CN114777418B - System for extracting helium from natural gas BOG by condensation method - Google Patents

System for extracting helium from natural gas BOG by condensation method Download PDF

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Publication number
CN114777418B
CN114777418B CN202210297595.6A CN202210297595A CN114777418B CN 114777418 B CN114777418 B CN 114777418B CN 202210297595 A CN202210297595 A CN 202210297595A CN 114777418 B CN114777418 B CN 114777418B
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bog
heat exchanger
methane
unit
natural gas
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CN114777418A (en
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孙大明
汪乘红
沈惬
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Zhejiang University ZJU
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Zhejiang University ZJU
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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
    • 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
    • F25J3/063—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 separated product stream
    • F25J3/0685—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 separated product stream separation of noble gases
    • F25J3/069—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 separated product stream separation of noble gases of helium
    • 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
    • F25J3/061—Natural gas or substitute natural gas
    • F25J3/0615—Liquefied natural gas
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01D—SEPARATION
    • B01D3/00—Distillation or related exchange processes in which liquids are contacted with gaseous media, e.g. stripping
    • B01D3/06—Flash distillation
    • 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
    • B01D53/002—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 condensation
    • C—CHEMISTRY; METALLURGY
    • C01—INORGANIC CHEMISTRY
    • C01B—NON-METALLIC ELEMENTS; COMPOUNDS THEREOF; METALLOIDS OR COMPOUNDS THEREOF NOT COVERED BY SUBCLASS C01C
    • C01B23/00—Noble gases; Compounds thereof
    • C01B23/001—Purification or separation processes of noble gases
    • 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
    • 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
    • F25B—REFRIGERATION MACHINES, PLANTS OR SYSTEMS; COMBINED HEATING AND REFRIGERATION SYSTEMS; HEAT PUMP SYSTEMS
    • F25B9/00—Compression machines, plants or systems, in which the refrigerant is air or other gas of low boiling point
    • F25B9/002—Compression machines, plants or systems, in which the refrigerant is air or other gas of low boiling point characterised by the refrigerant
    • 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
    • F25J3/061—Natural gas or substitute natural gas
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F25—REFRIGERATION OR COOLING; COMBINED HEATING AND REFRIGERATION SYSTEMS; HEAT PUMP SYSTEMS; MANUFACTURE OR STORAGE OF ICE; LIQUEFACTION SOLIDIFICATION OF GASES
    • F25J—LIQUEFACTION, SOLIDIFICATION OR SEPARATION OF GASES OR GASEOUS OR LIQUEFIED GASEOUS MIXTURES BY PRESSURE AND COLD TREATMENT OR BY BRINGING THEM INTO THE SUPERCRITICAL STATE
    • F25J3/00—Processes or apparatus for separating the constituents of gaseous or liquefied gaseous mixtures involving the use of liquefaction or solidification
    • F25J3/06—Processes or apparatus for separating the constituents of gaseous or liquefied gaseous mixtures involving the use of liquefaction or solidification by partial condensation
    • F25J3/063—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 separated product stream
    • F25J3/0635—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 separated product stream separation of CnHm with 1 carbon atom or more
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F25—REFRIGERATION OR COOLING; COMBINED HEATING AND REFRIGERATION SYSTEMS; HEAT PUMP SYSTEMS; MANUFACTURE OR STORAGE OF ICE; LIQUEFACTION SOLIDIFICATION OF GASES
