US20110232306A1

US20110232306A1 - Absorption refrigeration cycles using a lgwp refrigerant

Info

Publication number: US20110232306A1
Application number: US13/076,120
Authority: US
Inventors: Ryan Hulse; Christopher J. Seeton; Mark W. Spatz; Rajiv R. Singh
Original assignee: Honeywell International Inc
Current assignee: Honeywell International Inc
Priority date: 2008-04-30
Filing date: 2011-03-30
Publication date: 2011-09-29
Also published as: EP2553355A4; EP2553355A2; WO2011123592A3; JP2018136117A; CN102906515B; JP5864533B2; JP2016118383A; CN102906515A; WO2011123592A2; JP2013525724A

Abstract

An absorptive refrigeration method and refrigerant/absorbant pairs comprising fluorinated organic compounds, such as fluorinated organic compounds having from one to eight carbon atoms (C1-C8), including hydrofluoroolefin and/or hydrochlorofluoroolefin compounds. In certain embodiments, a fluorinated organic compound, including certain hydrofluoroolefin and/or hydrochlorofluoroolefin compounds (e.g. C2-C4 hydrofluoroolefin and/or hydrochlorofluoroolefin compounds) is/are utilized as the refrigerant, with the absorbant portion either being a fluorinated organic compound or a non-fluorinated oil.

Description

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is related to and claims the priority benefit of U.S. provisional application Ser. No. 61/320,305, filed Apr. 1, 2010, the contents of which are incorporated herein by reference.
The application is also a continuation-in-part of U.S. application Ser. No. 12/432,466, filed Apr. 29, 2009, which claims priority to United States provisional application serial number 61/049,069, filed Apr. 30, 2008, the contents each of which are incorporated herein by reference.

FIELD OF THE INVENTION

This invention relates to economical absorption refrigeration systems that employ refrigerants with low global warming potential (GWP) and low ozone depletion potential (ODP).

BACKGROUND OF THE INVENTION

Absorption refrigeration is a more economical alternative to compression refrigeration when a source of waste or other low-cost heat (e.g. solar heating) is available. As such, absorption refrigeration has the potential to play a very important role in reducing the environmental impact of cooling systems that operate in hot environments.
Both absorption refrigerators and vapor compression refrigerators use a refrigerant with a very low boiling point. In both types, when this refrigerant evaporates or boils, it takes some heat away with it, providing the cooling effect. However, absorption refrigeration and vapor compression refrigeration differ in the way the refrigerant is changed from a gas back into a liquid so that the cycle can repeat. A vapor compression refrigerator uses mechanical work, frequently supplied by an electrically-powered compressor, to increase the pressure on the gas, and then condenses the hot, high pressure gas back to a liquid by heat exchange with a cool fluid (usually air). An absorption refrigerator does not use mechanical work to increase the pressure of the pressure of the gas and changes the gas back into a liquid using a different method that needs only a low-power pump, or optionally only heat, thereby providing a system that has fewer moving parts, which increases the overall lifetime of the system.
Residential and commercial buildings are large consumers of energy and the major consumer of electricity with demand varying constantly. During low to moderate demand periods electricity is produced by the most efficient equipment utilizing nuclear, coal, or hydroelectric energy sources since this equipment is run nearly continuously. However during peak demand, less costly and less efficient equipment is used typically running on natural gas or fuel oil which raises concerns about fuel security in the case of oil use and price stability for natural gas. Peak demand also set the overall size of the electrical system that includes the generating and distribution systems. In addition, reducing demand at times when the generating or transmission systems are at their limit is an effective way to improve reliability of electricity supply and avoid interruptions that can have significant negative economic impact.
Solar energy can be utilized through the use of relatively inexpensive collector panels with the solar energy transferred to a working fluid which is typically water with glycols added to suppress the freezing point. This fluid then becomes the heat source that powers the absorption cooling system. In addition, when cooling is not required, this can be used to heat potable water. An additional benefit for new installations is that the base vapor compression cooling system can be downsized and thereby operate with less cycling that will improve the performance of this system. Also, absorption refrigeration can have an advantage is such environments because it holds the potential to use the same source of energy that typically increases the load on these systems, i.e. solar energy, to provide needed cooling.
Common examples of refrigeration cycles are food refrigerators and freezers and air conditioners. The reversible-cycle heat pumps for providing thermal comfort also work by exploiting the physical properties of evaporating and condensing a refrigerant. In heating, ventilation, and cooling (HVAC) applications, a heat pump normally refers to a refrigeration device that includes a reversing valve and optimized heat exchangers so that the direction of heat flow may be reversed. Most commonly, during the heating cycle, heat pumps draw heat from the air or from the ground, or even from water.
Although absorption systems have been in limited use for many years, applicants have come to recognize that conventional working fluids have had significant disadvantages that have limited their success. For example, the two most common absorption refrigeration pairs are NH₃-water and water-LiBr. NH₃-water use NH₃as the refrigerant and water as the absorbent. Although NH₃performs well as a refrigerant in many applications, the toxicity of NH₃limits it use in areas that can be occupied by the public. In addition, compatibility issues with one of the more common materials of construction in cooling systems, copper, can increase the cost of the installed systems based on NH₃-water by having to use less desirable and/or more expensive materials. With respect to water-LiBr, a problem arises because water is not a suitable refrigerant in many important cases of interest. Applicants have come to appreciate that water has two main drawbacks that limit its viability in certain important applications. The first is that due to the low pressures the equipment sizing becomes impractical for many applications. Second due to the freezing point of water it cannot be used at temperatures below 0° C. As a result, due to issues such as toxicity and/or flammability and/or corrosiveness and/or equipment cost, such systems are typically only used in industrial settings or to applications were only a very small charge of refrigerant is required (low capacity systems, ie some refrigerators in hotels and RVs, although even these have largely disappeared due to the toxicity of NH₃).
Accordingly, applicants have come to recognize a continuing need for safer and environmentally friendly refrigerant for absorption-type refrigeration systems. Applicants have also come to recognize a potential advantage to be gained by systems that can provide effective and environmentally acceptable fluids for use in a variety of applications from industrial heat recovery to residential solar assisted refrigeration.

