Patent Publication Number: US-8966934-B2

Title: Refrigeration system

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
     The present application claims the benefit of priority to Denmark Patent Application No. PA 2011 70306 titled “Refrigeration System” and filed on Jun. 16, 2011, the complete disclosure of which is hereby incorporated by reference for all purposes. 
     FIELD 
     The present invention relates to a refrigeration system primarily using CO 2  as refrigerant, which refrigeration system comprises at least one first compressor, from which compressor a pressure outlet tube is connected to at least one heat rejecting heat exchanger, which heat rejecting heat exchanger is connected to at least one first pressure reduction device and by tubing further connected to at least one receiver, which receiver comprises at least one first liquid outlet, which outlet is connected by tubing to one or more first pressure reduction devices, such as expansion valves, which expansion valves are connected to at least one first group of evaporators, which evaporators are connected by suction tubing to the suction side of the compressor, which receiver comprises at least one second outlet, which second outlet takes gas and is connected by tubing to a second pressure reduction device. 
     BACKGROUND 
     EP 1789732 discloses a CO2 refrigeration circuit for circulating a refrigerant in a predetermined flow direction, comprising in flow direction a heat-rejecting heat exchanging device, a receiver having a liquid portion and a flash gas portion, and subsequent to the receiver a medium temperature loop and a low temperature loop, wherein the medium and low temperature loops each comprise in flow direction an expansion device, an evaporator and a compressor, the refrigeration circuit further comprising a liquid line connecting the liquid portion of the receiver with at least one of the medium and low temperature loops and having an internal heat exchanging device, and a flash gas line connecting the flash gas portion of the receiver via the internal heat exchanging device with the inlet of the low temperature compressor, wherein the internal heat exchanging device transfers in use heat from the liquid flowing through the liquid line to the flash gas flowing through the flash gas line. 
     It is an object of the invention to reduce the energy consumption in CO 2  cooling systems, a further object is to protect one or more compressors against liquid CO 2  in the compressor inlet by heating the suction gas. 
     SUMMARY 
     The second pressure reduction device is connected by tubing to a first heat exchanging device, which first heat exchanging device is integrated in the receiver, either in liquid part, gas part or in both, in which first heat exchanging device the refrigerant is heated, which heated refrigerant is combined into the suction tubing. 
     Subsequent to the first pressure reduction device, gas and liquid is created and enters the receiver. Formation of gas in the receiver cannot be avoided, but the flash gas portion has to be removed to keep pressure low (30-45 bar) inside the receiver. Because the gas, from the top of the receiver is sent to a second pressure reduction device, the temperature is decreased in the gas and some liquid is created. The gas is sent into a heat exchanging device from which heat exchanging device the gas is sent to the suction side of the compressor group. By recirculating the gas portion after the second pressure reduction device back through the receiver, the temperature in the liquid part of a receiver will decrease and also some gas inside the receiver will condense. The efficiency of the whole cooling system is thereby improved. Not only is the flash gas of refrigerant in a receiver reduced, but the lower temperature in the liquid will also lead to higher efficiency in the evaporators that are supplied afterwards with liquid refrigerant through pressure reduction means. Because the flash gas is sent through the heat exchanging device in the receiver, the flash gas is heated inside the heat exchanging device and the flash gas is mixed with a suction gas increasing the temperature of the suction gas back to the compressor. In this way liquid refrigerant is avoided from being sent towards the suction side of the compressor. 
     The second pressure reduction device can be connected by tubing and combined with the suction gas into a combined line, which line is connected to the inlet to the heat exchanging device, which heat exchanging device is connected by tubing to the suction side of the compressor. Wherby heating of the suction gas is achieved, and the refrigerant in the receiver is further cooled. 
     The suction gas from the suction tubing is connected by tubing to a second heat exchanging device, which second heat exchanging device is integrated into the receiver, which second heat exchanging device is connected by tubing to the suction side of the compressor. Whereby the suction gas, coming from evaporators having a relatively low temperature, is heated in the heat exchanging device in the receiver. Further whereby the temperature inside the receiver is reduced, in a way where some condensation takes place so that the amount of gas inside the receiver is reduced. The suction gas that is sent through the heat exchanging device is in the same way being heated, and the temperature of the suction gas is then sufficiently high that liquid particles in the gas are avoided in the suction line towards the compressor. The suction gas leaving the evaporators can have a temperature only a few degrees below zero, and heating the gas up to approximately plus 10 degrees is sufficient to avoid any liquid particles in the gas. 
