AU2002306357B9 - Method of pelletizing, handling and transporting gas hydrate - Google Patents

Description

r VERIFICATION CERTIFICATE OF I, Shun KURITA of c/o Ogawa, Noguchi Saika International Patent Office, of Toranomon 11 Mori Building, 6-4, Toranomon 2-chome, Minato-ku, Tokyo, Japan state that the attached document is a true and complete translation to the best of my knowledge of International Patent Application No. PCT/JPO2/05224 with Article 34 amended pages attached.

Dated this 22nd day of January, 2004 Signature of Translator: METHOD OF HANDLING GAS HYDRATE FIELD OF THE INVENTION The present invention concerns a method of handling gas hydrate for handling so-called gas hydrate which is composed of a gas comprising methane as main component such as natural gas and water.

DETAILED DESCRIPTION OF THE RELATED ART Conventionally, the natural gas is transported or stored in the form of liquefied natural gas (LNG, hereinafter) or compressed natural gas.

However, it is necessary to transport or store LNG in a cargo whose temperature is kept at -162 C, and a special ship (LNG ship) or storing facility provided with an expensive reservoir manufactured especially for transport or storage is required. Furthermore, it is necessary to use a great quantity of energy for the manufacturing of the LNG so as to obtain solution of -162 0C. In addition, when the control of LNG becomes deficient, it vaporizes suddenly and is dangerous. Besides, LNG vaporizes rapidly and is inappropriate to store for a long time because it is extremely cold as described above.

On the other hand, gas comprising methane as main component such as natural gas attract attention as clean energy source or raw material of various structures. Researches for making the gas comprising methane as main component such as natural gas into gas hydrate artificially or industrially for the purpose of its transportation or storage is currently performed.

The gas hydrate has a crystalline structure where a gas molecule is contained one by one in a cage formed with water molecules. For instance, 1 m 3 of the methane hydrate (where the volume of water is 0.8 m 3 under the normal pressure is said to be capable of storing 164 m 3 of methane.

Thus, the methane hydrate attracts attention as a new transport and storage body of natural gas in place of LNG, because it has the abovementioned high capability of storage. The density of methane gas in the methane hydrate is about 1/3.5 of LNG, however, in case of producing it artificially or industrially, the energy efficiency may be largely improved because it has no necessity of cooling down to the liquefaction temperature (below 162 as LNG.

In case of producing methane hydrate artificially, for instance, water or antifreeze solution is sprayed from a spray means and, at the same time, natural gas (methane) is supplied from a supply pipe, into a pressure vessel where the temperature is kept 1 to 10 C and the pressure is kept 30 to 100 atmospheric pressure. Thereupon, water or antifreeze solution sprayed from the spray means and the natural gas (methane) are compounded to produce powdery methane hydrate. As the filling factor (volume of methane hydrate /volume of storage vessel) of the powdery methane hydrate is small, a reservoir of large capacity becomes necessary for transportation and storage thereof.

Furthermore, the powdery methane hydrate has a problem that it binds with each other by its own weight or others, and becomes like a rock making difficult to take it out (unloading), when a large quantity of it is stored for a long time.

SUMMARY OF THE INVENTION The present invention is devised in view of such problems of the related art and has an object of a method of handling gas hydrate allowing to improve the filling factor of gas hydrate, the safety during the transport and storage, and the easiness of handling.

In order to solve the aforementioned problems, the method of handling gas hydrate of the present invention comprises pelletizing a powdery gas 2 hydrate by compression-molding by a pelletizing device and thereafter loading the palletized gas hydrate into a ship or a storage tank in a storage facility and is characterized in that two or more kinds of palletized gas hydrate with different sizes are mixed and loaded into a ship or a storage tank in a storage facility.

Here, it is preferable to wet the gas hydrate previously by spraying solution over it before pelletizing the powdery gas hydrate.

