US 5,537,827 AGranted

Method for liquefaction of natural gas

OwnerWilliam R. Low, Clarence G. Houser +2inventors

InventorsWilliam R. Low, Clarence G. Houser, Douglas E. Yates, Donald L. Andress

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Abstract

A process for the liquefaction of natural gas having a pressure above atmospheric pressure, is disclosed in which a feed gas is cooled to sequentially lower temperatures, by passing the gas through a plurality of cooling stages, in heat exchange with at least three refrigerants, until the gas is substantially completely condensed in the last of the cooling stages. The pressure of the feed gas is reduced to near atmospheric pressure during the cooling of the feed gas by the use of hydraulic expanders which extract work during pressure reduction. Additionally, pressure reduction of the refrigerants within the refrigerant cycles is performed by similar hydraulic expanders. The work extracted by said hydraulic expanders is used to provide power to the liquefaction process, such as by helping to power compressors or pumps used in the liquefaction process.

Claims15

Dependent claims

A process for producing liquefied natural gas, from a pressurized natural gas feed stream, which is predominantly methane and has an initial pressure above 500 psia, comprising:

(a) introducing said feed stream into heat exchange contact with a first refrigerant cycle wherein the temperature of said feed stream is reduced by heat exchange with a first portion of a first refrigerant having a first boiling point, to thus produce a first cooled stream;
(b) introducing said first cooled stream into heat exchange contact with a second refrigerant cycle wherein the temperature of said first cooled stream is reduced by heat exchange with a second refrigerant, having a second boiling point lower than said first boiling point, to thus produce a second cooled stream and wherein within said second refrigerant cycle said second refrigerant is subsequently compressed and, at least partially, cooled and condensed by heat exchange with a second portion of said first refrigerant;
and
(c) reducing the pressure and temperature of said second cooled stream in a series of cooling and expansion steps utilizing at least one heat exchanger, at least one hydraulic expander and at least one separation vessel to produce a liquid natural gas stream at about atmospheric pressure, wherein said second cooled stream is cooled within said heat exchanger by heat exchange with a third refrigerant having a third boiling point lower than said second boiling point, said pressure of said second cooled stream is reduced in said hydraulic expander such that the temperature of said second cooled stream is further reduced and work is extracted during said pressure reduction, and a gaseous phase is separated from said second cooled stream in said separation vessel.

1 more element

A process for producing liquefied natural gas, from a pressurized natural gas feed stream, which is predominantly methane and has an initial pressure above 500 psia, comprising:

(a) introducing said feed stream into heat exchange contact with a first refrigerant cycle wherein the temperature of said feed stream is reduced by heat exchange with a first portion of a first refrigerant having a first boiling point, to thus produce a first cooled stream;
(b) introducing said first cooled stream into heat exchange contact with a second refrigerant cycle wherein the temperature of said first cooled stream is reduced by heat exchange with a second refrigerant having a second boiling point lower than said first boiling point, to thus produce a second cooled stream;
(c) compressing said second refrigerant after it has undergone heat exchange with said first cooled stream to increase said pressure of said second refrigerant;
(d) cooling said second refrigerant after said compressing of said second refrigerant by heat exchange with a second portion of said first refrigerant to thus decrease the temperature of said second refrigerant and at least partially condense it;
(e) reducing the pressure of said thus cooled second refrigerant in a second refrigerant hydraulic expander to further reduce the temperature of said second refrigerant wherein work is extracted from said second refrigerant during said reduction of pressure by means of said second refrigerant hydraulic expander;
(f) thereafter returning said second refrigerant for heat exchange with said first cooled feed stream;
(g) combining said first portion of said first refrigerant, after it has undergone heat exchange with said feed stream, with said second portion of said first refrigerant, after it has undergone heat exchange with said second refrigerant, to produce a first refrigerant stream;
(h) compressing said first refrigerant stream to increase the pressure of said first refrigerant stream;
(i) cooling said first refrigerant stream after said compressing of said first refrigerant stream by heat exchange with a cooling medium, to thus decrease the temperature of said first refrigerant stream and at least partially condense it;
(j) reducing the pressure of said thus cooled first refrigerant stream in a first refrigerant hydraulic expander to further reduce the temperature of said first refrigerant stream wherein work is extracted from said first refrigerant stream during said reduction of pressure by means of said first refrigerant hydraulic expander;
and
(k) thereafter splitting said first refrigerant stream into said first portion of said first refrigerant and said second portion of said first refrigerant and returning said first portion for heat exchange with said feed stream and returning said second portion for heat exchange with said second refrigerant.

9 more elements

Dependencies are inferred from the claim text.

Facts

Application: 08/484,398Filed 7 Jun 1995
Granted: 23 Jul 1996
Term ends: Not estimatedThe source records don’t support an estimate.

Classification16 codes

F25J 1/0281
Compression of refrigerant or internal recycle fluid, e.g. kind of compressor, accumulator, suction drum etc.: characterised by the type of prime…
F25J 1/0022
Characterised by the fluid to be liquefied: hydrocarbons, e.g. natural gas
F25J 1/0035
Using the feed stream itself or separated fractions from it, i.e. "internal refrigeration": by gas expansion with extraction of work
F25J 1/004
Using the feed stream itself or separated fractions from it, i.e. "internal refrigeration": by flash gas recovery