JP2007269874A - Method for transferring gas hydrate - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method and apparatus for continuously transferring a gas hydrate from a high-pressure production process to a low-pressure forming process while blocking the pressure difference. <P>SOLUTION: In the method for continuously transferring the gas hydrate from the high-pressure production process L1 to the low-pressure forming process L2 while blocking the pressure difference, a screw conveyer 1 provided with two screws 2, 3 juxtaposed parallel with each other is used. The flights of the two screws 2, 3 have an overlap h1 for crashing the gas hydrate clogging in the screw so that the transferred gas hydrate is consolidated to the extent coping with the pressure difference between the high pressure and the low pressure to form a material sheet state while transferring. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a method for transferring a gas hydrate to a system having a differential pressure, and directly transfers a gas hydrate generated at a high pressure and a low temperature to a molding machine or a storage tank held at a low pressure and a low temperature. It provides a way to

  Generally, when natural gas is transported, it is often performed in the state of liquefied natural gas (hereinafter referred to as LNG). Since this LNG has a large volume reduction rate per unit volume (1/600 of the original volume of natural gas), it is advantageous for mass transportation of natural gas. However, it is necessary to manufacture at a very low temperature (−162 ° C.), hold it at this very low temperature and transport it, and it is necessary to use a special metal for manufacturing, transport, and storage, which increases the cost.

  Recently, a method for transporting natural gas as natural gas hydrate (natural gas hydrate, hereinafter referred to as NGH) has been proposed. This NGH has a smaller volume reduction rate per unit volume than natural gas (natural gas). 1/170) does not require much cooling energy to continue to be maintained as a cryogenic liquid (-162 ° C.) like LNG. In addition, the “self-preserving effect” of NGH, that is, by maintaining the temperature (-30 to −10 ° C.) at which the decomposition is suppressed by wrapping the NGH surface with ice by the decomposition heat of NGH, There is a feature that it can be stably stored under atmospheric pressure, and there is an advantage that a large facility such as a gas tank is unnecessary.

  Since this NGH is usually obtained as a powdery snow-like crystal, it is not easy to handle as it is, and in order to improve the packing density, it is compression molded into a lump shape such as a sphere (diameter of about 10 to 100 mm) and stored. Or being transported.

  In general, NGH is manufactured in a production process held at a high pressure and low temperature (for example, 4 to 6 MPa, 2 to 7 ° C.) including a primary production process, a dehydration process, and a secondary production process. And it is stored in the storage tank hold | maintained at the low pressure and low temperature (for example, 0.1MPa (atmospheric pressure), -30 to -10 degreeC) through the formation process and the depressurization process from the said production | generation process, and is conveyed. The differential pressure at this time is remarkably large at 3.9 to 5.9 MPa.

  In the primary generation step, a reactor provided with a stirring blade and a natural gas supply nozzle is used below the pressure vessel, and the natural gas is fed into the nozzle while stirring the raw water contained in the reactor. From this, it is blown into the raw water, and a slurry (ice water) containing 10-20% NGH is obtained by gas / liquid contact.

  This slurry-like NGH is supplied from below the vertical gravitational dehydration tower having a cylindrical main body provided with drainage holes in the circumferential direction at an intermediate position in the longitudinal direction and a screw-type conveyor installed at the top of the main body. During the upward movement, the contained water is drained from the drain hole, and a semi-dehydrated NGH intermediate with a moisture content of about 50% is obtained. This semi-dehydrated NGH is transferred to the secondary generation step by a screw conveyor installed on the upper part of the cylindrical main body.

  In the secondary generation process, a reactor in which a natural gas ejection nozzle is installed below the pressure-resistant reactor is used, and the semi-dehydrated NGH transferred from the dehydration process to the reactor is discharged from the nozzle. NGH with a reduced water content is obtained by gas / liquid contact while being blown up into the reactor by the natural gas that is blown out and circulated in the reactor.

  NGH obtained in this secondary generation process is a fine powder (eg, several tens of μm to several mm) such as smooth powder snow, and has a property of adhering and solidifying.