SUMMARY OF THE INVENTION

Applicants have found that certain refrigerant/absorbant pairs comprising fluorinated organic compounds, including fluorinated organic compounds having from one to eight carbon atoms (C1-C8), and, in certain embodiments, certain hydrofluoroolefin and/or hydrochlorofluoroolefin compounds, are well suited for use as and have particular advantage in absorption refrigeration. In certain embodiments, a fluorinated organic compound in accordance with the present invention, particularly, though not exclusively, certain hydrofluoroolefin and/or hydrochlorofluoroolefin compounds, and/or C2-C4 hydrofluoroolefin and/or hydrochlorofluoroolefin compounds is/are utilized as the refrigerant, with the absorbant portion either being fluorinated organic compound and/or a non-fluorinated oil. Hydrofluoroolefins, such as, but not limited to, HFO-1234yf (e.g. 1,1,1,2-tetrafluoropropene) and HFO-1234ze(E) (e.g. 1,1,1,3-tetrafluoropropene), have been found to have excellent refrigeration capabilities and a very short atmospheric lifetime which makes them environmentally benign and are preferred for use, preferably as refrigerant, in accordance with the present invention. Hydrochlorofluoroolefins, particularly monofluorotrifluopropenes such as, but not limited to, HCFO-1233zd (1-chloro-3,3,3-trifluoropropene) have also been found to have excellent refrigeration capabilities and a very short atmospheric lifetime which makes them environmentally benign and are preferred for use, preferably as absorbent, in accordance with the present invention. These refrigerants also have the added benefit of being compatible with copper and aluminum. The use of copper and aluminum both increases the efficiency due to improved heat transfer and decreases the overall cost.
In certain embodiments, the absorption refrigeration fluids of the present invention comprises a first fluorinated organic compound which acts as an absorbent and has a relatively high boiling point and a second fluorinated organic compound which acts as a refrigerant and has a relatively low boiling point. In certain instances, the absorbent, which comprises the first fluorinated organic compound, has a boiling point that is at least 40° C. higher than the boiling point of the solute which comprises the second fluorinated organic compound. In further embodiments, the absorbent compound is a non-ionic compound and also has an aggregate number of carbon/oxygen atoms that is at least two (2) greater than the aggregate number of carbon/oxygen atoms in the refrigerant. Thus, in embodiments in which the refrigerant comprises one or more C1-C4 fluorinated compounds, or one or more C2-C4 hydrofluoroolefin and/or hydrochlorofluoroolefin compounds, the absorbant compounds comprise one or more C2-C8 fluorinated compounds, and in certain embodiments one or more C3-C8 hydrofluoroolefin and/or hydrochlorofluoroolefin compounds.
According to certain aspects of such embodiments, the absorbant portion of the fluid is selected from the group consisting of fluoroethers, fluoroketones, HFCs, HFOs (including HFCOs), and combinations of these, and the refrigerant portion of the pair is selected from the group consisting of HFCs, HFOs (including HFCOs), CO₂and combinations of these. A non-limiting example of a fluoroether for use as an absorbent in accordance with the present invention is methyl nonafluorobutyl ether. A nonlimiting example of fluoroketone for use as a absorbent in accordance with the present invention is perfluoro(2-methyl-3-pentanone). A nonlimiting example of an HFC for use as an absorbent in accordance with the present invention is HFC-245fa (e.g. 1,1,1,3,3-pentafluoropropane). A nonlimiting example of an HFO for use as a absorbent solvent in accordance with the present invention is HFO-1233zd, including HFO-1233zd(E). A nonlimiting example of an HFO for use as a refrigerant in accordance with the present invention is HFO-1234yf. A nonlimiting example of an HFC for use as a refrigerant in accordance with the present invention is HFC-32 (difluoromethane). Particularly preferred, though not exclusive, in accordance with the present invention are the refrigerant/absorbent pairs HFC32/HFC-245fa, HFC-32/HFC-1234yf, HFC-32/1233zd(E) and HFO-1234yf/1233zd(E), and most preferably, though not exclusively, the use of such pairs in connection with absorption refrigeration systems which comprise energy input in the form of solar power, and even more preferably, though not exclusively, the use of such solar power energy input to decrease the peak demand of a commercial system.
In certain other embodiments, the refrigerant portion of the pair in accordance with the present invention is selected from among certain hydrofluoroolefin and/or hydrochlorofluoroolefin compounds and the absorbent and/or solvent portion is or includes a nonfluoroinated oil, which may selected from organic oils, such as polyalkyene glycol oil, poly alpha olefin oil, mineral oil, and polyol ester oil, including combinations of these. It has been discovered that solutions of these refrigerants and oils enable the refrigerant to be used as a working fluid in an absorption-type refrigeration system. Many of these refrigerants are characterized as having a low-GWP (i.e., <1000, or <100 relative to CO₂), a low or no appreciable ozone depletion potential, and are non-toxic and non-flammable. One of skill in the art will appreciate that, in one aspect, the present invention includes a combination of the refrigerants, fluorinated absorbents and non-fluorinated oils.
Accordingly, an aspect of this invention involves a method for providing refrigeration comprising: (a) evaporating a first liquid-phase refrigerant stream comprising one or more fluorinated organic compounds having from one to eight carbon atoms, to produce a low-pressure vapor-phase refrigerant stream, wherein said evaporating transfers heat from a system to be cooled; (b) contacting said low-pressure vapor-phase refrigerant stream with a first liquid-phase solvent stream comprising one or more organic compounds having an aggregate number of carbon/oxygen atoms that is at least two (2) greater than an aggregate number of carbon/oxygen atoms in the refrigerant under conditions effective to dissolve substantially all of the refrigerant of the vapor-phase refrigerant stream into the solvent of the first liquid-phase solvent stream to produce a refrigerant-solvent solution stream; (c) increasing the pressure and temperature of the refrigerant-solvent solution stream; (d) thermodynamically separating said refrigerant-solvent solution stream into a high-pressure vapor-phase refrigerant stream and a second liquid-phase solvent stream; (e) recycling said second liquid-phase solvent stream to step (b) to produce said first liquid-phase solvent stream; (f) condensing said high-pressure vapor-phase refrigerant stream to produce a second liquid phase refrigerant stream; and (g) recycling said second liquid-phase refrigerant stream to step (a) to produce said first liquid-phase refrigerant stream.
As used herein, the terms “low-pressure vapor-phase refrigerant” and “high-pressure vapor-phase refrigerant” are relative to one another. That is, a low-pressure vapor-phase refrigerant has a pressure above 0 psia, but lower than thepressure of the high-pressure vapor-phase refrigerant. Likewise, the high-pressure vapor-phase refrigerant has a pressure below the composition's critical point, but higher than the pressure of the low-pressure vapor-phase refrigerant.
As used herein, the term “substantially all” with respect to a composition means at least about 90 weight percent based upon the total weight of the composition.
In another aspect, the invention provides an absorption refrigeration system comprising: (a) a refrigerant selected from the group consisting of one or more fluorinated organic compounds; (b) an absorbent comprising one or more fluorinated organic compounds having from one to eight carbon atoms (C1-C8) having a boiling point that is at least 40° C. higher than the boiling point of the refrigerant; (c) an evaporator suitable for evaporating said refrigerant; (d) a mixer suitable for mixing said refrigerant with said absorbent, wherein said mixer is fluidly connected to said evaporator; (e) an absorber suitable for dissolving at least a portion of said refrigerant into said absorbent to produce a solution, wherein said absorber is fluidly connect to said mixer; (f) a pump fluidly connected to said absorber; (g) a heat exchanger fluidly connected to said pump; (h) a separator suitable for thermodynamically separating said solution into a vapor refrigerant component and a liquid absorbent component, wherein said separator is fluidly connected to said heat exchanger; (i) an oil return line fluidly connected to said separator and said mixer, and (j) a condenser suitable for condensing said vapor refrigerant component, wherein said condenser is fluidly connected to said separator and said evaporator.
This invention is an environmentally friendly, economical refrigeration process.
In certain embodiments, the present methods and systems are powered, at least in part, by solar energy to provide cooling at times of greatest load. The absorption refrigerants are low global warming, safe to use, and energy efficient

