JP3320934B2 - Gas liquefaction method - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a method for liquefying a gas, for example, a method for liquefying a gas containing at least one low-boiling component such as natural gas.

[0002]

2. Description of the Related Art As a method for liquefying natural gas, for example, Japanese Patent Publication No. 47-29712 discloses that a methane-enriched gas feed stream is precooled by successively exchanging heat with a single-component coolant under a condition of successively lower temperatures. On the other hand, the pre-cooling is performed after separating the condensed portion and the vapor portion of the multi-component coolant pre-cooled until a portion is condensed by heat exchange with the single-component coolant, and deeply cooling and expanding the condensed portion. A first step of exchanging heat with the feed stream and passing the same through a heat exchange with the feed stream after liquefying and expanding the vapor portion.
The method of liquefaction according to the step is shown. 2, the lower part of the heat exchanger 50 is a first stage (high-temperature zone) 51, and the upper part is a second stage (low-temperature zone) 52. The pre-cooled gas stream 28 after pre-cooling the feed gas feed stream with a single-component coolant and further removing condensed high-boiling components by cooling with the single-component coolant is provided in a high-temperature zone 51. A high-pressure vapor stream (vapor section) 8 and a high-pressure condensate stream (condensation) in which a multi-component coolant that has been introduced from the lower part of the flow passage A and partially condensed by heat exchange with a single-component coolant are separated into gas and liquid. Portion 9 is also introduced from the lower part of each of the flow paths B and C provided in the high temperature zone 51. After the high-pressure condensate stream 9 of the multi-component coolant is further cooled while ascending in the flow path C in the high-temperature zone 51, the spray nozzle 5 passes through the expansion valve 53.
5 is sprayed into the high-temperature zone 51 to cool the fluid in the flow paths A, B and C. The high-pressure vapor stream 8 of the multi-component coolant flowing through the flow path B is cooled and liquefied here, and then introduced into the flow path F in the low-temperature zone 52. After being further cooled, the low-pressure zone flows from the spray nozzle 56 through the expansion valve 54. Spray 52 cools the fluid in channels E and F. The cooled gas flow 28 flowing through the flow path A in the high-temperature zone is introduced into the flow path E in the low-temperature zone 52, and is further cooled to be withdrawn as the liquefied gas 10 and recovered as a product. Spray nozzles 55, 56
The high-pressure condensate stream 9 of the multi-component coolant and the high-pressure vapor stream 8 of the liquefied multi-component coolant respectively sprayed from the channels A, B, C and the fluids flowing through the channels E, F are completely exchanged by heat. Vaporized multi-component coolant vapor stream 18
After being compressed by a compressor, the refrigerant is heat-exchanged with a single-component refrigerant in a heat exchanger and is circulated and used as a partially condensed multi-component coolant (not shown). In this method, a Hampson heat exchanger is employed as the heat exchanger between the pre-cooled gas feed stream and the multi-component coolant. This Hampson-type heat exchanger uses a method in which a wound tube made of aluminum is wound around the core metal several times, so the flow path of the heat exchanger becomes long and the pressure loss has to be large. The heat exchanger itself must be large because of the above structure. Also, if the flow of the fluid in the heat exchanger stops because the low temperature end of the low temperature fluid is at the top of the heat exchanger, the refrigerant liquid at the low temperature end flows back to the high temperature end due to gravity, and the high temperature stored at the bottom of the heat exchanger. This causes a problem in terms of safety because heat exchange occurs with the refrigerant vapor of the liquid and a sudden boiling of the low-temperature liquid occurs.

Japanese Patent Publication No. 54-40764 discloses a multi-component pre-cooling method in which a refrigerant containing multiple components is not pre-cooled by a single component refrigerant, but is pre-cooled until a part thereof is condensed by heat exchange with cooling water. The condensed part and the vapor part of the refrigeration agent are separated, and then the separated condensed part and the vapor part are mixed and introduced into the inlet of the plate-fin type heat exchanger, and the flow of the substance to be cooled, for example, natural gas, There is a method in which natural gas is liquefied by flowing the co-current high-temperature refrigerant, which consists of a mixture of the condensed part and the vapor part, countercurrently with the flow of the low-temperature refrigerant after cooling and expanding. It has been disclosed. In this method, a condensed part and a vapor part of a cryogen containing multi-components are mixed at a heat exchanger inlet and passed through the heat exchanger as a mixed phase. To take the method of super cooling to
The heat exchange amount is increased and a large heat exchanger is required as compared with the method disclosed in Japanese Patent Publication No. 712, which does not require supercondensing the condensed portion to a temperature in a low-temperature zone. Also, since the condensed part contains a lot of high-boiling components, in the high-temperature zone where the latent heat of vaporization of the high-boiling components is used, the temperature difference between the condensation curve of the fluid to be cooled and the evaporation curve of the refrigerant opens up, and the heat exchanger design Although it works effectively, in the low temperature zone where the condensed part is supercooled, the high boiling point component in the refrigerant mainly uses only sensible heat, so the temperature difference between the condensation curve of the fluid to be cooled and the evaporation curve of the refrigerant hardly opens, It is hard to say that the refrigerant heat is effectively used. For this reason, there is a disadvantage that a larger compressor horsepower is required as compared with the conventional method, and energy consumption is increased.

[0004]

SUMMARY OF THE INVENTION The present invention is directed to a method of producing a pre-cooled gas which is heat-exchanged with a single-component refrigerant under conditions of successively lower temperatures until a portion of the gas is condensed by heat exchange with the single-component refrigerant. By using a plate-fin type heat exchanger when exchanging heat with a pre-cooled high-pressure multi-component refrigerant to liquefy a gas, it is possible to avoid the drawbacks of the conventional method and to save energy by reducing the horsepower of the compressor. It is an object of the present invention to provide a liquefaction method.

