EP1929227B1 - Natural gas liquefaction process for lng - Google Patents
Natural gas liquefaction process for lng Download PDFInfo
- Publication number
- EP1929227B1 EP1929227B1 EP06760347.2A EP06760347A EP1929227B1 EP 1929227 B1 EP1929227 B1 EP 1929227B1 EP 06760347 A EP06760347 A EP 06760347A EP 1929227 B1 EP1929227 B1 EP 1929227B1
- Authority
- EP
- European Patent Office
- Prior art keywords
- gas stream
- heat exchange
- cooled
- expanded
- refrigerant
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
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- VNWKTOKETHGBQD-UHFFFAOYSA-N methane Chemical compound C VNWKTOKETHGBQD-UHFFFAOYSA-N 0.000 title claims description 68
- 238000000034 method Methods 0.000 title claims description 66
- 230000008569 process Effects 0.000 title claims description 60
- 239000003345 natural gas Substances 0.000 title description 21
- 239000007789 gas Substances 0.000 claims description 211
- 239000003507 refrigerant Substances 0.000 claims description 96
- 238000001816 cooling Methods 0.000 claims description 94
- IJGRMHOSHXDMSA-UHFFFAOYSA-N Atomic nitrogen Chemical compound N#N IJGRMHOSHXDMSA-UHFFFAOYSA-N 0.000 claims description 28
- 238000005057 refrigeration Methods 0.000 claims description 21
- 229910052757 nitrogen Inorganic materials 0.000 claims description 14
- 239000012809 cooling fluid Substances 0.000 claims description 6
- 238000011084 recovery Methods 0.000 claims 2
- 238000007906 compression Methods 0.000 description 37
- 230000006835 compression Effects 0.000 description 36
- 239000003949 liquefied natural gas Substances 0.000 description 29
- 239000000203 mixture Substances 0.000 description 10
- 239000000446 fuel Substances 0.000 description 8
- 239000007788 liquid Substances 0.000 description 7
- 230000000153 supplemental effect Effects 0.000 description 7
- 230000008901 benefit Effects 0.000 description 6
- 238000010586 diagram Methods 0.000 description 6
- 241000196324 Embryophyta Species 0.000 description 4
- ATUOYWHBWRKTHZ-UHFFFAOYSA-N Propane Chemical compound CCC ATUOYWHBWRKTHZ-UHFFFAOYSA-N 0.000 description 4
- 238000004519 manufacturing process Methods 0.000 description 4
- 230000004048 modification Effects 0.000 description 4
- 238000012986 modification Methods 0.000 description 4
- 239000000126 substance Substances 0.000 description 3
- 238000009833 condensation Methods 0.000 description 2
- 230000005494 condensation Effects 0.000 description 2
- 239000000356 contaminant Substances 0.000 description 2
- 239000002826 coolant Substances 0.000 description 2
- 238000004821 distillation Methods 0.000 description 2
- 230000010354 integration Effects 0.000 description 2
- 239000012071 phase Substances 0.000 description 2
- 239000000047 product Substances 0.000 description 2
- 239000001294 propane Substances 0.000 description 2
- 230000009467 reduction Effects 0.000 description 2
- OTMSDBZUPAUEDD-UHFFFAOYSA-N Ethane Chemical compound CC OTMSDBZUPAUEDD-UHFFFAOYSA-N 0.000 description 1
- VGGSQFUCUMXWEO-UHFFFAOYSA-N Ethene Chemical compound C=C VGGSQFUCUMXWEO-UHFFFAOYSA-N 0.000 description 1
- 239000005977 Ethylene Substances 0.000 description 1
- 241000183024 Populus tremula Species 0.000 description 1
- 230000005540 biological transmission Effects 0.000 description 1
- 239000001273 butane Substances 0.000 description 1
- 239000000498 cooling water Substances 0.000 description 1
- 239000010779 crude oil Substances 0.000 description 1
- 238000006073 displacement reaction Methods 0.000 description 1
- 230000008030 elimination Effects 0.000 description 1
- 238000003379 elimination reaction Methods 0.000 description 1
- 238000005516 engineering process Methods 0.000 description 1
- 230000002349 favourable effect Effects 0.000 description 1
- 239000007791 liquid phase Substances 0.000 description 1
- IJDNQMDRQITEOD-UHFFFAOYSA-N n-butane Chemical compound CCCC IJDNQMDRQITEOD-UHFFFAOYSA-N 0.000 description 1
- OFBQJSOFQDEBGM-UHFFFAOYSA-N n-pentane Natural products CCCCC OFBQJSOFQDEBGM-UHFFFAOYSA-N 0.000 description 1
- 238000010587 phase diagram Methods 0.000 description 1
- 238000004088 simulation Methods 0.000 description 1
- 239000013589 supplement Substances 0.000 description 1
- 230000007704 transition Effects 0.000 description 1
- XLYOFNOQVPJJNP-UHFFFAOYSA-N water Substances O XLYOFNOQVPJJNP-UHFFFAOYSA-N 0.000 description 1
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- F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
- F25—REFRIGERATION OR COOLING; COMBINED HEATING AND REFRIGERATION SYSTEMS; HEAT PUMP SYSTEMS; MANUFACTURE OR STORAGE OF ICE; LIQUEFACTION SOLIDIFICATION OF GASES
- F25J—LIQUEFACTION, SOLIDIFICATION OR SEPARATION OF GASES OR GASEOUS OR LIQUEFIED GASEOUS MIXTURES BY PRESSURE AND COLD TREATMENT OR BY BRINGING THEM INTO THE SUPERCRITICAL STATE
- F25J3/00—Processes or apparatus for separating the constituents of gaseous or liquefied gaseous mixtures involving the use of liquefaction or solidification
- F25J3/02—Processes or apparatus for separating the constituents of gaseous or liquefied gaseous mixtures involving the use of liquefaction or solidification by rectification, i.e. by continuous interchange of heat and material between a vapour stream and a liquid stream
- F25J3/0228—Processes or apparatus for separating the constituents of gaseous or liquefied gaseous mixtures involving the use of liquefaction or solidification by rectification, i.e. by continuous interchange of heat and material between a vapour stream and a liquid stream characterised by the separated product stream
- F25J3/0257—Processes or apparatus for separating the constituents of gaseous or liquefied gaseous mixtures involving the use of liquefaction or solidification by rectification, i.e. by continuous interchange of heat and material between a vapour stream and a liquid stream characterised by the separated product stream separation of nitrogen
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- F25J1/00—Processes or apparatus for liquefying or solidifying gases or gaseous mixtures
- F25J1/0002—Processes or apparatus for liquefying or solidifying gases or gaseous mixtures characterised by the fluid to be liquefied
- F25J1/0022—Hydrocarbons, e.g. natural gas
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- F25J1/003—Processes or apparatus for liquefying or solidifying gases or gaseous mixtures characterised by the kind of cold generation within the liquefaction unit for compensating heat leaks and liquid production
- F25J1/0032—Processes or apparatus for liquefying or solidifying gases or gaseous mixtures characterised by the kind of cold generation within the liquefaction unit for compensating heat leaks and liquid production using the feed stream itself or separated fractions from it, i.e. "internal refrigeration"
- F25J1/0035—Processes or apparatus for liquefying or solidifying gases or gaseous mixtures characterised by the kind of cold generation within the liquefaction unit for compensating heat leaks and liquid production using the feed stream itself or separated fractions from it, i.e. "internal refrigeration" by gas expansion with extraction of work
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- F25J3/0209—Natural gas or substitute natural gas
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- F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
- F25—REFRIGERATION OR COOLING; COMBINED HEATING AND REFRIGERATION SYSTEMS; HEAT PUMP SYSTEMS; MANUFACTURE OR STORAGE OF ICE; LIQUEFACTION SOLIDIFICATION OF GASES
- F25J—LIQUEFACTION, SOLIDIFICATION OR SEPARATION OF GASES OR GASEOUS OR LIQUEFIED GASEOUS MIXTURES BY PRESSURE AND COLD TREATMENT OR BY BRINGING THEM INTO THE SUPERCRITICAL STATE
- F25J3/00—Processes or apparatus for separating the constituents of gaseous or liquefied gaseous mixtures involving the use of liquefaction or solidification
- F25J3/02—Processes or apparatus for separating the constituents of gaseous or liquefied gaseous mixtures involving the use of liquefaction or solidification by rectification, i.e. by continuous interchange of heat and material between a vapour stream and a liquid stream
- F25J3/0228—Processes or apparatus for separating the constituents of gaseous or liquefied gaseous mixtures involving the use of liquefaction or solidification by rectification, i.e. by continuous interchange of heat and material between a vapour stream and a liquid stream characterised by the separated product stream
- F25J3/0233—Processes or apparatus for separating the constituents of gaseous or liquefied gaseous mixtures involving the use of liquefaction or solidification by rectification, i.e. by continuous interchange of heat and material between a vapour stream and a liquid stream characterised by the separated product stream separation of CnHm with 1 carbon atom or more
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- F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
- F25—REFRIGERATION OR COOLING; COMBINED HEATING AND REFRIGERATION SYSTEMS; HEAT PUMP SYSTEMS; MANUFACTURE OR STORAGE OF ICE; LIQUEFACTION SOLIDIFICATION OF GASES
- F25J—LIQUEFACTION, SOLIDIFICATION OR SEPARATION OF GASES OR GASEOUS OR LIQUEFIED GASEOUS MIXTURES BY PRESSURE AND COLD TREATMENT OR BY BRINGING THEM INTO THE SUPERCRITICAL STATE
- F25J2200/00—Processes or apparatus using separation by rectification
- F25J2200/70—Refluxing the column with a condensed part of the feed stream, i.e. fractionator top is stripped or self-rectified
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- F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
- F25—REFRIGERATION OR COOLING; COMBINED HEATING AND REFRIGERATION SYSTEMS; HEAT PUMP SYSTEMS; MANUFACTURE OR STORAGE OF ICE; LIQUEFACTION SOLIDIFICATION OF GASES
- F25J—LIQUEFACTION, SOLIDIFICATION OR SEPARATION OF GASES OR GASEOUS OR LIQUEFIED GASEOUS MIXTURES BY PRESSURE AND COLD TREATMENT OR BY BRINGING THEM INTO THE SUPERCRITICAL STATE
- F25J2205/00—Processes or apparatus using other separation and/or other processing means
- F25J2205/02—Processes or apparatus using other separation and/or other processing means using simple phase separation in a vessel or drum
- F25J2205/04—Processes or apparatus using other separation and/or other processing means using simple phase separation in a vessel or drum in the feed line, i.e. upstream of the fractionation step
