Energy efficient non-flammable refrigeration for co2-rich process streams

Abstract

Processes for chilling CO2 rich streams are described. The processes combine the use of a refrigerant mixture comprising CO2 and a first refrigerant capable of depressing the freezing point of CO2 to less than or equal to -60°C and a series of flash drums which reduce the temperature and pressure of the refrigerant mixture and concentrate the first refrigerant.

Description

H242187-WO PATENT APPLICATIONENERGY EFFICIENT NON-FLAMMABLE REFRIGERATIONFOR CO2-RICH PROCESS STREAMSCROSS-REFERENCES TO RELATED APPLICATIONS

[0001] This application claims priority to United States Non-Provisional Patent Application Ser. No. 19 / 357,832, filed on October 14, 2025, which claims the benefit of United States Provisional Patent Application Ser. No. 63 / 736,882, filed on December 20, 2024, the entirety of each of which is incorporated herein by reference.BACKGROUND

[0002] Traditional mixed refrigerants used in cryogenic capture of carbon dioxide may include carbon dioxide itself, along with a mixture of light hydrocarbons. These mixed refrigerants allow for efficient refrigeration; however they can require additional measures to be taken to reduce the risk of flammability. Pure CO2 may be used as a non-flammable refrigerant, but results in a less efficient scheme as the stream to be cooled is often near the CO2 freeze point.

[0003] More traditional hydrofluorocarbon (HFC) refrigerants may be used, but they can have high global warming potential (GWP) and high costs due to seal leakage in centrifugal compressors. These may also be flammable, depending on the refrigerant chosen.

[0004] Therefore, there is a need for a non-flammable refrigerant blend with low global warming potential that can provide efficient cooling.BRIEF DESCRIPTION OF THE DRAWINGS

[0005] Figures 1A and IB are graphs from a literature article showing freezing point depression of CO2 with HFOs.

[0006] Figure 2 is an illustration of one embodiment a process according to the present invention.

[0007] Figure 3 is an illustration of one embodiment of a secondary refrigeration loop suitable for use with the embodiment of Figure 2 or Figure 4.

[0008] Figure 4 is an illustration of one embodiment of a process according to the present invention.H242187-WO PATENT APPLICATIONDESCRIPTION

[0009] The unique process described in this application utilizes a mixture of low concentrations of a first refrigerant in CO2 to depress the freeze point of CO2 and allow for a more efficient flow scheme, while minimizing the GWP impacts and minimizing the cost of refrigerant, both in the initial inventory and any seal leakage. Suitable first refrigerants include, but are not limited to, hydro-fluoro-olefins (HFO) refrigerants, such as R-1234ze (trans-1,3,3,3 Tetrafluoropropene), R-1234yf (2,3,3,3-Tetrafluoropropene), and the like, or combinations thereof.

[0010] In addition, the HFO / CO2 refrigerant mixture is non-flammable, and some of the HFO refrigerants themselves can be classified as non-flammable, leading to an inherently safer process. This is particularly relevant for cryogenic units that concentrate oxygen in the process itself. The term “non-flammable” is defined according to the Al l method from European Regulation EC 440 / 2008.

[0011] The second refrigerant may comprise a pure hydrocarbon refrigerant, or a mixture of CO2 and one or more hydrocarbons, or a hydrofluorocarbon, or ammonia.

[0012] The scheme mentioned below further utilizes the freezing point depression to create a unique flow scheme wherein the concentration of the HFO in the liquid phase varies throughout the process and allows for the greatest freezing point depression in the coldest portion of the refrigeration loop. This allows for reduced concentrations of HFO in the warmer sections of the refrigerant flowscheme, leading to decreased refrigerant losses due to seal leakage and a more efficient process.

[0013] Examples of CO2 rich streams where these processes could be used include, but are not limited to, cryogenic fractionation and capture of CO2 from power generation sources such as coal, cryogenic fractionation and capture of CO2 from industrial sources such as steel or cement, cryogenic fractionation and capture of CO2 produced from oxycombustion in the industrial and power sources noted above, and liquefaction of captured CO2 from solvent, pressure swing adsorption or temperature swing adsorption processes. Examples of streams that can be processed potentially include but are not limited to, a cryogenic fractionator overhead vapor stream, a cryogenic fractionator feed stream, a pressure swing adsorption tail gas stream, or a vapor CO2 product stream, and combination thereof.H242187-WO PATENT APPLICATION

[0014] Freezing point depression of CO2 with FIFOs has been shown in the literature. For example, Figures. 1A-1B show Figures 2-3 from Di Nicola et. al., Solid-liquid equilibria measurements of the carbon dioxide + 2,3,3,3-tetrafluoroprop-l-ene and carbon dioxide + trans- 1,3,3,3-tetrafluoropropene mixtures, Fluid Phase Equilibria, 354 (2013) 54-58. These illustrate the benefits of having small amounts of the refrigerant in the CO2 itself to help lower the freeze point. Centrifugal compressors are an efficient choice of compressor, however seal leakage can be significant, at 0.5 to 3 scfm (see, e.g., https : / / 19j anuary2017 sna shot, epa. gov / sites / production / files / 2016- 06 / documents / ll_wetseals.pdf). The price of refrigerant is higher than that of CO2, especially in a unit that produces liquefied carbon dioxide as a product, so it is advantageous to add the minimum amount of the HFO. By staging multiple flashes in series, the heavier component (HFO) can be increased in concentration, leading to the highest HFO concentration at the lowest temperature flash. This allows for less HFO being charged to the system, and lower concentrations of seal leakage in the compressors themselves. An example of the concentration of HFOs across multiple stages can be seen below in Table 1. The concentration of 1234ze in the Stage 3 flash drum is 7.30%, which is 1.5 times higher than the 1234ze concentration in the HP Refrigerant from receiver. This allows the freeze point of the refrigerant stream to decrease by 2.7 °F. The freezing points were determined via the usage of Figure IB. The process conditions were determined with a process simulator and fluid package deemed suitable for the mixture.H242187-WO PATENT APPLICATION

