AU2015385052B2 - Natural gas liquefaction system and method - Google Patents

Natural gas liquefaction system and method Download PDF

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Publication number
AU2015385052B2
AU2015385052B2 AU2015385052A AU2015385052A AU2015385052B2 AU 2015385052 B2 AU2015385052 B2 AU 2015385052B2 AU 2015385052 A AU2015385052 A AU 2015385052A AU 2015385052 A AU2015385052 A AU 2015385052A AU 2015385052 B2 AU2015385052 B2 AU 2015385052B2
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gas
raw material
material gas
refrigerant
cooling
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AU2015385052A1 (en
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Yasuhiro Inoue
Masanori KAMETA
Toshiya MOMOSE
Yoshihiro Yamaguchi
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Chiyoda Corp
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Chiyoda Corp
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    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F25—REFRIGERATION OR COOLING; COMBINED HEATING AND REFRIGERATION SYSTEMS; HEAT PUMP SYSTEMS; MANUFACTURE OR STORAGE OF ICE; LIQUEFACTION SOLIDIFICATION OF GASES
    • F25J—LIQUEFACTION, SOLIDIFICATION OR SEPARATION OF GASES OR GASEOUS OR LIQUEFIED GASEOUS MIXTURES BY PRESSURE AND COLD TREATMENT OR BY BRINGING THEM INTO THE SUPERCRITICAL STATE
    • F25J1/00—Processes or apparatus for liquefying or solidifying gases or gaseous mixtures
    • F25J1/02—Processes or apparatus for liquefying or solidifying gases or gaseous mixtures requiring the use of refrigeration, e.g. of helium or hydrogen ; Details and kind of the refrigeration system used; Integration with other units or processes; Controlling aspects of the process
    • F25J1/0211—Processes or apparatus for liquefying or solidifying gases or gaseous mixtures requiring the use of refrigeration, e.g. of helium or hydrogen ; Details and kind of the refrigeration system used; Integration with other units or processes; Controlling aspects of the process using a multi-component refrigerant [MCR] fluid in a closed vapor compression cycle
    • F25J1/0214—Processes or apparatus for liquefying or solidifying gases or gaseous mixtures requiring the use of refrigeration, e.g. of helium or hydrogen ; Details and kind of the refrigeration system used; Integration with other units or processes; Controlling aspects of the process using a multi-component refrigerant [MCR] fluid in a closed vapor compression cycle as a dual level refrigeration cascade with at least one MCR cycle
    • F25J1/0215—Processes or apparatus for liquefying or solidifying gases or gaseous mixtures requiring the use of refrigeration, e.g. of helium or hydrogen ; Details and kind of the refrigeration system used; Integration with other units or processes; Controlling aspects of the process using a multi-component refrigerant [MCR] fluid in a closed vapor compression cycle as a dual level refrigeration cascade with at least one MCR cycle with one SCR cycle
    • F25J1/0216—Processes or apparatus for liquefying or solidifying gases or gaseous mixtures requiring the use of refrigeration, e.g. of helium or hydrogen ; Details and kind of the refrigeration system used; Integration with other units or processes; Controlling aspects of the process using a multi-component refrigerant [MCR] fluid in a closed vapor compression cycle as a dual level refrigeration cascade with at least one MCR cycle with one SCR cycle using a C3 pre-cooling cycle
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F25—REFRIGERATION OR COOLING; COMBINED HEATING AND REFRIGERATION SYSTEMS; HEAT PUMP SYSTEMS; MANUFACTURE OR STORAGE OF ICE; LIQUEFACTION SOLIDIFICATION OF GASES
    • F25J—LIQUEFACTION, SOLIDIFICATION OR SEPARATION OF GASES OR GASEOUS OR LIQUEFIED GASEOUS MIXTURES BY PRESSURE AND COLD TREATMENT OR BY BRINGING THEM INTO THE SUPERCRITICAL STATE
    • F25J1/00—Processes or apparatus for liquefying or solidifying gases or gaseous mixtures
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01D—SEPARATION
    • B01D53/00—Separation of gases or vapours; Recovering vapours of volatile solvents from gases; Chemical or biological purification of waste gases, e.g. engine exhaust gases, smoke, fumes, flue gases, aerosols
    • B01D53/14—Separation of gases or vapours; Recovering vapours of volatile solvents from gases; Chemical or biological purification of waste gases, e.g. engine exhaust gases, smoke, fumes, flue gases, aerosols by absorption
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01D—SEPARATION
    • B01D53/00—Separation of gases or vapours; Recovering vapours of volatile solvents from gases; Chemical or biological purification of waste gases, e.g. engine exhaust gases, smoke, fumes, flue gases, aerosols
    • B01D53/14—Separation of gases or vapours; Recovering vapours of volatile solvents from gases; Chemical or biological purification of waste gases, e.g. engine exhaust gases, smoke, fumes, flue gases, aerosols by absorption
