Mixed refrigerant system and method

Abstract

Provided are mixed refrigerant systems and methods and, more particularly, to a mixed refrigerant system and methods that provides greater efficiency and reduced power consumption.

Claims

1. A system for cooling a feed fluid with a mixed refrigerant comprising: a. a main heat exchanger including a warm end and a cold end with a feed fluid cooling passage extending therebetween, the feed fluid cooling passage being configured to receive a feed fluid at the warm end and to convey a cooled feed fluid out of the cold end, said main heat exchanger also including a high pressure vapor passage, a high pressure liquid passage, a cold separator vapor cooling passage, a cold separator liquid cooling passage and a primary refrigeration passage; b. a mixed refrigerant compressor system including: i) a compressor configured to receive a vapor phase or mixed phase refrigerant return stream from the primary refrigeration passage of the heat exchanger; ii) an aftercooler configured to receive a compressed refrigerant stream from the compressor, said aftercooler having an aftercooler outlet; and iii) a high pressure separation device having an inlet in fluid communication with the aftercooler outlet and a high pressure liquid outlet and a high pressure vapor outlet; c. said high pressure vapor passage of the heat exchanger configured to receive a high pressure vapor stream from the high pressure vapor outlet of the high pressure separation device and to cool the high pressure vapor stream to form a mixed phase stream; d. a cold vapor separator configured to receive the mixed phase stream from the high pressure vapor passage of the heat exchanger, said cold vapor separator having a cold separator liquid outlet and a cold separator vapor outlet; e. said cold separator vapor cooling passage of the heat exchanger configured to receive and condense a cold separator vapor stream from the vapor outlet of the cold vapor separator so that a condensed cold separator stream is formed; f. a first expansion device configured to receive and expand the condensed cold separator stream from the cold separator vapor cooling passage of the heat exchanger so that a cold temperature refrigerant stream is formed; g. said high pressure liquid passage of the heat exchanger having a first heat exchange passage length and configured to receive and subcool at least a portion of a mid-boiling refrigerant liquid stream from the high pressure liquid outlet of the high pressure separation device so that a subcooled mid-boiling refrigerant liquid stream is formed; h. said cold separator liquid cooling passage of the heat exchanger having a second heat exchange passage length, wherein the first heat exchange passage is separate and distinct from the second heat exchange passage and the first heat exchange passage length is greater than the second heat exchange passage length, said cold separator liquid cooling passage configured to receive and subcool a cold separator liquid stream from the cold separator liquid outlet so that a subcooled cold separator liquid stream is formed; i. a junction configured to combine the subcooled mid-boiling refrigerant liquid stream and the subcooled cold separator liquid stream while the subcooled mid-boiling refrigerant liquid stream is at, or colder via expansion than, the temperature of the subcooled mid-boiling refrigerant liquid stream in the subcooled state and the subcooled cold separator liquid stream is at, or colder via expansion than, the temperature of the subcooled cold separator liquid stream in the subcooled state so that a middle temperature refrigerant stream is formed; and j. said primary refrigeration passage of the heat exchanger configured to receive the cold temperature refrigerant stream from the first expansion device and the middle temperature stream from the junction and to thermally contact a feed fluid in the feed fluid cooling passage of the heat exchanger to form a cooled feed fluid in the feed fluid cooling passage and a vapor phase or mixed phase refrigerant return stream in the primary refrigeration passage.

2. The system of claim 1 wherein the junction includes a second expansion device configured to receive and expand the subcooled cold separator liquid stream from the cold separator liquid cooling passage of the heat exchanger and a third expansion device configured to receive and expand the subcooled mid-boiling refrigerant liquid stream from the high pressure liquid passage of the heat exchanger so that the subcooled cold separator liquid stream and the subcooled mid-boiling refrigerant liquid stream are combined while the subcooled cold separator liquid stream is colder via expansion than the temperature of the subcooled cold separator liquid stream in the subcooled state and the subcooled mid-boiling refrigerant liquid stream is colder via expansion than the temperature of the subcooled mid-boiling refrigerant liquid stream in the subcooled state.

3. The system of claim 2 further wherein the junction includes a junction accumulator separation device configured to receive and combine the expanded subcooled cold separator liquid stream and the expanded subcooled mid-boiling refrigerant liquid stream, said junction accumulator separation device having a vapor outlet and a fluid outlet in fluid communication with the primary refrigeration passage.

4. The system of claim 1 wherein the junction is configured to combine the subcooled cold separator liquid stream from the cold separator liquid cooling passage of the heat exchanger and the subcooled mid-boiling refrigerant liquid stream from the high pressure liquid passage of the heat exchanger so that a combined subcooled cold separator liquid and mid-boiling refrigerant liquid stream is formed and further comprising a fourth expansion device configured to receive and expand the combined subcooled cold separator liquid and mid-boiling refrigerant liquid stream so that the subcooled cold separator liquid stream and the subcooled mid-boiling refrigerant liquid stream are combined while the subcooled cold separator liquid stream is at the temperature of the subcooled cold separator liquid stream in the subcooled state and the subcooled mid-boiling refrigerant liquid stream is at the temperature of the subcooled mid-boiling refrigerant liquid stream in the subcooled state.

