Systems and methods for use in multi-stage regenerative cooling cycles

Abstract

Systems and methods for use in multi-stage regenerative cooling cycles that leverage an ejector as the motivating force to sub-cool a single refrigerant in a multi-stage regenerative cooling cycle. The multi-stage regenerative cooling cycle is more efficient than conventional muti-stage cooling cycles due to the placement of the ejector, which enables each stage to operate at a higher evaporating pressure and lower compression ratio.

Description

SYSTEMS AND METHODS FOR USE IN MULTI-STAGE REGENERATIVE COOLING CYCLESCROSS-REFERENCE TO RELATED APPLICATIONS

[0001] This application, PCT Application Nos. PCT / US21 / 49010 and PCT / US22 / 19352, and U.S. Patent Nos. 11,561,027, 10,514,201, 10,533,793, 10,465,983, 10,514,202, 11,725,858 and 12,078,394, which are each incorporated herein by reference, are commonly assigned to Bechtel Energy Technologies & Solutions, Inc.FIELD OF THE DISCLOSURE

[0002] The present disclosure generally relates to systems and methods for use in multistage regenerative cooling cycles. More particularly, the systems and methods leverage an ejector as the motivating force to sub-cool a single refrigerant in a multi-stage regenerative cooling cycle. The multi-stage regenerative cooling cycle is more efficient than conventional muti -stage cooling cycles due to the placement of the ejector, which enables each stage to operate at a higher evaporating pressure and lower compression ratio.BACKGROUND

[0003] Conventional refrigeration systems for use in muti-stage cooling cycles include the multi-stage recirculated liquid system 100 illustrated in FIG. 1. A compressed refrigerant 102 enters a condenser 104, which produces a condensed refrigerant 105. The condensed refrigerant 105 passes through an expansion valve 106 where it is expanded to form a two-phase refrigerant 107. The two-phase refrigerant 107 enters a medium temperature recirculator 108, which separates the two-phase refrigerant 107 into a vapor refrigerant 110 and a liquid refrigerant 112. The liquid refrigerant 112 is recirculated through a pump 114 and distributed to a medium temperature1008643.00094269337063cooling loop through an expansion valve 116 and a low temperature cooling loop through an expansion valve 122.

[0004] In the medium temperature cooling loop, the liquid refrigerant 112 is expanded by the expansion valve 116 into a two-phase refrigerant 117, which enters a medium temperature evaporator 118 where it is fully evaporated and is returned to the medium temperature recirculator 108 as an evaporated refrigerant 120.

[0005] In the low temperature cooling loop, the liquid refrigerant 112 is expanded by the expansion valve 122 into a two-phase refrigerant 123, which enters a low temperature evaporator 124 where it is fully evaporated and is sent to a low temperature recirculator 128 as an evaporated refrigerant 126. The low temperature recirculator 128 separates the evaporated refrigerant 126 into a vapor refrigerant 130 and a liquid refrigerant 132. The vapor refrigerant 130 enters a single-stage compressor 134 and the liquid refrigerant 132 is sent to the medium temperature recirculator 108 by a pump 140.

[0006] The single-stage compressor 134 is commonly used in multi-stage low-charge ammonia systems and includes a sideload port for the vapor refrigerant 110. A pressure control valve 138 controls the flow of the vapor refrigerant 110 to maintain a constant pressure in the medium temperature recirculator 108 based on the requirements of the single-stage compressor 134. This approach enables a multi-stage cooling cycle to utilize a single-stage compressor instead of multiple compression stages or multiple compressors. Implementing this approach, however, presents challenges in retrofit scenarios, particularly when a single-stage compressor sideload port is used at the medium temperature stage. Because the sideload port is in a fixed position, it prevents the ability to raise the evaporator pressure at the medium temperature stage.2008643.00094269337063

[0007] Other concepts, such as cascade refrigeration, have been proposed to sub-cool a refrigerant in a multi-stage cooling cycle with an ejector to reduce the total power consumption of the system. Cascade refrigeration systems, however, require two cascading loops and a refrigerant for each respective stage.BRIEF DESCRIPTION OF THE DRAWINGS

[0008] The detailed description is described below with reference to the accompanying drawing, in which like elements are referenced with like reference numbers, and in which:

[0009] FIG. 1 is a schematic diagram illustrating a conventional refrigeration system for use in a muti-stage cooling cycle with a single-stage sideload compressor.