    • B01D53/1456—Removing acid components
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01D—SEPARATION
    • B01D53/00—Separation of gases or vapours; Recovering vapours of volatile solvents from gases; Chemical or biological purification of waste gases, e.g. engine exhaust gases, smoke, fumes, flue gases, aerosols
    • B01D53/26—Drying gases or vapours
    • B01D53/263—Drying gases or vapours by absorption
    • C—CHEMISTRY; METALLURGY
    • C10—PETROLEUM, GAS OR COKE INDUSTRIES; TECHNICAL GASES CONTAINING CARBON MONOXIDE; FUELS; LUBRICANTS; PEAT
    • C10L—FUELS NOT OTHERWISE PROVIDED FOR; NATURAL GAS; SYNTHETIC NATURAL GAS OBTAINED BY PROCESSES NOT COVERED BY SUBCLASSES C10G, C10K; LIQUEFIED PETROLEUM GAS; ADDING MATERIALS TO FUELS OR FIRES TO REDUCE SMOKE OR UNDESIRABLE DEPOSITS OR TO FACILITATE SOOT REMOVAL; FIRELIGHTERS
    • C10L3/00—Gaseous fuels; Natural gas; Synthetic natural gas obtained by processes not covered by subclass C10G, C10K; Liquefied petroleum gas
    • C10L3/06—Natural gas; Synthetic natural gas obtained by processes not covered by C10G, C10K3/02 or C10K3/04
    • C10L3/10—Working-up natural gas or synthetic natural gas
    • C10L3/101—Removal of contaminants
    • C10L3/102—Removal of contaminants of acid contaminants
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F25—REFRIGERATION OR COOLING; COMBINED HEATING AND REFRIGERATION SYSTEMS; HEAT PUMP SYSTEMS; MANUFACTURE OR STORAGE OF ICE; LIQUEFACTION SOLIDIFICATION OF GASES
    • F25J—LIQUEFACTION, SOLIDIFICATION OR SEPARATION OF GASES OR GASEOUS OR LIQUEFIED GASEOUS MIXTURES BY PRESSURE AND COLD TREATMENT OR BY BRINGING THEM INTO THE SUPERCRITICAL STATE
    • F25J1/00—Processes or apparatus for liquefying or solidifying gases or gaseous mixtures
    • F25J1/0002—Processes or apparatus for liquefying or solidifying gases or gaseous mixtures characterised by the fluid to be liquefied
    • F25J1/0022—Hydrocarbons, e.g. natural gas
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F25—REFRIGERATION OR COOLING; COMBINED HEATING AND REFRIGERATION SYSTEMS; HEAT PUMP SYSTEMS; MANUFACTURE OR STORAGE OF ICE; LIQUEFACTION SOLIDIFICATION OF GASES
    • F25J—LIQUEFACTION, SOLIDIFICATION OR SEPARATION OF GASES OR GASEOUS OR LIQUEFIED GASEOUS MIXTURES BY PRESSURE AND COLD TREATMENT OR BY BRINGING THEM INTO THE SUPERCRITICAL STATE
    • F25J1/00—Processes or apparatus for liquefying or solidifying gases or gaseous mixtures
    • F25J1/003—Processes or apparatus for liquefying or solidifying gases or gaseous mixtures characterised by the kind of cold generation within the liquefaction unit for compensating heat leaks and liquid production
    • F25J1/0047—Processes or apparatus for liquefying or solidifying gases or gaseous mixtures characterised by the kind of cold generation within the liquefaction unit for compensating heat leaks and liquid production using an "external" refrigerant stream in a closed vapor compression cycle
    • F25J1/0052—Processes or apparatus for liquefying or solidifying gases or gaseous mixtures characterised by the kind of cold generation within the liquefaction unit for compensating heat leaks and liquid production using an "external" refrigerant stream in a closed vapor compression cycle by vaporising a liquid refrigerant stream
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F25—REFRIGERATION OR COOLING; COMBINED HEATING AND REFRIGERATION SYSTEMS; HEAT PUMP SYSTEMS; MANUFACTURE OR STORAGE OF ICE; LIQUEFACTION SOLIDIFICATION OF GASES
    • F25J—LIQUEFACTION, SOLIDIFICATION OR SEPARATION OF GASES OR GASEOUS OR LIQUEFIED GASEOUS MIXTURES BY PRESSURE AND COLD TREATMENT OR BY BRINGING THEM INTO THE SUPERCRITICAL STATE
    • F25J1/00—Processes or apparatus for liquefying or solidifying gases or gaseous mixtures
    • F25J1/006—Processes or apparatus for liquefying or solidifying gases or gaseous mixtures characterised by the refrigerant fluid used
    • F25J1/008—Hydrocarbons
    • F25J1/0087—Propane; Propylene
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F25—REFRIGERATION OR COOLING; COMBINED HEATING AND REFRIGERATION SYSTEMS; HEAT PUMP SYSTEMS; MANUFACTURE OR STORAGE OF ICE; LIQUEFACTION SOLIDIFICATION OF GASES
    • F25J—LIQUEFACTION, SOLIDIFICATION OR SEPARATION OF GASES OR GASEOUS OR LIQUEFIED GASEOUS MIXTURES BY PRESSURE AND COLD TREATMENT OR BY BRINGING THEM INTO THE SUPERCRITICAL STATE
    • F25J1/00—Processes or apparatus for liquefying or solidifying gases or gaseous mixtures
    • F25J1/02—Processes or apparatus for liquefying or solidifying gases or gaseous mixtures requiring the use of refrigeration, e.g. of helium or hydrogen ; Details and kind of the refrigeration system used; Integration with other units or processes; Controlling aspects of the process
    • F25J1/0243—Start-up or control of the process; Details of the apparatus used; Details of the refrigerant compression system used
    • F25J1/0279—Compression of refrigerant or internal recycle fluid, e.g. kind of compressor, accumulator, suction drum etc.
