TW201600817A - Centrifugal chiller system - Google Patents

Abstract

Chiller systems utilizing naturally occurring refrigerants. The refrigerants include methylene chloride and dichlorodifluoroethylene. The chiller systems utilizing these naturally occurring refrigerants have upgraded mechanical and electrical systems that are resistant to deterioration from the decomposition products of these refrigerants, permitting the use of environmentally friendly refrigerants such as methylene chloride and dichlorodifluoroethylene.

Description

Centrifugal chiller system Field of invention

The present invention is generally directed to a chiller system utilizing methylene chloride and dichlorodifluoroethylene as a refrigerant, and more particularly to a chiller system having an improved mechanical and electrical system, such improved machinery and The electrical system allows the use of environmentally friendly refrigerants such as methylene chloride and dichlorodifluoroethylene.

Background of the invention

A chiller system using a centrifugal compressor in a refrigeration circuit (hereinafter referred to as a centrifugal chiller system) is generally used to maintain temperature control within a structure, for example. The main challenge facing centrifugal chiller systems has been the ever-evolving refrigerants used in such systems. The main challenge with regard to the choice of refrigerants for use in refrigeration systems such as centrifugal refrigeration systems has been an environmental challenge caused by conventional refrigerants. For example, R11 and other chlorofluorocarbon refrigerants (CFCs) such as R22 have been phased out due to stratospheric ozone depletion. In the United States, such refrigerants are no longer available for new equipment that is put into service.

Current refrigerants used in centrifugal chiller systems include cryogens designated R134a and R123, and R134a is more commonly used. However, root According to the Montreal Protocol, R123 is scheduled to be phased out by 2030. R134a has also become problematic as it is facing rules regarding its global warming potential, which is attributed to R134a emissions into the atmosphere.

Due to concerns about the environmental and the effects of the refrigerant on the environment, natural refrigerants become the refrigerant of choice. Natural cryogens include natural materials such as certain hydrocarbons (such as propane and isobutane), CO ₂ , ammonia, water, and even air. Natural materials such as these are preferred over synthetic compositions used as cryogens because, unlike CFC, the natural mechanisms for removing such natural materials from the environment must exist. The use of such natural substances is unlikely to cause any unintended consequences due to unpredictable adverse effects on the environment, as these natural substances have been present in the environment for thousands of years, even for millions of years. In addition, after millions of years, the ecosystem has adapted to the existence of these materials and any decomposition products. Although new synthetic alternatives such as R1234yf, R1234ze(E) and R1234zd(E) have been developed to address environmental issues associated with CFCs and HFCs, the unintended consequences associated with these newly developed chemicals will be in the next few years. It is still unknown and unknowable, as the expected results of CFC and HFC have been unknown for decades.

One of the potential long-term problems with cryogens is their decomposition products. The olefin-based refrigerants such as R-1234yf, R1234ze(E), R-1336mzz(Z), and R1234zd(E) contain a CF ₃ group, which means that trifluoroacetic acid is a decomposition product. Although trifluoroacetic acid is known to be naturally present in the ocean, it can accumulate in other environments over time. Therefore, it is advantageous to develop a refrigerant which does not have such a decomposition product and which does not have a CF ₃ group.

While it is desirable to adapt natural chemicals for use as a cryogen, such natural chemicals must overcome the problems associated with the use of such natural chemicals in modern compressors. Some of these issues determine that such natural chemicals are not suitable for use in modern centrifugal compressors. Some of these materials have a low molecular weight such that they are not available due to impractical high compressor tip speeds and/or multi-stage centrifugal compressors. The explosive nature of hydrocarbons in the air excludes these hydrocarbons as a safe substitute. Butane and larger hydrocarbon molecules also experience problems with reduced cycle efficiency in the case of wet compression.

Ammonia is also undesirable to be flammable and has high acute toxicity. Ammonia is also incompatible with copper, which limits the use of ammonia with certain heat exchanger configurations, and ammonia has a very low molecular weight, severely limiting the use of ammonia with centrifugal compressors.

Carbon dioxide is undesirable because carbon dioxide must be used at very high operating pressures, which require extremely robust compressor construction, providing poor cycle efficiency and extremely high rotational speed requirements.

Water is undesirable as a cryogen because water has a very low vapor pressure and a very low molecular weight, requiring a large volume of steam movement in the case of a multi-stage compressor. The air is a gas under normal chiller operating conditions, so air cannot be used in conventional centrifugal chillers. Other natural inorganic compounds such as sulfur dioxide are highly toxic, and some such as hydrogen sulfide are highly flammable, both of which are also highly corrosive to materials used in both centrifugal compressor construction and associated refrigeration equipment.

Certain chemicals used as refrigerants in the past have ceased to be used for freezing Agents because these chemicals are not as effective as synthetic refrigerants that have been developed as replacements. Moreover, such refrigerants become inoperable due to design variations in the design of centrifugal compressors as a result of the use of synthetic refrigerants.

One such natural substance is dichloromethane. Natural sources of methylene chloride include phytoplankton, mangrove swamps and burning of organisms. Dichloromethane CH ₂ Cl _2, also known as R30, has been used as a cryogen in the last thirty years of the last world. Replaced by dichloromethane trichlorofluoromethane CFCl _3, as described in U.S. Patent 2,041,045. Since the replacement of methylene chloride in the 1920s and 1930s, various improvements in the design of centrifugal compressors have ruled out the use of methylene chloride. Such improvements in centrifugal compressors have made dichloromethane undesirable in the best case and in the worst case. For example, many modern centrifugal systems use varnish as the motor winding insulation and are used with magnetic bearings, and methylene chloride is incompatible with such varnishes. In addition, the aluminum used in mechanical bearings is also incompatible with methylene chloride. Gasket materials and shaft seals are also susceptible to attack by methylene chloride. In addition, long-term exposure to water can result in the formation of highly corrosive hydrochloric acid, and water leakage from water at higher pressures than the cryogen is not only for shell-and-tube heat exchangers commonly used in chillers, but also Other equipment exposed to acid in the refrigeration system causes problems. Another problem with the use of methylene chloride, which initially led to the replacement of methylene chloride, is the poor performance of methylene chloride compared to R-11, especially in multi-stage direct drive fixed speed compressors, which are multi-stage direct drive fixed. The speed compressor operates at 2 pole speeds at a maximum speed of 3600 rpm (rpm) powered by a 60 Hz utility line.

