WO2017192136A1 - Istallation for feeding a gas-consuming member with combustible gas and for liquefying said combustible gas - Google Patents

Istallation for feeding a gas-consuming member with combustible gas and for liquefying said combustible gas Download PDF

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Publication number
WO2017192136A1
WO2017192136A1 PCT/US2016/030793 US2016030793W WO2017192136A1 WO 2017192136 A1 WO2017192136 A1 WO 2017192136A1 US 2016030793 W US2016030793 W US 2016030793W WO 2017192136 A1 WO2017192136 A1 WO 2017192136A1
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WO
WIPO (PCT)
Prior art keywords
gas stream
combustible gas
phase
channel
vapour
Prior art date
Application number
PCT/US2016/030793
Other languages
French (fr)
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WO2017192136A9 (en
Original Assignee
Innovative Cryogenic Systems, Inc.
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Application filed by Innovative Cryogenic Systems, Inc. filed Critical Innovative Cryogenic Systems, Inc.
Priority to JP2018557009A priority Critical patent/JP6850305B2/en
Priority to KR1020177036719A priority patent/KR101943256B1/en
Priority to PCT/US2016/030793 priority patent/WO2017192136A1/en
Priority to KR1020197002018A priority patent/KR102190260B1/en
Priority to CN201680087173.9A priority patent/CN109563969B/en
Publication of WO2017192136A1 publication Critical patent/WO2017192136A1/en
Publication of WO2017192136A9 publication Critical patent/WO2017192136A9/en

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Classifications

    • 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
    • F17C9/00—Methods or apparatus for discharging liquefied or solidified gases from vessels not under pressure
    • F17C9/02—Methods or apparatus for discharging liquefied or solidified gases from vessels not under pressure with change of state, e.g. vaporisation
    • 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
    • F25J1/0025—Boil-off gases "BOG" from storages
    • 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
    • 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
    • F17C6/00—Methods and apparatus for filling vessels not under pressure with liquefied or solidified gases
    • 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"
    • F25J1/0045—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 vaporising a liquid return stream
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F25—REFRIGERATION OR COOLING; COMBINED HEATING AND REFRIGERATION SYSTEMS; HEAT PUMP SYSTEMS; MANUFACTURE OR STORAGE OF ICE; LIQUEFACTION SOLIDIFICATION OF GASES
    • F25J—LIQUEFACTION, SOLIDIFICATION OR SEPARATION OF GASES OR GASEOUS OR LIQUEFIED GASEOUS MIXTURES BY PRESSURE AND COLD TREATMENT OR BY BRINGING THEM INTO THE SUPERCRITICAL STATE
    • F25J1/00—Processes or apparatus for liquefying or solidifying gases or gaseous mixtures
    • F25J1/02—Processes or apparatus for liquefying or solidifying gases or gaseous mixtures requiring the use of refrigeration, e.g. of helium or hydrogen ; Details and kind of the refrigeration system used; Integration with other units or processes; Controlling aspects of the process
    • F25J1/0201—Processes or apparatus for liquefying or solidifying gases or gaseous mixtures requiring the use of refrigeration, e.g. of helium or hydrogen ; Details and kind of the refrigeration system used; Integration with other units or processes; Controlling aspects of the process using only internal refrigeration means, i.e. without external refrigeration
    • F25J1/0202—Processes or apparatus for liquefying or solidifying gases or gaseous mixtures requiring the use of refrigeration, e.g. of helium or hydrogen ; Details and kind of the refrigeration system used; Integration with other units or processes; Controlling aspects of the process using only internal refrigeration means, i.e. without external refrigeration in a quasi-closed internal refrigeration loop
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F25—REFRIGERATION OR COOLING; COMBINED HEATING AND REFRIGERATION SYSTEMS; HEAT PUMP SYSTEMS; MANUFACTURE OR STORAGE OF ICE; LIQUEFACTION SOLIDIFICATION OF GASES
    • F25J—LIQUEFACTION, SOLIDIFICATION OR SEPARATION OF GASES OR GASEOUS OR LIQUEFIED GASEOUS MIXTURES BY PRESSURE AND COLD TREATMENT OR BY BRINGING THEM INTO THE SUPERCRITICAL STATE
    • F25J1/00—Processes or apparatus for liquefying or solidifying gases or gaseous mixtures
    • F25J1/02—Processes or apparatus for liquefying or solidifying gases or gaseous mixtures requiring the use of refrigeration, e.g. of helium or hydrogen ; Details and kind of the refrigeration system used; Integration with other units or processes; Controlling aspects of the process
    • F25J1/0243—Start-up or control of the process; Details of the apparatus used; Details of the refrigerant compression system used
    • F25J1/0244—Operation; Control and regulation; Instrumentation
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F25—REFRIGERATION OR COOLING; COMBINED HEATING AND REFRIGERATION SYSTEMS; HEAT PUMP SYSTEMS; MANUFACTURE OR STORAGE OF ICE; LIQUEFACTION SOLIDIFICATION OF GASES
    • F25J—LIQUEFACTION, SOLIDIFICATION OR SEPARATION OF GASES OR GASEOUS OR LIQUEFIED GASEOUS MIXTURES BY PRESSURE AND COLD TREATMENT OR BY BRINGING THEM INTO THE SUPERCRITICAL STATE
    • F25J1/00—Processes or apparatus for liquefying or solidifying gases or gaseous mixtures
    • F25J1/02—Processes or apparatus for liquefying or solidifying gases or gaseous mixtures requiring the use of refrigeration, e.g. of helium or hydrogen ; Details and kind of the refrigeration system used; Integration with other units or processes; Controlling aspects of the process
    • F25J1/0243—Start-up or control of the process; Details of the apparatus used; Details of the refrigerant compression system used
    • F25J1/0244—Operation; Control and regulation; Instrumentation
    • F25J1/0254—Operation; Control and regulation; Instrumentation controlling particular process parameter, e.g. pressure, temperature
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F25—REFRIGERATION OR COOLING; COMBINED HEATING AND REFRIGERATION SYSTEMS; HEAT PUMP SYSTEMS; MANUFACTURE OR STORAGE OF ICE; LIQUEFACTION SOLIDIFICATION OF GASES
    • F25J—LIQUEFACTION, SOLIDIFICATION OR SEPARATION OF GASES OR GASEOUS OR LIQUEFIED GASEOUS MIXTURES BY PRESSURE AND COLD TREATMENT OR BY BRINGING THEM INTO THE SUPERCRITICAL STATE
    • F25J1/00—Processes or apparatus for liquefying or solidifying gases or gaseous mixtures
    • F25J1/02—Processes or apparatus for liquefying or solidifying gases or gaseous mixtures requiring the use of refrigeration, e.g. of helium or hydrogen ; Details and kind of the refrigeration system used; Integration with other units or processes; Controlling aspects of the process
    • F25J1/0243—Start-up or control of the process; Details of the apparatus used; Details of the refrigerant compression system used
    • F25J1/0257—Construction and layout of liquefaction equipments, e.g. valves, machines
    • F25J1/0262—Details of the cold heat exchange system
    • F25J1/0264—Arrangement of heat exchanger cores in parallel with different functions, e.g. different cooling streams
    • 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
    • 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
    • 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
    • F25J2210/04—Mixing or blending of fluids with the feed stream

