WO2019063658A1 - Natural gas production equipment and natural gas production method - Google Patents

Natural gas production equipment and natural gas production method Download PDF

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Publication number
WO2019063658A1
WO2019063658A1 PCT/EP2018/076202 EP2018076202W WO2019063658A1 WO 2019063658 A1 WO2019063658 A1 WO 2019063658A1 EP 2018076202 W EP2018076202 W EP 2018076202W WO 2019063658 A1 WO2019063658 A1 WO 2019063658A1
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WO
WIPO (PCT)
Prior art keywords
natural gas
distillation column
heat exchanger
component
liquid
Prior art date
Application number
PCT/EP2018/076202
Other languages
French (fr)
Inventor
Kenji Hirose
Loic Joly
Maxime RANCHOUX
Original Assignee
L'air Liquide, Societe Anonyme Pour L'etude Et L'exploitation Des Procedes Georges Claude
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 L'air Liquide, Societe Anonyme Pour L'etude Et L'exploitation Des Procedes Georges Claude filed Critical L'air Liquide, Societe Anonyme Pour L'etude Et L'exploitation Des Procedes Georges Claude
Priority to CN201880060781.XA priority Critical patent/CN111108336B/en
Priority to KR1020207010587A priority patent/KR102612287B1/en
Publication of WO2019063658A1 publication Critical patent/WO2019063658A1/en

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Classifications

    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F25—REFRIGERATION OR COOLING; COMBINED HEATING AND REFRIGERATION SYSTEMS; HEAT PUMP SYSTEMS; MANUFACTURE OR STORAGE OF ICE; LIQUEFACTION SOLIDIFICATION OF GASES
    • F25J—LIQUEFACTION, SOLIDIFICATION OR SEPARATION OF GASES OR GASEOUS OR LIQUEFIED GASEOUS MIXTURES BY PRESSURE AND COLD TREATMENT OR BY BRINGING THEM INTO THE SUPERCRITICAL STATE
    • F25J3/00—Processes or apparatus for separating the constituents of gaseous or liquefied gaseous mixtures involving the use of liquefaction or solidification
    • F25J3/02—Processes or apparatus for separating the constituents of gaseous or liquefied gaseous mixtures involving the use of liquefaction or solidification by rectification, i.e. by continuous interchange of heat and material between a vapour stream and a liquid stream
    • F25J3/0204—Processes or apparatus for separating the constituents of gaseous or liquefied gaseous mixtures involving the use of liquefaction or solidification by rectification, i.e. by continuous interchange of heat and material between a vapour stream and a liquid stream characterised by the feed stream
    • F25J3/0209—Natural gas or substitute natural gas
    • F25J3/0214—Liquefied 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
    • F25J3/00—Processes or apparatus for separating the constituents of gaseous or liquefied gaseous mixtures involving the use of liquefaction or solidification
    • F25J3/02—Processes or apparatus for separating the constituents of gaseous or liquefied gaseous mixtures involving the use of liquefaction or solidification by rectification, i.e. by continuous interchange of heat and material between a vapour stream and a liquid stream
    • F25J3/0228—Processes or apparatus for separating the constituents of gaseous or liquefied gaseous mixtures involving the use of liquefaction or solidification by rectification, i.e. by continuous interchange of heat and material between a vapour stream and a liquid stream characterised by the separated product stream
    • F25J3/0233—Processes or apparatus for separating the constituents of gaseous or liquefied gaseous mixtures involving the use of liquefaction or solidification by rectification, i.e. by continuous interchange of heat and material between a vapour stream and a liquid stream characterised by the separated product stream separation of CnHm with 1 carbon atom or more
    • 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
    • F25J3/00—Processes or apparatus for separating the constituents of gaseous or liquefied gaseous mixtures involving the use of liquefaction or solidification
    • F25J3/02—Processes or apparatus for separating the constituents of gaseous or liquefied gaseous mixtures involving the use of liquefaction or solidification by rectification, i.e. by continuous interchange of heat and material between a vapour stream and a liquid stream
    • F25J3/0228—Processes or apparatus for separating the constituents of gaseous or liquefied gaseous mixtures involving the use of liquefaction or solidification by rectification, i.e. by continuous interchange of heat and material between a vapour stream and a liquid stream characterised by the separated product stream
    • F25J3/0238—Processes or apparatus for separating the constituents of gaseous or liquefied gaseous mixtures involving the use of liquefaction or solidification by rectification, i.e. by continuous interchange of heat and material between a vapour stream and a liquid stream characterised by the separated product stream separation of CnHm with 2 carbon atoms or more
    • 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
    • F25J2200/00—Processes or apparatus using separation by rectification
    • F25J2200/04—Processes or apparatus using separation by rectification in a dual pressure main column system
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F25—REFRIGERATION OR COOLING; COMBINED HEATING AND REFRIGERATION SYSTEMS; HEAT PUMP SYSTEMS; MANUFACTURE OR STORAGE OF ICE; LIQUEFACTION SOLIDIFICATION OF GASES
    • F25J—LIQUEFACTION, SOLIDIFICATION OR SEPARATION OF GASES OR GASEOUS OR LIQUEFIED GASEOUS MIXTURES BY PRESSURE AND COLD TREATMENT OR BY BRINGING THEM INTO THE SUPERCRITICAL STATE
    • F25J2200/00—Processes or apparatus using separation by rectification
    • F25J2200/72—Refluxing the column with at least a part of the totally condensed overhead 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
    • F25J2210/00—Processes characterised by the type or other details of the feed stream
    • F25J2210/06—Splitting of the feed stream, e.g. for treating or cooling in different ways
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F25—REFRIGERATION OR COOLING; COMBINED HEATING AND REFRIGERATION SYSTEMS; HEAT PUMP SYSTEMS; MANUFACTURE OR STORAGE OF ICE; LIQUEFACTION SOLIDIFICATION OF GASES
    • F25J—LIQUEFACTION, SOLIDIFICATION OR SEPARATION OF GASES OR GASEOUS OR LIQUEFIED GASEOUS MIXTURES BY PRESSURE AND COLD TREATMENT OR BY BRINGING THEM INTO THE SUPERCRITICAL STATE
    • F25J2230/00—Processes or apparatus involving steps for increasing the pressure of gaseous process streams
    • F25J2230/08—Cold compressor, i.e. suction of the gas at cryogenic temperature and generally without afterstage-cooler
    • 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
    • F25J2230/00—Processes or apparatus involving steps for increasing the pressure of gaseous process streams
    • F25J2230/20—Integrated compressor and process expander; Gear box arrangement; Multiple compressors on a common shaft
    • 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
    • F25J2230/00—Processes or apparatus involving steps for increasing the pressure of gaseous process streams
    • F25J2230/32—Compression of the product 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
    • F25J2235/00—Processes or apparatus involving steps for increasing the pressure or for conveying of liquid process streams
    • F25J2235/60—Processes or apparatus involving steps for increasing the pressure or for conveying of liquid process streams the fluid being (a mixture of) hydrocarbons
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F25—REFRIGERATION OR COOLING; COMBINED HEATING AND REFRIGERATION SYSTEMS; HEAT PUMP SYSTEMS; MANUFACTURE OR STORAGE OF ICE; LIQUEFACTION SOLIDIFICATION OF GASES
    • F25J—LIQUEFACTION, SOLIDIFICATION OR SEPARATION OF GASES OR GASEOUS OR LIQUEFIED GASEOUS MIXTURES BY PRESSURE AND COLD TREATMENT OR BY BRINGING THEM INTO THE SUPERCRITICAL STATE
    • F25J2240/00—Processes or apparatus involving steps for expanding of process streams
    • F25J2240/02—Expansion of a process fluid in a work-extracting turbine (i.e. isentropic expansion), e.g. of the feed stream
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F25—REFRIGERATION OR COOLING; COMBINED HEATING AND REFRIGERATION SYSTEMS; HEAT PUMP SYSTEMS; MANUFACTURE OR STORAGE OF ICE; LIQUEFACTION SOLIDIFICATION OF GASES
    • F25J—LIQUEFACTION, SOLIDIFICATION OR SEPARATION OF GASES OR GASEOUS OR LIQUEFIED GASEOUS MIXTURES BY PRESSURE AND COLD TREATMENT OR BY BRINGING THEM INTO THE SUPERCRITICAL STATE
    • F25J2240/00—Processes or apparatus involving steps for expanding of process streams
    • F25J2240/02—Expansion of a process fluid in a work-extracting turbine (i.e. isentropic expansion), e.g. of the feed stream
    • F25J2240/04—Multiple expansion turbines in parallel
    • 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
    • F25J2245/00—Processes or apparatus involving steps for recycling of process streams
    • F25J2245/02—Recycle of a stream in general, e.g. a by-pass 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
    • F25J2280/00—Control of the process or apparatus
    • F25J2280/02—Control in general, load changes, different modes ("runs"), measurements

Definitions

  • the present invention relates to a filter
  • the present invention relates to natural gas production equipment using liquefied natural gas as a raw material and a natural gas production method, and more particularly, to natural gas production equipment and a useful supply method capable of supplying natural gas at a required pressure (for example, a high pressure such as 6 MPa to 10 MPa) while recovering natural gas liquid.
  • a required pressure for example, a high pressure such as 6 MPa to 10 MPa
  • Natural gas is stored as liquefied natural gas (LNG) for transport and storage convenience, and is vaporised before using mainly for thermal power generation or city gas. Since the shale gas boom, cheap LNG has become available on the LNG spot market and the number of cases using LNG from different countries of origin is increasing. When NG is used as a power generation fuel, for example, 100% methane is rather convenient for increasing combustion energy to achieve increased power generation.
  • components having more carbons such as ethane (hereafter sometimes called 'components such as ethane'), besides being valuable as a raw material in chemical plants, also have the advantage of being able to economise on usage of liquid propane gas (LPG) by using as high calorie LNG. Reflecting this situation, providing a highly energy-efficient process for separating LNG into the methane-rich gas of NG and components such as ethane is demanded at LNG consumption locations (LNG receiving terminals).
  • LPG liquid propane gas
  • An objective of technology for extracting natural gas liquid (NGL) from LNG to supply NG is to adjust the calorific value of fuel gas supplied mainly to power plants and pipelines, and in Patent Literature 1 , for example, the objective of adjusting the calorific value of an NG supply was achieved by first decompressing raw material LNG boosted to an NG supply pressure to a pressure allowing distillation before distilling to separate into NG and NGL, collecting the dilatational energy associated with decompression by an expansion turbine, and boosting the NG separated by a compressor powered by the turbine to the NG supply pressure again.
  • Patent Literature 2 to supply high pressure NG, all methane collected from the head of a distillation column was boosted by a compressor, then liquefied and further boosted by a pump before distilling to supply NG.
  • the components comprising a raw material LNG differ depending on where the LNG was produced, and may include a large amount of C3 and higher hydrocarbons such as propane or butane.
  • Such LNG has a higher boiling point, which reduces the recovery rate of methane when extracting methane-rich NG.