[0010] FIG. 2 is a schematic diagram illustrating one embodiment of a system for use in a multi-stage regenerative cooling cycle with a single-stage sideload compressor.

[0011] FIG. 3 is a Pressure-Enthalpy diagram comparing anticipated pressure / enthalpy values at state points for the regenerative refrigeration system illustrated in FIG. 2 and the conventional refrigeration system illustrated in FIG. 1.

[0012] FIG. 4 is a schematic diagram of the regenerative refrigeration system illustrated in FIG. 2 (without reference numbers) with the state points illustrated in FIG. 3.

[0013] FIG. 5 is a schematic diagram illustrating another embodiment of a system for use in a multi-stage regenerative cooling cycle with a pair of single-stage compressors arranged in parallel.

[0014] FIG. 6 is a schematic diagram illustrating another embodiment of a system for use in a multi-stage regenerative cooling cycle with a pair of single-stage compressors arranged in sequence.3008643.00094269337063

[0015] FIG. 7 is a schematic diagram illustrating another embodiment of a system for use in a multi-stage regenerative cooling cycle with a single-stage sideload compressor.

[0016] FIG. 8 is a schematic diagram illustrating another embodiment of a system for use in a multi-stage regenerative cooling cycle with a pair of single-stage compressors arranged in sequence.DETAILED DESCRIPTION OF THE ILLUSTRATIVE EMBODIMENTS

[0017] The subject matter of the present disclosure is described with specificity, however, the description itself is not intended to limit the scope of the disclosure. The subject matter thus, might also be embodied in other ways, to include different structures, steps and / or combinations similar to and / or fewer than those described herein, in conjunction with other present or future technologies. Although the term “step” may be used herein to describe different elements of methods employed, the term should not be interpreted as implying any particular order among or between various steps herein disclosed unless otherwise expressly limited by the description to a particular order. Other features and advantages of the disclosed embodiments will be or will become apparent to one of ordinary skill in the art upon examination of the following figures and detailed description. It is intended that all such additional features and advantages be included within the scope of the disclosed embodiments. Further, the illustrated figures described herein are only exemplary and are not intended to assert or imply any limitation with regard to the environment, architecture, design, or process in which different embodiments may be implemented. To the extent that temperatures, pressures and other dimensions are referenced in the following description, those conditions are merely illustrative and are not meant to limit the disclosure or exclude temperatures, pressures and other dimensions that are reasonably close to4008643.00094269337063(about) the same as understood by those with ordinary skill in the art. All streams described herein are carried by physical lines.

[0018] The systems and methods described herein improve conventional refrigeration systems by leveraging an ejector as the motivating force to sub-cool a single refrigerant in a multistage regenerative cooling cycle. The multi-stage regenerative cooling cycle is more efficient than conventional muti-stage cooling cycles due to the placement of the ejector, which enables each stage to operate at a higher evaporating pressure and lower compression ratio. An exemplary refrigerant is an R717 refrigerant with a cooling duty of 925 kW (263 RT) for cooling a cold storage facility from 95 °F (35 °C) to -12.5 °F (-25 °C). Other refrigerants, however, may be used with the systems and methods described herein.