5. The system of claim 1 wherein the mixed refrigerant compression system further includes: iv) an interstage separation device configured to receive cooled fluid from the aftercooler, said interstage separation device including a vapor outlet; v) a second stage compressor configured to receive a vapor stream from the vapor outlet of the interstage separation device; vi) a second stage aftercooler having an inlet configured to receive a compressed vapor stream from the second stage compressor and an outlet in fluid communication with the inlet of the high pressure accumulator.

6. The system of claim 5 wherein the interstage separation device includes a liquid outlet and the heat exchanger includes a pre-cool liquid passage and a pre-cool refrigeration passage, where the pre-cool liquid passage is configured to receive a high-boiling liquid stream from the liquid outlet of the interstage separation device and further comprising: k. a pre-cool expansion device configured to received and flash a subcooled high-boiling liquid stream from the pre-cool liquid passage of the heat exchanger and direct a flashed fluid stream to the pre-cool refrigeration passage of the heat exchanger.

7. The system of claim 6 wherein the primary refrigeration passage includes the pre-cool refrigeration passage.

8. The system of claim 6 further comprising a splitting intersection and an interstage expansion device, said splitting intersection configured to receive the mid-boiling refrigerant liquid stream from the high pressure liquid outlet of the high pressure separation device and direct a first portion of the mid-boiling refrigerant liquid stream to the high pressure liquid passage of the heat exchanger and a second portion of the mid-boiling refrigerant liquid stream to the interstage expansion device so that an expanded cooled interstage fluid stream is formed and said interstage expansion device configured to direct the expanded cooled interstage fluid stream to the interstage separation device.

9. The system of claim 6 further comprising a return passage in fluid communication with an outlet of the primary refrigeration passage and an outlet of the pre-cool refrigeration passage, said return passage having an outlet in fluid communication with an inlet of the compressor of the mixed refrigerant compressor system.

10. The system of claim 6 further comprising a header outside of the heat exchanger in fluid communication with an outlet of the primary refrigeration passage and an outlet of the pre-cool refrigeration passage and having an outlet in fluid communication with an inlet of the compressor of the mixed refrigerant compressor system.

11. The system of claim 6 wherein the compressor and the second stage compressor include a two-stage compressor.

12. The system of claim 5 wherein the compressor and the second stage compressor include a two-stage compressor.

13. The system of claim 1 wherein the inlet of said high pressure separation device is configured to receive a stream comprising two or more C1-C5 hydrocarbons and optionally N2.

14. The system of claim 1 further comprising a suction separation device having an inlet in fluid communication with the primary refrigeration passage of the heat exchanger and an outlet in fluid communication with an inlet of the compressor of the mixed refrigerant compressor system.

15. The system of claim 1 wherein the heat exchanger includes a single heat exchanger, one or more heat exchangers arranged in parallel, or one or more heat exchangers arranged in series, or a combination thereof.

16. The system of claim 1 wherein the mixed refrigerant includes two or more of methane, ethane, ethylene, propane, propylene, butane, N-butane, isobutane, butylenes, N-pentane, isopentane, and a combination thereof.

17. The system of claim 1 further comprising one or more of an external treatment, pre-treatment, post-treatment or integrated treatment system, or a combination thereof, independently in fluid communication with the feed fluid cooling passage and configured to treat the feed fluid.

18. The system of claim 17 wherein at least one of the external treatment, pre-treatment and post-treatment systems is configured to perform at least one process selected from the group consisting of desulfurizing, dewatering, removing CO.sub.2, removing one or more natural gas liquids (NGL), removing one or more freezing components, removing ethane, removing one or more olefins, removing one or more C6 hydrocarbons, removing one or more C6+ hydrocarbons and removing N.sub.2 from the feed fluid.

19. The system of claim 1 wherein the heat exchanger is a plate-fin heat exchanger.

20. The system of claim 1 wherein the feed fluid is a fluid from an acid gas distillation system and the cooled feed fluid is a reflux fluid stream and the feed fluid cooling passage of the heat exchanger is configured to direct the reflux fluid stream to a distillation column of the acid gas distillation system.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) FIG. 1 is a graphical representation of temperature-enthalpy curves for methane and a methane-ethane mixture.

(2) FIG. 2 is a process flow diagram and schematic illustrating an embodiment of a process and system of the invention.

(3) FIG. 3 is a process flow diagram and schematic illustrating a second embodiment of a process and system of the invention.

(4) FIG. 4 is a process flow diagram and schematic illustrating a third embodiment of a process and system of the invention.

(5) FIG. 5 is a process flow diagram and schematic illustrating a fourth embodiment of a process and system of the invention.

(6) FIG. 6 is a process flow diagram and schematic illustrating a fifth embodiment of a process and system of the invention.

(7) FIG. 7 is a process flow diagram and schematic illustrating a sixth embodiment of a process and system of the invention.

(8) FIG. 8 is a process flow diagram and schematic illustrating a seventh embodiment of a process and system of the invention.

(9) FIG. 9 is a process flow diagram and schematic illustrating an eighth embodiment of a process and system of the invention.

(10) FIG. 10 is a process flow diagram and schematic illustrating a ninth embodiment of a process and system of the invention.

