MXPA99011687A - Method for carrying out subambient temperature, especially cryogenic, separation using refrigeration from a multicomponent refrigerant fluid - Google Patents

Abstract

A method for low temperature separation of fluids wherein the separation process is sustained by refrigeration generated by a recirculating multicomponent refrigerant fluid.

Description

METHOD TO CARRY OUT SEPARATION ESPECIALLY CRIOGÉN ICA. A TEMPERATU RA YOUR B-AMBI ENTAL THAT USES REFRIGERATION FROM REFRIGERANT FLUID OF MULTIPLE COMPONENTS TECHNICAL FIELD ICO This invention relates generally to the provision of refrigeration for separation of mixtures at sub-ambient temperature, and is advantageous particularly for use with cryogenic separation.

BACKGROUND OF THE ICA TECHNIQUE In separations at sub-ambient temperature, refrigeration is provided to a mixture of gases to maintain low temperature conditions and thus facilitate the separation of the mixture into its components for recovery. Examples of such separations at sub-ambient temperature include cryogenic air separation, natural gas improvement, recovery of hydrogen from crude syngas, and production of carbon dioxide. One way to provide the cooling required to carry out the separation is by turbo-expansion of a fluid stream and using the cooling generated by the turbo-expansion, by heat exchange either directly or indirectly, to facilitate separation. Such a system, although effective, uses significant amounts of energy and can reduce product recovery and is thus costly to operate.

Cooling can also be generated using a refrigeration circuit wherein a refrigerant fluid is compressed and liquefied and then undergoes a phase change at a given temperature from a liquid to a gas thereby making its latent heat of evaporation available for cooling purposes. Such refrigeration circuits are commonly used in domestic refrigerators and air conditioners. Although such a refrigeration circuit is effective to provide cooling at a given temperature and at relatively high sub-ambient temperatures, it is not very efficient when cooling is desired at low temperatures and over a wide range of relatively high temperatures. Accordingly, it is an object of this invention to provide a method for carrying out a separation at sub-ambient temperature of a mixture of fluids, especially one carried out at cryogenic temperatures, more efficiently than with conventional separation systems and without the need for use turbo-expansion to generate some of the cooling required for separation.

