JPH1061599A - Submarine lng storage system - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a submarine LNG storage system for storing LNG near a city in large quantities over a long period. SOLUTION: An LNG supplying facility 1 is provided on the ground, a large- sized and concrete-made storage tank 5 having a simple structure and for giving prestress is installed on the bottom of the deep sea, they are linked to each other by a gas pipeline 11 and a liquid gas line 12, the cooling temperature required to hold liquefaction is maintained by taking evaporation heat from the liquid surface of the liquid phase by forcibly sucking gas in the upper space in the storage tank 5 through the gas pipeline 11 from the LNG supplying facility 1, LNG high-pressure gas generated in the LNG supplying facility 1 is partially recirculated into the storage tank 5 on the sea bottom through the gas pipeline 11 to pressurize the liquid surface, and therefore, LNG is transported to the ground through the liquid pipeline 12 without using any pump having possibility of failure.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a submarine LNG storage system applied to, for example, LNG storage.

[0002]

2. Description of the Related Art There is a movement to store LNG in the state stock just like oil. Currently, the annual domestic consumption of LNG is 40 million m ³ , and if this is to be stored in the state of oil for 100 days, the capacity will be 12 million m ³ .

In order to satisfy this, the current maximum capacity 2
For an LNG tank of 0 m ³ , 60 tanks are required, but at present, there are few places where the LNG tank can be constructed, and it is difficult to establish a location and economically. Especially LN
It has been pointed out that tankers transporting LNG frequently come and go in the bay where G-fired power plants are concentrated, which may cause a collision accident.

[0004]

On the other hand, LNG is conventionally stored in an LNG tank which is set above ground or semi-underground. However, this tank is difficult to withstand the pressure in the tank. A structure that gives a prestress, that is, a prestressed concrete structure has to be adopted, which complicates the tank structure and makes it difficult to realize economically. Specifically, the conventional LNG tank is given a pre-stress so that no tensile stress is generated in the concrete part even when the pressure in the tank rises. Tendon complicates the tank structure.

[0005] In addition, while LNG is used at a pressure close to the atmospheric pressure (about the atmospheric pressure), for liquefaction storage, the cooling temperature can be maintained at a very low temperature of -162 ° C. However, this is an absolute condition for safety, and maintaining this temperature is one of the obstacles. That is, in order to maintain the operating pressure at atmospheric pressure or less and the cooling temperature at -162 ° C. or less for a long time, forced cooling must be newly performed using energy.

In addition, to remove LNG from the inside of the LNG tank, a pump immersed in LNG is operated in the tank to pump LNG at -162 ° C. out of the tank, but the LNG is immersed in LNG. Once the pump breaks down, it must stop the plant, which is the lifeblood of the plant.

[0007] All of these locational, economical, cooling, and pumping conditions are difficult to solve and, in fact, it has been said that LNG cannot be stored over a long period like oil.

The present invention has been made in view of the above circumstances, and an object of the present invention is to provide a submarine LN capable of storing LNG in a large area for a long time near a city.
It is to provide a G storage system.

[0009]

According to a first aspect of the present invention, there is provided a submarine LNG storage system provided on the ground or on the sea, and an LNG supply system installed on the seabed, the LNG supply system and a gas supply system. Large storage tank made of concrete, which is connected via a pipeline for liquid and a pipeline for liquid and stores LNG sent from the LNG supply facility through the pipeline, and a part of high-pressure gas gasified by the LNG supply facility Pumping the LNG to the ground through the liquid pipeline by returning the LNG to the ground through the liquid pipeline by introducing the pressure into the upper space in the storage tank and applying pressure to the liquid level in the tank;
Cooling means for cooling the LNG by the heat of vaporization of the liquid in the tank by sucking the gas in the upper space in the storage tank from the G supply facility through the gas pipeline.

[0010] Thus, the storage tank is installed on the sea floor,
Storing LNG from LNG supply facilities on the ground or at sea will not be subject to location constraints. In other words, it can be installed on the sea floor near the city.

In addition, when a concrete tank is installed on the sea floor, a compressive force corresponding to the water depth is applied to the tank.
In effect, the tank is in the same state as the prestressed tank, and even if an internal pressure equivalent to the external pressure is applied, no tensile stress is generated in the concrete part. The condition is resolved.