    • F25J1/0296—Removal of the heat of compression, e.g. within an inter- or afterstage-cooler against an ambient heat sink
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01D—SEPARATION
    • B01D2256/00—Main component in the product gas stream after treatment
    • B01D2256/24—Hydrocarbons
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01D—SEPARATION
    • B01D2257/00—Components to be removed
    • B01D2257/70—Organic compounds not provided for in groups B01D2257/00 - B01D2257/602
    • B01D2257/702—Hydrocarbons
    • B01D2257/7022—Aliphatic hydrocarbons
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01D—SEPARATION
    • B01D2257/00—Components to be removed
    • B01D2257/70—Organic compounds not provided for in groups B01D2257/00 - B01D2257/602
    • B01D2257/702—Hydrocarbons
    • B01D2257/7027—Aromatic hydrocarbons
    • C—CHEMISTRY; METALLURGY
    • C10—PETROLEUM, GAS OR COKE INDUSTRIES; TECHNICAL GASES CONTAINING CARBON MONOXIDE; FUELS; LUBRICANTS; PEAT
    • C10L—FUELS NOT OTHERWISE PROVIDED FOR; NATURAL GAS; SYNTHETIC NATURAL GAS OBTAINED BY PROCESSES NOT COVERED BY SUBCLASSES C10G, C10K; LIQUEFIED PETROLEUM GAS; ADDING MATERIALS TO FUELS OR FIRES TO REDUCE SMOKE OR UNDESIRABLE DEPOSITS OR TO FACILITATE SOOT REMOVAL; FIRELIGHTERS
    • C10L2290/00—Fuel preparation or upgrading, processes or apparatus therefore, comprising specific process steps or apparatus units
    • C10L2290/06—Heat exchange, direct or indirect
    • C—CHEMISTRY; METALLURGY
    • C10—PETROLEUM, GAS OR COKE INDUSTRIES; TECHNICAL GASES CONTAINING CARBON MONOXIDE; FUELS; LUBRICANTS; PEAT
    • C10L—FUELS NOT OTHERWISE PROVIDED FOR; NATURAL GAS; SYNTHETIC NATURAL GAS OBTAINED BY PROCESSES NOT COVERED BY SUBCLASSES C10G, C10K; LIQUEFIED PETROLEUM GAS; ADDING MATERIALS TO FUELS OR FIRES TO REDUCE SMOKE OR UNDESIRABLE DEPOSITS OR TO FACILITATE SOOT REMOVAL; FIRELIGHTERS
    • C10L2290/00—Fuel preparation or upgrading, processes or apparatus therefore, comprising specific process steps or apparatus units
    • C10L2290/44—Deacidification step, e.g. in coal enhancing
    • 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
    • F25J2220/00—Processes or apparatus involving steps for the removal of impurities
    • F25J2220/60—Separating impurities from natural gas, e.g. mercury, cyclic hydrocarbons
    • F25J2220/64—Separating heavy hydrocarbons, e.g. NGL, LPG, C4+ hydrocarbons or heavy condensates in general
    • 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
    • F25J2220/00—Processes or apparatus involving steps for the removal of impurities
    • F25J2220/60—Separating impurities from natural gas, e.g. mercury, cyclic hydrocarbons
    • F25J2220/66—Separating acid gases, e.g. CO2, SO2, H2S or RSH
    • 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
    • F25J2220/00—Processes or apparatus involving steps for the removal of impurities
    • F25J2220/60—Separating impurities from natural gas, e.g. mercury, cyclic hydrocarbons
    • F25J2220/68—Separating water or hydrates
    • 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
    • F25J2240/40—Expansion without extracting work, i.e. isenthalpic throttling, e.g. JT valve, regulating valve or venturi, or isentropic nozzle, e.g. Laval

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  • Engineering & Computer Science (AREA)
  • Chemical & Material Sciences (AREA)
  • Oil, Petroleum & Natural Gas (AREA)
  • Physics & Mathematics (AREA)
  • Mechanical Engineering (AREA)
  • Thermal Sciences (AREA)
  • General Engineering & Computer Science (AREA)
  • Chemical Kinetics & Catalysis (AREA)
  • General Chemical & Material Sciences (AREA)
  • Analytical Chemistry (AREA)
  • Organic Chemistry (AREA)
  • Separation By Low-Temperature Treatments (AREA)

Abstract

[Problem] To raise the temperature of a reduced-pressure source gas during removal of acidic gas components in a system for liquefying natural gas, without needing to add outside energy. [Solution] Provided is a system 1 for liquefying natural gas, configured to be provided with: a pressure reduction device 2 for lowering the pressure of a source gas; a first heat exchanger 14 for heating the reduced-pressure source gas by heat exchange with a refrigerant; an acidic gas removal device 3 for removing acidic gas components from the heated source gas; a second heat exchanger 16 to which the refrigerant used in the first heat exchanger 14 is supplied, the second heat exchanger 16 cooling the source gas, from which acidic gas components have been removed by the acidic gas removal device 3, through heat exchange with the refrigerant; and a liquefaction device 6 for cooling the cooled source gas, thereby producing liquefied natural gas.