BRIEF DESCRIPTION OF THE INVENTION The above and other objects that will become apparent to the person skilled in the art upon reading this description are obtained by the present invention, an aspect of which is: a method for separating a mixture of fluids comprising : (A) compress a multi-component refrigerant fluid; (B) cooling the compressed multiple component refrigerant fluid to at least partially condense the multicomponent refrigerant fluid; (C) expanding the compressed multiple component refrigerant fluid to generate refrigeration; (D) employing said refrigeration to maintain low temperature conditions for a mixture of fluids; (E) separating the fluid mixture in at least one volatile vapor component and in at least one less volatile liquid component; and (F) recovering at least one of said more volatile vapor component (s) and less volatile liquid component (s). Another aspect of the invention is: A method for carrying out cryogenic rectification of feed air comprising: (A) passing feed air to a cryogenic rectification plant and separating the feed air by cryogenic rectification within the rectification plant cryogenic to produce at least one of the product nitrogen and oxygen product; (B) compressing a multicomponent refrigerant fluid by cooling the compressed multiple component refrigerant fluid to at least partially condensate the multicomponent refrigerant fluid, expanding the compressed multiple component refrigerant fluid, cooled to generate refrigeration, and employing such refrigeration to sustain said cryogenic rectification; and (C) recovering at least one of product nitrogen and oxygen product from the cryogenic rectification plant. As used herein, the term "refrigeration" means the ability to reject heat from a sub-environmental temperature system, such as a separation process at sub-ambient temperature, to the surrounding atmosphere. As used herein, the term "cryogenic rectification plant" means an installation for fractionally distilling a mixture by cryogenic rectification, comprising one or more columns and the pipe, valves and heat exchange equipment concomitant thereto. . As used herein, the term "feed air" means a mixture comprising primarily oxygen, nitrogen and argon, such as ambient air. As used herein, the term "column" means a fractionation distillation column or zone, i.e., a column or contact zone, wherein liquid and vapor phases are contacted in countercurrent to effect the separation of a mixing of fluids, such as, for example, contacting the vapor and liquid phases in a series of vertically separated trays or plates mounted within the column and / or on packing elements such as structured or random packing. For an additional discussion of distillation columns, see the Chemical Engineer's Manual, fifth edition, edited by R. H. Perry and C. H. Chilton, McGraw-Hill Book Company, New York, Section 1 3, The Continuous Distillation Process. The term "double column" is used to mean a higher pressure column having its upper portion in heat exchange relationship with the lower portion of a lower pressure column. An additional discussion of double columns appears in Ruheman's "Gas Separation," Oxford University Press, 1949, chapter VI, Commercial Air Separation. The processes of separation by contact of vapor and liquid depend on the difference of vapor pressures of the components. The component of high vapor pressure (or more volatile or low boiling) will tend to concentrate in the vapor phase, while the component of low vapor pressure (or less volatile or high boiling) will tend to concentrate in the liquid phase. Distillation is the separation process by which heating of a liquid mixture can be used to concentrate the more volatile component (s) in the vapor phase and hence the less volatile component (s). (is) in the liquid phase. Partial condensation is the separation process by which the cooling of a mixture of vapors can be used to concentrate the most volatile component (s) in the vapor phase and hence the component (s) less volatile (is) in the liquid phase. The rectification, or continuous distillation, is the separation process that successively combines vaporizations and partial condensations as obtained by a countercurrent treatment of the vapor and liquid phases. The countercurrent contact of the vapor and liquid phases can be adiabatic or non-adiabatic and can include integral contact (by stages) or differential (continuous) between the phases. The arrangements of the separation process that uses the principles of rectification to separate mixtures are often referred to interchangeably as rectification columns, distillation columns, or fractionation columns.

Cryogenic rectification is a rectification process carried out at least in part at temperatures of or below 150 degrees Kelvin (K). As used herein, the term "indirect heat exchange" means bringing the two fluid streams into a heat exchange relationship without any physical or intermixed contact of the fluids therebetween. As used herein, the terms "turbo-expander" and "turbo-expander" mean method and apparatus respectively for high-pressure fluid flow through a turbine to reduce the pressure and temperature of the fluid thereby generates cooling. As used herein, the term "expansion" means to make a reduction in pressure. As used herein, the term "nitrogen product" means a fluid having a nitrogen concentration of at least 99 mole percent. As used herein, the term "oxygen product" means a fluid having an oxygen concentration of at least 70 mole percent.

