KR101309963B1 - Re-liquefaction process for bog - Google Patents

Abstract

PURPOSE: A re-liquefaction method for boil-off gas is provided to divide a main stream into a gas phase stream and a liquid phase stream using a distillation tower and collect the liquid phase stream from the main stream. CONSTITUTION: A re-liquefaction method for boil-off gas is as follows. A main stream is compressed. The compressed main stream is cooled. The cooled main stream is expanded. The main stream is divided into a first gas phase stream and a second liquid phase stream at a distillation tower (150). The first gas phase stream is cooled. The cooled first gas phase stream is divided into a third gas phase stream and a fourth liquid phase stream. The fourth liquid phase stream is supplied to the distillation tower.

Description

Reliquefaction method of evaporated gas {RE-LIQUEFACTION PROCESS FOR BOG}

FIELD OF THE INVENTION The present invention relates to a method of reliquefaction of boil-off gas, and more particularly to a method of re-liquefaction of boil-off gas capable of recovering a liquid stream of higher recovery and purity from the boil-off gas.

Gases such as natural gas and carbon dioxide are usually liquefied and stored in storage tanks. That is, gases such as natural gas or carbon dioxide are generally stored in the form of liquefied natural gas or liquefied carbon dioxide. However, during such storage, a boil-off gas (BOG) is generated in which a part of the storage liquid is vaporized due to a cause such as external heat. However, the continuous generation of boil-off gas increases the pressure in the storage tank, so it is necessary to treat the boil-off gas in some way. The easiest way is to exhaust the evaporated gas as it is. However, evacuating the evaporated gas as such is not preferable for economic or environmental reasons. Therefore, various techniques for re-liquefying the evaporated gas to be introduced into the storage tank are currently being studied.

Recently, there has been disclosed a reliquefaction method that can simplify the structure and operation of the reliquefaction system (see Patent Document 1). However, the reliquefaction method of Patent Literature 1 has a problem of low recovery and purity despite various advantages. Therefore, there is an urgent need for a reliquefaction method capable of recovering the liquid stream from the evaporative gas with higher recovery rate and purity.

Korean Registered Patent Publication No. 1153103

Accordingly, the present invention has been made to solve the above problems, the object of the present invention is to provide a method of reliquefaction of the evaporated gas that can recover the liquid stream from the evaporated gas with a higher recovery rate and purity.

The reliquefaction method of the evaporation gas according to the present invention relates to a reliquefaction method of the evaporation gas for liquefying the main stream, which is an evaporation gas generated from a storage liquid stored in a storage tank by liquefying into a liquid phase in a gaseous phase. Compression step, a first cooling step of cooling the main stream after the compression step, a first expansion step of expanding the main stream after the first cooling step, and after the first expansion step, the main stream and A first separation step of separating the liquid stream into a second stream, a second cooling step of cooling the first stream after the first separation step, and a second stream of gaseous third and liquid phase fourth streams after the second cooling step A second separation step of separating into a stream, and a feeding step of feeding the fourth stream to the distillation column after the second separation step, wherein the second stream is at least partially The first being returned to the storage tank after the separation step, the third stream is at least in part is discharged to the outside after the second separation step.

The reliquefaction method of the boil-off gas according to the present invention separates the main stream into a gaseous part and a liquid phase part using a distillation column, so that the liquid stream is recovered from the main stream with higher recovery rate and purity even without cooling the main stream at a very low temperature. The effect is that you can.

1 is a flowchart showing a reliquefaction method according to Embodiment 1 of the present invention.
FIG. 2 is a flow chart showing a modification of the reliquefaction method of FIG.
3 is a flow chart showing a modification of the reliquefaction method of FIG.
4 is a flowchart showing a reliquefaction method according to Embodiment 2 of the present invention.
FIG. 5 is a flow chart showing a first modification of the reliquefaction method of FIG.
6 is a flowchart showing a second modification of the reliquefaction method of FIG.
7 is a flowchart showing a first modification of the reliquefaction method of FIG.
8 is a flow chart showing a second modification of the reliquefaction method of FIG.
9 is a flowchart showing a third modification of the reliquefaction method of FIG.
10 is a flowchart showing a reliquefaction method according to Embodiment 3 of the present invention.
FIG. 11 is a flowchart showing a modification of the reliquefaction method of FIG. 10.

Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the accompanying drawings. However, the present invention is not limited or limited by the following examples.

Example  One

1 is a flowchart illustrating a reliquefaction method according to Embodiment 1 of the present invention. The reliquefaction method according to Embodiment 1 of the present invention is applied to a method of reliquefaction of an evaporated gas (main stream) generated from a storage liquid stored in a storage tank by liquefying to a liquid phase in a gaseous phase. Such storage liquids are typically liquefied natural gas or liquefied carbon dioxide. However, the reliquefaction method according to the present embodiment is not applied only to the reliquefaction of liquefied natural gas or liquefied carbon dioxide.

Referring to Figure 1 will be described in more detail the reliquefaction method according to this embodiment. Firstly, the main stream enters the compression means 120 through the conduit 211 and is compressed (compression step). The compression means 120 here can be a conventional compressor, and can also be multistage. The main stream then enters and cools through the conduit 212 to the cooling means 131 (first cooling stage). Here, the cooling means 131 may be a water-cooled or air-cooled cooler. The same applies to other cooling means described later.

The main stream then enters the expansion means 141 and expands (first expansion step). This expansion allows the main stream to have a pressure equal to the pressure of the storage tank 110. The expansion means 141 may be a J-T (Joule-Thomson) valve. In one example, the expansion means 141 may be an expansion valve. The same is true for other expansion means described later. J-T valves can reduce the pressure and temperature of the stream through the J-T effect. Or the expansion means may be an expander.

The main stream is then introduced into a distillation column 150 and separated into a first stream in the gas phase and a second stream in the liquid phase (first separation step). Distillation columns can separate gaseous and liquid materials more precisely than conventional vapor-liquid separators. Thus, the use of a distillation column can recover the liquid stream to the storage tank 110 with higher recovery and purity.

The first stream separated from the main stream enters the cooling means 132 through the conduit 221 and is cooled (second cooling step). The first stream then enters separation means 161 through conduit 222 and is separated into a third stream in the gas phase and a fourth stream in the liquid phase (second separation step). The separation means 161 may be a conventional vapor-liquid separator. The same is true of the other separating means 162 which will be described later. The second stream separated from the main stream is then returned to storage tank 110 via conduit 231.

A third stream separated from the first stream is exhausted to the outside through conduit 241. Such exhaust can remove impurities from the storage liquid. And a fourth stream separated from the first stream is fed back to the distillation column 150 via a conduit 251 (feed step). As such, when the first stream is cooled and the liquid phase is separated therefrom and the distillation column 150 is supplied again, the liquid stream may be recovered to the storage tank 110 with higher purity. For reference, a pump 170 may be used to pump the fourth stream into the distillation column 150.

The reliquefaction method according to the present embodiment is characterized in that it basically uses a distillation column as described above. To recover the liquid stream with a higher recovery rate from the main stream (evaporation gas), the main stream generally needs to be cooled to very low temperatures. However, this cooling causes a problem that the structure of the reliquefaction system becomes complicated or the operation of the reliquefaction system becomes difficult. However, if the distillation column is used as in the reliquefaction method according to the present embodiment, the recovery rate and purity can be increased without cooling the main stream to a very low temperature.

Note that the conduits discussed above for reference may be different conduits or may be the same conduits according to reference numerals. That is, even one conduit may be given two reference numerals for convenience of description. Alternatively, two conduits may be provided with one reference numeral for convenience of explanation.

Meanwhile, the reliquefaction method of FIG. 1 may be modified as shown in FIG. 2. 2 is a flowchart illustrating a modification of the reliquefaction method of FIG. 1. As shown in FIG. 2, in this variant, the second stream is not returned directly to the storage tank 110. That is, in this variant, the second stream once enters the expansion means 142 and expands. This expansion allows the second stream to have a pressure equal to the pressure of the storage tank 110. For reference, in the present modification, the main stream may be expanded at a pressure higher than that of the storage tank 110 in the expansion means 141.