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- F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
- F25—REFRIGERATION OR COOLING; COMBINED HEATING AND REFRIGERATION SYSTEMS; HEAT PUMP SYSTEMS; MANUFACTURE OR STORAGE OF ICE; LIQUEFACTION SOLIDIFICATION OF GASES
- F25J—LIQUEFACTION, SOLIDIFICATION OR SEPARATION OF GASES OR GASEOUS OR LIQUEFIED GASEOUS MIXTURES BY PRESSURE AND COLD TREATMENT OR BY BRINGING THEM INTO THE SUPERCRITICAL STATE
- F25J2210/00—Processes characterised by the type or other details of the feed stream
- F25J2210/06—Splitting of the feed stream, e.g. for treating or cooling in different ways
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- F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
- F25—REFRIGERATION OR COOLING; COMBINED HEATING AND REFRIGERATION SYSTEMS; HEAT PUMP SYSTEMS; MANUFACTURE OR STORAGE OF ICE; LIQUEFACTION SOLIDIFICATION OF GASES
- F25J—LIQUEFACTION, SOLIDIFICATION OR SEPARATION OF GASES OR GASEOUS OR LIQUEFIED GASEOUS MIXTURES BY PRESSURE AND COLD TREATMENT OR BY BRINGING THEM INTO THE SUPERCRITICAL STATE
- F25J2220/00—Processes or apparatus involving steps for the removal of impurities
- F25J2220/60—Separating impurities from natural gas, e.g. mercury, cyclic hydrocarbons
- F25J2220/62—Separating low boiling components, e.g. He, H2, N2, Air
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- F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
- F25—REFRIGERATION OR COOLING; COMBINED HEATING AND REFRIGERATION SYSTEMS; HEAT PUMP SYSTEMS; MANUFACTURE OR STORAGE OF ICE; LIQUEFACTION SOLIDIFICATION OF GASES
- F25J—LIQUEFACTION, SOLIDIFICATION OR SEPARATION OF GASES OR GASEOUS OR LIQUEFIED GASEOUS MIXTURES BY PRESSURE AND COLD TREATMENT OR BY BRINGING THEM INTO THE SUPERCRITICAL STATE
- F25J2230/00—Processes or apparatus involving steps for increasing the pressure of gaseous process streams
- F25J2230/08—Cold compressor, i.e. suction of the gas at cryogenic temperature and generally without afterstage-cooler
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- F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
- F25—REFRIGERATION OR COOLING; COMBINED HEATING AND REFRIGERATION SYSTEMS; HEAT PUMP SYSTEMS; MANUFACTURE OR STORAGE OF ICE; LIQUEFACTION SOLIDIFICATION OF GASES
- F25J—LIQUEFACTION, SOLIDIFICATION OR SEPARATION OF GASES OR GASEOUS OR LIQUEFIED GASEOUS MIXTURES BY PRESSURE AND COLD TREATMENT OR BY BRINGING THEM INTO THE SUPERCRITICAL STATE
- F25J2230/00—Processes or apparatus involving steps for increasing the pressure of gaseous process streams
- F25J2230/30—Compression of the feed stream
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- F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
- F25—REFRIGERATION OR COOLING; COMBINED HEATING AND REFRIGERATION SYSTEMS; HEAT PUMP SYSTEMS; MANUFACTURE OR STORAGE OF ICE; LIQUEFACTION SOLIDIFICATION OF GASES
- F25J—LIQUEFACTION, SOLIDIFICATION OR SEPARATION OF GASES OR GASEOUS OR LIQUEFIED GASEOUS MIXTURES BY PRESSURE AND COLD TREATMENT OR BY BRINGING THEM INTO THE SUPERCRITICAL STATE
- F25J2270/00—Refrigeration techniques used
- F25J2270/04—Internal refrigeration with work-producing gas expansion loop
- F25J2270/06—Internal refrigeration with work-producing gas expansion loop with multiple gas expansion loops
Definitions
- Embodiments of the invention relate to a process for liquefaction of natural gas and other methane-rich gas streams, and more particularly to a process for producing liquefied natural gas (LNG).
- LNG liquefied natural gas
- LNG liquefied natural gas
- the refrigerants used may be a mixture of components such as methane, ethane, propane, butane, and nitrogen in multi-component refrigeration cycles.
- the refrigerants may also be pure substances such as propane, ethylene, or nitrogen in "cascade cycles.” Substantial volumes of these refrigerants with close control of composition are required. Further, such refrigerants may have to be imported and stored imposing logistics requirements.
- some of the components of the refrigerant may be prepared, typically by a distillation process integrated with the liquefaction process.
- the use of gas expanders to provide the feed gas cooling thereby eliminating or reducing the logistical problems of refrigerant handling has been of interest to process engineers.
- the expander system operates on the principle that the feed gas can be allowed to expand through an expansion turbine, thereby performing work and reducing the temperature of the gas.
- the low temperature gas is then heat exchanged with the feed gas to provide the refrigeration needed.
- Supplemental refrigeration is typically needed to fully liquefy the feed gas and this may be provided by a refrigerant system.
- the power obtained from the expansion is usually used to supply part of the main compression power used in the refrigeration cycle.
- the typical expander cycle for making LNG operates at the feed gas pressure, typically under about 6,895 kPa (1,000 psia).
- U.S. Patent No. 6,378,330 B1 is directed to liquefying a pressurized gas stream rich in methane, the process including withdrawing and entropically expanding a first fraction of the pressurized feed stream, preferably above 11.000 kPa, to a lower pressure and cooling a second fraction of the pressurized feed stream by indirect heat exchange with the expanded first fraction followed by expanding the second fraction to a lower pressure.
- 2003/0177785 A1 is directed to cooling and expanding a gas stream to liquefy the gas stream and subsequently withdrawing the liquefied gas stream as a pressurized product with a portion recycled through the heat exchanger to provide cooling which helps keep the cooling and compression of the gas stream in the supercritical region of the phase diagram.
- FR 2 714 722 is directed to liquefying a natural gas whereby during expansion of the gas stream the gas changes from a dense phase to a liquid phase without undergoing a phase transition.
- Embodiments of the present invention provide a process for liquefying natural gas and other methane-rich gas streams to produce liquefied natural gas (LNG) and/or other liquefied methane-rich gases.
- natural gas as used in this specification, including the appended claims, means a gaseous feed stock suitable for manufacturing LNG.
- the natural gas could comprise gas obtained from a crude oil well (associated gas) or from a gas well (non-associated gas).
- the composition of natural gas can vary significantly.
- natural gas is a methane-rich gas containing methane (C 1 ) as a major component.
- a process for liquefying a gas stream rich in methane comprising providing a gas stream rich in methane at a pressure less than 1,000 psia (6895 kPa); providing a refrigerant at a pressure of less than 1,000 psia (6895 kPa); compressing said refrigerant to a pressure greater than or equal to 1500 psia (10342 kPa) to provide a compressed refrigerant; cooling said compressed refrigerant by indirect heat exchange with a cooling fluid; expanding said compressed refrigerant to further cool said compressed refrigerant, thereby producing an expanded, cooled refrigerant; passing said expanded, cooled refrigerant to a heat exchange area; and passing said gas stream through said heat exchange area to cool at least part of said gas stream by indirect heat exchange with said expanded, cooled refrigerant, thereby forming a cooled gas stream.
- the providing the refrigerant at a pressure of less than 1,000 psia (6895 kPa) comprises withdrawing a portion of the gas at a pressure of less than 1,000 psia (6895 kPa) for use as the refrigerant.
- the portion of the gas stream to be used as the refrigerant is withdrawn from the gas stream before the gas stream is passed to the heat exchange area.
- the process according to the present invention further comprises providing at least a portion of the refrigeration duty for the heat exchange area using a closed loop charged with flash vapor produced in the process for liquefying the gas stream rich in methane. Additional embodiments according to the present invention will be apparent to those skilled in the art.
- Embodiments of the present invention provide a process for natural gas liquefaction using primarily gas expanders and eliminating the need for external refrigerants. That is the feed gas itself (e.g., natural gas) is used as the refrigerant in all refrigeration cycles. Such refrigeration cycles do not require supplemental cooling using external refrigerants (i.e., refrigerants other than the feed gas itself or gas that is produced at or near the LNG process plant) as typical proposed gas expander cycles do, yet such refrigeration cycles have a higher efficiency.
- cooling water or air are the only external sources of cooling fluids and are used for compressor inter-stage or after cooling.
- FIG. 1 illustrates one embodiment of the present invention in which an expander loop 5 (i.e., an expander cycle) and a sub-cooling loop 6 are used.
- expander loop 5 and sub-cooling loop 6 are shown with double-width lines in FIG. 1 .
- the terms "loop” and "cycle” are used interchangeably.
- feed gas stream 10 enters the liquefaction process at a pressure less than 1000 psia, or less than 900 psia (6205 kPa), or less than 800 psia (5516 kPa), or less than 700 psia (4826 kPa), or less than 600 psia (4137 kPa).
- the pressure of feed gas stream 10 will be about 800 psia (5516 kPa).
- Feed gas stream 10 generally comprises natural gas that has been treated to remove contaminants using processes and equipment that are well known in the art. Before it is passed to a heat exchanger, a portion of feed gas stream 10 is withdrawn to form side stream 11, thus providing, as will be apparent from the following discussion, a refrigerant at a pressure corresponding to the pressure of feed gas stream 10, namely any of the above pressures, including a pressure of less than 1000 psia (6895 kPa). Thus, in the embodiment shown in FIG. 1 , a portion of the feed gas stream is used as the refrigerant for expander loop 5. Although the embodiment shown in FIG.
- the present method is any of the other embodiments herein described, wherein the portion of the feed gas stream to be used as the refrigerant is withdrawn from the heat exchange area, expanded, and passed back to the heat exchange area to provide at least part of the refrigeration duty for the heat exchange area.