Definitions

  • the invention relates to the field of installations for treating a combustible gas, such as liquefied natural gas (LNG) .
  • a combustible gas such as liquefied natural gas (LNG)
  • the invention is more particularly directed towards an installation for, on the one hand, feeding a gas-consuming member with combustible gas and, on the other hand, liquefying said combustible gas.
  • Liquefied natural gas is stored in leaktight and heat-insulating tanks, in a liquid/vapour two-phase state of equilibrium, at cryogenic temperatures.
  • the heat- insulating barriers of liquefied natural gas storage tanks are the site of heat flow which tends to heat the content of the tanks, which is reflected by evaporation of the liquefied natural gas.
  • the gas derived from natural evaporation is generally used to feed a gas-consuming member so as to upgrade it.
  • the evaporated gas is used to feed the powertrain for propelling the ship or the power generators supplying the electricity required for the functioning of the onboard equipment.
  • such practice makes it possible to upgrade the gas derived from natural evaporation in the tanks, it does not make it possible to reduce its amount.
  • a first portion of the compressed gas is conveyed to one or more vapour-phase gas-consuming members in order to be burnt therein, while a second portion of the compressed gas is returned to the exchanger in order to transfer heat to the vapour-phase gas stream collected in the gaseous headspace of the tank.
  • the second portion of gas thus cooled and partially liquefied is then depressurized in an expansion device in which, by means of the Joule-Thomson effect, the temperature of the gas stream decreases further during its expansion so as at least partially to reliquefy it.
  • a phase separator allows the liquid phase and the vapour phase to be separated before conveying the liquid phase into the tank and sending the gas phase back into the vapour-phase gas collection circuit, upstream of the heat exchanger.
  • Such an installation is particularly advantageous in that compression of the gas stream is used, both to make one portion of the gas stream compatible with the working conditions of the gas-consuming members and to allow subsequent reliquefaction of the other portion of the gas stream.
  • the installation is thereby simplified and the cost of the additional reliquefaction function is limited.
  • the gaseous-phase natural gas derived from natural evaporation has a richer composition of volatile components, such as nitrogen, than the liquefied natural gas in the liquid state stored in the tank.
  • volatile components such as nitrogen
  • the gas derived from natural evaporation is liable to have a nitrogen concentration of the order of 14% to 15%.
  • the use of an expansion device using Joule-Thomson expansion and at the outlet of which the vapour phase is returned to the vapour-phase gas collection circuit leads to the nitrogen being concentrated in the gas stream treated by the installation.
  • the portion of the compressed gas that is conveyed to one or more gas-consuming members is liable to have a nitrogen concentration much higher than 20%.
  • high concentrations of nitrogen lead to imperfect combustion of the gas in the gas-consuming member and to operating defects of the gas- consuming member. Summary
  • An idea forming the basis of the invention is to propose an installation for feeding a gas-consuming member with combustible gas and for liquefying said combustible gas, which makes it possible to obtain an increased combustible gas liquefaction yield at least under certain critical operating conditions.
  • the invention provides an installation for feeding a gas-consuming member with combustible gas and for liquefying said combustible gas; the installation comprising:
  • a leaktight and heat-insulating tank comprising an inner space intended to be filled with combustible gas in a liquid-vapour two-phase state of equilibrium;
  • vapour-phase gas collection circuit comprising an admission emerging in the inner space of the tank and arranged to withdraw a vapour-phase combustible gas stream from the inner space of the tank;
  • a heat exchanger comprising a first and a second channels and heat- exchange walls for transferring heat from the second channel to the first channel, the first channel and the second channel each comprising an inlet and an outlet; the inlet of the first channel being connected to the vapour-phase gas collection circuit so as to heat the vapour-phase combustible gas stream in the heat exchanger;
  • a compressor which is connected upstream to the outlet of the first channel of the heat exchanger so as to compress the heated combustible gas stream in the heat exchanger and is connected downstream to a three-way connector that is capable of conveying a first portion of the combustible gas stream to the gas-consuming member and of conveying a second portion of the combustible gas stream to the inlet of the second channel of the heat exchanger in order to cool the second portion of the combustible gas;
  • an expansion device that is connected upstream to the outlet of the second channel of the heat exchanger via an intermediate circuit and is connected downstream to a return circuit leading to the tank; the expansion device being arranged to depressurize the second portion of the combustible gas stream coming from the intermediate circuit;
  • a cooling device which comprises a withdrawal circuit; said withdrawal circuit comprising an admission which emerges in the inner space of the tank and is arranged to withdraw a liquid-phase combustible gas stream in the inner space of the tank; said cooling device being arranged so as to transfer heat between the liquid-phase combustible gas stream withdrawn from the tank and a combustible gas stream to be cooled chosen from the vapour-phase combustible gas stream circulating in the vapour- phase gas collection circuit and the second portion of the combustible gas stream circulating in the intermediate circuit so as to vaporize the liquid-phase combustible gas stream withdrawn from the tank and to use the latent heat of vaporization of the liquid-phase combustible gas stream withdrawn from the tank to cool the combustible gas stream to be cooled.
  • the invention proposes to use the liquid phase of the combustible gas stored in the tank to even further reduce the temperature of the compressed gas at the inlet of the expansion device, this temperature reduction being able to be obtained either by acting directly on the second portion of the compressed gas stream circulating in the intermediate circuit, or by reducing the temperature of the gas at the inlet of the first channel of the heat exchanger such that the temperature at the outlet of the second channel of the exchanger will be reduced in consequence.
  • the temperature of the gas stream at the inlet of the expansion device its degree of liquefaction during its depressurization in the expansion device is substantially increased. This makes it possible to obtain an increased reliquefaction yield under certain critical operating conditions, especially when the temperature of the vapour that is present in the gaseous headspace of the tank is quite appreciably above the equilibrium temperature of the gas.
  • the combustible gas is a gaseous mixture of the LNG or LPG type comprising nitrogen in small proportion and when the cooling device is arranged so as to convey the vaporized gas stream in the vapour-phase gas collection circuit, such an installation makes it possible to perform dilution of the nitrogen of the gas stream intended to be conducted to the gas-consuming member so as to make it compatible with the operating conditions of the gas-consuming member, without substantially degrading the reliquefaction yield.
  • such an installation may comprise one or more of the following characteristics.
  • the combustible gas is a gaseous mixture of the LNG or LPG type comprising nitrogen.
  • the combustible gas is a gaseous mixture comprising nitrogen, nitrogen being the most volatile component of the gaseous mixture.
  • the cooling device is arranged so as to convey the vaporized gas stream in the cooling device to the vapour-phase gas collection circuit so as to reduce the nitrogen content of the combustible gas stream circulating in the vapour-phase gas collection circuit.
  • the combustible gas is constituted of a gaseous mixture comprising nitrogen
  • the vapour-phase gas at the inlet of the installation has a composition rich in volatile components, the greater will be the liquefaction yield. Consequently, by mixing the vaporized gas stream in the cooling device with a gas stream coming from natural evaporation, the nitrogen concentration of the resulting mixture is reduced, which makes it possible to increase the degree of liquefaction during depressurization in the expansion device.
  • the cooling device comprises an additional heat exchanger comprising a first and a second channels and heat-exchange walls for transferring heat from the first channel to the second channel of the additional heat exchanger, the first channel and the second channel each comprising an inlet and an outlet, the first channel being integrated into the intermediate circuit connecting the heat exchanger and the expansion device, the inlet of the second channel being connected to the admission of the cooling device and the outlet of the second channel being connected to the vapour-phase gas collection circuit.
  • the additional heat exchanger is superimposed above the heat exchanger and the outlet of the second channel of the additional heat exchanger is connected to the inlet of the first channel of the heat exchanger such that a liquid-phase gas stream can flow by gravity from the outlet of the second channel of the additional heat exchanger to the inlet of the first channel of the heat exchanger.
  • the cooling device comprises a second additional heat exchanger comprising a first channel integrated into the vapour-phase gas collection circuit and a second channel comprising an inlet connected to the withdrawal circuit and an outlet connected to the vapour-phase gas collection circuit.
  • the cooling device comprises a chamber integrated into the vapour-phase gas collection circuit between the admission of the vapour-phase gas collection circuit and the inlet of the first channel of the heat exchanger and a spraying member which is connected to the withdrawal circuit of the cooling device and is arranged to spray liquid-phase combustible gas into the chamber so as to cool the vapour-phase gas stream withdrawn from the inner space of the tank and to reduce the nitrogen content of the combustible gas stream circulating in the vapour-phase gas collection circuit.
  • the cooling device comprises a pumping device that can suck the liquid-phase combustible gas stream via the admission of the cooling device and deliver it into the withdrawal circuit.
  • the installation comprises a gas analyser that can deliver a representative measurement of the nitrogen concentration in the first portion of the combustible gas stream and the control unit is arranged to generate a control signal for the pumping device as a function of the representative measurement of the nitrogen concentration in the first portion of the combustible gas stream conveyed to the gas-consuming member so as to ensure a nitrogen concentration in the first portion of the combustible gas stream that is below a limit operating concentration of the gas-consuming member.
  • the gas analyser is capable of analysing the composition of a gas sample so as to deduce its nitrogen concentration therefrom.
  • the gas analyser is a machine for measuring the upper calorific power of a gas sample.
  • the control unit is arranged to generate a control signal for the pumping device as a function of a representative measurement of the nitrogen concentration in the first portion of the combustible gas stream and of a nominal concentration, below the limit operating concentration of the gas-consuming member, so as to enslave the nitrogen concentration in the first portion of the combustible gas stream to the nominal concentration.
  • control unit has:
  • a nitrogen concentration priority mode in which it generates a control signal for the pumping device as a function of a representative measurement of the nitrogen concentration in the first portion of the combustible gas stream and of a nominal concentration, below the limit operating concentration of the gas-consuming member, so as to enslave the nitrogen concentration in the first portion of the combustible gas stream to the nominal concentration;
  • a reliquefaction priority mode in which it generates a control signal for the pumping device as a function of a temperature measurement T1 of the second portion of the gas stream circulating in the intermediate circuit at the inlet of the expansion device and of a nominal temperature so as to enslave the temperature T1 to the nominal temperature;
  • control unit being arranged to switch from the nitrogen concentration priority mode to the reliquefaction priority mode as a function of the representative measurement of the nitrogen concentration in the first portion of the combustible gas stream.
  • the cooling device comprises a sensor that is capable of measuring the temperature T1 of the second portion of the gas stream circulating in the intermediate circuit at the inlet of the expansion device and a control unit arranged, at least in one operating mode, to generate a control signal for the pumping device as a function of the measurement of the temperature T1 and of a nominal temperature so as to enslave the temperature T1 to the nominal temperature.
  • the pumping device comprises a pump and the control unit is arranged to pilot the pump as a function of the control signal.
  • the liquid-phase gas flow rate delivered by the pump of the pumping device is varied to obtain the desired flow rate.
  • the pumping device comprises a pump, a return pipeline which, firstly, is connected to the withdrawal circuit downstream of the pump and, secondly, returns to the inner space of the tank and two valves that are installed, respectively, on the withdrawal circuit downstream of the return pipeline connector and on the return pipeline; the control unit being arranged to pilot one and/or the other of the two valves as a function of the control signal.
  • the pump of the pumping device operates at constant power and one and the other of the two valves are actuated in order to modify the distribution between the portion of the liquid-phase gas stream that is conveyed in the withdrawal circuit in order to be vaporized and the portion of the liquid-phase gas stream that returns into the tank via the return pipeline.
  • the expansion device is an expansion valve, also known as a Joule-Thomson valve.
  • the installation comprises a phase separator connected upstream to the expansion device and downstream, on the one hand, to a return circuit leading to the tank and, on the other hand, to a return pipe connected to the vapour-phase gas collection circuit; the phase separator being arranged to convey the liquid phase of the combustible gas stream to the return circuit and to convey the gas phase of the combustible gas stream to the return pipe.
  • the compressor is a multi-stage compressor.
  • the compressor comprises a plurality of compression stages and a plurality of intermediate heat exchangers, each of the intermediate heat exchangers being placed at the outlet of one of the compression stages.
  • the invention also provides a process for feeding a gas-consuming member with combustible gas and for liquefying said combustible gas by means of an abovementioned installation, the process comprising:
  • the combustible gas is a gaseous mixture comprising nitrogen and the vaporized gas stream in the cooling device is conveyed to the vapour-phase gas collection circuit.
  • a variable representative of the nitrogen concentration in the first portion of the combustible gas stream is measured and the flow rate of the liquid-phase combustible gas stream circulating in the withdrawal circuit of the cooling device is adjusted as a function of the variable representative of the nitrogen concentration in the first portion of the combustible gas stream.
  • the flow rate of the liquid-phase combustible gas stream circulating in the withdrawal circuit of the cooling device is adjusted as a function of the variable representative of the nitrogen concentration in the first portion of the combustible gas stream and of a nominal concentration so as to enslave the nitrogen concentration in the first portion of the combustible gas stream to the nominal concentration.
  • the temperature T1 of the second portion of the gas stream circulating in the intermediate circuit upstream of the expansion device is measured and the flow rate of the liquid-phase combustible gas stream circulating in the withdrawal circuit of the cooling device is adjusted as a function of the measurement of the temperature T1 and of a nominal temperature so as to enslave the temperature T1 to the nominal temperature.
  • the combustible gas is a liquefied natural gas and the nominal temperature T1 is between -145 and -160°C.
  • the invention provides a vessel comprising an abovementioned installation.
  • the invention also provides a process for loading or emptying such a vessel, in which combustible gas is conducted through cryogenic transfer pipes from or to a floating or land-based storage installation to or from the vessel's tank.