Description

The present invention relates to a natural gas liquefaction system and method for producing liquefied natural gas by cooling a raw material gas including natural gas.
BACKGROUND ART [0002]
Natural gas obtained from gas fields is liquefied in a liquefaction plant so that the gas may be stored and transported in liquid form; that is, as an LNG (liquefied natural gas). Cooled to around -162 degrees Celsius, liquefied natural gas advantageously has a significantly reduced volume as compared to gaseous natural gas, and is not required to be stored under a high pressure. Generally, a natural gas liquefaction process involves removing impurities such as moisture, acid gas components and mercury contained in a raw material gas in advance as necessary, and further involves, after removing heavy components (cyclohexane, benzene, toluene, xylene or the like) having a relatively high freezing point, liquefying the raw material gas by heat exchange with a refrigerant.
[0003]
In order to remove acid gas components from natural gas, a known natural gas liquefaction system includes, for example, an absorption tower for absorbing acid gases including carbon dioxide contained in a raw natural gas by bringing an acid-gas absorbing liquid (e.g., aminic solution) into contact with the raw natural gas, and a regeneration tower for separating the acid gases contained in the absorbing liquid. See W02009/093315A1 (Patent
Document 1).
-2 2015385052 14 Sep 2018
SUMMARY OF THE INVENTION
TASK TO BE ACCOMPFISHED BY THE INVENTION [0004]
Generally, heavy components contained in the natural gas are removed by separating liquefied heavy components from the natural gas in a distillation tower. In this connection, when natural gas to be liquefied has a relatively high pressure (e.g. over 80barA), it is necessary to reduce the pressure of the natural gas to a prescribed level since the separation of heavy components from methane becomes difficult under such a high pressure.
[0005]
However, when the natural gas is reduced in pressure, the temperature of the natural gas can be lowered below a temperature range suitable for the removal of acid gas components (e.g. 35 to 40 degrees Celsius). In particular, in cases where natural gas having a high pressure (e.g. more than lOObarA) undergoes pressure reduction, this excessive reduction of gas temperature tends to occur significantly more frequently.
[0006]
One possible solution to this problem is to heat the natural gas by heat exchange or by using heater to a temperature suitable for the removal of acid gas components at a location on the downstream side at which the temperature becomes relatively high (for example, before the removal of acid gases and before or after the removal of moisture). However, when the natural gas is heated by heat exchange before the removal of moisture, the heat exchange can lead to the generation of hydrates, which can cause the clogging of piping or the like, due to the presence of moisture in the natural gas. When the natural gas is heated at a further downstream location (after the removal of moisture), the natural gas at the location does not always have a temperature and/or a flow rate required for the temperature rise. When a heater is used, relatively large energy becomes necessary.
-3 2015385052 14 Sep 2018 [0007]
The present invention has been made in view of such problems of the prior art.
Certain objects and advantages of the present invention will become apparent from the following description, taken in connection with the accompanying drawings, wherein, by way of illustration and example, an embodiment of the present invention is disclosed.
MEANS TO ACCOMPLISH THE TASK [0008]
A first aspect provides a natural gas liquefaction system for producing liquefied natural gas by cooling a raw material gas including natural gas, the system comprising: a pressure reduction unit for reducing a pressure of the raw material gas, a first heat exchanger for heating, by heat exchange with a refrigerant, the raw material gas which has been reduced in pressure in the pressure reduction unit, an acid gas removal unit for removing an acid gas component from the raw material gas which has been heated in the first heat exchanger, a second heat exchanger for cooling the raw material gas from which the acid gas component has been removed in the acid gas removal unit, the raw material gas being cooled by heat exchange with the refrigerant which has been lowered in temperature in the first heat exchanger, and a liquefying unit for further cooling the raw material gas which has been cooled by the second heat exchanger to produce liquefied natural gas.
[0009]
In the natural gas liquefaction system according to the first aspect, since the raw material gas which has been lowered in temperature by the pressure reduction in the pressure reduction apparatus is heated by heat exchange with the refrigerant in the first heat exchanger, the system allows the temperature of the raw material gas to be increased with no (or minimized) additional energy supplied from outside so that the acid gas component can be
2015385052 14 Sep 2018
-4 removed from the raw material gas after the pressure reduction of the raw material gas.
