Method for refrigerating liquefied gas and installation therefor

• US 20040065113A1
• Filed: 11/03/2003
• Published: 04/08/2004
• Est. Priority Date: 12/18/2000
• Status: Active Grant

• Current Assignee: Technip France (TechnipFMC, plc)
• Original Assignee: Technip France (TechnipFMC, plc)
• Inventors: Paradowski, Henri
• Granted Patent: US 6,898,949 B2
• Time in Patent Office: Days
• US Class Current: 62/613
• CPC Class Codes: F25J 1/0022 Hydrocarbons, e.g. natural gas
• CPC Class Codes: F25J 1/0037 of a return stream
• 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 1/0055 originating from an incorporated cascade
• CPC Class Codes: F25J 1/0087 Propane; Propylene
• 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 1/0274 Retrofitting or revamping of an existing liquefaction unit
• CPC Class Codes: F25J 1/0283 Gas turbine as the prime mechanical driver
• CPC Class Codes: F25J 1/0285 Combination of different types of drivers mechanically coupled to the same refrigerant compressor, possibly split on multiple compressor casings
• CPC Class Codes: F25J 1/0288 using work extraction by mechanical coupling of compression and expansion of the refrigerant, so-called companders
• 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 2200/70 Refluxing the column with a condensed part of the feed stream, i.e. fractionator top is stripped or self-rectified
• CPC Class Codes: F25J 2205/04 in the feed line, i.e. upstream of the fractionation step
• CPC Class Codes: F25J 2215/04 Recovery of liquid products
• 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 2240/40 Expansion without extracting work, i.e. isenthalpic throttling, e.g. JT valve, regulating valve or venturi, or isentropic nozzle, e.g. Laval
• CPC Class Codes: F25J 2245/02 : Recycle of a stream in general, e.g. a by-pass stream
• CPC Class Codes: F25J 2270/04 : Internal refrigeration with work-producing gas expansion loop
• CPC Class Codes: F25J 2270/12 : External refrigeration with liquid vaporising loop
• CPC Class Codes: F25J 2270/18 : External refrigeration with incorporated cascade loop
• CPC Class Codes: F25J 2270/42 : Quasi-closed internal or closed external nitrogen refrigeration cycle
• 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 2270/66 : Closed external refrigeration cycle with multi component refrigerant [MCR], e.g. mixture of hydrocarbons
• CPC Class Codes: F25J 2280/02 : Control in general, load changes, different modes ("runs"), measurements
• CPC Class Codes: F25J 2290/80 : Retrofitting, revamping or debottlenecking of existing plant
• 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 3/0257 : separation of nitrogen from air F25J3/04, production of nitrogen in general C01B21/00
• CPC Class Codes: F25J 3/061 : Natural gas or substitute natural gas
• CPC Class Codes: F25J 3/0635 : separation of CnHm with 1 carbon atom or more
• CPC Class Codes: F25J 3/066 : separation of nitrogen from air F25J3/04, production of nitrogen in general C01B21/00

Abstract

The invention concerns a method for refrigerating liquefied natural gas under pressure (1), comprising a first step wherein the LNG (1) is cooled, expanded and separated (a) in a first base fraction (4) which is collected, and (b) a first top fraction (3) which is heated, compressed in a compressor (K1) and cooled into a first compressed fraction (5) which is collected; a second compressed fraction (6) is drawn from the fuel gas (5), cooled then mixed with the cooled and expanded LNG (1). The invention is characterised in that it comprises a second step wherein the second compressed fraction (6) is compressed and cooled, and a flux is (8) drawn and cooled, expanded and introduced in the compressor (K1). The invention also describes other embodiments.

Claims

1. A method for refrigerating a pressurized liquefied natural gas (1) containing methane and C₂ and higher hydrocarbons, comprising a first step (I) in which step (Ia) said pressurized liquefied natural gas (1) is expanded to provide an expanded liquefied natural gas stream (2), in which step (Ib) said expanded liquefied natural gas (2) is split into a relatively more volatile first top fraction (3) and a relatively less volatile first bottom fraction (4), in which step (Ic) the first bottom fraction (4) consisting of refrigerated liquefied natural gas is collected, in which step (Id) the first top fraction (3) is heated, compressed in a first compressor (K1) and cooled to provide a first fuel gas compressed fraction (5) which is collected, in which step (Ie) there is tapped off from the first compressed fraction (5) a second compressed fraction (6) which is then cooled, then mixed with the expanded liquefied natural gas stream (2), characterized in that the method comprises a second step (II) in which step (IIa) the second compressed fraction (6) is compressed in a second compressor (XK1) coupled to an expansion turbine (X1) to provide a third compressed fraction (7), in which step (IIb) the third compressed fraction (7) is cooled, then split into a fourth compressed fraction (8) and a fifth compressed fraction (9), in which step (IIc) the fourth compressed fraction (8) is cooled and expanded in the expansion turbine (X1) coupled to the second compressor (XK1) to provide an expanded fraction (10) which is then heated, then introduced into a medium-pressure first stage (11) of the compressor (K1), and in which step (IId) the fifth compressed fraction (9) is cooled, then mixed with the expanded liquefied natural gas stream (2).

