JP4625355B2 - Method for preventing purge gas generation during gas hydrate production - Google Patents

Description

  The present invention relates to a purge gas generation preventing method for preventing the generation of purge gas when pelletized gas hydrate is depressurized to normal pressure by a depressurization apparatus.

  As shown in FIG. 8, the conventional natural gas hydrate production system includes, for example, a first generator 1, a dehydrator 2, a second generator 3, a granulator 4, a decompressor 5, a cooler 6, and A storage tank 7 is provided, and natural gas (raw gas) g and water (raw water) w are introduced into the first generator 1, and the natural gas g and water w are actively added by a known method such as a bubbling method. It is made to contact and the natural gas hydrate n is produced | generated.

  Since the natural gas hydrate n in the first generator 1 is in the form of a slurry (natural gas hydrate content of about 20%), it is introduced into the dehydrator 2 and dehydrated by other methods such as mechanical or gravity dehydration. However, the content of the natural gas hydrate n is increased (for example, about 70%).

  The water w removed by the dehydrator 2 is returned to the first generator 1, and the natural gas hydrate n dehydrated by the dehydrator 2 is introduced into the second generator 3 and further dehydrated. ing. The second generator 3 reacts (hydration reaction) the unreacted natural gas g introduced from the first generator 1 and the water w attached to the natural gas hydrate n, thereby producing a natural gas hydrate. The content of n is further increased (for example, about 90%). The reaction heat generated in the first generator 1 and the second generator 3 is generally removed by a refrigerator (not shown).

  The natural gas hydrate n dehydrated in the second generator 3 is formed into pellets p having an arbitrary shape and size by the granulator 4 and then stored in the natural gas hydrate by the decompression device 5 for storage under normal pressure. The pressure is reduced from the rate generation pressure (for example, 54 ata (53 MPa)) to normal pressure.

  The pellet-shaped natural gas hydrate p after depressurization is cooled to a predetermined temperature (for example, about −20 ° C.) by the cooler 6 and then stored in the storage tank 7 under normal pressure.

On the other hand, the unreacted natural gas (purge gas) j removed by the depressurization device 5 is boosted to a predetermined pressure (for example, 54 data (53 MPa)) by the barge gas compressor 8 and then returned to the first generator 1. (For example, refer to Patent Document 1).
JP 2003-105362 A (page 11-12, FIG. 12)

  However, in the conventional natural gas hydrate production system, as described above, the unreacted natural gas j removed by the depressurization device 5 is boosted to a predetermined pressure (for example, 54 data (53 MPa)) by the purge gas compressor 8. Therefore, there is a problem that the power consumption for operating the purge gas compressor 8 or the power consumption for operating the refrigerator for removing heat increases.

  The present invention has been made to solve such problems, and it is an object of the present invention to suppress the generation of purge gas when storing natural gas hydrate produced under high pressure under normal pressure. is there.

  In order to achieve such an object, the present invention is configured as follows.

In the invention according to claim 1, natural gas as a raw material gas is hydrated with water to produce a gas hydrate, and the gas hydrate is formed into a pellet by a granulator, and then the pellet When the gas hydrate in the form is decompressed to normal pressure by a depressurizer and stored,
Mixer constituting the depressurization device, the subcooler, the lock hopper, vacuum drum, a condenser, out of the heater, the pellet introduction tube which projects into the mixer, to constitute the raw material gas A step of liquid-sealing with liquefied gas obtained by liquefying propane , which is one of the constituent gases,
While storing classified to pelletized gas hydrate the liquefied gas and pellets of gas hydrate discharged from the mixer into the lock hopper, the step of storing the liquefied gas to the subcooler in When,
A step of cooling to a predetermined temperature below the freezing point of the liquefied gas stored in the supercooled vessel utilizing LNG cold heat,
Cooling by introducing a pelletized gas hydrate and the subcooler liquefied gas that has been cooled to a predetermined temperature below the freezing point of the lock hopper into the vacuum within the drum supercooling pelletized gas hydrate below freezing Process,
Introducing propane gas vaporized in the decompression drum into the condenser and condensing using the cold heat of LNG;
A method for preventing the generation of purge gas during gas hydrate production comprising the step of raising the temperature of the liquid propane condensed in the condenser to a predetermined temperature by the heater when returning to the mixer .

