JPH08285192A - Residual liquid gasifying method of cryogenic liquid storage tank and its storage equipment - Google Patents

Abstract

PURPOSE: To provide a residual liquid gasifying method of a cryogenic liquid storage tank and its storage equipment by which a residual liquid can be efficiently gasified in a short time without requiring much cost. CONSTITUTION: A BOG return pipe 18 is connected to the middle of a receiving pipe 16 arranged in a lower part of a storage tank 15, and is constituted so that BOG after passing through a BOG compressor 27 is introduced into the storage tank 15 from the lower part of the storage tank 15, and the tip of a drain pipe 17 extending from a bottom part of the storage tank 15 is connected between a connecting point of the receiving pipe 16 and the BOG return pipe 18 and the storage tank 15, and a bottom part of the storage tank 15 and the receiving pipe 16 are communicated with each other by the drain pipe 17.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a residual liquid vaporizing method suitable for use during open inspection of a storage tank for storing low-temperature liquefied gas such as LNG, and particularly for a ground-based storage tank, and storage equipment therefor.

[0002]

2. Description of the Related Art Low temperature liquefied gas such as LNG (Liquefie)
d Natural gas (liquefied natural gas) has a basic process of receiving LNG, storing and regasifying LNG, and delivering it to LNG utilization facilities.
FIG. 2 shows an example of a storage facility (in the case of a ground type storage tank) at the LNG receiving terminal. LNG tanker and storage facility 1
In this example, three unloading arms 2a, 2b and 2b are provided (two for liquid and one for return gas), and two unloading arms 2b and 2 for liquid are provided.
b, LNG is stored in the storage tank 4 on the ground through the receiving pipe 3. On the other hand, when LNG is used, it is pumped out of the storage tank 4 by the LNG pump 5 and is vaporized by the vaporizer 6 into a gas having a pressure of about 20 kg / cm ² G, for example.
Supplied to NG utilization equipment.

Further, LNG is vaporized due to heat input into the receiving pipe 3, the storage tank 4, etc., and so-called boil off gas (hereinafter referred to as BOG) is generated, but when the LNG is received, BOG is generated. A part of this is returned to the LNG tanker by the return gas blower 7 via the return gas pipe 8 and the unloading arm 2a. And
The remaining BOG is pressurized to about 20 kg / cm ² G by the BOG compressor 10 provided in the BOG outlet pipe 9 and mixed with the gas produced by the vaporizer 6 described above. Further, in order to prevent surging, the BO after passing through the BOG compressor 10
A part of G is returned to the storage tank 4 through the BOG return pipe 11.

[0004]

By the way, the above-mentioned LN
When performing an open inspection of the storage tank 4 in the G storage facility 1,
It is necessary to completely discharge the LNG remaining in the storage tank 4. In that case, first, the LNG pump 5 discharges LNG to a level slightly higher than the position of the pipe through a pipe such as a discharge pipe provided at the bottom of the storage tank 4 (since the low temperature liquid pump used here is self-lubricating, In order to prevent the seizure of
I have to leave NG). After that, the remaining LNG was discharged using a temporary pump (not shown) through the drain pipe 12 at the bottom of the storage tank 4.

However, when LNG is discharged from the drain pipe 12, usually, in order to earn an effective NPSH of the temporary pump (that is, to secure a sufficient discharge capacity),
Although a hole was dug from the ground surface and a temporary pump was set at a position that was sufficiently lower than the liquid surface, it was not able to completely drain the residual liquid. There is also a problem that the cost of the temporary pump itself is very high. Therefore, in order to completely remove the LNG in the storage tank 4 after using the pump, it was necessary to rely on the vaporization of the residual liquid by natural heat input, but the vaporization by natural heat input takes a very long time, for example, several months. In addition to this, it takes a lot of time to hot-up the storage tank 4 after completion of vaporization, which hinders the open inspection work of the storage tank and causes a serious problem that the operating rate of the storage facility 1 is significantly reduced. It was

The present invention has been made to solve the above-mentioned problems, and does not require much cost.
An object of the present invention is to provide a residual liquid vaporization method for a low-temperature liquefied gas storage tank and a storage facility for the vaporization of residual liquid in a short time and with good efficiency.

[0007]

In order to achieve the above object, a method for vaporizing a residual liquid in a low temperature liquefied gas storage tank according to claim 1 is a boil-off gas for compressing a boil-off gas generated from a low-temperature liquefied gas. A method for vaporizing residual liquid in a low temperature liquefied gas storage tank provided with a compressor, characterized in that the gas after passing through the boil-off gas compressor is introduced into the storage tank from the lower part of the storage tank.