What is needed is that it can be designed for use with methylene chloride or for the day While other cryogens of the substance are used together and will not cause unpredictable consequences to the environment when cryogen leakage inevitably occurs, systems that provide effective freezing operations are still provided.

Summary of invention

The present invention is directed to a chiller system that utilizes a natural cryogen having a high critical temperature that improves high cycle efficiency, sufficiently low to allow operation of the chiller at a water temperature of 5 °C. Freezing point, low vapor pressure and low condensing pressure. The refrigerant will produce a vapor pressure at or below the vapor pressure of R123, which is a refrigerant that is currently being phased out due to its adverse environmental impact. The cryogen desirably has a high molecular weight of greater than 60. High molecular weight refrigerants with low vapor pressure result in lower moving impeller rotational speeds for centrifugal compressors but larger impeller diameters, simplifying compressor design. Desirably, the refrigerant should have a condensing pressure of no greater than the condensing pressure of R123, and the condensing pressure of R123 is 19 psia. Low condensing pressure allows the use of irregular pressure tanks in refrigeration systems.

Natural refrigerants that have a high critical temperature while being safe for use in a chiller system can be used in suitably modified chiller systems. Such natural refrigerants include dichloromethane and dichlorodifluoroethylene.

The chiller system utilizes standard components of the refrigeration system. These standard components include a compressor that compresses a natural cryogen that is in fluid communication with a condenser that condenses a natural cryogen that is in fluid communication with the evaporator. The expansion valve is in the middle of the condenser and evaporator to reduce condensation The pressure of the liquid cryogen. The condenser includes a heat exchanger to remove heat from the refrigerant during the condensation process. The evaporator includes a heat exchanger that cools water for the chiller system using an evaporative liquid cryogen in the form of a mist after passing through an expansion valve between the condenser and the evaporator. Cooling water is maintained in the chiller for use in cooling the building space as needed. While each of the components is typically found in all chiller systems, each of the components and interconnecting tubing must be modified to provide a system adapted to the natural cryogen.

A chiller system utilizing such natural refrigerants may necessarily include a filter desiccant that can be used to remove moisture and acid from the refrigeration system. These natural refrigerants decompose in the presence of water to form corrosive hydrochloric acid and hydrofluoric acid (for dichlorodifluoroethylene). Additionally, a stabilizer may be added to the cryogen to retard deterioration of the stabilizer.

The chiller system must also have a water detector and an isolation valve. Because the refrigeration system operated with such refrigerants operates below standard atmospheric pressure, and the chiller system operates at or above atmospheric pressure, water may leak into the refrigerant in the event of a leak. Once detected, the shut-off valve is activated to isolate leakage and prevent further contamination of the system.

The compressor in the chiller system using these natural refrigerants is a single-stage centrifugal compressor or a two-stage centrifugal compressor. The compressor must be modified to minimize corrosion problems. Therefore, the compressor assembly and heat exchanger assembly should exclude materials that are subject to attack by such natural refrigerants. Compressor mechanical bearings of either ball or liquid film type spheres should not include aluminum or aluminum alloys, while phase reactions are made of steel or ceramic materials. Not only from the compressor Aluminum (common electrical and heat exchange materials) and zinc should also be removed from the heat exchanger assembly. Therefore, these materials should also be replaced in compressor motors and magnetic bearings. The replacement of aluminum and zinc will include the removal of aluminum and zinc self-sealing and bonding materials. Ideally, the encapsulating material used in the compressor motor must be compatible with methylene chloride and dichlorodifluoroethylene. The aluminum rotor bars in the compressor motor must be replaced with copper rotor bars. Standard motor winding materials must be replaced with glass insulation. The compressor impeller is determined by its non-permeability to react with natural refrigerants.

All seals and gaskets in the chiller system must also be compatible with natural refrigerants. Therefore, all seals and gaskets desirably contain polytetrafluoroethylene (PTFE), Kapton ^® , epoxy or similar materials. Kapton ^® is a trademark of DuPont for polyimine having the chemical name poly(4,4'-oxyl-linked phenyl-pyromellitic acid diimine).

To improve compressor efficiency using these natural refrigerants, wet compression is utilized. Wet compression injects a small amount of liquid into the compressor suction. In addition, the rotational speed of the impeller is operated at a speed greater than 3600 rpm, such that the overall tip speed of the impeller is reduced. To produce such rotational speeds, the compressor unit or power supply must supply power at a frequency above 120 Hz design conditions, although other motors that can provide speeds greater than 3600 rpm can also be used.

The pipe for the heat exchanger in both the evaporator and the condenser should not only include aluminum, but can also be increased in size from a standard 5/8 inch diameter pipe to a pipe in the range of 3⁄4 inch to 1 inch. , thereby increasing the available surface area of each tube. The evaporator may have a flooding design or have a spray design to use a pump that eliminates the risk of leakage through the shaft sealed refrigerant.

As used herein, a high critical temperature means more than 210 ° C. Boundary temperature. As used herein, the term "natural cryogen" means natural, but may be suitable as a material for use as a refrigerant in a refrigeration system, which has a natural mechanism for removal from the environment with little or no The environmental impact of the decomposition. As used herein, the low vapor pressure is a vapor pressure of less than 6 psia. As used herein, the low condensing pressure is less than about 15 psia condensing pressure.

