KR20160015919A - Natural gas liquefaction process - Google Patents

Abstract

A liquefaction process according to the present invention primarily cools natural gas in a first heat exchange part by using a single closed loop cooling cycle applying a mixed coolant, and secondarily cools the natural gas in a second heat exchange part distinguished from the first heat exchange part. The subject of the present invention is to provide the natural gas liquefaction process having a simple structure of the liquefaction process, and not only having the liquefaction process easily operated, but also having excellent efficiency of the liquefaction process.

Description

NATURAL GAS LIQUEFACTION PROCESS

The present invention relates to a natural gas liquefaction process, and more particularly, to a natural gas liquefaction process having a simple structure of a liquefaction process, an easy operation of a liquefaction process, and an excellent liquefaction process.

Thermodynamic processes for liquefying natural gas and producing liquefied natural gas (LNG) have been developed since the 1970s to meet a variety of challenges, including higher efficiency and greater capacity requirements. Various attempts to liquefy natural gas using different refrigerants or using different cycles to meet these needs, i. E., To increase the efficiency and capacity of the liquefaction process, have continued to this day, but they have been used practically The number of liquefaction processes is very small.

One of the most prevalent and widely used liquefaction processes is the Propane Pre-cooled Mixed Refrigerant Process (or C3 / MR process). As shown in Figure 9, in the C3 / MR process, natural gas (NG) is first cooled to about 238 K through a Joule-Thomson cycle (or propane cycle) employing propane (C3) (pre-cooled). The natural gas is then liquefied and sub-cooled to approximately 123 K through a mixed refrigerant cycle using a mixed refrigerant (MR, Mixed Refrigerant or Multi-component Refrigerant). As described above, since the C3 / MR process uses a refrigeration cycle using a single refrigerant and a refrigeration cycle using a mixed refrigerant, the structure of the liquefaction process is complicated and the operation of the liquefaction process is difficult.

Another of the liquefaction processes in operation is the Cascade process by Conoco Phillips. As shown in Fig. 10, the cascade process by Conoco Phillips consists of three line-Thomson cycles using methane (C1), ethylene (C2) and propane (C3). Since the cascade process uses only a refrigeration cycle employing a single refrigerant, the operation of the liquefaction process is simple and the reliability of the liquefaction process is high. However, the cascade process has the disadvantage that the size of the liquefaction process can not be increased because each of the three refrigeration cycles requires a separate facility (e.g., a heat exchanger).

Another of the liquefaction processes in operation is the 'Single Mixed Refrigerant Process (or SMR process)'. As shown in FIG. 11, in the SMR process, natural gas is liquefied through one closed loop refrigeration cycle employing mixed refrigerant. This SMR process has the advantage that the structure of the liquefaction process is simple. However, the SMR process has a drawback that the efficiency of the liquefaction process is low.

SUMMARY OF THE INVENTION Accordingly, it is an object of the present invention to provide a natural gas liquefaction process which is simple in the structure of a liquefaction process, easy in operation of a liquefaction process, .

In the liquefaction process according to the present invention, the natural gas is first cooled in the first heat exchanging unit and the second heat exchanging unit, which is distinguished from the first heat exchanging unit, using the one closed loop refrigeration cycle employing the mixed refrigerant, Wherein the closed loop refrigeration cycle comprises a condensing step of partially condensing the mixed refrigerant, a second condensing step of condensing the mixed refrigerant into a first stream of the liquid phase and a second stream of the gas phase after the condensing step, A first inflow step for inflowing the first stream to the first heat exchanger after the first inflow step, a first inflation step for inflating the first stream discharged from the first heat exchanger after the first inflow step, 1 < / RTI > expansion step, the first stream is reintroduced into the first heat exchange unit and the first stream is cooled in the first heat exchange unit through the first stream, A first recovery step for recovering the first stream from the first heat exchange unit after the first cooling step, a second inflow step for introducing the second stream to the first heat exchange unit after the first separation step, a second inflow step after the second inflow step, A second separation step of separating the second stream discharged from the first heat exchange unit into a third stream of the liquid phase and a fourth stream of the gaseous phase, a third separation step of separating the third stream discharged from the third heat exchange unit into the third stream, A second-1 expansion step of expanding the third stream discharged from the second heat exchange unit after the first-flow-in step, the third stream after the second-1 expansion step, into the second heat exchange unit A second-1 cooling step of cooling the natural gas in the second heat exchanger through the third stream, a third-2 inflow step of introducing the fourth stream into the second heat exchanger after the second separation, After the inflow step, is discharged from the second heat exchange section A second-2 expansion step for expanding the fourth stream; a second-2 expansion step for introducing the fourth stream back into the second heat exchange section to cool the natural gas in the second heat exchange section through the fourth stream; And a second recovery step of recovering the third stream and the fourth stream from the second heat exchange section after the second cooling step and after the second and first cooling steps, Is sent to the condensation stage, and after the second recovery step, the third stream and the fourth stream are sent to the condensation stage as a second mixed stream mixed with each other.