Further, in the method for vaporizing the residual liquid in the low temperature liquefied gas storage tank according to claim 2, the low temperature liquefaction accumulated at the bottom of the storage tank in the flow of the gas when the gas is introduced into the storage tank. It is characterized in that the residual liquid of gas is injected.

Further, in the method for vaporizing the residual liquid of the low temperature liquefied gas storage tank according to claim 3, the introduction of the gas into the storage tank is continued even after the vaporization of the residual liquid of the low temperature liquefied gas is completed. It is what

Further, in the low temperature liquefied gas storage facility according to a fourth aspect of the present invention, a pipe which is a receiving pipe or a discharge pipe of the low temperature liquefied gas is connected to a lower portion of a storage tank which stores the low temperature liquefied gas, A drain pipe for discharging the residual liquid of the low temperature liquefied gas is connected to the bottom, and a boil-off gas return pipe for returning the boil-off gas discharged from the storage tank to the storage tank through a boil-off gas compressor is provided in the storage tank. In the low-temperature liquefied gas storage facility attached to, the boil-off gas return pipe is connected in the middle of the pipe, so that the gas after passing through the boil-off gas compressor is introduced into the storage tank from the lower part of the storage tank. And the tip of the drain pipe extending from the bottom of the storage tank is connected between the connection point of the pipe and the boil-off gas return pipe and the storage tank. Ri, is characterized in that said piping with the bottom of the reservoir is communicated with the drain pipe.

[0011]

According to the method for vaporizing the residual liquid in the low temperature liquefied gas storage tank according to claim 1, since the gas after passing through the boil-off gas compressor is sufficiently higher than the temperature of the low temperature liquefied gas, this hot By introducing the gas from the lower part of the storage tank, the hot gas is introduced into the residual liquid of the low temperature liquefied gas or accumulated on the liquid surface at a high flow rate, and the residual liquid is efficiently heated and vaporized.

Further, according to the method for vaporizing the residual liquid in the low temperature liquefied gas storage tank according to the second aspect, when the residual liquid is injected into the gas flow when the gas is introduced, the residual liquid vaporizes between the gas and the residual liquid. Since heat exchange is performed, vaporization of the residual liquid is further promoted.

Further, according to the method for vaporizing the residual liquid in the low temperature liquefied gas storage tank according to the third aspect, if the introduction of the gas is continued even after the vaporization of the residual liquid is completed, the storage tank can be heated up.

Further, according to the low-temperature liquefied gas storage facility of the fourth aspect, since the gas after passing through the boil-off gas compressor has a temperature sufficiently higher than the temperature of the low-temperature liquefied gas, this hot gas is generated. Boil-off gas Return pipe, receiving pipe or pay-out pipe is introduced into the storage tank by being introduced into the storage tank. The liquid is heated and vaporizes. On the other hand, since the tip of the drain pipe extending from the bottom of the storage tank was connected between the connection point between the pipe and the boil-off gas return pipe and the storage tank, the drain pipe functions as if it were a siphon connecting the bottom of the storage tank and the pipe. Will have. That is, when the hot gas flows in the pipe, the residual liquid in the storage tank is constantly sucked up to the pipe side through the drain pipe.Therefore, the hot gas and the residual liquid come into contact with each other to continuously perform heat exchange, Liquid vaporization is further promoted.

[0015]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT An embodiment of the present invention will be described below with reference to FIG. FIG. 1 is a diagram showing a main part of an LNG storage facility 14 (low temperature liquefied gas storage facility) of the present embodiment, and reference numeral 1 in the figure.
5 is a storage tank, 16 is a receiving pipe (pipe), 17 is a drain pipe,
18 is a BOG return pipe (boil-off gas return pipe).
Note that the features of the present invention can be shown in the main part of the equipment shown in FIG. 1, and the overall configuration of the LNG storage equipment 14 is almost the same as in FIG. 2 described as a conventional technique.

As shown in FIG. 1, a bottom cold insulation layer 20 made of a material having a high heat insulating property is formed on an upper portion of a base 19 formed on the ground, and a wall portion 21 of the tank body is provided above the bottom cold insulation layer 20. Are formed. The wall portion 21 is composed of a top plate portion 22, a side plate portion 23, and a bottom plate portion 24. Each of the plate portions 22, 23, 24 has a cold insulation layer formed of a material having high heat insulation and a liquid tightness. It is formed by a laminated structure of an inner shell plate and an outer shell plate, which are formed of a material for ensuring the above (not shown).

A receiving pipe 16 for receiving LNG from an LNG tanker or the like is fixed to a lower portion of the side plate portion 23 (a height of about 1.5 m for a storage tank having a height of 30 m as an example of dimensions). A storage tank source valve 29, a shutoff valve 30, and a valve 31 are sequentially installed on the receiving pipe 16 from the storage tank 15 side. Further, a BOG return pipe 18 is connected to the upstream side of the shutoff valve 30 in the receiving pipe 16, and a valve 25 is installed in the middle of the BOG return pipe 18. This BOG return pipe 18
Is a BOG outlet pipe 26 for the BOG discharged from the storage tank 15.
After passing through the BOG compressor 27 (boil-off gas compressor) through the BOG compressor 27, a BOG for returning a part thereof to the storage tank 15.
It is a branch from the return main 28.

