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
  • F25J1/02—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
  • F25J1/0243—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
• • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
  • F25—REFRIGERATION OR COOLING; COMBINED HEATING AND REFRIGERATION SYSTEMS; HEAT PUMP SYSTEMS; MANUFACTURE OR STORAGE OF ICE; LIQUEFACTION SOLIDIFICATION OF GASES
  • F25J—LIQUEFACTION, SOLIDIFICATION OR SEPARATION OF GASES OR GASEOUS OR LIQUEFIED GASEOUS MIXTURES BY PRESSURE AND COLD TREATMENT OR BY BRINGING THEM INTO THE SUPERCRITICAL STATE
  • F25J2210/00—Processes characterised by the type or other details of the feed stream
  • F25J2210/06—Splitting of the feed stream, e.g. for treating or cooling in different ways
• • 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
  • F25J2235/00—Processes or apparatus involving steps for increasing the pressure or for conveying of liquid process streams
  • F25J2235/42—Processes or apparatus involving steps for increasing the pressure or for conveying of liquid process streams the fluid being 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
  • F25J2240/00—Processes or apparatus involving steps for expanding of process streams
  • F25J2240/02—Expansion of a process fluid in a work-extracting turbine (i.e. isentropic expansion), e.g. of the feed stream
  • F25J2240/12—Expansion of a process fluid in a work-extracting turbine (i.e. isentropic expansion), e.g. of the feed stream the fluid being 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
  • F25J2270/00—Refrigeration techniques used
  • F25J2270/14—External refrigeration with work-producing gas expansion loop

Definitions

• the present invention relates generally to a method and a facility for liquefying a fuel gas with a high methane content.
• the global problem that the present invention seeks to solve is to liquefy gas with a high methane content (at least 80 mol%), typically natural gas from the gas transmission or distribution network, biomethane or gas evaporation.
• liquefied natural gas usually referred to as LNG.
• the process must incorporate a large amount of coolants in intermediate cycles to achieve the desired cooling (ultimately, the total mass flow of the refrigerant mixtures used is about 8 times that of the coolant to be cooled ), and
• the object of the present invention is therefore to overcome all or part of the disadvantages of the prior art, by setting up a hybrid process between on the one hand a process according to the Brayton cycle (or said relaxation) and on the other hand a conventional open cycle process.
• the method according to the invention instead of using a conventional open cycle which uses the only refrigerating power of the vaporization of the cold medium (typically liquid nitrogen), the method according to the invention firstly proposes to compress the cold medium and then, initially, to use its vaporization as cooling power, and finally in a second time, to relax it to generate additional cold.
• the subject of the present invention is a process for liquefying a fuel gas mainly comprising methane, in which the fuel gas circulates in a primary circuit from a source of combustible gas to a tank for liquefied gas, and a cooling mixture.
• formed of liquid nitrogen or at least partially vaporized circulates in an open secondary circuit from a nitrogen tank to be released to the atmosphere, the method comprising the following phases:
• a complete liquefaction phase during which the single stream of fuel gas leaving the cooling heat exchange zone is completely liquefied by cooling to a temperature T3 at least as low as bubble temperature of the fuel gas; this complete liquefaction phase being carried out in a liquefaction heat exchange zone comprising at least one heat exchanger;
• a subcooling phase during which the liquefied fuel gas leaving the liquefaction heat exchange zone is sub-cooled from the temperature 3 to a subcooling temperature T 4 , this subcooling phase being carried out in a sub-cooling heat exchange zone comprising at least one thermal exchange heat exchanger with a flow of initially liquid nitrogen gas from the liquid nitrogen tank and flowing against the flow of fuel gas .
• the flow sub-flow ⁇ 3 ⁇ 4 is injected into the heat exchanger of the liquefaction heat exchange zone in order to liquefy it completely and cool it to the temperature T3, by circulating the flow of at least partially vaporized nitrogen leaving the heat exchange sub-cooling zone;
• the flow sub-flow m 4 is injected into an auxiliary heat exchanger of the liquefaction heat exchange zone in order to liquefy it completely and to cool it to the temperature T3, by circulating therein countercurrently with the gas fuel, the flow of nitrogen leaving the turbine;
• the two fuel flow sub-flows of respective flow rates ⁇ 3 ⁇ 4 and m 4 respectively from each of the heat exchangers of the liquefaction heat exchange zone are brought together and reinjected into the d-zone; heat exchange sub-cooling.
• nitrogen is understood to mean a fluid comprising at least 97 mol% of nitrogen.
• heat exchanger means a subset or part of a heat exchange zone integrating the entire heat exchange line of the phase of the process of the invention.
• a heat exchange zone is understood to mean a set of heat exchangers in which all the heat exchanges of a given phase of the process of the invention take place, namely, the melt. -cooling, liquefaction or subcooling.
• heat exchange line means the succession of fluids exchanging heat with each other in the phase under consideration.
