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Publication numberUS3747359 A
Publication typeGrant
Publication dateJul 24, 1973
Filing dateJul 13, 1970
Priority dateAug 1, 1969
Also published asDE1939114A1, DE1939114B2
Publication numberUS 3747359 A, US 3747359A, US-A-3747359, US3747359 A, US3747359A
InventorsM Streich
Original AssigneeLinde Ag
Export CitationBiBTeX, EndNote, RefMan
External Links: USPTO, USPTO Assignment, Espacenet
Gas liquefaction by a fractionally condensed refrigerant
US 3747359 A
Abstract
A gas stream is liquefied by indirect heat exchange with a multi-component refrigerant in a closed cooling cycle. The refrigerant is fractionally condensed and the fractions are separately evaporated in the closed cycle to cool and liquefy the gas stream.
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Description  (OCR text may contain errors)

Patent: 1111 3,747,359

Streich July 24, 1973 [54] GAS LIQUEFACTION BY A FRACTIONALLY 2,823,523 2/1958 Eakin 62/40 CONDENSED REFRIGERANT 3,548,606 12/1970 Kuerston.... 62/40 3,218,816 11/1965 ,Grenier 62/28 [75] Inventor: Martin Str i h, Nl d' -Es h a h, 3,274,787 9/1966 Grenier 62/28 G FOREIGN PATENTS OR APPLICATIONS [731 8 P Aktiengmnschan, 652,208 11/1962 Canada 62 40 Wwsbaden, Germany 110,556 2/1961 Pakistan..... 62/40 Filed: J y 3, 1970 OTHER PUBLICATIONS [21] Appl. No.: 54,478 Kleemenko, One Flow Cascade Cycle, Pergamon Press 1960 Pgs. 34-39 in Prog. In Refrig. Sci. & Tech.

[30] Foreign Application Prlonty Data Primary Examiner Norman Yudkoff I Aug. 1, 1969 Germany P 19 39 114.1 Assistant Examiner Arthur R Purcell Att P 1 W. G b 52 115. CI 62/24,62/11, 62/40 at o [51 Int. Cl...., .Q F25j l/02, F25j 3/02 [58] Field of Search 62/23, 24, 27, 2s, [57] ABSTRACT 62/40 9 1 1 A gas stream is liquefied by indirect heat exchange with a multi-component refrigerant in a closed cooling cy- 5 R f ren e Cited cle. The refrigerant is fractionally condensed and the UNITED STATES PATENTS fractions are separately evaporated in the closed cycle to cool and llquefy the gas stream. 3,364,685 l/1968 Perret 62/23 3,407,052 10/1968 Huntress 62/23 4 Claims, 1 Drawing Figure PATENIEDJUI. 241m INVENTOR.

MARTIN STREICH BY m AGENT GAS LIQUEFACTION BY A FRACTIONALLY CONDENSED REFRIGERANT BACKGROUND OF THE INVENTION This invention relates to a process for the liquefaction of gases or gas mixtures by means of a cooling cycle in which is circulated a cooling medium or refrigerant composed of several components that are subjected to fractional condensation and in which the condensed fractions are separately evaporated. The process is especially-suitable for the liquefaction of natural gas.

From German Auslegeschrift 1,272,943, there is known a process of this type in which cooling media obtained by fractional condensation of components from the natural gas to be liquefied are decompressed to a common medium pressure, mixed, recompressed to the pressure of the natural gas flowing into the plant and again mixed therewith. It is characteristic of that process that the several cooling media are decompressed to a common medium pressure.

From German Offenlegungsschrift 1,501,690, it is also known to carry out the circulation of the cooling medium in a closed cycle in such process.

In comparison with the so-called classical cascade process, these processes have some advantages since only one cooling cycle with one compressor is needed. However, this single cooling cycle must be divided up into several circulation branches, with a corresponding division of the heat exchangers and with complicated connections resulting therefrom. Furthermore, the utilization of energy is higher than in the case of the classical cascade process.