The second stream then enters separation means 162 via conduit 2311 and is separated into a fifth stream of gaseous phase and a sixth stream of liquid phase. The separating means 162 may be a conventional gas-liquid separator. The fifth stream separated from the second stream is exhausted to the outside together with the third stream. To this end, the fifth stream may be incorporated into the third stream. Such incorporation may be accomplished by connecting one conduit 2312 to the other conduit 241. Alternatively, a separate configuration for incorporation may be employed. The third stream may then be expanded by the expansion means 143 before incorporation. The sixth stream separated from the second stream is then returned to storage tank 110 through conduit 2313.

The reliquefaction method according to this variant is characterized in that the main stream is first expanded through the expansion means 141 and then the second stream separated from the main stream is secondly expanded through the expansion means 142. . By expanding the stream in this manner it is possible to recover the liquid stream to the storage tank 110 with higher purity. It is also economically more useful because the cooling means 132 of this variant can cool the first stream at a higher temperature than the cooling means 132 of the first embodiment.

However, the reliquefaction method of FIG. 2 may be modified as shown in FIG. 3. 3 is a flowchart illustrating a modification of the reliquefaction method of FIG. 2. As shown in FIG. 3, in the present modification, the fifth stream is not exhausted to the outside. In other words, in the present modification, the fifth stream is mixed with the main stream as shown in FIG. 3 and then compressed together with the main stream by the compression means 120. Such incorporation may be accomplished by connecting one conduit 2314 to the other conduit 211. Alternatively, a separate configuration for incorporation may be employed. Alternatively, the main stream and the fifth stream may be introduced into the compression means 120 and then mixed in the compression means 120. In this way, when the fifth stream is supplied to the compression unit 120 again, the recovery rate can be increased rather than being exhausted as it is.

Example  2

4 is a flowchart illustrating a reliquefaction method according to Embodiment 2 of the present invention. For reference, the same (or equivalent) parts with the same (or equivalent) parts as those described above will be given the same reference numerals, and detailed description thereof will be omitted.

Hereinafter, the reliquefaction method according to the present embodiment will be described in more detail with reference to FIG. 4. First the main stream enters the first heat exchange zone 181 via conduit 311 (first inlet stage). In the first heat exchange zone 181, the main stream cools the main stream entering the first heat exchange zone 181 through the conduit 314. The main stream generated from the storage liquid has a relatively low temperature. The first heat exchange zone 181 is provided for recovering cold heat from the main stream having such a low temperature.

The main stream then enters the compression means 120 through the conduit 312 and is compressed (compression step). The main stream then enters and cools the cooling means 131 through the conduit 313. However, such cooling means 131 does not necessarily have to be provided. In some cases, cooling by the cooling means 131 may be replaced by cooling by the first heat exchange region 181. Or in some cases, cooling by the cooling means 131 may be unnecessary.

The main stream then flows back through the conduit 314 into the first heat exchange zone 181 (second inlet stage). In the first heat exchange zone 181, the main stream is cooled by the main stream entering the first heat exchange zone 181 through the conduit 311. The main stream then enters the expansion means 141 and expands (first expansion step). This expansion can lower the temperature of the main stream. Then, the main stream enters the distillation column 150 and is separated into a gaseous first stream and a liquid phase second stream (first separation step).

The first stream separated from the main stream enters the second heat exchange zone 182 via conduit 321 (third inflow step). In this case, the second heat exchange region 182 is physically distinguished from the first heat exchange region 181. In the second heat exchange zone 182, the first stream is cooled by a third stream entering the second heat exchange zone 182 through the conduit 341. The first stream then enters separation means 161 via conduit 322 and is separated into a third stream in the gas phase and a fourth stream in the liquid phase (second separation step). The second stream separated from the main stream is then returned to storage tank 110 via conduit 331.

A third stream separated from the first stream enters and expands into expansion means 144 and then enters second heat exchange zone 182 (fourth inflow step). The third stream may be lowered in temperature by expansion by the expansion means 144. In the second heat exchange zone 182, the third stream cools the first stream entering the second heat exchange zone 182 through the conduit 321. The third stream then exits the second heat exchange zone 182 and is exhausted outward through the conduit 342. And the fourth stream separated from the first stream is fed back to the distillation column 150 through the conduit 351 (feed step).

The reliquefaction method according to the present embodiment is characterized in that it has two heat exchange zones 181 and 182 as described above. At this time, the first heat exchange region 181 serves to recover the cold heat from the main stream generated from the storage liquid, and the second heat exchange region 182 serves to recover the cold heat from the third stream. The reliquefaction method according to the present embodiment has the advantage of improving the efficiency of the entire system by recovering the cold heat as described above.

