阅读说明：本技术 具有混合制冷剂冷却的脱氢分离装置 (Dehydrogenation separation device with mixed refrigerant cooling function ) 是由 D.A.小杜科特 B.A.海尔曼 T.P.古沙纳斯 R.霍普韦尔 于 2019-10-08 设计创作，主要内容包括：用于分离来自脱氢反应器的流出液流中的烯烃和氢气的系统,包括热交换器,该热交换器接收并部分地冷凝流出液流,从而形成混合相流出液流。初级分离装置接收并将混合相流出流分离成初级蒸汽流和初级液体产品流。热交换器接收并部分地冷凝初级蒸汽流,从而形成混合相初级流。二次分离装置接收混合相初级流并将该混合相初级流分离成二次蒸汽流和二次液体产品流。热交换器接收并加热二次蒸汽流以提供用于部分地冷凝流出液流的制冷,热交换器接收并加热二次蒸汽流以提供用于部分地冷凝初级蒸汽流的制冷。混合制冷剂压缩系统向热交换器提供制冷剂以提供制冷。(A system for separating olefins and hydrogen from an effluent stream from a dehydrogenation reactor includes a heat exchanger that receives and partially condenses the effluent stream to form a mixed phase effluent stream. The primary separation device receives and separates the mixed phase effluent stream into a primary vapor stream and a primary liquid product stream. The heat exchanger receives and partially condenses the primary vapor stream, forming a mixed-phase primary stream. The secondary separation device receives the mixed-phase primary stream and separates the mixed-phase primary stream into a secondary vapor stream and a secondary liquid product stream. The heat exchanger receives and heats the secondary vapor stream to provide refrigeration for partially condensing the effluent liquid stream, and the heat exchanger receives and heats the secondary vapor stream to provide refrigeration for partially condensing the primary vapor stream. A mixed refrigerant compression system provides refrigerant to a heat exchanger to provide refrigeration.)

1. A system for separating olefins and hydrogen in an effluent stream from a dehydrogenation reactor comprising:

a. a main heat exchanger configured to receive and partially condense an effluent stream, thereby forming a mixed phase effluent stream;

b. a primary separation device in fluid communication with the main heat exchanger to receive the mixed phase effluent stream and separate the mixed phase effluent stream into a primary vapor stream and a primary liquid product stream;

c. the main heat exchanger is configured to receive the primary vapor stream and partially condense the primary vapor stream, thereby forming a mixed-phase primary stream;

d. a secondary separation device in fluid communication with the main heat exchanger to receive the mixed-phase primary stream and separate the mixed-phase primary stream into a secondary vapor stream and a secondary liquid product stream;

e. the main heat exchanger is configured to receive the secondary vapor stream and heat the secondary vapor stream to provide refrigeration for partially condensing the effluent liquid stream and the primary vapor stream; and

f. a mixed refrigerant compression system configured to provide refrigerant to the primary heat exchanger.

2. The system of claim 1, wherein the primary heat exchanger comprises a primary refrigeration path, the mixed refrigerant compression system comprising:

i) a suction separation device configured to receive the primary refrigeration path from the main heat exchanger to receive a mixed phase refrigerant stream;

ii) a compressor having an inlet in fluid communication with the suction separation device;

iii) a cooling device having an inlet in fluid communication with an outlet of the compressor;

iv) an accumulator having an inlet in fluid communication with the outlet of the cooling device and a liquid outlet and a vapor outlet in fluid communication with the primary refrigeration passage of the primary heat exchanger.

3. The system of claim 2 wherein the cooling means comprises an air or water cooler followed by a propylene pre-cooler.

4. The system of claim 2, wherein the main heat exchanger is configured to partially condense a vapor stream from the vapor outlet of the accumulator to form a mixed phase accumulator stream, and further comprising a cold vapor separator having an inlet configured to receive the mixed phase accumulator stream, the cold vapor separator having a vapor outlet and a liquid outlet in fluid communication with the primary refrigeration passage of the heat exchanger.

