WO2013071789A1 - 采用单一混合工质制冷液化天然气的装置和方法 - Google Patents

采用单一混合工质制冷液化天然气的装置和方法 Download PDF

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Publication number
WO2013071789A1
WO2013071789A1 PCT/CN2012/081334 CN2012081334W WO2013071789A1 WO 2013071789 A1 WO2013071789 A1 WO 2013071789A1 CN 2012081334 W CN2012081334 W CN 2012081334W WO 2013071789 A1 WO2013071789 A1 WO 2013071789A1
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Prior art keywords
gas
heat exchange
liquid
heat exchanger
stage
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PCT/CN2012/081334
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English (en)
French (fr)
Inventor
何振勇
蔚龙
张生
傅建青
张晓哲
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新地能源工程技术有限公司
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Priority to US14/354,964 priority Critical patent/US20140283548A1/en
Priority to CA2856096A priority patent/CA2856096C/en
Publication of WO2013071789A1 publication Critical patent/WO2013071789A1/zh

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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
    • 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
    • F25J1/0055—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 originating from an incorporated cascade
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F25—REFRIGERATION OR COOLING; COMBINED HEATING AND REFRIGERATION SYSTEMS; HEAT PUMP SYSTEMS; MANUFACTURE OR STORAGE OF ICE; LIQUEFACTION SOLIDIFICATION OF GASES
    • F25J—LIQUEFACTION, SOLIDIFICATION OR SEPARATION OF GASES OR GASEOUS OR LIQUEFIED GASEOUS MIXTURES BY PRESSURE AND COLD TREATMENT OR BY BRINGING THEM INTO THE SUPERCRITICAL STATE
    • F25J1/00—Processes or apparatus for liquefying or solidifying gases or gaseous mixtures
    • F25J1/02—Processes or apparatus for liquefying or solidifying gases or gaseous mixtures requiring the use of refrigeration, e.g. of helium or hydrogen ; Details and kind of the refrigeration system used; Integration with other units or processes; Controlling aspects of the process
    • F25J1/0211—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
    • F25J1/0212—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 single flow MCR 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
    • 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.
    • F25J1/0291—Refrigerant compression by combined gas compression and liquid pumping
    • 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

Definitions

  • the present invention relates to liquefaction production of hydrocarbon-rich gas, and more particularly to a device and method for refrigerating liquefied natural gas with a single mixed working fluid. Background technique
  • Natural gas has become the best alternative to other fuels because of its environmental friendliness. Its application fields have gradually expanded to include power generation, automotive gas, industrial gas, urban residential gas, and chemical gas.
  • the more mature natural gas liquefaction processes mainly include: a cascade refrigeration process, an expansion refrigeration process, and a mixed refrigerant process.
  • the single mixed refrigerant refrigeration process is favored by medium-sized LNG plants.
  • the refrigerant compression system is secondary compression, and the natural gas liquefaction uses primary heat exchange.
  • the device used includes a motor-driven two-stage hybrid working fluid compressor, two coolers, two gas-liquid separators, two liquid pumps, and one plate.
  • Fin heat exchanger and a LNG storage tank the mixed working fluid consisting of Cl ⁇ C5 and N2 enters the inlet of the compressor after a reasonable ratio, and is compressed to 0.6 ⁇ lMPa after a period of time, and then cooled to 30 by the primary cooler. ⁇ 40°C, and then enter the first-stage gas-liquid separation tank for gas-liquid separation.
  • the gas separated at the top of the first-stage gas-liquid separation tank continues to enter the second inlet of the compressor, and is compressed to 1.6 ⁇ 2.5MPa by the second stage.
  • the liquid separated by the separation bottom is pressurized by the liquid pump and mixed with the gas at the outlet of the two-stage compressor to enter the secondary cooler to be cooled to 30 to 40 ° C.
  • the cooled mixed working medium then enters the secondary gas-liquid separation tank for gas.
  • the liquid is separated, and the separated liquid is pressurized by the secondary liquid pump, mixed with the gas obtained at the top of the separator, and then enters the plate-fin heat exchanger, pre-cooled to a certain temperature, and then throttled and returned to the plate-fin heat exchanger.
  • the gas through the plate-fin heat exchanger into the LNG storage tank.
  • the liquid at the bottom of the final gas-liquid separator must be pressurized to overcome the liquid outlet at the bottom of the separator to the plate-fin heat exchanger.
  • the column pressure caused by the difference in height at the top coolant inlet must be achieved by adding a final stage liquid pump.
  • the heat exchange process of the refrigerant and natural gas in the plate-fin heat exchanger is the first-order heat exchange, and the optimization of the heat transfer temperature difference between the streams is limited, the energy consumption of the device is high, and the variable load operation of the device is not very high. Good adaptability. Summary of the invention
  • the invention uses a single mixed refrigerant to liquefy natural gas.
  • the invention provides a device for refrigerating liquefied natural gas using a single mixed working fluid, which comprises a mixed refrigerant compression system and a cold box system, wherein the mixed refrigerant compression system is compressed by a two-stage mixed working fluid compressor, the compression system
  • the utility model comprises a two-stage mixed working fluid compressor, two coolers (ie, a first cooler and a second cooler) respectively connected to the first section and the second section of the two-stage mixed working fluid compressor, respectively a first gas-liquid separator and a second gas-liquid separator connected to the first cooler and the second cooler, and a first gas-liquid separator among the two gas-liquid separators a liquid pump connected
  • the cold box system comprises a set of plate fin heat exchanger groups connected to the liquid phase end of the second gas liquid separator of the two gas liquid separators, and the plate Two throttling devices connected to the heat exchange passage of the fin heat exchanger
  • the invention adopts a single mixed working medium refrigeration to liquefy natural gas, which is divided into a natural gas circulation and a mixed working medium refrigeration cycle.
