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
  • F25B—REFRIGERATION MACHINES, PLANTS OR SYSTEMS; COMBINED HEATING AND REFRIGERATION SYSTEMS; HEAT PUMP SYSTEMS
  • F25B7/00—Compression machines, plants or systems, with cascade operation, i.e. with two or more circuits, the heat from the condenser of one circuit being absorbed by the evaporator of the next circuit
• • 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
  • F25J1/0047—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 an "external" refrigerant stream in a closed vapor compression cycle
  • F25J1/0052—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 an "external" refrigerant stream in a closed vapor compression cycle by vaporising a liquid refrigerant stream
  • F25J1/0055—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 an "external" refrigerant stream in a closed vapor compression cycle by vaporising a liquid refrigerant stream originating from an incorporated cascade
• • 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
  • F25J1/0047—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 an "external" refrigerant stream in a closed vapor compression cycle
  • F25J1/0052—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 an "external" refrigerant stream in a closed vapor compression cycle by vaporising a liquid refrigerant stream
  • F25J1/0057—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 an "external" refrigerant stream in a closed vapor compression cycle by vaporising a liquid refrigerant stream after expansion of the liquid refrigerant stream 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
  • F25J1/006—Processes or apparatus for liquefying or solidifying gases or gaseous mixtures characterised by the refrigerant fluid used
  • F25J1/008—Hydrocarbons
  • F25J1/0087—Propane; Propylene
• • 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
  • F25J1/006—Processes or apparatus for liquefying or solidifying gases or gaseous mixtures characterised by the refrigerant fluid used
  • F25J1/008—Hydrocarbons
  • F25J1/009—Hydrocarbons with four or more carbon atoms
• • 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
  • F25J1/0257—Construction and layout of liquefaction equipments, e.g. valves, machines
  • F25J1/0262—Details of the cold heat exchange system
  • F25J1/0264—Arrangement of heat exchanger cores in parallel with different functions, e.g. different cooling streams
  • F25J1/0265—Arrangement of heat exchanger cores in parallel with different functions, e.g. different cooling streams comprising cores associated exclusively with the cooling of a refrigerant stream, e.g. for auto-refrigeration or economizer
  • F25J1/0267—Arrangement of heat exchanger cores in parallel with different functions, e.g. different cooling streams comprising cores associated exclusively with the cooling of a refrigerant stream, e.g. for auto-refrigeration or economizer using flash gas as heat sink
• • 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
  • F25J1/0257—Construction and layout of liquefaction equipments, e.g. valves, machines
  • F25J1/0262—Details of the cold heat exchange system
  • F25J1/0264—Arrangement of heat exchanger cores in parallel with different functions, e.g. different cooling streams
  • F25J1/0265—Arrangement of heat exchanger cores in parallel with different functions, e.g. different cooling streams comprising cores associated exclusively with the cooling of a refrigerant stream, e.g. for auto-refrigeration or economizer
  • F25J1/0268—Arrangement of heat exchanger cores in parallel with different functions, e.g. different cooling streams comprising cores associated exclusively with the cooling of a refrigerant stream, e.g. for auto-refrigeration or economizer using a dedicated refrigeration means
• • 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
  • 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.
  • F25J1/0296—Removal of the heat of compression, e.g. within an inter- or afterstage-cooler against an ambient heat sink
  • F25J1/0297—Removal of the heat of compression, e.g. within an inter- or afterstage-cooler against an ambient heat sink using an externally chilled fluid, e.g. chilled water
• • 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
  • F25B—REFRIGERATION MACHINES, PLANTS OR SYSTEMS; COMBINED HEATING AND REFRIGERATION SYSTEMS; HEAT PUMP SYSTEMS
  • F25B2400/00—General features or devices for refrigeration machines, plants or systems, combined heating and refrigeration systems or heat-pump systems, i.e. not limited to a particular subgroup of F25B
  • F25B2400/13—Economisers
• • 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
  • F25B—REFRIGERATION MACHINES, PLANTS OR SYSTEMS; COMBINED HEATING AND REFRIGERATION SYSTEMS; HEAT PUMP SYSTEMS
  • F25B2400/00—General features or devices for refrigeration machines, plants or systems, combined heating and refrigeration systems or heat-pump systems, i.e. not limited to a particular subgroup of F25B
  • F25B2400/23—Separators
• • 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
  • F25J2270/12—External refrigeration with liquid vaporising 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
  • F25J2270/00—Refrigeration techniques used
  • F25J2270/60—Closed external refrigeration cycle with single component refrigerant [SCR], e.g. C1-, C2- or C3-hydrocarbons

Definitions

• the present invention relates to a method for the liquefaction of a hydrocarbon-rich stream, preferably a natural gas containing stream, wherein the hydrocarbon- rich stream to be liquefied is heat exchanged against a refrigerant thereby cooling the hydrocarbon-rich stream.