As used herein, the term "variable charge refrigerant" means a mixture of two or more components in proportions such that the liquid phase of those components undergoes a continuous and increasing temperature change between the bubble point and the point of spray of the mixture. The bubble point of the mixture is the temperature, at a given pressure, where the mixture is all in the liquid phase, but the addition of heat will initiate the formation of a vapor phase in equilibrium with the liquid phase. The dew point of the mixture is the temperature, at a given pressure, where the mixture is all in the vapor phase, but the extraction of heat will initiate the formation of a liquid phase in equilibrium with the vapor phase. Hence, the region of temperature between the bubble point and the dew point of the mixture is the region where both liquid and vapor phases coexist in equilibrium. In the practice of this invention, the temperature differences between the bubble point and the dew point for the variable charge refrigerant is at least 10 ° K, preferably at least 20 ° K and more preferably at at least 50 ° K. As used herein, the term "fluorocarbon" means one of the following: tetrafluoromethane (CF), perfluoroethane (C? Fe), perfluoropropane (C3F8), perfluorobutane (C F10), perfluoropentane (C5F12) ), perfluoroethene (C2F), perfluoropropene (C3F6), perfluorobutene (C F8), perfluoropentene (C5F10), hexafluorocyclopropane (cyclo-C3F6), and octafluorocyclobutane (cyclo-C F8). As used herein, the term "hydrofluorocarbon" means one such axis: fluoroform (CH F3), pentafluoroethane (C? HFg), tetrafluoroethane (C2H2F4), heptafluoropropane (C3HF7), hexafluoropropane (C3H2F6), pentafluoropropane (C3H3F5) , tetrafluoropropane (C3H4F4), nonafluorobutane (C HF9), octafluorobutane (C4H2F8), undecafluoropentane (CsHFn), methyl fluoride (CH3F), difluoromethane (CH2F2), ethyl fluoride (C2H5F), difluoroethane (C2H4F2), trifluoroethane (C2H3F3) , difluoroethene (C2H2F2), trifluoroethene (C2HF3), fluoroethene (C2H3F), pentafluoropropene (C3HFS), tetrafluoropropene (C3H2F), trifluoropropene (C3H3F3), difluoropropene (C3H4F2), heptafluorobutene (C4HF7), hexafluorobutene (C H2F6), and nonafluoropentene ( C5HF9). As used herein, the term "fluoroether" means one of the following: trifluoromethoxy-perfluoromethane (CF3-O-CF3), difiuoromethoxy-perfluoromethane (CHF2-O-CF3), fluoromethoxy-perfluoromethane (CH2F-O-CF3) , difluoromethoxy-difluoromethane (CHF2-O-CHF2), difluoromethoxy-perfluoroethane (CHF2-O-C2F5), difluoromethoxy-1,2,2,2-tetrafluoroethane (CHF-O-C2HF), difluoromethoxy-1, 1,2,2-tetrafluoroethane (CHF2-O-C2HF), perfluoroethoxy-fluoromethane (C2F5-O-CH2F), perfluoromethoxy-1,1,2-trifluoroethane (CF3-O-C2H2F3), perf luoro methoxy-1,2,2-trifluoroethane (CF3-O-C2H2F3), cyclo-1,1,2,2-tetrafluoropropyl ether (cyclo-C3H2F -O-), cyclo-1,1,3,3-tetrafluoropropyl ether ( Cyclo-C3H2F -O-), perfluoromethoxy-1,1,2,2-tetrafluoroethane (CF3-O-C2HF4), cyclo-1,1,2,3,3-pentafluoropropyl ether (CÍCI0-C3H5-O-), perfluoromethoxy -perfluoroacetone (CF3-O-CF2-O-CF3), perfluoromethoxy-perfluoroethane (CF3-O-C2Fs), perfluoromethoxy-1, 2,2,2-tetrafluoroethane (CF3-O-C2HF4), perfluoromethoxy-2,2, 2-trifluoroethane (CF3-O-C2H2F3), cyclo-perfluoromethoxy-perfluoroacetone (cyclo-CF2-O-CF2-O-CF2-), and cyclo-perfluoropropyl ether (cyclo-C3F6-O). As used herein, the term "atmospheric gas" means one of the following: nitrogen (N2), argon (Ar), krypton (Kr), xenon (Xe), neon (Ne), carbon dioxide (CO2) , oxygen (O2), and helium (He). As used herein, the term "non-toxic" means not to pose an acute or chronic hazard when handled in accordance with acceptable exposure limits. As used herein, the term "non-flammable" means that either there is no flashing point or a very high flashing point of at least 600 ° K. As used herein, the term "low ozone reducer" "means that it has a lower ozone depleting potential than 0. 15 as defined by the Montreal Protocol convention where dichlorofluoromethane (CCI2F2) has an ozone depleting potential of 1.0. As used herein, the term "non-ozone depleting" means that it has no component that contains a chlorine, bromine or iodine atom. As used herein, the term "normal boiling point" means the boiling temperature at a pressure of a standard atmosphere, i.e., 1.034 kilograms per square centimeter-absolute.

