JP2005255075A - Transport ship and method for transporting natural gas hydrate - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a transport ship for transporting a natural gas hydrate with excellent transport efficiency capable of transporting the natural gas hydrate in the state of enclosing natural gas by a rather simple structure, and to provide a method for transporting the natural gas hydrate. <P>SOLUTION: In this transport ship, a closed storage part 10 is formed in a heat insulated structure so that an inner wall 13 and an outer wall 14 hold a heat insulator 15, and a heat inputted into the closed storage part 10 can be kept in balance with a heat outputted from the closed storage part 10. The initial temperature of the closed storage part 10 is set to approximately -20°C, the pellets 25 of the natural gas hydrate at the temperature of -20°C is filled into the closed storage part, and the natural gas hydrate is carried while keeping its temperature at -30 to -10°C (optimum temperature range) where the decomposing rate of the natural gas hydrate is minimized. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to a natural gas hydrate transport ship capable of efficiently transporting natural gas hydrate with a relatively simple structure and a transport method thereof.

  Normally, when transporting a refrigerated or refrigerated transported object on a ship, the transported object is stored in a storage part of a heat insulating structure, and the inside of the storage part is forcibly cooled and transported by a refrigeration system .

  In liquefied gas bulk carriers (LNG transport ships, etc.), a method is generally adopted in which cargo warehouses are pre-cooled and forced cooling is not performed during transportation.

However, when forced cooling is performed, a refrigeration apparatus is required, and in addition, the capacity of the storage unit is reduced by installing the refrigeration apparatus.
In addition, a sufficient heat insulation system is required when forced cooling is not performed at all by precooling.
That is, problems such as capital investment, an increase in running cost, and a decrease in transportation efficiency occur.

  By the way, in the transportation of natural gas hydrate, the transportation temperature is important. It is known that natural gas hydrate releases the contained gas (decomposition of gas hydrate) under atmospheric pressure, and the release rate (decomposition rate of gas hydrate) depends on temperature. That is, at about minus 10 ° C. or lower, the gas hydrate decomposition rate is slow due to the so-called self-preserving effect, so that gas can be stored for a long time. Therefore, it can be said that if the natural gas hydrate is transported while being held at a temperature at which the decomposition rate of the natural gas hydrate is the slowest, the natural gas hydrate can be transported in a state in which the natural gas is contained, so that it can be said that the transport efficiency is good.

  Regarding the transportation of natural gas hydrate, for example, it has been proposed to transport natural gas hydrate while maintaining it in a temperature range of minus 30 ° C. or more and 0 ° C. or less with a refrigeration apparatus (Patent Document 1). In this proposal, the temperature range is set as the condition with the least energy loss by comparing the energy of the gas released by natural decomposition of the natural gas hydrate with the energy required to freeze the natural gas hydrate. ing. The natural gas hydrate is forcibly cooled by a refrigeration apparatus and is kept within this temperature range.

However, this transportation method also requires a forced refrigeration system to maintain the natural gas hydrate at the set temperature, which increases capital investment, running costs, and reduces the transportation efficiency due to the reduction of the storage unit due to the installation of the refrigeration system Problem arises. In particular, in the case of a transport ship having a huge accommodating portion, the refrigeration apparatus becomes large-scale, and these influences become large.
For example, in a large transport ship, it is estimated that the refrigeration device occupies about 10% of the hull, and it is considered that the storage capacity must be greatly reduced.
JP2003-343798

The present invention has been made to solve the above-mentioned problems of the prior art. That is, it is an object of the present invention to provide a natural gas hydrate transport ship having a relatively simple structure, in which natural gas hydrate can be transported in a state where natural gas is embedded, that is, a transport method thereof.

  The natural gas hydrate transport ship according to claim 1 has an opening for charging and discharging the natural gas hydrate on the deck, and a sealed housing portion having a heat insulating structure for housing the natural gas hydrate, A natural gas hydrate transport ship having a cover portion that seals the opening, wherein the thermal decomposition structure of the natural gas hydrate accommodated in the hermetic housing portion has a minimum decomposition rate of minus 30 ° C. or more and minus 10 It was set to keep the temperature below ℃.

  The natural gas hydrate transport ship according to claim 2 is the natural gas hydrate transport ship according to claim 1, wherein the natural gas hydrate transport ship is made into small particles.

