TWI729379B - Mixed refrigerant liquefaction system and method with pre-cooling - Google Patents

Abstract

A system for cooling a gas includes a pre-cool heat exchanger and a liquefaction heat exchanger. The pre-cool heat exchanger uses a pre-cool refrigerant to pre-cool a feed gas stream prior to the stream being directed to a liquefaction heat exchanger. The liquefaction heat exchanger uses a mixed refrigerant to further cool the pre-cooled gas. The pre-cool heat exchanger also pre-cools the liquefaction mixed refrigerant used by the liquefaction heat exchanger.

Description

Mixed refrigerant liquefaction system and method with pre-cooling

This application claims the priority of U.S. Provisional Application No. 62/660,518 filed on April 20, 2018, and the content of the U.S. Provisional Application is hereby incorporated by reference.

The present invention relates generally to a system and method for cooling or liquefying gas, and more specifically, to a mixed refrigerant liquefaction system and method that uses cold vapor separation to separate high-pressure mixed refrigeration The refrigerant vapor is fractionated into liquid and vapor streams, and includes a subsystem for pre-cooling the feed gas stream and one or more mixed refrigerant streams using a second refrigerant.

Natural gas, mainly methane, and other gases are liquefied under pressure for storage and transportation. The reduction in volume caused by liquefaction allows more practical and economically designed containers to be used. Liquefaction is usually achieved by cooling the gas through indirect heat exchange through one or more refrigeration cycles. Such a refrigeration cycle is expensive in terms of both equipment cost and operation due to the complexity of the required equipment and the required performance efficiency of the refrigerant. Therefore, there is a need for gas cooling and liquefaction systems with improved refrigeration efficiency and reduced operating costs and reduced complexity.

The use of mixed refrigerant in the refrigeration cycle(s) used in the liquefaction system improves efficiency because the heating curve of the refrigerant more closely matches the cooling curve of the gas. The refrigeration cycle used in the liquefaction system will usually include a compression system for conditioning or processing the mixed refrigerant. A mixed refrigerant compression system usually includes one or more stages, where each stage includes a compressor, a cooler, and a separation and liquid accumulator device. The vapor leaving the compressor is cooled in a cooler, and the resulting two-phase or mixed-phase flow is directed to a separation and liquid accumulator device from which the vapor and liquid exit for further processing and / Or lead to the liquefaction heat exchanger.

The separated liquid and vapor phases of the mixed refrigerant from the compression system can be directed to the part of the heat exchanger to provide more effective cooling. Examples of such systems are provided in jointly owned U.S. Patent No. 9,441,877 by Gushanas et al., U.S. Patent Application Publication No. US 2014/0260415 by Ducote et al. and U.S. Patent Application Publication No. US 2016/0298898 by Ducote et al. , The content of each of the said patents is hereby incorporated by reference.

Further improvement in cooling efficiency and reduction in operating costs in gas cooling and liquefaction systems are desirable.

There are several aspects of the subject matter that can be embodied separately or together in the methods, devices, and systems described and required below. These aspects can be used alone or in combination with other aspects of the subject matter described herein, and the description of these aspects together is not intended to exclude the use of these aspects as set forth in the scope of the appended patents herein alone or these aspects alone or in different combinations Request.

In one aspect, a system for cooling gas using a pre-cooling refrigerant and a mixed refrigerant includes a pre-cooling heat exchanger having a feed gas inlet and an inlet adapted to receive a feed gas stream. Material gas outlet, pre-cooling refrigerant inlet and pre-cooling refrigerant outlet, as well as liquefied mixed refrigerant inlet and liquefied mixed refrigerant outlet. The pre-cooling heat exchanger is configured to use the pre-cooling refrigerant to cool the feed gas passing through the pre-cooling heat exchanger between the feed gas inlet and the feed gas outlet, and Cooling the liquefied mixed refrigerant passing through the pre-cooling heat exchanger between the liquefied mixed refrigerant inlet and the liquefied mixed refrigerant outlet. The pre-cooling compressor system includes a pre-cooling compressor having an inlet in fluid communication with the pre-cooling refrigerant outlet of the pre-cooling heat exchanger. The pre-cooling compressor system also has a pre-cooling condenser, and the pre-cooling condenser has an inlet in fluid communication with the outlet of the pre-cooling compressor. The pre-cooling condenser also has an outlet in fluid communication with the pre-cooling refrigerant inlet of the pre-cooling heat exchanger. The liquefaction heat exchanger includes a liquefaction channel in fluid communication with the feed gas outlet of the pre-cooling heat exchanger, a primary refrigeration channel, a high-pressure steam cooling channel, and a cold separator vapor cooling channel, wherein the cold separator vapor cooling The passage has an outlet in fluid communication with the primary refrigeration passage. mixing The refrigerant compression system includes a mixed refrigerant compressor having an inlet in fluid communication with the outlet of the primary refrigeration passage, and a mixed refrigerant cooler having an inlet in fluid communication with the outlet of the mixed refrigerant compressor. The mixed refrigerant cooler also has an outlet in fluid communication with the liquefied mixed refrigerant inlet of the pre-cooling heat exchanger. The mixed refrigerant compression system further has a high-pressure accumulator having an inlet in fluid communication with the liquefied mixed refrigerant outlet of the pre-cooling heat exchanger and the The inlet of the high-pressure steam cooling channel is in fluid communication with the steam outlet. The cold steam separator has an inlet in fluid communication with the outlet of the high-pressure steam cooling channel of the liquefaction heat exchanger, a steam outlet in fluid communication with the inlet of the cold separator steam cooling channel of the liquefaction heat exchanger, and A liquid outlet communicating with the primary refrigeration passage of the liquefaction heat exchanger.

In another aspect, a method for cooling a feed gas stream includes the steps of: pre-cooling the feed gas stream in a pre-cooling heat exchanger using a first refrigerant to form a pre-cooled feed gas stream, and The pre-cooled feed gas stream is further cooled by: i) cooling a high-pressure second refrigerant stream in the pre-cooling heat exchanger to form a cooled high-pressure second refrigerant stream, ii) separating the cooling Iii) Cool the high-pressure vapor stream in a liquefaction heat exchanger to form a mixed phase stream; iv) separate the mixed phase with a cold vapor separator Flow to form a cold separator vapor stream and a cold separator liquid stream, v) using the second refrigerant to condense and flash the cold separator vapor stream in the liquefaction heat exchanger to form cold temperature refrigeration Vi) directing the cold and warm refrigerant flow to the liquefaction heat exchanger, vii) subcooling the high-pressure liquid flow to form a supercooled high-pressure liquid flow and interacting with the liquid in the liquefaction heat exchanger The cold and warm refrigerant flow combination; viii) subcooling the cold separator liquid flow to form a subcooled cold separator liquid flow and combining with the cold and warm refrigerant flow in the liquefaction heat exchanger, And ix) bringing the pre-cooled gas stream in the liquefaction heat exchanger into thermal contact with the cold-temperature refrigerant stream.

