Patent Publication Number: US-10309719-B2

Title: De-superheater system and compression system employing such de-superheater system, and method of producing a pressurized and at least partially condensed mixture of hydrocarbons

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     The present application is a National Stage (§ 371) application of PCT/EP2015/062837, filed Jun. 9, 2015, which claims the benefit of European Application No. 14172746.1, filed Jun. 17, 2014, and also claims benefit of U.S. Provisional Application No. 62/010,890, filed Jun. 11, 2014, which is incorporated herein by reference in its entirety. 
    
    
     The present invention relates to a de-superheater system for de-superheating a compressed vaporous discharge stream. In another aspects, the present invention relates to a compression system for producing a pressurized and at least partially condensed mixture of hydrocarbons, and to a method of producing a pressurized and at least partially condensed mixture of hydrocarbons. 
     A pressurized and at least partially condensed mixture of hydrocarbons is frequently produced in refrigeration cycles, wherein the pressurized and at least partially condensed mixture of hydrocarbons is typically expanded and brought into indirect heat exchanging contact with a product stream to extract heat from the product stream. In such application, the mixture of hydrocarbons is typically referred to a mixed refrigerant (MR) or mixed component refrigerant (MCR). 
     An example of a single mixed refrigerant cycle is disclosed in CN103216998A. The method in this example comprises the steps of performing compressor first-section compression and inter-cooling on the mixed refrigerant; then, entering a second section and a third section for continuous compression; then, cooling the mixed refrigerant in two steps, and forming a gas phase and a liquid phase in last-step cooling. A compression suction pot is provided at the suction inlet of the compressor train. Anti-surge lines are provided to recycle a portion of the de-superheated mixed refrigerant from between the first-step cooling and last-step cooling to the compression suction pot. 
     The temperature of the de-superheated mixed refrigerant between the first-step cooling and last step cooling is between 65 and 100° C., and the temperature of the gas phase and liquid phase after the last-step cooling is between 20 and 50° C. These temperatures are controlled by a control valve, which controls the flow rate of the cooling streams which absorb the heat in the first-step cooling and last step cooling heat exchangers. 
     The system and method of CN103216998A may not be suitable when an ambient stream, particularly an ambient air stream, is used as the cooling stream. Ambient water streams, and ambient air streams more so, are subject to relatively large and unpredictable temperature variations and variations in humidity (in case of air). Hence, in order to guarantee that the de-superheated mixed refrigerant between the first-step cooling and last step cooling is fully vaporous, a relatively large margin needs to be observed between the target temperature of the de-superheated mixed refrigerant between the first-step cooling and last step cooling and the dew point of the mixed refrigerant between the first-step cooling and last step cooling. 
     In one aspect, the present invention provides a de-superheater system for de-superheating a compressed vaporous discharge stream, comprising:
         a de-superheater heat exchanger configured to bring at least a portion of the compressed vaporous discharge stream in indirect heat exchanging contact with an ambient stream in the de-superheater heat exchanger, whereby allowing heat to flow from the compressed vaporous discharge stream to the ambient stream;   a de-superheater bypass line comprising an temperature-controlled valve configured to selectively bypass the de-superheater heat exchanger over said temperature-controlled valve with a bypass portion of the compressed vaporous discharge stream;   a combiner configured downstream of the de-superheater heat exchanger for rejoining the bypass portion with the portion of the compressed vaporous discharge stream that has passed through the de-superheater heat exchanger thereby forming a rejoined stream; and   a mixer configured downstream of said combiner, to receive and mix the rejoined stream, and discharge the rejoined stream into a de-superheater discharge conduit as a de-superheated hydrocarbon stream.       

     Such de-superheater system may be employed in a compression system and/or a method of producing a pressurized and at least partially condensed mixture of hydrocarbons. 
