WO2017121042A1 - 一种膨胀制冷富甲烷气液化的方法及装置 - Google Patents

一种膨胀制冷富甲烷气液化的方法及装置 Download PDF

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WO2017121042A1
WO2017121042A1 PCT/CN2016/078263 CN2016078263W WO2017121042A1 WO 2017121042 A1 WO2017121042 A1 WO 2017121042A1 CN 2016078263 W CN2016078263 W CN 2016078263W WO 2017121042 A1 WO2017121042 A1 WO 2017121042A1
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gas
methane
heat exchanger
rich
low
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PCT/CN2016/078263
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English (en)
French (fr)
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张惊涛
母斌
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成都赛普瑞兴科技有限公司
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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
    • F25J1/0203—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 single-component refrigerant [SCR] fluid in a closed vapor compression cycle
    • F25J1/0208—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 single-component refrigerant [SCR] fluid in a closed vapor compression cycle in combination with an internal quasi-closed refrigeration loop, e.g. with deep flash recycle loop
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F25—REFRIGERATION OR COOLING; COMBINED HEATING AND REFRIGERATION SYSTEMS; HEAT PUMP SYSTEMS; MANUFACTURE OR STORAGE OF ICE; LIQUEFACTION SOLIDIFICATION OF GASES
    • F25J—LIQUEFACTION, SOLIDIFICATION OR SEPARATION OF GASES OR GASEOUS OR LIQUEFIED GASEOUS MIXTURES BY PRESSURE AND COLD TREATMENT OR BY BRINGING THEM INTO THE SUPERCRITICAL STATE
    • F25J3/00—Processes or apparatus for separating the constituents of gaseous or liquefied gaseous mixtures involving the use of liquefaction or solidification
    • F25J3/06—Processes or apparatus for separating the constituents of gaseous or liquefied gaseous mixtures involving the use of liquefaction or solidification by partial condensation
    • F25J3/0605—Processes or apparatus for separating the constituents of gaseous or liquefied gaseous mixtures involving the use of liquefaction or solidification by partial condensation characterised by 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
    • F25J1/00—Processes or apparatus for liquefying or solidifying gases or gaseous mixtures
    • F25J1/0002—Processes or apparatus for liquefying or solidifying gases or gaseous mixtures characterised by the fluid to be liquefied
    • F25J1/0022—Hydrocarbons, e.g. natural gas
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F25—REFRIGERATION OR COOLING; COMBINED HEATING AND REFRIGERATION SYSTEMS; HEAT PUMP SYSTEMS; MANUFACTURE OR STORAGE OF ICE; LIQUEFACTION SOLIDIFICATION OF GASES
    • F25J—LIQUEFACTION, SOLIDIFICATION OR SEPARATION OF GASES OR GASEOUS OR LIQUEFIED GASEOUS MIXTURES BY PRESSURE AND COLD TREATMENT OR BY BRINGING THEM INTO THE SUPERCRITICAL STATE
    • F25J1/00—Processes or apparatus for liquefying or solidifying gases or gaseous mixtures
    • F25J1/003—Processes or apparatus for liquefying or solidifying gases or gaseous mixtures characterised by the kind of cold generation within the liquefaction unit for compensating heat leaks and liquid production
    • F25J1/0032—Processes or apparatus for liquefying or solidifying gases or gaseous mixtures characterised by the kind of cold generation within the liquefaction unit for compensating heat leaks and liquid production using the feed stream itself or separated fractions from it, i.e. "internal refrigeration"
    • F25J1/0035—Processes or apparatus for liquefying or solidifying gases or gaseous mixtures characterised by the kind of cold generation within the liquefaction unit for compensating heat leaks and liquid production using the feed stream itself or separated fractions from it, i.e. "internal refrigeration" by gas expansion with extraction of work
    • F25J1/0037—Processes or apparatus for liquefying or solidifying gases or gaseous mixtures characterised by the kind of cold generation within the liquefaction unit for compensating heat leaks and liquid production using the feed stream itself or separated fractions from it, i.e. "internal refrigeration" by gas expansion with extraction of work of a return stream
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F25—REFRIGERATION OR COOLING; COMBINED HEATING AND REFRIGERATION SYSTEMS; HEAT PUMP SYSTEMS; MANUFACTURE OR STORAGE OF ICE; LIQUEFACTION SOLIDIFICATION OF GASES
    • F25J—LIQUEFACTION, SOLIDIFICATION OR SEPARATION OF GASES OR GASEOUS OR LIQUEFIED GASEOUS MIXTURES BY PRESSURE AND COLD TREATMENT OR BY BRINGING THEM INTO THE SUPERCRITICAL STATE
    • F25J1/00—Processes or apparatus for liquefying or solidifying gases or gaseous mixtures
    • F25J1/003—Processes or apparatus for liquefying or solidifying gases or gaseous mixtures characterised by the kind of cold generation within the liquefaction unit for compensating heat leaks and liquid production
    • F25J1/0032—Processes or apparatus for liquefying or solidifying gases or gaseous mixtures characterised by the kind of cold generation within the liquefaction unit for compensating heat leaks and liquid production using the feed stream itself or separated fractions from it, i.e. "internal refrigeration"
    • F25J1/004—Processes or apparatus for liquefying or solidifying gases or gaseous mixtures characterised by the kind of cold generation within the liquefaction unit for compensating heat leaks and liquid production using the feed stream itself or separated fractions from it, i.e. "internal refrigeration" by flash gas recovery
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F25—REFRIGERATION OR COOLING; COMBINED HEATING AND REFRIGERATION SYSTEMS; HEAT PUMP SYSTEMS; MANUFACTURE OR STORAGE OF ICE; LIQUEFACTION SOLIDIFICATION OF GASES
    • F25J—LIQUEFACTION, SOLIDIFICATION OR SEPARATION OF GASES OR GASEOUS OR LIQUEFIED GASEOUS MIXTURES BY PRESSURE AND COLD TREATMENT OR BY BRINGING THEM INTO THE SUPERCRITICAL STATE
    • F25J1/00—Processes or apparatus for liquefying or solidifying gases or gaseous mixtures
    • F25J1/003—Processes or apparatus for liquefying or solidifying gases or gaseous mixtures characterised by the kind of cold generation within the liquefaction unit for compensating heat leaks and liquid production
    • F25J1/0047—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
    • F25J1/005—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 expansion of a gaseous refrigerant stream with extraction of work
    • 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
    • F25J1/0082—Methane
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F25—REFRIGERATION OR COOLING; COMBINED HEATING AND REFRIGERATION SYSTEMS; HEAT PUMP SYSTEMS; MANUFACTURE OR STORAGE OF ICE; LIQUEFACTION SOLIDIFICATION OF GASES
