JP2012115880A - Device and method for forming gas hydrate pellet - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a device for forming gas hydrate pellets, which prevents sealing liquid absorption by solving the problem in prior art that in the course of immersing in a sealing liquid like hexane to detach the GH pellet (GHP) attached water which is generated in a gas hydrate (GH) production plant, the sealing liquid is absorbed because of depressurization in supplying the GHP to a sealing liquid chamber and gas layer formation is caused in a depressurizing process to facilitate GHP decomposition.SOLUTION: An upper portion of a sealing liquid chamber 30, which is filled with a sealing liquid L such as a liquid propane or a liquid hexane, is connected to an outlet 22a of a presser 21 for forming GHPs. In keeping the outlet 22a obstructed with a switching plunger 33, a compression plunger 21e is advanced within the presser 21 to press the GH slurry supplied to a pressing chamber 22 and squeeze water to form GHPs. After GHP formation, the compression plunger 21e is a little bit retreated to depressurize the GHPs, and then water is osmosed and absorbed. Next, the outlet 22a is opened to supply the GHPs to the sealing liquid chamber 30.

Description

  For example, the present invention provides a gas hydrate slurry from a gas hydrate slurry by a pellet forming apparatus installed in a natural gas hydrate production plant that produces natural gas hydrate existing under the seabed in a state suitable for transportation and storage. The present invention relates to an apparatus for molding gas hydrate pellets for molding gas hydrate pellets, in which decomposition is suppressed as much as possible when molding gas hydrate pellets and a stable state is maintained during storage and transportation.

  Natural gas hydrate (NGH), the main component of which is methane, exists under the seabed at a depth of 500 m or less in frozen land zones such as Siberia, Canada, and Alaska and in the continental area. This NGH is a water-like solid substance or clathrate hydrate that is composed of gas molecules such as methane and water molecules and is stable under low temperature and high pressure, and as clean energy that emits less carbon dioxide and air pollutants. It is attracting attention.

  Natural gas, after being liquefied, is stored and used as energy, but its production and storage are performed at an extremely low temperature of -162 ° C. On the other hand, natural gas hydrate has the advantage that it exhibits stable properties with almost no decomposition at −20 ° C. and can be handled as a solid. Because of these characteristics, it is possible to effectively use gas resources in undeveloped small and medium gas fields for reasons such as profitability existing all over the world, or short distance from small gas fields, small-scale transportation. In such a case, a natural gas hydrate system (NGH system) is expected in which natural gas is hydrated for transportation, storage, and regasification.

  In the NGH system, NGH suitable for transportation and storage is generated at NGH shipping bases such as small and medium gas fields, and transported to the desired NGH receiving base by transport ships and vehicles, etc., and the transported NGH is stored at the NGH receiving base. If necessary, it will be used as an energy source by the NGH gasifier. FIG. 8 is a schematic block diagram illustrating an example of the configuration of a gas hydrate generation plant used in the NGH shipping base. The mined raw material gas G is sufficiently mixed with water W in the generator 1 which is a high-pressure reaction vessel, and is hydrated to produce a low concentration gas hydrate slurry. The produced gas hydrate slurry is supplied to the dehydrator 3 by the supply pump 2 to produce a dehydrated highly concentrated gas hydrate slurry. At this time, the dehydrator 3 is supplied to the lowermost part of the dehydrator 3. When the supplied gas hydrate slurry ascends the dehydrator 3, it is dehydrated at a draining part (a part that separates hydrate particles and water through fine holes, slits, etc.) provided in the middle of the dehydrator 3. It is taken out from the upper end of the vessel 3. The extracted gas hydrate is extracted as a powdered gas hydrate powder. This gas hydrate powder is supplied to the pellet molding machine 4 and granulated, and gas hydrate pellets having an appropriate size for transportation and storage are molded. Next, after being cooled by the cooler 5 to a temperature at which it does not decompose even under normal pressure, it is supplied to the decompression device 6. That is, from the generator 1 to the pellet former 4, the treatment is performed under high pressure (temperature varies depending on the gas hydrate species and in the case of NGH, 2 to 10 ° C.), and the cooler 5 and the decompressor 6 Thus, it is processed at a temperature that hardly decomposes even under normal pressure (for example, in the case of NGH, approximately -20 ° C). Thereafter, the molded gas hydrate pellets are fed to a storage tank and stored.