[0019] In one embodiment, system for use in a closed-loop, multi-stage, cooling cycle is disclosed, which comprises: i) a liquid refrigerant line carrying a combined liquid refrigerant comprising a first liquid refrigerant from a medium temperature recirculator and a second liquid refrigerant from a low temperature recirculator; ii) an ejector fluidly connected to the liquid refrigerant line, the ejector configured to mix a first portion of the combined liquid refrigerant with a heated vapor refrigerant to produce a first two-phase refrigerant; iii) a sub-cooler fluidly connected to the liquid refrigerant line, the sub-cooler configured to exchange heat between a second two-phase refrigerant and a second portion of the combined liquid refrigerant to produce the heated vapor refrigerant and a cooled combined liquid refrigerant; and iv) an expansion valve fluidly connected to the liquid refrigerant line, the expansion valve configured to expand a third portion of the combined liquid refrigerant and produce the second two-phase refrigerant.

[0020] In another embodiment, closed-loop, multi-stage, cooling method is disclosed, which comprises: i) combining a first liquid refrigerant from a medium temperature recirculator5008643.00094269337063and a second liquid refrigerant from a low temperature recirculator to form a combined liquid refrigerant; ii) mixing a first portion of the combined liquid refrigerant and a heated vapor refrigerant to produce a first two-phase refrigerant; iii) exchanging heat between a second two- phase refrigerant and a second portion of the combined liquid refrigerant to produce the heated vapor refrigerant and a cooled combined liquid refrigerant; and iv) expanding a third portion of the combined liquid refrigerant to produce the second two-phase refrigerant.

[0021] Referring now to FIG. 2, one embodiment of a system 200 for use in a multi-stage regenerative cooling cycle is illustrated with a single-stage sideload compressor 134. The system 200 includes many of the same components as the system 100 illustrated in FIG. 1, which are reconfigured to incorporate additional components in a closed loop, multi-stage regenerative cooling cycle that enable each stage to operate at a higher evaporating pressure and lower compression ratio. The additional regenerative components include an ejector 202, an expansion valve 204 and a sub-cooler 206. The liquid refrigerant 112 from the medium temperature recirculator 108 is combined with the liquid refrigerant 132 pumped from the low temperature recirculator 128 to form a combined liquid refrigerant 208 that is recirculated through pump 114 and distributed to the medium temperature cooling loop through expansion valve 116 (in the same manner as the liquid refrigerant 112 described in reference to FIG. 1) and the low temperature cooling loop through the ejector 202, the expansion valve 204, and the sub-cooler 206.

[0022] One branch of the combined liquid refrigerant 208 is sent to the expansion valve 204 where it is expanded to reduce the pressure and temperature of the combined liquid refrigerant 208 and produce a two-phase refrigerant 210 with a pressure of about 17 psia and a temperature of about -23 °F (-30°C). The two-phase refrigerant 210 is then sent to sub-cooler 206 where heat is exchanged with another branch of the combined liquid refrigerant 208 sent to the sub-cooler 206,6008643.00094269337063which produces a heated vapor refrigerant 212 and a cooled combined liquid refrigerant 214. The sub-cooler 206 provides enough duty to reduce the temperature of the combined liquid refrigerant from about 14.8T (-9.5°C) to at least about 8°F (-13°C). The cooled combined liquid refrigerant 214 is then expanded by expansion valve 122 to reduce the pressure and temperature of the cooled combined liquid refrigerant 214 and produce the two-phase refrigerant 123 with a pressure of about 19 psia and a temperature of about -18.5°F (-28°C). The heated vapor refrigerant 212 is drawn into the ejector 202 by yet another branch of the combined liquid refrigerant 208 that flows through the ejector 202 as a motive fluid. The ejector 202 produces a two-phase refrigerant 216 that enters the low temperature recirculator 128 with the evaporated refrigerant 126 where both are separated into the vapor refrigerant 130 and the liquid refrigerant 132.