     The refrigeration system can comprise a second group of evaporators, which evaporators are connected by tubing to the receiver outlet towards pressure reduction devices such as expansion valves, which second evaporators are connected by tubing to the suction side of one or more second compressors, which second compressors have a pressure outlet, which pressure outlet is connected by tubing to the suction line of the first compressors. 
     The refrigeration system comprises a second group of evaporators, which evaporators are connected by tubing to the receiver outlet towards pressure reduction devices such as expansion valves, which second evaporators are connected by tubing to a third heat exchanging device, which third heat exchanging device is integrated in the receiver, from which third heat exchanging device tubing connects to the suction side of one or more second compressors, which second compressors have a pressure outlet, which pressure outlet is connected by tubing to the suction line of the first compressors. Whereby suction gas from a freezer group which is relatively cold and at least several degrees below zero is sent through a heat exchanging device inside the receiver, in that way the gas is heated, but the content of the receiver is being cooled down. Therefore, further condensation may take place inside the receiver and at least the outlet temperature of liquid refrigerant for the supply of expansion valves has a reduced temperature. At the same time, the suction gas which is sucked towards a suction compressor has an increased temperature so that all refrigerant is evaporated when it reaches the compressor. 
     The refrigeration system can comprise a second group of evaporators, which evaporators are connected by tubing to the receiver outlet towards pressure reduction devices such as expansion valves, which second evaporators are connected by tubing to a third heat exchanging device, which third heat exchanging device is integrated in the receiver, from which third heat exchanging device tubing connects to the suction side of one or more second compressors, which second compressors have a pressure outlet, which pressure outlet is connected by tubing to a mixing point, at which mixing point the gas is mixed with the line coming from the second pressure reduction device, which mixed gas is led by tubing into a heat exchanging device, which heat exchanging device is connected by tubing to a second mixing point, by which mixing point the gas is mixed with the suction gas in a line from the first evaporators, which second mixing point is connected to the suction side of the compressor or compressor group. 
     The refrigeration system can comprise a second group of evaporators, which evaporators are connected by tubing to the receiver outlet towards pressure reduction devices such as expansion valves, which second evaporators are connected by tubing to a third heat exchanging device, which third heat exchanging device is integrated in the receiver, from which third heat exchanging device tubing connects to the suction side of one or more second compressors, which second compressors have a pressure outlet, which pressure outlet is by tubing connected to a mixing point, at which mixing point the gas is mixed with the suction gas in line, which mixed gas is connected by tubing to a second mixing point, at which second mixing point the gas is mixed with the gas in line coming from the second pressure reduction device, which mixed gas is led by tubing into a heat exchanging device, which heat exchanging device is connected by tubing to the suction side of the compressor or compressor group. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  shows a cooling system in a first embodiment for the invention. 
         FIG. 2  show an alternative embodiment to the system disclosed at the  FIG. 1 . 
         FIG. 3  shows an alternative embodiment for the invention. 
         FIG. 4  shows a third embodiment for the invention. 
         FIG. 5  shows an alternative embodiment for the invention disclosed at  FIG. 4 . 
         FIG. 6  shows a further alternative embodiment for the invention disclosed at  FIG. 4 . 
         FIG. 7  shows a further alternative embodiment for the invention disclosed at  FIG. 4 . 
     
    
    
     DETAILED DESCRIPTION 
       FIG. 1  shows a first exemplary embodiment for the invention. At  FIG. 1  is indicated a cooling system  102  which comprises one or more compressors  104 , which compressor  104  has a pressure outlet line  106  connected to a heat rejecting heat exchanging device  108 . The heat rejecting heat exchanger  108  is connected through a high pressure control valve  109  through a line  110  into a receiver  112 . This receiver has an outlet  114  connected to a connection line  116  which is connected to pressure reduction means  118 , shown primarily as expansion valves  120 , into evaporators  122 . From the evaporators  122  is a line  124  connected to the compressor suction side  126 . The receiver  112  comprises further a gas outlet  128  connected over line  130  into a pressure reduction valve  132  and from here through a line  134  into a heat exchanging device  136  placed inside the receiver  112 . From the heat exchanging device  136  there is a connection line  137  which is combined with the suction line  124 . 
     In operation the system will function as a cooling system operating primarily with carbon dioxide as refrigerant. One difference to traditional cooling systems is that the pressure in the receiver is kept low by removing gas from the receiver and the gas from the receiver  112  is used for cooling the liquid and condensing the gas in the receiver. That is achieved by letting the flash gas flow through the pressure reduction valve  132  and then into the heat exchanging device  136 . Here is the relatively cool gas used for reducing the temperature in the refrigerant inside the receiver  112 . Whereby the gas inside the heat exchanging device  136  is heated and this heated gas is then transported through the line  137  combined with a suction gas, where the temperature of the suction gas further increased. By using the gas inside the receiver for further cooling of the liquid part of the receiver, the efficiency of the cooling system is increased. 