    • F25J—LIQUEFACTION, SOLIDIFICATION OR SEPARATION OF GASES OR GASEOUS OR LIQUEFIED GASEOUS MIXTURES BY PRESSURE AND COLD TREATMENT OR BY BRINGING THEM INTO THE SUPERCRITICAL STATE
    • F25J1/00—Processes or apparatus for liquefying or solidifying gases or gaseous mixtures
    • F25J1/02—Processes or apparatus for liquefying or solidifying gases or gaseous mixtures requiring the use of refrigeration, e.g. of helium or hydrogen ; Details and kind of the refrigeration system used; Integration with other units or processes; Controlling aspects of the process
    • F25J1/0201—Processes or apparatus for liquefying or solidifying gases or gaseous mixtures requiring the use of refrigeration, e.g. of helium or hydrogen ; Details and kind of the refrigeration system used; Integration with other units or processes; Controlling aspects of the process using only internal refrigeration means, i.e. without external refrigeration
    • F25J1/0202—Processes or apparatus for liquefying or solidifying gases or gaseous mixtures requiring the use of refrigeration, e.g. of helium or hydrogen ; Details and kind of the refrigeration system used; Integration with other units or processes; Controlling aspects of the process using only internal refrigeration means, i.e. without external refrigeration in a quasi-closed internal refrigeration loop
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F25—REFRIGERATION OR COOLING; COMBINED HEATING AND REFRIGERATION SYSTEMS; HEAT PUMP SYSTEMS; MANUFACTURE OR STORAGE OF ICE; LIQUEFACTION SOLIDIFICATION OF GASES
    • F25J—LIQUEFACTION, SOLIDIFICATION OR SEPARATION OF GASES OR GASEOUS OR LIQUEFIED GASEOUS MIXTURES BY PRESSURE AND COLD TREATMENT OR BY BRINGING THEM INTO THE SUPERCRITICAL STATE
    • 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 invention relates to the field of condensation and separation of methane-rich gas, in particular to a method and a device for liquefying expanded methane-rich gas.
  • the expansion refrigeration cycle mostly adopts an inverse Brayton cycle, in which the working medium is isentropically compressed by a compressor, cooled by an aftercooler, and then isentropically expanded and expanded in a turboexpander to perform external work, thereby obtaining a low-temperature airflow.
  • a turboexpander especially high speed gas bearing turboexpanders
  • the efficiency of the turbine reverse Brayton cycle has been significantly improved, and very low refrigeration temperatures and very low Wide range of cooling capacity with high reliability. Therefore, in recent decades, the reverse Bretton refrigeration cycle has been greatly developed, and the scope of application is becoming wider and wider.
  • the expansion refrigeration cycle mainly adopts three forms of nitrogen expansion refrigeration, nitrogen-methane hybrid expansion refrigeration and natural gas direct expansion refrigeration.
  • nitrogen expansion refrigeration is a variant of direct expansion refrigeration, which has the advantages of strong adaptability, high liquefaction capacity, simple process, flexible operation and convenient operation, but its energy consumption is high.
  • Nitrogen-methane hybrid expansion refrigeration is an improvement of the nitrogen expansion refrigeration cycle. It has the advantages of simple process, easy control, short start-up time, etc., and saves 10% of power consumption compared with pure nitrogen expansion refrigeration.
  • Natural gas direct expansion refrigeration directly uses high-pressure natural gas to adiabatically expand in the expander to liquefy natural gas, make full use of the pressure energy of natural gas itself, consume less energy, and save equipment investment.
  • the gas bearing turboexpander with small size, light weight, high efficiency and long-term reliable operation can effectively improve the system efficiency, and can be used in the peak-shaving device which is frequently operated and requires quick start and stop. It has developed into a multi-stage expansion liquefaction system, and the expansion chiller is also becoming mature, with long life, high reliability, low vibration, light weight, etc., and has good development prospects in natural gas liquefaction. Under the increasing demand of liquefied gas, the cycle has greater advantages: it has the advantages of compact equipment, low investment, flexible adjustment and reliable operation.
  • the object of the present invention is to provide a method for producing liquefied natural gas (GB 2522421A), which is difficult to separate heavy hydrocarbons, has complicated operation, high equipment investment, large methane loss, loss of expansion work, and high energy consumption.
  • the invention has the advantages of simple process, flexible operation, low equipment investment, small methane loss, good nitrogen separation effect and recovery expansion work, low energy consumption, low nitrogen content of liquefied methane-rich gas and strong adaptability of raw materials, and has good performance. Application prospects.
  • a method for liquefying an expanded refrigeration methane-rich gas comprises the following steps:
  • the operation of the step 1 is as follows: after the methane-rich feed gas is mixed with a part of the preheated gas, it is cooled to -10 to -90 ° C by a heat exchanger, and then de-heavy hydrocarbons are introduced into a heavy hydrocarbon separator to obtain a low-temperature dry gas and dried at a low temperature. After the gas is cooled by the heat exchanger, it is throttled and depressurized, and then gas-liquid separation is carried out. After separation, the liquefied methane-rich gas and the low-temperature flash vapor are respectively obtained, and the liquefied methane-rich gas is collected as a product, and the low-temperature flash vapor is exchanged through the heat exchanger. After the heat, pressurize and enter the next cycle;
  • the methane-rich feed gas is mixed with a portion of the preheated gas, directly cooled by a heat exchanger, and then subjected to throttling and depressurization, then gas-liquid separation is performed, and liquefied methane-rich gas is separately obtained after separation. , low temperature flash steam, liquefied methane enriched gas as product collection, low temperature flash vapor after heat exchange through the heat exchanger, pressurization, into the next cycle;
  • step 2 The operation of the step 2 is as follows: after the low temperature flash steam is exchanged by the heat exchanger, the preheating gas is obtained, and the preheating gas is pressurized, and after being pressurized, it is divided into the first material and the second material.
