Method and apparatus for cooling a hydrocarbon stream

• US 10,539,363 B2
• Filed: 02/12/2009
• Issued: 01/21/2020
• Est. Priority Date: 02/14/2008
• Status: Active Grant

• Current Assignee: Shell USA Incorporated (Shell Plc)
• Original Assignee: Shell Oil Company (Shell Plc)
• Inventors: Jager, Marco Dick, Meiring, Wouter Jan
• Primary Examiner(s): Pettitt, III, John F
• Application Number:
  US12/866,049
• Publication Number:
  US 20110023536A1
• Time in Patent Office: 3,995 Days
• Field of Search: 62618, 62619, 62620, 62630, 62611, 62612, 62613
• CPC Class Codes: F25J 1/0022 Hydrocarbons, e.g. natural gas
• CPC Class Codes: F25J 1/004 by flash gas recovery F25J1/0267 takes precedence
• CPC Class Codes: F25J 1/0042 by liquid expansion with extraction of work
• CPC Class Codes: F25J 1/0052 by vaporising a liquid refrigerant stream
• CPC Class Codes: F25J 1/0208 in combination with an internal quasi-closed refrigeration loop, e.g. with deep flash recycle loop F25J1/021 takes precedence
• CPC Class Codes: F25J 1/0216 using a C3 pre-cooling cycle
• CPC Class Codes: F25J 1/0219 in combination with an internal quasi-closed refrigeration loop, e.g. using a deep flash recycle loop
• CPC Class Codes: F25J 1/0231 for the working-up of the hydrocarbon feed, e.g. reinjection of heavier hydrocarbons into the liquefied gas
• CPC Class Codes: F25J 1/0241 wherein the overhead cooling comprises providing reflux for a fractionation step
• CPC Class Codes: F25J 1/0264 Arrangement of heat exchanger cores in parallel with different functions, e.g. different cooling streams F25J1/0272 takes precedence
• CPC Class Codes: F25J 1/0292 Refrigerant compression by cold or cryogenic suction of the refrigerant gas
• CPC Class Codes: F25J 2200/02 in a single pressure main column system
• CPC Class Codes: F25J 2200/04 in a dual pressure main column system
• CPC Class Codes: F25J 2200/40 Features relating to the provision of boil-up in the bottom of a column
• CPC Class Codes: F25J 2200/70 Refluxing the column with a condensed part of the feed stream, i.e. fractionator top is stripped or self-rectified
• CPC Class Codes: F25J 2200/74 Refluxing the column with at least a part of the partially condensed overhead gas
• CPC Class Codes: F25J 2205/04 in the feed line, i.e. upstream of the fractionation step
• CPC Class Codes: F25J 2210/06 Splitting of the feed stream, e.g. for treating or cooling in different ways
• CPC Class Codes: F25J 2215/02 Mixing or blending of fluids to yield a certain product
• CPC Class Codes: F25J 2215/62 Ethane or ethylene
• CPC Class Codes: F25J 2215/64 : Propane or propylene
• CPC Class Codes: F25J 2215/66 : Butane or mixed butanes
• CPC Class Codes: F25J 2220/62 : Separating low boiling components, e.g. He, H2, N2, Air
• CPC Class Codes: F25J 2240/30 : Dynamic liquid or hydraulic expansion with extraction of work, e.g. single phase or two-phase turbine
• CPC Class Codes: F25J 2245/02 : Recycle of a stream in general, e.g. a by-pass stream
• CPC Class Codes: F25J 2270/12 : External refrigeration with liquid vaporising loop
• CPC Class Codes: F25J 2270/60 : Closed external refrigeration cycle with single component refrigerant [SCR], e.g. C1-, C2- or C3-hydrocarbons
• CPC Class Codes: F25J 3/0209 : Natural gas or substitute natural gas
• CPC Class Codes: F25J 3/0233 : separation of CnHm with 1 carbon atom or more
• CPC Class Codes: F25J 3/0238 : separation of CnHm with 2 carbon atoms or more
• CPC Class Codes: F25J 3/0242 : separation of CnHm with 3 carbon atoms or more
• CPC Class Codes: F25J 3/0247 : separation of CnHm with 4 carbon atoms or more
• CPC Class Codes: F25J 3/0257 : separation of nitrogen from air F25J3/04, production of nitrogen in general C01B21/00

Abstract

A method and apparatus for cooling a hydrocarbon stream such as natural gas. An initial hydrocarbon stream is passed through a first separator to provide an initial overhead stream and a mixed hydrocarbon feed stream. The initial overhead stream is cooled to provide a cooled hydrocarbon stream such as LNG, and at least a C1 overhead stream and one or more C2, C3 and C4 overhead streams are separated from the mixed hydrocarbon feed stream. At least a fraction of at least one of the group comprising: the C2 overhead stream, the C3 overhead stream and the C4 overhead stream is cooled with the C1 overhead stream to provide a cooled stream, which is further cooled against at least a fraction of the cooled, preferably liquefied, hydrocarbon stream to provide an at least partly liquefied cooled stream.