  • the mixed working medium is compressed by the second stage, and the gas-liquid separation is carried out step by step in the stepwise compression process.
  • the liquid phase stream separated by the first stage compression does not participate in the subsequent compression process, and is effective.
  • the post-sequence gas compression power consumption is reduced; the gas phase and liquid phase mixed working fluid streams obtained by the compression respectively enter the different channel throttling heat exchange of the heat exchanger group, and the final stage liquid pump is omitted compared with the conventional process (ie, only The use of a liquid pump) and the use of secondary heat transfer to match the heat transfer curves of the heat and cold streams throughout the process.
  • the device for liquefying natural gas using a single mixed working fluid refrigeration comprises a two-stage mixed working fluid compressor, a cooler, a gas-liquid separator, a throttling device, a set of plate-fin heat exchanger groups and one set LNG storage tanks.
  • the mixed refrigerant compression system comprises a two-stage mixed working fluid compressor, two coolers, two gas-liquid separators and a liquid pump, and the cold box system comprises a set of plate-fin heat exchanger groups ( Secondary heat transfer), a heavy hydrocarbon separator (gas-liquid separator) and two throttling devices; mixed working fluid and natural gas complete the heat exchange process in the cold box system.
  • the outlet of the first compression section of the compressor is connected to the first stage cooler, and the first stage cooler is connected to the first stage gas-liquid separator, the gas phase of the first stage gas-liquid separator The end is connected to the second compression section, the bottom liquid phase end of the first stage gas-liquid separator is connected to a liquid pump, and the output pipe of the liquid pump is merged with the outlet pipe of the second compression section and connected to the second stage cooler
  • the second stage cooler is connected to the second stage gas-liquid separator, and the top gas phase end of the second stage gas-liquid separator is connected to the first heat exchange channel (gas phase channel) of the heat exchanger group; the second stage gas liquid a bottom liquid phase end of the separator is connected to the second heat exchange channel of the heat exchanger group;
  • the liquid phase end of the second stage gas-liquid separator derived from the mixed refrigerant compression system is connected to one end of the first throttle device through the second heat exchange passage in the heat exchanger group, the first section
  • the other end of the flow device is connected to the third heat exchange channel of the heat exchanger group
  • the gas phase end obtained at the top of the second stage gas-liquid separator is pre-cooled through the first heat exchange channel (gas phase channel) of the heat exchanger group, and then One end of the two throttling device is connected, and the other end of the second throttling device is connected to the third heat exchange channel of the heat exchanger group and then connected to the first compression section
  • the natural gas pipeline passes through the fourth heat exchange channel of the heat exchanger group Connected to the heavy hydrocarbon separator, the top gas phase end of the heavy hydrocarbon separator passes through the remaining heat exchangers of the heat exchanger group (for example, the fifth heat exchange passage;) and is connected to the LNG Storage tanks.
  • a device for refrigerating liquefied natural gas using a single mixed working fluid comprising a mixed refrigerant compression system and a cold box system, wherein the compression system comprises a two-stage mixed working fluid compressor, and the two-stage mixed working fluid compressor respectively a first cooler and a second cooler connected to the first and second sections, a first gas-liquid separator and a second unit respectively connected to the first cooler and the second cooler a gas-liquid separator and a liquid pump connected to the first of the two gas-liquid separators, and
  • the cold box system comprises: a set of plate-fin heat exchanger groups, comprising at least five heat exchange channels, ie comprising at least first, second, third, fourth and fifth heat exchange channels, said second The heat exchange passage and the first heat exchange passage are respectively connected to the liquid phase end and the gas phase end of the second gas-liquid separator in the mixed refrigerant compression system via the two pipes, and the third heat exchange passage is connected to the third heat exchange passage via the pipeline First compression section;
  • a first throttling device connected to the second heat exchange passage and the third heat exchange passage of the plate fin heat exchanger group; a first heat exchange passage and a third heat exchange passage with the plate fin heat exchanger group a second throttling device connected to the heat exchange channel;
  • a natural gas heavy hydrocarbon separator connected to a separate heat exchange passage of the plate fin heat exchanger group, that is, a fourth heat exchange passage
  • the gas phase end of the first gas-liquid separator in the two gas-liquid separators is connected to the second compression section of the two-stage mixed working fluid compressor, and the liquid phase end of the first gas-liquid separator is via a liquid pump
  • the outlet pipe of the second compression section is merged and connected to the second cooler of the two coolers, and the gas phase end and the liquid phase end of the second gas-liquid separator respectively exchange heat with the set of plate fins
  • the two heat exchange channels of the device group are connected to the first heat exchange channel and the second heat exchange channel; wherein the pipeline for conveying the purified natural gas is connected to the heavy through the above-mentioned independent heat exchange channel of the heat exchanger group, that is, the fourth heat exchange channel
  • the hydrocarbon separator, the top gas phase end of the heavy hydrocarbon separator is connected to the liquefied natural gas storage tank through a heat exchange passage of the heat exchanger group, that is, the fifth heat exchange passage.
  • top gas phase end of the heavy hydrocarbon separator passes through the fifth heat exchange passage of the heat exchanger group in turn and is further connected to the liquefied natural gas storage tank through the other sixth heat exchange passage of the heat exchanger group.
  • first segment compression or “segment compression” described herein is used interchangeably with the “first compression segment”, and so on.
  • the outlet gas of the first stage of the compressor enters the first-stage cooler and is cooled and passes through the first-stage gas-liquid separator.
  • Gas-liquid separation is carried out, and the separated gas phase continues to enter the second compression section, and the separated liquid phase is pressurized by the liquid pump and merged with the hot gas after the second stage compression, and then cooled by the second-stage cooler.
