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
  • F17—STORING OR DISTRIBUTING GASES OR LIQUIDS
  • F17C—VESSELS FOR CONTAINING OR STORING COMPRESSED, LIQUEFIED OR SOLIDIFIED GASES; FIXED-CAPACITY GAS-HOLDERS; FILLING VESSELS WITH, OR DISCHARGING FROM VESSELS, COMPRESSED, LIQUEFIED, OR SOLIDIFIED GASES
  • F17C13/00—Details of vessels or of the filling or discharging of vessels
  • F17C13/08—Mounting arrangements for vessels
  • F17C13/082—Mounting arrangements for vessels for large sea-borne storage vessels
• • 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
  • F25J1/006—Processes or apparatus for liquefying or solidifying gases or gaseous mixtures characterised by the refrigerant fluid used
  • F25J1/008—Hydrocarbons
• • 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
  • F25J1/0211—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 a multi-component refrigerant [MCR] fluid in a closed vapor compression cycle
  • F25J1/0214—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 a multi-component refrigerant [MCR] fluid in a closed vapor compression cycle as a dual level refrigeration cascade with at least one MCR cycle
• • 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
  • F25J1/0275—Construction and layout of liquefaction equipments, e.g. valves, machines adapted for special use of the liquefaction unit, e.g. portable or transportable devices
  • F25J1/0277—Offshore use, e.g. during shipping
  • F25J1/0278—Unit being stationary, e.g. on floating barge or fixed platform
• • 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.
  • F25J1/0291—Refrigerant compression by combined gas compression and liquid pumping
• • 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
• • 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
  • F25J2205/90—Mixing of components
• • 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
  • F25J2240/00—Processes or apparatus involving steps for expanding of process streams
  • F25J2240/60—Expansion by ejector or injector, e.g. "Gasstrahlpumpe", "venturi mixing", "jet pumps"

Definitions

• the present invention relates to a process for liquefying natural gas to produce LNG, or Liquefied Natural Gas, also called LNG in English. Even more particularly, the present invention relates to the liquefaction of natural gas comprising predominantly methane, preferably at least 85% methane, the other main constituents being chosen from nitrogen and alkanes at C-2 to C-4. namely ethane, propane, butane.
• the present invention also relates to a liquefaction plant disposed on a ship or floating support at sea, either at open sea or in a protected area, such as a port, or an onshore installation in the case of medium or large units of water. liquefaction of natural gas.
• Methane-based natural gas is either a by-product of oil fields, produced in small or medium quantities, usually associated with crude oil, or a major product in the case of gas fields, where it is then in combination with other gases, mainly C 2 -C 4 alkanes, CO 2, nitrogen.
• natural gas is associated with crude oil in small quantities, it is usually processed and separated and then used locally as fuel in turbines or piston engines to produce electrical energy and process calories. separation or production.
• quantities of natural gas are large, even considerable, it is sought to be transported so that it can be used in remote areas, usually on other continents, and to do this, the preferred method is to transport it to the mainland. state of cryogenic liquid (-165 ° C) substantially at ambient atmospheric pressure.
• LNG tankers Specialized transport vessels called “LNG tankers” have tanks of very large dimensions and with extreme insulation so as to limit evaporation during the voyage.
• the liquefaction of the gas for transport is generally carried out near the production site, generally on land, and requires considerable facilities to reach capacities of several million tons per year, the largest existing units include three or four liquefaction units of 3-4 Mt per year of unit capacity.
• This liquefaction process requires considerable amounts of mechanical energy, the mechanical energy generally being produced in situ by removing a portion of the gas to produce the energy required for the liquefaction process. Part of the gas is then used as fuel in gas turbines, steam boilers or piston engines.
• thermodynamic cycles have been developed to optimize overall energy efficiency.
• a first type based on the compression and expansion of coolant, with phase change
• a second type based on the compression and expansion of refrigerant gas without phase change.
• refrigerating fluid or "refrigerant gas”
• methane which gradually cools to reach its liquefaction temperature at atmospheric pressure, that is to say about - 165 ° C in the case of LNG.
