1. Technical Field
One or more embodiments of the present invention generally relate to systems and processes for cooling a feed gas stream with a single closed-loop mixed refrigerant cycle.
2. Description of Related Art
In recent years, natural gas has become a widely used source of fuel. In addition to its clean burning qualities and convenience, advances in exploration and production technology have permitted previously unreachable gas reserves to become accessible. Because many of these previously unreachable sources of natural gas are remote and are not connected to commercial markets or infrastructure by pipeline, cryogenic liquefaction of natural gas for transportation and storage has become increasingly important. In addition, liquefaction permits long term storage of natural gas, which can help balance out periodic fluctuations in supply and demand.
Several methods for liquefying natural gas are currently in practice. Although the specific configuration and/or operation of each facility may vary depending on, for example, the type of refrigeration system used, the rate and composition of feed gas, and other factors, most commercial facilities generally include similar basic components. For example, most facilities typically include a pretreatment area for removing one or more impurities from the incoming gas stream, a liquefaction zone for liquefying the gas stream, a refrigeration system for providing refrigeration to the liquefaction zone, and a storage and/or loading area for receiving, storing, and transporting the final liquefied product. Overall, the cost to construct and operate these facilities can vary widely, but in general, the cost of the refrigeration portion of the plant can account for up to 30 percent or more of the overall cost of the facility.
Thus, a need exists for an optimized refrigeration system capable of efficiently producing a liquefied gas product at a desired capacity, but with minimum amount of equipment. Ideally, the refrigeration system would be both robust and operationally flexible in order to handle variations in feed gas composition and flow rate, while still requiring minimal capital outlay and operating at the lowest possible cost.
One embodiment of the present invention concerns a process for producing liquefied natural gas (LNG). The process comprises the following steps: (a) cooling a natural gas stream in a first heat exchanger to provide a cooled natural gas stream; (b) compressing a mixed refrigerant stream to provide a compressed refrigerant stream; (c) cooling and at least partially condensing the compressed refrigerant stream to provide a two-phase refrigerant stream; (d) separating the two-phase refrigerant stream into a first refrigerant vapor stream and a first refrigerant liquid stream in a first vapor-liquid separator; (e) combining at least a portion of the first refrigerant vapor stream withdrawn from the first vapor-liquid separator with at least a portion of the first refrigerant liquid stream to provide a combined refrigerant stream; (f) cooling at least a portion of the combined refrigerant stream to provide a cooled combined refrigerant stream; (g) separating the cooled combined refrigerant stream into a second refrigerant vapor stream and a second refrigerant liquid stream in a second vapor-liquid separator; (h) dividing the second refrigerant liquid stream into a first refrigerant liquid fraction and a second refrigerant liquid fraction; (i) cooling at least a portion of the first and second refrigerant liquid fractions to provide respective first and second cooled liquid refrigerant fractions; and (j) introducing the first and second cooled liquid refrigerant fractions into separate inlets of the first heat exchanger, wherein the first and second cooled liquid refrigerant fractions are used to carry out at least a portion of the cooling of step (a).
Another embodiment of the present invention concerns a process for producing a liquefied gas stream. The process comprises the following steps: (a) compressing a stream of mixed refrigerant in a first compression stage of a compressor to provide a first compressed refrigerant stream; (b) cooling and at least partially condensing the first compressed refrigerant stream to provide a cooled, compressed refrigerant stream; (c) separating the cooled, compressed refrigerant stream into a first refrigerant vapor stream and a first refrigerant liquid stream; (d) compressing the first refrigerant vapor stream in a second compression stage of the compressor to provide a second compressed refrigerant stream; (e) cooling and at least partially condensing at least a portion of the second compressed refrigerant stream to provide a partially condensed refrigerant stream; (f) separating the partially condensed refrigerant into a second refrigerant vapor stream, a second refrigerant liquid stream, and a third refrigerant liquid stream; (g) cooling the second and third refrigerant liquid streams to provide respective cooled second and third refrigerant liquid streams; (h) expanding at least one of the cooled second and cooled third refrigerant liquid streams to provide at least one cooled, expanded refrigerant stream; (i) cooling a feed gas stream via indirect heat exchange with the at least one cooled, expanded refrigerant stream to provide a cooled feed gas stream and at least one warmed refrigerant stream.