  • the first strand of material is sent to the expander after heat exchange by the heat exchanger, and the expanded material is obtained.
  • the expanded material is mixed with the preheated gas after heat exchange by the heat exchanger, and enters the next cycle, and the second material is the second material. a part of the preheating gas mixed with the methane-rich feed gas in step 1;
  • the operation of the step 2 is as follows: after the low temperature flash vapor is exchanged by the heat exchanger, the preheating gas is obtained, the preheating gas is pressurized, and after being pressurized, the first material and the second material are separated. Two materials, the first material is directly sent into the expander to obtain the expanded material, and the expanded material is mixed with the preheated gas after heat exchange by the heat exchanger, and enters the next cycle, and the second material is the step 1 a portion of the preheated gas mixed with the methane-rich feed gas;
  • the operation of the step 1 is as follows: after the low temperature flash vapor is exchanged by the heat exchanger, the preheating gas is obtained, and the preheating gas is pressurized, and The methane-rich feed gas is mixed with the preheated gas, and the mixed materials are cooled to -10 to -90 ° C by a heat exchanger, and then de-heavy hydrocarbons are introduced into the heavy hydrocarbon separator to obtain low-temperature dry gas, and the low-temperature dry gas is passed through the heat exchanger. After cooling, after throttling and depressurization, gas-liquid separation is carried out.
  • liquefied methane-rich gas, low-temperature flash vapor, liquefied methane-rich gas are collected as products, and low-temperature flash vapor is superheated by heat exchanger.
  • the methane-rich feed gas is free of heavy hydrocarbons, the methane-rich feed gas is mixed with a portion of the preheated gas, directly cooled by a heat exchanger, and then subjected to throttling and depressurization, then gas-liquid separation, after separation Liquefied methane-rich gas, low-temperature flash steam, liquefied methane-rich gas are collected as products, and the low-temperature flash vapor is heated by the heat exchanger, and then pressurized to enter the next cycle;
  • step 2 After the cooling medium is pressurized, it is exchanged by the heat exchanger and enters the expander to obtain the expanded material. After the heat transfer material is exchanged by the heat exchanger, the pressure is returned to the next one. cycle;
  • step 2 the operation of the step 2 is as follows: after the cooling medium is pressurized, it is directly sent into the expander to obtain an expanded material, and the expanded material is then subjected to heat exchange by the heat exchanger, and then returned to the pressurization to enter the next cycle;
  • the methane-rich feed gas has a pressure of 1 MPaG to 20 MPaG and a temperature of -30 to 60 ° C, or the methane-rich feed gas is a self-evaporating gas of the LNG storage tank.
  • the partial preheating gas is mixed with the methane-rich raw material gas to form two materials into the heat exchanger; or the preheating gas is completely mixed with the methane-rich raw material gas, and then divided into two into the heat exchanger.
  • the throttling and depressurization are performed, and the number of stages of the throttling is first-stage throttling, two-stage throttling, three-stage throttling or four-stage throttling.
  • the low-temperature dry gas is cooled by the heat exchanger, then depressurized by the throttling, and then enters the first gas-liquid separator for gas-liquid separation, and the first liquid phase and the first gas phase are respectively obtained after separation.
  • the first liquid phase is a liquefied methane-rich gas
  • the first gas phase is a low-temperature flash vapor.
  • the first liquid phase is depressurized and then depressurized, and then enters the second gas-liquid separator for gas-liquid separation, and after separation, a second liquid phase and a second gas phase are respectively obtained, and the second liquid is obtained.
  • the phase is the liquefied methane-rich gas, and the first gas phase and the second gas phase are low temperature flash vapor.
  • pre-cooling step external cooling is connected to the heat exchanger, and other components in the heat exchanger are pre-cooled by external cooling.
  • a typical refrigerant used for the external cooling is one or more of propylene, propane, ammonia, freon, water, BOG, and lithium bromide.
  • Methane-laden liquefied gases can be extracted from any material in the system.
  • step 2 according to the pressure and temperature of the methane-rich feed gas, it is mixed with the preheated gas at a suitable position in the system.
  • the apparatus for the foregoing method for expanding and refrigerating methane-rich gas liquefaction includes a methane-rich gas liquefaction system and an open-cycle refrigeration system;
  • the methane-rich gas liquefaction system includes a raw material supply device for transporting a methane-rich feed gas, a heat exchanger, and a gas-liquid separator, and the raw material supply device, the heat exchanger, and the gas-liquid separator are sequentially connected through a pipeline;
  • the open-cycle refrigeration system includes a gas-liquid separator, a heat exchanger, a compressor, and an expander, and the gas-liquid separator, the heat exchanger, the compressor, and the expander form an open circulation system through a pipeline;
  • Providing another alternative device including a methane-rich gas liquefaction system, a closed cycle refrigeration system;
  • the methane gas liquefaction system includes a raw material supply device, a heat exchanger, a gas-liquid separator, and a compressor, and the raw material supply device, the heat exchanger, the gas-liquid separator, and the compressor are sequentially connected through a pipeline;
  • the closed cycle refrigeration system includes a compressor, a heat exchanger, and an expander, and the compressor, the heat exchanger, and the expander form a closed circulation system through a pipeline.
  • a methane-containing gas that is not easily liquefied e.g., one or more of nitrogen, hydrogen, argon, oxygen, or helium
  • the methane-containing, non-liquefied gas can be withdrawn from the first preheated gas or the first flash gas or the second preheated gas or the second flash gas.
  • external cooling in conjunction with a heat exchanger, typically one or more of propylene, propane, ammonia, freon, water, BOG, lithium bromide.
  • the invention has the advantages of rich regulation means, simple process, flexible operation, strong adaptability of raw materials, low equipment investment, small methane loss, good nitrogen separation effect and low energy consumption, and has good application prospect.
