Hybrid cycle liquefaction of natural gas with propane pre-cooling

Abstract

Natural gas is liquefied in a hybrid liquefaction cycle in which the gas feed is precooled using vaporizing liquefied refrigerant gas; liquefied using vaporizing mixed refrigerant comprising ethylene and at least one other refrigerant selected from hydrocarbons and halocarbons; and subcooled using a work expanded pressurized gaseous refrigerant stream. Preferably, the liquefied refrigerant gas used for precooling is propane, the mixed refrigerant does not contain ethane or nitrogen and the pressurized gaseous refrigerant is nitrogen.

1 . A method of liquefying natural gas which comprises:
 precooling a natural gas feed stream to a temperature below ambient temperature with refrigeration provided by vaporizing a liquefied refrigerant gas;   liquefying the precooled gas stream with refrigeration provided by vaporizing a mixed refrigerant comprising two or more refrigerants selected from hydrocarbons and halocarbons;   subcooling the liquefied stream with refrigeration by work expanding a pressurized gaseous refrigerant stream   characterized in that the mixed hydrocarbon refrigerant comprises ethylene.   
     
     
         2 . The method of  claim 1 , wherein the natural gas feed stream is precooled to a temperature not below about −40° F. (−40° C.) 
     
     
         3 . The method of  claim 2 , wherein the natural gas feed stream is precooled to a temperature not below about −35° F. (−37° C.) 
     
     
         4 . The method of  claim 3 , wherein the natural gas feed stream is precooled to a temperature of about −30° F. (−35° C.) 
     
     
         5 . The method of  claim 1 , wherein the liquefied refrigerant gas used for the pre-cooling consists of a single component. 
     
     
         6 . The method of  claim 5 , wherein the single component is propane. 
     
     
         7 . The method of  claim 1 , wherein the mixed refrigerant does not comprise ethane. 
     
     
         8 . The method of  claim 1 , wherein the mixed refrigerant comprises ethylene and one or more refrigerants selected from hydrocarbons and halocarbons 
     
     
         9 . The method of  claim 8 , wherein the mixed refrigerant consists of ethylene and one or more refrigerants selected from C 1  to C 5  hydrocarbons. 
     
     
         10 . The method of  claim 9 , wherein the mixed refrigerant does not comprise ethane. 
     
     
         11 . The method of  claim 1 , wherein the mixed refrigerant comprises methane, ethylene and propane. 
     
     
         12 . The method of  claim 11 , wherein the mixed refrigerant consist of methane, ethylene and propane. 
     
     
         13 . The method of  claim 1 , wherein the pressurized gaseous refrigerant stream is nitrogen. 
     
     
         14 . A method of liquefying natural gas which comprises:
 precooling a natural gas feed stream to a temperature not below about −40° F. (−40° C.) with refrigeration provided by vaporizing a single component liquefied refrigerant gas;   liquefying the precooled gas stream with refrigeration provided by vaporizing an essentially ethane-free mixed refrigerant comprising methane, ethylene and propane; and   subcooling the liquefied stream with refrigeration by work expanding a pressurized gaseous nitrogen stream.   
     
     
         15 . The method of  claim 14 , wherein the natural gas feed stream is precooled to a temperature of about −30° F. (−35° C.) 
     
     
         16 . The method of  claim 14 , wherein the liquefied refrigerant gas used for the pre-cooling is propane. 
     
     
         17 . The method of  claim 14 , wherein the mixed refrigerant consist of methane, ethylene and propane. 
     
     
         18 . A method of liquefying natural gas which comprises:
 precooling a natural gas feed stream to a temperature of about −30° F. (−35° C.) with refrigeration provided by vaporizing propane;   liquefying the precooled gas stream with refrigeration provided by vaporizing a mixed refrigerant consisting of methane, ethylene and propane; and   subcooling the liquefied stream with refrigeration by work expanding a pressurized gaseous nitrogen stream.