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"
  • F25J1/004—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
  • F25J1/003—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
  • F25J1/005—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 expansion of a gaseous 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
  • F25J1/003—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
• • 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
  • F25J1/0095—Oxides of carbon, e.g. CO2
• • 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
  • F25J1/0203—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 single-component refrigerant [SCR] fluid in a closed vapor compression cycle
  • F25J1/0208—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 single-component refrigerant [SCR] fluid in a closed vapor compression cycle in combination with an internal quasi-closed refrigeration loop, e.g. with deep flash recycle 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
  • F25J1/0203—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 single-component refrigerant [SCR] fluid in a closed vapor compression cycle
  • F25J1/0208—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 single-component refrigerant [SCR] fluid in a closed vapor compression cycle in combination with an internal quasi-closed refrigeration loop, e.g. with deep flash recycle loop
  • F25J1/0209—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 single-component refrigerant [SCR] fluid in a closed vapor compression cycle in combination with an internal quasi-closed refrigeration loop, e.g. with deep flash recycle loop as at least a three level refrigeration cascade
  • F25J1/021—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 single-component refrigerant [SCR] fluid in a closed vapor compression cycle in combination with an internal quasi-closed refrigeration loop, e.g. with deep flash recycle loop as at least a three level refrigeration cascade using a deep flash recycle 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
  • F25J1/0221—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 the cold stored in an external cryogenic component in an open 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
  • F25J1/0225—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 other external refrigeration means not provided before, e.g. heat driven absorption chillers
  • F25J1/0227—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 other external refrigeration means not provided before, e.g. heat driven absorption chillers within a refrigeration 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
  • F25J1/02—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
• • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
  • F25—REFRIGERATION OR COOLING; COMBINED HEATING AND REFRIGERATION SYSTEMS; HEAT PUMP SYSTEMS; MANUFACTURE OR STORAGE OF ICE; LIQUEFACTION SOLIDIFICATION OF GASES
  • F25J—LIQUEFACTION, SOLIDIFICATION OR SEPARATION OF GASES OR GASEOUS OR LIQUEFIED GASEOUS MIXTURES BY PRESSURE AND COLD TREATMENT OR BY BRINGING THEM INTO THE SUPERCRITICAL STATE
  • F25J2210/00—Processes characterised by the type or other details of the feed stream
  • F25J2210/42—Nitrogen
• • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
  • F25—REFRIGERATION OR COOLING; COMBINED HEATING AND REFRIGERATION SYSTEMS; HEAT PUMP SYSTEMS; MANUFACTURE OR STORAGE OF ICE; LIQUEFACTION SOLIDIFICATION OF GASES
  • F25J—LIQUEFACTION, SOLIDIFICATION OR SEPARATION OF GASES OR GASEOUS OR LIQUEFIED GASEOUS MIXTURES BY PRESSURE AND COLD TREATMENT OR BY BRINGING THEM INTO THE SUPERCRITICAL STATE
  • F25J2210/00—Processes characterised by the type or other details of the feed stream
  • F25J2210/66—Landfill or fermentation off-gas, e.g. "Bio-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
  • F25J2270/00—Refrigeration techniques used
  • F25J2270/90—External refrigeration, e.g. conventional closed-loop mechanical refrigeration unit using Freon or NH3, unspecified external refrigeration
• • 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
  • F25J2270/90—External refrigeration, e.g. conventional closed-loop mechanical refrigeration unit using Freon or NH3, unspecified external refrigeration
  • F25J2270/908—External refrigeration, e.g. conventional closed-loop mechanical refrigeration unit using Freon or NH3, unspecified external refrigeration by regenerative chillers, i.e. oscillating or dynamic systems, e.g. Stirling refrigerator, thermoelectric ("Peltier") or magnetic refrigeration
• • 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
  • F25J2290/00—Other details not covered by groups F25J2200/00 - F25J2280/00
  • F25J2290/34—Details about subcooling of liquids

Definitions

• the present invention relates to a process for liquefying a feed gas rich in methane, comprising purifying the feed gas to obtain a purified gas, pre-cooling the purified gas to obtain a gas precooled, liquefying the precooled gas to obtain a liquid stream, subcooling the liquid stream to obtain a subcooled liquid stream, and expanding the subcooled liquid stream to obtain a liquefied gas.