In another aspect, a system for cooling a feed gas using a mixed refrigerant includes a pre-cooling heat exchanger having a pre-cooling refrigerant inlet and a pre-cooling refrigerant configured to receive a pre-cooling refrigerant flow. Cooling refrigerant outlet and liquefied mixed refrigerant inlet and liquefied mixed refrigerant outlet. The pre-cooling heat exchanger is configured to use the pre-cooling refrigerant to cool the The liquefied mixed refrigerant passing through the pre-cooling heat exchanger between the mixed refrigerant inlet and the liquefied mixed refrigerant outlet. The liquefaction heat exchanger includes a liquefaction channel configured to receive the stream of the feed gas, a primary refrigeration channel, a high-pressure vapor cooling channel, and a cold separator vapor cooling channel, wherein the cold separator vapor cooling channel has the same relationship as the primary The outlet of the refrigeration channel in fluid communication. The mixed refrigerant compression system includes a mixed refrigerant compressor having an inlet in fluid communication with an outlet of the primary refrigeration passage. The mixed refrigerant compression system further includes a mixed refrigerant cooler having an inlet in fluid communication with an outlet of the mixed refrigerant compressor. The mixed refrigerant cooler has an outlet in fluid communication with the liquefied mixed refrigerant inlet of the pre-cooling heat exchanger. The mixed refrigerant compression system further includes a high-pressure accumulator having an inlet in fluid communication with the liquefied mixed refrigerant outlet of the pre-cooling heat exchanger and the The inlet of the high-pressure steam cooling channel is in fluid communication with the steam outlet. The cold steam separator has an inlet in fluid communication with the outlet of the high-pressure steam cooling channel of the liquefaction heat exchanger, a steam outlet in fluid communication with the inlet of the cold separator steam cooling channel of the liquefaction heat exchanger, and A liquid outlet communicating with the primary refrigeration passage of the liquefaction heat exchanger.

In another aspect, a method for cooling a feed gas stream includes the steps of: directing the feed gas stream into a liquefaction heat exchanger; cooling a high-pressure mixed refrigerant stream in a pre-cooling heat exchanger to form a cooling The high-pressure mixed refrigerant stream and the feed gas stream in the liquefaction heat exchanger are cooled by the following operations: i) separating the cooled high-pressure mixed refrigerant stream to form a high-pressure vapor stream and a high-pressure liquid stream, ii) Cool the high-pressure steam stream in the liquefaction heat exchanger to form a mixed phase stream, iii) separate the mixed phase stream with a cold steam separator to form a cold separator vapor stream and a cold separator liquid stream, iv) In the liquefaction heat exchanger, the cold separator vapor stream is condensed and flashed to form a cold-temperature refrigerant stream, v) the cold-temperature refrigerant stream is guided to the liquefaction heat exchanger, and vi) In the liquefaction heat exchanger, the high-pressure liquid flow is subcooled to form a subcooled high-pressure liquid flow and combined with the cold-temperature refrigerant flow in the liquefaction heat exchanger; vii) the cold separator liquid Flow through the cold to form a subcooled cold separator liquid flow and combine with the cold-temperature refrigerant flow in the liquefaction heat exchanger; and viii) make the gas flow in the liquefaction heat exchanger and the liquid The cold and warm refrigerant streams are in thermal contact.

