JP2011021705A - Method of gasifying gas hydrate, and device therefor - Google Patents

Abstract

A method and apparatus for efficiently decomposing gas hydrate pellets and taking out gas.
[Solution]
The gas hydrate pellets are supplied to the decomposition tank, and the pellets are dammed in the downstream side of the decomposition tank so that the pellets are densely packed. Gas hydrate decomposition method.
[Selection] Figure 1

Description

  The present invention relates to a method and apparatus for efficiently extracting gas by thermally decomposing gas hydrate pellets.

  In areas where pipelines are not installed, natural gas is once artificially liquefied and transported as liquefied natural gas (LNG) by a dedicated ship or lorry. LNG can contain about 600 times the volume of its gas by liquefaction, but the source gas is cooled to an extremely low temperature of -162 ° C and liquefied, so refrigeration power for liquefaction is required. In addition, high heat insulation performance is required for storage facilities.

  On the other hand, gas hydrate is a hydrate that has been converted into a solid by the reaction of gas and water, taking the gas into a cage made of water molecules. When the raw material gas is natural gas, a mixed gas containing methane as a main component is taken in, and this is called natural gas hydrate (NGH). NGH remains stable under low temperature and high pressure, and usually becomes a decomposition zone under normal temperature and pressure, so it exists in the permafrost region on land, and under the sea floor deeper than 500m where high water pressure is applied in the sea. To do.

  NGH has a unique property that the gas can contain about 160 times its volume in the structure, and the decomposition rate is relatively slow at temperatures from -10 ° C to -20 ° C under atmospheric pressure, which is the decomposition region. Are known. Therefore, for example, NGH is artificially manufactured at a pressure of about 5 MPa and a temperature of about 5 ° C., and then cooled and depressurized to store and transport hydrates using a gradual area where decomposition is suppressed. Natural gas transport is attracting attention.

  Hydrate itself is powdery snow (fine powder) and bulky, and it is rarely used as it is in terms of transport efficiency and storage stability. "For example, it is transported or stored as a molded product having a diameter of 2 to 3 cm. Therefore, when the gas in the pellet is used as a raw material or fuel, the pellet is thermally decomposed and the generated gas is sent to the consumer.

  An example of artificial NGH production and storage will be introduced. The fine powdery raw material obtained in the hydrate generator is compressed into a pellet state by a pair of roller-type presses or molding dies provided with concave portions on the surface, and cooled to the storage temperature. For example, even if the pellets are supplied into a large storage tank having a diameter of 30 m and a height of 60 m, the pellets are not broken or crushed and have a strength so that the shape can be maintained. Therefore, in order to decompose such a strong pellet into water and gas and take out the gas, an efficient “regasification step” is required separately.

  For example, Patent Document 1 discloses a regasification process. According to this document, pellets are filled in warm water in a horizontal rotary gasification vessel, and the generated gas and water are supplied to a gas-liquid separator. The gas is separated from the gas-liquid separator, and the gas is extracted from the gas-liquid separator. The water is extracted by a pump, heated, and then returned to the gasification vessel.

  Further, in Patent Document 2, a ring-shaped nozzle for supplying gas hydrate is arranged at the upper part in a vertically long gasification container, a rotating blade is provided at the lower end in the center of the container, and a crushing blade is provided at the upper part. There has been proposed an apparatus in which a rotating shaft provided is arranged, a thick cylindrical heat exchanger is formed around the stirring blade, and a bubble separation plate is provided at the bottom of the container.

JP 2001-279281 A Japanese Patent Laid-Open No. 2005-239782

  The regasification apparatus described in Patent Document 1 supplies warm water, a mass for gas hydrate destruction, and gas hydrate pellets in a horizontal processing container, and rotates the processing container itself to rotate the mass. While the gas hydrate is crushed by the body, it is vaporized with the heat of warm water to generate gas. Therefore, this apparatus has a drawback that a large driving power is required to rotate the agglomerates and pellets. In addition, the gas hydrate pellets are crushed and mixed with warm water and gasified while stirring, and this device configuration requires space for rotation and stirring power, as well as pellets to float. The gasification efficiency is extremely poor and it is not suitable for processing a large amount of gas hydrate pellets.