• US patent 6,272,882 discloses a plant and a process of liquefying a gaseous methane-rich feed to obtain liquefied natural gas.
• the plant comprises a pre-cooling stage for pre-cooling the feed, followed by a natural gas liquids extraction stage, followed by further cooling of the gaseous feed in a mixed-refrigerant operated main cryogenic heat exchanger to obtain a pressurised liquid natural gas.
• the pressurised liquid natural gas is finally flashed to atmospheric pressure in a flashing stage .
• the disclosed pre-cooling stage is based on a propane refrigerant cycle, wherein evaporated propane is compressed in a propane compressor.
• the propane is next condensed in an air cooler, where after the condensed propane at elevated pressure is passed to heat exchangers.
• heat exchangers heat is to be transferred from the product stream into the propane refrigerant.
• the condensed propane is allowed to expand to a high intermediate pressure over an expansion valve.
• a gaseous fraction of propane is formed by drawing heat from the product stream drawn from the heat exchangers and passed to an inlet in the propane compressor.
• the liquid fraction is passed to a consecutive heat exchanger.
• the propane Before entering in the consecutive heat exchanger, the propane is allowed to expand to a low intermediate pressure over another expansion valve.
• One or more of the above or other objects can be achieved according to the present invention by providing a method for the liquefaction of a hydrocarbon-rich stream, preferably a natural gas containing stream, wherein the hydrocarbon-rich stream to be liquefied is heat exchanged against a refrigerant, the method at least comprising the steps of:
• step (d) expanding the fully condensed compressed refrigerant thereby forming said liquid refrigerant; wherein, before expanding in step (d) , the fully condensed compressed refrigerant is further sub-cooled by indirect heat exchange against an auxiliary refrigerant being cycled in an auxiliary refrigerant cycle comprising an auxiliary compressing step followed by drawing heat from the fully condensed compressed refrigerant for its further sub-cooling.
• Further sub-cooling of the already fully condensed compressed refrigerant has an advantage that less flash vapour will be formed in the expanding. Such flash vapour has to be circulated through the refrigeration cycle, while it hardly contributes to refrigerating the product stream. Specifically, power is lost in recompressing the flash vapour.
• the fully condensed compressed refrigerant is sub-cooled to a temperature that is lower than ambient temperature.
• the further sub-cooling is preferably performed to a temperature that is less than 30 0 C above a bubble point temperature of the refrigerant after the subsequent expanding.
• the further sub-cooling is preferably performed to a temperature that is less than 10 0 C - more preferably less than 4 0 C - above a bubble point temperature of the refrigerant after the subsequent expanding.
• the auxiliary refrigerant is cycled in an auxiliary cycle comprising an auxiliary compressing step followed by drawing heat from the fully condensed compressed refrigerant.
• the auxiliary refrigerant cycle can be a dedicated auxiliary cycle, allowing to add-on to an existing process an additional sub-cooling process without having to modify the existing process in other places .
• Figure 1 schematically shows an apparatus for carrying out one embodiment of the method of the invention
• Figure 2 schematically shows cooling and depressurisation trajectories in a schematic phase diagram
• Figure 3 schematically shows an apparatus for carrying out a comparative method
• Figure 4 schematically shows an apparatus for carrying out an alternative embodiment of the method of the invention
• Figure 5 schematically shows an apparatus for carrying out another alternative embodiment of the method of the invention
• Figure 6 schematically shows an apparatus for carrying out another alternative embodiment of the method of the invention.
• Figure 7 schematically shows an apparatus for carrying out still another alternative embodiment of the method of the invention.
• a single reference number will be assigned to a line as well as a stream carried in that line. Same reference numbers refer to similar components.
• FIG. 1 schematically shows an apparatus representing a process scheme for refrigerating a hydrocarbon-rich product stream.
• the apparatus comprises a heat exchanger arrangement 1 in the form of so-called kettles Ia to Id wherein a liquid refrigerant 19 is allowed to evaporate using heat from the product stream (not shown) .
• a liquid refrigerant 19 is allowed to evaporate using heat from the product stream (not shown) .