It is also preferable that the ratio of diameter of two or more kinds of pelletized gas hydrate with different sizes is 1.5 to BRIEF DESCRIPTION OF THE DRAWINGS Fig. 1 illustrates a method of handling gas hydrate according to the present invention; Fig. 2 is an enlarged front view including a partial section of a pelletizing device; Fig. 3 is a cross-section of a carrying device; Fig. 4 illustrates a method of producing gas hydrate; Fig. 5 illustrates a case where two kinds of gas hydrate in large and small size are mixed; Fig. 6 illustrates a case of loading into a tank lorry; Fig. 7 is a section of a carrying ship; Fig. 8 is a section showing another example of the carrying ship.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT Fig. 1 illustrates a method of handling gas hydrate according to the present invention; however, before describing this method, a method for producing methane hydrate artificially shall be described briefly.

The methane hydrate can be produced by dry process and wet process and in case of producing by the wet process, it shall be produced, for instance, by a device shown in Fig. 4.

This device is composed of a cylindrical vessel 101, and the temperature in the vessel 101 is kept 1 to 10 C and the pressure is kept 30 to 100 atmospheric pressure. Water or antifreeze solution sprayed from a spray means 112 is compounded with natural gas (methane) supplied from a supply pipe 108 in a reactor 101A to produce powdery methane hydrate a, which drops on the surface layer of the water or antifreeze solution in a reservoir 101B. The powdery methane hydrate a floating on the surface layer of the water or antifreeze solution is sequentially collected towards a drain port 107, and discharged from the drain port 107. The powdery methane hydrate a discharged from the drain port 107 is stored in a not shown storage tank, after removing excessive water or antifreeze solution.

In Fig.4, 103 indicates a cooling jacket, 106 a coolant supply line, 102 a coolant exit line, 104 a water or antifreeze solution drain line, 105 a water or antifreeze solution circulation line, 110 a circulation pump, 111 a water or antifreeze solution drain line, and 113 a water or antifreeze solution supply line.

Next, the method of handling gas hydrate according to the present invention shall be described by using Fig. 1.

In Fig. 1, 1 indicates a storage tank for storing the powdery methane hydrate a, 2 a horizontal screw conveyer installed at the bottom of the storage tank 1. The screw conveyer 2 is composed of a cylindrical body 3, and a screw shaft 4 positively driven by an electric motor 5. The body 3 has a duct 6 directed downward to the bottom face of the end of the body 3.

A pelletizer (a palletizing device) 7 composed of two rollers 8a, 8b is installed just under a duct 6. The roller 8a rotates clockwise in the figure, while the roller 8b rotates counterclockwise, in synchronization with the roller 8a.

As shown in Fig. 2, outer peripheral faces of the rollers 8a, 8b are, respectively, provided with semispherical recesses 9 with a fixed interval in the circumferential direction. The shape of the recess 9 is not limited to the semisphere, for instance, semi-oval sphere, semi-cylinder or other desired shape may be adopted. Besides, the size thereof is also set to an arbitrary dimension.

It should be appreciated that the pelletizing device is not limited to the aforementioned roller system. The other systems may be used.

Referring again to Fig. 1, a water jet nozzle 10 is installed between the duct 6 and the pelletizer 7. Moreover, a horizontal carrying device 11 is installed just below the pelletizer 7. The carrying device 11 is composed of a belt conveyer 12 and a box-shaped body 13. The body 13 has a hopper 14 just under the pelletizer 7 and a duct 15 directed downward to the bottom face of the end of the body 13. In addition, the body 13 of the carrying device 11 is provided with a water jet nozzle 10 a downwards the hopper 14. The end of the water jet nozzle 10 a is directed to the upper face of the belt conveyer 12.

Furthermore, the aforementioned body 13 has a cooling jacket (not shown) on the outside thereof, for overcooling an object carried by the belt conveyer 12. Besides, the belt conveyer 12 is held by 2 to 3 rollers 16 per point, in a way to keep a dynamic repose angle (refer to Fig. 3).

It should be appreciated that the interval between the duct 6 of the screw conveyer 2 and the hopper 14 of the carrying device 11 is sealed with a not shown cover or the like, for preventing vaporized gas from leaking outside.

Next, a case of loading methane hydrate (NGH) into a carrying ship (bulk carrier) and transporting shall be described.

As shown in Fig. 1, when the duct 15 of the carrying device 11 is inserted into a loading port 32 of a hold (cargo tank) 31 of the bulk carrier 30 and, thereafter, an electric motor 5 of the screw conveyer 2 is driven, and the powdery methane hydrate a in the storage tank 1 is supplied to the pelletizer 7 by the horizontal screw conveyer 2.