Moreover, since the cold heat of the natural gas created by the pressure reduction is used for cooling the refrigerant, there is also an advantage that the energy efficiency in the refrigerant cycle can be enhanced.
[0010]
According to a second aspect, the natural gas liquefaction system further comprises a heating unit for heating the raw material gas which is supplied from the first heat exchanger to the acid gas removal unit.
[0011]
In the natural gas liquefaction system according to the second aspect, even when the raw material gas is not sufficiently heated by the first heat exchanger, the system can adjust the temperature of the raw material gas to be supplied to the acid gas removal apparatus within a suitable temperature range.
[0012]
According to a third aspect, the natural gas liquefaction system further comprises a heavy component removal unit provided between the acid gas removal unit and the second heat exchanger for removing a heavy hydrocarbon in the raw material gas.
[0013]
In the natural gas liquefaction system according to the third aspect, the system can remove the heavy hydrocarbons (heavy components) of the raw material gas to be supplied to the second heat exchanger, thereby avoiding troubles such as coagulation of heavy hydrocarbons in the second heat exchanger.
[0014]
According to a fourth aspect, the first and second heat exchangers constitute a pre-cooling refrigerant cycle for pre-cooling the raw material gas to be supplied to the
2015385052 14 Sep 2018
-5 liquefying unit, and wherein the natural gas liquefaction system further comprises: a compressor for compressing the refrigerant which has been used in the second heat exchanger, and an expansion valve provided between the first and second heat exchangers in the refrigerant cycle for throttling and expanding the refrigerant.
[0015]
In the natural gas liquefaction system according to the fourth aspect, since the cooled refrigerant which has been cooled by heat exchange with the raw material gas in the first heat exchanger is further cooled in the expansion valve and supplied to the second heat exchanger as a further cooled refrigerant, the system allows the load on the compressor in the refrigerant cycle to be reduced with a simple configuration.
[0016]
A fifth aspect provides a natural gas liquefaction method for producing liquefied natural gas by cooling a raw material gas including natural gas, the method comprising: a pressure-reducing step for reducing a pressure of the raw material gas, a first heat-exchanging step for heating, by heat exchange with a refrigerant, the raw material gas which has been reduced in pressure in the pressure-reducing step, an acid-gas-removal step for removing an acid gas component from the raw material gas which has been heated in the first heat exchanger, a second heat-exchanging step for cooling the raw material gas from which the acid gas component has been removed in the acid gas removal step, the raw material gas being cooled by heat exchange with the refrigerant which has been lowered in temperature in the first heat-exchanging step, and a liquefying step for further cooling the raw material gas which has been cooled by the second heat-exchanging step to produce liquefied natural gas.
EFFECT OF THE INVENTION [0017]
Advantageously, the natural gas liquefaction system disclosed herein allows the
2015385052 14 Sep 2018
-6temperature of the raw material gas to be increased with no (or minimized) additional energy supplied from outside so that the acid gas component can be removed from the raw material gas after the pressure reduction thereof.
BRIEF DESCRIPTION OF THE DRAWINGS [0018]
Figure 1 is a schematic diagram of a natural gas liquefaction system in accordance with an embodiment of the present invention.
DESCRIPTION OF THE PREFERRED EMBODIMENT(S) [0019]
Embodiments of the present invention are described in the following with reference to the appended drawings.
[0020]
Figure 1 is a schematic diagram of a natural gas liquefaction system 1 in accordance with an embodiment of the present invention. The liquefaction system 1 produces an LNG (liquefied natural gas) by cooling a raw material gas containing natural gas. The liquefaction system 1 includes a pressure reduction apparatus 2 for reducing a pressure of the raw material gas to a prescribed pressure, an acid gas removal apparatus 3 for removing an acid gas component(s) contained in the raw material gas, a moisture removal apparatus 4 for removing moisture contained in the raw material gas, a heavy component removal apparatus 5 for removing heavy components (e.g. benzene, toluene, xylene, heavier hydrocarbons such as C5+ hydrocarbons or hydrocarbons larger than pentane) in the raw material gas, and a liquefying apparatus 6 for producing the LNG by cooling the raw material gas by heat exchange with a refrigerant (hereinafter referred to as liquefying refrigerant or mixed refrigerant).
[0021]
The liquefaction system 1 also includes a pre-cooling system 7 for pre-cooling, by
2015385052 14 Sep 2018
-7 heat exchange with the refrigerant (hereinafter referred to as pre-cooling refrigerant), the raw material supplied to the liquefying apparatus 6. The acid gas removal apparatus 3 includes a heater 8 (heating device) provided to maintain the temperature of the supplied material gas within an appropriate temperature range by heating the raw material gas at a location upstream of the acid gas removal apparatus 3. As used herein, the term raw material gas refers to a processing target material flowing in the liquefaction system 1 (including the material in a partially liquefied state in the process), and does not strictly mean the material in a gaseous state.