5. The system of claim 4, wherein the mixed refrigerant compression system comprises:

i) an interstage separation device having an inlet in fluid communication with the cooling device, a liquid outlet in fluid communication with the primary refrigeration passage of the heat exchanger, and a vapor outlet;

ii) a compressor second stage having an inlet in fluid communication with the vapor outlet of the interstage separation device;

iii) a second stage cooling device having an inlet in fluid communication with the outlet of the compressor and an outlet in fluid communication with the accumulator.

6. The system of claim 5, wherein the compressor is a two-stage compressor comprising a first stage having an inlet in fluid communication with an outlet of the suction separation device and an outlet in fluid communication with the cooling device and a second stage having an inlet in fluid communication with the interstage separation device and an outlet in fluid communication with the second stage cooling device.

7. The system of claim 1, further comprising a combiner configured to receive and combine the primary liquid product stream and the secondary liquid product stream from the primary separation device and the secondary separation device, thereby forming a combined liquid product stream;

and wherein the main heat exchanger comprises a fresh feed cooling channel configured to receive and cool a fresh feed stream and a liquid product channel configured to receive and heat the combined liquid product stream to provide refrigeration to the fresh feed cooling channel, the fresh feed cooling channel having an outlet configured such that the cooled fresh feed stream is directed to and added to the secondary vapor stream.

8. The system of claim 7, wherein the fresh feed stream comprises primarily propane or primarily n-butane.

9. The system of claim 7, wherein the primary heat exchanger comprises: a cold box feed heat exchanger configured to receive and use refrigeration from the secondary vapor stream to partially condense the effluent feed stream; a mixed refrigerant heat exchanger configured to receive the cooling vapor stream and cool the primary vapor stream using refrigerant from the mixed refrigerant compression system; and a fresh feed heat exchanger configured to receive the fresh feed stream and to cool the fresh feed stream using refrigeration from the combined liquid product stream.

10. A system for separating olefins and hydrogen in an effluent stream from a dehydrogenation reactor comprising:

a. a cold box feed heat exchanger configured to receive and partially condense the effluent stream, forming a mixed phase effluent stream;

b. a primary separation device in fluid communication with the cold box feed heat exchanger to receive the mixed phase effluent stream and separate the mixed phase effluent stream into a primary vapor stream and a primary liquid product stream;

c. a mixed refrigerant heat exchanger configured to receive and partially condense the primary vapor stream, thereby forming a mixed phase primary stream;

d. a secondary separation device in fluid communication with the mixed refrigerant heat exchanger to receive the mixed phase primary stream and separate the mixed phase primary stream into a secondary vapor stream and a secondary liquid product stream;

e. the mixed refrigerant heat exchanger is configured to receive and heat the secondary vapor stream to provide refrigeration for partially condensing the primary vapor stream;

f. the cold box feed heat exchanger is configured to receive and further heat the secondary vapor stream after exiting the mixed refrigerant heat exchanger to provide refrigeration for partially condensing the effluent liquid stream; and

g. a mixed refrigerant compression system configured to provide refrigerant to the mixed refrigerant heat exchanger.

11. The system of claim 10, wherein the mixed refrigerant heat exchanger comprises a primary refrigeration path, the mixed refrigerant compression system comprising:

i) a suction separation device configured to receive a mixed phase refrigerant flow from the primary refrigeration passage of the mixed refrigerant heat exchanger;

ii) a compressor having an inlet in fluid communication with the suction separation device;

iii) a cooling device having an inlet in fluid communication with an outlet of the compressor;

iv) an accumulator having an inlet in fluid communication with the outlet of the cooling device and a liquid outlet and a vapor outlet in fluid communication with the primary refrigeration passage of the mixed refrigerant heat exchanger.

12. The system of claim 11 wherein the cooling means comprises an air or water cooler followed by a propylene pre-cooler.