  The invention described in claim 2 is the purge gas generation prevention method during gas hydrate production according to claim 1, characterized in that the pressure in the mixer is maintained at about the critical pressure of the liquefied gas.

  The invention according to claim 3 is the gas hydrate production according to claim 1, wherein the liquefied gas is flash-expanded in the decompression drum to cool the pellet-like gas hydrate to around -20 ° C. This is a method for preventing purge gas generation at the time.

  As described above, the invention according to claim 1, the raw material gas is hydrated with water to produce a gas hydrate, and the gas hydrate is formed into a pellet by a granulator. When this pellet-shaped gas hydrate is depressurized and stored to normal pressure by a depressurizer, the gas hydrate discharge port of the granulator is sealed with a liquefied gas of the same system as the raw material gas in the mixer. Therefore, when the pressure is reduced by the pressure reducing drum which is a pressure reducing device and the pellet-like gas hydrate is taken out under the atmospheric pressure, the unreacted source gas (purge gas) can be prevented from flowing out.

  Therefore, unlike the conventional case, it is not necessary to increase the pressure of the purge gas flowing out from the decompression device to the gas pressure of the raw material gas and return it to the upstream side of the first generator. it can. For this reason, the pellet-shaped gas hydrate cheaper than before can be manufactured.

  Furthermore, the present invention uses the cold heat of LNG (liquefied natural gas) to flush the liquefied gas cooled to a predetermined temperature to supercool the pellet-like gas hydrate below the freezing point, thus eliminating the need for a refrigerator. Therefore, there is an advantage that power consumption of the plant can be suppressed.

  Since the pressure in the mixer is maintained at about the critical pressure of the liquefied gas, the gas hydrate discharge port of the granulator is liquefied in the same system as the raw material gas in the mixer. It can be sealed with gas.

  According to the third aspect of the present invention, the liquefied gas is flash-expanded in the decompression drum under normal pressure to cool the pellet-like gas hydrate to around -20 ° C. The rate can be cooled, and the power consumption of the plant can be suppressed as compared with the conventional case. For this reason, the pellet-shaped gas hydrate cheaper than before can be manufactured.

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

  FIG. 1 is a schematic configuration diagram of a natural gas hydrate production system according to the present invention. A first generator 1, a dehydrator 2, a second generator 3, a granulator 4, a depressurizer 5, The raw material gas (natural gas) g having a predetermined pressure (for example, 54 ata (5.30 MPa)) and water w at normal temperature (for example, 4 ° C.) are introduced into the first generator 1. In addition, natural gas g and water w are reacted by an arbitrary method such as a bubbling method to generate natural gas hydrate (hereinafter referred to as gas hydrate) n. At that time, the heat of reaction is removed using the cold heat of LNG.

  Since this gas hydrate n is in a slurry state with a gas hydrate content of 20%, it is introduced into the dehydrator 2 for dehydration, and the gas hydrate content is increased to about 70%. The first generator 1 is returned.

  The gas hydrate n dehydrated by the dehydrator 2 is introduced into the second generator 3, the natural gas g from the first generator 1 is introduced, and the unreacted water w accompanying the gas hydrate n is introduced. To increase the hydrate conversion rate of gas hydrate to about 90%. In the second generator 3, similarly to the first generator 1, the reaction heat is removed using the cold of LNG (liquefied natural gas).

  The gas hydrate n substantially dehydrated in the second generator 3 is formed into pellets p having an arbitrary shape (for example, spherical shape) and size (for example, about 5 to 70 mm) by the granulator 4, and will be described later. The pressure is released to normal pressure by the pressure release device 5, and then stored in the storage tank 7 at normal pressure and below freezing (for example, about -20 ° C).

  As shown in FIG. 2, the depressurization device 5 includes a mixer 11, a supercooler 12, a lock hopper 13, a decompression drum 14, a condenser 15, and a heater 16. And the storage tank 7 is installed below the decompression drum 14. A valve 17 is provided in the pipe connecting the storage tank 7 and the decompression drum 14.