[0023] To assess the benefits of the regenerative refrigeration system illustrated in FIG. 2, modelling was conducted using an Aspen HYSYS vl4 simulator and GEA RTSelect 14.1.1.2 software to establish compressor performance. Tables 1 and 2 below compare the modelled results for the conventional refrigeration system illustrated in FIG. 1 and the regenerative refrigeration system illustrated in FIG. 2 using ammonia as the refrigerant (R717), a cooling duty of 925 kW (263 RT) and an assumption that increased subcooling by at least 5 °C results in an increased evaporator UA of at least 15%.Conventional Refrigeration Retrofitted RegenerativeSystem (FIG. 1) Refrigeration System (FIG. 2)Vapor quality, mass % 92% 96%Vapor rate, Ib / hr 316 178TABLE 1

[0024] As demonstrated by the results in Table 1, the vapor rate is reduced by 44%, which increases the quality of the low temperature evaporator 124 to 96%. To maintain stable operations,7008643.00094269337063the pressure of the low temperature evaporator 124 in the retrofitted regenerative refrigeration system (FIG. 2) is raised to 19 psia from about 18 psia in the conventional refrigeration system (FIG. 1)Conventional Retrofitted New RegenerativeRefrigeration Regenerative RefrigerationSystem (FIG. Refrigeration System (FIG. 2)1) System (FIG. 2)Capacity, RT / kW 789 / 925 789 / 925 789 / 925Energy Savings, kWh / % 202,849 / 5% 232, 898 / 6%TABLE 2

[0025] As demonstrated by the results in Table 2, the energy savings compared to the conventional refrigeration system (FIG. 1) is 5% for the retrofitted regenerative refrigeration system (FIG. 2) and is 6% for the new regenerative refrigeration system (FIG. 2). To maintain stable operations, the pressure of the low temperature evaporator 124 in each regenerative refrigeration system (FIG. 2) is raised to 19 psia from about 18 psia in the conventional refrigeration system (FIG. 1). Even when the pressure of the low temperature evaporator 124 in the retrofitted regenerative refrigeration system (FIG. 2) is 18 psia, a 3% energy savings is anticipated when compared to the conventional refrigeration system (FIG. 1).

[0026] The Pressure-Enthalpy diagram in FIG. 3 compares anticipated pressure / enthalpy values at state points for the regenerative refrigeration system 200 illustrated in FIG. 2 and the conventional refrigeration system 100 illustrated in FIG. 1. The dashed lines connect the state points for the conventional refrigeration system 100, the dashed / dotted lines connect the state points for the regenerative refrigeration system 200 and the dotted lines connect just the state points for the low temperature cooling loop in the regenerative refrigeration system 200. The Bubble8008643.00094269337063Point Curve represents the line beyond which the refrigerant is a liquid. The Dew Point Curve represents the line beyond which the refrigerant is a vapor.

[0027] In FIG. 4, the regenerative refrigeration system 200 in FIG. 2 is illustrated (without reference numbers) with the state points illustrated in FIG. 3. Based on the increased pressure of the low temperature evaporator at state point 002 (from 18 psia in the conventional refrigeration system (FIG. 1) to 19 psia), the impact of subcooling is shown to be incipient in the medium temperature cooling loop which is subcooled by at least 6°F below the saturation temperature

[0028] The impact of subcooling thus, results in an increased enthalpy difference at both evaporators, which facilitates a higher operating pressure as shown in FIG 3 by the comparison of state point 001 for the regenerative refrigeration system 200 (52 psia) and state point 001 for the conventional refrigeration system 100 (48 psia). The low temperature cooling loop in the regenerative refrigeration system 200 leverages the pump discharge pressure at state point 004 to increase the efficiency of the ejector and collectively function as a compressor in the low temperature cooling loop. The two-phase refrigerant discharged at state point 005 functions as a condenser in the low temperature cooling loop. The sub-cooler is positioned in the low temperature cooling loop so that its operating temperature is at least 3 °F lower than the operating temperature of the evaporator. This can be observed by comparing state point 006 and state point 003 in FIG 3. The placement of the sub-cooler in this manner is, therefore, crucial for achieving an economically viable regenerative refrigeration system 200. Efficient ejector operation requires a substantial pressure differential between the suction and motive pressures. Consequently, a subcooler with a lower operating temperature than the evaporator enables the ejector to function optimally. Additionally, it reduces the size of the required equipment, leading to significant cost9008643.00094269337063savings. The sub-cooler, for example, can be made three times smaller and the ejector can be made up to 50% smaller.

