JPH09158662A - Sea bottom gas hydrate decomposing system - Google Patents

Abstract

PROBLEM TO BE SOLVED: To previously disclose a concrete measure to gather gas from a sea bottom gas hydrate layer. SOLUTION: A sea bottom gas hydrate decomposing system is provided with seawater piping 5 to introduce warm seawater, a pump 9 to input this to a methane hydrate layer 2, a deep-sea nuclear reactor 10 being a motive power source of the pump 9, small piping 12 to inject this waste heat into the seawater piping 5, gas piping 13 to introduce decomposed gas aboveground, small piping 15 to complete decomposition by giving heat to this and a drain line 21 to discharge decomposed water 22 outside the layer 2. The seawater piping 5 is extended and contracted by a rope winder 24. Since warm seawater in the vicinity of the sea level is heated further by waste heat of the nuclear reactor, the methane hydrate layer can be easily decomposed.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a system for decomposing a gas hydrate layer existing on the sea floor, and more particularly to a system for decomposing gas from a gas hydrate layer by a seawater injection method.

[0002]

2. Description of the Related Art Gas hydrate is a gas hydrate in which gas molecules such as methane and carbon hydroxide are incorporated in a cage-shaped lattice formed by water molecules. Normally, the gas is confined in ice. It takes the form of a sherbet-like solid substance.

Among gas hydrates, methane hydrate in which methane is incorporated (CH ₄ , 5.75H ₂ O)
Is widely distributed in nature and is attracting attention as a new resource.
Methane hydrates are widely distributed in the frozen land zones of the Arctic and Antarctic regions and in the continental slope areas near the continent. Recently, it has been argued that the basic research plan of the Ministry of International Trade and Industry has begun to incorporate the trial drilling of methane hydrate and it can be used as a new energy resource in the 21st century. According to one calculation, the world's methane hydrate reserves are approximately tens of trillion m ^{3 on} land and thousands of trillion m ³ in sea. This is more than tens of times the world's proven natural gas reserves.

Generally, methane hydrate exists stably under conditions of low temperature and high pressure. FIG. 1 is a schematic cross-sectional view showing a stable region of methane hydrate in the sea area on the continental margin of the mid-latitude region. The vertical axis of the figure shows the depth. The water temperature depends on the depth of the continental shelf, continental slope, and continental rise.
It is assumed to vary between 1.5 and 18 ° C.

As shown in the figure, the stable region of methane hydrate begins at a water depth of about 400 m, and the thickness of the region increases as the depth increases. At a water depth of 3000 m, the thickness of the stable region reaches about 1800 m. Since the water pressure is high at a water depth of 3000 m, methane hydrate stably exists in a wide range up to about 25 ° C. On the other hand, at a water depth of 2400 m, since the water pressure is somewhat lowered, methane hydrate exists only up to a water temperature of about 21 ° C. Conversely, the water depth 2
At 400 m, if the temperature of seawater exceeds 21 ° C, methane hydrate will decompose into gas and water. If decomposed, methane gas can be taken out.

FIG. 2 shows "Monthly Earth" September 1994, No. 5
It is a gas production model figure published on page 67. As shown in the figure, this model collects relatively warm seawater near the sea surface, injects it into the gas hydrate layer on the seabed, and attempts to take out only the decomposed gas.
Hereinafter, this method is referred to as a seawater injection method.

[0007]

As shown in FIG. 2, the basic principle of the seawater injection method for producing gas from a seabed gas hydrate layer has already been proposed. However, there is no example that discloses a technique for realizing this principle at the system level, particularly, one that fully considers the power source and heat source required for the system. The object of the present invention is therefore to pioneer the disclosure of such systems.

[0008]

The present invention provides an injection means for guiding seawater having a temperature higher than that of seawater in the vicinity of the seabed gas hydrate layer to the seabed gas hydrate layer and injecting the seawater into the seawater gas hydrate layer.
And a discharge means for drawing out the decomposed gas warmed by the injected seawater to the outside of the seabed gas hydrate layer. That is, the present invention can be considered as a kind of seawater injection method.