Since the natural gas liquefaction process according to the present invention uses one closed loop refrigeration cycle employing a mixed refrigerant, the structure of the liquefaction process is simple and the operation of the liquefaction process is easy, and a single stream is divided into two streams Since the natural gas is cooled after being separated, the efficiency of the liquefaction process is excellent.

Further, the natural gas liquefaction process according to the present invention separates the second stream discharged from the first heat exchanging unit into a liquid-phase stream and a gaseous-phase stream, and then cools the natural gas in the second heat- There is an effect that natural gas can be cooled.

Further, the natural gas liquefaction process according to the present invention utilizes the third stream heavier than the fourth stream in the first heat exchange unit, so that not only can the natural gas be cooled more efficiently, but also the first stream is discharged from the second heat exchange unit So that the second heat exchanger can sufficiently cool the natural gas.

1 is a flowchart showing a natural gas liquefaction process according to a first embodiment of the present invention;
Fig. 2 is a flowchart showing a first modification of the natural gas liquefaction process according to Fig. 1
3 is a flowchart showing a second modification of the natural gas liquefaction process according to FIG.
Fig. 4 is a flowchart showing a third modification of the natural gas liquefaction process according to Fig. 1
5 is a flowchart showing a natural gas liquefaction process according to the second embodiment of the present invention.
6 is a flowchart showing a first modification of the natural gas liquefaction process according to FIG.
Fig. 7 is a flowchart showing a second modification of the natural gas liquefaction process according to Fig. 5
Fig. 8 is a flowchart showing a third modification of the natural gas liquefaction process according to Fig. 5
9 is a flow chart conceptually illustrating a conventional C3 / MR process.
10 is a flow chart conceptually illustrating a conventional cascade process.
11 is a flow chart conceptually illustrating a conventional SMR process.

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 flow chart showing a natural gas liquefaction process according to a first embodiment of the present invention. The liquefaction process according to the first embodiment of the present invention uses a closed loop refrigeration cycle as shown in FIG. 1 to cool natural gas (NG) to a liquefaction temperature to produce liquefied natural gas (LNG ). ≪ / RTI > Particularly, by using one closed loop refrigeration cycle employing a mixed refrigerant or a multi-component refrigerant, the natural gas is firstly cooled in the first heat exchanging section, and the second heat exchanging section To a natural gas liquefaction process which secondarily cools natural gas. For reference, the liquefaction process according to the present embodiment may further include a refrigeration cycle for cooling the mixed refrigerant or for cooling the natural gas.

Hereinafter, the liquefaction process according to the first embodiment of the present invention will be described in detail with reference to FIG. First, the mixed refrigerant (main stream to be described later) is partially condensed (condensation step). That is, the mixed refrigerant is partially condensed through a series of compressions or a series of compression and cooling. The mixed refrigerant thus comprises a liquid phase portion and a vapor phase portion. The mixed refrigerant then flows into the separating means 111 and is separated into a first stream in the liquid phase and a second stream in the vapor phase (first separation step). The separating means 111 may be a conventional vapor-liquid separator. This also applies to other separation means to be described later.

The first stream is introduced into the first heat exchanging unit 121 through the conduit 211 after the separation (first introduction step). Then, the first stream discharged from the first heat exchanging portion 121 flows into the expansion means 131 and is expanded (first expansion step). Whereby the temperature of the first stream can be lowered. The expansion means may comprise a J-T (Joule-Thomson) valve. For example, the expansion means may comprise a conventional expansion valve. Alternatively, the expansion means may comprise an expander. This also applies to other expansion means to be described later. J-T valves can reduce both the pressure and temperature of the stream through the J-T effect.