  However, in the conventional process, each apparatus of the dehydrator 3 and the pellet former 4 is required, which may increase the size of the gas hydrate production plant and make the production process complicated.

  On the other hand, the applicant of the present application has proposed a gas hydrate pellet molding apparatus in which the dehydrator and the pellet molding machine can be performed by a single apparatus and the continuous processing of the gas hydrate production plant is not impaired. (See Patent Document 1).

  The gas hydrate pellet forming apparatus disclosed in Patent Document 1 is connected to a compression chamber for filling and compressing the gas hydrate slurry generated by the generator, and the compression chamber, and is compressed in the compression chamber. A cooling chamber that receives and cools the gas hydrate pellets, a supply path that communicates with the cooling chamber and communicates with a depressurization step that depressurizes the cooled gas hydrate pellets, and a squeezing means provided in the squeezing chamber; A valve means for opening and closing between the compression chamber and the cooling chamber; and a pellet holding means having a holding chamber for moving between the cooling chamber and the supply path and receiving gas hydrate pellets. After squeezing the gas hydrate with the squeezing means, the valve means is opened, and the squeezing operation of the squeezing means is continued to supply gas hydrate pellets to the cooling chamber. Gas hydrate pellets are sequentially fed from the cooling chamber to the holding chamber of the pellet holding means, and the gas hydrate pellets are supplied to the supply path in a state where the cooling chamber is shut off by the moving operation of the pellet holding means. It is a thing.

  By the way, as described above, when the gas hydrate slurry is squeezed to remove moisture, for example, water is squeezed to 90% by weight. This squeezing step is performed under high pressure and molded. Further, moisture remains in the gas hydrate pellets, and some of the water exists as adhering water adhering to the surface of the gas hydrate pellets. Further, when forming into gas hydrate pellets, water splashes and the like are generated. On the other hand, in order to maintain the gas hydrate pellets in a stable state under normal pressure, the adhering water and the scattered water are frozen because it is cooled to about −20 ° C. There is a possibility that the gas hydrate pellets molded with ice are bonded to each other to form a lump of pellets inside the cooling device. In addition, the formed pellet lump grows in the cooling device to become a larger lump, which may block the cooling device. Furthermore, it accumulates on the heat transfer surface of the cooling device, lowering the heat transfer efficiency, and there is a possibility that the gas hydrate cannot be sufficiently cooled.

  For this reason, the applicant of the present application has proposed a gas hydrate adhering water separation device that reliably separates adhering water, splash water and the like accompanying the molded gas hydrate pellets (Patent Document 2). reference).

  The gas hydrate adhering water separator supplies a raw material gas and water to a generator and reacts under high pressure to generate a gas hydrate slurry, and after removing moisture from the gas hydrate slurry, a desired hydrate is separated. In a gas hydrate production plant that is formed into pellets of a small size, cooled, and then depressurized to normal pressure, the gas hydrate slurry is filled, and the gas hydrate slurry is compressed to form gas hydrate pellets. A gas hydrate pellet formed in the squeezing device in communication with the device and the squeezing device, a liquid having a density lower than that of water, and under pressure for producing a gas hydrate slurry Filled with a liquid seal that does not freeze in a temperature environment that maintains the liquefied state and stabilizes the state of the gas hydrate pellets A liquid chamber, a pellet transfer device disposed below the sealed liquid chamber, receiving a gas hydrate pellet settling in the sealed liquid chamber and transferring it to the next process, and below the pellet transfer device, A water separation plate that receives the gas hydrate that has settled in the sealed liquid chamber and allows water that descends through the sealed liquid chamber to pass therethrough.