  The fine powdery NGH is transferred to a supercooling device such as a screw conveyor system, and is cooled to a low temperature (for example, −30 to −10 ° C.) that exhibits self-storability while being transferred through the device. It is sent to the depressurization process.

  In the depressurization step, a depressurization device including a depressurization chamber having a supply valve, a discharge valve, and a pressure release valve is used.

  The NGH cooled through the cooling device is temporarily accommodated in the depressurization device, the pressure release valve is opened, and the depressurization chamber is depressurized from 4 to 6 MPa to 0.1 MPa (atmospheric pressure). When the pressure chamber becomes atmospheric pressure, the discharge valve is opened and NGH is discharged into the molding process.

  Then, the same operation is repeated, and NGH is intermittently transferred from the high pressure side to the low pressure side.

  The molding process uses, for example, a roll-type compression molding machine in which hemispherical pockets (molding recesses) are formed on a pair of roll-facing surfaces of the same diameter, and NGH enters the opposing pockets of both rolls to be consolidated. Then, it is formed into a spherical shape or other shapes. This molded NGH is transferred to a storage tank for storage or transportation.

  In such a series of conventional NGH manufacturing and storage processes, the production process and the molding process are continuously performed, but the depressurization process is intermittently received and released into the depressurizer. -It is essential to repeat the operation such as dispensing, and this depressurization step is necessarily intermittent, resulting in a problem that the production efficiency is remarkably lowered.

  Therefore, the present inventors set a large differential pressure (3.9 to 5.9 MPa) between the high pressure (4 to 6 MPa) in the NGH production process and the low pressure (0.1 MPa (atmospheric pressure)) in the molding process. A screw type conveyor was adopted as a means for continuously transferring NGH powder while blocking, and a method of material sealing the differential pressure with NGH itself was devised.

  NGH that has undergone the supercooling process is a fine powder such as smooth snow powder, and unexpectedly has poor sliding properties and has the property of adhering to each other and solidifying. Therefore, when this fine powdery NGH is transferred using a screw type conveyor, the NGH is solidified and clogged in the barrel inner wall surface and screw groove of the screw type conveyor. Furthermore, it was found that the NGH fixed on the inner wall surface of the barrel forms a thin ice layer, and a “co-rotation phenomenon” occurs in which the NGH solidified around the screw in contact with the NGH rotates together with the screw. In this state, there is a problem that not only the screw type conveyor cannot transfer NGH but also the material seal cannot be maintained.

  The present invention has been obtained in order to solve the above-mentioned problem, and in particular, fine powder NGH that has become powdery snow through a supercooling process is continuously stored in a storage tank or the like while blocking the differential pressure between high pressure and low pressure. It is an object to provide a method for transporting automatically.

In order to achieve the above object, a gas hydrate transfer method according to the present invention comprises:
1) In the method of continuously transferring a gas hydrate in a manufactured state or a high-pressure / low-temperature atmosphere close to it to a normal-pressure or low-pressure / low-temperature atmosphere by a screw conveyor, there are two screw conveyors. The flights 2b and 3b of these two screws 2 and 3 have the same or similar shape, pitch and height, and one of the screw shafts 2a. The flight 3b of the other screw shaft 3a is inserted between the flights 2b without contacting each other, and these screw shafts 2a and 3a rotate at the same speed in the same direction. The gas hydrate supplied from the supply port 12a can counter the differential pressure between the high pressure and the low pressure between the gas hydrate and the discharge port 12b. Wherein the transferring while forming a material seal state compacted to degrees.

Furthermore, a gas hydrate transfer device according to the present invention for achieving the above-described object is as follows.
2) In an apparatus for continuously transferring a gas hydrate in a manufactured or high pressure / low temperature atmosphere to a normal pressure or low pressure / low temperature atmosphere by a screw conveyor, there are two screw conveyors. The flights 2b and 3b of these two screws 2 and 3 have the same or similar shape, pitch and height, and one of the screw shafts 2a. The flights 3b of the other screw shaft 3a are inserted between the flights 2b without contacting each other, and these screw shafts 2a and 3a rotate at the same speed in the same direction. The gas hydrate transport amount between pitches is configured to gradually decrease.

