US 7,628,035 B2Granted

Method for processing a stream of LNG obtained by means of cooling using a first refrigeration cycle and associated installation

AssigneeTechnip France

InventorHenri Paradowski

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Abstract

In this method, the LNG stream is cooled using a refrigerating fluid in a first heat-exchanger. The refrigerating fluid is subjected to a second semi-open refrigeration cycle which is independent of the first cycle. The method comprises a step for introducing the stream of sub-cooled LNG into a distillation column and a step for recovering a stream of gas at the top of the column. The second refrigeration cycle comprises a step for forming a stream of refrigerating fluid from a portion of the top stream of gas, a step for compressing the stream of refrigerating fluid to a high pressure, then a step for expanding a portion of the stream of compressed refrigerating fluid in order to form a substantially liquid sub-cooling stream. The substantially liquid stream is evaporated in the first heat-exchanger.

Claims23

Dependent claims

Method for processing a stream of LNG obtained by means of cooling using a first refrigeration cycle, the method comprising the following steps:

(a) the stream of LNG which has been brought to a temperature of less than −100° C. is introduced into a first heat-exchanger;
(b) the stream of LNG is sub-cooled in the first heat-exchanger by means of heat-exchange with a refrigerating fluid in order to form a first stream of sub-cooled LNG;
and
(c) the refrigerating fluid is subjected to a second semi-open refrigeration cycle which is independent of the first cycle,
(d) the first stream of sub-cooled LNG is expanded in a dynamic manner in an intermediate turbine, maintaining the first stream of sub-cooled LNG substantially in the liquid state;
(e) the first stream of sub-cooled LNG from the intermediate turbine is cooled and expanded and then introduced into a distillation column;
(f) a stream of denitrogenated LNG at the bottom of the column and a stream of gas at the top of the column are recovered;
and
(g) the top stream of gas is compressed in a stage compressor, and, at an intermediate pressure stage of the compressor, a first portion of the top stream of gas, which is brought to an intermediate pressure PI, is extracted in order to form a stream of combustible gas;
performing a second refrigeration cycle comprising the following steps:
(i) an initial stream of refrigerating fluid is formed from a second portion of the top stream of gas which has been compressed at the intermediate pressure PI;
(ii) the initial stream of refrigerating fluid is compressed to a high pressure PH which is greater than the intermediate pressure PI in order to form a stream of compressed refrigerating fluid;
(iii) the stream of compressed refrigerating fluid is cooled in a second heat-exchanger;
(iv) the stream of compressed refrigerating fluid from the second heat-exchanger is separated into a main cooling stream and a second sub-cooling stream of the LNG;
(v) the second sub-cooling stream is cooled in a third heat-exchanger, then in the first heat-exchanger;
(vi) the first sub-cooling stream of LNG from the first heat-exchanger is expanded to a low pressure PB which is lower than the intermediate pressure PI in order to form a substantially liquid sub-cooling stream of the LNG;
(vii) the substantially liquid sub-cooling stream is evaporated in the first heat-exchanger in order to form a reheated sub-cooling stream;
(viii) the main cooling stream is expanded substantially to the low pressure PB in a main turbine and a cooling stream from the main turbine is mixed with the reheated sub-cooling stream in order to form a mixed stream;
(ix) the mixed stream is reheated successively in the third heat-exchanger, then in the second heat-exchanger in order to form a reheated mixed stream;
and
(x) the reheated mixed stream is introduced into the compressor at a low pressure stage located upstream of the intermediate pressure stage.

18 more elements

Installation for processing a stream of LNG obtained by means of cooling using a first refrigeration cycle, the installation comprising:

apparatus for sub-cooling the stream of LNG comprising a first heat-exchanger operable to bring the LNG stream into a heat-exchange relationship with a refrigerating fluid;
and
a second semi-open refrigeration cycle which is independent of the first refrigeration cycle,
an intermediate turbine for dynamic expansion of the stream of sub-cooled LNG from the first heat-exchanger;
a device operable for cooling and expanding the stream from the intermediate turbine;
a distillation column which is connected to the cooling and expansion device;
a device operable for recovering a stream of denitrogenated LNG at the bottom of the column, and a device operable for recovering a stream of gas at the top of the column,
a stage compressor which is connected to the device operable for recovering the stream of gas at the top of the column;
and
a device operable for extracting a first portion of the top stream of gas tapped at an intermediate pressure stage of the compressor in order to form a stream of combustible gas;
a second refrigeration cycle comprising:
a device operable for forming an initial stream of refrigerating fluid from a second portion of the top gas compressed to the intermediate pressure;
a device operable for compressing the initial stream of refrigerating fluid to a high pressure PH which is greater than the intermediate pressure PI in order to form a compressed stream of refrigerating fluid;
a second heat-exchanger operable to cool the compressed initial stream of refrigerating fluid;
a device operable for separating the compressed stream of refrigerating fluid from the second heat-exchanger into a main cooling stream and a sub-cooling stream of the LNG;
a third heat-exchanger for cooling the sub-cooling stream;
a device operable for introducing the sub-cooling stream from the third heat-exchanger into the first heat-exchanger;
a device operable for expanding the sub-cooling stream from the first heat-exchanger to a low pressure PB which is lower than the intermediate pressure PI in order to form a substantially liquid sub-cooling stream of the LNG;
a device operable for circulating the substantially liquid sub-cooling stream in the first heat-exchanger in order to form a reheated sub-cooling stream;
a main turbine operable for expanding the main cooling stream substantially to the low pressure PB;
a device operable for mixing the cooling stream from the main turbine with the sub-cooling stream which has been reheated in order to form a mixed stream;
a device operable for circulating the mixed stream successively in the third heat-exchanger then in the second heat-exchanger in order to form a reheated mixed stream;
a device operable for introducing the reheated mixed stream in the compressor at a low pressure stage which is located upstream of the intermediate pressure stage.

20 more elements

Dependencies are inferred from the claim text.

Facts

Application: 11/539,828Filed 9 Oct 2006
Priority: FR 05 1032910 Oct 2005
Published: US 2007/0095099 A13 May 2007
Granted: 8 Dec 2009
Term ends: Not estimatedThe source records don’t support an estimate.

Classification29 codes

F25J 3/0257
Characterised by the separated product stream: separation of nitrogen
F25J 1/0022
Characterised by the fluid to be liquefied: hydrocarbons, e.g. natural gas
F25J 1/0037
By gas expansion with extraction of work: of a return stream
F25J 1/004
Using the feed stream itself or separated fractions from it, i.e. "internal refrigeration": by flash gas recovery