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a graphic representation of data showing the solubility of HFC-1234ze(E) in a PAG lubricant;

FIG. 2 is a schematic view of an absorption refrigeration cycle according to one embodiment of the invention;

FIG. 3 is a schematic view of another absorption refrigeration cycle according to another embodiment of the invention;

FIG. 4 is a schematic view of one embodiment of an absorption compression system (B) and a vapor compression system (A);

FIG. 5 is a graphic representation of data showing GWP impact on Life Cycle Climate Performance (LCCP); and

FIG. 6 is a graphic representation of data showing GWP impact on LCCP, including impact of reduced efficiency.

DETAILED DESCRIPTION OF THE INVENTION

Absorption systems and vapor compression systems both operate via Carnot idealized energy conversion cycles moving heat energy from a low temperature reservoir (the cooling load) to a high temperature reservoir (the ambient) by the use of thermal energy, Qin, for absorption technology or shaft work, Wsh, or mechanical vapor compression. The illustration of FIG. 4 provides a simplified schematic of generalized versions of each of such systems. As can be seen by these figures, both absorption and vapor compression systems utilize a condenser to exchange heat with the ambient, an expansion device, and an evaporator to perform the cooling of the system. The primary difference is that absorption systems utilize thermal energy to serve as a “thermal” or “chemical” compressor through the use of the chemical potentials between the refrigerant and the absorbent while a vapor compression system utilizes mechanical compressors drawing shaft power that is frequently electric. Applicants have found an efficient absorption system by identifying suitable refrigerant-absorbent pairs that efficiently perform the compression of the refrigerant. In many embodiments, the only moving part in an absorption system is the pump which provides a long lifetime of the overall system.
In certain embodiments of the invention, certain refrigerant/absorbant pairs comprising fluorinated organic compounds, including fluorinated organic compounds having from one to eight carbon atoms (C1-C8), and, in certain embodiments, certain hydrofluoroolefin and/or hydrochlorofluoroolefin compounds, are well suited for use as and have particular advantage in absorption refrigeration. In certain embodiments, a fluorinated organic compound in accordance with the present invention, particularly, though not exclusively, certain hydrofluoroolefin and/or hydrochlorofluoroolefin compounds, and/or C2-C4 hydrofluoroolefin and/or hydrochlorofluoroolefin compounds is/are utilized as the refrigerant, with the absorbant portion either being a fluorinated organic compound or a non-fluorinated oil. Hydrofluoroolefins, such as, but not limited to, HFO-1234yf (e.g. 1,1,1,2-tetrafluoropropene) and HFO-1234ze(E) (e.g. 1,1,1,3-tetrafluoropropene), have been found to have excellent refrigeration capabilities and a very short atmospheric lifetime which makes them environmentally benign and are preferred for use, preferably as refrigerant, in accordance with the present invention. Hydrochlorofluoroolefins, particularly monofluorotrifluopropenes such as, but not limited to, HCFO-1233zd (1-chloro-3,3,3-trifluoropropene) have also been found to have excellent refrigeration capabilities and a very short atmospheric lifetime which makes them environmentally benign and are preferred for use, preferably as absorbent, in accordance with the present invention. These refrigerants also have the added benefit of being compatible with copper and aluminum. The use of copper and aluminum both increases the efficiency due to improved heat transfer and decreases the overall cost.
In certain embodiments, the absorption refrigeration fluids of the present invention comprises a first fluorinated organic compound which acts as an absorbent and has a relatively high boiling point and a second fluorinated organic compound which acts as a refrigerant and has a relatively low boiling point. In certain instances, the absorbent, which comprises the first fluorinated organic compound, has a boiling point that is at least 40° C. higher than the boiling point of the solute which comprises the second fluorinated organic compound. In further embodiments, the absorbent compound is a non-ionic compound and also has an aggregate number of carbon/oxygen atoms that is at least two (2) greater than the aggregate number of carbon/oxygen atoms in the refrigerant. Thus, in embodiments in which the refrigerant comprises one or more C1-C4 fluorinated compounds, or one or more C2-C4 hydrofluoroolefin and/or hydrochlorofluoroolefin compounds, the absorbant compounds comprise one or more C2-C8 fluorinated compounds, and in certain embodiments one or more C3-C8 hydrofluoroolefin and/or hydrochlorofluoroolefin compounds.
According to certain aspects of such embodiments, the absorbant portion of the fluid is selected from the group consisting of fluoroethers, fluoroketones, HFCs, HFOs (including HFCOs), and combinations of these, and the refrigerant portion of the pair is selected from the group consisting of HFCs, HFOs (including HFCOs), CO₂and combinations of these. A nonlimiting example of a fluoroether for use as a solvent in accordance with the present invention is methyl nonafluorobutyl ether. A nonlimiting example of fluoroketone for use as a absorbent in accordance with the present invention is perfluoro(2-methyl-3-pentanone). A nonlimiting example of an HFC for use as an absorbent in accordance with the present invention is HFC-245fa (e.g. 1,1,1,3,3-pentafluoropropane). A nonlimiting example of an HFO for use as a absorbent solvent in accordance with the present invention is HFO-1233zd, including HFO-1233zd(E). A nonlimiting example of an HFO for use as a refrigerant in accordance with the present invention is HFO-1234yf. A nonlimiting example of an HFC for use as a refrigerant in accordance with the present invention is HFC-32 (difluoromethane). Particularly preferred, though not exclusive, in accordance with the present invention are the pairs HFC32/HFC-245fa, HFC-32/HFO1234yf, HFC-32/1233zd(E) and HFO-1234yf/1233zd(E), and most preferably, though not exclusively, the use of such pairs in connection with absorption refrigeration systems which comprise energy input in the form of solar power, and even more preferably, though not exclusively, the use of such solar power energy input to decrease the peak demand of a commercial system.
