Refrigeration systems associated with cryogenic process plants for ethane or propane recovery from natural gas

Abstract

A method for an improved integration of refrigeration into conventional natural gas processing plants which use propane or similar hydrocarbon refrigerants either to supplement cooling by turbo-expanders or as the sole source of refrigeration.

What is claimed is: 
     
         1 . A closed cycle refrigeration method comprising:
 completely condensing a refrigerant stream at the bubble point pressure of said refrigerant at ambient temperatures to give liquid refrigerant, where the refrigerant stream is selected from the group consisting of ethane, propane, butane, and pentane.   
     
     
         2 . The closed cycle refrigeration method of  claim 1  further comprising sub-cooling of the condensed refrigerant in a multi-pass heat exchanger in combined service with the cooling of the inlet gas stream, such that when the pressure drop associated with cooling occurs there is less than 0.5% vaporization. 
     
     
         3 . The closed cycle refrigeration method of  claim 1  further comprising:
 dividing the sub-cooled liquid refrigerant into multiple refrigeration streams followed by 
 flashing of the sub-cooled liquid refrigerant to a predetermined pressure selected to provide cooling at predetermined temperatures. 
 
     
     
         4 . The closed cycle refrigeration method of  claim 3  further comprising:
 heating the multiple refrigeration streams such that they are completely vaporized and superheated to a close temperature approach of at least 2° F. and at most 30° F. with the inlet gas stream to supply refrigeration at a predetermined temperature. 
 
     
     
         5 . The closed cycle refrigeration method of any one of  claim 2  further comprising integration of the method into a single heat exchanger which also serves to cool the plant inlet gas and to warm various cold gas streams leaving the plant. 
     
     
         6 . The closed cycle refrigeration method of any one of  claim 2  further comprising heating of at least one of the multiple sub-cooled refrigerant streams in a reboiler associated exchanger such that this stream is vaporized and superheated to a close temperature approach to the inlet gas stream. 
     
     
         7 . A closed cycle hydrocarbon refrigeration system comprising:
 a condenser adapted to completely condense a refrigerant stream at the bubble point pressure of said refrigerant at ambient temperatures to give liquid refrigerant, where the refrigerant stream is selected from the group consisting of ethane, propane, butane, and pentane.   
     
     
         8 . The closed cycle hydrocarbon refrigeration system of  claim 7  further comprising a cooling pass adapted to sub-cool the condensed refrigerant in a multi-pass heat exchanger in combined service with the cooling of the inlet gas stream, such that when the pressure drop associated with cooling occurs there is less than 0.5% vaporization. 
     
     
         9 . The closed cycle hydrocarbon refrigeration system of  claim 7  further comprising lines dividing the sub-cooled liquid refrigerant into multiple refrigeration streams followed by a valve adapted to flash the sub-cooled liquid refrigerant to a predetermined pressure. 
     
     
         10 . The closed cycle hydrocarbon refrigeration system of  claim 9  further comprising heat exchangers adapted to heat the multiple refrigeration streams such that they are completely vaporized and superheated to a close temperature approach of at least 2° F. and at most 30° F. with the inlet gas stream. 
     
     
         11 . The closed cycle hydrocarbon refrigeration system of  claim 9  further comprising a single heat exchanger adapted to cool the plant inlet gas and to warm various cold gas streams leaving the plant. 
     
     
         12 . The closed cycle hydrocarbon refrigeration system of  claim 9  further comprising at least one reboiler heat exchanger adapted to heat at least one of the multiple sub-cooled refrigerant streams such that this stream is vaporized and superheated to a close temperature approach to the inlet gas stream. 
     
     
         13 . A closed cycle hydrocarbon refrigeration system comprising:
 a refrigerant condenser comprising:
 a refrigerant condenser configured to completely condense a refrigerant vapor stream into a condensed refrigerant stream directed to a multi-pass gas/gas/chiller/exchanger, where the refrigerant stream is at the bubble point pressure of said refrigerant at ambient temperatures to give liquid refrigerant, where the refrigerant stream is selected from the group consisting of ethane, propane, butane, and pentane; and 
   a pressure reduction device configured to flash the liquid refrigerant;   in the absence of a unit selected from the group consisting of a chiller, an economizer, and both.   
     
     
         14 . The closed cycle hydrocarbon refrigeration system of  claim 13  where the refrigerant stream consists essentially of propane. 
     
     
         15 . The closed cycle hydrocarbon refrigeration system of  claim 13  further comprising the pressure reduction device further configured such that when the pressure drop associated with cooling occurs there is less than 0.5% vaporization. 
     
     
         16 . The closed cycle hydrocarbon refrigeration system of  claim 13  further comprising heat exchangers adapted to heat the multiple refrigeration streams such that they are completely vaporized and superheated to a close temperature approach of at least 2° F. and at most 30° F. with the inlet gas stream. 
     
     
         17 . The closed cycle hydrocarbon refrigeration system of  claim 16  further comprising a single heat exchanger adapted to cool the plant inlet gas and to warm various cold gas streams leaving the plant. 
     
     
         18 . The closed cycle hydrocarbon refrigeration system of  claim 16  further comprising at least one reboiler heat exchanger adapted to heat at least one of the multiple sub-cooled refrigerant streams such that this stream is vaporized and superheated to a close temperature approach to the inlet gas stream.