    • F25J—LIQUEFACTION, SOLIDIFICATION OR SEPARATION OF GASES OR GASEOUS OR LIQUEFIED GASEOUS MIXTURES BY PRESSURE AND COLD TREATMENT OR BY BRINGING THEM INTO THE SUPERCRITICAL STATE
    • F25J3/00—Processes or apparatus for separating the constituents of gaseous or liquefied gaseous mixtures involving the use of liquefaction or solidification
    • F25J3/06—Processes or apparatus for separating the constituents of gaseous or liquefied gaseous mixtures involving the use of liquefaction or solidification by partial condensation
    • F25J3/063—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 separated product stream
    • F25J3/066—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 separated product stream separation of nitrogen
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F28—HEAT EXCHANGE IN GENERAL
    • F28D—HEAT-EXCHANGE APPARATUS, NOT PROVIDED FOR IN ANOTHER SUBCLASS, IN WHICH THE HEAT-EXCHANGE MEDIA DO NOT COME INTO DIRECT CONTACT
    • F28D9/00—Heat-exchange apparatus having stationary plate-like or laminated conduit assemblies for both heat-exchange media, the media being in contact with different sides of a conduit wall
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01D—SEPARATION
    • B01D2257/00—Components to be removed
    • B01D2257/10—Single element gases other than halogens
    • B01D2257/11—Noble gases
    • 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
    • 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
    • F25J2205/00—Processes or apparatus using other separation and/or other processing means
    • F25J2205/20—Processes or apparatus using other separation and/or other processing means using solidification of components
    • 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
    • F25J2205/00—Processes or apparatus using other separation and/or other processing means
    • F25J2205/24—Processes or apparatus using other separation and/or other processing means using regenerators, cold accumulators or reversible heat exchangers
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F25—REFRIGERATION OR COOLING; COMBINED HEATING AND REFRIGERATION SYSTEMS; HEAT PUMP SYSTEMS; MANUFACTURE OR STORAGE OF ICE; LIQUEFACTION SOLIDIFICATION OF GASES
    • F25J—LIQUEFACTION, SOLIDIFICATION OR SEPARATION OF GASES OR GASEOUS OR LIQUEFIED GASEOUS MIXTURES BY PRESSURE AND COLD TREATMENT OR BY BRINGING THEM INTO THE SUPERCRITICAL STATE
    • F25J2210/00—Processes characterised by the type or other details of the feed stream
    • F25J2210/62—Liquefied natural gas [LNG]; Natural gas liquids [NGL]; Liquefied petroleum gas [LPG]
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F25—REFRIGERATION OR COOLING; COMBINED HEATING AND REFRIGERATION SYSTEMS; HEAT PUMP SYSTEMS; MANUFACTURE OR STORAGE OF ICE; LIQUEFACTION SOLIDIFICATION OF GASES
    • F25J—LIQUEFACTION, SOLIDIFICATION OR SEPARATION OF GASES OR GASEOUS OR LIQUEFIED GASEOUS MIXTURES BY PRESSURE AND COLD TREATMENT OR BY BRINGING THEM INTO THE SUPERCRITICAL STATE
    • F25J2210/00—Processes characterised by the type or other details of the feed stream
    • F25J2210/90—Boil-off gas from storage
    • 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
    • F25J2215/00—Processes characterised by the type or other details of the product stream
    • F25J2215/30—Helium
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F25—REFRIGERATION OR COOLING; COMBINED HEATING AND REFRIGERATION SYSTEMS; HEAT PUMP SYSTEMS; MANUFACTURE OR STORAGE OF ICE; LIQUEFACTION SOLIDIFICATION OF GASES
    • F25J—LIQUEFACTION, SOLIDIFICATION OR SEPARATION OF GASES OR GASEOUS OR LIQUEFIED GASEOUS MIXTURES BY PRESSURE AND COLD TREATMENT OR BY BRINGING THEM INTO THE SUPERCRITICAL STATE
    • F25J2230/00—Processes or apparatus involving steps for increasing the pressure of gaseous process streams
    • F25J2230/08—Cold compressor, i.e. suction of the gas at cryogenic temperature and generally without afterstage-cooler
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F25—REFRIGERATION OR COOLING; COMBINED HEATING AND REFRIGERATION SYSTEMS; HEAT PUMP SYSTEMS; MANUFACTURE OR STORAGE OF ICE; LIQUEFACTION SOLIDIFICATION OF GASES
