Patent Publication Number: US-9897363-B2

Title: Transcritical carbon dioxide refrigeration system with multiple ejectors

Description:
TECHNICAL FIELD 
     The present application and the resultant patent relate generally to refrigeration systems and more particularly relate to a transcritical carbon dioxide refrigeration system using multiple ejectors at multiple temperatures for improved overall efficiency. 
     BACKGROUND OF THE INVENTION 
     Current refrigeration trends promote the use of carbon dioxide and other types of natural refrigerants as opposed to conventional hydrofluorocarbon based refrigerants. Although such carbon dioxide based refrigeration systems may be considered more environmentally friendly, such systems tend to be less efficient and, hence, may require more overall power usage given the low critical point and therefore high throttling losses between the heat rejection and heat absorption process in a conventional refrigeration cycle. 
     There is thus a desire for refrigeration systems using natural refrigerants such as carbon dioxide with improved efficiency and improved overall energy consumption. Preferably such an improved refrigeration system may be environmentally friendly with reduced overall operational and maintenance requirements. 
     SUMMARY OF THE INVENTION 
     The present application and the resultant patent thus provide a carbon dioxide based refrigeration system. The carbon dioxide based refrigeration system may include a mid temperature cycle with a mid temperature ejector, a low temperature cycle with a low temperature ejector, and a gas cooler/condenser in communication with the mid temperature cycle and the low temperature cycle. 
     The present application and the resultant patent further provide a method of operating a carbon dioxide based refrigeration system. The method may include the steps of flowing a first portion of a carbon dioxide refrigerant to a mid temperature ejector, accelerating the first portion of the flow of the carbon dioxide refrigerant in the mid temperature ejector, flowing the first portion of the flow of the carbon dioxide refrigerant to a mid temperature suction group, flowing a second portion of the carbon dioxide refrigerant to a low temperature ejector, accelerating the second portion of the flow of the carbon dioxide refrigerant in the low temperature ejector, and flowing the second portion of the flow of the carbon dioxide refrigerant to a low temperature suction group. 
     The present application and the resultant patent further provide a refrigeration system. The refrigeration system may include a flow of a carbon dioxide refrigerant, a mid temperature cycle with a mid temperature ejector, a low temperature cycle with a low temperature ejector and a gas cooler/condenser in communication with the mid temperature cycle, and the low temperature cycle. A first portion of the flow of the carbon dioxide refrigerant flows through the mid temperature cycle and a second portion of the flow of the carbon dioxide refrigerant flows through the low temperature cycle. 
     These and other features and improvements of the present application and the resultant patent will become apparent to one of ordinary skill in the art upon review of the following detailed description when taken in conjunction with the several drawings and the appended claims. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a schematic diagram of an ejector described herein. 
         FIG. 2  is a schematic diagram of a transcritical carbon dioxide refrigeration system as may be described herein. 
         FIG. 3  is an alternative embodiment of a transcritical carbon dioxide refrigeration system as may be described herein. 
         FIG. 4  is an alternative embodiment of a transcritical carbon dioxide refrigeration system as may be described herein. 
         FIG. 5  is an alternative embodiment of a transcritical carbon dioxide refrigeration system as may be described herein. 
     
    
    