The powdery methane hydrate a supplied to the pelletizer 7 is compression-molded into a spherical (ball shape) methane hydrate b by two rollers 8a, 8b having the semispherical recesses 9 on the outer peripheral surface. If the powdery methane hydrate a is not wet enough, water c is sprayed from the water jet nozzle 10 to wet the powdery methane hydrate a.

Accordingly, the consistency of the powdery methane hydrate a becomes firmer and breaks hardly even when it is dropped.

The ball shape methane hydrate (called the methane hydrate ball, hereinafter) b. is supplied from the pelletizer 7 onto the belt conveyer 12 of the carrying device 11 and, for instance, in case of loading into the hold (cargo tank) 31 of a large carrying ship (bulk carrier 30), the water c is sprayed from the water jet nozzle 10 a installed on the body 13 of the carrying device 11 to the methane hydrate ball b on the belt conveyer 12 so as to overcool it to -5 "C to 20 cC.

Then, the outer surface of the methane hydrate ball b is coated with an ice film (capsule), the strength of the methane hydrate ball b is further increased.

Hence, the methane hydrate ball b breaks hardly even when it is loaded into the hold (cargo tank) 31 of the large carrying ship (bulk carrier 30), and it seldom collapses by its own weight even if it is loaded by a large quantity.

The powdery methane hydrate a has a self-preservation effect as it has a crystalline structure where gas molecules are contained one by one in the cage formed with water molecules. There is an advantage that the self-preservation effect will be further improved, when the outer surface of the methane hydrate ball b is coated with the ice film (capsule), as mentioned above.

The methane hydrate ball b coated with the ice film is loaded into the hold (cargo tank) 31 of the bulk carrier 30. The inside of the hold (cargo tank) 31 is kept at a temperature (for instance, -5 C to -30 lower than the temperature where the methane hydrate ball b decomposes.

Those shown in Fig. 7 or Fig. 8 are used preferably as bulk carrier The bulk carrier 30 shown in Fig. 7 has a loading conveyer 33 and an unloading conveyer 35. It also has a baffle plate 38 which functions also as hatch for loading the gas hydrate ball b evenly. This baffle plate 38 which functions also as hatch can move vertically. In the figure, 31 indicates the hold, 34 a gate, 36 a ballast tank, 37 a cover and 39 an insulation material.

On the other hand, the bulk ship 30 of Fig. 8 is provided with a handling machine 50 that can move towards bow and stern of the ship. 31 indicates the hold, 37 the cover and 39 the insulation material.

In the above-mentioned, a case where the methane hydrate ball b is loaded into the hold (cargo tank) 31 by the belt conveyer type carrying device 11, a pneumatic transport method may be adopted as a carrying device, in case of loading directly from the pelletizer 7 into the hold (cargo tank) 31.

Besides, in case of loading methane hydrate ball b into a tank lorry also, it is loaded into a tank 41 of the tank lorry 40 by means of the belt conveyer type carrying device 11, similarly to the ship (refer to Fig. Further, in case of storing methane hydrate ball b in a storage facility also, it is transported by means of the belt conveyer type carrying device 11, similarly to the tank lorry.

The size of methane hydrate ball b is several centimeters to tens of centimeters and may, sometimes, be several meters. The bigger is the size, the smaller is the surface area ratio, and as less bridge is generated, the filling factor becomes higher. The filling factor of the methane hydrate ball b pelletized as mentioned above is about 60%. Since the filling factor of the powdery gas hydrate is 40%, it can be understood that the filling factor is largely improved by pelletizing the gas hydrate.

Fig. 5 shows a method for further increasing the filling factor of the methane hydrate ball. Namely, it is a method for combining a pelletizer 7' for producing a methane hydrate ball b' of larger grain diameter and a pelletizer 7" for producing a methane hydrate ball b" of smaller grain diameter. This method intends to fill a space filling factor) created by the large methane hydrate ball b' with the small methane hydrate ball The adoption of this method further increases the filling factor of the gas hydrate to about Here, what is important is to choose conveniently the ratio of the diameter of the large methane hydrate ball b' and the diameter of the small methane hydrate ball b"(the diameter ratio the diameter of the large methane hydrate ball/ the diameter of the small methane hydrate ball). According to an experiment, this diameter ratio is preferably within a range of 1.5 to 30, and more preferably within a range of 5 to In case of diameter ratio less than 1.5, the filling factor does not increase, because the small methane hydrate ball b" does not enter the space created by the large methane hydrate ball b'.

