JP4554322B2 - Gas hydrate pellet storage method - Google Patents

Description

  The present invention relates to a gas hydrate pellet storage method.

  At present, as a method of storing and transporting natural gas mainly composed of hydrocarbons such as methane, after collecting natural gas from a gas field, it is cooled to a liquefaction temperature and stored in a liquefied natural gas (LNG) state. The method of transport is common.

  However, for example, in the case of methane, which is the main component of LNG, extremely low temperature conditions such as −162 ° C. are necessary for liquefaction, and in order to store and transport while maintaining these conditions, a dedicated storage device or LNG A dedicated means of transportation such as a transport ship is required.

  Manufacturing, maintenance, and management of such devices and the like require very high costs, and therefore, low-cost storage and transportation methods that replace the above methods have been intensively studied.

  As a result of such research, natural gas is hydrated with water to produce a crystalline hydrate, that is, natural gas hydrate, and this gas hydrate is molded into pellets for storage or transportation. In recent years, it has been particularly promising.

  This method does not require cryogenic conditions as in the case of handling LNG. Moreover, since it is in the form of pellets, its handling is relatively easy.

  For this reason, a slightly improved version of the existing refrigeration apparatus or existing container ship can be used as a storage apparatus or a transportation means.

  Therefore, it is expected that the cost can be significantly reduced as compared with the case of handling LNG.

This natural gas hydrate is a kind of inclusion compound, and is a molecule constituting each component of natural gas, that is, methane (CH ₄ CH ₄₎ in a cubic cage inclusion lattice formed by a plurality of water molecules. ), Ethane (C ₂ H ₆ ), propane (C ₃ H ₈ ) and the like are included and included in the crystal structure.

The intermolecular distance between the natural gas constituent molecules included in the cubic cage inclusion lattice is shorter than the intermolecular distance in the gas cylinder when the natural gas is filled with high pressure. This means that natural gas is produced in close-packed crystals. For example, under conditions where hydrates of methane are stable, that is, at −80 ° C. and atmospheric pressure (1 kg / cm ² ). The volume can be about 1/170 compared to the gas state.

  Thus, natural gas hydrate can be produced and stably stored under conditions of temperature and pressure that can be obtained relatively easily.

In the above method, the natural gas collected from the gas field is removed from the acidic gas such as carbon dioxide (CO ₂ ) and hydrogen sulfide (H ₂ S) in the acidic gas removal step, and once stored in the gas storage unit, Thereafter, gas hydrate is formed in the gas hydrate generation step.

That is, natural gas and water are introduced into a gas hydrate generator and reacted at high pressure and low temperature (for example, 3 to 8 MPa, 0 to 7 ° C.), and high purity gas hydrate with little moisture is cooled by a cooling device. It is cooled to a predetermined temperature (for example, −10 ° C. to −30 ° C.), and then the gas hydrate is depressurized to atmospheric pressure (0.1 MPa) by alternately opening and closing two valves of the depressurization device, Further, the gas hydrate pellets are molded into pellets at atmospheric pressure, and the gas hydrate pellets are placed in the tank under atmospheric pressure (0.1 MPa) while maintaining the above cooling temperature (−10 ° C. to −30 ° C.). Storage has been proposed (see, for example, Patent Document 1).
Japanese Patent Laying-Open No. 2003-105362 (page 7-10, FIG. 2)

  However, during storage, for example, due to a rise in the temperature of the storage tank or an extension of the storage period, the raw material gas in the gas hydrate pellets is released, and the amount of gas contained in the gas hydrate pellets is reduced to about 30 to 50%. is there.

  In this case, in order to store and transport in a high gas storage rate again, the gas hydrate pellets are completely melted and returned to water, and reacted with the raw material gas again to produce gas hydrate pellets by the above method. There is a need to.

  The present invention has been made to solve such a problem, and its object is to regenerate gas hydrate pellets that have been decomposed during storage to reduce the amount of stored gas, thereby regenerating high quality. The gas hydrate pellets are to be transported or stored.

  In order to solve the above problems, the present invention is configured as follows.

  In the gas hydrate storage method according to the first aspect of the present invention, a gas hydrate is produced by reacting a raw material gas and water, the gas hydrate is molded into pellets, and the gas hydrate pellets are sub-freezing. In the gas hydrate pellet storage method of storing in a storage tank at atmospheric pressure, gas hydrate pellets having a reduced gas storage rate during storage are transferred to a regenerator, and a high-pressure raw material gas is supplied to the regenerator to supply gas. A gas hydrate pellet storage method characterized by refilling hydrate pellets.