• Said first type of cycle, with phase change, is generally used on installations with a large production capacity requiring a larger quantity of equipment.
• the refrigerants usually in the form of mixtures, consist of butane, propane, ethane and methane, these gases being dangerous because they risk, in case of leakage, to cause explosions or fires considerable .
• they despite the complexity of the equipment required, they remain the most efficient and require an energy of about 0.3 kWh per kg of LNG produced.
• separator tanks To collect the liquid phase and direct it to the heart of the heat exchangers where it will then vaporize on contact with methane to cool and liquefy, to obtain LNG.
• the second type of liquefaction process a process without phase change of the refrigerant gas
• This second type of process has an advantage in terms of safety, because the refrigerant gas of the cycle, in general nitrogen, is inert, therefore incombustible, which is very interesting when the installations are concentrated in a small space, for example on the deck of a floating support installed at open sea, said equipment being often installed on several levels, one above the other on a reduced surface to the strict minimum.
• the efficiency of this second type is lower, since it generally requires an energy of the order of 0.5 kWh / kg of LNG produced, ie approximately 20.84 kW x day / t.
• the phase change method is more sensitive to variations in the composition of the refrigerant gas.
• gas to be liquefied namely a natural gas consisting of a mixture in which methane predominates.
• the refrigerant fluid in order for the yields to remain optimal, the refrigerant fluid must be adapted to the nature and composition of the gas to be liquefied and the composition of the refrigerant fluid must, if necessary, be modified. over time, depending on the composition of the mixture of natural gas to be liquefied produced by the oil field.
• refrigerant fluids consisting of a mixture of compounds are used. More particularly, the object of the present invention is to provide an improved method of liquefying natural gas with phase change.
• the present invention relates to a method of liquefying a natural gas comprising predominantly methane, wherein said natural gas to be liquefied by circulating a stream of said natural gas in at least one cryogenic heat exchanger by circulating in circulation.
• first flow of first refrigerant fluid comprising a first mixture of compounds flowing in at least a first loop in closed circuit with phase change
• said first flow of first refrigerant entering at a temperature substantially equal to the temperature TO entering said natural gas into said first exchanger and at a pressure P1, passing therethrough cocurrently from said natural gas stream and exiting in the liquid state
• said first flow of first refrigerant fluid in the liquid state being relaxed in a first expander at the cold end of said first exchanger in the gauze state at a pressure P'1 less than P1 and at a temperature T1 lower than T0, then exiting at its hot end in the gaseous state and substantially at a temperature T0
• said first flow of first refrigerant fluid in the gaseous state then being at least partially reliquefied and conveyed to the hot inlet of said first exchanger to constitute the feed in said first flow of first refrigerant fluid in the liquid state circulating and closed circuit, liquefaction of said first flow of first refrigerant fluid
• the object of the present invention is therefore to provide a method of liquefaction of natural gas with phase change as defined above improved, in particular to solve the problem above.
• the present invention provides a method for liquefying a natural gas comprising predominantly methane, preferably at least 85% methane, the other components comprising essentially nitrogen and C-2 to C alkanes; -4, in which said natural gas to be liquefied is liquefied by circulation of a stream of said natural gas at a pressure PO greater than or equal to atmospheric pressure, preferably PO being greater than atmospheric pressure, in at least one heat exchanger cryogenic circuit by indirect contact with at least a first flow of first refrigerant fluid comprising a first mixture of compounds circulating in at least a first loop in closed circuit with phase change, said first flow of first refrigerant fluid entering said first exchanger to a first inlet of an end called “hot end” at a temperature substantially equal to the natural gas inlet temperature TO in said first exchanger and at a pressure P 1, passing through cocurrent of said natural gas stream and leaving at an end called “cold end” in the liquid state, said first flow first coolant fluid in the liquid state being expanded by a first expand
• said hot end e of said first exchanger for constituting said first flow of first refrigerant fluid in the liquid state, said first gaseous phase of said first high output refrigerant of said first separator being compressed at substantially the pressure P1 by a second compressor and then condensed at least partially in a second condenser, preferably after mixing with at least a portion of said first liquid phase of first refrigerant.