'In order to avoid these disadvantages, it has been proposed to divide up a cooling medium composed of several components and obtained byfractional condensation, to decompress one partial stream to a medium pressure and the other partial stream to approximately atmospheric pressure, to combine again the decompressed partial streams, to mix the combined streams with the gas mixture to be liquefied and to compress the total gas. The process is especially suitable for comparatively small natural gas liquefaction plants since it does not require a separate natural gas compressor. In such case, it is necessary that the natural gas is supplied at low pressure. However, these prerequisites-are not always fulfilled; Thus, for example, the natural gas is frequently supplied at a pressure which is already sufficiently high. Furthermore, the mixing of light natural gas and heavy hydrocarbons always leads to an. increased use of energy because of the increased entropy whichariSes. 1

It is an object of this invention to avoid these disadvantages and to make the process of universal applicability.

SUMMARY OF THE INVENTION A process has been found for the liquefaction of gas or gas mixtures by means of a closed cooling cycle in which a circulating multi-component refrigerant is compressed by a compressor, is separated by fractional condensation into fractions with different boiling ranges and these fractions are evaported as separate streams giving up refrigeration to the refrigerant undergoing fractional condensation and to the gas or gas mixture undergoing liquefaction, are recombined and again compressed. According to this invention, the

condensate fractions are separately evaporated and reheated to about ambient temperature and are again mixed together during recompression.

The process of this invention is especially advantageous for the liquefaction of natural gas since only two partial refrigerant streams fromm a single separator suffice for the liquefaction. Since the entropy increase by the mixing of cooling medium and natural gas is avoided, the energy requirement is relatively low. When using only two partial refrigerant streams, the one with the higher boiling fraction is decompressed to a medium absolute pressure, preferably five to 10 ats. (atmospheres), and the one with the lower boiling fraction is decompressed to a low absolute pressure, preferably one to five ats. When the gas mixture to be liquefied is natural gas, the refrigerant or cooling medium is preferably a hydrocarbon mixture.

When the process of this invention is applied to natural gas and nitrogen is to be removed therefrom, the

natural gas is preferably subjected, in the course of the I cooling thereof, to a preseparation before being further cooled and fractionated in a nitrogen rectification column.

BRIEF DESCRIPTION OF THE DRAWING charged in the gaseous state.

DESCRIPTION OF A PREFERRED EMBODIMENT The natural gas to be liquefied, which has the following composition:

N 14.3% by volume CH 82.4% by volume C Hq 2.6% by volume QH, 0.4% by volume C H 0.3% by volume enters the plant through pipe 1 at an absolute pressure of 20 ats. and at a temperature of 30 C. In purification plant 2, it is freed from impurities, especially from water and carbon dioxide, and then passed via pipe 3 successively through heat exchangers 4, 5 and 6. It is thereby cooled to a temperature of about -l00 C. and the heavy hydrocarbons condense out. These are separated in separator 7 and withdrawn through pipe 8. The gaseous portion which remains, consisting preponderantly of methane and nitrogen, flows through pipe 9 into heat exchanger 10 where it is cooled to about l20 C. and partially liquefied.

In order to simplify the separation of nitrogen in this stream in nitrogen rectification column 11, the liquid phase is separated from the gaseous phase in separator 12. The gaseous phase is enriched in nitrogen, whereas the liquid phase is depleted in nitrogen. The liquid and gaseous phases pass via pipes 13 and 14, respectively, into heat exchanger 15 where they are cooled to about l 40 C. and then used to heat the sump liquid of nitrogen column 11 by means of coils l7 and 16; respectively, whereby they are further cooled. The liquid phase is then decompressed via expansion valve 18 into the middle portion of nitrogen column 11, whereas the gaseous phase is first still further cooled in heat exchanger 19 to about 1 83 C. and thus liquefied before it is decompressed via expansion valve 20 into the top portion of nitrogen column 11.

In nitrogen column 11 which is at an absolute pressure of four ats., the nitrogen contained in the natural gas is completely separated and withdrawn via pipe 21 from the top of column 11 at a temperature of l83 C. It successively gives up its refrigeration in heat exchangers 19, l5, l0, 6, 5 and 4 and is then available at ambient temperature. It can also previously be decompressed to atmospheric pressure. Liquefied methane is withdrawn via pipe 22 from nitrogen column 11. It is then, in known manner, decompressed into a reservoir which is not illustrated in the drawing; the resulting flash and evaporation gases can also be utilized for recovering refrigeration therefrom.