  • the gas-liquid separation is carried out in the second-stage gas-liquid separator, and the separated gas phase enters the first heat exchange passage (gas phase passage) of the downstream heat exchanger; the liquid obtained at the bottom of the second-stage gas-liquid separator enters the downstream heat exchanger respectively The second liquid phase heat exchange channel.
  • the liquid liquid refrigerant from the bottom of the second stage gas-liquid separator of the refrigerant compression system enters the second liquid phase heat exchange channel of the heat exchanger group and is precooled and then passed through the first throttling device.
  • the throttled stream is returned to the third heat exchange channel of the heat exchanger group to provide a cooling capacity; the gas phase refrigerant from the top of the second stage gas-liquid separator is passed through the first heat exchange channel of the heat exchanger group After pre-cooling, the second throttling device is used for throttling, and the throttling stream is reversely fed into the third heat exchange channel of the heat exchanger group to provide cooling capacity.
  • the mixed refrigerant flowing from the third heat exchange passage is sent back to the first compression section. Natural gas First, the fourth heat exchange passage through the heat exchanger group is cooled to a certain temperature and then enters the heavy hydrocarbon separator for separation.
  • the bottom portion obtains the heavy hydrocarbon component, and the gas phase portion obtained at the top continues to enter the remaining stages of the heat exchanger group.
  • the heat exchanger (for example, the fifth heat exchange passage;) performs heat exchange, is cooled to a supercooled state, and the obtained LNG is stored in the LNG storage tank.
  • the method of cooling liquefied natural gas using a single mixed working fluid includes:
  • the purified raw material natural gas first enters the fourth heat exchange channel of the plate-fin heat exchanger group for pre-cooling, is cooled to -30 ° C ⁇ - 60 ° C and then enters the heavy hydrocarbon separator for gas-liquid separation.
  • the gas phase stream separated at the top of the separator continues to enter the remaining heat exchangers of the heat exchanger group (for example, the fifth heat exchange passage;) and is cooled therein to -130 ° C to - 166 ° C.
  • Liquefied natural gas is sent to the LNG storage tank for storage.
  • a mixed refrigerant composed of N 2 and C1 ⁇ C5 four (typically selected from Cl, C2, C3, C4 and C5 paraffins and the N 2, five or six, or volume ratio thereof in any according about Equivalent volume ratio, enter the inlet of the compressor, after the first stage is compressed to 0.6 ⁇ 1.8MPaA, enter the first stage cooler and cool to 30 °C ⁇ 40 °C, then enter the first stage gas-liquid separator for gas-liquid Separation, the gas separated at the top of the first-stage gas-liquid separator continues to enter the second inlet of the compressor, and is compressed to 1.2 ⁇ 5.4MPaA by the second stage, and the liquid separated at the bottom end of the liquid phase of the first-stage gas-liquid separator After the liquid pump is pressurized, it merges with the hot gas of the second-stage compression outlet pipe, and then enters the second-stage cooler and is cooled to 30 ° C to 40 ° C, and the cooled mixed working medium then enters the second-stage gas-liquid.
  • the separator performs gas-liquid separation.
  • the top gas of the second-stage gas-liquid separator then enters the first heat exchange channel of the main heat exchanger group to participate in heat exchange, and the liquid separated at the bottom of the second-stage gas-liquid separator enters the main heat exchange.
  • the second heat exchange channel of the group participates in heat exchange;
  • the liquid drawn from the bottom of the second-stage gas-liquid separator of the mixed working fluid compression system first enters the second heat exchange passage of the heat exchanger group, and is pre-cooled therein to about -30 ° C to - 80 ° C, After the throttle valve is throttled to 0.25 ⁇ 0.75MPaA, it merges with the first-stage heat exchange channel flowing through the main heat exchanger group and then returns through the second throttle valve to merge into the third stage.
  • the heat exchange channel provides a cooling capacity for the heat exchanger group and then returns to the first compression section, and the gas phase stream of the mixed working fluid separated by the top of the second stage gas-liquid separator passes through the gas phase channel of the heat exchanger group (first The heat exchange channel;) is cooled to -135 °C to -169 °C, and then throttled to 0.25 ⁇ 0.75MPaA by the second throttle valve, and then enters the third heat exchange channel of the heat exchanger group to provide heat exchanger Cooling capacity.
  • the pressure unit MPaA is MPa, absolute pressure.
  • the connection of one device to another device is achieved by piping.
  • the two-stage mixed refrigerant compressor is used in the device of the invention, and the mixed refrigerant is compressed step by step and separated step by step, thereby reducing the power consumption of gas compression.
  • the liquid stream at the bottom of the primary gas-liquid separator does not participate in the subsequent compression process, which reduces the influence of the fluctuation of the mixed refrigerant ratio on the operating conditions of the compressor unit to a certain extent, making the whole device easier to operate.
  • the gas-phase and liquid-phase mixed refrigerant streams obtained by the compression of the mixed refrigerant compressor enter the different heat exchange channels of the heat exchanger group respectively without the need of the final liquid pump (ie, using only one liquid pump), enabling The consumption is reduced, and the secondary heat exchange is used to make the heat transfer curves of the cold fluid and the hot fluid in the entire heat exchange process more matched, thereby effectively reducing the flow rate of the mixed refrigerant.
  • Figure 1 is a structural view of the prior art
  • FIG. 2 is a configuration diagram of a device of the two-stage hybrid working fluid compression system of the present invention. detailed description
  • the apparatus shown in Fig. 2 comprises a two-stage mixed working fluid compressor 1, a first cooler 21, a second cooler 22, a first gas-liquid separator 31, a second gas-liquid separator 32, and a heavy hydrocarbon separator 6. (gas-liquid separator), liquid pump 4, first throttling device 51, second throttling device 52, a set of plate-fin heat exchanger groups 7 (ie, main heat exchanger group;) and one LNG storage tank 8.