• the invention also relates to an installation adapted to implement such a method.
• the gas to be treated is, for example, biogas (from the fermentation of organic materials).
• the market concerned is for example that of retail LNG (Liquefied Natural Gas), with final storage of LNG produced at a pressure lower than 3 bars (10 5 Pa) absolute.
• This market requires relatively low liquefied gas production capacities, typically less than 20 tonnes of gas to be liquefied per day, or a mechanical power consumption of less than 1 MW.
• Liquefaction of the feed gas consists of cooling it to a sufficiently cold temperature so that it can remain in liquid form at thermodynamic equilibrium for pressures making it transportable by state storage techniques. art, that is to say at pressures less than 20 bars absolute and more often less than 3 bars absolute. At these pressures, the thermodynamic equilibrium of a methane-rich gas is reached at temperatures below -100°C and more often below -140°C.
• the feed gas To cool the feed gas to these temperatures, it is typically pretreated to remove any compounds that may crystallize at these cryogenic temperatures. Then, the feed gas can also be compressed to a pressure higher than its initial pressure. Then, cooling is generally carried out in three main stages summarized below.
• the gas is first pre-cooled, but not enough to condense at the pressure considered.
• This pressure is, except for pressure losses, the pressure at the outlet of the pretreatment and is generally higher than the final storage pressure of the liquefied gas.
• the gas then undergoes a condensation or liquefaction stage itself, during which it effectively liquefies and remains, except for pressure losses, at the cooling inlet pressure.
• the gas finally undergoes a subcooling stage which continues the cooling of the liquid and, after a final expansion allowing the storage pressure to be reached, the remaining liquid is collected and stored.
• cryogenic temperatures typically below -80°C, and are very expensive. Indeed, on the one hand, the heat extracted, in other words the cooling provided, at these low temperatures requires a lot of energy and, on the other hand, the equipment adapted to these cryogenic temperatures is much more specific and expensive than that designed for lower temperatures, such as pre-cooling.
• the feed gas is already at high pressure, greater than 40 bar absolute, because the gas comes either directly from a geological reservoir or of a network.
• subcooling is continued down to very low temperatures, around -150°C, in order to generate less than 10% by volume of steam during final expansion.
• the cold of the steam possibly produced is generally recovered and used to cool the feed gas over the entire cooling range, ie during pre-cooling, liquefaction and sub-cooling.
• - cooling in order to reduce the overall energy consumption of the cycle or cycles cooling refrigerants.
• this does not reduce the cost of the most expensive equipment, the contribution of which is significant in small capacity installations.
• An aim of the invention is therefore to propose a liquefaction process making it possible to reduce the overall production cost, in particular for capacities of less than 20 tonnes per day.
• the subject of the invention is a process for liquefying a feed gas comprising at least 40% by volume of methane, the process comprising the following steps:
• the process comprises one or more of the following characteristics, taken in isolation or in all technically possible combinations:
• the subcooling of the liquid stream comprises: a first subcooling of the liquid stream by heat exchange with the third stream of recycled gas, to obtain an intermediate subcooled liquid stream and the second flow recycled gas; and a second subcooling of the intermediate subcooled liquid stream to obtain the subcooled liquid stream;
• the second sub-cooling of the intermediate sub-cooled liquid stream is carried out by exchange with a flow of liquid nitrogen, the second sub-cooling producing the sub-cooled liquid stream and a flow of vaporized nitrogen, the second pre-cooling of the first pre-cooled gas being further produced by heat exchange the flow of vaporized nitrogen;
• the purified gas undergoes the first pre-cooling in a first pre-cooling unit including a pre-cooling refrigeration cycle, by heat exchange with a refrigerant fluid to form the first pre-cooled gas without heat exchange with the first flow of recycled gas, the refrigerant being produced by the pre-cooling refrigeration cycle;
• the liquid stream leaving the liquefaction unit has a temperature between -113°C and -90°C;
• the second pre-cooled gas is liquefied by the liquefaction unit with sub-cooling less than or equal to 5°C;
• the refrigeration liquefaction cycle is a Stirling cycle or an inverse Brayton cycle
• the expansion of the subcooled liquid stream is carried out in at least one Joule-Thomson valve or by expansion turbine.