13. The system of claim 11, wherein said suction separation device includes a vapor outlet and a liquid outlet, said vapor outlet being in fluid communication with an inlet of said compressor, said suction separation device further comprising a pump having a pump inlet in fluid communication with said liquid outlet of said suction separation device and a pump outlet in fluid communication with said outlet of said cooling device.

14. The system of claim 13, further comprising an interstage separation device, and wherein the compressor is a two-stage compressor comprising a first stage and a second stage, wherein the first stage has an inlet in fluid communication with the vapor outlet of the suction separation device and an outlet in fluid communication with an inlet of the interstage separation device, and wherein the second stage has an inlet in fluid communication with an outlet of the interstage separation device and an outlet in fluid communication with the cooling device, and wherein the inlet of the interstage separation device is also in fluid communication with the liquid outlet of the accumulator.

15. The system of claim 11, further comprising an interstage separation device, and wherein the compressor is a two-stage compressor comprising a first stage and a second stage, and wherein the first stage has an inlet in fluid communication with the vapor outlet of the suction separation device and an outlet in fluid communication with an inlet of the interstage separation device, and wherein the second stage has an inlet in fluid communication with an outlet of the interstage separation device and an outlet in fluid communication with the cooling device, and wherein an inlet of the interstage separation device is also in fluid communication with the liquid outlet of the accumulator.

16. The system of claim 10, further comprising a combiner configured to receive and combine the primary liquid product stream and the secondary liquid product stream from the primary separation device and the secondary separation device, thereby forming a combined liquid product stream;

a fresh feed heat exchanger comprising a fresh feed cooling channel configured to receive and cool a fresh feed stream and a liquid product channel configured to receive and heat the combined liquid product stream to provide refrigeration to the fresh feed cooling channel, the fresh feed cooling channel having an outlet configured such that the cooled fresh feed stream is directed to and joins the secondary vapor stream prior to entering the cold box feed heat exchanger.

17. The system of claim 16, wherein the fresh feed stream comprises primarily propane or primarily n-butane.

18. The system of claim 16, wherein the cold box feed heat exchanger, mixed refrigerant heat exchanger and fresh feed heat exchanger are incorporated into a main heat exchanger.

19. A process for separating olefins and hydrogen from an effluent stream from a dehydrogenation reactor comprising the steps of:

a. partially condensing the effluent stream, thereby forming a mixed phase effluent stream;

b. separating the mixed phase effluent stream into a primary vapor stream and a primary liquid product stream;

c. partially condensing the primary vapor stream using a mixed refrigerant, thereby forming a mixed-phase primary stream;

d. separating the mixed phase primary stream into a secondary vapor stream and a secondary liquid product stream; and

e. said secondary vapor stream is heated to provide refrigeration for partially condensing said effluent liquid stream.

20. The method of claim 19, further comprising the steps of:

f. combining the primary liquid product stream and the secondary liquid product stream to form a combined liquid product stream;

g. cooling the fresh feed stream by heating the combined liquid product stream, thereby forming a cooled fresh feed stream;

h. combining the cooled fresh feed stream and the secondary vapor stream to form a combined fresh feed and secondary vapor stream, the combined fresh feed and secondary vapor stream being heated in step e.

Background

Propane Dehydrogenation (PDH) separation systems are known in the art. One example of such a system is described in commonly owned U.S. patent No.6,333,445, the contents of which are incorporated herein by reference.

Current PDH separation system designs require the reactor effluent vapor stream to be compressed to high pressure (-12 Barg) using a reactor effluent compressor and then depressurized using two generator-or compressor-braked cryogenic turboexpanders to provide the refrigeration required for the separation and recovery of the liquid olefin product.

Disadvantages of such prior art systems include power consumption of the overall process, increased cost and maintenance requirements of the turboexpander/generator (or compressor) set, high requirements of the reactor effluent compressor discharge pressure (which increases capital and operating costs), and lack of flexibility to significantly adjust the olefin and hydrogen separation temperature.