[0015] Seal leakage recovery systems may also be used to further minimize the refrigerant losses from the compressor. Seal leakage recovery systems are well known in industry and have been offered or studied by companies including Crane, Borsig, Mitsubishi Heavy Industries Compressor Corporation and others. The losses of refrigerant, and optionally CO2, could be further reduced via adding a seal leakage recovery system to the centrifugal compressors, at the cost of additional capital and energy to recover this material. The process described in this application lowers the amount of refrigerant that would need to be recovered in the seal leakage system by lowering the concentration of refrigerant required in the compression stages.

[0016] This process, shown in Figure 2, is one embodiment of the invention, in which a three-stage mixed HFO / CO2 refrigeration system is used to chill and partially condense a CO2- rich stream 111 in brazed-aluminum exchanger (100) to form a cold two-phase outlet stream 141. Examples of the pressures, concentration of refrigerant components and estimated freeze points of the refrigerant are seen in Table 1. The process side temperatures may vary depending on the configuration, but will be warmer than the CO2 freeze point, and warmer than the corresponding temperatures of the refrigerant.

[0017] In this process, the mixed refrigerant contains enough HFO (mixed with CO2) to lower the freezing point of the liquid from the lowest-pressure flash drum to -60°C.

[0018] In this process, high-pressure liquid mixed HFO / CO2 refrigerant (205) flows from the Mixed Refrigerant Receiver (204), which is flashed across control valve (206) to form a two- phase stream (211) at lower pressure and temperature, which flows into the Stage 1 Flash Drum (210), whose pressure is controlled by the overhead valve (216).

[0019] Vapor (stream 219) from the Stage 1 Flash Drum (210), which may be equipped with a mist eliminator, flows to the third stage of the Mixed Refrigerant Compressor (260).

[0020] Part of the liquid (stream 213) from the Stage 1 Flash Drum (210), which is enriched in HFO compared to stream 205, flows by thermosiphon through the warm section of the exchanger (100) to chill the process stream (111). The two-phase mixed-refrigerant outlet stream (215) is returned to the Stage 1 Flash Drum (210) for separation of the liquid and vapor.

[0021] The remainder of the liquid (217) from the Stage 1 Flash Drum (210) is flashed across control valve (218) into the Stage 2 Flash Drum (220), whose pressure is controlled by overhead valve (226), at a lower pressure and temperature.H242187-WO PATENT APPLICATION

[0022] Vapor (stream 229) from the Stage 2 Flash Drum (220), which may be equipped with a mist eliminator, flows to the second stage of the Mixed Refrigerant Compressor (250).

[0023] Part of the liquid (stream 223) from the Stage 2 Flash Drum (220), which is enriched in HFO compared to stream 217 flows by thermosiphon through the middle section of the exchanger (100) to chill the process stream (111). The two-phase mixed-refrigerant outlet stream (225) is returned to the Stage 2 Flash Drum (220) for separation of the liquid and vapor.

[0024] The remainder of the liquid (227) from the Stage 2 Flash Drum (220) is flashed across control valve (228) into the Stage 3 Flash Drum (230), whose pressure is controlled by overhead valve (236), at the lowest pressure and temperature.

[0025] Vapor (stream 239) from the Stage 3 Flash Drum (230), which may be equipped with a mist eliminator, flows to the first stage of the Mixed Refrigerant Compressor (240).

[0026] Liquid (stream 233) from the Stage 3 Flash Drum (230), which is enriched in HFO compared to stream (227), flows by thermosiphon through the cold section of the exchanger (100) to chill the process stream (111). The mixed-refrigerant outlet stream (235) is returned to the Stage 3 Flash Drum (230) for separation of the liquid and vapor.

[0027] It should be noted that the successive flashes of mixed-refrigerant liquid tend to concentrate the HFO refrigerant (which is less volatile than CO2) in the liquid phase, so that the HFO concentration in the high-pressure mixed-refrigerant liquid (205) can be less than that required to lower the freezing point of the Stage 3 Flash Drum liquid (stream 233) to - 60°C. This reduces the amount of HFO refrigerant leaked through the vapor seals of a centrifugal compressor, and reduces the inventory of HFO refrigerant needed in the system.

[0028] If the refrigerant return from the exchanger (100) to a flash drum is two-phase as described above, the HFO tends to concentrate in the liquid to a higher degree. However, this has the disadvantage of increasing the temperature of the liquid from a flash drum at a given pressure, which tends to decrease temperature approaches and increase the required area of the exchanger (100). An alternative is to fully vaporize the refrigerant in the exchanger, leading to a vapor only return that bypasses the flash drum and optionally further cools the process before being returned to the respective stage of compression.

