JP4620359B2 - Gas hydrate delivery method - Google Patents

Description

  The present invention relates to a gas hydrate delivery method for supplying gas hydrate (NGH) to small-sized consumers such as suburban convenience stores, mass retailers, or small-scale offices where gas conduits are not yet laid. Is.

  Conventionally, natural gas has been imported as LNG (liquefied natural gas), but since LNG has an extremely low temperature (−160 ° C.), its storage and transportation are highly storage and transportation. Technology and expensive storage and transportation facilities are required.

  Therefore, as described above, LNG is applied technically and in terms of equipment for small-scale consumers such as suburban convenience stores, mass retailers, or small-scale business establishments where gas conduits are not laid. It was difficult.

  On the other hand, natural gas hydrate, which is a hydrate of natural gas and water, has attracted attention as an alternative to LNG, and its research has been conducted since the 1930s, but in recent years, only research on natural gas hydrate has been conducted. There is also research on storage and transportation.

  And as a natural gas hydrate transport method, water is stored in a transport container, the water is cooled, and natural gas is blown into the transport container to generate a natural gas hydrate, and the transport container is taken to a consumption place. A natural gas hydrate transport method has been proposed in which the transport container is heated to regasify the natural gas after transport (see, for example, Patent Document 1).

  Further, for the natural gas hydrate transport container, in the transportable transport container, while containing cooled water, a natural gas blowing pipe for generating natural gas hydrate by blowing natural gas is provided, There has been proposed a natural gas hydrate transport container provided with a natural gas discharge port for discharging the natural gas heated and regasified at the top of the transport container (see, for example, Patent Document 1).

Also, the tank for hydrate generation and the temperature and pressure inside the tank are selected from the conditions for generating hydrate, the conditions for storing hydrate, and the conditions for vaporizing hydrate. There has been proposed a hydrate tank apparatus including a temperature / pressure condition setting means for setting and maintaining one condition (for example, see Patent Document 2).
JP 2000-304196 A (page 2-3, FIG. 1) JP 2003-307299 A (page 4, FIG. 1)

  However, in any case, since natural gas hydrate is generated using “natural gas” as a raw material and “water” as a medium, the energy required for generating natural gas hydrate is low. There is a problem of becoming large (100 kcal / kg).

  By the way, the heat of generation when natural gas hydrate is generated and the heat of decomposition when natural gas hydrate is decomposed and gasified is 100 kcal / kg due to changes in water and source gas when the temperature is above freezing. If it is below the freezing point, it is 35 kcal / kg due to changes in ice and source gas.

  Therefore, it can be seen that if the medium that reacts with the raw material gas is supplied not by “water” but by “ice”, less energy is required to generate and decompose the natural gas hydrate. That is, it can be seen that if the medium that reacts with the raw material gas is supplied in the form of “ice” in advance, the energy required for generating and decomposing the natural gas hydrate may be about 1/3 that of “water”.

  On the other hand, if the generated gas hydrate is once decomposed and then gas hydrate is generated again, the reaction time is shortened. This is called the “memory effect” and is thought to be due to the remaining water molecule clusters having a structure suitable for the formation of gas hydrate nuclei.

  As described above, the gas hydrate formation reaction is a phase transfer that occurs when gas molecules are taken into water molecules and the subsequent supersaturated environment is triggered, which can be said to be a crystallization process. There are no established theories about the reaction time, the formation of nuclei, the reaction mechanism of gas hydrates, including crystal growth, and the kinetic analysis, and this is a hot research topic that researchers around the world are currently working on.

  In the present invention, as described above, if the medium that reacts with the raw material gas is supplied not by “water” but by “ice”, less energy is required for the production and decomposition of natural gas hydrate. The invention was invented based on the knowledge that the generated gas hydrate was once decomposed and then generated again for the "memory effect" because of the "memory effect". The object of the present invention is to provide a gas hydrate delivery method capable of reducing the energy required for the production and decomposition of natural gas hydrate and reducing the size of production facilities.

  In order to achieve the above object, the present invention is configured as follows.

  The invention described in claim 1 is a gas hydrate delivery method in which a gas hydrate produced by reacting a raw material gas and water is delivered to a consumer. The gas hydrate is supplied to a regasification zone. The gas hydrate is heated while being kept at a low temperature below the freezing point to be separated into a raw material gas and ice from which the raw material gas has escaped, and the extracted raw material gas is supplied to the consumer, and the raw material gas The ice that has escaped is returned to the gas hydrate regeneration zone, and then the gas hydrate is regenerated by supplying the raw material gas while maintaining the ice from which the raw material gas has escaped at a low temperature below the freezing point. This is a gas hydrate delivery method.