(11) FIG. 11 is a process flow diagram and schematic illustrating a tenth embodiment of a process and system of the invention.

(12) FIG. 12 is a process flow diagram and schematic illustrating an eleventh embodiment of a process and system of the invention.

(13) FIG. 13 is a process flow diagram and schematic illustrating an embodiment of a process and system of the invention for providing mixed refrigerant cooling for an acid gas distillation process.

(14) FIGS. 14A-14E show stream data for several embodiments of the invention and correlate with FIG. 6.

(15) FIGS. 15A-15F show stream data for several embodiments of the invention and correlate with FIG. 7.

BRIEF SUMMARY

(16) There are several aspects of the present subject matter which may be embodied separately or together in the devices and systems described and claimed below. These aspects may be employed alone or in combination with other aspects of the subject matter described herein, and the description of these aspects together is not intended to preclude the use of these aspects separately or the claiming of such aspects separately or in different combinations as set forth in the claims appended hereto.

(17) In one aspect, a system for cooling a feed fluid with a mixed refrigerant includes a main heat exchanger including a warm end and a cold end with a feed fluid cooling passage extending therebetween, the feed fluid cooling passage being configured to receive a feed fluid at the warm end and to convey a cooled feed fluid out of the cold end. The main heat exchanger also includes a high pressure vapor passage, a high pressure liquid passage, a cold separator vapor cooling passage, a cold separator liquid cooling passage and a primary refrigeration passage. A mixed refrigerant compressor system includes a compressor configured to receive a vapor phase or mixed phase refrigerant return stream from the primary refrigeration passage of the heat exchanger, an aftercooler configured to receive a compressed refrigerant stream from the compressor and a high pressure separation device having an inlet in fluid communication with the aftercooler outlet and a high pressure liquid outlet and a high pressure vapor outlet. The high pressure vapor cooling passage of the heat exchanger is configured to receive a high pressure vapor stream from the high pressure vapor outlet of the high pressure separation device and to cool the high pressure vapor stream to form a mixed phase stream. A cold vapor separator is configured to receive the mixed phase stream from the high pressure vapor cooling passage of the heat exchanger and has a cold separator liquid outlet and a cold separator vapor outlet. The cold separator vapor cooling passage of the heat exchanger is configured to receive and condense a cold separator vapor stream from the vapor outlet of the cold vapor separator so that a condensed cold separator stream is formed. A first expansion device is configured to receive and expand the condensed cold separator stream from the cold separator vapor cooling passage of the heat exchanger so that a cold temperature refrigerant stream is formed. The high pressure liquid cooling passage of the heat exchanger has a first heat exchange passage length and is configured to receive and subcool at least a portion of a mid-boiling refrigerant liquid stream from the high pressure liquid outlet of the high pressure separation device so that a subcooled mid-boiling refrigerant liquid stream is formed. The cold separator liquid cooling passage of the heat exchanger has a second heat exchange passage length, where the first heat exchange passage is separate and distinct from the second heat exchange passage and the first heat exchange passage length is greater than the second heat exchange passage length. The cold separator liquid cooling passage is configured to receive and subcool a cold separator liquid stream from the cold separator liquid outlet so that a subcooled cold separator liquid stream is formed. A junction is configured to combine the subcooled mid-boiling refrigerant liquid stream and the subcooled cold separator liquid stream while the subcooled mid-boiling refrigerant liquid stream is at, or colder via expansion than, the temperature of the subcooled mid-boiling refrigerant liquid stream in the subcooled state and the subcooled cold separator liquid stream is at, or colder via expansion than, the temperature of the subcooled cold separator liquid stream in the subcooled state so that a middle temperature refrigerant stream is formed. The primary refrigeration passage of the heat exchanger is configured to receive the cold temperature refrigerant stream from the first expansion device and the middle temperature stream from the junction and to thermally contact a feed fluid in the feed fluid cooling passage of the heat exchanger to form a cooled feed fluid in the feed fluid cooling passage and a vapor phase or mixed phase refrigerant return stream in the primary refrigeration passage.

DESCRIPTION OF THE SEVERAL EMBODIMENTS

(18) A process flow diagram and schematic illustrating an embodiment of a multi-stream heat exchanger is provided in FIG. 2.

(19) As illustrated in FIG. 2, one embodiment includes a multi-stream heat exchanger 170, having a warm end 1 and a cold end 2. The heat exchanger receives a feed fluid stream, such as a high pressure natural gas feed stream that is cooled and/or liquefied in cooling passage 162 via removal of heat via heat exchange with refrigeration streams in the heat exchanger. As a result, a stream of product fluid such as liquid natural gas is produced. The multi-stream design of the heat exchanger allows for convenient and energy-efficient integration of several streams into a single exchanger. Suitable heat exchangers may be purchased from Chart Energy & Chemicals, Inc. of The Woodlands, Tex. The plate and fin multi-stream heat exchanger available from Chart Energy & Chemicals, Inc. offers the further advantage of being physically compact.