     Accordingly, in a further aspect the present invention provides a compression system for producing a pressurized and at least partially condensed mixture of hydrocarbons, comprising:
         a compression suction scrubber comprising a suction scrubber outlet configured to discharge a vaporous compressor feed stream from the compression suction scrubber;   a train of one or more compressors, comprising a suction inlet fluidly connected to the suction scrubber outlet, and a compressor train discharge outlet, which train is configured to compress the vaporous compressor feed stream from the compression suction scrubber to a higher pressure whereby forming a compressed vaporous discharge stream at the discharge outlet;   a de-superheater system configured to form a de-superheated hydrocarbon stream out of the compressed vaporous discharge stream, said de-superheater system comprising a de-superheater heat exchanger arranged in fluid communication with the compressor train discharge outlet;   a condenser arranged to receive at least a portion of the de-superheated hydrocarbon stream and configured to further cool the portion of the de-superheated hydrocarbon stream by allowing indirect heat exchanging against a cooling stream, whereby said portion of the de-superheated hydrocarbon stream is at least partly condensed to form the pressurized and at least partially condensed mixture of hydrocarbons;   a de-superheater discharge conduit configured between the de-superheater system and the condenser, to establish a fluid connection between the de-superheater system and the condenser;   a compressor train surge recycle pathway arranged between the de-superheater discharge conduit and the suction scrubber inlet to convey a recycle flow of a recycle portion of the de-superheated hydrocarbon stream, at a recycle flow rate, from the de-superheater discharge conduit to the suction inlet of the train of one or more compressors via the compression suction scrubber;
 
wherein said de-superheater system is configured to bring at least a portion of the compressed vaporous discharge stream in indirect heat exchanging contact with an ambient stream in the de-superheater heat exchanger, whereby allowing heat to flow from the compressed vaporous discharge stream to the ambient stream, said de-superheater system further comprising a de-superheater bypass line comprising an temperature-controlled valve configured to selectively bypass the de-superheater heat exchanger over said temperature-controlled valve with a bypass portion of the compressed vaporous discharge stream, said de-superheater system further comprising a combiner configured downstream of the de-superheater heat exchanger for rejoining the bypass portion with the portion of the compressed vaporous discharge stream that has passed through the de-superheater heat exchanger thereby forming a rejoined stream, and a mixer separating the combiner and the de-superheater discharge conduit and configured to receive and mix the rejoined stream, and discharge the rejoined stream into the de-superheater discharge conduit in the form of said de-superheated hydrocarbon stream.
       

     Optionally, the compression system comprises
         a surge recycle valve configured in said compressor train surge recycle pathway, to control the recycle flow rate.       

     Controlling the recycle flow rate is done to maintain a flow rate through the train of one or more compressors to keep the train of one or more compressors from surging. 
     Furthermore, the present invention provides a method of producing a pressurized and at least partially condensed mixture of hydrocarbons, comprising:
         discharging a vaporous compressor feed stream from a compression suction scrubber;   compressing the vaporous compressor feed stream in a train of one or more compressors to a higher pressure whereby forming a compressed vaporous discharge stream;   de-superheating the compressed vaporous discharge stream in a de-superheater system comprising a de-superheater heat exchanger, comprising bringing at least a portion of the compressed vaporous discharge stream in indirect heat exchanging contact with an ambient stream in the de-superheater heat exchanger, whereby allowing heat to flow from the compressed vaporous discharge stream to the ambient stream, and comprising selectively bypassing the de-superheater heat exchanger over a temperature-controlled valve with a bypass portion of the compressed vaporous discharge stream, and rejoining the bypass portion with the portion of the compressed vaporous discharge stream that has passed through the de-superheater heat exchanger thereby forming a rejoined stream and subsequently passing the rejoined stream through a mixer, thereby forming a de-superheated hydrocarbon stream out of the compressed vaporous discharge stream;   passing at least a portion of the de-superheated hydrocarbon stream from the de-superheater system to a condenser via a de-superheater discharge conduit and further cooling the portion of the de-superheated hydrocarbon stream in said condenser by indirect heat exchanging said portion of the de-superheated hydrocarbon stream against a cooling stream, whereby said portion of the de-superheated hydrocarbon stream is at least partly condensed to form the pressurized and at least partially condensed mixture of hydrocarbons;   splitting off a recycle portion from the de-superheated hydrocarbon stream in the de-superheater discharge conduit and establishing a recycle flow from the de-superheater discharge conduit to the train of one or more compressors.       

     Optionally, establishing a recycle flow comprises establishing a recycle flow at a recycle flow rate from the de-superheater discharge conduit to the train of one or more compressors via a surge recycle valve and the compression suction scrubber, whereby controlling the recycle flow rate with the surge recycle valve. 
     Controlling the recycle flow rate is done to maintain a flow rate through the train of one or more compressors to keep the train of one or more compressors from surging. 
     The method includes the process step dealing with the compression suction scrubbing. Discharging a vaporous compressor feed stream from a compression suction scrubber therefore includes operating a compression suction scrubber, wherein operating the compression suction scrubber includes discharging the vaporous compressor feed stream from the compression suction scrubber. 
     Optionally, the method further comprises:
         providing a mixture of hydrocarbons in vapour phase;   passing at least some of the hydrocarbons in vapour phase to the compression suction scrubber;   expanding the pressurized and at least partially condensed mixture of hydrocarbons whereby forming at least one refrigeration stream;   passing the at least one refrigeration stream through a heat exchanger;   indirectly heat exchanging the at least one refrigeration stream against a product stream whereby the at least one refrigeration stream absorbs heat from the product stream and whereby a phase transition occurs in the at least one refrigeration stream from liquid phase to vapour phase;   discharging the at least one refrigeration stream in vapour phase from the heat exchanger in the form of the mixture of hydrocarbons in vapour phase.       