  • the operating temperature of the distillation column must be increased or the operating pressure of the distillation column must be reduced to maintain the recovery rate of methane.
  • One idea for increasing the operating temperature of a distillation column is to supply steam or hot water instead of the seawater, industrial water, or the like that is widely used in the reboiler of a distillation column for distilling LNG.
  • Steam or hot water uses natural gas or electricity as a heat source, and therefore has poor energy efficiency and high operating costs.
  • the NG supply pressure has tended to increase with the increasingly high pressure of the power generation equipment used for NG power generation. Because the most effective operating pressure during a distillation operation depends on the LNG composition and cannot be taken as fixed, in the case that the equipment disclosed by the Patent Literature 1 is used, the supply pressure of the raw material LNG differs greatly from the operating pressure of the distillation column. This pressure difference may lead to expansion of the raw material LNG, expansion of NG related to recompression, and increase in the compression rate, and may require an additional compressor to achieve the NG supply pressure.
  • the method disclosed by the Patent Literature 2 requires a pump for treating all of the supplied NG, and therefore is expensive.
  • the difference between the supply pressure of the raw material LNG and the operating pressure of the distillation column tends to be even greater because the operating pressure of the distillation column is determined by gas-liquid equilibrium based on the composition of the bottom liquid and the temperature of the reboiler heat source.
  • the present invention provides natural gas production equipment and a supply method capable of supplying NG at a required pressure (for example, a high pressure such as 6 MPa to 10 MPa) while maintaining the recovery rate of NGL, using seawater, for example, and without using an additional expensive heat source such as steam in the reboiler.
  • a required pressure for example, a high pressure such as 6 MPa to 10 MPa
  • the natural gas production equipment according to an aspect of the present invention is:
  • a raw material supply channel for introducing compressed liquefied natural gas in a supercooled state as a raw material through a raw material supply section, a first heat exchanger, a second heat exchanger, a first vaporiser, and a first expansion turbine, and through the second heat exchanger again to a first distillation column;
  • a first natural gas delivery channel for diverting a methane-rich gas component A drawn from the head of the first distillation column, and delivering one gas component B separated from the gas component A as the natural gas through a first compressor connected to the first expansion turbine;
  • the gas component C is condensed by at least some of the cold of the liquefied natural gas supplied from the raw material supply section to prepare the first reflux liquid;
  • the gas component E is cryocondensed by at least some of the cold of the liquefied natural gas supplied from the raw material supply section to prepare the second reflux liquid and the liquid component G.
  • Another aspect of the present invention is a method for extracting natural gas liquid from liquefied natural gas to produce natural gas, comprising the processes of:
  • the liquefied natural gas introduced to the first distillation column differs in composition and temperature, and is in a gas- liquid mixed state or a gaseous state.
  • ⁇ at least some of liquefied natural gas supplied from the raw material supply section may be introduced through a first heat exchanger, a second heat exchanger, a first vaporiser, and a first expansion turbine to a first distillation column as a raw material;
  • the gas component C may be condensed by at least some of the cold of the liquefied natural gas supplied from the raw material supply section to prepare a first reflux liquid to be introduced to an upper portion of the first distillation column;
  • some or all of the liquefied natural gas in a gaseous state drawn from the first expansion turbine may be cooled and condensed by the cold of the liquefied natural gas drawn from the first heat exchanger to prepare the raw material;
  • a methane-rich gas component E drawn from the head of the second distillation column may be liquefied through a third heat exchanger; and • in the third heat exchanger, the gas component E may be cryocondensed by at least some of the cold of the liquefied natural gas supplied from the raw material supply section to prepare the second reflux liquid and the liquid component G.
  • Raw material LNG is introduced to the first distillation column, where a methane-rich gas component A is obtained in the head by distillation and the liquid component D is stored in the bottom.
  • the liquid component D in the present invention may contain methane gas, unheated seawater, for example, may be used in the reboiler for heating the liquid component D without connecting a natural gas or electric heat source.
  • the first distillation column can be operated at a relatively high pressure, high pressure NG can be supplied without using multiple stages of compressors.
  • the liquid component D containing methane is introduced to the second distillation column and distilled.
  • the methane in the liquid component D is drawn from the head of the second distillation column as the methane-rice gas component E, and the components such as ethane in the liquid component D are drawn from the bottom of the second distillation column as the liquid component H and delivered as natural gas liquid.
  • the liquid component containing methane stored in the bottom of the first distillation column can be further distilled to obtain a methane-rich gas component and natural gas liquid. Therefore, even in the case that the raw material LNG contains many C3 or higher hydrocarbons, natural gas can be supplied while maintaining the recovery rate of NGL without connecting a heat source to the reboiler.
  • the operating pressure of the first distillation column can be increased when delivering natural gas at a high pressure.
  • Increasing the operating pressure of the first distillation column increases the methane component contained in the liquid component D stored in the bottom of the first distillation column.
  • the liquid component D containing methane can be further distilled in the second distillation column to obtain a methane-rich gas component and natural gas liquid, which also maintains the recovery rate of NGL.
  • the pressure of the methane-rich gas component A obtained from the head of the first distillation column is also high. Therefore, natural gas can be delivered at a high pressure even without multiple stages of compressors for compressing the gas component A.
  • ⁇ a second expansion turbine may be disposed after the first vaporiser in the raw material supply channel
  • a fourth heat exchanger and a second compressor may be disposed after the first compressor in the first natural gas delivery channel
  • the gas component B supplied from the first compressor may be delivered from the first natural gas delivery channel through the fourth heat exchanger and the second compressor as the natural gas;
  • some or all of the liquefied natural gas drawn from the first expansion turbine and the liquefied natural gas drawn from the second expansion turbine may be cooled and condensed by the cold of the liquefied natural gas drawn from the first heat exchanger to prepare the raw material.
  • the methane-rich gas component A can be further compressed by the second compressor to deliver the natural gas at an even higher pressure.
  • the gas component A compressed by the first compressor is also cooled by the fourth heat exchanger to more effectively compress by the second compressor.
  • Varying the pressure required by the natural gas to be delivered may also be considered, in which case, delivery may be controlled so that natural gas drawn from the first compressor is delivered directly when the required pressure is low, and natural gas drawn from the second compressor is delivered when the required pressure is high.
  • natural gas can be supplied at a wide range of pressures while maintaining the recovery rate of NGL, without connecting a heat source to the reboiler.
  • a branch bypass line may be disposed after the first compressor and before the fourth heat exchanger
  • a first shut-off valve may be disposed on the branch bypass line
  • the first shut-off valve may be controlled on the basis of a pressure value measured by a first pressure gauge arranged on the first natural gas delivery channel.
  • the second compressor disposed down-route may be shut off and the first shut-off valve on the branch bypass line disposed after the first compressor of the first stage may be opened to boost the natural gas using only the first compressor. If the natural gas supply pressure is higher than the predetermined pressure, the second compressor disposed down-route may be operated and the first shut-off valve may be closed to further boost the natural gas by a compressor following the first compressor.
  • the natural gas supply pressure can be measured by the first pressure gauge arranged on the first natural gas delivery channel. Although only the first compressor is used on the basis of the measured pressure, using both the first compressor and the second compressor may be selected to optimise the power used by the compressors.
  • a first generator may be disposed connected to the second compressor.
  • the second compressor is shut off as described earlier.
  • power recovered by an expansion turbine connected to the second compressor can be recovered as electric energy by the first generator connected to the second compressor. This can assure function under optimum conditions corresponding to fluctuation in the natural gas supply pressure, and assure power generation according to the operation of only the second expansion turbine.
  • a third expansion turbine may be arranged parallel to the second expansion turbine, and a second generator may be disposed connected to the third expansion turbine.
  • the second compressor is shut off as described earlier.
  • the second expansion turbine is also shut off, and the liquefied natural gas supplied from the first vaporiser is supplied to the third expansion turbine without supplying to the second expansion turbine.
  • the third expansion turbine is not connected to a compressor, but is connected to the second generator. This can assure function under optimum conditions corresponding to fluctuation in the natural gas supply pressure, and assure power generation according to the operation of only the third expansion turbine.
  • the temperature of the first reboiler may be 0°C to 30°C
  • the temperature of the second reboiler may be 0°C to 30°C
  • natural gas can be supplied at a wide range of pressures while maintaining the recovery rate of NGL, without connecting heat sources to the first reboiler and the second reboiler.
  • the range of the temperature of the first reboiler and the second reboiler is preferably 0°C to 30°C, and more preferably 5°C to 10°C.
  • unheated seawater for example, may be used in the reboilers, and there is no need to use steam or hot water obtained through heating by using electricity or burning natural gas. That is, there is no need for a heat source for heating such as by electricity or burning natural gas.
  • the heat exchangers can operate while restraining water turning to ice even if there is considerable fluctuation in the thermal load of the heat exchangers.
  • the upper limit of the temperature of the first reboiler and the second reboiler is about 10°C, seawater or industrial water having a seawater temperature or industrial water temperature of about 15°C can be used.
  • the liquid component D stored in the bottom of the first distillation column contains more methane due to the low temperature of the reboiler.
  • the liquid component D containing methane is introduced to the second distillation column and distilled.
  • the methane in the liquid component D is drawn from the head of the second distillation column as the methane-rice gas component E, and the components such as ethane in the liquid component D are drawn from the bottom of the second distillation column as the liquid component H and delivered as natural gas liquid.
  • the liquid component containing methane stored in the bottom of the first distillation column can be further distilled to obtain the methane-rich gas component E and natural gas liquid. Therefore, natural gas can be supplied while maintaining the recovery rate of NGL, without connecting a heat source to the reboiler.
  • the temperature of the liquefied natural gas introduced to the third heat exchanger may be -180°C to -125°C when introduced to the third heat exchanger.
  • the methane-rich gas component E drawn from the head of the second distillation column is cooled and condensed, and delivered as natural gas after the pressure has been boosted by a pump. Because methane cools and condenses when the temperature is -180°C to - 125°C, methane gas can be recovered effectively from an upper portion of the second distillation column.
  • the methane After being boosted by the compression means, the methane may be distilled by a warmer and delivered. According to this aspect of the present invention, the recovery rate of methane in raw material LNG can be increased even more because the methane component introduced to the second distillation column can be recovered and delivered as natural gas.
  • FIG. 1 is a diagram showing a configuration example of the natural gas production equipment of Embodiment 1 ;
  • FIG. 2 is a diagram illustrating verification results in a configuration example of the natural gas production equipment of Embodiment 1 ;
  • FIG. 3 is a diagram showing a configuration example of the natural gas production equipment of Embodiment 2;
  • FIG. 4 is a diagram illustrating verification results in a configuration example of the natural gas production equipment of Embodiment 2;
  • FIG. 5 is a diagram showing another configuration example of the natural gas production equipment of Embodiment 2;
  • FIG. 6 is a diagram showing another configuration example of the natural gas production equipment of Embodiment 2.
  • FIG. 7 is a diagram showing another configuration example of the natural gas production equipment of Embodiment 2.