For reference, the heat exchange regions described above may be provided in two heat exchange means, respectively. The heat exchange means here can be a conventional heat exchanger.

Meanwhile, the reliquefaction method of FIG. 4 may be modified as shown in FIG. 5. 5 is a flowchart illustrating a first modification of the reliquefaction method of FIG. 4. As shown in FIG. 5, in this variant, the second stream is not returned directly to the storage tank 110. That is, in this variant, the second stream once enters the expansion means 142 and expands. This expansion can lower the temperature of the second stream. The second stream then enters separation means 162 via conduit 3311 to separate the fifth stream in the gas phase and the sixth stream in the liquid phase.

The fifth stream separated from the second stream is expanded by the expansion means 145 and then enters the second heat exchange zone 182. The fifth stream may be lowered in temperature due to expansion. In the second heat exchange zone 182, the fifth stream cools the first stream entering the second heat exchange zone 182 through the conduit 321. The fifth stream is then exhausted outward through conduit 3313. In this case, the fifth stream may be exhausted together with the third stream. To this end, the third stream may be mixed into the fifth stream. Such incorporation may be accomplished by connecting one conduit 341 to the other conduit 3313. Alternatively, a separate configuration for incorporation may be employed. On the contrary, the fifth stream may be mixed in the third stream.

The reliquefaction method according to this variant is characterized in that the main stream is first expanded through the expansion means 141 and then the second stream separated from the main stream is secondly expanded through the expansion means 142. . By expanding the stream in stages as described above, there is an advantage that the liquid stream can be recovered to the storage tank 110 with higher purity. In addition, the reliquefaction method according to the present modification recovers cold heat from the fifth stream in the second heat exchange zone 182. Therefore, the reliquefaction method according to the present modification also has the advantage that the efficiency of the entire system is excellent.

The reliquefaction method of FIG. 4 may also be modified as in FIG. 6. 6 is a flowchart illustrating a second modification of the reliquefaction method of FIG. 4. As shown in FIG. 6, the reliquefaction method according to the present modification further cools the first stream in the second heat exchange zone 182 using a separate closed loop refrigeration cycle.

More specifically, the closed loop refrigeration cycle will be described. The refrigerant first enters the compression means 128 through the conduit 381 and is compressed. The refrigerant may be a pure refrigerant or a single-component refrigerant or a mixed refrigerant or a multi-component refrigerant. And the compression means 128 may be a conventional compressor, and may also be multistage. The refrigerant then enters and cools the cooling means 138 through conduits 382. Here, the cooling means 138 may be a water-cooled or air-cooled cooler.

The refrigerant then flows into the second heat exchange zone 182 through conduits 383. The refrigerant then enters and expands to expansion valve 148. This expansion can cause the refrigerant to cool down. The refrigerant then flows back into the second heat exchange zone 182 to cool the first stream entering the second heat exchange zone 182 through the conduit 321. In this case, the refrigerant may cool the refrigerant flowing into the second heat exchange region 182 through the conduit 383.

The reliquefaction process according to this variant is characterized by further cooling the first stream using a separate closed loop refrigeration cycle. As such, further cooling the first stream may further lower the temperature of the fourth stream supplied to the distillation column 150. In this way, if the temperature of the fourth stream is further lowered, the gaseous substance and the liquid substance can be separated more precisely in the distillation column, thereby increasing the recovery rate and purity.

However, the reliquefaction method of FIG. 6 may be modified as shown in FIG. 7. FIG. 7 is a flowchart illustrating a first modification of the reliquefaction method of FIG. 6. As shown in FIG. 7, in this variant, the second stream once enters and expands to expansion means 142. This expansion can lower the temperature of the second stream. The second stream then enters separation means 162 via conduit 3311 to separate the fifth stream in the gas phase and the sixth stream in the liquid phase.

The fifth stream separated from the second stream enters the first heat exchange zone 181 along with the main stream after being incorporated into the main stream. Such incorporation may be accomplished by connecting one conduit 3315 to the other conduit 311. Alternatively, a separate configuration for incorporation may be employed. As such, when the fifth stream is introduced into the first heat exchange region 181, the recovery rate may be further increased. Alternatively, the sixth stream is recovered to storage tank 110 through conduit 3314.