• the invention also relates to an installation adapted to implement a process as described above, comprising:
• a mixer for mixing the feed gas with the first flow of recycled gas and obtaining the gas to be treated, and at least one compressor adapted to compress the gas to be treated to the treatment pressure,
• a purification unit adapted to purify the gas to be treated and obtain the purified gas
• a first pre-cooling unit adapted to pre-cool the purified gas and obtain the first pre-cooled gas
• a second pre-cooling unit adapted to pre-cool the first pre-cooled gas by heat exchange with at least the second stream of recycled gas and to obtain the second pre-cooled gas and the first stream of recycled gas
• liquefaction unit for liquefying the second pre-cooled gas and obtaining the liquid stream
• the liquefaction unit including the liquefaction refrigeration cycle
• subcooling unit adapted to subcool the liquid stream to the subcooling temperature by heat exchange with at least the third recycled gas flow and to obtain the subcooled liquid flow and the second flow recycled gas
• the subcooling unit and the expansion unit being configured so that the third stream of recycled gas represents a fraction, relative to the subcooled liquid stream, less than 35 mol%.
• FIG. 1 is a schematic view of an installation according to the invention adapted to implement a method according to the invention.
• FIG. 2 is a schematic view of an installation according to the invention constituting a variant of the installation shown in Figure 1.
• upstream and downstream generally extend in relation to the normal direction of circulation of a fluid.
• 1 Nm 3 /h means in this document one cubic meter per hour at a pressure of 101325 Pa and a temperature of 0°C.
• an installation 10 is described.
• the installation is suitable for liquefying a feed gas 12 comprising at least 40% by volume of methane and obtaining a liquefied gas 14 (that is to say a liquid), for example with a view to marketing it on the market.
• a feed gas 12 comprising at least 40% by volume of methane
• a liquefied gas 14 that is to say a liquid
• retail LNG Liquefied Natural Gas
• the feed gas 12 is for example at low pressure, close to atmospheric pressure.
• the feed gas 12 is at a temperature close to ambient temperature, that is to say much hotter than its bubble temperature at atmospheric pressure (101325 Pa).
• the feed gas 12 is for example a biogas.
• the liquefied gas 14 is advantageously stored at a pressure of less than 3 bar absolute (300 kPa).
• the installation 10 comprises a mixer 16 for mixing the feed gas 12 with a first stream of recycled gas 18 and obtaining a gas to be treated 20.
• the installation 10 comprises at least one compressor 22 for compressing the gas to be treated 20, for example followed by a cooler 24 and a purification unit 26 adapted to purify the gas to be treated 20 and obtain a purified gas 28.
• the installation 10 comprises a first pre-cooling unit 30 adapted to pre-cool the purified gas 28 and obtain a first pre-cooled gas 32, the first pre-cooling unit including in the example a pre-cooling refrigeration cycle. cooling 34.
• cooling cycle we mean a set of pipes and elements (not shown), such as compressors or turbines, adapted to subject a fluid to a series of transformations with the aim of generating cold at a location. of the cycle, in a manner known in itself.
• the installation 10 comprises a second pre-cooling unit 36 adapted to pre-cool the first pre-cooled gas 32 by heat exchange with a second stream of recycled gas 38 and to obtain a second pre-cooled gas 40 and the first recycled gas flow 18.
• the installation 10 comprises a liquefaction unit 42 for liquefying the second pre-cooled gas 40 and obtaining a stream of liquid 44, the liquefaction unit including a refrigeration liquefaction cycle 46.
• the installation 10 comprises a sub-cooling unit 48 adapted to sub-cool the liquid stream 44 to a sub-cooling temperature by heat exchange with at least a third recycled gas flow 50 and to obtain a liquid stream subcooled 52 and the second flow of recycled gas 38.
• the installation 10 includes an expansion unit 54 for expanding the stream of sub-cooled liquid 52 and obtaining the liquefied gas 14, for example received in a storage 56, and the third flow of recycled gas 50.