  • the invention also provides a system for transferring a combustible gas, the system comprising the abovementioned vessel, cryogenic transfer pipes arranged so as to connect the tank installed in the vessel's hull to a floating or land-based storage installation, and a pump for driving a combustible gas stream through the cryogenic transfer pipes from or to the floating or land-based storage installation to or from the vessel 's tank.
  • FIG. 1 is a schematic illustration of an installation for feeding gas- consuming members with combustible gas and for liquefying said combustible gas according to a first embodiment.
  • FIG. 2 is a schematic illustration of an installation according to a second embodiment.
  • FIG. 3 is a schematic illustration of an installation according to a third embodiment.
  • FIG. 4 illustrates in detailed manner the arrangement of the two heat exchangers of figure 2 according to one embodiment variant.
  • FIG. 5 is a graph illustrating the nitrogen concentration of different natural gas streams of the installation of figure 2 as a function of the nitrogen concentration in the natural gas in the liquid state, when 70% of the flow of the combustible gas stream is returned to the heat exchanger in order to be reliquefied therein.
  • FIG. 6 is a graph similar to that of figure 5, when 70% of the flow of the combustible gas stream is returned to the heat exchanger in order to be reliquefied therein.
  • Figure 7 is a graph representing the difference between the flow rate of reliquefied gas and the flow rate of liquid-phase gas withdrawn from the tank as a function of the flow rate of the second portion of the combustible gas stream returning to the inlet of the second channel of the heat exchanger for the installation of figure 1 and that of figure 2.
  • FIG. 8 is a graph representing the nitrogen concentration of the first portion of the gas stream conveyed to the gas-consuming member as a function of the flow rate of the second portion of the combustible gas stream returning to the heat exchanger for an installation according to the prior art and an installation according to figure 1 or 2.
  • FIG. 9 is a graph representing the difference between the flow rate of reliquefied gas and the flow rate of liquid-phase gas withdrawn from the tank as a function of the flow rate of the second portion of the combustible gas stream returning to the heat exchanger for an installation according to the prior art and an installation according to figure 2.
  • FIG. 10 is a schematic representation of a vessel and of a transfer system for loading/unloading combustible gas.
  • combustion gas has a generic nature and refers without preference to a gas constituted of a single pure substance or a gaseous mixture constituted of a plurality of components.
  • an installation 1 for, on the one hand, feeding one or more gas- consuming members with combustible gas and, on the other hand, liquefying combustible gas is illustrated.
  • Such an installation 1 may be installed on land or on a floating structure.
  • the installation 1 may be intended for a liquefaction or regasification barge or for a liquefied natural gas cargo ship, such as a methane tanker, or may more generally be intended for any ship equipped with a gas-consuming member.
  • the installation 1 comprises three different types of combustible gas- consuming members, namely a burner 2, an electrical generator 3 and an engine 4 for propelling a ship.
  • the burner 2 may be integrated into a power production installation or may be integrated into a gas combustion unit (GCU) .
  • the power production installation may especially comprise a steam production boiler.
  • the steam may be intended to feed steam turbines for producing energy and/or to feed a heating network of the ship.
  • a burner 2 is capable of functioning with a combustible gas whose nitrogen concentration is high, for example greater than 30% to 35% for a standard gas combustion unit, but may be well above this by supplying fuel.
  • the electrical generator 3 comprises, for example, a diesel/natural gas mixed feed heat engine, for example of DFDE (dual-fuel diesel electric) technology.
  • a heat engine can burn a mixture of diesel and natural gas or use one or the other of these two fuels.
  • the natural gas feeding such a heat engine must have a pressure of the order of a few bar to a few tens of bar, for example from about 6 to 8 bar absolute.
  • the natural gas in order to allow compliant functioning of such a heat engine, the natural gas must have a nitrogen concentration below a limit operating concentration, of the order of 15% to 20%.
  • the engine 4 for propelling the ship is, for example, a dual fuel two-stroke low-speed engine of "ME-GI" technology, developed by the company MAN.
  • Such an engine 4 uses natural gas as combustible and a small amount of pilot fuel which is injected before the injection of the natural gas in order for it to ignite.
  • the natural gas must first be compressed at a high pressure of between 150 and 400 bar absolute, and more particularly between 250 and 300 bar absolute.
  • such an engine is extremely sensitive to the quality of the natural gas and, in order to allow compliant functioning, the natural gas must have a nitrogen concentration not exceeding a threshold of the order of 15% to 20%.
  • the installation 1 comprises one or more leaktight and heat-insulating tanks
  • each tank 5a, 5b, 5c, 5d is a membrane tank.
  • membrane tanks are described in patent applications WO 140/57221 , FR 2 691 520 and FR 2 877 638.
  • Such membrane tanks are intended to store combustible gas at pressures substantially equal to atmospheric pressure or slightly higher.
  • each tank 5a, 5b, 5c, 5d may also be a free-standing tank and may especially have a parallelepipedal, prismatic, spherical, cylindrical or multi-lobed shape. Certain types of tank 5a, 5b, 5c, 5d allow gas storage at pressures substantially higher than atmospheric pressure.
  • Each tank 5a, 5b, 5c, 5d comprises an inner space intended to be filled with combustible gas.
  • the combustible gas may especially be a liquefied natural gas (LNG), i.e. a gaseous mixture predominantly comprising methane and also one or more other hydrocarbons, such as ethane, propane, n-butane, i-butane, n-pentane, i-pentane, neopentane, and nitrogen in small proportion.
  • LNG liquefied natural gas
  • the combustible gas may also be ethane or a liquefied petroleum gas (LPG) , i.e. a mixture of hydrocarbons derived from oil refinery essentially comprising propane and butane and nitrogen in small proportion.
  • LPG liquefied petroleum gas
  • the combustible gas is stored in the inner space of each tank 5a, 5b, 5c, 5d in a liquid-vapour two-phase state of equilibrium.
  • the gas is thus present in the vapour phase in the upper part of the tank 5a, 5b, 5c, 5d, and in the liquid phase in the lower part of the tank 5a, 5b, 5c, 5d.
  • the equilibrium temperature of the liquefied natural gas corresponding to its liquid-vapour two-phase state of equilibrium is about - 162°C when it is stored at atmospheric pressure.
  • the installation 1 comprises a vapour-phase gas collection circuit 6 which comprises an admission 7a, 7b, 7c, 7d emerging in the gaseous headspace of each of the tanks 5a, 5b, 5c, 5d, i.e. above the maximum filling height of the tank.
  • Each of these admissions 7a, 7b, 7c, 7d is connected to the vapour-phase gas collection circuit 6 via a valve 24.
  • the vapour-phase gas collection circuit 6 leads to a heat exchanger 8.
  • the heat exchanger 8 comprises a first and a second channel 9, 10 each having an inlet 9a, 10a and an outlet 9b, 10b and heat-exchange walls for transferring heat from the second channel 10 to the first channel 9.
  • the heat exchanger 8 is a counter-current exchanger.
  • the inlet 9a of the first channel 9 is connected to the vapour-phase gas collection circuit 6 so as to heat the gas stream derived from natural evaporation collected in the tanks 5a, 5b, 5c, 5d.
  • the outlet 9b of the first channel 9 is connected to a compressor 1 1 for compressing the gas stream to pressures that are compatible with the operating of the gas- consuming members.
  • the compressor 1 1 is a multi-stage compressor.
  • the compressor 1 1 comprises a plurality of compression stages 1 1 a, 1 1 b, 1 1 c, 1 1 d, 1 1 e and intermediate heat exchangers 33a, 33b, 33c, 33d which are placed at the outlet of each of the compression stages 1 1 a, 1 1 b, 1 1 c, 1 1 d, 1 1 e.
  • the intermediate heat exchangers 33a, 33b, 33c, 33d are directed toward cooling the compressed gas between two compression stages 1 1 a, 1 1 b, 1 1 c, 1 1 d, 1 1 e.
  • the heat exchangers 33a, 33b, 33c, 33d may especially provide an exchange with seawater, thus making it possible to bring the compressed gas stream to a temperature substantially equal to that of the seawater.
  • the compressor 27 is dimensioned as a function of the combustible gas- consuming members intended to be fed and especially as a function of their maximum feed rate and of the pressure level at which the combustible gas must be distributed thereto.
  • the compressor 1 1 is dimensioned such that the gas stream leaving the compressor 1 1 typically has a pressure of between 250 and 300 bar absolute.
  • the installation 1 Downstream of the compressor 1 1 , the installation 1 comprises a three-way connector 12 for conveying a first portion of the gas stream to the engine 4 for propelling the ship, and a second portion of the gas stream to the inlet 10a of the second channel 10 of the heat exchanger 8.
  • This three-way connector 12 is piloted by a control unit 34.
  • the control unit 34 is thus capable of varying the proportions of gas circulating, respectively, to the engine 4 and to the inlet 10a of the second channel 10 of the heat exchanger 8 as a function of the combustible gas needs of the engine 4 and/or of the amount of gas to be reliquefied.
  • the installation 1 comprises an intermediate three-way connector 13 which is placed between two compression stages 1 1 b, 1 1 c and thus makes it possible to divert a portion of the gas stream to gas-consuming members, in this case the burner 2 and the electrical generator 3, before the outlet of the compressor 1 1 .
  • gas-consuming members in this case the burner 2 and the electrical generator 3, before the outlet of the compressor 1 1 .
  • Such an arrangement makes it possible to divert combustible gas to a combustible gas-consuming member once it has passed through a sufficient number of compression stages 1 1 a, 1 1 b to reach the feed pressure corresponding to said consuming member.
  • the second portion of the gas stream is cooled in the second channel 10 of the heat exchanger 8 during the transfer of its heat to the vapour-phase gas coming from the vapour-phase gas collection circuit 6.
  • the outlet 10b of the second channel 10 of the heat exchanger 8 is connected to a phase separator 25 via an expansion device 14 through which the combustible gas stream will be depressurized to a pressure substantially equal to the pressure prevailing in the tanks 5a, 5b, 5c, 5d, for example a pressure close to atmospheric pressure. Consequently, the gas stream undergoes an expansion which gives rise, via the Joule-Thomson effect, to a decrease of its temperature and its liquefaction, at least partially.
  • the expansion device 14 is, for example, an expansion valve.
  • the phase separator 25 occasionally referred to as a mist separator, allows the liquid phase to be separated from the gas phase. Downstream, the phase separator 25 is connected, on the one hand, to a return circuit 31 leading to the tanks 5a, 5b, 5c, 5d and, on the other hand, to a return pipe 32 which is connected to the vapour-phase gas withdrawal circuit 6.
  • the phase separator 25 thus conveys the liquid phase of the combustible gas to the tanks 5a, 5b, 5c, 5d, whereas the vapour phase is returned to the inlet 9a of the first channel 9 of the heat exchanger 8.
  • the installation 1 also comprises a cooling device 16 for cooling the vapour-phase gas stream circulating in the vapour-phase gas collection circuit 6.
  • the cooling device 16 comprises a chamber 20 which is integrated into the vapour-phase gas collection circuit 6 and inside which a liquid-phase combustible gas stream withdrawn from one of the tanks 5c is sprayed.
  • the sprayed combustible gas stream vaporizes, taking heat from the vapour-phase gas stream collected in the gaseous headspace of the tanks.
  • the spraying and vaporization of a fraction of liquid-phase combustible gas makes it possible to reduce the concentration of the most volatile components, especially nitrogen, in the gas stream intended to be, at least partly, conducted to the gas-consuming member 2, 3, 4.
  • the cooling device 16 comprises a withdrawal circuit 35.
  • the withdrawal circuit 35 has an admission 27 which emerges in the inner space of one of the tanks 5a, 5b, 5c, 5d, at the bottom part of the tank, close to the base of the tank, so as to withdraw the liquid phase of the combustible gas stored in the tank irrespective of its filling level.
  • the cooling device 16 also comprises a pumping device that is capable of sucking the liquid-phase combustible gas via the admission 27 of the cooling device 16 and of circulating it in the withdrawal circuit 35 to one or more spraying members 21 housed in the chamber 20.
  • the pumping device comprises:
  • the cooling device 16 also comprises a control unit 36 for controlling the pumping device.
  • the control unit 36 is connected to a temperature sensor 29 and to a gas analyser 40.
  • the sensor 29 is placed in the intermediate circuit 15 and is thus capable of delivering a temperature measurement T1 of the second portion of the compressed gas stream, circulating in the intermediate circuit 15, at the inlet of the expansion device 24.
  • the gas analyser 40 is capable of delivering a measurement representative of the nitrogen concentration in the gas stream intended to be conducted to the gas-consuming members 2, 3, 4.
  • the gas analyser 40 is capable of analysing the composition of a sample of the gas stream and is thus capable of determining the nitrogen concentration of the gas stream intended to be conducted to a gas- consuming member.
  • the gas analyser 40 is preferably arranged so as to withdraw a sample of gas between the outlet 9b of the second channel 9 of the heat exchanger 8 and the compressor 1 1 .
  • the analysed gas sample is, firstly, preheated and, secondly, at atmospheric pressure or virtually atmospheric pressure, which facilitates the analysis operations.
  • the gas analyser 40 may, however, be differently located.
  • the gas analyser 40 is a machine for measuring the upper calorific power of a combustible gas.
  • the upper calorific power being characteristic of the nitrogen concentration
  • the calorific power is a representative measurement of the nitrogen concentration of a gas stream.
  • a gas analyser 40 may advantageously be integrated into one or more of the gas-consuming members 2, 3, 4.
  • the control unit 34 is arranged to control the pumping device so as to ensure a nitrogen concentration in the gas stream intended to be conducted to the gas-consuming member(s) 2, 3, 4 which is below a limit operating concentration for the gas-consuming member(s) 2, 3, 4, i.e. a limit nitrogen concentration above which correct functioning of the gas-consuming member(s) 2, 3, 4 is no longer assured.
  • the amount of liquid-phase combustible gas stream delivered by the pump 26 is determined by means of a digital modelling tool.
  • This digital modelling tool makes it possible to determine a nominal liquid-phase combustible gas stream flow rate delivered by the pump 26, which, on the one hand, makes it possible to ensure a nitrogen concentration in the gas stream intended to be conducted to the gas-consuming member(s) 2, 3, 4 which is below the limit operating concentration for the gas-consuming member(s) 2, 3, 4, and which, on the other hand, makes it possible to optimize the degree of reliquefaction during the Joule-Thomson depressurization.
  • the modelling tool determines the nominal liquid-phase combustible gas stream flow rate withdrawn, especially as a function of the following inlet parameters: - the respective nitrogen concentrations in the liquid phase and/or in the gas phase of the combustible gas stored in the tank and/or in the gas stream intended to be conducted to the gas-consuming member(s) 2, 3, 4;
  • the control unit 36 operates in a reliquefaction priority mode in which the flow rate of the liquid-phase combustible gas stream withdrawn is determined so that the temperature T1 of the second portion of the gas stream circulating in the intermediate circuit 15 is enslaved to a nominal temperature.
  • the flow rate of the combustible gas stream is determined so as to optimize the degree of reliquefaction.
  • the nominal temperature for the second portion of the gas stream circulating in the intermediate circuit 15 is typically between - 145°C and -162°C, for example of the order of - 160°C.
  • the control unit 36 operates in a nitrogen concentration priority mode in which the flow rate of the liquid-phase combustible gas stream withdrawn is determined so that the representative measurement of the nitrogen concentration in the gas stream intended to feed the gas-consuming member(s) is enslaved to a target concentration.
  • the target nitrogen concentration is chosen slightly below, for example of the order of 2% to 3%, the limit concentration of the gas-consuming member(s) to be fed, above which correct functioning of the gas-consuming member(s) 2, 3, 4 is no longer assured.
  • the flow rate of liquid-phase combustible gas stream delivered by the pump 26 is regulated by a regulation of PI or PID type, for example, so that the representative measurement of the nitrogen concentration in the gas stream circulating in the vapour-phase gas collection circuit 6 is enslaved to a target concentration.