Yet another embodiment of the present invention concerns a system for cooling a natural gas stream. The system comprises a first heat exchanger for cooling a natural gas feed stream. The first heat exchanger comprises a first cooling pass having a feed gas inlet and a cool natural gas outlet, a second cooling pass for receiving and cooling a first stream of refrigerant liquid, wherein the second cooling pass has a first warm refrigerant inlet and a first cool refrigerant outlet; a third cooling pass for receiving and cooling a second stream of refrigerant liquid, wherein the third cooling pass has a second warm refrigerant inlet and a second cool refrigerant outlet; a first warming pass for receiving and warming a first stream of cooled refrigerant, wherein the first warming pass has a first cool refrigerant inlet and a first warm refrigerant outlet; and a second warming pass for receiving and warming a second stream of cooled refrigerant liquid, wherein the second warming pass has a second cool refrigerant inlet and a second warm refrigerant outlet. The first cool refrigerant outlet of the second cooling pass is in fluid flow communication with the first cool refrigerant inlet of the first warming pass, and the second cool refrigerant outlet of the third cooling pass is in fluid flow communication with the second cool refrigerant inlet of the second warming pass. The system also comprises at least one compressor for receiving and pressurizing a stream of mixed refrigerant. The compressor has a low pressure inlet and a high pressure outlet and the low pressure inlet is in fluid flow communication with at least one of the first warm refrigerant outlet of the first warming pass and the second warm refrigerant outlet of the second warming pass. The system also comprises a first cooler for cooling the pressurized stream of mixed refrigerant. The first cooler has a first warm fluid inlet and a first cool fluid outlet and the first warm fluid inlet is in fluid flow communication with the high pressure outlet of the compressor. The system also comprises a first vapor-liquid separator for separating a portion of the cooled refrigerant stream. The vapor-liquid separator comprises a first fluid inlet, a first vapor outlet, and a first liquid outlet and the first fluid inlet of the first vapor-liquid separator is in fluid flow communication with the first cool fluid outlet of the first cooler. The system also comprises a first liquid conduit for transporting at least a portion of the liquid exiting the first vapor-liquid separator. The first liquid conduit has a refrigerant liquid inlet and a pair of refrigerant liquid outlets. The refrigerant liquid inlet is in fluid flow communication with the first liquid outlet of the first vapor-liquid separator. One of the pair of refrigerant liquid outlets is in fluid flow communication with the first warm refrigerant inlet of the second cooling pass and the other of the pair of refrigerant liquid outlets is in fluid flow communication with the second warm refrigerant inlet of the third cooling pass.
Various embodiments of the present invention are described in detail below with reference to the attached Figures, wherein:
The following detailed description of embodiments of the invention references the accompanying drawings. The embodiments are intended to describe aspects of the invention in sufficient detail to enable those skilled in the art to practice the invention. Other embodiments can be utilized and changes can be made without departing from the scope of the claims. The following detailed description is, therefore, not to be taken in a limiting sense. The scope of the present invention is defined only by the appended claims, along with the full scope of equivalents to which such claims are entitled.
The present invention generally relates to processes and systems for liquefying a natural gas feed stream to thereby provide a liquefied natural gas (LNG) product. In particular, the present invention relates to optimized refrigeration processes and systems for cooling the incoming gas. As described in further detail below, the incoming feed gas stream can be cooled and at least partially condensed with a closed-loop refrigeration system employing a single mixed refrigerant. According to various embodiments of the present invention, the refrigeration system may be optimized to provide efficient cooling for the feed gas stream, while minimizing the expenses associated with the equipment and operating costs of the facility.
