JP4751110B2 - Natural gas hydrate decomposition method and decomposition apparatus - Google Patents

Description

  The present invention relates to a decomposition method and a decomposition apparatus for decomposing and gasifying natural gas hydrate.

  Currently, as a method of transporting domestically produced natural gas to the country, liquefied natural gas (hereinafter referred to as “LNG”) generated by cooling the natural gas to a temperature at which the natural gas is liquefied in a plant constructed in the production area. The method of performing in the state is adopted.

  However, the temperature at which natural gas is liquefied is as low as −162 ° C., and a large amount of capital is required to manufacture and hold storage facilities and transport ships that can maintain such a low temperature state. .

  Therefore, recently, a means for hydrated storage and transportation of natural gas has attracted attention. This hydrate of natural gas is called natural gas hydrate (hereinafter referred to as “NGH”), a molecule that forms the natural gas in a spherical shape created by water molecules or a soccer ball-like lattice formed by crushing it. For example, it has a structure in which methane, ethane, propane or the like is incorporated, and is classified as a kind of inclusion compound.

  Compared with LNG, NGH has a smaller volume reduction rate per unit volume (LNG: 1/600 vs. NGH: 1/170), but can be generated even in an extremely low temperature state like LNG (normally It is about -80 ° C under pressure and about 5 ° C at 5.4 MPa, and if it is cooled to about -20 ° C under normal pressure, it can be stored and transported stably because of its self-preserving property. It is expected that the cost for facilities and transport ships can be greatly reduced.

  Here, in the place where the transported NGH is received, it is necessary to generate natural gas by thermally decomposing NGH and gasifying it.

  Various methods have been proposed for the gasification of NGH.

  For example, in Japanese Patent Application Laid-Open No. 2001-279281, as shown in FIG. 4, the NGH 41 and the mass 42 are accommodated in the processing container 40, and the processing container 40 is rotated while supplying hot water 43 therein. Therefore, a decomposition apparatus that decomposes NGH 41 to generate natural gas 44 has been proposed. In this decomposition apparatus, the NGH 41 and the mass 42 collide with each other in the processing container 40, and the ice film formed on the surface of the NGH 41 is crushed by the self-preserving effect, so that the decomposition of the NGH 41 is promoted. It has become.

In Japanese Patent Application Laid-Open No. 2004-75849, as shown in FIG. 5, hot water 53 in which NGH (not shown) pulverized by a pulverizer 51 in a regasification tank 50 is stirred by a stirrer 52. There has been proposed a decomposition apparatus that decomposes NGH to generate natural gas 54 by introducing it into the interior.
This decomposition apparatus intends to promote the decomposition by previously pulverizing the solid pellet-shaped NGH and then stirring in a large amount of hot water 43.
JP 2001-279281 A JP 2004-75849 A

  However, in the above decomposition method and apparatus, the separation (gas-liquid separation) of natural gas and water (hereinafter referred to as “decomposed water”) generated by thermally decomposing NGH is stirred together with hot water used for the thermal decomposition. Therefore, there is a problem that gas-liquid separation takes time.

  In particular, when the produced natural gas is used in a gas turbine, the pressure in a vessel (gasification tank) in which gasification is performed is a gas pressure required by the gas turbine (for example, 1.0 to 5.0). Therefore, the natural gas generated from NGH is present in the water as extremely small bubbles of about several μm. Accordingly, the buoyancy applied to the bubbles in water is reduced, and it takes a longer time for gas-liquid separation. Therefore, it is necessary to enlarge the gasification tank to ensure the water retention time. The enormous gasification tank requires a large amount of construction costs and a large site, which increases the production cost of natural gas.

  The present invention has been made in view of such a problem, and an NGH decomposition method capable of promptly performing gas-liquid separation accompanying gasification of NGH even under a high pressure required by a gas turbine. And a disassembling apparatus.