    • F25J—LIQUEFACTION, SOLIDIFICATION OR SEPARATION OF GASES OR GASEOUS OR LIQUEFIED GASEOUS MIXTURES BY PRESSURE AND COLD TREATMENT OR BY BRINGING THEM INTO THE SUPERCRITICAL STATE
    • F25J2230/00—Processes or apparatus involving steps for increasing the pressure of gaseous process streams
    • F25J2230/30—Compression of the feed stream
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F25—REFRIGERATION OR COOLING; COMBINED HEATING AND REFRIGERATION SYSTEMS; HEAT PUMP SYSTEMS; MANUFACTURE OR STORAGE OF ICE; LIQUEFACTION SOLIDIFICATION OF GASES
    • F25J—LIQUEFACTION, SOLIDIFICATION OR SEPARATION OF GASES OR GASEOUS OR LIQUEFIED GASEOUS MIXTURES BY PRESSURE AND COLD TREATMENT OR BY BRINGING THEM INTO THE SUPERCRITICAL STATE
    • F25J2270/00—Refrigeration techniques used
    • F25J2270/12—External refrigeration with liquid vaporising 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
    • F25J2270/00—Refrigeration techniques used
    • F25J2270/14—External refrigeration with work-producing gas expansion 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
    • F25J2270/00—Refrigeration techniques used
    • F25J2270/42—Quasi-closed internal or closed external nitrogen refrigeration cycle
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    • 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
    • F25J2270/00—Refrigeration techniques used
    • F25J2270/90—External refrigeration, e.g. conventional closed-loop mechanical refrigeration unit using Freon or NH3, unspecified external refrigeration
    • F25J2270/908—External refrigeration, e.g. conventional closed-loop mechanical refrigeration unit using Freon or NH3, unspecified external refrigeration by regenerative chillers, i.e. oscillating or dynamic systems, e.g. Stirling refrigerator, thermoelectric ("Peltier") or magnetic refrigeration

Abstract

The invention discloses a system for extracting helium from natural gas BOG by a condensation method, which belongs to the technical field of BOG recovery of LNG factories and comprises a BOG buffer tank, a cold compressor, a first heat exchanger, a second heat exchanger, a heavy hydrocarbon separator, a methane solidification unit, a refrigerator unit and a liquid nitrogen separator which are connected in sequence; the second heat exchanger and the methane curing unit are connected with an external refrigeration unit; a first throttle valve is connected between the first heat exchanger and the heavy hydrocarbon separator; a second throttle valve is connected between the first heat exchanger and the liquid nitrogen separator. According to the invention, through reasonable process design, BOG does not need to be rewarmed, the system operates under normal pressure, the process flow is simple, the thermodynamic efficiency is high, the operation energy consumption is low, the equipment investment is small, the air source adaptability is strong, the methane content in the separated heavy hydrocarbon is not less than 88%, the nitrogen content in the separated liquid nitrogen is not less than 98%, and the product recycling rate is improved.

Description

System for extracting helium from natural gas BOG by condensation method
Technical Field
The invention relates to the technical field of BOG recovery of LNG factories, in particular to a system for extracting helium from natural gas BOG by a condensation method.
Background
Helium is an inert, non-flammable rare gas with a small molecular size and a low boiling point (about 4.2K) and is widely used in medical, scientific research and industrial production. With the development of economy and science, the demand for helium (mainly in china and india) has increased at a rate of 5-7% per year, facing the dilemma of global helium resource supply shortage. Although the atmosphere contains abundant helium (next to hydrogen), the concentration is generally lower than 5ppm, and the extraction difficulty is great, so helium gas for practical use is generally extracted from helium-rich natural gas (helium concentration is generally higher than 0.3%).