  • the target nitrogen concentration in the gas stream circulating in the vapour-phase gas collection circuit is determined as a function of the limit concentration of the gas-consuming member(s) 2, 3, 4 to be fed.
  • the control unit 33 has a correction factor for increasing the nominal flow rate when the drift of the flow rate of the first portion of the gas stream conveyed to the gas-consuming member(s) 2, 3,
  • the pump 26 operates at constant power giving a constant flow rate and the control unit 36 generates a signal for controlling one and/or the other of the two valves 38, 39 as a function of the nominal flow rate determined by the control unit 33.
  • the delivery rate of the pump 26 is constant and one and/or the other of the two valves 38, 39 is adjusted so as to vary the distribution between the portion of the liquid-phase combustible gas stream that is conveyed to the spraying member(s) 21 and that which returns to the tank 5c.
  • valve 38 is closed whereas valve 39 is open and the control unit 36 generates a signal for controlling the pump 26 so as to vary its delivery rate.
  • the installation 1 comprises an additional phase separator at the outlet of the chamber 20.
  • a phase separator is intended, firstly, to direct the liquid phase that has not been vaporized in the chamber 20 to the return circuit 31 leading to the tanks 5a, 5b, 5c, 5d and, secondly, to direct the gaseous phase to the inlet 9a of the first channel 9 of the heat exchanger 8.
  • an installation 1 according to a second preferred embodiment is shown. It differs from the preceding installation described only in the characteristics of the cooling device 16.
  • the cooling device 16 comprises an additional heat exchanger 17 which ensures transfer of heat without exchange of material between the compressed gas stream circulating in the intermediate circuit 15 and the liquid- phase gas stream collected in the tank.
  • the additional heat exchanger 17 comprises a first and a second channels 18, 19 each comprising an inlet 18a, 19a and an outlet 18b, 19b.
  • the additional heat exchanger 17 is advantageously a counter- current exchanger.
  • the first channel 18 is integrated into the intermediate circuit 15 connecting the heat exchanger 8 and the expansion device 14.
  • the inlet 18a of the first channel 18 is connected to the outlet 10b of the second channel 10 of the heat exchanger 8 whereas the outlet 18b of the first channel 18 is connected to the expansion device 14.
  • the inlet 19a of the second channel 19 is connected to the withdrawal circuit 35 whereas its outlet 19b is connected to the vapour-phase gas withdrawal circuit 6.
  • figure 2 is particularly advantageous in that:
  • the vaporized gas stream is injected into the gas stream circulating in the vapour-phase gas collection circuit 6, which is particularly advantageous as regards decreasing the nitrogen concentration in the gas stream intended to be conducted to the gas-consuming member(s) 2, 3, 4.
  • the pumping device represented in figure 2, is simplified relative to that described in relation with figure 1 , since it comprises only one pump 26.
  • the installation 1 comprises a gas analyser 40 for delivering a representative measurement of the nitrogen concentration in the gas stream intended to be conducted to the gas-consuming member(s) 2, 3, 4 and a sensor 28 for measuring the temperature T1 of the second portion of the gas stream, at the outlet 18b of the first channel 18 of the additional heat exchanger 17, i.e. at the inlet of the expansion device 14.
  • control unit 36 generates a signal for controlling the pump 26 so as to ensure a nitrogen concentration in the gas stream intended to be conducted to the gas-consuming member(s) 2, 3, 4 that is below a limit operating concentration of the gas-consuming member(s) 2, 3, 4.
  • the liquid-phase gas flow withdrawn from the tank 5a, 5b, 5c, 5d and intended to be injected as vapour phase into the vapour-phase gas collection circuit 6 may prove to be too high to be fully vaporized in the additional heat exchanger 17.
  • the gas stream at the outlet 19b of the second channel 19 of the additional heat exchanger 17 is liable to be in a liquid-vapour two- phase state.
  • the additional exchanger 17 in order to deal with difficulties associated with the possible presence of a gas stream in a liquid-vapour two-phase state at the outlet of the additional exchanger 17, the additional exchanger 17 is placed above the heat exchanger 8 such that the gas stream, at the outlet 19b of the second channel 19 of the additional heat exchanger 17, is capable of flowing by gravity to the inlet 9a of the first channel 9 of the heat exchanger 8.
  • the cooling device 16 comprises, in addition to the additional exchanger 1 7 described in relation with figure 2, a second additional heat exchanger 41 which transfers heat between the gas stream circulating in the vapour-phase gas collection circuit 6 and the liquid-phase gas stream withdrawn from the tank 5a, 5b, 5c, 5d
  • the second additional heat exchanger 41 comprises a first channel 42 integrated into the vapour-phase gas collection circuit 6 and a second channel 43 comprising an inlet 43a connected to the withdrawal circuit 35 and an outlet 43b connected to the vapour-phase gas collection circuit 6.
  • Each of the two additional exchangers 17, 41 is connected to the withdrawal circuit 35 via a respective valve 44, 45.
  • valves 44, 45 may be piloted so that only the excess amount of gas, i.e. the amount of gas that is not capable of being vaporized in the additional heat exchanger 17 if all of the liquid- phase gas stream withdrawn from the tank 5a, 5b, 5c, 5d were directed thereto, is directed to the second additional heat exchanger 41 .
  • Figure 5 represents the nitrogen concentration as a function of the nitrogen concentration in natural gas in the liquid state for the following natural gas streams:
  • Figure 5 represents operating conditions in which the vapour-phase gas stream withdrawn from the tank has a temperature of -120°C and 70% of the flow of the combustible gas stream is returned to the heat exchanger 8 in order to be reliquefied therein. It is observed in relation with figure 5 that the spraying of liquid at the inlet 9a of the first channel 9 of the heat exchanger 8 makes it possible to substantially reduce the nitrogen concentration of the gas stream intended to be conveyed to the gas-consuming member(s) 2, 3, 4 so as to make it compatible with the operating modes of the gas-consuming member(s) 2, 3, 4. This is also achieved without degrading the reliquefaction yield.
  • Figure 6 represents a similar graph when only 50% of the flow of the combustible gas stream is returned to the heat exchanger 8 in order to be reliquefied therein.
  • Figure 7 is a graph representing the difference between the flow rate of reliquefied gas and the flow rate of liquid-phase gas withdrawn from the tank as a function of the flow rate of the second portion of the combustible gas stream returning to the heat exchanger 8 in order to be reliquefied therein.
  • the reliquefaction performance qualities with an installation as illustrated in figure 1 are represented on curve a and those with an installation as illustrated in figure 2 are represented on curve b.
  • the operating conditions of the installations are as follows: the nitrogen concentration of the vapour-phase natural gas collected from the tank 5a, 5b, 5c, 5d is 20% and its temperature is -140°C, the total flow rate of the natural gas stream at the inlet 9a of the first channel 9 of the heat exchanger 8 is 4700 kg/hour and the flow rate of the liquid-phase natural gas stream withdrawn from the tank is regulated such that the temperature T1 of the second portion of the gas stream circulating in the intermediate circuit 22 is enslaved to a nominal temperature of -160°C.
  • Figure 7 thus demonstrates the increased efficacy of the installation of figure 2.
  • Figure 8 represents the nitrogen concentration of the first portion of the gas stream intended to be conveyed to a gas-consuming member 2, 3, 4 as a function of the flow rate of the second portion of the combustible gas stream returning to the heat exchanger 8 in order to be reliquefied therein.
  • Curve a corresponds to the nitrogen content with an installation of the prior art, i.e. when no flow of gas withdrawn in the liquid phase from the tank and then vaporized is added to the vapour-phase gas collection circuit 6, whereas curve b corresponds to the nitrogen content when gas is withdrawn in the liquid phase from the tank 5a, 5b, 5c, 5d, vaporized and injected into the vapour-phase gas collection circuit 6 by means of an installation as described in figures 1 and 2.
  • FIG. 9 is a graph representing the difference between the flow rate of reliquefied gas and the flow rate of liquid-phase gas withdrawn from the tank as a function of the flow rate of the second portion of the combustible gas stream returning to the heat exchanger 8.
  • Curve a corresponds to the reliquefaction performance qualities with an installation according to the prior art, i.e.
  • curve b corresponds to the reliquefaction performance qualities when gas is withdrawn in the liquid phase from the tank, vaporized and injected into the vapour-phase gas collection circuit by means of an installation as described in figure 2.
  • Figure 10 shows a transfer system 40 for loading/unloading combustible gas such as liquefied natural gas and forming the interface between a vessel 41 and a floating or land-based installation, not shown.
  • the vessel 41 is equipped with an installation for feeding gas-consuming members with combustible gas and for liquefying said combustible gas as described above.
  • the fluid-tight and insulated tank not shown, is of generally prismatic form and is mounted in the double hull of the vessel.
  • the product transfer is ensured by immersed cryogenic lines denoted 42.
  • the transfer system 40 forming the interface between the vessel 41 and the floating or land-based installation comprises at least one platform 43 bearing a storage/handling gantry 44 and a main platform 45 to take all the equipment that allows connecting the immersed cryogenic lines 42 to flexible transfer pipes 46.
  • Each flexible transfer pipe 46 is intended to be connected to a vessel's manifold 47 through a connection module 48.
  • the vessel's manifolds 47 are connected to the tank by means of loading/unloading pipelines arranged on the upper deck of the vessel 41 in order to transfer a cargo of liquefied gas from or to the tank.
  • gantry 44 The chief function of gantry 44 is to enable handling and storage of transfer parts, namely each connection module 48 and the mobile ends of the flexible transfer pipe 46, by means of a crane and winches.
  • the transfer system comprises three parallel flexible transfer pipes 46, two of which make it possible to transfer the liquefied natural gas between the floating or land-based installation and the vessel, whereas the third transfer pipe makes it possible to transfer gas in order to balance the pressures in the gaseous headspaces of the tank of the vessel.
  • on-board pumps in the vessel 41 are used, and/or pumps installed in the land-based installation, and/or pumps fitted to transfer system 40.
  • a leaktight and heat-insulating tank (5a, 5b, 5c, 5d) comprising an inner space intended to be filled with combustible gas in a liquid-vapour two-phase state of equilibrium;
  • a vapour-phase gas collection circuit (6) comprising an admission (7a, 7b, 7c, 7d) emerging in the inner space of the tank (5a, 5b, 5c, 5d) and arranged to withdraw a vapour-phase combustible gas stream from the inner space of the tank (5a, 5b, 5c, 5d);
  • a heat exchanger (8) comprising a first and a second channels (9, 10) and heat-exchange walls for transferring heat from the second channel (10) to the first channel (9), the first channel (9) and the second channel (10) each comprising an inlet (9a, 10a) and an outlet (9b, 10b); the inlet (9a) of the first channel (9) being connected to the vapour-phase gas collection circuit (6) so as to heat the vapour- phase combustible gas stream in the heat exchanger (8);
  • a compressor (1 1 ) which is connected upstream to the outlet (9b) of the first channel (9) of the heat exchanger (8) so as to compress the combustible gas stream at the outlet of the first channel (9) of the heat exchanger (8) and is connected downstream to a three-way connector (12, 13) that is capable of conveying a first portion of the combustible gas stream to the gas-consuming member (2, 3, 4) and of conveying a second portion of the combustible gas stream to the inlet (10a) of the second channel (10) of the heat exchanger (8) in order to cool the second portion of the combustible gas stream; and
  • an expansion device (14) that is connected upstream to the outlet (10b) of the second channel (10) of the heat exchanger (8) via an intermediate circuit (15) and is connected downstream to a return circuit (31 ) leading to the tank (5a, 5b, 5c, 5d) ; the expansion device (14) being arranged to depressurize the second portion of the combustible gas stream coming from the intermediate circuit (15) ;
  • the installation (1 ) being characterized in that it also comprises a cooling device (16) which comprises a withdrawal circuit (35) ; said withdrawal circuit comprising an admission (27) which emerges in the inner space of the tank (5a, 5b, 5c, 5d) and is arranged to withdraw a liquid-phase combustible gas stream from the inner space of the tank (5a, 5b, 5c, 5d); said cooling device (16) being arranged so as to transfer heat between the liquid-phase combustible gas stream withdrawn from the tank and a combustible gas stream to be cooled chosen from the vapour-phase combustible gas stream circulating in the vapour-phase gas collection circuit (6) and the second portion of the combustible gas stream circulating in the intermediate circuit (15) so as to vaporize the liquid-phase combustible gas stream withdrawn from the tank and to use the latent heat of vaporization of the liquid-phase combustible gas stream withdrawn from the tank to cool the combustible gas stream to be cooled.
  • the cooling device (16) comprises an additional heat exchanger (17) comprising a first and a second channels (18, 19) and heat-exchange walls for transferring heat from the first channel (18) to the second channel (19) of the additional heat exchanger (17), said first channel (18) and said second channel (19) each comprising an inlet (18a, 19a) and an outlet (18b, 19b), said first channel (18) being integrated into the intermediate circuit (15) connecting the heat exchanger (8) and the expansion device (14), the inlet (19a) of said second channel (19) being connected to the withdrawal circuit (35) of the cooling device (16) and the outlet (19b) of said second channel (19) being connected to the vapour-phase gas collection circuit (6).
  • the cooling device (16) comprises a chamber (20) integrated into the vapour-phase gas collection circuit (6) between the admission (7a, 7b, 7c, 7d) of the vapour-phase gas collection circuit (6) and the inlet (9a) of the first channel (9) of the heat exchanger (8) and a spraying member (21 ) which is connected to the withdrawal circuit (35) of the cooling device (16) and is arranged to spray liquid-phase combustible gas into the chamber (20) so as to cool the vapour-phase gas stream withdrawn from the inner space of the tank and to reduce the nitrogen content of the combustible gas stream circulating in the vapour-phase gas collection circuit (6).
  • cooling device (16) comprises a pumping device (26) that can suck the liquid-phase combustible gas stream via the admission (27) of the cooling device (16) and deliver it into the withdrawal circuit (35) .
  • control unit (36) is arranged to generate a control signal for the pumping device (26) as a function of a representative measurement of the nitrogen concentration in the first portion of the combustible gas stream and of a nominal concentration, below the limit operating concentration of the gas-consuming member, so as to enslave the nitrogen concentration in the first portion of the combustible gas stream to the nominal concentration.
  • - a nitrogen concentration priority mode in which it generates a control signal for the pumping device (26) as a function of a representative measurement of the nitrogen concentration in the first portion of the combustible gas stream and of a nominal concentration, below the limit operating concentration of the gas-consuming member, so as to enslave the nitrogen concentration in the first portion of the combustible gas stream to the nominal concentration; and - a reliquefaction priority mode in which it generates a control signal for the pumping device (26) as a function of a temperature measurement T1 of the second portion of the gas stream circulating in the intermediate circuit (15) at the inlet of the expansion device (14) and of a nominal temperature so as to enslave the temperature T1 to the nominal temperature;
  • control unit (36) being arranged to switch from the nitrogen concentration priority mode to the reliquefaction priority mode as a function of the representative measurement of the nitrogen concentration in the first portion of the combustible gas stream.
  • FIG. 19 System for transferring a combustible gas, the system comprising a vessel (40) according to Clause 17, cryogenic transfer pipes (42, 46) arranged so as to connect the tank installed in the vessel's hull to a floating or land- based storage installation, and a pump for driving a combustible gas stream through the insulated pipelines from or to the floating or land-based storage installation to or from the vessel's tank.