8: Mixed refrigerant liquefaction system

10: Heat exchanger

12: warm end

14: cold end

16: Pre-cooling natural gas feed stream

18: Liquefaction channel

20: Liquid natural gas (LNG) product flow

22: Mixed refrigerant compressor system

24, 46, 264: first stage suction drum

26: Mixed refrigerant vapor flow

27: Steam mixed refrigerant flow

28, 352: Primary refrigeration channel

32: The first stage compressor

34, 38: cooler

35, 88, 284, 342: second stage suction drum

36: second stage compressor

40: Pre-cooling system

42a, 372a: Pre-cooling and warming heat exchanger

42b, 372b: pre-cooling cold heat exchanger

44, 262: Pre-cooling compressor system

48: Propane refrigerant vapor flow

52, 272: Steam flow

54: Pre-cooling compressor

56, 274: pre-cooling condenser

58: Propane refrigerant liquid stream

62: Pre-cooling refrigerant accumulator

64: Propane refrigerant liquid flow

66, 94, 144, 174, 216, 222, 244, 296, 348, 366: expansion device

72, 96: Two-phase flow

74, 98, 378, 382: shell

76: Liquid level sensor

78, 104, 114, 118, 194, 196, 226, 236, 374: core

82, 84, 84’: Natural gas feed stream

86: Warm propane refrigerant vapor flow

92: Propane refrigerant liquid stream

102: Liquid level sensor

112: High-pressure mixed refrigerant flow

116: Mixed refrigerant flow

122: Mixed refrigerant (MR) mixed phase flow

124, 418: high pressure accumulator

125: High pressure liquid cooling channel

126: High-pressure vapor refrigerant flow

127, 204, 286, 306: steam flow

128: High-pressure liquid refrigerant flow

129, 162: flashing

131: Warm temperature separator

132: Mixed phase cold separator feed stream

133, 142, 212, 234, 362: liquid flow

134, 208, 358, 410: cold steam separator

135: High-pressure steam cooling channel

136: Cold separator steam flow

138: Cold separator liquid flow

141: Cold separator steam cooling channel

143: Liquid cooling channel of cold separator

146: Cold and warm separator

152: Cold and warm liquid flow

154: Cold and warm steam flow

160: Subcooled cold separator liquid

164, 368: Medium temperature separator

166: The resulting liquid stream

168, 232: Obtained steam flow

172: Liquefied Natural Gas Stream

182: The flow of the second stage compression and cooling cycle

186: The resulting cooled MR stream

188: The first high-pressure MR accumulator

192: Obtained steam MR flow

198, 218, 238: the resulting cooling flow

202: The second high-pressure MR accumulator

206, 214, 220, 242, 294, 324, 326, 346, 356, 364: (cooling) channel

224: Discharge stream of the first stage compression and cooling cycle

228: MR low pressure accumulator

252: Warm mixed refrigerant (MR) pre-cooling system

254: Warm MR pre-cooling heat exchanger

256: Pre-cooling channel

266: Pre-cooling MR steam flow

268: Pre-cooling primary refrigeration channel

276: Pre-cooling MR accumulator

278, 298: Valve

292, 312: Liquid pre-cooling MR flow

302: Pre-cooling cold separator

304: Secondary pre-cooling refrigeration channel

308: Steam pre-cooling MR flow

314: The resulting cooled natural gas stream

316: Liquefied Compressor System

318: First stage liquefaction MR flow

322: Second stage liquefaction MR flow

328, 334: resulting mixed phase flow

332: Liquefied MR low pressure accumulator

336: Liquefied MR high pressure accumulator

338, 354: Liquefied MR steam flow

344: Liquefied MR liquid stream

350, 420: Liquefied heat exchanger

370: Propane pre-cooling system

376: inner head

384, 404: discharge flow from the second compression and cooling stage

386, 406: Liquefied MR compressor system

402: cold water cooling system

408: MR Liquefaction System

412: Pump

414: Coolant Heat Exchanger

416: Cooled MR stream

422: warm riser

424: Medium temperature riser

426: Cold and warm riser

Fig. 1 is a process flow and schematic diagram showing the first embodiment of the system and method of the present invention; Fig. 2 is a process flow and schematic diagram showing the second embodiment of the system and method of the present invention; The process flow and schematic diagram of the third embodiment of the system and method of the present invention; FIG. 4 is a process flow and schematic diagram showing the fourth embodiment of the system and method of the present invention; and FIG. 5 is a process flow and schematic diagram showing the system and method of the present invention The process flow and schematic diagram of the fifth embodiment.

Embodiments of the mixed refrigerant liquefaction system and method of the present invention are illustrated in FIGS. 1-5. It should be noted that although embodiments are illustrated and described below in terms of liquefying natural gas to produce liquid natural gas, the present invention can be used to liquefy or cool other types of gas.

The embodiment of the present invention may use the commonly owned U.S. Patent No. 9,441,877 of Gushanas et al.; U.S. Patent Application Publication No. 2014/0260415 of Ducote et al., U.S. Patent Application No. 14/218,949, and U.S. Patent of Ducote et al. The mixed refrigerant liquefaction system and process described in Application No. 62/561,417, and the contents of each of the patents are hereby incorporated herein by reference.

It should be noted herein that both channels and streams are sometimes referred to by the same reference numerals listed in the figure. In addition, as used herein, and as known in the art, a heat exchanger is a device or device in which indirect heat exchange occurs between two or more streams at different temperatures, or between streams and the environment Area. As used herein, the terms "communication/communicating" etc. usually refer to Fluid communication unless otherwise specified. Furthermore, although two fluids in communication can exchange heat when mixed, this exchange will not be considered the same as the heat exchange in the heat exchanger, although this exchange may occur in the heat exchanger. As used herein, the term "reducing the pressure of" (or its deformation) does not involve a phase change, and the term "flashing" (or its deformation) involves a phase change, even a partial phase change. As used herein, the terms "high", "intermediate", "medium", "warm", etc., are relative to comparable streams, as is customary in the art.

In general, referring to FIG. 1, the system of the first embodiment of the present invention includes a mixed refrigerant liquefaction system generally indicated by 8, and the mixed refrigerant liquefaction system includes a multi-stream liquefaction heat exchanger generally indicated by 10, The multi-stream liquefaction heat exchanger has a warm end 12 and a cold end 14. The heat exchanger receives a pre-cooled natural gas feed stream 16, which is liquefied in the cooling or liquefaction channel 18 by heat removal via heat exchange with the refrigerated stream in the heat exchanger. As a result, a liquid natural gas (LNG) product stream 20 is produced. The multi-flow design of the heat exchanger allows several flows to be conveniently and energy-efficiently integrated into a single exchanger. Suitable heat exchangers include welded aluminum heat exchangers available from Chart Energy & Chemicals, Inc. of The Woodlands, Texas. Such a plate-fin multi-flow heat exchanger offers the further advantage of being physically compact.

The system of Figure 1 includes a heat exchanger 10, which can be configured to perform other gas treatment options known in the art. These treatment options may require the gas stream to leave and re-enter the heat exchanger one or more times, and may include, for example, natural gas liquid recovery or nitrogen removal.

The heat removal is achieved in the heat exchanger using a mixed refrigerant that is processed and reconditioned using the liquefaction system mixed refrigerant compressor system indicated generally at 22. The mixed refrigerant compressor system includes a first stage suction drum 24 that receives the mixed refrigerant vapor flow 26 from the primary refrigeration passage 28 of the heat exchanger 10. The vapor stream is compressed in the first stage compressor 32 (the first stage compressor may be a single compressor or one stage of a single multi-stage compressor) and then cooled by the first stage heat exchanger or cooler 34. The resulting mixed refrigerant vapor flows into the second-stage suction drum 35 and then to the second-stage compressor 36 (the second-stage compressor may be a single compressor or one stage of a single multi-stage compressor), and is compressed After that, it is cooled in the second-stage heat exchanger or cooler 38.

As known in the art, the first stage suction drum 24 and the second stage suction drum 35, as well as the remaining suction drums described below, prevent liquid from being delivered to its subsequent compressor, and are optional.

In addition to the liquefied heat exchanger 10 and the associated components described in Ducote et al. U.S. Patent Application No. 14/218,949 below and incorporated herein by reference, and the mixed refrigerant compressor system 22, The system of FIG. 1 includes a pre-cooling system indicated generally at 40. The pre-cooling system includes a pre-cooling warm heat exchanger generally indicated at 42a and a pre-cooling cold heat exchanger generally indicated at 42b. As just one example, the pre-cooling warm heat exchanger 42a and the pre-cooling cold heat exchanger 42b may be CORE-IN-KETTLE heat exchangers available from Chart Energy & Chemicals, Inc. of The Woodlands, Texas. Alternative types of heat exchangers include, but are not limited to, shell and tube type, or thermosiphon type heat exchangers can be used to pre-cool the warm heat exchanger 42a and pre-cool the cold heat exchanger 42b. The pre-cooling system may optionally have a single pre-cooling heat exchanger or more than two pre-cooling heat exchangers.

The pre-cooling system also includes a compressor system indicated generally at 44 for processing and reconditioning the pre-cooling system refrigerant, such as propane, butane, ammonia, or chlorofluorocarbons. Although the pre-cooling system in the embodiments described herein uses propane, alternative refrigerants that can be used include, but are not limited to, butane, ammonia, or liquid fluorinated hydrocarbons.