[0022]
The raw material gas to be processed in the liquefaction system 1 includes, but not limited to, natural gas extracted from known gas fields. Note that the raw material gas to be processed in the present invention is a raw gas having a relatively high pressure (a pressure of at least 80 barA, more preferably 100 barA or more). Since such a raw material gas has a high pressure upon extraction as well as a low pressure drop in the process from the extraction to the feed to the liquefaction system 1, and is pressurized upon extraction (for example, a gas separated from crude oil in an FPSO (Floating Production, Storage and Offloading system)), the raw material gas is fed to the liquefaction system 1 in a high pressure state.
[0023]
The pressure reduction apparatus 2 includes a known expander which reduces the pressure of the flowing raw material by isentropic expansion. In the present embodiment, the raw material gas supplied to the liquefaction system 1 (the pressure reduction apparatus 2 in this context) has a temperature of about 20 degrees Celsius, a pressure of 150 to 200 barA, and a flow rate of about 500,000 kg/hr, but the present invention is not limited thereto, and the temperature, pressure and flow rate of the raw material gas can be changed as necessary. The pressure of the raw material gas is reduced to a prescribed pressure (70 to 80 barA in this case)
2015385052 14 Sep 2018
-8 by the pressure reduction apparatus 2 so that the raw material gas can be properly processed in the heavy component removal apparatus 5 as described in detail later.
[0024]
The raw material gas which has been reduced in pressure in the pressure reduction apparatus 2 is heated by heat exchange (heating) with the refrigerant in the cooling apparatus 14 for refrigerant as described in detail later, further heated by a heater 8 to a prescribed temperature and then introduced into the acid gas removal apparatus 3. The temperature the raw material gas introduced into the acid gas removal apparatus 3 is within the range from about 25 to 60 degrees Celsius, more preferably from 35 to 40 degrees Celsius. If the temperature of the raw material gas is less than 20 degrees Celsius, the fluidity of an acid gas absorbing medium or absorption liquid decreases, causing problems such as operation failure of the apparatus. If the temperature of the raw material gas exceeds 60 degrees Celsius, a problem of reduction in the acid gas removal efficiency occurs.
[0025]
The pressure reduction apparatus 2 may be any known apparatus other than the expander (e.g. expansion valve) as long as the apparatus can reduce the pressure of the raw material to a desired level. Various known heat sources can be used as the heater 8 as long as it can raise the temperature of the raw material gas to a desired temperature.
[0026]
The acid gas removal apparatus 3 includes an absorption tower for removing acid gases contained in the raw material gas by a chemical absorption method. Also, the acid gas removal apparatus 3 is provided with a regeneration tower (not shown) for regenerating the absorption liquid used in the absorption tower. The absorption tower is a plate tower provided with shelves at regular intervals inside the tower and brings the absorption liquid into countercurrent contact with the supplied raw material gas to thereby cause acid gas components
2015385052 14 Sep 2018
-9 (carbon dioxide and the like) to be absorbed in the absorption liquid. The absorption liquid may be an alkanolamine aqueous solution such as monoethanolamine, diethanolamine, triethanolamine, methyl diethanolamine, diisopropanolamine, diglycolamine, or
2-amino-2-methyl-1 -propanol. The regeneration tower treats the absorption liquid at a prescribed pressure (1 to 2 barA in this case) and at a temperature (130 to 140 degrees Celsius in this case) to remove the acid gas components from the absorption liquid, causing the regenerated absorption liquid to circulate to the absorption tower. The raw material gas from which the acid gas components have been removed in the acid gas removal apparatus 3 is fed to the moisture removal apparatus 4.
[0027]
The moisture removal apparatus 4 includes a dewatering tower fdled with a moisture absorbent (in this case, molecular sieve) which physically adsorbs moisture. In the moisture removal apparatus 4, dehydration treatment is performed so that the moisture content in the raw material gas is preferably less than 0.1 ppmv (volume parts per million). Removal of the moisture in the raw material gas prevents troubles caused due to freezing or like in the subsequent liquefaction process. The moisture removal apparatus 4 may be any known apparatus (or configuration) as long as it can remove the moisture content in the raw material gas to a desired level or less. The raw material gas from which moisture has been removed by the moisture removal apparatus 4 is fed to the heavy component removal apparatus 5.
[0028]
The heavy component removal apparatus 5 is composed primarily of a rectifying tower including shelves therein, and removes heavy components contained in the raw material gas which heavy components have relatively high freezing points; that is, each heavy component is reduced to a desired concentration or less. In the rectifying tower, a liquid containing relatively high levels of heavy components is discharged from the bottom of the
2015385052 14 Sep 2018
- 10tower. Also, in the rectifying tower, the raw material gas (light component(s)) containing methane, which has a low boiling point, as a main component is separated as a distillate to be discharged from the top of the tower. The separated raw material gas is cooled (pre-cooled) by heat exchange with the refrigerant in an evaporator 16 for refrigerant described in detail later, and then introduced into the liquefying apparatus 6.