Disclosure of Invention

Several aspects of the inventive subject matter may be embodied separately or together in the devices and systems described and claimed below. These aspects may be used alone or in combination with other aspects of the subject matter described herein, the description of which together is not intended to exclude the use of these aspects alone or in different combinations as described in the appended claims.

In one aspect, a system for separating olefins and hydrogen in an effluent stream from a dehydrogenation reactor includes a main heat exchanger configured to receive and partially condense the effluent stream, thereby forming a mixed phase effluent stream. The primary separation device is in fluid communication with the main heat exchanger to receive the mixed phase effluent stream and separate it into a primary vapor stream and a primary liquid product stream. The main heat exchanger is configured to receive and partially condense the primary vapor stream, thereby forming a mixed-phase primary stream. A secondary separation device is in fluid communication with the main heat exchanger for receiving the mixed phase primary stream and separating it into a secondary vapor stream and a secondary liquid product stream. The primary heat exchanger is configured to receive and heat the secondary vapor stream to provide refrigeration for partially condensing the effluent liquid stream and the primary vapor stream. The mixed refrigerant compression system is configured to also provide refrigerant to the main heat exchanger.

In another aspect, a system for separating olefins and hydrogen in an effluent stream from a dehydrogenation reactor includes a cold box feed heat exchanger configured to receive and partially condense the effluent stream, thereby forming a mixed phase effluent stream. The primary separation device is in fluid communication with the cold box feed heat exchanger to receive the mixed phase effluent stream and separate it into a primary vapor stream and a primary liquid product stream. The mixed refrigerant heat exchanger is configured to receive and partially condense a primary vapor stream, thereby forming a mixed phase primary stream. A secondary separation device is in fluid communication with the mixed refrigerant heat exchanger to receive the mixed phase primary stream and separate it into a secondary vapor stream and a secondary liquid product stream. The mixed refrigerant heat exchanger is configured to receive and heat the secondary vapor stream to provide refrigeration for partially condensing the primary vapor stream. The cold box feed heat exchanger is configured to receive and further heat the secondary vapor stream after exiting the mixed refrigerant heat exchanger to provide refrigeration for partially condensing the effluent stream. The mixed refrigerant compression system is configured to provide refrigerant to the mixed refrigerant heat exchanger.

In yet another aspect, a process for separating olefins and hydrogen in an effluent stream from a dehydrogenation reactor comprises the steps of: the method includes partially condensing an effluent stream to form a mixed phase effluent stream, separating the mixed phase effluent stream into a primary vapor stream and a primary liquid product stream, partially condensing the primary vapor stream to form a mixed phase primary vapor stream, separating the mixed phase primary stream into a secondary vapor stream and a secondary liquid product stream, heating the secondary vapor stream to provide refrigeration for partially condensing the effluent stream and the primary vapor stream, and providing refrigerant from the mixed refrigerant compression system to a main heat exchanger.

Drawings

FIG. 1 is a schematic diagram of a first embodiment of a system of the present disclosure;

FIG. 2 is a schematic diagram of a second embodiment of the system of the present disclosure;

FIG. 3 is a schematic diagram of a third embodiment of the system of the present disclosure;

FIG. 4 is a schematic diagram of a fourth embodiment of the system of the present disclosure;

fig. 5 is a schematic diagram of a fifth embodiment of the system of the present disclosure.

Detailed Description

The present invention is a dehydrogenation separation unit wherein a Mixed Refrigerant (MR) system consisting of an MR compressor with a heat exchanger and drum is used to provide the refrigeration required to separate and recover liquid olefin products. For example only, the MR system may use a single mixed refrigerant system, or a single mixed refrigerant system that is pre-cooled using a second refrigerant.

While achieving the same product recovery as prior art systems, some benefits may include: 1) the overall process is less energy intensive, 2) two sets of turboexpander/generator (or compressor) units are eliminated, 3) the required reactor effluent compressor discharge pressure is significantly reduced, saving capital and operating costs, 4) the MR process improves the operation, maintenance and reliability of the separation system compared to the turboexpander process, 5) the MR process allows for a more robust and more durable design of the main feed heat exchanger, and 6) the MR process provides a separate means to adjust the refrigeration level of the separation system without affecting the recycled effluent compressor.