Japanese Patent Application No. 2009-087565 Japanese Patent Application No. 2010-143348

  If the gas hydrate slurry is squeezed to a desired concentration, the gas hydrate adhering water separation device will feed the sealed liquid chamber, but at that time, the squeezing device and the sealed liquid chamber It will communicate between them. For example, the door which has closed between the pressing device and the sealing chamber is opened. At this time, since the gas hydrate pellets formed in a pressurized state for squeezing are decompressed to the pressure before squeezing, the gas hydrate pellets expand slightly, and a liquid in the sealed liquid chamber, for example, a sealed liquid such as hexane or propane. Is absorbed into the gas hydrate pellets. The state in which the sealing liquid is absorbed is a high-pressure atmosphere in which gas hydrate is generated. However, if the sealing liquid is subjected to a subsequent depressurization step from this state, the atmosphere is at atmospheric pressure. Vaporizes and a fine gas layer is formed in the gas hydrate pellets. Furthermore, this fine gas layer increases the specific surface area of the gas hydrate pellets, and as a result, the gas hydrate pellets may be easily decomposed.

  Therefore, the present invention prevents the sealing liquid such as hexane from being absorbed into the molded gas hydrate pellets, suppresses the formation of a gas layer at the time of depressurization, and further decomposes the gas hydrate pellets. An object of the present invention is to provide a molding apparatus and a molding method for gas hydrate pellets capable of suppressing the above.

  As a technical means for achieving the above object, the gas hydrate pellet forming apparatus according to the present invention supplies a raw material gas and water to a generator and reacts them under high pressure to generate a gas hydrate slurry. In a gas hydrate production plant for forming pellets of a desired size while removing moisture from the gas hydrate slurry, the gas hydrate slurry is filled and compressed to form gas hydrate pellets. A pressure device for forming a gas hydrate slurry, the gas hydrate pellets formed by the pressure device, and having a density lower than that of water. In a temperature environment that maintains a liquefied state and stabilizes the state of the gas hydrate pellets. Becomes liquid from the sealing liquid chamber which is filled as a working liquid, after said gas hydrate pellets formed by the squeezing device is vacuum is characterized by supplying the gas hydrate pellets in the sealing liquid chamber.

  When the formed gas hydrate pellets are depressurized from the pressure after squeezing to, for example, the pressure before squeezing, the gas hydrate pellets are slightly expanded, and at that time, the gas hydrate pellets are compressed around the gas hydrate pellets. Water is sucked (absorbed) into the gas hydrate pellets and permeates into the gas hydrate pellets. Therefore, even if the gas hydrate pellets are supplied to the sealing liquid chamber, the sealing liquid such as hexane is not absorbed by the gas hydrate pellets. Therefore, a gas layer due to vaporization of the sealing liquid in a depressurized state is not formed, and decomposition of the gas hydrate pellets is not promoted.

  A molding apparatus for gas hydrate pellets according to the invention of claim 2 is an open / close plunger that switches between a communication state and a blocking state between the pressing device and a sealed liquid chamber by an advancing and retracting operation, and the pressing device to the pressing device. A squeezing plunger that advances and retreats with respect to the sealed liquid chamber, the squeezing device is advanced in a state where the squeezing device and the sealed liquid chamber are shut off by the opening and closing plunger, and the gas hydrate slurry is compressed to gas hydrate Forming pellets, retreating the compression plunger to depressurize the gas hydrate pellets and absorbing water into the gas hydrate pellets, moving the open / close plunger to communicate the compression device and the sealing chamber The gas hydrate pellets are supplied to a sealing chamber.

  If the gas hydrate pellet is formed, the shut-off state is maintained by the open / close plunger and the squeezing plunger is moved backward to reduce the gas hydrate pellet from the pressure after squeezing to, for example, the pressure before squeezing. Thereby, the water squeezed so far is sucked (absorbed) and permeates into the gas hydrate pellets. Note that the amount of retraction at this time is small, and the gas hydrate pellets formed are retreated to a position where the expansion becomes stable. It is set according to conditions such as the dimensions of the gas hydrate pellets, the shape and dimensions of the squeezing device, the area of the head portion of the squeezing plunger, the dimensions of the passage through which the sucked water passes.