  • liquefied natural gas is introduced to a first distillation column as a raw material
  • methane-rich natural gas is prepared from a gas component drawn from the top of the first distillation column
  • a liquid component drawn from the bottom is introduced to a second distillation column
  • methane-rich natural gas is prepared from a gas component drawn from the top of the second distillation column
  • natural gas liquid is prepared from a liquid component drawn from the bottom.
  • the production equipment is provided with a raw material supply channel for introducing compressed liquefied natural gas in a supercooled state as a raw material through a raw material supply section, a first heat exchanger, a second heat exchanger, a first vaporiser, and a first expansion turbine, then through the second heat exchanger again to a first distillation column;
  • a first reboiler for heating a liquid component D in the bottom of the first distillation column
  • a first natural gas delivery channel for diverting a methane-rich gas component A drawn from the head of the first distillation column, and delivering one gas component B as the natural gas through a first compressor connected to the first expansion turbine; a first reflux channel for introducing the other gas component C through the first heat exchanger to an upper portion of the first distillation column as a first reflux liquid;
  • a bottom supply channel for introducing the liquid component D drawn from the bottom of the first distillation column to a second distillation column
  • a second reflux channel for diverting a methane-rich gas component E from the head of the second distillation column through a third heat exchanger after liquefying, and introducing one liquid component F to an upper portion of the second distillation column as a second reflux liquid;
  • a second natural gas supply channel for supplying the other liquid component G through a compression means and a second vaporiser as the natural gas;
  • a second reboiler for heating a liquid component H in the bottom of the second distillation column
  • a natural gas liquid delivery channel for delivering the liquid component H drawn from the bottom of the second distillation column as the natural gas liquid.
  • the gas component C is condensed by at least some of the cold of the liquefied natural gas supplied from the raw material supply section to prepare the first reflux liquid;
  • some or all of the liquefied natural gas in a gaseous state drawn from the first expansion turbine may be cooled and condensed by the cold of the liquefied natural gas drawn from the first heat exchanger to prepare the raw material;
  • the gas component E is cryocondensed by at least some of the cold of the liquefied natural gas supplied from the raw material supply section to prepare the second reflux liquid and the liquid component G.
  • the natural gas production equipment of Embodiment 1 will be described with reference to FIG. 1 .
  • the natural gas production equipment 100 of Embodiment 1 With the natural gas production equipment 100 of Embodiment 1 :
  • Liquefied natural gas is introduced from a raw material supply section 101 to a first distillation column 7 as a raw material
  • methane-rich natural gas is prepared from a gas component drawn from the top of the first distillation column 7
  • a liquid component drawn from the bottom is introduced to a second distillation column 9
  • methane-rich natural gas is prepared from a gas component drawn from the top of the second distillation column 9
  • natural gas liquid is prepared from a liquid component drawn from the bottom.
  • Some of the compressed LNG supplied from the raw material supply section 101 is vaporised in a cold release process comprising a first heat exchanger 1 , a second heat exchanger 2, a first vaporiser 3, and a first expansion turbine 4, and the vaporised LNG passes through the second heat exchanger 2 to form a gas-liquid mixture which is introduced to the first distillation column 7 as a raw material.
  • the U-turned LNG is subjected to heat exchange in a counter-current with the LNG itself to use the cold of the LNG in the emission process to cool and condense the temporarily vaporised LNG itself. That is, the cold of the LNG is released during the flow of LNG in the raw material preparation process introduced in the distillation column, but some of the released cold is stored to reuse the cold more effectively.
  • the natural gas production equipment is provided with a raw material supply channel 102 for introducing compressed LNG in a supercooled state as a raw material to the first distillation column 7 through the raw material supply section 101 , the first heat exchanger 1 , the second heat exchanger 2, the first vaporiser 3, and the first expansion turbine 4, then through the second heat exchanger 2 again.
  • Low-temperature and high-pressure (for example, about -135°C and about 10 MPa) LNG is supplied from the raw material supply section 101 as a liquid, and the cold is successively released through the first heat exchanger 1 and the second heat exchanger 2 before the LNG is vaporised by the first vaporiser 3.
  • the vaporised LNG is both vaporised and cooled to a low temperature by the first expansion turbine 4, then compressed to an predetermined optimum pressure for a raw material (for example, 3.2 MPa) to become low-temperature and low-pressure gaseous LNG.
  • the gaseous LNG is cooled again by the second heat exchanger 2 to a predetermined optimum temperature for a raw material.
  • This predetermined temperature refers to the temperature at which LNG of a predetermined composition condenses to form a gas-liquid state at an optimum pressure; for example, in the case of LNG having the composition illustrated below in Table 1 , the optimum temperature at about 3.2 MPa is about -80°C.
  • the condensed LNG is introduced to the first distillation column 7.
  • the first distillation column 7 is provided with a first reboiler 201 for heating the liquid component D stored in the bottom of the first distillation column 7.
  • the first reboiler 201 heats the liquid component D by heat exchange between the liquid component D and a heat transfer medium in the first reboiler 201 .
  • the temperature of the first reboiler 201 may be any temperature that seawater or industrial water can maintain; specifically, a range of 0°C to 30°C. Therefore, specifically, unheated seawater may be used, and there is no need to dispose a heating means for heating the thermal transfer medium in the first reboiler 201 .
  • the liquid component D heated in the first reboiler 201 is reintroduced to the bottom of the first distillation column 7, and after distilling in the first distillation column 7, the methane-rich gas component A is introduced from the head of the first distillation column 7 and the liquid component D is drawn from the bottom of the first distillation column 7.
  • the methane-rich gas component A drawn from the head of the first distillation column 7 is diverted, and one gas component B separated from the gas component A is delivered as the natural gas through a first compressor 5 connected to the first expansion turbine 4.
  • the gas component A drawn from the head of the first distillation column 7 is a low-temperature and low-pressure (for example, about -95°C and about 3.2 MPa) methane-rich NG.
  • the gas component A can be subjected to heating and boosting treatments, without introducing additional energy, by adiabatic compression by the first compressor 5 connected to the first expansion turbine 4 used to prepare the raw material.
  • the gas component A drawn from the first compressor 5 is supplied as NG as is, but may be heated by a warmer 6 arranged after the first compressor 5 to extract as a product NG having a predetermined temperature and pressure (for example, 15°C and about 10.6 MPa).
  • the other gas component C separated from the gas component A drawn from the head of the first distillation column 7 is cooled and condensed through the first heat exchanger 1 , and introduced to an upper portion of the first distillation column 7 as a first reflux liquid.
  • a first reflux channel 104 is provided for introducing the other gas component C through the first heat exchanger 1 to an upper portion of the first distillation column 7 as a first reflux liquid.
  • the low- temperature and low-pressure gas component A (for example, about 95°C and about 3.2 MPa) is cooled and condensed by heat exchange with supercooled LNG before introducing to the first distillation column 7.
  • the liquid component D stored in the bottom of the first distillation column 7 is introduced from a bottom liquid supply channel 105 to the second distillation column 9.
  • the liquid component D contains a predetermined quantity of methane. Therefore, distilling in the distillation column 9 obtains the methane-rich component E from the head of the second distillation column 9 and the liquid component H from the bottom of the second distillation column 9.
  • a reboiler arranged in the bottom of the second distillation column 9 for superheating the liquid component H need not be a high temperature, and may be, for example, a temperature of 0°C to 30°C. Therefore, specifically, unheated seawater may be used, and there is no need to dispose a heating means for heating the thermal transfer medium in the first reboiler 201 .
  • the methane-rich gas component E drawn from the head of the second distillation column 9 is cooled by heat exchange with supercooled LNG in a third heat exchanger 8.
  • the raw material LNG is diverted after the raw material supply section 101 , some is supplied to the third heat exchanger 8, and the remainder is supplied to the first heat exchanger 1 .
  • the gas component E subjected to heat exchange in the third heat exchanger 8 is cooled and condensed, for example, to -1 10°C, and the liquid component F comprising a portion separated from the gas component E is introduced from a second reflux channel 1 1 1 to an upper portion of the second distillation column 9 as a second reflux liquid.
  • the other liquid component G separated from the gas component E after detouring via the third heat exchanger 8 is boosted by a compression means 10 and vaporised and heated in the second vaporiser 1 1 to prepare a product NG having a predetermined temperature and pressure (for example, 15°C and about 10 MPa).
  • the liquid component H drawn from the bottom of the second distillation column 9 is a liquid containing many components such as ethane, and is delivered as natural gas liquid.
  • raw material LNG is distilled by a first distillation column 7 to obtain a methane-rich gas component A, and a liquid component D containing a methane component from the bottom of the first distillation column 7.
  • the liquid component D containing a methane component can be further distilled in a second distillation column 9 to supply NG while maintaining the recovery rate of NGL.
  • the first distillation column 7 can be operated at a high pressure and can therefore supply high pressure NG.
  • the present embodiment can provide natural gas production equipment having high energy efficiency without requiring that a heat source be connected to the reboiler.
  • the LNG supplied in the present equipment has a composition such as illustrated below in Table 1 , for example, has variable components depending on the place of origin, and differs in the temperature and pressure conditions for storing in a high pressure tank.
  • the LNG is stored under a temperature condition of about -120°C to -160°C and a pressure condition of about 5-10 MPa.
  • the LNG according to the present invention includes shale gas as described earlier, and unrefined LNG as well as refined LNG. TABLE 1
  • the first heat exchanger 1 , the second heat exchanger 2, and the third heat exchanger 8 are not specifically limited, and may be, for example, plate-fin heat exchangers or shell and tube heat exchangers.
  • the compression means 10 is not specifically limited, and may be, for example, a liquid delivery pump.
  • a second expansion turbine 13 is disposed after the first vaporiser 3 in the raw material supply channel 102.
  • the LNG vaporised in the first vaporiser 3 is diverted, some is introduced to the first expansion turbine 4, and the remainder is introduced to the second expansion turbine 13.
  • the gaseous LNG depressurised by the first expansion turbine 4 and the gaseous LNG depressurised by the second expansion turbine 13 converge and are introduced to the second heat exchanger 2.
  • the LNG is cooled by heat exchange in the second heat exchanger 2, and the condensed LNG is introduced to the first distillation column 7.
  • a fourth heat exchanger 15 is disposed after the first compressor 5, and a second compressor 14 is disposed connected to the second expansion turbine 13.
  • the gas component B supplied from the first compressor 5 is cooled in the fourth heat exchanger 15 by LNG supplied from the raw material supply section 101 .
  • the LNG cooled in the fourth heat exchanger 15 becomes, for example, -54°C, and is introduced to the second compressor 14. Cooling in the fourth heat exchanger 15 contributes to improving compression efficiency in the second compressor 14.
  • the gas component B boosted to a predetermined pressure (for example, 1 1 .2 MPa) in the second compressor 14 is delivered from the first natural gas delivery channel 103 as the product NG. Because the product NG is a predetermined temperature (for example, 15°C), the warmer 6 may be arranged after the second compressor 14 to heat the gas component B.
