JP2003343798A - Storage method, transport method, and transport system for natural gas - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To hold gas hydrate stably and supply natural gas as an energy source stably and inexpensively in a process of transport in which it is expected that natural gas is transported over a long distance for a long period of time. <P>SOLUTION: In a transport method for natural gas in which natural gas is hydrated for transport, the hydrated natural gas, namely, natural gas hydrate is frozen, and the natural gas hydrate is stored in a transport vessel 20 and is transported by keeping it in a temperature scope of -30°C or more and 0°C or less. <P>COPYRIGHT: (C)2004,JPO

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for transporting natural gas containing hydrocarbons such as methane as a main component from an excavation site to a consumption site.

[0002]

2. Description of the Related Art Currently, boring is carried out in various places on the earth for the purpose of crude oil mining. All of these are places where it is recognized that crude oil is likely to exist from the ground structure and geological point of view, but there are only a few layers where crude oil can be actually mined.

[0003] Many of the trial drilling sites where crude oil mining has been unsuccessful correspond to the natural gas layer, but at such trial drilling sites, natural gas cannot be discharged into the atmosphere.
The current situation is that it is burned exclusively at the processing tower installed in the test pit.

In recent years, with the increasing awareness of environmental problems, how to treat natural gas in such natural gas mining areas has become a problem. The heat generated by the combustion of natural gas can contribute to global warming. Therefore, attempts have been made to recover natural gas and use it as an energy source even in the above-mentioned mining areas.

In general, natural gas is produced into liquefied natural gas at a production plant constructed at or near a mining site, transported over the ocean by a dedicated transport ship, and stored at a storage base constructed at a consuming site, and then sequentially. Consumed. However,
This is the case when the mining site is onshore, for example when the mining site is offshore, it is difficult to realize because huge capital is required to construct the production plant. Also, whether on land or offshore, the amount of natural gas reserves at the mining site is sufficient to meet the invested capital, but in reality there are few mining sites with such reserves, and it is difficult to realize it. .

[0006] Therefore, what is currently attracting attention is a method of transporting natural gas in the form of hydrate. Hydrate of natural gas (hereinafter referred to as gas hydrate) has a smaller volume reduction rate per unit volume than liquefied natural gas (while liquefied natural gas becomes 1/600 of the original volume, The gas hydrate is 1/170), but it can be produced even under the condition of cryogenic temperature such as liquefied natural gas. Therefore, the capital required for the construction of the production plant is not so large as that of liquefied natural gas, and the plant construction on the ocean is not impossible. In addition, it is not necessary to use cryogenic conditions such as liquefied natural gas for its handling, and a special transport ship equipped with cryogenic refrigeration equipment is not particularly required for transportation. Can be used to reduce costs. Furthermore, when the mining site is offshore, the production plant will be constructed as a movable float facility, and if one mining site is exhausted, it will move to the next mining site and move to the next mining site for new mining. There is also.

From the above viewpoint, Japanese Patent Laid-Open No. 2000-2
In Japanese Patent No. 80592, the following proposal is made as a more specific method for hydrating natural gas and transporting it. The transportation method is to hydrate natural gas in a production plant adjacent to the method mining site, store the hydrated natural gas in a transportation container, and install the transportation container containing the natural gas hydrate in a ship or the like. It is loaded on a transportation means and transported, and a natural gas hydrate is taken out from a transportation container in a regasification plant adjacent to the place of consumption and decomposed and gasified. According to this transportation method, transportation of natural gas can be realized at a low cost which is unrivaled in comparison with liquefied natural gas.

[0008]

As described above, the technology for converting natural gas into gas hydrate and transporting it is a very effective measure in considering future use of natural gas, but it is stable and stable. It is undeniable that further technological innovation is necessary to realize low-cost supply.

The present invention has been made in view of the above circumstances, and in the process of transportation, which is expected to move over a long distance over a long period of time, stably holds gas hydrates and uses natural gas as an energy source. The aim is to realize a stable and inexpensive supply of gas.

[0010]

As means for solving the above problems, a natural gas storage method, transportation method and transportation system having the following configurations are adopted. The method for storing natural gas according to claim 1 of the present invention is characterized in that the natural gas hydrate is stored while being kept in a temperature range of -30 ° C to 0 ° C.

The method for transporting natural gas according to claim 2 is a method for transporting natural gas by hydrating natural gas, wherein the hydrated natural gas, that is, natural gas hydrate is frozen. , Storing the natural gas hydrate in a transport container -30
It is characterized in that it is transported while being kept in a temperature range of 0 ° C or higher and 0 ° C or lower.

