Abstract:
A multistage compression refrigerating machine is disclosed, which efficiently cools a rotating machine such as an electric motor and lubricating oil by using a refrigerant and increases the amount of refrigerant to be used to provide the refrigerating capacity in the evaporator, thereby improving the refrigerating capacity. The machine comprises a condenser for supplying a condensed refrigerant to an evaporator via an intercooler: a multistage compression system for absorbing the above refrigerant, absorbing a refrigerant evaporated from the intercooler, from an intermediate position between adjacent compressors, compressing the absorbed refrigerants together, and discharging it to the condenser; a rotating-machine cooler for cooling a rotating machine for driving the multistage compression system; and a lubricating-oil cooler for cooling lubricating oil. The refrigerant extracted from the intercooler is supplied to the rotating-machine cooler and the lubricating-oil cooler, and this refrigerant is returned to the evaporator after cooling.

Description:
BACKGROUND OF THE INVENTION  
         [0001]    1. Field of the Invention  
           [0002]    The present invention relates to a multistage compression refrigerating machine such as a centrifugal chiller, screw chiller, or the like.  
           [0003]    2. Description of the Related Art  
           [0004]    Multistage compression refrigerating machines are widely used in air conditioning systems of general buildings, factories, and the like. For example, the two-stage compression refrigerating machine as shown in FIG. 3 comprises an evaporator  51 , a first-stage compressor  53  and a second-stage compressor  54  which are rotationally driven by an electric motor  52  (abbreviated to the motor  52 , hereinbelow), a condenser  55 , an intercooler  56 , a motor cooler  57  for cooling the motor  52  by using a refrigerant, and a lubricating-oil cooler  58  for cooling lubricating oil by using a refrigerant.  
           [0005]    In the evaporator  51 , a liquid refrigerant is heated by cold water  60  having a temperature of 12° C. passing through a tube  59 , so that vaporized refrigerant  61  is generated. In this process, the cold water  60  is cooled to approximately 7° C. thorough the heat exchange in the evaporator  51 , and it is then delivered outside. Therefore, the temperature in the evaporator  51  is maintained to be approximately 5° C.  
           [0006]    The vaporized refrigerant  61  generated in the evaporator  51  is absorbed into the first-stage compressor  53  and second-stage compressor  54 , and the absorbed refrigerant is two-stage-compressed by using impellers which are rotated by the motor  52 , thereby discharging high-temperature and high-pressure vaporized refrigerant  61   a.  Here, vaporized refrigerant  61   b  from the intercooler  56  is also introduced (or absorbed) into a path between the first-stage and second-stage compressors  53  and  54  (i.e., the upstream side of the second-stage compressor  54 ), and the absorbed vaporized refrigerant  61   b  is also compressed together with the vaporized refrigerant  61  from the evaporator  51 .  
           [0007]    In the condenser  55 , the high-temperature and high-pressure vaporized refrigerant  61   a  discharged from the second-stage compressor  54  is cooled using cooling water  63  which flows through a tube  62 , thereby condensing the vaporized refrigerant  61   a  into a liquid. In this process, the cooling water  63  is heated through the heat exchange in the condenser  55  and is then discharged outside. The condensed liquid refrigerant  64  is collected at the bottom of the condenser  55 ; thus, the temperature inside the condenser  55  is approximately 40° C.  
           [0008]    The pressure of the liquid refrigerant  64   a  supplied from the condenser  55  is reduced to an intermediate pressure by using a first-stage expansion valve  65 , so that the refrigerant  64   a  is expanded, and a portion of the expanded refrigerant is output from the intercooler  56  as vaporized refrigerant  61   b  . As explained above, this vaporized refrigerant  61   b  is supplied to an intermediate position between the first-stage compressor  53  and the second-stage compressor  54 . On the other hand, the pressure of the remaining refrigerant  64   a  cooled through the evaporation of the refrigerant  64   a  is further reduced using a second-stage expansion valve  66  and is then supplied to the evaporator  51 .  
           [0009]    In addition, a portion  64   b  of the refrigerant  64 , which is collected at the bottom of the condenser  55 , is used for cooling the motor  52  and the lubricating oil. More specifically, the refrigerant  64   b  is first supplied to the lubricating-oil cooler  58  so as to cool the lubricating oil and is then supplied to the motor cooler  57  so as to cool the motor  52 . After that, the refrigerant  64   b  including a vaporized portion is returned to the evaporator  51 .  