In the present invention, a deep-sea reactor is used as a power source for the injection means. For example, when the injection means uses a pump, a motor or the like for carrying seawater, the power generation by the deep-sea nuclear reactor is the power source for these. On the other hand, at this time, heat such as waste heat is generated from the deep sea reactor. Therefore, this heat is used to further raise the temperature of the high-temperature seawater. Thereafter, this seawater is injected into the seabed gas hydrate layer.

In the present invention, the injection means further includes a seawater pipe connecting the undersea gas hydrate layer relatively close to the sea surface, and the system includes a pipe length control means for controlling expansion and contraction of the seawater pipe. Good. "Relatively close to the sea level"
Means a depth of about 50 to 200 meters from the sea surface. Since the seawater near the sea surface is relatively warm, we will guide and use it. At this time, the seawater pipe is protected by pulling this seawater pipe toward the seabed when the movement of seawater is strong.

Although the gas and water are decomposed by warm seawater by the above system, it is considered that some gas hydrate remains in the gas in this state. Therefore, in the present invention, the discharging means may utilize the heat to completely decompose the remaining gas hydrate to remove the water component, and then discharge the gas.

[0012]

BEST MODE FOR CARRYING OUT THE INVENTION Here, preferred embodiments for carrying out the present invention will be described with reference to the drawings.

FIG. 3 is an overall configuration diagram of the seabed gas hydrate decomposition system according to this embodiment. Below sea level 1,
Methane hydrate layer 2 on the seabed deeper than about 1000 m
Exists. This layer is sandwiched between an upper stratum 3 and a lower stratum 4 such as bedrock.

[Injection side] The seawater pipe 5 is for guiding warm seawater near the sea surface 1 to the gas hydrate layer 2. The seawater pipe 5 is made of, for example, a soft synthetic resin. This is to respond flexibly to ocean currents. The periphery of the seawater pipe 5 is covered with a heat insulating material 6. In order to make the seawater pipe 5 stand upright, a buoyancy container 7 is placed above it.
Is attached.

The lower portion 25 of the seawater pipe 5 has a bellows structure and can be expanded and contracted in this portion. Expansion and contraction is performed by winding up and unwinding the rope 23 by the rope winding device 24 installed on the rock. The stretchable length is preferably 500 meters or more. The reasons for this are: The whole seawater pipe 5 is inclined by the flow of seawater. This is because the distance d between the opening of the seawater pipe 5 and the sea surface 1 can be varied from 0 to 200 meters even when there is no seawater flow. 2. It is desirable that the distance d is about 0 to 100 m when warmer seawater is taken in, while 10 is required when the seawater pipe 5 is protected from storms or the like.
This is because it is desirable that the length is 0 m or more.

Further, below the seawater pipe 5, a pump 9 for drawing in seawater is provided. Deep sea reactor 10
Supplies power to the pump 9. Power is power cable 1
1 transmitted.

According to these configurations, electric power is generated by the operation of the deep sea reactor 10 and the pump 9 is operated. Therefore, warm seawater is drawn in from the opening of the seawater pipe 5 and moves in the direction of arrow 8. The temperature of the drawn seawater may be considered to be an average annual water temperature of about 20 ° C near the sea level 1.

On the other hand, the operation of the deep sea reactor 10 produces waste heat. As will be described later, this deep sea reactor 10 is cooled by cooling gas and sea water. Here, it is assumed that the cooling seawater is heated to about 50 to 80 ° C. by the waste heat. This hot water is injected into the seawater pipe 5 through the small pipe 12. Seawater after the temperature rise is injected into the gas hydrate layer 2, and the gas hydrate is decomposed into gas 20 and water 22.

[Discharge Side] The decomposed water 22 is discharged to the outside of the gas hydrate layer 2 by the drain line 21. On the other hand, the methane gas 20 is collected on the ground through the gas pipe 13. At the tip of the gas pipe 13, there is a methane gas manufacturing plant (not shown).