  • the mixing system of the mixed refrigerant comprises a two-stage mixed working fluid compressor 1, two coolers 21, 22, two gas-liquid separators 31, 32, a liquid pump 4, and the cold box system includes a group Plate-fin heat exchanger group 7 (two-stage heat exchange), one heavy hydrocarbon separator 6 (gas-liquid separator) and two throttling devices 51, 52; mixed working fluid and natural gas complete in the cold box system Heat exchange process.
  • the outlet of the first stage of the compressor 1 is connected to the first stage cooler 21, and the first stage cooler 21 is connected to the first stage gas-liquid separator 31, the first stage gas-liquid separator
  • the gas phase end of 31 is connected to the second compression section
  • the bottom liquid phase end of the first stage gas-liquid separator 31 is connected to the liquid pump 4
  • the output end of the liquid pump 4 is merged with the outlet pipe of the second compression section, and then connected to the second
  • the second stage cooler 22 is further connected to the second stage gas-liquid separator 32, the top gas phase end of the second stage gas-liquid separator 32 and the first heat exchange channel of the heat exchanger group 7 (gas phase channel) Connecting
  • the bottom liquid phase of the second stage gas-liquid separator 32 is connected to the second liquid phase heat exchange channel of the heat exchanger group 7;
  • the liquid phase end of the second stage gas-liquid separator 32 from the mixed refrigerant compression system is connected to one end of the first throttle device 51 through the second heat exchange passage in the heat exchanger group 7,
  • the other end of the flow device 51 is connected to the third heat exchange channel of the heat exchanger group 7;
  • the gas phase end obtained at the top of the second gas-liquid separator 32 is pre-cooled through the first heat exchange channel of the heat exchanger group 7,
  • the second throttling device 52 Further connected to the second throttling device 52, the other end of the second throttling device 52 is connected to the third heat exchange channel of the heat exchanger group 7 and then connected to the first compression section;
  • the natural gas pipeline passes through the heat exchanger group
  • the fourth heat exchange passage is connected to the heavy hydrocarbon separator 6, and the top gas phase end of the heavy hydrocarbon separator 6 sequentially passes through the remaining heat exchangers of the heat exchanger group 7 (for example, the fifth heat exchange passage, optionally also After passing through the sixth heat exchange passage), it is connected to
  • the purified raw material natural gas is first pre-cooled into the fourth heat exchange passage in the plate-fin type main heat exchanger group 7 (two-stage heat exchange), and is cooled to -30 ° C. - After 60 ° C, it enters the heavy hydrocarbon separator 6 for gas-liquid separation, and the gas phase stream separated by the top of the heavy hydrocarbon separator 6 continues to enter the remaining heat exchangers of the main heat exchanger group 7, and is After cooling to -130 ° C to -166 ° C, the obtained liquefied natural gas is sent to the LNG storage tank 8 for storage, and the bottom of the heavy hydrocarbon separator 6 is supplied with liquefied petroleum gas (LPG).
  • LPG liquefied petroleum gas
  • the gas separated at the top of the first-stage gas-liquid separator 31 continues to enter the second inlet of the compressor, and is compressed to 1.2 to 5.4 MPaA by the second stage, and the liquid separated from the bottom liquid phase of the first-stage gas-liquid separator 31 is liquid.
  • the pump 4 After the pump 4 is pressurized, it merges with the hot gas of the two-stage compression outlet, and then enters the second-stage cooler 22 to be cooled to 30 ° C to 40 ° C, and the cooled mixed working medium then enters the second-stage gas-liquid separator 32.
  • the gas at the top of the second-stage gas-liquid separator 32 then enters the first heat exchange channel of the main heat exchanger group 7 to participate in the heat exchange, and the liquid separated at the bottom of the second-stage gas-liquid separator 32 enters the main exchange.
  • the second heat exchange channel of the heat exchanger group 7 participates in heat exchange;
  • the liquid drawn from the bottom of the second stage gas-liquid separator 32 of the mixed working fluid compression system first enters the second heat exchange passage of the heat exchanger group, where it is pre-cooled to about -30 ° C to - 80 ° C,
  • the throttle valve 51 is throttled to 0.25 to 0.75 MPaA and is returned to the mixed working fluid stream from the heat exchanger group 7 after the first stage heat exchanger (ie, flowing through the first heat exchange passage and the second throttle valve;
  • Combining the reverse into the pre-stage heat exchanger ie, the third heat exchange channel) provides cooling capacity for the heat exchanger group 7, and the gas phase stream of the mixed working fluid separated by the top of the second-stage gas-liquid separator 32 is exchanged.
  • the gas phase channel of the heat exchanger group 7 (ie, the first heat exchange channel) is cooled to -135 ° C to -169 ° C, and then throttled to 0.25 to 0.75 MPaA through the second throttle valve 52, and then enters the heat exchanger group.
  • the third heat exchange passage of 7 supplies a heat to the heat exchanger group and then returns to the first compression section.