  The small particle here means a particle having a particle size of 10 to 100 mm, preferably 20 to 50 mm, and means a so-called pellet. The shape is not limited to a spherical shape, and may be a distorted spherical shape or the like, and generally includes particles of this size.

  The natural gas hydrate transport ship according to claim 3 is the natural gas hydrate transport ship according to claim 1 or claim 2, wherein the natural gas hydrate transport ship according to claim 1 or 2 is decomposed and released. It is equipped with a gas storage tank for storing

  The natural gas hydrate transport ship according to claim 4 is the natural gas hydrate transport ship according to any one of claims 1 to 3, wherein the natural gas hydrate transport ship is forced to be contained in a sealed housing portion. It has a decomposing means for decomposing automatically.

  The natural gas hydrate transport ship according to claim 5 is the natural gas hydrate transport ship according to claim 4, in which the gas is circulated through the hermetic housing portion as the decomposition means.

  The method for transporting a natural gas hydrate according to claim 6 has an opening for charging and discharging the natural gas hydrate on the deck, and a sealed housing portion having a heat insulating structure for housing the natural gas hydrate, Natural gas hydrate is accommodated in the hermetic housing portion of a natural gas hydrate transport ship provided with a cover portion that seals the opening, and the decomposition rate of natural gas hydrate is minimized to minus 30 ° C. or more and minus 10 ° C. It is transported while maintaining the following temperature.

  It is known that natural gas hydrates have different rates (decomposition rate) of releasing the contained gas depending on temperature under atmospheric pressure, and the decomposition rate is extremely slow when the temperature is about minus 10 ° C. or less. This is the so-called self-preserving effect, where gas hydrate dissolves due to decompression and ambient heat, and decomposition begins, gas is released and water covers the surface, but the water forms an ice film due to the endothermic effect of decomposition. It is said to cover natural gas hydrate and confine natural gas for thermal protection.

The present inventors left natural gas hydrate pellets having a particle diameter of 20 mm under atmospheric pressure in various atmospheric temperatures, measured the decomposition rate of natural gas hydrate, and obtained the results shown in FIG. That is, it has been found that the decomposition rate of natural gas hydrate has a peculiar tendency, and the decomposition rate is minimized in the temperature range centered at minus 20 ° C. (253 K), and has the slowest decomposition rate characteristic.
Here, the decomposition rate is the percentage of the amount of gas released per unit time with respect to the amount of gas initially contained in the natural gas hydrate.

  From this result, in order to store and transport the natural gas hydrate most efficiently, the natural gas hydrate should be minus 30 ° C. or more and minus 10 ° C. or less (hereinafter, the optimum temperature range), preferably minus 25 ° C. or more and minus 15 ° C. or less. Further, it has been found that it is necessary to maintain at −20 ° C. preferably.

  However, if the hermetic housing portion is cooled by a refrigeration apparatus in order to keep the natural gas hydrate at about minus 20 ° C., the same problem as in the prior art occurs.

  Therefore, the present inventors have endothermic action when natural gas hydrate is decomposed, and even if the natural gas hydrate is maintained at minus 20 ° C. by controlling the temperature under atmospheric pressure, the endothermic action is decomposed. We focused on the point where this happens.

  In other words, by applying a heat insulation structure that transmits the same heat as the heat absorption generated by the decomposition of the natural gas hydrate stored in the hermetic housing part to the hermetic housing part, the heat input to and output from the hermetic housing part is balanced and stored in the hermetic housing part. The gas hydrate can be kept at a constant temperature.

  Therefore, if the heat insulation structure of the sealed housing part is set appropriately, the natural gas hydrate can be kept in the optimum temperature range by the endotherm due to the decomposition of the natural gas hydrate without using a refrigeration system. The natural gas can be transported in an embedded state, and efficient transport becomes possible.

  In addition, even if a refrigeration system is necessary to pre-cool the sealed housing and finely adjust the temperature, an extremely small-scale refrigeration system is sufficient, so that conventional problems such as capital investment, increased running costs, and reduction of the storage volume are eliminated. Can greatly improve. That is, the following effects can be obtained by the present invention.