[0029] Referring now to FIG. 5, another embodiment of a system 500 for use in a multistage regenerative cooling cycle is illustrated with a pair of single-stage compressors 502, 504 arranged in parallel. The system 500 is commonly applied in CO2 refrigeration applications and includes many of the same components as the system 200 illustrated in FIG. 2, which are reconfigured to incorporate the single-stage compressors 502, 504. The vapor refrigerant 110 is sent to the single-stage compressor 502, which functions as a booster compressor, where it is compressed into a compressed refrigerant 503. The vapor refrigerant 130 is sent to the single-stage compressor 504 where it is compressed into a compressed refrigerant 505. The compressed refrigerants 503, 505 are then combined to form a combined compressed refrigerant 506 that is sent to the condenser 104, which produces the condensed refrigerant 105. The remainder of the system 500 operates in the same manner as the system 200.

[0030] In FIG. 6, another embodiment a system 600 for use in a multi-stage regenerative cooling cycle is illustrated with a pair of single-stage compressors 504, 602 arranged in sequence. The system 600 includes many of the same components as the system 200 illustrated in FIG. 2, which are reconfigured to incorporate the single-stage compressors 504, 602. The vapor refrigerant 130 is sent to the single-stage compressor 504 where it is compressed into a compressed refrigerant 505. The compressed refrigerant 505 is combined with the vapor refrigerant 110 to form a combined vapor refrigerant 601 that is sent to another single-stage compressor 602 where it is compressed into another compressed refrigerant 604. The another compressed refrigerant 604 is then sent to the condenser 104, which produces the condensed refrigerant 105. The remainder of the system 600 operates in the same manner as the system 200. The systems illustrated in FIGS.10008643.000942693370635 and 6 provide more operational flexibility to establish the medium temperature pressure level independent of the low temperature pressure level, while also leveraging the benefits of the regenerative system 200 to sub-cool both temperature levels.

[0031] Referring now to FIG. 7, another embodiment a system 700 for use in a multi-stage regenerative cooling cycle is illustrated with a single-stage sideload compressor 134. The system 700 includes many of the same components as the system 200 illustrated in FIG. 2, which are reconfigured to incorporate another ejector 702. The evaporated refrigerant 120 is drawn into the ejector 702 by vacuum pressure created by the condensed refrigerant 105 that flows through the ejector 702 as a motive fluid. The ejector 702 produces a two-phase refrigerant 704 that enters the medium temperature recirculator 108 where it is separated into the vapor refrigerant 110 and the liquid refrigerant 112. The remainder of the system 700 operates in the same manner as the system 200

[0032] In FIG. 8, another embodiment a system 800 for use in a multi-stage regenerative cooling cycle is illustrated with a pair of single-stage compressors 504, 602 arranged in sequence. The system 800 includes many of the same components as the system 200 illustrated in FIG. 2, which are reconfigured to incorporate the single-stage compressors 504, 602 and the ejector 702 from the systems illustrated in FIGS. 6-7, respectively. Thus, the single-stage compressors 504, 602 function in the same manner described in reference to FIG. 6 and the ejector 702 functions in the same manner described in reference to FIG. 7. The remainder of the system 800 operates in the same manner as the system 200.

