JPH11130700A - Production of methane hydrate and device for producing the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a method for efficiently producing highly concentrated methane hydrate by allowing methane to react with water, and to obtain a device for producing the same. SOLUTION: This method for producing methane hydrate comprises circulating a aqueous phase L from an upflow chamber 6 through an upper chamber 8, a downflow chamber 7 and an aqueous phase-circulating pump 9 in a reaction vessel 1 having a partition plate 5, supplying methane from a methane-charging port 10 into the upflow chamber 6 to allow the methane to react with the water, and recovering the produced methane hydrate layer MH floated on the surface of the aqueous phase from a liquid phase-extracting port 16.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a method for efficiently producing high-concentration methane hydrate by reacting methane with water and an apparatus for producing the same.

[0002]

2. Description of the Related Art It is known that natural gas components such as methane are distributed in large quantities as hydrates underground in cold regions. Since these hydrates exist stably under the condition of low temperature and high pressure, they are expected as the next generation natural gas source. In particular, methane hydrate (hereinafter “methane hydrate”)
) Means that the intermolecular distance of methane in the hydrate lattice is shorter than that in the gas cylinder filled with high pressure, and it is in a tightly packed state, so that storage and transport in the hydrated state is expected, and methane and water Since this reaction is a reversible equilibrium reaction and generates a large heat of hydration, its application to heat storage materials, refrigerators and heat pumps is also being studied. On the other hand, since various applications are expected as described above, research for efficiently synthesizing methane hydrate in addition to relying on natural resources is also in progress. However, methane hydrate is generally difficult to handle because it requires a low temperature and a high pressure in order to exist stably, for example, a pressure that can exist stably at 15 ° C. is 100 kg / cm ² or more. Therefore, various stabilizers have been sought so that the methane hydrate formation equilibrium can be shifted to a high temperature and a low pressure side even a little. For example, aliphatic amines such as isobutylamine and isopropylamine (Japanese Patent Publication No. 53-15082), 3-dioxolan, cyclobutanone, tetrahydrofuran, cyclopentanone, acetone, etc. (Seiichi Yokoi et al., The Chemical Society of Japan, 1993,
(4), pp. 387-394) were found to be effective as stabilizers.

In synthesizing the methane hydrate, an apparatus shown in FIG. 2, for example, has conventionally been generally used. In FIG. 2, this methane hydrate synthesizing apparatus
The pressure vessel 50 is provided with an aqueous phase injection pipe 51, a methane introduction pipe 52 for introducing methane gas, an exhaust port 53, and a stirring blade 54. The pressure vessel 50 is immersed in a thermostat 55. This synthesizer includes a gas phase temperature T ₁ measuring device, a liquid phase temperature T ₂ measuring device, a container pressure P measuring device, a rotating speed R measuring device of the stirring blade 53, and a temperature T ₃ measuring device in the thermostatic chamber 55. Vessels are installed.

[0004] Methane hydrate is produced using the above apparatus.
To synthesize, for example, first, methane is introduced into the pressure vessel 50.
Methane gas is introduced from the inlet pipe 52 to eliminate air in the container
Then, a predetermined concentration of a stabilizer is contained from the aqueous phase injection pipe 51.
The aqueous solution is injected as an aqueous phase.
Stabilize to temperature. Meta under stirring by the stirring blade 54
Methane gas is introduced from the gas introduction pipe 52 until it reaches a predetermined pressure.
I do. If stirring is continued in this state, a hydration reaction occurs and
As the pressure P in the vessel drops, the heat of hydration causes the liquidus temperature
T_TwoRises. If necessary, methane gas can be
The pressure P in the container is adjusted by evacuating a part,
Liquid phase temperature T in hot bath 55_TwoAnd gas phase temperature T ₁Matches
When left still, the temperature T_TwoWith formation equilibrium pressure P at
Methane hydrate is obtained as a liquid phase.