In the natural gas industry, natural gas is often produced as liquefied natural gas (Liquefied Natural Gas, LNG) (which has a volume of about 1/600 of the original gaseous volume) for ease of storage and transportation. In LNG production, it is necessary to reduce the liquefaction pressure to tank pressure through a final throttling valve. The boiling points of the components in the natural Gas are different (helium: 4.22K, hydrogen: 20.28K, nitrogen: 77.36K and methane 111.7K under normal pressure), the throttling process is equivalent to simple evaporation of LNG at the storage tank pressure, gas molecules with lower boiling points are firstly escaped from the LNG and are called flash gases (BOG), and because hydrocarbon gases are liquefied, non-condensable gases such as helium and the like are enriched in the BOG to a certain degree. In addition, the gas-liquid mixture formed after LNG flows through the throttle valve is sent to the BOG buffer tank for storage through a low-temperature pipeline, BOG is also generated due to heat leakage of the storage tank in the storage process, and the components of the BOG are mainly nitrogen and methane. In general, the concentration of helium in BOG is higher than that of raw natural gas, and even a small amount of BOG has high utilization value.
The existing natural gas helium stripping technology comprises the following steps: membrane separation technology, pressure swing adsorption technology, and low temperature technology. The low-temperature process is widely adopted for good economy, and the principle is that the temperature of the natural gas is gradually reduced by refrigeration circulation by utilizing the difference of boiling points of all components of the natural gas, and cryogenic separation is carried out, so that hydrocarbon gas and nitrogen are sequentially removed, and coarse helium is obtained.
Common low temperature processes include: condensation, rectification, and a combination of condensation and rectification. The product obtained by the BOG helium extraction system by the rectification method has high purity, but the process is complex, the investment is high, the BOG needs to be pressurized after being rewarmed to normal temperature, then the BOG is cooled and liquefied for the second time, and then the BOG is separated, thereby increasing the heat exchange processLoss, equipment investment (e.g., compressor train, multi-stream heat exchanger) and system complexity. The system adopting the condensation method has the characteristics of simple and compact structure, low energy consumption and strong operability, but in the system for extracting helium by the BOG of the condensation method, the flow of raw material gas in a hydrocarbon gas removal link is much larger than that in a nitrogen removal link, so that the cooling capacity required by cooling is also much.
Disclosure of Invention
The invention provides a system for extracting helium from natural gas BOG by a condensation method, which can extract crude helium from the BOG and has the characteristics of low energy consumption, simple and compact structure and high product recycling rate.
A system for extracting helium from natural gas BOG by a condensation method comprises a BOG buffer tank, a cold compressor, a first heat exchanger, a second heat exchanger, a heavy hydrocarbon separator, a methane solidification unit, a refrigerator unit and a liquid nitrogen separator which are connected in sequence;
the second heat exchanger and the methane curing unit are connected with an external refrigeration unit; a first throttle valve is connected between the first heat exchanger and the heavy hydrocarbon separator; a second throttle valve is connected between the first heat exchanger and the liquid nitrogen separator;
the inlet of the BOG buffer tank is connected with the gas phase space of the LNG storage tank; the cold compressor is used for pressurizing the BOG from the BOG buffer tank; the first heat exchanger is used for precooling the BOG after being pressurized by the cold compressor; the second heat exchanger is used for partially liquefying the BOG from the first heat exchanger; the heavy hydrocarbon separator is used for separating the BOG gas-liquid mixture from the second heat exchanger; the first throttle valve is used for throttling the liquid phase obtained by the heavy hydrocarbon separator; the methane solidifying unit is used for cooling the gas phase mixture obtained by the heavy hydrocarbon separator; the refrigerator unit is used for cooling the BOG from the methane curing unit; the liquid nitrogen separator is used for separating a gas-liquid mixture from the refrigerator unit; the second throttle valve is used for throttling the liquid phase obtained by the liquid nitrogen separator; the external refrigeration unit is used for providing the cooling capacity required by the heavy hydrocarbon separation and methane solidification process.
Further, the BOG temperature at the outlet of the second heat exchanger is lower than the saturation temperature of methane but higher than the three-phase point thereof.