  In addition, the gas hydrate pellet forming method according to the present invention supplies a raw material gas and water to a generator and reacts under high pressure to generate a gas hydrate slurry, and removes moisture from the gas hydrate slurry. Meanwhile, in the gas hydrate production plant for forming into pellets of a desired size, the gas hydrate slurry is filled, the gas hydrate slurry is squeezed, and water is squeezed to form gas hydrate pellets. The gas hydrate pellets formed by depressurization are decompressed, the gas hydrate pellets absorb an appropriate amount of the squeezed water, and the gas hydrate pellets that have absorbed the squeezed water have a density lower than that of water. And maintaining the liquefied state under pressure for the production of gas hydrate slurry, Is characterized by supplying a liquid that condition does not freeze in a temperature environment to stabilize the in working liquid.

  The gas hydrate slurry is squeezed to squeeze out moisture to form gas hydrate pellets in which the gas hydrate is hardened. When the formed gas hydrate pellets are decompressed, the gas hydrate pellets are slightly expanded, and the compressed water is sucked and absorbed. Next, even if it is supplied into the sealing liquid, the sealing liquid is suppressed from being absorbed. Therefore, even when the pressure is released in the subsequent process, a gas layer is not formed.

  The “appropriate amount” of the squeezed water to be absorbed is an amount corresponding to the expansion amount of the gas hydrate pellets when the pressure is reduced, and when the gas hydrate pellets are supplied into the sealing liquid, they are sealed. It is a grade which occupies the ratio in a gas hydrate pellet until there is almost no room for liquid absorption.

  According to the gas hydrate pellet molding apparatus according to the present invention or the gas hydrate molding method according to the invention of claim 3, when the formed gas hydrate pellets are immersed in a sealing liquid such as hexane. The sealing liquid is not sucked (absorbed) into the gas hydrate pellets. For this reason, the gas layer by the sealing liquid vaporized in the subsequent depressurization process is not formed, and it is possible to stabilize the gas hydrate pellets during transportation and storage and to suppress decomposition. Therefore, the efficiency of transportation and storage of gas hydrate pellets is improved, and the convenience of gas hydrate is increased.

  According to the gas hydrate pellet molding apparatus of the second aspect of the present invention, the gas hydrate pellet molding pressure and molding speed can be arbitrarily selected, and the formed gas hydrate pellet can be reliably decompressed. be able to. Moreover, since the water squeezed so far is infiltrated, the squeezed water in the discharge path can be sucked in, and there is no need to separately provide a water passage for infiltration, and the gas has a simple structure. Stability of hydrate pellets can be improved.

It is a schematic diagram for demonstrating the shaping | molding apparatus of the gas hydrate pellet which concerns on this invention. It is a figure explaining operation | movement of the shaping | molding apparatus of the gas hydrate pellet which concerns on this invention, and has shown the state filled with gas hydrate slurry. The state which pressed the filled gas hydrate slurry and formed the gas hydrate pellet is shown. It shows a state in which the gas hydrate pellets are decompressed from the pressure after pressing to the pressure before pressing after forming the gas hydrate pellets. The state which supplies the formed gas hydrate pellet to a sealing liquid chamber is shown. It is a graph which shows the condition decomposed | disassembled by progress of the time of the formed NGH pellet, and has shown the case where the decompression process of a NGH pellet is performed. It is a graph which shows the condition decomposed | disassembled by progress of the time of the formed NGH pellet, and has shown the case where the decompression process (from the pressure after pressing to the pressure before pressing) of the NGH pellet is not performed. It is a schematic block diagram explaining an example of a structure of the production plant of NGH used for the shipping base of NGH.

  The gas hydrate pellet molding apparatus according to the present invention will be described in detail below based on the preferred embodiments shown in the drawings.