In addition, the reliquefaction method of FIG. 6 may be modified as shown in FIG. 8. 8 is a flowchart illustrating a second modification of the reliquefaction method of FIG. 6. As shown in FIG. 8, the reliquefaction method according to the present modification uses the turbo expander 149 to expand the refrigerant in the refrigeration cycle. It is more effective to use turbo expander 149 when the refrigeration cycle uses a refrigerant such as nitrogen to form a gas cycle.

Furthermore, the reliquefaction method of FIG. 6 may be modified as shown in FIG. 9. 9 is a flowchart illustrating a third modification of the reliquefaction method of FIG. 6. As shown in FIG. 9, the reliquefaction method according to the present modification is basically the same as the reliquefaction method of FIG. 7. However, the reliquefaction method of FIG. 7 uses the expansion valve 148 to expand the refrigerant in the refrigeration cycle, whereas the reliquefaction method of FIG. 8 uses the turbo expander 149 to expand the refrigerant.

Example  3

10 is a flowchart illustrating a reliquefaction method according to Embodiment 3 of the present invention. For reference, the same (or equivalent) parts with the same (or equivalent) parts as those described above will be given the same reference numerals, and detailed description thereof will be omitted.

Hereinafter, the reliquefaction method according to the present embodiment will be described in detail with reference to FIG. 10. First the main stream enters the heat exchange zone 180 via conduit 411 (first inlet stage). The main stream then enters compression means 120 through conduit 412 and is compressed (compression step). The main stream then enters and cools the cooling means 131 through the conduit 413. However, such cooling means 131 does not necessarily have to be provided. In some cases, cooling by the cooling means 131 may be replaced by cooling by the heat exchange area 180. Or in some cases, cooling by the cooling means 131 may be unnecessary.

The main stream then flows back through the conduit 414 into the heat exchange zone 180 (second inlet stage). The main stream then enters the expansion means 141 and expands (first expansion step). This expansion can lower the temperature of the main stream. Then, the main stream enters the distillation column 150 and is separated into a gaseous first stream and a liquid phase second stream (first separation step).

The first stream separated from the main stream enters the heat exchange zone 180 via conduit 421 (third inflow step). The first stream then enters separation means 161 via conduit 422 and is separated into a third stream in the gas phase and a fourth stream in the liquid phase (second separation step). The second stream separated from the main stream is then returned to storage tank 110 through conduit 431.

The third stream separated from the first stream enters the expansion means 144 and expands and then enters the heat exchange zone 180 (fourth inflow step). The third stream may be lowered in temperature by expansion by the expansion means 144. The third stream then exits the heat exchange zone 180 and is exhausted outward through conduit 442. And a fourth stream separated from the first stream is fed back to the distillation column 150 via a conduit 451 (feed step).

For reference, the main stream introduced into the heat exchange region 180 through the conduit 411 and the third stream introduced into the heat exchange region 180 through the conduit 441 may be the heat exchange region 180 through the conduit 414. The first stream introduced into the heat exchange zone 180 is cooled through the main stream and the conduit 421 introduced thereto.

The reliquefaction method according to the present embodiment is characterized in that one heat exchange area is used as compared with the reliquefaction method according to the second embodiment. Thus, using one heat exchange zone has the advantage of cooling the first stream through the low temperature of the main stream. That is, the first stream introduced into the heat exchange region 180 through the conduit 421 may also be cooled by using the main stream introduced into the heat exchange region 180 through the conduit 411. Such cooling may further lower the temperature of the fourth stream fed to the distillation column 150. In this way, if the temperature of the fourth stream is further lowered, the gaseous substance and the liquid substance can be separated more precisely in the distillation column, thereby increasing the recovery rate and purity.

Meanwhile, the reliquefaction method of FIG. 10 may be modified as shown in FIG. 11. 11 is a flowchart illustrating a modification of the reliquefaction method of FIG. 10. As shown in FIG. 11, in this variant, the second stream is not returned directly to the storage tank 110. That is, in this variant, the second stream once enters the expansion means 142 and expands. This expansion can lower the temperature of the second stream. The second stream then enters separation means 162 to separate the fifth stream in the gas phase and the sixth stream in the liquid phase.