    
    
     
       The invention will be further illustrated hereinafter by way of example only, and with reference to the non-limiting drawing in which; 
         FIG. 1  schematically shows a de-superheater system according to an embodiment of the invention; 
         FIG. 2  schematically shows a compression system for producing a pressurized and at least partially condensed mixture of hydrocarbons according to embodiments of the invention, wherein incorporated is the de-superheater system of  FIG. 1 ; 
         FIG. 3  schematically shows a refrigeration system for refrigerating a product stream, which incorporates the de-superheater system of  FIG. 1  and the compression system of  FIG. 2 ; and 
         FIG. 4  schematically shows an alternative refrigeration system for refrigerating a product stream, which also incorporates the de-superheater system of  FIG. 1  and the compression system of  FIG. 2 . 
     
    
    
     For the purpose of this description, a single reference number will be assigned to a line as well as a stream carried in that line. Same reference numbers refer to similar components. The person skilled in the art will readily understand that, while the invention is illustrated making reference to one or more a specific combinations of features and measures, many of those features and measures are functionally independent from other features and measures such that they can be equally or similarly applied independently in other embodiments or combinations. 
     The present disclosure involves a de-superheater system and method, for de-superheating a compressed vaporous discharge stream. The de-superheater system comprises a de-superheater heat exchanger to remove excess heat from the compressed vaporous discharge stream which has been added during compression of a vaporous compressor feed stream. In the presently proposed de-superheater system, the temperature of the de-superheated stream as it is being discharged from the de-superheater system is controlled by allowing a bypass portion of the compressed vaporous discharge stream to bypass the de-superheater heat exchanger over a temperature-controlled valve. The bypass portion of the compressed vaporous discharge stream is re-joined with the portion that has passed through the de-superheater heat exchanger, and the rejoined stream is passed through a mixer. The presently disclosed temperature controlled bypass functionality in combination with the mixer provides a much more direct and complete temperature control of the de-superheated stream than is the case in the prior art system of CN103216998A. These measures facilitate that the de-superheated stream being discharged from the de-superheater system is kept at high enough temperature whereby formation of condensation liquids is avoided. The mixer ensures that the heat from the bypass portion is evenly absorbed in the portion of the compressed vaporous discharge stream that has passed through the de-superheater heat exchanger. With these measures, the heat transfer rate in the de-superheater heat exchanger is not a critical parameter any more. This facilitates the use of an ambient stream as the heat sink in the de-superheater heat exchanger, as the actual temperature of the ambient stream may fluctuate significantly over the seasons and the 24 hour cycle of each day. 
     Furthermore, employing the proposed de-superheater system allows maintaining a de-superheated stream in the vapour phase at a temperature much closer to the dew point temperature of the de-superheated stream being discharged from the de-superheater system. 
     The de-superheater system can be incorporated in a system for refrigerating a product stream, as will be illustrated herein below. 
     First, however,  FIG. 1  illustrates a de-superheater system  1  as outlined above, for de-superheating a compressed vaporous discharge stream  40 . The de-superheater system  1  comprises a de-superheater heat exchanger  170  and a de-superheater bypass line  50 . The de-superheater system  1  is configured to bring at least a portion  60  of the compressed vaporous discharge stream  40  in indirect heat exchanging contact with an ambient stream  65  in the de-superheater heat exchanger  170 , whereby allowing heat to flow from the portion  60  of compressed vaporous discharge stream  40  to the ambient stream  65 . The de-superheater bypass line  50  comprises a temperature-controlled valve  52 . This bypass line is configured to selectively bypass the de-superheater heat exchanger  170  over the temperature-controlled valve  52 , with a bypass portion of the compressed vaporous discharge stream  40 . The bypass portion typically is formed by the remainder of the compressed vaporous discharge stream  40  that is not fed to the de-superheater heat exchanger  170 . 
     The de-superheater system  1  further comprises a combiner  220 , that is configured downstream of the de-superheater heat exchanger  170  for rejoining the bypass portion with the portion of the compressed vaporous discharge stream that has passed through the de-superheater heat exchanger  170 . Together, these streams form a rejoined stream  70 . Furthermore, a mixer  180  is configured downstream of the combiner  220 , to receive and mix the rejoined stream  70 , and to discharge the rejoined stream  70  into a de-superheater discharge conduit  80 . 