A natural gas transportation system according to a third aspect of the present invention is a natural gas transportation system for transporting hydrated natural gas, the transportation system containing hydrated natural gas, that is, natural gas hydrate. It is characterized by comprising a container and a refrigerating device for holding the natural gas hydrate stored in the transportation container in a frozen state.

The natural gas transportation system according to claim 4 is the natural gas transportation system according to claim 3,
It is characterized by comprising a transportation means for loading and transporting the transportation container.

The natural gas transportation system according to claim 5 is the natural gas transportation system according to claim 4,
An area for loading the transportation container and the refrigeration apparatus are separately arranged in the transportation means.

A natural gas transportation system according to claim 6 is the natural gas transportation system according to any one of claims 3 to 5, wherein the natural gas hydrate is placed in a temperature range of -30 ° C to 0 ° C. Characterized by transporting while keeping.

The transport container according to claim 7 is a transport container for transporting the natural gas in a hydrated form, wherein the natural gas hydrate contained in the transport container is fed from a refrigeration unit provided separately. It is characterized in that it is provided with a cooling means for receiving and cooling.

When a natural gas hydrate is kept at a temperature of 0 ° C. or lower, the water molecules constituting itself freeze to form a shell, and the natural gas is confined inside to stabilize (the self-preserving property ( self-preserzation))). Furthermore, it can be said that “self-preservation” is an essential condition for natural gas hydrate to exist as a hydrate, and this property is effectively used for transporting natural gas hydrate. Should be used. On the other hand, in order to stably retain the natural gas hydrate by utilizing the above-mentioned self-preserving property, it is desirable to keep the natural gas hydrate under the lowest possible temperature condition. 0
This is because even if it freezes below 0 ° C, the closer it is to 0 ° C, the higher the ratio of spontaneous decomposition and gasification.
However, the lower the condition temperature, the more the energy consumption required for freezing increases, which is not preferable for the purpose of low cost natural gas transportation. Therefore, the present inventors have found a temperature range suitable for the cryopreservation of the natural gas hydrate from the balance between the energy of the gas that spontaneously decomposes and the energy required for freezing.

FIG. 4 shows the relationship between the storage temperature of the natural gas hydrate and the energy of the decomposed gas, and the relationship between the storage temperature and the energy required for freezing. Here, the energy of the cracked gas is the electric power obtained by generating power (power generation efficiency; converted at 30%) with the heat of burning methane, which occupies most of the components of the cracked gas, and the energy required for freezing. Is the power consumed by the refrigeration system.

Since the natural gas hydrate self-preserving property is utilized as described above, the upper limit of the storage temperature is absolutely 0 ° C. When the storage temperature is lowered from 0 ° C., the amount of gas that spontaneously decomposes decreases, so that the energy of the decomposed gas also gradually decreases. On the other hand, the energy required for freezing increases as the storage temperature is lowered.

All of these energies are energy which is naturally or intentionally consumed in keeping the natural gas hydrate in a frozen state. Therefore, when considering the consumed energy that is the sum of both energies, when the storage temperature is lowered from 0 ° C, the consumed energy gradually decreases, showing the lowest value between -15 ° C and -20 ° C and turning to an increase. , −30 ° C., the energy consumption becomes almost the same as that at 0 ° C., and thereafter continues to rise. From this, it can be seen that when the storage temperature is set lower than −30 ° C., more energy is wasted than when the absolutely set upper limit temperature of 0 ° C. is consumed. Therefore, the storage temperature of the natural gas hydrate is preferably set in a temperature range of -30 ° C or higher and 0 ° C or lower, with a lower limit temperature of -30 ° C, and more specifically, a temperature of -20 ° C or higher and -15 ° C or lower. It is more desirable to set the range.

In the present invention, the natural gas hydrate is kept in a frozen state in the course of transportation which is expected to move over a long distance over a long period of time, thereby utilizing the self-preserving property as described above. It becomes possible to stably hold the gas hydrate.

[0022]

DESCRIPTION OF THE PREFERRED EMBODIMENTS A first embodiment according to the present invention will be described with reference to FIGS. Fig. 1 shows a natural gas transportation system from the offshore natural gas mining site (hereinafter referred to as a gas field) to the consumption site. Reference numeral 1 in the figure
Is a gas hydrate production plant constructed offshore,
Reference numeral 2 is a transportation ship (transportation means) for carrying gas hydrate, and 3 is a gas hydrate regasification plant constructed at a receiving terminal adjacent to the coast of the consumption area.