Further, the BOG temperature at the outlet of the methane curing unit is below the triple point of methane but above the saturation temperature of nitrogen.
Further, the methane curing unit at least comprises a group of heat exchangers which work alternately, and preferably a plate-fin heat exchanger with high fins and large channels is adopted.
Furthermore, the methane curing unit adopts an automatic control technology, and realizes the automatic switching of the heat exchanger by monitoring the pressure at two sides of the heat exchanger channel.
Further, the BOG temperature at the outlet of the refrigerator unit is below the saturation temperature of nitrogen but above its three-phase point.
Further, the refrigerator unit comprises 1 or more cryocoolers, preferably Stirling coolers.
Further, nitrogen after the cold recovery through the first heat exchanger is used as a purge gas for the methane curing unit.
Further, the external refrigeration unit adopts a dividing wall type refrigerator, preferably adopts a nitrogen expansion refrigeration technology and a liquid nitrogen throttling refrigeration technology.
Further, the dividing wall type refrigerator adopts a liquid nitrogen throttling refrigeration technology to provide the cold energy required by the second heat exchanger and the methane solidifying unit, and divides the nitrogen-liquid mixture generated by liquid nitrogen throttling into two streams to respectively provide the cold energy required by the second heat exchanger and the methane solidifying unit.
Compared with the prior art, the invention has the following beneficial effects:
the invention separates heavy hydrocarbon and nitrogen in BOG to prepare coarse helium by condensation method, and has the characteristics of low energy consumption, simple and compact structure and high product recycling rate. BOG does not need to be rewarmed to normal temperature, and avoids the rewarming and secondary cooling processesLoss. The system has low operating pressure, only needs to overcome the flow resistance, and reduces the requirements on equipment and pipelines. The content of methane in the liquid phase obtained by the heavy hydrocarbon separator is not less than 88 percent, the content of nitrogen in the liquid phase obtained by the liquid nitrogen separator is not less than 98 percent, the product utilization rate is high, and the system economy is good.
2. In the invention, the external refrigeration unit in the heavy hydrocarbon separation and methane solidification link adopts the dividing wall type refrigerator, the required cold energy is preferably provided by a nitrogen gas, the thermodynamic efficiency is high, the required refrigerant flow is small, and the air source adaptability is strong; the cold energy required by the nitrogen separation link is provided by the regenerative refrigerator, so that the use of refrigeration cycle with hydrogen or helium as a working medium is avoided, the complexity of the system is reduced, and the industrial feasibility is enhanced.
Drawings
Fig. 1 is a schematic diagram of a system for extracting helium from natural gas BOG by condensation according to an embodiment of the present invention.
In the figure: BOG buffer tank 1, cold compressor 2, first heat exchanger 3, second heat exchanger 4, heavy hydrocarbon separator 5, first throttle valve 6, methane solidification unit 7, refrigerator unit 8, liquid nitrogen separator 9, second throttle valve 10, external refrigeration unit 11.
Detailed Description
The invention will be described in further detail with reference to the drawings and examples, it being noted that the examples described below are intended to facilitate the understanding of the invention and are not intended to limit the invention in any way.
As shown in fig. 1, a system for extracting helium from natural gas BOG by a condensation method comprises a BOG buffer tank 1, a cold compressor 2, a first heat exchanger 3, a second heat exchanger 4, a heavy hydrocarbon separator 5, a methane solidifying unit 7, a refrigerator unit 8 and a liquid nitrogen separator 9 which are connected in sequence; also included are an external refrigeration unit 11 connected to the second heat exchanger 4 and the methane solidification unit 7, a first throttle valve 6 connected to the first heat exchanger 3 and the heavy hydrocarbon separator 5, and a second throttle valve 10 connected to the first heat exchanger 3 and the liquid nitrogen separator 9.