The pre-cooling compressor system 44 includes a first stage suction drum 46 that receives the propane refrigerant vapor stream 48 from the pre-cooling cold heat exchanger 42b, as described in more detail below. The vapor stream 52 from the first stage suction drum travels to the pre-cooling compressor 54 and the resulting compressed stream enters the pre-cooling condenser 56. The resulting propane refrigerant liquid flows into the pre-cooling refrigerant accumulator 62. The propane refrigerant liquid stream 64 travels from the accumulator to the expansion device 66 so that the two-phase stream 72 enters the housing 74 of the pre-cooling warming heat exchanger 42a. The liquid level sensor 76 controls the setting of the expansion device 66 so that a proper liquid level is maintained in the housing 74.

As in the case of all expansion devices referred to herein, the expansion device 66 may be an expansion valve such as a Joule-Thomson valve, or another type of expansion device including but not limited to a turbine or an orifice.

The housing 74 of the pre-cooling warming heat exchanger 42 a houses a core 78 that receives the natural gas feed stream 82. As just one example, the core 78 of the warm feed gas heat exchanger, and all such cores discussed below may be brazed aluminum heat exchangers (BAHX) or other heat exchanger types such as microchannels or welded Plates, tubes or coils, printed circuit heat exchangers, etc. The natural gas stream is cooled by propane liquid refrigerant in the core 78, and the cooled natural gas stream exits the pre-cooling warming heat exchanger 42a as stream 84. In an alternative embodiment in which the natural gas stream 82 is colder than the pre-cooling warm heat exchanger 42a, the gas stream may be transported directly to the pre-cooling cold heat exchanger 42b, as indicated by the dashed line 84' in FIG. In such an embodiment, the core 78 may be omitted.

The warm propane refrigerant vapor stream 86 leaves the shell 74 of the pre-cooling warm heat exchanger 42 a and travels to the second stage suction drum 88 and enters the inlet of the pre-cooling compressor 54.

The propane refrigerant liquid stream exits the shell of the warm heat exchanger as stream 92 and travels to the expansion device 94 so that the two-phase stream 96 enters the shell 98 of the pre-cooling cold heat exchanger 42b. The liquid level sensor 102 controls the setting of the expansion device 94 so that a proper liquid level is maintained in the housing 98.

The housing 98 of the pre-cooling cold heat exchanger 42b houses the core 104, which receives the natural gas feed stream 84 (or natural gas feed stream 84'). The natural gas stream 84 is further cooled (or cooled) by propane liquid refrigerant in the core 104, and the cooled natural gas stream exits the pre-cooling cold heat exchanger 42 b as the pre-cooling stream 16 and enters the liquefaction channel 18 of the liquefaction heat exchanger 10. In an alternative embodiment where the natural gas stream 82 is colder than both the pre-cooling warm heat exchanger 42a and the pre-cooling cold heat exchanger 42b, the gas stream 84' of FIG. 1 may be directly sent to the liquefaction heat exchanger. aisle. In such an embodiment, the core 104 may be omitted.

The propane refrigerant vapor stream 48 leaves the shell 98 of the pre-cooling cold heat exchanger 42 b and travels to the first stage suction drum 46.

The high pressure mixed refrigerant flow 112 from the second stage compressor 36 and heat exchanger 38 of the mixed refrigerant compression system travels to the core 114 located within the housing 74 of the pre-cooling warming heat exchanger 42a. The mixed refrigerant flowing through the core 114 is cooled by the liquid propane refrigerant in the housing 74, and the resulting cooled mixed refrigerant flow 116 is directed into the housing 98 located in the pre-cooling cold heat exchanger 42b 的cold mixed refrigerant core 118. The mixed refrigerant flowing through the core 118 is cooled by the liquid propane refrigerant in the housing 98, and the resulting mixed refrigerant (MR) mixed phase flow 122 is directed to the high-pressure accumulator 124. Although the accumulator drum is exemplified as the high-pressure accumulator 124, alternative separation devices may be used, including, but not limited to, another type of vessel, cyclone separator, distillation unit, coalescing separator, or sieve or vane demister Device. The same situation applies to the remaining separation devices or drums discussed herein.

The high-pressure vapor refrigerant flow 126 exits the vapor outlet of the accumulator 124 and travels to the warm end of the heat exchanger 10.

The high-pressure liquid refrigerant stream 128 exits the liquid outlet of the accumulator 124 and also travels to the warm end of the heat exchanger. After cooling in the heat exchanger 10, passing through the high-pressure liquid cooling channel 125, it is flashed at 129 and travels to the warm temperature separator 131. The vapor flow 127 and the liquid flow 133 travel from the warm-temperature separator 131 to the primary refrigeration passage 28 of the heat exchanger 10.

The heat exchanger 10 also receives and cools the high-pressure steam stream 126 from the high-pressure accumulator 124 through the high-pressure steam cooling passage 135, and cools the high-pressure steam stream so that it is partially condensed. The resulting mixed phase cold separator feed stream 132 is provided to the cold vapor separator 134 so that a cold separator vapor stream 136 and a cold separator liquid stream 138 are produced.

The cold separator vapor stream 136 is cooled and condensed in the heat exchanger 10 through the cold separator vapor cooling channel 141, enters the liquid stream 142, flashes through the expansion device 144, and is directed to the cold and warm separator 146 to form a cold and warm liquid The flow 152 and the cold and warm vapor flow 154, the cold and warm liquid flow and the cold and warm vapor flow are directed to the primary refrigeration passage 28 of the heat exchanger 10 as a cold and warm refrigerant flow.

The cold separator liquid stream 138 is cooled in the heat exchanger 10 by the cold separator liquid cooling channel 143 to form a subcooled separator liquid 160, which flashes at 162 and is directed into the Temperature separator 164. The resulting liquid stream 166 and the resulting vapor stream 168 are directed to the primary refrigeration passage 28 of the heat exchanger 10.

The combined refrigerant streams from the warm-temperature separator 131, the intermediate-temperature separator 164, and the cold-temperature separator 146 provide refrigeration for liquefying the pre-cooled feed gas stream 16 in the liquefaction or cooling channel 18 of the heat exchanger 10 , And leave the primary refrigeration passage 28 of the liquefaction heat exchanger as a combined return system The refrigerant flow 26, the combined return refrigerant flow is preferably in the vapor phase. The return refrigerant flow 26 flows to the suction drum 24, which produces a vapor mixed refrigerant flow 27, as previously mentioned.

The liquefied natural gas stream 172 exits the cold side of the heat exchanger and can optionally be expanded using an expansion device 174, and is transported to storage or processing.