BRIEF DESCRIPTION OF THE DIAMETER The only Figure is a schematic representation of a preferred embodiment of the invention wherein the separation is cryogenic air separation and a cooling circuit of multi-component cooling fluid serves to generate cooling to cool and thereby maintain the low temperatures inside the cryogenic air separation plant.

DETAILED DESCRIPTION The invention will be described in detail with reference to the Drawing. In the Figure there is illustrated a cryogenic air separation plant having three columns, a double column having higher and lower pressure columns, and a column with argon side arm. Referring now to the Figure, feed air 60 is compressed by passing through the base load compressor 30 at a pressure generally within the range of 2.46 to 18 kilograms per absolute square centimeter (kcca). The resulting compressed feed air 61 is cooled from the heat of compression in a post-cooler (not shown) and is then cleaned of high boiling impurities such as water vapor, carbon dioxide and hydrocarbons by passage through the purifier 50 and then the purified feed air stream 62 is divided into two designated portions 65 and 63. The portion 65, which generally comprises from 20 to 35 percent of the feed air stream 62, is further compressed by passage through the compressor 31 reinforcement at a higher pressure, which can be up to 70.37 kcca. The resultant additionally compressed feed air stream 66 is cooled from the heat of compression in a post-cooler (not shown) and is cooled and at least partially condensed by indirect heat exchange in the primary or primary heat exchanger 1 with currents return. The resultant cooled feed air stream 67 is then divided into stream 68 which is passed to column 10 of higher pressure through valve 120 and stream 69 which is passed through valve 70 and as current 71 to column 1 1 of lower pressure. The remaining portion 63 of the supply air stream 62 is cooled by e (passage through the main heat exchanger 1 by indirect heat exchange with the return streams and current 64 is passed to the column 10 of higher pressure. which is operating at a pressure generally within the range of 2.46 to 18 kaka.In column 10 of higher pressure the feed air is separated by cryogenic rectification in steam enriched in nitrogen and liquid enriched in oxygen.The steam enriched in nitrogen is withdrawn from the upper portion of the column 10 of higher pressure in stream 77 and condensed in the reboiler boiler 2 by indirect heat exchange with boiling liquid from the lower pressure column .. The resulting liquid nitrogen-enriched 78 is returned to column 10 as reflux A portion of liquid 79 enriched in nitrogen is passed from column 1 0 to the superheater 6 where it is subcooled to form the subcooled stream 80. If desired, a portion 81 of stream 80 can be recovered as a liquid nitrogen product having a nitrogen concentration of at least 99 mole percent. The remainder of current 80 is passed in stream 82 to the upper portion of column 1 1 as reflux. The oxygen enriched liquid is removed from the lower portion of the higher pressure column 10 in the stream 83 and passed to the superheater 7 where it is subcooled. The resultant subcooled oxygen enriched liquid 84 is then divided into portion 85 and portion 88. Portion 85 is passed through valve 86 and stream 87 to column 1 1 of less pressure. The portion 88 is passed through the valve 95 and the condenser 3 of the argon column where it is partially evaporated. The resulting vapor is removed from condenser 3 in stream 94 and passed to column 1 1 of lower pressure. The remaining oxygen enriched liquid is withdrawn from condenser 3 in stream 93, combined with stream 94 to form stream 96 and then passed to column 1 1 of lower pressure. The lower pressure column 1 1 is operated at a lower pressure than that of the column 10 of higher pressure and within generally the range from 1.05 to 7.03 kcca. Within column 1 1 of lower pressure the various feeds are separated by cryogenic rectification in nitrogen-rich vapor and oxygen-rich liquid. The nitrogen-rich vapor is removed from the upper portion of column 1 1 in stream 101, heated by passage through heat exchangers 6, 7 and 1, and recovered as product nitrogen in stream 104 having a nitrogen concentration of at least 99 mole percent, preferably at least 99.9 mole percent, and most preferably 99.999 mole percent. For purposes of purity control of the product, a waste stream 97 is withdrawn from column 1 1 from a level below the point of extraction of stream 101, heated by passage through heat exchangers 6, 7 and 1 , and removed from the system in stream 100. The oxygen-rich liquid is withdrawn from the lower portion of column 1 1 in stream 105 having an oxygen concentration within generally from 90 to 99.9 mol percent. If desired, a portion 106 of stream 105 can be recovered by running liquid oxygen product. The remaining portion 107 of the stream 105 is pumped at a higher pressure by passing through the pump 35 for liquid and the pressurized stream 108 is evaporated in the main heat exchanger 1 and recovered as gas 109 of high pressure oxygen product. The fluid comprising oxygen and argon is passed in the stream 1 10 of column 1 1 of lesser pressure to column 12 of argon where it is separated by cryogenic rectification in fluid richer in argon and fluid richer in oxygen. The oxygen-rich fluid is passed from the lower portion of column 12 in stream 11 1 to column 1 1 of lower pressure. The fluid richer in argon is passed from the upper portion of the column 12 in the steam stream 89 to the condenser 3 of the argon column where it is condensed by indirect heat exchange with the liquid enriched in subcooled oxygen partially evaporated aforementioned. The resulting richer liquid in argon is extracted from condenser 3 in stream 90.