  • a branch bypass line 30 may be disposed after the first vaporiser 3 and a first shut-off valve 31 may be disposed on the branch bypass line 30 as shown in FIG. 5.
  • the first shut-off valve 31 is controlled on the basis of a pressure value measured by a pressure gauge 32 arranged on the first natural gas delivery channel 103.
  • the first shut-off valve 31 may be opened and the second compressor 14 stopped at the same time to increase the natural gas supply pressure, and in the case that the pressure measured by the pressure gauge 32 is a predetermined value (for example, 6 MPa) or greater, the first shut-off valve 31 may be closed and the second compressor 14 controlled to operate at the same time.
  • a predetermined value for example, 6 MPa
  • the predetermined value may be determined on the basis of the compression ratio of the first compressor 5 to the second compressor 14, the pressure of the natural gas before being introduced to the first compressor 5, and the pressure of the natural gas delivered from the natural gas delivery channel 103.
  • the first compressor 5 can boost the natural gas to 6 MPa, and therefore, the predetermined value for the pressure measured by the pressure gauge 32 may be 6 MPa.
  • the first shut-off valve is controlled to open, and if the measured pressure is 6 MPa or greater, the first shut-off valve is controlled to close.
  • the second compressor 14 In the case that the first shut-off valve 31 is opened, the second compressor 14 is stopped, and in the case that the first shut-off valve 31 is closed, the second compressor 14 is operated to compress the natural gas.
  • the natural gas can be boosted to the required pressure by boosting by the first compressor 5 before compressing by the second compressor 14.
  • the equipment can be operated under optimum conditions by using only the first compressor 5 to boost pressure without using the second compressor 14.
  • a first generator 33 may be disposed connected to the second compressor 14 as shown in FIG. 6.
  • the second expansion turbine 13 connected to the second compressor 14 operates even in the case that the natural gas supply pressure is low and the second compressor 14 has been stopped.
  • the first generator 33 connected to the second compressor 14 assures the power required for operating the second expansion turbine 13 in the case that the second compressor 14 has been stopped.
  • a third expansion turbine 34 arranged parallel with the second expansion turbine 13 is disposed down-route from the first vaporiser 3 and a second generator 35 is disposed connected to the third expansion turbine 34 as shown in FIG. 7.
  • the liquefied natural gas delivered from the first vaporiser 3 is switched to a new channel by a second shut-off valve 36 or a third shut-off valve to supply to the second expansion turbine 13 or the third expansion turbine 34.
  • the second shut-off valve 36 is closed and the third shut-off valve 37 is opened.
  • the natural gas delivered from the first vaporiser 3 is detoured via the third shut-off valve 37 to introduce to the third expansion turbine 34.
  • the second generator 35 connected to the third expansion turbine 34 assures the power required to operate the third expansion turbine 34.
  • the second generator 35 connected to the third expansion turbine 34 can assure the power required to operate the third expansion turbine 34.
  • the pressure (MPaA), temperature (°C), flow rate (kg/h), and composition (wt%) in each section were simulated to verify supply of LNG having the composition illustrated in Table 1 using the natural gas production equipment according to Embodiment 1 .
  • A is located at the exit of the raw material supply section 101 .
  • B is located after the raw material supply section 101 and just in front of the inlet of the first heat exchanger 1 .
  • C is located after the first heat exchanger 1 and before the second heat exchanger 2.
  • D is located after the raw material supply section 101 and before the third heat exchanger 8.
  • E is located after the third heat exchanger 8 and just in front of where the channel from the first heat exchanger 1 merges with the channel to the second heat exchanger 2.
  • F is located after the second heat exchanger 2 and before the first vaporiser 3.
  • G is located after the first vaporiser 3 and before the first expansion turbine 4.
  • H is located at the exit after the first expansion turbine.
  • J is located just in front of where the gas component B obtained from the head of the first distillation column 7 is introduced to the first compressor 5, and before the first compressor 5.
  • K is located after the first compressor 5 and before the warmer 6.
  • L is located on the first natural gas delivery channel 103 and after the warmer 6.
  • M is located in the bottom liquid supply channel 105 extending from the bottom of the first distillation column 7 and at the exit portion of the bottom of the first distillation column 7.
  • N is located in the bottom liquid supply channel 105 and just before where liquid is introduced to the second distillation column 9.
  • O is located after the third heat exchanger 8 and before the compression means 10.
  • P is located after the compression means 10 and before the second vaporiser 1 1 .
  • Q is located after the second vaporiser 1 1 and just in front of where the channel merges with the first natural gas delivery channel 103.
  • R is located in the natural gas liquid delivery channel 1 13 and after the second distillation column 9.
  • Example 1 a natural gas supply apparatus without a second distillation column
  • Comparative Example 1 a conventional natural gas supply apparatus without a second distillation column was used in which methane- rich NG is delivered from the head of the first distillation column and natural gas liquid is delivered from the bottom of the first distillation column.
  • Table 3 shows a comparison between Example 1 and Comparative Example 1 .
  • Example 1 and Comparative Example 1 were verified when raw material LNG having the same temperature and pressure was used, and the methane recovery rate, the ethane recovery rate, and the propane recovery rate were all 99.9% or higher.
  • Example 1 an NG supply pressure of 10.57 MPa could be obtained using unheated seawater (temperature: 10°C) in the first reboiler and the second reboiler.
  • the pressure (MPaA), temperature (°C), flow rate (kg/h), and composition (wt%) in each section were simulated to verify supply of LNG having the composition illustrated in Table 1 using the natural gas production equipment according to Embodiment 2.
  • the locations of the sections A-R in FIG. 4 are the same as the locations of the sections A-R in FIG. 2.
  • the locations of the sections D2-K2 in FIG. 4 are as follows.
  • D2 is located after the raw material supply section 101 and just in front of the inlet to the fourth heat exchanger 15.
  • E2 is located at the exit of the fourth heat exchanger 15.
  • G1 is located just after a branch intersection after branching following the first vaporiser 3, and before the first expansion turbine 4.
  • G2 is located just after a branch intersection after branching following the first vaporiser 3, and before the second expansion turbine 13.
  • H1 is located at the exit portion of the first expansion turbine 4.
  • H2 is located after branching following the first vaporiser 3, and at the inlet portion of the second expansion turbine 13.
  • K1 is located after the fourth heat exchanger 15 and before the second compressor 14.
  • K2 is located after the second compressor 14 and before the warmer 6.

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Abstract

The natural gas production equipment is provided with a raw material supply section 101 for introducing compressed liquefied natural gas (LNG) in a supercooled state as a raw material to the first distillation column 7 through the raw material supply section 101, the first heat exchanger 1, the second heat exchanger 2, the first vaporiser 3, and the first expansion turbine 4, then through the second heat exchanger 2 again. A methane-rich gas component drawn from the head of a first distillation column 7 is delivered as natural gas. A liquid component stored in the bottom of the first distillation column 7 is introduced to a second distillation column 9. A methane-rich gas component drawn from the head of the second distillation column 9 is delivered as natural gas. Natural gas liquid is delivered from the bottom of the second distillation column 9.

Description

Natural Gas Production Equipment and Natural Gas Production Method
The present invention relates to a filter The present invention relates to natural gas production equipment using liquefied natural gas as a raw material and a natural gas production method, and more particularly, to natural gas production equipment and a useful supply method capable of supplying natural gas at a required pressure (for example, a high pressure such as 6 MPa to 10 MPa) while recovering natural gas liquid.
Natural gas (NG) is stored as liquefied natural gas (LNG) for transport and storage convenience, and is vaporised before using mainly for thermal power generation or city gas. Since the shale gas boom, cheap LNG has become available on the LNG spot market and the number of cases using LNG from different countries of origin is increasing. When NG is used as a power generation fuel, for example, 100% methane is rather convenient for increasing combustion energy to achieve increased power generation. On the other hand, components having more carbons, such as ethane (hereafter sometimes called 'components such as ethane'), besides being valuable as a raw material in chemical plants, also have the advantage of being able to economise on usage of liquid propane gas (LPG) by using as high calorie LNG. Reflecting this situation, providing a highly energy-efficient process for separating LNG into the methane-rich gas of NG and components such as ethane is demanded at LNG consumption locations (LNG receiving terminals).
An objective of technology for extracting natural gas liquid (NGL) from LNG to supply NG is to adjust the calorific value of fuel gas supplied mainly to power plants and pipelines, and in Patent Literature 1 , for example, the objective of adjusting the calorific value of an NG supply was achieved by first decompressing raw material LNG boosted to an NG supply pressure to a pressure allowing distillation before distilling to separate into NG and NGL, collecting the dilatational energy associated with decompression by an expansion turbine, and boosting the NG separated by a compressor powered by the turbine to the NG supply pressure again.
In Patent Literature 2, to supply high pressure NG, all methane collected from the head of a distillation column was boosted by a compressor, then liquefied and further boosted by a pump before distilling to supply NG. PRIOR ART LITERATURE:
- PATENT LITERATURE 1 Japanese Unexamined Patent Publication No. 2016-156581
- PATENT LITERATURE 2 United States Patent Application Publication
No. 2009/0282865
The components comprising a raw material LNG differ depending on where the LNG was produced, and may include a large amount of C3 and higher hydrocarbons such as propane or butane. Such LNG has a higher boiling point, which reduces the recovery rate of methane when extracting methane-rich NG. The operating temperature of the distillation column must be increased or the operating pressure of the distillation column must be reduced to maintain the recovery rate of methane.
One idea for increasing the operating temperature of a distillation column is to supply steam or hot water instead of the seawater, industrial water, or the like that is widely used in the reboiler of a distillation column for distilling LNG. Steam or hot water, however, uses natural gas or electricity as a heat source, and therefore has poor energy efficiency and high operating costs.
Previously, however, when seawater is used in a reboiler to reduce the operating pressure of a distillation column, no heat source such as natural gas or electricity has been required, but there is concern that the resulting NG pressure may not meet the pressure required according to the application.
The NG supply pressure has tended to increase with the increasingly high pressure of the power generation equipment used for NG power generation. Because the most effective operating pressure during a distillation operation depends on the LNG composition and cannot be taken as fixed, in the case that the equipment disclosed by the Patent Literature 1 is used, the supply pressure of the raw material LNG differs greatly from the operating pressure of the distillation column. This pressure difference may lead to expansion of the raw material LNG, expansion of NG related to recompression, and increase in the compression rate, and may require an additional compressor to achieve the NG supply pressure.
The method disclosed by the Patent Literature 2, on the other hand, requires a pump for treating all of the supplied NG, and therefore is expensive. Especially in the case that the raw material LNG contains more C3 or higher hydrocarbon components such as propane, the difference between the supply pressure of the raw material LNG and the operating pressure of the distillation column tends to be even greater because the operating pressure of the distillation column is determined by gas-liquid equilibrium based on the composition of the bottom liquid and the temperature of the reboiler heat source.