Since in many PDH plantsRefrigeration is used with propylene, so the MR process described herein uses propylene refrigeration to pre-cool the MR refrigerant and reduce MR compressor power consumption. Precooling also allows simplification of the MR composition mixture, requiring only methane, ethylene (or ethane) and propylene (or propane), preferably ethylene and propylene. Absence of C in the MR mixture₄Or C₅The possibility of reactor catalyst contamination is reduced.

Although the explanation of the invention given below is directed to a propane dehydrogenation unit, the same process can be used for butane dehydrogenation.

Referring to fig. 1, the reactor effluent gas is compressed to about 7.2 bar in the REC compressor and removed before the heat of compression is used as cold box vapor feed 8 to the cryogenic separation system. The gas is sent to a cold box feed heat exchanger 9 where it is partially condensed and then flows to an outlet primary separator 10. The vapour and liquid are separated, the liquid stream containing a portion C₃The olefin product, vapor stream 17, contains hydrogen and residual olefin product.

The vapor stream 17 flows to the mixed refrigerant heat exchanger 11(MR exchanger) where it is further cooled to the desired temperature and partially condensed to achieve the desired product recovery. The partially condensed stream flows to the secondary separator 12 and is separated into a liquid olefin product and a hydrogen rich vapor stream 21. The hydrogen-rich stream is reheated in the MR exchanger and then split into two streams-recycle gas 13 (which is the hydrogen required for the combined reactor feed) and net steam 16 (which is the balance of the hydrogen stream and will be exported from the separation system.

The net vapor stream is reheated in a fresh feed heat exchanger (having cold end 26 and warm end 32) and refrigeration is recovered. The liquid product streams (from the primary and secondary separators 10 and 12) combine to form a combined liquid product stream 18 and flow to the fresh feed heat exchangers 26, 32.

The cold box steam feed 8 ("reactor effluent") is first cooled in a cold box feed exchanger. It is initially cooled by the combined reactor feed 14 and is secondarily cooled by outputting a portion 24 of the net steam product 16. The combined reactor feed provides most of the refrigeration by combining the recycle gas stream 13 with a cold fresh feed liquid stream 15 (such as propane or n-butane) and vaporizing the combined stream in the cold box feed heat exchanger 9. The cold fresh feed liquid stream 15 is formed from a fresh feed inlet stream 23 which fresh feed inlet stream 23 is subcooled (sub-cooled) at 26 and 32 in the fresh feed heat exchanger before entering the cold box feed heat exchanger 9. Refrigeration of the fresh feed is provided by recovering refrigeration from the C3 olefin product 18 and from a portion of the net vapor product 16.

Flash gas (recycle) 19 is produced by partially heating the separator liquid in the cold end section 26 of the fresh feed exchanger. The resulting vapor-liquid mixture 27 is separated in a liquid product tank 28. The vapor from drum 28 is heated in the warm end portion 32 of the fresh feed exchanger and the flash gas 19 is recycled to the suction of the upstream reactor effluent compressor (see figure 1 of U.S. patent No.6,333,445). The liquid product from tank 28 is pumped via pump 34 and additional cold is recovered in the warm end portion 32 of the fresh feed exchanger.