The inlet of the BOG buffer tank 1 is connected with the gas phase space of the LNG storage tank; the cold compressor 2 is used for pressurizing the BOG from the BOG buffer tank 1; the first heat exchanger 3 is used for precooling the BOG after being pressurized by the cold compressor 1; the second heat exchanger 4 is used for partially liquefying the BOG from the first heat exchanger 3; a heavy hydrocarbon separator 5 for separating the BOG gas-liquid mixture from the second heat exchanger 4; the first throttle valve 6 is used for throttling the liquid phase obtained from the heavy hydrocarbon separator 5; the methane solidification unit 7 is used for cooling the gas phase mixture obtained by the heavy hydrocarbon separator 5; the refrigerator unit 8 is used for cooling the BOG from the methane curing unit 7; the liquid nitrogen separator 9 is used for separating the gas-liquid mixture from the refrigerator unit 8; the second throttle valve 10 is used for throttling the liquid phase obtained by the liquid nitrogen separator 9; the external refrigeration unit 11 is used to provide the refrigeration required for the heavy hydrocarbon separation and methane solidification process.
The cold compressor 2 only needs to boost the BOG from the storage tank 1 to overcome the subsequent flow resistance.
In this embodiment, the BOG temperature at the outlet of the second heat exchanger 4 is below the saturation temperature of methane but above its three-phase point. The BOG temperature at the outlet of the methane solidifying unit 7 is lower than the triple point of methane but higher than the saturation temperature of nitrogen.
The methane curing unit 7 comprises at least one set of heat exchangers which work alternately, preferably plate-fin heat exchangers with high fins and large channels. The methane solidifying unit 7 adopts an automatic control technology, and realizes the automatic switching of the heat exchanger by monitoring the pressure at two sides of the heat exchanger channel.
The BOG temperature at the outlet of the refrigerator unit 8 is below the saturation temperature of nitrogen but above its three-phase point. The refrigerator unit 8 comprises 1 or more cryocoolers, preferably a stirling cooler.
The external refrigeration unit 11 adopts a dividing wall type refrigerator, preferably adopts a nitrogen expansion refrigeration technology and a liquid nitrogen throttling refrigeration technology; further, the liquid nitrogen throttling refrigeration technology provides the cold energy required by the second heat exchanger 4 and the methane solidifying unit 7, preferably divides the nitrogen-liquid mixture generated by liquid nitrogen throttling into two streams, and provides the cold energy required by the second heat exchanger 4 and the methane solidifying unit 7 respectively.
The nitrogen after the recovery of cold energy through the first heat exchanger 3 is preferably used as a purge gas for the methane solidifying unit 7.
In the invention, BOG from the BOG buffer tank does not need to be rewarmed, is pressurized by the cold compressor 2 in sequence, is partially liquefied by cooling, and then enters the heavy hydrocarbon separator 5 to remove most heavy hydrocarbon and methane; the liquid phase mixture obtained after the separation of the heavy hydrocarbon separator 5 is throttled to provide partial cold energy required by BOG cooling, and the separated gas phase mixture is further cooled to a triple point of methane, so that the methane is solidified on the surface of a heat exchanger channel, and the methane is removed; the gas phase mixture after removing methane is further cooled to the saturation temperature of nitrogen, and part of the gas phase mixture after being liquefied enters a liquid nitrogen separator 9 to remove most of nitrogen. The cold required for the heavy hydrocarbon separation and methane solidification process is provided by an external refrigeration unit.
Through testing, the content of methane in the liquid phase obtained by the heavy hydrocarbon separator 5 is not less than 88%, and the content of nitrogen in the liquid phase product obtained by the liquid nitrogen separator 9 is not less than 98%. The product utilization rate is high, and the system economy is good.
The foregoing embodiments have described in detail the technical solution and the advantages of the present invention, it should be understood that the foregoing embodiments are merely illustrative of the present invention and are not intended to limit the invention, and any modifications, additions and equivalents made within the scope of the principles of the present invention should be included in the scope of the invention.