- Side stream 11 is passed to compression unit 20 where it is compressed to a pressure greater than or equal to 1500 psia (10342 kPa), thus providing compressed refrigerant stream 12.
- side stream 11 is compressed to a pressure greater than or equal to 1600 psia (11032 kPa), or greater than or equal to 1700 psia (11721 kPa), or greater than or equal to 1800 psia (12411 kPa), or greater than or equal to 1900 psia (13100 kPa), or greater than or equal to 2000 psia (13790 kPa), or greater than or equal to 2500 psia (17237 kPa), or greater than or equal to 3000 psia (20684 kPa), thus providing compressed refrigerant stream 12.
- compression unit means any one type or combination of similar or different types of compression equipment, and may include auxiliary equipment, known in the art for compressing a substance or mixture of substances.
- a “compression unit” may utilize one or more compression stages.
- Illustrative compressors may include, but are not limited to, positive displacement types, such as reciprocating and rotary compressors for example, and dynamic types, such as centrifugal and axial flow compressors, for example.
- compressed refrigerant stream 12 is passed to cooler 30 where it is cooled by indirect heat exchange with a suitable cooling fluid to provide a compressed, cooled refrigerant.
- cooler 30 is of the type that provides water or air as the cooling fluid, although any type of cooler can be used.
- the temperature of compressed refrigerant stream 12 as it emerges from cooler 30 depends on the ambient conditions and the cooling medium used and is typically from about 35 °F (1.7 °C) to about 105 °F (40.5 °C).
- Cooled compressed refrigerant stream 12 is then passed to expander 40 where it is expanded and consequently cooled to form expanded refrigerant stream 13.
- expander 40 is a work-expansion device, such as gas expander producing work that may be extracted and used for compression.
- Expanded refrigerant stream 13 is passed to heat exchange area 50 to provide at least part of the refrigeration duty for heat exchange area 50.
- heat exchange area means any one type or combination of similar or different types of equipment known in the art for facilitating heat transfer.
- a "heat exchange area” may be contained within a single piece of equipment, or it may comprise areas contained in a plurality of equipment pieces. Conversely, multiple heat exchange areas may be contained in a single piece of equipment.
- feed gas stream 10 is sub-cooled by sub-cooling loop 6 (described below) to produce sub-cooled stream 10a.
- Sub-cooled stream 10a is then expanded to a lower pressure in expander 70, thereby partially liquefying sub-cooled stream 10a to form a liquid fraction and a remaining vapor fraction.
- Expander 70 may be any pressure reducing device, including, but not limited to a valve, control valve, Joule Thompson valve, Venturi device, liquid expander, hydraulic turbine, and the like.
- Partially liquefied sub-cooled stream 10a is passed to surge tank 80 where the liquefied fraction 15 is withdrawn from the process as LNG having a temperature corresponding to the bubble point pressure.
- flash vapor stream 16 is used as fuel to power the compressor units and/or as a refrigerant in sub-cooling loop 6 as described below. Prior to being used as fuel, all or a portion of flash vapor stream 16 may optionally be passed from surge tank 80 to heat exchange areas 50 and 55 to supplement the cooling provided in such heat exchange areas.
- a portion of flash vapor 16 is withdrawn through line 17 to fill sub-cooling loop 6.
- a portion of the feed gas from feed gas stream 10 is withdrawn (in the form of flash gas from flash gas stream 16 ) for use as the refrigerant in sub-cooling loop 6.
- make-up gas i.e., additional flash vapor from line 17
- expanded stream 18 is discharged from expander 41 and drawn through heat exchange areas 55 and 50.
- Expanded flash vapor stream 18 (the sub-cooling refrigerant stream) is then returned to compression unit 90 where it is re-compressed to a higher pressure and warmed.
- the re-compressed sub-cooling refrigerant stream is cooled in cooler 31, which can be of the same type as cooler 30, although any type of cooler may be used.
- the re-compressed sub-cooling refrigerant stream is passed to heat exchange area 50 where it is further cooled by indirect heat exchange with expanded refrigerant stream 13, sub-cooling refrigerant stream 18, and, optionally, flash vapor stream 16.
- the present method is any of the other embodiments disclosed herein further comprising providing cooling using a closed loop (e.g., sub-cooling loop 6 ) charged with flash vapor resulting from the LNG production (e.g., flash vapor 16 ).
- feed gas stream 10 passes from one heat exchange area to another, the temperature of feed gas stream 10 will be reduced until ultimately a sub-cooled stream is produced.
- mass flow rate of feed gas stream 10 will be reduced.
- Other modifications, such as compression, may also be made to feed gas stream 10. While each such modification to feed gas stream 10 could be considered to produce a new and different stream, for clarity and ease of illustration, the feed gas stream will be referred to as feed gas stream 10 unless otherwise indicated, with the understanding that passage through heat exchange areas, the taking of side streams, and other modifications will produce temperature, pressure, and/or flow rate changes to feed gas stream 10.
- FIG. 2 illustrates an unclaimed embodiment of the present invention that is similar to the embodiment shown in FIG. 1 , except that expander loop 5 has been replaced with expander loop 7.
- Expander loop 7 is shown with double-width lines in FIG. 2 for clarity. Expander loop 7 utilizes substantially the same equipment as expander loop 5 (for example, compressor 20, cooler 30, and expander 40, all of which have been described above).
- the gaseous refrigerant in expander loop 7 however, is de-coupled from the feed gas and may therefore have a different composition than the feed gas. That is, expander loop 7 is essentially a closed loop and is not connected to feed gas stream 10.
- the refrigerant for expander loop 7 is therefore not necessarily the feed gas, although it may be.
- Expander loop 7 may be charged with any suitable refrigerant gas that is produced at or near the LNG process plant in which expander loop 7 is utilized.
- the refrigerant gas used to charge expander loop 7 could be a feed gas, such as natural gas, that has only been partially treated to remove contaminants.
- expander loop 7 is a high pressure gas loop.
- Stream 12a exits compression unit 20 at a pressure greater than or equal to about 1500 psia (10342 kPa), or greater than or equal to about 1600 psia (11032 kPa), or greater than or equal to about 1700 psia (11721 kPa), or greater than or equal to about 1800 psia (12411 kPa), or greater than or equal to about 1900 psia (13100 kPa), or greater than or equal to about 2000 psia (13790 kPa), or greater than or equal to about 2500 psia (17237 kPa), or greater than or equal to about 3000 psia (20684 kPa).
- the temperature of compressed refrigerant stream 12a as it emerges from cooler 30 depends on the ambient conditions and the cooling medium used and is typically about from about 35 °F (1.7 °C) to about 105 °F (40.5 °C). Cooled compressed refrigerant stream 12a is then passed to expander 40 where it is expanded and further cooled to form expanded refrigerant stream 13a. Expanded refrigerant stream 13a is passed to heat exchange area 50 to provide at least part of the refrigeration duty for heat exchange area 50, where feed gas stream 10 is at least partially cooled by indirect heat exchange with expanded refrigerant stream 13a. Upon exiting heat exchange area 50, expanded refrigerant stream 13a is returned to compression unit 20 for re-compression.
- expander loops 5 and 7 may be used interchangeably. For example, in an embodiment utilizing expander loop 5, expander loop 7 may be substituted for expander loop 5.
- FIG. 3 shows another embodiment for producing LNG in accordance with the process of the invention.
- the process illustrated in FIG. 3 utilizes a plurality of work expansion cycles to provide supplemental cooling for the feed gas and other streams.
- the use of such work expansion cycles results in overall improved efficiency for the liquefaction process.
- feed gas stream 10 again enters the liquefaction process at the pressures described above.
- side stream 11 is fed to expander loop 5 in the manner previously described, but it will be apparent in an unclaimed aspect of the invention that closed expander loop 7 could be utilized in the place of expander loop 5, in which case side stream 11 would not be necessary.
- Expander loop 5 operates in the same manner as described above for the embodiment shown in FIG. 1 , except that expanded refrigerant stream 13 is passed through heat exchange area 56, described in detail below, to provide at least a part of the refrigeration duty for heat exchange area 56.
- feed gas stream 10 is passed to heat exchange area 56 where it is cooled, at least in part, by indirect heat exchange with expanded refrigerant stream 13 and other streams described below.
- feed gas stream 10 is passed through heat exchange areas 57 and 58 where it is further cooled by indirect heat exchange with additional streams described below.
- first and second work expansion cycles are utilized for improved efficiency as follows: before feed gas stream 10 enters heat exchange area 57, side stream 11b is taken from feed gas stream 10. After feed gas stream 10 exits heat exchange area 57, but before it enters heat exchange area 58, side stream 11c is taken from feed gas stream 10.
- side streams 11b and 11c are taken from feed gas stream 10 at different stages of feed gas stream cooling. That is, each side stream is withdrawn from the feed gas stream at a different point on the cooling curve of the feed gas such that each successively withdrawn side stream has a lower initial temperature than the previously withdrawn side stream.
- expanded streams 13b and 13c are passed to compression units 61 and 62, respectively, where they are re-compressed and combined to form stream 14a.
- Stream 14a is cooled by cooler 32 prior to being re-combined with feed gas stream 10.
- Cooler 32 can be the same type of cooler or cooler types as coolers 30 and 31.
- Expanders 42 and 43 are work expansion devices of the type well know to those of skill in the art. Illustrative, non-limiting examples of suitable work expansion devices include liquid expanders and hydraulic turbines.
- the feed gas stream is further cooled using a plurality of work expansion devices. It will be apparent to those of ordinary skill in the art that additional work expansion cycles can be added to the embodiment illustrated in FIG.
- each of the work expansion devices expands a portion of the feed gas stream and thereby cools such portion, wherein each of the portions of the feed gas stream expanded in the work expansion devices is withdrawn from the feed gas stream at a different stage of feed gas stream cooling (i.e., at a different feed gas stream temperature).
- the work expansion devices are utilized by withdrawing one or more side streams from the feed gas stream; passing said one or more side streams to one or more work expansion devices; expanding said one of more side streams to expand and cool said one or more side streams, thereby forming one or more expanded, cooled side streams; passing said one or more expanded, cooled side streams to at least one heat exchange area; passing said gas stream through said at least one heat exchange area; and at least partially cooling said gas stream by indirect heat exchange with said one or more expanded, cooled side streams.