(20) In one embodiment, referring to FIG. 2, a feed fluid cooling passage 162 includes an inlet at the warm end 1 and a product outlet at the cold end 2 through which product exits the feed fluid cooling passage 162. A primary refrigeration passage 104 (or 204—see FIG. 3) has an inlet at the cold end for receiving a cold temperature refrigerant stream 122, a refrigerant return stream outlet at the warm end through which a vapor phase refrigerant return stream 104A exits the primary refrigeration passage 104, and an inlet adapted to receive a middle temperature refrigerant stream 148. In the heat exchanger, at the latter inlet, the primary refrigeration passage 104/204 is joined by the middle temperature refrigerant passage 148, where the cold temperature refrigerant stream 122 and the middle temperature refrigerant stream 148 combine. In one embodiment, the combination of the middle temperature refrigerant stream and the cold temperature refrigerant stream forms a middle temperature zone in the heat exchanger generally from the point at which they combine and downstream from there in the direction of the refrigerant flow toward the primary refrigerant outlet.

(21) It should be noted herein that the passages and streams are sometimes both referred to by the same element number set out in the figures. Also, as used herein, and as known in the art, a heat exchanger is that device or an area in the device wherein indirect heat exchange occurs between two or more streams at different temperatures, or between a stream and the environment. As used herein, the terms “communication”, “communicating”, and the like generally refer to fluid communication unless otherwise specified. And although two fluids in communication may exchange heat upon mixing, such an exchange would not be considered to be the same as heat exchange in a heat exchanger, although such an exchange can take place in a heat exchanger. A heat exchange system can include those items though not specifically described are generally known in the art to be part of a heat exchanger, such as expansion devices, flash valves, and the like. As used herein, the term “reducing the pressure of” does not involve a phase change, while the term, “flashing”, does involve a phase change, including even a partial phase change. As used herein, the terms, “high”, “middle”, “warm” and the like are relative to comparable streams, as is customary in the art. The stream tables of FIGS. 14A-14E and 15A-15F set out exemplary values as guidance, which are not intended to be limiting unless otherwise specified.

(22) In an embodiment, the heat exchanger includes a high pressure vapor passage 166 adapted to receive a high pressure vapor stream 34 at the warm end and to cool the high pressure vapor stream 34 to form a mixed phase cold separator feed stream 164, and including an outlet in communication with a cold vapor separator VD4, the cold vapor separator VD4 adapted to separate the cold separator feed stream 164 into a cold separator vapor stream 160 and a cold separator liquid stream 156. In one embodiment, the high pressure vapor 34 is received from a high pressure accumulator separation device on the compression side.

(23) In an embodiment, the heat exchanger includes a cold separator vapor passage having an inlet in communication with the cold vapor separator VD4. The cold separator vapor is cooled passage 168 condensed into liquid stream 112, and then flashed with 114 to form the cold temperature refrigerant stream 122. The cold temperature refrigerant 122 then enters the primary refrigeration passage at the cold end thereof. In one embodiment, the cold temperature refrigerant is a mixed phase.

(24) In an embodiment, the cold separator liquid 156 is cooled in passage 157 to form subcooled cold vapor separator liquid 128. This stream can join the subcooled mid-boiling refrigerant liquid 124, discussed below, which, thus combined, are then flashed at 144 to form the middle temperature refrigerant 148, such as shown in FIG. 2. In one embodiment, the middle temperature refrigerant is a mixed phase.

(25) In an embodiment, the heat exchanger includes a high pressure liquid passage 136. In one embodiment, the high pressure liquid passage receives a high pressure liquid 38 from a high pressure accumulator separation device on the compression side. In one embodiment, the high pressure liquid 38 is a mid-boiling refrigerant liquid stream. The high pressure liquid stream enters the warm end and is cooled to form a subcooled refrigerant liquid stream 124. As noted above, the subcooled cold separator liquid stream 128 is combined with the subcooled refrigerant liquid stream 124 to form a middle temperature refrigerant stream 148. In an embodiment, the one or both refrigerant liquids 124 and 128 can independently be flashed at 126 and 130 before combining into the middle temperature refrigerant 148, as shown for example in FIG. 4.

(26) In an embodiment, the cold temperature refrigerant 122 and middle temperature refrigerant 148, thus combined, provide refrigeration in the primary refrigeration passage 104, where they exit as a vapor phase or mixed phase refrigerant return stream 104A/102. In an embodiment, they exit as a vapor phase refrigerant return stream 104A/102. In one embodiment, the vapor is a superheated vapor refrigerant return stream.

(27) As shown in FIG. 2, the heat exchanger may also include a pre-cool passage adapted to receive a high-boiling refrigerant liquid stream 48 at the warm end. In one embodiment, the high-boiling refrigerant liquid stream 48 is provided by an interstage separation device between compressors on the compression side. The high-boiling liquid refrigerant stream 48 is cooled in pre-cool liquid passage 138 to form subcooled high-boiling liquid refrigerant 140. The subcooled high-boiling liquid refrigerant 140 is then flashed or has its pressure reduced at expansion device 142 to form the warm temperature refrigerant stream 158, which may be a mixed vapor liquid phase or liquid phase.

(28) In an embodiment, the warm temperature refrigerant stream 158 enters the pre-cool refrigerant passage 108 to provide cooling. In an embodiment, the pre-cool refrigerant passage 108 provides substantial cooling for the high pressure vapor passage 166, for example, to cool and condense the high pressure vapor 34 into the mixed phase cold separator feed stream 164.