  The invention described in claim 2 is the gas hydrate delivery method according to claim 1, wherein the regeneration / decomposition conditions of the gas hydrate are in the range of -20 ° C to -5 ° C and 1.5 MPa to 0.1 MPa. is there.

  As described above, the invention described in claim 1 is a gas hydrate delivery method in which a gas hydrate produced by reacting a raw material gas and water is delivered to a consumer. While transporting to the regasification zone and maintaining the gas hydrate at a low temperature below the freezing point, it is separated into source gas and ice from which the source gas has escaped, and the extracted source gas is supplied to consumers At the same time, the ice from which the source gas has escaped is returned to the gas hydrate regeneration zone, and then the source gas is supplied to regenerate the gas hydrate while maintaining the ice from which the source gas has escaped at a low temperature below the freezing point. It is characterized by doing.

  As already explained, the heat of formation for generating gas hydrate by reacting the raw material gas and water, or the heat of decomposition for decomposing the raw material gas and water by heating the gas hydrate is 100 kcal / kg. On the other hand, as in the present invention, the heat of formation for reacting the raw material gas and ice to generate gas hydrate or the heat of decomposition for heating the gas hydrate to decompose into raw material gas and ice is 35 kcal / kg. It is.

  Therefore, since the present invention requires about 1/3 of the conventional energy, significant energy saving is possible.

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

  FIG. 2 is an explanatory diagram of a tank that also serves as a generation / storage / decomposition tank applied to the implementation of the gas hydrate delivery method according to the present invention.

  As shown in FIG. 2, natural gas hydrate is once decomposed (regasified) in a pressure-resistant tank (hereinafter referred to as a tank) 10 that also serves as a gas hydrate production / storage / decomposition tank. The ice a which has released natural gas is stored. The ice a is placed on a perforated plate 11 such as a mesh.

  Here, the natural gas hydrate is produced by reacting a raw material gas (natural gas) and water as a medium as usual, and has a pellet shape or a powder shape.

  The tank 10 is covered with a heat insulating material (not shown) so that the ice a contained therein is not melted by heat, and the inside thereof is maintained at predetermined conditions, for example, a pressure of 1.5 MPa and a temperature of −5 ° C. ing.

  In addition, although the pressure and temperature in the tank 10 can be suitably set as desired, the pressure in the tank 10 is preferably in the range of 1.5 to 0.1 MPa, for example. Moreover, the temperature in the tank 10 is preferably in the range of -20 ° C to -5 ° C, for example.

  The tank 10 has connection pipes 15 and 16 for connecting circulation pipes equipped with heat exchangers and blowers at both upper and lower ends, and a connection pipe 18 for connecting a raw material gas supply pipe to the side surface thereof. have. Furthermore, a pressure gauge 19 for measuring the pressure in the tank is provided in the upper part of the tank 10. The connecting pipes 15, 16 and 18 are each provided with a valve 20.

  As described above, when the gas hydrate is generated using the ice a which has been degassed in advance, the source gas supply pipe 17 is connected to the third connection pipe 18 as shown in FIG. At the same time, the circulation pipe 14 a including the cooling heat exchanger 12 a and the blower 13 a is connected to the first and second connection pipes 15 and 16. Subsequently, the wiring 23 of the pressure gauge 19 is connected to the controller 25a for controlling the flow rate adjusting valve 22a provided in the refrigerant supply pipe 21 of the cooling heat exchanger 12a.

  Then, after the valves 20 of the connection pipes 15, 16, and 18 are respectively opened, the raw material gas (natural gas) b having a predetermined pressure (for example, 1.5 MPa) is supplied from the raw material gas supply pipe 17 into the tank 10. At the same time, when the blower 13 is started while supplying the low-temperature refrigerant c to the cooling heat exchanger 12a, the natural gas b in the tank 10 is cooled to a predetermined temperature (for example, −20 ° C.).

In the meantime, that is, while the temperature in the tank 10 decreases from −5 ° C. to −20 ° C., as already explained, the natural gas b is contained in the ice a due to the “memory effect” that the ice a has. It is taken in and natural gas hydrate d is produced again. The reason why the natural gas hydrate d is generated at a low temperature below the freezing point is that the code X as the generation condition is located on the equilibrium line Z as shown in FIG. The regeneration of the natural gas hydrate is performed over several hours, for example, 2 to 8 hours. When the natural gas hydrate is regenerated, the inside of the tank 10 is maintained in an equilibrium state, that is, 1.5 MPa and −20 ° C. (refer to the symbol X in FIG. 3).