       FIG. 2  discloses an alternative embodiment to  FIG. 1 .  FIG. 1   a  illustrates a cooling system  102  which comprises one or more compressors  104 , which compressor  104  has a pressure outlet line  106  connected to a heat rejecting heat exchanger  108 . The heat rejecting heat exchanger  108  is connected through a high pressure control valve  109  through a line  110  into a receiver  112 . This receiver has an outlet  114  connected to a connection line  116  which is connected to pressure reduction means  118 , shown primarily as expansion valves  120 , into evaporators  122 . From the evaporators  122  is a line  124  connected to the compressor suction side  126 . The receiver  112  comprises further a gas outlet  128  connected over line  130  into a pressure reduction valve  132  and from here through a line  134  into a connection point where the suction line  124  and the line  134  are combined into line  140 , which line  140  is connected to the heat exchanging device  136  placed inside the receiver  112 . The heat exchanging device has an outlet connected by line  137  into the compressor suction line  126 . 
       FIG. 3  shows another alternative embodiment to what is shown at  FIG. 1 .  FIG. 3  shows a cooling system  202  which cooling system comprises a compressor or a compressor group  204  which has a pressure outlet  206 . This pressure outlet  206  is connected to a heat rejecting heat exchanger  208  and the heat rejecting heat exchanger  208  is further connected to a high pressure control valve  209  from where a line  210  leads to a receiver  212 . From this receiver, an outlet  214  is sending liquid refrigerant towards expansion means, such as expansion valves  218 ,  220 , and from where the expanded refrigerant is sent through evaporators  222 . The evaporators  222  are connected into a suction line  224 . The line  224  is connected to an inlet  240  into the receiver  212  and further into a heat exchanging device  242  placed in the top of the receiver  212 . An outlet  244  from the receiver  212  is connected to the suction line  226  towards the compressor group  204 . 
     The suction gas that is leaving the evaporators  222  is relatively cool as it is flowing through the line  224  and into the heat exchanging device  242 . Thereby the suction gas is heated in the heat exchanging device, and the gas inside the receiver  212  is cooled down to a lower temperature which is intended to lead to condensation in the gas so that further liquid refrigerant is generated. The heated suction gas that is leaving through the outlet  244  and sent to the compressor through the suction line  226  is thereby increased in temperature so that liquid particles can be avoided in the part of the gas that is sucked into the compressor, whereby further security is achieved against liquid hammer in a piston compressor and the total effectivity of the system is increased. 
       FIG. 4  shows a cooling system  302  comprises a compressor group  304  which is through a pressure line  306  connected to a heat rejecting heat exchanger  308  according to a second exemplary embodiment. From this heat rejecting heat exchanger  308 , the refrigerant flows through a high pressure control valve  309  into a line  310  into a receiver  312 . From this receiver a liquid outlet  314  is connected into pressure reduction means, shown as expansion valves  318 ,  320 , into evaporators  322  from where the refrigerant is sent through a suction line  324  to the compressor suction side  326 . The liquid outlet  314  from the receiver  312  is further connected to low temperature evaporators through pressure reduction means, shown as expansion valves  354 ,  356 , into the low temperature evaporators  350 , which evaporators  350  are connected by tubing  352  to the receiver outlet  314  towards pressure reduction devices  354  such as expansion valves  356 , which second evaporators  350  are connected by tubing  358  to the suction side  364  of one or more second compressors  366 , which second compressors have a pressure outlet  368 , which pressure outlet  368  is connected by tubing  370  to the suction line  324  to the first compressors  304 . 
       FIG. 5  shows a third exemplary embodiment for the invention. A cooling system  302  comprises a compressor group  304  which is connected through a pressure line  306  to a heat rejecting heat exchanger  308 . From this heat rejecting heat exchanger  308 , the refrigerant flows through a high pressure control valve  309  into a line  310  into a receiver  312 . From this receiver  312 , a liquid outlet  314  is connected into pressure reduction means, shown as expansion valves  318 ,  320 , into evaporators  322  from where the refrigerant is sent through a suction line  324  to the compressor suction side  326 . The liquid outlet  314  from the receiver  312  is further connected to low temperature evaporators through pressure reduction means, shown as expansion valves  354 ,  356 , into the low temperature evaporators  350 . The outlet from the evaporators  350  is sent through a line  358  through a heat exchanging device  360  integrated in the receiver  312 . The outlet from the heat exchanging device  362  is connected to a suction line  364  of a further low temperature compressor or compressor group  366  which has an outlet  368  which is connected by line  370  to the suction line  326 , whereby the relatively cool suction gas from the evaporators used in freezers is used for a temperature reduction in the receiver  312 . Thereby the liquid content and also the gas content of the receiver is cooled to a lower temperature which may also lead to condensation of the gas in the receiver  312 . At the same time, it leads to heating the suction inside the heat exchanging device  360  to a temperature level where the entire refrigerant is evaporated, before the refrigerant reaches the low temperature compressor  366 . 