Refrigerants for this invention are not limited to the foregoing embodiments and also include hydrofluoroolefins and hydrochlorofluoroolefins of the formula C_wH_xF_yCl_zwhere w is an integer from 3 to 5, x is an integer from 1 to 3, and z is an integer from 0 to 1, and where y=(2·w)−x−z. Certain refrigerants include hydrohalopropenes, including tetrahalopropenes, e.g. tetrafluoropropenes and mono-chloro-trifluoropropenes, or tetrahalopropenes having a —CF₃moiety, e.g. 1,1,1,2-tetrafluoropropene, 1,3,3,3-tertafluoropropene, 1-chloro-3,3,3-trifluoropropene, including all stereoisomers thereof, such as trans-1,3,3,3-tertafluoropropene, cis-1,3,3,3-tertafluoropropene, trans-l-chloro-3,3,3-trifluoropropene, cis-l-chloro-3,3,3-trifluoropropene and 3,3,3-trifluoropropene. Certain useful refrigerants also comprise a mixture of two or more hydrofluoroolefins, hydrochlorofluoroolefins, as well as mixtures of both hydrofluoroolefins and hydrochlorofluoroolefins.
In certain embodiments of the invention, a hydrofluoroolefin and/or hydrochlorofluoroolefin refrigerant is used in an absorption-type refrigeration system as a working fluid, i.e., a fluid that changes states from gas to liquid or vice versa via a thermodynamic cycle. This phase change is facilitated by dissolving the vapor-phase refrigerant in an oil solvent (as an absorbent with an with an additional absorbent provided herein) to form a solution. Preferably, though not exclusively, a pump and heat exchanger are used to efficiently increase the solution's pressure and temperature, respectively. The pressurized and heated solution is then flashed to produce a refrigerant vapor at high pressure. This high pressure vapor is then passed through a condenser and evaporator to transfer heat from a system to be cooled.
Solvents useful in the present invention may be selected from the group consisting of polyalkyene glycol oil, a poly alpha olefin oil, a mineral oil and a polyolester oil. The oils selected are generally thermally stable, have very low vapor pressures, and are non-toxic and non-corrosive. Certain oils that fit these criteria and can be used with various olefins above are poly-ethylene glycol oils, polyol ester oils, polypropylene glycol dimethyl ether-based and mineral oil. Such oils, as discussed herein, may also act in a absorbent capacity either alone, or in combination with one or more of the fluorinated absorbent discussed herein. To this end, the discussion herein with respect to the mixing of refrigerant and solvent is equally applicable to solutions including the refrigerant, fluorinated absorbent and solvent.
In certain embodiments, the refrigerant and solvent are mixed in proportions and under conditions effective to form a solution in which the refrigerant is dissolved in the solvent. Preferably, though not exclusively, the mixture of refrigerant and solvent is in proportions in which a substantial portion, or substantially all, of the refrigerant mixed with the solvent is dissolved in the solvent. That is, in certain embodiments, the amount of refrigerant to be mixed with the solvent is below the saturation point of the solvent at the operating temperature and pressure of the refrigerant system. Maintaining the refrigerant concentration below the saturation point decreases the likelihood that vapor refrigerant will reach the pump, where it could lead to cavitations.
The refrigerant and solvent may be mixed by a mixer. Such mixers include, but are not limited to, static mixers and aspirators (i.e., venturi pump). In certain embodiments, the mixer is a simple junction of two transfer lines (e.g., pipes, tubes, hoses, and the like) that produces a turbulent flow, such as a T-fitting.
Dissolution of the low-pressure vapor phase refrigerant in the oil solvent may occur at refrigerant temperature of about −10° C. to about 30° C., or about 0° C. to about 10° C.
The dissolution of the refrigerant in the solvent may occur, at least to a major portion, in an absorber. The absorber can be of any type that is suitable for dissolving a refrigerant gas into an oil-based solvent. Examples of absorbers include heat exchangers through or around which a cooling medium is circulated.
The solution comprising the refrigerant and solvent is pumped against a means of resistance to increase the pressure of the solution. Pumping the liquid solution to a high operating pressure typically requires significantly less energy compared to compressing a vapor refrigerant using a compressor. In addition to expending less energy, pumps are typically less costly to install and maintain compared to compressors. This energy and cost savings is a distinct advantage of the present invention over conventional compression-type refrigeration systems.
The solution is also heated, in certain embodiments, after being pressurized. Heating may be accomplished using a heat exchanger, such as shell-and-tube heat exchangers and plate heat exchangers or a distillation column. In certain embodiments, heating the solution involves a waste-heat recovery unit (WHRU) (i.e., a heat exchanger that recovers heat from a hot gas or liquid stream, such as, but not limited to, exhaust gas from a gas turbine, heat generated in a solar collector or waste gas from a power plant or refinery). The WHRU working medium may include water-either pure or with triethylene glycol (TEG)—thermal oil or other mediums conducive to heat transfer. In other embodiments, heating the solution involves the use of geothermal, solar derived heat or direct heating from combustion of a fuel such a propane.