One portion 91 is passed to column 12 of argon as reflux and another portion 92 is recovered as argon product having an argon concentration generally in the range of 95 to 99.9 mole percent. Now we will describe in more detail the operation of the multicomponent refrigerant circuit that serves to generate all the cooling passed to the cryogenic rectification plant, thereby eliminating the need for any turbo-expansion of a process stream to produce refrigeration for the separation. The separation processes at sub-environmental temperatures require refrigeration for several purposes. First, since the process equipment operates at low temperatures, there is heat leakage from the ambient atmosphere to the equipment that is a function of the surface areas of the equipment, the temperature of the local operation, and the insulation of the equipment. Second, since the processes generally involve heat exchange between feed and return streams, there is net heat input to the process associated with temperature differences for heat exchange. Third, if the process produces liquid product from gaseous feed, sufficient refrigeration must be provided for liquefaction. Fourth, for those processes that use cold fluid pumping, such as pumping liquids, the pumping energy must be rejected from the process system. Fifth, for those processes that use liquid pumping and evaporation to provide gaseous product at high pressure, commonly referred to as product heater processes, heat pumping is required between the two temperature levels associated with the evaporation of liquid at the levels of low and high pressure. Such pumping of heat is often provided by a fraction of the feed air at a high pressure level, but can be supplemented by external cooling of the system. Finally, there may be another intake of miscellaneous heat or cooling needs for the process. The satisfactory operation of the separation process at sub-ambient temperature requires sufficient cooling to compensate all the heat input to the system and thereby maintain the low temperatures associated with the process. As can be visualized from the various refrigeration requirements listed above, the typical sub-ambient temperature preparation process has a variable refrigeration requirement in the entire temperature range associated with the separation, that is, from the ambient temperature to the temperature colder inside the separation process. Generally the heat exchangers used to cool the feed streams versus the return streams will include the full temperature range associated with the separation process. Therefore, that interchanger is adequate to provide the required cooling. The multicomponent refrigerant fluid can be incorporated into that heat exchanger to provide variable refrigeration over the entire temperature range. . The provision of variable refrigeration, as it is necessary in each temperature, allows the equalization of the cooling and heating curves of the composite heat exchanger and with this the energy requirements of the separation process are reduced. Such cooling equalization required and supplied at all temperature levels within the heat exchanger allows the heat exchanger to operate at uniform or approximately uniform temperature differences over its entire length. Although the above-described situation is the preferred practice for the invention, it is understood that some deviation can be allowed for acceptable practice. For example, it is well known that the equalization of cooling and heating curves is more important at lower temperatures. Therefore, an acceptable system could have a more closed curve equalization below 200 ° K than in the temperature region of 200 ° K to 300 ° K. Also, although it is preferred to incorporate the multi-component refrigerant circuit throughout the entire length of the heat exchanger, it may be acceptable to include the refrigerant circuit within only a portion of the length of the heat exchanger. The following description illustrates the multi-component coolant system for providing cooling throughout the primary heat exchanger one. The multicomponent refrigerant fluid in stream 201 is compressed by passing through the recycle compressor 34 at a pressure generally within the range of 4.22 to 42.22 kcca to produce compressed refrigerant 202. The compressed refrigerant fluid is cooled from the compression heat by passing through the post-cooler 4 and can be partially condensed. The multicomponent refrigerant fluid in stream 203 is then passed through the heat exchanger 1 where it is further cooled and is at least partially condensed and can be completely condensed. Cooled, compressed multiple component refrigerant 204 is then expanded or throttled through valve 205. The throttle partially evaporates the multi-component refrigerant fluid, cooling the fluid and generating refrigeration. Under some limited circumstances, dependent on the conditions of the heat exchanger, the compressed fluid 204 may be liquid subcooled prior to expansion, and may remain as a liquid until the initial expansion. Subsequently, by heating in the heat exchanger, the fluid will have two phases. The pressure expansion of the fluid through a valve would provide cooling by the Joule-Thomson effect, ie, lowering the fluid temperature due to pressure expansion at constant enthalpy. However, under some circumstances, fluid expansion could occur using a two-phase or liquid expansion turbine, such that the fluid temperature would be decreased due to the expansion work. The multicomponent two-phase refrigerant fluid stream 206 which undergoes the cooling is then passed through the heat exchanger 1 where it is heated and completely evaporated thus serving by indirect heat exchange to cool the stream 203 and also to transfer refrigeration to the process streams within the heat exchanger, including the feed air streams 66 and 63, thus passing the cooling generated by the multi-component cooling fluid cooling circuit to the cryogenic rectification plant to sustain the separation process . The resulting heated multi-component refrigerant fluid in the vapor stream 201 is then recirculated to the compressor 34 and the refrigeration cycle begins again. In the cooling cycle of the multi-component refrigerant fluid while the high pressure mixture is condensed, the low pressure mixture is boiled against it, ie the condensation heat boils the low pressure liquid. At each temperature level, the net difference between evaporation and condensation provides cooling. For a given combination of refrigerant components, the mixture composition, flow rate and pressure levels determine the refrigeration available at each temperature level. The multicomponent refrigerant fluid contains two or more components in order to provide the refrigeration required at each temperature. The selection of refrigerant components will depend on the refrigeration load versus temperature for the application of the particular process. Suitable components will be selected depending on their normal boiling points, heat beating, and flammability, toxicity, and ozone reduction potential.