[0005]

A gas liquefaction method according to the present invention is characterized in that a gas pre-cooled by exchanging heat with a single-component refrigerant under a condition of sequentially lowering the temperature is converted into one by heat exchange with the single-component refrigerant. When the gas is liquefied by exchanging heat with the high-pressure multi-component refrigerant pre-cooled until the part condenses, (1) the high-pressure multi-component refrigerant partially condensed by heat exchange with the single-component refrigerant is condensed with the high-pressure vapor stream and the high-pressure vapor (2) A plate provided with a plate surface standing upright and provided with a high-temperature zone having at least four types of flow paths on the upper side and a low-temperature zone having at least three types of flow paths on the lower side A gas flow, a high-pressure vapor flow of a multi-component refrigerant, and a high-pressure condensate flow of a multi-component refrigerant are respectively introduced from the upper portions of three types of flow passages in the high-temperature zone of the fin heat exchanger. Low-pressure multi-component refrigerant stream of one of the high-temperature zones Was introduced from the lower part of the road, the gas stream, the high-pressure condensate flow of the high pressure vapor stream and a multi-component refrigerant of the multicomponent refrigerant first by low pressure multi-component refrigerant flow and is heat exchanged and cooled, (3)
The gas flow cooled in the high-temperature zone and the high-pressure vapor flow of the multi-component refrigerant are introduced from the upper portions of two of the flow channels in the low-temperature zone of the plate fin heat exchanger, and a second low pressure The multi-component refrigerant stream is introduced from the lower part of one of the channels in the low-temperature zone, and the gas stream and the high-pressure vapor stream of the multi-component refrigerant are heat-exchanged with the second low-pressure multi-component refrigerant stream to be further cooled; (4)
A liquefied gas stream is extracted and collected from the lower part of the low-temperature zone, and (5) a vapor part and a condensed part obtained by expanding the high-pressure vapor stream of the liquefied multi-component refrigerant extracted from the lower part of the low-temperature zone are vaporized. Liquid separation, the separated vapor portion and the condensed portion are mixed and introduced as a second low-pressure multi-component refrigerant stream from the lower part of one of the flow paths in the low-temperature zone, and the low-temperature zone is shifted from the upper part to the lower part. After heat exchange with the passing gas stream and the high-pressure vapor stream of the multi-component refrigerant, withdraw from the upper part of the low temperature zone,
(6) Mixing the second low-pressure multi-component refrigerant stream extracted from the upper part of the low-temperature zone with the flow obtained by expanding the high-pressure condensate stream of the multi-component refrigerant after passing through the high-temperature zone, and Separated, the separated vapor portion and condensed portion are mixed and introduced as a first low-pressure multi-component refrigerant stream from the lower part of one of the flow paths in the high-temperature zone, and pass through the high-temperature zone from the upper part to the lower part. After heat exchange with the flowing gas stream, the high-pressure vapor stream of the multi-component refrigerant, and the high-pressure condensate flow of the multi-component refrigerant, it was extracted as steam from the upper part of the high-temperature zone, and (7) extracted as steam from the upper part of the high-temperature zone. After compressing the first low-pressure multi-component refrigerant stream, the partially condensed high-pressure multi-component refrigerant obtained by heat exchange with the single-component refrigerant is circulated to the step (1) and used again for gas liquefaction. Consisting of

This will be described more specifically with reference to FIG. In the present invention, the gas pre-cooled by exchanging heat with the single-component refrigerant under the condition of sequentially lowering the temperature is exchanged with the high-pressure multi-component refrigerant pre-cooled until partly condensed by heat exchange with the single-component refrigerant. At this time, a plate-fin heat exchanger is used as the heat exchanger. The plate fin type heat exchanger has a linear and short flow path inside the heat exchanger, so the pressure loss is significantly smaller than that of a conventional Hampson heat exchanger with a long flow path in which a wound tube is wound many times. Can be. Reducing the pressure loss on the side of the cooled fluid flowing through the heat exchanger tends to cause the condensation curve of the cooled fluid to move to the higher temperature side (see the description of FIG. 8 described later). Therefore, if the heat transfer area of the heat exchanger is reduced, or if the heat exchanger is designed with a temperature difference equivalent to that of the Hampson-type heat exchanger, the load on the compressor can be reduced. The plate-fin type heat exchanger 20 used in the present invention has a high-temperature zone 21 having at least four types of flow paths A, B, C, and D provided on an upper side and having at least three channels at a lower side. A low-temperature zone 22 having seed flow paths E, F, and G is provided (partial description of constituent feature 2). In the present invention, the multi-component refrigerant includes a composition having a boiling point lower than the temperature at which the fluid to be cooled is to be cooled, that is, the liquefaction temperature of the gas, including a plurality of refrigerant components having sequentially lower boiling points. To tell. The multi-component refrigerant may be appropriately selected according to the composition, temperature, and pressure of the source gas. For example,
A mixture of components selected from nitrogen and hydrocarbons having 1 to 5 carbon atoms can be used, and a mixture of nitrogen, methane, ethane and propane is preferred. Further nitrogen 2-14
Mol%, 30 to 45 mol% of methane, 32 to 45 mol% of ethane, and 9 to 21% of propane are preferred. Propylene may be used instead of ethylene or propane in place of ethane in the mixture. As the single component refrigerant, a hydrocarbon having a low boiling point can be used, and propane is preferable. In addition, 4 in the upper side of the plate fin type heat exchanger
The kind flow path and the three kinds of flow paths on the lower side are indispensable constituent elements for carrying out the present invention, but in addition to the above, a flow path is provided in a high temperature zone and / or a low temperature zone, and other It does not preclude its use for cooling fluids (gas, liquid or gas-liquid mixed phase fluids).

As the raw material gas in the present invention, a gas containing at least one low-boiling component such as methane and ethane can be used. An example is natural gas. Feed gas stream 1 containing at least one low-boiling component, for example 4
Natural gas at 9.9 barA (absolute pressure) and 21 ° C. is pre-cooled in a group of heat exchangers 2 and 3, which are set under conditions of successively lower temperatures with a single-component refrigerant such as propane.
The pre-cooling temperature depends on the type of the source gas, but is determined in consideration of the energy consumption of the entire system. The pre-cooled gas stream 4 is separated from high-boiling substances by a high-boiling substance separator 7 provided with a reboiler 5 as necessary to increase the purity of low-boiling components. It is introduced from the upper part of the flow channel A of 21 (partial description of the constituent requirement 2).
In FIG. 1, 48.4 barA, −
The gas stream 27 introduced at 33 ° C. and cooled to −45 ° C. is once extracted, introduced into the reflux drum 6, and the high-boiling-point condensate separated by the reflux drum 6 is refluxed to the upper part of the high-boiling-point separator 7. The gas stream 28 from which the condensate has been removed by the reflux drum 6 and the purity of the low-boiling components has been increased is introduced into the flow path A of the high-temperature zone 21. The gas flow introduced into the flow path A of the high-temperature zone 21 flows downward in the high-temperature zone 21. In order to cool the gas stream 27 withdrawn from the top of the high boiler separator 7 and separate the condensate, a plate-fin type heat exchanger 20
Instead of the high temperature zone 21, a cooler using a single component refrigerant can be provided. In that case, the gas stream from which the condensate has been separated and removed is introduced into the upper part of the high-temperature zone 21 of the heat exchanger 20,
It is possible to pass through the high-temperature zone as it is without extracting it from the middle.