• said first gaseous phase of said first refrigerant fluid at the outlet of said second compressor is cooled in a desuperheater by contact with a part of said first liquid phase of first refrigerant at the outlet of said first separator, said part of first liquid phase first refrigerant fluid being micronized and vaporized, preferably fully vaporized, within said desuperheater, before said condensation in said second condenser.
• said portion of first liquid phase of first refrigerant is less than 10% mass flow, more preferably 2 to 5% of the flow rate of said first liquid phase of first refrigerant, so that it either completely vaporized within said desuperheater and that the first refrigerant at the outlet of said desuperheater is entirely in the gas phase before its at least partial condensation in said second condenser, the flow rate of said portion of first liquid phase of first refrigerant being adjusted using at least one control valve.
• the vaporization of the first and second streams of first refrigerant fluid by said first and second expansers constitutes the bulk of the heat exchange within said first cryogenic exchanger by cooling said first and second streams of first refrigerant in the gaseous state at within said first exchanger and causing a caloric absorption and cooling of said natural gas stream at a temperature T1 lower than T0 and thus the cooling of said first and second flow of first coolant in the liquid state.
• Micronization (still known as
• the micronization of a controlled amount constituting a small portion of said first liquid phase of first refrigerant fluid allows it to be fully brought to the gaseous state and to cool said first gaseous phase of first refrigerant, which remains entirely at the gaseous state.
• Pre-cooling of said gaseous phase of first refrigerant by mixing with a portion of the micronized liquid phase within the desuperheater is advantageous in that it allows condensation of a larger portion of the gaseous phase in said second condenser. or even an integral condensation.
• said first gas phase of said first refrigerant fluid at the outlet of said first separator tank is more easily condensed in said second condenser after mixing with at least a portion of said first liquid phase of the first refrigerant fluid after micronization and vaporization, because said resulting gas phase is then condensable at a higher temperature and a lower pressure than those required in the prior art, and therefore by implementing a lower power at said second compressor.
• said gaseous phase of the first coolant cooled at the outlet of said desuperheater is partially condensed in said second condenser, then a second phase separation is carried out in a second separator tank separating a second liquid phase from a first refrigerant fluid and a second gaseous phase from a first refrigerant fluid, said second liquid phase of a first refrigerant fluid at the bottom outlet from said second separator tank being mixed with the remainder of said first liquid first fluid phase refrigerant and conveyed to said first inlet of the hot end of said first exchanger to form said first flow of first refrigerant fluid in the liquid state substantially at the temperature T0 and substantially at the pressure P1, and, said second gaseous phase at the upper outlet of the second separator tank being conveyed at said substantially P1 pressure and said temperature substantially T0 to a second inlet at the hot end of said first exchanger to form a second flow of first refrigerant flowing through the gaseous
• FIG. 3 The above embodiment (Fig. 3) is preferred because it allows mixing said liquid first refrigerant phases to form said first flow under good stability conditions on the one hand and, on the other hand, it does not require the implementation of a total condenser.
• said gas phase of first refrigerant fluid cooled in said desuperheater is totally condensed in said second condenser, then is conveyed in the liquid state at substantially said pressure.
• said natural gas leaving the cold end of said first exchanger at a temperature substantially equal to T1 is cooled and at least partially liquefied in at least a second cryogenic exchanger, in which said natural gas to be liquefied by circulation is liquefied.
• said natural gas leaving the cold end of said second exchanger at a temperature substantially equal to T2 partially liquefied is cooled and fully liquefied at a temperature T3 less than T2 in at least a third cryogenic exchanger, in wherein said natural gas circulates in indirect cocurrent contact with at least a third flow of second refrigerant fluid supplied by said second second refrigerant fluid stream in gaseous state exiting the cold end of said second heat exchanger at substantially temperature T2 and at the pressure P2, said third flow of second refrigerant flowing through the gaseous state said third exchanger co-current of said stream of liquefied natural gas and leaving substantially in the gaseous state and being expanded by a fourth regulator at the level of of the cold end of said third exchanger to find itself in the gaseous state at a pressure P2 'less than P2 and at a temperature T3 less than T2 inside said third exchanger on the cold end side, and then emerging at an orifice at its hot end in the state gaseous and substantially at
• said expansion valves comprise valves whose opening percentage is suitable for being controlled in real time.