Referring initially to
As shown in
According to one embodiment, the feed gas stream in conduit 110 can comprise at least about 65, at least about 75, at least about 85, at least about 95, at least 99 weight percent methane, based on the total weight of the stream. Typically, heavier components such as C2, C3, and heavier hydrocarbons, and trace amounts of components such as hydrogen and nitrogen, can make up the balance of the composition fo the feed gas stream. As discussed previously, the stream in conduit 110 may have undergone one or more pretreatment steps to reduce the amount of or remove one or more components other than methane from the feed gas stream. In one embodiment, the feed gas stream in conduit 110 comprises less than about 25, less than about 20, less than about 15, less than about 10, or less than about 5 percent of components other than methane. Depending on the source and composition of the feed gas stream, the undesired components removed in the pretreatment steps can include, but are not limited to, water, mercury, sulfur compounds, and other materials.
As shown in
Primary heat exchanger 16 shown in
Referring back to
As shown in
As shown in one embodiment depicted in
Turning now the embodiment of refrigeration system 12 of LNG facility 10 depicted in
According to one embodiment of the present invention, the refrigerant utilized in closed-loop refrigeration cycle 12 may be a mixed refrigerant. As used herein, the term “mixed refrigerant” refers to a refrigerant composition comprising two or more constituents. In one embodiment, the mixed refrigerant utilized by refrigeration cycle 12 may be a single mixed refrigerant and can comprise two or more components selected from the group consisting of methane, ethylene, ethane, propylene, propane, isobutane, n-butane, isopentane, n-pentane, and combinations thereof. In some embodiments, the refrigerant composition can comprise methane, ethane, propane, normal butane, and isopentane and can exclude certain components, including, for example, nitrogen or halogenated hydrocarbons. Various specific refrigerant compositions are contemplated according to embodiments of the present invention. Table 1, below, summarizes broad, intermediate, and narrow ranges for several exemplary components that may be employed in refrigerant mixtures suitable for use in refrigerant cycle 12, according to various embodiments of the present invention.
In some embodiments of the present invention, it may be desirable to adjust the composition of the mixed refrigerant to thereby alter its cooling curve and, therefore, its refrigeration potential. Such a modification may be utilized to accommodate, for example, changes in composition and/or flow rate of the feed gas stream introduced into LNG facility 10. In one embodiment, the composition of the mixed refrigerant can be adjusted such that the heating curve of the vaporizing refrigerant more closely matches the cooling curve of the feed gas stream. One method for such curve matching is described in detail in U.S. Pat. No. 4,033,735, the disclosure of which is incorporated herein by reference in its entirety and to the extent not inconsistent with the present disclosure. In some embodiments, ability to alter the composition and, consequently, the heating curve of the refrigerant provides increased flexibility and operability to the facility, enabling it to receive and efficiently process feed streams having a wider variety of gas compositions.
Referring again to refrigeration cycle 12 shown in the embodiment of facility 10 in
As shown in
The combined refrigerant stream in conduit 138 can then be introduced into a refrigerant condenser 38, wherein the stream may be cooled and at least partially condensed via indirect heat exchange with a coolant stream (e.g., cooling water). The resulting cooled, at least partially condensed refrigerant stream in conduit 140 may then be introduced into a refrigerant accumulator 40, wherein the vapor and liquid phases may be separated. As shown in
According to one embodiment of the present invention, the liquid refrigerant stream withdrawn from refrigerant accumulator 40 via conduit 144 can be pressurized via refrigerant pump 40 and the resulting stream discharged into conduit 146 may be passed through a dividing device 50, which can be configured to divide the pressurized liquid refrigerant into two separate portions in conduits 148 and 150. As shown in
As shown in
As shown in
According to one embodiment of the present invention, the second portion of the liquid refrigerant stream withdrawn from refrigerant accumulator 40 via conduit 150 can be separately introduced into a second refrigerant cooling pass 52 disposed within primary heat exchanger 16. As the liquid stream travels vertically downward through cooling pass 52, it is cooled and condensed via indirect heat exchange with one or more refrigerant streams. The resulting liquid refrigerant stream exiting cooling pass 52 in conduit 152 can then be passed through expansion device 54, wherein the pressure of the stream can be reduced to thereby flash a portion of the stream. Although generally depicted as being an expansion valve or Joule-Thompson (JT) valve in
The resulting cooled, two-phase refrigerant stream in conduit 154 may then be reintroduced into another refrigerant warming pass 56 of primary heat exchanger 16, wherein the stream can be warmed to thereby providing refrigeration to one or more other fluid streams being cooled in primary heat exchanger 16, including the refrigerant streams in conduits 150 and 158 in respective cooling passes 52 and 58, the natural gas feed stream in conduit 110 in cooling pass 18, and/or the overhead vapor stream in conduit 114 in cooling pass 22.