  The gas hydrate storage method according to the invention of claim 2 is characterized in that the raw material gas is refilled into gas hydrate pellets under conditions of 3 to 5 MPa and -10 ° C to 5 ° C. Item 2. A gas hydrate pellet storage method according to Item 1.

  A gas hydrate storage method according to a third aspect of the invention is characterized in that the gas hydrate pellets refilled with the raw material gas are stored and transported at 0.1 MPa, −20 ° C. to −30 ° C. The gas hydrate pellet storage method according to claim 1.

  As described above, the invention according to claim 1 reacts the raw material gas with water to generate gas hydrate, and the gas hydrate is molded into pellets. In a gas hydrate pellet storage method for storing in a storage tank under atmospheric pressure, gas hydrate pellets having a reduced gas storage rate during storage are transferred to a regenerator, and a gas hydrate is supplied by supplying high-pressure raw material gas in the regenerator. Since the pellets are refilled, gas hydrate pellets are produced from the raw material gas and water, cooled, depressurized and taken out to the atmospheric pressure, and again through the step of pelletizing under atmospheric pressure, 80 to 90% again. High quality gas hydrate pellets with encapsulated gas content can be provided for transport or storage.

  Moreover, when the gas hydrate pellet from which the raw material gas has escaped is regenerated, the stability of the hydrate pellet is significantly improved compared to the newly generated gas hydrate.

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

  In FIG. 1, 1 is a gas hydrate generating device, 2 is a dehydrating device, 3 is a cooling device, 4 is a depressurizing device, 5 is a granulating device, 6 is a storage tank, and is introduced into the gas hydrate generating device 1. Natural gas g and water w are reacted under high pressure (for example, 3 to 5 MPa) and low temperature (for example, 0 to 5 ° C.), and as shown in FIG. A gas hydrate n having a crystal structure in which the molecules 8 are accommodated one by one is generated.

  Since the gas hydrate n generated by the gas hydrate generator 1 is in a semi-dehydrated state (for example, a water content of about 50%), it is dehydrated by the dehydrator 2 and has a high purity (for example, a water content of 10%). The gas hydrate is n. The gas hydrate n having a high purity (for example, a water content of 10%) is cooled below the freezing point (for example, −20 ° C.) by the cooling device 3.

  The gas hydrate n cooled below the freezing point is depressurized from a high pressure (for example, 3 to 5 MPa) to an atmospheric pressure (0.1 MPa) by the depressurizer 4 and is pelletized by the granulator 5 at the atmospheric pressure. The molded solid (hereinafter referred to as pellets) p is stored in the storage tank 6 as it is.

  By the way, as already explained, while the gas hydrate pellets p are stored in the storage tank 6, the raw material gas contained in the cage made of water molecules escapes due to temperature rise, storage period extension, etc. The amount of gas stored in the pellet p may be reduced to about 30%.

  For this reason, in the present invention, gas hydrate pellets that have been decomposed during storage to reduce the amount of stored gas are regenerated to provide high-quality gas hydrate for transportation or storage.

  That is, as shown in FIG. 3, the gas hydrate pellets p are directly transferred from the storage tank 6 to the regenerator 11 before shipment, and the natural pressure is increased (for example, 2 to 5 MPa) to the regenerator 11 by the booster pump 12. Supply gas g. Then, the molecules of the raw material gas 8 are accommodated in an empty water molecule basket 7 from which the raw material gas has escaped (see FIG. 2), and the amount of gas stored in the gas hydrate pellet p is the original state (the amount of stored gas 80 ~ 90%). In FIG. 3, 13 is a gas storage tank.

  Here, the cracked gas amount of the gas hydrate pellets p stored in the storage tank 6 can be measured by a flow meter 14 provided in the pipeline. Further, the gas content of the gas hydrate pellet p is obtained by separating a sample of the gas hydrate pellet p and calculating the water content from the amount of water and gas (decomposition-weight measuring device), differential thermal analyzer. Measurement can be performed using a Raman spectrum spectrometer, a laser Raman spectrometer, or the like.