In view of this situation, the present invention provides natural gas production equipment and a supply method capable of supplying NG at a required pressure (for example, a high pressure such as 6 MPa to 10 MPa) while maintaining the recovery rate of NGL, using seawater, for example, and without using an additional expensive heat source such as steam in the reboiler.
The natural gas production equipment according to an aspect of the present invention is:
• equipment for extracting natural gas liquid from liquefied natural gas and supplying natural gas, provided with:
• a raw material supply channel for introducing compressed liquefied natural gas in a supercooled state as a raw material through a raw material supply section, a first heat exchanger, a second heat exchanger, a first vaporiser, and a first expansion turbine, and through the second heat exchanger again to a first distillation column;
· a first reboiler for heating a liquid component D in the bottom of the first distillation column;
• a first natural gas delivery channel for diverting a methane-rich gas component A drawn from the head of the first distillation column, and delivering one gas component B separated from the gas component A as the natural gas through a first compressor connected to the first expansion turbine;
• a first reflux channel for introducing the other gas component C separated from the gas component A through the first heat exchanger to an upper portion of the first distillation column as a first reflux liquid;
• a bottom supply channel for introducing the liquid component D drawn from the bottom of the first distillation column to a second distillation column;
• a second reflux channel for diverting a methane-rich gas component E drawn from the head of the second distillation column through a third heat exchanger after liquefying, and introducing one liquid component F separated from the gas component E to an upper portion of the second distillation column as a second reflux liquid;
• a second natural gas supply channel for supplying the other liquid component G separated from the gas component E through a compression means and a second vaporiser as the natural gas;
• a second reboiler for heating a liquid component H in the bottom of the second distillation column; and
• a natural gas liquid delivery channel for delivering the liquid component H drawn from the bottom of the second distillation column as the natural gas liquid;
· in the first heat exchanger, the gas component C is condensed by at least some of the cold of the liquefied natural gas supplied from the raw material supply section to prepare the first reflux liquid;
• in the second heat exchanger, some or all of the liquefied natural gas in a gaseous state drawn from the first expansion turbine is cooled and condensed by the cold of the liquefied natural gas drawn from the first heat exchanger to prepare the raw material to be introduced to the first distillation column; and
• in the third heat exchanger, the gas component E is cryocondensed by at least some of the cold of the liquefied natural gas supplied from the raw material supply section to prepare the second reflux liquid and the liquid component G.
Another aspect of the present invention is a method for extracting natural gas liquid from liquefied natural gas to produce natural gas, comprising the processes of:
(1 ) introducing at least some of the liquefied natural gas supplied from a raw material supply section to a first distillation column after expelling some of the cold of the liquefied natural gas;
(2) introducing a methane-rich gas component A from the head of the first distillation column;
(3) diverting the gas component A and boosting one gas component B separated from the gas component A before delivering as the natural gas;
(4) cooling the other gas component C separated from the gas component A before introducing to an upper portion of the first distillation column as a first reflux liquid;
(5) heating a liquid component D stored in the bottom of the first distillation column through a first reboiler; (6) introducing at least some of a liquid component D drawn from the bottom of the first distillation column to a second distillation column;
(7) cooling a methane-rich gas component E drawn from the head of the second distillation column;
(8) introducing one liquid component F separated from the liquefied, then diverted liquid component E to an upper portion of the second distillation column as a second reflux liquid, and boosting and vaporising the other liquid component G separated from the gas component E before supplying as the natural gas;
(9) heating a liquid component H stored in the bottom of the second distillation column through a second reboiler; and
(10) delivering the liquid component H drawn from the bottom of the second distillation column as the natural gas liquid.
In the process (1 ) for introducing at least some of liquefied natural gas supplied from a raw material supply section to a first distillation column after expelling some of the cold of the liquefied natural gas, the liquefied natural gas introduced to the first distillation column differs in composition and temperature, and is in a gas- liquid mixed state or a gaseous state.
In the method for producing natural gas according to an aspect of the present invention:
· at least some of liquefied natural gas supplied from the raw material supply section may be introduced through a first heat exchanger, a second heat exchanger, a first vaporiser, and a first expansion turbine to a first distillation column as a raw material;
• in the first heat exchanger, the gas component C may be condensed by at least some of the cold of the liquefied natural gas supplied from the raw material supply section to prepare a first reflux liquid to be introduced to an upper portion of the first distillation column;
• in the second heat exchanger, some or all of the liquefied natural gas in a gaseous state drawn from the first expansion turbine may be cooled and condensed by the cold of the liquefied natural gas drawn from the first heat exchanger to prepare the raw material;
• a methane-rich gas component E drawn from the head of the second distillation column may be liquefied through a third heat exchanger; and • in the third heat exchanger, the gas component E may be cryocondensed by at least some of the cold of the liquefied natural gas supplied from the raw material supply section to prepare the second reflux liquid and the liquid component G.
Raw material LNG is introduced to the first distillation column, where a methane-rich gas component A is obtained in the head by distillation and the liquid component D is stored in the bottom. Because the liquid component D in the present invention may contain methane gas, unheated seawater, for example, may be used in the reboiler for heating the liquid component D without connecting a natural gas or electric heat source. Because the first distillation column can be operated at a relatively high pressure, high pressure NG can be supplied without using multiple stages of compressors.
When raw material LNG containing many C3 or higher hydrocarbons is introduced to a first distillation column having a reboiler that does not use a natural gas or electric heat source, the methane-rich gas component A is obtained at the head upon distillation, but the liquid component D stored in the bottom contains more methane. This is because the boiling point of the raw material LNG is increased by containing C3 or higher hydrocarbons.
The liquid component D containing methane is introduced to the second distillation column and distilled. The methane in the liquid component D is drawn from the head of the second distillation column as the methane-rice gas component E, and the components such as ethane in the liquid component D are drawn from the bottom of the second distillation column as the liquid component H and delivered as natural gas liquid.
Thus, with this aspect of the present invention, the liquid component containing methane stored in the bottom of the first distillation column can be further distilled to obtain a methane-rich gas component and natural gas liquid. Therefore, even in the case that the raw material LNG contains many C3 or higher hydrocarbons, natural gas can be supplied while maintaining the recovery rate of NGL without connecting a heat source to the reboiler.
According to this aspect of the present invention, the operating pressure of the first distillation column can be increased when delivering natural gas at a high pressure. Increasing the operating pressure of the first distillation column increases the methane component contained in the liquid component D stored in the bottom of the first distillation column. The liquid component D containing methane, however, can be further distilled in the second distillation column to obtain a methane-rich gas component and natural gas liquid, which also maintains the recovery rate of NGL. Because the operating pressure of the first distillation column is high, the pressure of the methane-rich gas component A obtained from the head of the first distillation column is also high. Therefore, natural gas can be delivered at a high pressure even without multiple stages of compressors for compressing the gas component A.
With the natural gas production equipment according to an aspect of the present invention:
· a second expansion turbine may be disposed after the first vaporiser in the raw material supply channel;
• at least some of the liquefied natural gas supplied from the first vaporiser may be introduced through the second expansion turbine to the first distillation column;
· a fourth heat exchanger and a second compressor may be disposed after the first compressor in the first natural gas delivery channel;
• the gas component B supplied from the first compressor may be delivered from the first natural gas delivery channel through the fourth heat exchanger and the second compressor as the natural gas; and
· in the second heat exchanger, some or all of the liquefied natural gas drawn from the first expansion turbine and the liquefied natural gas drawn from the second expansion turbine may be cooled and condensed by the cold of the liquefied natural gas drawn from the first heat exchanger to prepare the raw material.
According to this aspect of the present invention, the methane-rich gas component A can be further compressed by the second compressor to deliver the natural gas at an even higher pressure. The gas component A compressed by the first compressor is also cooled by the fourth heat exchanger to more effectively compress by the second compressor.
Varying the pressure required by the natural gas to be delivered may also be considered, in which case, delivery may be controlled so that natural gas drawn from the first compressor is delivered directly when the required pressure is low, and natural gas drawn from the second compressor is delivered when the required pressure is high. Thus, according to this aspect of the present invention, natural gas can be supplied at a wide range of pressures while maintaining the recovery rate of NGL, without connecting a heat source to the reboiler.
With the natural gas production equipment according to an aspect of the present invention:
• a branch bypass line may be disposed after the first compressor and before the fourth heat exchanger;
• a first shut-off valve may be disposed on the branch bypass line; and
• the first shut-off valve may be controlled on the basis of a pressure value measured by a first pressure gauge arranged on the first natural gas delivery channel.
According to this aspect of the present invention, in the case that the natural gas supply pressure fluctuates, if the natural gas supply pressure is lower than a predetermined pressure, the second compressor disposed down-route may be shut off and the first shut-off valve on the branch bypass line disposed after the first compressor of the first stage may be opened to boost the natural gas using only the first compressor. If the natural gas supply pressure is higher than the predetermined pressure, the second compressor disposed down-route may be operated and the first shut-off valve may be closed to further boost the natural gas by a compressor following the first compressor.
The natural gas supply pressure can be measured by the first pressure gauge arranged on the first natural gas delivery channel. Although only the first compressor is used on the basis of the measured pressure, using both the first compressor and the second compressor may be selected to optimise the power used by the compressors.
In the natural gas production equipment according to another aspect of the present invention, a first generator may be disposed connected to the second compressor.
If the pressure of the natural gas supplied from the first natural gas supply channel is lower than a predetermined pressure value, the second compressor is shut off as described earlier. In this case, power recovered by an expansion turbine connected to the second compressor can be recovered as electric energy by the first generator connected to the second compressor. This can assure function under optimum conditions corresponding to fluctuation in the natural gas supply pressure, and assure power generation according to the operation of only the second expansion turbine.
In the natural gas production equipment according to another aspect the present invention, a third expansion turbine may be arranged parallel to the second expansion turbine, and a second generator may be disposed connected to the third expansion turbine.
If the pressure of the natural gas supplied from the first natural gas supply channel is lower than a predetermined pressure value, the second compressor is shut off as described earlier. In this case, the second expansion turbine is also shut off, and the liquefied natural gas supplied from the first vaporiser is supplied to the third expansion turbine without supplying to the second expansion turbine. The third expansion turbine is not connected to a compressor, but is connected to the second generator. This can assure function under optimum conditions corresponding to fluctuation in the natural gas supply pressure, and assure power generation according to the operation of only the third expansion turbine.
In the method for producing natural gas according an aspect of the present invention, the temperature of the first reboiler may be 0°C to 30°C, and the temperature of the second reboiler may be 0°C to 30°C.
Thus, according to this aspect of the present invention, natural gas can be supplied at a wide range of pressures while maintaining the recovery rate of NGL, without connecting heat sources to the first reboiler and the second reboiler. The range of the temperature of the first reboiler and the second reboiler is preferably 0°C to 30°C, and more preferably 5°C to 10°C.
Within this temperature range, unheated seawater, for example, may be used in the reboilers, and there is no need to use steam or hot water obtained through heating by using electricity or burning natural gas. That is, there is no need for a heat source for heating such as by electricity or burning natural gas.