When LNG gas in the upper portion of the tank is forcibly sucked by the gas pipeline, the gas takes heat of vaporization from the liquid surface of LNG and cools the liquid phase. The required cooling temperature is maintained. That is, a cooling system is configured inside the tank, and the cooling of LNG can be performed autonomously, so that the cooling conditions are also solved. Of course, by controlling the amount of gas, the cooling capacity is controlled. This cooling is realized because the pressure resistance of the tank is substantially increased by installation on the sea floor.

When a part of the LNG high-pressure gas generated in the LNG supply facility is recirculated through the gas pipeline into the storage tank at the bottom of the sea, pressure is also applied to the liquid level in the tank, so that the liquid extending from the lower part of the tank is reduced. LNG will be pumped to the ground through the pipeline. That is, since the pumping (transport) of LNG can be performed autonomously by the pump system configured inside the tank without using a pump that may cause a failure, the pumping condition is also solved. Of course, by controlling the amount of gas,
The pumping amount is controlled. This pumping is realized because the pressure resistance of the tank is substantially increased by installation on the sea floor.

[0014]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The method of the present invention will be described below with reference to one embodiment shown in FIGS. FIG. 1 shows a configuration of a submarine LNG storage system to which the present invention is applied,
In the figure, reference numeral 1 denotes, for example, an LNG ground facility (LN
G supply equipment). The LNG ground facility 1 is provided with, for example, a facility of a pumping means 2 for receiving and pumping LNG to be stored. Further, the LNG ground facility 1 is provided with a facility of gasification means 3 having a function of gasifying LNG to a desired high pressure and a function of providing a desired use pressure, for example. Station, for example, a power plant or factory, home, etc.

Reference numeral 5 denotes L, which is installed on, for example, a seabed, for example, a deep-sea bedrock 8 at a depth of 500 m near the city.
This is a horizontal cylindrical concrete storage tank for storing NG.

In the storage tank 5, the tank itself is covered with heavy concrete, and this concrete part is effectively used as a heat insulating material without using a constituent material of the tank, and in particular, without using a heat insulating material. A concrete tank is used. For example, a large-sized compression-type concrete tank that can withstand a pressure of 50 kg / cm ² of seawater outside the tank when the tank is empty is used.

More specifically, as shown in FIG. 4, the storage tank 5 has a tank outer surface and a tank inner surface facing each other made of a steel plate (or stainless steel). High strength concrete in between (800
kg / cm ² ) 5z is driven into the peripheral wall, for example, a horizontal type having an inner diameter r1 of 53.3 m, an outer diameter r2 of 70.0 m, and a total length of 363.32 m, having a storage capacity of 3.3 million Kl / l. It consists of a cylindrical tank.

To install the storage tank 5, for example, a horizontal tank support 6 having a size corresponding to the outer shape of the tank is installed on the seabed rock 8 via the base plate 7 in advance at the seabed installation position. For example, while holding the entire storage tank from the sea with a sea crane, the storage tank 5
The entire tank is immersed in the sea while adjusting the buoyancy by pouring water into the installation ballast tank 5a provided in the
Is carried out so as to fit into the concave portion 6a.

Due to the installation in the deep sea, a compressive force corresponding to the water depth is applied to the entire tank from the outside, and the tank is substantially in the same state as the tank having the prestress structure. That is, the storage tank 5 has a structure in which no tensile stress is generated in the concrete portion even when an internal pressure of the same level as the external pressure acts.

By utilizing this behavior, the storage tank 5 is made to have a structure that is simple in structure, yet is structurally stable even when it is empty and full of LNG and is in a seaside condition. is there.

A gas port 9 is provided at the upper part of the storage tank 5, and a liquid port 10 is provided at the lower part. The gas inlet / outlet 9 and the LNG ground facility 1, and the liquid inlet / outlet 10 and the LNG ground facility 1 are connected by two systems, a gas pipeline 11 and a liquid pipeline 12, and are sent from the LNG ground facility 1. LNG can be stored. Then, the LNG ground equipment 1 can be reduced by gas or liquid as required.

Of the two pipelines 11 and 12, at least the liquid pipeline 12 employs a multi-layered heat insulating structure for shutting off seawater temperature or atmospheric temperature in the outside world.