According to one embodiment depicted in
As shown in
Turning now to
As shown in
According to one embodiment, the addition of refrigerant pump 64 to the lower liquid conduit 122 of refrigeration suction drum 28 may permit refrigeration cycle 12 to utilize refrigerants having different compositions than those suitable for use in the embodiment of LNG facility 10 shown in
Turning now to
As shown in
As shown in
Referring again to
Although described herein with respect to liquefying a natural gas stream, it should it should also be understood that processes and systems of the present invention may also be suitable for use in other gas processing and separation applications, including, but not limited to, ethane recovery and liquefaction, recovery of natural gas liquids (NGL), syngas separation and methane recovery, and cooling and separation of nitrogen and/or oxygen from various hydrocarbon-containing gas streams.
The preferred forms of the invention described above are to be used as illustration only, and should not be used in a limiting sense to interpret the scope of the present invention. Obvious modifications to the exemplary one embodiment, set forth above, could be readily made by those skilled in the art without departing from the spirit of the present invention. The inventors hereby state their intent to rely on the Doctrine of Equivalents to determine and assess the reasonably fair scope of the present invention as pertains to any apparatus not materially departing from but outside the literal scope of the invention as set forth in the following claims.
Number | Name | Date | Kind |
---|---|---|---|
2976695 | Meade | Oct 1961 | A |
3191395 | Maher et al. | Jun 1965 | A |
3210953 | Reed | Oct 1965 | A |
3271967 | Karbosky | Sep 1966 | A |
3596472 | Streich | Aug 1971 | A |
3729944 | Kelley et al. | May 1973 | A |
3800550 | Delahunty | Apr 1974 | A |
3932154 | Coers et al. | Jan 1976 | A |
4033735 | Swenson | Jul 1977 | A |
4036028 | Mandrin | Jul 1977 | A |
4217759 | Shenoy | Aug 1980 | A |
4249387 | Crowley | Feb 1981 | A |
4311496 | Fabian | Jan 1982 | A |
4411677 | Pervier et al. | Oct 1983 | A |
4525187 | Woodward et al. | Jun 1985 | A |
4584006 | Apffel | Apr 1986 | A |
4662919 | Davis | May 1987 | A |
4676812 | Kummann | Jun 1987 | A |
4707170 | Ayres et al. | Nov 1987 | A |
4714487 | Rowles | Dec 1987 | A |
4720294 | Lucadamo et al. | Jan 1988 | A |
4727723 | Durr | Mar 1988 | A |
4869740 | Campbell et al. | Sep 1989 | A |
4878932 | Phade et al. | Nov 1989 | A |
5051120 | Pahade et al. | Sep 1991 | A |
5148680 | Dray | Sep 1992 | A |
5182920 | Matsuoka et al. | Feb 1993 | A |
5275005 | Campbell et al. | Jan 1994 | A |