[0029] Vapor from the Stage 3 Flash Drum (230) is compressed by the first stage of the Mixed Refrigerant Compressor (240). It may be cooled by a water-cooled or air-cooled exchanger (246), and the discharge (247) mixes with vapor (251) from the Stage 2 Flash Drum (220).H242187-WO PATENT APPLICATION

[0030] This vapor stream (253) is compressed by the second stage of the Mixed Refrigerant Compressor (250). It may be cooled by a water-cooled or air-cooled exchanger (256), and the discharge (257) mixes with vapor (261) from the Stage 1 Flash Drum (210).

[0031] This vapor stream (263) is compressed by the third stage of the Mixed Refrigerant Compressor (260), and the discharge (265) is cooled by a water-cooled or air-cooled exchanger (266).

[0032] The first-stage intercooler (246) and / or the second-stage intercooler (256) may be omitted if the compressor discharge temperatures are similar to or lower than the outlet temperature from a water-cooled or air-cooled exchanger, as this results in a reduction of total required compressor power.

[0033] High-pressure mixed-refrigerant vapor (267) is condensed in the Mixed Refrigerant Condenser (202) by heat exchange against a vaporizing stream of a second pure HFO refrigerant liquid (323) at a lower temperature, which is part of a second refrigeration cycle, (shown as box 300 on Figure 2.). The condensed Mixed Refrigerant liquid (203) flows to the Mixed Refrigerant Receiver (204), thereby completing the Mixed Refrigerant cycle.

[0034] The details of the second pure HFO refrigerant cycle are shown in Figure 3, where liquid streams are shown as solid lines, and vapor streams or two-phase streams are shown as dashed lines.

[0035] High-pressure pure HFO liquid (303) flows from the Pure HFO Receiver (302) and is flashed through valve (304) to form stream 311, which flows into an Economizer Drum (312), which operates at an intermediate temperature and pressure between those of streams 323 and 303. The pressure of the Economizer Drum 312 is regulated by control valve (318).

[0036] Vapor (319) from the Economizer Drum (312) flows to a side port in the Pure HFO Compressor (340). Liquid (313) from the Economizer Drum is flashed through control valve (314) to form stream 321, which flows into a Pure HFO Flash Drum (322), whose pressure is controlled by overhead valve (328), at a temperature less than the condensing temperature of the Mixed Refrigerant (203).

[0037] Liquid (323) from the Pure HFO Flash Drum (322) flows by thermosiphon through the shell side of the Mixed Refrigerant Condenser (202), in which it is partially vaporized to condense the Mixed Refrigerant, and returns to the Pure HFO Flash Drum (322).H242187-WO PATENT APPLICATION

[0038] Vapor (327) from the Pure HFO Flash Drum (322) flows through pressure control valve (328) to the Pure HFO Suction Drum (330), which may be equipped with a mist eliminator.

[0039] Vapor (331) from the Pure HFO Suction Drum (330) is compressed by the Pure HFO Compressor (340), and the discharge is condensed in the Pure HFO Condenser (342), which can be a water-cooled or air-cooled exchanger.

[0040] The Pure HFO Compressor (340) may be an oil-flooded screw compressor package, including one or more oil-flooded screw compressors in parallel, each equipped with an oil separator, and lubrication oil pumps, coolers, and filters. Screw compressors are advantageous for pure HFO services, to minimize losses of expensive HFO refrigerant to the atmosphere. However, screw compressors tend to be less efficient than centrifugal compressors, so they are better suited to services with lower power requirements.

[0041] Condensed high-pressure liquid HFO refrigerant (343) flows from the Condenser (342) to the Pure HFO Receiver (302), thereby completing the Pure HFO refrigerant cycle.

[0042] The Economizer Drum (312) and its associated control valves (318) and (314) may be omitted from the Pure HFO refrigeration cycle (300), with high-pressure liquid HFO (303) flashed directly into the Pure HFO Flash Drum (322).

[0043] However, the use of an economizer drum in the second (pure HFO) refrigeration cycle reduces the power requirement of the Pure HFO Compressor (340), and its operating pressure can be varied to minimize the power consumption. The operating conditions of the Economizer Drum (312), if present, has no effect on the Mixed Refrigerant cycle.

[0044] While the above system has been discussed as using an HFO, the process is not limited only to using HFOs. Hydrocarbons or other traditional refrigerants may also be used, provided that they reach a temperature cool enough to cool stream 203 to the desired temperature without dropping below the freeze point of stream 203. It is advantageous to use the HFO in this loop however, as it reduces the number of refrigerants required on site.

[0045] Figure 4 illustrates a variation of the basic three-stage process described above, which is used to provide chilling duty to partially condense the total overhead stream from a CO2 Fractionator (stream 121), and to cool and partially condense the feed (stream 111) to a CO2 Fractionator.

[0046] In this process, the mixed refrigerant contains enough HFO (mixed with CO2) to lower the freezing point of the liquid from the Stage 3 Flash Drum to - 60°C. This enables theH242187-WO PATENT APPLICATION reflux drum of the CO2 Fractionator to operate at - 55°C or less, which minimizes loss of CO2 into the vapor. In some configurations, this will increase the recovery of CO2 in the unit. In other configurations, this reduces the power requirement of the pressure-swing adsorption (PSA) process to separate CO2 from the remaining gases in the net vapor stream from the CO2 Fractionator.