     The de-superheater system  1  further comprises a temperature controller  56 . The temperature controller  56  is functionally coupled to the temperature-controlled valve  52  to change a valve opening setting in response to a temperature of de-superheated stream in the de-superheater discharge conduit  80 . The temperature controller  56  is programmed to keep the temperature of the de-superheated stream in the de-superheater discharge conduit  80  above a dew point temperature of the de-superheated stream in the de-superheater discharge conduit  80 . 
     The temperature controller is preferably programmed to keep the temperature of the de-superheated hydrocarbon stream between 1° C. and 15° C. above said dew point temperature. More preferably, the temperature controller is programmed to keep the temperature of the de-superheated hydrocarbon stream between 1° C. and 10° C. above said dew point temperature. The most preferred target temperature for the temperature controller is (about) 5° C. above said dew point temperature. 
     Suitably, the heat transfer rate in the de-superheater heat exchanger  170  is controlled as well. To this end, the flow rate of the ambient stream  65  in the de-superheater heat exchanger  170  may also be controlled via said temperature controller  56 , possibly in concert the temperature-controlled valve  52 . In the case the ambient stream  65  is a stream of ambient air, this may be accomplished by varying the speed of a fan  172  which drives the stream of ambient air through the de-superheater heat exchanger  170 . The speed of the fan  172  may suitably be varied by varying the motor speed of motor  174  which drives the fan  172 . However, alternatives have been conceived, including varying air inlet vanes. 
     An advantage of the mixer  180  is that if inadvertently some condensation may have occurred in the de-superheater heat exchanger  170 , and small droplets or mist of liquid particulates are discharged from the de-superheater heat exchanger  170 , the mixer facilitates the direct heat transfer between the bypass portion and the small droplets or mist of liquid particulates are discharged from the de-superheater heat exchanger  170  so that these can evaporate prior to being discharged in the de-superheater discharge conduit  80  in the form of the de-superheated stream. The mixer may suitably be provided in the form of a static mixer. Static mixers as such are known in the art, and they typically comprise a conduit defining a flow path for the rejoined stream  70 , with static (stationary) flow-disrupting internals configured in the flow path. The advantage of a static mixer is that it functions autonomously because it contains no moving parts. Commercially available examples for various flow regimes are described in for instance an information brochure “Mixing and Reaction Technology” published by Sulzer Chemtech Ltd. 
     The de-superheater system  1  can be used in a variety of industrial refrigeration processes to de-superheat a compressed vaporous discharge stream. Typically in such industrial refrigeration processes a hydrocarbon refrigerant is cycled in a refrigeration cycle. The compressed vaporous discharge stream  40  is obtained in such a refrigeration cycle by compressing a vaporous compressor feed stream in a train of one or more compressors to a higher pressure. The compression typically adds heat (enthalpy) to the vaporous compressor feed stream such that the compressed vaporous discharge stream  40  thus formed is typically superheated by more than 60° C. above the dew point temperature of the compressed vaporous discharge stream as it is being discharged from the last compressor (or last compression stage) in the train of one or more compressors. 
       FIG. 2  illustrates one example of a compression system  2  for producing a pressurized and at least partially condensed mixture of hydrocarbons, which may form part of such an industrial refrigeration processes as meant above. The illustrated compression system  2  comprises a compression suction scrubber  160 . The compression suction scrubber  160  suitably comprises a suction drum provided with at least a suction scrubber outlet  166  configured to discharge the vaporous compressor feed stream  30  from the compression suction scrubber  160 . The compression suction scrubber  160  also comprises a suction scrubber inlet  162  provided in the suction drum. 
     The suction scrubber outlet  166  is in direct fluid communication with the train of one or more compressors. This train of one or more compressors is represented in  FIG. 2  as a single compressor  230 , which may consist of one or multiple compression stages optionally connected to each other with intercooling. However, the train of one or more compressors may also comprise a plurality of compressors connected in sequence with each other optionally with intercooling. Any intercooling may comprise additional suction drums to ensure that no liquid droplets or particulates can pass from the intercooling into the next compressor or compressor stage. 
     Regardless of the number of compressors or compression stages, the train of one or more compressors comprises  232  a suction inlet fluidly connected to the feed scrubber vapour outlet  166 , as well as a compressor train discharge outlet  236 . 
     The train of one or more compressors is configured to compress the vaporous compressor feed stream  30  from the compression suction scrubber  160  to a higher pressure, whereby forming the compressed vaporous discharge stream  40  at the discharge outlet  236 . The discharge outlet  236  is in fluid communication with the de-superheater system  1  as described above. 