  The method for decomposing NGH according to the present invention includes a step of pulverizing NGH, a step of holding the pulverized NGH on the upper surface of a porous support, and a step of thermally decomposing by spraying hot water on the held NGH. It consists of

  The NGH decomposition apparatus according to the present invention includes a gasification tank that reacts NGH and hot water to generate natural gas, a supply unit that supplies the NGH from an upper part of the gasification tank, and the gasification tank. An NGH decomposition apparatus comprising circulation means for heating water discharged from the gasification tank and supplying it to the gasification tank; and exhaust means for exhausting the generated natural gas to the outside of the gasification tank, The chemical conversion tank includes an NGH pulverizing means supplied by the supplying means, a porous support disposed below the pulverizing means and holding the pulverized NGH, and between the pulverizing means and the porous support. And spraying means for spraying hot water to the held NGH.

  According to the present invention, the gas-liquid separation accompanying the gasification of NGH can be performed promptly even under a high pressure required by the gas turbine, so the gasification tank can be downsized to reduce the supply cost of natural gas. It becomes possible to do.

  An embodiment according to the present invention will be described with reference to FIG.

  FIG. 1 is a system diagram of an NGH decomposition apparatus according to the present invention.

  The NGH decomposition apparatus includes a gasification tank 1 where NGH is thermally decomposed, an NGH supply means 2 provided at the upper part of the gasification tank 1, a hot water circulation means 3 for thermally decomposing NGH, and a generated natural gas. It comprises gas discharging means 4.

  The gasification tank 1 is a steel container and has a strength that can sufficiently withstand a pressure (for example, 1.0 to 5.0 MPa) required by a gas turbine. At the top of the gasification tank 1, a pulverizer 6, which is a pulverizing means for pulverizing the NGH 5 supplied by the supplying means 2 to a size of several millimeters, is disposed. Although there are various types of the pulverizer 6, it is preferable to use a rotor type granulator as shown in FIG. 2 because of its simple structure and excellent durability.

  This rotor type granulator is composed of a cylindrical rotor 30 that is horizontally placed and rotated, and a screen 31 that is attached so as to surround the lower half of the rotor. A push plate 32 is provided on the outer periphery of the rotor 30. Are attached at equal intervals, and the inclined surface 33 at the tip of the push plate 32 faces the inner surface of the screen 31. The screen 31 is composed of a metal mesh having a mesh size of several mm square.

  The NGH 5 thrown from above the rotor 30 rotates while being sandwiched between the rotor 30 and the screen 31 and is pressed against the screen 31 by the inclined surface 33 of the push plate 32, so that the NGH 5a having a size of several mm is obtained. And is supplied downward through the mesh of the screen 31.

  A porous support 7 is provided below the pulverizer 6 so as to cover the entire radial cross section of the gasification tank 1. The pores of the porous support 7 are manufactured to be finer (less than 1 mm square) than the size of the pulverized NGH 5a. The porous support 7 is preferably a stainless steel wire mesh from the viewpoint of excellent corrosion resistance.

  Between the pulverizer 6 and the porous support 7, a ring-shaped spray tube 8, which is a means for spraying hot water 9, is disposed. The ring-shaped spray tube 8 is composed of a ring-shaped pipe attached so as to be in contact with the radially inner surface of the gasification tank 1, and the surface of the pipe is uniformly warm water on the entire upper surface of the porous support 7. A plurality of injection holes are provided so that 9 can be dispersed.

  Connected to the bottom of the gasification tank 1 is a conduit for guiding the stored water 10 comprising hot water after reacting with the pulverized NGH 5a and decomposed water generated by the decomposition of the NGH 5a to the circulation means.

  The NGH supply means 2 provided in the upper part of the gasification tank 1 includes a first introduction pipe 11, a first gate valve 12 provided in the middle thereof, a second introduction pipe 14 and a second gate provided in the middle thereof. It consists of a valve 15 and an introduction tank 13 connecting the first introduction pipe 11 and the second introduction pipe 14. These have a function as a kind of air lock as a whole, and NGH 5 can be supplied to the gasification tank 1 maintained in a high pressure state by proper valve operation without breaking airtightness. Yes.