For example, a group of heat exchangers 31, which are set in such a manner that a high-pressure multi-component refrigerant consisting of nitrogen, methane, ethane and propane is successively cooled down by the same single-component refrigerant used for pre-cooling of the raw material gas, The pre-cooled high-pressure multi-component refrigerant is heat-exchanged sequentially at 32 and 33 until a part thereof is condensed.
The high-pressure vapor stream 8 is introduced from the upper part of the flow path B in the high-temperature zone 21 of the plate-fin heat exchanger 20, and the high-pressure condensate stream 9 is introduced from the upper part of the flow path D. The first described later
The low-pressure multi-component refrigerant flow (gas-liquid multiphase flow) of
And flows countercurrently to the gas flow in the flow path A, the high-pressure vapor flow in the flow path B, and the high-pressure condensate flow in the flow path D to perform heat exchange.
Since the first low-pressure multi-component refrigerant flow (gas-liquid mixed-phase flow) in the flow path C has a low temperature, for example, 4.0 barA and -128 ° C (the inlet of the high-temperature zone), the gas flow in the flow path A, the flow path The high-pressure vapor stream in B and the high-pressure condensate stream in flow path D are cooled by heat exchange with the high-pressure condensate stream (partial description of Requirement 1 and Requirement 2).

The gas flow 28 cooled in the flow path A of the high-temperature zone 21 and the high-pressure vapor flow 8 of the multi-component refrigerant cooled in the flow path B are introduced from the upper portions of the flow paths E and F of the low-temperature zone 22. And a second low-pressure multi-component refrigerant flow (gas-liquid multiphase flow) to be described later.
Is introduced from the lower part of the flow path G in the low temperature zone, and flows countercurrently to the gas flow 28 of the flow path E and the high-pressure steam flow 8 of the flow path F to perform heat exchange. Since the second low-pressure multi-component refrigerant flow (gas-liquid multiphase flow) in the flow path G has a lower temperature, for example, 4.1 barA, -168 ° C (the inlet of the low-temperature zone), the gas flows 28 and The high-pressure steam flow 8 in the flow path F is further cooled. (Description of Configuration Requirement 3). When the gas flow 28 passing through the flow path A of the high temperature zone 21 is introduced into the flow path E of the low temperature zone 22, it is expanded as shown in FIG. 1, and the liquefied gas flow 10 is extracted from the lower part of the low temperature zone and further expanded. Then, the pressure is reduced to a low pressure (not shown), and the product is recovered as a product of about 1 atm and about −162 ° C. (description of constituent requirement 4).

The vaporized portion and the condensed portion obtained by expanding the liquefied, high-pressure steam flow 11 of a multicomponent refrigerant of, for example, 47.0 barA, -162 ° C., extracted from the lower part of the low-temperature zone by the expansion valve 42 are vaporized. 3. A gas-liquid separation is performed by the liquid separator 25, and the separated vapor portion 12 and condensed portion 13 are mixed.
1 barA, a second low-pressure multi-component refrigerant flow of about -168 ° C. is introduced into the flow path G from the lower part of the low-temperature zone to the gas flow in the flow path E and the flow path F which pass from the upper part to the lower part in the low-temperature zone. After heat exchange by flowing countercurrent to the high-pressure vapor flow of the component refrigerant, it is extracted from the upper part of the low-temperature zone (description of constituent element 5).

The second low-pressure multi-component refrigerant stream 14 extracted from the upper part of the low-temperature zone through the flow path G and, for example, 47.0 barA, -124 after passing through the high-temperature zone flow path D.
The high-pressure condensed liquid stream 15 of the multi-component refrigerant at 40 ° C. is mixed with the 4.0 bar A, −128 ° C. stream obtained by expanding the expansion valve 41 at the expansion valve 41, and gas-liquid separation is performed by the gas-liquid separator 24. The separated vapor portion 16 and condensed portion 17 are mixed and introduced as a first low-pressure multi-component refrigerant flow from the lower portion of the flow path C in the high-temperature zone. After heat exchange by flowing countercurrently to the high-pressure vapor flow of the multi-component refrigerant in the passage B and the high-pressure condensate flow of the multi-component refrigerant in the passage D, 3.6 from the top of the high-temperature zone.
BarA is extracted as steam at about −36 ° C. (description of constituent requirement 6). The flow path of the low-pressure multi-component refrigerant flow (flow path G +
It is preferred that the pressure loss in channel C) is not more than 0.5 bar.

The first low-pressure multi-component refrigerant stream 18 withdrawn from the upper part of the flow path C in the high-temperature zone is compressed by the compressor 26, and is cooled by the multi-component refrigerant cooler 34 with a non-hydrocarbon refrigerant, for example, air or water. After cooling by heat exchange, the heat exchanger group 31,
The high-pressure multi-component refrigerant 19 having a mixed phase of about 48.0 barA and about -33 ° C., partly condensed by heat exchange with the single-component refrigerant at 32 and 33, is circulated to the step (1) to liquefy the gas again. Used (description of configuration requirement 7). The same single-component refrigerant is used for the pre-cooling of the raw material gas and the high-pressure multi-component refrigerant by the single-component refrigerant. This single-component refrigerant cooling system usually compresses the single-component refrigerant, cools it and completely condenses it, and then sequentially heat-exchanges with the fluid to be cooled at a low pressure and low temperature. A method of circulating through the cycle consisting of compressing the vapor of the component refrigerant is employed. Further, the pre-cooling of the raw material gas and the pre-cooling of the high-pressure multi-component refrigerant can be configured in one closed cycle of the single-component refrigerant. For example, in FIG. 1, a single-component medium-pressure refrigerant (liquid) obtained by compressing and cooling a single-component
And a single-component low-pressure refrigerant (gas-liquid mixed phase) obtained by expanding the single-component medium-pressure refrigerant (liquid) extracted from the precooler 2 into the precooler 3. Then, the raw material gas stream cooled by the precooler 2 is further cooled at low pressure and low temperature. The vapor of the single-component refrigerant vaporized by heat exchange with the raw material gas stream is sent from each precooler to the compressor, where the pressure is increased.
Subsequently, it is condensed by air or water and used again for cooling the raw material gas stream. Also, in the case of pre-cooling the high-pressure multi-component refrigerant with a single-component refrigerant until a part thereof is condensed, it can be performed by sequentially performing heat exchange at a low pressure and a low temperature in the same manner as described above. For example, the single-component high-pressure refrigerant (liquid) is introduced into the multi-component refrigerant precooler 31 to cool the high-pressure multi-component refrigerant, and the single-component high-pressure refrigerant (liquid) extracted from the multi-component refrigerant precooler 31 is expanded. The single-component medium-pressure refrigerant (gas-liquid mixed phase) obtained by the above is introduced into the multi-component refrigerant precooler 32, and the high-pressure multi-component refrigerant cooled by the precooler 31 is cooled at a low pressure and a low temperature, The single-component low-pressure refrigerant (gas-liquid mixed phase) obtained by expanding the single-component medium-pressure refrigerant (liquid) extracted from the multi-component refrigerant precooler 32 is introduced into the multi-component refrigerant precooler 33, The high-pressure multi-component refrigerant that has been cooled in the step (c) is further cooled at a lower pressure and a lower temperature to condense a part of the high-pressure multi-component refrigerant. The vapor of the single-component refrigerant vaporized by heat exchange with the multi-component refrigerant is sent from each precooler to the compressor to increase the pressure, then condensed by air or water, and again as a single-component high-pressure refrigerant (liquid). It can be used for cooling a refrigerant. The cooling cycle of the single-component refrigerant for pre-cooling the raw material gas and the cooling cycle of the single-component refrigerant for pre-cooling the multi-component refrigerant are one closed by sharing the compressor for the single-component refrigerant. Make up the cycle.