• the overall principle of the process according to the invention is therefore to take advantage of both cooling by evaporation of the liquid nitrogen and its expansion. Therefore, this means, from a conceptual point of view, that the refrigerant (i.e. liquid or vaporized nitrogen will be used twice on a part of the heat exchange zone (this is on the same temperature range) But the nitrogen will not be in the same state during these two passages:
• the refrigerant i.e. liquid or vaporized nitrogen
• the two phases of redistribution of the fuel gas can be carried out under the following conditions:
• the flow ⁇ 3 ⁇ 4 of the fuel gas sub-flow injected into the heat exchanger of the liquefaction heat exchange zone representing at least 60% of the initial flow rate m of fuel gas, and at most the value of ⁇ 3 ⁇ 4.
• the liquid nitrogen from the liquid nitrogen tank can be pumped at a pressure of at least 1.2 MPa, depending on the nature of the fuel gas to be liquefied.
• the stream of at least partially vaporized nitrogen at the outlet of the heat exchanger of the cooling heat exchange zone can be expanded in the turbine (preferably a pressure turbine) at an equal pressure. or less than 0.2 MPa (ie approximately
• the gas to be liquefied may contain methane in a molar proportion of at least 80%.
• the method according to the invention makes it possible to keep the advantages of a conventional open cycle by limiting its main disadvantage, namely its consumption of liquid nitrogen, and consequently the cost associated with this consumption.
• a total absence of phenomena of the "sudden evaporation" type (usually referred to in English as "flash gas") during the final relaxation of the LNG because the LNG is under -cooled enough so that it does not generate steam (“flash”) during this final relaxation. This allows to save the economy of a recompression of gas.
• abrupt evaporation is meant, in the sense of the present invention a partial vaporization in the liquid line (during relaxation), which occurs when the LNG under pressure (to facilitate its liquefaction) is expanded either by means of a valve Joule-Thomson, a liquid or even two-phase turbine.
• the costs of developing or supplying non-consumable parts are moderate: in the absence of cold to be created by intermediate cycles (as in the case of closed cycles), the number of rotating machines to implement to operate the process according to the invention (compressor, turbine) is drastically reduced compared to conventional closed cycle processes, as well as the size of the exchange line.
• OPEX operating costs
• the subject of the present invention is also a liquefaction plant for a fuel gas for implementing the method according to the invention, this installation comprising a primary circuit connected to a source of combustible gas and to a tank for liquefied gas, a an open secondary circuit connected to a liquid nitrogen tank, and four heat exchange zones arranged in cascade for cooling and liquefying the fuel gas circulating in the primary circuit, each of the thermal zones being traversed by the primary and secondary circuits disposed in such a manner that the fuel gas and the nitrogen circulate there against the current according to the following configuration:
• a heat exchange zone pre ⁇ cooling comprising at least one heat exchanger
• a cooling heat exchange zone comprising a heat exchanger and an auxiliary exchanger, the cooling heat exchange zone being connected, in the primary circuit, to the heat exchange zone (100) of pre-cooling by
• auxiliary heat exchanger in the liquefaction heat exchange zone
• a turbine disposed in the secondary circuit between the outlet of the heat exchanger of the heat exchange zone and the inlet of the heat exchanger of the liquefaction heat exchange zone, to relax and cool the at least partially vaporized nitrogen leaving the heat exchanger of the cooling heat exchange zone before injecting it into the auxiliary heat exchanger of the a liquefaction heat exchange zone
• the installation according to the invention has the advantage of being very compact thanks to the reduction of the inventory of cooling fluids (that is to say the quantity and the refrigerant mass flow rate) and the size and the number of rotating machines; this compactness thus allowing its mobility (on truck, barge, boat, train, etc.).
• FIG. 1 represents a general block diagram of a preferred embodiment of the installation according to the invention, on which the arrangement of the various heat exchangers and of the fuel gas distribution zones has been represented;
• FIG. 2 represents the same general block diagram as that represented in FIG. 1, showing in particular the different phases of the method of the invention
• FIG. 3 represents a general block diagram of a plant according to the prior art comprising an open cycle with liquid nitrogen.
• FIG. 3 is a device according to the prior art for implementing a method for liquefying a fuel gas known from the prior art operating with an open cycle with liquid nitrogen. This method serves as a point of comparison for the numerical simulations presented hereinafter in the examples.
• FIG. 1 there is shown a general block diagram of a preferred embodiment of the installation according to the invention.
• This installation comprises: a primary circuit 1 connected to a source 1 of combustible gas and a tank for liquefied gas),
• an open secondary circuit 34 connected to a liquid nitrogen reservoir 3, and four heat exchange zones 100, 200, 300, 400 disposed in cascade for cooling and liquefying the fuel gas circulating in the primary circuit 12, each of the thermal zones 100, 200, 300, 400 being traversed by the primary circuits 12 and secondary 34 arranged so that the fuel gas and nitrogen circulate there against the current.
• the heat exchange zones 100, 200, 300, 400 are distributed according to the following configuration:
• FIG. 1 further shows that a turbine 22 (preferably a detent) is disposed in the secondary circuit 34, connecting the outlet of the heat exchanger 20 of the heat exchange zone 200 and the cooling inlet.