More specifically, for example, the liquid pipeline 1
2, a pipe inner tube 13 and a pipe outer tube 14 are used on the inner surface and the outer surface of the pipeline as shown in FIG. 5, and a pipe middle tube 15 is provided between these pipes. A heat insulating material 16 is provided between the middle pipe 15 and a high-strength concrete 17 is provided between the middle pipe 15 and the outer pipe 14. A multilayer insulation structure including an air layer to be formed and a concrete layer formed of high-strength concrete 17, and has a structure for shutting off the inside and outside seawater and the atmosphere.

The LNG ground equipment 1 is provided with a suction means 18 (corresponding to a cooling means) for forcibly sucking the LNG gas in the upper part of the tank by the gas pipeline 11. The suction means 18 is, for example, a control means 18a
Accordingly, the detection temperature of the sensor 18b for monitoring the LNG temperature is set to operate before the temperature exceeds an allowable level, and the temperature does not exceed the allowable level.

Further, the LNG ground equipment 1 includes a reflux means 19 (corresponding to a pump means) for refluxing a part of the high-pressure gas generated in the LNG ground equipment 1 into the storage tank 5 through the gas pipeline 11. Facilities are provided.

According to the seafloor storage system configured as described above, when LNG is stored, the LNG is transferred from the ground to, for example, a gas pipeline using the pumping means 2 of the LNG ground facility 1 on the ground. 11. Through the liquid pipeline 12, through the deep sea near the city (for example, at a depth of 500
m), the LNG is stored utilizing the deep sea that satisfies the locational conditions.

At this time, the storage tank 5 installed in the deep sea has already been pushed from outside the tank with 50 kg / cm ² of seawater, and is in the same state as the tank of the prestressed structure. However, only the compressive force of the concrete part is reduced, and no tensile stress is generated in the concrete part.

That is, when the storage tank 5 is installed in the deep sea,
The simple structure provides the necessary strength and solves the difficult economic conditions of the tank. Here, water depth 50
As can be seen from the following table, the 0 m storage tank 5
Allowable internal pressure 50 kg / cm ² is, for exceeding the waterfront pressure 46 kg / cm ² of methane LNG principal components are retained in the liquid.

That is, since LNG is mainly composed of methane and the boiling point of methane is lower than that of other components, if methane is liquefied, other components are cooled and the LNG temperature is lowered by -16.
Even when the temperature changes from 2 ° C. to −82.5 ° C., if the pressure is higher than the critical pressure, the liquid phase is formed.

[0030]

[Table 1]

Here, a trial calculation of the heat insulation performance per unit length of the tank cylinder cross section is as follows. First, the heat input Q / L per unit of the cylinder cross section is: Q / L = 2π (θ ₁ −θ ₂ ) / ( 1 / λ) ln (r2 / r1) where L: cylindrical length, r1: 53.3 m, r2: 70.0
m, λ: 0.8 to 1.4 w / m in high-strength concrete
k (1.0), θ ₁ : -162 at LNG temperature
° C, θ ₂ : 4 ° C at seawater temperature.

From the above, it can be seen that: 2π (−162-4) / (1/1) ln (70 / 53.3) = 3827 w / m, and gasification outside the tank (the cooling effect of evaporation heat) heat capacity T per cylinder section unit length and unit temperature for not be expected) ^{is, T = π · r1 2 ·} ρ · C P where, [rho: density, C _P: specific heat (3.517kJ / kg K) = π53 .3 become ^{2 · 10 3 · 0.72 · 3.517} = 2.26 · 10 7 kJ / (k · m) = 2.26 · 10 10 w · SEC / (k · m).

From this, the time Δt per unit temperature of rise
If you ask for The number of days required to increase by 5 ° C. is 340 days,
Once a month, if LNG is reinforced, the temperature of the tank will hardly rise during operation.

This is because the storage tank 5 has a wall thickness of 16.7 m.
This is a result of the very large thermal insulation effect provided by the concrete. Then, when the gas is further gasified in the tank, the temperature actually rises, and the cooling starts, and finally, the solidification occurs.

Specifically, before the LNG temperature reaches an allowable temperature or more, the suction means 18 is operated, and the LNG ground equipment 1 is operated.
Then, the LNG gas in the upper part of the tank is forcibly sucked through the gas pipeline 11 as shown in FIG.

Thus, a cooling system in which the gas removes heat of vaporization from the liquid surface of the LNG and cools the liquid phase is formed inside the tank. If the amount of gas to be sucked is controlled and gasification is performed while keeping the balance inside and outside the tank, storage can be performed on a yearly basis while adjusting the temperature of the tank.