In the present invention, the precooled gas stream 28 as the fluid to be cooled, the high-pressure vapor stream 8 of the multi-component refrigerant and the high-pressure condensate stream 9 of the multi-component refrigerant are introduced so as to flow below the upper part of the heat exchanger. Is done. On the other hand, the first low-pressure multi-component refrigerant flow (16 + 17) and the second low-pressure multi-component refrigerant flow (12 + 13), which are cooling fluids, are directed from the lower part to the upper part in the zone in the heat exchanger through which each fluid passes. It is introduced to flow. By doing so, the fluid to be cooled introduced into the upper part of the heat exchanger is condensed while reaching the lower part of the zone through which the fluid passes while being cooled. And the pressure loss is canceled. As a result, the actual pressure loss becomes extremely small, and the temperature difference between the condensation curve of the fluid to be cooled and the evaporation curve of the cooling fluid tends to increase, so that the heat transfer area of the heat exchanger can be reduced. This is advantageous for vessel design. Alternatively, if the temperature difference between the condensation curve of the fluid to be cooled and the evaporation curve of the cooling fluid is maintained at the same level as before, the load on the compressor is reduced by reducing the flow rate of the multi-component refrigerant or adjusting the refrigerant composition. You can also.

When the flow of the fluid in the heat exchanger stops, when the low temperature end of the low temperature fluid is at the top of the heat exchanger as in the heat exchanger described in Japanese Patent Publication No. 47-29712, the low temperature Because the refrigerant liquid at the end remains at the bottom of the high-temperature end due to gravity without heat exchange, heat exchange occurs with the high-temperature refrigerant vapor collected at the bottom of the heat exchanger, causing a sudden rise in the temperature of the low-temperature liquid, This causes a pressure increase in the exchanger. Further, the temperature difference of the aluminum tube may exceed the design value, which may cause thermal stress fatigue of the aluminum material.However, in the present invention, even if the flow of the fluid in the heat exchanger stops, the backflow of the low-temperature liquid due to gravity is prevented. Since no accident occurs, safety can be maintained.

In order for the heat exchanger to perform to its full potential, the fluids must be evenly distributed in their respective flow paths. Therefore, in the present invention, the gas-liquid mixed phase fluid obtained after expansion as described above is separated into a vapor portion and a condensed portion by installing a separator, and then the separated vapor portion and condensed portion are sufficiently separated. And introduced into the inlet of the heat exchanger. That is, with respect to the vaporized stream 11 of the liquefied multi-component refrigerant, after the vapor portion and the condensed portion obtained after expansion are separated by the gas-liquid separator 25, the separated vapor portion 12 and the condensed portion 13 are sufficiently mixed. In this state, a second low-pressure multi-component refrigerant flow is introduced into the flow path G from the lower part of the low-temperature zone as a gas flow in the flow path E passing through the low-temperature zone and a high-pressure vapor flow of the multi-component refrigerant in the flow path F. Allow heat exchange. The mixing of the separated vapor portion 12 and the condensing portion 13 is preferably performed immediately before being introduced into the low temperature zone. As a mixing method, there is a method in which a vapor portion and a condensed portion are respectively supplied in a single phase up to the inlet of the heat exchanger, and a multiphase flow is formed at once at the inlet. For example, a dispersing core (multi-layered fluid path assembly device) for supplying a vapor phase (gas) and a condensing part (liquid) in a single phase to the heat exchanger is attached to the fluid inlet of the heat exchanger. Dispersion fins for gas (multi-layered fluid passages) and dispersion fins for liquid are provided adjacent to each other in the core, and the gas and liquid flowing through each adjacent dispersion fin are two-phase (mixed phase).
A gas-liquid dispersing device (Japanese Patent Publication No. 63-52313) in which a gas flows into a diversion distribution fin and merges into a gas-liquid mixed-phase flow, and a gas-liquid comprising a gas-liquid merged layer and a flow path layer in a heat exchanger header A gas-liquid dispersing device having a dispersing core and allowing gas and liquid to flow in separately and to join in a confluent layer (Japanese Patent Publication No. 63-52)
No. 312), gas and liquid are separately supplied to an inlet of an effective fin of a heat exchanger or a center bar (a central distribution pipe having a through groove on a side surface) provided at an intermediate portion thereof, and are joined by the center bar. Liquid dispersion device (Japanese Patent Laid-Open No. 58-86396)
Publication). Alternatively, a heat exchanger (US Pat. No. 3,559,722) in which a hole is formed in a plate that separates adjacent fluid passages to mix gas and liquid inside the core can be used. Is preferred.