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Abstract

一种采用单一混合工质制冷来液化天然气的装置和方法，该装置包括一台电机驱动的二段式混合工质压缩机（1）、两台冷却器（21，22）、一台液体泵（4）、三台气液分离器（31，32，6）、两个节流装置（51，52）、一组板翅式换热器组（7）和一台LNG储罐（8）；该方法采用了二段式混合工质压缩机（1），将混合工质逐级压缩并逐级分离，经分离得到的气相和液相混合工质流股分别进入换热器组（7）的不同通道节流换热，且采用二级换热使整个换热过程的冷流体和热流体的换热曲线更为匹配，有效减少了混合工质的流量。

Description

采用单一混合工质制冷液化天然气的装置和方法
技术领域
本发明涉及富含烃类气体的液化生产， 具体涉及一种单一混合工质制冷液化天然气的装 置和方法。 背景技术
天然气由于其环保性而成为取代其他说燃料的最佳物质， 其应用领域已逐渐扩大到发电、 汽车用气、 工业用气、 城市居民用气、 化工用气等方面。
随着天然气消费量的增长， 作为天然气最有效的供用形式之一， 液化天然气的贸易量也 已成为能源市场增长最快的领域之一。 液化天然气书工业的不断发展， 则对天然气液化方法和 装置在能耗、 投资和效率等方面提出了更高的要求。
目前， 比较成熟的天然气液化工艺主要有： 阶式制冷工艺、 膨胀制冷工艺和混合工质制 冷工艺。 其中的单一混合工质制冷工艺则比较受中型 LNG装置的青睐。
现有的单一混合工质制冷的天然气液化方法中， 冷剂压缩***为二级压缩， 天然气液化 采用一级换热。
现有工艺技术： 如图 1所示， 其使用的装置包括一台电机驱动的二段式混合工质压缩机， 二台冷却器， 二台气液分离器， 二台液体泵， 一台板翅式换热器和一台 LNG储罐； 由 Cl〜 C5和 N2组成的混合工质经过合理配比后进入压缩机的入口， 经一段压缩至 0.6〜lMPa， 进 入一级冷却器冷却至 30〜40°C， 再进入一级气液分离罐进行气液分离， 一级气液分离罐顶部 分离出的气体继续进入压缩机的二段入口，经二段压缩至 1.6〜2.5MPa，一级分离底部分离得 到的液体通过液体泵加压后与二段压缩机出口的气体混合进入二级冷却器冷却至 30〜40°C， 冷却后的混合工质随后进入二级气液分离罐进行气液分离， 分离后的液体通过二级液体泵加 压后与该分离器顶部得到的气体混合后进入板翅式换热器， 预冷至一定温度后节流再返回该 板翅式换热器， 为整个换热过程提供冷量， 天然气通过板翅式换热器后进入 LNG储罐内。
在上述工艺， 为保证液体和气体进入同一个板翅式换热器通道参与换热， 末级气液分离 器底部的液体必须要加压以克服分离器底部液体出口到板翅式换热器顶部冷剂入口的高度差 所带来的液柱压力， 必须通过增加末级液体泵来实现。 冷剂和天然气在板翅式换热器中的换 热过程为一级换热， 流股间换热温差的优化受到一定限制， 装置能耗较高， 此外， 对装置的 变负荷运转没有很好的适应性。 发明内容
本发明采用单一混合工质制冷使天然气液化。 本发明提供了一种采用单一混合工质制冷液化天然气的装置， 其包括混合冷剂压缩*** 和冷箱***， 其中混合冷剂压缩***采用二段式混合工质压缩机进行压缩， 该压缩***包括 二段式混合工质压缩机、 分别与所述二段式混合工质压缩机的第一段和第二段连接的两台冷 却器 (即第一冷却器和第二冷却器)、 分别与所述第一台冷却器和第二台冷却器连接的第一台 气液分离器和第二台气液分离器和与所述两台气液分离器当中的第一台气液分离器连接的一 台液体泵， 其中冷箱***包含与所述两台气液分离器中的第二台气液分离器的液相端连接的 一组板翅式换热器组、 与所述板翅式换热器组的换热通道连接的两台节流装置和与所述板翅 式换热器组的一个独立换热通道连接的一台天然气重烃分离器， 其中两台气液分离器中的第 一台气液分离器的气相端与二段式混合工质压缩机的第二压缩段连接， 第一台气液分离器的 液相端经由一台液体泵与第二压缩段的出口管道汇合后连接至所述两台冷却器中的第二台冷 却器， 第二台气液分离器的气相端和液相端分别与所述一组板翅式换热器组的两个换热通道 连接； 其中天然气管道通过换热器组的上述独立换热通道连接到重烃分离器， 重烃分离器的 顶部气相端通过换热器组的一个换热通道后连接到 LNG储罐。
本发明采用单一混合工质制冷来液化天然气的装置， 其分为天然气循环和混合工质制冷 循环。 在混合工质回路中， 混合工质经二级压缩， 在其逐级压缩过程中同时伴随逐级的气液 分离， 一级压缩分离出的液相流股不参与后续的压缩过程， 有效的减少了后序气体压缩功耗； 经压缩得到的气相和液相混合工质流股分别进入换热器组的不同通道节流换热， 相比传统工 艺省去了末级液体泵 (即仅仅使用一台液体泵)， 且采用二级换热使整个过程中热流股和冷流 股的换热曲线更为匹配。
本发明所述采用单一混合工质制冷来液化天然气的装置， 包括二段式混合工质压缩机、 冷却器、 气液分离器、 节流装置、 一组板翅式换热器组和一台 LNG储罐。 其混合制冷剂的压 缩***包括一台二段式混合工质压缩机、 两台冷却器、 两台气液分离器和一台液体泵， 冷箱 ***包括一组板翅式换热器组（二级换热）、一台重烃分离器（气液分离器）和两台节流装置； 混合工质和天然气在冷箱***中完成整个换热过程。