  A natural gas hydride having an opening for charging and discharging the natural gas hydrate on the deck, a sealed housing portion having a heat insulating structure for housing the natural gas hydrate, and a cover portion for sealing the opening. The heat insulation structure of the rate transport ship is set so as to maintain a temperature of minus 30 ° C. or more and minus 10 ° C. or less at which the decomposition rate of the natural gas hydrate accommodated in the hermetic accommodation portion is minimized, Contain and transport natural gas hydrate.

  As a result, the natural gas hydrate contained in the hermetic housing part absorbs heat by decomposition, while the heat insulating structure of the hermetic housing part suppresses heat input from outside and allows heat input corresponding to this heat absorption. Therefore, the stored natural gas hydrate can be maintained at minus 30 ° C. or more and minus 10 ° C. or less. Natural gas hydrate has the slowest decomposition rate in this optimum temperature range. That is, natural gas hydrate can be efficiently transported without cooling with a forced refrigeration system.

  Moreover, even if the refrigeration apparatus is used for pre-cooling the hermetic housing portion or finely adjusting the temperature, a small-scale refrigeration apparatus is sufficient. In addition, the heat insulation structure of the sealed housing part only needs to secure a heat insulation property that balances the heat absorption due to the decomposition of natural gas hydrate and the heat input from the outside, and it is not necessary to have a complete heat insulation property. This is advantageous from the viewpoint of cost increase and reduction of the storage volume.

  When natural gas hydrate is made into small granules (pellets), the decomposition rate can be made slower than in other states such as powders. According to the inventors' experiments, it was found that the decomposition speed of the small particles (pellets) is slower than that of the powder. From this result, when natural gas hydrate is pelletized, the amount of gas released by decomposition of natural gas hydrate during transportation is reduced, and transportation efficiency is improved.

  Small particles with different particle diameters can be mixed and accommodated. In this case, the small particles enter between the small particles, so that the filling rate can be increased, leading to improved transport efficiency. .

  In addition, by providing the transport ship with a gas storage tank, it is possible to store the gas released by the decomposition of the natural gas hydrate stored in the hermetic housing portion during transportation. Natural gas hydrate decomposes a little and always releases gas. If this gas is left untreated, resources are wasted. Since the stored gas can be utilized as a resource such as fuel, the natural gas hydrate transportation system as a whole can effectively utilize the resource.

In addition, by having a decomposition means for forcibly decomposing natural gas hydrate, if it falls outside the optimum temperature range with the best transport efficiency, the natural gas hydrate is forcibly decomposed to generate endotherm. Natural gas hydrate can be matched to the optimum temperature range.
As a result, the amount of decomposition of the natural gas hydrate increases temporarily, but the amount of gas that is finally decomposed and released can be reduced, and efficient transportation becomes possible.

  If gas is circulated through the hermetic housing portion and the natural gas hydrate is forcibly decomposed, a simple structure can be used, so that an increase in cost burden and running cost can be suppressed. For example, a circulation pipe can be passed inside and outside the sealed housing and the atmosphere can be circulated in the circulation pipe, so that the natural gas hydrate can be maintained in the optimum temperature range with a simple structure. Efficient transportation is possible.

Hereinafter, an embodiment of a natural gas hydrate transport ship according to the present invention will be described with reference to FIGS. In the following, the transportation method according to the present invention will also be described. FIG. 2 shows the entire transport ship, in which four hermetic accommodating portions 10 for accommodating natural gas hydrate small particles are arranged side by side in the longitudinal direction. An opening 11 is provided in the upper part of each hermetic housing part 10, and the hermetic housing part 10 is in a hermetically sealed state by closing a cover part 12 that seals the opening 11. The natural gas hydrate is charged and discharged from the opening 11 by the cargo handling device 40 disposed above the cover 12.
The arrangement position of the cargo handling device 40 is not limited to that shown in FIG. 2. The entire deck 21 is sealed with the cover portion 12, and the cargo handling device 40 is arranged below the cover portion 12, that is, inside the sealed housing portion 10. It is also possible to perform.

  As shown in FIG. 1, the hermetic housing portion 10 has a heat insulating structure in which an inner wall 13 and an outer wall 14 sandwich a heat insulating material 15. In particular, it is not limited to this heat insulation structure, and other structures may be used as long as the hermetic housing portion 10 can be insulated. A space is formed between the outer wall 14 and the hull outer plate 20.

  Although hard foam polyurethane, wood, etc. are used as the heat insulating material 15, it is not necessary to specifically limit to these heat insulating materials 15, and the general heat insulating material 15 can be used.