  • the methane-rich gas is pre-cooled, expanded, and then cooled, and has a better refrigeration effect than the prior art
  • the throttle valve is used for decompression, although the efficiency is slightly lower, but the cooling capacity is equivalent, the operation is simpler, and the equipment investment is smaller;
  • the invention adopts step-by-step throttling, and the pressure drop of each stage is small, so that the invention has the advantages of lower energy consumption, less methane loss and high nitrogen separation coefficient;
  • the present invention enables the expansion work to be transmitted to the compression device through the mutual cooperation between the components, thereby effectively reducing energy consumption, saving cost, and having a good application prospect;
  • the invention has flexible operation, small methane loss, low energy consumption and good application prospect.
  • Embodiment 1 is a schematic diagram of the principle of Embodiment 1.
  • T1 is the pretreatment system
  • P1 is the expander
  • C1 and C2 are the recycle gas compressors
  • E1 and E2 are the coolers
  • E3 is the heat exchanger
  • V2 is the heavy hydrocarbon separator
  • V1 is the gas-liquid separator
  • V3 is an LNG storage tank.
  • Embodiment 2 is a schematic diagram of the principle of Embodiment 2.
  • T1 is the pretreatment system
  • P1 is the expander
  • C1 and C2 are the recycle gas compressors
  • C3 is the methane-rich recycle gas compressor
  • E1, E2, E3 are the coolers
  • E4 is the heat exchanger
  • V1 is The gas-liquid separator
  • V2 is a heavy hydrocarbon separator
  • V3 is an LNG storage tank.
  • the schematic diagram of the flow of this embodiment is shown in Figure 1.
  • the process includes a pretreatment system (T1), an expander (P1), a recycle gas compressor (C1, C2), a cooler (E1, E2), and a heat exchanger ( E3), a heavy hydrocarbon separator (V2), a gas-liquid separator (V1), an LNG storage tank (V3), etc., and a methane-rich gas liquefaction system and an open-cycle refrigeration system are formed by piping between the components.
  • the untreated methane-rich feed gas 1 is treated with a pretreatment system T1 to obtain a methane-rich feed gas 2 .
  • the methane-rich feed gas 2 is mixed with a portion of the preheated gas 16 (mentioned below) to obtain the material 3, which is cooled by the heat exchanger E3 to obtain the material 4.
  • the material 4 exits the heat exchanger E3, enters the heavy hydrocarbon separator V2 to de-heavigate the hydrocarbon, the heavy hydrocarbon is taken out from the material 6, and the low-temperature dry gas material 5 is further cooled into the heat exchanger E3 to obtain the material 7.
  • the material 7 is taken out of the heat exchanger E3 and throttled by the first throttle valve I to obtain the material 8.
  • the material 8 enters the gas-liquid separator V1 for gas-liquid separation, and the liquid phase 10 separated by the gas-liquid separator V1 continues to perform two-stage throttling, and the low-temperature flash vapor 9 separated by the gas-liquid separator V1 enters the heat exchanger E3.
  • the preheating gas 11 is taken out.
  • the preheating gas 11 extracts two materials 12 and 13, the material 12 is taken out as a non-liquefied gas, and the material 13 is mixed with the material 28 (mentioned below) to obtain the material 25.
  • the material 25 is mixed with the material 22 (mentioned below)
  • the material 23 is obtained, and the material 23 is pressurized by the circulating gas compressor C2.
  • the material 24 is cooled by the cooler E2, and the material 14 is divided into the material 15 With material 16, material 16 is mixed with methane-rich feed gas 2 for the next cycle.
  • the liquid phase 10 separated by the gas-liquid separator V1 is throttled by the secondary throttle valve II to obtain the material 17.
  • the material 17 enters the LNG storage tank V3 for gas-liquid separation, and the separated liquid phase product is stored in the tank and transported through the material 18;
  • the low temperature flash steam 19 enters the heat exchanger E3 to reheat, the preheating gas 20 is taken out, and the preheating gas 20 is pressurized into the circulating gas compressor C1 to obtain the material 21.
  • the material 21 is cooled by the cooler E1
  • the material 22 is taken out and the material 22 is mixed with the material 25.
  • the material 15 of the preheated gas 14 is cooled in the heat exchanger E3 to obtain the material 26.
  • Material 26 enters expander P1, and after expansion, material 27 is withdrawn.
  • the material 15 is directly sent to the expander P1 for expansion without heat exchange by the heat exchanger E3, and the material 27 is taken out.
  • Material 27 enters heat exchanger E3 to provide refrigeration and heat exchanger to obtain material 28. After the material 28 is mixed with the preheated gas 13, it proceeds to the next cycle.
  • the temperature of the methane-rich feed gas 2 is 40 ° C and the pressure is 6000 kPaA; the liquefied gas (ie, material 12) is 37 ° C and the pressure is 1080 kPa A; the temperature of the product LNG is -160.5 ° C, and the pressure is 120 kPaA. All are absolutely pressure.
  • the schematic diagram of the flow of this embodiment is shown in FIG. 2, and the process includes a pretreatment system (T1), an expander (P1), a circulating gas compressor (C1, C2), a methane-rich circulating gas compressor (C3), and a cooler. (E1, E2, E3), heat exchanger (E4), gas-liquid separator (V1), heavy hydrocarbon separator (V2), LNG storage tank (V3), and methane-rich gas liquefaction system formed by pipes between the components And closed cycle refrigeration systems.
  • T1 pretreatment system
  • P1 a circulating gas compressor
  • C3 methane-rich circulating gas compressor
  • E4 heat exchanger
  • V1 gas-liquid separator
  • V2 heavy hydrocarbon separator
  • LNG storage tank V3
  • methane-rich gas liquefaction system formed by pipes between the components And closed cycle refrigeration systems.
  • the untreated methane-rich feed gas 1 is treated with a pretreatment system T1 to obtain a methane-rich feed gas 2 .
  • Methane-rich feed gas 2 is mixed with preheated gas 16 (mentioned below) to give material 3.
  • preheated gas 16 (mentioned below) to give material 3.
  • the heat exchanger E4 is discharged from the material 4
  • the heavy hydrocarbon separator V2 is de-heavier
  • the heavy hydrocarbon is taken out by the material 6
  • the low-temperature dry gas material 5 is re-entered into the heat exchanger E4 to be cooled by the material.