The fifth stream separated from the second stream is expanded by expansion means 145 and then enters heat exchange zone 180. The fifth stream is then exhausted outward through conduit 4313. In this case, the fifth stream may be exhausted together with the third stream. To this end, the fifth stream may be incorporated into the third stream. Such incorporation may be accomplished by connecting one conduit 4313 to the other conduit 4421. Alternatively, a separate configuration for incorporation may be employed. On the contrary, the third stream may be mixed in the fifth stream. Alternatively, the sixth stream separated from the second stream is recovered to storage tank 110 through conduit 4314.

The reliquefaction method according to this variant is characterized in that the main stream is first expanded through the expansion means 141 and then the second stream separated from the main stream is secondly expanded through the expansion means 142. . By expanding the stream in stages as described above, there is an advantage that the liquid stream can be recovered to the storage tank 110 with higher purity. In addition, the reliquefaction method according to the present modification recovers cold heat from the fifth stream in the heat exchange zone 180. Therefore, the reliquefaction method according to the present modification also has the advantage that the efficiency of the entire system is excellent.

120: compression means 131, 132: cooling means
141, 142, 143, 144, 145: expansion means
150: distillation column 161, 162: separation means
180, 181, 182: heat exchange zone

Claims (12)

A method of reliquefaction of an evaporated gas for liquefying a main stream, which is an evaporated gas generated from a storage liquid stored in a storage tank by liquefying to a liquid phase in a gaseous phase,
Compressing the main stream;
A first cooling step of cooling the main stream after the compression step;
A first expansion step of expanding the main stream after the first cooling step;
A first separation step of separating the main stream into a gaseous first stream and a liquid phase second stream in the distillation column after the first expansion step;
A second cooling step of cooling the first stream after the first separation step;
A second separation step of separating the first stream into a gaseous third stream and a liquid fourth stream after the second cooling step; And
A feed step of feeding the fourth stream to the distillation column after the second separation step,
Wherein the second stream is at least partially recovered to the storage tank after the first separation step and the third stream is at least partially exhausted to the outside after the second separation step. Way. The method according to claim 1,
A second expansion step of expanding the second stream after the first separation step; and a third separation step of separating the second stream into a fifth gaseous stream and a sixth liquid stream after the second expansion step. More,
The fifth stream is evacuated with the third stream after the third separation step, and the sixth stream is recovered to the storage tank after the third separation step. Way. The method according to claim 1,
A second expansion step of expanding the second stream after the first separation step; and a third separation step of separating the second stream into a fifth gaseous stream and a sixth liquid stream after the second expansion step. More,
The fifth stream is mixed into the main stream after the third separation step and sent to the compression step together with the main stream, and the sixth stream is returned to the storage tank after the third separation step. A reliquefaction method of the evaporated gas to be. A method of reliquefaction of an evaporated gas for liquefying a main stream, which is an evaporated gas generated from a storage liquid stored in a storage tank by liquefying to a liquid phase in a gaseous phase,
A first inflow step of introducing the main stream into a first heat exchange region;
Compressing the main stream discharged from the first heat exchange zone after the first inlet step;
A second inflow step of introducing the main stream back into the first heat exchange area after the compression step;
A first expansion step of expanding the main stream discharged from the first heat exchange zone after the second inflow step;
A first separation step of separating the main stream into a gaseous first stream and a liquid phase second stream in the distillation column after the first expansion step;
A third inflow step of introducing the first stream into a second heat exchange area distinct from the first heat exchange area after the first separation step;
A second separation step of separating the first stream discharged from the second heat exchange zone after the third inflow step into a gaseous third stream and a liquid phase fourth stream;
A fourth inflow step of expanding the third stream and introducing the second heat exchange zone after the second separation step; And
A feed step of feeding the fourth stream to the distillation column after the second separation step,
The second stream is at least partially recovered to the storage tank after the first separation step, and the third stream is at least partially discharged from the second heat exchange zone after the fourth inflow step to be exhausted to the outside A method for reliquefying an evaporated gas, characterized by the above-mentioned. The method of claim 4,