After the solution is heated and pressurized, it is subjected to a thermodynamic separation process to produce a vapor refrigerant fraction and a liquid solvent fraction. Examples of such thermodynamic separation processes include column distillation and flashing. Since the two fractions are in different phases, they can be separated easily.
In certain embodiments, the liquid solvent phase is recirculated back to the mixer, while the vapor phase comprising the refrigerant is transferred to a condenser where at least a portion, or substantially all, of the refrigerant is converted from its vapor phase to a liquid phase.
The types of condenser useful in the invention are not particularly limited provided that they are suitable for condensing a hydrofluoroolefin or hydrochlorofluoroolefin refrigerant. Examples of condensers include horizontal or vertical in-shell condensers and horizontal or vertical in-tube condensers.
The liquid phase refrigerant is passed through an expansion valve to lower the pressure of the refrigerant and, correspondingly, cool the refrigerant. The cooled, throttled refrigerant can be in a liquid-phase, vapor-phase, or a mixed-phase.
The refrigerant is then passed through an evaporator wherein the cooling capacity of the refrigerant during evaporation is used to extract heat (i.e., refrigerate) the system to be cooled. Preferably, though not exclusively, the material to be cooled in the system is water, with or without a heat transfer additive such as PEG, which can be used, for example, as chilled water circulated to air handlers in a distribution system for air conditioning. However, the material to be cooled can also be air used directly for air conditioning. In addition, the external material can also be any flowable material that needs to be cooled, and if water or air, the cooled materials can be used for purposes other than air conditioning (e.g., chilling food or other products).
The type of evaporator used to evaporate the liquid-phase refrigerant is not particularly limited provided that it is suitable for evaporating a hydrofluoroolefin or hydrochlorofluoroolefin refrigerant. Examples of useful evaporators include forced circulation evaporators, natural circulation evaporator, long-tube and short-tube vertical evaporators, falling film evaporators, horizontal tube evaporators, and plate evaporators.
After the refrigerant is evaporated, it becomes a low-pressure vapor-phase refrigerant typically, though not exclusively, having a temperature of about 30° C. to about 60° C., in certain embodiments about 40° C. to about 50° C. The low-pressure vapor-phase refrigerant is recirculated back to the mixer.
The processes of the present invention are, in certain embodiments, closed-loop systems wherein both the refrigerant and solvent are recirculated. Absorption refrigeration systems according to this invention involve a single, double, or triple effect absorption refrigeration process. Single and double effect processes are described in the Examples and figures described below.
Consideration of non-ideal behavior properties such as viscous friction (pressure drops), thermal mixing (exergy exchange), mass mixing (rate of absorption and desorption), heat transfer effects and basic control of the system can play an important role in the selection of the refrigerant and other system parameters. In addition, working pair solubilities and thermophysical properties could be determined and considered in connection with determining the mixture parameters and operating parameters. The mixing (thermal and mass) of the working fluid pairs can also be important to the design of the absorber, which frequently is the most engineering complex component. The rate of absorption can also be important to determine and evaluate for different refrigerant flow configurations, and consideration of transient system startup effects may be necessary. Furthermore, consideration of the environmental effects on refrigeration systems may involve evaluation of direct contribution due to fluid leakage (direct effect fluid GWP), the amount of energy it consumes (indirect effect), the amount of energy used to produce the device (indirect), and the amount of energy used to decommission the device (indirect). By limiting only to technologies that have a low direct effect does not correctly solve the overall problem of energy usage and impact to our environments. As explained below, LCCP analysis can be used to evaluate the choices in technology development. Not only should working fluids have a low overall fluid GWP, they must also have a good societal payback through reduced energy consumption toward energy independence and technology development. In order to determine the environmental impact of the choice of refrigerants for this application, an analysis of both the direct and indirect contributions to global warming were conducted. The direct contributions come from refrigerant emissions and the indirect contributions are due to the burning of fossil fuels to supply the power consumed by the equipment.
To determine the power consumption of a typical heat pump over the course of a year, a bin analysis was performed using averaged weather data for an average of 29 cities across the U.S. Data from an Air Conditioning, Heating and Refrigeration Institute Standard for chillers (AHRI Std 550) was used for average U.S. weather. Assumptions for this analysis included a value of 0.65 kg of CO2 per kW-hr of electrical production for the U.S., a 5% annual leakage rate and a 15% end-of-life loss, and a 15-year life. The impacts were determined by:
Direct=Refrigerant Charge×(Annual loss rate×Lifetime +End-of-life loss)×GWP
Indirect=Annual Power Consumption×Lifetime×0.65
Using this information a Life Cycle Climate Performance (LCCP) analysis was performed and is shown in FIGS. 5 and 6 herein. It is very clear from these results that the indirect contributors dominate any contributions from refrigerant emissions. Any reduction below the 400 level has no significant impact on the total.
The following examples are given as specific illustrations of the invention. It should be noted, however, that the invention is not limited to the specific details set forth in the examples.