  • 7 leads to the heat exchanger E4.
  • the material 8 is obtained.
  • the material 8 enters the gas-liquid separator V1 for gas-liquid separation, and the separated liquid phase 10 continues to perform secondary throttling.
  • the separated low-temperature flash vapor 9 enters the heat exchanger E4 to reheat, and then the preheated gas 11 is taken out, and the preheating is performed.
  • the gas 11 leads to two materials 12 and 13. Wherein the material 12 is taken out as a liquefied gas, and the material 13 is mixed with the material 22 (mentioned below) to obtain the material 14.
  • the material 14 is pressurized by the circulating gas compressor C2, and the material 15 which is taken out after being pressurized is cooled by the cooler E2 to obtain the material 16. Material 16 is mixed with dry gas 2 for the next cycle.
  • the liquid phase 10 separated by the gas-liquid separator V1 is throttled by the secondary throttle valve II to obtain the material 17.
  • the material 17 enters the LNG storage tank V3 for gas-liquid separation, and the separated liquid phase product is stored in the tank and transported through the material 18; the separated low-temperature flash steam 19 enters the heat exchanger E4 to reheat, and the preheating gas 20 is taken out.
  • preheating gas 20 enters the recycle gas compressor C1 is pressurized to obtain material 21. After the material 21 is cooled by the cooler E1, the material 22 is taken out and the material 22 is mixed with the material 13.
  • the material 23 is taken out. After the material 23 is cooled by the cooler E3, the material 24 is obtained. Material 24 enters heat exchanger E4 for further cooling and is withdrawn from material 25. After the material 25 is expanded by the expander P1, the material 26 is obtained. Alternatively, the material 24 is directly sent to the expander P1 for expansion without heat exchange by the heat exchanger E4, and the material 26 is taken out. Material 26 enters heat exchanger E4 to provide refrigeration for the heat exchanger and draws material 27 into rich methane recycle gas compressor C3 to begin the next cycle.
  • the temperature of the methane-rich feed gas 2 is 40 ° C and the pressure is 5000 kPaA; the liquefied gas (ie, material 12) is 37 ° C, the pressure is 1080 kPa A; the temperature of the product LNG is -160.5 ° C, and the pressure is 120 kPaA. All are absolutely pressure.
  • the invention is not limited to the specific embodiments described above.
  • the invention extends to any new feature or any new combination disclosed in this specification, as well as any novel method or process steps or any new combination disclosed.

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Abstract