           [0010]    However, in the conventional multistage compression refrigerating machines, the refrigerant  64   b  (a portion of the liquid refrigerant  64 ) collected at the bottom of the condenser  55  having a temperature of approximately 40° C. is used for cooling the motor  52  and the lubricating oil, and the refrigerant  64   b  after the cooling process is returned to the evaporator  51  whose inner temperature is approximately 5° C. Therefore, the liquid refrigerant  64   b  expands due to a pressure difference between the condenser  55  and the evaporator  51 , and as a result, the refrigerant  64   b  evaporates in the evaporator  51 . Accordingly, the amount of the liquid refrigerant to be used to provide or increase the refrigerating capacity is reduced, thereby decreasing the refrigerating capacity.  
         SUMMARY OF THE INVENTION  
         [0011]    In consideration of the above circumstances, an object of the present invention is to provide a multistage compression refrigerating machine for efficiently cooling a rotating machine such as an electric motor and lubricating oil by using a refrigerant and increasing the amount of refrigerant to be used to provide the refrigerating capacity in the evaporator, thereby improving the refrigerating capacity.  
           [0012]    Therefore, the present invention provides a multistage compression refrigerating machine comprising:  
           [0013]    an evaporator;  
           [0014]    a condenser for condensing a refrigerant and supplying the condensed refrigerant to the evaporator via an intercooler:  
           [0015]    a multistage compression system having a plurality of compressors which are connected in series, for:  
           [0016]    absorbing the refrigerant evaporated in the evaporator;  
           [0017]    absorbing a refrigerant evaporated from the intercooler, from an intermediate position between adjacent compressors in the multistage compression system; and  
           [0018]    compressing the absorbed refrigerants together and discharging the compressed refrigerant to the condenser;  
           [0019]    a rotating machine for driving the multistage compression system;  
           [0020]    a rotating-machine cooler for cooling the rotating machine; and  
           [0021]    a lubricating-oil cooler for cooling lubricating oil for lubricating the rotating machine, and wherein:  
           [0022]    the refrigerant extracted from the intercooler is supplied to the rotating-machine cooler and the lubricating-oil cooler, and this refrigerant is returned to the evaporator after cooling.  
           [0023]    According to the present invention, the rotating machine and the refrigerant can be efficiently cooled, and the amount of the liquid refrigerant (in the evaporator) to be used to provide or increase the refrigerating capacity can be reduced, thereby improving the refrigerating capacity and reducing the running cost.  
           [0024]    It is possible that:  
           [0025]    one or more intercoolers connected in series are provided for supplying the evaporated refrigerant from each intercooler to each intermediate position between adjacent compressors of the multistage compression system; and  
           [0026]    the refrigerant supplied to the lubricating-oil cooler and the rotation-machine cooler is extracted from the intercooler positioned at a position most downstream of the intercoolers connected in series.  
           [0027]    In this case, the refrigerant capacity can be further improved and the cost can be further reduced.  
           [0028]    Typically, the rotating machine is an electric motor. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0029]    [0029]FIG. 1 is a diagram showing the general structure of a multistage compression refrigerating machine of the first embodiment according to the present invention.  
         [0030]    [0030]FIG. 2 is a diagram showing the general structure of a multistage compression refrigerating machine of the second embodiment according to the present invention.  
         [0031]    [0031]FIG. 3 is a diagram showing the general structure of a conventional multistage compression refrigerating machine. 
     
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0032]    Hereinafter, embodiments according to the present invention will be explained in detail with reference to the drawings.  
         [0033]    [0033]FIG. 1 is a diagram showing the general structure of a multistage compression refrigerating machine of the first embodiment according to the present invention. In this multistage compression refrigerating machine having a two-stage compressor system, (i) a refrigerant condensed in a condenser is supplied via an intercooler to an evaporator, (ii) first vaporized refrigerant obtained by evaporating the refrigerant in the evaporator is absorbed by the two-stage compressor system, (iii) second vaporized refrigerant obtained by evaporating the refrigerant through the intercooler is absorbed from an intermediate position between the two stages, (iv) and the first vaporized refrigerant and the second vaporized refrigerant are compressed and discharged into a condenser.  