  After the regeneration of the natural gas hydrate, as shown in FIG. 1 (b), the valves 20 of the connection pipes are respectively closed, and the raw material gas supply pipe 17, the cooling heat exchanger 12a, the blower 13a and the like are supplied from the tank 10. The circulation pipe 14a provided with is removed. After that, the tank 10 is temporarily stored, or placed on a transport vehicle (not shown) such as a trailer, and a suburban convenience store or mass retailer where a gas conduit is not yet laid, or a small-scale business Land transported to small customers such as offices.

  A small-sized consumer who has received the tank 10 filled with the natural gas hydrate d connects the gas delivery pipe 26 to the third connection pipe 18 as shown in FIG. A circulation pipe 14b having 12b and a blower 13b is connected to the first and second connection pipes 15 and 16. Subsequently, the wiring 23 of the pressure gauge 19 is connected to the controller 25b for controlling the flow rate adjustment valve 22b provided in the heat medium supply pipe 27 to the heating heat exchanger 12b.

  Then, after each of the valves 20 of the connection pipes is “open”, the blower 13b is started while supplying the heating medium e to the heating heat exchanger 12b, and the residual gas (natural gas) heated by the heating heat exchanger 12b is then started. The natural gas hydrate d in the tank 10 is heated by the gas b). Then, the natural gas b escapes from the natural gas hydrate d in the form of powder or pellets. These natural gases b are supplied to devices such as a small gas turbine generator and a fuel cell through the gas delivery pipe 26.

  When the natural gas hydrate d in the tank 10 is heated, there is a device for applying heat. As already described, the tank 10 is in an equilibrium state (1.5 MPa, −20 ° C.) (see reference X in FIG. 3).

Therefore, if heat is applied to the natural gas hydrate d in the tank 10, the equilibrium state is lost (see symbol Y in FIG. 3), and the natural gas hydrate d is decomposed to generate natural gas b. If the natural gas b is released to the outside of the tank 10, the pressure (1.5 MPa) in the tank 10 is maintained, but the heat applied to the natural gas hydrate is such that the natural gas hydrate is below freezing point, and Should be given between the equilibrium temperatures. Thereby, the medium from which the natural gas has escaped maintains the ice state. The reason why the natural gas hydrate d is decomposed at a low temperature below the freezing point is that, as shown in FIG. 3, the symbol Y, which is the point of the final gas loss state, is located on the low pressure side from the equilibrium line Z. . In FIG. 3, the symbol Z indicates a balanced line.

  As described above, the heat of decomposition is given from the outside through the heat exchanger 12b. For example, if the working gas in the tank 10 is −5 ° C. and 1.5 MPa, the ice is returned to the initial state shown in FIG. That is, the driving force for gasification is the difference between −5 ° C. and −20 ° C., and the driving force for natural gas hydrate regeneration is the difference between the cooling side temperature (for example, −30 ° C.) and −20 ° C. .

  Therefore, the required energy can be reduced as compared with the conventional case where natural gas hydrate is produced from water and raw material gas.

  Here, as shown in FIG. 4, the tank 10 has a bottom portion 30 and an upper portion 31 each having a conical shape. In addition, connection pipes 15 and 18 are provided on the upper part 31 and connection pipes 18 corresponding to the connection pipes 15 are provided on the bottom part. A plurality of tip ends of the connection pipes 18 are provided. The circulation gas spreads throughout the entire area.

  In the above explanation, the fuel supply method for private power generation for small consumers such as convenience stores, mass retailers, or small-scale establishments has been explained. However, the present invention is also applicable to the following cases. Can do. It can also be applied to the delivery of gases other than natural gas.

(A) Substitution of gas holder for city gas FIG. 5 shows an alternative example of a gas holder for coping with changes in gas demand. Regenerate and store in tank for a time. When the gas demand increases, the gas hydrate is regasified into natural gas, which is sent out to the city, and sent at an intermediate pressure A (10 data (0.89 MPa)). The gas is reduced to an intermediate pressure B (3 data (0.29 MPa)) and sent to a consumer at a so-called “governor station”.

  That is, since the gas hydrate is generated under the condition of 15.3 at (1.5 MPa) from the gas delivered at the medium pressure A (10 at (0.89 MPa)), the booster 33 for boosting is necessary. When the gas hydrate is generated at the supply pressure (10 ata (0.89 MPa)), it is necessary to cool to −20 ° C. or lower, and since it is not advantageous from the viewpoint of self-preservation, a booster 33 is provided.