The embodiment of Figure 1 therefore shows the propane (C3) pre-cooling mixed refrigerant (MR) process in combination with the cold vapor separator (CVS) located in the main liquefaction section of the process. The combination of C3 pre-cooling and MR and CVS results in a more efficient process than pre-cooling without CVS, and has lower equipment costs and also promotes higher equipment yields. The combination of pre-cooling and CVS allows the C3 system to operate with high efficiency at significantly warmer temperatures such as approximately -5°C and -35°C to -40°C as just one example, which reduces the cost and power consumption of the propane system.

The process of Figure 1 can be used with any MR liquefaction process using CVS.

It should be noted that although FIG. 1 shows two stages of pre-cooling in the pre-cooling system 40, one or more stages of pre-cooling may be used instead.

In addition, although FIG. 1 shows the MR liquefaction system 8 with separate warm-temperature separators, medium-temperature separators, and cold-temperature separators, any of these separators can be combined, or can be eliminated in some cases Splitter. Furthermore, although these separators are exemplified as standpipes, alternative types of separators known in the art may be used.

Except as discussed below, the embodiments of FIGS. 2-4 have the same mixed refrigerant compressor system, mixed refrigerant liquefaction system, and pre-cooling compressor system components and operations as described above with reference to FIG. 1, and thus Common reference numerals are used to indicate these parts of the system, and common components.

A second embodiment of the system of the invention is presented in FIG. 2. In this embodiment, two high-voltage MR accumulators are used instead of the single high-voltage MR accumulator 124 of FIG. 1. More specifically, the flow 182 leaving the second stage compression and cooling cycle of the MR compressor system 22 is directed to the core 114 of the pre-cooling warm heat exchanger 42a. The core 114 uses the liquid propane refrigerant in the housing 74 to cool the stream 182. The resulting cooled MR stream 186 travels to the first high-pressure MR accumulator 188. Obtained steam MR The stream 192 travels to the core 194 positioned in the pre-cooling cold heat exchanger 42 b, where the vapor MR stream is cooled by the liquid propane refrigerant in the housing 98. The resulting cooled stream 198 travels to the second high-pressure MR accumulator 202.

The steam flow 204 leaving the second high-pressure MR accumulator 202 is cooled in the liquefaction heat exchanger 10 through the passage 206 and directed to the cold steam separator 208. The steam stream leaving the cold steam separator is processed as described above with respect to FIG. 1.

The liquid stream 212 leaving the second high-pressure MR accumulator 202 is cooled in the liquefaction heat exchanger 10 through the passage 214, flashed through the expansion device 216 and directed to the intermediate temperature separator 164, where it is combined with the cold vapor separator 208 Combination of cooling and flashing liquid streams. The vapor and liquid streams leaving the intermediate temperature separator are directed to the primary refrigeration passage 28.

The liquid MR leaving the first high pressure MR accumulator 188 flows into the core 196 positioned in the pre-cooling cold heat exchanger 42b, where it is cooled by the liquid propane refrigerant in the housing 98. The resulting cooled stream 218 is cooled in the liquefaction heat exchanger 10 through the passage 220, and the resulting cooled liquid stream is flashed through the expansion device 222 and sent to the warm temperature separator 131. The vapor and liquid streams leaving the warm-temperature separator are directed to the primary refrigeration passage 28.

In addition, in the embodiment of FIG. 2, the pre-cooling system is used to cool the discharge stream 224 leaving the first stage compression and cooling cycle of the MR compressor system 22. More specifically, the pre-cooling warming heat exchanger 42 a includes a core 226 that receives the flow 224 through the interstage mixed refrigerant inlet and uses the propane liquid refrigerant in the housing 74 to cool the flow. The resulting cooled stream exits the core through the interstage mixed refrigerant outlet and travels to the interstage or MR low pressure accumulator 228. The resulting vapor stream 232 is directed to the input of the second stage compressor 36 of the MR compressor system 22. The liquid stream 234 leaving the MR low pressure accumulator 228 is received by the core 236 positioned within the housing 98 of the pre-cooling cold heat exchanger 42b. The resulting cooled stream 238 is cooled in the passage 242 of the liquefaction heat exchanger 10, flashed through the expansion device 244 and directed to the primary refrigeration passage 28 of the heat exchanger 10.

It should be understood that with regard to the embodiment of FIG. 2, in the second stage, the discharge stream (224) of the first compression and cooling stage of the MR compressor system 22 is pre-cooled before compression and the first MR high pressure is accumulated The second MR high-pressure accumulator and the second MR high-pressure accumulator (188 and 202) are different and independent in processing, and can be used in combination or separately.

In addition, the pre-cooled liquid stream 224 from the first compression and cooling stage is separately introduced into the MR liquefaction system 8, as shown in FIG. 2, or with any of the other refrigeration streams in the separator of the MR liquefaction system 8. A combination or in some cases without any separator.

A third embodiment of the system of the invention is presented in FIG. 3. In this embodiment, a warm mixed refrigerant (MR) pre-cooling system indicated generally at 252 is used instead of the propane pre-cooling system of FIGS. 1 and 2.

The MR pre-cooling system includes a warm MR pre-cooling heat exchanger indicated generally at 254 that includes a pre-cooling passage 256 that receives a natural gas feed stream 82.

The MR pre-cooling system also includes a pre-cooling compressor system 262. The pre-cooling compressor system includes a first-stage suction drum 264 that receives the pre-cooling primary refrigeration passage 268 from the heat exchanger 254. The MR steam stream 266 is cooled. The vapor stream 272 from the first stage suction drum travels to the inlet of the pre-cooling compressor 272, and the resulting compressed stream enters the pre-cooling condenser 274. The resulting MR liquid flows into the pre-cooled MR accumulator 276. The steam flow from the accumulator 276 may be discharged through the valve 278 or directed to the second stage suction drum 284 through a second valve. The vapor stream 286 from the second stage suction drum 284 travels to the inlet of the pre-cooling compressor 272.

The liquid pre-cooled MR stream 292 travels from the accumulator 276 through the cooling channel 294 of the heat exchanger 254, and the resulting cooled liquid flows into the expansion device 296 and is flashed, where the resulting mixed phase stream enters the pre-cooled cold separator 302. A portion (or all) of the cooled liquid flow leaving the passage 294 of the heat exchanger may be directed to the secondary pre-cooling refrigeration passage 304 of the heat exchanger using a valve 298 depending on the system temperature and operating requirements. The steam flow 306 leaving the secondary pre-cooling refrigeration passage 304 is directed to the second stage suction drum 284. The vapor and liquid pre-cooling MR streams from the pre-cooling cold separator 302 (308 and 312, respectively) are directed to the pre-cooling primary refrigeration passage 268 of the heat exchanger 254.