[0047] As discussed above, the successive flashes of mixed-refrigerant liquid tend to concentrate the HFO refrigerant (which is less volatile than CO2) in the liquid phase, so that the HFO concentration in the high-pressure mixed-refrigerant liquid can be less than that required to lower the freezing point of the Stage 3 Flash Drum liquid to -60°C. This tends to reduce the amount of HFO refrigerant leaked through the vapor seals of a centrifugal compressor.

[0048] In this process, the cold net overhead vapor stream (151) from the CO2 Fractionator Reflux Drum is warmed in the CO2 Fractionator Condensers (120 and 130) and CO2 Fractionator Feed Chiller (110), in order to help chill the CO2 Fractionator total overhead stream and feed stream (121), thereby reducing the power required by the mixed-refrigerant compressor.

[0049] In this configuration, the two-phase or vapor refrigerant outlet streams from the chillers do not flow back to the flash drums, but are mixed with vapor from the flash drum (at the same pressure) and flow through warmer chillers so that they enter the mixed-refrigerant compressor as superheated vapor. In some cases, this heat exchange can reduce the power requirement of the mixed-refrigerant compressor.

[0050] This configuration also includes an additional Refrigerant Subcooler exchanger (270), in which high-pressure liquid mixed refrigerant from the Mixed Refrigerant Condenser is subcooled by heat exchange against cold refrigerant vapor streams and the CO2 Fractionator net vapor stream (157). This subcooling reduces the flow rate of vapor flashed from the Stage 1 Flash Drum (210), and thereby reduces the power requirement of the third stage of the Mixed Refrigerant Compressor.

[0051] This process is illustrated in Figure 4, where vapor or two-phase streams are shown as dashed lines, and liquid streams are shown as solid lines. High-pressure mixed-refrigerant liquid (205) from the Mixed Refrigerant Receiver (204) flows to the Mixed Refrigerant Subcooler (270), in which it is subcooled by heat exchange against three cold refrigerant vapor streams (at different pressures) and the CO2 Fractionator net vapor stream (157). This exchange with multiple streams may be achieved with a brazed aluminum heat exchanger.H242187-WO PATENT APPLICATION

[0052] The subcooled high-pressure refrigerant liquid is then flashed across control valve (208) into the Stage 1 Flash Drum (210), to a temperature slightly below the outlet temperature of stream 113 from the CO2 Fractionator Feed Chiller (110). The pressure of the Stage 1 Flash Drum (210) is controlled by overhead valve (216).

[0053] A portion of the liquid from the Stage 1 Flash Drum (stream 213) is vaporized in the CO2 Fractionator Feed Chiller (110), then mixes with the vapor (411) from the Stage 1 Flash Drum and flows through the Refrigerant Subcooler (270).

[0054] The remainder of the liquid from the Stage 1 Flash Drum (217) is flashed into the Stage 2 Flash Drum (220), to a lower temperature and pressure. The pressure of the Stage 2 Flash Drum is controlled by the overhead valve (226).

[0055] A portion of the liquid from the Stage 2 Flash Drum (stream 223) is vaporized in the Warm CO2 Fractionator Condenser (120), which chills and partially condenses the CO2 Fractionator total overhead vapor (stream 125), to a temperature slightly above that of the Stage 2 Flash Drum liquid.

[0056] The partially or totally vaporized stream (225) from the Stage 2 Flash Drum then mixes with the vapor (421) from the Stage 2 Flash Drum (at the same pressure) and is warmed in the CO2 Fractionator Feed Chiller (110) and the Refrigerant Subcooler (270).

[0057] The remainder of the liquid (227) from the Stage 2 Flash Drum is flashed through control valve (228) into the Stage 3 Flash Drum (230), to a temperature less than the required temperature in the CO2 Fractionator Reflux Drum (140). The pressure in the Stage 3 Flash Drum is controlled by the overhead valve (236).

[0058] Liquid from the Stage 3 Flash Drum (stream 233) is vaporized in the Cold CO2 Fractionator Condenser (130), which chills and partially condenses the two-phase CO2 Fractionator total overhead stream (125) down to the required temperature in the CO2 Fractionator Reflux Drum (140).

[0059] The CO2 Fractionator Reflux Drum (140) separates the two-phase outlet stream (135) from the Cold CO2 Fractionator Condenser (130) into the liquid reflux stream to the Fractionator (stream 141), and the net CO2 Fractionator overhead vapor (151), which flows back through the CO2 Fractionator Condensers (130 and 120), CO2 Feed Chiller (110), and Refrigerant Subcooler (270).H242187-WO PATENT APPLICATION

[0060] The partially or totally vaporized stream (235) from the Stage 3 Flash Drum then mixes with the vapor (stream 431) from the Stage 3 Flash Drum (at the same pressure), and is warmed in the Warm CO2 Fractionator Condenser (130 and 120), the CO2 Fractionator Feed Chiller (110) and the Refrigerant Subcooler (270).

[0061] The Warm (120) and Cold (130) CO2 Fractionator Condensers, which are shown in Figure 4 as separate exchangers, could be combined into a single exchanger where the Stage 2 liquid and Stage 3 vapor enter at an appropriate location along the length of the combined exchanger.