The production plant 1 is constructed as a float facility that can be moved over the ocean, and a production device 5 for recovering natural gas to form a gas hydrate and a slurry gas hydrate are provided on the floating body 4. A forming and solidifying device 6 for forming and solidifying, a freezing storage facility 7 for temporarily storing the formed and solidified gas hydrate until shipment, and a loading facility 8 for loading the gas hydrate from the freezing storage facility 7 onto the transport ship 2. , Are provided.

As shown in FIG. 2, the transport vessel 2 includes a transport container 20 for storing the molded and solidified gas hydrate, and a refrigerating device 21 for holding the gas hydrate stored in the transport container 20 in a frozen state. Is provided. On the transport ship 2, a region for loading the plurality of transport containers 20 is provided from the bow to the center of the hull, and the refrigeration system 21 is provided on the stern side. These are arranged separately for explosion protection, and are connected by a pipe 22 for supplying brine (refrigerant).

The regasification plant 3 has an unloading facility 9 for unloading the gas hydrate from the transport ship 2, a frozen storage facility 10 for temporarily storing the unloaded gas hydrate until it is decomposed, and a storage facility. A decomposing device 11 for decomposing and gasifying the gas hydrate is provided.

In the above transportation system, the gas hydrate produced in the production plant 1 is transported to the transportation container 2
0, and stored in the refrigeration storage facility 7 until shipping. When transporting, the transport container 20 is loaded on the transport ship 2 and transported to the receiving terminal, and the transport container 20 is transferred to the regasification plant 3 as it is. , Used as a raw material container. Therefore, the transport container 20 includes the refrigerating device 21 and the pipe 2.
It has a structure that can be freely attached to and detached from 2.

As shown in FIG. 3, in the loading area of the transportation vessel 2, a receiving portion 23 corresponding to each of the plurality of transportation containers 20 is provided.
A plurality of shipping containers 2 are provided and connected to these.
At 0, a cooling coil (cooling means) 24 connected to a pipe 22 for circulating and supplying brine is provided.

The receiving part 23 has a box-shaped frame 25 for receiving and connecting and fixing the transport container 20, and two couplers 26, 27 which are respectively attached to and detached from the brine introducing end 24a and the extracting end 24b of the cooling coil 24. I have it. These two
Each of the two couplers 26 and 27 is provided so as to project from one surface of the frame body 25.

One coupler 26 has a flexible hose 26a on the upstream side of the pipe 22 through which cooler brine flows.
It is supported by a flexible support 26b which is connected via the hydraulic coil 26c and sucks the displacement at the time of connection with the cooling coil 24. While being connected with the cooling coil 24, the hydraulic cylinder 26c constantly presses the brine introduction end 24a. Has become. The other coupler 27 is connected to the downstream side of the pipe 22 via a flexible hose 27a and is also supported by a flexible support 27b. Similarly, while being connected to the cooling coil 24, the hydraulic cylinder 27c is also connected.
Is always pressed against the brine outlet end 24b.

The cooling coil 24 is bent in a meandering state so as to come into contact with a wide area of the side surface of the transport container 20. The entire surface of the transport container 20 is covered with a cold insulating material (not shown). As the refrigerating device 21, a vapor compression refrigerating machine is adopted like the LNG carrier. As these driving fuels, natural gas stored in the transportation container 20 and naturally decomposed is used.

The natural gas blown out from the gas field on the sea floor is recovered through a flexible pipe system and is generated in the generator 5 to be a gas hydrate in the form of slurry.
The slurry-like gas hydrate is dehydrated, cooled, and depressurized, and then is molded and solidified in the molding and solidifying apparatus 6 into a shape suitable for transportation. The molded and solidified gas hydrate is stored in the transportation container 20 and temporarily stored in the frozen storage facility 7, and then loaded into the transportation vessel 2 together with the transportation container 20 by the loading facility 8 and transported to the receiving terminal. To be done. In the transport ship 2, the transport container 20 is a refrigerating device 21.
It is controlled so that the storage temperature of the gas hydrate stored inside is maintained in the range of -30 ° C or higher and 0 ° C or lower (desirably -20 ° C or higher and -15 ° C or lower). .

