Classifications

• • 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
  • 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
• • 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
  • F25J1/00—Processes or apparatus for liquefying or solidifying gases or gaseous mixtures
  • 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
• • 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
  • F25J1/00—Processes or apparatus for liquefying or solidifying gases or gaseous mixtures
  • 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
  • F25J1/0037—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 of a return stream
• • 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
  • F25J1/00—Processes or apparatus for liquefying or solidifying gases or gaseous mixtures
  • 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"
  • F25J1/004—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 flash gas recovery
• • 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
  • F25J1/00—Processes or apparatus for liquefying or solidifying gases or gaseous mixtures
  • 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"
  • F25J1/0042—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 liquid expansion with extraction of work
• • 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
  • F25J1/00—Processes or apparatus for liquefying or solidifying gases or gaseous mixtures
  • F25J1/02—Processes or apparatus for liquefying or solidifying gases or gaseous mixtures requiring the use of refrigeration, e.g. of helium or hydrogen ; Details and kind of the refrigeration system used; Integration with other units or processes; Controlling aspects of the process
  • F25J1/0201—Processes or apparatus for liquefying or solidifying gases or gaseous mixtures requiring the use of refrigeration, e.g. of helium or hydrogen ; Details and kind of the refrigeration system used; Integration with other units or processes; Controlling aspects of the process using only internal refrigeration means, i.e. without external refrigeration
  • F25J1/0202—Processes or apparatus for liquefying or solidifying gases or gaseous mixtures requiring the use of refrigeration, e.g. of helium or hydrogen ; Details and kind of the refrigeration system used; Integration with other units or processes; Controlling aspects of the process using only internal refrigeration means, i.e. without external refrigeration in a quasi-closed internal refrigeration loop
• • 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
  • F25J1/00—Processes or apparatus for liquefying or solidifying gases or gaseous mixtures
  • F25J1/02—Processes or apparatus for liquefying or solidifying gases or gaseous mixtures requiring the use of refrigeration, e.g. of helium or hydrogen ; Details and kind of the refrigeration system used; Integration with other units or processes; Controlling aspects of the process
  • F25J1/0243—Start-up or control of the process; Details of the apparatus used; Details of the refrigerant compression system used
  • F25J1/0244—Operation; Control and regulation; Instrumentation
  • F25J1/0254—Operation; Control and regulation; Instrumentation controlling particular process parameter, e.g. pressure, temperature
• • 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
  • F25J1/00—Processes or apparatus for liquefying or solidifying gases or gaseous mixtures
  • F25J1/02—Processes or apparatus for liquefying or solidifying gases or gaseous mixtures requiring the use of refrigeration, e.g. of helium or hydrogen ; Details and kind of the refrigeration system used; Integration with other units or processes; Controlling aspects of the process
  • F25J1/0243—Start-up or control of the process; Details of the apparatus used; Details of the refrigerant compression system used
  • F25J1/0279—Compression of refrigerant or internal recycle fluid, e.g. kind of compressor, accumulator, suction drum etc.
  • F25J1/0292—Refrigerant compression by cold or cryogenic suction of the refrigerant gas
• • 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
  • F25J2220/64—Separating heavy hydrocarbons, e.g. NGL, LPG, C4+ hydrocarbons or heavy condensates in general
• • 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

• the present invention relates to a method and system for liquefying a natural gas feed stream.
• hydrocarbon-containing gas streams Methods of liquefying hydrocarbon-containing gas streams are well known in the art. It is desirable to liquefy a hydrocarbon-containing gas stream such as natural gas stream for a number of reasons. As an example, natural gas can be stored and transported over long distances more readily as a liquid than in gaseous form, because it occupies a smaller volume and does not need to be stored at high pressures. Typically, before being liquefied, the contaminated hydrocarbon-containing gas stream is treated to remove one or more contaminants (such as H2O, CO2, H2S and the like) which may freeze out during the liquefaction process.
• contaminants such as H2O, CO2, H2S and the like
• Processes of liquefaction are known from the prior art in which one or more closed refrigerant cycles are used to cool and liquefy the hydrocarbon-containing gas stream. Examples are a C3-MR process or a DMR process.
• a C3-MR process a first cooling stage uses propane as refrigerant and the second cooling stages uses a mixture of two or more refrigerants, such as a mixture of propane, ethane, methane and nitrogen.
• two refrigerant cycles are used, each comprising a mixed refrigerant .