- feed gas stream 10 after being cooled in heat exchange areas 56, 57, and 58, is then passed to heat exchange area 59 where it is further cooled to produce sub-cooled stream 10a.
- the principal function of heat exchange area 59 is to sub-cool feed gas stream 10.
- Sub-cooled stream 10a is then expanded to a lower pressure in expander 85, thereby partially liquefying sub-cooled stream 10a to form a liquid fraction and a remaining vapor fraction.
- Expander 85 may be any pressure reducing device, including, but not limited to a valve, control valve, Joule Thompson valve, Venturi device, liquid expander, hydraulic turbine, and the like.
- Partially liquefied sub-cooled stream 10a is passed to surge tank 80 where the liquefied fraction 15 is withdrawn from the process as LNG having a temperature corresponding to the bubble point pressure.
- the remaining vapor fraction (flash vapor) stream 16 is used as fuel to power the compressor units and/or as a refrigerant in sub-cooling loop 8 in a manner substantially the same as previously described for sub-cooling loop 6.
- sub-cooling loop 8 is similar to sub-cooling loop 6, except that sub-cooling loop 8 supplies cooling to four heat exchange areas (heat exchange areas 56, 57, 58, and 59 ).
- FIG. 4 illustrates yet another embodiment of the present invention.
- the embodiment shown in FIG. 4 is substantially the same as the embodiment shown in FIG. 3 , except that compression unit 25 and expander 35 have been added.
- Expander 35 may be any type of liquid expander or hydraulic turbine. Expander 35 is placed between heat exchange areas 58 and 59 such that feed gas stream 10 flows from heat exchange area 58 into expander 35 where it is expanded, and consequently cooled to produce expanded feed gas stream 10b. Stream 10b then is passed to heat exchange area 59 where it is sub-cooled to produce sub-cooled stream 10c.
- the overall cooling load on sub-cooling loop 8 is advantageously reduced.
- the present method is any of the other embodiments disclosed herein further comprising expanding at least a portion of the cooled feed gas stream to produce a cooled, expanded feed gas stream (e.g., stream 10b ); and further cooling the cooled, expanded feed gas stream by indirect heat exchange with a closed loop (e.g., sub-cooling loop 6 or 8 ) charged with flash vapor resulting from the LNG production (e.g., flash vapor 16 ).
- a closed loop e.g., sub-cooling loop 6 or 8
- compression unit 25 is utilized to increase the pressure of feed gas stream 10 prior to entry into the liquefaction process.
- feed gas stream 10 is passed to compression unit 25 where it is compressed to a pressure above the feed gas supply pressure or, in one or more unclaimed embodiments, to a pressure greater than about 1200 psia (8274 kPa).
- feed gas stream 10 is compressed to a pressure greater than or equal to about 1300 psia (8963 kPa), or greater than or equal to about 1400 psia (9653 kPa), or greater than or equal to about 1500 psia (10342 kPa), or greater than or equal to about 1600 psia (11032 kPa), or greater than or equal to about 1700 psia (11721 kPa), or greater than or equal to about 1800 psia (12411 kPa), or greater than or equal to about 1900 psia (13100 kPa), or greater than or equal to about 2000 psia (13790 kPa), or greater than or equal to about 2500 psia (17237 kPa), or greater than or equal to about 3000 psia (20684 kPa).
- feed gas stream 10 is passed to cooler 33 where it is cooled prior to being passed to heat exchange area 56. It will be appreciated that to the extent compression unit 25 is used to compress feed gas stream 10 (and, hence, side stream 11 ) to a lower pressure than that desired for compressed refrigerant stream 12, compression unit 20 may be used to boost the pressure.
- feed gas stream 10 as described above provides three benefits. First, by increasing the pressure of the feed gas stream, the pressures of side streams 11b and 11c are also increased, with the result that the cooling performance of work expansion devices 42 and 43 is enhanced. Second, the heat transfer coefficient in the heat exchange areas is improved. Thus, in one or more embodiments, the process for producing LNG described herein is carried out according to any of the other embodiments described herein wherein the feed gas is compressed to the pressures described above prior to entry into a heat exchange area.
- the present method comprises providing supplemental cooling for the feed gas stream from a plurality of work expansion devices, each of the work expansion devices expanding a portion of the feed gas stream and thereby cooling the portion to form one or more expanded, cooled side streams, wherein each of the portions of the feed gas stream expanded in the work expansion devices is withdrawn from the feed gas stream at a different stage of feed gas stream cooling (i.e., at a different feed gas stream temperature); and cooling said feed gas stream by indirect heat exchange with said one or more expanded, cooled side streams.
- each of the above-described portions of feed gas has a pressure, prior to expansion, greater than about 1200 psia (8274 kPa), or greater than or equal to about 1300 psia (8963 kPa), or greater than or equal to about 1400 psia (9653 kPa), or greater than or equal to about 1500 psia (10342 kPa), or greater than or equal to about 1600 psia (11032 kPa), or greater than or equal to about 1700 psia (11721 kPa), or greater than or equal to about 1800 psia (12411 kPa), or greater than or equal to about 1900 psia (13100 kPa), or greater than or equal to about 2000 psia (13790 kPa), or greater than or equal to about 2500 psia (17237 kPa), or greater than or equal to about 3000 psia (206
- the present method is any of the other embodiments described herein further comprising compressing the feed gas stream to any of the pressures described above to produce a pressurized feed gas stream; feeding the pressurized feed gas stream to a work expansion device, or to a plurality of work expansion devices; expanding the compressed feed gas stream through the work expansion device, or through a plurality of work expansion devices, to provide supplemental cooling for the feed gas stream.
- a third benefit obtained by compression the feed gas stream as described above is that the cooling capacity of expander 35 is improved, with the result that expander 35 is able to even further reduce the cooling load on sub-cooling loop 8.
- compression unit 25 and/or expander 35 could also be advantageously added to other embodiments described herein to provide similar reductions in the cooling load on the sub-cooling loops utilized in those embodiments or other improvements in cooling, and that compression unit 25 and expander 35 may be used independently of each other in any embodiment herein.
- the cooling capacity of expander 35 (or the work expansion devices 42 and 43 ) will be improved, even without compression of the feed stream, to the extent the feed stream is supplied at a pressure above the bubble point pressure of the LNG.
- FIG. 5 is a schematic flow diagram of a fifth embodiment for producing LNG in accordance with the process of this invention that is similar to the embodiment shown in FIG. 4 , but utilizes yet another expansion step to provide sub-cooling.
- sub-cooling loop 8 is not present in the embodiment shown in FIG. 5 .
- side stream 11d is taken from stream 10b and passed to expansion device 105 where it is expanded and consequently cooled to form expanded stream 13d.
- Expansion device 105 is a work-producing expander, many types of which are readily available. Illustrative, non-limiting examples of such devices include liquid expanders and hydraulic turbines.
- Expanded stream 13d is passed through heat exchange areas 59, 58, 57, and 56 to provide at least part of the refrigeration duty for those heat exchange areas.
- stream 10b is also cooled by indirect heat exchange with expanded stream 13d, as well as by the flash vapor stream 16.
- the inventive process further comprises expanding at least a portion of the cooled gas stream (feed gas stream 10 ) in expander 35 before the final heat exchange step (for example, prior to heat exchange area 59 ) to produce an expanded, cooled gas stream (for example, stream 10b ); passing a portion of said expanded, cooled gas stream to a work-producing expander; further expanding said expanded, cooled gas stream in said work-producing expander; and passing the stream emerging from said work-producing expander (for example, stream 13d ) to a heat exchange area to further cool said expanded, cooled gas stream by indirect heat exchange in said heat exchange area.
- expanded stream 13d is passed to compression unit 95 where it is re-compressed and combined with the streams emerging from compression units 61 and 62 to form part of stream 14a, which is cooled and then re-cycled to feed stream 10 as before.
- FIG. 6 A further embodiment shown in FIG. 6 is similar to the embodiment shown in FIG.1 and described above, except that sub-cooling loop 6 has been modified such that after exiting heat exchange area 50, the re-compressed and cooled sub-cooling refrigerant stream is further cooled in heat exchange area 55 prior to being expanded through expander 41.
- This embodiment is favorable where a cooling fluid is used that does not present much condensation after expander 41.
- FIG. 7 depicts another embodiment in which sub-cooling loop 6a uses a portion of feed gas 10.
- the portion of feed gas 10 is re-pressurized in compressor 25 and cooled in cooler 33 from 201, in the same fashion as in FIG. 4 .
- FIG. 8 is another embodiment similar to FIG. 7 showing an alternative arrangement for the sub-cooling loop 6.
- an additional compressor (not shown) may be used to prevent condensation in the sub-cooling loop or to ensure adequate line pressures.
- FIG. 9 depicts an embodiment for use with certain feed gas 10 compositions and/or pressures.
- an expansion valve 82 or other expander e.g., a Joules-Thompson valve
- FIG. 10 represents another embodiment showing the integration of a nitrogen rejection stage using distillation column 81 or equivalent device, for the case where nitrogen rejection is needed, based on feed gas 10 composition. This may be needed to meet the nitrogen specification of product LNG for transmission and end use.
- FIG. 11 represents another embodiment showing the integration of a nitrogen rejection unit, where the flash vapor from the nitrogen rejection unit is used as refrigerant for the sub-cooling loop.
- the resulting refrigerant is therefore rich in nitrogen.
- the volume of flash vapor stream 16 is controlled to match the fuel requirements of the compression units and other equipment.
- the temperature at state point 207 can be controlled to produce more or less flash vapor (stream 16 ) depending on the fuel requirements. Higher temperatures at state point 207 will result in the production of more flash vapor (and hence more available fuel), and vice-versa.
- the temperature may be adjusted such that the flash vapor flow rate is higher than the fuel requirement, in which case the excess flow above the fuel flow requirement may be recycled after compression and cooling.
Description
- Embodiments of the invention relate to a process for liquefaction of natural gas and other methane-rich gas streams, and more particularly to a process for producing liquefied natural gas (LNG).