When the gas hydrate transported on the ocean arrives at the receiving terminal, it is unloaded together with the transportation container 20 and temporarily stored in the frozen storage facility 10. Frozen storage facility 10
The gas hydrate stored in is directly discharged from the transport container 20 to the decomposition device 11 using this as a raw material, gasified, and sent to the consumer through the lifeline.

In the above transportation system, the refrigerating device 2
Naturally decomposed natural gas is used as fuel for No. 1, but if the storage temperature is lowered in order to reduce the rate of natural decomposition of gas hydrate, the amount of gasified natural gas will be consumed. turn into.

Therefore, by keeping the storage temperature of the gas hydrate in the range of -30 ° C. to 0 ° C. during the transportation process, the gas hydrate is naturally or intentionally held in the frozen state. The energy consumed can be reduced, resulting in an overall low loss natural gas transport.

Further, it is possible to save the time and labor involved in exchanging the gas hydrate between the containers. Furthermore, when loading and landing on the transport ship 2, it becomes possible to carry out cargo handling work together with the storage container 12, so that transport efficiency is significantly improved.

By the way, in the above embodiment, the transport container 20 and the refrigerating device 21 are provided separately. This is a refrigeration system 2 that uses natural gas as fuel and has many electrical components.
1 is to prevent contact between the gas hydrate and the gas hydrate to avoid the risk of ignition of natural gas. However, if such explosion-proof measures are taken, the refrigeration system 21 should be installed in the transport container 20. An integrated structure may be adopted. Further, the present invention is effective not only when transporting the gas hydrate, but also when storing it for a long period of time.

[0037]

As described above, according to the present invention,
By keeping natural gas hydrate in a frozen state during the process of transportation that is expected to travel over long distances over a long period of time, gas hydrate can be stably maintained and natural gas as an energy source can be stabilized. In addition, inexpensive supply can be realized.

[Brief description of drawings]

FIG. 1 is a diagram showing an embodiment of a natural gas transportation method according to the present invention, and is a conceptual diagram showing a natural gas transportation system to which the method is applied.

FIG. 2 is a diagram showing a structure of a transportation ship that constitutes a part of a transportation system.

FIG. 3 is a diagram showing details of a transportation container in the transportation ship and a receiving portion thereof.

FIG. 4 is a graph showing the relationship between the energy naturally or intentionally consumed for holding a natural gas hydrate in a frozen state and the storage temperature of the natural gas hydrate.

[Explanation of symbols]

1 generation plant 2 Transport vessels (transportation means) 3 Regasification plant 20 shipping containers 21 Refrigerator 22 Piping 23 Reception Department 24 Cooling coil (cooling means)

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁷ Identification code FI theme code (reference) B63J 2/12 C10L 3/00 A (72) Inventor Minoru Mineda 1-chome, Wadazaki-cho, Hyogo-ku, Kobe-shi, Hyogo No. 1-1 Mitsubishi Heavy Industries, Ltd. Kobe Shipyard (72) Inventor Katsuo Ito 1-1-1, Wadasaki-cho, Hyogo-ku, Kobe City, Hyogo Prefecture Mitsubishi Heavy Industries Ltd. Kobe Shipyard F-term (reference) 3E070 AA02 AB01 EA04 3E072 EA10

Claims (7)

[Claims] 1. A method for storing natural gas, which comprises storing the natural gas hydrate while maintaining the temperature range from −30 ° C. to 0 ° C. 2. A method for transporting natural gas by hydrated natural gas for transportation, comprising freezing hydrated natural gas, that is, natural gas hydrate, and transporting the natural gas hydrate. The method for transporting natural gas, which is characterized in that the gas is transported while being kept in a temperature range of -30 ° C to 0 ° C. 3. A natural gas transport system for transporting hydrated natural gas, comprising: a transport container for storing the hydrated natural gas, that is, a natural gas hydrate; and a transport container housed in the transport container. A natural gas transportation system, comprising: a refrigerating device for holding the natural gas hydrate in a frozen state. 4. The natural gas transportation system according to claim 3, further comprising transportation means for loading and transporting the transportation container. 5. The natural gas transportation system according to claim 4, wherein an area in which the transportation container is loaded and the refrigeration apparatus are separately arranged in the transportation means. 6. The natural gas hydrate is -30 ° C. or higher and 0 ° C.
The natural gas transportation system according to any one of claims 3 to 5, wherein the transportation is carried out while maintaining the temperature range below. 7. A transport container for hydrating and transporting natural gas, wherein natural gas hydrate contained therein is cooled by receiving a refrigerant supply from a refrigerating device provided separately. A transportation container comprising cooling means.