Other features and advantages of the present invention will be apparent from the following description of the preferred embodiments of the invention.

10‧‧‧ motor

12‧‧‧Compressor

14‧‧‧Refrigerant steam

16‧‧‧Condenser

18‧‧‧Cooling fluid

20‧‧‧Refrigerant fluid

24‧‧‧Expansion device

26‧‧‧Evaporator

28‧‧‧Heat transfer fluid

30‧‧‧Refrigerant steam

32‧‧‧Selective variable frequency drive

34‧‧‧Control panel

302‧‧‧Selective condenser design

304‧‧‧cooler

306‧‧‧Condenser shell

308‧‧‧Non-circular shell

310‧‧‧Condenser tube sheet

320‧‧‧Refrigerant export

Figure 1 is a graph depicting the relative cycle efficiency and cooling capacity of possible refrigerants.

2 depicts a refrigerant circuit showing the components utilized in the present invention.

3 depicts a selective condenser design incorporating a subcooler for use in the refrigeration circuit of FIG.

Detailed description of the preferred embodiment

Global environmental issues advance the reassessment of refrigerant selection. The present invention is directed to a chiller system that has been modified to effectively utilize natural cryogens. Stability and flammability issues impose additional constraints on the choice of compounds used as refrigerants.

The group of compounds of interest for use as a refrigerant is based on a halogenated derivative of ethylene (also known as ethene, CH ₂ =CH ₂ ). The double bond will give a very short atmospheric lifetime, which leads to a very low global warming potential for chlorine-containing compounds and negligible ozone depletion potential. Of particular interest in this group is 1,2-dichloro 1,2-difluoroethylene, CClF = CClF. Tests have shown that trichloroethylene is weakly flammable in air, while tetrachloroethylene (CCl ₂ = CCl ₂ ) is non-flammable. In general, the substitution of fluorine for chlorine increases flammability, so only fully halides may be non-flammable. Nonetheless, tetrafluoroethylene (CF ₂ =CF ₂ ) is flammable and readily polymerizable, so only perhalogenated chlorine-containing compounds may be stable and non-flammable.

In general, compounds having a CF ₂ = group have serious toxicity problems. For example, CF ₂ = CFCl is considered highly toxic, flammable and Qieyi stability problems. This constraint also eliminates CCl ₂ =CF ₂ as a possible option. However, 1,2-dichloro 1,2-difluoroethylene may have relatively low toxicity, non-flammability or reduced flammability and make 1,2-dichloro 1,4-difluoroethylene suitable for advanced Other physical properties used as a refrigerant in chiller systems. Dichlorodifluoroethylene has a critical temperature of 221 °C. This compound exists as two isomers, that is, a cis isomer and a trans isomer having a boiling point of 21 ° C and a boiling point of 22 ° C in the trans, which makes the compound suitable for Used as a refrigerant in most chiller applications. The cis isomer has a liquid to solids transition temperature of -119.6 °C, while the trans isomer has a liquid to solids transition temperature of -93.3 °C. This compound may also be referred to as R1112 using standard cryogen numbers and nomenclature.

The two dichlorodifluoroethylene isomers have suitable boiling points for use as a refrigerant for most chiller applications. Although any of these isomers can be used alone in chiller applications, the mixture of these two isomers The compound is commercially available. Because the isomers are very close to the same boiling point, a substantially azeotropic mixture of two isomers that are desirable as a cryogen in a centrifugal chiller can be used. However, the trans isomers in the two isomers may be more stable and less flammable. The simple structure of dichlorodifluoroethylene will give high cycle efficiency and reduce the cost of the refrigerant. The high molecular weight of dichlorodifluoroethylene is desirable, which will allow for a reduction in compressor speed, which simplifies compressor design and allows for easy use of the direct drive induction motor. As used herein, a substantially azeotropic mixture is a mixture having a temperature slip of no more than 1.0 ° C (1.0 ° K). A substantially azeotropic mixture of a mixture having a temperature slip of 1.0 ° C (1.0 ° K) between or among the components can generally ignore the effect of separation during such phase transitions. To achieve this temperature slip, the boiling point of the components of the mixture (here the isomer of dichlorodifluoroethylene) cannot be disproportionate.

A natural refrigerant of interest for use in advanced applications quencher methylene chloride, also identified as CH ₂ Cl _2. Dichloromethane is a liquid having a boiling point of 40 ° C at room temperature. Dichloromethane is a commonly used industrial chemical used as a solvent, as a paint stripper, in caffeine for coffee removal, in pharmaceutical production, as a foaming foaming agent, and in many other applications. Historical review shows that methylene chloride was used as a refrigerant in centrifugal chillers and domestic refrigerators in the 1920s and 1930s, but with the development of more effective refrigerants, methylene chloride was used. The use of the refrigerant stops. Today, methylene chloride is used as a common industrial chemical, as a solvent, as a paint stripper, in caffeine for coffee removal, in pharmaceutical production, as a foam blowing agent and many other applications. . Recently, atmospheric science has shown that there are a large number of natural sources for methylene chloride.

A number of studies have identified a number of natural sources of methylene chloride in the environment. Analysis of the air trapped in Antarctic ice showed an atmospheric concentration of approximately 1.4 parts per trillion produced by significant industries earlier than dichloromethane. As shown in Table 1, this concentration corresponds to a natural emissions of approximately 50,000 tons per year. The mass of the substances in Table 1 is calculated based on the measured atmospheric concentration and the mass of the atmosphere. The rate of emission is the mass in the atmosphere divided by the lifetime of the atmosphere. The source of emissions is mainly from the burning of organisms, and the ocean with mangrove swamps is a secondary source.