Claims (10)

1. The system for extracting helium from natural gas BOG by a condensation method is characterized by comprising a BOG buffer tank (1), a cold compressor (2), a first heat exchanger (3), a second heat exchanger (4), a heavy hydrocarbon separator (5), a methane solidifying unit (7), a refrigerator unit (8) and a liquid nitrogen separator (9) which are connected in sequence;
the second heat exchanger (4) and the methane curing unit (7) are connected with an external refrigeration unit (11); a first throttle valve (6) is connected between the first heat exchanger (3) and the heavy hydrocarbon separator (5); a second throttle valve (10) is connected between the first heat exchanger (3) and the liquid nitrogen separator (9);
the inlet of the BOG buffer tank (1) is connected with a gas phase space of the LNG storage tank; the cold compressor (2) is used for pressurizing the BOG from the BOG buffer tank (1); the first heat exchanger (3) is used for precooling the BOG after being pressurized by the cold compressor (2); the second heat exchanger (4) is used for partially liquefying the BOG from the first heat exchanger (3); the heavy hydrocarbon separator (5) is used for separating the BOG gas-liquid mixture from the second heat exchanger (4); the first throttling valve (6) is used for throttling the liquid phase obtained by the heavy hydrocarbon separator (5); the methane solidifying unit (7) is used for cooling the gas phase mixture obtained by the heavy hydrocarbon separator (5); the refrigerator unit (8) is used for cooling the BOG from the methane curing unit (7); the liquid nitrogen separator (9) is used for separating a gas-liquid mixture from the refrigerator unit (8); the second throttle valve (10) is used for throttling the liquid phase obtained by the liquid nitrogen separator (9); the external refrigeration unit (11) is used for providing the cooling capacity required by the heavy hydrocarbon separation and methane solidification process.
2. The system for extracting helium from natural gas BOG by condensation process according to claim 1, wherein the BOG temperature at the outlet of the second heat exchanger (4) is lower than the saturation temperature of methane but higher than the triple point thereof.
3. The system for extracting helium from natural gas BOG by condensation process according to claim 1, wherein the BOG temperature at the outlet of the methane solidifying unit (7) is lower than the triple point of methane but higher than the saturation temperature of nitrogen.
4. The system for extracting helium from natural gas BOG by condensation method according to claim 1, wherein the methane solidifying unit (7) at least comprises a group of heat exchangers which work alternately, and the heat exchangers adopt plate-fin heat exchangers with high fins and large channels.
5. The system for extracting helium from natural gas BOG by condensation method according to claim 4, wherein the methane solidifying unit (7) adopts an automatic control technology, and realizes automatic switching of the heat exchanger by monitoring the pressure at two sides of the heat exchanger channel.
6. A system for helium stripping of natural gas BOG according to claim 1, characterized in that the BOG temperature at the outlet of the refrigerator unit (8) is below the saturation temperature of nitrogen but above its triple point.
7. The system for extracting helium from natural gas BOG by condensation process according to claim 1, wherein the refrigerator unit (8) comprises 1 or more cryocoolers, and the cryocoolers are stirling cryocoolers.
8. The system for extracting helium from natural gas BOG by condensation process according to claim 1, wherein nitrogen after cold recovery through the first heat exchanger (3) is used as purge gas for the methane solidification unit (7).
9. The system for extracting helium from natural gas BOG by condensation method according to claim 1, wherein the external refrigeration unit (11) adopts a dividing wall type refrigerator, and adopts a nitrogen expansion refrigeration technology and a liquid nitrogen throttling refrigeration technology.
10. The system for extracting helium from natural gas BOG by condensation method according to claim 9, wherein the dividing wall type refrigerator adopts a liquid nitrogen throttling refrigeration technology to provide cold energy required by the second heat exchanger (4) and the methane solidifying unit (7), and divides a nitrogen-liquid mixture generated by liquid nitrogen throttling into two streams to respectively provide cold energy required by the second heat exchanger (4) and the methane solidifying unit (7).
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