• the compounds of the natural gas and the refrigerant fluids are chosen from methane, nitrogen, ethane, ethylene, propane, butane, and pentane. More particularly, the composition of the natural gas to be liquefied is included in the following ranges for a total of 100% of the following compounds:
• butane from 0 to 20%.
• composition of the refrigerant fluids is included in the following ranges for a total of 100% of the following compounds:
• temperatures have the following values:
• - T0 is are from 10 to 60 ° C
• - Tl is -30 to -70 ° C
• T2 is from -100 to-140 ° C
• - T3 is -160 to -170 ° C.
• the pressures have the values:
• P0 is from 0.5 to 10 MPa (substantially 5 to 100 bar).
• PI 1.5 to 10 MPa (approximately 15 to 100 bar)
• P2 is 2.5 to 10 MPa (substantially 25 to 100 bar).
• a method according to the invention is implemented on board a floating support.
• the present invention also provides an on-board installation on a floating support for implementing a method according to the present invention, characterized in that it comprises:
• At least one said first exchanger comprising at least:
• a first expander between the cold outlet of said first duct and a first inlet at the cold end of the enclosure of said first exchanger
• a second expander between the cold outlet of said second duct and a second inlet at the cold end of the enclosure of said first exchanger
• a first compressor with a connection line between an outlet at the hot end of the enclosure of said first exchanger and the inlet of said first compressor
• a first condenser with a connecting line between the output of said first compressor and the inlet of said first condenser
• a first separator tank with a connecting line between the outlet of said first condenser and said first separator tank, and
• a second compressor with a connecting line between an upper outlet of said first separator tank and the inlet of said second compressor
• connection line between the output of said pump and the inlet of said first refrigerant first conduit
• an installation according to the present invention further comprises:
• a second separator tank with a connecting line between the outlet of said second condenser and said second separator tank, and
• connection line between the upper outlet of said second separator tank and the inlet of said second refrigerant first conduit
• an installation according to the present invention further comprises:
• a second cryogenic exchanger comprising:
• a third exchanger comprising:
• a third separator tank A third separator tank, and
• connection line between a lower outlet of said third separator tank and an outlet orifice at the hot end of said second exchanger
• connection line between an upper outlet of said third separator tank and the hot end of said second conduit of said second exchanger
• a third expander between the cold outlet of said first conduit of said second exchanger and a first inlet to the cold end of the enclosure of said second exchanger
• a third compressor with a connecting pipe between an outlet at the hot end of the enclosure of said second heat exchanger and the inlet of said second compressor, and
• a gas heat exchanger with a connecting pipe between the outlet of said second compressor and the inlet of said gas cooler, and
• a fourth expander between the cold outlet of said first duct of said third exchanger and an inlet at the cold end of the enclosure of said third exchanger
• FIG. 1A represents the diagram of a standard double-loop phase-change liquefaction process using coiled cryogenic exchangers
• FIG. 1B is a variant of FIG. 1A in which the second and third cryogenic exchangers C2 and C3 are in continuity and of the type called "brazed aluminum" (in English “cold box”),
• FIG. 2 is a diagram of a liquefaction process according to the invention comprising, at the level of the primary refrigeration loop, a circuit for recycling a portion of the refrigerant fluid in the liquid state to the portion of the cooling fluid. in the gaseous state, at a desuperheater (in English "desuperheater”), located upstream of a coolant condenser, FIG. 2A details in a broken side view the desuperheater of FIG. 2,
• FIG. 3 represents the diagram of a liquefaction process according to a preferred version of the invention, comprising, at the level of the primary refrigeration loop, a liquid and gaseous phase separator tank downstream of the condenser of FIG. downstream of a desuperheater,
• FIG. 1A shows the PFD (Process Flow Diagram), ie the flow diagram of a standard double-loop phase change liquefaction process called "DMR" (in English Dual Mixed Refrigerant).