Table 1 also shows that based on the measured atmospheric concentrations in 2003, the natural emissions of methane before 1940 were approximately two orders of magnitude higher than the emissions of R123. Operating in a vacuum combined with the use of a high efficiency flushing system, the use of methylene chloride as a refrigerant substitute for R123 will result in a cooler discharge below the emissions from the R123 chiller. Therefore, methylene chloride refrigerant emissions from well-maintained chillers will only result in a small portion of natural emissions for rational use based on the cryogen treatment program, which is similar to that used in modern chiller equipment. R123 refrigerant treatment program.

Possible emissions from the use of refrigerants are also orders of magnitude lower than existing emissions from other uses. Industrial emissions worldwide are around 650,000 tons per year, which is approximately 1000 times higher than the possible refrigerant emission rate. The very low emissions from the chiller means that the use of the refrigerant will not cause a significant increase in the atmospheric concentration of methylene chloride.

Dichloromethane has advantageous properties in terms of global environmental effects. For a 100-year time horizon, the global warming potential (GWP) is 9 compared to carbon dioxide, and the atmospheric lifetime of methylene chloride is 0.4 years. R30 is not regulated under the Montreal Protocol. The US EPA recognizes R30 as a non-ozone depletion alternative and solvent in foam foaming.

Figures 1 and 2 compare cycle efficiency and cooling capacity for various refrigerants. The analysis is for an ideal cycle with 6 ° C evaporation temperature, 36 ° C condensation temperature, 5K (5 ° C) liquid subcooling and no suction port overheating. Perform the use of cryogen properties from NIST REFPROP.

The general trend is that low pressure refrigerants have better cycle efficiency and reduced cooling capacity, and methylene chloride provides the highest cycle efficiency of any cryogen in the analysis. Based on the cooling capacity (kJ/m ³ ) data in Table 1, it is expected that a centrifugal compressor using dichloromethane as a refrigerant has a size comparable to that of using R123 as a refrigerant.

For comparison purposes, carbon dioxide is included even if the condensing temperature exceeds a critical point. For this condition, the execution is based on adjusting the high side pressure adjustment to give optimum cycle efficiency rather than saturation conditions.

Commercially available chillers use various types of reinforced tubes in the evaporator and condenser. These reinforced tubes are designed for use by chiller tube manufacturers and the general correlation to estimate the heat transfer efficiency of such reinforced tubes is not available. In the absence of generalization for the quench tube, the transport properties of the cryogen are compared in Table 3 below to infer the heat transfer performance of methylene chloride relative to other cryogens.

Table 3 summarizes the transport properties of several refrigerants having relative capacities and efficiencies close to the capacity and efficiency of dichloromethane and R134a. The data in Table 2 was saturated at 20 ° C for all refrigerant systems. The properties of all refrigerants used in addition to dichloromethane are from NIST REFPROP. The properties of methylene chloride are available from ASHRAE (1993) and Dow (1998).

As can be seen from Table 2, methylene chloride has the highest liquid thermal conductivity among the listed refrigerants. The liquid viscosity of methylene chloride is lower than the liquid viscosity of R123 and R1233zd(E), but higher than the liquid viscosity of R134a, butane and pentane. The latent heat of R30 is higher than the latent heat of R123, R134a and R1233zd(E), but lower than the latent heat of butane and pentane. Based on the transport properties data from Table 2, the heat exchanger performance of methylene chloride is expected to be the same as or better than the heat exchanger of R123 or R1233zd(E). Higher pressure refrigerants such as R134a and butane are expected to have the same or better heat transfer efficiency than dichloromethane. There is no significant difference in planned heat transfer between dichloromethane and pentane.

The vapor pressure of methylene chloride contributes to evaporation and condensation on the shell side. Dichloromethane has the advantage that its low vapor pressure protects the tank from the pressure bath rules. On the other hand, the refrigerant pressure drop will limit the effectiveness of the methylene chloride in the direct expansion heat exchanger.

Material compatibility issues can also affect heat exchanger design. Dichloromethane has significant advantages over ammonia because methylene chloride can be used with reinforced copper tubes that are incompatible with ammonia. The disadvantage of methylene chloride is the possible compatibility with aluminum. The compatibility issue limits the choice of materials and other components for the heat exchanger.

The processing requirements of the cryogen can be complex and depend on regional or regionally different regulations. To simplify the analysis, we will limit the review of methane treatment requirements to the US and China. These two countries have the two largest markets for centrifugal chillers, and reviewers in the US and China also provide a good starting point in assessing processing requirements in other parts of the world.

In the United States, the current ASHRAE Standard 34 for methylene chloride is classified as B1, which corresponds to higher toxicity without flame propagation. Dichloromethane previously had a classification B2, but this classification has recently been revised to indicate to B1. Extensive flammability testing of methylene chloride was carried out in the 1970s, indicating no flame propagation in air at atmospheric pressure for temperatures below 100 °C. The ASHRAE Standard 34 (ASHRAE 2103a) requirement for flameless propagation is based on measurements at 60 °C. As with other refrigerants, elevated pressures, extreme temperatures, addition of combustible components, etc., can produce a combustible mixture in the air. Dichloromethane can be burned and/or decomposed in contact with the flame or in contact with the hot surface due to the continuous supply of heat that drives the reaction. The flammability limits are sometimes shown for methylene chloride based on conditions different from those used by the ASHRAE classification system.

Dichloromethane has a long history as an industrial chemical and there are many studies on the long-term toxicity of methylene chloride in humans and in animals. Although some animal studies have shown increased cancer rates for long-term exposure at high concentrations, other studies in workers and animals have shown no increase. Although methylene chloride can cause cancer risk, the risk is due to animals and humans. The difference between them is negligible due to the intermittent nature of the exposure to methylene chloride.