[0005]

The above-mentioned method for producing methane hydrate has the following problems. That is, the reaction between methane and water occurs first by the absorption of methane into the aqueous phase at the gas-liquid interface. On the other hand, the methane hydrate generated by the reaction has a density lower than that of water (theoretical density of 0.915 g / cm ³ ) and floats near the liquid surface to form a methane hydrate layer. Absorption will be hindered by the product.
Further, the viscosity of the aqueous phase increases with the generation of methane hydrate, and the stirring effect decreases. As a result, it becomes difficult to obtain a high concentration of methane hydrate. Although the concentration of methane hydrate in the aqueous phase increases with the introduction of methane gas from the methane introduction pipe 52, the proportion of water remaining in the aqueous phase decreases due to the reaction, so that the production equilibrium is reached at that temperature and pressure. Then, the reaction does not proceed any further, and it is not possible to obtain a high concentration of methane hydrate in this regard. The present invention has been made in order to solve the above-mentioned problems, and therefore, an object of the present invention is to provide a method for efficiently producing high-concentration methane hydrate by reacting methane and water, and an apparatus for producing the same. To provide.

[0006]

SUMMARY OF THE INVENTION In order to solve the above-mentioned problems, the present invention provides a method for producing methane hydrate by reacting methane and water. And a method for producing methane hydrate in which methane is supplied to the circulating flow to react with water, and a methane hydrate layer generated by the reaction and floating near the liquid surface of the aqueous phase is recovered. In the above, it is preferable to supply a new aqueous phase to the system so that the liquid level of the aqueous phase is maintained at a constant level. In the above, it is preferable that unreacted methane gas released from the liquid surface ascending in the aqueous phase be supplied to the circulating flow and reacted with water. The present invention also provides
A reaction vessel having a temperature control means, a means for forming a circulating flow composed of an ascending flow and a descending flow in an aqueous phase introduced into the reaction vessel, a means for supplying methane to the circulating flow, Means for recovering the methane hydrate layer floating near the liquid surface of the aqueous phase. This manufacturing apparatus includes a means for replenishing a new aqueous phase into the reaction vessel so that the liquid level of the aqueous phase maintains a constant level, and an unreacted methane gas that has been ascended in the aqueous phase and released from the liquid level. It is preferable to have a means for supplying to the circulation flow.

[0007]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Embodiments of the present invention will be described below in detail with reference to examples. FIG. 1 shows an embodiment of a methane hydrate production apparatus and a production method using this apparatus in this embodiment. In FIG. 1, reference numeral 1 denotes a sealed reaction vessel. This reaction vessel 1 has a jacket 2, a brine tank 3 and a brine pump 4
Reaction vessel 1 by brine circulated through
The aqueous phase L introduced into the container can be kept in a predetermined temperature range of, for example, 2 to 5 ° C.

The lower space of the reaction vessel 1 is divided into two chambers by a partition plate 5 extending from the bottom of the reactor, while the upper part of the vessel is an integral space that is not partitioned by the partition plate 5. Hereinafter, one of the lower spaces divided by the partition plate 5 is referred to as an upflow chamber 6 and the other is referred to as a downflow chamber 7. A space without a partition formed above the partition plate 5 is referred to as an upper chamber 8. The bottom of the ascending flow chamber 6 and the bottom of the descending flow chamber 7 of the reaction vessel 1 are connected via an aqueous phase circulation pump 9 that circulates the aqueous phase L from the descending flow chamber 7 to the ascending flow chamber 6.

A methane inlet 10 is provided at the bottom of the upward flow chamber 6, and methane gas is supplied to the methane inlet 10 from a methane storage tank 11 via a gas supply pump 12 and a flow control valve 13. It has become. on the other hand,
A gas pipe 14 is drawn from the top of the reaction vessel 1, and the gas accumulated at the top of the vessel is supplied to the gas pipe 14 and a gas circulation pump 15.
Through the methane inlet 10.

In the reaction vessel 1, a liquid layer discharge port 16 is provided on the side wall of the upper chamber 8, and a relatively low-density methane hydride floating near the liquid surface S of the aqueous phase L is provided from the liquid layer discharge port 16. The rate layer MH is recovered in the methane hydrate recovery tank 18 via the extraction pump 17.
An aqueous phase supply port 19 is provided at the top of the reaction vessel 1,
A new aqueous phase is supplied from the aqueous phase tank 20 into the reaction vessel 1 via the aqueous phase supply pump 21.