The natural gas feed stream flowing through the pre-cooling passage 256 of the pre-cooling heat exchanger 254 is pre-cooled through the refrigeration passages 268 and 304 of the heat exchanger, and the resulting cooled natural gas stream 314 is directed to the liquefaction heat exchanger 10 to be liquefied.

Similar to the embodiment of FIGS. 1 and 2, the liquefaction compressor system 316 has a first stage compression and cooling cycle that generates a first stage liquefied MR stream 318 and a second stage compression and cooling cycle that generates a second stage liquefied MR stream 322. The liquefied MR streams 318 and 322 are further cooled in the pre-cooling heat exchanger 254 through channels 324 and 326, and the resulting mixed phase stream 328 leaving the channel 324 travels to the liquefied MR low-pressure accumulator 332, and the resulting mixed phase stream 334 travels to liquefaction MR high pressure accumulator 336.

The liquefied MR vapor stream 338 travels from the liquefied MR low pressure accumulator 332 to the second stage suction drum 342 of the liquefied compressor system 316, where the resulting vapor stream is directed to the second stage compression and cooling cycle. The liquefied MR liquid stream 344 from the liquefied MR low pressure accumulator 332 is cooled in the passage 346 of the liquefaction heat exchanger 350, flashed through the expansion device 348 and directed to the primary refrigeration passage 352 of the heat exchanger 350.

The liquefied MR steam stream 354 leaving the liquefied MR high-pressure accumulator 336 is cooled by the passage 356 in the liquefied heat exchanger 350 and is directed to the cold steam separator 358. The steam stream leaving the cold steam separator can be treated as described above with respect to FIG. 1.

The liquid stream 362 leaving the liquefied MR high-pressure accumulator 336 is combined with the cooling and flashing liquid stream from the cold vapor separator 358 (this is functionally equivalent to the stream in the combined mid-temperature separator, as shown in Figure 2 After the instruction), it is cooled in the liquefaction heat exchanger 350 through the passage 364, flashed through the expansion device 366, and is led to the medium temperature separator 368. The vapor and liquid streams leaving the intermediate temperature separator are directed to the primary refrigeration passage 352 of the heat exchanger 350.

It should be noted that with regard to the embodiment of FIG. 3, pre-cooling the first stage discharge (318) of the liquefied MR compression system 316 before compression in the second stage is an optional feature and can be utilized in combination with other features or completely Do not use. In addition, the mixed refrigerant used in the pre-cooling system and the liquefaction system may have the same or different compositions.

In addition, it should be noted that the MR pre-cooling system illustrated at 262 in FIG. 3 is only an example of a suitable MR system-other MR systems and non-mixed refrigerant systems known in the art may alternatively be used as the pre-cooling system .

Except for the configuration of the pre-cooling heat exchanger, the embodiment of the system illustrated in FIG. 4 is essentially the same as the embodiment of FIG. 1, including a propane pre-cooling system indicated generally at 370. More specifically, in the embodiment of the system illustrated in FIG. 4, the pre-cooling system 370 includes a pre-cooling warm heat exchanger generally indicated at 372a and a pre-cooling cold heat exchanger generally indicated at 372b. As just one example, the warm heat exchanger 372a and the cold heat exchanger 372b may be CORE-IN-KETTLE heat exchangers available from Chart Energy & Chemicals, Inc. of The Woodlands, Texas. Alternative types of heat exchangers that can be used include, but are not limited to, shell and tube or thermosyphon type heat exchangers.

In the embodiment of FIG. 4, the core 374 (just as an example, the core may be a brazed aluminum heat exchanger (BAHX) or other heat exchanger types such as microchannels or welded plates, etc.) The shells 378 and 382 of the exchanger 372a and the cold heat exchanger 372b extend through the inner head 376, so that the processing flow is continuous through the core 374, and the processing flow is the first from the liquefied MR compressor system 386. The discharge stream 384 of the second compression and cooling stage. The advantage of this configuration is that the cooled and partially condensed process streams are not affected by the uneven distribution of the two-phase flow, which adversely affects the system performance, as can be piped in series in the heat exchanger design The case of multiple cores is encountered, as shown in Figure 1. The configuration of FIG. 4 reduces the power consumption of the treatment (propane system or liquefaction system or both) caused by uneven distribution, or simplifies the equipment count and reduces the cost to eliminate the uneven distribution effect.

It should be noted that the warm heat exchanger 372a and the cold heat exchanger 372b can utilize any shape of the inner head 376, including flat plates. In addition, although Figure 4 shows a propane (C3) pre-cooling MR process, the embodiment of Figure 4 can be used with any process that utilizes at least two boiling refrigerant cooling steps. In addition, although propane (C3) is described as the coolant used in the pre-cooling system of FIG. 4, any refrigerant may be used, such as but not limited to butane, ammonia, or liquid fluorinated hydrocarbons. In addition, although the system of FIG. 4 shows two stages of pre-cooling, two or more stages of cooling may be used. In addition, although FIG. 4 shows a separate feed exchanger, the feed exchanger may be combined with an MR exchanger.

In the embodiment illustrated in FIG. 5, the cold water cooling system indicated generally at 402 is used to pre-cool the discharge stream 404 from the second compression and cooling stage of the liquefied MR compressor system 406. More specifically, water is pumped to the coolant heat exchanger 414 by the pump 412. The heat exchanger also receives the MR exhaust stream 404 and cools the MR exhaust stream. Chilled water is water or water/glycol mixture cooled in a pre-cooling refrigerant system that can be but not limited to mechanical coolers or adsorption coolers or thermoelectric coolers or thermoacoustic coolers, and is always better than the air that can pass through Cooling or water evaporative cooling achieves colder temperatures.

The cooled MR stream 416 then flows to the high pressure accumulator 124, where the resulting liquid and vapor stream is directed to the liquefaction heat exchanger 420 of the MR liquefaction system 408, as in the previous embodiment.

Although a single chiller heat exchanger 414 is illustrated in FIG. 5, multiple chiller heat exchangers in parallel or in series may be used instead.

As in the previous embodiment, the liquefied MR compressor system provides refrigerant to the MR liquefaction system 408, which includes a cold vapor separator (CVS) 410. The combination of pre-cooling and cold water cooling systems and MR and CVS results in a more efficient process and lower equipment costs than pre-cooling without CVS and also promotes higher equipment yields. The combination of pre-cooling and CVS allows the cold water cooling system to operate at significantly warmer temperatures, generally -5°C versus -35°C to -40°C. It also allows the chiller equipment to be located away from the hydrocarbon-containing equipment, which reduces system costs and provides area planning flexibility. The treatment can be used with any MR liquefaction treatment using CVS.