2. The method as claimed in claim 1, characterized in that the expanded liquefied natural gas stream (2) is split, prior to step (Ib), into a second top fraction (12) and a second bottom fraction (13), in that the second top fraction (12) is heated, then introduced into the first compressor (K1) in an intermediate medium-pressure second stage (14) between the medium-pressure first stage (11) and a low-pressure stage (15), and in that the second bottom fraction (13) is split into the first top fraction (3) and the first bottom fraction (4).

3. The method as claimed in claim 1 or claim 2, characterized in that each compression step is followed by a cooling step.

4. A refrigerated liquefied natural gas (4) obtained by the method as claimed in any one of the preceding claims.

5. The fuel gas (5) obtained by the method as claimed in any one of claims 1-3.

6. An installation for refrigerating a pressurized liquefied natural gas (1) containing methane and C₂ and higher hydrocarbons, comprising means for carrying out a first step (I) in which step (Ia) said pressurized liquefied natural gas (1) is expanded to provide an expanded liquefied natural gas stream (2), in which step (Ib) said expanded liquefied natural gas (2) is split into a relatively more volatile first top fraction (3) and a relatively less volatile first bottom fraction (4), in which step (Ic) the first bottom fraction (4) consisting of refrigerated liquefied natural gas is collected, in which step (Id) the first top fraction (3) is heated, compressed in a first compressor (K1) and cooled to provide a first fuel gas compressed fraction (5) which is collected, in which step (Ie) there is tapped off from the first compressed fraction (5) a second compressed fraction (6) which is then cooled, then mixed with the expanded liquefied natural gas stream (2), characterized in that the installation comprises means for carrying out a second step (II) in which step (IIa) the second compressed fraction (6) is compressed in a second compressor (XK1) coupled to an expansion turbine (X1) to provide a third compressed fraction (7), in which step (IIb) the third compressed fraction (7) is cooled, then split into a fourth compressed fraction (8) and a fifth compressed fraction (9), in which step (IIc) the fourth compressed fraction (8) is cooled and expanded in the expansion turbine (X1) coupled to the second compressor (XK1) to provide an expanded fraction (10) which is then heated, then introduced into a medium-pressure first stage (11) of the compressor (K1), and in which step (IId) the fifth compressed fraction (9) is cooled, then mixed with the expanded liquefied natural gas stream (2).

7. The installation as claimed in claim 6, characterized in that it comprises means for splitting the expanded liquefied natural gas stream (2), prior to step (Ib), into a second top fraction (12) and a second bottom fraction (13), in that the installation comprises means for heating, then introducing the second top fraction (12) into the first compressor (K1) in an intermediate medium-pressure second stage (14) between the medium-pressure first stage (11) and a low-pressure stage (15), and in that it comprises means for splitting the second bottom fraction (13) into the first top fraction (3) and the first bottom fraction (4).

8. The installation as claimed in claim 6 or claim 7, characterized in that the first top fraction (3) and the first bottom fraction (4) are separated in a first separating vessel (V1).

9. The installation as claimed in claim 6 or claim 7, characterized in that the first top fraction (3) and the first bottom fraction (4) are separated in a distillation column (C1).

10. The installation as claimed in any one of claims 6-9, characterized in that the expanded liquefied natural gas stream (2) is split into the second top fraction (12) and the second bottom fraction (13) in a second separating vessel (V2).

11. The installation as claimed in claim 9, characterized in that the distillation column (C1) comprises at least one lateral and/or column-bottom reboiler (16), in that liquid tapped off a plate (17) of the distillation column (C1) passing through said reboiler (16) is heated in a heat exchanger (E2), then reintroduced into the distillation column (C1) at a stage below said plate (17), and in that the expanded liquefied natural gas stream (2) is cooled in said heat exchanger (E2).

12. The installation as claimed in any one of claims 6 to 11, characterized in that the cooling of the first top fraction (3) and of the expanded fraction (10), and the heating of the fourth compressed fraction (6) and of the fifth compressed fraction (9) take place in one and the same first heat exchanger (E1).

13. The installation as claimed in any one of claims 6 to 12, in conjunction with claim 7, characterized in that the second top fraction (12) is heated in the first heat exchanger (E1).