一种膨胀制冷富甲烷气液化的方法及装置，包括富甲烷气与部分预热气混合后进入换热器（E3、E4）冷却，冷却后的物料再脱重烃，随后依次经节流阀（Ⅰ）节流和气液分离器（V1）分离，被分离成液相物料和低温闪蒸气。液相物料作为产品收集；低温闪蒸气依次经换热器（E3、E4）换热、压缩机（C2）增压，增压后分成两部分物料，一部分与富甲烷气混合进入换热器（E3、E4），另一部分依次进入换热器（E3、E4）、膨胀机（P1）分别被冷却、膨胀，膨胀后的物料进入换热器（E3、E4）提供冷量，换热后返回增压，进入下一个循环。

Description

一种膨胀制冷富甲烷气液化的方法及装置 技术领域
本发明涉及富甲烷气冷凝分离领域，具体为一种膨胀制冷富甲烷气液化的方法及装置。
背景技术
膨胀制冷循环多采用逆布雷顿循环，在该循环中，工质通过压缩机等熵压缩，经后冷却器冷却，然后在透平膨胀机内等熵绝热膨胀并对外做功，从而获得低温气流，来制取冷量。随着低温透平膨胀机(尤其是高速气体轴承透平膨胀机)和高效紧凑换热器的发展，透平逆布雷顿循环的效率得到了显著提高，而且可获得很低的制冷温度和很宽制冷量范围，具有高可靠性。因此，近几十年来，逆布雷顿制冷循环得到了很大的发展，应用范围越来越广。
在天然气液化过程中，膨胀制冷循环主要采用氮膨胀制冷、氮气-甲烷混合膨胀制冷和天然气直接膨胀制冷三种形式。其中，氮膨胀制冷是直接膨胀制冷的一种变型，其具有适应性强，液化能力高，流程简单，运行灵活，操作方便等优点，但其能耗较高。氮气-甲烷混合膨胀制冷则是氮膨胀制冷循环的一种改进，具有流程简单、控制容易、启动时间短等优点，比纯氮气膨胀制冷节省10％的动力消耗。
天然气直接膨胀制冷是直接利用高压天然气在膨胀机中绝热膨胀而使天然气液化，充分利用天然气本身的压力能，消耗电能很少，节省了设备投资。采用体积小、重量轻、效率高、长期可靠运行的气体轴承透平膨胀机，能有效提高***效率，可用于操作频繁且要求快速启停的调峰型装置中。现已发展到多级膨胀的液化***，并且膨胀制冷机也日趋成熟，具有长寿命、高可靠性、低振动、重量轻等特点，在天然气液化方面有良好的发展前景。在液化气量日趋加大的要求下，该循环具有更大的优势：具有设备紧凑、投资少、调节灵活、工作可靠等优点。
现有专利GB 2522421A公开了一种液化天然气的生产过程(LNG production process)，其具有如下缺点：
(1)重烃分离困难；
(2)操作繁琐，设备投资较高；
(3)甲烷损失大，且氮气分离效果不好，液化天然气中含氮量较高；
(4)膨胀功损失掉，能耗较高。
基于GB 2522421A存在的上述缺点，开发一种流程简单、操作灵活、设备投资低、甲烷损失小，且氮气分离效果良好和回收膨胀功的工艺显得尤其重要。
发明内容
本发明的发明目的在于：针对现有液化天然气的生产方法(GB 2522421A)存在重烃分离困难，操作繁琐，设备投资较高，甲烷损失大，膨胀功损失掉，能耗较高等的问题，提供一种膨胀制冷富甲烷气液化的方法及装置。本发明具有流程简单、操作灵活、设备投资低、甲烷损失小，氮气分离效果良好和回收膨胀功等优点，能耗低、液化富甲烷气含氮量低和原料适应性强，具有较好的应用前景。
为了实现上述目的，本发明采用如下技术方案：
一种膨胀制冷富甲烷气液化的方法，包括如下步骤：
(1)富甲烷气液化：
所述步骤1的操作如下：富甲烷原料气与部分预热气混合后，经换热器冷却至-10～-90℃，再进入重烃分离器脱重烃，得到低温干气，低温干气再经换热器冷却后，经节流降压，再进行气液分离，分离后分别得到液化富甲烷气、低温闪蒸气，液化富甲烷气作为产品收集，低温闪蒸气经换热器换热后，进行增压，进入下一个循环；
若富甲烷原料气无重烃，则富甲烷原料气与部分预热气混合后，直接经换热器冷却，再经节流降压后，进行气液分离，分离后分别得到液化富甲烷气、低温闪蒸气，液化富甲烷气作为产品收集，低温闪蒸气经换热器换热后，进行增压，进入下一个循环；
(2)开式循环制冷：
所述步骤2的操作如下：低温闪蒸气经换热器换热后，得到预热气，将预热气进行增压，增压后将其分为第一股物料、第二股物料两股物料，第一股物料经换热器换热后送入膨胀机中，得到膨胀物料，膨胀物料经换热器换热后与预热气混合，进入下一个循环，第二股物料即为所述步骤1中与富甲烷原料气混合的部分预热气；
或者，所述步骤2的操作如下：低温闪蒸气经换热器换热后，得到预热气，将预热气进行增压，增压后将其分为第一股物料、第二股物料两股物料，第一股物料直接送入膨胀机中，得到膨胀物料，膨胀物料经换热器换热后与预热气混合，进入下一个循环，第二股物料即为所述步骤1中与富甲烷原料气混合的部分预热气；
提供另一种替换方法，包括如下步骤：
(1)富甲烷气液化：
所述步骤1的操作如下：低温闪蒸气经换热器换热后，得到预热气，将预热气进行增压，并 将富甲烷原料气与预热气混合，混合的物料经换热器冷却至-10～-90℃，再进入重烃分离器脱重烃，得到低温干气，低温干气再经换热器冷却后，经节流降压，再进行气液分离，分离后分别得到液化富甲烷气、低温闪蒸气，液化富甲烷气作为产品收集，低温闪蒸气经换热器换热后，进行增压，进入下一个循环；若富甲烷原料气无重烃，则富甲烷原料气与部分预热气混合后，直接经换热器冷却，再经节流降压后，进行气液分离，分离后分别得到液化富甲烷气、低温闪蒸气，液化富甲烷气作为产品收集，低温闪蒸气经换热器换热后，进行增压，进入下一个循环；
(2)闭式循环制冷
所述步骤2的操作如下：冷却介质经增压后，再经换热器换热，进入膨胀机中，得到膨胀物料，膨胀物料再经换热器换热后，返回增压，进入下一个循环；
或者，所述步骤2的操作如下：冷却介质经增压后，直接送入膨胀机中，得到膨胀物料，膨胀物料再经换热器换热后，返回增压，进入下一个循环；
所述步骤1中，富甲烷原料气的压力为1MPaG～20MPaG、温度为-30～60℃，或所述富甲烷原料气为LNG储罐的自蒸发气。
所述部分预热气与富甲烷原料气混合，形成两股物料进入换热器；或预热气与富甲烷原料气完全混合，再分为两股进入换热器。
所述步骤1中，低温干气经换热器冷却后，再进行节流降压，节流的级数为一级节流、二级节流、三级节流或四级节流。
所述步骤1中，低温干气经换热器冷却后，再经节流降压，然后进入第一气液分离器进行气液分离，分离后分别得到第一液相物、第一气相物，该第一液相物即为液化富甲烷气，该第一气相物即为低温闪蒸气。
所述步骤1中，第一液相物再经节流降压后，进入第二气液分离器进行气液分离，分离后分别得到第二液相物、第二气相物，该第二液相物即为液化富甲烷气，该第一气相物和第二气相物即为低温闪蒸气。
还包括预冷步骤：将外部冷却与换热器相连，通过外部冷却对换热器中的其他部件进行预冷。