[0033] To assess the benefits of the regenerative refrigeration systems illustrated in FIGS. 7-8, modelling was conducted using an Aspen HYSYS vl4 simulator and GEA RTSelect 14.1.1.2 software to establish compressor performance. Table 3 below compares the modelled results for11008643.00094269337063the conventional refrigeration system illustrated in FIG. 1 and the regenerative refrigeration systems illustrated in FIGS. 7-8 using ammonia as the refrigerant (R717), a cooling duty of 925 kW (263 RT) and an assumption that increased subcooling by at least 5 °C results in an increased evaporator UA of at least 15%.Conventional Regenerative RegenerativeRefrigeration Refrigeration RefrigerationSystem (FIG. System (FIG. 7) System (FIG. 8)1)Capacity, RT / kW 789 / 925 789 / 925 789 / 925Energy Savings, - 202,849 / 5% 316,619 / 8% kWh / %TABLE 3

[0034] As demonstrated by the results in Table 3, the energy savings compared to the conventional refrigeration system (FIG. 1) is 5% for the regenerative refrigeration system in FIG. 7 and is 8% for the regenerative refrigeration system in FIG. 8. To maintain stable operations, the pressure of the low temperature evaporator 124 in each regenerative refrigeration system (FIGS. 7-8) is raised to 19 psia from about 18 psia in the conventional refrigeration system (FIG. 1). The regenerative refrigeration systems illustrated in FIGS. 7-8 are best suited as new installations because each system will perform best if the medium temperature cooling loop pressure can be adjusted through the selection of a single-stage sideload compressor (FIG. 7) or with a pair of single-stage compressors (FIG. 8).

[0035] The systems and methods described herein, therefore, improve conventional refrigeration systems by leveraging the ejector 202 as the motivating force to sub-cool a single refrigerant in a multi-stage regenerative cooling cycle. The placement of the ejector 202 relative to the low temperature cooling loop and the medium temperature cooling loop facilitates a retrofit12008643.00094269337063of conventional refrigeration systems used in multi-stage cooling cycles, like the system 100 illustrated in FIG. 1, with the ejector 202, expansion valve 204 and sub-cooler 206 while providing substantially the same performance advantages as the new system 200 illustrated in FIG. 2. As illustrated in FIG. 5, the system 500 can also be modified in a retrofit scenario with a single-stage compressor 502 to raise the medium temperature evaporator pressure without having to adjust a compressor sideload port or employ a multi-stage compressor to better optimize the medium temperature section pressure.

[0036] While the present disclosure has been described in connection with presently preferred embodiments, it will be understood by those skilled in the art that it is not intended to limit the disclosure of those embodiments. It is therefore contemplated that various alternative embodiments and modifications may be made to the disclosed embodiments without departing from the spirit and scope of the disclosure defined by the appended claims and equivalents thereof.13008643.00094269337063

Claims

CLAIMS1. A system for use in a closed-loop, multi-stage, cooling cycle, which comprises: a liquid refrigerant line carrying a combined liquid refrigerant comprising a first liquid refrigerant from a medium temperature recirculator and a second liquid refrigerant from a low temperature recirculator; an ejector fluidly connected to the liquid refrigerant line, the ejector configured to mix a first portion of the combined liquid refrigerant with a heated vapor refrigerant to produce a first two-phase refrigerant; a sub-cooler fluidly connected to the liquid refrigerant line, the sub-cooler configured to exchange heat between a second two-phase refrigerant and a second portion of the combined liquid refrigerant to produce the heated vapor refrigerant and a cooled combined liquid refrigerant; and a first expansion valve fluidly connected to the liquid refrigerant line, the expansion valve configured to expand a third portion of the combined liquid refrigerant and produce the second two-phase refrigerant.

2. The system of claim 1, wherein the medium temperature recirculator is configured to separate at least one of a third two-phase refrigerant and an evaporated refrigerant into the first liquid refrigerant and a first vapor refrigerant.

3. The system of claim 2, wherein the low temperature recirculator is fluidly connected to the ejector and is configured to separate the first two-phase refrigerant into the second liquid refrigerant and a second vapor refrigerant.