  Since the transfer device 1 used in the NGH transfer method according to the present invention crushes NGH in the gap between the flight of one screw shaft and the other screw shaft, there is a “co-rotation phenomenon” that inhibits the material seal phenomenon. Therefore, the NGH can be transferred continuously and stably while blocking the differential pressure between the high pressure and the low pressure, so that the production efficiency is greatly improved.

Embodiments of the present invention will be described with reference to the drawings. FIG. 1 is a schematic diagram showing a process from a primary generation process to a storage tank, and is also a schematic diagram of a transfer device that continuously transfers NGH while blocking a differential pressure between high and low pressure atmospheres.
(Overview)
NGH is generated by the manufacturing apparatus L1 that is maintained at a high pressure and low temperature (4 to 6 MPa, 2 to 7 ° C.) including the primary generation process P1, the dehydration process P2, and the secondary generation process P3. Through the pressure sealing process P4 of NGH according to the present invention, the differential pressure (3.9 to 5.9 MPa) is shut off to the device L2 held at low pressure and low temperature (atmospheric pressure, −30 to −10 ° C.). However, it is continuously transferred, formed into a lump by the forming step P5, and stored in the storage tank 31.
(Primary generation process P1)
In the primary production step P1, for example, a primary production reaction device 20 in which a stirring blade 20a and a natural gas supply nozzle 20b are provided below the pressure vessel 20c is used. This apparatus 20 is maintained at high pressure and low temperature (4 to 6 MPa, 2 to 7 ° C.).

When the natural gas g is bubbled from the nozzle 20b into the primary production reactor 20c filled with a predetermined amount of raw material water w and the raw material water w is stirred by the stirring blade 20a, NGH is reduced to 10 to 10 by gas / liquid contact. A slurry (ice water) containing 20% is obtained. This NGH slurry is pumped by the slurry pump 28 to the dehydration process P2.
(Dehydration process P2)
This dewatering step P2 uses, for example, a cylinder 21c having a plurality of drain holes 21b in the middle portion 21a in the longitudinal direction, and a vertical gravity dewatering tower 21 in which a screw type conveyor 25 is installed above the cylinder 21c. Has been.

The NGH slurry pushed down the vertical gravitational dehydration tower 21 is drained from the drain hole 21b while moving upward in the cylinder 21c of the dehydration tower 21 and has a water content of about 50%. A dehydrated NGH slurry is obtained. This NGH slurry is transferred to the secondary production step P3 by a screw conveyor 25 installed at the top of the dehydration tower 21.
(Secondary generation process P3)
In the secondary production step P3, the secondary production reactor 22 provided with a natural gas jet nozzle below the reaction vessel 22c is used.

The semi-dehydrated NGH transferred to the secondary production reactor 22 is blown up into the reaction vessel 22 by a jet flow from the natural gas jet nozzle 22a and is circulated in the reactor 22 while the gas / liquid is circulated. NGH with reduced water content is obtained by contact. This NGH is in the form of fine powder (several tens of μm to several mm) and is continuously transferred to the supercooling step P4 by the screw type conveyor 26 arranged in the reactor 22 (supercooling step P4).
In the supercooling step P4, a screw conveyor type cooling device 11 is used, a refrigerant is circulated in a jacket formed in the device 11, and the temperature at which the transferred NGH has a self-preserving effect (-30 to -10). ° C) and continuously transferred to the transfer step P5 according to the present invention.
( NGH transfer process P5 )
In the transfer step P5, the transfer device 1 according to the present invention is used. The transfer device 1 is provided with two screws 2 and 3 that rotate at the same speed in the same direction, and the flights 2b and 3b of both the screws 2 and 3 have the same or similar shape, pitch, and height. . As shown in the front sectional view of FIG. 2, the flights 3b of the other screw shaft 3a are disposed so as to overlap each other between the flights 2b of the one screw shaft 2a. This flight overlap h1 is formed so that NGH clogged during the flight is crushed by each other's flight.