A preferable embodiment of the multicomponent refrigerant fluid useful in the practice of this invention comprises at least two components of the group consisting of fluorocarbons, hydrofluorocarbons, and fluoroethers. Another preferable embodiment of the multicomponent refrigerant fluid useful in the practice of this invention comprises at least u? component of the group consisting of fluorocarbons, hydrofluorocarbons and fluoroethers, and at least one atmospheric gas. Another preferable embodiment of the multicomponent refrigerant fluid useful in the practice of this invention comprises at least two components of the group consisting of fluorocarbons, hydrofluorocarbons and fluoroethers, and at least two atmospheric gases. Another preferable embodiment of the multicomponent refrigerant fluid useful in the practice of this invention comprises at least one fluoroether and at least one component of the group consisting of fluorocarbons, hydrofluorocarbons, fluoroethers and atmospheric gases. In a preferred embodiment, the multicomponent refrigerant fluid consists solely of fluorocarbons. In another preferred embodiment, the multicomponent refrigerant fluid consists solely of fluorocarbons and hydrofluorocarbons. In another preferred embodiment, the multicomponent refrigerant fluid consists solely of fluorocarbons and atmospheric gases. In another preferred embodiment, the multicomponent refrigerant fluid consists solely of fluorocarbons, hydrofluorocarbons and fluoroethers. In another preferred embodiment, the multicomponent refrigerant fluid consists solely of fluorocarbons, fluoroethers, and atmospheric gases. The multicomponent refrigerant fluid useful in the practice of this invention may contain other components such as hydrochlorofluorocarbons and / or hydrocarbons. Preferably, the multicomponent refrigerant fluid does not contain hydrochlorofluorocarbons. In another preferred embodiment of the invention, the multicomponent refrigerant fluid does not contain hydrocarbons. Most preferably, the multicomponent refrigerant fluid does not contain hydrochlorofluorocarbons or hydrocarbons. Most preferably, the multicomponent refrigerant fluid is non-toxic, non-flammable and non-ozone depleting and most preferably, each component of the multicomponent refrigerant fluid is either a fluorocarbon, hydrofluorocarbon, fluoroether or atmospheric gas. The invention is particularly advantageous for use in efficiently achieving cryogenic temperatures from ambient temperatures. Tables 1-5 list preferred examples of multicomponent refrigerant blends useful in the practice of this invention. The concentration ranges given in the Tables are in percent mol.