This manufacturing apparatus is operated as follows.
The air in the reaction vessel 1 is replaced with methane gas in advance, and then the aqueous phase L is introduced from the aqueous phase tank 20 into the reaction vessel 1 so that the liquid surface S is above the liquid layer outlet 16. This aqueous phase may contain stabilizers if necessary. Next, the aqueous phase circulation pump 9 is operated to move the liquid phase L in the container from the upward flow chamber 6 to the upward flow chamber 6 again via the upper chamber 8, the downward flow chamber 7, and the aqueous phase circulation pump 9. Circulate. At this time, the brine in the brine tank 3 is simultaneously circulated through the jacket 2 to cool the liquid phase L in the container to a predetermined temperature range of, for example, 2 to 5 ° C., and thereafter, the temperature is controlled so that this temperature is maintained.

When the temperature of the liquid phase L is stabilized at a predetermined temperature, methane in the methane storage tank 11 is continuously introduced from the methane inlet 10 into the bottom of the rising flow chamber 6 as bubbles while continuing the liquid phase circulation. As a result, at least a portion of methane is absorbed from the gas-liquid interface of the bubbles into the aqueous phase, reacts with water, and is converted into methane hydrate.

The methane hydrate generated by the reaction floats in the aqueous phase because its density is smaller than that of water, and accumulates below the liquid surface S of the upper chamber 8 to form a methane hydrate layer MH. The methane hydrate layer MH is extracted from the liquid layer extraction port 16 by an extraction pump 17 and collected in a methane hydrate recovery tank 18.

Unreacted methane gas not absorbed in the aqueous phase in the upflow chamber 6 is released from the liquid surface S and accumulates as a gas phase at the top of the reaction vessel 1. This methane gas merges with new methane gas from the methane storage tank 11 via the gas pipe 14 and the gas circulation pump 15 and circulates from the methane inlet 10 to the upflow chamber 6. The supply flow rate of the new methane gas from the methane storage tank 11 is changed to the methane hydrate recovery tank 18.
Is controlled by the flow control valve 13 so as to correspond to the amount of methane consumed in the synthesis of the methane hydrate recovered in the first step.

As the methane hydrate layer MH is withdrawn from the liquid layer withdrawal outlet 16, the liquid level S of the aqueous phase falls, so that a new aqueous phase is formed so that the level of the liquid level S is kept constant. Water is supplied from the aqueous phase tank 20 into the reaction vessel 1 via the aqueous phase supply pump 21.

The aqueous phase flowing under the methane hydrate layer MH due to the reflux of the aqueous phase L flows into the descending flow chamber 7 beyond the upper side of the partition plate 5, and further flows into the ascending flow chamber 6 by the aqueous phase circulation pump 9. Circulated. Since this circulated aqueous phase contains nuclides of methane hydrate, methane hydrate is produced immediately upon contact with methane gas. In this system, the bubbles of methane rise in the aqueous phase, so that the bubble interface can be constantly brought into contact with new water molecules without being covered with a high-viscosity reaction product, and the reaction is promoted. By continuing this operation in a stable state, high-concentration methane hydrate can be efficiently and continuously recovered in the methane hydrate recovery tank 18.