         [0034]    Therefore, as shown in FIG. 1, the multistage compression refrigerating machine in the present embodiment comprises an evaporator  1 , a first-stage compressor  3  and a second-stage compressor  4  which are rotationally driven by an electric motor  2  (abbreviated to the motor  2 , hereinbelow), a condenser  5 , an intercooler  6 , a motor cooler  7  for cooling the motor  2  by using a refrigerant, and a lubricating-oil cooler  8  for cooling lubricating oil by using a refrigerant.  
         [0035]    The evaporator  1  and the first-stage compressor  3  are joined to each other via a pipe line  9 . The first-stage compressor  3  and the second-stage compressor  4  are joined to each other via a pipe line  10 . The second-stage compressor  4  and the condenser  5  are joined to each other via a pipe line  11 . The condenser  5  and the intercooler  6  are joined to each other via a pipe line  12 . The intercooler  6  and the evaporator  1  are joined to each other via a pipe line  13 . The intercooler  6 , the lubricating-oil cooler  8 , and the motor cooler  7  are joined to each other via a pipe line  14 . The intercooler  6 , the first-stage compressor  3 , the second-stage compressor  4  are joined to each other via a pipe line  15  and the pipe line  10 , and the motor cooler  7  and the evaporator  1  are joined to each other via a pipe line  16 .  
         [0036]    In the evaporator  1 , cold water  18  having a temperature of 12° C. passes through a tube  17  which is arranged in the evaporator  1 , as shown in FIG. 1, and a liquid refrigerant is heated by the cold water  18 , so that vaporized refrigerant  19  is generated. In this process, the cold water  18  is cooled to approximately 7° C. thorough the heat exchange in the evaporator  1 , and it is then delivered outside the evaporator  1 . As a result, the temperature of the evaporator  1  is approximately 5° C.  
         [0037]    The vaporized refrigerant  19  generated in the evaporator  1  is absorbed into the first-stage compressor  3  and second-stage compressor  4  via the pipe line  9 , and the absorbed refrigerant is compressed by using an impeller of the first-stage compressor  3  which is rotated by the motor  2 . This compressed vaporized refrigerant is absorbed into the second-stage compressor  4  via the pipe line  10  and is further compressed by using an impeller of the second-stage compressor  4 , thereby discharging high-temperature and high-pressure vaporized refrigerant  19   a . Here, vaporized refrigerant  19   b  from the intercooler  6  via the pipe line  15  is also introduced (or absorbed) into an intermediate position of the pipe line  10  between the first-stage and second-stage compressors  3  and  4  (i.e., the upstream side of the second-stage compressor  4 ), and the absorbed vaporized refrigerant  19   b  is also compressed together with the vaporized refrigerant  19  from the evaporator  1 .  
         [0038]    In the condenser  5 , cooling water  21  passes through a tube  20  which is arranged in the condenser  5 , as shown in FIG. 1. The high-temperature and high-pressure vaporized refrigerant  19   a  discharged from the second-stage compressor  4  and supplied via the pipe line  11  is cooled using the cooling water  21 , thereby condensing the vaporized refrigerant  19   a  into a liquid. In this process, the cooling water  21  is heated through the heat exchange in the condenser  5  and is then discharged outside the condenser  5 . The condensed liquid refrigerant  22  is collected at the bottom of the condenser  5 . As a result, the temperature inside the condenser  5  is approximately 40° C.  
         [0039]    The intercooler  6  is provided for maintaining a specific pressure difference between the condenser  5  and the evaporator  1 , evaporating a portion of the refrigerant  22 , and increasing latent heat in the evaporator  1 . Therefore, in the intercooler  6 , the pressure of the liquid refrigerant  22  supplied from the condenser  5  is reduced to an intermediate pressure by using a first-stage expansion valve  23  provided in the middle of the pipe line  12 , so that the refrigerant  22  is expanded. A portion of the expanded refrigerant is used as vaporized refrigerant  19   b . As explained above, this vaporized refrigerant  19   b  is supplied to the pipe line  10  between the first-stage compressor  3  and the second-stage compressor  4 . On the other hand, the pressure of the remaining refrigerant cooled through the evaporation of the refrigerant  22  is further reduced using a second-stage expansion valve  24  in the middle of the pipe line  13  and is then supplied to the evaporator  1 . As a result, the temperature inside the intercooler  6  is approximately 20° C.  
         [0040]    In addition, a portion of the refrigerant  22  in the intercooler  6  is extracted as refrigerant  25  used for cooling the motor  2  and the lubricating oil. More specifically, the refrigerant  25  is first supplied to the lubricating-oil cooler  8  via the pipe line  14  and the like so as to cool the lubricating oil and is then further supplied to the motor cooler  7  so as to cool the motor  2 . After that, the refrigerant  25  including a vaporized portion is returned to the evaporator  1  via the pipe line  16 .  
