Method and apparatus for liquefying a hydrocarbon-containing feed stream

Abstract

Method and apparatus for liquefying a hydrocarbon stream such as natural gas from a feed stream. The method comprises at least the steps of: first cooling the feed stream ( 10 ) against a first cooling refrigerant being cycled in a first cooling refrigerant circuit ( 100 ), wherein the first cooling refrigerant comprises >90 mol % propane, second cooling the cooled gas stream ( 20 ) to obtain a liquefied stream ( 60 ) against a first mixed refrigerant being cycled in a first mixed refrigerant circuit ( 200 ), wherein said second cooling is in two or more heat exchangers ( 42, 44 ), at least two of which are operating at different pressures and sub-cooling the liquefied stream ( 60 ) against a second mixed refrigerant or against a nitrogen refrigerant being cycled in a sub-cooling refrigerant circuit ( 300 ), thereby obtaining a sub-cooled hydrocarbon stream ( 70 ).

1 .- 15 . (canceled) 
     
     
         16 . Method of liquefying a feed stream comprising a gaseous hydrocarbon stream, the method at least comprising the steps of:
 (a) providing the feed stream;   (b) first cooling the feed stream in one or more first heat exchangers against a first cooling refrigerant being cycled in a first cooling refrigerant circuit, thereby obtaining a cooled gas stream, wherein the first cooling refrigerant comprises >90 mol % propane;   (c) second cooling the cooled gas stream obtained in step (b) into a liquid against a first mixed refrigerant being cycled in a first mixed refrigerant circuit, wherein said second cooling is in two or more heat exchangers arranged in series such that the cooled gas stream passes through each heat exchanger, at least two of which, a second and a third heat exchanger, are operating at different pressures, thereby obtaining a liquefied stream; and   (d) sub-cooling the liquefied stream obtained in step (c) against a second mixed refrigerant or against a nitrogen refrigerant being cycled in a sub-cooling refrigerant circuit against a fourth heat exchanger, thereby obtaining a sub-cooled hydrocarbon stream; wherein the cooled gas stream from the second heat exchanger in step (c) passes through a separation vessel, so as to provide a lighter gas stream, being methane-enriched, and a heavier liquid stream, which lighter gas stream is passed to the third heat exchanger.   
     
     
         17 . Method according to  claim 16  wherein at least two of the heat exchangers in the second cooling of step (c) are spool-wound heat exchangers. 
     
     
         18 . Method according to  claim 16  wherein a fraction of the first mixed refrigerant in the second cooling of step (c) does not pass through every heat exchanger of the second cooling. 
     
     
         19 . Method according to  claim 16  wherein the first mixed refrigerant is separated into two or more fractions after passing through at least the first heat exchanger in the second cooling of step (c), and at least one of said fractions is expanded and returned to the first heat exchanger. 
     
     
         20 . Method according to  claim 16  wherein the first cooling refrigerant used in step (b) comprises >95 mol % propane. 
     
     
         21 . Method according to  claim 16  wherein the first cooling in step (b) comprises cooling in at least two first heat exchangers. 
     
     
         22 . Method according to  claim 21  wherein each first heat exchanger of the first cooling involves a different first cooling refrigerant pressure. 
     
     
         23 . Method according to  claim 16  wherein the first mixed refrigerant used in step (c) comprises: >50 mol % of a compound selected from the group consisting of ethane and ethylene or a mixture thereof; and >10 mol % of a compound selected from the group consisting of propane and propylene or a mixture thereof. 
     
     
         24 . Method according to  claim 16  wherein step (d) uses a second mixed refrigerant, and the second mixed refrigerant comprises: >30 mol % of a compound selected from the group consisting of ethane and ethylene or a mixture thereof; and >30 mol % methane. 
     
     
         25 . Method according to  claim 16  wherein in step (c) the circulation of the first mixed refrigerant comprises compressing, cooling, and separating the refrigerant into a subsequent first high pressure fraction and a subsequent second low pressure fraction, evaporation of the first and second fractions in different heat exchangers, and recollecting of the first and second evaporated fractions, 
       wherein the high pressure fraction is evaporated at a higher temperature than the low pressure fraction. 
     