In general, the reaction between methane and water proceeds at a pressure of 60 kg / cm ² G or more, for example, when the reaction temperature is 10 ° C. Therefore, the reaction vessel 1 must have a pressure resistance of at least 6
Requires a high pressure vessel of 0 kg / cm ² G or more. When it is desired to carry out the reaction at a higher temperature and lower pressure, it is preferable to add a stabilizer to the aqueous phase L. Examples of stabilizers that can shift the methane hydration reaction to higher temperatures and lower pressures include aliphatic amines such as isobutylamine and isopropylamine;
Alicyclic ethers such as dioxolane, tetrahydrofuran, and furan; alicyclic ketones such as cyclobutanone and cyclopentanone; aliphatic ketones such as acetone; Since all of these stabilizers have a hydrocarbon group and a polar group in the molecule, each polar group attracts a water molecule and the hydrocarbon group attracts a methane molecule, thereby reducing the intermolecular distance. It is thought to promote the hydration reaction. For example, the reaction at 10 ° C. and 20 kg / cm ² G becomes possible by adding an aliphatic amine,
10 ° C, 10kg / c depending on the addition of tetrahydrofuran
Reaction at m ² G or less is also possible. These stabilizers are preferably added in the range of 0.1 to 10 mol per 1000 g of pure water.

The reaction temperature depends on the above-mentioned production equilibrium relation and the aqueous phase L
It is better to be as low as possible. For example, it is preferable to control the temperature of the aqueous phase in the reaction vessel 1 to be in the range of 2 to 5 ° C. As a result, the solubility of methane in water can be increased, and the production equilibrium pressure can be reduced. The reaction between water and methane is an exothermic reaction, and when the reaction is started in the reaction vessel 1, the temperature of the system rises due to the heat of hydration, so that the temperature in the system is always maintained within a predetermined range. It is preferable to perform temperature control.

In the embodiment shown in FIG. 1 described above, the jacket 2 is used as the temperature control means, but is not limited to this. For example, the reaction vessel may be composed of a double tube or a multi-tube, and brine may be circulated in either one of the gaps, a cooling coil or a radiator may be inserted in the reaction vessel, or a combination thereof may be used. Is also good.

In the upflow chamber 6, the methane gas is absorbed by the water phase from the gas-liquid interface of the rising bubbles and reacts with water. Therefore, it is preferable to make the interface area of the bubbles as large as possible.
Since this is achieved by minimizing the particle diameter of the bubbles as much as possible, it is preferable that the gas blowing portion of the methane inlet 10 be a spherical or flat porous plate. If the particle size of the bubbles is reduced, there is also an effect of improving the cooling efficiency of local heat generation at the bubble interface.

When methane gas comes into contact with water in the ascending flow chamber 6 of the reaction vessel 1 and the reaction proceeds, methane hydrate generated by the reaction has a theoretical density of 0.915 g / cm ³ , which is smaller than the density of water. Therefore, the circulating liquid phase L is
, And rises to the vicinity of the liquid surface S, forming a methane hydrate layer MH below the liquid surface. This methane hydrate layer MH is a hydrate layer having a high methane content ratio, and can be used as it is as a methane hydrate product. The ratio of methane and water in the obtained methane hydrate product
Is determined by the gas-liquid equilibrium conditions and the stabilizer, and therefore the temperature and pressure of the system, and when the stabilizer is added, vary depending on the type and amount of the stabilizer.

In the method of the present invention, it is not always necessary to supply a new aqueous phase into the reaction vessel. Without replenishment of the aqueous phase, batch production is required. Even in this case, the reaction proceeds because the reaction product does not prevent the contact between methane and water. However, the proportion of water in the liquid phase decreases with the progress of the reaction, and the reaction stops when the temperature reaches near the production equilibrium at the temperature and pressure of the system. From this point of view, as in the above-described embodiment, continuous supply of a new aqueous phase to the reaction vessel 1 continuously or intermittently, and continuous or intermittent withdrawal of the methane hydrate layer MH floating near the liquid surface S Manufacturing method is preferred,
As a result, the liquid phase in the reaction vessel is always on the water excess side of the production equilibrium, and the reaction proceeds rapidly, while the liquid surface S is maintained at a constant level, and the liquid layer with a high concentration of methane hydrate fixed therein is drained. It is possible to continuously withdraw from the outlet 16.

When a new aqueous phase is supplied to the reaction vessel, it may be supplied to the top of the reaction vessel 1 as shown in FIG. 1, but in this case, the methane hydrate layer MH is diluted with water. Since there is a possibility that the water layer may be disturbed or the layer may be disturbed, the water phase supply port 19 is extended to the inside of the water phase L, preferably to the inside of the descending flow chamber 7, and a new water phase from the water phase tank 20 is circulated. Preferably, it is supplied in a water stream.