(B) Coastal tanker (sea transport)
Conventionally, in a gas production base (LNG gasification base), a means for transporting LNG to a small and medium city by a conventional coastal tanker has been adopted, but the present invention can be substituted for it. The transportation cost is much lower than that of transporting LNG at −162 ° C., and regasification is simple, leading to the spread of natural gas.

  A large number of containers (tanks) can be “loaded and unloaded” on a coastal tanker, or the tanker itself can be regarded as a container (tank). In this case, a barge transportation method is desirable. That is, since the barge is moored at the regasification base and the empty barge is carried back to the gas production base by the towed ship, the operating rate of the towed ship can be increased.

(C) CNG replacement (replacement of current CNG vehicles)
In recent years, natural gas vehicles have been sought to spread in order to use gas with excellent environmental characteristics as fuel for vehicles. However, CNG (compressed natural gas) has an ultra-high pressure of 250 atmospheres, and the weight of the container itself and the compressor that pressurizes the gas compress the cost, thereby inhibiting the spread. In addition, as the gas remaining in the container is 30 atm, there is a large amount of unused gas in the container, which is not economical.

  Therefore, the present invention is at most about 15 atm, and there is little danger even if it is mounted on an automobile. In addition, since the amount of unused gas is extremely small, it is thought that it will lead to the spread of gas as automobile fuel.

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

(Example)
(1) Gas hydrate generation / decomposition conditions, etc.
・ Production conditions: −20 ° C., 1.5 MPa
Decomposition conditions: -5 ° C, 1.5 MPa
・ Container capacity: 5m ³
-NGH amount: 4.75 m ³
-NGH amount: 3.8 t
・ Gas content: 0.481t
Heat of reaction (NGH reaction heat below freezing point): 35 kcal / kg (NGH)
-Container size: Diameter 1.3m x Height 3.8m
・ Container wall thickness: 9.6 mm
-Container weight: 5.3t (including NGH)
(2) Generation of gas hydrate
・ Generation of natural gas blown into ice held at -5 ° C and 1.5 MPa to generate NGH
・ Sensible heat of ice: 2.7 × 10 ³ kcal / container
Heat of reaction: 16.8 × 10 ³ kcal / container
・ Material gas cooling: 8.4 × 10 ³ kcal / container
Total: 27.9 × 10 ³ kcal / container
-Time required to generate NGH corresponding to the above capacity: 2 hours
At this time, it is necessary to prepare a 9.6 kW refrigerator.
(3) Decomposition of gas hydrate
・ Amount of gas to be supplied for 10 hours of power generation (daytime peak cut) after installing the above containers in factories, etc .: 670 Nm ³
・ Power generation: 270 kW (fuel cell)
It becomes.

          The amount of heat at this time uses waste heat of the engine (fuel cell) 34 (see FIG. 6), but basically heat is supplied so as to maintain a state of 1.5 MPa. However, at the time of regasification, since the gas is generated so as to maintain the original conditions (−20 ° C., 1.5 MPa), the generated gas is −20 ° C., so it is heated with waste heat when supplied to the engine. There is a need to.

  In FIG. 6, 35 is a gas heater and 36 is a pressure reduction control valve.

  As described above, the container has a diameter of 1.3 m × a height of 3.8 m, a container thickness of 9.6 mm, and a container weight of 5.3 t (including NGH). there is no problem.

(A)-(c) is explanatory drawing for demonstrating embodiment of the gas hydrate delivery method concerning this invention. It is a schematic diagram of a gas hydrate manufacturing tank. It is production | generation / decomposition | disassembly explanatory drawing of gas hydrate. It is sectional drawing of a gas hydrate manufacturing tank. It is explanatory drawing which shows the example of application of the method of this invention. It is gas hydrate decomposition | disassembly process explanatory drawing applied in the Example of this invention method.

Explanation of symbols

a Porous ice husks from which source gas has escaped b Source gas d Gas hydrate

Claims (2)

In a gas hydrate delivery method in which a gas hydrate generated by reacting a raw material gas and water is delivered to a consumer, the gas hydrate is transferred to a regasification zone, and the gas hydrate is cooled to freezing point. While maintaining the following low temperature, it is heated and separated into raw material gas and ice from which the raw material gas has escaped, and the extracted raw material gas is supplied to the consumer, and the ice from which the raw material gas has escaped is supplied to the gas hydrate regeneration zone The gas hydrate delivery method is characterized in that the gas hydrate is regenerated by supplying the raw material gas while maintaining the ice from which the raw material gas has escaped at a low temperature below the freezing point. The gas hydrate delivery method according to claim 1, wherein the gas hydrate regeneration / decomposition conditions are in a range of -20 ° C to -5 ° C and 1.5 MPa to 0.1 MPa.

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