  The specifications of the material, thickness, heat insulation structure, etc. of the heat insulating material 15 take into consideration the size and shape of the hermetic housing portion 10, the temperature conditions of the transportation route, etc., and when natural gas hydrate of about minus 20 ° C. is accommodated, The amount of heat absorbed by the decomposition of the natural gas hydrate and the amount of heat entering and exiting the hermetic housing portion 10 by this heat insulating structure are taken into consideration. That is, by utilizing the decomposition rate characteristic of natural gas hydrate as shown in FIG. 3, the heat input to the sealed housing portion 10 and the heat output from the sealed housing portion 10 are balanced to accommodate the stored natural gas hydrate. The heat insulation structure of the hermetic housing portion 10 is set so that the rate is −30 ° C. or more and −10 ° C. or less, and the decomposition rate of the natural gas hydrate is minimized and slowed down. By adopting such a heat insulating structure, it becomes possible to maintain the stored natural gas hydrate at a constant temperature without a forced refrigeration device, and minus 30 ° C. or more and minus 10 ° C. or less (optimum transportation efficiency) It is also easy to keep the temperature within the optimum temperature range.

  In addition, with such a heat insulation structure, even if the stored natural gas hydrate is outside the optimum temperature range, only a slight temperature adjustment is required, and even if a refrigeration unit is required, a small-scale one is sufficient, so capital investment, Impacts such as an increase in running costs and a reduction in storage capacity are small. In trial calculations, even if a refrigeration unit is required, it is considered that only a small one occupying 1% or less of the hull is sufficient.

  Further, the heat insulating material 15 is not required to be completely heat-insulating, and it is sufficient that the heat input to the sealed housing portion 10 and the heat output are balanced, so the cost burden is small and the housing volume is not reduced so much.

  Since the sealed housing portions 10 are independent of each other, natural gas hydrates with different specifications can be housed in each sealed housing portion 10 and can be housed under different conditions.

  A metal distribution pipe 18 is installed on the bottom surface of the hermetic housing portion 10 so that a gas such as the atmosphere can flow through the distribution pipe 18. The position, size, and the like of the distribution pipe 18 are determined as appropriate. For example, the distribution pipe 18 may be provided on the side surface or may pass through the central portion of the hermetic housing portion 10. Further, the distribution pipe 18 can be omitted.

  It is desirable that the cover 12 also has a heat insulating structure like the hermetic housing part 10 or improves the heat insulating property of the hermetic housing part 10 using a material having low thermal conductivity.

  Further, as shown in FIG. 2, a gas storage tank 30 is provided on the deck 21 for storing the gas released by the decomposition of the natural gas hydrate.

Next, how to use this transport ship will be described.
First, the natural gas hydrate pellets 25 are charged into the sealed housing 10 from the opening 11 by the cargo handling device 40, and when the filling is completed, the cover is closed and the sealed housing 10 is in a sealed state. Then, the natural gas hydrate pellets 25 are sequentially filled in another hermetic housing portion 10.

Since the hermetic housing part 10 has a heat insulating structure as described above, the initial temperature of the hermetic housing part 10 when natural gas hydrate is filled is about minus 20 ° C., and natural gas hydrate pellets of about minus 20 ° C. 25 is preferably filled.
If the sealed container 10 is about minus 20 ° C. from the beginning of filling, it is relatively easy to maintain the optimum temperature range during transportation.

  Using natural gas hydrate as pellets 25 has a slower decomposition rate than other states such as powders, and natural gas hydrate can be transported in a state of containing natural gas, that is, it can be transported efficiently. Because.

  When the initial temperature of the hermetic housing part 10 deviates more than minus 20 ° C., it can be maintained in the optimum temperature range by forced pre-cooling or the like.

  Also, for example, when the initial temperature of the hermetic housing 10 is 0 ° C., the natural gas hydrate pellet 25 of about −30 ° C. is charged without pre-cooling or maintaining the temperature using a refrigeration apparatus, The initial temperature can be adjusted to about minus 20 ° C.

  The natural gas hydrate pellets 25 accommodated in the hermetic housing 10 are transported to their destinations over several weeks, for example, in a hermetically sealed state. During transportation, the temperature of the outside air changes temporally, regionally, and seasonally, and the natural gas hydrate pellets 25 contained therein are also affected by temperature.