5351491 | Fabian | Oct 1994 | A |
5377490 | Howard et al. | Jan 1995 | A |
5379597 | Howard et al. | Jan 1995 | A |
5398497 | Suppes | Mar 1995 | A |
5497626 | Howard et al. | Mar 1996 | A |
5502972 | Howard et al. | Apr 1996 | A |
5555748 | Campbell et al. | Sep 1996 | A |
5566554 | Vijayaraghavan et al. | Oct 1996 | A |
5568737 | Campbell et al. | Oct 1996 | A |
5596883 | Bernhard et al. | Jan 1997 | A |
5615561 | Houshmand et al. | Apr 1997 | A |
5657643 | Price | Aug 1997 | A |
5771712 | Campbell et al. | Jun 1998 | A |
5791160 | Mandler et al. | Aug 1998 | A |
5799507 | Wilkinson et al. | Sep 1998 | A |
5881569 | Campbell et al. | Mar 1999 | A |
5890377 | Foglietta | Apr 1999 | A |
5890378 | Rambo et al. | Apr 1999 | A |
5950453 | Bowen et al. | Sep 1999 | A |
5979177 | Sumner et al. | Nov 1999 | A |
5983664 | Campbell et al. | Nov 1999 | A |
5983665 | Howard et al. | Nov 1999 | A |
5992175 | Yao et al. | Nov 1999 | A |
6003603 | Breivik et al. | Dec 1999 | A |
6021647 | Ameringer et al. | Feb 2000 | A |
6023942 | Thomas et al. | Feb 2000 | A |
6035651 | Carey | Mar 2000 | A |
6053008 | Arman et al. | Apr 2000 | A |
6070430 | McNeil et al. | Jun 2000 | A |
6085546 | Johnston | Jul 2000 | A |
6105390 | Bingham et al. | Aug 2000 | A |
6112550 | Bonaquist et al. | Sep 2000 | A |
6182469 | Campbell et al. | Feb 2001 | B1 |
6260380 | Arman et al. | Jul 2001 | B1 |
6266977 | Howard et al. | Jul 2001 | B1 |
6295833 | Hoffart et al. | Oct 2001 | B1 |
6298688 | Brostow | Oct 2001 | B1 |
6311516 | Key et al. | Nov 2001 | B1 |
6311519 | Gourbier et al. | Nov 2001 | B1 |
6330811 | Arman et al. | Dec 2001 | B1 |
6347531 | Roberts | Feb 2002 | B1 |
6363728 | Udischas et al. | Apr 2002 | B1 |
6367286 | Price | Apr 2002 | B1 |
6401486 | Lee et al. | Jun 2002 | B1 |
6405561 | Mortko et al. | Jun 2002 | B1 |
6412302 | Foglietta | Jul 2002 | B1 |
6425263 | Bingham et al. | Jul 2002 | B1 |
6425266 | Roberts | Jul 2002 | B1 |
6427483 | Rashad et al. | Aug 2002 | B1 |
6438994 | Rashad et al. | Aug 2002 | B1 |
6449982 | Fischer | Sep 2002 | B1 |
6449983 | Pozivil | Sep 2002 | B2 |
6460350 | Johnson et al. | Oct 2002 | B2 |
6560989 | Roberts et al. | May 2003 | B1 |
6578379 | Paradowski | Jun 2003 | B2 |
6581410 | Johnson et al. | Jun 2003 | B1 |
6662589 | Roberts et al. | Dec 2003 | B1 |
6725688 | Elion et al. | Apr 2004 | B2 |
6745576 | Granger | Jun 2004 | B1 |
6823691 | Ohta | Nov 2004 | B2 |
6823692 | Patel et al. | Nov 2004 | B1 |
6915662 | Wilkinson et al. | Jul 2005 | B2 |
6925837 | Eaton | Aug 2005 | B2 |
6945075 | Wilkinson et al. | Sep 2005 | B2 |
7051553 | Mak et al. | May 2006 | B2 |
7069744 | Patel et al. | Jul 2006 | B2 |