• four kettles are depicted, each operating at a different pressure level, but the invention can also employ other types of heat exchangers or a different number of heat exchangers including a single heat exchanger.
• part of the liquid refrigerant in kettle Ia is evaporated, using heat from the product stream, whereby a liquid fraction of the liquid refrigerant is retained and separated from the evaporated part to be fed to the next kettle Ib, from where another part can be evaporated and so on.
• Evaporated refrigerant is removed from the kettles Ia to Id via lines 3a to 3d, and fed to a compressor 5 wherein the evaporated refrigerant is subsequently compressed.
• the compressor 5 has consecutive pressure compression stages 5a to 5d, and the lines 3a to 3d fluidly connect with corresponding pressure level inlets 6a to 6d.
• a train of compressors with different pressure levels can be employed, or a single compressor.
• Another possible alternative for the present invention is a split compressor arrangement as published in US patent 6,637,238.
• the compressed refrigerant is expelled from compressor 5 via line 8 and contains a lot of heat, notably super heat in the vapour phase and evaporation heat.
• the compressed refrigerant is cooled against ambient in ambient cooler 10, here provided in the form of an air cooler, whereby the super heat and the evaporation heat is removed from the compressed refrigerant resulting in a fully condensed compressed refrigerant 12.
• ambient cooler 10 here provided in the form of an air cooler
• a water cooler can be employed instead of or in combination with the air cooler 10.
• the fully condensed compressed refrigerant 12 may be sub-cooled against the ambient when some additional heat is removed from the refrigerant by the ambient.
• Figure 2 schematically depicts a phase diagram for a typical refrigerant, where enthalpy H is set out on a horizontal axis and pressure P on a vertical axis.
• Line 20 represents a phase envelope, underneath which liquid and vapour phases of the refrigerant coexist and separate.
• Point W represents the compressed refrigerant 8 at high pressure Po and high enthalpy (or temperature) .
• the compressed refrigerant is cooled to point Y, i.e. its enthalpy is lowered, at essentially constant pressure.
• the removal of super heat is indicated by line 22 and the removal of evaporation heat is indicated by line 24.
• X represents the refrigerant as it has just fully condensed at the given pressure level P 0 .
• the optional sub-cooling against ambient to point Y is indicated via line 26.
• the fully condensed compressed refrigerant 12 is further sub-cooled by indirect heat exchange against an auxiliary refrigerant 40, for instance in an auxiliary heat exchanger arrangement 14, resulting in a further sub-cooled fully condensed compressed refrigerant stream 16.
• the auxiliary heat exchanger arrangement 14 can comprise one single heat exchanger or a set of two or more heat exchangers arranged in series, wherein the auxiliary refrigerant is allowed to evaporate at one or more pressure levels.
• the pressure is essentially maintained at the compressed level.
• the resulting further sub- cooled fully condensed compressed refrigerant 16 is represented by point Z, and the further sub-cooling at constant pressure by line 28.
• the sub-cooled fully condensed compressed refrigerant 16 is expanded in an expansion means, for instance over a Joule-Thompson valve 18, and the resulting refrigerant stream 19 is fed into the first kettle Ia where it is allowed to evaporate using heat extracted from the product stream.
• no expander is present between cooler 10 and the auxiliary heat exchanger 14; in other words, the pressure drop of the refrigerant between the cooling in cooler 10 and the sub- cooling against the auxiliary refrigerant in auxiliary heat exchanger 14 is less than 10 bar, preferably less than 5 bar, more preferably less than 2 bar, even more preferably less than 1 bar.
• the invention at least also covers an alternative embodiment, wherein the first heat exchange stage Ia is performed in two or more kettles or heat exchangers arranged in parallel with each other.
• the further subcooled fully condensed compressed refrigerant 16 can be split in two or more branches and expanded over two or more valves provided in the branches. Both the evaporated fractions as well as the liquid fractions drawn from the parallel heat exchangers are recombined, whereby the evaporated fraction is subjected to recompression and the liquid fraction fed to a consecutive serially arranged second cooling stage.
• An example of such parallel first stage is shown in US patent 6,389,844.
• the further sub-cooled fully condensed compressed refrigerant 16 is expanded in one expansion means such as the Joule- Thompson valve 18 of the embodiment of Figure 1, and subsequently split over the two or more branches as discussed in the above-paragraph.