  In the case of the apparatus described in Patent Document 2, when this apparatus is used, gas hydrate is supplied from the nozzle while circulating hot water in the container, and is crushed by crushing blades. The mixture is further gasified while being stirred in the heat exchanger and transferred to the lower part of the container, hot water is extracted from the lower end of the container, and the gas generated by gasification at the upper part of the container is discharged to the gas discharge pipe. It is configured to discharge more.

  The gas hydrate regasification apparatus cited above crushes pellets in a container, decomposes the crushed material with mixing and stirring with warm water, and heat exchangers that produce warm water in the container. Various devices are required. In addition, there is a problem that the power used for the crushing and stirring is large, and the equipment cost and operation cost are high, and it is difficult to employ industrially.

  Therefore, the present inventors conducted the following experiment, paying attention to the arrangement of pellets and gasification efficiency as aggregates.

FIG. 4 shows a gasification vessel 30 having an inner diameter of 9.3 cm and a height of 20 cm. Thermometers 31a to 31d, a pump 32, a water supply tank 33, a water thermometer 34, A test device 40 comprising a flow meter 35, a gas-liquid separation tank 36, a gas flow meter 37, and a water flow rate measuring device 38 is prepared, and a methane hydrate pellet q having a diameter of 2 to 3 cm has an average filling rate of 66% (pellet volume). : 66%, water and gas volume: 34%), water is supplied from the water supply tank 33 using the pump 32, and the generated methane gas g is passed through the packed bed J filled with the pellets q. The Reynolds number (Re) of the feed water and the Nusselt number (Nu) indicating the heat transfer amount are calculated from the experimental results while being separated in the gas-liquid separation tank 36 and discharged through the gas flow meter 37, and FIG. Displayed as curve A.

  For comparison, curve B is the Nusselt number (Nu) calculated from the Lantz equation indicating the general heat transfer amount in the state of being filled with a solid object, and curve C is the Lantz indicating the general heat transfer amount of a single sphere. -Nusselt number (Nu) calculated from Marshall's equation is displayed for Reynolds number (Re).

  From the experimental result of curve A filled with pellets, when gasification is performed by filling pellets, for example, the heat transfer amount with Re of 250 is 2.0 times the heat transfer amount in the packed state shown in curve B, as well. When Re is 500, the ratio is 2.3 times, and as Re increases, the ratio further increases. The hot water passes through the gap between the pellets q filled in the gasification vessel 30 and the pellets q are gradually decomposed to generate gas. This gas is mixed into the hot water to form a mixed flow. When this generated gas is added to the supply water, the volume of the fluid is increased and becomes larger than the apparent Re calculated from the voids of the pellet. Moreover, when the pellets were gasified, it was possible to observe from experiments that bubbles were generated from the pellet surface, and that the generated gas collided with the pellet surface filled on the downstream side.

  Hydrate gasification in the filling tank has the effect of disturbing the flow of the pellet surface and actively stimulating the boundary layer (hereinafter referred to as turbulent flow effect), and a large heat transfer amount compared to the filling state without gasification. Can be obtained.

  In this way, with the hydrate pellets in a packed state, the feed water to which the generated gas is added is gasified by passing water from one direction and gasifying, and further, near the pellet surface As a result, a larger amount of heat transfer than the general heat transfer was obtained due to the turbulent flow effect caused by the bubble generation and the downstream collision.

  Since a high heat transfer amount can be obtained, the contact area between the solid pellet and the fluid as the heat source or the temperature difference between them can be reduced, and gasification can be efficiently performed.

[Comparison of regasification characteristics of the two methods]
(First stirring method apparatus)
The first regasification apparatus 10 shown in FIG. 6 is an apparatus that decomposes the pellet p by stirring it in the hot water h in a floating state and receives the heat while the pellet p freely moves in the hot water h. Is. In this type of solid-liquid contact state, heat transfer is received and decomposed while changing the relative position of the surface of the pellets p and the hot water h floating by mechanical stirring.