     A condenser  190  is arranged in fluid connection with the de-superheater system  1  via the de-superheater discharge conduit  80 , which is configured between the de-superheater system  1  and the condenser  190 , to receive at least a portion  85  of the de-superheated hydrocarbon stream  80 . The condenser  190  is configured to further cool the portion of the de-superheated hydrocarbon stream  80 , by allowing indirect heat exchanging against a cooling stream  165 , whereby said portion  85  of the de-superheated hydrocarbon stream  80  is at least partly condensed to form a pressurized and at least partially condensed mixture of hydrocarbons  90 . Suitably, the heat transfer rate in the condenser  190  is controlled by a temperature controller  196  on the at least partially condensed mixture of hydrocarbons  90 . To this end, the flow rate of the ambient stream in the condenser  190  may be controlled via said temperature controller  196 . In the case the ambient stream is a stream of ambient air, this may be accomplished by varying the speed of fan  192  which drives the stream of ambient air through the condenser  190 . The speed of the fan  192  may suitably be varied by varying the motor speed of motor  194  which drives the fan  192 . However, alternatives have been conceived, including varying air inlet vanes. 
     In embodiments wherein both the de-superheater heat exchanger  170  and the condenser  190  are provided in the form of air-cooled heat exchangers, the de-superheater heat exchanger may be referred to as first air-cooled heat exchanger cooled by a first stream of ambient air, while the condenser may be referred to as second air-cooled heat exchanger cooled by a second stream of the ambient air. 
     A compressor train surge recycle pathway is arranged between the de-superheater discharge conduit  80  and the suction scrubber inlet  162 . Herewith a recycle flow consisting of a recycle portion  120  of the de-superheated hydrocarbon stream, at a recycle flow rate, can be conveyed from the de-superheater discharge conduit  80  to the suction inlet  232  of the train of one or more compressors  230  via the compression suction scrubber  160 . A surge recycle valve  250  is configured in said compressor train surge recycle pathway, to control the recycle flow rate. 
     Optionally, a surge recycle separator drum  210  is configured in said compressor train surge recycle pathway in addition to the surge recycle valve  250 . The optional surge recycle separator drum  210  is arranged to remove and drain liquid constituents from the recycle portion  120  of the de-superheated hydrocarbon stream via a liquid drain outlet  218  into a liquid drain conduit  140 . A drain control valve  240  may be provided in the liquid drain conduit  140  to control the flow rate of the liquid constituents being drained. Suitably the drain control valve  240  is controlled by a level controller  246  to keep the level of liquid constituents that has accumulated in the surge recycle separator drum  210  within a predetermined range. The recycle vapour outlet  216  of the optional surge recycle separator drum  210  is fluidly connected with the compression suction scrubber  160  via the surge recycle valve  250  and suitably via the suction scrubber inlet  162  to allow vapour constituents of the recycle portion  120  to continue the journey along the compressor train surge recycle pathway and reach the suction scrubber inlet  162 . 
     The suction scrubber inlet  162  may be connected directly to a feed vapour source via a feed line  10 , for providing a mixture of hydrocarbons in vapour phase into the suction scrubber  160 . Advantageously, however, an additional feed scrubber  150  separates the feed line  10  from the suction scrubber inlet  162 . If provided, such feed scrubber  150  may comprise a feed drum provided with at least a feed scrubber inlet  152  connected to the feed line  10 , and a feed scrubber vapour outlet  156 . The feed vapour source may thus be connected to the feed drum via the feed scrubber inlet  152 . The feed scrubber vapour outlet  156  is suitably connected with the suction scrubber inlet  162 . 
     If the compression system  2  is provided with both the optional surge recycle separator drum  210  and the optional feed scrubber  150 , the liquid drain outlet  218  of the surge recycle separator drum  210  is suitably fluidly connected via the liquid drain conduit  140  to the feed scrubber  150 . The liquid constituents drained from the recycle portion of the de-superheated hydrocarbon stream may thus be fed into the feed drum, wherein these liquid constituents mix with the mixture of hydrocarbons in vapour phase and re-vaporize in direct heat exchange with the mixture of hydrocarbons in vapour phase. In such embodiments, the feed drum preferably comprises a liquid recycle inlet  154  as a separate inlet in addition to the feed scrubber inlet  152 , whereby the liquid drain conduit fluidly connects the liquid drain outlet of the surge recycle separator drum  210  with the feed drum via the liquid recycle inlet  154 . The liquid recycle inlet  154  is suitably configured gravitationally lower than the feed scrubber inlet  152 . 
     Regardless of whether the optional feed scrubber  150  is provided or not, the compression system  2  may be incorporated in a refrigeration system. In such a refrigeration system, the feed line  10  is ultimately fed from the pressurized and at least partially condensed mixture of hydrocarbons  90 .  FIGS. 3 and 4  schematically show two examples. In both examples, the feed vapour source comprises an expansion system  3 . The expansion system  3  is configured to receive the pressurized and at least partially condensed hydrocarbon stream  90  from the condenser  190  in the compression system  2 , and configured to expand the pressurized and at least partially condensed mixture of hydrocarbons whereby forming at least one refrigeration stream. 