• WO2014/166925 describes a method of liquefying a contaminated hydrocarbon-containing gas stream, the method comprising at least the steps of: (1) providing a contaminated hydrocarbon-containing gas stream;
• step (4) expanding the liquid stream obtained in step (4) thereby obtaining a multiphase stream, the multiphase stream containing at least a vapour phase, a liquid phase and a solid phase;
• step (10) combining the compressed gas stream obtained in step (9) with the contaminated hydrocarbon-containing gas stream provided in step (1) .
• the method as described in WO2014/166925 allows liquefying a contaminated hydrocarbon-containing gas stream with a relatively low equipment count, without the need of a refrigerant cycle, thereby providing a simple and cost-effective method of liquefying a contaminated hydrocarbon-containing gas stream, in particular a methane-containing contaminated gas stream such as natural gas .
• the contaminant may be C02.
• step (5) uses a freeze out process scheme to remove C02.
• the process conditions in the liquid stream obtained in step (4) are just outside the C02 freeze out envelope (the process conditions are for example 20 bar, -120°C, 1 mol% C02) such that any further temperature reduction will provoke freeze out of C02.
• the temperature reduction is achieved in step (5) by pressure reduction over a Joule Thomson valve. The pressure reduction evaporates part of the liquid methane, thus cooling the remaining liquid.
• US3616652 describes a process for liquefying natural gas comprising flashing the stream to a low pressure level to form a low pressure liquid and a flash gas and recirculating the flash gas in a circuit arranged to assist in the cooling of the natural gas at the upper pressure level by indirect heat exchange therewith.
• a method of liquefying a natural gas feed stream comprising at least the steps of : (a) providing a process feed stream (11) by mixing the natural gas feed stream (1) with a recycle stream (105) ,
• the pressure of the compressed process stream may be in the range of 120 - 200 bar or in the range of 130 - 190 bar,
• step (b) is well above the critical pressure (supercritical pressure) , preferably at least 50 bars above the critical pressure, which results in a relatively constant temperature profile in the first heat exchanger (40, step c2) for the compressed process stream (31), because of a relatively constant heat capacity at supercritical conditions, as opposed to a pressure that would be in the proximity of the critical point, where heat capacity variations with temperature are large.
• critical pressure supercritical pressure
• the temperature profiles are substantially straight lines (in a temperature vs heat (Q) diagram) , reducing the temperature difference between hot and cold streams and thus reducing
• a pressure close to the critical point would result in a divergence between the two heat exchanging streams at the cold of the heat exchanger, thereby resulting in inefficiencies, meaning that the compressed process stream (31) is less precooled (i.e. leaves the first heat exchanger (40) at a higher temperature) .
• the precooling pressure i.e. the pressure of the expanded first split-off stream (34) is an optimized parameter.
• a lower pressure results in a colder expanded first split-off stream (34) but requires more
• the optimum precooling pressure may therefore be determined by an iterative process.
• the precooling pressure may further be adjusted during operation to take into account changes in operation conditions, such as a changing ambient temperature.
• Fig. 1 schematically shows a process scheme according to an embodiment
• Fig. 2 schematically shows a process scheme according to an alternative embodiment .
• a natural gas feed stream 1 is provided.
• the natural gas feed stream 1 may also be referred to as a hydrocarbon feed stream 1.
• the natural gas feed stream 1 mainly comprises methane.
• the natural gas feed stream 1 is not particularly limited, it preferably is a methane-rich gas stream, preferably comprising at least 50 mol% methane, more preferably at least 80 mol% and more preferably at least 95 mol% methane.
• the remainder of the natural gas feed stream 1 is primarily formed of hydrocarbon molecules comprising two, three or four carbon atoms (ethane, propane, butane) .
• the natural gas feed stream 1 may originate from a gas treatment stage in which the contaminants and C5+ molecules are removed. As will be understood by the skilled person, the exact line-up of the gas treatment stage may depend on the gas composition upstream of the gas treatment stage and the liquid natural gas
• Contaminants and hydrocarbon molecules comprising five or more carbon atoms are preferably removed
• the natural gas feed stream 1 is formed by contaminants and hydrocarbon molecules comprising five or more carbon atoms after removal.
• the natural gas feed stream 1 comprises less than 0.15 mol% hydrocarbon molecules comprising five or more carbon atoms.
• the amount of hydrocarbon molecules comprising five or more carbon atoms may be in the range of 0.10 - 0.15 mol%.
• the contaminants and hydrocarbon molecules comprising five or more carbon atoms may be removed in between the first and second heat exchangers 40, 60, instead of upstream removal.