• DMR Dual Mixed Refrigerant
• the natural gas is cooled by giving up calories to the coolants, which heat up vaporizing as described below and must permanently undergo complete thermodynamic cycles with phase change in order to continuously extract calories to natural gas entering AA. So the natural gas route is shown on the left of the coolants, which heat up vaporizing as described below and must permanently undergo complete thermodynamic cycles with phase change in order to continuously extract calories to natural gas entering AA. So the natural gas route is shown on the left of the coolants, which heat up vaporizing as described below and must permanently undergo complete thermodynamic cycles with phase change in order to continuously extract calories to natural gas entering AA. So the natural gas route is shown on the left of the
• the gaseous phases are represented in dotted lines; the two-phase phases are represented in normal lines.
• thermodynamic cycles of the refrigerant fluids of the two loops as described below.
• cryogenic exchangers EC1, EC2 and EC3 consist, in known manner, of at least two fluid circuits juxtaposed but not communicating with each other at said fluids, the fluids circulating in said circuits exchanging heat along the route within said heat exchanger.
• Many types of heat exchangers have been developed for the various industries and in the context of cryogenic exchangers two types prevail in a known manner: - on the one hand coiled exchangers, on the other hand the so-called "brazed" aluminum plate heat exchangers called "cold box".
• exchangers EC1, EC2 and EC3 of coiled type refers to exchangers EC1, EC2 and EC3 of coiled type.
• Coiled exchangers of this type are known to those skilled in the art and marketed by the companies LINDE (Germany) or FIVE Cryogenie (France).
• These exchangers comprise a sealed and insulated enclosure 6, and the natural gas as well as the cooling fluids circulate in lines in the form of coils Sg, S1 and S2, said coils being disposed in said sealed and insulated enclosure vis-à-vis the outside so that the heat exchange is between the internal volume of the chamber and the different coils, with a minimum of thermal losses to the outside, that is to say the ambient environment.
• gases and liquids may be respectively expanded or vaporized directly in the enclosure and not in a conduit within the enclosure as described below.
• FIG. 1B shows a variant of FIG. 1A in which the cryogenic exchangers are of the plate heat exchanger type: all the circuits are in thermal contact with one another to exchange calories, but the sealed and insulated enclosure 6 is simply to thermally isolate the various conduits it contains, no fluid can be introduced directly, all fluids that circulate there can not mix.
• Exchangers of this type with so-called "cold box” plates are known to those skilled in the art and marketed by CHART (USA).
• the method comprises a first loop called Primary Loop or in English "PMR" (Primary Mixed Refrigerant) constituted as follows.
• a flow d1 of a first flow of first refrigerant fluid enters AA1 at the hot end AA of the first cryogenic exchanger EC1 at a temperature substantially equal to T0 and a pressure P1, for example P1 being from 1.5 to 10 MPa.
• Said first refrigerant fluid passes through the first heat exchanger EC1 in a liquid state in a first serpentine pipe SI.
• a first expansion valve D1 consisting of a controlled valve, said valve being in communication with BB1 inside the chamber 6 of the first exchanger EC1 on the cold end side of the exchanger EC1. Due to its expansion at a pressure P'1 below P1, in particular P'1 being equal to 2 to 5 MPa, the liquid of the first refrigerant vaporizes by absorbing the calories of the circuit Sg of natural gas and the calories of the other circuits of the first loop within the first exchanger described hereinafter as well as, where appropriate, the calories of the ducts forming part of the second loop described hereinafter, or even other loops in the case of multi-loop circuits called "MMR".
• MMR multi-loop circuits
• the first refrigerant fluid in the gaseous state BB1 crosses against the current chamber and leaves the enclosure of the first heat exchanger EC1 AA3 of the hot side AA always in the gaseous state and substantially at a temperature T0. Said first flow of refrigerant fluid in the gaseous state will then be reliqued and conveyed to the hot inlet AA1 of said first exchanger EC1 to constitute the supply of a said first flow of first refrigerant fluid in the liquid state to the inside the duct SI, thus circulating in a closed circuit.