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Abstract

The invention relates to an installation (1) for feeding a gas-consuming member (2, 3, 4) with combustible gas and for liquefying said combustible gas; the installation comprising: - a leaktight and heat-insulating tank (5a, 5b, 5c, 5d); - a vapour-phase gas collection circuit (6) for withdrawing a combustible gas stream from the tank (5a, 5b, 5c, 5d); - a heat exchanger (8) comprising a first channel (9) connected to the vapour-phase gas collection circuit (6); - a compressor (1 1) connected to the first channel (9) of the heat exchanger (8) and connected to a three-way connector (12, 13) that is capable of conveying combustible gas to the gas-consuming member (2, 3, 4) and combustible gas to the second channel (10) of the heat exchanger (8); and - an expansion device (14) which is connected to the second channel (10) of the heat exchanger (8) via an intermediate circuit (15); - a cooling device (16) arranged so as to transfer heat between a liquid- phase combustible gas stream withdrawn from the tank and a combustible gas stream to be cooled, chosen from the vapour-phase combustible gas stream circulating in the vapour-phase gas collection circuit (6) and the second portion of the combustible gas stream circulating in the intermediate circuit (15).

Description

INSTALLATION FOR FEEDING A GAS-CONSUMING MEMBER WITH COMBUSTIBLE GAS AND FOR LIQUEFYING SAID COMBUSTIBLE GAS
Technical field
The invention relates to the field of installations for treating a combustible gas, such as liquefied natural gas (LNG) .
The invention is more particularly directed towards an installation for, on the one hand, feeding a gas-consuming member with combustible gas and, on the other hand, liquefying said combustible gas.
Technological background
Liquefied natural gas is stored in leaktight and heat-insulating tanks, in a liquid/vapour two-phase state of equilibrium, at cryogenic temperatures. The heat- insulating barriers of liquefied natural gas storage tanks are the site of heat flow which tends to heat the content of the tanks, which is reflected by evaporation of the liquefied natural gas. The gas derived from natural evaporation is generally used to feed a gas-consuming member so as to upgrade it. Thus, on a methane tanker, for example, the evaporated gas is used to feed the powertrain for propelling the ship or the power generators supplying the electricity required for the functioning of the onboard equipment. However, although such practice makes it possible to upgrade the gas derived from natural evaporation in the tanks, it does not make it possible to reduce its amount.
Thus, the prior art, and especially US 2015/0 316 208, discloses installations which can both upgrade part of the gas derived from natural evaporation via one or more gas-consuming members and liquefy another part of the gas derived from natural evaporation. Such an installation comprises a collection circuit which withdraws vapour-phase gas in the gaseous headspace of the tank and then conveys it to a heat exchanger to be heated therein. On leaving the exchanger, the heated gas stream is compressed to high pressures that are compatible with the operating conditions of the gas-consuming members. Thereafter, a first portion of the compressed gas is conveyed to one or more vapour-phase gas-consuming members in order to be burnt therein, while a second portion of the compressed gas is returned to the exchanger in order to transfer heat to the vapour-phase gas stream collected in the gaseous headspace of the tank. The second portion of gas thus cooled and partially liquefied is then depressurized in an expansion device in which, by means of the Joule-Thomson effect, the temperature of the gas stream decreases further during its expansion so as at least partially to reliquefy it. On leaving the expansion device, a phase separator allows the liquid phase and the vapour phase to be separated before conveying the liquid phase into the tank and sending the gas phase back into the vapour-phase gas collection circuit, upstream of the heat exchanger.
Such an installation is particularly advantageous in that compression of the gas stream is used, both to make one portion of the gas stream compatible with the working conditions of the gas-consuming members and to allow subsequent reliquefaction of the other portion of the gas stream. Thus, the installation is thereby simplified and the cost of the additional reliquefaction function is limited.
However, an installation of this type is not entirely satisfactory. In particular, under certain critical operating conditions, for example when the tank is only partially filled, the reliquefaction yield is low. Specifically, when the tank is only partially filled, the temperature of the vapour that is present in the gaseous headspace of the tank is liable to rise quite appreciably above the equilibrium temperature of the gas. Thus, the exchange of heat between the gas stream collected in the tank and the second portion of the compressed gas to be liquefied risks being insufficient to reliquefy a large proportion of the second portion of the compressed gas.
Moreover, the gaseous-phase natural gas derived from natural evaporation has a richer composition of volatile components, such as nitrogen, than the liquefied natural gas in the liquid state stored in the tank. Thus, for a liquefied natural gas cargo with a molar concentration of nitrogen of 0.5%, the gas derived from natural evaporation is liable to have a nitrogen concentration of the order of 14% to 15%. Furthermore, the use of an expansion device using Joule-Thomson expansion and at the outlet of which the vapour phase is returned to the vapour-phase gas collection circuit leads to the nitrogen being concentrated in the gas stream treated by the installation. Thus, the portion of the compressed gas that is conveyed to one or more gas-consuming members is liable to have a nitrogen concentration much higher than 20%. Now, high concentrations of nitrogen lead to imperfect combustion of the gas in the gas-consuming member and to operating defects of the gas- consuming member. Summary
An idea forming the basis of the invention is to propose an installation for feeding a gas-consuming member with combustible gas and for liquefying said combustible gas, which makes it possible to obtain an increased combustible gas liquefaction yield at least under certain critical operating conditions.
According to one embodiment, the invention provides an installation for feeding a gas-consuming member with combustible gas and for liquefying said combustible gas; the installation comprising:
- a leaktight and heat-insulating tank comprising an inner space intended to be filled with combustible gas in a liquid-vapour two-phase state of equilibrium;
- a vapour-phase gas collection circuit comprising an admission emerging in the inner space of the tank and arranged to withdraw a vapour-phase combustible gas stream from the inner space of the tank;
- a heat exchanger comprising a first and a second channels and heat- exchange walls for transferring heat from the second channel to the first channel, the first channel and the second channel each comprising an inlet and an outlet; the inlet of the first channel being connected to the vapour-phase gas collection circuit so as to heat the vapour-phase combustible gas stream in the heat exchanger;
- a compressor which is connected upstream to the outlet of the first channel of the heat exchanger so as to compress the heated combustible gas stream in the heat exchanger and is connected downstream to a three-way connector that is capable of conveying a first portion of the combustible gas stream to the gas-consuming member and of conveying a second portion of the combustible gas stream to the inlet of the second channel of the heat exchanger in order to cool the second portion of the combustible gas; and
- an expansion device that is connected upstream to the outlet of the second channel of the heat exchanger via an intermediate circuit and is connected downstream to a return circuit leading to the tank; the expansion device being arranged to depressurize the second portion of the combustible gas stream coming from the intermediate circuit;
the installation being noteworthy in that it also comprises a cooling device which comprises a withdrawal circuit; said withdrawal circuit comprising an admission which emerges in the inner space of the tank and is arranged to withdraw a liquid-phase combustible gas stream in the inner space of the tank; said cooling device being arranged so as to transfer heat between the liquid-phase combustible gas stream withdrawn from the tank and a combustible gas stream to be cooled chosen from the vapour-phase combustible gas stream circulating in the vapour- phase gas collection circuit and the second portion of the combustible gas stream circulating in the intermediate circuit so as to vaporize the liquid-phase combustible gas stream withdrawn from the tank and to use the latent heat of vaporization of the liquid-phase combustible gas stream withdrawn from the tank to cool the combustible gas stream to be cooled.
Thus, the invention proposes to use the liquid phase of the combustible gas stored in the tank to even further reduce the temperature of the compressed gas at the inlet of the expansion device, this temperature reduction being able to be obtained either by acting directly on the second portion of the compressed gas stream circulating in the intermediate circuit, or by reducing the temperature of the gas at the inlet of the first channel of the heat exchanger such that the temperature at the outlet of the second channel of the exchanger will be reduced in consequence. Thus, by reducing the temperature of the gas stream at the inlet of the expansion device, its degree of liquefaction during its depressurization in the expansion device is substantially increased. This makes it possible to obtain an increased reliquefaction yield under certain critical operating conditions, especially when the temperature of the vapour that is present in the gaseous headspace of the tank is quite appreciably above the equilibrium temperature of the gas.
In addition, when the combustible gas is a gaseous mixture of the LNG or LPG type comprising nitrogen in small proportion and when the cooling device is arranged so as to convey the vaporized gas stream in the vapour-phase gas collection circuit, such an installation makes it possible to perform dilution of the nitrogen of the gas stream intended to be conducted to the gas-consuming member so as to make it compatible with the operating conditions of the gas-consuming member, without substantially degrading the reliquefaction yield.
According to embodiments, such an installation may comprise one or more of the following characteristics. According to one embodiment, the combustible gas is a gaseous mixture of the LNG or LPG type comprising nitrogen.
According to one embodiment, the combustible gas is a gaseous mixture comprising nitrogen, nitrogen being the most volatile component of the gaseous mixture.
According to one embodiment, the cooling device is arranged so as to convey the vaporized gas stream in the cooling device to the vapour-phase gas collection circuit so as to reduce the nitrogen content of the combustible gas stream circulating in the vapour-phase gas collection circuit.
Thus, when the combustible gas is constituted of a gaseous mixture comprising nitrogen, this leads to reducing the nitrogen concentration in the vapour phase treated in the installation since the vaporized gas stream in the cooling device comes from a gas stream withdrawn in the liquid phase from the tank which has a reduced concentration of the most volatile compounds, such as nitrogen. This consequently makes it possible to keep the nitrogen concentration in the gas treated by the installation within a range that is compatible with correct functioning of the gas-consuming member. In addition, the less the vapour-phase gas at the inlet of the installation has a composition rich in volatile components, the greater will be the liquefaction yield. Consequently, by mixing the vaporized gas stream in the cooling device with a gas stream coming from natural evaporation, the nitrogen concentration of the resulting mixture is reduced, which makes it possible to increase the degree of liquefaction during depressurization in the expansion device.
According to a first embodiment, the cooling device comprises an additional heat exchanger comprising a first and a second channels and heat-exchange walls for transferring heat from the first channel to the second channel of the additional heat exchanger, the first channel and the second channel each comprising an inlet and an outlet, the first channel being integrated into the intermediate circuit connecting the heat exchanger and the expansion device, the inlet of the second channel being connected to the admission of the cooling device and the outlet of the second channel being connected to the vapour-phase gas collection circuit.
According to a first embodiment variant, the additional heat exchanger is superimposed above the heat exchanger and the outlet of the second channel of the additional heat exchanger is connected to the inlet of the first channel of the heat exchanger such that a liquid-phase gas stream can flow by gravity from the outlet of the second channel of the additional heat exchanger to the inlet of the first channel of the heat exchanger.
According to a second embodiment variant, the cooling device comprises a second additional heat exchanger comprising a first channel integrated into the vapour-phase gas collection circuit and a second channel comprising an inlet connected to the withdrawal circuit and an outlet connected to the vapour-phase gas collection circuit.
According to a second embodiment, the cooling device comprises a chamber integrated into the vapour-phase gas collection circuit between the admission of the vapour-phase gas collection circuit and the inlet of the first channel of the heat exchanger and a spraying member which is connected to the withdrawal circuit of the cooling device and is arranged to spray liquid-phase combustible gas into the chamber so as to cool the vapour-phase gas stream withdrawn from the inner space of the tank and to reduce the nitrogen content of the combustible gas stream circulating in the vapour-phase gas collection circuit.
According to a variant of any of the three abovementioned embodiments, the cooling device comprises a pumping device that can suck the liquid-phase combustible gas stream via the admission of the cooling device and deliver it into the withdrawal circuit.
According to one embodiment, the installation comprises a gas analyser that can deliver a representative measurement of the nitrogen concentration in the first portion of the combustible gas stream and the control unit is arranged to generate a control signal for the pumping device as a function of the representative measurement of the nitrogen concentration in the first portion of the combustible gas stream conveyed to the gas-consuming member so as to ensure a nitrogen concentration in the first portion of the combustible gas stream that is below a limit operating concentration of the gas-consuming member.
According to one embodiment, the gas analyser is capable of analysing the composition of a gas sample so as to deduce its nitrogen concentration therefrom. According to another embodiment, the gas analyser is a machine for measuring the upper calorific power of a gas sample. According to one embodiment variant, the control unit is arranged to generate a control signal for the pumping device as a function of a representative measurement of the nitrogen concentration in the first portion of the combustible gas stream and of a nominal concentration, below the limit operating concentration of the gas-consuming member, so as to enslave the nitrogen concentration in the first portion of the combustible gas stream to the nominal concentration.
According to another embodiment variant, the control unit has:
- a nitrogen concentration priority mode in which it generates a control signal for the pumping device as a function of a representative measurement of the nitrogen concentration in the first portion of the combustible gas stream and of a nominal concentration, below the limit operating concentration of the gas-consuming member, so as to enslave the nitrogen concentration in the first portion of the combustible gas stream to the nominal concentration; and
- a reliquefaction priority mode in which it generates a control signal for the pumping device as a function of a temperature measurement T1 of the second portion of the gas stream circulating in the intermediate circuit at the inlet of the expansion device and of a nominal temperature so as to enslave the temperature T1 to the nominal temperature;
said control unit being arranged to switch from the nitrogen concentration priority mode to the reliquefaction priority mode as a function of the representative measurement of the nitrogen concentration in the first portion of the combustible gas stream.
According to one embodiment, the cooling device comprises a sensor that is capable of measuring the temperature T1 of the second portion of the gas stream circulating in the intermediate circuit at the inlet of the expansion device and a control unit arranged, at least in one operating mode, to generate a control signal for the pumping device as a function of the measurement of the temperature T1 and of a nominal temperature so as to enslave the temperature T1 to the nominal temperature.
According to a first variant, the pumping device comprises a pump and the control unit is arranged to pilot the pump as a function of the control signal. In other words, the liquid-phase gas flow rate delivered by the pump of the pumping device is varied to obtain the desired flow rate. According to a second variant, the pumping device comprises a pump, a return pipeline which, firstly, is connected to the withdrawal circuit downstream of the pump and, secondly, returns to the inner space of the tank and two valves that are installed, respectively, on the withdrawal circuit downstream of the return pipeline connector and on the return pipeline; the control unit being arranged to pilot one and/or the other of the two valves as a function of the control signal. In other words, the pump of the pumping device operates at constant power and one and the other of the two valves are actuated in order to modify the distribution between the portion of the liquid-phase gas stream that is conveyed in the withdrawal circuit in order to be vaporized and the portion of the liquid-phase gas stream that returns into the tank via the return pipeline.
According to one embodiment, the expansion device is an expansion valve, also known as a Joule-Thomson valve.
According to one embodiment, the installation comprises a phase separator connected upstream to the expansion device and downstream, on the one hand, to a return circuit leading to the tank and, on the other hand, to a return pipe connected to the vapour-phase gas collection circuit; the phase separator being arranged to convey the liquid phase of the combustible gas stream to the return circuit and to convey the gas phase of the combustible gas stream to the return pipe.
According to an advantageous variant, the compressor is a multi-stage compressor. Advantageously, the compressor comprises a plurality of compression stages and a plurality of intermediate heat exchangers, each of the intermediate heat exchangers being placed at the outlet of one of the compression stages.
According to one embodiment, the invention also provides a process for feeding a gas-consuming member with combustible gas and for liquefying said combustible gas by means of an abovementioned installation, the process comprising:
- conveying a vapour-phase combustible gas stream from the admission of the vapour-phase gas collection circuit to the inlet of the first channel of the heat exchanger;
- transferring heat from the second channel to the first channel of the heat exchanger; - compressing the combustible gas stream exiting the first channel of the heat exchanger;
- conveying a first portion of the compressed combustible gas stream to the gas-consuming member and a second portion of the compressed gas stream to the inlet of the second channel of the heat exchanger;
- conveying the second portion of the combustible gas stream from the second channel of the heat exchanger to the expansion device via the intermediate circuit;
- depressurizing the second portion of the combustible gas stream coming from the intermediate circuit;
- conveying at least one liquid-phase portion of the second portion of the depressurized combustible gas stream to the tank;
- withdrawing a liquid-phase combustible gas stream from the inner space of the tank;
- transferring heat between the liquid-phase combustible gas stream withdrawn from the tank and a gas stream to be cooled chosen from the vapour- phase gas stream circulating in the vapour-phase gas collection circuit and the second portion of the gas stream circulating in the intermediate circuit so as to vaporize the liquid-phase combustible gas stream withdrawn from the tank and to use the latent heat of vaporization of the liquid-phase combustible gas stream withdrawn from the tank to cool the gas stream to be cooled.
According to one embodiment, the combustible gas is a gaseous mixture comprising nitrogen and the vaporized gas stream in the cooling device is conveyed to the vapour-phase gas collection circuit.
According to one embodiment, a variable representative of the nitrogen concentration in the first portion of the combustible gas stream is measured and the flow rate of the liquid-phase combustible gas stream circulating in the withdrawal circuit of the cooling device is adjusted as a function of the variable representative of the nitrogen concentration in the first portion of the combustible gas stream.
According to an embodiment variant, the flow rate of the liquid-phase combustible gas stream circulating in the withdrawal circuit of the cooling device is adjusted as a function of the variable representative of the nitrogen concentration in the first portion of the combustible gas stream and of a nominal concentration so as to enslave the nitrogen concentration in the first portion of the combustible gas stream to the nominal concentration.
According to one embodiment, in at least one operating mode, the temperature T1 of the second portion of the gas stream circulating in the intermediate circuit upstream of the expansion device is measured and the flow rate of the liquid-phase combustible gas stream circulating in the withdrawal circuit of the cooling device is adjusted as a function of the measurement of the temperature T1 and of a nominal temperature so as to enslave the temperature T1 to the nominal temperature.
According to an advantageous variant, the combustible gas is a liquefied natural gas and the nominal temperature T1 is between -145 and -160°C.
According to one embodiment, the invention provides a vessel comprising an abovementioned installation.
According to one embodiment, the invention also provides a process for loading or emptying such a vessel, in which combustible gas is conducted through cryogenic transfer pipes from or to a floating or land-based storage installation to or from the vessel's tank.
According to one embodiment, the invention also provides a system for transferring a combustible gas, the system comprising the abovementioned vessel, cryogenic transfer pipes arranged so as to connect the tank installed in the vessel's hull to a floating or land-based storage installation, and a pump for driving a combustible gas stream through the cryogenic transfer pipes from or to the floating or land-based storage installation to or from the vessel 's tank.
Brief description of the figures
The invention will be better understood and further aims, details, characteristics and advantages thereof will appear more clearly from the following description of several particular embodiments of the invention, given merely for illustration and without limitation, with reference to the attached drawings.