EXAMPLES

Example 1

The solubility of trans-1,3,3,3-tertafluoropropene (1234ze(E)) in Ford Motor craft oil (a PAG refrigerant compressor oil meeting Ford specification No. WSH-M1C231-B) was measured by means of a micro-balance. The solubility that was measured along with the correlation of the data using the Non-Random Two Liquid (“NRTL”) activity coefficient model (Renon H., Prausnitz J. M., “Local Compositions in Thermodynamic Excess Functions for Liquid Mixtures,” AlChE J., 14(1), S.135-144, 1968)) is shown in FIG. 1. From these data it is seen that the Ford Motor Craft oil has nearly negligible vapor pressure and that the NRTL model can accurately represent the data.

Example 2

The data from examples 1 was used to develop a single effect absorption cycle. A representative schematic of a single effect absorption system of this invention is illustrated in FIG. 2.
In FIG. 2, a Ford Motorcraft polypropylene glycol dimethyl ether-based oil from line 10 is mixed with a liquid 1234ze(Z) refrigerant from line 4 in a closed mixer 20 (which can be a simple “T” joint connecting lines 4 and 10 to line 5). The mixture in passed though line 5 to an absorber 22 where the gaseous 1234ze(Z) dissolves into the oil. The liquid mixture is passed though line 6 to pump 24 that pressurizes the mixture and passes the mixture through line 7 to heat exchanger/boiler 26. In boiler 26, heat is exchanged with the mixture. The source of that heat can be waste heat from an industrial operation (e.g., power generation) external to the heat exchanger. The temperature of the mixture is raised to a temperature where the 1234ze(Z) refrigerant can separate from the oil. The heated mixture is removed through line 8 from the heat exchanger and introduced to a separator 28 whereby the refrigerant separates substantially in a vapor state from the oil that remains substantially in a liquid state. The oil is then returned through line 9 and through an oil valve 30 where its pressure is decreased to match the pressure in line 4. From valve 30 the oil is returned via line 10 to mixer 20 where it is again mixed with the refrigerant to repeat the process.
From separator 28, the refrigerant vapor is passed through line 1 to a condenser 32 so as to liquefy it. The liquid is passed through line 2 through an expansion valve 34, throttling the liquid refrigerant to cool the refrigerant. The cooled, throttled refrigerant can be liquid, vapor or a combination depending on the operator's choice. The cooled refrigerant is passed through an evaporator 36 whereby the cooling ability of the refrigerant is utilized to cool a material (water or air) that is in a heat-exchanging relationship with evaporator 36. The refrigerant is then returned from evaporator 36 through line 4 to mixer 20 where it is again mixed with the oil to repeat the process again.
The input parameters for the single effect absorption cycle of FIG. 2 are:
1) Evaporator 28: 2° C.
2) Condenser 32: 40° C.
3) 3000 kJ/hr supplied to boiler 26
4) Saturated liquid leaving absorber 22
5) Superheat leaving the evaporator 36 through line 4: 3° C.
6) The composition of stream 8 is 90 wt % oil and 10 wt % refrigerant.
With these parameters, the calculated coefficient of performance (“COP”) using 1234ze(Z) and the Ford motor craft oil is 4.56.