[0062] In this particular configuration, the outlet temperature from the CO2 Fractionator Feed Chiller (stream 113) is higher than the inlet temperature (stream 121) to the Warm CO2 Fractionator Condenser, so that these are shown as separate exchangers.

[0063] If there is a temperature overlap between the CO2 Fractionator Feed Chiller (110) and the Warm CO2 Fractionator Condenser (120), it may be advantageous for these to be combined into a single exchanger, where the Stage 1 liquid and Stage 2 vapor enter at an appropriate location along the length of the combined exchanger.

[0064] In some cases, the use of cold refrigerant streams to help chill the CO2 Fractionator Feed and subcool the high-pressure mixed-refrigerant liquid offers an advantage over directly returning the warmed refrigerant to the flash drum.

[0065] Low-pressure mixed refrigerant vapor (241), which has been warmed in the Cold (130) and Warm (120) CO2 Fractionator Condensers, the CO2 Fractionator Feed Chiller (110), and the Refrigerant Subcooler (270) flows to the Mixed Refrigerant Compressor, and is compressed in the first stage of compression (240).

[0066] The first-stage discharge (245) may or may not be cooled by cooling water (or an air-cooled exchanger) (246), and is then mixed with second-stage vapor (251), which has been warmed in the CO2 Fractionator Feed Chiller (110), and the Refrigerant Subcooler (270), and flows to the second stage of compression (250).

[0067] Second-stage discharge (255) may or may not be cooled by cooling water (or an air-cooled exchanger) (256) and is then mixed with first-stage vapor (261), which has been warmed in the Refrigerant Subcooler (270), and flows to the third stage of compression (260).

[0068] Third-stage discharge (265) from the Mixed Refrigerant Compressor (260) flows to the Mixed Refrigerant Aftercooler (266), where it is cooled using cooling water (or an air-cooledH242187-WO PATENT APPLICATION exchanger), then flows to the Mixed Refrigerant Condenser (202), where it is condensed by heat exchange against vaporizing pure HFO refrigerant in a separate refrigeration loop, which is shown in Figure 3, and described earlier in this document..

[0069] While the above system has been discussed as using an HFO, the process is not limited only to using HFOs. Hydrocarbons or other traditional refrigerants may also be used, provided that they reach a temperature cool enough to cool stream 203 to the desired temperature without dropping below the freeze point of stream 203. It is advantageous to use the HFO in this loop however as it reduces the number of refrigerants required on site

[0070] Condensed high-pressure mixed refrigerant liquid (203) flows to the Mixed Refrigerant Receiver (204), which completes the mixed-refrigerant cycle.

[0071] An example of key variables from Figure 4 can be seen below. It can be seen that the flash drum pressures are similar to what is shown in Table 1. The process conditions will vary however as the liquid from each receiver is not returned to the vessel in Figure 4, and as the heat integration with the process varies. The process conditions were determined with a process simulator and fluid package deemed suitable for the mixture.SPECIFIC EMBODIMENTS

[0072] While the following is described in conjunction with specific embodiments, it will be understood that this description is intended to illustrate and not limit the scope of the preceding description and the appended claims.