- Figure 1 is a schematic illustration of an installation for feeding gas- consuming members with combustible gas and for liquefying said combustible gas according to a first embodiment. - Figure 2 is a schematic illustration of an installation according to a second embodiment.
- Figure 3 is a schematic illustration of an installation according to a third embodiment.
- Figure 4 illustrates in detailed manner the arrangement of the two heat exchangers of figure 2 according to one embodiment variant.
- Figure 5 is a graph illustrating the nitrogen concentration of different natural gas streams of the installation of figure 2 as a function of the nitrogen concentration in the natural gas in the liquid state, when 70% of the flow of the combustible gas stream is returned to the heat exchanger in order to be reliquefied therein.
- Figure 6 is a graph similar to that of figure 5, when 70% of the flow of the combustible gas stream is returned to the heat exchanger in order to be reliquefied therein.
- Figure 7 is a graph representing the difference between the flow rate of reliquefied gas and the flow rate of liquid-phase gas withdrawn from the tank as a function of the flow rate of the second portion of the combustible gas stream returning to the inlet of the second channel of the heat exchanger for the installation of figure 1 and that of figure 2.
- Figure 8 is a graph representing the nitrogen concentration of the first portion of the gas stream conveyed to the gas-consuming member as a function of the flow rate of the second portion of the combustible gas stream returning to the heat exchanger for an installation according to the prior art and an installation according to figure 1 or 2.
- Figure 9 is a graph representing the difference between the flow rate of reliquefied gas and the flow rate of liquid-phase gas withdrawn from the tank as a function of the flow rate of the second portion of the combustible gas stream returning to the heat exchanger for an installation according to the prior art and an installation according to figure 2.
- Figure 10 is a schematic representation of a vessel and of a transfer system for loading/unloading combustible gas.
Detailed description of embodiments In the description and the claims, the term "combustible gas" has a generic nature and refers without preference to a gas constituted of a single pure substance or a gaseous mixture constituted of a plurality of components.
In figure 1 , an installation 1 for, on the one hand, feeding one or more gas- consuming members with combustible gas and, on the other hand, liquefying combustible gas is illustrated. Such an installation 1 may be installed on land or on a floating structure. In the case of a floating structure, the installation 1 may be intended for a liquefaction or regasification barge or for a liquefied natural gas cargo ship, such as a methane tanker, or may more generally be intended for any ship equipped with a gas-consuming member.
The installation 1 comprises three different types of combustible gas- consuming members, namely a burner 2, an electrical generator 3 and an engine 4 for propelling a ship.
The burner 2 may be integrated into a power production installation or may be integrated into a gas combustion unit (GCU) . The power production installation may especially comprise a steam production boiler. The steam may be intended to feed steam turbines for producing energy and/or to feed a heating network of the ship. A burner 2 is capable of functioning with a combustible gas whose nitrogen concentration is high, for example greater than 30% to 35% for a standard gas combustion unit, but may be well above this by supplying fuel.
The electrical generator 3 comprises, for example, a diesel/natural gas mixed feed heat engine, for example of DFDE (dual-fuel diesel electric) technology. Such a heat engine can burn a mixture of diesel and natural gas or use one or the other of these two fuels. The natural gas feeding such a heat engine must have a pressure of the order of a few bar to a few tens of bar, for example from about 6 to 8 bar absolute. In addition, in order to allow compliant functioning of such a heat engine, the natural gas must have a nitrogen concentration below a limit operating concentration, of the order of 15% to 20%.
The engine 4 for propelling the ship is, for example, a dual fuel two-stroke low-speed engine of "ME-GI" technology, developed by the company MAN. Such an engine 4 uses natural gas as combustible and a small amount of pilot fuel which is injected before the injection of the natural gas in order for it to ignite. To feed such an engine 4, the natural gas must first be compressed at a high pressure of between 150 and 400 bar absolute, and more particularly between 250 and 300 bar absolute. In addition, such an engine is extremely sensitive to the quality of the natural gas and, in order to allow compliant functioning, the natural gas must have a nitrogen concentration not exceeding a threshold of the order of 15% to 20%.
The installation 1 comprises one or more leaktight and heat-insulating tanks
5a, 5b, 5c, 5d. According to one embodiment, each tank 5a, 5b, 5c, 5d is a membrane tank. By way of example, such membrane tanks are described in patent applications WO 140/57221 , FR 2 691 520 and FR 2 877 638. Such membrane tanks are intended to store combustible gas at pressures substantially equal to atmospheric pressure or slightly higher. According to other alternative embodiments, each tank 5a, 5b, 5c, 5d may also be a free-standing tank and may especially have a parallelepipedal, prismatic, spherical, cylindrical or multi-lobed shape. Certain types of tank 5a, 5b, 5c, 5d allow gas storage at pressures substantially higher than atmospheric pressure.
Each tank 5a, 5b, 5c, 5d comprises an inner space intended to be filled with combustible gas. The combustible gas may especially be a liquefied natural gas (LNG), i.e. a gaseous mixture predominantly comprising methane and also one or more other hydrocarbons, such as ethane, propane, n-butane, i-butane, n-pentane, i-pentane, neopentane, and nitrogen in small proportion. The combustible gas may also be ethane or a liquefied petroleum gas (LPG) , i.e. a mixture of hydrocarbons derived from oil refinery essentially comprising propane and butane and nitrogen in small proportion.
The combustible gas is stored in the inner space of each tank 5a, 5b, 5c, 5d in a liquid-vapour two-phase state of equilibrium. The gas is thus present in the vapour phase in the upper part of the tank 5a, 5b, 5c, 5d, and in the liquid phase in the lower part of the tank 5a, 5b, 5c, 5d. The equilibrium temperature of the liquefied natural gas corresponding to its liquid-vapour two-phase state of equilibrium is about - 162°C when it is stored at atmospheric pressure.
The installation 1 comprises a vapour-phase gas collection circuit 6 which comprises an admission 7a, 7b, 7c, 7d emerging in the gaseous headspace of each of the tanks 5a, 5b, 5c, 5d, i.e. above the maximum filling height of the tank. Each of these admissions 7a, 7b, 7c, 7d is connected to the vapour-phase gas collection circuit 6 via a valve 24. The vapour-phase gas collection circuit 6 leads to a heat exchanger 8. The heat exchanger 8 comprises a first and a second channel 9, 10 each having an inlet 9a, 10a and an outlet 9b, 10b and heat-exchange walls for transferring heat from the second channel 10 to the first channel 9. So as to optimize the heat exchanges, the heat exchanger 8 is a counter-current exchanger. The inlet 9a of the first channel 9 is connected to the vapour-phase gas collection circuit 6 so as to heat the gas stream derived from natural evaporation collected in the tanks 5a, 5b, 5c, 5d. The outlet 9b of the first channel 9 is connected to a compressor 1 1 for compressing the gas stream to pressures that are compatible with the operating of the gas- consuming members.
In the embodiment shown, the compressor 1 1 is a multi-stage compressor. In other words, the compressor 1 1 comprises a plurality of compression stages 1 1 a, 1 1 b, 1 1 c, 1 1 d, 1 1 e and intermediate heat exchangers 33a, 33b, 33c, 33d which are placed at the outlet of each of the compression stages 1 1 a, 1 1 b, 1 1 c, 1 1 d, 1 1 e. The intermediate heat exchangers 33a, 33b, 33c, 33d are directed toward cooling the compressed gas between two compression stages 1 1 a, 1 1 b, 1 1 c, 1 1 d, 1 1 e. By way of example, the heat exchangers 33a, 33b, 33c, 33d may especially provide an exchange with seawater, thus making it possible to bring the compressed gas stream to a temperature substantially equal to that of the seawater.
The compressor 27 is dimensioned as a function of the combustible gas- consuming members intended to be fed and especially as a function of their maximum feed rate and of the pressure level at which the combustible gas must be distributed thereto. Thus, when one of the gas-consuming members is an engine 4 of ME-GI type as described previously, the compressor 1 1 is dimensioned such that the gas stream leaving the compressor 1 1 typically has a pressure of between 250 and 300 bar absolute.
Downstream of the compressor 1 1 , the installation 1 comprises a three-way connector 12 for conveying a first portion of the gas stream to the engine 4 for propelling the ship, and a second portion of the gas stream to the inlet 10a of the second channel 10 of the heat exchanger 8. This three-way connector 12 is piloted by a control unit 34. The control unit 34 is thus capable of varying the proportions of gas circulating, respectively, to the engine 4 and to the inlet 10a of the second channel 10 of the heat exchanger 8 as a function of the combustible gas needs of the engine 4 and/or of the amount of gas to be reliquefied. Moreover, in the event that the combustible gas-consuming members have different feed pressures as in the embodiment shown, the installation 1 comprises an intermediate three-way connector 13 which is placed between two compression stages 1 1 b, 1 1 c and thus makes it possible to divert a portion of the gas stream to gas-consuming members, in this case the burner 2 and the electrical generator 3, before the outlet of the compressor 1 1 . Such an arrangement makes it possible to divert combustible gas to a combustible gas-consuming member once it has passed through a sufficient number of compression stages 1 1 a, 1 1 b to reach the feed pressure corresponding to said consuming member.
The second portion of the gas stream is cooled in the second channel 10 of the heat exchanger 8 during the transfer of its heat to the vapour-phase gas coming from the vapour-phase gas collection circuit 6.
The outlet 10b of the second channel 10 of the heat exchanger 8 is connected to a phase separator 25 via an expansion device 14 through which the combustible gas stream will be depressurized to a pressure substantially equal to the pressure prevailing in the tanks 5a, 5b, 5c, 5d, for example a pressure close to atmospheric pressure. Consequently, the gas stream undergoes an expansion which gives rise, via the Joule-Thomson effect, to a decrease of its temperature and its liquefaction, at least partially. The expansion device 14 is, for example, an expansion valve.
The phase separator 25, occasionally referred to as a mist separator, allows the liquid phase to be separated from the gas phase. Downstream, the phase separator 25 is connected, on the one hand, to a return circuit 31 leading to the tanks 5a, 5b, 5c, 5d and, on the other hand, to a return pipe 32 which is connected to the vapour-phase gas withdrawal circuit 6. The phase separator 25 thus conveys the liquid phase of the combustible gas to the tanks 5a, 5b, 5c, 5d, whereas the vapour phase is returned to the inlet 9a of the first channel 9 of the heat exchanger 8.
The installation 1 also comprises a cooling device 16 for cooling the vapour-phase gas stream circulating in the vapour-phase gas collection circuit 6. To do this, the cooling device 16 comprises a chamber 20 which is integrated into the vapour-phase gas collection circuit 6 and inside which a liquid-phase combustible gas stream withdrawn from one of the tanks 5c is sprayed. Thus, the sprayed combustible gas stream vaporizes, taking heat from the vapour-phase gas stream collected in the gaseous headspace of the tanks. In addition, the spraying and vaporization of a fraction of liquid-phase combustible gas makes it possible to reduce the concentration of the most volatile components, especially nitrogen, in the gas stream intended to be, at least partly, conducted to the gas-consuming member 2, 3, 4.
The cooling device 16 comprises a withdrawal circuit 35. The withdrawal circuit 35 has an admission 27 which emerges in the inner space of one of the tanks 5a, 5b, 5c, 5d, at the bottom part of the tank, close to the base of the tank, so as to withdraw the liquid phase of the combustible gas stored in the tank irrespective of its filling level. The cooling device 16 also comprises a pumping device that is capable of sucking the liquid-phase combustible gas via the admission 27 of the cooling device 16 and of circulating it in the withdrawal circuit 35 to one or more spraying members 21 housed in the chamber 20.
In the embodiment shown, the pumping device comprises:
- a pump 26 for sucking the liquid-phase combustible gas stream and delivering it;
- a return pipeline 37 which, on the one hand, is connected to the withdrawal circuit 35 downstream of the pump 26 and, on the other hand, emerges in the inner space of the tank 5c; and
- two valves 38, 39 which are installed, respectively, on the return pipeline 37 and on the withdrawal circuit 35 downstream of the connection of the return pipeline 37 to said withdrawal circuit 35.
The cooling device 16 also comprises a control unit 36 for controlling the pumping device. The control unit 36 is connected to a temperature sensor 29 and to a gas analyser 40. The sensor 29 is placed in the intermediate circuit 15 and is thus capable of delivering a temperature measurement T1 of the second portion of the compressed gas stream, circulating in the intermediate circuit 15, at the inlet of the expansion device 24. The gas analyser 40 is capable of delivering a measurement representative of the nitrogen concentration in the gas stream intended to be conducted to the gas-consuming members 2, 3, 4. According to one embodiment, the gas analyser 40 is capable of analysing the composition of a sample of the gas stream and is thus capable of determining the nitrogen concentration of the gas stream intended to be conducted to a gas- consuming member. In this case, as shown in figure 1 , the gas analyser 40 is preferably arranged so as to withdraw a sample of gas between the outlet 9b of the second channel 9 of the heat exchanger 8 and the compressor 1 1 . Thus, the analysed gas sample is, firstly, preheated and, secondly, at atmospheric pressure or virtually atmospheric pressure, which facilitates the analysis operations. The gas analyser 40 may, however, be differently located.
According to another embodiment, the gas analyser 40 is a machine for measuring the upper calorific power of a combustible gas. The upper calorific power being characteristic of the nitrogen concentration, the calorific power is a representative measurement of the nitrogen concentration of a gas stream. In such a case, a gas analyser 40 may advantageously be integrated into one or more of the gas-consuming members 2, 3, 4.
The control unit 34 is arranged to control the pumping device so as to ensure a nitrogen concentration in the gas stream intended to be conducted to the gas-consuming member(s) 2, 3, 4 which is below a limit operating concentration for the gas-consuming member(s) 2, 3, 4, i.e. a limit nitrogen concentration above which correct functioning of the gas-consuming member(s) 2, 3, 4 is no longer assured.
According to a first predictive approach, the amount of liquid-phase combustible gas stream delivered by the pump 26 is determined by means of a digital modelling tool. This digital modelling tool makes it possible to determine a nominal liquid-phase combustible gas stream flow rate delivered by the pump 26, which, on the one hand, makes it possible to ensure a nitrogen concentration in the gas stream intended to be conducted to the gas-consuming member(s) 2, 3, 4 which is below the limit operating concentration for the gas-consuming member(s) 2, 3, 4, and which, on the other hand, makes it possible to optimize the degree of reliquefaction during the Joule-Thomson depressurization.
The modelling tool determines the nominal liquid-phase combustible gas stream flow rate withdrawn, especially as a function of the following inlet parameters: - the respective nitrogen concentrations in the liquid phase and/or in the gas phase of the combustible gas stored in the tank and/or in the gas stream intended to be conducted to the gas-consuming member(s) 2, 3, 4;
- the vapour-phase gas stream flow rate circulating in the vapour-phase gas collection circuit 6; and
the ratio between the first portion of the compressed combustible gas stream conveyed to the gas-consuming member(s) 2, 3, 4 and the second portion of the compressed combustible gas stream returned to the exchanger 8.
As long as the nitrogen concentration in the gas stream intended to be conducted to the gas-consuming member(s) 2, 3, 4 is below a critical threshold, the control unit 36 operates in a reliquefaction priority mode in which the flow rate of the liquid-phase combustible gas stream withdrawn is determined so that the temperature T1 of the second portion of the gas stream circulating in the intermediate circuit 15 is enslaved to a nominal temperature. Thus, in this reliquefaction priority mode, the flow rate of the combustible gas stream is determined so as to optimize the degree of reliquefaction. When the combustible gas is a liquefied natural gas, stored at atmospheric pressure, the nominal temperature for the second portion of the gas stream circulating in the intermediate circuit 15 is typically between - 145°C and -162°C, for example of the order of - 160°C.
In contrast, when the nitrogen concentration in the gas stream intended to be conducted to the gas-consuming member(s) 2, 3, 4 is greater than or equal to a critical threshold, the control unit 36 operates in a nitrogen concentration priority mode in which the flow rate of the liquid-phase combustible gas stream withdrawn is determined so that the representative measurement of the nitrogen concentration in the gas stream intended to feed the gas-consuming member(s) is enslaved to a target concentration. The target nitrogen concentration is chosen slightly below, for example of the order of 2% to 3%, the limit concentration of the gas-consuming member(s) to be fed, above which correct functioning of the gas-consuming member(s) 2, 3, 4 is no longer assured.
According to a second approach, the flow rate of liquid-phase combustible gas stream delivered by the pump 26 is regulated by a regulation of PI or PID type, for example, so that the representative measurement of the nitrogen concentration in the gas stream circulating in the vapour-phase gas collection circuit 6 is enslaved to a target concentration. The target nitrogen concentration in the gas stream circulating in the vapour-phase gas collection circuit is determined as a function of the limit concentration of the gas-consuming member(s) 2, 3, 4 to be fed.
According to one embodiment, it is possible to combine the first and second abovementioned approaches.
Moreover, an increase in the consumption of the gas-consuming member(s) 2, 3, 4 is liable to give rise to a momentary increase in the nitrogen concentration in the gas stream at the inlet 9a of the first channel 9 of the heat exchanger 8. Specifically, during an increase in the flow rate of the first portion of the combustible gas stream conveyed to the gas-consuming member 2, 3, 4 relative to that of the second portion of the stream which returns to the exchanger 8, a transient phenomenon has been observed which promotes at the inlet 9a of the first channel 9 of the exchanger 8 the gas stream circulating in the intermediate circuit 32 to the benefit of the gas stream coming from the gaseous headspaces of the tanks, which leads to a transient increase in the nitrogen concentration of the gas stream at the inlet 9a of the first channel 9 of the exchanger 8. Thus, according to one embodiment, to compensate for this phenomenon, the control unit 33 has a correction factor for increasing the nominal flow rate when the drift of the flow rate of the first portion of the gas stream conveyed to the gas-consuming member(s) 2, 3, 4 is positive.
According to a first embodiment, the pump 26 operates at constant power giving a constant flow rate and the control unit 36 generates a signal for controlling one and/or the other of the two valves 38, 39 as a function of the nominal flow rate determined by the control unit 33. Thus, the delivery rate of the pump 26 is constant and one and/or the other of the two valves 38, 39 is adjusted so as to vary the distribution between the portion of the liquid-phase combustible gas stream that is conveyed to the spraying member(s) 21 and that which returns to the tank 5c.
According to a second embodiment, valve 38 is closed whereas valve 39 is open and the control unit 36 generates a signal for controlling the pump 26 so as to vary its delivery rate.
According to an embodiment variant which is not shown, the installation 1 comprises an additional phase separator at the outlet of the chamber 20. Such a phase separator is intended, firstly, to direct the liquid phase that has not been vaporized in the chamber 20 to the return circuit 31 leading to the tanks 5a, 5b, 5c, 5d and, secondly, to direct the gaseous phase to the inlet 9a of the first channel 9 of the heat exchanger 8.
In relation with figure 2, an installation 1 according to a second preferred embodiment is shown. It differs from the preceding installation described only in the characteristics of the cooling device 16.
In figure 2, the cooling device 16 comprises an additional heat exchanger 17 which ensures transfer of heat without exchange of material between the compressed gas stream circulating in the intermediate circuit 15 and the liquid- phase gas stream collected in the tank.
To do this, the additional heat exchanger 17 comprises a first and a second channels 18, 19 each comprising an inlet 18a, 19a and an outlet 18b, 19b. In order to optimize the heat exchanges, the additional heat exchanger 17 is advantageously a counter- current exchanger. The first channel 18 is integrated into the intermediate circuit 15 connecting the heat exchanger 8 and the expansion device 14. In other words, the inlet 18a of the first channel 18 is connected to the outlet 10b of the second channel 10 of the heat exchanger 8 whereas the outlet 18b of the first channel 18 is connected to the expansion device 14. The inlet 19a of the second channel 19 is connected to the withdrawal circuit 35 whereas its outlet 19b is connected to the vapour-phase gas withdrawal circuit 6.
In other words, the embodiment of figure 2 is particularly advantageous in that:
- firstly, heat is withdrawn from the second portion of the compressed gas stream circulating in the intermediate circuit 15, which is particularly advantageous as regards the reliquefaction performance; and in that
- secondly, the vaporized gas stream is injected into the gas stream circulating in the vapour-phase gas collection circuit 6, which is particularly advantageous as regards decreasing the nitrogen concentration in the gas stream intended to be conducted to the gas-consuming member(s) 2, 3, 4.
