JP2003294198A - Boil-off gas re-liquefying device for liquefied natural gas - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To reduce load of a cold storage tank 20 by performing an effective recovery of cold heat when re-liquefying a boil-off gas (BOG) of the normal temperature from a LNG storage tank and to minimize a heat exchanger 30 by reducing the capacity of a cold storage material in a BOG re-liquefying device for liquefied natural gas (LNG). <P>SOLUTION: A second heat exchanger 30A performing heat exchange between BOG from the LNG storage tank 1 and re-liquefied BOG is provided, and after pre-cooling BOG by passing through the second heat exchanger 30A, BOG is sent into the first heat exchanger 30 in the cold storage tank 20. <P>COPYRIGHT: (C)2004,JPO

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to a boil-off gas reliquefaction apparatus for liquefied natural gas, which relates to liquefied natural gas (LN).
The present invention relates to a boil-off gas reliquefaction device for liquefied natural gas so that the boil-off gas (BOG) generated in the storage tank of G) can be reliquefied efficiently and at low cost.

[0002]

2. Description of the Related Art Generally, LNG stored in an LNG base
After being pressurized by a dedicated pump, it is vaporized by the LNG vaporizer and supplied as natural gas to the demand area. This LNG
In the supply system, in the LNG storage tank, LN
BOG containing methane gas evaporated from G as a main component is generated. The BOG is extracted from the storage tank, compressed by a compressor, mixed with natural gas, and used. For example, in the device shown in FIG. 3, the LN in the LNG storage tank 1
G is sent to the outside of the storage tank by the first pump 2, the pressure of the second pump 3 is increased by the second pump 3, and the carburetor 5 is passed through the LNG pipe 4.
It is heated by seawater and vaporized to produce natural gas. On the other hand, the BOG generated in the LNG storage tank 1 is
The BOG compressor 6 in the middle of the pipe 7 raises the pressure to the same level as the natural gas, and then joins the natural gas.

When LNG remains in the LNG storage tank 1 for a long period of time, if BOG is continuously extracted from the LNG storage tank 1,
It is possible that the methane component in LNG contained in the storage tank decreases and the concentration of other components increases. Therefore, in order to prevent such concentration of LNG, a device is also known in which BOG is once extracted from the storage tank, and then compressed and reliquefied to be refluxed to the storage tank.

FIG. 2 shows an example of such an arrangement.
The LNG pump 3 for discharging NG is connected, and the LNG pump 3 is passed through the LNG pipe 4 on the downstream side of the LNG pump 3.
Is sent to the LNG vaporizer 5 to be gasified and supplied. L
A cold storage tank 20 is installed on the downstream side of the NG pump 3, and a branch pipe 11 from the LNG pipe 4 is connected to the booster pump 1.
2, the cold storage tank 20 through the flow rate adjusting valve 13 and the opening / closing valve 14.
Connected to the inlet side of the heat exchanger 30 immersed in the
When the on-off valve 14 is open, the low temperature L from the LNG storage tank 1
NG is supplied into the heat exchanger 30.
The cold storage tank 20 contains a cold storage material 21 such as n-butane or n-pentane.

On the other hand, the BOG from the LNG storage tank 1 is a BOG.
It is pressurized by the compressor 6 and sent to the heat exchanger 30 through the BOG pipe 7. The BOG pipe 7 is provided with an opening / closing valve 15, and the BOG pressurized when the opening / closing valve 15 is opened is supplied into the heat exchanger 30. The on-off valve 14 and the on-off valve 15
On the other hand, opening and closing control is alternately performed so that when one is open, the other is closed.

A pipe 31 on the outlet side of the heat exchanger 30 joins the LNG pipe 4 at a position upstream of the vaporizer 5, and an on-off valve 16 is provided on the way. The outlet pipe 31 is the on-off valve 16
A branch pipe 32 is provided at the upstream position of the branch pipe 32, and the branch pipe 32 is connected to the inlet side of the condensate drum 40 via the opening / closing valve 17. And the condensate drum 40
The outlet side of the outlet pipe 3 via the delivery pump 50
It joins 1 again. There is also a configuration in which the outlet side of the condensate drum 40 is connected to the LNG storage tank 1, and a configuration in which the connection to the outlet pipe 31 and the connection to the LNG storage tank 1 can be selectively switched. is there.