• the compressor 22 is adapted to compress the gas to be treated 20 to a treatment pressure of between 19 and 70 bar absolute, which makes the gas to be treated 20, after purification, liquefiable at cryogenic temperatures, nevertheless remaining above - 113°C .
• the treatment pressure is advantageously less than 45 bar absolute.
• the purification unit 26 is adapted to remove from the gas to be treated the compounds likely to crystallize downstream.
• the purification unit 26 is conventionally adapted to eliminate volatile compounds and heavy hydrocarbons (called “C6+”), for example using activated carbons (not shown and known per se).
• C6+ volatile compounds and heavy hydrocarbons
• the purification unit 26 includes for example a condensation system (not shown).
• a membrane system (not shown) is for example used.
• molecular sieves can be used (not shown).
• the purified gas 28 contains at least 90%, or even 99%, of methane by volume.
• the first pre-cooling unit 30 comprises for example a heat exchanger 58 adapted to carry out a heat exchange between the purified gas 28 and a refrigerating fluid 60 produced by the pre-cooling refrigeration cycle 34, without heat exchange with the first recycled gas flow 18.
• the pre-cooling refrigeration cycle 34 is disjoint from the liquefaction refrigeration cycle 46.
• disjoint we mean that the two refrigeration cycles do not share a refrigerating fluid which would be common to them.
• the pre-cooling refrigeration cycle 34 used is for example a brine cycle, a CO2 cycle, an ammonia cycle, a freon cycle, or a propane cycle, known in themselves and which will not be described. in detail.
• the temperature of the first pre-cooled gas 32 is between -40°C and -15°C.
• the second pre-cooling unit 36 comprises for example a heat exchanger 62 to carry out the heat exchange with the second flow of recycled gas 38.
• the liquefaction unit 42 comprises for example a heat exchanger 64 adapted to carry out a heat exchange between the second pre-cooled gas 40 and a refrigerating fluid 66 produced by the refrigerating liquefaction cycle 46, without heat exchange with the second flow of recycled gas 38.
• the liquefaction refrigeration cycle 46 is adapted to provide all the cold necessary to the liquefaction unit 42.
• the refrigeration liquefaction cycle 46 is for example a Stirling cycle.
• the refrigeration liquefaction cycle 46 is for example an inverse Brayton cycle, also known in itself to those skilled in the art.
• the subcooling unit 48 and the expansion unit 54 are configured so that the third stream of recycled gas 50 represents a fraction, relative to the stream of subcooled liquid 52, less than 35 molar%, and preferably between 10% and 30 mol%. This is particularly possible by sufficiently lowering the temperature of the subcooled liquid stream 52.
• the sub-cooling unit 48 comprises a first heat exchanger 68, a second heat exchanger 70 and a sub-cooling refrigeration cycle 72.
• the first heat exchanger 68 is adapted to carry out a first sub-cooling of the liquid stream 44 by heat exchange with the third flow of liquid. recycled gas 50, and to obtain an intermediate subcooled liquid stream 74 and the second stream of recycled gas 38.
• the second heat exchanger 70 is adapted to carry out a second sub-cooling of the intermediate sub-cooled liquid stream 74 to obtain the sub-cooled liquid stream 52, by heat exchange with a refrigerating fluid 76 produced by the sub-cooling refrigeration cycle. -cooling 72, without heat exchange with the third flow of recycled gas 50.
• the expansion unit 54 advantageously comprises an expansion member 78 for expanding the stream of sub-cooled liquid 52 and obtaining a relaxed sub-cooled stream 80, for example at a pressure less than 3 bar absolute.
• the expansion unit 54 comprises for example a flash drum 82 to separate the expanded subcooled stream 80 into the liquefied gas 14 and a vapor forming the third stream of recycled gas 50.
• the expansion member 78 is for example a Joule-Thomson valve or an expansion turbine.
• the feed gas 12 and the first flow of recycled gas 18 are mixed by the mixer 16 to form the gas to be treated 20.
• the gas to be treated 20 is compressed in the compressor 22, then cooled to approximately ambient temperature, for example 20°C, in the cooler 24. Then the gas to be treated 20 is purified in the purification unit 26 to form the purified gas 28.