所述外部冷却采用的典型冷剂为丙烯、丙烷、氨、氟利昂、水、BOG、溴化锂中的一种或多种。
含甲烷的不易液化气体能从***的任何物料中引出。
步骤2中，根据富甲烷原料气的压力和温度，在***合适的位置与预热气混合。
用于前述膨胀制冷富甲烷气液化的方法的装置，包括富甲烷气液化***、开式循环制冷***；
所述富甲烷气液化***包括用于输送富甲烷原料气的原料供应装置、换热器、气液分离器，所述原料供应装置、换热器、气液分离器通过管道依次相连；
所述开式循环制冷***包括气液分离器、换热器、压缩机、膨胀机，所述气液分离器、换热器、压缩机、膨胀机通过管道构成开式循环***；
提供另一种替换装置，包括富甲烷气液化***、闭式循环制冷***；
所述甲烷气液化***包括原料供应装置、换热器、气液分离器、压缩机，所述原料供应装置、换热器、气液分离器、压缩机通过管道依次相连；
所述闭式循环制冷***包括压缩机、换热器、膨胀机，所述压缩机、换热器、膨胀机通过管道构成闭式循环***。
本发明中，含甲烷的不易液化的气体(如：氮气、氢气、氩气、氧气或氦气等的一种或几种)可以在富甲烷气液化***的任何物料中引出。作为优选，含甲烷的不易液化气体能从第一预热气或第一闪蒸气或第二预热气或第二闪蒸气中引出。还包括与换热器相配合的外部冷却，外部冷却使用的冷却剂典型为丙烯、丙烷、氨、氟利昂、水、BOG、溴化锂中的一种或多种。
本发明具有调节手段丰富、流程简单、操作灵活、原料适应性强、设备投资低、甲烷损失小，氮气分离效果良好、能耗低等优点，具有较好的应用前景。
综上所述，由于采用了上述技术方案，本发明的有益效果是：
(1)本发明中，富甲烷气经预冷、膨胀后再冷却，相对现有技术，具有更好的制冷效果；
(2)本发明中，采用节流阀减压，虽效率略低，但冷量相当，操作更为简便，设备投资更小；
(3)本发明中采用逐级节流，各级压降小，使得本发明具有能耗更低、甲烷损失小、氮气分离系数高的优点；
(4)本发明通过部件之间的相互配合，使得膨胀功能够传递给压缩装置，有效降低能耗，节约成本，具有较好的应用前景；
(5)本发明操作灵活，甲烷损失小，能耗低，具有较好的应用前景。
附图说明
本发明将通过例子并参照附图的方式说明，其中：
图1是实施例1的原理示意图。
图1中，T1为预处理***，P1为膨胀机，C1、C2为循环气压缩机，E1、E2为冷却器，E3为换热器，V2为重烃分离器，V1为气液分离器，V3为LNG储罐。
图2是实施例2的原理示意图。
图2中，T1为预处理***，P1为膨胀机，C1、C2为循环气压缩机，C3为富甲烷循环气压缩机，E1、E2、E3为冷却器，E4为换热器，V1为气液分离器，V2为重烃分离器，V3为LNG储罐。
具体实施方式
本说明书中公开的所有特征，或公开的所有方法或过程中的步骤，除了互相排斥的特征和/或步骤以外，均可以以任何方式组合。
本说明书中公开的任一特征，除非特别叙述，均可被其他等效或具有类似目的的替代特征加以替换。即，除非特别叙述，每个特征只是一系列等效或类似特征中的一个例子而已。
实施例1
本实施例的流程示意图如图1所示，本流程包含预处理***(T1)，膨胀机(P1)，循环气压缩机(C1、C2)，冷却器(E1、E2)，换热器(E3)，重烃分离器(V2)，气液分离器(V1)，LNG储罐(V3)等，各部件之间通过管道构成富甲烷气液化***和开式循环制冷***。
本实施例工艺步骤如下：
(1)富甲烷气液化：
未经处理富甲烷原料气1经预处理***T1处理后，得到富甲烷原料气2。富甲烷原料气2与部分预热气16(下文中提到)混合后得到物料3，进入换热器E3冷却后，得到物料4。物料4出换热器E3，进入重烃分离器V2脱重烃，重烃由物料6引出，低温干气物料5再进入换热器E3冷却得到物料7。将物料7引出换热器E3，经一级节流阀Ⅰ节流后，得到物料8。物料8进入气液分离器V1进行气液分离，经气液分离器V1分离得到的液相10继续进行二级节流，经气液分离器V1分离得到的低温闪蒸气9进入换热器E3复热后，引出预热气11。预热气11引出两股物料12和13，物料12作为不易液化气引出界外，物料13与物料28(下文中提到)混合得到物料25。物料25与物料22(下文中提到)混合后，得到物料23，物料23进入循环气压缩机C2增压，增压后引出的物料24经冷却器E2冷却后，由物料14分为物料15和物料16，物料16与富甲烷原料气2混合，进入下一个循环。
气液分离器V1分离出的液相10经二级节流阀Ⅱ节流后，得到物料17。物料17进入LNG储罐V3进行气液分离，分离得到的液相产品储存在罐内，通过物料18外运；分离得 到的低温闪蒸气19进入换热器E3复热后，引出预热气20，预热气20进入循环气压缩机C1中增压，得到物料21。物料21经冷却器E1冷却后，引出物料22，并将物料22与物料25混合。
(2)开式循环制冷：
预热气14分得的物料15进入换热器E3冷却后，得到物料26。物料26进入膨胀机P1中，膨胀后，引出物料27。或者物料15不经换热器E3换热而直接送入膨胀机P1中膨胀，引出物料27。物料27进入换热器E3提供冷量，换热后得到物料28。物料28与预热气13混合后，进入下一个循环。
本实施例中，富甲烷原料气2的温度为40℃，压力为6000kPaA；不易液化气(即物料12)为37℃，压力为1080kPaA；产品LNG的温度为-160.5℃，压力为120kPaA。均为绝压。
实施例2
本实施例的流程示意图如图2所示，本流程包含预处理***(T1)、膨胀机(P1)、循环气压缩机(C1、C2)、富甲烷循环气压缩机(C3)、冷却器(E1、E2、E3)、换热器(E4)、气液分离器(V1)、重烃分离器(V2)、LNG储罐(V3)，各部件之间通过管道构成富甲烷气液化***和闭式循环制冷***。
该装置的工作步骤如下：
(1)富甲烷气液化：
未经处理富甲烷原料气1经预处理***T1处理后，得到富甲烷原料气2。富甲烷原料气2与预热气16(下文中提到)混合后得到物料3。物料3进入换热器E4冷却后由物料4出换热器E4，进入重烃分离器V2脱重烃，重烃由物料6引出，低温干气物料5再进入换热器E4冷却后由物料7引出换热器E4。物料7经一级节流阀Ⅰ节流后，得到物料8。物料8进入气液分离器V1进行气液分离，分离得到的液相10继续进行二级节流，分离得到的低温闪蒸气9进入换热器E4复热后，引出预热气11，预热气11引出两股物料12和物料13。其中，物料12作为不易液化气引出界外，物料13与物料22(下文中提到)混合，得到物料14。物料14进入循环气压缩机C2增压，增压后引出的物料15经冷却器E2冷却后，得到物料16。物料16与干燥气体2混合，进入下一个循环。