  The mixer 11 encloses a hydrocarbon-based liquefied gas i such as liquid propane in the container, and the lower end portion of the pellet introduction pipe 18 protruding into the mixer 11 by the liquefied gas i is liquid-sealed. It has become. In addition, the mixer 11 is provided with a pressure equalizing pipe 19 at the upper end thereof, and a part of the gas j accumulated in the upper space of the mixer 11 is communicated with the first generator 1.

  At that time, the pressure A of the gas j existing in the upper space of the mixer 11 is the operating pressure of the generation process.

  Accordingly, the liquefied gas i is maintained at the pressure A by the heater 16 so as to reach the operating temperature of the production process. When the liquefied gas i is propane, A exceeds the critical pressure of propane.

  The pipe connecting the mixer 11 and the subcooler 12 has a pressure reducing valve 22, and the pipe connecting the supercooler 12 and the pressure reducing drum 14 has an expansion valve 23. Further, the supercooler 12 is provided with a sieve 24 inside to separate the pellet-like gas hydrate p and the liquefied gas i. The sieve 24 is provided to be inclined so that the pellet-like gas hydrate p rolls down.

  Further, the pipe connecting the upper side surface of the subcooler 12, that is, the upper space of the subcooler 12 divided by the sieve 24, and the decompression drum 14 includes the first valve 25, the lock hopper 13, and the first Two valves 26 are provided in this order.

  As shown in FIG. 3 (a), the pressure reducing valve 22 has a plurality of guide vanes 29 that are spirally bent above the hydraulic slide valve 28, so that the pellet-like gas hydrate p and the liquefied gas i are supplied. When discharging, as shown in FIG. 3 (b), the pellet-shaped gas hydrate p and the liquefied gas i fall while spirally turning.

  2, the liquefied gas return pipe 31 connecting the decompression drum 14 and the mixer 11 includes a valve 32, a blower 33, a condenser 15, a pump 35, and a heater 16. It is provided in order. The heater 16 uses fresh water k as a heat medium, but the fresh water supply amount is controlled by a temperature control valve 38 provided in the pipe 37.

  Further, the storage tank 7 is provided with a pressure equalizing discharge pipe 39 so as to return the purge gas j ′ generated in the storage tank 7 to the liquefied gas return pipe 31.

  FIG. 4 shows a state diagram of propane.

  In FIG. 4, f → a is a propane cooling process by LNG cold heat in the condenser 15. a → b is a process in which the pressure of the propane liquid condensed by the condenser 15 is increased by the pump 35. b → c is a heating process with fresh water k (temperature adjustment). c → d is the pressure reduction by the pressure reducing valve 22. The pellet-like gas hydrate n and the propane liquid i are separated here. d → e is a process in which the separated propane solution is supercooled by LNG cold heat (5 ° C. → −40 ° C.). e → a takes heat from the pellet-like gas hydrate p delivered from the lock hopper 13 in the process of the expansion valve 23, evaporates all propane and cools the pellet-like gas hydrate n to −20 ° C. . The freezing effect at that time is a process of a → f.

  Here, the freezing effect (a → f) is 101 kcal / kg.

  The flow rate ratio between the pellet-like gas hydrate and liquid propane is determined by cooling the pellet-like gas hydrate from 5 ° C. to −20 ° C. due to the cooling effect.

That is, when the circulation amount of propane is m and the removal amount of the pellet-like gas hydrate is G, the following equation is obtained.
G / m = 8.08

Next, the operation of the decompression device will be described with reference to FIGS.
As shown in FIG. 5, when the pressure reducing valve 22 and the first valve 25 at the top of the lock hopper are switched from “closed” to “open”, the pellet-shaped gas hydrate p in the mixer 11 and liquid propane which is a liquefied gas i flows into the subcooler 12.

  The liquid propane i flowing into the subcooler 12 passes through the sieve 24 and accumulates in the subcooler 12. On the other hand, the pellet-shaped gas hydrate p blocked by the sieve 24 rolls along the inclined surface of the sieve 24 and is stored in the lock hopper 13 through the first valve 25.

  The liquid propane i stored in the supercooler 12 is cooled to −40 ° C. by the intermediate refrigerant s cooled using the cold heat of LNG.