• the fully condensed compressed refrigerant stream is sub- cooled to such an extent that the expanded refrigerant stream in line 19 stays fully in the liquid region of the phase diagram. Any vapour that is formed over the expansion, so-called flash vapour, is lost for cooling purposes, but still has to go through the compression cycle via the first kettle Ia and line 3a.
• the fully condensed compressed refrigerant 12 is preferably sub-cooled to a temperature whereby the subsequent expanding brings the temperature below the bubble point temperature of the refrigerant after the subsequent expanding, to avoid flashing during the expansion step altogether.
• refrigerant stream 16 is preferably flash-expanded from point Z via line 30 to point Zl where the pressure P a represents the pressure level of operation of the first kettle Ia.
• the fully condensed compressed refrigerant in line 12 has been sub-cooled to a temperature between the temperature in the first kettle Ia and 9 0 C higher than that temperature, preferably between the temperature in the first kettle Ia and 5 0 C higher than that temperature, more preferably the temperature in the first kettle Ia and 3 °C higher than that temperature.
• the present invention also covers alternative routes from X to Zl, such as for instance sub-cooling against ambient from point X to Y, and then further sub-cooling while simultaneously letting off pressure; or such as for instance sub-cooling against ambient from point X to Y, letting off pressure to an intermediate value that is higher than P a , then further sub-cooling, and then letting off more pressure and so on until point Zl is reached.
• alternative routes from X to Zl such as for instance sub-cooling against ambient from point X to Y, and then further sub-cooling while simultaneously letting off pressure; or such as for instance sub-cooling against ambient from point X to Y, letting off pressure to an intermediate value that is higher than P a , then further sub-cooling, and then letting off more pressure and so on until point Zl is reached.
• the auxiliary refrigerant 40 can be at least partially evaporated after having picked up enthalpy from the refrigerant stream 12 in heat exchanger arrangement 14.
• the auxiliary refrigerant is cycled in an auxiliary cycle 55, whereby the auxiliary refrigerant stream is recompressed in an auxiliary compressor 45.
• the auxiliary compressor 45 optionally comprises two or more compression stages 45a and 45b.
• a fully compressed auxiliary refrigerant stream 42 is then cooled against ambient in heat exchanger 44.
• the resulting fully compressed cooled auxiliary refrigerant stream 46 is then optionally separated in a liquid fraction 52 and a vapour fraction 50 in separator 48, whereby the vapour fraction 50 is fed back to the auxiliary compressor 45 at an intermediate pressure inlet point.
• the fully compressed cooled auxiliary refrigerant stream 46 is partly flashed off by letting down the pressure upstream of the separator 48.
• a Joule- Thompson valve 54 can be provided, optionally preceded by a dynamic expansion device if possible.
• Such so-called “economizer” line-up reduces power consumption as part of the flash vapour is circulated at a higher pressure level than if the full pressure drop were made in one expansion step in valve 56.
• the pressure in the auxiliary refrigerant stream 52 can be let down, for which a Joule- Thompson valve 56 can be provided, optionally preceded by a dynamic expansion device if possible.
• the bubble point temperature can be chosen in accordance with the desired temperature to be reached in the fully condensed compressed refrigerant 16.
• the auxiliary refrigerant 40 can be derived from a cold slip stream from somewhere else in the process.
• the auxiliary refrigerant can for instance be a slip stream of so-called end-flash gas.
• An advantage of such alternative is that no additional refrigeration cycle has to be built and operated and that the additional heat integration within the entire process can increase the power-efficiency of the entire process.
• a single component refrigerant typically propane (i.e.
• auxiliary refrigerant comprising at least 90 mol% propane, preferably substantially 100%
• propane a suitable choice for the auxiliary refrigerant is butane (i.e. comprising at least 90 mol% butane, preferably substantially 100%). Butane is suitable because it has a slightly higher boiling temperature than propane refrigerant when determined under equal pressure condition. This enables a suitable selection of heat exchange conditions in heat exchanger arrangement 14 whereby the auxiliary refrigerant 40 can evaporate by picking up heat from the fully condensed compressed refrigerant 12.
• auxiliary refrigerant 40 Another reason making butane suitable as a choice for the auxiliary refrigerant 40 is that it has a higher heat of evaporation than the fully condensed compressed refrigerant 12. Therefore sub-cooling of a certain flow rate of the fully condensed compressed refrigerant 12 can be achieved using a smaller flow rate of the auxiliary refrigerant 40.