After the temperature of the first stream is lowered by the expansion, it flows back to the first heat exchanging part 121 through the conduit 212 to cool the natural gas NG in the first heat exchanging part 121 (first cooling step) . The first stream flowing into the first heat exchanging unit 121 through the conduit 212 flows into the first heat exchanging unit 121 through the conduit 211 and the first stream flowing into the first heat exchanging unit 121 through the conduit 221, The second stream introduced into the heat exchanging unit 121 can be cooled together with the natural gas. Through such cooling, the natural gas can be precooled. After the cooling, the first stream is recovered from the first heat exchanger 121 (first recovery step). The first stream is then sent via conduit 213 to the condensation stage.

Meanwhile, the second stream is introduced into the first heat exchanging unit 121 through the conduit 221 after the separation (second inflow step). Then, the second stream discharged from the first heat exchanging unit 121 flows into the separating unit 112 through the conduit 222 and is separated into the third liquid stream and the fourth stream in the vapor phase (second separation step) .

The third stream is introduced into the second heat exchanger 122 through the conduit 2221 after separation (Step 3-1). Then, the third stream discharged from the second heat exchange portion 122 flows into the expansion means 132 and is expanded (a second-1 expansion step). The third stream is lowered in temperature by expansion and then flows back to the second heat exchanger 122 through the conduit 2222 to cool the natural gas NG in the second heat exchanger 122 step).

The fourth stream is introduced into the second heat exchanger 122 through the conduit 2223 after the separation (third-2 inflow step). Then, the fourth stream discharged from the second heat exchange portion 122 flows into the expansion means 133 and is expanded (a second-2 expansion step). The fourth stream is lowered in temperature by expansion and then flows back to the second heat exchanger 122 through the conduit 2224 to cool the natural gas NG in the second heat exchanger 122 step). Natural gas can be liquefied by cooling by the third stream and cooling by the fourth stream.

After the cooling, the third stream and the fourth stream are recovered from the second heat exchange unit 122 (second recovery step). The third stream and the fourth stream are then sent via conduit 224 to the condensation stage. At this time, the third stream and the fourth stream are mixed with each other and sent to the condensation stage. This mixed stream will be referred to as the second mixed stream.

For reference, the first heat exchanger 121 is preferably a SWHE (Spiral Wound Heat Exchanger) type heat exchanger. This also applies to the second heat exchanging part 122. More specifically, in the case of the natural gas liquefaction process, a heat exchanger of a Plate Fin Heat Exchanger (PFHE) type or a spiral heat exchanger (SWHE) type is generally used for heat exchange. Since the PFHE type heat exchanger and the SWHE type heat exchanger have different structures, the liquefaction process based on the PFHE type heat exchanger may not be directly applicable to the liquefaction process using the SWHE type heat exchanger.

The liquefaction process according to this embodiment distinguishes the first heat exchanging unit 121 and the second heat exchanging unit 122 from each other in order to use the SWHE type heat exchanger. For example, in the liquefaction process according to the present embodiment, the first heat exchanging unit 121 is formed by one SWHE type heat exchanger, and the second heat exchanging unit 122 is formed by another SWHE type heat exchanger. The SWHE type heat exchanger is advantageous when the capacity of the liquefaction system is very large. The SWHE type heat exchanger is also advantageous for maintenance of the liquefaction system. However, any one of the first heat exchanging unit 121 and the second heat exchanging unit 122 may be a PFHE type heat exchanger.

As described above, the liquefaction process according to the present embodiment liquefies natural gas using one closed loop refrigeration cycle. Therefore, the liquefaction process according to the present embodiment is advantageous in that the structure of the liquefaction process is simple and the liquefaction process is easy to operate. The liquefaction process according to the present embodiment also isolates one stream into two streams and then cools the natural gas. Therefore, the liquefaction process according to the present embodiment is advantageous in that the liquefaction process efficiency is excellent as it includes one refrigeration cycle but includes two refrigeration cycles. Furthermore, in the liquefaction process according to the present embodiment, the second stream discharged from the first heat exchanging unit 121 is separated into a liquid stream and a gaseous stream, and then the natural gas is cooled in the second heat exchanging unit 122 . In this case, the natural gas can be cooled more efficiently than when the natural gas is cooled in the second heat exchanger 122 through one stream.