From the standpoint of heat exchanger operation, if the lower limit of the temperature of the first reboiler and the second reboiler is about 5°C, the heat exchangers can operate while restraining water turning to ice even if there is considerable fluctuation in the thermal load of the heat exchangers. If the upper limit of the temperature of the first reboiler and the second reboiler is about 10°C, seawater or industrial water having a seawater temperature or industrial water temperature of about 15°C can be used.
With the configuration of this aspect of the present invention, the liquid component D stored in the bottom of the first distillation column contains more methane due to the low temperature of the reboiler. The liquid component D containing methane is introduced to the second distillation column and distilled. The methane in the liquid component D is drawn from the head of the second distillation column as the methane-rice gas component E, and the components such as ethane in the liquid component D are drawn from the bottom of the second distillation column as the liquid component H and delivered as natural gas liquid.
Thus, with this aspect of the present invention, the liquid component containing methane stored in the bottom of the first distillation column can be further distilled to obtain the methane-rich gas component E and natural gas liquid. Therefore, natural gas can be supplied while maintaining the recovery rate of NGL, without connecting a heat source to the reboiler.
With the method for supplying natural gas according to this aspect of the present invention, the temperature of the liquefied natural gas introduced to the third heat exchanger may be -180°C to -125°C when introduced to the third heat exchanger.
With this aspect of the present invention, by introducing some of the -180°C to
-125°C raw material LNG directly to the third heat exchanger, the methane-rich gas component E drawn from the head of the second distillation column is cooled and condensed, and delivered as natural gas after the pressure has been boosted by a pump. Because methane cools and condenses when the temperature is -180°C to - 125°C, methane gas can be recovered effectively from an upper portion of the second distillation column.
After being boosted by the compression means, the methane may be distilled by a warmer and delivered. According to this aspect of the present invention, the recovery rate of methane in raw material LNG can be increased even more because the methane component introduced to the second distillation column can be recovered and delivered as natural gas. BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a diagram showing a configuration example of the natural gas production equipment of Embodiment 1 ;
FIG. 2 is a diagram illustrating verification results in a configuration example of the natural gas production equipment of Embodiment 1 ;
FIG. 3 is a diagram showing a configuration example of the natural gas production equipment of Embodiment 2;
FIG. 4 is a diagram illustrating verification results in a configuration example of the natural gas production equipment of Embodiment 2;
FIG. 5 is a diagram showing another configuration example of the natural gas production equipment of Embodiment 2;
FIG. 6 is a diagram showing another configuration example of the natural gas production equipment of Embodiment 2; and
FIG. 7 is a diagram showing another configuration example of the natural gas production equipment of Embodiment 2.
Several embodiments of the present invention will be described hereinafter. The embodiments described hereinafter describe an example of the present invention. The present invention is not in any way limited to the following embodiments, and includes various modifications executed within a range that does not alter the essence of the present invention. The configurations described hereinafter are not necessarily all of the essential configurations of the present invention.
Natural gas production equipment according to the present invention
With the natural gas production equipment according to the present invention, liquefied natural gas (LNG) is introduced to a first distillation column as a raw material, methane-rich natural gas (NG) is prepared from a gas component drawn from the top of the first distillation column, a liquid component drawn from the bottom is introduced to a second distillation column, methane-rich natural gas (NG) is prepared from a gas component drawn from the top of the second distillation column, and natural gas liquid (NGL) is prepared from a liquid component drawn from the bottom.
The production equipment is provided with a raw material supply channel for introducing compressed liquefied natural gas in a supercooled state as a raw material through a raw material supply section, a first heat exchanger, a second heat exchanger, a first vaporiser, and a first expansion turbine, then through the second heat exchanger again to a first distillation column;
a first reboiler for heating a liquid component D in the bottom of the first distillation column;
a first natural gas delivery channel for diverting a methane-rich gas component A drawn from the head of the first distillation column, and delivering one gas component B as the natural gas through a first compressor connected to the first expansion turbine; a first reflux channel for introducing the other gas component C through the first heat exchanger to an upper portion of the first distillation column as a first reflux liquid;
a bottom supply channel for introducing the liquid component D drawn from the bottom of the first distillation column to a second distillation column;
a second reflux channel for diverting a methane-rich gas component E from the head of the second distillation column through a third heat exchanger after liquefying, and introducing one liquid component F to an upper portion of the second distillation column as a second reflux liquid; a second natural gas supply channel for supplying the other liquid component G through a compression means and a second vaporiser as the natural gas;
a second reboiler for heating a liquid component H in the bottom of the second distillation column; and
a natural gas liquid delivery channel for delivering the liquid component H drawn from the bottom of the second distillation column as the natural gas liquid.
In the first heat exchanger, the gas component C is condensed by at least some of the cold of the liquefied natural gas supplied from the raw material supply section to prepare the first reflux liquid;
in the second heat exchanger, some or all of the liquefied natural gas in a gaseous state drawn from the first expansion turbine may be cooled and condensed by the cold of the liquefied natural gas drawn from the first heat exchanger to prepare the raw material; and
in the third heat exchanger, the gas component E is cryocondensed by at least some of the cold of the liquefied natural gas supplied from the raw material supply section to prepare the second reflux liquid and the liquid component G. Embodiments of the present invention will be described hereinafter while referring to the appended drawings.
Embodiment 1
The natural gas production equipment of Embodiment 1 will be described with reference to FIG. 1 . With the natural gas production equipment 100 of Embodiment 1 :
Liquefied natural gas (LNG) is introduced from a raw material supply section 101 to a first distillation column 7 as a raw material, methane-rich natural gas (NG) is prepared from a gas component drawn from the top of the first distillation column 7, a liquid component drawn from the bottom is introduced to a second distillation column 9, methane-rich natural gas (NG) is prepared from a gas component drawn from the top of the second distillation column 9, and natural gas liquid (NGL) is prepared from a liquid component drawn from the bottom.
Some of the compressed LNG supplied from the raw material supply section 101 is vaporised in a cold release process comprising a first heat exchanger 1 , a second heat exchanger 2, a first vaporiser 3, and a first expansion turbine 4, and the vaporised LNG passes through the second heat exchanger 2 to form a gas-liquid mixture which is introduced to the first distillation column 7 as a raw material. In the second heat exchanger 2, the U-turned LNG is subjected to heat exchange in a counter-current with the LNG itself to use the cold of the LNG in the emission process to cool and condense the temporarily vaporised LNG itself. That is, the cold of the LNG is released during the flow of LNG in the raw material preparation process introduced in the distillation column, but some of the released cold is stored to reuse the cold more effectively.
Specifically, the natural gas production equipment is provided with a raw material supply channel 102 for introducing compressed LNG in a supercooled state as a raw material to the first distillation column 7 through the raw material supply section 101 , the first heat exchanger 1 , the second heat exchanger 2, the first vaporiser 3, and the first expansion turbine 4, then through the second heat exchanger 2 again. Low-temperature and high-pressure (for example, about -135°C and about 10 MPa) LNG is supplied from the raw material supply section 101 as a liquid, and the cold is successively released through the first heat exchanger 1 and the second heat exchanger 2 before the LNG is vaporised by the first vaporiser 3. The vaporised LNG is both vaporised and cooled to a low temperature by the first expansion turbine 4, then compressed to an predetermined optimum pressure for a raw material (for example, 3.2 MPa) to become low-temperature and low-pressure gaseous LNG. The gaseous LNG is cooled again by the second heat exchanger 2 to a predetermined optimum temperature for a raw material. This predetermined temperature refers to the temperature at which LNG of a predetermined composition condenses to form a gas-liquid state at an optimum pressure; for example, in the case of LNG having the composition illustrated below in Table 1 , the optimum temperature at about 3.2 MPa is about -80°C. The condensed LNG is introduced to the first distillation column 7.
The first distillation column 7 is provided with a first reboiler 201 for heating the liquid component D stored in the bottom of the first distillation column 7. The first reboiler 201 heats the liquid component D by heat exchange between the liquid component D and a heat transfer medium in the first reboiler 201 . The temperature of the first reboiler 201 may be any temperature that seawater or industrial water can maintain; specifically, a range of 0°C to 30°C. Therefore, specifically, unheated seawater may be used, and there is no need to dispose a heating means for heating the thermal transfer medium in the first reboiler 201 .
The liquid component D heated in the first reboiler 201 is reintroduced to the bottom of the first distillation column 7, and after distilling in the first distillation column 7, the methane-rich gas component A is introduced from the head of the first distillation column 7 and the liquid component D is drawn from the bottom of the first distillation column 7.
The methane-rich gas component A drawn from the head of the first distillation column 7 is diverted, and one gas component B separated from the gas component A is delivered as the natural gas through a first compressor 5 connected to the first expansion turbine 4.
Specifically, the gas component A drawn from the head of the first distillation column 7 is a low-temperature and low-pressure (for example, about -95°C and about 3.2 MPa) methane-rich NG. With the present embodiment, the gas component A can be subjected to heating and boosting treatments, without introducing additional energy, by adiabatic compression by the first compressor 5 connected to the first expansion turbine 4 used to prepare the raw material. The gas component A drawn from the first compressor 5 is supplied as NG as is, but may be heated by a warmer 6 arranged after the first compressor 5 to extract as a product NG having a predetermined temperature and pressure (for example, 15°C and about 10.6 MPa).
The other gas component C separated from the gas component A drawn from the head of the first distillation column 7 is cooled and condensed through the first heat exchanger 1 , and introduced to an upper portion of the first distillation column 7 as a first reflux liquid.
Specifically, a first reflux channel 104 is provided for introducing the other gas component C through the first heat exchanger 1 to an upper portion of the first distillation column 7 as a first reflux liquid. In the first heat exchanger 1 , the low- temperature and low-pressure gas component A (for example, about 95°C and about 3.2 MPa) is cooled and condensed by heat exchange with supercooled LNG before introducing to the first distillation column 7.
The liquid component D stored in the bottom of the first distillation column 7 is introduced from a bottom liquid supply channel 105 to the second distillation column 9. The liquid component D contains a predetermined quantity of methane. Therefore, distilling in the distillation column 9 obtains the methane-rich component E from the head of the second distillation column 9 and the liquid component H from the bottom of the second distillation column 9.
Because the second distillation column 9 is operated at a lower pressure than the first distillation column 7 (for example, 1 .8 MPa), a reboiler arranged in the bottom of the second distillation column 9 for superheating the liquid component H need not be a high temperature, and may be, for example, a temperature of 0°C to 30°C. Therefore, specifically, unheated seawater may be used, and there is no need to dispose a heating means for heating the thermal transfer medium in the first reboiler 201 .
The methane-rich gas component E drawn from the head of the second distillation column 9 is cooled by heat exchange with supercooled LNG in a third heat exchanger 8. The raw material LNG is diverted after the raw material supply section 101 , some is supplied to the third heat exchanger 8, and the remainder is supplied to the first heat exchanger 1 .
The gas component E subjected to heat exchange in the third heat exchanger 8 is cooled and condensed, for example, to -1 10°C, and the liquid component F comprising a portion separated from the gas component E is introduced from a second reflux channel 1 1 1 to an upper portion of the second distillation column 9 as a second reflux liquid.