Example 3

A representative schematic of a double effect absorption is illustrated in FIG. 3.
In FIG. 3, a Ford Motorcraft polypropylene glycol dimethyl ether-based oil from line 17 is mixed with a liquid 1234ze(Z) refrigerant from line 4 in a closed mixer 40. The mixture is passed though line 5 to a first absorber 42 where the gaseous 1234ze(Z) dissolves into the oil. The mixture is passed though line 6 to first pump 44 that pressurizes the mixture and passes the mixture through line 7 to first heat exchanger/boiler 46. In boiler 46, heat is exchanged with the mixture. The source of that heat can be waste heat from an industrial operation (e.g., power generation) external to heat exchanger 46. The temperature of the mixture is raised. The heated mixture is removed through line 8 from heat exchanger 46 and introduced to a second mixer 48 where it is mixed with oil from line 15. The mixture from mixer 48 is taken through line 9 and introduced to second absorber 50 to ensure that all of the 1234ze(Z) is dissolved in the oil. From second absorber 50, the mixture is drawn through line 10 to a second pump 52 that pumps the mixture to a second boiler 54 where the temperature of the mixture is raised to a temperature where the 1234ze(Z) refrigerant can separate from the oil. A source of heat to boiler 54 is provided to accomplish this, which source can be of the type described above.
The mixture is taken from second boiler 54 through line 12 to separator 56 whereby the refrigerant separates substantially in a vapor state from the oil that remains substantially in a liquid state. The oil is then returned through line 13 to tee 58 where it is split between line 14 and 16. Line 14 sends oil through a second oil valve 60 and through line 15 to second mixer 48. Line 16 sends oil through a first oil valve 62 where the pressure is decreased to match the pressure in line 4. The oil then passes through line 17 to mixer 40 where it is again mixed with the refrigerant to repeat the process.
From separator 56, the refrigerant vapor is passed through line 1 to a condenser 64 so as to liquefy it. The liquid is passed through line 2 through an expansion valve 66, throttling the liquid refrigerant to cool the refrigerant. The cooled, throttled refrigerant can be liquid, vapor or a combination depending on the operator's choice. The cooled refrigerant is passed through an evaporator 68 whereby the cooling ability of the refrigerant is utilized to cool a material (water or air) external of evaporator 68. The refrigerant is then returned from evaporator 68 through line 4 to mixer 40 where it is again mixed with the oil to repeat the process again. The input parameters for the double effect absorption cycle of FIG. 3 are:
1) Evaporator 68: 2° C.
2) Condenser 64 40° C.
3) Pressure exiting Pump 44 is exp(1n(√{square root over (P_evap·P_cond)}))
4) 1500 kJ/hr supplied to boiler 46
5) Saturated liquid leaving both Absorber 42 and Absorber 50
6) Superheat leaving the evaporator 68: 3° C.
7) Tee 58 splits the flow 30% to stream 14 and 70% to stream 16.
8) The composition of stream 12 is 90 wt % oil and 10 wt % refrigerant.
With these parameters the calculated COP using 1234ze(Z) and Ford motor craft oil is 5.04.
One skilled in the art will recognize that there are other variations of the absorption refrigeration systems disclosed above that can be practiced. For example, Perry's Chemical Engineers' Handbook; Green. D. W.; Perry, R. H.; McGraw-Hill (2008) pg 11-90-11-93 discloses other variations of absorptive refrigeration cycles using liquids different than we use, but many of those variations otherwise can be employed in the practice of this invention.
In addition, various additives can be added to the refrigerant system of this invention. For example, to avoid polymerization of the olefin refrigerant during service, stabilizers may be added. Such stabilizers are known, for example, and include terpenes, epoxides and the like. Other optional additives to add to the refrigerant include

- 1. antioxidants e.g., phenol based such as BHT
- 2. extreme pressure additives—chlorinated materials, phosphorous based materials—tricresyl phosphate, sulfur based materials
- 3. antifoam additives (e.g., silicones)
- 4. oiliness additives (e.g., organic acids and esters)
- 5. acid catchers (e.g.,) epoxides

Example 4

With particular reference to the figure provided above, the efficiency of the absorption cycle is calculated as Qcooling/(Qin+WP). Even though Qin is considered waste heat and is a “free” source of energy this is the best way to compare potential refrigerant pairs. A typical NH3-water absorption cycle operates with a COP=˜0.5-0.6 at an evaporator temperature of 5° C. and an ambient temperature of 40° C. One absorption refrigeration pair according to the present invention is HFO-1234yf and a PAG oil. This particular absorption pair benefits from the fact that the PAG oil has a negligible vapor pressure so that the separation in the generator becomes very simple. When operated at an evaporator temperature of 2° C. and a ambient temperature of 40° C. the COP of this cycle is ˜0.6 which is nearly identical to that of an ideal NH3-water system.

Claims

1. A method for providing refrigeration, comprising:

a. evaporating a first liquid-phase refrigerant stream comprising one or more fluorinated organic compounds having from one to eight carbon atoms, to produce a low-pressure vapor-phase refrigerant stream, wherein said evaporating transfers heat from a system to be cooled;

b. contacting said low-pressure vapor-phase refrigerant stream with a first liquid-phase solvent stream comprising one or more organic compounds having an aggregate number of carbon/oxygen atoms that is at least two (2) greater than an aggregate number of carbon/oxygen atoms in the refrigerant under conditions effective to dissolve substantially all of the refrigerant of the vapor-phase refrigerant stream into the solvent of the first liquid-phase solvent stream to produce a refrigerant-solvent solution stream;

c. increasing the pressure and temperature of the refrigerant-solvent solution stream;

d. thermodynamically separating said refrigerant-solvent solution stream into a high-pressure vapor-phase refrigerant stream and a second liquid-phase solvent stream;

e. recycling said second liquid-phase solvent stream to step (b) to produce said first liquid-phase solvent stream;

f. condensing said high-pressure vapor-phase refrigerant stream to produce a second liquid phase refrigerant stream; and

g. recycling said second liquid-phase refrigerant stream to step (a) to produce said first liquid-phase refrigerant stream.