  FIG. 8A shows a model of this state, the pellet p has a sufficient interval so that it can rotate and move, the flow of the hot water h is represented by f, and the vortex is represented by v, The rotation of the pellet p is indicated by an arrow. The contact between the pellet p and the hot water h occurs during the movement of the pellet p. Therefore, depending on the relative speed between the hot water h by stirring and the surface of the pellet p that rotates and moves in synchronization with the flow. Although the amount of heat received is determined, it is difficult to generate a relative speed by tuning, and it can be determined that the amount of heat received is not very large.

In the thermal decomposition apparatus shown in FIG. 6, the pellet p is decomposed by the rotation speed of the stirring blade 2a and the temperature of the hot water h, and the amount of gas generated changes. Furthermore, in this embodiment, since the generated gas only floats in the floating pellet near the hot water surface in a state where the pellet is floating, the effect of increasing the speed by the generated gas cannot be expected. Therefore, in order to increase the amount of heat transfer, the pellet p itself is small in order to increase the contact area with the fluid, is destroyed in advance, or the gasification vessel itself is enlarged to increase the gasification rate. There is a way. Accordingly, the amount of gas generated is determined in relation to the stirring speed, the size of the pellet p and the container, and the temperature of the hot water.

(Second pellet compaction system)
In the second regasification apparatus 10 </ b> A shown in FIG. 7, the pellets p are transferred to the cracking cylinder 14 constituting the cracking unit 11 from the lower direction along with the flow of the hot water h, and are arranged on the upper part of the cracking unit 14. It is stopped by the obstacles on the screen 16 and densely packed into a dumpling state, and itself cannot move freely, the relative position with respect to the gasification vessel is almost fixed, and the displacement of the pellet p can be shifted in a small range by changing the size and shape of the pellet p. It comes to move with it.

  Even if these pellets are densely packed and each is restricted, a flow path formed by a narrow gap exists between the pellets p, and a mixed flow of water, warm water, and gas g generated by the decomposition of the pellets p. Is supplied to the gas separation unit 12 by a pipe 17, and water supplies pellets p to the flow from a circulation line 13, a pump 20, a heat exchanger 21, and a pellet supply device 22 connected to the circulation line 13. It is configured to be supplied to the disassembly cylinder 14 more.

  As shown in FIG. 8B, the hot water h flowing through the circulation pipe 13 including the pipe 17 flows through the gap between the aggregates of the pellets p in an arbitrary direction as shown by arrows, but the gap is fine. The contact between the hot water h and the pellet surface is forced. In other words, the hot water h that is forcibly supplied flows while strongly disturbing the interface with the pellet p, and gives a quantity of heat in the meantime to promote the thermal decomposition of the pellet p, and is a hot water forced contact decomposition device. It can be said.

  The fluid resistance when the hot water h passes through a narrow gap between the pellets p is related to the size of the pellets p, the thickness of the layers, the surface condition of the pellets changing with the decomposition, and the flow velocity. As the fluid resistance increases, the pump power used for water flow increases, but there is no need for mechanical agitation and pre-crushing unlike the first agitation system shown in FIG. It can be said that it can be done.

(Conclusion)
As described above, when compared with the first agitation type regasification device and the second regasification device, that is, the forced-passage type regasification device of the hot water of the pellet dense type, the latter device is more It can be understood that the thermal decomposition performance of the pellet is excellent. In the latter device, the gasification vessel itself can be miniaturized because of its excellent regasification performance, and there is little mechanical stirring and crushing power, and gasification with excellent maintainability in terms of equipment. The device can be realized.

  The gas hydrate decomposition method according to the present invention is configured as follows.

1. It is characterized in that gas hydrate pellets are supplied to the decomposition tank, the pellets are densely packed on the downstream side of the decomposition tank, and warm water is passed through the dense pellet layer to decompose into water and gas.
2. A screen is provided on the downstream side of the decomposition tank to prevent the hydrate lump from flowing out and separate water and gas generated by decomposition.

  The gas hydrate decomposition apparatus according to the present invention is configured as follows.