The other liquid component G separated from the gas component E after detouring via the third heat exchanger 8 is boosted by a compression means 10 and vaporised and heated in the second vaporiser 1 1 to prepare a product NG having a predetermined temperature and pressure (for example, 15°C and about 10 MPa).
The liquid component H drawn from the bottom of the second distillation column 9 is a liquid containing many components such as ethane, and is delivered as natural gas liquid.
Thus, with the natural gas production equipment of the present embodiment, raw material LNG is distilled by a first distillation column 7 to obtain a methane-rich gas component A, and a liquid component D containing a methane component from the bottom of the first distillation column 7. The liquid component D containing a methane component can be further distilled in a second distillation column 9 to supply NG while maintaining the recovery rate of NGL.
According to the present embodiment, because the recovery rate of LNG can be maintained even if the liquid component D stored in the bottom of the first distillation column 7 contains a methane component, the first distillation column 7 can be operated at a high pressure and can therefore supply high pressure NG.
Because the first distillation column 7 can be operated at a low temperature, the present embodiment can provide natural gas production equipment having high energy efficiency without requiring that a heat source be connected to the reboiler.
The LNG supplied in the present equipment has a composition such as illustrated below in Table 1 , for example, has variable components depending on the place of origin, and differs in the temperature and pressure conditions for storing in a high pressure tank.
Specifically, the LNG is stored under a temperature condition of about -120°C to -160°C and a pressure condition of about 5-10 MPa. Besides what is conventionally called LNG, the LNG according to the present invention includes shale gas as described earlier, and unrefined LNG as well as refined LNG. TABLE 1
Figure imgf000019_0001
The first heat exchanger 1 , the second heat exchanger 2, and the third heat exchanger 8 are not specifically limited, and may be, for example, plate-fin heat exchangers or shell and tube heat exchangers.
The compression means 10 is not specifically limited, and may be, for example, a liquid delivery pump.
Embodiment 2
The LNG storage system of Embodiment 2 will be described referring to FIG.
3. Elements labelled with the same reference numerals as the natural gas production equipment 100 of Embodiment 1 have the same function and will not be described again.
With the natural gas production equipment 100 of Embodiment 2, a second expansion turbine 13 is disposed after the first vaporiser 3 in the raw material supply channel 102. The LNG vaporised in the first vaporiser 3 is diverted, some is introduced to the first expansion turbine 4, and the remainder is introduced to the second expansion turbine 13. The gaseous LNG depressurised by the first expansion turbine 4 and the gaseous LNG depressurised by the second expansion turbine 13 converge and are introduced to the second heat exchanger 2. The LNG is cooled by heat exchange in the second heat exchanger 2, and the condensed LNG is introduced to the first distillation column 7.
In a first natural gas delivery channel 103, a fourth heat exchanger 15 is disposed after the first compressor 5, and a second compressor 14 is disposed connected to the second expansion turbine 13. The gas component B supplied from the first compressor 5 is cooled in the fourth heat exchanger 15 by LNG supplied from the raw material supply section 101 . The LNG cooled in the fourth heat exchanger 15 becomes, for example, -54°C, and is introduced to the second compressor 14. Cooling in the fourth heat exchanger 15 contributes to improving compression efficiency in the second compressor 14. The gas component B boosted to a predetermined pressure (for example, 1 1 .2 MPa) in the second compressor 14 is delivered from the first natural gas delivery channel 103 as the product NG. Because the product NG is a predetermined temperature (for example, 15°C), the warmer 6 may be arranged after the second compressor 14 to heat the gas component B.
Another embodiment
As another embodiment, a branch bypass line 30 may be disposed after the first vaporiser 3 and a first shut-off valve 31 may be disposed on the branch bypass line 30 as shown in FIG. 5. The first shut-off valve 31 is controlled on the basis of a pressure value measured by a pressure gauge 32 arranged on the first natural gas delivery channel 103. Specifically, in the case that the natural gas supply pressure is low and the pressure measured by the pressure gauge 32 is lower than a predetermined value (for example, 6 MPa), the first shut-off valve 31 may be opened and the second compressor 14 stopped at the same time to increase the natural gas supply pressure, and in the case that the pressure measured by the pressure gauge 32 is a predetermined value (for example, 6 MPa) or greater, the first shut-off valve 31 may be closed and the second compressor 14 controlled to operate at the same time.
When the first shut-off valve 31 is opened to the branch bypass line 30 side, a valve (not shown) on the inlet side of the fourth heat exchanger 15 is controlled to close.
When the first shut-off valve 31 is closed to the branch bypass line 30 side, the valve (not shown) on the inlet side of the fourth heat exchanger 15 is controlled to open.
The predetermined value may be determined on the basis of the compression ratio of the first compressor 5 to the second compressor 14, the pressure of the natural gas before being introduced to the first compressor 5, and the pressure of the natural gas delivered from the natural gas delivery channel 103. For example, in the case that the pressure of the natural gas before being introduced to the first compressor 5 is 3 MPa and the compression ratio of the first compressor 5 is 2, the first compressor 5 can boost the natural gas to 6 MPa, and therefore, the predetermined value for the pressure measured by the pressure gauge 32 may be 6 MPa.
If the pressure measured by the pressure gauge 32 is less than the predetermined value of 6 MPa, the first shut-off valve is controlled to open, and if the measured pressure is 6 MPa or greater, the first shut-off valve is controlled to close.
In the case that the first shut-off valve 31 is opened, the second compressor 14 is stopped, and in the case that the first shut-off valve 31 is closed, the second compressor 14 is operated to compress the natural gas.
By controlling in this way, in the case that natural gas must be supplied at a pressure of 6 MPa or greater, the natural gas can be boosted to the required pressure by boosting by the first compressor 5 before compressing by the second compressor 14.
In the case that natural gas is to be supplied at a pressure less than 6 MPa, however, the equipment can be operated under optimum conditions by using only the first compressor 5 to boost pressure without using the second compressor 14.
Another embodiment
As still another embodiment, a first generator 33 may be disposed connected to the second compressor 14 as shown in FIG. 6.
The second expansion turbine 13 connected to the second compressor 14 operates even in the case that the natural gas supply pressure is low and the second compressor 14 has been stopped.
Therefore, the first generator 33 connected to the second compressor 14 assures the power required for operating the second expansion turbine 13 in the case that the second compressor 14 has been stopped.
Another embodiment
As still another embodiment, a third expansion turbine 34 arranged parallel with the second expansion turbine 13 is disposed down-route from the first vaporiser 3 and a second generator 35 is disposed connected to the third expansion turbine 34 as shown in FIG. 7. The liquefied natural gas delivered from the first vaporiser 3 is switched to a new channel by a second shut-off valve 36 or a third shut-off valve to supply to the second expansion turbine 13 or the third expansion turbine 34.
More specifically, in the case that the natural gas supply pressure is low and the first shut-off valve 31 is opened and the second compressor 14 is stopped, the second shut-off valve 36 is closed and the third shut-off valve 37 is opened.
As a result, the natural gas delivered from the first vaporiser 3 is detoured via the third shut-off valve 37 to introduce to the third expansion turbine 34. The second generator 35 connected to the third expansion turbine 34 assures the power required to operate the third expansion turbine 34.
In the case that the natural gas supply pressure is high, however, and the first shut-off valve 31 is closed and the second compressor 14 is operating, the second shut-off valve 36 is opened and the third shut-off valve 37 is closed.
As a result, the natural gas delivered from the first vaporiser 3 is detoured via the second shut-off valve 36 to introduce to the second expansion turbine 13.
Therefore, by operating the third expansion turbine 34 even in the case that the natural gas supply pressure is low and the second compressor 14 is stopped, the second generator 35 connected to the third expansion turbine 34 can assure the power required to operate the third expansion turbine 34.
Example 1
The pressure (MPaA), temperature (°C), flow rate (kg/h), and composition (wt%) in each section were simulated to verify supply of LNG having the composition illustrated in Table 1 using the natural gas production equipment according to Embodiment 1 .
Results
When LNG (-135°C and 9.96 MPa) was supplied at 572 and 373 kg/h, the results illustrated below in Table 2 were obtained for the pressure (MPaA), temperature (°C), flow rate (kg/h), and composition (wt%) in sections A-R in FIG. 2.
The locations of the sections A-R in FIG. 2 are as follows.
A is located at the exit of the raw material supply section 101 .
B is located after the raw material supply section 101 and just in front of the inlet of the first heat exchanger 1 . C is located after the first heat exchanger 1 and before the second heat exchanger 2.
D is located after the raw material supply section 101 and before the third heat exchanger 8.
E is located after the third heat exchanger 8 and just in front of where the channel from the first heat exchanger 1 merges with the channel to the second heat exchanger 2.
F is located after the second heat exchanger 2 and before the first vaporiser 3.
G is located after the first vaporiser 3 and before the first expansion turbine 4. H is located at the exit after the first expansion turbine.
I is located in the raw material supply channel 102 just before where natural gas is introduced into the first distillation column 7.
J is located just in front of where the gas component B obtained from the head of the first distillation column 7 is introduced to the first compressor 5, and before the first compressor 5.
K is located after the first compressor 5 and before the warmer 6.
L is located on the first natural gas delivery channel 103 and after the warmer 6.
M is located in the bottom liquid supply channel 105 extending from the bottom of the first distillation column 7 and at the exit portion of the bottom of the first distillation column 7.
N is located in the bottom liquid supply channel 105 and just before where liquid is introduced to the second distillation column 9.
O is located after the third heat exchanger 8 and before the compression means 10.
P is located after the compression means 10 and before the second vaporiser 1 1 .
Q is located after the second vaporiser 1 1 and just in front of where the channel merges with the first natural gas delivery channel 103.
R is located in the natural gas liquid delivery channel 1 13 and after the second distillation column 9. TABLE 2
Figure imgf000024_0001
Comparative Example 1
Next, the correlation of the recovery rate with the NG supply pressure was verified for the Example 1 and Comparative Example 1 (a natural gas supply apparatus without a second distillation column). In Comparative Example 1 , a conventional natural gas supply apparatus without a second distillation column was used in which methane- rich NG is delivered from the head of the first distillation column and natural gas liquid is delivered from the bottom of the first distillation column. Table 3 shows a comparison between Example 1 and Comparative Example 1 .
The reboiler temperatures in Example 1 and Comparative Example 1 were verified when raw material LNG having the same temperature and pressure was used, and the methane recovery rate, the ethane recovery rate, and the propane recovery rate were all 99.9% or higher.
In Example 1 , an NG supply pressure of 10.57 MPa could be obtained using unheated seawater (temperature: 10°C) in the first reboiler and the second reboiler.
In Comparative Example 1 , by contrast, a temperature of 45°C was required in the first reboiler and the second reboiler to obtain a comparable NG supply pressure (10.46 MPa). Therefore, steam had to be used in the first reboiler and the second reboiler.