• the auxiliary compression power is further lowered by the fact that the required compression ratio is smaller provided that the temperature to which the compressed auxiliary refrigerant 42 is cooled against ambient in heat exchanger 44 is the same as the temperature of the fully condensed compressed refrigerant 12.
• the fully condensed compressed refrigerant 12 is best sub-cooled to a temperature whereby the subsequent expanding in valve 18 brings the temperature below the bubble point temperature of the liquid refrigerant 19 after the subsequent expanding and before subsequent expanding in valve 2a.
• Comparative example Figure 3 represents a comparative apparatus for carrying out a comparative process. The difference with the embodiment of Figure 1 is that the auxiliary heat exchanger arrangement 14 and the auxiliary refrigerant cycle is not present. Thus, the further sub-cooling step of the invention is not employed. This can result in that the fully condensed compressed refrigerant 12 (corresponding to point Y in Figure 2) is partly wasted to flash vapour during expansion in valve 18, as is schematically represented in Figure 2 wherein line 32 crosses the phase envelope 20 on its way to point Yl.
• the refrigerant phase- separates into a liquid fraction in point Zl and vapour fraction in point U whereby the total available enthalpy Hy is divided over the liquid fraction in which an enthalpy of R ⁇ will be vested and a the vapour fraction in which an enthalpy of H ⁇ j will be vested.
• part of the liquid refrigerant 19 is evaporated in a first stage in the first kettle Ia, using heat from the product stream, after expanding the liquid refrigerant over valve 18.
• a retained liquid fraction of the refrigerant is drawn from the first kettle Ia and let down to a lower pressure level over valve 2a (or equivalent means, optionally in combination with a dynamic expander) before it is fed to the second kettle Ib where cooling of the product stream can proceed in a second stage. In this way even more consecutive cooling stages, each time at a lower pressure level, can be executed using the same liquid refrigerant to each time enable vapourisation at a lower temperature.
• the total amount of propane that is cycled through line 12 in the process of Figure 1 is 456 kg/s, while in the process of Figure 2 a propane flow of 589.3 kg/s was required to maintain the same heat transfer rate (chiller duty) of 148.7 MW in the kettles Ia to Id.
• a flow rate of only 104.2 kg/s of auxiliary refrigerant in the form of butane through line 40 was needed, and only a total flow rate of 116.5 kg/s of butane needed to be cycled in line 46.
• the propane cycle can be provided with smaller piping, or with the same piping a smaller pressure loss will be experienced. Also, safety flaring capacity could likely be reduced, as the largest refrigerant circuit (in this case the propane main refrigerant circuit) needs to contain less refrigerant.
• Figure 1 is sub-cooled by 27 °C more than the propane stream in line 12 of Figure 2, bringing the temperature of the propane stream in line 16 upstream of the valve 18 to only 2.8 0 C above the temperature in the first kettle Ia.
• this embodiment is based on the embodiment of Figure 1 modified by the provision of a second auxiliary refrigerant cycle 155.
• the second auxiliary refrigerant cycle 155 can comprise a second auxiliary compressor 145, an optional second separator 148, a second ambient heat exchanger 144.
• the second auxiliary compressor 145 optionally comprises two or more compression stages 145a and 145b.
• the second auxiliary refrigerant stream is recompressed m the second auxiliary compressor 145.
• a fully compressed second auxiliary refrigerant stream 142 is then cooled against ambient in heat exchanger 144.
• the resulting fully compressed cooled second auxiliary refrigerant stream 146 is then optionally separated in a second liquid fraction 152 and a second vapour fraction 150 in second separator 148, whereby the second vapour fraction 150 is fed back to the second auxiliary compressor 145 at an intermediate pressure inlet point.
• More optionally the fully compressed cooled second auxiliary refrigerant stream 146 is partly flashed off by letting down the pressure upstream of the second separator 148.
• Joule-Thompson valve 154 can be provided, optionally in combination with a dynamic expansion device.
• the second liquid fraction 152 is led to second auxiliary heat exchanger arrangement 114 where it draws heat from the liquid refrigerant leaving the first kettle Ia by indirect heat exchange. After being discharged from the second auxiliary heat exchanger arrangement 114, the second auxiliary refrigerant is recompressed in second auxiliary compressor 145.
• the pressure in the second auxiliary refrigerant stream 152 can be let down, for which a Joule-Thompson valve 156 can be provided, optionally in combination with a dynamic expansion device .