Although FIG. 5 shows a cold water pre-cooling MR process, any refrigerated cooling fluid can be used, such as, but not limited to, ammonia, water, water glycol mixture, lithium bromide solution, liquid fluorinated hydrocarbon, liquid hydrocarbon, and the like. In addition, although FIG. 5 shows a shell and tube heat exchanger for the pre-cooling system heat exchanger 414, any heat exchanger type may be used. In addition, although FIG. 5 shows separate warm-temperature riser 422, medium-temperature riser 424, and cold-temperature riser 426, any of these risers can be combined, or in some cases, the riser can be eliminated. tube. Although not explicitly shown, the cold water cooling system can also be used to cool the feed gas and/or to cool the first-stage emissions as shown in Figure 2 or to provide cooling or cooling of the turbine inlet air for the gas turbine drive. A liquefaction system.

There are several aspects of the subject matter that can be embodied separately or together in the methods, devices, and systems described and required below. These aspects can be used alone or in combination with other aspects of the subject matter described herein, and the description of these aspects together is not intended to exclude the use of these aspects alone or these aspects alone or in different ways as set forth in the appended claims herein. Combination requirements.

Although the preferred embodiments of the present invention have been shown and described, it will be obvious to those skilled in the art that changes and modifications can be made in the present invention without departing from the spirit of the present invention, and the scope of the present invention is defined by the appended The scope of patent application is limited.

8‧‧‧Mixed refrigerant liquefaction system

10‧‧‧Heat exchanger

12‧‧‧Warm End

14‧‧‧Cold End

16‧‧‧Pre-cooled natural gas feed stream

18‧‧‧Liquefaction Channel

20‧‧‧Liquid natural gas (LNG) product stream

22‧‧‧Mixed refrigerant compressor system

24, 46‧‧‧First stage suction drum

26‧‧‧Mixed refrigerant vapor flow

27‧‧‧Steam mixed refrigerant flow

28‧‧‧Primary refrigeration channel

32‧‧‧First-stage compressor

34、38‧‧‧Cooler

35、88‧‧‧Second stage suction drum

36‧‧‧Second-stage compressor

40‧‧‧Pre-cooling system

42a‧‧‧Pre-cooling and warming heat exchanger

42b‧‧‧Pre-cooling cold heat exchanger

44‧‧‧Pre-cooling compressor system

48‧‧‧Propane refrigerant vapor flow

52‧‧‧The steam flow of the first stage suction drum

54‧‧‧Pre-cooling compressor

56‧‧‧Pre-cooling condenser

62‧‧‧Pre-cooling refrigerant accumulator

64‧‧‧Propane refrigerant liquid flow

66、94、144、174‧‧‧Expansion device

72, 96‧‧‧Two-phase flow

74‧‧‧Shell

76‧‧‧Liquid level sensor

78, 104, 114, 118‧‧‧Core

82, 84, 84’‧‧‧Natural gas feed stream

86‧‧‧Warm propane refrigerant vapor flow

92‧‧‧Propane refrigerant liquid stream

102‧‧‧Liquid level sensor

112‧‧‧High-pressure mixed refrigerant flow

116‧‧‧Mixed refrigerant flow

122‧‧‧Mixed refrigerant (MR) mixed phase flow

124‧‧‧High pressure accumulator

125‧‧‧High pressure liquid cooling channel

126‧‧‧High pressure vapor refrigerant flow

127‧‧‧Steam flow

128‧‧‧High pressure liquid refrigerant flow

129、162‧‧‧Flash

131‧‧‧Warm temperature separator

132‧‧‧Mixed phase cold separator feed stream

133、142‧‧‧Liquid flow

134‧‧‧Cold steam separator

135‧‧‧High pressure steam cooling channel

136‧‧‧Cold separator steam flow

138‧‧‧cold separator liquid flow

141‧‧‧Cold separator steam cooling channel

143‧‧‧Cool separator liquid cooling channel

146‧‧‧Cold and warm separator

152‧‧‧cold and warm liquid flow

154‧‧‧Cold and warm steam flow

160‧‧‧Subcooled cold separator liquid

164‧‧‧Medium temperature separator

166‧‧‧The resulting liquid stream

168‧‧‧obtained steam flow

172‧‧‧Liquefied natural gas stream

Claims (17)