3. A decomposition tank for filling gas hydrate pellets and thermally decomposing them, a gas-liquid separation tank for separating water and gas generated by decomposition, a water tank for storing surplus water, and a gas generated in the decomposition tank; It has an upper pipe for communicating a mixture with water with a gas-liquid separation tank, and a lower pipe for heating water in the gas-liquid separation tank by a heater and supplying the water from below the decomposition tank.
4). A screen for separating gas hydrate pellets, generated gas and water is provided inside the decomposition tank.
5. The means for heating the water supplied to the decomposition tank is an external heater incorporated in a pipe or a heater for heating the decomposition tank itself.

  In the present invention, when gas hydrate pellets are decomposed into water and gas and the gas is taken out, and the gas is used as a fuel or as a raw material, the stirring power and, depending on the case, the pellet may be reduced as in the conventional apparatus. There is no need to crush, and warm water is supplied to an aggregate of pellets (in a dense state), and the warm water is allowed to pass through a slight gap formed between the pellets.

  The hot water flows on the surface of the pellets to generate gas, but the gas is mixed in the hot water and apparently the hot water increases and the flow of hot water becomes faster. Furthermore, the generated gas bubbles disturb the pellet surface on the downstream side, and as a result, it is thought that the heat transfer characteristics on the surface of the hot water and the pellet are improved. Can be disassembled.

  Moreover, since this invention does not stir a pellet in warm water, the stirring power is not consumed and the cost required for operation can be reduced. Further, since the heat transfer rate is remarkably improved and the pellet does not need to be suspended in the gasification tank, the apparatus can be reduced in size as a whole.

It is the schematic of the regasification apparatus of the 1st Example of this invention. It is the schematic of the regasification apparatus of a 2nd Example. It is the schematic of the regasification apparatus of a 3rd Example. It is the schematic of the experimental apparatus of gasification of a pellet. It is a graph which shows the experimental data of Reynolds number and a heat transfer coefficient. It is the schematic of the conventional stirring type regasification apparatus. 1 is a schematic diagram of a pellet dense regasification apparatus according to the present invention. (A) is explanatory drawing of the decomposition | disassembly state in a stirring regasification apparatus, (B) is the description of the state which makes warm water forcibly pass through the clearance gap between the pellets of a pellet dense regasification apparatus, and performs heat transfer. FIG.

  Next, a gas hydrate pellet decomposition apparatus according to the present invention will be described with reference to the drawings.

  FIG. 1 is a schematic diagram of a decomposition apparatus according to the first embodiment, in which a gas-liquid separation tank 52 is connected by a pipe 51 connected to an upper portion of a filling tank 50 (decomposition tank: diameter 1500 mm, height 4 m), A lower portion of the tank 52 and a bottom portion of the filling tank 50 are connected by a pipe 53. The bottom of the filling tank 50 is connected to a normal pressure tank 54 that stores water.

  A pellet p (diameter 2 to 3 cm) supplied from a pellet manufacturing apparatus (not shown) or a pellet storage tank (for example, normal pressure) is filled from a large-diameter supply pipe 56 with a large rotary valve 55 (pellet feeder). 50 is intermittently supplied and filled by the rotation of the rotary valve 55, and then the rotary valve 55 is closed and decomposed in a batch manner.

  The hot water h stored in the gas-liquid separation tank 52 maintained at a high pressure is supplied from the bottom of the filling tank 50 via the pump 57, the heat exchanger 58, and the valve 59, and decomposes in contact with the pellet p. However, it flows in the upper pipe 51 as a mixed flow (g + h) of the generated gas g and hot water h. A screen 60 is provided on the top of the filling tank 50, and the pellet p being decomposed is in contact with the hot water h in a state of being blocked by this, and decomposes to the end.

  The pipe 51 is provided with an automatic flow rate adjusting valve 61, and the pipe 53 is provided with an automatic flow rate adjusting valve 59. By the cooperative operation of these valves, the hot water h is changed depending on the remaining amount of pellets p in the filling tank 50. The pellet p is decomposed while controlling the flow rate. Although the water w which formed the pellet p is generated with the decomposition of the pellet p, the water w flows into the gas-liquid separation tank 52 and is separated into the gas g and the water w in the tank 52. Is supplied to the user through the pipe 62 and the automatic control valve 63. Symbols 64 and 65 indicate a plurality of series of devices of the same type.