• the natural gas feed stream 1 preferably has a pressure in the range of 50 - 80 bar, more preferably in the range of 55 - 75 bar, e.g. 65 bar.
• the natural gas feed stream 1 preferably has a temperature in the range of 0 - 40°C, e.g. 17°C.
• a process feed stream 11 is formed by mixing/combining the natural gas feed stream 1 with a recycle stream 105 by means of a combiner 2.
• the recycle stream 105 will be described in more detail below.
• step (b) the process stream 11 is passed to a compressor stage 20 to obtain a compressed process stream 25, having a pressure of at least 120 bars and a first temperature below 40°C.
• the pressure of the compressed process stream may be in the range of 120 - 200 bar or in the range of 130 - 190 bar,
• the compressor stage 20 comprises a single compressor 21 with an associated intercooler 22 positioned downstream of the compressor 21.
• the compressor stage 20 comprises a multi-stage compressor with intercoolers .
• the compressor stage 20 may comprise a multi-stage compressor 20 having any suitable number of compressors and
• the compressor stage 20 may comprise a first compressor 21 to receive the process stream 11, subsequently followed by a first intercooler 22, a second compressor 23 and a second intercooler 24.
• the intercooler ( s ) preferably cool(s) the process stream against ambient, such as against ambient air or ambient water.
• step (cl) the compressed process stream 25 is fed to a first splitter 30 to obtain a first split-off stream 32.
• the first splitter 30 may be any suitable type of splitter, including a simple T- or Y- unction.
• the first splitter 30 may also be a controllable splitter to actively control and adjust the split-off portion during operation.
• the controllable splitter may comprise one or two controllable valves positioned downstream of the junction to control the split ratio.
• the split ratio is defined as the mass flow of the split-off stream 32 (MF 32 ) divided by the mass flow of the compressed process stream 25 (MF25) , MF32 : MF25.
• the split ratio is in the range of 0.5 - 0.65.
• the first split-off stream 32 is expanded and thereby cooled in a precool expander 33.
• the expansion typically has a pressure ratio in the range of 4 - 6, e.g. 5, to provide sufficient cold to precool the remainder of the compressed process stream 31.
• the pressure ratio is defined as the pressure ( P 32 ) upstream of the precool expander 33 divided by the pressure ( P 34 ) downstream of the precool expander 33.
• the expanded first split-off stream 34 may have a pressure P 34 in the range of 26 - 38 bar, preferably 29 - 35 bar, more preferably in the range of 31 - 33 bar.
• the expanded first split-off stream 34 typically has a temperature in the range of minus 60° - minus 80°C, typically minus 70°C.
• step (c2) the remainder of the compressed process stream 31 is fed to a warm-side of a first heat exchanger 40 and the expanded first split-off stream 34 is fed to a cold-side of the first heat exchanger 40 to allow the two streams to exchange heat, in particular to allow the expanded first split-off stream 34 to precool the remainder of the compressed process stream 31.
• the first heat exchanger 40 may be any type of suitable heat exchanger including a coil wound heat exchanger or a plate (fin) heat exchanger.
• the first heat exchanger 40 may comprise a plurality of serial and/or parallel sub-heat exchangers (not shown) . From the first heat exchanger 34 a precooled process stream 41 is obtained on the cold-side and a warmed first split-off stream 42 is obtained on the warm-side. The warmed first split-off stream 42 is forwarded to the recompression stage 200 to be comprised in the recycle stream 105 as will be described in more detail below.
• the warmed first split-off stream 42 may have a temperature in the range of 0°C - 40°C, e.g. 15°C.
• the precooled process stream 41 may have a temperature in the range of minus 50°C - minus 70°C, e.g. minus 60 °C.
• the precooled process stream 41 is passed to a second splitter 50 to obtain a second split-off stream 52.
• the second splitter 50 may be any suitable type of splitter, including a simple T- or Y- unction.
• the second splitter 50 may also be a controllable splitter to actively control and adjust a second split-off portion during operation.
• the second controllable splitter 50 may comprise one or two controllable valves positioned downstream of the junction to control the second split ratio .
• the second split ratio is defined as the mass flow of the second split-off stream 52 (MF52) divided by the mass flow of the precooled process stream 41 (MF41), MF52 : MF41.
• the second split ratio is in the range of 0.75 - 0.85.