• Figure 5 relates to an embodiment wherein the first- mentioned auxiliary refrigerant cycle has been modified in that the optional separator 48 of Figure 1 is provided in the form of a kettle 58 or a heat exchanger. Line 12 passes through that kettle as its warm side. In operation, the fully condensed compressed refrigerant 12 is further sub-cooled by indirect heat exchange against the auxiliary refrigerant in at least two stages including the kettle 48 and the heat exchanger arrangement 14 at two pressure levels.
• the auxilary refrigerant circuit of the embodiment of Figure 5 can also be advantageously applied in an embodiment such as shown Figure 1 which is not provided with a second auxiliary refrigerant circuit. However, in another advantageous embodiment shown in
• FIG 6 the apparatus of Figure 5 is modified in that line 146 is also passed though kettle 48.
• line 146 is also passed though kettle 48.
• the fully compressed cooled second auxiliary refrigerant stream 146 is sub-cooled or further sub-cooled by indirect heat exchange against the first- mentioned auxiliary refrigerant before expanding it in expansion device 154.
• the sub-cooling or further sub-cooling is applied on the second auxilary refrigerant in order to avoid unnecessary circulation of vapour through the second compressor stage 145a thereby saving a little more compression power in the second auxilary refrigerant cycle 155.
• the second auxiliary refrigerant should preferably be selected to have a lower bubble point temperature than that of the auxiliary refrigerant, but higher than that of the main liquid refrigerant, when determined under equal-pressure condition.
• propane as a main refrigerant
• butane as the auxiliary refrigerant
• iso-butane is a suitable choice for the second auxiliary refrigerant.
• a third and fourth auxiliary refrigerant cycles can be employed between second and third, respectively third and fourth main refrigerant pressure stages.
• the possible power reduction is expected to be less with each stage, as the compression power put into each compression stage of 5a to 5d is lower with each consecutive stage.
• more of the product stream can be refrigerated before the maximum suction flow of the compressor 5 is reached. This is of particular importance in a colder ambient, as then the refrigerant pressure can be lower while at the same time the flow has to be higher in order to achieve the required volumetric flow.
• the lower refrigerant flow through lines 3c and 3d would help to maximise the amount of refrigerated product stream that can be produced.
• FIG. 7 This embodiment employs a similar amount of hard ware as the embodiment described above with reference to Figure 1, but allows for further sub-cooling of the liquid refrigerant at two pressure levels in two consecutive stages.
• the compressor 5 is arranged in two compression sections 5a and 5b.
• separator 48 of Figure 1 a kettle 58 is employed wherein after letting off pressure in valve 54 the auxiliary refrigerant is both separated into vapour 50 and liquid 52 fractions and is allowed to further evaporate using heat drawn from the fully condensed compressed refrigerant 12.
• the fully condensed compressed refrigerant 12 is thereby further sub-cooled using kettle 58 for the function of heat exchanger arrangement 14 of Figure 1.
• the resulting further sub-cooled fully condensed compressed refrigerant 16 is expanded over valve 18 and fed to the first kettle Ia where it is allowed to evaporate against heat drawn from the product stream.
• the residual liquid fraction is drawn from the kettle Ia and before expanding in valve 2, the liquid fraction is again further sub-cooled by indirect heat exchange in heat exchanger arrangement 14 against a second auxiliary refrigerant in the form of the liquid fraction 52 drawn from kettle 58.
• the pressure level in of the second auxiliary refrigerant in heat exchanger arrangement 14 can be lowered relative to the pressure level in kettle 58 to a desired pressure level by means of for instance Joule Thompson valve 56.
• the further sub-cooling before expanding the second time in valve 2 can reduce or avoid flash vapour formation in a similar way as before in kettle 58.
• auxiliary refrigerant in the embodiment of Figure 7 is best selected by considering the bubble-point requirement in the second stage 14 using similar considerations as explained above.
• the bubble-point requirement in kettle 58 can then be achieved by selecting suitable pressure drops over valves 54 and 56.
• a suitable auxiliary refrigerant is iso-butane.
• LNG liquefied natural gas
• the compressors are driven by a suitable motor, such as for instance a gas turbine or an electrically driven motor or a combination thereof.

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• 2006
  • 2006-03-07 EP EP06724956A patent/EP1864064A1/en not_active Withdrawn
  • 2006-03-07 RU RU2007137274/06A patent/RU2386090C2/ru not_active IP Right Cessation
  • 2006-03-07 US US11/885,795 patent/US20080173043A1/en not_active Abandoned
  • 2006-03-07 AU AU2006222005A patent/AU2006222005B2/en not_active Ceased
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