Further, the tip of a drain pipe 17 extending from the bottom plate portion 24 of the storage tank 15 through the bottom cold insulating layer 20 and the base 19 is connected between the storage tank source valve 29 and the shutoff valve 30 in the receiving pipe 16. In the middle of the drain pipe 17, a drain valve 32 and a valve 33 are sequentially installed from the storage tank 15 side. Therefore, the bottom of the storage tank 15 and the receiving pipe 16 are in communication with each other by the U-shaped drain pipe 17. In addition, BOG
Valve 25 on the return pipe 18 and valve 33 on the drain pipe 17
For LNG storage facility 14, a size suitable for residual liquid vaporization is used from the stage of construction of LNG storage facility 14.

When discharging the LNG residual liquid in the storage tank 15 in the LNG storage facility 14 having the above-mentioned structure, the following procedure is performed. First, LNG is discharged through the receiving pipe 16 to a level almost equal to that of the receiving pipe 16. Then, among the six valves shown in FIG. 1, only the valve 31 on the receiving pipe is “closed” and the remaining valves are all “open”, and the BOG after passing through the BOG compressor 27 is returned to the BOG. B through the main pipe 28
It is injected into the OG return pipe 18 side. Then, the BOG compressor 2
BOG after passing 7 is normal temperature gas and LNG in the storage tank 15
Since the temperature is sufficiently higher than the temperature of
When G is ejected into the storage tank 15 through the BOG return pipe 18 and the receiving pipe 16, the hot gas flows into the LNG residual liquid accumulated in the storage tank 15 or on the liquid surface at a high flow rate,
The residual liquid is heated and vaporized.

On the other hand, since the tip of the drain pipe 17 extending from the bottom of the storage tank 15 is connected between the connection point A of the receiving pipe 16 and the BOG return pipe 18 and the storage tank 15, the drain pipe 17 is connected to the bottom of the storage tank 15. It has a function as a siphon that connects the receiving tube 16 with the receiving tube 16. That is, when the hot BOG flows in the receiving pipe 16, the residual liquid in the storage tank 15 is constantly sucked up to the receiving pipe 16 side through the drain pipe 17, so that the hot BOG and the residual liquid come into gas-liquid contact with each other in the receiving pipe 16. The heat exchange is performed while flowing, and the vaporization of the residual liquid is further promoted. Then, even after the residual liquid is completely vaporized, hot BOG is continuously injected to hot-up the storage tank 15 itself.

In the LNG storage facility 14 of this embodiment, hot BOG produced by the BOG compressor 27 is used instead of the conventional method that relies on pumping in a liquid state and vaporization by natural heat input. By positively promoting vaporization, it is possible to efficiently vaporize the LNG residual liquid. In other words, according to the present embodiment, it is not necessary to install an expensive temporary pump, which takes time and effort as in the conventional case, so that the cost is low and the residual liquid vaporization is required as compared with the case of natural heat input. It can save a lot of time.

Then, not only the residual liquid in the storage tank 15 is heated by hot BOG, but also the residual liquid in the storage tank 15 circulates through the drain pipe 17 by constructing a siphon with the drain pipe 17, so that the liquid vapor Since the contact is actively performed, the efficiency of the residual liquid vaporization can be further increased. Further, by continuously injecting the hot BOG even after the completion of the vaporization of the residual liquid, the hot-up of the storage tank 15 can be accelerated. Therefore, according to the residual liquid vaporization method using the LNG storage facility 14 of the present embodiment, the open inspection work of the storage tank 15 can be efficiently performed, and the LNG storage facility 1
The operating rate of 4 can be improved.

In order to realize the configuration of the LNG storage facility 14, in addition to the conventional facility configuration at the construction stage of the LNG storage facility 14, the piping work of the BOG return pipe 18 branched from the BOG return main pipe 28 is performed. It suffices to add only the work of connecting the drain pipe 17 to the receiving pipe 16.
Furthermore, since no special power source is required for hot BOG injection or circulation of LNG residual liquid, the LNG storage facility 14 of this embodiment can be rationalized without spending a great deal of cost.
Can be realized.