The methane treatment requirements required by OSHA are generally consistent with the practices required by ASHRAE Standard 15 (ASHRAE 2013b). For example, if the methylene chloride concentration is expected to exceed 12.5 ppm, OSHA requires periodic monitoring of the methylene chloride concentration. ASHRAE Standard 15 (ASHRAE 2013b) requires continuous monitoring in equipment rooms with alarms at 10 ppm; ASHRAE Standard 15 requirements are more restrictive than OSHA requirements. The purification and fluid transfer procedures are generally similar for dichloromethane and R123.

Table 3 summarizes the comparison of data related to the handling of dichloromethane and other refrigerants. For acute exposure due to accident release, methylene chloride is similar to R123 because the IDLH values and leakage conditions are similar. Although not shown in the table, CFC11 and CFC113 also have similar IDLH values of 2000 ppm and have an empirical history of safe use in chillers.

In Table 3, for R123, there is no approved IDLH value or PEL value, so instead the one hour exposure limit and AEL (acceptable exposure limit) values from DuPont (2012) are used. The IDLH value comes from the CDC (2014). The PEL value comes from OSHA (2014). The LFL values for ammonia and pentane are from ASHRAE (2013a).

A comparison with R123 indicates that it is possible that the extremely low equipment room exposure is properly handled. Based on measurements from the early 1990s, the R123 standard for equipment room concentrations was 1 ppm. Unlike R123, the entire refrigeration cycle for R30 is typically below atmospheric pressure, which means that air leaks through the flushing system and exits the outside of the building, rather than the refrigerant leaking into the equipment room. This analysis indicates that the normal equipment room concentration should be several orders of magnitude lower than the allowable duty station exposure limit for methylene chloride.

Pentane or other hydrocarbons have a significant fire risk that is not present in the case of methylene chloride and other non-flammable refrigerants. According to current US safety regulations, hydrocarbons are prohibited from being used in commercial air conditioning applications, even in water chillers.

The handling of methylene chloride is usually more problematic than the handling of ammonia. The acute toxicity of methylene chloride is much less acute than the acute toxicity of ammonia. In addition, Leakage in the ammonia system can result in a large amount of immediate release, so ammonia is used as steam at room temperature and dichloromethane is a liquid. Ammonia also has flammability problems that are not present in the case of methylene chloride. These advantages give dichloromethane a competitive advantage over ammonia in the chiller prior to the introduction of CFC and will contribute to the use of methylene chloride as a natural refrigerant in modern chillers.

In China, methylene chloride is mainly used as a solvent, extractant, detergent, foaming agent, mold release agent and raw materials for R32 production. China recognizes that methylene chloride is flammable under open flame or high temperature conditions, and the thermal decomposition of methylene chloride can give off high toxicity phosgene in a manner similar to the thermal decomposition of R22. When using or exposure to methylene chloride, smoking, eating and drinking are prohibited on the spot. Non-permeable gloves for hand protection and safety glasses for eye protection are required. Two key emergency treatments and treatments for first-aid measures are: if skin exposure occurs, remove contaminated clothing and thoroughly wash the skin with soap and water for at least 15 minutes, and if eye exposure occurs, use flow cleaning Wash eyes with water or saline. The feeding and storage requirements for methylene chloride need to keep the ignition source away and avoid contact with alkali metals, alkaline earth metals and nitric acid. Due to the B1 classification of ASHRAE, the requirement to treat methylene chloride as a cryogen in a chiller is expected to be similar to that of R123.

Dichloromethane currently lacks refrigerant classification in national standards, but ongoing revisions will soon address this issue. The Chinese cryoclassification standard lacks a classification for methylene chloride. An earlier version of the Chinese refrigerant classification listed the methylene chloride as a B2 refrigerant, but is expected to be revised in 2015, which will provide a classification as a B1 refrigerant.

Adapted in Figure 2 to adapt dichloromethane or dichlorodifluoroethane A basic embodiment of a chiller system in which a olefin is used as a refrigerant. Motor 10 drives compressor 12, which vents refrigerant vapor 14 to condenser 16. Cooling fluid 18 cools the refrigerant vapor in the condenser to produce refrigerant fluid 20. The cooling fluid is in fluid communication with a heat exchanger, not shown. The refrigerant fluid 20 flows via an expansion device 24 to an evaporator 26 that boils to cool the heat transfer fluid 28. A heat transfer fluid, typically water or brine, is in fluid communication with the chiller reservoir that supplies, for example, the cooling waters of the area of the building where cooling is desired. The refrigerant vapor 30 then exits the evaporator and enters the end of the suction port of the compressor 12. The selective variable frequency drive 32 supplies power to the motor 10. The selective variable frequency drive can be controlled from the control panel 34.

Variable speed drive systems available in centrifugal compressor systems allow centrifugal compressors to be rotated at speeds greater than 3600 rpm, such as by using a 4-pole motor. In past designs, the rotational speed of the impeller has been specified by a three-stage variable speed motor. However, the variable speed drive system provides frequencies in excess of 120 Hz so that the impeller can rotate at speeds in excess of 3,600 rpm. In the past, the limitation at the compressor speed of 3,600 rpm required a system with multiple stages (three more) in order to achieve the required cooling capacity using methylene chloride. In past designs, CFC refrigerants also provided increased cooling capacity due to higher evaporation pressures. However, the ability to rotate the compressor at speeds greater than 3600 rpm allows for methylene chloride and dichlorodifluoroethylene in a two-stage centrifugal compressor system and preferably in a single-stage centrifugal compressor system that utilizes a smaller compressor size. Used in the middle. Alternatively, one or more gears can be used to increase the speed to the compressor moving impeller to achieve a speed greater than 3600 rpm. The gear configuration can use a hermetic motor or an air-cooled motor with a shaft seal. other Motor designs include permanent magnet motors, switched reluctance motors, and other types of induction motors.