  FIG. 1 is a diagram for explaining a gas hydrate pellet forming apparatus according to the present invention. As in the case of the gas hydrate production plant shown in FIG. 8, the gas hydrate is fed to the generator 1 with a raw material gas G and water W. Are supplied from the raw material gas supply pipe 11 and the reaction water supply pipe 12, respectively. In the generator 1, the raw material gas G and water W react to generate a gas hydrate slurry, which is fed to the pressing device 21 of the pellet forming device 20 through the slurry supply pipe 13. Further, unreacted water is recovered from the return pipe 1b from the generator 1 via the unreacted water recirculation pump 1a. The discharge side of the unreacted water recirculation pump 1a is connected to the reaction water supply pipe 12. The reaction water supply pipe 12 is provided with a regulating valve 12a, and the opening degree of the regulating valve 12a is adjusted based on the measured value of the pressure gauge 11c that measures the internal pressure of the generator 1.

  The squeezing device 21 includes a cylindrical inner cylinder 21a and an outer cylinder 21b that accommodates the inner cylinder 21a. The inner cylinder 21a can be moved forward and backward by sliding in the direction of the axis O of the inner cylinder 21a. An appropriate squeezing plunger 21e is accommodated. The squeezing plunger 21e is advanced and retracted by actuation of a hydraulic cylinder 21f as a drive source. A part of the inner cylinder 21a is provided with a screen portion 21c having a through hole of an appropriate size.

  A slurry recovery pipe 21d connected to the suction side of the slurry circulation pump 11a is connected to the lower part of the squeezing device 21, and the raw material gas supply pipe 11 is connected to the discharge side of the slurry circulation pump 11a. . The discharge side of the source gas supply pump 11b is connected to the suction side of the slurry circulation pump 11a. That is, as will be described later, the squeezed water generated when the gas hydrate slurry is generated by the squeezing device 21 merges with the raw material supplied from the raw material gas supply pump 11b and is supplied to the generator 1 by the slurry circulation pump 11a. It has been returned. In addition, the middle of the slurry supply pipe 13 and the slurry recovery pipe 21d are connected by a return pipe 13a, and a return valve 13b is provided in the middle of the return pipe 13a. A gas / water buffer 21h is connected to a back pressure chamber 21g on the rear side of the compression plunger 21e via a back pressure pipe 21i. The gas / water buffer 21h is connected to the slurry recovery pipe 21d via a regulating valve 21j.

  The front end of the squeezing chamber 22 that is the front side of the squeezing plunger 21e of the squeezing device 21 is a pellet outlet 22a, and the pellet outlet 22a has an upper portion of a cylindrical sealed chamber 30 whose longitudinal direction is the longitudinal direction. Are connected, and the compression chamber 22 and the sealed liquid chamber 30 are communicated with each other. The sealed liquid chamber 30 is filled with a sealed liquid L which is a liquid having a density lower than that of water. The gas hydrate is generated at room temperature under a high pressure of about 5.4 MPa, the outer cylinder 21b of the pressing device 21 is formed of a so-called high pressure vessel, and the sealed chamber 30 is also formed of a high pressure vessel. Has been. For this reason, the sealing liquid L is assumed to maintain a liquid state under a high pressure of about 5.4 MPa. For example, liquid propane or liquid hexane is used. A cushion tank 31 is provided in the sealing liquid chamber 30, and the sealing liquid L is always filled with the sealing liquid L by supplying the sealing liquid L to the sealing liquid chamber 30. A portion of the sealing chamber 30 facing the pellet outlet 22a of the squeezing chamber 22 is provided with a scraper 32 that can slide along the outlet surface of the pellet outlet 22a by the operation of the drive cylinder 32a.

  In addition, an open / close plunger 33 that can be moved back and forth with respect to the pellet outlet 22a of the compression chamber 22 is disposed. When the opening / closing plunger 33 is advanced and pressed against the pellet outlet 22a, the pellet outlet 22a is closed, the pressing chamber 22 and the sealing liquid chamber 30 are blocked, and the pellet outlet 22a is opened by moving backward. It is made to do. The opening / closing plunger 33 is advanced and retracted by, for example, the operation of the closing cylinder 33a.