         [0041]    As explained above, in the two-stage compression refrigerating machine in the first embodiment, as shown in FIG. 1, a portion of the liquid refrigerant  22  of the intercooler  6  is extracted, where the temperature of the intercooler  6  is approximately 20° C. which is lower than the temperature of the condenser  5  (i.e., 40° C.), and the pressure difference between the intercooler  6  and the evaporator  1  is lower than that between the condenser  5  and the evaporator  1 . This extracted liquid refrigerant  25  is used for cooling the motor  2  and the lubricating oil, and after cooling, the refrigerant is returned to the evaporator  1  whose inner temperature is approximately 5° C. Therefore, the amount of the liquid refrigerant  25  which expands due to a pressure difference between the intercooler  6  and the evaporator  1  is smaller in comparison with the case in which the refrigerant is taken from the condenser  5 .  
         [0042]    Therefore, the amount of the liquid refrigerant, which evaporates in the evaporator  1  and thus can be used to provide or increase the refrigerating capacity, is increased, and the flow rate of the refrigerant per unit refrigerating capacity is reduced. Accordingly, the COP (coefficient of performance) can be improved and a two-stage compression refrigerating machine having a superior refrigerating efficiency can be obtained. Here, the COP is defined as “the refrigerating capacity/the motor input”.  
         [0043]    [0043]FIG. 2 is a diagram showing the structure of the multistage compression refrigerating machine of the second embodiment according to the present invention. The distinctive feature of the second embodiment in comparison with the first embodiment is the provision of a four-stage compression refrigerating machine having a third-stage compressor  26  and a fourth-stage compressor  27  in addition to the first-stage compressor  3  and the second-stage compressor  4 . Therefore, two intercoolers  28  and  29 , pipe lines  30  to  35  for joining these elements, and third and fourth expansion valves  36  and  37  are also added in the second embodiment.  
         [0044]    The pressure in the intercoolers  28  and  29  provided at the downstream side of the intercooler  6  which is provided immediately after the condenser  5  is further reduced using the expansion valves  24  and  36 , and these intercoolers  28  and  29  are cooled through the evaporation of the refrigerant  22  through the intercoolers  6  and  28 . Therefore, the temperature of the intercooler  28  is approximately 15° C., and the temperature of the intercooler  29  is approximately 10° C.  
         [0045]    The refrigerant  25  extracted from the intercooler  29  at the most downstream side is used for cooling the motor  2  and the lubricating oil. The other structural elements and functions are similar to those of the first embodiment.  
         [0046]    As shown in FIG. 2, in the four-stage compression refrigerating machine of the second embodiment, a portion of the refrigerant  22  of the intercooler  29  at the most downstream side is extracted, where the temperature of the intercooler  29  is approximately 10° C., which is considerably lower than the temperature of the condenser  5 , that is, approximately 40° C., and the pressure difference between the intercooler  29  and the evaporator  1  is much smaller. This extracted refrigerant  25  is used for cooling the motor  2  and the lubricating oil, and after cooling, the refrigerant is returned to the evaporator  1  having an inner temperature of approximately 5° C. Therefore, the amount of the refrigerant (for cooling) which self-expands due to the pressure difference between the intercooler  29  and the evaporator  1  is much more reduced in comparison with the case in which the refrigerant for cooling is taken from the condenser  5 . Accordingly, the amount of the liquid refrigerant which evaporates in the evaporator  1  and is used to provide the refrigerating capacity is considerably increased. As a result, the flow rate of the refrigerant per unit refrigerating capacity is reduced and the COP is increased, thereby obtaining a four-stage compression refrigerating machine having a superior refrigerating efficiency.  
         [0047]    The embodiments of the present invention have been explained above. However, the present invention is not limited to these embodiments, and various variations and modifications are possible within the scope and spirit of the present invention.  
         [0048]    For example, the number of stages of the multistage compression refrigerating machine is not limited to two or four in the above embodiments, and three or more than four is also possible.  
         [0049]    In addition, the rotating machine is an electric motor in the above embodiment. However, the present invention can be applied to multistage compression refrigerating machines employing other kinds of rotating machine, such as a gas engine, Diesel engine, steam turbine, gas turbine, and the like.