2. The method of claim 1 wherein said one or more organic compounds in said first liquid-phase solvent stream has a boiling point that is at least 40° C. higher than the boiling point of the one or more organic compounds in said first liquid-phase refrigerant stream.

3. The method of claim 1 wherein one or more organic compounds in said first liquid-phase refrigerant stream are selected from the group consisting of HFCs, HFOs, HFCOs, CO2, and combinations thereof.

4. The method of claim 3 wherein said one or more organic compounds in said first liquid-phase refrigerant stream are selected from one or more of 1,1,1,2-tetrafluoropropene, difluoromethane, trans-1,1,1,3-tetrafluoropropene, cis-1,1,1,3-tertafluoropropene, 3,3,3-trifluoropropene, and combinations thereof.

5. The method of claim 1 wherein said one or more organic compounds in said first liquid-phase solvent stream are selected from the group consisting of fluoroethers, fluoroketones, HFC, HFOs, HFCOs, and combination thereof.

6. The method of claim 5 wherein the organic compounds in said first liquid-phase solvent stream are selected from the group consisting of nonafluorobutyl ether, perfluoro(2-methyl-3-pentanone), 1,1,1,3,3-pentafluoropropane, 1-chloro-3,3,3-trifluoropropene, and combinations thereof.

7. The method of claim 1 wherein said one or more organic compounds in said first liquid-phase refrigerant stream are selected from one or more of 1,1,1,2-tetrafluoropropene, difluoromethane, trans-1,1,1,3-tertafluoropropene, cis-1,1,1,3-tertafluoropropene, 3,3,3-trifluoropropene, and combinations thereof and said organic compounds in said first liquid-phase solvent stream are selected from the group consisting of nonafluorobutyl ether, perfluoro(2-methyl-3-pentanone), 1,1,1,3,3-pentafluoropropane, 1-chloro-3,3,3-trifluoropropene, and combinations thereof.

8. The method of claim 1 wherein said one or more organic compounds in said first liquid-phase refrigerant stream comprises at least one compound having the formula C_wH_xF_yCl_zwhere w is an integer from 3 to 5, x is an integer from 1 to 3, z is an integer from 0 to 1, and y=2w−x−z.

9. The method of claim 1 wherein said solvent is selected from the group consisting of poly-ethylene glycol oils, polyol ester oils, polypropylene glycol dimethyl ether-based and mineral oil.

10. The method of claim 1 wherein said increasing the temperature of said solution in step (c) involves the transfer of heat from a source of industrial waste heat to said solution.

11. The method of claim 1 wherein said increasing the temperature of said solution in step (c) involves the transfer of geothermal heat to said solution.

12. The method of claim 1 wherein said increasing the temperature of said solution in step (c) involves the transfer of solar heat to said solution.

13. An absorption refrigeration system comprising:

a. a refrigerant selected from the group consisting of one or more fluorinated organic compounds

b. an absorbent comprising one or more fluorinated organic compounds having from one to eight carbon atoms (C1-C8) having a boiling point that is at least 40° C. higher than the boiling point of the refrigerant;

c. an evaporator suitable for evaporating said refrigerant;

d. a mixer suitable for mixing said refrigerant with said absorbent, wherein said mixer is fluidly connected to said evaporator;

e. an absorber suitable for dissolving at least a portion of said refrigerant into said absorbent to produce a solution, wherein said absorber is fluidly connect to said mixer;

f. a pump fluidly connected to said absorber;

g. a heat exchanger fluidly connected to said pump;

h. a separator suitable for thermodynamically separating said solution into a vapor refrigerant component and a liquid absorbent component, wherein said separator is fluidly connected to said heat exchanger;

i. an oil return line fluidly connected to said separator and said mixer, and

j. a condenser suitable for condensing said vapor refrigerant component, wherein said condenser is fluidly connected to said separator and said evaporator.

14. The method of claim 13 wherein the refrigerant is selected from the group consisting of HFCs, HFOs, HFCOs, CO2, and combinations thereof.

15. The method of claim 14 wherein the refrigerant is selected from one or more of 1,1,1,2-tetrafluoropropene, difluoromethane, trans-1,1,1,3-tertafluoropropene, cis-1,1,1,3-tertafluoropropene, 3,3,3-trifluoropropene, and combinations thereof.

16. The method of claim 13 wherein the absorbent is selected from the group consisting of fluoroethers, fluoroketones, HFC, HFOs, HFCOs, and combination thereof.

17. The method of claim 16 wherein the absorbent is selected from the group consisting of nonafluorobutyl ether, perfluoro(2-methyl-3-pentanone), 1,1,1,3,3-pentafluoropropane, 1-chloro-3,3,3-trifluoropropene, and combinations thereof.

18. The system of claim 13 wherein said refrigerant comprises at least one compound having the formula C_wH_xF_yCl_zwhere w is an integer from 3 to 5, x is an integer from 0 to 3, z is an integer from 0 to 1, and y=2w−x−z, provided that x and z are not both zero.