[0007] In this apparatus, the opening / closing valves 14, 15, 16 and 17 are operated during a period when the load of city gas production is high, and a part of the LNG discharged from the LNG storage tank 1 and flowing through the LNG pipe 4 or The whole is boosted by the boosting pump 12 and sent to the inlet side of the heat exchanger 30 arranged in the cold storage tank 20. The cold heat of LNG is stored in the cold storage material 21 by cooling and solidifying the cold storage material 21. The LNG after heat exchange with the regenerator material 21 reaches the carburetor 5 after joining the LNG pipe 4 from the heat exchanger 30 through the outlet pipe 31.

During times when the load of city gas production is low,
The BOG is reliquefied by using the cold heat stored in the cool storage material 21 in the cool storage tank 20 as described above. In this case, the on-off valves 14, 15, 16, 17 are re-operated so that the heat exchanger 3
While stopping the inflow of LNG to 0, the BOG compressed by the BOG compressor 6 up to the liquefaction pressure at which the cold heat stored can be condensed is sent to the heat exchanger 30 in the cold storage tank 20. The BOG cooled and condensed by heat exchange with the regenerator material 21 passes through the branch pipe 32 from the outlet pipe 31 of the heat exchanger 30 and enters the condensate drum 40. The condensed and liquefied BOG is sent out from the outlet side of the condensate drum 40, pressurized by the pump 50, sent out to the outlet pipe 31, merged with the LNG pipe 4, and then sent to the vaporizer 5. Although not shown, the reliquefied BOG is
As described above, it may be returned to the LNG storage tank 1.
For such a technique, reference is made to JP-A-9-60799.

[0009]

In the BOG reliquefaction apparatus of the above-described form, when a cold storage material such as n-butane or n-pentane is used, cold storage is performed by utilizing latent heat of solidification of the cold storage material and melting. Since the BOG is cooled and liquefied by the latent heat, the scale of the regenerator can be significantly reduced as compared with an apparatus using only sensible heat of the liquid. Further, since the LNG and the BOG are switched so as to pass through one heat exchanger, the regenerator can be further downsized.

In the BOG reliquefaction apparatus, as described above, for a BOG at room temperature compressed to a pressure (for example, about 0.6 to 0.9 MPa) that can be condensed at the temperature of cold heat stored by the cold storage material, , BOG re-liquefied (condensed) by the supply of cold heat from the cold storage material in the cold storage tank
Is finally gasified by warming with seawater in a vaporizer. In other words, all the cold heat stored in the refrigerant (cooling material) is discharged into seawater. The cold heat discharged to seawater is a loss of cold heat, and means that the load of the cold storage tank increases correspondingly in terms of equipment. The present invention has been made in view of the above circumstances, and in the BOG reliquefaction apparatus for liquefied natural gas in the above-described mode, cold heat is recovered in the apparatus, thereby reducing the load of the cold storage tank. , The purpose is to further reduce the size of the cold storage tank.

[0011]

A boil-off gas reliquefaction apparatus for liquefied natural gas according to the present invention for solving the above-mentioned problems, includes a storage tank for storing liquefied natural gas and a cold storage for storing cold heat of the liquefied natural gas. At least a tank and a first heat exchanger provided in the cold storage tank are provided, and the liquefied natural gas and the boil-off gas from the storage tank are alternately fed to the first heat exchanger, and the boil-off is performed. A boil-off gas reliquefaction device for liquefied natural gas, wherein the gas is reliquefied by passing through the heat exchanger, wherein the boil-off gas from the storage tank and the re-liquefied boil-off gas and / or the storage tank A second heat exchanger for exchanging heat with said liquefied natural gas, said boil-off gas passing through said second heat exchanger and being pre-cooled before said first boil-off gas. Characterized in that it adapted to be fed into the heat exchanger.

Boil-off gas (BO) of this liquefied natural gas
G) According to the reliquefaction device, BOG for compressing and compressing BOG
The BOG compressed to a pressure (for example, about 0.6 to 0.9 MPa) that can be condensed at the temperature of the cold heat stored in the regenerator material in the regenerator by the compressor passes through the first heat exchanger. Before passing through the second heat exchanger. There, the BO, which has been reliquefied by passing through the first heat exchanger,
G (or liquefied natural gas from the storage tank) is exchanged with heat to receive supply of cold heat and precooling (that is, recovery of cold heat) is performed. Since the BOG thus precooled passes through the first heat exchanger, the load of the cold storage tank can be reduced and the cold storage material capacity can be reduced. As a result, the heat exchanger can be downsized.