The second low-pressure multi-component refrigerant stream 14 that has passed through the flow path G of the low-temperature zone 22 and has been extracted from the upper part is the high-pressure condensate liquid stream 15 of the multi-component refrigerant that has passed through the high-temperature zone flow path D. Is mixed with a stream obtained by expansion to perform gas-liquid separation. Since the flow obtained by expanding the high-pressure condensate liquid stream 15 of the multi-component refrigerant and the second low-pressure multi-component refrigerant stream 14 extracted through the low-temperature zone are different in temperature, composition, and gas-liquid ratio, Mixing may increase the temperature. The outlet temperature in the high-temperature zone of the high-pressure condensate stream of the multi-component refrigerant and the outlet temperature in the low-temperature zone of the second low-pressure multi-component refrigerant stream are optimally adjusted so as to minimize the temperature rise due to this mixing. It is desirable. For this purpose, it is preferable that the temperature of the high-pressure condensate stream of the multi-component refrigerant at the outlet of the high-temperature zone be in the range of −110 to −130 ° C. The temperature of the second low-pressure multi-component refrigerant stream at the outlet of the low-temperature zone is preferably 5 to 10 ° C. lower than the temperature of the high-pressure condensate stream of the multi-component refrigerant at the outlet of the high-temperature zone. A stream obtained by expanding the high-pressure condensate stream 15 of the multi-component refrigerant and a second low-pressure multi-component refrigerant stream 14 extracted through the low-temperature zone.
Mixing and gas-liquid separation may be performed simultaneously by introducing both streams into the gas-liquid separator 24 as shown in FIG. 1, or both may be mixed before being introduced into the gas-liquid separator. After mixing, the mixture may be introduced into the gas-liquid separator 24. In a state where the separated vapor portion 16 and the condensing portion 17 are sufficiently mixed in order to make the gas-liquid mixing ratio in the flow path uniform, a first low-pressure multi-component refrigerant flow is formed from the lower portion of the high-temperature zone. The gas flow introduced into the flow path C and passing through the flow path A in the high-temperature zone, the high-pressure vapor flow of the multi-component refrigerant passing through the flow path B, and the high-pressure condensate flow of the multi-component refrigerant passing through the flow path D and heat Let me exchange. The mixing of the separated vapor portion 16 and the condensing portion 17 is preferably carried out immediately before being introduced into the high-temperature zone.
This mixing method can be performed in the same manner as in the case of mixing the vapor portion 12 and the condensing portion 13 introduced into the low temperature zone. Specifically, the above-mentioned JP-B-63-52313,
JP-B-63-52312, JP-A-58-8639
No. 6 publication can be used.

In the case where the low-pressure multi-component refrigerant is introduced into either the high-temperature zone or the low-temperature zone, the low-pressure multi-component refrigerant in the gas-liquid mixed phase is separated into gas and liquid at the inlet of each zone of the heat exchanger. By introducing as a completely mixed multiphase fluid, the vaporization curve of the low-pressure multi-component refrigerant is lower than the method in which the gas phase and the liquid phase are separately introduced into the high or low temperature zone of the heat exchanger after gas-liquid separation. Has a low evaporation temperature over a long temperature range, a large logarithmic average temperature difference with the fluid to be cooled can be obtained, and the heat transfer area of the heat exchanger can be reduced. For example, (1) a low-pressure multi-component refrigerant is introduced as a multiphase fluid in a low-temperature zone, and a gas-phase and a liquid-phase are separately introduced in a high-temperature zone (FIG. 4). In the present invention, which is introduced as a multi-phase fluid, the vapor curve of the low-pressure multi-component refrigerant in the high-temperature zone (FIG. 6) has an evaporation temperature lower by about 7 ° C. over a long temperature range. (2) In the low-temperature zone, the gas phase and the liquid phase of the low-pressure multi-component refrigerant are separately introduced, and in the high-temperature zone, the mixed-phase fluid is introduced into both the low-temperature zone and the high-temperature zone, as compared with the method (FIG. 5). The present invention, which is introduced as a fluid, has a lower evaporation temperature of about 2 ° C. over a long temperature range in the evaporation curve of the low-pressure multi-component refrigerant in the low temperature zone (FIG. 7). Also,
According to (1) and (2), the present invention in which a low-pressure multi-component refrigerant is introduced as a multi-phase fluid in both the low-temperature zone and the high-temperature zone, the gas phase and the liquid phase of the low-pressure multi-component refrigerant are changed in any zone. 3 has a lower evaporation temperature over a longer temperature range in the evaporation curve of the low-pressure multi-component refrigerant in the low-temperature zone and the high-temperature zone, as compared with the case of separately introducing the heat exchanger (FIG. 3). This is advantageous in terms of design and the like.

In the case of the method shown in FIG. 3 (Comparative Example 1), seven types of flow paths A,
A high-temperature zone 21 composed of B, D, K, L, M, and N;
Source gas precooled from the upper part of the flow path A in the flow path of the high temperature zone 21 of the plate fin heat exchanger 20 having the low temperature zone 22 composed of four types of flow paths E, F, H, and J at the lower part Stream 28, high pressure vapor stream 8 of the multi-component refrigerant from the top of flow path B,
The introduction of the high-pressure condensate stream 9 of the multi-component refrigerant from the upper part of the flow path D is the same as in the case of the present invention shown in FIG. However, the flow obtained by expanding the high-pressure condensed liquid stream 15 of the multicomponent refrigerant after passing through the flow path D in the high-temperature zone by the expansion valve 41 is subjected to gas-liquid separation by the gas-liquid separator 24, and the separated vapor portion 16 Is introduced from the lower part of the flow path M, the condensing part 17 is introduced from the lower part of the flow path N, and the gas flow of the flow path A passing through the high-temperature zone, the high-pressure vapor flow of the multi-component refrigerant in the flow path B, and the flow path D After the heat exchange by flowing countercurrent to the high-pressure condensate flow of the multi-component refrigerant, it is extracted as steam 18 from the upper part of the high-temperature zone, that is, the plate-fin type heat exchange is performed separately without mixing the steam portion 16 and the condensing portion 17. The present invention differs from the present invention in that they are respectively introduced into different flow paths of the vessel. The flow path E of the low-temperature zone 22 is a raw material gas flow 28 that flows through the flow path A of the high-temperature zone and is cooled. The flow path F is a high-pressure vapor of the multi-component refrigerant that flows through the flow path B of the high-temperature zone and is cooled. The introduction of the respective streams 8 is the same as in the case of the invention shown in FIG. 1, however, the high-pressure vapor stream 11 of the multicomponent refrigerant after liquefaction through the low-temperature zone flow path F is expanded. The stream obtained by expansion at 42 is subjected to gas-liquid separation by the gas-liquid separator 25, and the separated vapor portion 12 is introduced from the lower part of the flow path H, and is subsequently introduced to the lower part of the flow path K in the high-temperature zone, and is condensed. The part 13 is introduced from the lower part of the flow path J, and subsequently introduced into the lower part of the flow path L in the high-temperature zone, and after being countercurrently exchanged with the fluid to be cooled for heat exchange, is extracted as steam 18 from the upper part of the high-temperature zone; That is, the vapor portion 12 and the condensing portion 13 are separately mixed without being mixed. And a vapor portion 16 and a condensing portion 17 in which the flow obtained by expanding the high-pressure condensate stream 15 of the multi-component refrigerant with the expansion valve 41 is separated into gas and liquid. Is different from the present invention in that it passes through the flow path in the low temperature zone independently.