The pumping device, represented in figure 2, is simplified relative to that described in relation with figure 1 , since it comprises only one pump 26. Moreover, the installation 1 comprises a gas analyser 40 for delivering a representative measurement of the nitrogen concentration in the gas stream intended to be conducted to the gas-consuming member(s) 2, 3, 4 and a sensor 28 for measuring the temperature T1 of the second portion of the gas stream, at the outlet 18b of the first channel 18 of the additional heat exchanger 17, i.e. at the inlet of the expansion device 14. As in the embodiment of figure 1 , the control unit 36 generates a signal for controlling the pump 26 so as to ensure a nitrogen concentration in the gas stream intended to be conducted to the gas-consuming member(s) 2, 3, 4 that is below a limit operating concentration of the gas-consuming member(s) 2, 3, 4.
Under certain operating conditions, especially when the nitrogen concentration of the gas stream intended to be conducted to the gas-consuming member(s) 2, 3, 4 is high, the liquid-phase gas flow withdrawn from the tank 5a, 5b, 5c, 5d and intended to be injected as vapour phase into the vapour-phase gas collection circuit 6 may prove to be too high to be fully vaporized in the additional heat exchanger 17. In other words, the gas stream at the outlet 19b of the second channel 19 of the additional heat exchanger 17 is liable to be in a liquid-vapour two- phase state.
Thus, in an embodiment variant illustrated in figure 4, in order to deal with difficulties associated with the possible presence of a gas stream in a liquid-vapour two-phase state at the outlet of the additional exchanger 17, the additional exchanger 17 is placed above the heat exchanger 8 such that the gas stream, at the outlet 19b of the second channel 19 of the additional heat exchanger 17, is capable of flowing by gravity to the inlet 9a of the first channel 9 of the heat exchanger 8.
In another embodiment illustrated in figure 5, in order to avoid the presence of a gas stream in a liquid-vapour two-phase state at the outlet of the additional exchanger 17, the cooling device 16 comprises, in addition to the additional exchanger 1 7 described in relation with figure 2, a second additional heat exchanger 41 which transfers heat between the gas stream circulating in the vapour-phase gas collection circuit 6 and the liquid-phase gas stream withdrawn from the tank 5a, 5b, 5c, 5d
To do this, the second additional heat exchanger 41 comprises a first channel 42 integrated into the vapour-phase gas collection circuit 6 and a second channel 43 comprising an inlet 43a connected to the withdrawal circuit 35 and an outlet 43b connected to the vapour-phase gas collection circuit 6.
Each of the two additional exchangers 17, 41 is connected to the withdrawal circuit 35 via a respective valve 44, 45. Thus, the distribution of the gas stream withdrawn as liquid phase from the tank 5a, 5b, 5c, 5d between the two additional exchangers 1 7, 41 is able to be adjusted. In particular, valves 44, 45 may be piloted so that only the excess amount of gas, i.e. the amount of gas that is not capable of being vaporized in the additional heat exchanger 17 if all of the liquid- phase gas stream withdrawn from the tank 5a, 5b, 5c, 5d were directed thereto, is directed to the second additional heat exchanger 41 .
Figure 5 represents the nitrogen concentration as a function of the nitrogen concentration in natural gas in the liquid state for the following natural gas streams:
- the vapour-phase gas stream withdrawn from the tank (curve a) ;
- the first portion of the compressed combustible gas stream intended to be conveyed to a gas-consuming member 2, 3, 4 in an installation according to the prior art (curve b) ; and
- the first portion of the compressed combustible gas stream intended to be conveyed to a gas-consuming member 2, 3, 4 in an installation according to figure 2 in which the flow rate of the gas withdrawn as liquid phase from the tank 5a, 5b, 5c, 5d and vaporized in the additional heat exchanger 17 is adjusted so as to optimize the reliquefaction yield (curve c) .
Figure 5 represents operating conditions in which the vapour-phase gas stream withdrawn from the tank has a temperature of -120°C and 70% of the flow of the combustible gas stream is returned to the heat exchanger 8 in order to be reliquefied therein. It is observed in relation with figure 5 that the spraying of liquid at the inlet 9a of the first channel 9 of the heat exchanger 8 makes it possible to substantially reduce the nitrogen concentration of the gas stream intended to be conveyed to the gas-consuming member(s) 2, 3, 4 so as to make it compatible with the operating modes of the gas-consuming member(s) 2, 3, 4. This is also achieved without degrading the reliquefaction yield. Figure 6 represents a similar graph when only 50% of the flow of the combustible gas stream is returned to the heat exchanger 8 in order to be reliquefied therein.
Figure 7 is a graph representing the difference between the flow rate of reliquefied gas and the flow rate of liquid-phase gas withdrawn from the tank as a function of the flow rate of the second portion of the combustible gas stream returning to the heat exchanger 8 in order to be reliquefied therein. The reliquefaction performance qualities with an installation as illustrated in figure 1 are represented on curve a and those with an installation as illustrated in figure 2 are represented on curve b. The operating conditions of the installations are as follows: the nitrogen concentration of the vapour-phase natural gas collected from the tank 5a, 5b, 5c, 5d is 20% and its temperature is -140°C, the total flow rate of the natural gas stream at the inlet 9a of the first channel 9 of the heat exchanger 8 is 4700 kg/hour and the flow rate of the liquid-phase natural gas stream withdrawn from the tank is regulated such that the temperature T1 of the second portion of the gas stream circulating in the intermediate circuit 22 is enslaved to a nominal temperature of -160°C. Figure 7 thus demonstrates the increased efficacy of the installation of figure 2.
Figure 8 represents the nitrogen concentration of the first portion of the gas stream intended to be conveyed to a gas-consuming member 2, 3, 4 as a function of the flow rate of the second portion of the combustible gas stream returning to the heat exchanger 8 in order to be reliquefied therein. Curve a corresponds to the nitrogen content with an installation of the prior art, i.e. when no flow of gas withdrawn in the liquid phase from the tank and then vaporized is added to the vapour-phase gas collection circuit 6, whereas curve b corresponds to the nitrogen content when gas is withdrawn in the liquid phase from the tank 5a, 5b, 5c, 5d, vaporized and injected into the vapour-phase gas collection circuit 6 by means of an installation as described in figures 1 and 2. The operating conditions of the installation are identical to those described in relation with figure 7. It is thus observed that the installations as illustrated in figures 1 and 2 make it possible to markedly reduce the nitrogen concentration of the first portion of the gas stream conveyed to a gas-consuming member 2, 3, 4 so as to make it compatible with the operating requirements of said gas-consuming member 2, 3, 4. Figure 9 is a graph representing the difference between the flow rate of reliquefied gas and the flow rate of liquid-phase gas withdrawn from the tank as a function of the flow rate of the second portion of the combustible gas stream returning to the heat exchanger 8. The operating conditions of the installation are identical to those described in relation with figure 7. Curve a corresponds to the reliquefaction performance qualities with an installation according to the prior art, i.e. when no flow of gas withdrawn in the liquid phase from the tank 5a, 5b, 5c, 5d and then vaporized is added to the vapour-phase gas collection circuit, whereas curve b corresponds to the reliquefaction performance qualities when gas is withdrawn in the liquid phase from the tank, vaporized and injected into the vapour-phase gas collection circuit by means of an installation as described in figure 2.
It is thus observed that the use of a cooling device as described in relation with figure 2 makes it possible to reduce the nitrogen concentration of the gas stream intended to be conducted to the gas-consuming member 2, 3, 4, while simultaneously increasing the reliquefaction yield up to a certain flow rate value of the second portion of the combustible gas stream and without considerably reducing the reliquefaction yield beyond said flow rate value of the second portion of the combustible gas stream.
It should also be noted that the higher the temperature of the natural gas in the vapour phase withdrawn from the tank 5a, 5b, 5c, 5d, the more the reliquefaction yield comparison will favour the installation as described in figure 2 relative to an installation according to the prior art.
Figure 10 shows a transfer system 40 for loading/unloading combustible gas such as liquefied natural gas and forming the interface between a vessel 41 and a floating or land-based installation, not shown. The vessel 41 is equipped with an installation for feeding gas-consuming members with combustible gas and for liquefying said combustible gas as described above. As an example, the fluid-tight and insulated tank, not shown, is of generally prismatic form and is mounted in the double hull of the vessel.
The product transfer is ensured by immersed cryogenic lines denoted 42.
The transfer system 40 forming the interface between the vessel 41 and the floating or land-based installation comprises at least one platform 43 bearing a storage/handling gantry 44 and a main platform 45 to take all the equipment that allows connecting the immersed cryogenic lines 42 to flexible transfer pipes 46. Each flexible transfer pipe 46 is intended to be connected to a vessel's manifold 47 through a connection module 48. The vessel's manifolds 47 are connected to the tank by means of loading/unloading pipelines arranged on the upper deck of the vessel 41 in order to transfer a cargo of liquefied gas from or to the tank.
The chief function of gantry 44 is to enable handling and storage of transfer parts, namely each connection module 48 and the mobile ends of the flexible transfer pipe 46, by means of a crane and winches.
According to an embodiment, the transfer system comprises three parallel flexible transfer pipes 46, two of which make it possible to transfer the liquefied natural gas between the floating or land-based installation and the vessel, whereas the third transfer pipe makes it possible to transfer gas in order to balance the pressures in the gaseous headspaces of the tank of the vessel.
To create the pressure necessary for the transfer of liquefied gas, on-board pumps in the vessel 41 are used, and/or pumps installed in the land-based installation, and/or pumps fitted to transfer system 40.
Although the invention has been described in connection with several particular embodiments, it is evident that it is in no way limited thereto and comprises all technical equivalents of the means described and their combinations if these fall within the scope of the invention.
The use of the verb "comprise" or "contain" or "include" and its conjugated forms does not exclude the presence of elements or steps other than those stated in a claim.
As such, the methods and installations implemented in accordance with some non-limiting embodiments of the present technology can be represented as follows, presented in numbered clauses.
[Clause 1] Installation (1) for feeding a gas-consuming member (2, 3, 4) with combustible gas and for liquefying said combustible gas; the installation comprising:
- a leaktight and heat-insulating tank (5a, 5b, 5c, 5d) comprising an inner space intended to be filled with combustible gas in a liquid-vapour two-phase state of equilibrium; - a vapour-phase gas collection circuit (6) comprising an admission (7a, 7b, 7c, 7d) emerging in the inner space of the tank (5a, 5b, 5c, 5d) and arranged to withdraw a vapour-phase combustible gas stream from the inner space of the tank (5a, 5b, 5c, 5d);
- a heat exchanger (8) comprising a first and a second channels (9, 10) and heat-exchange walls for transferring heat from the second channel (10) to the first channel (9), the first channel (9) and the second channel (10) each comprising an inlet (9a, 10a) and an outlet (9b, 10b); the inlet (9a) of the first channel (9) being connected to the vapour-phase gas collection circuit (6) so as to heat the vapour- phase combustible gas stream in the heat exchanger (8);
- a compressor (1 1 ) which is connected upstream to the outlet (9b) of the first channel (9) of the heat exchanger (8) so as to compress the combustible gas stream at the outlet of the first channel (9) of the heat exchanger (8) and is connected downstream to a three-way connector (12, 13) that is capable of conveying a first portion of the combustible gas stream to the gas-consuming member (2, 3, 4) and of conveying a second portion of the combustible gas stream to the inlet (10a) of the second channel (10) of the heat exchanger (8) in order to cool the second portion of the combustible gas stream; and
- an expansion device (14) that is connected upstream to the outlet (10b) of the second channel (10) of the heat exchanger (8) via an intermediate circuit (15) and is connected downstream to a return circuit (31 ) leading to the tank (5a, 5b, 5c, 5d) ; the expansion device (14) being arranged to depressurize the second portion of the combustible gas stream coming from the intermediate circuit (15) ;
the installation (1 ) being characterized in that it also comprises a cooling device (16) which comprises a withdrawal circuit (35) ; said withdrawal circuit comprising an admission (27) which emerges in the inner space of the tank (5a, 5b, 5c, 5d) and is arranged to withdraw a liquid-phase combustible gas stream from the inner space of the tank (5a, 5b, 5c, 5d); said cooling device (16) being arranged so as to transfer heat between the liquid-phase combustible gas stream withdrawn from the tank and a combustible gas stream to be cooled chosen from the vapour-phase combustible gas stream circulating in the vapour-phase gas collection circuit (6) and the second portion of the combustible gas stream circulating in the intermediate circuit (15) so as to vaporize the liquid-phase combustible gas stream withdrawn from the tank and to use the latent heat of vaporization of the liquid-phase combustible gas stream withdrawn from the tank to cool the combustible gas stream to be cooled.
[Clause 2] Installation (1) according to Clause 1 , in which the combustible gas is a gaseous mixture comprising nitrogen and in which the cooling device (16) is arranged so as to convey the vaporized gas stream in the cooling device (16) to the vapour-phase gas collection circuit (6) so as to reduce the nitrogen content of the combustible gas stream circulating in the vapour-phase gas collection circuit (6).
[Clause 3] Installation according to Clause 2, in which the cooling device (16) comprises an additional heat exchanger (17) comprising a first and a second channels (18, 19) and heat-exchange walls for transferring heat from the first channel (18) to the second channel (19) of the additional heat exchanger (17), said first channel (18) and said second channel (19) each comprising an inlet (18a, 19a) and an outlet (18b, 19b), said first channel (18) being integrated into the intermediate circuit (15) connecting the heat exchanger (8) and the expansion device (14), the inlet (19a) of said second channel (19) being connected to the withdrawal circuit (35) of the cooling device (16) and the outlet (19b) of said second channel (19) being connected to the vapour-phase gas collection circuit (6).
[Clause 4] Installation according to Clause 3, in which the additional heat exchanger (17) is superimposed above the heat exchanger (8) and the outlet of the second channel (19) of the additional heat exchanger (17) is connected to the inlet (9a) of the first channel (9) of the heat exchanger (8) such that a liquid-phase gas stream can flow by gravity from the outlet of the second channel (19) of the additional heat exchanger (17) to the inlet (9a) of the first channel (9) of the heat exchanger (8).
[Clause 5] Installation according to Clause 3, in which the cooling device (16) comprises a second additional heat exchanger (41) comprising a first channel
(42) integrated into the vapour-phase gas collection circuit (6) and a second channel
(43) comprising an inlet (43a) connected to the withdrawal circuit (35) and an outlet (43b) connected to the vapour-phase gas collection circuit (6).
[Clause 6] Installation according to Clause 2, in which the cooling device (16) comprises a chamber (20) integrated into the vapour-phase gas collection circuit (6) between the admission (7a, 7b, 7c, 7d) of the vapour-phase gas collection circuit (6) and the inlet (9a) of the first channel (9) of the heat exchanger (8) and a spraying member (21 ) which is connected to the withdrawal circuit (35) of the cooling device (16) and is arranged to spray liquid-phase combustible gas into the chamber (20) so as to cool the vapour-phase gas stream withdrawn from the inner space of the tank and to reduce the nitrogen content of the combustible gas stream circulating in the vapour-phase gas collection circuit (6).
[Clause 7] Installation according to any one of Clauses 2 to 6, in which the cooling device (16) comprises a pumping device (26) that can suck the liquid-phase combustible gas stream via the admission (27) of the cooling device (16) and deliver it into the withdrawal circuit (35) .
[Clause 8] Installation according to Clause 7, comprising a gas analyser (40) that can deliver a representative measurement of the nitrogen concentration in the first portion of the combustible gas stream and in which the control unit (36) is arranged to generate a control signal for the pumping device (26) as a function of the representative measurement of the nitrogen concentration in the first portion of the combustible gas stream conveyed to the gas-consuming member (2, 3, 4) so as to ensure a nitrogen concentration in the first portion of the combustible gas stream that is below a limit operating concentration of the gas-consuming member.
[Clause 9] Installation according to Clause 8, in which the control unit (36) is arranged to generate a control signal for the pumping device (26) as a function of a representative measurement of the nitrogen concentration in the first portion of the combustible gas stream and of a nominal concentration, below the limit operating concentration of the gas-consuming member, so as to enslave the nitrogen concentration in the first portion of the combustible gas stream to the nominal concentration.
[Clause 10] Installation according to Clause 8, in which the control unit (36) has:
- a nitrogen concentration priority mode in which it generates a control signal for the pumping device (26) as a function of a representative measurement of the nitrogen concentration in the first portion of the combustible gas stream and of a nominal concentration, below the limit operating concentration of the gas-consuming member, so as to enslave the nitrogen concentration in the first portion of the combustible gas stream to the nominal concentration; and - a reliquefaction priority mode in which it generates a control signal for the pumping device (26) as a function of a temperature measurement T1 of the second portion of the gas stream circulating in the intermediate circuit (15) at the inlet of the expansion device (14) and of a nominal temperature so as to enslave the temperature T1 to the nominal temperature;
said control unit (36) being arranged to switch from the nitrogen concentration priority mode to the reliquefaction priority mode as a function of the representative measurement of the nitrogen concentration in the first portion of the combustible gas stream.
[Clause 11] Installation according to any one of Clauses 1 to 10, in which the expansion device (23) is an expansion valve.
[Clause 12] Installation according to any one of Clauses 1 to 1 1 , comprising a phase separator (25) connected upstream to the expansion device (14) and downstream, on the one hand, to a return circuit (31 ) leading to the tank and, on the other hand, to a return pipe (32) connected to the vapour-phase gas collection circuit (6) ; the phase separator (25) being arranged to convey the liquid phase of the combustible gas stream to the return circuit (31 ) and to convey the gas phase of the combustible gas stream to the return pipe (32).
[Clause 13] Process for feeding a gas-consuming member with combustible gas and for liquefying said combustible gas by means of an installation according to any one of Clauses 1 to 12, comprising:
- conveying a vapour-phase combustible gas stream from the admission (7a, 7b, 7c, 7d) of the vapour-phase gas collection circuit (6) to the inlet (9a) of the first channel (9) of the heat exchanger (8) ;
- transferring heat from the second channel (10) to the first channel (9) of the heat exchanger (8);
- compressing the combustible gas stream exiting the first channel (9) of the heat exchanger (8);
- conveying a first portion of the compressed combustible gas stream to the gas-consuming member (2, 3, 4) and a second portion of the compressed gas stream to the inlet (10a) of the second channel (10) of the heat exchanger (8) ; - conveying the second portion of the combustible gas stream from the second channel of the heat exchanger (8) to the expansion device (14) via the intermediate circuit (15) ;
- depressurizing the second portion of the combustible gas stream coming from the intermediate circuit (15) ;
- conveying at least one liquid-phase portion of the second portion of the depressurized combustible gas stream to the tank (5a, 5b, 5c, 5d) ;
- withdrawing a liquid-phase combustible gas stream from the inner space of the tank (5a, 5b, 5c, 5d) ;
- transferring heat between the liquid-phase combustible gas stream withdrawn from the tank and a gas stream to be cooled chosen from the vapour- phase gas stream circulating in the vapour-phase gas collection circuit (6) and the second portion of the gas stream circulating in the intermediate circuit (1 5) so as to vaporize the liquid-phase combustible gas stream withdrawn from the tank and to use the latent heat of vaporization of the liquid-phase combustible gas stream withdrawn from the tank to cool the gas stream to be cooled.
[Clause 14] Process according to Clause 13, in which the combustible gas is a gaseous mixture comprising nitrogen and in which the vaporized gas stream in the cooling device (16) is conveyed to the vapour-phase gas collection circuit (6).
[Clause 15] Process according to Clause 14, in which a variable representative of the nitrogen concentration in the first portion of the combustible gas stream is measured and in which the flow rate of the liquid-phase combustible gas stream circulating in the withdrawal circuit (35) of the cooling device (16) is adjusted as a function of the variable representative of the nitrogen concentration in the first portion of the combustible gas stream.
[Clause 16] Process according to Clause 15, in which the flow rate of the liquid-phase combustible gas stream circulating in the withdrawal circuit (35) of the cooling device (16) is adjusted as a function of the variable representative of the nitrogen concentration in the first portion of the combustible gas stream and of a nominal concentration so as to enslave the nitrogen concentration in the first portion of the combustible gas stream to the nominal concentration. [Clause 17] Vessel (40) comprising an installation (1 ) according to any one of Clauses 1 to 12.
[Clause 18] Process for loading or emptying a vessel (40) according to Clause 17, in which combustible gas is conducted through cryogenic transfer pipes (42, 46) from or to a floating or land-based storage installation to or from the vessel's tank.
[Clause 19] System for transferring a combustible gas, the system comprising a vessel (40) according to Clause 17, cryogenic transfer pipes (42, 46) arranged so as to connect the tank installed in the vessel's hull to a floating or land- based storage installation, and a pump for driving a combustible gas stream through the insulated pipelines from or to the floating or land-based storage installation to or from the vessel's tank.