(29) In an embodiment, the warm temperature refrigerant stream exits the pre-cool refrigeration passage 108 as a vapor phase or mixed phase warm temperature refrigerant return stream 108A. In an embodiment, the warm temperature refrigerant return stream 108A returns to the compression side either alone—such as shown in FIG. 8, or in combination with the refrigerant return stream 104A to form return stream 102. If combined, the return streams 108A and 104A can be combined with a mixing device. Examples of non-limiting mixing devices include but are not limited to static mixer, pipe segment, header of the heat exchanger, or combination thereof.

(30) In an embodiment, the warm temperature refrigerant stream 158, rather than entering the pre-cool refrigerant passage 108, instead is introduced to the primary refrigerant passage 204, such as shown in FIG. 3. The primary refrigerant passage 204 includes an inlet downstream from the point where the middle temperature refrigerant 148 enters the primary refrigerant passage but upstream of the outlet for the return refrigerant stream 202. The cold temperature refrigerant stream 122, which was previously combined with the middle temperature refrigerant stream 148, and the warm temperature refrigerant stream 158 combine to provide warm temperature refrigeration in the corresponding area, e.g., between the refrigerant return stream outlet and the point of introduction of the warm temperature refrigerant 158 in the primary refrigeration passage 204. An example of this is shown in the heat exchanger 270 at FIG. 3. The combined refrigerants 122, 148, and 158 exit as a combined return refrigerant stream 202, which may be a mixed phase or a vapor phase. In an embodiment, the refrigerant return stream from the primary refrigeration passage 204 is a vapor phase return stream 202.

(31) FIG. 5, like FIG. 4 discussed above, shows alternate arrangements for combining the subcooled cold separator liquid stream 128 and subcooled refrigerant liquid stream 124 to form the middle temperature refrigerant stream 148. In an embodiment, the one or both refrigerant liquids 124 and 128 can independently be flashed at 126 and 130 before combining into the middle temperature refrigerant 148.

(32) Referring to FIGS. 6 and 7, in which embodiments of a compression system, generally referenced as 172, are shown in combination with a heat exchanger, exemplified by 170. In an embodiment, the compression system is suitable for circulating a mixed refrigerant in a heat exchanger. Shown is a suction separation device VD1 having an inlet for receiving a low return refrigerant stream 102 (or 202, although not shown) and a vapor outlet and a vapor outlet 14. A compressor 16 is in fluid communication with the vapor outlet 14 and includes a compressed fluid outlet for providing a compressed fluid stream 18. An optional aftercooler 20 is shown for cooling the compressed fluid stream 18. If present, the aftercooler 20 provides a cooled fluid stream 22 to an interstage separation device VD2. The interstage separation device VD2 has a vapor outlet for providing a vapor stream 24 to the second stage compressor 26 and also a liquid outlet for providing a liquid stream 48 to the heat exchanger. In one embodiment the liquid stream 48 is a high-boiling refrigerant liquid stream.

(33) Vapor stream 24 is provided to the compressor 26 via an inlet in communication with the interstage separation device VD2, which compresses the vapor 24 to provide compressed fluid stream 28. An optional aftercooler 30 if present cools the compressed fluid stream 28 to provide an a high pressure mixed phase stream 32 to the accumulator separation device VD3. The accumulator separation device VD3 separates the high pressure mixed phase stream 32 into high pressure vapor stream 34 and a high pressure liquid stream 36, which may be a mid-boiling refrigerant liquid stream. In an embodiment, the high pressure vapor stream 34 is sent to the high pressure vapor passage of the heat exchanger.

(34) An optional splitting intersection is shown, which has an inlet for receiving the mid-high pressure liquid stream 36 from the accumulator separation device VD3, an outlet for providing a mid-boiling refrigerant liquid stream 38 to the heat exchanger, and optionally an outlet for providing a fluid stream 40 back to the interstage separation device VD2. An optional expansion device 42 for stream 40 is shown which, if present provides a an expanded cooled fluid stream 44 to the interstage separation device, the interstage separation device VD2 optionally further comprising an inlet for receiving the fluid stream 44. If the splitting intersection is not present, then the mid-boiling refrigerant liquid stream 36 is in direct fluid communication with mid-boiling refrigerant liquid stream 38.

(35) FIG. 7 further includes an optional pump P, for pumping low pressure liquid refrigerant stream 14l, the temperature of which in one embodiment has been lowered by the flash cooling effect of mixing 108A and 104A before suction separation device VD1 for pumping forward to intermediate pressure. As described above, the outlet stream 18l from the pump travels to the interstage drum VD2.

(36) FIG. 8 shows an example of different refrigerant return streams returning to suction separation device VD1. FIG. 9 shows several embodiments including feed fluid outlets and inlets 162A and 162B for external feed treatment, such as natural gas liquids recovery or nitrogen rejection, or the like.

(37) Furthermore, while the present system and method are described below in terms of liquefaction of natural gas, they may be used for the cooling, liquefaction and/or processing of gases other than natural gas including, but not limited to, air or nitrogen.