     In the example of  FIG. 3 , the expansion system  3  comprises an expansion device  35 . This expansion device  35  is for easy understanding illustrated in the form of a Joule-Thomson valve but it may be embodied in any suitable manner. For instance, the expansion device  35  may comprise an expansion turbine instead of or in combination with the Joule-Thomson valve. 
     The feed vapour source further comprises a cryogenic heat exchanger  300 . The expansion system  3  is optionally separated from the compression system  2  by the cryogenic heat exchanger  300 , configured to further cool the pressurized and at least partially condensed mixture of hydrocarbons prior to expanding it. However, this is not a requirement. The cryogenic heat exchanger  300  is arranged to receive the at least one refrigeration stream ( 95 , in  FIG. 3 ), and configured to allow the at least one refrigeration stream to pass. In addition, a product stream  400  is allowed to pass through the cryogenic heat exchanger  300 , in an indirectly heat exchanging contact with the at least one refrigeration stream  95 . The at least one refrigeration stream  95  absorbs heat from the product stream  400  during this indirect heat exchanging, whereby a phase transition occurs in the at least one refrigeration stream  95  from liquid phase to vapour phase. A discharge conduit  310  from the cryogenic heat exchanger  300  fluidly connects the cryogenic heat exchanger  300  with the feed line  10 . This completes the vapour feed source. 
     The feed line  10 , as described above, is connected to the compression system  2  optionally via the optional feed scrubber  150  if provided. 
     In the example of  FIG. 4 , the compression system  2  for producing the pressurized and at least partially condensed mixture of hydrocarbons is connected to a gas/liquid phase separator  200 , whereby the at least partially condensed mixture of hydrocarbons  90  is phase-separated in a liquid mixture of hydrocarbons  100  and a vaporous mixture of hydrocarbons  110 . The gas/liquid phase separator  200  may be provided with internals to facilitate said phase-separating, including an inlet distributer  202  and a de-misting device  204 . This refrigeration system is suitable if the at least partially condensed mixture of hydrocarbons is partially and not fully condensed. If the at least partially condensed mixture of hydrocarbons is fully condensed, this gas/liquid phase separator  200  is not necessary, such as illustrated in  FIG. 3 . 
     The expansion system  3  in  FIG. 4  comprises two expansion devices  35   a  and  35   b . Similar to expansion device  35  described above, each of expansion devices  35   a  and  35   b  may be embodied in any suitable manner. The expansion system  3  of  FIG. 4  thus receives the pressurized and at least partially condensed hydrocarbon stream from the condenser in the form of two phase-separated streams corresponding the liquid mixture of hydrocarbons  100  and the vaporous mixture of hydrocarbons  110 . The resulting refrigeration stream initially comprises an expanded heavy refrigerant fraction stream  105  and an expanded light refrigerant fraction stream  115 . The cryogenic heat exchanger  300  is arranged to receive the expanded heavy refrigerant fraction stream  105  and expanded light refrigerant fraction stream  115 , which streams are reunited within the cryogenic heat exchanger  300 . 
     The expansion system  3  as shown in the example of  FIG. 4  is separated from the compression system  2  by the cryogenic heat exchanger  300 . Hence the cryogenic heat exchanger  300  is configured to further cool the pressurized and at least partially condensed mixture of hydrocarbons prior to expanding it. This way, the liquid mixture of hydrocarbons  100  can be sub-cooled by rejecting heat to the refrigeration stream that passes from the expansion system  3  through the cryogenic heat exchanger  300  to the discharge conduit  310 . Similarly, the vaporous mixture of hydrocarbons  110  can be condensed and subsequently sub-cooled by rejecting heat to the refrigeration stream that passes from the expansion system  3  through the cryogenic heat exchanger  300  to the discharge conduit  310 . 
     Regardless of the type of refrigeration system, the product stream  400  may be a hydrocarbon stream that for at least 80 mol. % consists of methane. 
     In operation, the compression system  2  may be used in a method of producing a pressurized and at least partially condensed mixture of hydrocarbons  90 . A vaporous compressor feed stream  30  is discharged from the compression suction scrubber  160 , and compressed to a higher pressure whereby forming the compressed vaporous discharge stream  40 . 