Specifically, in order to prevent the temperature rise due to heat input by latent heat of vaporization during gasification, at least the weight to be vaporized per second is (Q / L) /510=7.5 g / (m · sec) Therefore, if the total length of the tank is 363.32 m, if 2.7 kg of methane is vaporized per second, the cooling temperature required for liquefaction and preservation is maintained without using new energy. Cold insulation will be performed.

Here, the storage tank 5 has a capacity of 3.3 million m ³ · 2.
Since 380,000 tons of methane can be stored, it will be stably consumed for a considerably long period of time. Such autonomous cooling of the LNG also solves the difficult cooling condition.

Needless to say, such autonomous cooling performed inside the tank is realized on the premise that the tank has an increased pressure-resistant capability due to installation on the sea floor.

As shown in FIG. 3, a part of the LNG high-pressure gas generated in the LNG supply facility 1 is returned to the storage tank 5 on the seabed through the gas pipeline 11 by using the reflux means 19 as shown in FIG. When L is pressurized, pressure is applied to the liquid level of the liquid phase in the tank, and LNG is transported (pumped) from the lower part of the tank to the ground through a liquid pipeline.

As a result, the LNG can be pumped autonomously by its own pump system formed inside the tank without using a pump that may cause a failure, and the pumping conditions can be solved.

Of course, by controlling the amount of recirculating gas, the amount of pumping can be controlled. Of course, this pumping is also realized because the pressure resistance of the tank is increased by installation on the sea floor.

Thus, the submarine LNG storage system can solve all of the location, economic, cooling, and pumping conditions, and can store LNG near a city in a large amount for a long time.

Moreover, since the liquid pipeline 12 has a multi-layered heat insulating structure including an air layer and a concrete layer that block the seawater temperature or the atmospheric temperature in the outside world, it is possible to prevent frost damage to seawater and the atmosphere around the pipeline. Can be.

In one embodiment, an LNG ground base is provided on land and LNG is stored in a deep-sea storage tank. However, an LNG ground base is provided on sea and LNG is stored in a deep-sea storage tank. You may make it do.

Further, such a storage system may be applied to a deep sea power storage system for storing surplus electric power or to a submarine oil storage system for storing oil. Further, as a preferred embodiment, an example in which a storage tank of a certain size is used has been described, but the present invention is not limited to this, and a large tank of another different shape and a different size may be used as the storage tank.

[0047]

As described above, according to the first aspect of the present invention, various conditions such as locational conditions, economical conditions, cooling conditions, and pumping conditions, which are difficult when storing a large amount of LNG, are considered. As the conditions are resolved, LNG can be stored in large quantities and for long periods in suburban areas.

[Brief description of the drawings]

FIG. 1 is a diagram for explaining an entire submarine LNG storage system according to an embodiment of the present invention.

FIG. 2 is a cross-sectional view illustrating a state in which LNG gas in a tank is sucked to cool LNG.

FIG. 3 shows a high-pressure gas being fed (refluxed) into a tank to produce LNG.
Sectional drawing for demonstrating the situation which transports to the ground.

FIG. 4 is a side sectional view of a storage tank.

FIG. 5 is a side sectional view of a liquid pipeline extending from a lower portion of the storage tank.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 ... LNG ground equipment (LNG supply equipment) 5 ... Storage tank 5x ... Outer steel plate 5y ... Inner steel plate 5z ... High-strength concrete 6 ... Tank pedestal 11 ... Gas pipeline 12 ... Liquid pipeline 16 ... Insulation material 17 ... High-strength concrete 18: suction means (cooling means) 19: reflux means (pump means)

Claims (1)

[Claims] 1. An LNG supply facility provided on the ground or at sea, installed on the seabed, and connected to the LNG supply facility via a gas pipeline and a liquid pipeline,
A large-sized concrete storage tank for storing LNG sent from the LNG supply facility through the pipeline; and a part of the high-pressure gas gasified by the LNG supply facility is returned to the gas pipeline by the gas pipeline. A pump means for guiding LNG to the ground through the liquid pipeline by guiding the liquid to the upper space in the storage tank and applying pressure to the liquid level in the tank; and a liquid pipeline through the gas pipeline from the LNG supply facility. A submarine LNG storage system, comprising: cooling means for cooling a liquid in the tank by sucking gas in an upper space in the storage tank.