(38) The removal of heat is accomplished in the heat exchanger using a single mixed refrigerant in the systems described herein. Exemplary refrigerant compositions, conditions and flows of the streams of the refrigeration portion of the system, as described below, which are not intended to be limiting, are presented in FIGS. 14A-14E and 15A-15F.

(39) In one embodiment, warm, high pressure, vapor refrigerant stream 34 is cooled, condensed and subcooled as it travels through high pressure vapor passage 166/168 of the heat exchanger 170. As a result, stream 112 exits the cold end of the heat exchanger 170. Stream 112 is flashed through expansion valve 114 and re-enters the heat exchanger as stream 122 to provide refrigeration as stream 104 traveling through primary refrigeration passage 104. As an alternative to the expansion valve 114, another type of expansion device could be used, including, but not limited to, a turbine or an orifice.

(40) Warm, high pressure liquid refrigerant stream 38 enters the heat exchanger 170 and is subcooled in high pressure liquid passage 136. The resulting stream 124 exits the heat exchanger and is flashed through expansion valve 126. As an alternative to the expansion valve 126, another type of expansion device could be used, including, but not limited to, a turbine or an orifice. Significantly, the resulting stream 132 rather than re-entering the heat exchanger 170 directly to join the primary refrigeration passage 104, first joins the subcooled cold separator vapor liquid 128 to form a middle temperature refrigerant stream 148. The middle temperature refrigerant stream 148 then re-enters the heat exchanger wherein it joins the low pressure mixed phase stream 122 in primary refrigeration passage 104. Thus combined, and warmed, the refrigerants exit the warm end of the heat exchanger 170 as vapor refrigerant return stream 104A, which may be optionally superheated.

(41) In one embodiment, vapor refrigerant return stream 104A and stream 108A which, may be mixed phase or vapor phase, may exit the warm end of the heat exchanger separately, e.g., each through a distinct outlet, or they may be combined within the heat exchanger and exit together, or they may exit the heat exchanger into a common header attached to the heat exchanger before returning to the suction separation device VD1. Alternatively, streams 104A and 108A may exit separately and remain so until combining in the suction separation device VD1, or they may, through vapor and mixed phase inlets, respectively, and are combined and equilibrated in the low pressure suction drum. While a suction drum VD1 is illustrated, alternative separation devices may be used, including, but not limited to, another type of vessel, a cyclonic separator, a distillation unit, a coalescing separator or mesh or vane type mist eliminator. As a result, a low pressure vapor refrigerant stream 14 exits the vapor outlet of drum VD1. As stated above, the stream 14 travels to the inlet of the first stage compressor 16. The blending of mixed phase stream 108A with stream 104A, which includes a vapor of greatly different composition, in the suction drum VD1 at the suction inlet of the compressor 16 creates a partial flash cooling effect that lowers the temperature of the vapor stream traveling to the compressor, and thus the compressor itself, and thus reduces the power required to operate it.

(42) In one embodiment, a pre-cool refrigerant loop enters the warm side of the heat exchanger 170 and exits with a significant liquid fraction. The partially liquid stream 108A is combined with spent refrigerant vapor from stream 104A for equilibration and separation in suction drum VD1, compression of the resultant vapor in compressor 16 and pumping of the resulting liquid by pump P. In the present case, equilibrium is achieved as soon as mixing occurs, i.e., in the header, static mixer, or the like. In one embodiment, the drum merely protects the compressor. The equilibrium in suction drum VD1 reduces the temperature of the stream entering the compressor 16, by both heat and mass transfer, thus reducing the power usage by the compressor.

(43) Other embodiments shown in FIG. 9 include various separation devices in the warm, middle, and cold refrigeration loops. In one embodiment, warm temperature refrigerant passage 158 is in fluid communication with a separation device.

(44) In one embodiment, the warm temperature refrigerant passage 158 is in fluid communication with an accumulator separation device VD5 having a vapor outlet in fluid communication with a warm temperature refrigerant vapor passage 158v and a liquid outlet in fluid communication with a warm temperature refrigerant liquid passage 158l.

(45) In one embodiment, the warm temperature refrigerant vapor and liquid passages 158v and 158l are in fluid communication with the low pressure high-boiling stream passage 108.

(46) In one embodiment, the warm temperature refrigerant vapor and liquid passages 158v and 158l are in fluid communication with each other either inside the heat exchanger or in a header outside the heat exchanger.

(47) In one embodiment, the flashed cold separator liquid stream passage 134 is in fluid communication with an accumulator separation device VD6 having a vapor outlet in fluid communication with a middle temperature refrigerant vapor passage 148v, and a liquid outlet in fluid communication with a middle temperature refrigerant liquid passage 148l.

(48) In one embodiment, the middle temperature refrigerant vapor and liquid passages 148v and 148l are in fluid communication with the low pressure mixed refrigerant passage 104.

(49) In one embodiment, the middle temperature refrigerant vapor and liquid passages 148v and 148l are in fluid communication with each other either inside the heat exchanger or in a header outside the heat exchanger.