In the case of the method shown in FIG. 4 (Comparative Example 2), a high-temperature zone 21 composed of five types of flow paths A, B, D, O, and P is provided on the upper portion where the plate surface is set upright. In a plate fin type heat exchanger 20 having a low-temperature zone 22 composed of three types of flow paths E, F, and G at the lower part, a source gas flow precooled from the upper part of the flow path A in the high-temperature zone 21 28, a high-pressure vapor flow 8 of the multi-component refrigerant from the upper part of the flow path B,
The high-pressure condensate flow 9 of the multi-component refrigerant is introduced from the upper part of the flow channel D, passes through the high-temperature zone flow channel B, and further passes through the low-temperature zone flow channel F. Expansion valve 4
The gas obtained by expansion in step 2 is subjected to gas-liquid separation by a gas-liquid separator 25, and the separated vapor portion 12 and condensed portion 13 are mixed and introduced into the flow channel G from the lower part of the low temperature zone as a mixed phase. After the heat exchange with the gas flow in the flow path E passing through the zone and the high-pressure steam flow in the flow path F, the second flow starts from the upper part of the low temperature zone.
1 is extracted as the low-pressure multi-component refrigerant 14 and mixed with the flow obtained by expanding the high-pressure condensate flow 9 of the multi-component refrigerant after passing through the flow path D in the high-temperature zone with the expansion valve 41. Same as the present invention. However, the flow path D in the high temperature zone
The high-pressure condensate flow 9 of the multi-component refrigerant after passing through the
1 and the flow obtained by expansion in the second low-pressure multi-component refrigerant 1
4 and gas-liquid separation by a gas-liquid separator 24. The separated vapor part 16 is introduced into the lower part of the flow path P, and the condensed part 17 is introduced into the lower part of the flow path O to pass through the high-temperature zone. That is, the present invention is different from the present invention in that the separated vapor portion 16 and condensed portion 17 are not mixed and passed through a flow path in a high-temperature zone as a gas-liquid mixed phase.

FIG. 6 is a diagram for explaining the difference in the evaporation curve characteristics of the cooling fluid in the high temperature zone between the method of the present invention shown in FIG. 1 and the method of FIG. 6, the horizontal axis represents the heat exchange amount Q, the vertical axis represents the temperature T (° C.), the line A is the evaporation curve of the first low-pressure multi-component refrigerant flow in the present invention having the configuration shown in FIG. FIG. 9 is a diagram obtained by synthesizing an evaporation curve of a low-pressure multi-component refrigerant in a high-temperature band in Comparative Example 2 having the configuration shown in FIG. 4 (evaporation curve of flow path O + evaporation curve of flow path P);
Since the line A shows an evaporation temperature about 7 ° C. lower than the line B over a long temperature range, a logarithmic average temperature difference with the fluid to be cooled can be increased, and the heat transfer area of the heat exchanger can be reduced. .

In the case of the method shown in FIG. 5 (Comparative Example 3), a high-temperature zone 21 composed of four types of flow paths A, B, D, and R is provided at an upper portion where the plate surface is set upright, and a lower portion is provided at a lower portion. 4
In the plate fin type heat exchanger 20 having the low temperature zone 22 composed of the flow paths E, F, H, and J of the species, the raw material gas stream 28 pre-cooled from the upper part of the flow path A in the flow path of the high temperature zone 21 , A high-pressure vapor flow 8 of the multi-component refrigerant from the upper part of the flow path B,
The high-pressure condensate flow 9 of the multi-component refrigerant is introduced from the upper part of the flow path D, passes through the high-temperature zone flow path B, and further passes through the low-temperature zone flow path F
The high-pressure vapor flow 8 of the multi-component refrigerant after passing through the
The point that the flow obtained by the expansion in the step is gas-liquid separated by the gas-liquid separator 25 is the same as that of the present invention shown in FIG. However, the vapor portion 12 and the condensed portion 13 separated by the gas-liquid separator 25 are separately introduced into the flow path H and the flow path J from the lower part of the low-temperature zone without being mixed. The present embodiment differs from the present invention shown in FIG. 1 in that heat is exchanged by flowing countercurrently to the gas flow in the passage E and the high-pressure steam flow in the passage F. The low-pressure multi-component refrigerant stream 14 extracted from the upper part of the low-temperature zone through the channels H and J is obtained by expanding the high-pressure condensate stream 15 after passing through the high-temperature zone channel D by the expansion valve 41. And a gas-liquid separator 24 to separate the vapor and liquid, and the separated vapor portion 16 and the condensed portion 17 are mixed to form a first low-pressure multi-component refrigerant flow at a lower portion of the flow path R in the high-temperature zone. And heat exchange with the gas flow in the flow channel A, the high-pressure vapor flow of the multi-component refrigerant in the flow channel B, and the high-pressure condensate flow of the multi-component refrigerant in the flow channel D that pass through the high-temperature zone. Is the same as in the present invention.

FIG. 7 is a diagram for explaining the difference in the evaporation curve characteristics of the cooling fluid in the low temperature zone between the method of the present invention of FIG. 1 and the method of FIG. In FIG. 7, the horizontal axis represents the heat exchange amount Q, the vertical axis represents the temperature T (° C.), the line C is the evaporation curve of the second low-pressure multi-component refrigerant flow of the present invention having the configuration shown in FIG. 9 is a diagram obtained by synthesizing an evaporation curve of a low-pressure multi-component refrigerant in a low-temperature zone in Comparative Example 3 having the configuration shown in FIG. 5 (evaporation curve of flow path H + evaporation curve of flow path J);
Since the line C shows the evaporation temperature of the low-pressure multi-component refrigerant which is lower by about 2 ° C. than the line D over the long temperature range, the logarithmic average temperature difference with the fluid to be cooled can be increased, and the heat transfer area of the heat exchanger can be reduced. Can be reduced.