  The gas hydrate pellets p regenerated in this way are transported to the import destination by a transport ship (not shown). The gas hydrate pellets p unloaded from the transport ship are decomposed by the gasifier 15, the natural gas g is supplied as fuel, and the water w is used as cold heat. This can also be applied to land transportation performed using a tank truck or the like.

  According to the regeneration method of the present invention, the amount of gas contained can be recovered and the stability can be improved with the gas hydrate pellets intact, so that the pellets are decomposed to generate gas hydrates from the raw material gas and water and cooled. The gas hydrate pellets can be stored and transported again without going through the depressurizing and pelletizing step.

  The gas hydrate pellet regeneration method includes a batch type (batch type) and a continuous type, and each method will be described.

(1) Batch type (batch type)
First, the batch type (batch type) will be described.

  In the case of the batch type (batch type), the gas hydrate pellets p are transferred from the storage tank 6 to the regeneration tank 17 as shown in FIG. At this time, the pressure in the regeneration tank 17 is atmospheric pressure (0.1 MPa), and the temperature of the gas hydrate pellet p is −20 ° C.

  Next, as shown in FIG. 4 (b), after attaching a lid 18 to the regeneration tank 17, high-pressure (2-5 MPa) natural gas g is supplied into the regeneration tank 17 to embed gas hydrate pellets p. The gas is regenerated to 80-90%. At this time, the pressure in the regeneration tank 17 is 2 to 5 MPa. During the regeneration of the gas hydrate pellets p, the temperature of the gas hydrate pellets p rises due to the reaction heat, but the heat is removed by a cooling device (not shown), and the temperature of the gas hydrate pellets p is suppressed to −10 to 5 ° C. Further, the amount of gas contained in the gas hydrate pellet p is measured by the method described above.

  Next, as shown in FIG.4 (c), the gas hydrate pellet p is cooled to -20 degreeC with the cooling device which is not shown in figure. Further, the unreacted natural gas g in the regeneration tank 17 is removed, and the pressure in the regeneration tank 17 is returned to atmospheric pressure (0.1 MPa).

  Next, as shown in FIG. 4 (d), the gas hydrate pellets p in the regeneration tank 17 are stored in the storage tank 6. The storage conditions of the gas hydrate pellet p are 0.1 MPa and −20 ° C.

(2) Continuous type Next, the continuous type will be described.

  In the case of the continuous system, as shown in FIG. The regeneration conditions are 2 to 5 MPa and −10 to 5 ° C. as in the batch type (batch type).

  The gas hydrate pellet p regenerated by the regenerator 23 is cooled to −20 ° C. by the cooler 24. The gas hydrate pellet p cooled by the cooler 24 is depressurized to atmospheric pressure (0.1 MPa) by a depressurization device 25 having two valves 26 and 27, and then stored in a storage tank (not shown).

  The regenerator 23 continuously transfers the gas hydrate pellets p by the conveyor 30 provided in the regenerator body 28, and the cooler 24 is supplied by the conveyor 31 provided in the cooler body 29. Are to be transferred continuously.

It is a schematic block diagram of the gas hydrate storage method which concerns on this invention. It is a schematic diagram which shows the single-piece | unit structure of gas hydrate. It is a system diagram of the gas hydrate storage method of the present invention. (A)-(d) It is an action explanatory view of a batch type. It is a continuous operation explanatory view. It is a schematic block diagram of a reproducing | regenerating apparatus and a cooling device.

Explanation of symbols

g Raw material gas n Gas hydrate w Water 1 Gas hydrate generator 6 Storage tank 7 Basket made of water molecules 8 Molecule of raw material gas 11 Regenerator

Claims (3)

A gas hydrate pellet storage method in which a raw material gas and water are reacted to form a gas hydrate, the gas hydrate is molded into pellets, and the gas hydrate pellets are stored in a storage tank below freezing point and atmospheric pressure. Gas hydrate pellets having a reduced gas occluding rate during storage in a regenerator, and supplying high-pressure raw material gas to the gas hydrate pellets in the regenerator Storage method. The gas hydrate pellet storage method according to claim 1, wherein the raw material gas is refilled into gas hydrate pellets under conditions of 3 to 5 MPa and -10 ° C to 5 ° C. The gas hydrate pellet storage method according to claim 1, wherein the gas hydrate pellets refilled with the raw material gas are stored and transported at 0.1 MPa, -20 ° C to -30 ° C.

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