On the other hand, if the diameter ratio exceeds 30, the small methane hydrate balls b" increase, and creates bridges easily; therefore the filling factor does not increase. It should be appreciated that the diameter of the methane hydrate ball b other than the sphere such as oval sphere corresponds to the diameter of the intercontact sphere.

The adoption of this method reduces the size of the hold (cargo tank) or the tank of the tank lorry 1/2 or less compared to the case of loading the powdery methane hydrate a. The number of kind of the methane hydrate ball is preferably 2 or more and, for instance, if methane hydrate balls are prepared in three sizes (large, middle, small), it becomes possible to further increase the filling factor.

As mentioned above, if the present invention is adopted, the temperature state lower than the decomposition temperature of the methane hydrate ball is held, the methane hydrate balls maintains the sintered state each other, because the contact surface between adjacent methane hydrate balls is small.

Consequently, the assembly of the methane hydrate balls to be transported can be crushed easily, and unloaded by a glove or the like.

Though, in the above-mentioned description, the case of loading the methane hydrate ball in the hold or the tank lorry, the present invention can be also applied to a case of storing the methane hydrate ball in a tank of a storage facility.

Moreover, the present invention can be applied to the pelletizing, handling, and storage and carrying of gas hydrate other than methane, such as propane, carbon dioxide.

As mentioned above, the present invention can make a gas hydrate into solidified one with a homogenous shape and quality by industrially palletizing the powdery gas hydrate. Consequently, the flow ability of the gas hydrate increases dramatically, facilitating the handling and transport.

Besides, according to the present invention, by industrially palletizing the powdery gas hydrate, the filling factor is largely increased compared to the powdery gas hydrate and economical efficiency in its carriage and storage can be secured.

Further, the gas hydrate does not vaporizes suddenly even if the temperature control becomes deficient, because it has the crystalline structure where gas molecules are contained one by one in the cage formed with water molecules, making the safety higher than the LNG. Furthermore, as it evaporates slowly, it is more appropriate for long time storage than the LNG.

In addition, ball-like gas hydrates maintains the sintered state, because the contact surface area is small for the ball gas hydrate. Consequently, the assembly of methane hydrate balls agglomerated during the transport or the storage can be crushed easily, and unloaded easily, for instance, by a glove or the like.

Besides, according to the present invention, as the surface of the methane hydrate ball is coated with th6 ice film (capsule), created by spraying water over the ball gas hydrate and overcooling, the strength of the methane hydrate ball is further increased and, thus, it hardly breaks. Consequently, it can be transported or stored by a large quantity.

Finally, according to the present invention, as two or more kinds of balllike gas hydrate with different sizes are mixed and loaded, the filling factor can further be increased compared to a case where only ball gas hydrates of the same diameter are loaded.

The present invention having the aforementioned excellent effects can be used extremely effectively for pelletizing, handling and transporting gas hydrate.

Claims (4)

1. A method of handling gas hydrate, comprising pelletizing powdery gas hydrate by compression-molding by a pelletizing device and thereafter loading the pelletized gas hydrate into a ship or in a storage tank in a storage facility, characterized in that two or more kinds of pelletized gas hydrate different in size are mixed and loaded into the ship or in the storage tank in the storage facility.

2. The method of handling gas hydrate of claim 1, characterized in that said powedry gas hydrate is humidified by spraying liquid over it, before palletizing said powedry gas hydrate.

3. The method of handling gas hydrate of claim 1, charcterized in that the solid gas hydrate is humidified by spraying liquid over it, and thereafter overcooled.

4. The method of handling gas hydrate of claim 1, characterized in that the diameter ratio of two or more kinds of the pelletized gas hydrate different in size is set to 1.5 to A method of handling gas hydrate, substantially as described with reference to the drawings. DATED this 2 4 th day of January, 2006 Mitsui Engineering Shipping Co. by DAVIES COLLISON CAVE Patent Attorneys for the applicant