On the other hand, the condensation step can be more specifically described as follows. The second mixed stream flows from the second heat exchanger 122 through the conduit 224 into the compression means 141 and is compressed (first compression step). Here, the compression means 141 may be a conventional compressor, and may also be a single compressor. This also applies to other compression means to be described later. The second mixed stream then flows into the cooling means 151 through the conduit 231 and is cooled. Here, the cooling means 151 may be a water-cooled type or an air-cooled type cooler. This also applies to other cooling means to be described later. Cooling means 151 may be provided when it is necessary to cool the compressed stream. This also applies to other cooling means.

The second mixed stream is mixed with the first stream after such cooling. That is, the first stream is incorporated into the second mixed stream (first mixing step). Such incorporation can be achieved by connecting one conduit 213 to another conduit 232. Or a separate configuration for incorporation may be employed. Such incorporation forms the main stream. That is, the main stream is a stream in which the first stream and the second mixed stream are mixed. The main stream is compressed by the compression means 142 (second compression step). The main stream then flows into the cooling means 152 through the conduit 233 and is cooled. Through this series of processes, the main stream is partially condensed and then flows into the separation means 111 through the conduit 234.

For reference, incorporation is a relative concept. Depending on the configuration of the conduit, the first stream may be considered to be incorporated into the second mixed stream and the second mixed stream may be considered incorporated into the first stream. The first stream and the second mixed stream may also be respectively introduced into the compression means 142 and then mixed in the compression means 142. And the conduits discussed above may be different conduits or may be the same conduits according to the reference numerals. That is, even one conduit may be given two numerals for convenience of explanation. Alternatively, two conduits may be provided with one reference numeral for convenience of explanation.

Meanwhile, the liquefaction process according to the present embodiment can be modified as shown in FIG. 2 is a flow chart showing a first modification of the natural gas liquefaction process according to FIG. As shown in Fig. 2, the liquefaction process according to the present modification further includes a third compression step and a fourth compression step. More specifically, in the liquefaction process according to the present modification, the main stream is cooled by the cooling means 152 and then flows into the compression means 143 through the conduit 2341 and is compressed (third compression step). The main stream then flows into the cooling means 153 via conduit 2342 and is cooled.

Then, the main stream is introduced into the separating means 113 through the conduit 2343 to be separated into the fifth stream of the liquid phase and the sixth stream of the gaseous phase (third separation step). The fifth stream is then incorporated into the main stream of conduit 2341 through conduit 2344 (second entraining step). Wherein the fifth stream may be inflated by the inflation means 134 and then incorporated into the main stream. The fifth stream then flows into the compression means 143 together with the main stream.

Then, the sixth stream flows into the compression means 144 through the conduit 2345 and is compressed (fourth compression step). The sixth stream then flows into the cooling means 154 through conduit 2346 and is cooled. Through this series of processes, the sixth stream is partially condensed and then flows into the separation means 111 through the conduit 2347.

However, it is preferable that the compression means (for example, compression means 144) is supplied with the gaseous refrigerant. However, when the refrigerant is mixed with the first stream and the second mixed stream, or the refrigerant is compressed or cooled, a liquid-phase refrigerant may be generated. At this time, when the separating means 113 is used as in the present modified example, only the gaseous refrigerant can be supplied to the compression means.

The liquefaction process according to the present embodiment may be modified as shown in FIG. 3 is a flow chart showing a second modification of the natural gas liquefaction process according to FIG. As shown in FIG. 3, in the liquefaction process according to the present modification, the second mixed stream flows into the compression means 141 through the conduit 224 and is compressed (first compression step). The second mixed stream then flows into the cooling means 151 through the conduit 231 and is cooled. Then, the first stream flows into the compression means 142 through the conduit 213 and is compressed (second compression step). The first stream then flows into the cooling means 152 through conduit 291 and is cooled.

The first stream is then introduced via conduit 292 into the second mixed stream of conduits 232 (first entraining step). With such mixing, the main stream is formed. That is, the main stream is a stream in which the first stream and the second mixed stream are mixed. The main stream is compressed by the compression means 143 (third compression step). The main stream then flows into the cooling means 153 through the conduit 233 and is cooled. Through this series of processes, the main stream is partially condensed and then flows into the separation means 111 through the conduit 234.

The liquefaction process according to the present embodiment can be modified as shown in FIG. 4 is a flowchart showing a third modification of the natural gas liquefaction process according to FIG. As shown in FIG. 4, in the liquefaction process according to the present modification, the second mixed stream flows into the compression means 141 through the conduit 224 and is compressed (first compression step). The second mixed stream then flows into the cooling means 151 through the conduit 241 and is cooled. Then, the first stream flows into the compression means 142 through the conduit 213 and is compressed (second compression step). The first stream then flows into the cooling means 152 through conduit 251 and is cooled.