A system for cooling gas using a pre-cooling refrigerant and a mixed refrigerant, the system comprising: a) a pre-cooling heat exchanger, which has a feed gas inlet and a feed gas outlet suitable for receiving a feed gas stream, and a pre-cooling Cooling refrigerant inlet and pre-cooling refrigerant outlet, and liquefied mixed refrigerant inlet and liquefied mixed refrigerant outlet, the pre-cooling heat exchanger is configured to use the pre-cooling refrigerant to cool the feed gas inlet and The feed gas passes through the pre-cooling heat exchanger between the feed gas outlets, and is cooled through the pre-cooling heat exchange between the liquefied mixed refrigerant inlet and the liquefied mixed refrigerant outlet B) a pre-cooling compressor system, which includes: i) a pre-cooling compressor, which has an inlet in fluid communication with the pre-cooling refrigerant outlet of the pre-cooling heat exchanger; ii) A pre-cooling condenser having an inlet in fluid communication with the outlet of the pre-cooling compressor, the pre-cooling condenser also having an outlet in fluid communication with the pre-cooling refrigerant inlet of the pre-cooling heat exchanger; c) A liquefaction heat exchanger, which includes a liquefaction channel in fluid communication with the feed gas outlet of the pre-cooling heat exchanger, a primary refrigeration channel, a high-pressure steam cooling channel, and a cold separator steam cooling channel, wherein the cold The separator vapor cooling passage has an outlet in fluid communication with the primary refrigeration passage; d) a mixed refrigerant compression system, which includes: i) a mixed refrigerant compressor, which has an inlet in fluid communication with the outlet of the primary refrigeration passage ； ii) A mixed refrigerant cooler having an inlet in fluid communication with the outlet of the mixed refrigerant compressor, the mixed refrigerant cooler having an inlet fluid with the liquefied mixed refrigerant of the pre-cooling heat exchanger A communicating outlet, iii) a high-pressure accumulator having an inlet fluidly communicating with the liquefied mixed refrigerant outlet of the pre-cooling heat exchanger and an inlet fluid of the high-pressure vapor cooling channel of the liquefaction heat exchanger Connected steam outlet; e) a cold steam separator having an inlet fluidly connected to the outlet of the high-pressure steam cooling channel of the liquefaction heat exchanger, and an inlet that is in fluid communication with the cold separator steam cooling channel of the liquefaction heat exchanger The steam outlet in fluid communication with the inlet and the liquid outlet in communication with the primary refrigeration passage of the liquefaction heat exchanger, wherein the pre-cooling heat exchanger includes a warm pre-cooling heat exchanger and a cold pre-cooling heat exchanger, wherein Each of the warm pre-cooling heat exchanger and the cold pre-cooling heat exchanger includes a housing that receives the pre-cooling refrigerant, and the warm pre-cooling heat exchanger and the cold pre-cooling heat exchanger At least one of them includes a feed gas core that receives the feed gas. The system according to claim 1, wherein each of the warm pre-cooling heat exchanger and the cold pre-cooling heat exchanger includes a liquefied mixed refrigerant core, the liquefied mixed refrigerant core It is configured to cool the liquefied mixed refrigerant passing through the pre-cooling heat exchanger between the liquefied mixed refrigerant inlet and the liquefied mixed refrigerant outlet. The system described in the first item of the patent application, wherein a single liquefied mixed refrigerant core extends within the shell of both the warm pre-cooling heat exchanger and the cold pre-cooling heat exchanger, and is configured To cool the liquefied mixed refrigerant passing through the pre-cooling heat exchanger between the liquefied mixed refrigerant inlet and the liquefied mixed refrigerant outlet. The system according to claim 1, wherein the inner head extends between the inner space of the housing of the warm pre-cooling heat exchanger and the cold pre-cooling heat exchanger, and the single The liquefied mixed refrigerant core extends through the inner head. The system according to claim 1, wherein the mixed refrigerant compression system further includes a mixed refrigerant second compressor or compression stage having an inlet in fluid communication with the outlet of the mixed refrigerant cooler , A second mixed refrigerant cooler having an inlet in fluid communication with the outlet of the mixed refrigerant second compressor or compression stage, the second cooler having the liquefaction mixing with the pre-cooling heat exchanger The refrigerant inlet is in fluid communication with the outlet. The system according to the fifth item of the scope of patent application, wherein the pre-cooling heat exchanger includes an inter-stage mixed refrigerant inlet and an inter-stage mixed refrigerant outlet, and wherein the mixed refrigerant cooler has the same type as the pre-cooling The inter-stage mixed refrigerant inlet of the heat exchanger is in fluid communication with an outlet, and the inter-stage mixed refrigerant outlet of the pre-cooling heat exchanger is in fluid communication with an inter-stage accumulator, the inter-stage accumulator having and A vapor outlet in fluid communication with the inlet of the second compressor or second compression stage and a liquid outlet in fluid communication with the primary refrigeration passage of the liquefaction heat exchanger. The system according to claim 1, wherein the high-pressure accumulator includes a liquid outlet, and the liquefaction heat exchanger further includes a high-pressure liquid cooling channel, the high-pressure liquid cooling channel having a connection with the high-pressure accumulator An inlet in fluid communication with the liquid outlet and an outlet in fluid communication with the primary refrigeration passage of the liquefaction heat exchanger. The system described in item 1 of the scope of patent application, wherein the pre-cooling refrigerant is propane, butane, ammonia or chlorofluorocarbon. The system described in item 1 of the scope of patent application, wherein the pre-cooling refrigerant is a mixed refrigerant. In the system described in item 9 of the scope of patent application, the pre-cooling heat exchanger is a plate-fin heat exchanger. A method for cooling a feed gas stream, the method comprising the following steps: a) using a first refrigerant to pre-cool the feed gas stream in a pre-cooling heat exchanger to form a pre-cooled feed gas stream; b) Further cooling the pre-cooled feed gas stream by the following operations: i) cooling the high-pressure second refrigerant stream in the pre-cooling heat exchanger to form a cooled high-pressure second refrigerant stream; ii) separating the cooled high-pressure second refrigerant stream to form a high-pressure vapor stream and a high-pressure liquid Iii) cooling the high-pressure steam stream in a liquefaction heat exchanger to form a mixed-phase stream; iv) separating the mixed-phase stream with a cold steam separator to form a cold separator vapor stream and a cold separator liquid stream; v) Use the second refrigerant to condense and flash vaporize the cold separator vapor stream in the liquefaction heat exchanger to form a cold-temperature refrigerant stream; vi) direct the cold-temperature refrigerant stream to The liquefaction heat exchanger; vii) making the high-pressure liquid flow subcooled to form a subcooled high-pressure liquid flow and combining with the cold-temperature refrigerant flow in the liquefaction heat exchanger; vii) making the cold The separator liquid flow is subcooled to form a subcooled cold separator liquid flow and combined with the cold and warm refrigerant flow in the liquefaction heat exchanger; and ix) making the preheating in the liquefaction heat exchanger The cooled gas stream is in thermal contact with the cold and warm refrigerant stream, wherein the high pressure liquid stream and the cold separator liquid stream are subcooled in the liquefaction heat exchanger. The method described in item 11 of the scope of the patent application, wherein step b) further comprises the following steps: cooling the low-pressure mixed refrigerant stream in the pre-cooling heat exchanger, and separating the cooled low-pressure mixed refrigerant stream to A low-pressure mixed refrigerant vapor stream and a low-pressure mixed refrigerant liquid stream are formed, the low-pressure mixed refrigerant vapor stream is compressed to form a high-pressure mixed refrigerant stream, and then the high-pressure mixed refrigerant stream is cooled to form the cooled high-pressure mixed refrigerant And direct the low-pressure mixed refrigerant liquid flow to the liquefaction heat exchanger. The method according to claim 12, wherein the high-pressure mixed refrigerant stream is cooled in the pre-cooling heat exchanger to form the cooled high-pressure mixed refrigerant stream. The method according to claim 12, wherein the high-pressure mixed refrigerant stream is cooled in both the pre-cooling heat exchanger and the liquefaction heat exchanger to form the cooled high-pressure mixed refrigerant stream . The method according to item 11 of the scope of patent application, wherein the first refrigerant is propane, butane, ammonia or chlorofluorocarbon. The method described in item 11 of the scope of patent application, wherein the first refrigerant is a mixed refrigerant. The method described in item 11 of the scope of patent application, wherein step a) includes a first pre-cooling stage using a warm pre-cooling heat exchanger and a second pre-cooling stage using a cold pre-cooling heat exchanger.

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