     
         26 . Method according to  claim 16  wherein step (d) uses a second mixed refrigerant, and in step (d) the circulation of the second mixed refrigerant comprises compressing, cooling, and separating the second mixed refrigerant into a first heavy fraction and a second light fraction, evaporating the first and second fractions in different zones at wholly or substantially the same pressure, and collecting the first and second fractions. 
     
     
         27 . Method according to  claim 16  wherein the sub-cooling refrigerant circuit passes through the second cooling of step (c) to cool the second mixed refrigerant or nitrogen refrigerant prior to step (d). 
     
     
         28 . Method according to  claim 16  wherein step (d) uses a nitrogen refrigerant, and the sub-cooling refrigerant circuit includes a single-component refrigerant heat exchanger to cool the nitrogen refrigerant prior to its use to sub-cool the liquefied stream. 
     
     
         29 . Method according to  claim 16  wherein the heavier liquid stream is recycled in the liquefaction plant or used for production of other hydrocarbon streams. 
     
     
         30 . Apparatus for liquefying a hydrocarbon stream from a feed stream, the apparatus at least comprising:
 a first cooling stage comprising one or more heat exchangers arranged in series to receive the feed stream and to pass the cooled gas stream through each heat exchanger and to provide a cooled gas stream, the first cooling stage including a first cooling refrigerant circuit using a first refrigerant for removing heat from the feed stream, wherein the first cooling refrigerant comprises >90 mol % propane;   a second cooling stage comprising a plurality of heat exchangers arranged to receive the cooled gas stream from the first cooling stage and to provide a liquefied stream, the second cooling stage including a second refrigerant circuit using a first mixed refrigerant for removing heat from the cooled gas stream, wherein at least two of the heat exchangers, a second and a third heat exchanger, of the second cooling stage are adapted to operate at different pressures; and   a sub-cooling stage comprising one or more sub-cooling heat exchangers arranged to receive the liquefied stream from the second cooling stage and to provide a sub-cooled liquefied hydrocarbon product stream, the sub-cooling stage including a sub-cooling refrigerant circuit using a second mixed refrigerant or a nitrogen refrigerant for removing heat from the liquefied stream; and   a separation vessel arranged to receive the cooled gas stream from the second heat exchanger as provided in the second cooling stage so as to provide a lighter gas stream being methane-enriched and a heavier liquid stream, whereby the third heat exchanger as provided in the second cooling stage is arranged to receive the lighter gas stream.   
     
     
         31 . Apparatus according to  claim 30  wherein the sub-cooling refrigerant circuit uses a mixed refrigerant, and includes a separator adapted to provide a first light fraction and a second heavier fraction for use in the one or more sub-cooling heat exchangers. 
     
     
         32 . Method of liquefying a feed stream comprising a gaseous hydrocarbon stream, the method at least comprising the steps of:
 (a) providing the feed stream;   (b) first cooling the feed stream in one or more first heat exchangers against a first cooling refrigerant being cycled in a first cooling refrigerant circuit, thereby obtaining a cooled gas stream, wherein the first cooling refrigerant comprises >90 mol % propane;   (c) second cooling the cooled gas stream obtained in step (b) into a liquid against a first mixed refrigerant being cycled in a first mixed refrigerant circuit, wherein said second cooling is in two or more heat exchangers arranged in series such that the cooled gas stream passes through each heat exchanger, at least two of which, a second and a third heat exchanger, are operating at different pressures, thereby obtaining a liquefied stream; and   (d) sub-cooling the liquefied stream obtained in step (c) against a second mixed refrigerant or against a nitrogen refrigerant being cycled in a sub-cooling refrigerant circuit against a fourth heat exchanger, thereby obtaining a sub-cooled hydrocarbon stream; wherein the cooled gas between the second and third heat exchangers of step (c) provides an intermediate temperature stream which is used to provide reflux for a scrub column.