And the second mixed stream flows into the compression means 143 through the conduit 242 and is compressed (third compression step). The second mixed stream then flows into the cooling means 153 through conduit 243 and is cooled. The second mixed stream is then mixed with the first stream. That is, the first stream is introduced into the second mixing stream of conduit 244 via conduit 252 after cooling (first mixing step). With such mixing, the main stream is formed.

The main stream flows into the separating means 113 and is separated into a fifth stream in the liquid phase and a sixth stream in the gaseous phase (third separation step). The fifth stream is then introduced via conduit 245 into the second mixing stream of conduit 242 (second entraining step). Wherein the fifth stream may be expanded by the expansion means 135 and then incorporated into the second mixing stream. The fifth stream then flows into the compression means 143 together with the second mixed stream.

And the sixth stream is introduced into the compression means 144 through the conduit 246 and compressed (fourth compression step). The sixth stream then flows into the cooling means 154 through conduit 247 and is cooled. Through this series of processes, the sixth stream is partially condensed and then flows into the separating means 111 through the conduit 248.

For reference, in the present modification, the second compression step and the cooling step by the cooling means 152 may be omitted. That is, the first stream may be incorporated into the second mixing stream of conduit 244 directly through conduit 213.

Example  2

5 is a flowchart showing a natural gas liquefaction process according to a second embodiment of the present invention. For reference, the same or substantially equivalent parts as those in the above-described configuration are denoted by the same or corresponding reference numerals, and a detailed description thereof will be omitted.

As shown in FIG. 5, the mixed refrigerant (main stream to be described later) is first partially condensed (condensation step). That is, the mixed refrigerant is partially condensed through a series of compressions or a series of compression and cooling. The mixed refrigerant then flows into the separating means 111 and is separated into a first stream in the liquid phase and a second stream in the vapor phase (first separation step).

The first stream is introduced into the first heat exchanging unit 121 through the conduit 211 after the separation (first introduction step). Then, the first stream is partially separated in the first heat exchanging unit 121 (first additional separating step). The stream thus separated from the first stream will be referred to as a first sub-stream. Such a separation can be achieved by connecting one conduit to another conduit. Or a separate configuration for separation may be employed

After the separation, the first sub-stream is discharged from the first heat exchanger 121 and introduced into the expansion means 131. The first sub-stream is expanded by the expansion means 131 (first expansion step). The first sub-stream is lowered in temperature due to expansion and then flows into the first heat exchanging unit 121 through the conduit 212 to cool the natural gas NG in the first heat exchanging unit 121 (first cooling step) .

Meanwhile, the second stream is introduced into the first heat exchanging unit 121 through the conduit 221 after the separation (second inflow step). Then, the second stream discharged from the first heat exchanging unit 121 flows into the separating unit 112 through the conduit 222 and is separated into the third liquid stream and the fourth stream in the vapor phase (second separation step) .

The third stream flows into the expansion means 1311 after the separation and is expanded (first additional expansion step). The third stream is lowered in temperature due to expansion, and then flows into the first heat exchanging unit 121 through the conduit 2221 to cool the natural gas NG in the first heat exchanging unit 121 (first cooling step). The natural gas can be precooled by cooling by the first sub-stream and cooling by the third stream.

After the cooling, the first sub-stream and the third stream are recovered from the first heat exchanging unit 121 (first collecting step). The first sub-stream and the third stream are then sent via conduit 213 to the condensation stage. At this time, the first sub stream and the third stream are mixed with each other and sent to the condensing step. This mixed stream will be referred to as the third mixed stream.

Meanwhile, the fourth stream is introduced into the second heat exchanger 122 through the conduit 2223 after the separation (third introduction step). Then, the fourth stream discharged from the second heat exchanging portion 122 flows into the expansion means 133 and is expanded (second expansion step). The fourth stream is lowered in temperature by expansion and then flows into the second heat exchanger 122 again through the conduit 2224 to cool the natural gas NG in the second heat exchanger 122 (second cooling step) .