The small pipe 15 supplies a part of seawater warmed by the waste heat of the deep sea reactor 10 to the vicinity of the inlet of the gas pipe 13. The flow of hot water through the small pipe 15 is intended to surely decompose the undecomposed methane hydrate remaining in the methane gas 20. The steam separator 17 is provided for completely separating water from the methane gas 20 containing water and discarding the water. As the steam separator 17, for example, a centrifugal separator can be adopted.

The above is the configuration and operation of the injection and discharge sides of this embodiment.

Here, the deep sea reactor 10 will be described.

FIG. 4 is a diagram showing the structure of the deep-sea nuclear reactor 10. This fast reactor is obtained by adding the above-mentioned small pipes 12 and 15 to the one disclosed in Japanese Patent Application No. 2-402271 previously proposed by the present applicant. As shown in the figure, the main components of the deep sea reactor 10 are all pressure shells 1.
It is built into 00. This is to improve the pressure resistance performance. The pressure-resistant shell 100 can be made of, for example, stainless steel, and the top opening thereof is a detachable lid 100.
It is sealed with a. A reactor main body 102 is installed in the lower part of the pressure-resistant shell 100, and a heat exchanger 10 installed above the reactor main body 102.
The primary coolant circulation path A is formed between the primary coolant circulation path A and the primary coolant circulation path A. Pressure shell 1
A turbine 104, a generator 105, and a compressor 106 are arranged in the upper part of 00, and a rotating shaft 107 of the turbine 104 drives the generator 105 and the compressor 106. A steel plate is arranged on the inner surface of the pressure-resistant shell 100 to form a closed space, which functions as the gas cooler 108. By installing the fins 108a in the gas cooler 108, the cooling effect is improved.

By connecting these members by piping, the heat exchanger 103 → turbine 104 → gas cooler 108 →
A secondary system gas coolant circulation path B is formed from the compressor 106 to the heat exchanger 103. Compressor 106 of secondary system gas coolant circulation path B → heat exchanger 1
Between the gas flow path 03 and the turbine 104 → gas cooler 1
An economizer 109 is provided which allows heat exchange with the gas passages between 08 and 08. This can improve the energy balance. Further, by disposing the radiation shielding material 110 between the reactor body 102 and the heat exchanger 103, the turbine 104 and the like are prevented from being deteriorated by the influence of radiation.

A seawater flow passage 119 is provided outside the pressure-resistant shell 100, and the small pipes 12 and 15 shown in FIG. 3 are attached to the seawater flow passage 119. The wastewater heats the seawater inside the seawater channel 119. In order to generate a flow in the seawater flow passage 119, the pumps 120 and 121 are respectively provided in the seawater flow passage 119.
It is provided at the entrance of the.

It is desirable to use a high temperature fast reactor or a high temperature gas reactor for the reactor body 102. When these are adopted, the temperature difference between the surface inside and outside the pressure shell becomes larger than that in the light water reactor, the cooling effect is enhanced, and there is no problem of water quality control of the primary cooling water required in the case of the light water reactor.

[Result of Examination of Effectiveness of Utilization of Waste Heat] One of the features of the present invention is that hot water is injected after the piping through the small piping 12. Applicants have calculated the effect of this feedback.

(1) Study conditions-Depth of sea water depth 2000m-Output heat of deep-sea reactor 10: 2MWt Electricity: 400kWe (thermal efficiency 20%)-Length of seawater pipe 5 2500m (500m considers inclination) -Seawater pipe 5 Inner diameter 40 cm-Seawater velocity in seawater pipe 5 2 m / sec-Seawater temperature in seawater pipe 5 20 ° C-Methane hydrate layer 2 temperature 3-17 ° C (average 1
0 ° C) -Methane gas separation temperature 17 ° C (2) Calculation results-At 400kWe, it is possible to send 68t / day of seawater by the pump 9 by installing three seawater pipes 5 described above.

To raise the temperature of seawater by 1 ° C.,
A heat quantity of 3.3 MWt is required.

Therefore, at a waste heat of 1.6 MWt, 0.5
It is possible to raise the temperature by ℃.