       FIG. 6  shows a cooling system  302  which comprises a compressor group  304  which is connected through a pressure line  306  to a heat rejecting heat exchanger  308 . From this heat rejecting heat exchanger  308 , the refrigerant flows through a high pressure control valve  309  into a line  310  into a receiver  312 . From this receiver  312 , a liquid outlet  314  is connected into pressure reduction means, shown as expansion valves  318 ,  320 , into evaporators  322  from where the refrigerant is sent through a suction line  324  to the compressor suction side  326 . The liquid outlet  314  from the receiver  312  is further connected to low temperature evaporators through pressure reduction means, shown as expansion valves  354 ,  356 , into the low temperature evaporators  350 , which evaporators  350  are connected by tubing  352  to the receiver outlet  314  towards pressure reduction devices  354  such as expansion valves  356 , which second evaporators  350  are connected by tubing  358  to a third heat exchanging device  360 , which third heat exchanging device  360  is integrated in the receiver  312 , from which third heat exchanging device  360  connects by tubing  362  to the suction side  364  of one or more second compressors  366 , which second compressors  366  have a pressure outlet  368 , which pressure outlet  368  is connected by tubing  380  to a mixing point  390 , at which mixing point the gas is mixed with the gas in line  334  coming from the second pressure reduction device  332 , which mixed gas is led by tubing into a heat exchanging device  336 , which heat exchanging device  336  is connected by tubing  337  to a second mixing point  395 , by which mixing point  395  the gas is mixed with the suction gas in a line  324  from the first evaporators  322 , which second mixing point  395  is connected to the suction side  326  of the compressor or compressor group  304 . 
       FIG. 7  shows a cooling system  302 , which comprises a compressor group  304  which is through a pressure line  306  connected to a heat rejecting heat exchanger  308 . From this heat rejecting heat exchanger  308 , the refrigerant flows through a high pressure control valve  309  into a line  310  into a receiver  312 . From this receiver  312  a liquid outlet  314  is connected into pressure reduction means, shown as expansion valves  318 ,  320 , into evaporators  322  from where the refrigerant is sent through a suction line  324  to the compressor suction side  326 . The liquid outlet  314  from the receiver  312  is further connected to low temperature evaporators through pressure reduction means, shown as expansion valves  354 ,  356 , into the low temperature evaporators  350 , which evaporators  350  are connected by tubing  352  to the receiver outlet  314  towards pressure reduction devices  354  such as expansion valves  356 , which second evaporators  350  are connected by tubing  358  to a third heat exchanging device  360 , which third heat exchanging device  360  is integrated in the receiver  312 , from which third heat exchanging device  360  connects by tubing  364  to the suction side of one or more second compressors  366 , which second compressors  366  have a pressure outlet  368 , which pressure outlet  368  is connected by tubing  370  to a mixing point  390 , at which mixing point  390  the gas is mixed with the suction gas in line  324 , which mixed gas is connected by tubing to a second mixing point  395 , at which second mixing point  395  the gas is mixed with the gas in line  334  coming from the second pressure reduction device  332 , which mixed gas is led by tubing into a heat exchanging device  336 , which heat exchanging device  336  is connected by tubing  337  to the suction side  326  of the compressor or compressor group  304 . 
     In a preferred embodiment, all the different heat exchanging devices described in  FIG. 1-7  can be combined into a common system where all or some heat exchanging devices are placed inside the same receiver. All heat exchanging devices described in  FIG. 1-7  are configured as a volume and a surface capable of holding a refrigerant volume and exchanging heat between refrigerant inside the heat exchanging device and the refrigerant in the receiver. The heat exchanging device could be designed as a vessel, coil or a plate construction. Position of exchangers can vary from gas part of receiver to liquid part of the receiver. Drawings with more than one heat exchanging device showing the position of these heat exchanging devices can be placed independently from each other. 
     Also, many different types of heat exchanger devices can be used, which may be plate hear exchangers or tube heat exchangers. Heat exchangers in the form of a coil placed outside the receivers are also possible. 
     Further, mixing points ( 190 , 195 , 290 , 295 , 390 , 395 ) on same refrigerant lines can be placed independently from each other and at various positions.