In the boil-off gas reliquefaction apparatus for liquefied natural gas of the present invention, the form of utilization of BOG after reliquefaction is arbitrary and may be the same as in the conventional BOG reliquefaction apparatus of this type. For example, the liquefied natural gas discharged from the storage tank may be combined with the liquefied natural gas and sent to the vaporizer, or may be returned to the storage tank. Both of them can be selectively switched by a switching valve or the like. It may be a mode.

[0014]

BEST MODE FOR CARRYING OUT THE INVENTION An embodiment of the present invention will be described in detail below with reference to the drawings. FIG. 1 is a schematic configuration diagram according to an embodiment of a boil-off gas (BOG) reliquefaction apparatus for liquefied natural gas according to the present invention, in which the BOG compressed by the BOG compressor 6 is disposed in the cold storage layer 20. The pipeline system shown in FIG. 2 is different from that of the BOG reliquefaction apparatus described with reference to FIG. 2 in that the pipeline system up to the exchanger (first heat exchanger 30) is different from that of the BOG reliquefaction apparatus. It is the same as the BOG reliquefaction device shown. Therefore, in the apparatus shown in FIG. 1, members having the same functions as those shown in FIG. 2 are designated by the same reference numerals, and detailed description thereof will be omitted.

In this BOG reliquefaction apparatus for liquefied natural gas, the outlet side of the condensate drum 40, to which the branch pipe 32 from the outlet pipe 31 of the first heat exchanger 30 immersed in the cold storage tank 20 is connected, is a delivery pump. It is similar to the device shown in FIG. 2 in that it rejoins the outlet pipe 31 via 50, but a second heat exchanger 30A is provided on the upstream side of rejoining the outlet pipe 31. The difference is that.

The room temperature BOG from the LNG storage tank 1
After being compressed by the BOG compressor 6, the BOG pipe 7 is adapted to be connected to the inlet side of the first heat exchanger 30 after passing through the second heat exchanger 30A. The compressed gaseous BOG passing through the BOG pipe 7 and the reliquefied BOG sent from the outlet side of the condensate drum 40 exchange heat in the second heat exchanger 30A.

The operation mode of the above-mentioned BOG reliquefaction apparatus for liquefied natural gas is substantially the same as that of the apparatus shown in FIG.
That is, during a time period when the load of city gas production is high, the on-off valve 14 is opened, the on-off valve 15 is closed, the on-off valve 16 is opened, and the on-off valve 17 is closed, and the LNG storage tank 1 is dispensed with L.
A part or all of LNG flowing through the NG pipe 4 is pressurized by the boost pump 12 and fed to the inlet side of the heat exchanger 30 arranged in the cold storage tank 20. The cold energy of LNG is cold storage material 21
The LNG that has been stored in the cold storage and has exchanged heat with the cold storage material 21 merges with the LNG pipe 4 from the heat exchanger 30 through the outlet pipe 31 and then reaches the vaporizer 5, where it is warmed by seawater and gasified.

During times when the load of city gas production is low,
The opening / closing valve 14 is closed, the opening / closing valve 15 is opened, the opening / closing valve 16 is closed, and the opening / closing valve 17 is opened. As a result, the inflow of LNG into the heat exchanger 30 is stopped, while the BO in the LNG storage tank 1 is stopped.
G is compressed by the BOG compressor 6,
It passes through the pipe 7 and reaches the second heat exchanger 30A. Reliquefied B sent from the outlet side of the condensate drum 40 to the second heat exchanger 30A by the pump 50.
OG is flowing in, where heat exchange between the room temperature gaseous BOG and the reliquefied BOG proceeds. By this heat exchange, cold heat is recovered, and the gaseous BOG is precooled.

That is, the BOG from the LNG storage tank 1 is
Since it passes through the first heat exchanger 30 housed in the cold storage tank 20 in the precooled state in this way, the load on the cold storage tank 20 is reduced as compared with the conventional reliquefaction device of this type. Is possible. Therefore, the capacity of the regenerator material 21 can be reduced, and the heat exchanger 30 can be downsized.

In the above-mentioned BOG reliquefaction apparatus, the reliquefied BOG merges with the liquefied natural gas discharged from the LNG storage tank 1 and is sent to the vaporizer 5, where it is sent to a gasification gas conduit heated by seawater. . Although not shown, as described above, the BOG after reliquefaction is stored in the LNG storage tank 1
It is also possible to recirculate to. Further, a mode in which both modes are selectively switched by a switching valve or the like is also possible. Further, the second heat exchanger 30A is connected to the LNG
It can also be provided at a position on the upstream side of the carburetor 5 which is a conduit after the pipe 4 and the outlet pipe 31 have joined.