• first refrigerant fluid leaving the gaseous state of the cold end of the enclosure of the first heat exchanger EC1 AA3 is first compressed from P'1 to P "1, P" 1 being between P'1 and P1, in a first compressor C1, and then partially condensed in a first condenser HO.
• the biphasic mixture of first coolant leaving the first condenser HO undergoes a phase separation in a first separator tank RI.
• a first liquid phase of the first refrigerant fluid is extracted in the lower part of the first separator tank RI and re-conveyed at a flow rate dla and a pressure P1 substantially by a pump PP to the inlet of a second condenser H1.
• a gaseous phase of first refrigerant fluid is extracted from the upper side of the separator tank RI and compressed to substantially the pressure PI and a flow dlb by a second compressor CIA, the outlet temperature of said compressor being of the order of 80-90 ° vs.
• this gaseous phase dlb it is mixed with the liquid phase dla before introducing the biphasic mixture dl obtained in the second condenser Hl.
• the condensation of the gaseous phase at the outlet of the second condenser H1 is not complete and the fluid leaving it can still be two-phase.
• the gases contained in it cause the pressure rise of the refrigerant.
• a calibrated safety valve is generally inserted at a pressure slightly below the limit pressure tolerable by the pipes, said valve (not shown) being connected to a flare 5, in which the combustion gases are removed by combustion because the quantities are small compared to the coolant mass of the loop.
• the composition of the cooling mixture is generally determined in C1, C2, C3 and C4 alkane compounds described below to reach a minimum temperature T1 of the order of -50 ° C. But, as some of the lighter compounds are removed, the composition of the mixture changes and the minimum temperature T1 then becomes -40 or -45 ° C, or -35 ° C. This results in a decrease in the efficiency of the primary loop and therefore a decrease in the overall efficiency of the liquefaction process.
• an additional accumulator tank R'1 is introduced downstream of the condenser H1 whose function is to receive a liquid phase, and if necessary a multiphase phase so that the gas contained in the multiphase phase gathers in the upper part of said accumulator tank and is trapped therein, the liquid phase contained in R'1 being taken from the bottom of said accumulator tank and conveyed to EC1. If the amount of gas in R'1 increases, the pressure within R'1 increases and said gas condenses and mixes with the liquid phase before being discharged to the cryogenic exchanger EC1.
• FIGS. 1 to 3 comprise a second loop of second refrigerant fluid cooperating with the three cryogenic exchangers EC1, EC2 and EC3 as described below.
• the natural gas at temperature T1 is partially liquefied and then passes into the second cryogenic exchanger EC2, from which it leaves at the temperature T2 partially liquefied before being cooled to a fully liquefied state.
• a second refrigerant mixture circulates in a second closed circuit loop with phase change as follows.
• the second refrigerant fluid arrives at the hot end CC of EC2 in CCI in the liquid state at the temperature T1 and at the pressure P2, P2 being for example 2.5 to 10 MPa.
• the second coolant in the liquid state passes through the second exchanger EC2 in a coil-shaped conduit S2 co-current of the natural gas fluid in Sg.
• This first flow of second refrigerant fluid in the liquid state of flow d2a is then expanded in a D2 expander at the cold end DD of the second exchanger EC2 in DD1 at a pressure P'2 less than P2 and at a temperature T2 lower than T1 within the chamber of the second exchanger EC2. Then, this first flow of second refrigerant fluid leaves the second chamber at a CC3 orifice at the hot end of the second exchanger EC2, in the gaseous state and substantially at a pressure P'2 and a temperature Tl.
• second refrigerant fluid in the gaseous state is then compressed from P'2 to P2 in a compressor C2 from which it comes out at a temperature of about 80-100 ° C, before being cooled in a temperature-cooling exchanger H2 including it always comes out in the gaseous state at a temperature substantially equal to T0 (20-30 ° C).
