in Conventional Example 2, the annual power consumption of the gas compressor and the refrigerator is 24,000 MWh, and the electricity bill is 300 to 400 million yen per year.

Further, when the amount of CO ₂ produced oil-fired thermal power plant and 0.7kgCO ₂ / kW, in the conventional example 1, the amount of CO ₂ produced per year is 20,000 tons.

It is a schematic block diagram of the gas hydrate manufacturing apparatus which concerns on this invention. It is a schematic block diagram of a gas hydrate production | generation plant. It is a schematic block diagram of a gas hydrate gasification plant. It is a schematic block diagram of the gas hydrate manufacturing apparatus which concerns on this invention. It is a schematic block diagram of the conventional gas hydrate manufacturing apparatus. It is a schematic block diagram of the conventional gas hydrate manufacturing apparatus.

Explanation of symbols

a Natural gas mainly composed of methane b Water c Gas hydrate d Natural cold water e Hot water f Ice and snow g Spring water 1 High pressure gas supply line 2 LNG base 3 City 4 Gas hydrate generation plant 5 Gas conduit 6 Generated water supply line 7 Spray nozzle 8 Gas hydrate generator 9 Water pipe 10 Circulation line 11,16 Heat exchanger 12 Water tank 13 Vehicle 14 Gasification plant 15 Storage tank 17 Gas pipe 18 Mountain slope 19 Cave 20 Pipeline 21 Gas compressor 22 refrigerator

Claims (3)

A method for producing a gas hydrate in which a natural gas mainly composed of methane introduced into a pressure-resistant vessel and generated water are reacted at a predetermined pressure and temperature to generate a gas hydrate that is a hydrate thereof. In the above, the high-pressure natural gas extracted from the existing high-pressure transport pipeline and the generated water extracted from the generated water supply line are introduced into the pressure vessel to produce a gas hydrate that is a hydrate of both. Natural ice and snow, stream of mountain stream and valley river, spring water of mountain tunnel, etc. are stored in a reservoir constructed in the mountain, and gas hydrate is generated using the cold heat stored in the natural cold water stored in this reservoir A method for producing a gas hydrate characterized by removing generated heat generated. The method for producing a gas hydrate according to claim 1, wherein the gas pressure of the high-pressure natural gas extracted from the existing high-pressure transport pipeline is 5 to 7 MPa. The method for producing a gas hydrate according to claim 1, wherein the temperature of natural cold water stored in a water tank constructed in the mountains is 0 ° C to 5 ° C.

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