• the purified gas 28 undergoes a first pre-cooling in the first pre-cooling unit 30, by heat exchange with the refrigerant fluid 60, to form the first pre-cooled gas 32.
• the first pre-cooled gas 32 undergoes a second pre-cooling in the second pre-cooling unit 36, by heat exchange with the second flow of recycled gas 38, to form the second pre-cooled gas 40.
• the second flow of recycled gas 38 heats up and becomes the first flow of recycled gas 18.
• the second pre-cooled gas 40 is liquefied in the liquefaction unit 42 and forms the liquid stream 44.
• the second pre-cooling unit 36 does not carry out liquefaction.
• Liquefaction is entirely carried out by liquefaction unit 42.
• the second pre-cooled gas 40 is liquefied by the liquefaction unit 42, with subcooling advantageously less than or equal to 5°C, for example approximately 3°C.
• the temperature of the liquid stream 44 leaving the liquefaction unit 42 is for example 3°C below the bubble temperature of the second precooled gas 40.
• the temperature of the liquid stream 44 leaving the liquefaction unit is preferably between -90°C and -113°C.
• the refrigeration liquefaction cycle 46 advantageously provides all the cold allowing the liquefaction of the second pre-cooled gas 40.
• the liquid stream 44 is then subcooled in the subcooling unit 48 to form the subcooled liquid stream 52, by heat exchange with at least the third recycled gas flow 50, i.e. i.e. the steam coming from the flash tank 82.
• the third flow of recycled gas 50 heats up and becomes the second flow of recycled gas 38.
• the liquid stream 44 undergoes a first subcooling in the first heat exchanger 68 by heat exchange with the third flow of recycled gas 50, then a second subcooling in the second heat exchanger 70 by heat exchange. heat with the refrigerant fluid 76 to form the subcooled liquid stream 52.
• the subcooling applied makes it possible to reduce the evaporation rate at the outlet of the flash tank 82 to a value less than 35 mol%.
• the evaporation rate remains greater than or equal to 20 mol%.
• the subcooled liquid stream 52 is expanded in the expansion member 78 to form the expanded subcooled stream 80, which is received in the flash tank 82.
• the liquefied gas 14 is for example recovered at the bottom of the flash tank. flash 82 and sent to storage 56.
• the steam from the flash drum 82 is recycled in the gas to be treated 20.
• This steam forms the third flow of recycled gas 50, which first becomes the second flow of recycled gas 38 after its passage through the sub-unit. cooling 48, then becomes the first flow of recycled gas 18 after its passage into the second pre-cooling unit 36.
• This vapor does not pass into the liquefaction unit 42, or in any case this vapor does not release cold to the liquefaction unit 42.
• this vapor does not pass into the first pre-cooling unit 30 either, or in any case does not transfer cold to the first pre-cooling unit 30.
• this steam can release part of its cold into the pre-cooling unit 30, in particular depending on the size of the installation 10. For example, if the production of liquefied gas 14 is less than 20 tonnes per day, the cold recovery in the first pre-cooling unit 30 coming from the first flow of recycled gas 18 will be avoided, as shown in Figure 1.
• the production of liquefied gas 14 is greater than or equal to 20 tonnes per day for example, this recovery will be preferred.
• the first stream of recycled gas 18 is passed through the first pre-cooling unit 30.
• an installation 100 according to the invention constituting a variant of the installation 10.
• the installation 100 is similar to the installation 10 shown in Figure 1. Similar elements bear the same numerical references and will not be described again. Only the differences will be described in detail below.
• the first pre-cooling of the purified gas 28 is carried out by heat exchange with a refrigeration liquefaction cycle 146.
• the liquefaction unit 42 and the first pre-cooling unit 30 share the same refrigeration cycle 146, which provides the cold used for the first pre-cooling and for liquefaction.
• the refrigerating fluid 66 gives up cold to the second pre-cooled gas 40 in the heat exchanger 64 of the liquefaction unit 42, and becomes the refrigerating fluid 60.
• the refrigerating fluid 60 gives up cold to the purified gas 28 in the exchanger thermal 58 of the first pre-cooling unit 30.
• the second pre-cooling unit 36 of installation 100 does not receive cold from the refrigeration cycle 146.