  Next, as shown in FIG. 6, after the pressure reducing valve 22 and the first valve 25 at the upper part of the lock hopper are switched from “open” to “closed”, the second valve 26 at the lower part of the lock hopper, the expansion valve 23, and the valve 32. Is switched from “closed” to “open”, the pellet-like gas hydrate p in the lock hopper 13 is supplied into the decompression drum 14 through the second valve 26.

  On the other hand, the liquid propane i in the supercooler 12 is flushed in the decompression drum 14 by the expansion valve 23. Then, when evaporating along with the flash, the pellet-shaped gas hydrate p supplied into the decompression drum 14 is cooled to -20 ° C.

  The vaporized propane gas i 'is supplied to the condenser 15 by the blower 33, where it is condensed and returned to the liquid propane i. Here, an intermediate refrigerant s cooled using the cold heat of LNG is used as the refrigerant of the condenser 15.

  The liquid propane i condensed by the condenser 15 is supplied to the mixer 11 by the pump 35. At that time, the liquid propane i is heated from −40 ° C. to 5 ° C. by the fresh water k while passing through the heater 16.

  In this case, the liquid propane i and the pellet-like gas hydrate p are at substantially the same temperature, and the mutual heat exchange is negligibly small.

  Next, after switching the second valve 26, the expansion valve 23, and the valve 32 below the lock hopper from "open" to "closed", as shown in FIG. When “open”, the pellet-shaped gas hydrate p in the decompression drum 14 is supplied to the storage tank 7 through the valve 17. The pressure equalizing pipe 39 communicates the pressure reducing drum 14 and the storage tank 7.

It is a schematic block diagram of the natural gas hydrate manufacturing system which concerns on this invention. It is a block diagram of the decompression apparatus in this invention. (A) It is sectional drawing of a pressure-reduction valve, (b) It is action explanatory drawing of a pressure-reduction valve. It is a state diagram of propane. It is explanatory drawing which discharges the pellet-form gas hydrate and liquid propane in a mixer. It is explanatory drawing which flushes the liquid propane in a subcooler, while supplying the pellet-form gas hydrate in a lock hopper in a pressure reduction tank. It is explanatory drawing which supplies the pellet-shaped gas hydrate in a decompression tank in a storage tank. It is a schematic block diagram of the conventional natural gas hydrate manufacturing system.

Explanation of symbols

g Raw gas i Liquefied gas n Gas hydrate p Pellet gas hydrate w Water 4 Granulator 5 Depressurizer 7 Storage tank 11 Mixer 12 Supercooler 13 Rock hopper 14 Decompression drum 18 Gas hydrate outlet 24 Classification means

Claims (3)

Natural gas as raw material gas is hydrated with water to produce gas hydrate, and this gas hydrate is formed into pellets by a granulator, and then the pellet-like gas hydrate is depressurized. When storing to normal pressure by the device,
Mixer constituting the depressurization device, the subcooler, the lock hopper, vacuum drum, a condenser, out of the heater, the pellet introduction tube which projects into the mixer, to constitute the raw material gas A step of liquid-sealing with liquefied gas obtained by liquefying propane , which is one of the constituent gases,
While storing classified to pelletized gas hydrate the liquefied gas and pellets of gas hydrate discharged from the mixer into the lock hopper, the step of storing the liquefied gas to the subcooler in When,
A step of cooling to a predetermined temperature below the freezing point of the liquefied gas stored in the supercooled vessel utilizing LNG cold heat,
Cooling by introducing a pelletized gas hydrate and the subcooler liquefied gas that has been cooled to a predetermined temperature below the freezing point of the lock hopper into the vacuum within the drum supercooling pelletized gas hydrate below freezing Process,
Introducing propane gas vaporized in the decompression drum into the condenser and condensing using the cold heat of LNG;
A method for preventing the generation of purge gas during gas hydrate production, comprising the step of raising the temperature of the liquid propane condensed in the condenser to a predetermined temperature when returning to the mixer. 2. The method for preventing purge gas generation during gas hydrate production according to claim 1, wherein the pressure in the mixer is maintained at about the critical pressure of liquefied gas. The pelletized gas hydrate is cooled to around -20 ° C by expanding the liquefied gas in the decompression drum at a pressure close to normal pressure. Purge gas generation prevention method.

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