• the liquid phase is sent at a flow rate d2a at CC3 to the hot side CC of the second exchanger EC2 to constitute the supply of said first flow of second coolant in the liquid state within the coil S2 to perform a new cycle as described herein. -above.
• the flow rate d2b of the vapor phase leaving the second separator tank R2 is also directed towards the hot side CC of the second exchanger EC2 at substantially T1 and substantially P2 for supplying CC2 with another serpentine duct S2A within the second exchanger EC2.
• cryogenic exchangers are plate heat exchangers as described above and the gases of the fluids vaporized by the regulators D1, D2 and D3 are channeled in serpentine conduits SIC, S2B and S2C within the respectively first heat exchanger EC1, second heat exchanger EC2, third heat exchanger EC3 to emerge at the hot ends of the first exchanger EC1 at AA3 and second heat exchanger EC2 respectively at CC3.
• the second and third exchangers EC2 and EC3 as well as said lines S2A and S3 are in continuity from the hot end CC of the second exchanger EC2 to the cold end FF of the third exchanger EC3.
• the return of the gaseous phase from the expander D3 to FF1 at the cold end of the third exchanger to the outlet CC3 at the hot end of the second exchanger EC2 is in a serpentine duct S2C.
• the return of the gaseous phase from the expander D2 to DD1 at the cold end of the second exchanger in DD1 to CC3 at the hot end of the second exchanger takes place in a serpentine pipe S2B.
• FIGS. 1A and 1B show two variants of the method according to the invention.
• the modifications with respect to the method of the prior art of FIGS. 1A and 1B are at the level of the first loop of the first refrigerant.
• a flow part dlc representing a mass flow ratio of 2-5% with respect to the initial flow dla is sent to a desuperheater DS, the gas phase dlb at the outlet of the second compressor CIA also joining the inlet of the desuperheater DS whose operation will be explained below.
• the fraction of flow liquid dlc sent to the desuperheater DS is adjusted thanks to the combined action of the controlled valve VI and the first expander D1 described below.
• This fraction dlc represents 2-10%, preferably 3-5%, of the flow rate dla of the pump PP.
• FIG. 2A there is shown in side view and torn off the desuperheater DS, whose function is to cool the gaseous phase dlb before it enters the condenser H1.
• the desuperheater DS is formed in a known manner of a gas inlet pipe 1 connected to an inner ramp 3 in the form of a perforated tube having a plurality of orifices 4 of small section distributed along and around the periphery of said ramp.
• a liquid supply pipe 2 from the pump PP whose flow dlc is controlled by the valve VI serves to supply the ramp 3 in liquid so as to create a mist of fine liquid droplets out of the orifices 4 of the fact the liquid spraying pressure through said ramp 3.
• the fine liquid droplets then have a large specific surface exchange with the gas phase arriving via the feed pipe 1. And, the latent heat of evaporation of the liquid phase has the effect of cooling the incoming gas phase.
• Said gaseous phase has indeed a temperature at the inlet of the desuperheater DS of about 80-90 ° C, and its outlet temperature of the desuperheater is only 55-65 ° C because of the calories absorbed by the vaporization of the liquid fluid dlc.
• the quantity of liquid dlc injected into the desuperheater DS is adjusted precisely so that the entire flow leaving the desuperheater DS is in the gaseous state and therefore has a homogeneous gas composition.
• a desuperheater DS of this type is marketed by the company FISHER-EMERSON (France).
• FISHER-EMERSON France
• the first refrigerating fluid leaving the desuperheater DS is thus completely in the gaseous state at a temperature of approximately +55-65 ° before being completely condensed in a second condenser H1 which is here a total condenser. .
• the first refrigerant fluid is completely in the liquid state and represents a flow dl 'routed to the temperature TO and the pressure substantially PI to the hot inlet AA2 of the first exchanger EC1 that it passes through the in a serpentine conduit S1A co-current of fluids passing through the serpentine pipes Sg and SI and S1B before being directed to a second regulator D1A also consisting of a slave valve, the second regulator D1A being in communication with the inside of exchanger EC1 at its cold end BB2.