[0073] A first embodiment of the invention is a process for chilling a CO2 rich stream, comprising flashing a high-pressure liquid refrigerant stream from a mixed refrigerant receiver toH242187-WO PATENT APPLICATION partially vaporize and cool the high-pressure liquid refrigerant stream, the liquid refrigerant stream comprising a mixture of CO2 and a first refrigerant, wherein a concentration of the first refrigerant is sufficient to reduce a freezing point of the mixture to less than or equal to -60°C in the lowest pressure section; separating the partially vaporized and cooled high-pressure liquid refrigerant stream into a first refrigerant liquid stream and a first refrigerant vapor stream in a first flash drum; cooling the CO2 rich stream with a first portion of the first refrigerant liquid stream from the first flash drum in a first cooler forming a first cooled CO2 rich stream and a first warmed refrigerant stream; flashing a second portion of the first refrigerant liquid stream from the first flash drum to partially vaporize and cool the second portion of the first refrigerant liquid stream from the first flash drum; separating the partially vaporized and cooled second portion of the first refrigerant liquid stream from the first flash drum stream into a second refrigerant liquid stream and a second refrigerant vapor stream in a second flash drum, the second flash drum having a lower temperature and a lower pressure than the first flash drum; further cooling the CO2 rich stream or cooling a second CO2 rich stream with a first portion of the second refrigerant liquid stream from the second flash drum in a second cooler forming a second cooled CO2 rich stream and a second warmed refrigerant stream; compressing the second refrigerant vapor stream from the second flash drum in a second compressor stage forming a second compressed refrigerant vapor stream; combining the first refrigerant vapor stream from the first flash drum and the second compressed refrigerant vapor stream from the first stage compressor to form a first combined refrigerant stream; compressing the first combined refrigerant stream to form a first combined compressed refrigerant stream; condensing the first combined compressed refrigerant stream with a cold stream to form a condensed high-pressure liquid refrigerant stream; passing the condensed high-pressure liquid refrigerant stream to the mixed refrigerant receiver. An embodiment of the invention is one, any or all of prior embodiments in this paragraph up through the first embodiment in this paragraph further comprising passing the first warmed refrigerant stream to the first flash drum; and passing the second warmed refrigerant stream to the second flash drum An embodiment of the invention is one, any or all of prior embodiments in this paragraph up through the first embodiment in this paragraph further comprising combining the first refrigerant vapor stream and the first warmed refrigerant stream to form a fourth combined refrigerant stream; and wherein combining the first refrigerant vapor stream from the first flash drum and the second compressed refrigerant vapor stream from the second compressor comprises combining the fourth combined refrigerant streamH242187-WO PATENT APPLICATION and the second compressed refrigerant vapor stream from the second compressor; combining the second refrigerant vapor stream and the second warmed refrigerant stream to form a fifth combined refrigerant stream; and wherein combining the second refrigerant vapor stream from the second flash drum and the second compressed refrigerant vapor stream from the second compressor comprises combining the fourth combined refrigerant stream and the first compressed refrigerant vapor stream from the first compressor. An embodiment of the invention is one, any or all of prior embodiments in this paragraph up through the first embodiment in this paragraph further comprising sub-cooling the first cooled CO2 rich stream with the fourth combined refrigerant stream in a fourth condenser; or sub-cooling the second cooled CO2 rich stream with the fifth combined refrigerant stream in the third condenser or the fourth condenser or both; or both. An embodiment of the invention is one, any or all of prior embodiments in this paragraph up through the first embodiment in this paragraph wherein the cold stream comprises a secondary refrigerant stream from a secondary refrigerant loop, wherein the secondary refrigerant stream comprising a second refrigerant. An embodiment of the invention is one, any or all of prior embodiments in this paragraph up through the first embodiment in this paragraph wherein the second refrigerant comprises a pure hydro-fluoro-olefin (HFO) refrigerant. An embodiment of the invention is one, any or all of prior embodiments in this paragraph up through the first embodiment in this paragraph wherein the secondary refrigerant loop comprises a screw compressor. An embodiment of the invention is one, any or all of prior embodiments in this paragraph up through the first embodiment in this paragraph wherein the first compressor or the second compressor or both comprise a centrifugal compressor having a seal leakage recovery system. An embodiment of the invention is one, any or all of prior embodiments in this paragraph up through the first embodiment in this paragraph wherein the first condenser and the second condenser comprise stages in a single heat exchanger unit. An embodiment of the invention is one, any or all of prior embodiments in this paragraph up through the first embodiment in this paragraph wherein the liquid refrigerant stream is non-flammable as defined by the Al l method from European Regulation EC 440 / 2008. An embodiment of the invention is one, any or all of prior embodiments in this paragraph up through the first embodiment in this paragraph wherein the first refrigerant is an HFO refrigerant. An embodiment of the invention is one, any or all of prior embodiments in this paragraph up through the first embodiment in this paragraph further comprising flashing a second portion of the second refrigerant liquid stream from the second flash drum to partially vaporize and cool the secondH242187-WO PATENT APPLICATION portion of the second refrigerant liquid stream from the second flash drum; separating the partially vaporized and cooled second portion of the second refrigerant liquid stream from the second flash drum into a third refrigerant liquid stream and a third refrigerant vapor stream in a third flash drum, the third flash drum having a lower temperature and a lower pressure than the second flash drum; further cooling the CO2 rich stream or cooling a second CO2 rich stream with a first portion of the third refrigerant liquid stream from the third flash drum in a third condenser to form a third cooled CO2 rich stream and a third warmed refrigerant stream; compressing the third refrigerant vapor stream from the third flash drum in a third compressor stage forming a third compressed refrigerant vapor stream; combining the third compressed refrigerant vapor stream from the third compressor and the second refrigerant vapor stream from the second flash drum to form a third combined refrigerant stream; and wherein compressing the second refrigerant vapor stream comprises compressing the third combined refrigerant stream. An embodiment of the invention is one, any or all of prior embodiments in this paragraph up through the first embodiment in this paragraph further comprising passing the third warmed refrigerant stream to the third flash drum. An embodiment of the invention is one, any or all of prior embodiments in this paragraph up through the first embodiment in this paragraph further comprising combining the third refrigerant vapor stream and the third warmed refrigerant stream to form a fifth combined refrigerant stream; wherein compressing the third refrigerant vapor stream from the third flash drum comprises compressing the fifth combined refrigerant stream forming a fifth compressed combined refrigerant stream; and wherein combining the third compressed refrigerant vapor stream from the third compressor stage and the second refrigerant vapor stream from the second flash drum comprises combining the fifth compressed combined refrigerant stream and the second refrigerant vapor stream to form a sixth combined refrigerant vapor stream; and wherein compressing the second refrigerant vapor stream comprises compressing the sixth combined refrigerant stream.