  A gap h2 between the flights 2b, 3b and the barrel inner wall surface 4a is formed so as to peel off the NGH fixed to the barrel inner wall surface 4a.

  The screw shafts 2a and 3a are formed in a tapered shape with a gradually increasing diameter from the supply port 12a toward the discharge port 12b, or formed so that the flight pitch becomes smaller. Further, a pressure holding unit 5 is provided between the discharge port 12b and the tip of the screw shaft so as to form a material seal with NGH itself at a high pressure. In addition, resistance generating means for applying a deterrent to NGH discharge is installed on the discharge port 12b side.

  This resistance generating means is provided with a valve body 9a for pressing NGH discharged from the discharge port 12b, and a gas flow meter F for measuring the flow rate of gas that changes according to the state of the material seal is provided in the pipe line 17. is set up.

  The finely powdered NGH transferred from the secondary generation reaction device 22 is introduced into the supply port 12a of the transfer device 1, and the NGH is transferred to the discharge port 12b side with the rotation of the screws 2 and 3. . As the screw shafts 2a, 3a gradually increase in diameter, the gap between the barrel inner wall surface 4a and the screw shafts 2a, 3a decreases, and NGH is compressed and the pressure of the NGH itself increases accordingly. Then, the discharge of the NGH is suppressed by holding down the discharge port 12a by the valve body 9a, and the pressure of the NGH itself further increases, and the differential pressure between the high pressure and the low pressure is cut off, that is, the NGH itself acts as a plug. A seal is formed on the pressure holding unit 5.

  At this time, when the gas flows in the pipe line 17 exceeding a predetermined flow rate, the pressure applied to the valve body 9a is increased to increase the pressure applied to the material seal itself, so that the gas production apparatus L1 having a high pressure is used. Is prevented from flowing into the normal pressure device L2, for example, in the initial state where the transfer device 1 is driven, since the NGH is not tightly clogged, the material sealing force is insufficient. 12b is closed. Further, after the material seal is formed, the pressing force of the valve body 9a is lowered when the gas flow rate in the pipe line 17 is reduced below a predetermined value so as not to excessively pressurize the material seal. In addition to the gas flow meter, a gas pressure gauge may be installed to control the valve body 9a according to this pressure change.

Thus, the sealing force of the material seal is adjusted, and NGH is continuously transferred to the molding step P6 while maintaining this sealing force.
(Molding process P6, storage P7)
In the forming step P6, for example, a roll forming machine 30 in which hemispherical dents are formed on the opposing surfaces of a pair of rolls 30a having the same diameter is used. It is consolidated into a spherical shape or other lump shape, and is continuously transferred to the storage tank 31 for storage.

  As described above, the NGH transfer method and apparatus according to the present invention continuously transfer NGH while sealing the differential pressure between the high-pressure manufacturing apparatus L1 and the low-pressure apparatus L2, greatly improving production efficiency. To do. In addition, since the molding step P6 is performed at normal pressure, adjustment and operation of the molding apparatus 30 are facilitated, and safety is further improved.

  Next, FIG. 3 shows a second embodiment. In FIG. 3, the same members as those in the first embodiment are denoted by the same reference numerals.

  The transfer device 1 is provided with two screws 2 and 3 that rotate at the same speed in the same direction, and the flights 2b and 3b of both the screws 2 and 3 have the same or similar shape, pitch, and height. Yes. As shown in the front sectional view of FIG. 2, the flights 3b of the other screw shaft 3a are disposed so as to overlap each other between the flights 2b of the one screw shaft 2a. This flight overlap h1 is formed so that NGH clogged during the flight is crushed by each other's flight.

  A gap h2 between the flights 2b, 3b and the barrel inner wall surface 4a is formed so as to peel off the NGH fixed to the barrel inner wall surface 4a.

  The screw shafts 2a and 3a are formed in a tapered shape with a gradually increasing diameter from the supply port 12a toward the discharge port 12b, or formed so that the flight pitch becomes smaller. Further, a pressure holding unit 5 is provided between the discharge port 12b and the tip of the screw shaft so as to form a material seal with NGH itself at a high pressure.