(50) In one embodiment, the flashed mid-boiling refrigerant liquid stream passage 132 is in fluid communication with an accumulator separation device VD6 having a vapor outlet in fluid communication with a middle temperature refrigerant vapor passage 148v and a liquid outlet in fluid communication with a middle temperature refrigerant liquid passage 148l.

(51) In one embodiment, the middle temperature refrigerant vapor and liquid passages 148v and 148l are in fluid communication with the low pressure mixed refrigerant passage 104.

(52) In one embodiment, the middle temperature refrigerant vapor and liquid passages 148v and 148l are in fluid communication with each other either inside the heat exchanger or in a header outside the heat exchanger.

(53) In one embodiment, the flashed mid-boiling refrigerant liquid stream 132 and the flashed cold separator liquid stream 134 are in fluid communication with an accumulator separation device VD6 having a vapor outlet in fluid communication with a middle temperature refrigerant vapor passage 148v and a liquid outlet in fluid communication with a middle temperature refrigerant liquid passage 148l.

(54) In one embodiment, the middle temperature refrigerant vapor and liquid passages 148v and 148l are in fluid communication with the low pressure mixed refrigerant passage 104.

(55) In one embodiment, the middle temperature refrigerant vapor and liquid passages 148v and 148l are in fluid communication with each other either inside the heat exchanger or in a header outside the heat exchanger.

(56) In one embodiment, the flashed mid-boiling refrigerant liquid stream 132 and the flashed cold separator liquid stream 134 are in fluid communication with each other prior to fluidly communicating with the accumulator separation device VD6.

(57) In one embodiment, the low pressure mixed phase stream passage 122 is in fluid communication with an accumulator separation device VD7 having a vapor outlet in fluid communication with a cold temperature refrigerant vapor passage 122v, and a cold temperature liquid passage 122l.

(58) In one embodiment, the cold temperature refrigerant vapor passage 122v and a cold temperature liquid passage 122l are in fluid communication with the low pressure mixed refrigerant passage 104.

(59) In one embodiment, the cold temperature refrigerant vapor passage 122v and cold temperature liquid passage 122l are in fluid communication with each other either inside the heat exchanger or in a header outside the heat exchanger.

(60) In one embodiment, each of the warm temperature refrigerant passage 158, flashed cold separator liquid stream passage 134, low pressure mid-boiling refrigerant passage 132, low pressure mixed phase stream passage 122 is in fluid communication with a separation device.

(61) In one embodiment, one or more precooler may be present in series between elements 16 and VD2.

(62) In one embodiment, one or more precooler may be present in series between elements 30 and VD3.

(63) In one embodiment, a pump may be present between a liquid outlet of VD1 and the inlet of VD2. In some embodiments, a pump may be present between a liquid outlet of VD1 and having an outlet in fluid communication with elements 18 or 22.

(64) In one embodiment, the pre-cooler is a propane, ammonia, propylene, ethane, pre-cooler.

(65) In one embodiment, the pre-cooler features 1, 2, 3, or 4 multiple stages.

(66) In one embodiment, the mixed refrigerant comprises 2, 3, 4, or 5 C1-C5 hydrocarbons and optionally N2.

(67) In one embodiment, the suction separation device includes a liquid outlet and further comprising a pump having an inlet and an outlet, wherein the outlet of the suction separation device is in fluid communication with the inlet of the pump, and the outlet of the pump is in fluid communication with the outlet of the aftercooler.

(68) In one embodiment, the mixed refrigerant system a further comprising a pre-cooler in series between the outlet of the intercooler and the inlet of the interstage separation device and wherein the outlet of the pump is also in fluid communication with the pre-cooler.

(69) In one embodiment, the suction separation device is a heavy component refrigerant accumulator whereby vaporized refrigerant traveling to the inlet of the compressor is maintained generally at a dew point.

(70) In one embodiment, the high pressure accumulator is a drum.

(71) In one embodiment, an interstage drum is not present between the suction separation device and the accumulator separation device.

(72) In one embodiment, the first and second expansion devices are the only expansion devices in closed-loop communication with the main process heat exchanger.

(73) In one embodiment, an aftercooler is the only aftercooler present between the suction separation device and the accumulator separation device.

(74) In one embodiment, the heat exchanger does not have a separate outlet for a pre-cool refrigeration passage.

(75) In an alternative embodiment, described below with reference to FIG. 13, the technology of the disclosure may advantageously be used to provide cooling for an acid gas distillation process and system.

(76) A conventional cascade refrigeration layout for acid gas distillation units has several issues, including high operating power and a high equipment count. The latter leads to higher capital expenditures and a larger plot space requirement. When applying the technology of the disclosure as a refrigeration system for an acid gas distillation unit, the refrigeration equipment count is significantly reduced. The multiple pure component refrigeration loops with multiple compression stages associated with a cascade refrigeration layout are replaced with a single mixed refrigerant loop with preferably a two-stage compressor. The use of a mixed refrigerant system and associated brazed aluminum heat exchangers (BAHX) also allows for additional process heating and cooling loads from the acid gas distillation unit to be integrated with the refrigeration system. This results in a further reduction in the total equipment count, and the required refrigeration flow/duty. This provides a significant reduction in operating power, and a reduction in the size of the refrigerant compressor and associated equipment.