[0024]

According to the method for producing methane hydrate of the present invention, the aqueous phase is circulated up and down, methane is supplied to this circulating flow to react with water, and the methane hydrate layer floating near the liquid surface is recovered. The reaction between methane and water is not hindered by the reaction products, and the methane hydrate production equilibrium in the reaction system is always on the excess water side, and the reaction proceeds smoothly, resulting in extremely high efficiency. Methane hydrate can be produced well. At this time, if a new aqueous phase is supplied to the system, methane hydrate can be continuously produced, and the production efficiency can be further improved. If the unreacted methane gas discharged from the liquid level is supplied to the circulation flow, the methane utilization rate can be improved and it is economical.

[Brief description of the drawings]

FIG. 1 is a configuration diagram showing a specific example of a manufacturing method and a manufacturing apparatus of the present invention.

FIG. 2 is a configuration diagram showing a specific example of a conventional method and apparatus for producing methane hydrate.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 ... Reaction container 2 ... Jacket 3 ... Brine tank 4 ... Brine pump 5 ... Partition plate 6 ... Upflow chamber 7 ... Downflow chamber 8 ... Upper chamber 9 ... Water phase circulation pump 10 ... Methane inlet 11 ... Methane storage tank 12 ... Gas supply pump 13 ... Flow control valve 14 ... Gas pipe 15 ... Gas circulation pump 16 ... Liquid layer outlet 17 ... Extraction pump 18 ... Methane hydrate recovery tank 19 ... Aqueous phase supply port 20 ... Aqueous phase tank 21 ... Aqueous phase Supply pump L: water phase MH: methane hydrate layer S: liquid level

 ──────────────────────────────────────────────────続 き Continued on the front page (72) Inventor Shoji Watanabe 2-1-1 Shinhama, Arai-machi, Takasago City, Hyogo Prefecture Inside the Takasago Research Laboratory, Mitsubishi Heavy Industries, Ltd. (72) Inventor Yoshito Soma Wadazaki, Hyogo-ku, Kobe City, Hyogo Prefecture 1-1-1, Machi Kobe Shipyard, Mitsubishi Heavy Industries, Ltd. (72) Yoshimasa Ando 1-1-1, Wadasaki-cho, Hyogo-ku, Kobe, Hyogo Prefecture, Japan Kobe Shipyard, Mitsubishi Heavy Industries, Ltd. (72) Kiyoshinori Nishida Takaishi Engineering Co., Ltd. 2-2-19-1 Shinhama, Arai-machi, Takasago City, Hyogo Prefecture

Claims (5)

[Claims] When producing methane hydrate by reacting methane and water, a circulating flow consisting of an upward flow and a downward flow is formed in an aqueous phase, and methane is supplied to the circulating flow to react with water. And recovering a methane hydrate layer generated by the reaction and floating near the liquid surface of the aqueous phase. 2. The method for producing methane hydrate according to claim 1, wherein a new aqueous phase is supplied to the system so that the liquid level of the aqueous phase is maintained at a constant level. 3. The methane hydride according to claim 1, wherein unreacted methane gas that has risen in the aqueous phase and has been released from the liquid surface is supplied to the circulating flow to react with water. Rate production method. 4. An apparatus for producing methane hydrate by reacting methane and water, comprising: a reaction vessel having a temperature control means; and an up-flow and a down-flow in an aqueous phase introduced into the reaction vessel. A means for forming a circulating flow, a means for supplying methane to the circulating flow, and a means for collecting a methane hydrate layer generated by reaction and floating near the liquid surface of the aqueous phase. Methane hydrate production equipment. 5. A means for replenishing the reaction vessel with a new aqueous phase so that the liquid level of the aqueous phase maintains a constant level, and means for unreacted methane gas rising from the aqueous phase and discharged from the liquid level. The apparatus for producing methane hydrate according to claim 4, further comprising means for supplying a circulating flow.