Also, the first stream is introduced into the second heat exchanger 122 through the conduit 2121 after the first sub-stream is separated (fourth inflow step). Then, the first stream discharged from the second heat exchange portion 122 flows into the expansion means 132 and is expanded (a second additional expansion step). The first stream is lowered in temperature due to expansion and then flows back to the second heat exchanger 122 through the conduit 2122 to cool the natural gas NG in the second heat exchanger 122 ). Natural gas can be liquefied by cooling by the first stream and cooling by the fourth stream.

After the cooling, the first stream and the fourth stream are recovered from the second heat exchange unit 122 (second recovery step). The first stream and the fourth stream are then sent via conduit 224 to the condensation stage. At this time, the first stream and the fourth stream are mixed with each other and sent to the condensing stage. This mixed stream will be referred to as the fourth mixed stream.

As described above, the liquefaction process according to the present embodiment liquefies natural gas using one closed loop refrigeration cycle. Therefore, the liquefaction process according to the present embodiment is advantageous in that the structure of the liquefaction process is simple and the liquefaction process is easy to operate. The liquefaction process according to the present embodiment also isolates one stream into two streams and then cools the natural gas. Therefore, the liquefaction process according to the present embodiment is advantageous in that the liquefaction process efficiency is excellent as it includes one refrigeration cycle but includes two refrigeration cycles.

Furthermore, the liquefaction process according to the present embodiment can cool natural gas more efficiently. Because the third stream is a liquid stream, it is heavier than the fourth stream, which is a gaseous stream. Whereby the third stream is suitable as a refrigerant which is applied at a higher temperature than the fourth stream. As a result, it is more preferable that the third stream is utilized in the first heat exchanger 121 as in the present embodiment. However, when the third stream is utilized in the first heat exchanging unit 121, it may be difficult to sufficiently cool the natural gas in the second heat exchanging unit 122. The liquefaction process according to this embodiment utilizes the first stream in the second heat exchanger 122 to sufficiently cool the natural gas.

On the other hand, the condensation step can be more specifically described as follows. The condensing step may be configured as shown in FIG. Since this is the same as the condensing step of FIG. 1, a detailed description thereof will be omitted. The liquefaction process according to the present embodiment can be modified as shown in FIG. FIG. 6 is a flowchart showing a first modification of the natural gas liquefaction process according to FIG. The condensing step of FIG. 6 is the same as the condensing step of FIG. 2, so a detailed description thereof will be omitted. The liquefaction process according to the present embodiment can be modified as shown in FIG. 7 is a flow chart showing a second modification to the natural gas liquefaction process according to Fig. The condensing step of FIG. 7 is the same as the condensing step of FIG. 3, so a detailed description thereof will be omitted. Further, the liquefaction process according to the present embodiment can be modified as shown in Fig. FIG. 8 is a flowchart showing a third modification of the natural gas liquefaction process according to FIG. The condensing step of FIG. 8 is the same as the condensing step of FIG. 4, so a detailed description thereof will be omitted.

111, 112, 113: separation means
121, 122: heat exchanger
131, 132, 133, 134, 135: expansion means
141, 142, 143, 144: compression means
151, 152, 153, 154: cooling means

Claims (14)