     The vaporous compressor feed stream  30  and the compressed vaporous discharge stream  40  may comprise a mixture comprising two or more selected from N 2 , C 1 , C 2 , C 3 , C 4 , C 5 , whereby N 2  denotes nitrogen, C 1  denotes methane, C 2  denotes ethane and/or ethylene, C 3  denotes propane and/or propylene, C 4  denotes i-butane and/or n-butane, and C 5  denotes one or more of the pentanes, such as i-pentane and/or n-pentane. In one embodiment, between 20 and 80 mol. % consists of C 2  and/or C 3  of which at least 10 mol. % C 3 , and at least 20 mol. % consists of one or more selected from C 1 , C 4 , and C 5 . In another embodiment, between 20 and 60 mol. % consists of C 1  and/or C 2 , supplemented with up to 20 mol. % of N 2  and at least 20 mol. % selected from C 3 , C 4 , and C 5 . In all cases the total amount of N 2 , C 1 , C 2 , C 3 , C 4 , and C 5  in the mixture is at least 98 mol. %, preferably at least 99 mol. %, of the total mixture, whereby the maximum amount of N 2  is 20 mol. %. The pressure the compressed vaporous discharge stream  40  is suitably in pressure range of from 30 to 50 bara. 
     The compressed vaporous discharge stream  40  is then de-superheated in the de-superheater system  1 . In the course of de-superheating, at least the portion  60  of the compressed vaporous discharge stream  40  is brought in indirect heat exchanging contact with the ambient stream  65  in the de-superheater heat exchanger  170 . Hereby, heat is allowed to flow from the compressed vaporous discharge stream  40  to the ambient stream  65 . However, the de-superheater heat exchanger  170  is selectively bypassed over the temperature-controlled valve  52  with the bypass portion  50  of the compressed vaporous discharge stream  40 . The bypass portion  50  is rejoined with the portion  60  of the compressed vaporous discharge stream  40  that has passed through the de-superheater heat exchanger  170 , thereby forming the rejoined stream  70 . The rejoined stream  70  is subsequently passed through the mixer  180 . This way, the de-superheated hydrocarbon stream  80  is formed out of the compressed vaporous discharge stream  40 . 
     The de-superheated hydrocarbon stream  80 , or at least a portion thereof, passes from the de-superheater system  1  to the condenser  190  via the de-superheater discharge conduit  80 . The portion of the de-superheated hydrocarbon stream in the condenser  190  is further cooled by indirect heat exchanging said portion of the de-superheated hydrocarbon stream against the cooling stream  165 . During the further cooling, the portion of the de-superheated hydrocarbon stream is at least partly condensed, to form the pressurized and at least partially condensed mixture of hydrocarbons  90 . As stated above, the de-superheated hydrocarbon stream may be fully condensed or partially condensed in the condenser  190 . 
     A recycle portion  120  may be split off from the de-superheated hydrocarbon stream  80  in the de-superheater discharge conduit, to establish a recycle flow at a recycle flow rate from the de-superheater discharge conduit  80  to the train of one or more compressors. The recycle flow passes via the surge recycle valve  250  and the compression suction scrubber  160 . The recycle flow rate is controlled with the surge recycle valve  250 . Typically the recycle flow rate is determined with the object to keep the train of one or more compressors from surging by ensuring there is sufficient flow rate through the train of one or more compressors. 
     This may for instance be done by known surge control techniques, such as by measuring the flow rate through the train of one or more compressors and monitoring the operation of the train of one or more compressors and controlling the recycle flow rate in response thereto. 
     The temperature-controlled valve  52  is preferably controlled in response to a temperature of de-superheated hydrocarbon stream in the de-superheater discharge conduit  80 . Preferably, the temperature of the de-superheated hydrocarbon stream  80  is kept above a dew point temperature of the de-superheated hydrocarbon stream in the de-superheater discharge conduit  80 . The dew point temperature depends on composition of the de-superheated hydrocarbon stream and the pressure in the de-superheater discharge conduit  80 . The temperature of the de-superheated hydrocarbon stream is preferably kept between 1° C. and 15° C., more preferably between 1° C. and 10° C., above the dew point temperature. If desired a larger safety margin may be applied, whereby the temperature of the de-superheated hydrocarbon stream is kept at least 2 or 3° C. above the dew point temperature instead of only 1° C. The optimum temperature of the de-superheated hydrocarbon stream is conceived to be 5° C. (or about 5° C.) above the dew point temperature. About 5° C. above the dew point temperature is understood to include temperatures between 3 and 7° C. above the dew point temperature. 
     The method described above is preferably carried out surrounded by ambient air having an actual temperature. The ambient stream  65  may be a steam of the ambient air at the actual temperature. 
     The cooling stream  165  in the condenser  190  may be a chilled stream at a temperature below the actual temperature, or a second ambient air stream at the actual temperature. An approach temperature, in the condenser  190 , between the temperature of the cooling stream  165  and the pressurized and at least partially condensed mixture of hydrocarbons  90  is suitably between 1° C. and 10° C. Preferably, the approach temperature is in a range of from 3° C. to 10° C., more preferably in a range of from 3° C. to 7° C. A typical optimum approach temperature for the condenser  190  is 5° C. 