在混合冷剂压缩***中， 压缩机的第一压缩段的出口连接到第一级冷却器， 第一级冷却 器再与第一级气液分离器连接， 第一级气液分离器的气相端连接到第二压缩段， 第一级气液 分离器的底部液相端连接到一台液体泵， 该液体泵的输出管道与第二压缩段的出口管道汇合 后连接到第二级冷却器， 第二级冷却器再与第二级气液分离器连接， 第二级气液分离器的顶 部气相端与换热器组的第一换热通道 （气相通道） 连接； 第二级气液分离器的底部液相端与 换热器组的第二换热通道连接；
在冷箱***中， 由混合冷剂压缩***导出的第二级气液分离器的液相端通过换热器组中 的第二换热通道连接到第一节流装置的一端， 第一节流装置的另一端与换热器组的第三换热 通道连接； 第二级气液分离器顶部得到的气相端通过换热器组第一换热通道 （气相通道） 预 冷， 再与第二节流装置的一端连接， 第二节流装置的另一端连接到换热器组的第三换热通道 后再连接到第一压缩段； 天然气管道通过换热器组的第四换热通道连接到重烃分离器， 重烃 分离器的顶部气相端依次通过换热器组的其余各级换热器 (例如第五换热通道；)后连接到 LNG 储罐。
本发明的技术方案概括如下：
采用单一混合工质制冷液化天然气的装置， 该装置包括混合冷剂压缩***和冷箱***， 其中该压缩***包括二段式混合工质压缩机、 分别与所述二段式混合工质压缩机的第一 段和第二段连接的第一台冷却器和第二台冷却器、 分别与所述第一台冷却器和第二台冷却器 连接的第一台气液分离器和第二台气液分离器和与所述两台气液分离器当中的第一台连接的 一台液体泵， 和
其中冷箱***包括： 一组板翅式换热器组， 它包含至少五个换热通道， 即至少包含第一、 第二、 第三、 第四和第五换热通道， 所述第二换热通道和第一换热通道经由两根管道分别与 所述混合冷剂压缩***中的第二台气液分离器的液相端和气相端连接， 和第三换热通道经由 管道连接到第一压缩段；
与所述板翅式换热器组的第二换热通道和第三换热通道连接的第一台节流装置； 与所述板翅式换热器组的第一换热通道和第三换热通道连接的第二台节流装置； 禾口
与所述板翅式换热器组的一个独立换热通道即第四换热通道连接的一台天然气重烃分离 器，
其中两台气液分离器中的第一台气液分离器的气相端与二段式混合工质压缩机的第二压 缩段连接， 第一台气液分离器的液相端经由液体泵与第二压缩段的出口管道汇合后连接到所 述两台冷却器中的第二台冷却器， 第二台气液分离器的气相端和液相端分别与所述一组板翅 式换热器组的两个换热通道即第一换热通道和第二换热通道连接； 其中用于输送净化天然气 的管道通过换热器组的上述独立换热通道即第四换热通道连接到重烃分离器， 重烃分离器的 顶部气相端通过换热器组的一个换热通道即第五换热通道后连接到液化天然气储罐。
另外， 重烃分离器的顶部气相端依次通过换热器组的第五换热通道后进一步通过换热器 组的另外第六换热通道连接到液化天然气储罐。
这里所述的"第一段压缩"或"一段压缩"与"第一压缩段"可互换使用， 以此类推。
下面描述采用单一混合工质制冷液化天然气的方法。
本发明所述二段式混合工质压缩***的装置， 在其混合冷剂压缩***中， 压缩机第一段 的出口气体进入第一级冷却器中被冷却后通过第一级气液分离器进行气液分离， 分离后的气 相继续进入第二压缩段， 分离后的液相经液体泵加压后与经过第二段压缩后的热气体汇合， 再经第二级冷却器冷却后进入第二级气液分离器中进行气液分离， 分离后的气相进入下游换 热器的第一换热通道（气相通道）； 第二级气液分离器底部得到的液体分别进入下游换热器的 第二液相换热通道。 在冷箱***中， 由冷剂压缩***的第二级气液分离器底部来的液体冷剂 进入换热器组的第二液相换热通道被预冷后再通过第一节流装置， 节流后的该流股返回至换 热器组的第三换热通道中提供冷量； 由第二级气液分离器顶部来的气相冷剂经由换热器组的 第一换热通道被预冷后再流经第二节流装置进行节流， 节流后的该流股反向进入换热器组的 第三换热通道中提供冷量。 从第三换热通道流出的混合冷剂被输送回到第一压缩段。 天然气 首先经过换热器组的第四换热通道被冷却至一定温度后进入重烃分离器中进行分离， 底部得 到重烃组分， 顶部得到的气相部分继续进入换热器组的其余各级换热器 (例如第五换热通道；) 进行换热， 冷却至过冷状态， 得到的 LNG进入 LNG储罐中被储存。
采用单一混合工质制冷液化天然气的方法包括：
天然气循环：
净化后的原料天然气首先进入板翅式换热器组的第四换热通道进行预冷， 被冷却至 -30°C〜- 60°C后进入重烃分离器进行气液分离， 由重烃分离器顶部分离出的气相流股继续进 入换热器组的其余各级换热器 (例如第五换热通道；)， 并在其中被冷却至 -130°C〜- 166°C， 得到 的液化天然气送入 LNG储罐中储存。
混合冷剂循环：
由 C1〜C5和 N2组成的混合工质（， 通常选自 Cl、 C2、 C3、 C4和 C5链烷烃和 N2中的 四种、 五种或六种， 它们按照任意体积比例或按照大约等同的体积比例， 进入压缩机的入口， 经第一段压缩至 0.6〜1.8MPaA，进入第一级冷却器冷却至 30°C〜40°C，再进入第一级气液分 离器进行气液分离， 第一级气液分离器顶部分离出的气体继续进入压缩机的第二段入口， 经 二段压缩至 1.2〜5.4MPaA，第一级气液分离器底部液相端分离出的液体经液体泵加压后与第 二段压缩出口管道的热气体汇合后， 再进入第二级冷却器中被冷却至 30°C〜40°C， 冷却后的 混合工质随后进入第二级气液分离器进行气液分离， 第二级气液分离器的顶部气体随后进入 主换热器组的第一换热通道参与换热， 第二级气液分离器底部分离出的液体进入主换热器组 的第二换热通道参与换热；