气液分离器V1分离出的液相10经二级节流阀Ⅱ节流后，得到物料17。物料17进入LNG储罐V3进行气液分离，分离得到的液相产品储存在罐内，通过物料18外运；分离得到的低温闪蒸气19进入换热器E4复热后，引出预热气20，预热气20进入循环气压缩机 C1增压，得到物料21。物料21经冷却器E1冷却后，引出物料22，并将物料22与物料13混合。
(2)闭式循环制冷：
富甲烷气经富甲烷循环气压缩机C3增压后，引出物料23。物料23经冷却器E3冷却后，得到物料24。物料24进入换热器E4进一步冷却，由物料25引出。物料25经膨胀机P1膨胀后，得到物料26。或者物料24不经换热器E4换热而直接送入膨胀机P1中膨胀，引出物料26。物料26进入换热器E4为换热器提供冷量，并引出物料27进入富甲烷循环气压缩机C3，开始下一个循环。
本实施例中，富甲烷原料气2的温度为40℃，压力为5000kPaA；不易液化气(即物料12)为37℃，压力为1080kPaA；产品LNG的温度为-160.5℃，压力为120kPaA。均为绝压。
本发明并不局限于前述的具体实施方式。本发明扩展到任何在本说明书中披露的新特征或任何新的组合，以及披露的任一新的方法或过程的步骤或任何新的组合。

Claims (10)

  1. 一种膨胀制冷富甲烷气液化的方法，其特征在于，包括如下步骤：
    (1)富甲烷气液化：
    所述步骤1的操作如下：富甲烷原料气与部分预热气混合后，经换热器冷却至-10～-90℃，再进入重烃分离器脱重烃，得到低温干气，低温干气再经换热器冷却后，经节流降压，再进行气液分离，分离后分别得到液化富甲烷气、低温闪蒸气，液化富甲烷气作为产品收集，低温闪蒸气经换热器换热后，进行增压，进入下一个循环；
    若富甲烷原料气无重烃，则富甲烷原料气与部分预热气混合后，直接经换热器冷却，再经节流降压后，进行气液分离，分离后分别得到液化富甲烷气、低温闪蒸气，液化富甲烷气作为产品收集，低温闪蒸气经换热器换热后，进行增压，进入下一个循环；
    (2)开式循环制冷：
    所述步骤2的操作如下：低温闪蒸气经换热器换热后，得到预热气，将预热气进行增压，增压后将其分为第一股物料、第二股物料两股物料，第一股物料经换热器换热后送入膨胀机中，或者第一股物料不经换热器换热而直接送入膨胀机中，得到膨胀物料，膨胀物料经换热器换热后与预热气混合，进入下一个循环，第二股物料即为所述步骤1中与富甲烷原料气混合的部分预热气；
    提供另一种替换方法，包括如下步骤：
    (1)富甲烷气液化：
    所述步骤1的操作如下：低温闪蒸气经换热器换热后，得到预热气，将预热气进行增压，并将富甲烷原料气与预热气混合，混合的物料经换热器冷却至-10～-90℃，再进入重烃分离器脱重烃，得到低温干气，低温干气再经换热器冷却后，经节流降压，再进行气液分离，分离后分别得到液化富甲烷气、低温闪蒸气，液化富甲烷气作为产品收集，低温闪蒸气经换热器换热后，进行增压，进入下一个循环；
    若富甲烷原料气无重烃，则富甲烷原料气与部分预热气混合后，直接经换热器冷却，再经节流降压后，进行气液分离，分离后分别得到液化富甲烷气、低温闪蒸气，液化富甲烷气作为产品收集，低温闪蒸气经换热器换热后，进行增压，进入下一个循环；
    (2)闭式循环制冷
    所述步骤2的操作如下：冷却介质经增压后，再经换热器换热，进入膨胀机中，或者冷却介质经增压后不经换热器换热而直接送入膨胀机中，得到膨胀物料，膨胀物料再经换热器换热后，返回增压，进入下一个循环；
    所述步骤1中，富甲烷原料气的压力为1MPaG～20MPaG、温度为-30～60℃，或所述富甲烷 原料气为LNG储罐的自蒸发气。
  2. 根据权利要求1所述膨胀制冷富甲烷气液化的方法，其特征在于，所述部分预热气与富甲烷原料气混合，形成两股物料进入换热器；或预热气与富甲烷原料气完全混合，再分为两股进入换热器。
  3. 根据权利要求1或2所述膨胀制冷富甲烷气液化的方法，其特征在于，所述步骤1中，低温干气经换热器冷却后，再进行节流降压，节流的级数为一级节流、二级节流、三级节流或四级节流。
  4. 根据权利要求1所述膨胀制冷富甲烷气液化的方法，其特征在于，所述步骤1中，低温干气经换热器冷却后，再经节流降压，然后进入第一气液分离器进行气液分离，分离后分别得到第一液相物、第一气相物，该第一液相物即为液化富甲烷气，该第一气相物即为低温闪蒸气。
  5. 根据权利要求4所述膨胀制冷富甲烷气液化的方法，其特征在于，所述步骤1中，第一液相物再经节流降压后，进入第二气液分离器进行气液分离，分离后分别得到第二液相物、第二气相物，该第二液相物即为液化富甲烷气，该第一气相物和第二气相物即为低温闪蒸气。
  6. 根据权利要求1～5任一项所述膨胀制冷富甲烷气液化的方法，其特征在于，还包括预冷步骤：将外部冷却与换热器相连，通过外部冷却对换热器中的其他部件进行预冷。
  7. 根据权利要求6所述膨胀制冷富甲烷气液化的方法，其特征在于，所述外部冷却采用的典型冷剂为丙烯、丙烷、氨、氟利昂、水、BOG、溴化锂中的一种或多种。
  8. 根据权利要求1～7任一项所述膨胀制冷富甲烷气液化的方法，其特征在于，含甲烷的不易液化气体能从***的任何物料中引出。
  9. 根据权利要求1～8任一项所述膨胀制冷富甲烷气液化的方法，其特征在于，步骤2中，根据富甲烷原料气的压力和温度，在***合适的位置与预热气混合。
  10. 用于前述权利要求1～9任一项所述方法的装置，其特征在于，包括富甲烷气液化***、开式循环制冷***；
    所述富甲烷气液化***包括用于输送富甲烷原料气的原料供应装置、换热器、气液分离器，所述原料供应装置、换热器、气液分离器通过管道依次相连；
    所述开式循环制冷***包括气液分离器、换热器、压缩机、膨胀机，所述气液分离器、换热器、压缩机、膨胀机通过管道构成开式循环***；
    提供另一种替换装置，包括富甲烷气液化***、闭式循环制冷***；
    所述甲烷气液化***包括原料供应装置、换热器、气液分离器、压缩机，所述原料供应装置、换热器、气液分离器、压缩机通过管道依次相连；
    所述闭式循环制冷***包括压缩机、换热器、膨胀机，所述压缩机、换热器、膨胀机通过管道构成闭式循环***。
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