Claims

1. A method, comprising at least the steps of:

(a) passing an initial hydrocarbon stream through a first separator to provide an initial overhead stream and a mixed hydrocarbon feed stream;

(b) cooling the initial overhead stream in a main heat exchanger to provide a cooled hydrocarbon stream;

(c) separating a C1 overhead stream from the mixed hydrocarbon feed stream, and subsequently separating one or more C2, C3 and C4 overhead streams from the mixed hydrocarbon feed stream;

(d) admixing one or more of the C2 overhead stream, the C3 overhead stream and the C4 overhead stream with the C1 overhead stream to provide a cooled stream, thereby bypassing the main heat exchanger;

(e) passing the cooled hydrocarbon stream through a first valve to provide an expanded cooled hydrocarbon stream and passing the expanded cooled hydrocarbon stream into an end gas/liquid separator to provide;

an end-flash gas stream, and

a liquefied product stream;

(f) passing the cooled stream to a second heat exchanger, thereby still bypassing the main heat exchanger, and further indirectly cooling the cooled stream against the end-flash gas stream in the second heat exchanger to provide an at least partly liquefied cooled stream, and subsequently

(g) combining the at least partly liquefied cooled stream with the expanded cooled hydrocarbon stream.

2. The method according to claim 1, wherein the cooling in step (b) comprises liquefying such that the cooled hydrocarbon stream is a liquefied hydrocarbon stream.

3. The method according to claim 1, wherein said further cooling the cooled stream comprises sub-cooling of the cooled stream, such that the at least partly liquefied cooled stream is a sub-cooled liquefied stream.

4. The method according to claim 1, wherein the at least partly liquefied cooled stream is within 40°

C. of temperature of the end-flash gas stream of step (e).

5. The method according to claim 1, wherein step (d) comprises at least the steps of:

(i) passing at least a fraction of the mixed hydrocarbon feed stream into a first distillation column to provide the C1 overhead stream and a first bottom stream;

(ii) passing at least a fraction of the first bottom stream into at least one of the group comprising;

a second distillation column, a third distillation column and a fourth distillation column;

to provide at least one of the group comprising;

the C2 overhead stream, the C3 overhead stream and the C4 overhead stream.

6. The method according to claim 5, wherein the second distillation column, the third distillation column, and the fourth distillation column provides the C2 overhead stream, the C3 overhead stream and the C4 overhead stream, respectively.

7. The method as claimed in claim 6, wherein at least a fraction of each of the C2 overhead stream, the C3 overhead stream and the C4 overhead stream is cooled by the C1 overhead stream.

8. The method according to claim 1, wherein the cooled stream has a temperature below 0°

C.

9. The method according to claim 1, wherein the initial hydrocarbon stream comprises natural gas and the liquefied product stream is LNG.

10. The method according to claim 1, wherein the at least partly liquefied cooled stream is within 10°

C. of the end-flash gas stream.

11. The method according to claim 1, further comprising precooling a hydrocarbon stream to provide a precooled hydrocarbon stream, the precooled hydrocarbon stream being the initial hydrocarbon stream.

12. The method according to claim 1,

the step of passing the cooled stream to the second heat exchanger comprising passing the cooled stream directly to the second heat exchanger,

the step of combining the at least partly liquefied cooled stream with the expanded cooled hydrocarbon stream comprising:

passing the at least partly liquefied cooled stream through a second valve to provide a reduced-pressure cooled stream, and subsequently

combining the reduced-pressure cooled stream with the expanded cooled hydrocarbon stream.

13. The method according to claim 12, the step of combining the reduced-pressure cooled stream with the expanded cooled hydrocarbon stream comprising:

passing the expanded cooled hydrocarbon stream to a first inlet of the end gas/liquid separator; and

passing the reduced-pressure cooled stream to a second inlet of the end gas/liquid separator.

14. The method according to claim 1, the step of combining the at least partly liquefied cooled stream with the expanded cooled hydrocarbon stream comprising:

passing the expanded cooled hydrocarbon stream to a first inlet of the end gas/liquid separator; and

passing the at least partly liquefied cooled stream to a second inlet of the end gas/liquid separator.