Methods and apparatus for generating a mixed refrigerant for use in natural gas processing and production of high purity liquefied natural gas

Abstract

A novel method and system for liquefying and distilling raw natural gas into NGL and liquid methane (LNG) product streams, with at least one novel feature including the use of a mixed refrigerant comprising naturally occurring natural gas liquids that were recovered from the inlet gas stream being processed. Heat exchangers and distillation towers are configured to produce high purity liquefied natural gas (LNG) and NGL product streams, utilizing liquid NGL as the process refrigerant for both systems.

1 . A method of operating a gas processing plant by using an NGL product from the gas processing plant as a mixed refrigerant for liquefying an inlet hydrocarbon gas being introduced to said gas processing plant, wherein said liquefied inlet hydrocarbon gas is further processed into the NGL product and a methane rich residue gas the method comprising:
 introducing the inlet hydrocarbon gas to a first heat exchange unit utilizing a mixed refrigerant to produce a cooled hydrocarbon gas having a liquid portion and a vapor portion;   flowing the liquid and vapor portions to a first pressurized distillation tower;   flowing a vapor product of hydrocarbons comprising methane rich residue gas from the first pressurized distillation tower;   flowing NGL product from the first pressurized distillation tower;   flowing said NGL product to at least the first heat exchange unit said NGL product to be used as the mixed refrigerant to aid in cooling of the hydrocarbon gas.   
     
     
         2 . The method of  claim 1 , further comprising vaporizing at least a portion of the mixed refrigerant forming a mixed refrigerant vapor portion and a mixed refrigerant liquid portion, separating the mixed refrigerant vapor portion from the mixed refrigerant liquid portion, recompressing and condensing that vapor portion and recombining with the liquid portion to form a final NGL product. 
     
     
         3 . The method of  claim 1 , wherein the NGL product contains a percentage of ethane and methane, the method further comprising:
 flowing the methane rich residue gas to an LNG liquefaction unit utilizing a mixed refrigerant;   providing the NGL product to the LNG liquefaction unit for use as the mixed refrigerant; and,   liquefying the methane rich natural gas in the LNG liquefaction unit using the NGL product as the mixed refrigerant to liquefy the methane rich natural gas into Liquid Natural Gas (LNG).   
     
     
         4 . The method of  claim 3 , further comprising vaporizing at least a portion of the mixed refrigerant forming a mixed refrigerant vapor portion and a mixed refrigerant liquid portion and separating the mixed refrigerant vapor portion from the mixed refrigerant liquid portion. 
     
     
         5 . The method of  claim 4 , wherein the mixed refrigerant vapor portion is utilized as the mixed refrigerant in the process used to liquefy methane rich natural gas (LNG) while the mixed refrigerant liquid portion is delivered as a final NGL product. 
     
     
         6 . The method of  claim 5 , wherein the mixed refrigerant generated for use in the LNG process may be used in an open loop process or as make-up into a closed loop process. 
     
     
         7 - 16 . (canceled) 
     
     
         17 - 19 . (canceled) 
     
     
         20 . A method of operating a liquefaction unit to liquefy methane rich natural gas into liquid natural gas (LNG), the method comprising:
 introducing methane rich natural gas from a gas processing plant to a liquefaction unit utilizing a mixed refrigerant;   providing NGL product to the liquefaction unit for use as the mixed refrigerant, wherein the NGL product contains methane and ethane, and wherein the NGL product is from said gas processing plant, or another gas processing plant; and,   liquefying the methane rich natural gas in the liquefaction unit using the NGL product as the mixed refrigerant to liquefy the methane rich natural gas into Liquid Natural Gas (LNG).