从混合工质压缩***的第二级气液分离器底部引出的液体首先进入换热器组的第二换热 通道， 在其中被预冷至约 -30°C〜- 80°C， 经第一节流阀节流至 0.25~0.75MPaA后与流过主换 热器组的第一级换热通道和然后经过第二节流阀返回的混合工质流股汇合并反向进入第三级 换热通道为换热器组提供冷量和然后返回到第一压缩段， 由第二级气液分离器顶部分离出的 混合工质的气相流股通过换热器组的气相通道 (第一换热通道；)冷却至 -135 °C〜- 169°C， 再经第 二节流阀节流至 0.25〜0.75MPaA后反向进入换热器组的第三换热通道为换热器提供冷量。
这里， 压力单位 MPaA为兆帕， 绝对压力。 在本发明中， 一般而言， 一个设备与另一个 设备的连接是通过管道来实现的。
本发明的优点：
1. 本发明装置中采用了二段式混合冷剂压缩机， 将混合冷剂逐级压缩并逐级分离， 减少 了气体压缩的功耗。
2. 一级气液分离器底部液体流股不参与后续的压缩过程，在一定程度上减少了混合冷剂 配比的波动对压缩机组运行工况的影响程度， 使得整个装置更易于操作。
3. 经混合冷剂压缩机压缩得到的气相和液相混合冷剂流股分别进入换热器组的不同换 热通道而不需末级液体泵（即仅仅使用一台液体泵）， 使得能耗有所降低， 且采用二级换热使 得整个换热过程的冷流体和热流体的换热曲线更为匹配， 有效减少了混合冷剂的流量。
4. 对装置的变负荷运转有很好的适应性， 可有效避免冷箱底部积液， 从而保证在低负荷 工况时， 产品能耗与正常工况能耗接近。 附图说明
图 1是现有技术的一种结构图；
图 2是本发明所述二段式混合工质压缩***的装置配置图。 具体实施方式
下面结合附图进一步说明。
图 2所示的装置包括二段式混合工质压缩机 1， 第一冷却器 21、 第二冷却器 22， 第一气 液分离器 31、 第二气液分离器 32、 重烃分离器 6 (气液分离器）， 液体泵 4， 第一节流装置 51、 第二节流装置 52， 一组板翅式换热器组 7(即主换热器组;)和一台 LNG储罐 8。 其混合制 冷剂的压缩***包括一台二段式混合工质压缩机 1，两台冷却器 21、 22，两台气液分离器 31、 32, 一台液体泵 4， 冷箱***包括一组板翅式换热器组 7 (两级换热）、一台重烃分离器 6 (气 液分离器） 和两台节流装置 51、 52； 混合工质和天然气在冷箱***中完成整个换热过程。 在 混合冷剂压缩***中， 压缩机 1第一段的出口连接到第一级冷却器 21， 第一级冷却器 21再 与第一级气液分离器 31连接， 第一级气液分离器 31的气相端连接到第二压缩段， 第一级气 液分离器 31底部液相端连接到液体泵 4， 液体泵 4的输出端与第二压缩段的出口管道汇合后 再连接到第二级冷却器 22， 第二级冷却器 22再与第二级气液分离器 32连接， 第二级气液分 离器 32顶部气相端与换热器组 7的第一换热通道 （气相通道） 连接； 第二级气液分离器 32 底部液相端与换热器组 7的第二液相换热通道连接；
在冷箱***中，由混合冷剂压缩***来的第二级气液分离器 32液相端通过换热器组 7中 的第二换热通道连接到第一节流装置 51的一端， 第一节流装置 51的另一端与换热器组 7的 第三换热通道连接；二级气液分离器 32顶部得到的气相端通过换热器组 7的第一换热通道被 预冷， 再与第二节流装置 52—端连接， 第二节流装置 52的另一端连接到换热器组 7的第三 换热通道后再连接到第一压缩段； 天然气管道通过换热器组的第四换热通道连接到重烃分离 器 6，重烃分离器 6的顶部气相端依次通过换热器组 7的其余各级换热器 (例如第五换热通道， 任选地还可以经过第六换热通道)后连接到 LNG储罐 8。
使用图 2的装置的工艺流程如下：
天然气循环：
如附图 2中所示， 净化后的原料天然气首先进入板翅式主换热器组 7 (两级换热） 中的 第四换热通道中被预冷， 被冷却至 -30°C〜- 60°C后进入重烃分离器 6 中进行气液分离， 由重 烃分离器 6顶部分离出的气相流股继续进入主换热器组 7的其余各级换热器， 并在其中被冷 却至 -130°C〜- 166°C， 得到的液化天然气送入 LNG储罐 8中储存， 重烃分离器 6的底部得到 液化石油气 （LPG)。
混合冷剂循环： 由 C1〜C5和 N2组成的混合工质， 通常选自 Cl、 C2、 C3、 C4和 C5链烷烃和 N2中的四 种、 五种或六种， 它们按照任意体积比例或按照大约等同的体积比例， 进入压缩机 1的入口， 经一段压缩至 0.6〜1.8MPaA， 进入一级冷却器 21冷却至 30°C〜40°C， 再进入一级气液分离 器 31进行气液分离， 一级气液分离器 31顶部分离出的气体继续进入压缩机的第二段入口， 经二段压缩至 1.2〜5.4MPaA， 第一级气液分离器 31底部液相端分离出的液体经液体泵 4加 压后与二段压缩出口的热气体汇合后， 再进入第二级冷却器 22冷却至 30°C〜40°C， 冷却后 的混合工质随后进入第二级气液分离器 32中进行气液分离， 第二级气液分离器 32顶部气体 随后进入主换热器组 7的第一换热通道参与换热，第二级气液分离器 32底部分离出的液体进 入主换热器组 7的第二换热通道参与换热；