Liquid injection improves the efficiency of methylene chloride and dichlorodifluoroethylene used as a refrigerant in a centrifugal compressor chiller system. The liquid is injected into the compressor to route a small amount of condensed refrigerant from the high pressure side of the refrigeration circuit, and the condensed refrigerant is injected into the suction port of the compressor having the refrigerant vapor 30, and the superheat is reduced. This liquid injection is referred to as wet compression, and the amount of condensed refrigerant liquid is throttled from the high pressure side of the compressor to the compressor inlet, reducing the refrigerant gas quality from 100% saturated steam to 95% quality. Therefore, the excretion temperature of the refrigerant is lowered, and the stability of the refrigerant can be improved. Liquid injection also allows the use of a moving impeller having a slightly larger diameter, thereby increasing the desired diameter from about 8.6 Torr without wet compression to about 9 Torr with wet compression. Although wet compression is typically achieved to reduce the noise of the centrifugal compressor, the efficiency of the system is improved by about 3.0% for the natural refrigerant used with the chiller system of the present invention, and the calculated efficiency is 2.9%. The amount of condensed refrigerant liquid that is throttled from the high pressure side to the compressor inlet will vary based on compressor capacity, and larger compressors will throttle more condensing refrigerant than small centrifugal compressors. The compressor speed can also affect the amount of condensed liquid refrigerant that is throttled to the suction port, such as for a compressor with variable speed performance. The amount of condensed cryogen liquid that is throttled can be up to 5% of the total mass of the refrigerant at the inlet of the compressor. The use of methylene chloride advantageously provides a liquid retentate which improves the calculated cycle efficiency and thus reduces the size and pressure drop of the mist scrubber. Although liquid injection into the compressor suction port improves performance, the theoretical optimum corresponds to a small (~20°F) row. Overheating, this condition can also serve as the basis for system control. The optimal injection can be different from the theoretical optimum, and the amount can be optimized based on the test data. The size and amount of droplets of the injected liquid should be limited to reduce the risk of compressor damage.

Regarding the compressor impeller, the decomposition of hydrochloric acid from methylene chloride (and phosgene gas) and the decomposition of hydrochloric acid and hydrofluoric acid from dichlorodifluoroethylene have been presented for prior art steel impellers or lightweight aluminum impellers. Survivability problems, because both are attacked by both hydrochloric acid and hydrofluoric acid, both hydrochloric acid and hydrofluoric acid are extremely corrosive. There are several solutions for this problem that are not available in the case of centrifugal chillers that previously used dichloromethane as a refrigerant. One such solution is the use of stainless steel impellers to limit the attack of hydrochloric acid and hydrofluoric acid. Preferably, the stainless steels are cast stainless steel and are austenitic stainless steels, preferably in the 300 series of austenitic stainless steels. Because even stainless steel can withstand such acid attack by the decomposition of methylene chloride and dichlorodifluoroethylene in the presence of water, it can be coated by a thin layer of non-permeable material through the acid. These stainless steel castings are included to further extend the useful life of these stainless steel castings. Of course, these coatings can also be applied to the aluminum impeller. Such coatings include Teflon ^® (polytetrafluoroethylene -PTFE), epoxy resin and other polymers.

Hydrochloric acid formed by decomposition of methylene chloride hydrochloric acid in the presence of water and hydrofluoric acid formed by decomposition of dichlorodifluoroethylene circulate through the system and have an impeller in addition to the centrifugal compressor in the attack system. The potential of various components, including aluminum, zinc, aluminum and zinc Gold and / or fat iron steel. Therefore, mechanical bearings and parts of the motor are also subjected to such acid attacks. Preferably, the mechanical bearing is designed to replace the steel or aluminum portion with stainless steel such that the bearing is a stainless steel bearing. Alternatively, ceramic bearings can be used as replacements for metal bearings. The motor housing may be replaced by a stainless steel motor housing or a housing having a coating of a material resistant to such acid attack. This is especially desirable when the refrigerant is also used as a coolant for the motor. The aluminum rotor bars and aluminum wiring used in the windings of the motor are replaced with copper rotor bars and copper wire windings. The decomposition products of methylene chloride and dichlorodifluoroethylene also attack the package used on the stator windings in the motor. KAPTON® can be used as insulation for wires, and KAPTON® is a polyimide film available from Du Pont. Additionally, the varnish used for encapsulation and which can be attacked by decomposition products of the refrigerant or cryogen is preferably replaced with an acid-resistant encapsulating compound such as a glass encapsulant or an epoxy resin.

Aluminum has also been used in heat exchanger shells and tubes. Again, aluminum must be removed from the heat exchanger shell and tube that is in contact with the refrigerant. For the shell, the shell is replaced by a stainless steel shell. Alternatively, the shell may be coated with a coating such as epoxy or PTFE that protects the substrate from attack from decomposition products of methylene chloride or dichlorodifluoroethylene. The aluminum tube should be replaced with a copper tube.

The use of methylene chloride and dichlorodifluoroethylene also allows for other modifications in the design of the heat exchanger. The standard tube diameter for tubes used in shell/tubular heat exchangers is 5/8 inch. Increasing the size of the tubes used in these shell/tube heat exchangers to a size in the range of 3⁄4 吋 to 1 将 will provide more surface area for heat exchange, which is desirable because of Reduce the mass flow and density of methylene chloride and dichlorodifluoroethylene compared to CFC refrigerant degree. A cycle comparison for dichloromethane compared to other CFC refrigerants is set forth in Table 4. In addition, the tube can be provided with a reinforced surface on both the shell side and the water/tube side for better efficiency and improved capacity to be improved compared to CFC refrigerants having better mass flow and higher density. Heat exchange characteristics with such refrigerants. Such enhanced surface features include spiral internal reinforcement and/or high performance nuclear boiling surfaces.