When the natural gas hydrate pellet 25 deviates from the optimum temperature range, the natural gas hydrate contained therein is decomposed by circulating the outside air through the distribution pipe 18 to generate heat and maintain the optimum temperature range. Control to do.
Thus, the natural gas hydrate accommodated can be decomposed | disassembled by distribute | circulating gas through the airtight accommodating part 10 indirectly using the distribution | circulation pipe 18. FIG.

  Therefore, it is desirable to provide a plurality of temperature sensors 17 in the hermetic housing portion 10 and maintain an optimum temperature range by a signal from the temperature sensor 17.

  If only the air is allowed to flow through the flow pipe, a flow device such as a pump may be provided, and a refrigeration device is not necessary. Even the pump can be omitted.

  The stored natural gas hydrate decomposes at any temperature, so that the gas released by the decomposition is stored in the gas storage tank 30 provided on the deck 21 shown in FIG. Yes. The stored gas is used as a resource such as fuel, and natural gas hydrate is used to the maximum extent. The size, shape, location, etc. of the gas storage tank 30 are determined as appropriate.

  When the transport ship arrives at the destination, the pellets 25 of natural gas hydrate are discharged in the procedure opposite to the filling.

  Although this embodiment is for a transport ship, the natural gas hydrate is provided with an airtight structure containing an opening and containing a natural gas hydrate, and a cover portion for sealing the opening. As a transport vehicle, if the natural gas hydrate is transported while maintaining a temperature of −30 ° C. or higher and −10 ° C. or lower by heat absorption caused by decomposition of the natural gas hydrate stored in the hermetic housing portion, the transport efficiency is improved. A good natural gas hydrate transport vehicle.

  Similarly, a natural gas hydrate storage tank having an opening and a sealed housing portion having a heat insulating structure for containing the natural gas hydrate and a cover portion for sealing the opening portion is provided in the sealed housing portion. If the natural gas hydrate is kept at a temperature of minus 30 ° C. or more and minus 10 ° C. or less by endotherm generated by decomposition of the stored natural gas hydrate, a storage tank of natural gas hydrate with high storage efficiency can be obtained.

It is a longitudinal cross-sectional view with respect to the hull front direction which shows the internal structure of the transport ship of embodiment of this invention (pellet filling state). It is a partially cutaway perspective view showing an overall outline of a transport ship according to an embodiment of the present invention. It is a figure which shows the change of the decomposition rate with the temperature of the pellet of a natural gas hydrate.

Explanation of symbols

10 Sealing housing 11 Opening 12 Cover
13 Inner wall 14 Outer wall 15 Thermal insulation
17 Temperature sensor 18 Distribution pipe
20 Hull outer plate 21 Deck 25 Natural gas hydrate pellets (small particles)
30 Gas storage tank 40 Handling equipment

Claims (6)

A sealed housing portion having a heat insulating structure for housing the natural gas hydrate, having an opening for charging and discharging the natural gas hydrate on the deck;
A cover for sealing the opening;
A natural gas hydrate transport ship equipped with
The heat insulation structure is a natural gas hydrate transport ship set so as to maintain a temperature of minus 30 ° C. or more and minus 10 ° C. or less at which the decomposition rate of the natural gas hydrate accommodated in the hermetic accommodating portion is minimized. The natural gas hydrate transport ship according to claim 1, wherein the natural gas hydrate is a small particle. The natural gas hydrate transport ship according to claim 1 or 2, further comprising a gas storage tank for storing a gas released by decomposition and release of the natural gas hydrate stored in the hermetic housing portion. The natural gas hydrate transport ship according to any one of claims 1 to 3, further comprising a decomposing means for forcibly decomposing the natural gas hydrate accommodated in the hermetic accommodating portion. The natural gas hydrate transport ship according to claim 4, wherein the decomposing means circulates the gas in the hermetic housing portion. A sealed housing portion having a heat insulating structure for housing the natural gas hydrate, having an opening for charging and discharging the natural gas hydrate on the deck;
A cover for sealing the opening;
A natural gas hydrate transport ship equipped with a natural gas hydrate is accommodated in the hermetic container, and the natural gas hydrate is transported in such a manner that the decomposition rate of the natural gas hydrate is kept at a temperature of minus 30 ° C. or more and minus 10 ° C. or less. How to transport natural gas hydrate.

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