Patent ID: 9506690
Filing Date: 2016-11-29
CPC Classification: F25J

Claim Text:
1. A process for the production of a subcooled liquefied natural gas stream from a natural gas feed stream, the method comprising the following steps: precooling the natural gas feed stream by passing the natural gas feed stream through a first heat exchanger for obtaining a feed stream precooled to a temperature below −20° C.; liquefying the precooled feed stream by passing the precooled feed stream through a second heat exchanger for obtaining at least one liquefied natural gas stream at a temperature below −80° C.; subcooling the liquefied natural gas stream by passing the liquefied natural gas stream through a third heat exchanger for obtaining a liquefied natural gas stream subcooled to a temperature below −120° C.; during the precooling, placing the natural gas feed stream in a heat exchange relationship in the first heat exchanger with a first stream of substantially gaseous refrigerant and producing the substantially gaseous refrigerant in a first refrigeration cycle from a first gaseous stream of expanded refrigerant fluid issuing from a first dynamic gas expansion turbine; during the liquefying, placing the precooled feed stream in a heat exchange relationship in the second heat exchanger with a second stream of gaseous refrigerant circulating in a second refrigeration cycle, producing the second gaseous refrigerant stream from a second gaseous stream of expanded fluid issuing from a second dynamic gas expansion turbine separate from the first dynamic gas expansion turbine; during the subcooling, placing the liquefied natural gas stream in a heat exchange relationship in the third heat exchanger with a third refrigerant stream circulating in a third refrigeration cycle, producing the third refrigerant stream at least partly from a third gaseous stream of expanded fluid issuing from a third dynamic expansion turbine separate from the first and the second dynamic gas expansion turbines; conveying a first stream of heated refrigerant obtained at an outlet of the first heat exchanger to a first compression device without passing the first stream of heated refrigerant through the second or the third heat exchangers; conveying a second stream of heated refrigerant issuing from the second heat exchanger to a second compression device without passing the second stream of heated refrigerant through the first or the third heat exchangers; and conveying a third stream of heated refrigerant issuing from the third heat exchanger to a third compression device without passing the third stream of heated refrigerant through the first or the second heat exchangers.