[0029]
The liquefying apparatus 6 is a main heat exchanger for liquefying the raw material gas, from which unnecessary components such as acid gases and heavy components have been removed as described above, by heat exchange with a mixed refrigerant. In this case, the liquefying apparatus 6 is composed primarily of a spool-wound type heat exchanger; that is, heat transfer tubing (tube bundle), in which the raw material gas and the mixed refrigerant flow, wound in a coil shape and accommodated in a shell. However, in the liquefying apparatus 6, any other known configuration such as plate fin type heat exchanger and the like can be used as long as at least the liquefaction of the raw material gas is possible. The raw material gas (LNG) at a low temperature (about -162 degrees Celsius) liquefied by the liquefying apparatus 6 is fed to and stored in an LNG storage facility (not shown).
[0030]
In the liquefying apparatus 6 in the present embodiment, a hydrocarbon mixture including methane, ethane and propane blended with nitrogen is used as the mixed refrigerant for cooling the raw material gas. However the mixed refrigerant is not limited to this, and may be a liquefying refrigerant composed of other known components. Although not shown, the liquefying apparatus 6 is provided with equipment (compressor, condenser and the like) for implementing a known refrigerant cycle (refrigeration cycle) for a mixed refrigerant.
[0031]
The pre-cooling system 7 primarily includes a compressor 11 for compressing the
2015385052 14 Sep 2018
- 11 pre-cooling refrigerant, a condenser 12 for condensing the pre-cooling refrigerant, a subcooler for supercooling the pre-cooling refrigerant, a cooling apparatus (first heat exchanger) 14 for cooling the pre-cooling refrigerant by heat exchange with the raw material gas, an expansion valve 15 for throttling and expanding the refrigerant, and an evaporator (second heat exchanger)
16 for cooling the raw material gas by heat exchange with the refrigerant, so that the pre-cooling system 7 implements a refrigerant cycle for pre-cooling the raw material gas to be liquefied in the liquefying apparatus 6. In this case, propane is used as the pre-cooling refrigerant. However, the pre-cooling refrigerant is not limited to this, and any other known component can be adopted.
[0032]
The compressor 11 is a centrifugal compressor that compresses the mixed refrigerant which has been used for cooling the raw material gas in the evaporator 16. In this case, the flow rate of the mixed refrigerant introduced into the compressor 11 (that is, to be used in the refrigerant cycle) is about 800,000 kg/hr, and the temperature and pressure of the refrigerant compressed by the compressor 11 are about 70 degrees Celsius and about 30 barA, respectively.
[0033]
The pre-cooling refrigerant which has been compressed by the compressor 11 is condensed in the condenser 12 and further supercooled to about 30 degrees Celsius by air or water in the subcooler 13. Thereafter, the pre-cooling refrigerant is supplied from the subcooler
13 to the cooling apparatus 14, in which heat exchange is performed between the pre-cooling refrigerant and the raw material gas. By the heat exchange in the cooling apparatus 14, the pre-cooling refrigerant is cooled to about -10 degrees Celsius, while the raw material gas is heated to about 25 degrees Celsius by the heat from the pre-cooling refrigerant.
[0034]
Subsequently, the pre-cooling refrigerant is supplied from the cooling apparatus 14 to
2015385052 14 Sep 2018
- 12 the expansion valve 15, where the pre-cooling refrigerant is throttling and expanded to exhibit a low temperature and a low pressure (the temperature is about -50 degrees Celsius and the pressure is about 3.5 bar A). Next, the pre-cooling refrigerant is supplied from the expansion valve 15 to the evaporator 16, in which heat exchange is performed between the pre-cooling refrigerant and the raw material gas. By the heat exchange in the evaporator 16, the pre-cooling refrigerant is heated up to about 10 degrees Celsius by the heat from the raw material gas and evaporates, while the raw material gas is cooled to about -40 degrees Celsius. The pre-cooling refrigerant from the evaporator 16 is supplied again to the compressor 11 so that the pre-cooling refrigerant is circulated.
[0035]
As described above, in the liquefaction system 1, since the raw material gas which has been lowered in temperature by the pressure reduction in the pressure reduction apparatus 2 is heated by heat exchange with the pre-cooling refrigerant in the cooling apparatus 14, the system allows the temperature of the raw material gas to be increased with no (or minimized) additional energy supplied from outside so that the acid gas components can be removed from the raw material gas after the pressure reduction of the raw material gas.
[0036]
Moreover, in the liquefaction system 1, since the cold heat of the natural gas created by the pressure reduction on the upstream side is used for cooling the pre-cooling refrigerant which is for cooling the raw material gas on the downstream side (in this case, the raw material gas from which heavy components have been removed), the load of the compressor 11 is reduced to provide another advantage that the energy efficiency in the refrigerant cycle can be enhanced. This allows the circulating amount of the pre-cooling refrigerant to be reduced in the pre-cooling system 7. In some cases, the subcooler 13 may be omitted. Furthermore, since the cooling capacity of the raw material gas by the pre-cooling system 7 is improved as compared
2015385052 14 Sep 2018
- 13 with cases where the cooling apparatus 14 is not used, the throughput of the natural gas in the liquefaction system 1 (that is, the production volume of LNG) can be increased.