4. The system of claim 3, further comprising a compressor fluidly connected to at least one of the medium temperature recirculator and the low temperature recirculator and configured to compress at least one of the first vapor refrigerant and the second vapor refrigerant.14008643.000942693370635. The system of claim 1 , further comprising a pump fluidly connected to the low temperature recirculator and configured to pump only the second liquid refrigerant.

6. The system of claim 5, further comprising another pump fluidly connected to the medium temperature recirculator and the low temperature recirculator and configured to pump the combined liquid refrigerant in the liquid refrigerant line.

7. The system of claim 4, further comprising a second expansion valve fluidly connected to the medium temperature recirculator and configured to expand a condensed refrigerant and produce the third two-phase refrigerant.

8. The system of claim 4, further comprising another ejector fluidly connected to the medium temperature recirculator and configured to mix a condensed refrigerant with the evaporated refrigerant to produce the third two-phase refrigerant.

9. The system of claim 7, further comprising another compressor fluidly connected to the medium temperature recirculator and the compressor, the another compressor configured to compress the first vapor refrigerant and a compressed refrigerant from the compressor.

10. The system of claim 8, further comprising another compressor fluidly connected to the medium temperature recirculator and the compressor, the another compressor configured to compress the first vapor refrigerant and a compressed refrigerant from the compressor.

11. The system of claim 7, further comprising another compressor fluidly connected to the medium temperature recirculator and configured to compress the first vapor refrigerant.

12. The system of claim 3, wherein the second vapor refrigerant is about -18.5 °F and about 19 psia.

13. The system of claim 12, wherein the second two-phase refrigerant is about -22.7 °F and about 17 psia.15008643.0009426933706314. The system of claim 3, wherein a temperature of the second two-phase refrigerant is at least 3 °F lower than a temperature of the second vapor refrigerant.

15. A closed-loop, multi-stage, cooling method, which comprises: combining a first liquid refrigerant from a medium temperature recirculator and a second liquid refrigerant from a low temperature recirculator to form a combined liquid refrigerant; mixing a first portion of the combined liquid refrigerant and a heated vapor refrigerant to produce a first two-phase refrigerant; exchanging heat between a second two-phase refrigerant and a second portion of the combined liquid refrigerant to produce the heated vapor refrigerant and a cooled combined liquid refrigerant; and expanding a third portion of the combined liquid refrigerant to produce the second two- phase refrigerant.

16. The method of claim 15, further comprising separating at least one of a third two-phase refrigerant and an evaporated refrigerant into the first liquid refrigerant and a first vapor refrigerant.

17. The method of claim 16, further comprising separating the first two-phase refrigerant into the second liquid refrigerant and a second vapor refrigerant.

18. The method of claim 17, further comprising compressing at least one of the first vapor refrigerant and the second vapor refrigerant to produce a compressed refrigerant.

19. The method of claim 15, further comprising pumping only the second liquid refrigerant to be combined with the first liquid refrigerant.

20. The method of claim 19, further comprising pumping the combined liquid refrigerant through a liquid refrigerant line.16008643.0009426933706321 . The method of claim 18, further comprising expanding a condensed refrigerant to produce the third two-phase refrigerant.

22. The method of claim 18, further comprising mixing a condensed refrigerant with the evaporated refrigerant to produce the third two-phase refrigerant.

23. The method of claim 21, further comprising compressing the first vapor refrigerant and the compressed refrigerant to produce another compressed refrigerant.

24. The method of claim 22, further comprising compressing the first vapor refrigerant and the compressed refrigerant to produce another compressed refrigerant.

25. The method of claim 21, further comprising compressing the first vapor refrigerant to produce another compressed refrigerant.

26. The method of claim 17, wherein the second vapor refrigerant is about -18.5 °F and about19 psia.

27. The method of claim 26, wherein the second two-phase refrigerant is about -22.7 °F and about 17 psia.

28. The method of claim 17, wherein a temperature of the second two-phase refrigerant is at least 3 °F lower than a temperature of the second vapor refrigerant.17008643.00094269337063

Images