A process using the plate fin type heat exchanger shown in FIG. 1 (the present invention), and only the heat exchanger 20 in the process shown in FIG. 1 is replaced with the Hampson type heat exchanger shown in FIG. Table 1 shows the process (Comparative Example 4).
FIG. 8 shows the relationship between the heat exchange amount Q and the temperature T when producing LNG shown in Table 1 from the raw material gas shown in FIG. Table 2 shows the result of calculating the power consumption of the compressor of the present invention.
Shown in In Comparative Example 4, as in the present invention, the gas flow passing through the high-temperature zone was expanded and then introduced into the low-temperature zone. The LNG product is obtained by extracting the liquefied gas 10 from the low temperature zone of the heat exchanger and expanding it further (not shown).

[0024]

[Table 1]

[0025]

[Table 2]

In FIG. 8, the horizontal axis represents the heat exchange amount Q, the vertical axis represents the temperature T (° C.), the line E (solid line) represents the condensation curve of the fluid to be cooled in Comparative Example 4, and the line F (dotted line) represents the present invention. 7 is a condensation curve of the fluid to be cooled in FIG. The line F (dotted line) partially exceeds the line E (solid line), that is, since the condensation curve of the fluid to be cooled moves to the high temperature side, the heat transfer area of the heat exchanger is reduced, or the Hampson type If the heat exchanger is designed with the same temperature difference as the heat exchanger, the load on the compressor can be reduced. The degree of reduction of the load is about several MW in the case of the compressor power shown in Table 2.

[0027]

【The invention's effect】

(1) In the present invention, when exchanging heat between a pre-cooled gas and a high-pressure multi-component refrigerant, the use of a plate-fin type heat exchanger makes it possible to reduce the pressure loss as compared with the conventional method using a Hampson-type heat exchanger. Can be significantly reduced, so that the temperature difference between the condensation curve of the fluid to be cooled and the evaporation curve of the cooling fluid tends to increase. Therefore, the heat transfer area of the heat exchanger can be reduced, or if the heat exchanger is designed with the same temperature difference as the Hampson heat exchanger, the load on the compressor can be reduced. (2) In the present invention, the precooled gas stream, the high-pressure vapor stream and the high-pressure condensate stream of the multi-component refrigerant, which are the fluids to be cooled, flow from the upper part to the lower part of the heat exchanger. The first low-pressure multi-component refrigerant and the second low-pressure multi-component refrigerant are in a zone in a heat exchanger through which each fluid passes,
Since the fluid to be cooled flows from the lower part to the upper part, the fluid to be cooled in the flow path condenses while reaching the lower part and generates a large static pressure of the liquid, so that the pressure loss is canceled. Therefore, the temperature difference between the condensation curve of the fluid to be cooled and the evaporation curve of the cooling fluid tends to increase, so that the heat transfer area of the heat exchanger can be reduced or the load on the compressor can be further reduced. it can. (3) Further, in the present invention, since the low-temperature end of the low-temperature fluid is at the bottom of the heat exchanger, even if the flow of the fluid in the heat exchanger stops, backflow of the low-temperature liquid does not occur due to gravity. Can be. (4) In the present invention, a gas-liquid mixed-phase low-pressure multi-component refrigerant is gas-liquid separated, and then mixed and introduced at the inlet of a heat exchanger, so that the gas phase and the liquid phase after the gas-liquid separation are separated. Compared to the case where the refrigerant is introduced into the heat exchanger, the low-pressure multi-component refrigerant has a low evaporation temperature over a long temperature range in the evaporation curve, so that the logarithmic average temperature difference with the fluid to be cooled can be increased, and the transfer of the heat exchanger can be increased. The heat area can be reduced. (5) In the present invention, compared with the conventional method using a Hampson heat exchanger, the amount of circulating multi-component refrigerant can be reduced or the amount of single-component refrigerant for pre-cooling, for example, propane, can be reduced. By reducing or increasing the composition of the multi-component refrigerant, a gas liquefaction method that can further reduce the horsepower of the compressor and save energy can be expected.

[Brief description of the drawings]

FIG. 1 is a diagram for explaining a configuration of a gas liquefaction method according to the present invention.

FIG. 2 is a diagram for explaining a configuration of a conventional gas liquefaction method using a Hampson-type heat exchanger.

FIG. 3 is an explanatory diagram of a method (Comparative Example 1) of separately introducing a steam flow and a condensate flow after expansion of a multi-component refrigerant in both a high-temperature zone and a low-temperature zone to a heat exchanger.

FIG. 4 shows a method of separately introducing a steam flow and a condensate flow after expansion of a multi-component refrigerant in a high-temperature zone into a heat exchanger (Comparative Example 2).
FIG.

FIG. 5 shows a method of separately introducing a vapor flow and a condensate flow after expansion of a multi-component refrigerant in a low-temperature zone into a heat exchanger (Comparative Example 3).
FIG.

6 is a diagram showing a relationship between a heat exchange amount Q and a temperature T in a high temperature zone in the method of the present invention in FIG. 1 and the method in FIG. 4;

7 is a diagram showing a relationship between a heat exchange amount Q and a temperature T in a low temperature zone in the method of the present invention in FIG. 1 and the method in FIG. 5;

FIG. 8 is a diagram showing a relationship between a heat exchange amount Q and a temperature T in a case where a plate fin type heat exchanger is used as a heat exchanger and in a case where a Hampson type heat exchanger is used in the process shown in FIG. 1; It is.

[Explanation of symbols]

REFERENCE SIGNS LIST 1 raw material gas stream 2 precooler (using single-component medium-pressure refrigerant) 3 precooler (using single-component low-pressure refrigerant) 4 precooled raw material gas stream 5 reboiler of high-boiling material separator 6 reflux of high-boiling material separator Drum 7 High-boiling material separator in raw material gas 8 Multi-component refrigerant high-pressure vapor flow 9 Multi-component refrigerant high-pressure condensate flow 10 Liquefied gas flow 11 High-pressure vapor flow of liquefied multi-component refrigerant 12 High-pressure vapor of liquefied multi-component refrigerant A low-pressure vapor portion where the flow is expanded and gas-liquid separated 13 A low-pressure condensed flow portion where the high-pressure vapor flow of the liquefied multi-component refrigerant is expanded and gas-liquid separated 14 A second low-pressure multi-component refrigerant flow 15 The high pressure of the cooled multi-component refrigerant Condensed liquid flow 16 Vapor portion separated by gas and liquid in gas-liquid separator 24 17 Condensed portion separated in gas and liquid by gas-liquid separator 24 18 First low-pressure multi-component refrigerant flow 19 High-pressure multi-component refrigerant partially condensed 20 Plate Heat exchanger 21 High temperature zone of plate fin heat exchanger 22 Low temperature zone of plate fin heat exchanger 23 Gas-liquid separator (for high-pressure multi-component refrigerant) 24 Gas-liquid separator (for low-pressure multi-component refrigerant) 25 Gas-liquid separator (for low-pressure multi-component refrigerant) 26 Compressor 27 Gas stream at the top of high-boiling-point separator 28 Gas stream with high purity of low-boiling components 31 Multi-component refrigerant precooler (using single-component high-pressure refrigerant) 32 Multi-component refrigerant pre-cooler (using single-component medium-pressure refrigerant) 33 Multi-component refrigerant pre-cooler (using single-component low-pressure refrigerant) 34 Multi-component refrigerant cooler (water-cooled) 41 Expansion valve 42 Expansion valve

