Modularized LNG separation device and flash gas heat exchanger

Patent metadata

Field	Value
Publication number	US-10982898-B2
Application number	US-201815977535-A
Country	US
Kind code	B2
Filing date	May 11, 2018
Priority date	May 11, 2018
Publication date	Apr 20, 2021
Grant date	Apr 20, 2021

Abstract

Described herein are methods and systems for the liquefaction of natural gas to produce a LNG product. The methods and systems use an apparatus for separating a flash gas from a liquefied natural gas (LNG) stream to produce a LNG product and recovering refrigeration from the flash gas. The apparatus includes a shell casing enclosing a heat exchange zone comprising a coil wound heat exchanger, and a separation zone. The heat exchange zone is located above and in fluid communication with the separation zone. Flash gas is separated from the LNG product in the separation zone and flows upwards from the separation zone into the heat exchange zone where refrigeration is recovered from the separated flash gas.

First claim

The invention claimed is:

1. A system for producing a liquefied natural gas (LNG) product, and for recovering refrigeration from the flash gas, the system comprising:
a main cryogenic heat exchanger (MCHE) for cooling and liquefying a natural gas feed stream so as to produce an LNG stream;
a refrigeration circuit in fluid flow communication with the MCHE for circulating a main refrigerant and passing one or more cold streams of the refrigerant through the MCHE so as to provide cooling duty for liquefying the natural gas stream, the one or more cold streams of refrigerant being warmed in the MCHE via indirect heat exchange with the natural gas stream;
a first pressure reduction device in fluid flow communication with the MCHE for reducing the pressure of all or a portion of the LNG stream to form a reduced pressure LNG stream;
an apparatus, in fluid flow communication with the first pressure reduction device, for separating flash gas from the reduced pressure LNG stream and recovering refrigeration from the separated flash gas to produce an LNG product stream and a warmed flash gas stream, the apparatus comprising a shell casing enclosing a heat exchange zone and a separation zone, the heat exchange zone being located above and in fluid communication with the separation zone, the separation zone configured to separate the flash gas from the LNG product and the heat exchange zone being configured to recover refrigeration from the separated flash gas;
wherein the heat exchange zone comprises at least one coil wound tube bundle defining a tube side and a shell side of the heat exchange zone, the tube side defining one or more passages through the heat exchange zone for cooling and/or liquefying a first fluid stream, and the shell side defining a passage through the heat exchange zone for warming separated flash gas;
wherein the separation zone is configured such that flash gas separated from the LNG product in the separation zone flows upwards from the separation zone into and through the shell side of the heat exchange zone;
and wherein the shell casing has:
a first inlet in fluid flow communication with the tube side of the heat exchange zone for introducing the first fluid stream to be cooled and/or liquefied;
a first outlet in fluid flow communication with the tube side of the heat exchange zone for withdrawing a first cooled and/or liquefied fluid stream;
a second outlet in fluid flow communication with the shell side of the heat exchange zone for withdrawing the warmed flash gas stream;
a second inlet in fluid flow communication with the separation zone for introducing the reduced pressure LNG stream containing flash gas to be separated; and
a third outlet in fluid flow communication with the separation zone for withdrawing the LNG product stream.

2. A system according to claim 1 , wherein the first fluid stream is an auxiliary natural gas feed stream to be cooled and liquefied in the heat exchange zone to produce an auxiliary LNG stream, the system is configured to reduce the pressure of the auxiliary LNG stream, and the apparatus for separating flash gas from the reduced pressure LNG stream and recovering refrigeration from the separated flash gas is configured to also receive the reduced pressure auxiliary LNG stream, separate flash gas from the reduced pressure auxiliary LNG stream, and recover refrigeration from the separated flash gas.

3. A system according to claim 1 , wherein the refrigeration circuit is in fluid flow communication with the apparatus for separating flash gas from the reduced pressure LNG stream and recovering refrigeration from the separated flash gas the first fluid stream is a stream of gaseous refrigerant to be cooled and/or liquefied in the heat exchange zone to provide a stream of cooled and/or liquefied refrigerant, and the refrigeration circuit is configured to introduce the stream of gaseous refrigerant into the first inlet of the apparatus, to withdraw the stream of cooled and/or liquefied refrigerant from the first outlet of the apparatus, and to pass the stream of cooled and/or liquefied refrigerant through the MCHE.

4. A system according to claim 1 , wherein the apparatus for separating flash gas from the reduced pressure LNG stream and recovering refrigeration from the separated flash gas further comprising a mist eliminator positioned between the heat exchange zone and the separation zone.

5. A system according to claim 1 , wherein a first section of the shell casing enclosing the heat exchange zone and a second section of the shell casing enclosing the separation zone have substantially the same diameter.

6. A system according to claim 1 , wherein a second section of the shell casing enclosing the separation zone has a larger diameter than a first section of the shell casing enclosing the heat exchange zone.

7. A system according to claim 1 , wherein the separation zone comprises one or more mass transfer devices for bringing downward flowing fluid into contact with upward rising vapor and wherein the second inlet is positioned above one or more of the mass transfer devices.

8. A system according claim 1 , wherein the apparatus for separating flash gas from the reduced pressure LNG stream and recovering refrigeration from the separated flash gas further comprises a reboiler heat exchanger for re-boiling a portion of the LNG from a bottom end of the separation zone so as to generate upward flowing vapor through the separation zone.

9. A system according to claim 1 , wherein the separation zone is an empty section of the shell casing defining a sump zone for collection of LNG and a head space zone above the sump zone and below the heat exchange zone for collection of flash gas.

10. A system according claim 1 , wherein the at least one coil wound tube bundle comprises a first coil wound tube bundle located above a second coil wound tube bundle for warming separated flash gas;
wherein the tube side defined by the first tube bundle is in fluid flow communication with the first inlet and defines at least one passage for cooling and/or liquefying the first fluid stream;
wherein the shell casing has a fourth outlet in fluid flow communication with the tube side of the first tube bundle for withdrawing a cooled and/or liquefied portion of the first fluid stream from the first tube bundle; and
wherein the tube side defined by the second tube bundle is in fluid flow communication with the tube side of the first tube bundle and with the first outlet, and defines at least one passage for further cooling and/or liquefying another portion of the first fluid stream from the first tube bundle.

11. A system according to claim 1 , the wherein the shell casing has a fourth outlet in fluid flow communication with the shell side of the heat exchange zone, and located below the second outlet, for withdrawing a partially warmed flash gas stream at a lower temperature than the warmed flash gas stream withdrawn from the second outlet.

Assignees

• Air Prod & Chem

Inventors

• Chen Fei
• Ott Christopher Michael
• Weist Annemarie Ott
• Roberts Mark Julian

Classifications

• F25J2270/08

  Internal refrigeration by flash gas recovery loop · CPC title

• F25J2215/04

  Recovery of liquid products · CPC title

• F25J2210/60

  Natural gas or synthetic natural gas [SNG] · CPC title

• F25J1/0267

  using flash gas as heat sink · CPC title

• F25J1/004 Primary

  by flash gas recovery (F25J1/0267 takes precedence) · CPC title