- Because of its clean burning qualities and convenience, natural gas has become widely used in recent years. Many sources of natural gas are located in remote areas, great distances from any commercial markets for the gas. Sometimes a pipeline is available for transporting produced natural gas to a commercial market. When pipeline transportation is not feasible, produced natural gas is often processed into liquefied natural gas (which is called "LNG") for transport to market.
- In the design of an LNG plant, one of the most important considerations is the process for converting the natural gas feed stream into LNG. Currently, the most common liquefaction processes use some form of refrigeration system. Although many refrigeration cycles have been used to liquefy natural gas, the three types most commonly used in LNG plants today are: (1) the "cascade cycle," which uses multiple single component refrigerants in heat exchangers arranged progressively to reduce the temperature of the gas to a liquefaction temperature; (2) the "multi-component refrigeration cycle," which uses a multi-component refrigerant in specially designed exchangers; and (3) the "expander cycle," which expands gas from feed gas pressure to a low pressure with a corresponding reduction in temperature. Most natural gas liquefaction cycles use variations or combinations of these three basic types.
- The refrigerants used may be a mixture of components such as methane, ethane, propane, butane, and nitrogen in multi-component refrigeration cycles. The refrigerants may also be pure substances such as propane, ethylene, or nitrogen in "cascade cycles." Substantial volumes of these refrigerants with close control of composition are required. Further, such refrigerants may have to be imported and stored imposing logistics requirements. Alternatively, some of the components of the refrigerant may be prepared, typically by a distillation process integrated with the liquefaction process.
- The use of gas expanders to provide the feed gas cooling thereby eliminating or reducing the logistical problems of refrigerant handling has been of interest to process engineers. The expander system operates on the principle that the feed gas can be allowed to expand through an expansion turbine, thereby performing work and reducing the temperature of the gas. The low temperature gas is then heat exchanged with the feed gas to provide the refrigeration needed. Supplemental refrigeration is typically needed to fully liquefy the feed gas and this may be provided by a refrigerant system. The power obtained from the expansion is usually used to supply part of the main compression power used in the refrigeration cycle. The typical expander cycle for making LNG operates at the feed gas pressure, typically under about 6,895 kPa (1,000 psia).
- Previously proposed expander cycles have all been less efficient thermodynamically, however, than the current natural gas liquefaction cycles based on refrigerant systems. Expander cycles have therefore not offered any installed cost advantage to date, and liquefaction cycles involving refrigerants are still the preferred option for natural gas liquefaction.
- Because expander cycles result in a high recycle gas stream flow rate and high inefficiency for the pre-cooling (warm) stage, gas expanders have typically been used to further cool feed gas after it has been pre-cooled to temperatures well below -20°C using an external refrigerant in a closed cycle, for example. Thus, a common factor in most proposed expander cycles is the requirement for a second, external refrigeration cycle to pre-cool the gas before the gas enters the expander. Such a combined external refrigeration cycle and expander cycle is sometimes referred to as a "hybrid cycle." While such refrigerant-based pre-cooling eliminates a major source of inefficiency in the use of expanders, it significantly reduces the benefits of the expander cycle, namely the elimination of external refrigerants. Additional cooling may also be required after the expander cooling and may be provided by another external refrigerant system, such as nitrogen or a cold mixed refrigerant.
U.S. Patent No. 6,378,330 B1 is directed to liquefying a pressurized gas stream rich in methane, the process including withdrawing and entropically expanding a first fraction of the pressurized feed stream, preferably above 11.000 kPa, to a lower pressure and cooling a second fraction of the pressurized feed stream by indirect heat exchange with the expanded first fraction followed by expanding the second fraction to a lower pressure.U.S. Patent Publication No. 2003/0177785 A1 is directed to cooling and expanding a gas stream to liquefy the gas stream and subsequently withdrawing the liquefied gas stream as a pressurized product with a portion recycled through the heat exchanger to provide cooling which helps keep the cooling and compression of the gas stream in the supercritical region of the phase diagram.FR 2 714 722 - Accordingly, there is still a need for an expander cycle that eliminates the need for external refrigerants and has improved efficiency, at least comparable to that of technologies currently in use.
- Embodiments of the present invention provide a process for liquefying natural gas and other methane-rich gas streams to produce liquefied natural gas (LNG) and/or other liquefied methane-rich gases. The term natural gas as used in this specification, including the appended claims, means a gaseous feed stock suitable for manufacturing LNG. The natural gas could comprise gas obtained from a crude oil well (associated gas) or from a gas well (non-associated gas). The composition of natural gas can vary significantly. As used herein, natural gas is a methane-rich gas
containing methane (C1) as a major component. - In one or more other embodiments according to the present invention, a process for liquefying a gas stream rich in methane is provided, said process comprising providing a gas stream rich in methane at a pressure less than 1,000 psia (6895 kPa); providing a refrigerant at a pressure of less than 1,000 psia (6895 kPa); compressing said refrigerant to a pressure greater than or equal to 1500 psia (10342 kPa) to provide a compressed refrigerant; cooling said compressed refrigerant by indirect heat exchange with a cooling fluid; expanding said compressed refrigerant to further cool said compressed refrigerant, thereby producing an expanded, cooled refrigerant; passing said expanded, cooled refrigerant to a heat exchange area; and passing said gas stream through said heat exchange area to cool at least part of said gas stream by indirect heat exchange with said expanded, cooled refrigerant, thereby forming a cooled gas stream.
- The providing the refrigerant at a pressure of less than 1,000 psia (6895 kPa) comprises withdrawing a portion of the gas at a pressure of less than 1,000 psia (6895 kPa) for use as the refrigerant. In other embodiments, the portion of the gas stream to be used as the refrigerant is withdrawn from the gas stream before the gas stream is passed to the heat exchange area. In still other embodiments, the process according to the present invention further comprises providing at least a portion of the refrigeration duty for the heat exchange area using a closed loop charged with flash vapor produced in the process for liquefying the gas stream rich in methane. Additional embodiments according to the present invention will be apparent to those skilled in the art.
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FIG. 1 is a schematic flow diagram of one embodiment for producing LNG in accordance with the process of this invention. -
FIG. 2 is a schematic flow diagram of a second example process not according to the invention for producing LNG that is similar to the process shown inFIG. 1 , except that the gaseous refrigerant in the compressed, cooled and expanded loop is de-coupled from the feed gas and may therefore have a different composition than the feed gas. -
FIG. 3 is a schematic flow diagram of a third embodiment for producing LNG in accordance with the process of this invention that uses a plurality of work expansion steps for improved efficiency. -
FIG. 4 is a schematic flow diagram of a fourth example process for producing LNG not in accordance with this invention that uses a plurality of work expansion steps similar toFIG. 3 , but also incorporates an additional expansion step as well as compression of the feed gas to improve performance of the expansion steps. -
FIG. 5 is a schematic flow diagram of a fifth example process for producing LNG not in accordance with this invention that is similar to the embodiment shown inFIG. 4 , but utilizes an additional side stream and expansion of process gas to provide sub-cooling. -
FIG. 6 is another embodiment according to the invention similar to the embodiments shown inFIG. 1 andFIG. 2 in which the refrigerant for the sub-cooling loop is cooled in the sub-cooling heat exchanger prior to expansion. -
FIG. 7 is another example process not according to the invention in which the sub-cooling loop is coupled to the feed gas. -
FIG. 8 is another embodiment according to the invention showing an alternative arrangement for the sub-cooling loop. -
FIG. 9 is a similar embodiment according to the invention to that ofFIG. 8 but using split expanded streams through the sub-cooler wherein an expansion valve, Joules-Thompson valve, or similar expansion device is used for improved efficiency in the sub-cooler. -
FIG. 10 is another embodiment in which a nitrogen rejection stage has been integrated for situations in which nitrogen rejection may be needed. -
FIG. 11 is yet another embodiment in which the refrigerant for the sub-cooling loop is derived from the flash vapor from the nitrogen rejection unit and is therefore rich in nitrogen content. - Embodiments of the present invention provide a process for natural gas liquefaction using primarily gas expanders and eliminating the need for external refrigerants. That is the feed gas itself (e.g., natural gas) is used as the refrigerant in all refrigeration cycles. Such refrigeration cycles do not require supplemental cooling using external refrigerants (i.e., refrigerants other than the feed gas itself or gas that is produced at or near the LNG process plant) as typical proposed gas expander cycles do, yet such refrigeration cycles have a higher efficiency. In one or more embodiments, cooling water or air are the only external sources of cooling fluids and are used for compressor inter-stage or after cooling.