  The hot water circulation means 3 includes a pump 16 for leading the water stored in the gasification tank 1 to the outside, a bubble separator 17 for removing bubbles remaining in the water pressurized by the water pump, And the heater 18 which heats the isolate | separated water and produces | generates warm water is comprised.

  Further, exhaust means for exhausting the natural gas generated in the gasification tank 1 to the outside includes a first exhaust pipe 19 and a first exhaust valve 20 that communicate with the upper space of the pulverizer 2, a pulverizer 6 and a ring-shaped spray pipe 8. The second exhaust pipe 21 and the second exhaust valve 22 communicated with the space between them, and the third exhaust pipe 23 and the third exhaust valve 24 communicated with the space between the porous support 7 and the stored water 10. Each is connected to the gas turbine 25.

  Next, a process of decomposing NGH using the decomposing apparatus configured as described above will be described.

  With the first gate valve 11 opened and the second gate valve 15 closed, NGH 5 is supplied from the NGH storage facility (not shown) to the introduction tank 13 through the first introduction pipe 11. After the NGH 5 is stored in the introduction tank 13, the first gate valve 12 is closed and then the second gate valve 15 is opened to supply the NGH 5 to the upper side of the pulverizer 6. In addition, after supplying NGH5, the 2nd gate valve 15 is closed again.

  By performing such a valve opening / closing operation, the influence on the gasification tank 1 in a high pressure state can be suppressed.

  The NGH 5 supplied to the pulverizer 6 is pulverized to a size of several millimeters, and dropped and held on the porous support 7 disposed below the pulverizer 6. And the warm water 9 is sprayed from the ring-shaped spray pipe 8 to the held NGH 5a, and the NGH 5a is decomposed by heating to be decomposed into natural gas and decomposed water.

  At this time, the NGH 5a contacts and reacts with the amount of hot water required for decomposition, and excess hot water is removed through the porous support 7, so that gas-liquid separation of the generated natural gas and decomposed water is prevented. It will be done instantly.

  In addition, since NGH 5a is always in contact with warm water at a constant temperature, the temperature difference between them (gasification driving force) can be increased compared to the conventional stirring of NGH in warm water. Natural gas can be stably generated.

  The natural gas generated here is mainly supplied to the gas turbine 25 via the second exhaust pipe 21, but a part of the natural gas flows back to the upper side of the pulverizer 6, so that it is recovered from the first exhaust pipe 19. Will be.

  Most of the natural gas produced by the decomposition of NGH will be recovered here.

  NGH, which has become smaller due to the progress of the decomposition reaction, passes through the holes of the porous support 7 and falls into the stored water 10 composed of hot water 9 and decomposition water. This reduced NGH is further decomposed in the stored water 10 to produce natural gas. The natural gas generated here is separated from the stored water 10 during the storage period, and is supplied to the gas turbine 25 through the third exhaust pipe 23.

  The stored water 10 is led out of the gasification tank 1 by a pump 16 provided in a conduit connected to the bottom of the gasification tank 1. The fine gas state natural gas remaining without being recovered in the gasification tank 1 is removed by the bubble separator 17 and sent to the gas turbine 25. Since the amount of natural gas remaining until this time is extremely small, the bubble separator 17 can also be reduced in size, and the manufacturing cost of the separation device can be further reduced.

  The water separated by the bubble separator 17 is heated by the heater 18 and supplied to the ring-shaped spray tube 8 again.

  The temperature of the hot water 9 is determined by the internal pressure of the gasification tank 1, the amount of NGH, the amount of circulating water, and the like.

  Another embodiment according to the present invention will be described with reference to FIG. FIG. 3 shows a system diagram of an NGH decomposition apparatus according to the present invention. In addition, the cross section of the gasification tank 1 corresponds to the thing from the direction which rotated FIG. 1 90 degree | times to the axial direction. Moreover, although the same code | symbol is attached | subjected about the part which is common in FIG. 1, a part of supply means 1 is abbreviate | omitted and shown.