A natural gas liquefaction process in which natural gas is first cooled in a first heat exchanging unit and second natural gas is cooled in a second heat exchanging unit distinguished from the first heat exchanging unit by using one closed loop refrigeration cycle employing a mixed refrigerant In this case,
The closed-loop refrigeration cycle includes:
A condensing step of partially condensing the mixed refrigerant;
A first separation step of separating the mixed refrigerant into a liquid first stream and a gaseous second stream after the condensing step;
A first inflow step of introducing the first stream into the first heat exchange unit after the first separation step;
A first expansion step of expanding the first stream discharged from the first heat exchange section after the first introduction step;
A first cooling step of flowing the first stream back into the first heat exchanger after the first expansion step and cooling the natural gas in the first heat exchanger through the first stream;
A first recovery step of recovering the first stream from the first heat exchange unit after the first cooling step;
A second inflow step of introducing the second stream to the first heat exchange unit after the first separation step;
A second separation step of separating the second stream discharged from the first heat exchange unit after the second introduction step into a third stream in the liquid phase and a fourth stream in the vapor phase;
(3-1) introducing the third stream into the second heat exchanger after the second separator;
A 2nd-1 expansion step of expanding the third stream discharged from the second heat exchange unit after the 3rd-1st inflow step;
A second-1 cooling step of flowing the third stream back into the second heat exchanger after the second-1 expansion step and cooling the natural gas in the second heat exchanger through the third stream;
A third-2 inflow step of introducing the fourth stream into the second heat exchanger after the second separation;
A second-2 expansion step of expanding the fourth stream discharged from the second heat exchange unit after the third-2 inflow step;
A second 2-2 cooling step of introducing the fourth stream back into the second heat exchanger after the 2nd-2 expansion step and cooling the natural gas in the second heat exchanger through the fourth stream; And
And a second recovery step of recovering the third stream and the fourth stream from the second heat exchanger after the second and first cooling stages,
Wherein the first stream is sent to the condensing stage after the first collecting step and after the second collecting step the third stream and the fourth stream are sent to the condensing stage as a second mixed stream mixed with each other Natural gas liquefaction process characterized by. The method according to claim 1,
The first condensing step comprises a first compression step of compressing the second mixed stream, a first mixing step of mixing the first stream into the second mixed stream after the first compression step to form a main stream, And a second compression step of compressing the main stream after the first mixing step. The method of claim 2,
Wherein the condensing step includes a third compression step of compressing the main stream after the second compression step and a third compression step of separating the main stream into a fifth stream of liquid phase and a sixth stream of liquid phase after the third compression step, A second mixing step of mixing the fifth stream into the main stream after the third splitting step and a fourth compression step of compressing the sixth stream after the third splitting step,
The fifth stream is sent to the third compression step together with the main stream after the second incorporation step and the sixth stream is sent to the first separation step after the fourth compression step Natural gas liquefaction process. The method according to claim 1,
Wherein the condensing step includes a first compression step of compressing the second mixed stream, a second compression step of compressing the first stream, a second compression step of compressing the first stream after the first compression step and the second compression step, 2 mixed stream to form a main stream; and a third compression step of compressing the main stream after the first incorporation step,
And the main stream is sent to the first separating step after the third compressing step. The method according to claim 1,
The condensing step comprises a first compression step for compressing the second mixed stream, a second compression step for compressing the first stream, a third compression step for compressing the second mixed stream after the first compression step, A first mixing step of mixing the first stream into the second mixing stream after the second compression step and the third compression step to form a main stream; 5 stream and a gaseous sixth stream, a second mixing step of admixing the fifth stream after the third separation step into the second mixed stream, and a third mixing step of mixing the fifth stream with the third stream, And a fourth compression step of compressing the sixth stream,
Characterized in that said fifth stream is sent to said third compression stage together with said second mixed stream after said second mixing stage and said sixth stream is sent to said first separation stage after said fourth compression stage The natural gas liquefaction process. The method according to claim 1,
Wherein said condensing comprises a first compression step for compressing said second mixed stream, a third compression step for compressing said second mixed stream after said first compression step, a third compression step for compressing said first stream after said third compression step, A third separation step of separating the main stream into a liquid fifth stream and a gaseous sixth stream after the first introduction step, a third separation step of separating the main stream into a liquid fifth stream and a gaseous sixth stream after the first introduction step, A third mixing step of mixing the fifth stream after the third splitting step into the second mixing stream and a fourth compression step of compressing the sixth stream after the third splitting step,
Characterized in that said fifth stream is sent to said third compression stage together with said second mixed stream after said second mixing stage and said sixth stream is sent to said first separation stage after said fourth compression stage The natural gas liquefaction process. The method according to any one of claims 1 to 6,
Wherein at least one of the first heat exchanger and the second heat exchanger is a SWHE type heat exchanger. A natural gas liquefaction process in which natural gas is first cooled in a first heat exchanging unit and second natural gas is cooled in a second heat exchanging unit distinguished from the first heat exchanging unit by using one closed loop refrigeration cycle employing a mixed refrigerant In this case,