• step (dl) the second split-off stream 52 is passed to an expander 53, e.g. a dense phase expander, to expand and thereby cool the second split-off stream 52 to enter the two phase region thereby obtaining an expanded and cooled multiphase second split-off stream 54.
• the cooled multiphase second split-off stream 54 is typically expanded to a pressure in the range of 5 - 20 bar, e.g. in the range 8 - 12 bar and to a third temperature in the range of minus 110°C - minus 130 °C.
• the expander 53 may function as a dense phase expander, i.e. an expander 53 which is suitable to receive a pressurized supercritical flow at an inlet of the expander 53 and arranged to discharge a multiphase stream 54 via an outlet of the expander 53.
• multiphase stream 54 may be a two phase stream comprising a vapour/gas phase and a liquid phase.
• step (d2) the expanded and cooled multiphase second split-off stream 54 is flashed in a phase
• the phase separator 55 may be any suitable vapour- liquid separator, such as a flash drum or knock-out vessel.
• step (d3) the remainder of the precooled
• compressed process stream 51 is fed to a warm-side of a second heat exchanger 60 and the vapour stream 56 is fed to a cold-side of the second heat exchanger 60 to allow the two streams to exchange heat, in particular to allow the vapour stream 56 to further cool the remainder of the precooled compressed process stream 51. Thereby, a further cooled process stream 61 and a warmed vapour stream 62 are obtained.
• the warmed vapour stream 62 may be forwarded to the recompression stage 200 to be comprised in the recycle stream 105 as will be described in more detail below. According to an embodiment, the warmed vapour stream 62 is first forwarded to the first heat exchanger 40 and then forwarded to the recompression stage 200, as will be described in more detail below.
• the second heat exchanger 60 may be any type of suitable heat exchanger including a coil wound heat exchanger or a plate (fin) heat exchanger.
• the second heat exchanger 60 may comprise a plurality of serial and/or parallel sub-heat exchangers (not shown) .
• the warmed vapour stream 62 may have a temperature
• T62 in the range of minus 65°C - minus 85°C and a
• the precooled process stream 51 may enter the second heat exchanger 60 having a temperature T51 in the range of minus 60°C - minus 80°C and the further cooled process stream 61 may leave the second heat exchanger 60 having a temperature ⁇ in the range of minus 110°C - minus 130°C and a pressure which is still substantially equal to the pressure of the compressed process stream 25, except for a (undeliberate) pressure drop resulting from flowing through the piping and first and second heat exchangers.
• the further cooled process stream 61 may be in a
• step (e ) the further cooled process stream 61 is expanded in a liquid expander 70 thereby obtaining a liquid natural gas stream 71 having a pressure in the range of 8 - 15 bar, e.g. 10 bar, and a temperature equal to the boiling temperature of the composition at that pressure (e.g. approximately minus 125°C at 10 bar) .
• the liquid natural gas stream 71 may be passed to a flash vessel 80 thereby obtaining liquid natural gas at a pressure in the range of 1 - 3 bar, e.g. atmospheric pressure.
• Flash vessel 80 may be a storage vessel.
• liquid natural gas is passed from flash vessel 80 to a subsequent storage vessel.
• the method further comprises passing the liquid natural gas stream 71 to a flash vessel 80 and obtaining a liquid natural gas product stream 81 as bottom stream from the flash vessel 80.
• the liquid natural gas product stream 81 may be passed to a LNG storage tank such as a LNG storage tank on a LNG carrier vessel/ship or floating LNG facility.
• the method comprises obtaining a flash gas stream 82 as top stream from the flash vessel 80, passing the flash gas stream 82 to the recompression stage 200, wherein the flash gas stream 82 is optionally at least partially passed through a third heat exchanger 75, 75' to provide cooling to at least part of the liquid stream 57 obtained in (d2) .
• the method comprises
• the first pressure reduction device may be a (Joule- Thomson) valve or an expander.
• the second pressure reduction device may be a (Joule-Thomson) valve or an expander.
• the first pressure reduction device is an expander and the second pressure reduction device is a Joule-Thomson valve.
• This embodiment provides the advantage that the splitting in (el) makes it possible to control the flow rate of the second liquid portion through the third heat exchanger and thereby allows for a better matching of the heating curves in the third heat exchanger 75, yielding a lower logarithmic mean temperature difference (LMTD) and hence lower exergy losses in the third heat exchanger 75.
• LMTD logarithmic mean temperature difference
• the splitting in (el) may be a predetermined split, e.g. may provide for a predetermined flow rate of the second liquid portion through the third heat exchanger.