The overall refrigeration balance of the separation system is provided by the Mixed Refrigerant (MR) compression system (generally designated 38 in fig. 1) via final cooling in the MR exchanger (MRHX) 11). A C is described₃Pre-cooling the MR system; however, a single MR system may also be used. FIG. 1 shows a single stage MR compressor 40, followed by an air or water cooler 42, followed by C₃A (propylene) pre-cooler 44. The precooler may utilize as many refrigeration stages as necessary to achieve the desired temperature, two stages being shown for simplicity. The MR refrigerant is separated into vapor and liquid phase streams 31 and 33, respectively, via separator 46 and sent to the MRHX 11. The MR vapor stream 31 is cooled and condensed in the MRHX 11 and flashed at 35 to produce the coldest refrigerant for the process and a low pressure refrigerant stream 37. The MR liquid stream 33 is also cooled in the MRHX, flashed at 41 and sent to the low pressure refrigerant stream 37 where it joins and mixes with the low pressure refrigerant stream 37 at the warmer temperature. The common refrigerant return stream 47 exits the MRHX as a mixed phase vapor/liquid stream. Prior to compression, the vapor and liquid are separated via separator 48. The liquid is pumped to a higher pressure via pump 49 and the vapor is compressed in compressor 40 to a desired discharge pressureForce. The system uses a typical MR composition adapted to the specific design conditions.

The heat exchangers shown in fig. 1 and described above may be added or integrated into a single main heat exchanger.

Referring to fig. 2, in a second embodiment of the system, the suction drum of the MR compressor may also be designed to function as a heavy component refrigerant accumulator. MR systems can be used with excess heavy components (such as C) in the refrigerant₃、C₄Or C₅) The resulting MR is, at least temporarily, a two-phase flow 52 leaving the exchanger 11. This excess heavy component is separated in the compressor suction drum 50 and remains in the drum. The refrigerant vapor flowing to the MR compressor 40 is now at its dew point and the system operates automatically at dew point conditions. When "make-up" refrigerant is added to the system, the accumulated heavy components will then equilibrate with the light components to the dew point at suction pressure and temperature. If desired, the heavies may be removed from the refrigeration system, preferably at the suction accumulator, or preferably added and maintained in the suction drum.

In a third embodiment of the system, as shown in fig. 3, the reactor effluent gas is compressed to about 7.2 bar in the REC compressor and the heat of compression is removed via ambient exchanger (air or water) cooling before entering the cryogenic separation system as cold box steam feed 108. The gas is sent to a main heat exchanger 110 where it is cooled and partially condensed before flowing to a primary separator 112. The vapor and liquid are separated, with liquid stream 114 containing a portion of the C3 olefin product and vapor stream 116 containing hydrogen and the remaining olefin product. The vapor stream flows back to the main heat exchanger 110 where it is further cooled and partially condensed to achieve the desired product recovery. The partially condensed stream 118 flows to a secondary separator 122 and is separated into a liquid olefin product 124 and a hydrogen-rich stream 126. The hydrogen rich vapor stream is reheated in the main heat exchanger and then split at 130 into two streams-recycle gas 132 (which is the hydrogen required for the combined reactor feed 133) and net vapor 134 (which is the balance of the hydrogen stream and will be output from the separation system). The net vapor stream is reheated and refrigeration is recovered in the main heat exchanger.

The heated fresh propane feed 138 is sent to the main heat exchanger 110 and cooled to the same temperature as the primary separator 112. The cooled fresh propane feed 142 is then mixed with the recycle gas 132 to form the combined reactor feed 133. This stream is reheated and refrigeration is recovered in the main heat exchanger. This provides most of the refrigeration for the cryogenic separation system.

Liquid product streams 114 and 124 (from primary and secondary separators 112 and 122) are fed to main heat exchanger 110 at appropriate locations relative to their respective temperatures. The liquid product stream is heated and partially vaporized. The liquid product stream exits the main heat exchanger through a common header to form a liquid product stream 146. This orientation of the liquid product flow increases efficiency, reduces piping complexity, and reduces the risk of freezing.

The partially vaporized mixed C3 liquid product stream 146 is sent to a liquid product tank 150. Vapor 152 (flash gas) from the liquid product drum is warmed in the main heat exchanger and then recycled as flash gas stream 154 to the suction of the upstream reactor effluent compressor. Liquid 156 (liquid product) from the liquid product tank is pumped via pump 158 and then warmed in the main heat exchanger for additional energy recovery. The heated liquid product exits the main heat exchanger as C3 product stream 162.