The refrigeration necessary for cooling and liquefying the natural gas is produced in a closed cooling cycle in which a multicomponent refrigerant is circulated and subjected to fractional condensation. The refrigerant or cooling medium is preponderantly composed of methane, ethane, propane and butane. At about ambient temperature, one fraction of the refrigerant enters compressor 24 at an absolute pressure of two ats. and the other fraction enters compressor 24 at an absolute pressure of seven ats. The fractions thus recombined are compressed to about 25 ats. absolute and cooled in water cooler 25 to about 30 C. The refrigerant is then further cooled in heat exchanger 4 to about C., whereby it is partially liquefied. lt passes via pipe 26 into separator 27 in which the liquid phase is separated from the gaseous phase. The two separated phases now provide the two fractions or partial refrigerant streams. The partial refrigerant stream formed from the liquid phase and containing only a little methane and the heavier hydrocarbons, ethane, propane and butane in about equal parts, is first passed by means of pipe 28 through heat exchanger to effect further cooling of the partial stream and then is decompressed by expansion valve 29 to an absolute pressure of about 7.5 ats. This partial stream then evaporates at this pressure while giving up refrigeration in heat exchangers 5 and 4 and is returned to an intermediate stage of compressor 24.

The partial refrigerant stream obtained from the gaseous phase leaving separator 26 consists preponderantly of methane and has a modest content of ethane and propane, whereas the content of butane is small. This second partial stream in pipe 30 is first cooled in heat exchangers 5, 6, and to about l40 C. and thus liquefied and then, according to this invention, is decompressed by expansion valve 31 to an absolute pressure of about 2.5 ats. Thereafter, this second stream evaporates, successively gives up refrigeration in heat exchangers l5, l0, 6, 5 and 4 and finally passes via pipe 23 back into compressor 24.

A special advantage of the process of this invention is that it can be carried out with only a single subdivision of the closed cooling cycle.

I claim:

1. A process for the liquefaction of gas or a mixture of gases by indirect heat exchange with a compressed multi-component refrigerant circulated in a closed cooling cycle comprising thefollowing steps:

a. cooling, fractionally condensing and separating said compressed multi-component refrigerant into higher boiling liquid and lower boiling gaseous fractions,

b. subcooling all of said higher boiling liquid fractions and further cooling, liquefying and subcooling said lower boiling gaseous fractions,

c. expanding all of said subcooled higher boiling and lower boiling liquid fractions to different pressures, said subcooled higher boiling liquid fractions being expanded to a higher pressure, and said subcooled lower boiling liquid fractions being expanded to a lower pressure,

d. separately evaporating and heating to ambient temperature said subcooled liquid fractions expanded to different pressures by indirect heat exchange with said higher boiling and lower boiling fractions of said multi-component refrigerant and with said gas or gaseous mixture to be liquefied, without mixing said higher boiling and lower boiling fractions during evaporation and heating to ambient temperature,

e. separately recycling said evaporated fractions previously expanded to different pressures to a multistage compressor and mixing said evaporated fractions only during the compression.

2. A process for the liquefaction of natural gas by indirect heat exchange with a compressed multicomponent refrigerant circulated in a closed cooling cycle comprising the following steps:

a. cooling, fractionally condensing and separating said compressed multi-component refrigerant into only a single higher boiling liquid and a single lower boiling gaseous fraction,

b. subcooling all of said higher boiling liquid fraction and further cooling, liquefying and subcooling said lower boiling gaseous fraction,

c. expanding all of said subcooled higher boiling and lower boiling liquid fractions to different pressures, said subcooled higher boiling liquid fraction being expanded to a higher pressure, and said subcooled lower boiling liquid fraction being expanded to a lower pressure,

(1. separately evaporating and heating to ambient temperature said subcooled liquid fractions expanded to different pressures by indirect heat exchange with said higher boiling and lower boiling fractions of said multi-component refrigerant and with said natural gas to be liquefied, without mixing said higher boiling and lower boiling fractions during evaporation and heating to ambient temperature,

e. separately recycling said two evaporated fractions previously expanded to different pressures to a multi-stage compressor and mixing said two evaporated fractions only during the compression.

3. The process of claim 2 wherein the subcooled higher boiling liquid fraction is expanded to an absolute pressure of not less than about 5 atmospheres and the subcooled lower boiling liquid fraction is expanded to a lower absolute pressure of'less than about 5 atmospheres.

4. The process of claim 2 wherein the subcooled boiling liquid fraction is expanded to an absolute pressure in the range of about five to 10 atmospheres and the subcooled lower boiling liquid fraction is expanded to a lower absolute pressure in the range of about one to five atmospheres.