  A neck portion 30a having a reduced diameter is formed at an intermediate portion of the sealing chamber 30, and a gas hydrate pellet P that settles in the sealing chamber 30 is sealed under the neck portion 30a as will be described later. A pellet transfer device 34 for transferring to the next process while being discharged to the outside of the chamber 30 is provided. A water separation plate 35 is provided below the pellet transfer device 34 and inside the sealed liquid chamber 30. The water separation plate 35 allows water to pass therethrough and prevents gas hydrate pellets P from passing through. For example, the water separation plate 35 is formed with a through hole that allows water to pass therethrough. ing. The bottom of the sealed chamber 30 below the water separation plate 35 is a water storage section 36.

  The water storage part 36 is connected to the suction side of a water recovery pump 37, and the water recovery pump 37 is operated to discharge water remaining in the water storage part 36. It is preferable that the discharged water is returned to the generator 1 and used as water W for reacting the raw material gas G. Further, a water level detector 37a for detecting the water level staying in the storage part 36 is provided, and the water recovery pump 37 is driven based on an output signal of the water level detector 37a.

  The operation of the gas hydrate pellet forming apparatus according to the present invention configured as described above will be described below.

  FIG. 2 shows the pressing device 21 in a state in which the gas hydrate slurry generated by the generator 1 is supplied. At this time, as shown in FIG. 2, the compression plunger 21e is in a position where the inner cylinder 21a is retracted to the rear. The opening / closing plunger 33 is in a position where the pellet outlet 22a of the pressing device 21 is closed by moving forward. In this state, gas hydrate slurry is supplied from the slurry supply pipe 13 to the pressing chamber 22. Unreacted water entrained in the supplied gas hydrate is filtered by the screen portion 21c of the inner cylinder 21a and flows into the outer cylinder 21b, and is generated through the slurry recovery pipe 21d by the slurry circulation pump 11a. Collected in vessel 1. When the gas hydrate slurry is filled into the inner cylinder 21a, the squeezing plunger 21e moves forward to squeeze the gas hydrate slurry and squeeze water from the gas hydrate slurry as shown in FIG. Thereby, the gas hydrate pellet P is formed as a lump of gas hydrate. As shown in FIG. 3, the pressing plunger 21e advances to the front part of the inner cylinder 21a. At this time, for example, when about 10% by weight of gas hydrate slurry is filled, the operation of the squeezing means is adjusted so that water is squeezed to about 90% by weight and gas hydrate pellets P are formed.

  Once the water is squeezed to the desired concentration to form the gas hydrate pellet P, the squeezing plunger 21e is slightly retracted from the position shown in FIG. 3 to the position shown in FIG. The retraction amount is such that the pressure is reduced in the same manner as the pressure reduction state generated in the gas hydrate pellet P when the opening / closing plunger 33 described later is retreated and the pellet outlet 22a is opened in the state shown in FIG. In addition, the retraction amount is sucked by the pressing pressure when forming the gas hydrate pellet P, the size of the formed gas hydrate pellet P, the shape and size of the pressing device 21, the area of the head portion of the pressing plunger 21e, It is preferable that the gas hydrate pellets P are set in accordance with conditions such as a passage size through which the water passes, and are moved backward to a position where the expansion of the formed gas hydrate pellets P becomes stable.

  When the gas hydrate pellet P is depressurized by the retraction of the squeezing plunger 21e, the water squeezed until then flows in the reverse direction and is absorbed by the gas hydrate pellet P. In the vicinity of the forward end of the squeezing plunger 21e, the squeezed water flows out to the rear of the head portion of the squeezing plunger 21e through the gap between the squeezing plunger 21e and the outer peripheral surface and the inner peripheral surface of the pressing chamber 22. When the compression plunger 21e is retracted, the gas hydrate pellets P penetrate through the gap.