──────────────────────────────────────────────────続 き Continuation of the front page (56) References JP-A-6-159928 (JP, A) JP-A-60-50370 (JP, A) JP-A-6-299174 (JP, A) 29712 (JP, B1) (58) Fields investigated (Int. Cl. ⁷ , DB name) F25J 1/00-5/00

Claims (9)

(57) [Claims] 1. A gas pre-cooled by heat exchange with a single-component refrigerant under a condition of sequentially lowering the temperature is exchanged with a high-pressure multi-component refrigerant pre-cooled until partly condensed by heat exchange with the single-component refrigerant. When the gas is liquefied, (1) the high-pressure multi-component refrigerant partially condensed by heat exchange with the single-component refrigerant is separated into a high-pressure vapor stream and a high-pressure condensate stream, and (2) the plate surface is upright. Of a high-temperature zone having at least four types of flow paths on the upper side, and a low-temperature zone having at least three types of flow paths on the lower side. The gas flow, the high-pressure vapor flow of the multi-component refrigerant, and the high-pressure condensate flow of the multi-component refrigerant are respectively introduced from the upper portions of the three types of flow paths, and the first low-pressure multi-component refrigerant flow described later is divided into one of the high-temperature zones. Introduced from the lower part of the seed flow path, the gas flow, multi-component refrigerant high Cooling the high-pressure condensate stream of the high-pressure vapor stream and the multi-component refrigerant by heat exchange with the first low-pressure multi-component refrigerant stream;
(3) The gas flow cooled in the high-temperature zone and the high-pressure vapor flow of the multi-component refrigerant are introduced from the upper portions of two of the flow channels in the low-temperature zone of the plate fin heat exchanger, respectively. And introducing a gas stream and a high-pressure vapor stream of the multi-component refrigerant into a second low-pressure multi-component refrigerant stream by introducing the low-pressure multi-component refrigerant stream from the lower portion of one of the flow paths in the low-temperature zone. Cool down,
(4) A liquefied gas stream is extracted and recovered from the lower part of the low-temperature zone, and (5) A vapor part and a condensing part obtained by expanding the high-pressure vapor stream of the liquefied multi-component refrigerant extracted from the lower part of the low-temperature zone. And a separated vapor portion and a condensed portion are mixed and introduced as a second low-pressure multi-component refrigerant stream from the lower part of one of the flow paths in the low-temperature zone. After exchanging heat with the gas flow passing through the lower part and the high-pressure vapor flow of the multi-component refrigerant, withdraw from the upper part of the low-temperature zone,
(6) Mixing the second low-pressure multi-component refrigerant stream extracted from the upper part of the low-temperature zone with the flow obtained by expanding the high-pressure condensate stream of the multi-component refrigerant after passing through the high-temperature zone, and Separated, the separated vapor portion and condensed portion are mixed and introduced as a first low-pressure multi-component refrigerant stream from the lower part of one of the flow paths in the high-temperature zone, and pass through the high-temperature zone from the upper part to the lower part. After heat exchange with the flowing gas stream, the high-pressure vapor stream of the multi-component refrigerant, and the high-pressure condensate flow of the multi-component refrigerant, it was extracted as steam from the upper part of the high-temperature zone, and (7) extracted as steam from the upper part of the high-temperature zone. After compressing the first low-pressure multi-component refrigerant stream, the partially condensed high-pressure multi-component refrigerant obtained by heat exchange with the single-component refrigerant is circulated to the step (1) and used again for gas liquefaction. Gas liquefaction method comprising: 2. A gas flow is introduced from one upper part of a flow path in a high-temperature zone of a plate fin type heat exchanger and cooled, and a part of the gas flow is extracted to separate a condensed high-boiling component. The gas liquefaction method according to claim 1, wherein after the removal, the gas stream from which the high-boiling components have been removed is introduced from an upper portion of another flow path in a high-temperature zone from a location where the gas stream was extracted. 3. A vapor part and a condensed part obtained by expanding a high-pressure vapor flow of a liquefied multi-component refrigerant extracted from a lower part of a low temperature zone are subjected to gas-liquid separation, and the separated vapor part and condensed part are separated. 3. The gas according to claim 1, wherein the mixture of the gas and the condensed portion is performed immediately before the mixture is introduced into the low-temperature zone. Liquefaction method. 4. A method of mixing a second low-pressure multi-component refrigerant stream extracted from the upper part of the low-temperature zone with a flow obtained by expanding a high-pressure condensate stream of the multi-component refrigerant after passing through the high-temperature zone. The mixture of the vapor and the condensed part is introduced into the high-temperature zone when the vapor-liquid separation and the separated vapor and the condensed part are mixed and introduced from the lower part of one of the channels in the high-temperature zone. The gas liquefaction method according to claim 1, 2 or 3, which is performed immediately before. 5. The gas flow that has passed through the high-temperature zone flow path of the plate-fin heat exchanger is expanded and then introduced from above the low-temperature zone flow path. Item 5. The gas liquefaction method according to Item 4. 6. The first low-pressure multi-component refrigerant stream extracted as vapor from the upper part of the high-temperature zone is compressed, cooled with a non-hydrocarbon refrigerant, and then heat-exchanged with a single-component refrigerant to partially condense. The gas liquefaction method according to claim 1, wherein the high-pressure multi-component refrigerant is used. 7. The multi-component refrigerant is a mixture of components selected from nitrogen and hydrocarbons having 1 to 5 carbon atoms. The gas liquefaction method according to claim 6. 8. The gas liquefaction method according to claim 7, wherein the multi-component refrigerant is a mixture of nitrogen, methane, ethane and propane. 9. The gas liquefaction method according to claim 1, wherein the single-component refrigerant is propane.