In the present embodiment, the case where the pipe under the storage tank 15 is the receiving pipe 16 has been described, but even if this pipe is a payout pipe, the same effect as that of the present embodiment can be obtained. . Further, if the effect of this embodiment in which the drain pipe 17 is a siphon is not required, the residual liquid in the storage tank 15 may be injected into the flow of the hot BOG by any other means. Further, the arrangement of the valves provided in each pipe is not limited to this embodiment, and may be appropriately changed. And, as the low temperature liquefied gas, for example, LPG,
The present invention can be applied to low temperature liquefied gas other than LNG.

[0025]

As described in detail above, claim 1 is as follows.
In the low-temperature liquefied gas storage tank residual liquid vaporization method described in,
Since the residual liquid of the low temperature liquefied gas can be vaporized by the high temperature gas, the time required for vaporizing the residual liquid can be shortened as compared with the case of the conventional natural heat input. Therefore, the open inspection work of the storage tank can be efficiently performed, and the operation rate of the low temperature liquefied gas storage facility can be improved.

In the method for vaporizing the residual liquid in the low temperature liquefied gas storage tank according to claim 2, heat exchange is performed between the gas and the residual liquid by injecting the residual liquid into the flow of the high temperature gas. Since the residual liquid vaporization can be further promoted, the residual liquid can be efficiently vaporized, and the time required for the residual liquid vaporization can be much shortened as compared with the conventional natural heat input. it can. Therefore, the open inspection work of the storage tank can be efficiently performed, and the operation rate of the low temperature liquefied gas storage facility can be improved.

In the method for vaporizing the residual liquid of the low temperature liquefied gas storage tank according to the third aspect, the time required for hot-up of the storage tank is shortened by continuing the gas blowing even after the vaporization of the residual liquid is completed. can do.

Further, in the low temperature liquefied gas storage facility according to claim 4, the high temperature gas is a boil-off gas return pipe,
The residual liquid of the low-temperature liquefied gas is vaporized by being introduced into the storage tank through the pipe, while the drain pipe has a function as a siphon, so that heat exchange between the gas and the residual liquid is continuously performed, and the residual liquid Vaporization is promoted more. Therefore, it is possible to efficiently vaporize the residual liquid, and it is not necessary to install an expensive temporary pump, which takes time and effort as in the conventional case, so that the cost can be reduced and compared to the case of natural heat input. The time required for vaporizing the residual liquid can be shortened sufficiently.
Therefore, the open inspection work of the storage tank can be efficiently performed, and the operation rate of the storage facility can be improved.

[Brief description of drawings]

FIG. 1 is a diagram showing a main part of an LNG storage facility according to an embodiment of the present invention.

FIG. 2 is a diagram showing an example of the configuration of a general LNG storage facility.

[Explanation of symbols]

 14 LNG storage facility (low-temperature liquefied gas storage facility) 15 Storage tank 16 Receiving pipe (piping) 17 Drain pipe 18 BOG return pipe (boil-off gas return pipe) 27 BOG compressor (boil-off gas compressor) 28 BOG return main pipe

Claims (4)

[Claims] 1. A method for vaporizing residual liquid in a low-temperature liquefied gas storage tank provided with a boil-off gas compressor for compressing boil-off gas generated from low-temperature liquefied gas, wherein the gas after passing through said boil-off gas compressor is said A method for vaporizing a residual liquid in a low temperature liquefied gas storage tank, characterized by introducing the liquid from a lower portion of the storage tank. 2. The low-temperature liquefaction method for a low-temperature liquefied gas storage tank according to claim 1, wherein when the gas is introduced into the storage tank, the low-temperature liquefaction accumulated at the bottom of the storage tank in the flow of the gas. A method for vaporizing a residual liquid in a low temperature liquefied gas storage tank, which comprises injecting a residual liquid of gas. 3. The method for vaporizing a residual liquid in a low temperature liquefied gas storage tank according to claim 1, wherein the introduction of the gas into the storage tank is continued even after the vaporization of the residual liquid of the low temperature liquefied gas is completed. A method for vaporizing a residual liquid in a low-temperature liquefied gas storage tank, comprising: 4. A pipe which is a receiving pipe or a pay-out pipe for the low temperature liquefied gas is connected to a lower portion of a storage tank for storing the low temperature liquefied gas, and a residual liquid of the low temperature liquefied gas is discharged to a bottom portion of the storage tank. In the low-temperature liquefied gas storage facility in which a boil-off gas return pipe for recirculating boil-off gas discharged from the storage tank to the storage tank through a boil-off gas compressor is attached to the storage tank, By connecting the boil-off gas return pipe in the middle of the, the gas after passing through the boil-off gas compressor is introduced into the storage tank from the lower part of the storage tank, and the pipe and the boil-off gas return pipe are connected. Since the tip of the drain pipe extending from the bottom of the storage tank is connected between the point and the storage tank, the bottom of the storage tank and the pipe are connected to the drain. Low-temperature liquefied gas storage facility, characterized in that it communicates with the tube.