     DETAILED DESCRIPTION 
     Referring now to the drawings, in which like numerals refer to like elements throughout the several views,  FIG. 1  shows an example of an ejector  100  as may be described herein. Generally described, the ejector  100  may be a mechanical device with or without any moving parts. Instead, the ejector  100  mixes two fluid streams based upon a momentum transfer between a motive fluid and a suction fluid. A motive inlet  110  may be in communication with a first flow under pressure. The ejector  100  also may include a suction inlet  120  in communication with a second flow. The ejector  100  also may include a mixing tube  130  and a diffuser  140 . The motive flow may be reduced in pressure as the suction flow is accelerated therein. The flows are mixed in the mixing tube  130  and flow through the diffuser  140  as a mixed flow. The mixed flow may be discharged at an outlet  150  at a pressure greater than the suction flow but less than the motive flow. The overall suction capability for the ejector  100  may be based upon the net positive suction head available therein. Other component and other configurations also may be used herein. 
       FIG. 2  shows an example of a carbon dioxide based refrigeration system  160  as may be described herein. The transcritical carbon dioxide based refrigeration system  160  may include a number of the ejectors  100  in a parallel configuration  170 . In this example, a medium temperature ejector  180  may be used in a medium temperature cycle  190  and a low temperature ejector  200  may be used in a low temperature cycle  210 . Other components and other configurations also may be used herein. As the names imply, the mid temperature cycle  190  and the low temperature cycle  210  operate at different temperatures. 
     The mid temperature cycle  190  may include any number of mid temperature suction groups  220  or compressors. The mid temperature suction groups  220  may be used herein in a parallel configuration or otherwise. The mid temperature suction groups  220  compress a flow of a carbon dioxide refrigerant  230 . Other types of refrigerant flows may be used herein. The carbon dioxide refrigerant  230  may be forwarded to a gas cooler/condenser  240 . The carbon dioxide refrigerant  230  may lose or reject heat in the gas cooler/condenser. The mid temperature cycle  190  also may include a mid temperature suction line heat exchanger  250 . The mid temperature suction line heat exchanger  250  may exchange heat between the flow of refrigerant  230  entering the mid temperature suction groups  220  and the flow of refrigerant  230  leaving the gas cooler/condenser  240 . Other components and other configurations also may be used herein. 
     A first portion  260  of the flow of refrigerant  230  leaving the gas cooler/condenser  240  may be directed to the mid temperature ejector  180 . The first portion  260  of the refrigerant flow  230  may be substantially gaseous. The mid temperature ejector  180  also may be in communication with a mid temperature flash tank  270  and one or more mid temperature evaporators  280 . The mid temperature evaporators  280  may be evenly or unevenly sized to cover a certain capacity range and modulation. The first portion  260  of the flow  230  may enter the mid temperature ejector  180  at the motive inlet  110  as the motive flow. The flow of refrigerant  230  from the mid temperature evaporators  280  may enter the suction inlet  120  in a liquid state as the suction flow. The motive flow of refrigerant  230  thus may be accelerated and reduced in pressure upon leaving the outlet  150 . The flow of refrigerant  230  then may again be separated into vapor and liquid form in the temperature flash tank  270 . The vaporized refrigerant  230  may be returned to the mid temperature suction groups  220  via the mid temperature suction line heat exchanger  250  while the liquid flow may be sent to the mid temperature evaporators  280  and back to the mid temperature ejector  180 . Other components and other configurations also may be used herein. 
     A second portion  290  of the flow of refrigerant  230  from the gas cooler/condenser  240  may be routed to the low temperature ejector  220  of the low temperature cycle  210 . The second portion  290  of the flow of refrigerant  230  may first pass through a low temperature suction line heat exchanger  300 . The low temperature ejector  200  also may be in communication with a low temperature flash tank  310  and one or more low temperature evaporators  320 . The low temperature evaporators  320  may be evenly or unevenly sized to cover a certain capacity range and modulation. The second portion  290  of the flow of refrigerant  230  thus may enter the motive inlet  110  of the low temperature ejector  200  while the flow of refrigerant  230  from the low temperature evaporator  320  may enter at the suction inlet  120 . Again the mixed flow may be accelerated and reduced in pressure. The mixed flow thus leaves the outlet  150  of the low temperature ejector  200  and flows to the low temperature flash tank  310 . The vaporized portion of the flow of refrigerant  230  may flow through the low temperature suction line heat exchanger  300  and towards a number of low temperature suction groups  330  or compressors. The flow of refrigerant  230  then may be forwarded to the mid temperature flash tank  270  or directly back to the gas cooler/condenser  240 . The liquid portion of the flow of refrigerant  230  may pass through the low temperature evaporator  320  and back to the low temperature ejector  200 . The cycle then may be repeated. 
     The use of the ejectors  180 ,  200  serves to recover pressure/work herein. The work recovered from the expansion process may be used to compress the vaporized refrigerant before entering into the compressors/suction groups. Accordingly, the pressure ratio of the suction groups (and thus the overall power consumption) may be reduced for a given evaporator pressure. The quality of the refrigerant also may be reduced. The overall number of pumps also may be reduced and/or eliminated. 
       FIG. 3  shows an alternative embodiment of a carbon dioxide refrigeration system  160 . In this example, the ejectors  100  may be positioned in a series configuration  340 . Specifically, a medium temperature cycle  350  and a low temperature cycle  360  may be positioned in a series configuration  340 . Other components and other configurations may be used herein. 
     The mid temperature cycle  350  may include the mid temperature suction groups  220 , the gas cooler/condenser  240 , and the mid temperature suction line heat exchanger  250  substantially as described above. In this example, however, the entire flow of refrigerant  230  may be directed to the mid temperature ejector  180 . The mid temperature ejector  180  also may be in communication with the mid temperature flash tank  270  and the mid temperature evaporator  280 . In this example, a first portion  370  of the fluid refrigerant  230  may be directed to the mid temperature evaporators  280  while a second portion  380  may be forwarded to the low temperature cycle  360 . 
     The lower temperature cycle  360  also may include the low temperature suction line heat exchanger  300  and the low temperature ejector  200  in communication with the low temperature flash tank  310  and the low temperature evaporator  320 . The low temperature cycle  360  also includes the low temperature suction groups  330 . The flow of refrigerant  230  thus flows first through the mid temperature cycle  350  and then through the low temperature cycle  360  before being returned to either the mid temperature flash tank  270  and/or the gas cooler/condenser  240 . Other components and other configurations may be used herein. 
       FIG. 4  shows an alternative embodiment of  FIG. 2 . In this example, an evaporator  390  or an assembly of evaporators  390  in a parallel configuration are positioned between the outlet of the low temperature ejector  200  and the inlet of the low temperature flash tank  310 . Further, the flash tank liquid outlet is fed into the ejector suction port  120  in the low temperature cycle  210 . This alternative embodiment enables overfeeding of the evaporator coils with liquid such that they can have heat transfer performance enhancement. 
       FIG. 5  shows an alternative embodiment of the transcritical carbon dioxide based refrigeration system  160  of  FIG. 3 . In this example, an evaporator  400  or an assembly of evaporators  400  in a parallel configuration are positioned in between the outlet of the low temperature ejector  200  and the inlet of the low temperature flash tank  310 . Further, the flash tank liquid outlet is fed into the ejector suction port  120  in the low temperature cycle  210 . This alternative embodiment also enables overfeeding of the evaporator coils with liquid such that they can have heat transfer performance enhancement. 
     It should be apparent that the foregoing relates only to certain embodiments of the present application and the resultant patent. Numerous changes and modifications may be made herein by one of ordinary skill in the art without departing from the general spirit and scope of the invention as defined by the following claims and the equivalents thereof.