• the second flow of first refrigerant fluid in the liquid state is vaporized by absorbing the calories of the natural gas conduit Sg as well as the calories of the flow of the conduit SI, the conduit S1A and the conduit S1B.
• first heat exchanger EC1 but pass through the first heat exchanger EC1 in two separate ducts S1 and S1A is also advantageous because the two flows have different compositions of the first refrigerant fluid, and moreover they are at different pressures, so that their mixture would lead to instabilities more problematic than those of the prior art It would however be possible to control the mixing of said two liquid streams with the aid of appropriate control systems, for example control valves, but this would go against the simplicity and the reliability sought in this type of installation.
• FIG. 3 shows a preferred embodiment of the invention, in which the second condenser H1 is not a total condenser, only part of the gas stream leaving the desuperheater DS is condensed in the second condenser H1.
• the biphasic fluid leaving at a die flow rate of the second condenser H1 undergoes a phase separation in a second separator tank R1A in which a second liquid phase and a second gas phase of the first refrigerant fluid are separated.
• the second coolant liquid phase at the low output of R1A is routed to the pipe SI and represents a flow dlf.
• the flow dla at the pump outlet PP is separated into two flow rates, respectively dlc to the desuperheater DS, flow adjusted by the first control valve VI, the dld residue being adjusted by a second control valve VIA, the two said valves being controlled in close combination with each other; said residue dld being then mixed with the liquid flow dlf, then conveyed to the conduit SI at the hot end of the cryogenic exchanger ECl, substantially at the pressure Pl.
• the second gaseous phase of the first high-output refrigerant of the second separator tank R1A represents a flow rate dl ".It is conveyed at the temperature TO and at the pressure P1 substantially to the inlet AA2 of the hot end.
• the second expansion valve DIA relaxes at a pressure P'1 less than P1 at BB2, the gas of the second gaseous phase of the first refrigerant, this expansion of the gas in BB2 of SIA by DIA then absorbs the calories of Sg, S1, S1 and S1b by promoting their cooling, and, where appropriate, absorbs the calories of other loops in the case of multi-loop circuits, referred to as MMRs as mentioned above .
• the gaseous fluid exiting at BB2 from the second expander DIA mixes the first portion of the first refrigerant vaporized BB1 to exit AA3 at a rate dl and be compressed from P'1 to P "1, P" 1 being between P'1 and P1 by the first compressor Cl.
• the expander D1 is a liquid-to-gas expander
• the expander DIA is a gas-to-gas expander
• FIG. 3 is preferred because the control valve VIA associated with the control valve VI and with the expander D1 allows the mixing of the two liquid phases and their vaporization in good stability conditions on the one hand, and on the other hand, it does not require the implementation of a total condenser, which increases the overall stability of the process and therefore its industrial reliability.
• the liquid flow d1 represents approximately 95% of the mass flow of first refrigerant gas, the gaseous flow dl "representing the complement, that is to say about 5%.
• Condensers HO and H1 and cooler H2 may consist of water exchangers, for example a seawater or river heat exchanger, or cold air type air cooler known to those skilled in the art.
• compositions of the first and second refrigerant fluids are related to the technologies selected in terms of cryogenic exchangers and condensers and each manufacturer or supplier recommends his own compositions.
• these compositions are also closely related to the composition of the natural gas to be liquefied, and the components of the refrigerant fluids are advantageously adjusted over time as soon as the characteristics of the natural gas change significantly.
• the first refrigerant fluid operating in a loop in the exchanger EC1 therefore the ordinary temperature T0 (20-30 ° C), to a minimum temperature Tl of -50 ° C approximately, consists of following mixture:
• the "hot" loop is identical, but the "cold” loop is replaced by two independent loops each comprising a clean refrigerant fluid, generally a second loop operating at the exchanger EC2, that is to say between -50 ° C and -120 ° C, the third loop operating at the exchanger EC3, that is to say between -120 ° C and -165 ° C.
• the so-called "hot" loop corresponding to the exchanger EC1 remains substantially the same as that described with reference to FIG. 1A.
• the invention applies to virtually all methods of liquefaction of natural gas with multiple independent loops and phase change.

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