  When a rotor-type granulator as shown in FIG. 2 is used for the pulverizer 6, an unground NGH 5 is formed from a gap generated between the axial end of the rotor 30 and the inner wall of the gasification tank 1. Is likely to fall into the stored water 10. If the amount of NGH 5 that falls in this way increases, the temperature of the stored water 10 decreases and the driving force for gasification decreases, and galling occurs between the rotor 6 and the inner wall, thereby improving the performance of the pulverizer 6. May deteriorate.

  Therefore, since it is necessary to limit the supply amount of NGH5 so that unprocessed NGH5 is not deposited on the rotor 30 as much as possible, there is a possibility that the processing amount of the decomposition apparatus is greatly limited.

  Therefore, in the present embodiment, as shown in FIG. 3, by providing two rotor-type granulators in parallel in the gasification tank 1, the amount of NGH 5 deposited on the rotor 30 is reduced, and the gas An inclined plate 36 is provided between the inner wall of the chemical conversion tank 1 and the screen 31 to prevent the unground NGH 5 from falling. The supply means 1 for NGH 5 is provided for each pulverizer 6, and the NGH 5 supplied into the gasification tank 1 is guided through a cage-like wire mesh 35 provided on each rotor 30. , Will be supplied to each pulverizer 6.

  In this embodiment, since the pulverizer 6 is housed in the gasification tank 1, the gasification tank 1 having a conventional shape is used as it is instead of the gasification tank 1 having a special shape as shown in FIG. Since it can be used, the construction cost of the decomposition apparatus can be further reduced.

1 is a system diagram of a gas hydrate decomposition apparatus according to the present invention. It is sectional drawing of a rotor type granulator. It is a systematic diagram of other embodiment of a gas hydrate decomposition | disassembly apparatus. It is a systematic diagram of the conventional gas hydrate decomposition | disassembly apparatus. It is a systematic diagram of another conventional gas hydrate decomposition | disassembly apparatus.

Explanation of symbols

1 Gasification tank 2 NGH supply means 3 Circulating water supply means 4 Natural gas exhaust means 5 NGH
5a NGH after grinding
6 Crusher 7 Porous support 8 Ring spray pipe 9 Sprinkled water 10 Reserved water 11 First introduction pipe 12 First gate valve 13 Introduction tank 14 Second introduction pipe 15 Second gate valve 16 Pump 17 Bubble separator 18 Heating 19 First exhaust pipe 20 First exhaust valve 21 Second exhaust pipe 22 Second exhaust valve 23 Third exhaust pipe 24 Third exhaust valve 25 Gas turbine 30 Rotor 31 Screen 32 Push plate 33 Inclined surface 34 Electric motor 35 Cage-shaped Wire mesh 36 Inclined plate 40 Processing vessel 41 NGH
42 NGH mass 43 Hot water 44 Natural gas 45 Gas-liquid separator 50 Regasification tank 51 Crusher 52 Stirrer 53 Hot water 54 Natural gas 55 Gas hydrate supply device 56 Electric motor 57 Circulation pipe

Claims (3)

A natural gas hydrate decomposition method for producing natural gas from natural gas hydrate,
Crushing natural gas hydrate;
Holding the pulverized natural gas hydrate on the upper surface of the porous support;
Sprinkling hot water on the retained natural gas hydrate and thermally decomposing,
A natural gas hydrate decomposition method comprising: A gasification tank that reacts natural gas hydrate with hot water to produce natural gas;
Supply means for supplying the natural gas hydrate from the upper part of the gasification tank;
A circulation means for heating and discharging water discharged from the gasification tank to the gasification tank;
Exhaust means for exhausting the generated natural gas to the outside of the gasification tank;
A natural gas hydrate decomposition apparatus comprising:
The gasification tank is
Pulverizing means for natural gas hydrate supplied by the supplying means;
A porous support disposed below the pulverizing means and holding the pulverized natural gas hydrate;
Spraying means for spraying hot water on the retained natural gas hydrate disposed between the pulverizing means and the porous support;
Natural gas hydrate decomposition equipment equipped with. 3. The natural gas hydrate decomposition apparatus according to claim 2, wherein the pulverizing means is a rotor type granulator.

Images