Title of Invention

A REFRIGERANT COMPOSITION FOR REFRIGERANTION SYSTEMS

Abstract

A refrigerant composition for precooled multistage mixed refrigeration systems comprising: more than 36 molar percent but less than 60 molar percent of Nitrogen,, 21 to 40 molar percent of Methane , atleast one of the gases: Ethane and/or Ethylene (5 to 30 molar percent in all), at least one of the gases: propane and/or n—Butane and/or Iso-Butane (up to 15 molar percent in all), at 1 east one of the gases: Neon and/or Helium (up to 20 molar percent in all)-

Full Text

This invention relates to a refrigerant composition for refrigeration systems, more particularly precooled multistage mixed refrigeration systems. Simple refrigeration systems use a method called vapor compression cycle. The vapor compression cycle is a method in which a compressor such as a piston compressor compresses a low-pressure refrigerant vapor. In a next stage, a condenser condenses the warm compressed vapor, resulting in a partial or complete condensation of the vapor. This condensed refrigerant then passes through a fine capillary tube or other constriction into a larger chamber at low pressure. As the refrigerant enters the larger chamber, it evaporates and absorbs heat, resulting in the vapor. This refrigerant vapor is then routed to the intake of the compressor, thus closing the cycle. This is the so-called closed loop refrigeration system. A single stage refrigerant system is used to achieve temperatures up to -40°C. For temperatures in the range -50 °C to -80 °C a two-stage cascaded vapor compression system has been proposed. This method uses a single refrigerant per stage and two compressors, one for each stage. For still lower refrigeration temperatures, more cascaded stages are required. Typically, four stage cascade vapor compression systems are proposed for reaching cryogenic temperatures, lower than -150T. An advance in technology has been achieved by using a single compression system with a composition of refrigerants. This method has been used to achieve temperatures far below those that can be achieved using a cascaded multi-stage system, for example, the range -100 °C to -210 °C. This method uses a composition of several refrigerants each of which with different boiling points. The low temperatures can be achieved using different process systems, some employing one or more phase separators and some that don't employ any phase separators. Systems that employ phase separators are commonly known as multistage mixed refrigerant systems, and those that don't employ phase separators as single stage mixed refrigerant systems. In all the systems, the high pressure refrigerant is cooled to a low temperature and expanded to a low pressure to provide the necessary refrigeration to cool a load. The low pressure refrigerant leaving the evaporator provides the necessary refrigerant to cool the high pressure refrigerant to low temperatures. Phase separators are employed to remove some of the high boiling point components and lubricating oil carried over from the compressor from reaching low temperatures where they may freeze. In the phase separators, the liquid consists mostly of the high boiling point components, and the vapour phase preferably does not contain any high boiling components. The liquid is expanded to a lower pressure, mixed with the low pressure refrigerant returning from the evaporator at an intermediate temperature and returned to the compressor. The expanded liquid also provides the necessary cooling to cool and condense the vapour stream leaving the phase separator. The use of phase separators allow balancing the refrigeration needed to cool the high pressure refrigerant at different temperatures. It is also possible to replace the phase separators with stream splitters such that both liquid and vapour phases are present in the two outlet streams of the stream splitter. One of the streams is expanded to provide the refrigeration required to cool the other stream. Sometimes part of the refrigeration needed to cool the high pressure refrigerant is provided by another refrigerator or a cold stream. Such systems are known as precooled systems. Precooling can be used in both single and multistage mixed refrigerant systems. This invention relates to a refrigerant composition for multistage refrigeration systems precooled to a temperature at least 20 K below the ambient temperature, and more preferably precooled to a temperature of230 to 250K. Researchers have proposed different refrigerant compositions for precooled systems. There is still a need for a refrigerant composition that can achieve better efficiency or a greater amount of cooling or both. This disclosure is directed toward a composition of refrigerants for use in precooled multi stage mixed refrigerant systems to provide refrigeration below 150 Kelvin. Applications for such composition of refrigerants include household or commercial refrigeration systems such as refrigerators, electronic circuit cooling, medical applications, cryo-vacuum pumps, storing of biological specimens and tissues at low temperatures, cooling of Gamma-ray, Infra Red and X-ray detectors, cryosurgery and the like. In one aspect, disclosed herein is a composition of refrigerant consisting of more than 36 molar percent but less than 60 molar percent of Nitrogen, 15 to 40 molar percent of Methane, at least one the gases: Ethane and Ethylene (5 to 30 molar percent in all), at least one the gases: propane, n-Butane and Iso-Butane (up to 20 molar percent in all), at least one the gases: Neon and Helium (up to 20 molar percent in all) We have ascertained that a new combination of refrigerants as defined herein results in an efficient cooling system (higher refrigeration capacity, or higher efficiency or both) for precooled single and multistage mixed refrigerant systems. The advantages in using the disclosed refrigerant composition are illustrated with the help of three examples. The following are common for all the examples. • The refrigerant leaving the precooled multistage mixed refrigerant system is passed to the compressor directly, • No pressure drop occurs in the heat exchangers, evaporator, phase separators or connecting piping, • The systems are well insulated, • The efficiency of the phase separators is 100%j • The refrigerating temperature is considered to be the temperature of the refrigerant leaving the evaporator, • The ambient temperature is 300 K, • The exergy efficiency (T|ex) quoted is the internal exergy efficiency defined as follows: where Q is the heat added to the refrigerant in the evaporator in Joules per mol of refrigerant circulating through the system, Tambient and Tevap,out are the ambient temperature and the temperature of the refrigerant leaving the evaporator respectively. The term exhp,in refers to the exergy of the high pressure refrigerant leaving the precooler and entering the coldbox of the multistage refrigeration system, and exipout refers to the exergy of the low pressure stream leaving the refrigeration system to the compressor inlet, in Joules per mol. The multistage system considered in the examples is a refrigerant system with one phase separator, two 2-stream counter flow heat exchangers. The refrigerant is compressed in a compressor. The heat of compression of the high pressure refrigerant is removed in an after cooler and further cooled in a precooler. A part of the high pressure refrigerant is in the liquid phase and the rest in the vapour phase at this stage. The liquid and vapour phases are separated in a phase separator. The high pressure vapour separated in the phase separator is passed to the first of the two heat exchangers (HXl). The liquid separated from the phase separator is expanded and mixed with the low pressure stream between the first (HXl) and second heat exchangers (HX2). The high pressure stream is cooled to a low temperature in the two heat exchangers regeneratively, and is expanded to a lower pressure in a throttling device (JT). The low temperature and low pressure refrigerant provides the refrigeration to cool the load in the evaporator. The low pressure refrigerant leaving the evaporator warms up in the two heat exchangers, and cools the high pressure refrigerant. The low pressure refrigerant leaving HXl is passed to the compressor where it gets compressed to a higher pressure, thus completing the cycle. The table shows the refrigerant compositions passing through the compressor of a precooled multistage refrigeration systems described above at different operating conditions. The minimum temperature difference in each of the heat exchanger and other operating/design conditions assumed to arrive at the above compositions is also given. The compositions were arrived at for a compressor with a certain volumetric efficiency characteristic. The compositions will be different when the operating/design conditions and hardware such as the compressor used are different. It is also possible to obtain even higher exergy efficiencies and/or larger amount of refrigeration than that shown in Table with appropriate changes to the refrigerant composition and/or the operating/design conditions such as the amount of subcooling of the refrigerant at the inlet of the expansion valve connected to the evaporator etc. It should be understood that the use of a refrigerant composition that falls within the claims in this specification is not to be taken in isolation, but in conjunction with other parameters such as those indicated below to achieve a high efficiency and high refrigeration. Only an appropriate composition can result in optimum performance. The efficiency and the quantity of refrigeration obtained from different systems depend not only on the type of refrigerant composition employed, but also on the hardware used as well as operating parameters such as the operating pressures used etc. The type of system to be employed (number of phase separators or heat exchangers to be used etc.) depends on several factors such as the temperature at which refrigeration is needed, type of lubricating oil used, type of oil separation/filtration systems used, compressor used, the quantity of refrigeration required etc. The optimum composition for one type of system may not be optimum for other type of systems, operating temperatures and pressures. The components used in the refrigerant composition also depend on other factors as well. For example, We Claim; 1. A refrigerant composition for precooled multistage mixed refrigeration systems comprisings more than 36 molar percent but lese than 60 molar percent of Nitrogen, 21. to 40 molar percent of Methane, at least one of the gases Ethane and/or Ethylene (5 to 30 molar percent in all), at 1 east one of the gases: propane and/or n-Butane and/or Iso-Botane (up to 15 molar percent in all), at 1 east one of the gases : Neon and/or Helium Cup to 20 molar percent in all), 2. A refrigerant composition for precooled multistage mixed refrigeration systems substantialy as herein described and illustrated with reference to the Examplest Dated this the 14th day of -July 2003.

Documents:

573-che-2003 claims duplicate.pdf

573-che-2003 description (complete) duplicate.pdf

573-che-2003-abstract.pdf

573-che-2003-claims.pdf

573-che-2003-correspondnece-others.pdf

573-che-2003-correspondnece-po.pdf

573-che-2003-description(complete).pdf

573-che-2003-form 1.pdf

573-che-2003-form 19.pdf

573-che-2003-form 26.pdf