TABLE 1 COMPONENT CONCENTRATION RATE CsF? 2 5-25 C4F? O 0- 15 C3F8 10-40 C2F8 0-30 CF4 10-50 Ar 0-40 N2 10-80 10 TABLE 2 COMPONENT RANGE OF CONCENTRATION C3F8 10-40 CHF3 0-30 CF4 10-50 Ar 0-40 N2 10-80 TABLE 3 COM SPEAKER CONCENTRATION RANGE C3H3Fs 5-25 C3H3Fe 0-1 5 C2HF5 5-20 C2F8 0-30 CF4 10-50 Ar 0-40 N2 10-80 TABLE 4 COMPONENT CONCENTRATION RANGE CHF2-O-C2H F4 5-25 C H-? O 0-1 5 CF3-O-CHF2 10-40 CF3-O-CF3 0-20 C2F8 0-30 CF4 10-50 Ar 0-40 N2 10-80 TABLE 5 COMPONENT CONCENTRATION RANGE C3H3F5 5-25 C3H2F8 0-15 CF3-O-CHF2 10-40 CHF3 0-30 CF4 0-25 Ar 0-40 N2 10-80 The invention is especially useful for providing refrigeration over a wide temperature range, particularly one that encompasses cryogenic temperatures. In a preferred embodiment of the invention each of the two or more components of the refrigerant mixture has a normal boiling point which differs by at least 5 degrees Kelvin, more preferably at least 10 degrees Kelvin, and most preferably by at least 20 degrees Kelvin, of the normal boiling point of each other component in that refrigerant mixture. This increases the effectiveness to provide cooling over a wide temperature range, particularly one that encompasses cryogenic temperatures. In a particularly preferred embodiment of the invention, the normal boiling point of the highest boiling component of the. Multi-component refrigerant fluid is at least 50 ° K, preferably at least 100 ° K, most preferably at least 200 ° K, greater than the normal boiling point of the lower boiling component of the component cooling fluid multiple Although the multi-component refrigerant fluid flow circuit illustrated in the Drawing is a single closed-loop flow circuit, it may be desirable to use other arrangements for specific applications. For example, it may be desirable to use multiple independent flow circuits, each with its own refrigerant blends and process conditions. Such multiple circuits could more rapidly provide cooling at different temperature ranges and reduce the complexity of the refrigerant system. Also, it may be desirable to include phase separations in the flow circuit at one or more temperatures to allow internal recycling of some of the refrigerant liquid. Such internal recycling of the coolant would prevent unnecessary cooling of the coolant and prevent the freezing of the coolant. The components and their concentrations making the multicomponent refrigerant fluid useful in the practice of this invention are such that they form a variable charge multi-component refrigerant fluid and preferably maintain such a variable charge characteristic over the entire temperature range of the method of the invention. This greatly increases the efficiency with which the cooling can be generated and used over such a wide temperature range. The preferred defined group of components has an added benefit because they can be used to form fluid mixtures that are non-toxic, non-flammable, and low or non-ozone depleting. This provides additional advantages over conventional refrigerants which are typically toxic, flammable and / or ozone depleting. A preferred variable charge multiple component refrigerant fluid useful in the practice of this invention which is non-toxic, non-flammable and non-ozone depleting comprises two or more components of the group consisting of CSF12, CHF2-O-C2HF, CHF9 , C3H3Fs, C2F5-O-CH2F, CsHzFß, CHF2-O-CHF2, C4F? O, CF3-O-C2H2F3, C3HF7, CH2F-O-CF3, C2H2F4, CHF2-O-CF3, C3F8, C2H F5, CF3-O-CF3, C2F6, CHF3, CF4, O2, Ar, N2, Ne and He. Although the invention has been described in detail with reference to a certain preferred embodiment, those skilled in the art will recognize that there are other embodiments of the invention within the spirit and scope of the claims. For example, the invention can be practiced in conjunction with other cryogenic air separation systems and with other cryogenic separation systems such as natural gas enhancement and recovery of hydrogen or helium. It can also be used to carry out non-cryogenic separations at sub-environmental temperatures such as carbon dioxide recovery.