  When an appropriate amount of water is absorbed in the gas hydrate pellet P, the opening / closing plunger 33 is retracted to open the pellet outlet 22a of the pressing device 21, as shown in FIG. When the pressing plunger 21e moves forward in this state, the formed gas hydrate pellets P are pushed out from the pellet outlet 22a to the sealing chamber 30. At this time, when the gas hydrate pellets P continuously extruded are too large for the treatment in the sealed liquid chamber 30, the scraper plate 32 is driven by the drive cylinder 32a and slides along the exit surface. The gas hydrate pellet P is cut. When the gas hydrate pellets P are extruded into the sealing liquid chamber 30, they are immersed in the sealing liquid L filled in the sealing liquid chamber 30. Since the density of the sealing liquid L is smaller than that of water, the gas hydrate pellet P settles the sealing liquid L. Moreover, the water adhering to the surface at the time of formation of the gas hydrate pellet P will also settle similarly. The adhering water is separated from the surface of the gas hydrate pellet P by receiving the surface tension due to the density difference from the sealing liquid L.

  When the gas hydrate pellets P settle and reach the pellet transfer device 34, they are received by the pellet transfer device 34 and discharged from the sealed liquid chamber 30 to the outside. Since the pellet transfer device 34 is also filled with the sealing liquid L, the sealing liquid L is also discharged together with the gas hydrate pellets P. Further, when the gas hydrate pellets P reach the water separation plate 35 provided below the pellet transfer device 34 in the sealed liquid chamber 30, the water separation plate 35 stops the sedimentation. On the other hand, the water separated from the gas hydrate pellets P passes through the water separation plate 35 and stays in the water storage section 36 below the water separation plate 35. The accumulated water is returned to the generator 1 by the water recovery pump 37.

  The gas hydrate pellets P transferred by the pellet transfer device 34 are cooled in the next step. At this time, since the sealing liquid L is also transferred to the cooling step along with the gas hydrate pellets P, the sealing liquid P is also cooled. In the cooling step, the gas hydrate pellet P is maintained at a normal pressure even under normal pressure so that it can be maintained in a stable state. For this reason, the sealing liquid L is also exposed to an atmosphere of −20 ° C., and it is preferable to use a liquid that does not freeze in this atmosphere. As described above, liquid propane, liquid hexane, or the like is used. Is suitable.

  The cooled gas hydrate pellets P are depressurized to normal pressure and are in a state suitable for storage, and are fed to the storage tank. Since the gas hydrate pellets P are infiltrated with water and the sealing liquid L such as hexane is not absorbed, the formation of a gas layer such as hexane is suppressed during the depressurization. The cause of promoting the decomposition of the hydrate pellet P is eliminated as much as possible.

Next, in the case where the formed gas hydrate pellets P are NGH pellets, the decomposition speed was compared between the case where the compression plunger 21e was not retracted and the case where the compression plunger 21e was retracted. That is, when the compressed plunger 21e is retracted, water is infiltrated into the formed NGH pellet P and absorbed, and then immersed in the sealing liquid L for stabilization (hereinafter referred to as “water-containing NGH pellet”). ) And the case where it is stabilized after absorbing the sealing liquid L by immersing it in the sealing liquid L without retracting the compression plunger 21e (hereinafter referred to as “sealing liquid-containing NGH pellet”). The speed was measured. In addition, the formation conditions of NGH pellet P set the pressing pressure by pressing plunger 21e to 15.4 (MPa), and measured the change of the NGH rate shown by the following formula for 2 weeks after stabilizing each.
NGH rate (wt%) = {(weight of NGH in pellet) / (weight of pellet)} × 100 Formula 1
Here, the “NGH weight in the pellet” of the denominator was obtained from the following equation based on the actually measured pellet weight and the weight of water after decomposition.
NGH weight in pellet = natural gas weight x
{1 + ((hydration number of NGH × molecular weight of water) ÷ molecular weight of natural gas)} Equation 2
In addition,
Natural gas weight = pellet weight-weight of water after decomposition
Hydration number of NGH (number ratio of gas molecules to water molecules in NGH) = 6.19
Number of water molecules = 18 g / mol
Natural gas molecular weight (average molecular weight) = 16.94 g / mol
As sought.
The initial NGH rate is 82 (wt%) for water-containing NGH pellets and 84 (wt%) for sealing liquid-containing NGH pellets, and the sample weight is 42 (g) for water-containing NGH pellets, including sealing liquid. The NGH pellet was 49 (g). The NGH rate after 2 weeks was 72 (wt%) for the water-containing NGH pellets and 44 (wt%) for the sealant-containing NGH pellets.