Claims

CLAIMS What is claimed is:
1 . Installation for feeding a gas-consuming member with combustible gas and for liquefying said combustible gas; the installation comprising:
- a leaktight and heat-insulating tank comprising an inner space intended to be filled with combustible gas in a liquid-vapour two-phase state of equilibrium;
- a vapour-phase gas collection circuit comprising an admission emerging in the inner space of the tank and arranged to withdraw a vapour-phase combustible gas stream from the inner space of the tank;
- a heat exchanger comprising a first and a second channels and heat-exchange walls for transferring heat from the second channel to the first channel, the first channel and the second channel each comprising an inlet and an outlet ; the inlet of the first channel being connected to the vapour-phase gas collection circuit so as to heat the vapour-phase combustible gas stream in the heat exchanger
- a compressor which is connected upstream to the outlet of the first channel of the heat exchanger so as to compress the combustible gas stream at the outlet of the first channel of the heat exchanger and is connected downstream to a three-way connector that is capable of conveying a first portion of the combustible gas stream to the gas-consuming member and of conveying a second portion of the combustible gas stream to the inlet of the second channel of the heat exchanger in order to cool the second portion of the combustible gas stream; and
- an expansion device that is connected upstream to the outlet of the second channel of the heat exchanger via an intermediate circuit and is connected downstream to a return circuit leading to the tank ; the expansion device being arranged to depressurize the second portion of the combustible gas stream coming from the intermediate circuit ;
the installation being characterized in that it also comprises a cooling device which comprises a withdrawal circuit ; said withdrawal circuit comprising an admission which emerges in the inner space of the tank and is arranged to withdraw a liquid- phase combustible gas stream from the inner space of the tank ; said cooling device being arranged so as to transfer heat between the liquid-phase combustible gas stream withdrawn from the tank and a combustible gas stream to be cooled chosen from the vapour-phase combustible gas stream circulating in the vapour-phase gas collection circuit and the second portion of the combustible gas stream circulating in the intermediate circuit so as to vaporize the liquid-phase combustible gas stream withdrawn from the tank and to use the latent heat of vaporization of the liquid- phase combustible gas stream withdrawn from the tank to cool the combustible gas stream to be cooled.
2. Installation according to Claim 1 , in which the combustible gas is a gaseous mixture comprising nitrogen and in which the cooling device is arranged so as to convey the vaporized gas stream in the cooling device to the vapour-phase gas collection circuit so as to reduce the nitrogen content of the combustible gas stream circulating in the vapour-phase gas collection circuit.
3. Installation according to Claim 2, in which the cooling device comprises an additional heat exchanger comprising a first and a second channels and heat-exchange walls for transferring heat from the first channel to the second channel of the additional heat exchanger, said first channel and said second channel each comprising an inlet and an outlet, said first channel being integrated into the intermediate circuit connecting the heat exchanger and the expansion device, the inlet of said second channel being connected to the withdrawal circuit of the cooling device and the outlet of said second channel being connected to the vapour-phase gas collection circuit .
4. Installation according to Claim 3, in which the additional heat exchanger is superimposed above the heat exchanger and the outlet of the second channel of the additional heat exchanger is connected to the inlet of the first channel of the heat exchanger such that a liquid-phase gas stream can flow by gravity from the outlet of the second channel of the additional heat exchanger to the inlet of the first channel of the heat exchanger.
5. Installation according to Claim 3, in which the cooling device comprises a second additional heat exchanger comprising a first channel integrated into the vapour-phase gas collection circuit and a second channel comprising an inlet connected to the withdrawal circuit and an outlet connected to the vapour- phase gas collection circuit.
6. Installation according to Claim 2, in which the cooling device comprises a chamber integrated into the vapour-phase gas collection circuit between the admission of the vapour-phase gas collection circuit and the inlet of the first channel of the heat exchanger and a spraying member which is connected to the withdrawal circuit of the cooling device and is arranged to spray liquid-phase combustible gas into the chamber so as to cool the vapour-phase gas stream withdrawn from the inner space of the tank and to reduce the nitrogen content of the combustible gas stream circulating in the vapour-phase gas collection circuit.
7. Installation according to any one of Claims 2 to 6, in which the cooling device comprises a pumping device that can suck the liquid-phase combustible gas stream via the admission of the cooling device and deliver it into the withdrawal circuit
8. Installation according to Claim 7, comprising a gas analyser that can deliver a representative measurement of the nitrogen concentration in the first portion of the combustible gas stream and in which the control unit is arranged to generate a control signal for the pumping device as a function of the representative measurement of the nitrogen concentration in the first portion of the combustible gas stream conveyed to the gas-consuming member so as to ensure a nitrogen concentration in the first portion of the combustible gas stream that is below a limit operating concentration of the gas-consuming member.
9. Installation according to Claim 8, in which the control unit is arranged to generate a control signal for the pumping device as a function of a representative measurement of the nitrogen concentration in the first portion of the combustible gas stream and of a nominal concentration, below the limit operating concentration of the gas-consuming member, so as to enslave the nitrogen concentration in the first portion of the combustible gas stream to the nominal concentration.
10. Installation according to Claim 8, in which the control unit has:
- a nitrogen concentration priority mode in which it generates a control signal for the pumping device as a function of a representative measurement of the nitrogen concentration in the first portion of the combustible gas stream and of a nominal concentration, below the limit operating concentration of the gas-consuming member, so as to enslave the nitrogen concentration in the first portion of the combustible gas stream to the nominal concentration; and - a reliquefaction priority mode in which it generates a control signal for the pumping device as a function of a temperature measurement T1 of the second portion of the gas stream circulating in the intermediate circuit at the inlet of the expansion device and of a nominal temperature so as to enslave the temperature T1 to the nominal temperature;
said control unit being arranged to switch from the nitrogen concentration priority mode to the reliquefaction priority mode as a function of the representative measurement of the nitrogen concentration in the first portion of the combustible gas stream.
1 1 . Installation according to any one of Claims 1 to 6, in which the expansion device is an expansion valve.
12. Installation according to any one of Claims 1 to 6, comprising a phase separator connected upstream to the expansion device and downstream, on the one hand, to a return circuit leading to the tank and, on the other hand, to a return pipe connected to the vapour-phase gas collection circuit; the phase separator being arranged to convey the liquid phase of the combustible gas stream to the return circuit and to convey the gas phase of the combustible gas stream to the return pipe.
13. Process for feeding a gas-consuming member with combustible gas and for liquefying said combustible gas by means of an installation according to claim 1 , comprising:
- conveying a vapour-phase combustible gas stream from the admission of the vapour-phase gas collection circuit to the inlet of the first channel of the heat exchanger;
- transferring heat from the second channel to the first channel of the heat exchanger;
- compressing the combustible gas stream exiting the first channel (9) of the heat exchanger ;
- conveying a first portion of the compressed combustible gas stream to the gas- consuming member and a second portion of the compressed gas stream to the inlet of the second channel of the heat exchanger; - conveying the second portion of the combustible gas stream from the second channel of the heat exchanger to the expansion device via the intermediate circuit;
- depressurizing the second portion of the combustible gas stream coming from the intermediate circuit;
- conveying at least one liquid-phase portion of the second portion of the depressurized combustible gas stream to the tank;
- withdrawing a liquid-phase combustible gas stream from the inner space of the tank;
- transferring heat between the liquid-phase combustible gas stream withdrawn from the tank and a gas stream to be cooled chosen from the vapour-phase gas stream circulating in the vapour-phase gas collection circuit and the second portion of the gas stream circulating in the intermediate circuit so as to vaporize the liquid-phase combustible gas stream withdrawn from the tank and to use the latent heat of vaporization of the liquid-phase combustible gas stream withdrawn from the tank to cool the gas stream to be cooled.
14. Process according to Claim 13, in which the combustible gas is a gaseous mixture comprising nitrogen and in which the vaporized gas stream in the cooling device is conveyed to the vapour-phase gas collection circuit.
15. Process according to Claim 14, in which a variable representative of the nitrogen concentration in the first portion of the combustible gas stream is measured and in which the flow rate of the liquid-phase combustible gas stream circulating in the withdrawal circuit of the cooling device is adjusted as a function of the variable representative of the nitrogen concentration in the first portion of the combustible gas stream.
16. Process according to Claim 15, in which the flow rate of the liquid- phase combustible gas stream circulating in the withdrawal circuit of the cooling device is adjusted as a function of the variable representative of the nitrogen concentration in the first portion of the combustible gas stream and of a nominal concentration so as to enslave the nitrogen concentration in the first portion of the combustible gas stream to the nominal concentration.
17. Vessel comprising an installation according to claim 1 .
18. Process for loading or emptying a vessel according to Claim 17, in which combustible gas is conducted through cryogenic transfer pipes from or to a floating or land-based storage installation to or from the vessel's tank.
19. System for transferring a combustible gas, the system comprising a vessel according to Claim 17, cryogenic transfer pipes arranged so as to connect the tank installed in the vessel's hull to a floating or land-based storage installation, and a pump for driving a combustible gas stream through the insulated pipelines from or to the floating or land-based storage installation to or from the vessel's tank.
PCT/US2016/030793 2016-05-04 2016-05-04 Istallation for feeding a gas-consuming member with combustible gas and for liquefying said combustible gas WO2017192136A1 (en)

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JP2018557009A JP6850305B2 (en) 2016-05-04 2016-05-04 Equipment for supplying flammable gas to gas consuming parts and for liquefying this flammable gas
KR1020177036719A KR101943256B1 (en) 2016-05-04 2016-05-04 An apparatus for feeding a combustible gas to a gas consuming member and liquefying the combustible gas
PCT/US2016/030793 WO2017192136A1 (en) 2016-05-04 2016-05-04 Istallation for feeding a gas-consuming member with combustible gas and for liquefying said combustible gas
KR1020197002018A KR102190260B1 (en) 2016-05-04 2016-05-04 Installation for feeding a gas-consuming member with combustible gas and for liquefying said combustible gas
CN201680087173.9A CN109563969B (en) 2016-05-04 2016-05-04 Device for supplying a combustible gas to a gas consuming member and for liquefying said combustible gas

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JP2019522758A (en) 2019-08-15
JP6850305B2 (en) 2021-03-31
CN109563969A (en) 2019-04-02
KR101943256B1 (en) 2019-01-29
KR20190009848A (en) 2019-01-29
KR20180015161A (en) 2018-02-12
WO2017192136A9 (en) 2018-02-01
CN109563969B (en) 2021-02-12
KR102190260B1 (en) 2020-12-11

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