As an example, the BOG temperature at the time of discharging the BOG compressor 6 is 20 ° C., the pressure is 0.8 MPa, the BOG temperature in the regenerator 20 and the condensate drum 40 is -135.
When the BOG temperature is −90 ° C. (saturation temperature + 10 ° C.) and the pressure is 6 MPa after the provision of cold heat, that is, after passing through the second heat exchanger 30A, the pressure is transmitted (recovered) to the BOG. When the amount of cold heat and the scale of the cold storage tank are calculated, BOG 14t / h (20
The load of the cold storage tank 20 is 2.7 Mkcal at 000 m ³ ).
/ H, but due to cold heat recovery, BOG is-
It is 60 ° C., and the load of the cold heat tank is 2.1 Mkcal / h, which means that the load of the cold storage tank can be reduced by about 20%.

[0022]

As described above, according to the boil-off gas reliquefaction apparatus for liquefied natural gas according to the present invention, the reliquefied B is reliquefied when the room temperature BOG from the LNG storage tank is reliquefied.
Since the heat is exchanged with the OG and the heat is passed through the cold storage tank, the cold heat is effectively recovered, the load on the cold storage tank itself can be reduced, and the capacity of the cold storage material can be reduced. As a result, the heat exchanger can be downsized.

[Brief description of drawings]

FIG. 1 is a schematic configuration diagram according to an embodiment of a boil-off gas reliquefaction apparatus for liquefied natural gas according to the present invention.

FIG. 2 is a schematic configuration diagram according to another embodiment of a boil-off gas reliquefaction apparatus for liquefied natural gas.

FIG. 3 is a schematic configuration diagram illustrating another usage mode of boil-off gas.

[Explanation of symbols]

1 ... LNG storage tank, 2, 3 ... pump, 4 ... LNG piping, 5
... vaporizer, 6 ... BOG compressor, 7 ... BOG piping, 11 ...
Branch pipe, 12 ... Boost pump, 13 ... Flow control valve, 14,
15, 16, 17 ... On-off valve, 20 ... Regenerator, 30 ... First
Heat exchanger, 30A ... Second heat exchanger, 31 ... Outlet piping, 32 ... Branching pipe, 40 ... Condensate drum, 50
… Delivery pump

   ─────────────────────────────────────────────────── ─── Continued front page    (72) Inventor Kazuhide Hori             1-5-20 Kaigan, Minato-ku, Tokyo Tokyo Gas             Within the corporation (72) Inventor Koichiro Tsugane             1-5-20 Kaigan, Minato-ku, Tokyo Tokyo Gas             Within the corporation (72) Inventor Nobuhiko Tsui             1-5-20 Kaigan, Minato-ku, Tokyo Tokyo Gas             Within the corporation (72) Inventor Yoshio Komi             3-2-16 Toyosu, Koto-ku, Tokyo Ishikawajima             Harima Heavy Industries Tokyo Engineering Co., Ltd.             Tar (72) Inventor Kazuhiro Saigo             3-2-16 Toyosu, Koto-ku, Tokyo Ishikawajima             Harima Heavy Industries Tokyo Engineering Co., Ltd.             Tar F-term (reference) 3E073 DB04 DD07

Claims (3)

[Claims] 1. A storage tank for storing liquefied natural gas, a cold storage tank for storing cold heat of the liquefied natural gas, and a first heat exchanger provided in the cold storage tank. Liquefied natural gas and boil-off gas from the storage tank are alternately fed to the heat exchanger, and the boil-off gas is reliquefied by passing through the heat exchanger. The boil-off device further comprises a second heat exchanger for exchanging heat between the boil-off gas from the storage tank and the re-liquefied boil-off gas and / or liquefied natural gas from the storage tank. A boil-off gas reliquefaction apparatus for liquefied natural gas, characterized in that the gas is passed through the second heat exchanger and precooled before being fed into the first heat exchanger. . 2. The liquefied natural gas according to claim 1, wherein the boil-off gas reliquefied by passing through the heat exchanger merges with the liquefied natural gas discharged from the storage tank and is sent to the vaporizer. Boil-off gas reliquefaction device. 3. The boil-off gas reliquefaction apparatus for liquefied natural gas according to claim 1, wherein the boil-off gas reliquefied by passing through the heat exchanger is recirculated to the storage tank.