(3) Examination Considering the average temperature of the methane hydrate layer 2 of 10 ° C. as a reference, 20-1 of the seawater temperatures can be effectively used.
It becomes 0 = 10 ° C. Therefore, the effect of increasing the temperature using waste heat is 0.5 / 10 × 100 = 5%. Furthermore, when only the lower 1/3 (12.7 to 17 ° C.) of the methane hydrate layer 2 having a higher temperature is targeted for mining, the average temperature of this part is 14.9 ° C.
The following calculation result is obtained.

20-14.9 = 5.1 ° C. 0.5 ÷ 5.1 × 100 = 10% That is, an increase of 10%.

Although the average seawater temperature is set to 20 ° C. here, it is considered to fluctuate at 15 to 25 ° C. seasonally. At this time, since the seawater temperature is lower than the methane gas separation temperature of 17 ° C in the season of 17 ° C or lower, it is theoretically impossible to mine the methane gas. But even in this case,
Considering the temperature rise due to the waste heat of 0.5 ° C., the minable period increases.

The above is the outline of the present embodiment.

In this embodiment, the necessity of the buoyancy container 7 should be considered. That is, when the heat insulating material 6 itself has a sufficient buoyancy, the buoyancy container 7 becomes unnecessary. For example, when the heat insulating material 6 made of glass balls is adopted, the buoyancy container 7 may be unnecessary.

Further, in the present embodiment, the lower portion 25 has a bellows structure in order to make the seawater pipe 5 extendable and contractible. This may of course be another structure as long as it achieves a similar purpose.

[0037]

According to the present invention, the decomposition of gas hydrate and the extraction of gas can be realized at the system level. At this time, since a deep-sea reactor is used as a power source, it is possible to extract gas with higher efficiency by using waste heat that is not normally useful. Since the output of the deep-sea nuclear reactor is about 10% of that of a normal nuclear reactor, it is possible to continue the operation for a long period of 10 to 20 years with one refueling.

Further, in the present invention, when the pipe on the injection side can be expanded and contracted, seawater can be pumped from an optimum depth depending on the situation.

Further, in the present invention, by utilizing the waste heat on the discharge side as well, the gas hydrate component remaining in the gas can be completely decomposed and removed, so that a good quality gas can be collected. .

[Brief description of the drawings]

FIG. 1 is a schematic cross-sectional view showing a stable region of methane hydrate in a sea area on the continental margin of the mid-latitude region.

FIG. 2 is a model diagram of gas production by the seawater injection method.

FIG. 3 is an overall configuration diagram of a seabed gas hydrate decomposition system of the present invention.

FIG. 4 is a configuration diagram of a deep-sea nuclear reactor 10.

[Explanation of symbols]

2 Methane hydrate layer, 5 Seawater piping, 6 Insulation, 7 Buoyancy vessel, 9 Pump, 10 Deep sea reactor, 11
Power cable, 12,15 small piping, 13 gas piping,
17 steam separator, 21 drain line, 23 rope,
24 Rope winding device.

Claims (3)

[Claims] 1. An injection means for guiding seawater having a temperature higher than that of seawater in the vicinity of the seabed gas hydrate layer to the seabed gas hydrate layer and injecting it into the seawater gas hydrate layer, The deep sea reactor is used as a power source for the injecting means, and the temperature of the high-temperature seawater is further raised by the heat generated from the deep sea reactor. A submarine gas hydrate decomposition system characterized by injecting this into the submarine gas hydrate layer. 2. The seabed gas hydrate decomposition system according to claim 1, wherein the injecting means includes seawater piping that connects the seabed and a seabed gas hydrate layer relatively close to the sea surface, and the system includes the seawater piping. A submarine gas hydrate decomposition system comprising a pipe length control means for controlling expansion and contraction of the seabed. 3. The seabed gas hydrate decomposition system according to claim 1, wherein the discharging unit decomposes gas hydrate remaining in the gas by heat generated from the deep-sea nuclear reactor. , A submarine gas hydrate decomposition system that discharges gas after removing water components.