7100399 | Eaton | Sep 2006 | B2 |
7107788 | Patel et al. | Sep 2006 | B2 |
7114342 | Oldham et al. | Oct 2006 | B2 |
7152428 | Lee et al. | Dec 2006 | B2 |
7152429 | Paradowski | Dec 2006 | B2 |
7159417 | Foglietta et al. | Jan 2007 | B2 |
7191617 | Cuellar et al. | Mar 2007 | B2 |
7204100 | Wilkinson et al. | Apr 2007 | B2 |
7210311 | Wilkinson et al. | May 2007 | B2 |
7216507 | Cuellar et al. | May 2007 | B2 |
7219513 | Mostafa | May 2007 | B1 |
7234321 | Maunder et al. | Jun 2007 | B2 |
7234322 | Hahn et al. | Jun 2007 | B2 |
7266975 | Hupkes et al. | Sep 2007 | B2 |
7310972 | Yoshida et al. | Dec 2007 | B2 |
7316127 | Huebel et al. | Jan 2008 | B2 |
7357003 | Ohara et al. | Apr 2008 | B2 |
7484385 | Patel et al. | Feb 2009 | B2 |
7614241 | Mostello | Nov 2009 | B2 |
7644676 | Lee et al. | Jan 2010 | B2 |
7713497 | Mak | May 2010 | B2 |
7793517 | Patel et al. | Sep 2010 | B2 |
7818979 | Patel et al. | Oct 2010 | B2 |
7841288 | Lee et al. | Nov 2010 | B2 |
7856847 | Patel et al. | Dec 2010 | B2 |
8505312 | Mak et al. | Aug 2013 | B2 |
8549876 | Kaart et al. | Oct 2013 | B2 |
8650906 | Price et al. | Feb 2014 | B2 |
8671699 | Rosetta et al. | Mar 2014 | B2 |
20020166336 | Wilkinson et al. | Nov 2002 | A1 |
20030029190 | Trebble | Feb 2003 | A1 |
20030046953 | Elion et al. | Mar 2003 | A1 |
20040159122 | Patel et al. | Aug 2004 | A1 |
20050056051 | Roberts et al. | Mar 2005 | A1 |
20050204625 | Briscoe et al. | Sep 2005 | A1 |
20060260355 | Roberts et al. | Nov 2006 | A1 |
20060260358 | Kun | Nov 2006 | A1 |
20070157663 | Mak et al. | Jul 2007 | A1 |
20070231244 | Shah et al. | Oct 2007 | A1 |
20080264076 | Price et al. | Oct 2008 | A1 |
20090193846 | Foral et al. | Aug 2009 | A1 |
20090205367 | Price | Aug 2009 | A1 |
20090217701 | Minta et al. | Sep 2009 | A1 |
20100043488 | Mak et al. | Feb 2010 | A1 |
20100064725 | Chieng et al. | Mar 2010 | A1 |
20100132405 | Nilsen | Jun 2010 | A1 |
20110289963 | Price | Dec 2011 | A1 |
20120000245 | Currence et al. | Jan 2012 | A1 |
20120090324 | Rosetta et al. | Apr 2012 | A1 |
20120137726 | Currence | Jun 2012 | A1 |
20130213807 | Hanko et al. | Aug 2013 | A1 |
Number | Date | Country |
---|---|---|
201463463 | May 2010 | CN |
200018049 | Jan 2000 | JP |
20025398 | Jan 2002 | JP |
2003232226 | Aug 2003 | JP |
2005045338 | May 2005 | WO |
WO2009151418 | Dec 2009 | WO |
Entry |
---|
International Search Report and Written Opinion for PCT/US2015/016551 dated May 22, 2015, 8 pages. |
Gas Processors Suppliers Association (GPSA) Engineering Databook, Section 16, “Hydrocarbon Recovery,” p. 16-13 through 16-20, 12th ed. (2004). |
Number | Date | Country | |
---|---|---|---|
20150260451 A1 | Sep 2015 | US |