In addition to the separate use of each of the fluids, mixtures of such fluids with each other or with other fluids of similar vapor pressure may be suitable as a substantially azeotropic refrigerant blend. Other components preferably have a short atmospheric lifetime such as hydrofluoroolefins (HFO) and hydrochlorofluoroolefins (HCFO). Particularly desirable fluids include the isomers of R-1336mzz(Z), R-1233zd(E), R1336mzz(E), R-143, R-245. Hydrocarbons can also be used, but flammability is a problem. Short-lived HFCs such as R-143, R-245ea, R-245eb, and R-245ca are also alternatives.

The use of dichloromethane and dichlorodifluoroethylene also allows for changes to the evaporator configuration. The evaporator is preferably an overflow evaporator, eliminating the need for a pump for the refrigerant. Of course, the pump is subjected to decomposition products of methylene chloride and dichlorodifluoroethylene, and the elimination of the pump reduces maintenance due to pump leakage and possible downtime. In another embodiment, a spray design can be utilized. Although this configuration of the evaporator can utilize a refrigerant pump that eliminates the risk of leakage from the shaft seal. Such pumps include a magnetically coupled centrifugal refrigerated pump, an airlift pump that uses flash gas as the drive fluid, and a hermetic motor driven pump. In another preferred embodiment, the evaporator can have a falling film type that also uses a pump to pump the refrigerant through the tubes in the tube bundle. An "air lift" pump or ejector can be used to deliver liquid cryogen to the dispenser in the evaporator.

In one embodiment, the shell is generally circular to minimize material and labor costs as compared to conventional rectangular shell configurations. In one embodiment, the shell has a greater width than the height to allow the centrifugal compressor to be mounted vertically to minimize the refrigerant pressure drop into and out of the compressor. In an embodiment, the shell includes a concave shell side, a top and a bottom, and outwardly extending reinforcing ribs to create a rectangular outer boundary. In an embodiment, the evaporator housing contains a controlled orifice or valve for flow into a dispenser at the top of the evaporator.

Because the refrigerants methylene chloride and dichlorodifluoroethylene are in the presence of water The decomposition products in the case of the operation cause problems in the operation of the centrifugal compressor chiller system, so that several remediation systems can be built into the chiller system. One such system includes a water detection system that detects the presence of water in the cryogen. The water detection system includes a series of sensors placed on the refrigerant side of the chiller system. Because the refrigerant operates below the standard pressure of 15 psia and the water side of the system operates above the standard pressure, any leakage between the water side of the system and the refrigerant side of the system, such as at the condenser and evaporator, will result in Water leaks into the refrigerant side of the system. These sensors measure the conductivity or dielectric properties of the fluid flowing on the refrigerant side. The change in the measurement of the cryogen is an indication of the water in the cryogen. In response to a leak, the chiller can be shut down, or the leak can be isolated by various water side shutoff valves within the system. The leak can then be repaired. Additionally, the remediation system can include a filter desiccant for the cryogen or stabilizer that is added to the cryogen to remove moisture or acid from the cryogen in the system. The sensor in the equipment room can also be used to detect leakage of methylene chloride or dichlorofluoroethylene refrigerant into the equipment room. In one embodiment, a metal flat disk can be used to collect the liquid cryogen in the event of a cryogen leakage. In another embodiment, a concrete flat disk having a non-permeable coating can be used to collect a liquid cryogen in the presence of a cryogen leakage, the liquid cryogen being a liquid at ambient temperature and pressure.

In one embodiment, the expansion device is an actuated butterfly valve that is responsive to condenser level control. In one embodiment, if a subcooler is used, the condenser level control is preferred. Alternatively, the fixed orifice can be used to reduce system cost and refrigerant feed requirements without a subcooler.

Due to methylene chloride, dichlorodifluoroethylene and its decomposition products The corrosive nature of these materials, the materials used for sealing and bonding in contact with the refrigerant should be compatible with the refrigerant. Welding and brazing are good options in many situations. Compatible gasket materials for flanges and O-rings include various fluoropolymers marketed under various brand names such as Chemraz® and Kalrez®. Teflon® (PTFE) is another compatible gasket material. In some cases, if the expansion does not create operational problems, a less expensive material can be used.

FIG. 3 shows a selective condenser design 302 with a subcooler 304. As further shown in FIG. 3, the subcooler 304 has a non-circular shell 308 that is welded to the outside of the condenser shell 306 and that is welded to the condenser tube sheet 310 at the end of the subcooler shell. This setting reduces refrigerant feed requirements while improving performance with additional subcooling. This subcooler is designed to be particularly desirable in the case of irregular tanks that can be used with methylene chloride.

While the invention has been described with respect to the preferred embodiments of the embodiments of the embodiments of the invention . In addition, many modifications may be made to adapt a particular situation or material to the teachings of the invention. Therefore, it is intended that the invention not be limited to the particular embodiments of the invention

10‧‧‧ motor

12‧‧‧Compressor

14‧‧‧Refrigerant steam

16‧‧‧Condenser

18‧‧‧Cooling fluid

20‧‧‧Refrigerant fluid

24‧‧‧Expansion device

26‧‧‧Evaporator

28‧‧‧Heat transfer fluid

30‧‧‧Refrigerant steam

32‧‧‧Selective variable frequency drive

34‧‧‧Control panel

Claims (22)