A second expansion step of expanding the second stream after the first separation step, a third separation step of separating the second stream into a fifth gaseous stream and a sixth liquid stream after the second expansion step; And a fifth inflow step of expanding the fifth stream and introducing the second heat exchange zone into the second heat exchange zone after the third separation step.
The fifth stream is discharged from the second heat exchange zone after the fifth inflow stage and exhausted to the outside together with the third stream, and the sixth stream is recovered to the storage tank after the third separation stage. A method for reliquefying an evaporated gas, characterized by the above-mentioned. The method of claim 4,
And further cooling the first stream further in the second heat exchange zone by using a separate closed loop refrigeration cycle. The method of claim 6,
The closed loop refrigeration cycle may include a refrigerant compression step of compressing a refrigerant, a first refrigerant inflow step of introducing the refrigerant into the second heat exchange area after the refrigerant compression step, and a second heat exchange after the first refrigerant inflow step A refrigerant expansion step of expanding the refrigerant discharged from the region through an expansion valve, and a second refrigerant introduction step of introducing the refrigerant back into the second heat exchange region after the refrigerant expansion step,
And the refrigerant is discharged from the second heat exchange area after the second refrigerant inflow step and sent back to the refrigerant compression step. The method of claim 7,
A second expansion step of expanding the second stream after the first separation step; and a third separation step of separating the second stream into a fifth gaseous stream and a sixth liquid stream after the second expansion step. More,
The fifth stream is mixed into the main stream after the third separation step and sent to the first inlet step together with the main stream, and the sixth stream is returned to the storage tank after the third separation step. Reliquefaction method of the boil-off gas, characterized in that. The method of claim 6,
The closed loop refrigeration cycle may include a refrigerant compression step of compressing a refrigerant, a first refrigerant inflow step of introducing the refrigerant into the second heat exchange area after the refrigerant compression step, and a second heat exchange after the first refrigerant inflow step A refrigerant expansion step of expanding a refrigerant discharged from the region through a turbo expander, and a second refrigerant introduction step of introducing the refrigerant back into the second heat exchange area after the refrigerant expansion step,
And the refrigerant is discharged from the second heat exchange area after the second refrigerant inflow step and sent back to the refrigerant compression step. The method according to claim 9,
A second expansion step of expanding the second stream after the first separation step; and a third separation step of separating the second stream into a fifth gaseous stream and a sixth liquid stream after the second expansion step. More,
The fifth stream is mixed into the main stream after the third separation step and sent to the first inlet step together with the main stream, and the sixth stream is returned to the storage tank after the third separation step. Reliquefaction method of the boil-off gas, characterized in that. A method of reliquefaction of an evaporated gas for liquefying a main stream, which is an evaporated gas generated from a storage liquid stored in a storage tank by liquefying to a liquid phase in a gaseous phase,
A first inflow step of introducing the main stream into a heat exchange zone;
Compressing the main stream discharged from the heat exchange zone after the first inlet step;
A second inflow step of introducing the main stream back into the heat exchange area after the compression step;
A first expansion step of expanding the main stream discharged from the heat exchange zone after the second inflow step;
A first separation step of separating the main stream into a gaseous first stream and a liquid phase second stream in the distillation column after the first expansion step;
A third inflow step of introducing the first stream into the heat exchange zone after the first separation step;
A second separation step of separating the first stream discharged from the heat exchange zone after the third inflow step into a gaseous third stream and a liquid phase fourth stream;
A fourth inlet step of expanding the third stream and introducing the heat exchange zone after the second separation step; And
A feed step of feeding the fourth stream to the distillation column after the second separation step,
The second stream is at least partially recovered to the storage tank after the first separation step, and the third stream is at least partially discharged from the heat exchange zone after the fourth inflow step and exhausted to the outside Reliquefaction method of the evaporated gas. The method of claim 11,
A second expansion step of expanding the second stream after the first separation step, a third separation step of separating the second stream into a fifth gaseous stream and a sixth liquid stream after the second expansion step; And a fifth inflow step of expanding the fifth stream and introducing the heat exchange zone after the third separation step.
The fifth stream is discharged from the heat exchange zone after the fifth inflow stage and is exhausted to the outside together with the third stream, and the sixth stream is returned to the storage tank after the third separation stage. Reliquefaction method of the evaporated gas.

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