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FIG. 1 illustrates one embodiment of the present invention in which an expander loop 5 (i.e., an expander cycle) and asub-cooling loop 6 are used. For clarity, expanderloop 5 andsub-cooling loop 6 are shown with double-width lines inFIG. 1 . In this specification and the appended claims, the terms "loop" and "cycle" are used interchangeably. InFIG. 1 , feedgas stream 10 enters the liquefaction process at a pressure less than 1000 psia, or less than 900 psia (6205 kPa), or less than 800 psia (5516 kPa), or less than 700 psia (4826 kPa), or less than 600 psia (4137 kPa). Typically, the pressure offeed gas stream 10 will be about 800 psia (5516 kPa).Feed gas stream 10 generally comprises natural gas that has been treated to remove contaminants using processes and equipment that are well known in the art. Before it is passed to a heat exchanger, a portion offeed gas stream 10 is withdrawn to formside stream 11, thus providing, as will be apparent from the following discussion, a refrigerant at a pressure corresponding to the pressure offeed gas stream 10, namely any of the above pressures, including a
pressure of less than 1000 psia (6895 kPa). Thus, in the embodiment shown inFIG. 1 , a portion of the feed gas stream is used as the refrigerant forexpander loop 5. Although the embodiment shown inFIG. 1 utilizes a side stream that is withdrawn fromfeed gas stream 10 beforefeed gas stream 10 is passed to a heat exchanger, the side stream of feed gas to be used as the refrigerant inexpander loop 5 may be withdrawn from the feed gas after the feed gas has been passed to a heat exchange area. Thus, in one or more embodiments, the present method is any of the other embodiments herein described, wherein the portion of the feed gas stream to be used as the refrigerant is withdrawn from the heat exchange area, expanded, and passed back to the heat exchange area to provide at least part of the refrigeration duty for the heat exchange area. -
Side stream 11 is passed tocompression unit 20 where it is compressed to a pressure greater than or equal to 1500 psia (10342 kPa), thus providing compressedrefrigerant stream 12. Alternatively,side stream 11 is compressed to a pressure greater than or equal to 1600 psia (11032 kPa), or greater than or equal to 1700 psia (11721 kPa), or greater than or equal to 1800 psia (12411 kPa), or greater than or equal to 1900 psia (13100 kPa), or greater than or equal to 2000 psia (13790 kPa), or greater than or equal to 2500 psia (17237 kPa), or greater than or equal to 3000 psia (20684 kPa), thus providing compressedrefrigerant stream 12. As used in this specification, including the appended claims, the term "compression unit" means any one type or combination of similar or different types of compression equipment, and may include auxiliary equipment, known in the art for compressing a substance or mixture of substances. A "compression unit" may utilize one or more compression stages. Illustrative compressors may include, but are not limited to, positive displacement types, such as reciprocating and rotary compressors for example, and dynamic types, such as centrifugal and axial flow compressors, for example. - After exiting
compression unit 20, compressedrefrigerant stream 12 is passed to cooler 30 where it is cooled by indirect heat exchange with a suitable cooling fluid to provide a compressed, cooled refrigerant. In one or more embodiments, cooler 30 is of the type that provides water or air as the cooling fluid, although any type of cooler can be used. The temperature of compressedrefrigerant stream 12 as it emerges from cooler 30 depends on the ambient conditions and the cooling medium used and is typically from about 35 °F (1.7 °C) to about 105 °F (40.5 °C). Cooled compressedrefrigerant stream 12 is then passed to expander 40 where it is expanded and consequently cooled to form expandedrefrigerant stream 13. In one or more embodiments,expander 40 is a work-expansion device, such as gas expander producing work that may be extracted and used for compression. - Expanded
refrigerant stream 13 is passed to heatexchange area 50 to provide at least part of the refrigeration duty forheat exchange area 50. As used in this specification, including the appended claims, the term "heat exchange area" means any one type or combination of similar or different types of equipment known in the art for facilitating heat transfer. Thus, a "heat exchange area" may be contained within a single piece of equipment, or it may comprise areas contained in a plurality of equipment pieces. Conversely, multiple heat exchange areas may be contained in a single piece of equipment. - Upon exiting
heat exchange area 50, expandedrefrigerant stream 13 is fed tocompression unit 60 for pressurization to formstream 14, which is then joined withside stream 11. It will be apparent that onceexpander loop 5 has been filled with feed gas fromside stream 11, only make-up feed gas to replace losses from leaks is required, the majority of the gas enteringcompressor unit 20 generally being provided bystream 14. The portion offeed gas stream 10 that is not withdrawn asside stream 11 is passed to heatexchange area 50 where it is cooled, at least in part, by indirect heat exchange with expandedrefrigerant stream 13. After exitingheat exchange area 50, feedgas stream 10 is passed to heatexchange area 55. The principal function ofheat exchange area 55 is to sub-cool the feed gas stream. Thus, inheat exchange area 55feed gas stream 10 is sub-cooled by sub-cooling loop 6 (described below) to producesub-cooled stream 10a.Sub-cooled stream 10a is then expanded to a lower pressure inexpander 70, thereby partially liquefyingsub-cooled stream 10a to form a liquid fraction and a remaining vapor fraction.Expander 70 may be any pressure reducing device, including, but not limited to a valve, control valve, Joule Thompson valve, Venturi device, liquid expander, hydraulic turbine, and the like. Partially liquefiedsub-cooled stream 10a is passed tosurge tank 80 where the liquefied
fraction 15 is withdrawn from the process as LNG having a temperature corresponding to the bubble point pressure. The remaining vapor fraction (flash vapor)stream 16 is used as fuel to power the compressor units and/or as a refrigerant insub-cooling loop 6 as described below. Prior to being used as fuel, all or a portion offlash vapor stream 16 may optionally be passed fromsurge tank 80 to heatexchange areas - Referring again to
FIG. 1 , a portion offlash vapor 16 is withdrawn throughline 17 to fillsub-cooling loop 6. Thus, a portion of the feed gas fromfeed gas stream 10 is withdrawn (in the form of flash gas from flash gas stream 16) for use as the refrigerant insub-cooling loop 6. It will again be apparent that oncesub-cooling loop 6 is fully charged with flash gas, only make-up gas (i.e., additional flash vapor from line 17) to replace losses from leaks is required. Insub-cooling loop 6, expandedstream 18 is discharged fromexpander 41 and drawn throughheat exchange areas compression unit 90 where it is re-compressed to a higher pressure and warmed. After exitingcompression unit 90, the re-compressed sub-cooling refrigerant stream is cooled in cooler 31, which can be of the same type as cooler 30, although any type of cooler may be used. After cooling, the re-compressed sub-cooling refrigerant stream is passed to heatexchange area 50 where it is further cooled by indirect heat exchange with expandedrefrigerant stream 13, sub-coolingrefrigerant stream 18, and, optionally,flash vapor stream 16. After exitingheat exchange area 50, the re-compressed and cooled sub-cooling refrigerant stream is expanded throughexpander 41 to provide a cooled stream which is then passed throughheat exchange area 55 to sub-cool the portion of the feed gas stream to be finally expanded to produce LNG. The expanded sub-cooling refrigerant stream exiting fromheat exchange area 55 is again passed throughheat exchange area 50 to provide supplemental cooling before being re-compressed. In this manner the cycle insub-cooling loop 6 is continuously repeated. Thus, in one or more embodiments, the present method is any of the other embodiments disclosed herein further comprising providing cooling using a closed loop (e.g., sub-cooling loop 6) charged with flash vapor resulting from the LNG production (e.g., flash vapor 16). - It will be apparent that in the embodiment illustrated in
FIG. 1 (and in the other embodiments described herein) that asfeed gas stream 10 passes from one heat exchange area to another, the temperature offeed gas stream 10 will be reduced until ultimately a sub-cooled stream is produced. In addition, as side streams are taken fromfeed gas stream 10, the mass flow rate offeed gas stream 10 will be reduced. Other modifications, such as compression, may also be made to feedgas stream 10. While each such modification to feedgas stream 10 could be considered to produce a new and different stream, for clarity and ease of illustration, the feed gas stream will be referred to asfeed gas stream 10 unless otherwise indicated, with the understanding that passage through heat exchange areas, the taking of side streams, and other modifications will produce temperature, pressure, and/or flow rate changes to feedgas stream 10. -
FIG. 2 illustrates an unclaimed embodiment of the present invention that is similar to the embodiment shown inFIG. 1 , except thatexpander loop 5 has been replaced withexpander loop 7. The other items inFIG. 2 have been previously described above.Expander loop 7 is shown with double-width lines inFIG. 2 for clarity.Expander loop 7 utilizes substantially the same equipment as expander loop 5 (for example,compressor 20, cooler 30, andexpander 40, all of which have been described above). The gaseous refrigerant inexpander loop 7 however, is de-coupled from the feed gas and may therefore have a different composition than the feed gas. That is,expander loop 7 is essentially a closed loop and is not connected to feedgas stream 10. The refrigerant forexpander loop 7 is therefore not necessarily the feed gas, although it may be.Expander loop 7 may be charged with any suitable refrigerant gas that is produced at or near the LNG process plant in whichexpander loop 7 is utilized. For example, the refrigerant gas used to chargeexpander loop 7 could be a feed gas, such as natural gas, that has only been partially treated to remove contaminants. - Like
expander loop 5,expander loop 7 is a high pressure gas loop.Stream 12a exitscompression unit 20 at a pressure greater than or equal to about 1500 psia (10342 kPa), or greater than or equal to about 1600 psia (11032 kPa), or greater than or equal to about 1700 psia (11721 kPa), or greater than or equal to about 1800 psia (12411 kPa), or greater than or equal to about 1900 psia (13100 kPa), or greater than or equal to about 2000 psia (13790 kPa), or greater than or equal to about 2500 psia (17237 kPa), or greater than or equal to about 3000 psia (20684 kPa). The temperature of compressedrefrigerant stream 12a as it emerges from cooler 30 depends on the ambient conditions and the cooling medium used and is typically about from about 35 °F (1.7 °C) to about 105 °F (40.5 °C). Cooled compressedrefrigerant stream 12a is then passed to expander 40 where it is expanded and further cooled to form expandedrefrigerant stream 13a. Expandedrefrigerant stream 13a is passed to heatexchange area 50 to provide at least part of the refrigeration duty forheat exchange area 50, wherefeed gas stream 10 is at least partially cooled by indirect heat exchange with expandedrefrigerant stream 13a. Upon exitingheat exchange area 50, expandedrefrigerant stream 13a is returned tocompression unit 20 for re-compression. In any of the embodiments described herein,expander loops expander loop 5,expander loop 7 may be substituted forexpander loop 5. -
FIG. 3 shows another embodiment for producing LNG in accordance with the process of the invention. The process illustrated inFIG. 3 utilizes a plurality of work expansion cycles to provide supplemental cooling for the feed gas and other streams. The use of such work expansion cycles results in overall improved efficiency for the liquefaction process. Referring toFIG. 3 , feedgas stream 10 again enters the liquefaction process at the pressures described above. In the particular embodiment shown inFIG. 3 ,side stream 11 is fed toexpander loop 5 in the manner previously described, but it will be apparent in an unclaimed aspect of the invention that closedexpander loop 7 could be utilized in the place ofexpander loop 5, in whichcase side stream 11 would not be necessary.Expander loop 5 operates in the same manner as described above for the embodiment shown inFIG. 1 , except that expandedrefrigerant stream 13 is passed throughheat exchange area 56, described in detail below, to provide at least a part of the refrigeration duty forheat exchange area 56. - The portion of
feed gas stream 10 that is not withdrawn asside stream 11 is passed to heatexchange area 56 where it is cooled, at least in part, by indirect heat exchange with expandedrefrigerant stream 13 and other streams described below. After exitingheat exchange area 56, feedgas stream 10 is passed throughheat exchange areas feed gas stream 10 entersheat exchange area 57,side stream 11b is taken fromfeed gas stream 10. Afterfeed gas stream 10 exits heatexchange area 57, but before it entersheat exchange area 58,side stream 11c is taken fromfeed gas stream 10. Thus,side streams feed gas stream 10 at different stages of feed gas stream cooling. That is, each side stream is withdrawn from the feed gas stream at a different point on the cooling curve of the feed gas such that each successively withdrawn side stream has a lower initial temperature than the previously withdrawn side stream. -
Side stream 11b, which is part of the first work expansion cycle, is passed to expander 42 where it is expanded and consequently cooled to form expandedstream 13b.Expanded stream 13b is passed throughheat exchange areas heat exchange areas side stream 11c, which is part of the second work expansion cycle, is passed to expander 43 where it is expanded and consequently cooled to form expandedstream 13c. Expandedstream 13c is then passed throughheat exchange areas heat exchange areas gas stream 10 is also cooled inheat exchange areas streams heat exchange area 58feed gas stream 10 is also cooled by additional indirect heat exchange with expandedstream 13c. - Upon exiting
heat exchange area 56, expandedstreams compression units stream 14a.Stream 14a is cooled by cooler 32 prior to being re-combined withfeed gas stream 10.Cooler 32 can be the same type of cooler or cooler types ascoolers Expanders FIG. 3 , the feed gas stream is further cooled using a plurality of work expansion devices. It will be apparent to those of ordinary skill in the art that additional work expansion cycles can be added to the embodiment illustrated inFIG. 3 , or that a single work expansion cycle could be employed. Generally, therefore, one or more work expansion devices may be employed in the manner described above. Each of the work expansion devices expands a portion of the feed gas stream and thereby cools such portion, wherein each of the portions of the feed gas stream expanded in the work expansion devices is withdrawn from the feed gas stream at a different stage of feed gas stream cooling (i.e., at a different feed gas stream temperature). - The work expansion devices are utilized by withdrawing one or more side streams from the feed gas stream; passing said one or more side streams to one or more work expansion devices; expanding said one of more side streams to expand and cool said one or more side streams, thereby forming one or more expanded, cooled side streams; passing said one or more expanded, cooled side streams to at least one heat exchange area; passing said gas stream through said at least one heat exchange area; and at least partially cooling said gas stream by indirect heat exchange with said one or more expanded, cooled side streams.
