Patent ID: 11892233
Assignee: EXXONMOBIL TECHNOLOGY AND ENGINEERING COMPANY
Field: Chemical engineering (Chemistry)
Classification: CPC F | IPC F

Claim 5:
6. A system for liquefying a feed gas stream rich in methane and having a pressure less than 1,200 psia, comprising:
at least one first compressor for compressing the feed gas stream to a pressure of at least 1,500 psia to form a compressed gas stream;
a cooler for cooling the compressed gas stream by indirect heat exchange with an ambient temperature air or water to form a cooled, compressed gas stream;
at least one first work producing expander for expanding the cooled, compressed gas stream to a pressure that is less than 2,000 psia and no greater than the pressure to which the feed gas stream was compressed to form a chilled gas stream;
a first heat exchanger zone downstream from the at least one first work producing expander for receiving the chilled gas stream therefrom, the first heat exchanger zone comprising a first main heat exchanger, a second main heat exchanger, and a sub-cooling heat exchanger sequentially downstream from the at least one first work producing expander;
a compressed refrigerant stream with a pressure greater than or equal to 1,500 psia;
a refrigerant cooler for cooling the compressed refrigerant stream by indirect heat exchange with an ambient temperature air or water to produce a compressed, cooled refrigerant stream;
wherein the compressed, cooled refrigerant stream is directed through a second heat exchanger zone comprising at least one heat exchanger to be additionally cooled below ambient temperature to produce a compressed, additionally cooled refrigerant stream;

at least one second work producing expander for expanding the compressed, additionally cooled refrigerant stream to produce an expanded, cooled refrigerant stream;
wherein the expanded, cooled refrigerant stream is passed through the second main heat exchanger of the first heat exchanger zone but not the sub-cooling heat exchanger to form a first warm refrigerant stream having a temperature that is cooler, by at least 5° F., than a highest fluid temperature within the first heat exchanger zone;

wherein the chilled gas stream is passed sequentially through the first main heat exchanger, the second main heat exchanger, and the sub-cooling heat exchanger to cool at least part of the chilled gas stream by indirect heat exchange with the expanded, cooled refrigerant stream to form a liquefied gas stream, and
neither the chilled gas stream nor the liquefied gas stream are passed through the second heat exchanger zone; and

wherein a first portion of the first warm refrigerant stream is directed to the second heat exchanger zone to cool by indirect heat exchange the compressed, cooled refrigerant stream to form a second warm refrigerant stream, a second portion of the first warm refrigerant stream bypasses the second heat exchanger zone and is directed to the first main heat exchanger to form a third warm refrigerant stream exiting the first main heat exchanger, and the second warm refrigerant stream and the third warm refrigerant stream are combined to produce a fourth warm refrigerant stream; and
at least one second compressor for compressing the fourth warm refrigerant stream to produce the compressed refrigerant stream.