• the splitting may be a controllable split provided by a controllable splitter, which provides for an adjustable split, which can be controlled actively during operation.
• the second liquid natural gas stream 73 and the third liquid natural gas stream 76 are typically at the same pressure, being close to atmospheric (in the range 1
• step (e3) the second liquid portion 74 is cooled in the third heat exchanger 75 against at least part of the flash gas stream 82, thereby obtaining a warmed flash gas stream 77, which is passed to the recompression stage 200.
• the third liquid natural gas stream 76 which is a sub-cooled liquid, can effectively be reduced in
• the method comprises
• Expander 78' may more generally be a pressure reduction device, such as a (Joule-Thomson) valve.
• Further liquid natural gas stream 76' may have a pressure in the range of 1 - 1.25 bar, e.g. 1.05 bar, and a temperature in the range minus 160 - minus 162°C, e.g. minus 160.6°C.
• the warmed flash gas stream 77 may be at atmospheric pressure, e.g. 1 bar, and at a temperature in the range of minus 120 - minus 130°C, e.g. minus 125°C.
• the pressure in the flash vessel 80 is substantially equal to atmospheric pressure and the collected liquid natural gas is at its boiling point.
• the warmed vapour stream 62 obtained from the second heat exchanger 60 in (d3) is passed through the first heat exchanger 40 to provide cooling to the remainder of the compressed process stream 31 thereby obtaining a further warmed vapour stream 43 before being passed to the recompression stage 200.
• step ( f) the warmed first split-off stream 43 and the warmed vapour stream 62 originating from the expanded and cooled multiphase second split-off stream 54 are combined to be comprised in the recycle stream 105 in the recompression stage 200.
• ( f) comprises separately passing the warmed first split-off stream 42 and one of the warmed vapour stream 62 and the further warmed vapour stream 43 to the recompression stage 200 to obtain the recycle stream 105.
• the recompression stage 200 may be a multi-stage re- compressor stage.
• the first split-off stream 42 and one of the warmed vapour stream 62 and the further warmed vapour stream 43 are preferably fed to different
• warmed vapour stream 43 is passed through the first heat exchanger 40, it is the further warmed vapour stream 43 that is passed to the first heat exchanger 40.
• ( f) further comprises passing the flash gas stream (82) or the warmed flash gas stream 77 to the recompression stage 200.
• the flash gas stream 82 or warmed flash gas stream 77 is passed to the recompression stage separately from the warmed first split-off stream 42, the warmed vapour stream 62 and the further warmed vapour stream 43.
• the flash gas stream 82 or warmed flash gas stream 77, the warmed first split-off stream 42, the warmed vapour stream 62 or the further warmed vapour stream 43 are preferably fed to different (pressure) stages of the recompression stage 200.
• the recompression stage 200 may comprise a number of recompression stages positioned in series, each
• the number of recompression stages may be equal to the number of streams being passed to the recompression stage 200, e.g. three according to the embodiment depicted in Fig. 1.
• One or more recompression stages may comprise one or more associated intercoolers .
• the recompression stage 200 may then be referred to as an intercooled multi-stage re- compressor stage.
• the recompression stage 200 is a three-stage recompressor stage 200 comprising three recompression stages
• a pre-recompression stage positioned in series, i.e. a pre-recompression stage, an intermediate recompression stage and a final
• the pre-recompression stage may comprise a first compressor 90 comprising two serial sub-compressors, arranged to receive the warmed flash gas stream 77 and compress the warmed flash gas stream 77 thereby obtaining a first recompressed stream 91 having a temperature T91 in the range of 15°C - 20°C.
• the pressure P91 of the first recompressed stream is substantially equal to the pressure P43 of the warmed vapour stream 43, e.g. in the range of 8 - 12 bar, e.g. 10 bar.
• flash gas stream 82 typically having a temperature of -162°C
• warmed flash gas stream 77 typically having a temperature of approximately minus
• the pre-compressed stream 91 and the further warmed vapour stream 43 (or warmed vapour stream 62) are combined and are fed to the intermediate recompression stage as combined stream 92.
• the intermediate recompression stage comprises an intermediate compressor 93 and associated intermediate intercooler 97 positioned downstream of the intermediate compressor 93.
• the intermediate recompression stage is arranged to receive the combined stream 92 and further recompress and cool the combined stream 92 to obtain intermediate compressed stream 98 typically having an intermediate pressure P98 in the range of 25 - 35 bar, e.g. 32 bar.