[0074] A second embodiment of the invention is a process for chilling a CO2 rich stream, comprising flashing a high-pressure liquid refrigerant stream from a mixed refrigerant receiver to partially vaporize and cool the high-pressure liquid refrigerant stream, the liquid refrigerant stream comprising a mixture of CO2 and a first refrigerant, wherein a concentration of the first refrigerant is sufficient to reduce a freezing point of the mixture to less than or equal to -60°C; separating the partially vaporized and cooled high-pressure liquid refrigerant stream into a first refrigerant liquid stream and a first refrigerant vapor stream in a first flash drum; cooling the CO2 rich streamH242187-WO PATENT APPLICATION with a first portion of the first refrigerant liquid stream from the first flash drum in a first cooler forming a first cooled CO2 rich stream and a first warmed refrigerant stream; flashing a second portion of the first refrigerant liquid stream from the first flash drum to partially vaporize and cool the second portion of the first refrigerant liquid stream from the first flash drum; separating the partially vaporized and cooled second portion of the first refrigerant liquid stream from the first flash drum stream into a second refrigerant liquid stream and a second refrigerant vapor stream in a second flash drum, the second flash drum having a lower temperature and a lower pressure than the first flash drum; further cooling the CO2 rich stream or cooling a second CO2 rich stream with a first portion of the second refrigerant liquid stream from the second flash drum in a second cooler forming a second cooled CO2 rich stream and a second warmed refrigerant stream; compressing the second refrigerant vapor stream from the second flash drum in a second compressor stage forming a second compressed refrigerant vapor stream; combining the first refrigerant vapor stream from the first flash drum and the second compressed refrigerant vapor stream from the first stage compressor to form a first combined refrigerant stream; compressing the first combined refrigerant stream to form a first combined compressed refrigerant stream; condensing the first combined compressed refrigerant stream with a secondary refrigerant stream comprising a second refrigerant from a secondary refrigerant loop to form a condensed high-pressure liquid refrigerant stream, wherein the secondary refrigerant loop comprises a screw compressor; passing the condensed high-pressure liquid refrigerant stream to the mixed refrigerant receiver. An embodiment of the invention is one, any or all of prior embodiments in this paragraph up through the second embodiment in this paragraph further comprising passing the first warmed refrigerant stream to the first flash drum; and passing the second warmed refrigerant stream to the second flash drum An embodiment of the invention is one, any or all of prior embodiments in this paragraph up through the second embodiment in this paragraph further comprising combining the first refrigerant vapor stream and the first warmed refrigerant stream to form a fourth combined refrigerant stream; and wherein combining the first refrigerant vapor stream from the first flash drum and the second compressed refrigerant vapor stream from the second compressor comprises combining the fourth combined refrigerant stream and the second compressed refrigerant vapor stream from the second compressor; combining the second refrigerant vapor stream and the second warmed refrigerant stream to form a fifth combined refrigerant stream; and wherein combining the second refrigerant vapor stream from the second flash drum and the second compressedH242187-WO PATENT APPLICATION refrigerant vapor stream from the second compressor comprises combining the fourth combined refrigerant stream and the first compressed refrigerant vapor stream from the first compressor. An embodiment of the invention is one, any or all of prior embodiments in this paragraph up through the second embodiment in this paragraph further comprising sub-cooling the first cooled CO2 rich stream with the fourth combined refrigerant stream in a fourth condenser; or sub-cooling the second cooled CO2 rich stream with the fifth combined refrigerant stream in the third condenser or the fourth condenser or both. An embodiment of the invention is one, any or all of prior embodiments in this paragraph up through the second embodiment in this paragraph wherein the first refrigerant is an hydro-fluoro-olefin refrigerant. An embodiment of the invention is one, any or all of prior embodiments in this paragraph up through the second embodiment in this paragraph wherein the second refrigerant comprises a pure hydro-fluoro-olefin refrigerant.

[0075] Without further elaboration, it is believed that using the preceding description that one skilled in the art can utilize the present invention to its fullest extent and easily ascertain the essential characteristics of this invention, without departing from the spirit and scope thereof, to make various changes and modifications of the invention and to adapt it to various usages and conditions. The preceding preferred specific embodiments are, therefore, to be construed as merely illustrative, and not limiting the remainder of the disclosure in any way whatsoever, and that it is intended to cover various modifications and equivalent arrangements included within the scope of the appended claims.

[0076] In the foregoing, all temperatures are set forth in degrees Celsius and, all parts and percentages are by weight, unless otherwise indicated.

Claims

H242187-WO PATENT APPLICATIONWhat is claimed is:

1. A process for chilling a CO2 rich stream, comprising: flashing a high-pressure liquid refrigerant stream (205) from a mixed refrigerant receiver (204) to partially vaporize and cool the high-pressure liquid refrigerant stream (205), the liquid refrigerant stream (205) comprising a mixture of CO2 and a first refrigerant, wherein a concentration of the first refrigerant is sufficient to reduce a freezing point of the mixture to less than or equal to -60°C; separating the partially vaporized and cooled high-pressure liquid refrigerant stream (211) into a first refrigerant liquid stream (213) and a first refrigerant vapor stream (219) in a first flash drum (210); cooling the CO2 rich stream (111) with a first portion of the first refrigerant liquid stream (213) from the first flash drum in (210) a first cooler forming a first cooled CO2 rich stream and a first warmed refrigerant stream (215); flashing a second portion (217) of the first refrigerant liquid stream (213) from the first flash drum (210) to partially vaporize and cool the second portion (217) of the first refrigerant liquid stream (213) from the first flash drum (210); separating the partially vaporized and cooled second portion (221) of the first refrigerant liquid stream (213) from the first flash drum into a second refrigerant liquid stream (223) and a second refrigerant vapor stream (229) in a second flash drum (220), the second flash drum (220) having a lower temperature and a lower pressure than the first flash drum (210); further cooling the CO2 rich stream (111) or cooling a second CO2 rich stream with a first portion of the second refrigerant liquid stream (223) from the second flash drum (220) in a second cooler forming a second cooled CO2 rich stream and a second warmed refrigerant stream (225); compressing the second refrigerant vapor stream (229) from the second flash drum (220) in a second compressor stage (250) forming a second compressed refrigerant vapor stream (255); combining the first refrigerant vapor stream (219) from the first flash drum (210) and the second compressed refrigerant vapor stream (255) from the second compressor stage (250) to form a first combined refrigerant stream (263);H242187-WO PATENT APPLICATION compressing the first combined refrigerant stream (263) in a first compressor stage (260) to form a first combined compressed refrigerant stream (265); condensing the first combined compressed refrigerant stream (265) with a cold stream to form a condensed high-pressure liquid refrigerant stream (203); and passing the condensed high-pressure liquid refrigerant stream (203) to the mixed refrigerant receiver (204).