Patent Citations
Cited PatentFiling datePublication dateApplicantTitle
US2823523 *Mar 26, 1956Feb 18, 1958Inst Gas TechnologySeparation of nitrogen from methane
US3218816 *May 23, 1962Nov 23, 1965Air LiquideProcess for cooling a gas mixture to a low temperature
US3274787 *Sep 2, 1965Sep 27, 1966Air LiquideMethod for cooling a gaseous mixture to a low temperature
US3364685 *Mar 16, 1966Jan 23, 1968Cie Francaise D Etudes Et De CMethod and apparatus for the cooling and low temperature liquefaction of gaseous mixtures
US3407052 *Aug 17, 1966Oct 22, 1968Conch Int Methane LtdNatural gas liquefaction with controlled b.t.u. content
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CA652208A *Nov 13, 1962Shell Oil CoGas liquefaction
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Non-Patent Citations
Reference
1 *Kleemenko, One Flow Cascade Cycle, Pergamon Press 1960 Pgs. 34 39 in Prog. In Refrig. Sci. & Tech.
Referenced by
Citing PatentFiling datePublication dateApplicantTitle
US4251247 *Jun 28, 1979Feb 17, 1981Compagnie Francaise D'etudes Et De Construction TechnipMethod and apparatus for cooling a gaseous mixture
US4321795 *Sep 22, 1980Mar 30, 1982Helmut BrandtProcess for the purification of gaseous chlorine
US4445917 *May 10, 1982May 1, 1984Air Products And Chemicals, Inc.Process for liquefied natural gas
US4461634 *Apr 15, 1982Jul 24, 1984Petrocarbon Developments LimitedSeparation of gas mixtures by partial condensation
US4584006 *Oct 3, 1983Apr 22, 1986Flexivol, Inc.Process for recovering propane and heavier hydrocarbons from a natural gas stream
US4664686 *Feb 7, 1986May 12, 1987Union Carbide CorporationProcess to separate nitrogen and methane
US4666483 *Dec 26, 1984May 19, 1987L'air Liquide, Societe Anonyme Pour L'etude Et L'exploitation Des Procedes George ClaudeMethod and installation for recovering the heaviest hydrocarbons from a gaseous mixture
US5051120 *Jun 12, 1990Sep 24, 1991Union Carbide Industrial Gases Technology CorporationFeed processing for nitrogen rejection unit
US5535594 *Apr 5, 1994Jul 16, 1996Gaz De France (Service National)Process and apparatus for cooling a fluid especially for liquifying natural gas
US5613373 *May 10, 1996Mar 25, 1997Gaz De France (Service National)Process and apparatus for cooling a fluid especially for liquifying natural gas
US5950453 *Jun 18, 1998Sep 14, 1999Exxon Production Research CompanyMulti-component refrigeration process for liquefaction of natural gas
US6041619 *Jun 22, 1998Mar 28, 2000Institute Francais Du PetroleMethod of liquefying a natural gas with two interconnected stages
US6250105Dec 16, 1999Jun 26, 2001Exxonmobil Upstream Research CompanyDual multi-component refrigeration cycles for liquefaction of natural gas
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US20080016910 *Jul 21, 2006Jan 24, 2008Adam Adrian BrostowIntegrated NGL recovery in the production of liquefied natural gas
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US20100189508 *Jun 6, 2007Jul 29, 2010Jose LourencoMethod of increasing storage capacity of natural gas storage caverns
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WO1994024500A1 *Apr 5, 1994Oct 27, 1994Gaz De FranceFluid cooling process and plant, especially for natural gas liquefaction
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WO2006094675A1 *Feb 28, 2006Sep 14, 2006Linde AktiengesellschaftMethod for liquefaction of a stream rich in hydrocarbons
Classifications
U.S. Classification62/623
International ClassificationF25J3/02, F25J1/02
Cooperative ClassificationF25J2220/64, F25J2205/04, F25J1/004, F25J3/0257, F25J3/0233, F25J1/0211, F25J3/0209, F25J2200/02, F25J1/0055, F25J2200/70, F25J2270/66, F25J2270/18, F25J1/0022, F25J1/0212
European ClassificationF25J3/02A2, F25J1/02D2, F25J1/00A6, F25J1/00C4V2, F25J1/00C2F, F25J1/02D, F25J3/02C12, F25J3/02C2