(77) An example of a cryogenic acid gas distillation system and process suitable for use with the technology of the disclosure is described in U.S. Pat. No. 9,945,605 to Pellegrini, issued Apr. 17, 2018, the contents of which is hereby incorporated by reference. The system and process disclosed by the Pellegrini '605 patent requires an external refrigeration source to generate the reflux for one or more distillation columns. This external refrigeration requirement can be met with a single mixed refrigerant system, such as the system indicated in general at 310 in FIG. 13.

(78) The mixed refrigerant system of FIG. 13 utilizes a two-stage centrifugal compressor, indicated in general at 312, forming a first stage compressor 314a and a second stage compressor 314b. Alternatively, independent compressors may be used to provide the first and second compressor stages. The first stage discharge and the second stage discharge are cooled by a first stage aftercooler 316a and a second stage aftercooler 316b, respectively. As an example only, the aftercoolers 316a and 316b may use air or water cooling (ambient cooling). The discharge of the first stage compressor 314a is de-superheated via ambient cooling in the first stage aftercooler 316a and then sent to an interstage separation device, such as second stage suction drum 318. The second stage suction drum 318 removes any potential liquids, and the vapor is sent to the second stage compressor 314b. The discharge of the second stage compressor 314b is de-superheated and partially condensed via second stage aftercooler 316b. Optional additional condensing duty can be performed after ambient cooling using aftercooler 320 against process side cold loads.

(79) With continued reference to FIG. 13, the partially condensed mixed refrigerant flow is sent to a high pressure accumulator 322. The vapor stream 324 and liquid stream 326 from the high pressure accumulator are separately fed to different passes in a heat exchanger 332. In a preferred embodiment, heat exchanger 332 is a brazed aluminum heat exchanger (BAHX) positioned within a cold box 334 for additional cooling. The high pressure accumulator vapor is partially condensed in a high pressure vapor passage 336 of the heat exchanger and sent to a cold vapor separator 340. The vapor stream 342 and liquid stream 344 from the cold vapor separator 340 are separately fed back to the heat exchanger for additional cooling in a cold separator vapor passage 346 and a cold separator liquid passage 348, respectively.

(80) The cold vapor separator vapor stream 342 is condensed and subcooled in passage 346 and then is flashed across an expansion device 352, such as a Joules Thomson (T) valve. The resulting mixed phase refrigerant stream is directed to primary refrigeration passage 354.

(81) The liquid stream 344 from the cold vapor separator is subcooled in the cold separator liquid cooling passage, while the liquid stream 326 from the high pressure accumulator 322 is subcooled in a high pressure liquid passage 358. The resulting subcooled streams can independently be flashed via expansion devices at 362 and 364 before combining into the middle temperature refrigerant stream 366, which is directed to the primary refrigeration passage 354.

(82) The streams from passages 346, 348 and 358 exit the heat exchanger at appropriate locations based on the optimized amount of subcooling for each stream. The flashed mixed refrigerant streams are then fed back to the heat exchanger at the appropriate locations based on the stream temperatures. The flashing provides the temperature driving force/duty required for the acid gas distillation process cooling loads as well as the aforementioned cooling of fluid flowing in passages 346, 348 and 358.

(83) The use of a BAHX/Cold Box system allows for multiple process side heating and cooling loads, and mixed refrigerant heating and cooling loads to be integrated into a single heat exchanger service. This helps to minimize the refrigeration load as multiple variables of the mixed refrigerant system (suction pressure, mixed refrigerant composition, subcooling temperatures, etc.) can be adjusted to provide cooling at the exact temperature ranges required. Additionally, the high surface area to volume ratio of BAHX allows for a low mean temperature differential and minimum internal temperature approaches resulting in lower refrigerant flow/duty requirements.

(84) The net result is a compact refrigeration system, with a low refrigeration equipment count and equipment sizes relative to the process capacity. The number of exchanger services and expansion device locations, etc. of FIG. 13 can be adjusted to match the process requirements. While FIG. 13 shows two process side streams 370 and 372 for cooling process fluids for an acid gas distillation system, such as cooling feed fluid streams from the acid gas distillation system to generate reflux streams as the cooled feed fluid streams that are directed to the distillation columns of the Pellegrini '605 patent incorporated by reference above, the cold box can integrate significantly more process side streams if/when desirable. The system of FIG. 13 possesses the ability to integrate all of the acid gas distillation system and process cooling/heating loads with the mixed refrigerant in a heat exchanger (such as a BAHX) in order to improve the refrigeration efficiency, and reduce overall equipment count.

INCORPORATION BY REFERENCE

(85) The contents of U.S. Pat. No. 10,345,039 to Gushanas et al., issued Jul. 9, 2019; U.S. Pat. No. 9,441,877 to Gushanas et al., issued Sep. 13, 2016; U.S. Pat. No. 6,333,445 to O'Brien, issued Dec. 25, 2001, and U.S. Pat. No. 9,945,605 to Pellegrini, issued Apr. 17, 2018, are hereby incorporated by reference.

(86) While the preferred embodiments of the invention have been shown and described, it will be apparent to those skilled in the art that changes and modifications may be made therein without departing from the spirit of the invention, the scope of which is defined by the claims and elsewhere herein.