2. The process of claim 1 further comprising: passing the first warmed refrigerant stream (215) to the first flash drum (210); and passing the second warmed refrigerant stream (225) to the second flash drum (220).

3. The process of claim 1 further comprising: combining the first refrigerant vapor stream (219) and the first warmed refrigerant stream (215) to form a fourth combined refrigerant stream (417); wherein combining the first refrigerant vapor stream (219) from the first flash drum (210) and the second compressed refrigerant vapor stream (255) from the second compressor stage (250) comprises combining the fourth combined refrigerant stream (417) and the second compressed refrigerant vapor stream (255) from the second compressor stage; and combining the second refrigerant vapor stream (229) and the second warmed refrigerant stream (225) to form a fifth combined refrigerant stream (425); wherein compressing the second refrigerant vapor stream (229) from the second flash drum (220) in a second compressor stage (250) forming a second compressed refrigerant vapor stream (255) comprises compressing the fifth combined refrigerant stream (425) to form a fifth combined compressed refrigerant stream (255); wherein combining the first refrigerant vapor stream (219) from the first flash drum (220) and the second compressed refrigerant vapor stream (255) from the second compressor stage (250) comprises combining the fourth combined refrigerant stream (417) and the fifth combined compressed refrigerant vapor stream (255).

4. The process of claim 3 further comprising:H242187-WO PATENT APPLICATION sub-cooling the first cooled CO2 rich stream (111) with the fourth combined refrigerant stream (417) in a fourth condenser; or sub-cooling the second cooled CO2 rich stream with the fifth combined refrigerant stream (425) in the third condenser or the fourth condenser or both; or both.

5. The process of claim 1 wherein the cold stream comprises a secondary refrigerant stream (323) from a secondary refrigerant loop, wherein the secondary refrigerant stream (323) comprising a second refrigerant comprising a pure hydro-fluoro-olefin refrigerant, and wherein the secondary refrigerant loop comprises a screw compressor.

6. The process of claim 1 wherein the first compressor stage or the second compressor stage or both comprise a centrifugal compressor having a seal leakage recovery system.

7. The process of claim 1 wherein the first refrigerant is an HFO refrigerant.

8. The process of claim 1 further comprising: flashing a second portion (227) of the second refrigerant liquid stream (223) from the second flash drum (210) to partially vaporize and cool the second portion (227) of the second refrigerant liquid stream (223) from the second flash drum (220); separating the partially vaporized and cooled second portion (227) of the second refrigerant liquid stream (223) from the second flash drum (220) into a third refrigerant liquid stream (233) and a third refrigerant vapor stream (239) in a third flash drum (230), the third flash drum (230) having a lower temperature and a lower pressure than the second flash drum (220); further cooling the CO2 rich stream (111) or cooling a second CO2 rich stream with a first portion of the third refrigerant liquid stream (233) from the third flash drum (230) in a third condenser to form a third cooled CO2 rich stream and a third warmed refrigerant stream (235); compressing the third refrigerant vapor stream (239) from the third flash drum (230) in a third compressor stage (240) forming a third compressed refrigerant vapor stream (245);H242187-WO PATENT APPLICATION combining the third compressed refrigerant vapor stream (245) from the third compressor stage (240) and the second refrigerant vapor stream (229) from the second flash drum (220) to form a third combined refrigerant stream (253); and wherein compressing the second refrigerant vapor stream (229) comprises compressing the third combined refrigerant stream (253).

9. The process of claim 8 further comprising: passing the third warmed refrigerant stream (235) to the third flash drum (230).

10. The process of claim 8 further comprising: combining the third refrigerant vapor stream (239) and the third warmed refrigerant stream (235) to form a fifth combined refrigerant stream (433); wherein compressing the third refrigerant vapor stream (239) from the third flash drum (230) comprises compressing the fifth combined refrigerant stream (433) forming a fifth compressed combined refrigerant stream (245); wherein combining the third compressed refrigerant vapor stream (245) from the third compressor stage (240) and the second refrigerant vapor stream (229) from the second flash drum (220) comprises combining the fifth compressed combined refrigerant stream (245) and the second refrigerant vapor stream (425) to form a sixth combined refrigerant vapor stream (253); and wherein compressing the second refrigerant vapor stream (229) comprises compressing the sixth combined refrigerant stream (253).

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