从混合工质压缩***的第二级气液分离器 32 底部引出的液体首先进入换热器组的第二 换热通道， 在其中被预冷至约 -30°C〜- 80°C， 经节流阀 51节流至 0.25〜0.75MPaA后与从换 热器组 7 后一级换热器返回 (即流过第一换热通道和第二节流阀;)的混合工质流股汇合并反向 进入前一级换热器 (即第三换热通道)为换热器组 7提供冷量， 由第二级气液分离器 32顶部分 离出的混合工质的气相流股通过换热器组 7 的气相通道 (即第一换热通道)冷却至 -135 °C〜 -169 °C , 再经第二节流阀 52节流至 0.25〜0.75MPaA后反向进入换热器组 7的第三换热通道 中为换热器组提供冷量， 然后返回到第一压缩段。

Claims

权 利 要 求
1、采用单一混合工质制冷液化天然气的装置， 其特征在于， 该装置包括混合冷剂压缩系 统和冷箱***，
其中该压缩***包括二段式混合工质压缩机、 分别与所述二段式混合工质压缩机的第一 段和第二段连接的第一台冷却器和第二台冷却器、 分别与所述第一台冷却器和第二台冷却器 连接的第一台气液分离器和第二台气液分离器和与所述两台气液分离器当中的第一台连接的 一台液体泵， 和
其中冷箱***包括：
一组板翅式换热器组， 它包含至少五个换热通道： 第一、 第二、 第三、 第四和第五换热 通道， 所述第二换热通道和第一换热通道经由两根管道分别与所述混合冷剂压缩***中的第 二台气液分离器的液相端和气相端连接， 和第三换热通道经由管道连接到第一压缩段； 与所述板翅式换热器组的第二换热通道和第三换热通道连接的第一台节流装置； 与所述板翅式换热器组的第一换热通道和第三换热通道连接的第二台节流装置； 禾口
与所述板翅式换热器组的一个独立换热通道即第四换热通道连接的一台天然气重烃分离 器，
其中两台气液分离器中的第一台气液分离器的气相端与二段式混合工质压缩机的第二压 缩段连接， 第一台气液分离器的液相端经由液体泵与第二压缩段的出口管道汇合后连接到所 述两台冷却器中的第二台冷却器， 第二台气液分离器的气相端和液相端分别与所述一组板翅 式换热器组的两个换热通道即第一换热通道和第二换热通道连接； 其中用于输送净化天然气 的管道通过换热器组的上述独立换热通道即第四换热通道连接到重烃分离器， 重烃分离器的 顶部气相端依次通过换热器组的一个换热通道即第五换热通道后连接到液化天然气储罐。
2、 根据权利要求 1所述的采用单一混合工质制冷液化天然气的装置， 其特征在于： 重烃分离器的顶部气相端依次通过换热器组的第五换热通道后进一步通过换热器组的另 外第六换热通道连接到液化天然气储罐。
3、 一种采用单一混合工质制冷来液化天然气的方法， 其特征在于， 该方法包括： 天然气循环：
净化后的原料天然气首先进入板翅式换热器组的第四换热通道进行预冷， 被冷却至 -30°C〜- 60°C后进入重烃分离器进行气液分离， 由重烃分离器顶部分离出的气相流股继续进 入换热器组的第五换热通道，并在其中被冷却至 -130°C〜- 166°C，得到的液化天然气送入 LNG 储罐中储存；
混合冷剂循环：
由 C1〜C5和 N2组成的混合工质进入压缩机的入口， 经第一段压缩至 0.6〜1.8MPaA， 进入第一级冷却器冷却至 30°C〜40°C， 再进入第一级气液分离器进行气液分离， 第一级气液 分离器顶部分离出的气体继续进入压缩机的第二段入口， 经二段压缩至 1.2〜5.4MPaA， 第一 级气液分离器底部液相端分离出的液体经液体泵加压后与第二段压缩出口管道的热气体汇合 后， 再进入第二级冷却器中被冷却至 30°C〜40°C， 冷却后的混合工质随后进入第二级气液分 离器进行气液分离， 第二级气液分离器的顶部气体随后进入主换热器组的第一换热通道参与 换热， 第二级气液分离器底部分离出的液体进入主换热器组的第二换热通道参与换热；
从混合工质压缩***的第二级气液分离器底部引出的液体首先进入换热器组的第二换热 通道， 在其中被预冷至约 -30°C〜- 80°C， 经第一节流阀节流至 0.25~0.75MPaA后与流过主换 热器组的第一级换热通道和然后经过第二节流阀返回的混合工质流股汇合并反向进入第三级 换热通道为换热器组提供冷量和然后返回到第一压缩段， 由第二级气液分离器顶部分离出的 混合工质的气相流股通过换热器组的第一换热通道冷却至 -135 °C〜- 169°C， 再经第二节流阀 节流至 0.25〜0.75MPaA后反向进入换热器组的第三换热通道为换热器提供冷量。
4. 根据权利要求 3所述的采用单一混合工质制冷来液化天然气的方法， 其特征在于， 所 述混合工质选自 Cl、 C2、 C3、 C4和 C5链烷烃和 N2中的四种、 五种或六种， 它们按照任意 体积比例或按照大约等同的体积比例。
5. 根据权利要求 3或 4所述的采用单一混合工质制冷来液化天然气的方法，其特征在于， 重烃分离器的顶部气相端依次通过换热器组的第五换热通道后进一步通过换热器组的另外第 六换热通道连接到液化天然气储罐。
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