     In one example carried out in Honeywell UniSim™ process simulation software, a pressurized and at least partially condensed mixture of hydrocarbons  90  was produced using the method described above. The vaporous compressor feed stream  30  had the following composition: 
                                         Components   Mol. %                                                N2   10.0           C1   25.0           C2   36.0           C3   12.0           C4   0.00           C5   17.0                    
The resulting pressurized and at least partially condensed mixture of hydrocarbons  90 , after compressing, de-superheating and partially condensing against an air stream having an actual temperature of 40° C., had a temperature of 45° C. and a pressure of 38.3 bara. A molar fraction of 0.76 was in vapour phase having an average molar mass of 28.67 g; a molar fraction of 0.24 was in liquid phase having an average molar mass of 52.84 g. This resulting pressurized and at least partially condensed mixture of hydrocarbons  90  was intended as refrigerant in a single mixed refrigerant process for liquefying a product stream of natural gas.
 
     The method described above may form part of a method of refrigerating a product stream. In such method of refrigerating, a mixture of hydrocarbons in vapour phase is obtained from the pressurized and at least partially condensed mixture of hydrocarbons  90  and passed to the compression suction scrubber  160 . To this end, the the pressurized and at least partially condensed mixture of hydrocarbons  90  is expanded, whereby forming at least one refrigeration stream, such as but not limited to the refrigeration stream  95  in  FIG. 3  or the expanded heavy refrigerant fraction stream  105  and the expanded light refrigerant fraction stream  115  of  FIG. 4 . 
     Regardless the precise nature of the at least one refrigeration stream, the at least one refrigeration stream is then passed through the cryogenic heat exchanger  300  where it is exposed to indirectly heat exchanging against the product stream. During this indirect heat exchanging, the at least one refrigeration stream absorbs heat from the product stream  400  whereby a phase transition occurs in the at least one refrigeration stream from liquid phase to vapour phase. The product stream  400  is thereby cooled and discharged from the cryogenic heat exchanger  300  as refrigerated product stream  450 . Optionally, heat from the pressurized and at least partially condensed hydrocarbon stream  90  is simultaneously absorbed by the at least one refrigeration stream. 
     The at least one refrigeration stream is discharged in vapour phase from the cryogenic heat exchanger  300  in the form of the mixture of hydrocarbons in vapour phase. 
     The product stream may be a hydrocarbon stream that for at least 80 mol. % consists of methane. Examples of such a hydrocarbon stream include natural gas and pipeline gas from a natural gas grid. Synthetic gas 
     Regardless of the precise nature of the product stream  400 , during or after said indirectly heat exchanging the at least one refrigeration stream against the product stream  400  the product stream may be allowed to condense to form a liquefied hydrocarbon product stream. The liquefied hydrocarbon product stream may be a liquefied natural gas stream. 
     Although not shown in the drawings, a pressure reduction system may be arranged in the refrigerated product stream  450  downstream of the cryogenic heat exchanger  300  and in fluid communication therewith, to receive refrigerated product stream  450  and to reduce its pressure. An end-flash separator may be arranged downstream of the pressure reduction system, and in fluid communication therewith, to receive the refrigerated product stream from the pressure reduction system. The pressure reduction system may comprise a dynamic unit, such as an expander turbine, a static unit, such as a Joule Thomson valve, or a combination thereof. If an expander turbine is used, it may optionally be drivingly connected to a power generator. Many arrangements are possible and known to the person skilled in the art. 
     With these provisions it is possible to pass the product stream  400  through the cryogenic heat exchanger  300  in pressurized condition, for instance at a pressure of between 30 and 120 bar absolute, or between 30 and 80 bar absolute, while storing any liquefied part of the refrigerated product stream at substantially atmospheric pressure, such as between 1 and 2 bar absolute. 
     Depending on the separation requirements, the end flash separator may be provided in the form of a simple drum which separates vapour from liquid phases in a single equilibrium stage, or a more sophisticated vessel such as a distillation column. Non-limiting examples of possibilities are disclosed in U.S. Pat. Nos. 5,421,165; 5,893,274; 6,014,869; 6,105,391; and pre-grant publication US 2008/0066492. In some of these examples, the more sophisticated vessel is connected to a reboiler whereby the refrigerated product stream  450 , before being expanded in said pressure reduction system, is led to pass though a reboiler in indirect heat exchanging contact with a reboil stream from the vessel, whereby the refrigerated product stream  450  is caused to give off heat to the reboil stream. 
     The person skilled in the art will understand that the present invention can be carried out in many various ways without departing from the scope of the appended claims.