• the second heat exchanger 70 does not receive cold from a refrigeration cycle dedicated to sub-cooling, but from an open loop 172 with liquid nitrogen.
• a flow of liquid nitrogen 174 (coming from a source not shown, such as a liquid nitrogen storage) transfers cold to the stream of intermediate subcooled liquid 74 in the second heat exchanger 70 of the sub-cooling unit 48, and vaporizes to become a flow of nitrogen gas 176.
• the flow of nitrogen gas 176 then transfers cold to the first pre-cooled gas 32 in the heat exchanger 62, and becomes a flow of nitrogen 178.
• a nitrogen make-up 180 is made in the gaseous nitrogen flow 176 before the latter enters the second pre-cooling unit 36.
• This make-up 180 has a temperature lower than that of the flow of nitrogen. nitrogen gas 176 before topping up.
• the supplement 180 is advantageously produced in liquid form.
• the second pre-cooling is carried out by heat exchange, on the one hand, with the second flow of recycled gas 38 and, on the other hand, advantageously with the flow of gaseous nitrogen 176, possibly increased by the make-up 180.
• installation 100 is similar to that of installation 10.
• the second heat exchanger 70 of the sub-cooling unit 48 is absent, as well as the sub-cooling refrigeration cycle 72 (figure 1) or the open loop 172 (figure 2).
• the sub-cooling carried out by the sub-cooling unit 48 is then carried out only in the first exchanger 68, by heat exchange with the third flow of recycled gas 50.
• the treatment pressure is 40 bars absolute (pressure of the gas to be treated after compression by compressor 22).
• the second pre-cooled gas 40 has a temperature of -53.5°C.
• the liquid stream 44, leaving the liquefaction unit 42, has a temperature of -90°C.
• the subcooling unit 48 and the expansion unit 54 are configured to obtain an evaporation rate of between 20% and 30 molar%.
• Case 2 (example according to the invention): with recovery of the cold contained in the flash gas (the third gas flow 50 passes through the exchangers 68 and 62), but no open loop 172 with liquid nitrogen. Case 2 corresponds substantially to Figure 1;
• Case 4 (example according to the invention): with recovery of the cold contained in the flash gas (the third gas flow 50 passes through the exchangers 68 and 62), and presence of the loop 172 open to liquid nitrogen. Case 4 corresponds substantially to Figure 2.
• Case 1 represents a simple process, namely just liquefaction without subcooling and without cold recovery on the flash. We then seek to evaluate the energy gains resulting from the progressive addition of cold recovery systems using flash gas and liquid nitrogen sub-cooling systems.
• case 4 makes it possible to reduce the size of the liquefaction unit by 44%, resulting in a significant reduction in the overall production cost of liquefied gas.
• the process makes it possible to reduce the overall production cost of liquefied gas 14, in particular for production capacities of less than 20 tonnes per day.
• the treatment pressure between 19 and 70 bar absolute, is sufficiently high so that the liquefaction temperature is not too low, ie preferably greater than -90°C.
• the equipment used is less specific and less expensive.
• the weight of the investment being significant for small capacities, this has a favorable impact on the unit production cost.
• the energy spent to provide cold is also lower when the temperature of the fluid to be cooled is lower.
• the processing pressure remains relatively low and allows a sufficiently low subcooling temperature, which maintains the volume fraction of flash gas recycled upstream of the compressor in a reasonable proportion, which reduces the energy spent for compressing the gas to be treated 20.
• the lower pressure also allows savings on equipment, which does not have to withstand very high pressures.
• the cold present in the recycled flash gas (third recycled gas flow 50) is used specifically to amplify the pre-cooling of the gas to be treated and its sub-cooling. This cold is not used in the liquefaction unit 42. This reduces the cooling range of the liquefaction unit 42, and reduces the size of the liquefaction refrigeration cycles 46, 146. In addition, this avoids having to to modify the refrigeration liquefaction cycles themselves to integrate a flow of recycled gas.
• the sub-cooling is advantageously carried out with liquid nitrogen, the cold of which is for example also used to amplify the pre-cooling.

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• 2022
  • 2022-03-23 FR FR2202570A patent/FR3133908A1/fr active Pending
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