• compressor 93 typically has a temperature of above 100°C and is cooled by intercooler 97 typically to a
• the final recompression stage comprises a final compressor 102 and associated intercooler 104 positioned downstream of the final compressor 102.
• the final recompression stage is arranged to receive the further combined stream 101 and further recompress and cool the further combined stream 101 to obtain recycle stream 105.
• the recycle stream 105 typically has a pressure Pios substantially equal to the pressure of the natural gas feed stream 1, typically in the range of 50 - 80 bar, more preferably in the range of 55 - 75 bar, e.g. 65 bar.
• the method further comprises
• the fuel stream 95 is obtained at an intermediate position at which the nitrogen concentration is relatively high.
• the flash gas stream 77, 82 and the vapour stream 56 contain a relatively high amount of nitrogen compared to the first split-off stream 32, 42
• the fuel stream 95 is preferably obtained upstream from the position at which the warmed first split-off stream 42 enters the multi-stage re-compressor unit 200.
• the fuel stream 95 is preferably obtained as a side stream of stream 96 leaving intermediate compressor 93.
• the fuel stream 95 is obtained at an intermediate position in between the intermediate compressor 93 and associated intermediate intercooler 97. This results in an effective fuel stream having a relatively high amount of nitrogen and reduces the amount of nitrogen being recycled.
• the process feed stream 11 is obtained by mixing the natural gas feed stream 1, taken after dew pointing to meet the C5+ specification
• a (booster) compressor stage 20 comprising two stages with intercooling rises the pressure from 65 bar to 160 bar.
• the process feed stream 11 is cooled down by the intercooler ( s ) to approximately 17°C using water as a cooling media.
• the thereby obtained compressed process stream 25 is split in two fractions, the first split-off stream 32 (0.57 mass fraction) and a remainder of the compressed process stream (0.43 mass fraction) .
• the first split-off stream is expanded in the precool expander 33, being a 30 MW expander, with a pressure ration of approximately 5. Thereby the expanded first split-off stream 34 is obtained to provide cold for the remainder of the compressed process stream.
• These streams exchange heat in the first heat exchanger 40.
• the hot outlet reaches -75° C and the cold outlet is directed to the recompression stage 200.
• the precooled process stream 41 is subsequently split into a second split-off stream 52 (0.8 mass fraction), which is expanded to 10 bar in expander 53, thereby cooling itself to approximately minus 123°C, entering the two phase region thereby obtaining the expanded and cooled multiphase second split-off stream 54.
• the expanded and cooled multiphase second split-off stream 54 is flashed in a high pressure separator 55 to obtain the vapour stream 56 (0.34 mole fraction) .
• the vapor stream 56 is employed to further cool the remainder of the precooled compressed process stream 51 in the second heat exchanger 60 to approximately -123 C. Subsequently, the vapor stream 56 (now being warmed vapour stream 62) provides cold in the first heat exchanger 40.
• the liquid stream 57 obtained from the separator 55 is split into two.
• the first liquid portion or main stream 71 (0.89 mass fraction) is expanded through a first pressure reduction device, for instance liquid expander 72, whereas the second liquid portion 74 or minor fraction (0.19 mass fraction) is subcooled against the flash gas stream 82 in third heat exchanger 75 and subsequently let down in pressure with a second pressure reduction device, such as a J-T valve 78 before being passed to the flash vessel 80.
• a first pressure reduction device for instance liquid expander 72
• a second liquid portion 74 or minor fraction (0.19 mass fraction
• the flash gas stream 82 after having cooled at least part of the liquid stream 57 in the third heat exchanger 75, is forwarded to the recompression stage 200.
• the warmed flash gas stream 77 is directed to cold
• the outlet temperature of the first compressor 90 has risen to 17°C.
• the outlet stream of the first compressor 90 is mixed with the 10 bar

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• 2017
  • 2017-03-20 WO PCT/EP2017/056520 patent/WO2017162566A1/en active Application Filing
  • 2017-03-20 CN CN201780018963.6A patent/CN108779953A/zh active Pending
  • 2017-03-20 CA CA3017839A patent/CA3017839A1/en not_active Abandoned
  • 2017-03-20 US US16/086,491 patent/US20190049174A1/en not_active Abandoned
  • 2017-03-20 EP EP17712106.8A patent/EP3433556A1/en not_active Withdrawn
  • 2017-03-20 AU AU2017237356A patent/AU2017237356B2/en not_active Ceased
  • 2017-03-20 RU RU2018136794A patent/RU2730090C2/ru active

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