- Referring again to
FIG. 3 , feedgas stream 10, after being cooled inheat exchange areas exchange area 59 where it is further cooled to producesub-cooled stream 10a. The principal function ofheat exchange area 59 is to sub-coolfeed gas stream 10.Sub-cooled stream 10a is then expanded to a lower pressure inexpander 85, thereby partially liquefyingsub-cooled stream 10a to form a liquid fraction and a remaining vapor fraction.Expander 85 may be any pressure reducing device, including, but not limited to a valve, control valve, Joule Thompson valve, Venturi device, liquid expander, hydraulic turbine, and the like. Partially liquefiedsub-cooled stream 10a is passed tosurge tank 80 where
the liquefiedfraction 15 is withdrawn from the process as LNG having a temperature corresponding to the bubble point pressure. The remaining vapor fraction (flash vapor)stream 16 is used as fuel to power the compressor units and/or as a refrigerant insub-cooling loop 8 in a manner substantially the same as previously described forsub-cooling loop 6. As can be seen fromFIG. 3 ,sub-cooling loop 8 is similar tosub-cooling loop 6, except thatsub-cooling loop 8 supplies cooling to four heat exchange areas (heat exchange areas -
FIG. 4 illustrates yet another embodiment of the present invention. The embodiment shown inFIG. 4 is substantially the same as the embodiment shown inFIG. 3 , except thatcompression unit 25 andexpander 35 have been added.Expander 35 may be any type of liquid expander or hydraulic turbine.Expander 35 is placed betweenheat exchange areas feed gas stream 10 flows fromheat exchange area 58 intoexpander 35 where it is expanded, and consequently cooled to produce expandedfeed gas stream 10b.Stream 10b then is passed to heatexchange area 59 where it is sub-cooled to producesub-cooled stream 10c. By expanding and consequently coolingfeed gas stream 10 inexpander 35 to producestream 10b, the overall cooling load onsub-cooling loop 8 is advantageously reduced. Thus, in one or more embodiments, the present method is any of the other embodiments disclosed herein further comprising expanding at least a portion of the cooled feed gas stream to produce a cooled, expanded feed gas stream (e.g.,stream 10b); and further cooling the cooled, expanded feed gas stream by indirect heat exchange with a closed loop (e.g.,sub-cooling loop 6 or 8) charged with flash vapor resulting from the LNG production (e.g., flash vapor 16). - Continuing to refer to
FIG. 4 ,compression unit 25 is utilized to increase the pressure offeed gas stream 10 prior to entry into the liquefaction process. Thus, feedgas stream 10 is passed tocompression unit 25 where it is compressed to a pressure above the feed gas supply pressure or, in one or more unclaimed embodiments, to a pressure greater than about 1200 psia (8274 kPa). Alternatively, feedgas stream 10 is compressed to a pressure greater than or equal to about 1300 psia (8963 kPa), or greater than or equal to about 1400 psia (9653 kPa), or greater than or equal to about 1500 psia (10342 kPa), or greater than or equal to about 1600 psia (11032 kPa), or greater than or equal to about 1700 psia (11721 kPa), or greater
than or equal to about 1800 psia (12411 kPa), or greater than or equal to about 1900 psia (13100 kPa), or greater than or equal to about 2000 psia (13790 kPa), or greater than or equal to about 2500 psia (17237 kPa), or greater than or equal to about 3000 psia (20684 kPa). After compression, feedgas stream 10 is passed to cooler 33 where it is cooled prior to being passed to heatexchange area 56. It will be appreciated that to theextent compression unit 25 is used to compress feed gas stream 10 (and, hence, side stream 11) to a lower pressure than that desired for compressedrefrigerant stream 12,compression unit 20 may be used to boost the pressure. - The compression of
feed gas stream 10 as described above provides three benefits. First, by increasing the pressure of the feed gas stream, the pressures ofside streams work expansion devices - In still other unclaimed embodiments, each of the above-described portions of feed gas has a pressure, prior to expansion, greater than about 1200 psia (8274 kPa), or greater than or equal to about 1300 psia (8963 kPa), or greater than or equal to about 1400 psia (9653 kPa), or greater than or equal to about 1500 psia (10342 kPa), or greater than or equal to about 1600 psia (11032 kPa), or greater than or equal to about 1700 psia (11721 kPa), or greater than or equal to about 1800 psia (12411 kPa), or greater than or equal to about 1900 psia (13100 kPa), or greater than or equal to about 2000 psia (13790 kPa), or greater than or equal to about 2500 psia (17237 kPa), or greater than or equal to
about 3000 psia (20684 kPa). In yet other unclaimed embodiments, the present method is any of the other embodiments described herein further comprising compressing the feed gas stream to any of the pressures described above to produce a pressurized feed gas stream; feeding the pressurized feed gas stream to a work expansion device, or to a plurality of work expansion devices; expanding the compressed feed gas stream through the work expansion device, or through a plurality of work expansion devices, to provide supplemental cooling for the feed gas stream. - A third benefit obtained by compression the feed gas stream as described above is that the cooling capacity of
expander 35 is improved, with the result that expander 35 is able to even further reduce the cooling load onsub-cooling loop 8. It will be appreciated thatcompression unit 25 and/orexpander 35 could also be advantageously added to other embodiments described herein to provide similar reductions in the cooling load on the sub-cooling loops utilized in those embodiments or other improvements in cooling, and thatcompression unit 25 andexpander 35 may be used independently of each other in any embodiment herein. Moreover, it will also be appreciated that the cooling capacity of expander 35 (or thework expansion devices 42 and 43) will be improved, even without compression of the feed stream, to the extent the feed stream is supplied at a pressure above the bubble point pressure of the LNG. For example, if the feed gas is supplied at any of the pressures described above resulting from compression of the feed gas, the benefit of such pressure will obviously be obtainable without additional compression. Therefore, in interpreting this specification the use of work expansion devices and/orexpander 35 to expand streams having pressures above about 1200 psia (8274 kPa) should not be construed as requiring the use or presence ofcompression unit 25 or of any other compressor or compression step. -
FIG. 5 is a schematic flow diagram of a fifth embodiment for producing LNG in accordance with the process of this invention that is similar to the embodiment shown inFIG. 4 , but utilizes yet another expansion step to provide sub-cooling. Referring toFIG. 5 , it will be seen thatsub-cooling loop 8 is not present in the embodiment shown inFIG. 5 . Instead,side stream 11d is taken fromstream 10b and passed toexpansion device 105 where it is expanded and consequently cooled to
form expandedstream 13d.Expansion device 105 is a work-producing expander, many types of which are readily available. Illustrative, non-limiting examples of such devices include liquid expanders and hydraulic turbines. Expandedstream 13d is passed throughheat exchange areas FIG. 5 ,stream 10b is also cooled by indirect heat exchange with expandedstream 13d, as well as by theflash vapor stream 16. Thus, in one or more embodiments, the inventive process further comprises expanding at least a portion of the cooled gas stream (feed gas stream 10) inexpander 35 before the final heat exchange step (for example, prior to heat exchange area 59) to produce an expanded, cooled gas stream (for example,stream 10b); passing a portion of said expanded, cooled gas stream to a work-producing expander; further expanding said expanded, cooled gas stream in said work-producing expander; and passing the stream emerging from said work-producing expander (for example,stream 13d) to a heat exchange area to further cool said expanded, cooled gas stream by indirect heat exchange in said heat exchange area. - Upon exiting
heat exchange area 56, expandedstream 13d is passed tocompression unit 95 where it is re-compressed and combined with the streams emerging fromcompression units stream 14a, which is cooled and then re-cycled to feedstream 10 as before. - A further embodiment shown in
FIG. 6 is similar to the embodiment shown inFIG.1 and described above, except thatsub-cooling loop 6 has been modified such that after exitingheat exchange area 50, the re-compressed and cooled sub-cooling refrigerant stream is further cooled inheat exchange area 55 prior to being expanded throughexpander 41. This embodiment is favorable where a cooling fluid is used that does not present much condensation afterexpander 41. -
FIG. 7 depicts another embodiment in whichsub-cooling loop 6a uses a portion offeed gas 10. The portion offeed gas 10 is re-pressurized incompressor 25 and cooled in cooler 33 from 201, in the same fashion as inFIG. 4 . -
FIG. 8 is another embodiment similar toFIG. 7 showing an alternative arrangement for thesub-cooling loop 6. Depending on the composition offeed gas 10, an additional compressor (not shown) may be used to prevent condensation in the sub-cooling loop or to ensure adequate line pressures. -
FIG. 9 depicts an embodiment for use withcertain feed gas 10 compositions and/or pressures. To better match the cooling curve of thefeed gas 10 being cooled for LNG collection, to the cooling curve of that portion offeed gas 10 being used for cooling in sub-coolingheat exchange area 55, it may be necessary to further expand a split of the portion of the refrigerant gas going to thesub-cooling loop 6. This is accomplished using anexpansion valve 82 or other expander (e.g., a Joules-Thompson valve) to provide supplemental cooling insub-cooling loop 6. -