A centrifugal chiller system comprising: an electric drive centrifugal compressor having a moving impeller having a rotational speed greater than 3600 rpm, the compressor further comprising an electric motor driven by an electric motor housing a moving impeller and a bearing selected from the group consisting of an electromagnetic bearing, a ceramic bearing and a stainless steel bearing; a condenser in fluid communication with the compressor; an evaporator in fluid communication with the condenser and the compressor; an expansion a device interposed between the condenser and the evaporator and in fluid communication with both the condenser and the evaporator; a chiller in heat exchange connection with the evaporator having a chiller fluid, the chiller fluid Circulating from the chiller to the evaporator in which the chiller fluid is cooled; a refrigerant circulating through a refrigerant circulatory system, the refrigerant circulatory system further comprising a line that compresses the compressor fluid Connected to the condenser, fluidly connect the condenser to the evaporator, and fluidly connect the evaporator to the compressor, the refrigerant is further The step comprises a non-flammable natural organic compound having a molecular weight of greater than about 60 and a condensation pressure of no greater than 19 psia; in at least the condenser and a water detector in the evaporator, the water detector detects water Leaking into the refrigerant circulating through the condenser and the evaporator; a shut-off valve that isolates the quench fluid in the chiller when water leakage is detected in the cryogen; wherein the evaporator is selected from a flooding evaporator, a falling film a group consisting of an evaporator and a spray evaporator; wherein the compressor further comprises an electric motor characterized by substantially no aluminum, zinc and aluminum zinc alloys, the electric motor further comprising copper windings and copper rotor bars And a moving impeller characterized by a material resistant to attack by decomposition products of the cryogen; and wherein the refrigerant circulation system is substantially free of alloys of aluminum, zinc, aluminum and zinc, and ferrite Profile steel contact. The centrifugal chiller system of claim 1, wherein the compressor electric motor is insulated from a group selected from the group consisting of glass insulation, epoxy, and polyimide. The centrifugal chiller system of claim 1, wherein the centrifugal compressor further comprises a liquid cryogen injection system that throttles up to 5% of the suction enthalpy of one of the centrifugal compressors Liquid cryogen. The centrifugal chiller system of claim 1, wherein the natural refrigerant has an ideal gas heat capacity of less than about 100 kJ/kg mol/K at 20 ° C and a vapor pressure of at least 0.05 bar at 0 ° C, at least 0 One of the freezing point of °C and a vapor pressure of less than about 1 bar at 35 °C. The centrifugal chiller system of claim 3, wherein the chiller system One step includes a single stage centrifugal compressor. The centrifugal chiller system of claim 4, wherein the natural refrigerant is selected from the group consisting of dichloromethane and dichlorodifluoroethylene. The centrifugal chiller system of claim 6, wherein when the natural refrigerant is dichlorodifluoroethylene, the refrigerant further comprises cis-dichlorodifluoroethylene having a boiling point of 21 ° C and having a boiling point of 22 ° C A substantially azeotropic combination of trans-dichlorodifluoroethylene and cis-dichlorodifluoroethylene and trans-dichlorodifluoroethylene. The centrifugal chiller system of claim 6 further comprising an HFO in combination with the natural cryogen, and an HFC or an HFCO, the combination forming a substantially azeotropic refrigerant blend. The centrifugal chiller system of claim 8, wherein the HFO, HFC or the HFCO is selected from the group consisting of R-1336mzz (Z), R-1233zd (E), R1336mzz (E), R-143, and R-245. At least one cryogen of the group consisting of R-245ea, R-245eb, and R-245ca. The centrifugal chiller system of claim 1 wherein the system further comprises a seal and a gasket compatible with the natural refrigerant in the chiller system. The term centrifugal chiller system 10 of the request, and wherein the gasket seal comprises those selected from the group consisting of PTFE, a group of materials consisting of Kapton ^®, a combination of epoxy resin and those of the above. The centrifugal chiller system of claim 1, wherein one or both of the evaporator and the condenser comprise a tube having a diameter or 3⁄4 吋 to 1 。. The centrifugal chiller system of claim 1, wherein the system further comprises A filter desiccant is included which removes water and acid from the cryogen. A method of limiting the global environmental effects of a cryogen, the method comprising: selecting a cryogen fluid comprising a non-combustible natural organic compound having a molecular weight greater than about 60 and at 20 Less than about 100 kJ/kg mol/K of one mole of the desired gas heat capacity at ° C, and a vapor pressure of at least 0.05 bar at 0 ° C and a freezing point of at least 0 ° C. The method of claim 14, further comprising the steps of: providing a centrifugal chiller system, the step comprising circulating the selected refrigerant fluid to a centrifugal compressor in fluid communication with a condenser, the condenser An evaporator is in fluid communication, the evaporator being in fluid communication with the centrifugal compressor, the evaporator also being in fluid communication with a chiller using water or an aqueous solution. The method of claim 15 wherein the step of providing a chiller system further comprises providing a single stage centrifugal compressor or a two stage centrifugal compressor. The method of claim 16, wherein the step of providing a single stage compressor or a two stage compressor further comprises providing a variable speed drive that operates at a frequency of at least 120 Hz while rotating at a rotational speed of more than 3600 rpm. A compressor moves the impeller. The method of claim 16, wherein the step of providing a chiller system further comprises providing a liquid injection to the suction side of the centrifugal compressor in. The method of claim 16, wherein the non-flammable natural organic compound has a vapor pressure of less than about 1 bar at 35 °C. The method of claim 16, wherein the non-flammable natural organic compound comprises an organic compound selected from the group consisting of dichloromethane and dichlorodifluoroethylene. The centrifugal chiller system of claim 20, further comprising an HFO in combination with the natural cryogen, and HFC or an HFCO, the combination forming a substantially azeotropic refrigerant blend. The centrifugal chiller system of claim 21, wherein the HFO, HFC or the HFCO is selected from the group consisting of R-1336mzz (Z), R-1233zd (E), R1336mzz (E), R-143, and R-245. At least one cryogen of the group consisting of R-245ea, R-245eb, and R-245ca.