The closed-loop refrigeration cycle includes:
A condensing step of partially condensing the mixed refrigerant;
A first separation step of separating the mixed refrigerant into a liquid first stream and a gaseous second stream after the condensing step;
A first inflow step of introducing the first stream into the first heat exchange unit after the first separation step;
A first further separating step of separating a first sub-stream which is a part of the first stream from the first stream in the first heat exchange unit after the first introduction step;
A first expansion step of expanding the first sub-stream discharged from the first heat exchange unit after the first additional separation step;
A first cooling step of introducing the first sub-stream to the first heat exchanger after the first expansion step and cooling the natural gas in the first heat exchanger through the first sub-stream;
A second inflow step of introducing the second stream to the first heat exchange unit after the first separation step;
A second separation step of separating the second stream discharged from the first heat exchange unit after the second introduction step into a third stream in the liquid phase and a fourth stream in the vapor phase;
A first further expansion step of expanding the third stream after the second separation step;
A first additional cooling step of introducing the third stream to the first heat exchanger after the first further expansion step and cooling the natural gas in the first heat exchanger through the third stream;
A first recovery step of recovering the first sub-stream and the third stream from the first heat exchange unit after the first cooling step and the first additional cooling step;
A third inflow step of introducing the fourth stream into the second heat exchange unit after the second separation step;
A second expansion step of expanding the fourth stream discharged from the second heat exchange section after the third introduction step;
A second cooling step of flowing the fourth stream back into the second heat exchanger after the second expansion step and cooling the natural gas in the second heat exchanger through the fourth stream;
A fourth inflow step of introducing the first stream discharged from the first heat exchange unit to the second heat exchange unit after the first additional separation step;
A second further expansion step of expanding the first stream discharged from the second heat exchange section after the fourth inflow step;
A second additional cooling step of introducing the first stream back into the second heat exchanger after the second further expansion step and cooling the natural gas in the second heat exchanger through the first stream; And
And a second recovery step of recovering the first stream and the fourth stream from the second heat exchange unit after the second cooling step and the second additional cooling step,
After the first collecting step, the first sub-stream and the third stream are sent to the condensing stage as a third mixed stream mixed with each other, and after the second collecting step, the first stream and the fourth stream And the mixed gas is sent to the condensing step as a fourth mixed stream mixed with each other. The method of claim 8,
The first condensing step comprises a first compression step of compressing the fourth mixed stream, a first mixing step of mixing the third mixed stream into the fourth mixed stream after the first compression step to form a main stream, and And a second compression step of compressing the main stream after the first mixing step. The method of claim 9,
Wherein the condensing step includes a third compression step of compressing the main stream after the second compression step and a third compression step of separating the main stream into a fifth stream of liquid phase and a sixth stream of liquid phase after the third compression step, A second mixing step of mixing the fifth stream into the main stream after the third splitting step and a fourth compression step of compressing the sixth stream after the third splitting step,
The fifth stream is sent to the third compression step together with the main stream after the second incorporation step and the sixth stream is sent to the first separation step after the fourth compression step Natural gas liquefaction process. The method of claim 8,
Wherein the condensing step comprises a first compression step for compressing the fourth mixed stream, a second compression step for compressing the third mixed stream, and a second compression step for compressing the third mixed stream after the first compression step and the second compression step. And a third compression step of compressing the main stream after the first incorporation step, wherein the third compression step comprises the steps of:
And the main stream is sent to the first separating step after the third compressing step. The method of claim 8,
Wherein the condensing step comprises a first compression step for compressing the fourth mixed stream, a second compression step for compressing the third mixed stream, a third compression step for compressing the fourth mixed stream after the first compression step, A first mixing step of mixing the third mixed stream into the fourth mixed stream to form a main stream after the second compressing step and the third compressing step, And a sixth stream of the gaseous phase; a second mixing step of mixing the fifth stream after the third separation step into the fourth mixed stream; And a fourth compression step of compressing the sixth stream into the second stream,
Characterized in that said fifth stream is sent to said third compression stage together with said fourth mixed stream after said second mixing stage and said sixth stream is sent to said first separation stage after said fourth compression stage The natural gas liquefaction process. The method of claim 8,
Wherein the condensing step comprises a first compression step for compressing the fourth mixed stream, a third compression step for compressing the fourth mixed stream after the first compression step, a third compression step for compressing the third mixed stream after the third compression step, A third separation step of separating the main stream into a liquid fifth stream and a gaseous sixth stream after the first introduction step, A second mixing step of mixing the fifth stream after the third separation step into the fourth mixing stream and a fourth compression step of compressing the sixth stream after the third separation step,
Characterized in that said fifth stream is sent to said third compression stage together with said fourth mixed stream after said second mixing stage and said sixth stream is sent to said first separation stage after said fourth compression stage The natural gas liquefaction process. The method according to any one of claims 8 to 13,
Wherein at least one of the first heat exchanger and the second heat exchanger is a SWHE type heat exchanger.

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