FIG. 10 represents another embodiment showing the integration of a nitrogen rejection stage usingdistillation column 81 or equivalent device, for the case where nitrogen rejection is needed, based onfeed gas 10 composition. This may be needed to meet the nitrogen specification of product LNG for transmission and end use. -
FIG. 11 represents another embodiment showing the integration of a nitrogen rejection unit, where the flash vapor from the nitrogen rejection unit is used as refrigerant for the sub-cooling loop. The resulting refrigerant is therefore rich in nitrogen. - A hypothetical mass and energy balance was carried out to illustrate the embodiment shown in
FIG. 4 , and the results are shown in the Table below. The data were obtained using a commercially available process simulation program called HYSYS™ (available from Hyprotech Ltd. of Calgary, Canada); however, other commercially available process simulation programs can be used to develop the data, including for example HYSIM™, PROII™, and ASPEN PLUS™, which are familiar to those of ordinary skill in the art. This example assumed thatfeed gas stream 10 had the following composition in mole percent: C1: 90.25%; C2: 5.70%; C3: 0.01%;
N2: 4.0%; He: 0.04%. The data presented in the Table are offered to provide a better understanding of the embodiment shown inFIG. 4 , but the invention is not to be construed as unnecessarily limited thereto. The temperatures, pressures, and flow rates can have many variations in view of the teachings herein. The specific temperature, pressure, and flow rate calculated for state points 201 through 214 (at the locations shown inFIG. 4 ) are set forth in the Table. - In one embodiment of the inventive method, by controlling the temperature of the stream emerging from the final heat exchange area, the volume of
flash vapor stream 16 is controlled to match the fuel requirements of the compression units and other equipment. For example, referring toFIG. 4 , the temperature atstate point 207 can be controlled to produce more or less flash vapor (stream 16) depending on the fuel requirements. Higher temperatures atstate point 207 will result in the production of more flash vapor (and hence more available fuel), and vice-versa. Alternatively, the temperature may be adjusted such that the flash vapor flow rate is higher than the fuel requirement, in which case the excess flow above the fuel flow requirement may be recycled after compression and cooling.TABLE State Point Temperature (deg. F) [deg. C] Pressure (psia) [kPa] Flow (lb-mole/hr) [kg-mol/hr] 201 262 [128] 985 [6791] 3.35 x 105 [1.52 x 105] 202 100 [38] 1500 [10342] 1.08 x 106 [4.90 x 105] 203 -36 [-38] 1480 [10204] 4.85 x 105 [2.20 x 105] 204 -130 [-90] 1470 [10135] 3.35 x 105 [1.52 x 105] 205 -213 [-136] 1460 [10066] 3.35 x 105 [1.52 x 105] 206 -229 [-145] 48 [331] 3.35 x 105 [1.52 x 105] 207 -236 [-149] 42 [290] 3.35 x 105 [1.52 x 105] 208 -254 [-159] 18 [124] 3.35 x 105 [1.52 x 105] 209 -217 [-138] 71 [490] 3.12 x 105 [1.42 x 105] 210 -140 [-96] 420 [2896] 2.29 x 104 [1.04 x 104] 211 100 [38] 126 [869] 2.57 x 104 [1.17 x 104] 212 -240 [-151] 44 [303] 2.57 x 104 [1.17 x 104] 213 100 [38] 3000 [20684] 8.57 x 105 [3.89 x 105] 214 -40 [-40] 895 [6171] 8.57 x 105 [3.89 x 105] - A person skilled in the art, particularly one having the benefit of the teachings herein, will recognize many modifications and variations to the specific embodiments disclosed above. For example, features shown in one embodiment may be added to other embodiments to form additional embodiments.
Claims (20)
- A process for liquefying a gas stream (10) rich in methane, said process comprising:providing said gas stream at a pressure less than 1,000 psia (6895 kPa);providing a refrigerant at a pressure of less than 1,000 psia (6895 kPa) by withdrawing a portion (11) of said gas stream at a pressure of less than 1,000 psia (6895 kPa) for use as said refrigerant;compressing said refrigerant to a pressure greater than or equal to 1500 psia (10342 kPa) to provide a compressed refrigerant (12);cooling said compressed refrigerant by indirect heat exchange with a cooling fluid;expanding said compressed refrigerant to further cool said compressed refrigerant, thereby producing an expanded, cooled refrigerant (13);passing said expanded, cooled refrigerant to a heat exchange area (50, 56); andpassing said gas stream through said heat exchange area to cool at least part of said gas stream by indirect heat exchange with said expanded, cooled refrigerant, thereby forming a cooled gas stream (10a).
- The process of claim 1 wherein said portion of said gas stream is withdrawn before said gas stream is passed to said heat exchange area.
- The process of claim 1 wherein said portion of said gas stream is withdrawn from said heat exchange area.
- The process of claim 1 further comprising providing at least a portion of the refrigeration duty for said heat exchange area using a closed loop (6, 8) charged with a flash vapor (16) produced in said process for liquefying a gas stream rich in methane.
- The process of claim 4 further comprising:expanding at least a portion of said cooled gas stream to produce an expanded, cooled gas stream; andfurther cooling said expanded, cooled gas stream by indirect heat exchange with said closed loop charged with the flash vapor.
- The process of claim 1 further comprising:expanding at least a portion of said cooled gas stream to produce an expanded, cooled gas stream; andfurther cooling said expanded, cooled gas stream by indirect heat exchange in one or more additional heat exchange areas.
- The process of claim 1 further comprising:cooling said gas stream using a plurality of work expansion devices (42, 43), each of said work expansion devices expanding a portion of the feed gas stream and thereby cooling said portion to form one or more expanded, cooled side streams (13b, 13c), wherein each of said portions of the feed gas stream expanded in said work expansion devices is withdrawn from said feed gas stream at a different stage of feed gas stream cooling; andcooling said feed gas stream by indirect heat exchange with said one or more expanded, cooled side streams.
- The process of claim 1 further comprising:withdrawing one or more portions of said gas stream (11b, 11c);passing each of said one or more portions of said gas stream to one or more work expansion devices (42, 43) and expanding each of said one of more portions of said gas stream to expand and cool said one or more portions, thereby forming one or more expanded, cooled side streams (13b, 13c);passing said one or more expanded, cooled side streams to at least one heat exchange area (57, 58);passing said gas stream through said at least one heat exchange area; andat least partially cooling said gas stream by indirect heat exchange with said one or more expanded, cooled side streams.
- The process of claim 1 further comprising an expansion stage of said cooled gas stream before a final heat exchange step and prior to expansion to produce LNG.
- The process of claim 1 further comprising:expanding at least a portion of said cooled gas stream before a final heat exchange step to produce an expanded, cooled gas stream;passing a portion of said expanded, cooled gas stream to a work-producing expander and further expanding said portion of said expanded, cooled gas stream in said work-producing expander; andpassing the stream emerging from said work-producing expander to a heat exchange area to further cool the balance of said expanded, cooled gas stream by indirect heat exchange in said heat exchange area.
- The process of claim 1 wherein said refrigerant is compressed to a pressure greater than or equal to 3,000 psia (20684 kPa) to provide a compressed refrigerant.
- The process of claim 1 wherein said heat exchange area comprises multiple heat exchange chambers.
- The process of claim 1 further comprising:a sub-cooling heat exchange area (55, 59) receiving said gas stream and cooled by expansion of a second refrigerant to provide a sub-cooled gas stream;followed by final expansion of said sub-cooled gas stream and recovery of LNG.
- The process of claim 13 wherein said second refrigerant is sub-cooled in said sub-cooling heat exchange area prior to expansion of said second refrigerant.
- The process of claim 14 wherein said gas stream rich in methane is re-pressurized before passing through said heat exchange area, said cooled gas stream is expanded, and a portion of said expanded, cooled gas stream is further expanded and used as said second refrigerant in said sub-cooling heat exchange area.
- The process of claim 14 wherein a portion of said sub-cooled gas stream is expanded and a portion thereof is said second refrigerant.
- The process of claim 16 wherein said portion of said sub-cooled gas stream is split into two partial streams, one of said partial streams is further expanded, and both of said partial streams comprise said second refrigerant.
- The process of claim 1 further comprising rejecting nitrogen with LNG recovery.
- The process of claim 1, wherein said gas stream is provided at a pressure less than 900 psia (6205 kPa).
- The process of claim 1, wherein said refrigerant is compressed to a pressure greater than or equal to 2000 psia (13790 kPa).
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- 2006-05-24 CA CA2618576A patent/CA2618576C/en active Active
- 2006-05-24 AU AU2006280426A patent/AU2006280426B2/en active Active
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2008
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JP5139292B2 (en) | 2013-02-06 |
RU2008108998A (en) | 2009-09-20 |
EP1929227A1 (en) | 2008-06-11 |
RU2406949C2 (en) | 2010-12-20 |
NO20081190L (en) | 2008-05-07 |
AU2006280426A1 (en) | 2007-02-22 |
US20090217701A1 (en) | 2009-09-03 |
CA2618576C (en) | 2014-05-27 |
JP2009504838A (en) | 2009-02-05 |
AU2006280426B2 (en) | 2010-09-02 |
WO2007021351A1 (en) | 2007-02-22 |
CA2618576A1 (en) | 2007-02-22 |
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