  A comparison of the decomposition rates is shown in FIGS. 6 and 7. FIG. 6 shows a change in the NGH rate for the water-containing NGH pellet, and FIG. 7 shows a change in the NGH rate for the sealant-containing NGH pellet. When the decomposition rate was determined from the change in the NGH rate in these graphs, 0.67 (wt% / day) was obtained for the water-containing NGH pellets and 2.9 (wt% / day) was obtained for the sealant-containing NGH pellets. That is, the water-containing NGH pellets had a lower decomposition rate and were more stable over a longer period.

  According to the apparatus for molding gas hydrate pellets according to the present invention, gas hydrate pellets with suppressed decomposition can be molded, and the stability of gas hydrate pellets during transportation and storage can be ensured. Contributes to promoting the use of pellets.

G Raw material gas W Water L Sealing liquid 1 Generator
21 Squeezer
21a Inner cylinder
21b outer cylinder
21e compression plunger
22 Press room
22a Pellet outlet
30 Sealing chamber
32 scraper
33 Opening / closing plunger
34 Pellet transfer device
35 Water separator
36 Water reservoir
37 Water recovery pump

Claims (3)

Raw material gas and water are supplied to the generator and reacted under high pressure to produce a gas hydrate slurry, and gas hydrate is produced into pellets of the desired size while removing moisture from the gas hydrate slurry. In the plant
A pressing device for filling the gas hydrate slurry and pressing the gas hydrate slurry to form gas hydrate pellets;
The gas hydrate pellets formed by the squeezing device in communication with the squeezing device are supplied, the density is lower than that of water, and the state is liquefied under the pressure for generating the gas hydrate slurry. And a sealing chamber filled with a liquid that does not freeze as a sealing liquid in a temperature environment that stabilizes the state of the gas hydrate pellets,
An apparatus for molding gas hydrate pellets, comprising: depressurizing gas hydrate pellets formed by the squeezing device, and then supplying the gas hydrate pellets to the sealing chamber. An open / close plunger that switches between a communication state and a blocking state between the pressing device and the sealing chamber by an advance / retreat operation;
A pressing plunger that moves forward and backward with respect to the sealed chamber in the pressing device,
The pressing plunger is advanced in a state where the pressing device and the sealing liquid chamber are blocked by the opening and closing plunger, and the gas hydrate slurry is pressed to form a gas hydrate pellet,
Retract the compression plunger to depressurize the gas hydrate pellet and absorb the compressed water into the gas hydrate pellet,
2. The gas hydrate pellet forming apparatus according to claim 1, wherein the gas hydrate pellets are supplied to the sealing chamber by moving the opening / closing plunger to communicate the squeezing device and the sealing chamber. . Raw material gas and water are supplied to the generator and reacted under high pressure to produce a gas hydrate slurry, and gas hydrate is produced into pellets of the desired size while removing moisture from the gas hydrate slurry. In the plant
Filling the gas hydrate slurry and pressing the gas hydrate slurry, squeezing to form gas hydrate pellets,
Depressurizing the gas hydrate pellets formed by squeezing the water, allowing the gas hydrate pellets to absorb an appropriate amount of the squeezed water,
The gas hydrate pellets that have absorbed the squeezed water are liquids having a density lower than that of water, and maintain a state of being liquefied under a pressure for producing a gas hydrate slurry. A method for forming a gas hydrate pellet, characterized in that a liquid that does not freeze in a temperature environment that stabilizes the temperature is supplied into the sealing liquid.

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