The overall refrigeration balance of the separation system is provided by a Mixed Refrigerant (MR) system, generally indicated at 168. The embodiment of fig. 3 uses a two-stage MR compressor 172 with air or water intercooling and discharge cooling. The discharge 174 of the first MR compressor stage is partially condensed at 175 and sent to an MR interstage drum 176. Vapor 178 is sent to the second MR compressor stage and liquid 182 is sent to the main heat exchanger 110. Second MR compressor stage discharge 184 is partially condensed at 185 and separated in MR accumulator 186. MR accumulator vapor 192 and liquid 194 are sent to main heat exchanger 110. The MR accumulator vapor is partially condensed in the main heat exchanger and the resulting stream 196 is sent to cold vapor separator drum 202 to increase process efficiency. Cold steam separator vapor 204, cold steam separator liquid 206, MR accumulator liquid 194, and MR interstage liquid 182 are all condensed and subcooled (sub-cooled) within main heat exchanger 110. All of these streams exit the exchanger, are flashed across JT valves (by way of example only), and the resulting mixed phase stream is separated and returned to the main heat exchanger via standpipes 212, 213, 214, and 216 at appropriate temperatures to provide the refrigeration balance required by the separation system. Additional details regarding the operation of the MR system 168 can be found in commonly owned U.S. patent application publication No. US2014/0260415 to Ducote, jr.

The flashed low pressure MR streams are combined within the main heat exchanger and exit as a single superheated vapor stream 220 that is sent to the MR compressor suction drum 224. The system uses a typical MR composition adapted to the specific design conditions.

MR systems allow the integration of additional heat transfer services at ambient temperature or colder into the main heat exchanger. As an example, fig. 3 shows the integration of the deethanizer rectification condenser (deethanizer overhead inlet stream 226 and deethanizer overhead outlet stream 228) with the main heat exchanger. This increases the size of the MR system because of the additional refrigeration load required, but removes the need for a separate C3 refrigeration system for the deethanizer rectification condenser service, which reduces the total equipment count for the dehydrogenation plant.

In a fourth embodiment of the system of the present disclosure, an interstage separation device 406 is added to the system of fig. 1, as shown in fig. 4. Mixed phase MR stream 402 from MR heat exchanger 11 (which is produced as a liquid discharge from separator 46 prior to entering the MR heat exchanger) is combined with mixed phase MR stream 404 from the first stage discharge of compressor 40. The combined stream is directed to an inlet of a separation device 406 and the resulting vapor stream 408 is directed to an inlet of a second stage of the compressor 40. The discharge of second stage compressor 40 is directed to cooling devices 42 and 44, and then the processing of the MR stream continues as described above with reference to FIG. 1, except that stream 33 is not joined with low pressure refrigerant stream 37 after being cooled in mixed refrigerant heat exchanger 11 and flashed via valve 41. However, in an alternative embodiment, a portion of stream 33 may be combined with the low pressure refrigerant stream 37 after being cooled in the mixed refrigerant heat exchanger 11 and flashed via valve 41.

In a fifth embodiment of the system of the present disclosure, an interstage separation device 506 is added to the system of fig. 2, as shown in fig. 5. The mixed phase MR flow 502 from the MR heat exchanger 11 is combined with the mixed phase MR flow 504 from the outlet of the first stage of the MR compressor. The combined flow is directed to the inlet of the separation device 506, and the resulting vapor stream 508 is directed to the inlet of the second stage of the MR compressor. The discharge of the second stage of the MR compressor is directed to one or more cooling devices, and then the processing of the MR flow continues as described above with reference to FIG. 4.

The heat exchangers referred to in the specification can be combined with the use of multi-flow heat exchangers, such as brazed aluminum plate fin heat exchangers, to simplify piping design, equipment layout or performance. Examples of combinations may be a fresh feed-1 exchanger with a fresh feed-2 exchanger, or two fresh feed exchangers with a cold box feed exchanger. Other combinations may also be required.

While 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 may be made therein without departing from the scope of the present invention.