  FIG. 2 shows a regasification apparatus 70 according to the second embodiment. A pellet supply rotary valve 72 is disposed below a pellet p storage tank 71, and piping connected to the rotary valve 72 is shown in FIG. The pellet p is intermittently supplied to the decomposition tank 74 via 73 and decomposed. The decomposition tank 74 has a decomposition chamber 76 in which jackets 75 are respectively arranged, and the pellet p fed through the rotary valve 72 is thermally decomposed in the decomposition chamber 76 to produce water w, gas g, and the like. The water w is again supplied to the upstream side of the rotary valve 72 via the pipe 77, the pump 78, and the pipe 79, and the pellet p that is sent along with the rotating operation of the rotary valve 72 is fed into the pipe 73. It is configured. In addition, 80 is a bypass pipe and 81 is a pellet discharge pipe.

  A hot water supply pipe 82 as a high heat source is connected to the decomposition tank 74, and the high temperature water is supplied to the shacket 75 to heat the decomposition chamber 76 from the surroundings. A screen 82 is provided at the top of the decomposition chamber 76 to prevent the undecomposed pellets p from being discharged together with the water w, and to efficiently decompose the pellets p to the end by receiving heat from the jacket 75. It is configured.

  The flow in the decomposition chamber 76 is accelerated by the generated gas g. Further, bubbles pass near the inner surface, and heat is actively transferred to the high-temperature water supplied from the supply pipe 82 by the turbulent flow effect. In addition, the gas g separated in the decomposition tank 74 is configured to be sent to the user through a gas supply line 83.

  FIG. 3 shows a third embodiment, in which an apparatus similar to the pellet storage tank 71 in FIG. 2 is described by adding “71a” and the letter a. In the second embodiment shown in FIG. 2, the “heating means integrated type” decomposition tank 74 in which the jacket 75 is provided inside the decomposition tank 74 is shown. In contrast, in the embodiment shown in FIG. 3, an external heater 93 is provided, and the water w discharged from the decomposition tank 90 (filling tank) in which the screen 91 is arranged is connected to the external heat exchanger via the pipe 92. 93 is heated to a predetermined temperature, and the obtained hot water is recirculated to the circulation path 79a via the pump 78a. The gas g generated in the decomposition tank 90 is configured to be supplied to the user through the gas supply line 94.

  In the present invention, when the gas hydrate NGH is decomposed and the gas g is taken out and the gas g is used as a fuel or as a raw material, as described above, it is much more efficient than the conventional stirring type cracking apparatus. Therefore, the gas g can be supplied with energy saving, and the apparatus can be miniaturized.

50 Decomposition tank (filling tank)
52 Gas-liquid separation tank 53 Normal pressure tank 55 Rotary valve 57 Pump 58 Heat exchanger 59 Automatic flow control valve 60 Screen 61 Automatic flow control valve 70 Second regasification device 72 Pellet supply rotary valve 73 Upper piping 74 Decomposition tank 75 Jacket 76 Decomposition chamber 79 Lower piping

Claims (5)

  A gas characterized in that gas hydrate pellets are supplied to the decomposition tank, the pellets are densely packed downstream in the decomposition tank, and hot water is passed through the dense pellet layer to decompose into water and gas. How to decompose hydrate.   2. The gas hydrate pellets according to claim 1, wherein a screen is provided on the downstream side of the decomposition tank to prevent the hydrate lump from flowing out and to separate water and gas generated by the decomposition. Disassembly method.   A decomposition tank for filling gas hydrate pellets and thermally decomposing them, a gas-liquid separation tank for separating water and gas generated by decomposition, a water tank for storing surplus water, and a gas generated in the decomposition tank; A gas hydrate comprising: a pipe for connecting a mixture with water to a gas-liquid separation tank; and a pipe for heating the water in the gas-liquid separation tank by a heater and supplying the water from below the decomposition tank Disassembly equipment.   The gas hydrate decomposition apparatus according to claim 3, wherein a screen for separating gas hydrate pellets, generated gas and water is provided inside the decomposition tank.   The gas hydrate decomposition apparatus characterized in that the means for heating water supplied to the decomposition tank is an external heater incorporated in a pipe or a heater for heating the decomposition tank itself.

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