Claims (10)

1. CLAIMS 1. A method for separating a fluid mixture comprising: (A) compressing a multicomponent refrigerant fluid; (B) cooling the compressed multiple component refrigerant fluid until at least partially condensing the multicomponent refrigerant fluid; (C) expanding the compressed, cooled multiple component refrigerant fluid to generate refrigeration; (D) employing said refrigeration to maintain low temperature conditions for a mixture of fluids; (E) separating the fluid mixture in at least one more volatile vapor component and in at least one less volatile liquid component; and (F) recovering at least one of said more volatile vapor component (s) and less volatile liquid component (s).
2. 2. The method of claim 1, wherein the separation of the fluid mixture is carried out in a cryogenic rectification plant.
3. The method of claim 1, wherein the expansion of the cooled, compressed, multiple component refrigerant fluid produces a two-phase multi-component refrigerant fluid.
4. The method of claim 1, wherein the multicomponent refrigerant fluid comprises at least one component of the group consisting of fluorocarbons, hydrofluorocarbons and fluoroethers and at least one atmospheric gas.
5. 5. The method of claim 1, wherein the multicomponent refrigerant fluid comprises at least two components of the group consisting of fluorocarbons, hydrofluorocarbons and fluoroethers and at least two atmospheric gases.
6. The method of claim 1, wherein the multicomponent refrigerant fluid comprises at least one fluoroether and at least one component of the group consisting of fluorocarbons, hydrofluorocarbons, fluoroethers, and atmospheric gases.
7. The method of claim 1, wherein the normal boiling point of the highest boiling component of the multicomponent refrigerant is at least 50 ° K greater than the normal boiling point of the lower boiling component of the fluid multi-component refrigerant.
8. 8. A method for carrying out the cryogenic rectification of feed air comprising: (A) passing feed air to a cryogenic rectification plant and separating the feed air by cryogenic rectification within the cryogenic rectification plant to produce by at least one of the product nitrogen and product oxygen; (B) compressing a multi-component refrigerant fluid, cooling the compressed multi-component refrigerant fluid to at least partially condensate the multi-component refrigerant fluid, expanding the compressed multiple component refrigerant fluid, cooled to generate refrigeration, and employing said refrigeration to sustain said cryogenic rectification; and (C) recovering at least one of the product nitrogen and oxygen product from the cryogenic rectification plant. The method of claim 8, wherein the cooling generated by the expansion of the multicomponent refrigerant fluid is the only refrigeration used to sustain the cryogenic rectification. The method of claim 8, wherein the compression, cooling and expansion of the multicomponent refrigerant fluid is carried out in a closed circuit. RESU M EN A method for separating fluids at low temperature where the separation process is sustained by cooling generated by a recirculating multi-component refrigerant fluid.