• a turbine 22 preferably a detent
• this turbine 33 can relax and cool the vaporized nitrogen leaving the heat exchanger 20 of the heat exchange zone 200 cooling, before its injection into the heat exchanger annex 31 of the heat exchange zone 300 of liquefaction.
• FIG. 2 shows the implementation of the method according to the invention on the installation according to the invention shown in FIG. 1.
• the various phases of the process of the invention have been indicated at the level of the heat exchangers where they are realized.
• FIG. 2 shows in particular that the process according to the invention consists in liquefying a fuel gas comprising predominantly methane, by circulating it in a primary circuit I open from a source of combustible gas to a tank for liquefied gas 2, while a refrigerant mixture consisting of liquid nitrogen or at least partially vaporized circulates in a secondary circuit 34 open from a nitrogen reservoir 3 to be released to the atmosphere.
• the initially completely liquid nitrogen, coming from the tank 3, is injected into the heat exchanger 40 of the heat exchange zone 400 of subcooling, in which it flows in counter-current flow of fuel gas. Then, in the subcooling zone 400, the nitrogen stream partially vaporizes. On leaving the zone 400, the partially vaporized nitrogen is injected into the heat exchanger 30 of the heat exchange zone 300 of liquefaction to liquefy a portion of the fuel gas stream, between 3 and T 2.
• This step makes it possible to adjust at best the flow rate of fuel gas to be liquefied so as to optimize the process according to the invention, and to facilitate its technical implementation since then at T 2 , the nitrogen is totally vaporized, so that the exchangers involved ( exchangers 30 and 40) have purely monophasic input-output.
• the completely vaporized nitrogen is, at the temperature T 2 , injected into the heat exchanger 20 of the cooling heat exchange zone 200, in which it circulates countercurrently with a part of the combustible gas which there is cooled between the temperature T1 of pre-cooling to the temperature T 2 of dew.
• the nitrogen at a temperature close to ⁇ , is totally vaporized, but still at high pressure.
• the vaporized nitrogen is then expanded in the expansion turbine 22 (typically from a pressure of 1.2 MPa to less than 0.2 MPa, the precise values depending on the fuel gas to be cooled).
• This makes it possible to obtain a stream of nitrogen that is admittedly vaporized, but at a cryogenic temperature typically of the order of -160 ° C. (again the precise values depend on the case studied).
• the nitrogen obtained is at a temperature well below 3 (which is the bubble temperature of the gas to be liquefied).
• cold, completely vaporized, low pressure nitrogen is obtained which is used to liquefy the remainder of the fuel stream that has not been liquefied.
• this phase 1000 of pre-cooling the fuel gas (initial m speed) is cooled to the ambient temperature T to a temperature pre ⁇ Ti cooling above the dew point 2 of the combustible gas, this stage of pre -cooling being performed by heat exchange with a stream of vaporized nitrogen and low pressure circulating countercurrent flow of fuel gas in the heat exchanger 10 of the heat exchange zone 100 of pre- cooling.
• cooling phase 2000 the combustible gas, once divided into two sub-flows of flow rates mi and n3 ⁇ 4, is cooled from the pre-cooling temperature ⁇ to the dew point temperature 2 of the fuel gas.
• cooling phase being carried out in the heat exchange zone 200 of cooling comprising the heat exchanger 20 and the exchanger annex 21, according to the following steps:
• this complete liquefaction phase 3000 is carried out in the heat exchange zone 300 as follows:
• the flow sub-flow ⁇ 3 ⁇ 4 is injected into the heat exchanger 30 of the liquefaction heat exchange zone 300 in order to liquefy it completely and cool it to the temperature T3, by circulating it in countercurrent. at least partially vaporized nitrogen flow exiting the heat exchange zone 400 subcooling;
• the flow sub-flow m 4 is injected 3005 into the heat exchanger annex 31 of the liquefaction heat exchange zone 300 in order to liquefy it completely and cool it down to the temperature T3, by circulating there, against the current of the fuel gas, the flow of nitrogen leaving the turbine 22; at the temperature 3 of the fuel gas;
• the two fuel flow sub-streams of respective flow rates ⁇ 3 ⁇ 4 and m 4 respectively from each of the heat exchangers 30, 31 of the liquefaction heat exchange zone 300 are brought together to reinject them into the heat exchange zone. 400 subcooling.
• this phase 4000 the liquefied fuel gas leaving the liquefaction heat exchange zone 300 is sub-cooled from the temperature T3 to a subcooling temperature T 4 , this subcooling phase 4000 being performed in the heat exchange zone 400 subcooling comprising at least one heat exchanger 40 by heat exchange with the flow of nitrogen gas initially completely liquid circulating countercurrent flow of fuel gas.
• the process according to the invention comprises 5 major process control parameters:

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• 2015
  • 2015-12-17 FR FR1562705A patent/FR3045796A1/fr active Pending
• 2016
  • 2016-01-26 FR FR1650632A patent/FR3045794B1/fr active Active
  • 2016-12-16 EP EP16834023.0A patent/EP3390938B1/de active Active
  • 2016-12-16 WO PCT/FR2016/053523 patent/WO2017103535A1/fr active Application Filing

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