[0037]
In addition, since the temperature of the raw material gas is raised by heat exchange with the pre-cooling refrigerant, the energy consumption is reduced as compared with cases where the temperature of the raw material gas is raised only by the heater 8 provided to the acid gas removal apparatus 3, the heater 8 can be downsized, and in some cases the heater 8 can be omitted. There is also an advantage that, by raising the temperature of the raw material gas both by heat exchange with the pre-cooling refrigerant and the heat from the heater 8, even when the raw material gas is not sufficiently heated by the cooling apparatus 14, the heater 8 can be used to adjust the temperature of the raw material gas to be supplied to the acid gas removal apparatus 3 within a suitable temperature range.
[0038]
Although the specific embodiments have been described above, the present invention is not limited to the above-described embodiments. All the elements of the natural gas liquefaction system and method of the present invention in the above-described embodiments are not necessarily essential and can be appropriately selected without departing from the scope of the present invention.
[0039]
Throughout the specification and the claims that follow, unless the context requires otherwise, the words “comprise” and “include” and variations such as “comprising” and “including” will be understood to imply the inclusion of a stated integer or group of integers, but not the exclusion of any other integer or group of integers.
[0040]
2015385052 14 Sep 2018
- 14 The reference to any prior art in this specification is not, and should not be taken as, an acknowledgement of any form of suggestion that such prior art forms part of the common general knowledge.
[0041]
It will be appreciated by those skilled in the art that the invention is not restricted in its use to the particular application described. Neither is the present invention restricted in its preferred embodiment with regard to the particular elements and/or features described or depicted herein. It will be appreciated that the invention is not limited to the embodiment or embodiments disclosed, but is capable of numerous rearrangements, modifications and substitutions without departing from the scope of the invention as set forth and defined by the following claims.
- 15 2015385052 14 Sep 2018

Claims (5)

1. A natural gas liquefaction system for producing liquefied natural gas by cooling a raw material gas including natural gas, the system comprising:
5 a pressure reduction unit for reducing a pressure of the raw material gas, a first heat exchanger for heating, by heat exchange with a refrigerant, the raw material gas which has been reduced in pressure in the pressure reduction unit, a heating unit for heating the raw material gas which is supplied from the first heat exchanger,
10 an acid gas removal unit for removing an acid gas component from the raw material gas which has been heated in the heating unit, a second heat exchanger for cooling the raw material gas from which the acid gas component has been removed in the acid gas removal unit, the raw material gas being cooled by heat exchange with the refrigerant which has been lowered in temperature in the first heat
15 exchanger, and a liquefying unit for further cooling the raw material gas which has been cooled by the second heat exchanger to produce liquefied natural gas.
2. The natural gas liquefaction system according to claim 1, further comprising a heavy
20 component removal unit provided between the acid gas removal unit and the second heat exchanger for removing a heavy hydrocarbon in the raw material gas.
3. The natural gas liquefaction system according to any one of claims 1 or 2, wherein the first and second heat exchangers constitute a pre-cooling refrigerant cycle for pre-cooling the
25 raw material gas to be supplied to the liquefying unit, and
2015385052 14 Sep 2018
- 16wherein the natural gas liquefaction system further comprises:
a compressor for compressing the refrigerant which has been used in the second heat exchanger, and an expansion valve provided between the first and second heat exchangers in
5 the refrigerant cycle for throttling and expanding the refrigerant.
4. A natural gas liquefaction method for producing liquefied natural gas by cooling a raw material gas including natural gas, the method comprising:
a pressure-reducing step for reducing a pressure of the raw material gas,
10 a first heat-exchanging step for heating, by heat exchange with a refrigerant, the raw material gas which has been reduced in pressure in the pressure-reducing step, a heating step for heating the raw material gas which has been heated in the first heat-exchanging step, an acid-gas-removal step for removing an acid gas component from the raw material
15 gas which has been heated in the heating step, a second heat-exchanging step for cooling the raw material gas from which the acid gas component has been removed in the acid gas removal step, the raw material gas being cooled by heat exchange with the refrigerant which has been lowered in temperature in the first heat-exchanging step, and
20 a liquefying step for further cooling the raw material gas which has been cooled by the second heat-exchanging step to produce liquefied natural gas.
il
TO
5 '§
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CC TO £
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US4012212A (en) * 1975-07-07 1977-03-15 The Lummus Company Process and apparatus for liquefying natural gas

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GB997802A (en) * 1964-04-08 1965-07-07 Conch Int Methane Ltd Cold separation of gas mixtures
US3503220A (en) * 1967-07-27 1970-03-31 Chicago Bridge & Iron Co Expander cycle for natural gas liquefication with split feed stream
SU1499079A1 (en) * 1986-06-02 1989-08-07 Краснодарский политехнический институт Method of treating oil gas
US5473900A (en) * 1994-04-29 1995-12-12 Phillips Petroleum Company Method and apparatus for liquefaction of natural gas
CN101796359B (en) * 2007-07-09 2012-05-23 液化天然气技术有限公司 A method and system for production of liquid natural gas

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* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US4012212A (en) * 1975-07-07 1977-03-15 The Lummus Company Process and apparatus for liquefying natural gas

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