  Furthermore, a roll forming machine in which hemispherical dents are formed on the two roll surfaces as used in the forming step P6 is disposed at the discharge port 12b.

  The finely powdered NGH transferred from the secondary generation reaction device 22 is introduced into the supply port 12a of the transfer device 1, and the NGH is transferred to the discharge port 12b side with the rotation of the screws 2 and 3. . As the screw shafts 2a, 3a gradually increase in diameter, the gap between the barrel inner wall surface 4a and the screw shafts 2a, 3a decreases, and NGH is compressed and the pressure of the NGH itself increases accordingly. And the discharge of NGH is suppressed by the roll 30a of the roll forming machine provided in the discharge port 12b, the pressure of NGH itself rises, and the material seal which interrupts | blocks the differential pressure of high pressure and low pressure forms in the pressure holding part 5 Is done.

  At this time, if the gas flows in the pipe line 17 exceeding a predetermined flow rate, the rotation speed of the roll 30a is decreased to reduce the discharge amount of NGH, the pressure applied to the material seal itself is increased, This prevents the high-pressure manufacturing apparatus L1 from flowing into the normal-pressure apparatus L2. In addition, when the gas flow rate in the pipe line 17 is reduced below a predetermined value so as not to pressurize the material seal excessively, the rotational speed of the roll 30a is increased to increase the discharge amount of NGH, and the material seal itself is applied. Reduce pressure. In addition to the gas flow meter, a gas pressure gauge may be installed to control the valve body 9a according to this pressure change.

  In this way, the sealing force of the material seal is adjusted, and NGH is continuously transferred to the storage tank 31 and stored while maintaining this sealing force.

  As described above, the NGH transfer method and apparatus according to the present invention continuously transfer NGH while sealing the differential pressure between the high-pressure manufacturing apparatus L1 and the low-pressure apparatus L2, greatly improving production efficiency. To do. Moreover, since shaping | molding is performed immediately after discharging from the transfer apparatus 1, the shaping | molding process P6 is abbreviate | omitted.

  Further, the coolant may be supplied to the cooling jacket of the transfer device 1 so that the NGH cooled in the supercooling step P4 is cooled and held.

  Furthermore, it is also possible to place a gear pump in place of the roll forming machine at the discharge port of the transfer device and limit the discharge of NGH from the discharge port 12b by this gear pump. The operation of the gear pump can be controlled by a gas flow meter, a gas pressure gauge, or the like.

It is a schematic block diagram of the transfer method and transfer apparatus which concern on embodiment of this invention. It is a front view of the transfer device concerning an embodiment of the present invention. It is a schematic block diagram of the transfer apparatus which concerns on other embodiment of this invention.

Explanation of symbols

n NGH M motor L1 generation process L2 post-process 1 transfer device 2 screw 2a, 3a screw shaft 2b, 3b flight 4 barrel 4a barrel inner wall surface

Claims (2)

In a method of continuously transferring a gas hydrate in a manufactured state or a high pressure / low temperature atmosphere close to this to a normal pressure or a low pressure / low temperature atmosphere close to this by a screw type conveyor,
The screw type conveyor has two screws arranged in parallel, and these two screws have the same or similar shape, pitch, and flight height,
And, between the flights of one screw shaft, the flights of the other screw shaft are arranged so as not to contact each other, these screw shafts are driven at the same speed in the same direction,
The gas hydrate supplied from the supply port of the screw-type conveyor is transferred to the discharge port while being consolidated to a level that can counter the differential pressure between the high pressure and the low pressure to form a material seal state. To transfer gas hydrate. In an apparatus for continuously transferring a gas hydrate in a manufactured or high pressure / low temperature atmosphere to a normal pressure or low pressure / low temperature atmosphere by a screw conveyor.
The screw type conveyor has two screws arranged in parallel, and these two screws have the same or similar shape, pitch, and flight height,
In addition, the flights of the other screw shaft are arranged so as not to contact each other between the flights of one screw shaft, and these screw shafts rotate in the same direction at the same speed, and A gas hydrate transfer apparatus, characterized in that the transport amount of gas hydrate between one pitch is gradually reduced.

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