Where no additional heat source was required in Example 1 , an additional heat source was required in Comparative Example 1 to use steam in the reboilers. TABLE 3
Figure imgf000025_0001
Example 2
The pressure (MPaA), temperature (°C), flow rate (kg/h), and composition (wt%) in each section were simulated to verify supply of LNG having the composition illustrated in Table 1 using the natural gas production equipment according to Embodiment 2.
Results
When LNG (-135°C and 9.96 MPa) was supplied at 572 and 373kg/h, the results illustrated below in Table 4 were obtained for the pressure (MPaA), temperature (°C), flow rate (kg/h), and composition (wt%) in sections A-R and D2- K2 in FIG. 4.
The locations of the sections A-R in FIG. 4 are the same as the locations of the sections A-R in FIG. 2. The locations of the sections D2-K2 in FIG. 4 are as follows.
D2 is located after the raw material supply section 101 and just in front of the inlet to the fourth heat exchanger 15.
E2 is located at the exit of the fourth heat exchanger 15.
G1 is located just after a branch intersection after branching following the first vaporiser 3, and before the first expansion turbine 4. G2 is located just after a branch intersection after branching following the first vaporiser 3, and before the second expansion turbine 13.
H1 is located at the exit portion of the first expansion turbine 4.
H2 is located after branching following the first vaporiser 3, and at the inlet portion of the second expansion turbine 13.
K1 is located after the fourth heat exchanger 15 and before the second compressor 14.
K2 is located after the second compressor 14 and before the warmer 6.
TABLE 4
Pressure Temperatu Mass flow Methane Ethane Propane i-Butane n-Butane Nitrogen
: MPaA deg.C kg/h wt % wt % wt % wt % wt % wt %
A 9.96 -135.0 572,373 89.50 5.00 3.00 1.00 1.00 0.50
B 9.96 -135.0 349,685 89.50 5.00 3.00 1.00 1.00 0.50
C 9.86 -99.5 349,685 89.50 5.00 3.00 1.00 1.00 0.50
D 9.96 -135.0 142,688 89.50 5.00 3.00 1.00 1.00 0.50
E 9.86 -109.1 142,688 89.50 5.00 3.00 1.00 1.00 0.50
F 9.76 -49.5 572,373 89.50 5.00 3.00 1.00 1.00 0.50
G 9.66 16.0 572,373 89.50 5.00 3.00 1.00 1.00 0.50
H 3.24 -40.9 572,373 89.50 5.00 3.00 1.00 1.00 0.50
I 3.19 -83.1 572,373 89.50 5.00 3.00 1.00 1.00 0.50
J 3.19 -94.6 442,741 99.44 0.00 0.00 0.00 0.00 0.56
K 10.01 -25.7 442,741 99.44 0.00 0.00 0.00 0.00 0.56
L 11.10 15.0 442,741 99.44 0.00 0.00 0.00 0.00 0.56
M 3.20 10.9 129,632 11.00 44.50 26.70 8.90 8.90 0.00
N 1.85 -2.5 129,632 11.00 44.50 26.70 8.90 8.90 0.00
0 1.75 -110.6 5,413 98.93 1.07 0.00 0.00 0.00 0.00
P 10.01 -100.1 5,413 98.93 1.07 0.00 0.00 0.00 0.00
Q 9.96 15.0 5,413 98.93 1.07 0.00 0.00 0.00 0.00
R 1.86 11.7 124,197 1.70 49.07 29.54 9.85 9.85 0.00
D2 9.96 -135.0 80,000 89.50 5.00 3.00 1.00 1.00 0.50
E2 9.76 -50.3 80,000 89.50 5.00 3.00 1.00 1.00 0.50
Gl 9.66 16.0 367,861 89.50 5.00 3.00 1.00 1.00 0.50
G2 9.66 16.0 204,512 89.50 5.00 3.00 1.00 1.00 0.50
HI 3.24 -40.9 367,861 89.50 5.00 3.00 1.00 1.00 0.50
H2 3.24 -40.9 204,512 89.50 5.00 3.00 1.00 1.00 0.50
Kl 7.35 -54.2 442,741 99.44 0.00 0.00 0.00 0.00 0.56
K2 11.15 -30.2 442,741 99.44 0.00 0.00 0.00 0.00 0.56 KEY TO REFERENCE NUMERALS
1 First heat exchanger
2 Second heat exchanger
3 First vaporiser
4 First expansion turbine
5 First compressor
6 Warmer
7 First distillation column
8 Third heat exchanger
9 Second distillation column
10 Compression means
1 1 Second vaporiser
13 Second expansion turbine
14 Second compressor
30 Branch bypass line
31 First shut-off valve
32 Pressure gauge
33 First generator
34 Third expansion turbine
35 Second generator
100 Natural gas production equipment
101 Raw material supply section
102 Raw material supply channel 103 First natural gas delivery channel
104 First reflux channel
105 Bottom liquid supply channel
1 1 1 Second reflux channel
1 12Second natural gas supply channel
1 13Natural gas liquid delivery channel

Claims

1 . Equipment for extracting natural gas liquid from liquefied natural gas and supplying natural gas, provided with:
• a raw material supply channel for introducing compressed liquefied natural gas in a supercooled state as a raw material through a raw material supply section, a first heat exchanger, a second heat exchanger, a first vaporiser, and a first expansion turbine, then through the second heat exchanger again to a first distillation column;
• a first reboiler for heating a liquid component D in the bottom of the first distillation column;
• a first natural gas delivery channel for diverting a methane-rich gas component A drawn from the head of the first distillation column, and delivering one gas component B separated from the gas component A as the natural gas through a first compressor connected to the first expansion turbine;
• a first reflux channel for introducing the other gas component C separated from the gas component A through the first heat exchanger to an upper portion of the first distillation column as a first reflux liquid;
· a bottom supply channel for introducing the liquid component D drawn from the bottom of the first distillation column to a second distillation column;
• a second reflux channel for diverting a methane-rich gas component E drawn from the head of the second distillation column through a third heat exchanger after liquefying, and introducing one liquid component F separated from the gas component E to an upper portion of the second distillation column as a second reflux liquid;
• a second natural gas supply channel for supplying the other liquid component G separated from the gas component E through a compression means and a second vaporiser as the natural gas;
· a second reboiler for heating a liquid component H in the bottom of the second distillation column; and
• a natural gas liquid delivery channel for delivering the liquid component H drawn from the bottom of the second distillation column as the natural gas liquid; • in the first heat exchanger, the gas component C is condensed by at least some of the cold of the liquefied natural gas supplied from the raw material supply section to prepare the first reflux liquid;
• in the second heat exchanger, some or all of the liquefied natural gas in a gaseous state drawn from the first expansion turbine is cooled and condensed by the cold of the liquefied natural gas drawn from the first heat exchanger to prepare the raw material to be introduced to the first distillation column; and
• in the third heat exchanger, the gas component E is cryocondensed by at least some of the cold of the liquefied natural gas supplied from the raw material supply section to prepare the second reflux liquid and the liquid component G.
2. Natural gas production equipment according to Claim 1 , characterized in that a second expansion turbine is disposed after the first vaporiser in the raw material supply channel;
· at least some of the liquefied natural gas supplied from the first vaporiser is introduced through the second expansion turbine to the first distillation column;
• a fourth heat exchanger and a second compressor connected to the second expansion turbine are disposed after the first compressor in the first natural gas delivery channel;
· the gas component B supplied from the first compressor is delivered from the first natural gas delivery channel through the fourth heat exchanger and the second compressor as the natural gas; and
• in the second heat exchanger, some or all of the liquefied natural gas drawn from the first expansion turbine and the liquefied natural gas drawn from the second expansion turbine are cooled and condensed by the cold of the liquefied natural gas drawn from the first heat exchanger to prepare the raw material.
3. Natural gas production equipment according to Claim 2, characterized in that a branch bypass line is disposed after the first compressor and before the fourth heat exchanger;
• a first shut-off valve is disposed on the branch bypass line; and • the first shut-off valve is controlled on the basis of a pressure value measured by a first pressure gauge arranged on the first natural gas delivery channel. 4. Natural gas production equipment according to Claim 3, characterized in that a first generator is disposed connected to the second compressor.
5. Natural gas production equipment according to Claim 3, characterized in that a third expansion turbine is disposed parallel to the second expansion turbine, and a second generator is disposed connected to the third expansion turbine.
6. Method for producing natural gas liquid, being a method for extracting natural gas liquid from liquefied natural gas to produce natural gas, comprising the processes of:
(1 ) introducing at least some of the liquefied natural gas supplied from a raw material supply section to a first distillation column after expelling some of the cold of the liquefied natural gas;
(2) introducing a methane-rich gas component A from the head of the first distillation column;
(3) diverting the gas component A and boosting one gas component B separated from the gas component A before delivering as the natural gas;
(4) cooling the other gas component C separated from the gas component A before introducing to an upper portion of the first distillation column as a first reflux liquid;
(5) heating a liquid component D stored in the bottom of the first distillation column through a first reboiler;
(6) introducing at least some of a liquid component D drawn from the bottom of the first distillation column to a second distillation column;
(7) cooling a methane-rich gas component E drawn from the head of the second distillation column and diverting after liquefying, and introducing one liquid component F separated from the gas component E to an upper portion of the second distillation column as a second reflux liquid;
(8) boosting the pressure of the other liquid component G separated from the gas component E and vaporising before supplying as the natural gas;
(9) heating a liquid component H stored in the bottom of the second distillation column through a second reboiler; and
(10) delivering the liquid component H drawn from the bottom of the second distillation column as the natural gas liquid.
7. Natural gas production equipment according to Claim 3, wherein at least some of the liquefied natural gas supplied from the raw material supply section is introduced through a first heat exchanger, a second heat exchanger, a first vaporiser, and a first expansion turbine to a first distillation column as a raw material;
♦ in the first heat exchanger, the gas component C is condensed by at least some of the cold of the liquefied natural gas supplied from the raw material supply section to prepare a first reflux liquid to be introduced to an upper portion of the first distillation column;
• in the second heat exchanger, some or all of the liquefied natural gas in a gaseous state drawn from the first expansion turbine may be cooled and condensed by the cold of the liquefied natural gas drawn from the first heat exchanger to prepare the raw material;
• a methane-rich gas component E drawn from the head of the second distillation column is liquefied through a third heat exchanger; and
· in the third heat exchanger, the gas component E is cryocondensed by at least some of the cold of the liquefied natural gas supplied from the raw material supply section to prepare the second reflux liquid and the liquid component G.
8. Natural gas production method according to Claim 3 or Claim 4, wherein the temperature of the first reboiler is 0°C to 30°C, and the temperature of the second reboiler is 0°C to 30°C.
9. Natural gas production method according to any one of Claims 3 to 5, characterized in that the temperature of the liquefied natural gas introduced to the third heat exchanger is -180°C to -125°C when introduced to the third heat exchanger.
PCT/EP2018/076202 2017-09-29 2018-09-27 Natural gas production equipment and natural gas production method WO2019063658A1 (en)

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